[Federal Register Volume 76, Number 248 (Tuesday, December 27, 2011)]
[Proposed Rules]
[Pages 81328-81358]
[FR Doc No: 2011-32843]

Vol. 76

Tuesday,

No. 248

December 27, 2011

Part VIII

Environmental Protection Agency

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40 CFR Part 63

 National Emission Standards for Hazardous Air Pollutants From the Pulp
and Paper Industry; Proposed Rule

Federal Register / Vol. 76 , No. 248 / Tuesday, December 27, 2011 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2007-0544; FRL-9609-8]
RIN 2060-AQ41

National Emission Standards for Hazardous Air Pollutants From the
Pulp and Paper Industry

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing amendments to the national emission
standards for hazardous air pollutants for the pulp and paper industry
to address the results of the residual risk and technology review that
the EPA is required to conduct under sections 112(d)(6) and (f)(2) of
the Clean Air Act. These proposed amendments include revisions to the
kraft pulping process condensates standards; a requirement for 5-year
repeat emissions testing for selected process equipment; revisions to
provisions addressing periods of startup, shutdown and malfunction;
additional test methods for measuring methanol; and technical and
editorial changes.

DATES: Comments. Comments must be received on or before February 27,
2012. Under the Paperwork Reduction Act, comments on the information
collection provisions are best assured of having full effect if the
Office of Management and Budget receives a copy of your comments on or
before January 26, 2012.
    Public Hearing. If anyone contacts the EPA requesting to speak at a
public hearing by January 6, 2012, a public hearing will be held on
January 11, 2012.

ADDRESSES: Submit your comments, identified by Docket ID Number EPA-HQ-
OAR-2007-0544, by one of the following methods:
     Federal eRulemaking Portal: http://www.regulations.gov.
Follow the online instructions for submitting comments.
     Agency Web site: http://www.epa.gov/oar/docket.html.
Follow the instructions for submitting comments on the EPA Air and
Radiation Docket Web site.
     Email<EMAIL_ADDRESS>Include EPA-HQ-OAR-2007-
0544 in the subject line of the message.
     Fax: Fax your comments to:<PHONE_NUMBER>, Attention
Docket ID Number EPA-HQ-OAR-2007-0544.
     Mail: Send your comments to: EPA Docket Center (EPA/DC),
Environmental Protection Agency, Mailcode: 2822T, 1200 Pennsylvania
Ave. NW., Washington, DC 20460, Attention: Docket ID Number EPA-HQ-OAR-
2007-0544. 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 or Courier: In person or by courier, deliver
comments to the EPA Docket Center, EPA West (Air Docket), Room 3334,
1301 Constitution Ave. NW., Washington, DC 20460, Attention: Docket ID
Number EPA-HQ-OAR-2007-0544. Such deliveries are only accepted during
the Docket's normal hours of operation (8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays), and special arrangements
should be made for deliveries of boxed information. Please include two
copies.
    Instructions. Direct your comments to Docket ID Number EPA-HQ-OAR-
2007-0544. The EPA 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 or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be confidential business information 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 avoid the use
of special characters, any form of encryption and be free of any
defects or viruses. For additional information about the EPA public
docket, visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID Number EPA-HQ-OAR-2007-0544. All documents in the docket are
listed in the http://www.regulations.gov index. Although listed in the
index, some information is not publicly available (e.g., confidential
business information or other information whose disclosure is
restricted by statute). Certain other material, such as copyrighted
material, will be publicly available only in hard copy. Publicly
available docket materials are available either electronically in
http://www.regulations.gov or in hard copy at the EPA Docket Center,
EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. The
Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through
Friday, excluding legal holidays. The telephone number for the Public
Reading Room is<PHONE_NUMBER>, and the telephone number for the EPA
Docket Center is<PHONE_NUMBER>.
    Public Hearing. If a public hearing is held, it will begin at 10
a.m. on January 11, 2012 and will be held at the EPA campus in Research
Triangle Park, North Carolina, or at an alternate facility nearby.
Persons interested in presenting oral testimony or inquiring as to
whether a public hearing is to be held should contact Ms. Joan Rogers,
Office of Air Quality Planning and Standards, Sector Policies and
Programs Division, Natural Resources Group (E143-03), U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Mr. John Bradfield, Office of Air Quality Planning and
Standards, (E143-03), 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. James Hirtz, Health and Environmental Impacts Division
(C539-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>For information about the
applicability of the national emission standards for hazardous air
pollutants to a particular entity, contact the appropriate person
listed in Table 1 to this preamble.

 Table 1--List of EPA Contacts for the NESHAP Addressed in This Proposed
                                 Action
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           NESHAP for:             OECA Contact \1\   OAQPS Contacts \2\
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Pulp and Paper..................  Sara Ayres (202)    John Bradfield
                                   564-5391<PHONE_NUMBER>
<EMAIL_ADDRESS> bradfield.john@ep
                                   v..                 a.gov.
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\1\ EPA's Office of Enforcement and Compliance Assurance.
\2\ EPA's Office of Air Quality Planning and Standards.

SUPPLEMENTARY INFORMATION:

Preamble Acronyms and Abbreviations

    Several acronyms and terms used to describe industrial processes,
data inventories and risk modeling are included in this preamble. While
this may not be an exhaustive list, to ease the reading of this
preamble and for reference purposes, the following terms and acronyms
are defined here:
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
ASME American Society of Mechanical Engineers
ATSDR Agency for Toxic Substances and Disease Registry
BACT Best Available Control Technology
BBDR Biologically-Based Dose-Response
CAA Clean Air Act
CalEPA California Environmental Protection Agency
CBI Confidential Business Information
CCA Clean Condensate Alternative
CD ROM Compact Disk Read Only Memory
CDX Central Data Exchange
CEEL Community Emergency Exposure Levels
CEMS Continuous Emissions Monitoring System
CFR Code of Federal Regulations
CIIT Chemical Industry Institute of Toxicology
EIA Economic Impact Analysis
EJ Environmental Justice
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
ERT Electronic Reporting Tool
ft Feet
ft\3\ Cubic Feet
FTE Full-Time Equivalents
HAP Hazardous Air Pollutants
HEM-3 Human Exposure Model version 3
HI Hazard Index
HON Hazardous Organic National Emissions Standards for Hazardous Air
Pollutants
HQ Hazard Quotient
hr Hour
HVLC High Volume Low Concentration
ICR Information Collection Request
IRIS Integrated Risk Information System
ISIS Industrial Sectors Integrated Solution Model
km Kilometer
LAER Lowest Achievable Emission Rate
lb Pounds
LVHC Low Volume High Concentration
m\3\ Cubic Meters
MACT Maximum Achievable Control Technology
MACT Code Code within the NEI used to identify processes included in
a source category
MEK Methyl Ethyl Ketone
mg Milligrams
MIR Maximum Individual Risk
MRL Minimal Risk Level
NAC/AEGL National Advisory Committee for Acute Exposure Guideline
Levels for Hazardous Substances
NAICS North American Industry Classification System
NAS National Academy of Sciences
NATA National Air Toxics Assessment
NCASI National Council for Air and Stream Improvement
NEI National Emissions Inventory
NESHAP National Emissions Standards for Hazardous Air Pollutants
NIOSH National Institutes for Occupational Safety and Health
NRC National Research Council
NSPS New Source Performance Standard
NTTAA National Technology Transfer and Advancement Act of 1995
O&M Operation and Maintenance
OAQPS EPA's Office of Air Quality Planning and Standards
ODTP Oven-Dried Tons of Pulp
OECA EPA's Office of Enforcement and Compliance Assurance
OMB Office of Management and Budget
PB-HAP Hazardous air pollutants known to be persistent and bio-
accumulative in the environment
POM Polycyclic Organic Matter
ppm Parts Per Million
ppmw Parts Per Million by Weight
PRA Paperwork Reduction Act
QA Quality Assurance
QC Quality Control
RACT Reasonably Available Control Technology
RBLC RACT/BACT/LAER Clearinghouse
REL Reference Exposure Level
RFA Regulatory Flexibility Act
RfC Reference Concentration
RfD Reference Dose
RTR Residual Risk and Technology Review
SAB Science Advisory Board
SBA Small Business Administration
SCC Source Classification Code
Sec Second
SISNOSE Significant Impact on a Substantial Number of Small Entities
SOP Standard Operating Procedures
SSM Startup, Shutdown, and Malfunction
TOSHI Target Organ-Specific Hazard Index
TPY Tons Per Year
TRI Toxics Release Inventory
TRIM Total Risk Integrated Modeling System
TRIM.FaTE Fate, Transport and Environmental Exposure module of EPA's
Total Risk Integrated Modeling System
TTN Technology Transfer Network
UF Uncertainty Factor
UMRA Unfunded Mandates Reform Act of 1995
URE Unit Risk Estimate
VCS Voluntary Consensus Standards
VOC Volatile Organic Compound
WWW Worldwide Web
[mu]g Micrograms

Organization of This Document

    The information in this preamble is organized as follows:

I. General Information
    A. What is the statutory authority for this action?
    B. Does this action apply to me?
    C. Where can I get a copy of this document and other related
information?
    D. What should I consider as I prepare my comments for the EPA?
II. Background
    A. What is this source category and how did the MACT standard
regulate its HAP emissions?
    B. What data collection activities were conducted to support
this action?
III. Analyses Performed
    A. How did we estimate risks posed by the source category?
    B. How did we consider the risk results in making decisions for
this proposal?
    C. How did we perform the technology review?
    D. What other issues are we addressing in this proposal?
IV. Analytical Results and Proposed Decisions
    A. What are the results of the risk assessments?
    B. What are our proposed decisions regarding risk acceptability
and ample margin of safety?
    C. What are the results and proposed decisions based on our
technology review?
    D. What other actions are we proposing?
    E. Compliance Dates
V. Summary of Cost, Environmental and Economic Impacts
    A. What are the affected sources?
    B. What are the air quality impacts?
    C. What are the cost impacts?
    D. What are the economic impacts?
    E. What are the benefits?
VI. Request for Comments
VII. Submitting Data Corrections
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review

    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. What is the statutory authority for this action?

    Section 112 of the 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)
calls for us to promulgate 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, these technology-based standards must reflect the maximum
degree of emissions reductions of HAP achievable (after considering
cost, energy requirements and nonair quality health and environmental
impacts) and are commonly referred to as MACT standards.
    Maximum achievable control technology standards must require the
maximum degree of emissions reduction through the application of
measures, processes, methods, systems or techniques, including, but not
limited to, measures that: (A) Reduce the volume of or eliminate
pollutants through process changes, substitution of materials or other
modifications; (B) enclose systems or processes to eliminate emissions;
(C) capture or treat pollutants when released from a process, stack,
storage or fugitive emissions point; (D) are design, equipment, work
practice or operational standards (including requirements for operator
training or certification); or (E) 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: (A) A pollutant cannot be emitted through
a conveyance designed and constructed to emit or capture the
pollutants, or that any requirement for, or use of, such a conveyance
would be inconsistent with law; or (B) the application of measurement
methodology to a particular class of sources is not practicable due to
technological and economic limitations (CAA sections 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 emission control that is achieved in practice by the
best-controlled similar source. The MACT floors for existing sources
can be less stringent than floors for new sources, but they cannot be
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, we must also consider control options that are more
stringent than the floor. We may establish standards more stringent
than the floor based on the consideration of the cost of achieving the
emissions reductions, any nonair quality health and environmental
impacts and energy requirements.
    The EPA is then required to review these technology-based standards
and to revise them ``as necessary (taking into account developments in
practices, processes, and control technologies)'' no less frequently
than every 8 years, under CAA section 112(d)(6). In conducting this
review, the EPA is not obliged to completely recalculate the prior MACT
determination and, in particular, is not obligated to recalculate the
MACT floors. NRDC v. EPA, 529 F.3d 1077, 1084 (DC Cir., 2008).
    The second stage in standard-setting focuses on reducing any
remaining ``residual'' risk according to CAA section 112(f). This
provision requires, first, that the EPA prepare a Report to Congress
discussing (among other things) methods of calculating the risks posed
(or potentially posed) by sources after implementation of the MACT
standards, the public health significance of those risks, and the EPA's
recommendations as to legislation regarding such remaining risk. The
EPA prepared and submitted this report (Residual Risk Report to
Congress, EPA-453/R-99-001) in March 1999. Congress did not act in
response to the report, thereby triggering the EPA's obligation under
CAA section 112(f)(2) to analyze and address residual risk.
    Section 112(f)(2) of the CAA requires us to determine, for source
categories subject to certain MACT standards, whether those emissions
standards provide an ample margin of safety to protect public health.
If the MACT standards apply to a source category emitting a HAP that is
``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 (CAA section 112(f)(2)(A)).
This requirement is procedural. It mandates that the EPA establish CAA
section 112(f) residual risk standards if certain risk thresholds are
not satisfied but does not determine the level of those standards. NRDC
v. EPA, 529 F. 3d at 1083. The second sentence of CAA section 112(f)(2)
sets out the substantive requirements for residual risk standards:
Protection of public health with an ample margin of safety based on the
EPA's interpretation of this standard in effect at the time of the CAA
amendments. Id. This refers to the Benzene NESHAP, described in the
next paragraph. The EPA may adopt residual risk standards equal to
existing MACT standards (or to standards adopted after the technology
review required by CAA section 112(d)(6)) if the EPA determines that
the existing standards are sufficiently protective, even if (for
example) excess cancer risks to a most exposed individual are not
reduced to less than 1 in 1 million. Id. at 1083, (``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''). Section 112(f)(2) of the CAA further
authorizes the EPA to adopt more stringent standards, if necessary,
``to prevent, taking into consideration costs, energy, safety and other
relevant factors, an adverse environmental effect.'' \1\
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    \1\ ``Adverse environmental effect'' is defined in CAA section
112(a)(7) 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.
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    As just noted, CAA section 112(f)(2) expressly preserves our use of
the two-step process for developing standards to address any residual
risk and our

interpretation of ``ample margin of safety'' developed in the 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
(Benzene NESHAP) (54 FR 38044, September 14, 1989). The first step in
this process is the determination of acceptable risk. The second step
provides for an ample margin of safety to protect public health, which
is the level at which the standards are set (unless a more stringent
standard is required to prevent, taking into consideration costs,
energy, safety and other relevant factors, an adverse environmental
effect).
    The terms ``individual most exposed,'' ``acceptable level,'' and
``ample margin of safety'' are not specifically defined in the CAA.
However, CAA section 112(f)(2)(B) preserves the EPA's interpretation
set out in the Benzene NESHAP, and the Court in NRDC v. EPA concluded
that the EPA's interpretation of CAA section 112(f)(2) is a reasonable
one. See NRDC v. EPA, 529 F.3d at 1083 (D. C. Cir. 2008), which says
``[S]ubsection 112(f)(2)(B) expressly incorporates 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, volume 1, p. 877 (Senate debate
on Conference Report). We also notified Congress in the Residual Risk
Report to Congress that we intended to use the Benzene NESHAP approach
in making CAA section 112(f) residual risk determinations (EPA-453/R-
99-001, p. ES-11).
    In the Benzene NESHAP, we stated as an overall objective:

* * * in protecting public health with an ample margin of safety, we
strive 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 facility would have
if he or she were exposed to the maximum pollutant concentrations
for 70 years.

    The agency also stated that, ``The 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.'' The agency
went on to conclude that ``estimated incidence would be weighed along
with other health risk information in judging acceptability.'' As
explained more fully in our Residual Risk Report to Congress, the EPA
does not define ``rigid line[s] of acceptability,'' but rather
considers broad objectives to be weighed with a series of other health
measures and factors (EPA-453/R-99-001, p. ES-11). 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'' (Residual Risk
Report to Congress, p. 178, quoting the D.C. Circuit's en banc Vinyl
Chloride decision at 824 F.2d 1165) 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 1 in 10 thousand, that risk level is considered
acceptable.'' 54 FR 38045. We discussed the maximum individual lifetime
cancer risk 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 acknowledge 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
maximum individual lifetime cancer risk as a metric for determining
acceptability, we acknowledged in the 1989 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. Id. Further, in the Benzene NESHAP, we
noted that, ``Particular 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 1989 Benzene NESHAP the following:
``In establishing a presumption for MIR [maximum individual cancer
risk], 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.
    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 explained in the Benzene NESHAP, ``[e]ven though
the risks judged ``acceptable'' by the EPA in the first step of the
Vinyl Chloride inquiry are already low, 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.''
    In NRDC v. EPA, 529 F.3d 1077, 1082 (D.C. Cir. 2008), the Court of
Appeals held that section 112(f)(2) ``incorporates EPA's
`interpretation' of the Clean Air Act from the Benzene Standard, and
the text of this provision draws no distinction between carcinogens and
non-carcinogens.'' Additionally, the

Court held there is nothing on the face of the statute that limits the
agency's section 112(f) assessment of risk to carcinogens. Id. at 1081-
82. In the NRDC case, the petitioners argued, among other things, that
section 112(f)(2)(B) applied only to non-carcinogens. The D.C. Circuit
rejected this position, holding that the text of that provision ``draws
no distinction between carcinogens and non-carcinogens,'' Id., and that
Congress' incorporation of the Benzene standard applies equally to
carcinogens and non-carcinogens.
    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. 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 CAA section 112(f). 54 FR
38046.

B. Does this action apply to me?

    The regulated industrial source category that is the subject of
this proposal is listed in Table 2 of this preamble. Table 2 of this
preamble is not intended to be exhaustive, but rather provides a guide
for readers regarding the entities likely to be affected by this
proposed action. This standard, and any changes considered in this
rulemaking, would be directly applicable to affected sources. Federal,
state, local and tribal government entities are not affected by this
proposed action. As defined in the Source Category Listing Report
published by the EPA in 1992, the pulp and paper production source
category includes any facility engaged in the production of pulp and/or
paper. This category includes, but is not limited to, integrated mills
(where pulp and paper or paperboard are manufactured on-site), non-
integrated mills (where either pulp or paper/paperboard are
manufactured on-site, but not both), and secondary fiber mills (where
waste paper is used as the primary raw material). Examples of pulping
methods include kraft, soda, sulfite, semi-chemical and mechanical.

    Table 2--NESHAP and Industrial Source Categories Affected By This
                             Proposed Action
------------------------------------------------------------------------
                                                 NAICS code   MACT code
       Source category              NESHAP          \1\          \2\
------------------------------------------------------------------------
Pulp and Paper...............  Pulp and Paper.          322       1626-1
------------------------------------------------------------------------
\1\ North American Industry Classification System.
\2\ Maximum Achievable Control Technology.

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

    In addition to being available in the docket, an electronic copy of
this proposal will also be available on the WWW through the EPA's TNN.
Following signature by the EPA Administrator, a copy of this proposed
action will be posted on the TTN's policy and guidance page for newly
proposed or promulgated rules at the following address: http://www.epa.gov/ttn/atw/rrisk/rtrpg.html. The TTN provides information and
technology exchange in various areas of air pollution control.
    Additional information is available on the RTR Web page at http://www.epa.gov/ttn/atw/rrisk/rtrpg.html. This information includes source
category descriptions and detailed emissions estimates and other data
that were used as inputs to the risk assessments.

D. 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 comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket. If
you submit a CD ROM or disk that does not contain CBI, mark the outside
of the disk or CD ROM clearly that it does not contain CBI. Information
not marked as CBI will be included in the public docket and the EPA's
electronic public docket without prior notice. Information marked as
CBI will not be disclosed except in accordance with procedures set
forth in 40 CFR part 2. Send or deliver information identified as CBI
only to the following address: Roberto Morales, OAQPS Document Control
Officer (C404-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, Attention Docket ID Number EPA-HQ-OAR-2007-0544.

II. Background

A. What is this source category and how did the MACT standard regulate
its HAP emissions?

    The pulp and paper production source category includes any facility
engaged in the production of pulp and/or paper. This category includes,
but is not limited to, integrated mills (where pulp and paper or
paperboard are manufactured on-site), non-integrated mills (where
paper/paperboard or pulp are manufactured, but not both), and secondary
fiber mills (where waste paper is used as the primary raw material).
The pulp and paper production process includes operations such as
pulping, bleaching, chemical recovery and papermaking. Different
pulping processes are used, including chemical processes (kraft, soda,
sulfite and semi-chemical) and mechanical, secondary fiber or non-wood
processes.
    The NESHAP from the pulp and paper Industry (or MACT rule) was
promulgated on April 15, 1998 (63 FR 18504) and codified at 40 CFR part
63, subpart S. As promulgated in 1998, the subpart S MACT standard
applies to major sources of HAP emissions from the pulp production
areas (e.g., pulping system vents, pulping process condensates) at
chemical, mechanical, secondary fiber and non-wood pulp mills;
bleaching operations; and papermaking systems. A separate NESHAP (40
CFR part 63, subpart MM) applicable to chemical recovery processes at
kraft, soda, sulfite and stand-alone semi-chemical pulp mills was
promulgated on January 12, 2001 (66 FR 3180). However, only subpart S
is undergoing the RTR that is the subject of this proposal.
    This is the first in a series of rules being developed for the pulp
and paper

industrial sector. This proposal includes both a risk assessment and a
technology review of the emission sources in subpart S, as well as a
risk assessment of the whole facility. The whole facility risk
assessment includes emissions from the other sources in the pulp and
paper industrial sector: boilers covered under subpart DDDDD, chemical
recovery systems covered under subpart MM, various sources covered
under the NSPS for kraft pulp mills (40 CFR part 60, subpart BB), and
other applicable MACT emission sources. In the future, we will also
conduct a RTR for the subpart MM category, as well as a review of the
kraft pulp mills NSPS, subpart BB. When we conduct the RTR for the
subpart MM rule, subpart S emission sources will be included in the
facilitywide risk assessment.
    According to results of the EPA's 2011 pulp and paper ICR, there
are a total of 171 major sources in the United States including:
     111 major sources that carry out chemical wood pulping
(kraft, sulfite, soda or semi-chemical);
     33 major sources that carry out mechanical, groundwood,
secondary fiber and non-wood pulping (without chemical wood pulping);
     94 major sources that perform bleaching; and
     156 major sources that manufacture paper or paperboard
products.
    Facilities in the category perform at least one of several pulp and
papermaking operations (e.g., chemical pulping, bleaching and
papermaking; pulping and unbleached papermaking; etc.).
    Subpart S includes numerical emission limits for pulping system
vents, pulping process condensates and bleaching system vents. The
control systems used by most mills to meet the subpart S emission
limits are as follows:
     Pulping system vents--thermal oxidizers, power boilers,
lime kilns and recovery furnaces.
     Pulping process condensates--steam strippers, biological
treatment and recycling to pulping equipment that is controlled by the
pulping vent standards.
     Bleaching system vents--caustic scrubbers (for chlorinated
HAPs, other than chloroform) and process modifications to eliminate the
use of chlorine and hypochlorite.
    Facilities that only purchase pre-consumer paper or paperboard
stock products and convert them into other products (i.e., converting
operations) are not part of the subpart S source category and are not
affected by today's action.

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

    In February 2011, the EPA issued an ICR, pursuant to CAA section
114, to United States pulp and paper manufacturers to gather
information needed to conduct the regulatory reviews required under CAA
sections 112(d)(6) and (f)(2). The ICR was divided into three parts,
with each part due on a different date. Part I requested available
information regarding subpart S process equipment, control devices,
pulp and paper production, bleaching and other aspects of facility
operations, to support the subpart S technology review and a later
review of the kraft pulp mills NSPS under 40 CFR part 60, subpart BB.
Part II requested updated inventory data for all pulp and paper
emission sources, to support the residual risk assessment for the pulp
and paper sector (including subparts S and MM) and to both supplement
and update the NEI for the source category. Part III requested
available information on subpart MM chemical recovery combustion
equipment, control devices, etc., to support a later subpart MM
technology review (which will include a source category and a
facilitywide risk assessment) and a subpart BB NSPS review. Responses
to all three parts of the ICR have been received and data from the
first two parts of the ICR have been compiled. The response rate for
the subpart S ICR was 100 percent.\2\
---------------------------------------------------------------------------

    \2\ Part II of the ICR will be available for download on the RTR
Web page at: http://www.epa.gov/ttn/atw/rrisk/rtrpg.html.
---------------------------------------------------------------------------

III. Analyses Performed

    In this section, we describe the analyses performed to support the
proposed decisions for the RTR for this source category.

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

    The EPA conducted risk assessments that provided estimates of (1)
the MIR posed by the HAP emissions from the 171 pulp and paper mills in
the source category, (2) the distribution of cancer and noncancer risks
within the exposed populations, (3) the total cancer incidence, (4)
estimates of the maximum TOSHI for chronic exposures to HAP with the
potential to cause chronic noncancer health effects, (5) worst-case
screening estimates of HQ for acute exposures to HAP with the potential
to cause noncancer health effects, and (6) an evaluation of the
potential for adverse environmental effects. The risk assessments
consisted of seven primary steps, as discussed below.\3\ The methods
used to assess risks (as described in the seven primary steps below)
are consistent with those peer-reviewed by a panel of the EPA's SAB in
2009 and described in their peer review report issued in 2010; they are
also consistent with the key recommendations contained in that report.
---------------------------------------------------------------------------

    \3\ The docket for this rulemaking contains the following
document which provides more information on the risk assessment
inputs and models: Draft Residual Risk Assessment for Pulp and Paper
Source Category.A27DE2.
---------------------------------------------------------------------------

1. Establishing the Nature and Magnitude of Actual Emissions and
Identifying the Emissions Release Characteristics
    As discussed in section II.B of this preamble, we used data from
Part II of the pulp and paper ICR as the basis for the risk assessment.
Part II of the ICR, which concluded in June 2011, targeted facilities
that are major sources of HAP emissions and involved an update of pre-
populated NEI data spreadsheets (or creation of new NEI datasets). The
NEI is a database that contains information about sources that emit
criteria air pollutants, their precursors and HAP. The NEI database
includes estimates of actual annual air pollutant emissions from point
and volume sources; emission release characteristic data such as
emission release height, temperature, diameter, velocity and flow rate;
and location latitude/longitude coordinates.
    The actual annual emissions data in the NEI database were based on
data from actual emissions tests and estimates of actual emissions
(based on emission factors) provided by subpart S sources surveyed in
Part II of the ICR. We received a comprehensive set of emissions test
data and emissions estimates that enabled us to conduct risk modeling
of detectable HAP emissions for all major source facilities in the pulp
and paper category.
    Two substantial QA efforts were conducted on the Part II data in
order to create the modeling files needed for the residual risk
assessment, which included: (1) QA of the updated inventory
spreadsheets submitted by each mill prior to import into the compiled
database; and (2) QA and standardization of the compiled database.
    We reviewed the NEI datasets to ensure that the major pulp and
paper processes and pollutants were included and properly identified,
to ensure that emissions from the various processes were allocated to
the correct source category (e.g., MACT code 1626-1), and to identify
emissions and other data anomalies that could affect risk

estimates. We also standardized the various codes (e.g., SCCs,
pollutant codes), eliminated duplicate records and checked geographic
coordinates. We reviewed emissions release parameters for data gaps and
errors, assigned the proper default parameters where necessary,
segregated the emission points into logical emission process groups and
ensured that fugitive release dimensions were specified or given
default values where necessary. We made changes based on available
information, including updated information voluntarily submitted by
pulp and paper mills.\4\
---------------------------------------------------------------------------

    \4\ For more information, see the memorandum in the docket
titled, Inputs to the Pulp and Paper Industry October 2011 Residual
Risk Modeling.
---------------------------------------------------------------------------

    We assigned emissions process groups to distinguish between
processes with related SCCs. For mills with VOC emissions data but no
HAP emissions data, we developed HAP-to-VOC ratios to estimate HAP
emissions, using HAP and VOC emission factors provided by NCASI.\5\
However, as noted above, most emissions factors were based on actual
tests or actual tests conducted at similar sources (see NCASI Technical
Bulletin No. 973).\6\ Additionally, the largest HAP emission compound
in the category, methanol, at approximately 86 percent of the HAP in
the category, is required to be quantified in each compliance test
referenced in the standard. Consequently, the greatest proportion of
HAP emissions at each facility are based on emission factors derived
from actual source specific tests.
---------------------------------------------------------------------------

    \5\ Ibid.
    \6\ A. Someshwar, NCASI. Compilation of ``Air Toxic'' and Total
Hydrocarbon Emissions Data for Pulp and Paper Mill Sources--A Second
Update. Technical Bulletin No. 973. February 2010.
---------------------------------------------------------------------------

    For purposes of risk modeling, we reviewed emissions data for
chromium, mercury, POM and glycol ether in order to properly speciate
emissions. Chromium emissions were speciated as hexavalent chromium
(chromium VI) and trivalent chromium (chromium III).\7\ Mercury
emissions were speciated as particulate divalent mercury, gaseous
divalent mercury and elemental gaseous mercury.\8\ Total POM emissions
were speciated differently for each emission unit type (e.g., gas- or
oil-fired paper machine dryers) based on the most common POM compounds
emitted from that unit (e.g., phenanthrene, fluorene, pyrene,
fluoranthene and/or 2-methylnaphthalene). We speciated all total glycol
ether records as 1,2-dimethoxyethane, since this pollutant represents
99 percent of all emissions reported under the glycol ether compounds
category from pulp and paper emission sources.\9\ Acrolein emissions
were removed from the subpart S modeling file due to uncertainty in the
emissions estimates.\10\
---------------------------------------------------------------------------

    \7\ For more information, see the memorandum in the docket
titled, Inputs to the Pulp and Paper Industry October 2011 Residual
Risk Modeling.
    \8\ Ibid.
    \9\ Ibid.
    \10\ Ibid.
---------------------------------------------------------------------------

    In addition, we reviewed facilitywide data included in the NEI
dataset from the EPA's TRI to ensure that combustion-related dioxin/
furan emissions were apportioned to the proper MACT code (0107 or 1626-
2). As expected, there were no dioxin/furan emissions data for subpart
S sources (MACT code 1626-1).\11\
---------------------------------------------------------------------------

    \11\ Ibid.A27DE2.
---------------------------------------------------------------------------

    The Part II NEI emissions dataset for the pulp and paper (subpart
S) source category shows 45,000 tpy of total HAP emissions from the 171
mills in the dataset. Methanol, acetaldehyde, cresol/cresylic acid
(mixed isomers), phenol, chloroform, formaldehyde, hydrochloric acid,
biphenyl, hexachloroethane, xylenes, propionaldehyde and 1,2,4-
trichlorobenzene account for the majority of the HAP emissions reported
for pulp and paper production (approximately 43,900 tpy, or 97
percent). The remaining 3 percent of the HAP, reported in lesser
quantities, include acetophenone, benzene, cumene, carbon disulfide,
chlorine, methyl isobutyl ketone, methylene chloride (dichloromethane),
naphthalene, styrene, tetrachloroethylene (perchloroethylene), toluene,
trichloroethylene and 56 others. Methanol, which accounts for about 86
percent of the total HAP mass emissions, is the HAP emitted by the
largest number of facilities, with methanol reported for 166 out of 171
mills in the dataset (or 97 percent). Emissions of the following PB-HAP
were identified in the emissions inventory for the pulp and paper
(subpart S) source category: cadmium compounds, lead compounds, mercury
compounds and POM. As a standard practice in conducting risk
assessments for source categories, the EPA conducts a two-step process:
(1) Are PB-HAPs being emitted; and (2) are they being released above
screening thresholds? If these releases are significantly above the
screening thresholds and the EPA has detailed information on the
releases and the site, a complete multipathway analysis of the site
will be conducted to estimate pathway risks for the source category.
Further information about the analysis performed for this category
follows in section III.B.4 of this preamble.
2. Establishing the Relationship Between Actual Emissions and MACT-
Allowable Emissions Levels
    The available emissions data in the Part II NEI emissions dataset
include estimates of the mass of HAP actually emitted during the 2009
time period covered under the survey. These ``actual'' emissions levels
are often lower than the emissions levels that a facility might be
allowed to emit and still comply with the MACT standards. The emissions
levels allowed to be emitted by the MACT standards are referred to as
the ``MACT-allowable'' emissions levels. These represent the highest
emissions levels that could be emitted by the facility without
violating the MACT standards.
    We discussed the use of both MACT-allowable and actual emissions in
the final Coke Oven Batteries residual risk rule (70 FR 19998-19999,
April 15, 2005) and in the proposed and final HON 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 at which sources could emit while still
complying with the MACT standards. However, we also explained that it
is reasonable to consider actual emissions, where such data are
available, in both steps of the risk analysis, in accordance with the
Benzene NESHAP (54 FR 38044, September 14, 1989). It is reasonable to
consider actual emissions because sources typically seek to perform
better than required by emissions standards to provide an operational
cushion to accommodate the variability in manufacturing processes and
control device performance. Facilities' actual emissions may also be
significantly lower than MACT-allowable emissions for other reasons
such as state requirements, better performance of control devices than
required by the MACT standards or reduced production.
    As described earlier in this section, actual emissions were based
on the Part II NEI emissions dataset. To estimate emissions at the
MACT-allowable level, we developed a ratio of MACT-allowable to actual
emissions for each source type for the facilities in the source
category. This ratio is based on the level of control required by the
subpart S MACT standards compared to the level of reported actual
emissions and available information from the Part I survey on the level
of control achieved by the emissions controls in use. For example, if
survey data indicated that

an emission point type was being controlled by 92 percent, while the
MACT standard required only 87 percent control, we would estimate that
MACT-allowable emissions from that emission point type could be as much
as 1.6 times higher (13 percent allowable emissions compared with 8
percent actually emitted), and the ratio of MACT-allowable to actual
would be 1.6:1 for this emission point type.\12\
---------------------------------------------------------------------------

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

    After developing these ratios for each emission point type in this
source category, we next applied these ratios on an emission process
unit basis to the Part II actual emissions data to obtain risk
estimates based on MACT-allowable emissions.\13\
---------------------------------------------------------------------------

    \13\ Ibid.
---------------------------------------------------------------------------

3. Conducting Dispersion Modeling, Determining Inhalation Exposures and
Estimating Individual and Population Inhalation Risks
    Both long-term and short-term inhalation exposure concentrations
and health risks from the source category addressed in this proposal
were estimated using the HEM-3 human exposure model. The HEM-3 performs
three of the primary risk assessment activities listed above: (1)
Conducting dispersion modeling to estimate the concentrations of HAP in
ambient air, (2) estimating long-term and short-term inhalation
exposures to individuals residing within 50 km of the modeled sources,
and (3) estimating individual and population-level inhalation risks
using the exposure estimates and quantitative dose-response
information.
    The dispersion model used by HEM-3 is AERMOD, which is one of the
EPA's preferred models for assessing pollutant concentrations from
industrial facilities.\14\ 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 of hourly
surface and upper air observations for 130 meteorological stations,
selected to provide coverage of the United States and Puerto Rico. A
second library of United States Census Bureau census block \15\
internal point locations and populations provides the basis of human
exposure calculations based on the year 2000 U.S. Census. 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.
---------------------------------------------------------------------------

    \14\ 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).
    \15\ A census block is generally 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 concentration of each of the
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 primarily used as a surrogate for the chronic inhalation
exposure concentration for all the people who reside in that census
block. There were two exceptions to this. In those cases where we
identified census block centroids which were located on-site, these
centroids were re-assigned to a nearby residential location. In those
cases where nearby census blocks were abnormally large, additional
residential receptors were placed within those census blocks at
observable residences to ensure an adequate representation of chronic
risks to the nearby residences. 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 an inhabited
census block. 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) by its URE, which is an upper
bound estimate of an individual's probability of contracting cancer
over a lifetime of exposure to a concentration of 1 microgram of the
pollutant per cubic meter of air. In general, for residual risk
assessments, we use URE values from the EPA's IRIS.\16\ For
carcinogenic pollutants without the EPA IRIS values, we look to other
reputable sources of cancer dose-response values, often using CalEPA
URE values, where available. In cases where new, scientifically
credible dose-response values have been developed in a manner
consistent with EPA guidelines and have undergone a peer review process
similar to that used by the EPA, we may use such dose-response values
in place of, or in addition to, other values, if appropriate.
---------------------------------------------------------------------------

    \16\ The IRIS information is available at http://www.epa.gov/IRIS.
---------------------------------------------------------------------------

    In 2004, the EPA determined that the CIIT cancer dose-response
value for formaldehyde (5.5 x 10-9 per [mu]g/m\3\) was based
on better science than the IRIS dose-response value (1.3 x
10-5 per [mu]g/m\3\), and we switched from using the IRIS
value to the CIIT value in risk assessments supporting regulatory
actions. Based on subsequent published research, however, the EPA
changed its determination regarding the CIIT model, and, in 2010, the
EPA returned to using the 1991 IRIS value. The NAS completed its review
of the EPA's draft assessment in April of 2011 (http://www.nap.edu/catalog.php?record id=13142), and the EPA has been working on revising
the formaldehyde assessment. The EPA will follow the NAS Report
recommendations and will present results obtained by implementing the
BBDR model for formaldehyde. The EPA will compare these estimates with
those currently presented in the External Review draft of the
assessment and will discuss their strengths and weaknesses. As
recommended by the NAS committee, appropriate sensitivity and
uncertainty analyses will be an integral component of implementing the
BBDR model. The draft IRIS assessment will be revised in response to
the NAS peer review and public comments and the final assessment will
be posted on the IRIS database. In the interim, we will present
findings using the 1991 IRIS value as a primary estimate and may also
consider other information as the science evolves.
    We note here that POM, a carcinogenic HAP with a mutagenic mode of
action, is emitted by some of the facilities in this category.\17\ For
this compound,\18\ the ADAF described in the EPA's Supplemental
Guidance for Assessing Susceptibility from Early-Life Exposure to
Carcinogens \19\ were applied. This adjustment has the effect of
increasing the estimated lifetime risks for this pollutant by a factor
of 1.6. In addition, although only a small fraction

of the total POM emissions were not reported as individual compounds,
the EPA expresses carcinogenic potency for compounds in this group in
terms of benzo[a]pyrene equivalence, based on evidence that
carcinogenic POM has the same mutagenic mechanism of action as does
benzo[a]pyrene. For this reason, the EPA's Science Policy Council \20\
recommends applying the Supplemental Guidance to all carcinogenic
polycyclic aromatic hydrocarbons for which risk estimates are based on
relative potency. Accordingly, we have applied the ADAF to the
benzo[a]pyrene equivalent portion of all POM mixtures.
---------------------------------------------------------------------------

    \17\ U.S. EPA, 2006. Performing risk assessments that include
carcinogens described in the Supplemental Guidance as having a
mutagenic mode of action. Science Policy Council Cancer Guidelines
Implementation Work Group Communication II: Memo from W.H. Farland,
dated June 14, 2006.
    \18\ See the Risk Assessment for Source Categories document
available in the docket for a list of HAP with a mutagenic mode of
action.
    \19\ U.S. EPA, 2005. Supplemental Guidance for Assessing Early-
Life Exposure to Carcinogens. EPA/630/R-03/003F. http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf.
    \20\ U.S. EPA, 2006. Science Policy Council Cancer Guidelines
Implementation Workgroup Communication II: Memo from W.H. Farland,
dated June 14, 2006.
---------------------------------------------------------------------------

    Incremental individual lifetime cancer risks associated with
emissions from the source category were estimated 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 \21\) emitted by the
modeled source. Cancer incidence and the distribution of individual
cancer risks for the population within 50 km of the source were also
estimated for the source category as part of these assessments by
summing individual risks. A distance of 50 km is consistent with both
the analysis supporting the 1989 Benzene NESHAP (54 FR 38044) and the
limitations of Gaussian dispersion models, including AERMOD.
---------------------------------------------------------------------------

    \21\ 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
NATA titled, NATA--Evaluating the National-scale Air Toxics
Assessment 1996 Data--an SAB Advisory, available at: http://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
---------------------------------------------------------------------------

    To assess risk of noncancer 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 TOSHI). The HQ
is the estimated exposure divided by the chronic reference value, which
is either the EPA RfC, defined as ``an estimate (with uncertainty
spanning perhaps an order of magnitude) of a continuous inhalation
exposure to the human population (including sensitive subgroups) that
is likely to be without an appreciable risk of deleterious effects
during a lifetime,'' or, in cases where a RfC is not available, the
ATSDR chronic MRL or the CalEPA Chronic REL. The REL is defined as
``the concentration level at or below which no adverse health effects
are anticipated for a specified exposure duration.'' As noted above, in
cases where new, scientifically credible dose-response values have been
developed in a manner consistent with EPA guidelines and have undergone
a peer review process similar to that used by the EPA, we may use those
dose-response values in place of or, in addition to, other values.
    Worst-case screening estimates of acute exposures and risks were
also evaluated for each of the HAP at the point of highest offsite
exposure for each facility (i.e., not just the census block centroids)
assuming that a person was located at this spot at a time when both the
peak (hourly) emission rate and hourly dispersion conditions occurred.
In general, acute HQ values were calculated using best available,
short-term dose-response value. These acute dose-response values
include REL, AEGL and ERPG for 1-hour exposure durations. As discussed
below, we used conservative assumptions for emission rates, meteorology
and exposure location for our acute analysis.
    As described in the CalEPA's Air Toxics Hot Spots Program Risk
Assessment Guidelines, Part I, The Determination of Acute Reference
Exposure Levels for Airborne Toxicants, an acute REL value (http://www.oehha.ca.gov/air/pdf/acuterel.pdf) is defined as ``the
concentration level at or below which no adverse health effects are
anticipated for a specified exposure duration.'' Reference exposure
level values are based on the most sensitive, relevant, adverse health
effect reported in the medical and toxicological literature. Reference
exposure level values are designed to protect the most sensitive
individuals in the population by the inclusion of margins of safety.
Since margins of safety are incorporated to address data gaps and
uncertainties, exceeding the REL does not automatically indicate an
adverse health impact.
    Acute Exposure Guideline Levels were derived in response to
recommendations from the 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/opptintr/aegl/pubs/sop.pdf),\22\ ``the NRC's previous name for acute exposure
levels--CEEL--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.'' 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 8
hours.'' The document lays out the purpose and objectives of AEGL by
stating (page 21) that ``the primary purpose of the AEGL program and
the NAC/AEGL Committee is to develop guideline levels for once-in-a-
lifetime, short-term exposures to airborne concentrations of acutely
toxic, high-priority chemicals.'' In detailing the intended application
of AEGL values, the document states (page 31) that ``[i]t is
anticipated that the AEGL values will be used for regulatory and
nonregulatory purposes by United States 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.''
---------------------------------------------------------------------------

    \22\ NAS, 2001. Standing Operating Procedures for Developing
Acute Exposure Levels for Hazardous Chemicals, page 2.
---------------------------------------------------------------------------

    The AEGL-1 value is then specifically defined as ``the airborne
concentration of a substance above which it is predicted that the
general population, including susceptible individuals, could experience
notable discomfort, irritation, or certain asymptomatic nonsensory
effects. However, the effects are not disabling and are transient and
reversible upon cessation of exposure.'' The document also notes (page
3) 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.'' Similarly, the document defines
AEGL-2 values as ``the airborne concentration (expressed as ppm or mg/
m\3\) 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.''
    Emergency Response Planning Guidelines values are derived for use
in emergency response, as described in the American Industrial Hygiene

Association's document titled, Emergency Response Planning Guidelines
(ERPG) Procedures and Responsibilities (http://www.aiha.org/1documents/committees/ERPSOPs2006.pdf) which states that, ``Emergency Response
Planning Guidelines were developed for emergency planning and are
intended as health-based guideline concentrations for single exposures
to chemicals.'' \23\ 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.'' 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 1 hour
without experiencing or developing irreversible or other serious health
effects or symptoms which could impair an individual's ability to take
protective action.''
---------------------------------------------------------------------------

    \23\ ERP Committee Procedures and Responsibilities. November 1,
2006. American Industrial Hygiene Association.
---------------------------------------------------------------------------

    As can be seen from the definitions above, the AEGL and ERPG values
include the similarly-defined severity levels 1 and 2. For many
chemicals, a severity level 1 value AEGL or ERPG has not been
developed; in these instances, higher severity level AEGL-2 or ERPG-2
values are compared to our modeled exposure levels to screen for
potential acute concerns.
    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
threshold (usually the AEGL-1 and/or the ERPG-1 value).
    To develop screening estimates of acute exposures, we first
developed estimates of maximum hourly emission rates by multiplying the
average actual annual hourly emission rates by a factor to cover
routinely variable emissions. An acute multiplication factor of 1.6 was
used for papermaking equipment (e.g., paper machines, stock
preparation, repulping) based on a paper machine peak-to-mean analysis.
Similarly, a peak-to-mean multiplier of 2 was used for pulp and paper
wastewater treatment units based on analysis of data from pulp and
paper primary clarifiers and aerated stabilization basins. Peak-to-mean
multipliers ranging from 1 to 3.1 were developed for other types of
pulp and paper equipment based on the routine annual emissions data and
peak hourly emissions data obtained from Part II survey data.\24\
---------------------------------------------------------------------------

    \24\ More information supporting the use of these factors for
Pulp and Paper production is presented in the memorandum, Inputs to
the Pulp and Paper Industry October 2011 Residual Risk Modeling,
which is available in the docket for this action.
---------------------------------------------------------------------------

    In cases where all acute HQ values from the screening step were
less than or equal to 1, acute impacts were deemed negligible and no
further analysis was performed. In the 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. The data refinements included using site-
specific facility layouts, as available, to distinguish facility
property from an area where the public could access and be exposed.
These refinements are discussed in the draft risk assessment documents,
which are available in the docket for this source category. 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 emission rates over a year would allow us to
perform a probabilistic analysis to estimate potential threshold
exceedances and their frequency of occurrence. Such an evaluation could
include a more complete statistical treatment of the key parameters and
elements adopted in this screening analysis. However, we recognize that
having this level of data is rare, and hence our use of the multiplier
approach.
4. Multipathway Exposure and Risk Screening
    The potential for significant human health risks due to exposures
via routes other than inhalation (i.e., multipathway exposures) and the
potential for adverse environmental impacts were evaluated in a three-
step process. In the first step, we determined whether any facilities
emitted any HAP known to be persistent and bio-accumulative in the
environment (PB-HAP). There are 14 PB-HAP compounds or compound classes
identified for this screening in the EPA's Air Toxics Risk Assessment
Library (available at http://www.epa.gov/ttn/fera/risk_atra_vol1.html). They are cadmium compounds, chlordane, chlorinated
dibenzodioxins and furans, dichlorodiphenyldichloroethylene,
heptachlor, hexachlorobenzene, hexachlorocyclohexane, lead compounds,
mercury compounds, methoxychlor, polychlorinated biphenyls, POM,
toxaphene and trifluralin. Emissions of four different PB-HAP were
identified in the Part II NEI emissions dataset for the pulp and paper
(subpart S) source category: cadmium compounds, lead compounds, mercury
compounds and POM. These four compounds plus chlorinated dibenzodioxins
and furans were identified in the NEI dataset for the entire mill,
which includes sources inside and outside the subpart S category (e.g.,
boilers, chemical recovery combustion sources). In the second step of
the screening process, 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 or
environmental risks. To facilitate this step, we have developed
emission rate thresholds for each PB-HAP using a hypothetical screening
exposure scenario developed for use in conjunction with the TRIM.FaTE
model. The hypothetical screening scenario was subjected to a
sensitivity analysis to ensure that its key design parameters were
established such that environmental media concentrations were not
underestimated (i.e., to minimize the occurrence of false negatives or
results that suggest that risks might be acceptable when, in fact,
actual risks are high), and to also minimize the occurrence of false
positives for human health endpoints. We call this application of the
TRIM.FaTE model TRIM-Screen. The facility specific emission rates of
each of the PB-HAP in each source category were compared to the
emission threshold values for each of the PB-HAP identified in the
source category datasets.
    For all of the facilities in the source category addressed in this
proposal, all of the PB-HAP emission rates were less than the emission
threshold values, except for one facility with POM emissions as
benzo(a)pyrene that exceeded the screening emission rate by a factor of
2. For POM, exceeding the screening emission rate relates to a
potential for creating a cancer risk in excess of 1 in a million. In
performing the screening for potential multipathway exposures and risks
of

concern, we determined that emissions of POM were not significant
enough to pose multipathway impacts of concern for human health or the
environment. If the emission rates of the PB-HAP had been determined to
be significant, the source category would have been further evaluated
for potential non-inhalation risks and adverse environmental effects in
a third step through site-specific refined assessments using the EPA's
TRIM.FaTE model.
    For further information on the multipathway analysis approach, see
the residual risk documentation as referenced in section IV.A of this
preamble.
5. Assessing Risks Considering Emissions Control Options
    This rulemaking does not require the installation of any new
emission controls to reduce risk; therefore, no risk modeling was
conducted to estimate risk reductions following installation of
emission controls for this proposal.
6. Conducting Facilitywide Risk Assessments
    To put the source category risks in context, we also 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 of interest but also emissions of HAP from all other
emissions sources at the facility. Nearly all 171 major sources in the
subpart S category include boilers, and 111 of the 171 major sources
include chemical recovery combustion sources (e.g., recovery furnace,
smelt dissolving tank, lime kiln). Pulp and paper mills also include
paper coating, landfills, petroleum storage and transfer and other
operations. Therefore, where data were available, we performed a
facilitywide risk assessment for these major sources as part of today's
action.
    We estimated the risks due to the inhalation of HAP that are
emitted ``facilitywide'' for the populations residing within 50 km of
each facility, consistent with the methods used for the source category
analysis described above. For these facilitywide risk analyses, the
modeled source category risks were compared to the facilitywide risks
to determine the portion of facilitywide risks that could be attributed
to the source categories addressed in this proposal. We specifically
examined the facilities associated with the highest estimates of risk
and determined the percentage of that risk attributable to the source
category of interest. The risk documentation available through the
docket for this action provides all the facilitywide risks and the
percentage of source category contribution for all source categories
assessed.
    The methodology and the results of the facilitywide analyses for
each source category are included in the residual risk documentation as
referenced in section IV.A of this preamble, which is available in the
docket for this action.
7. Considering Uncertainties in Risk Assessment
    Uncertainty and the potential for bias are inherent in all risk
assessments, including that performed for the source category addressed
in this proposal. Although uncertainty exists, we believe the approach
that we took, which used conservative tools and assumptions to bridge
data gaps, ensures that our decisions are health-protective. A brief
discussion of the uncertainties in the emissions dataset, dispersion
modeling, inhalation exposure estimates and dose-response relationships
follows below.\25\
---------------------------------------------------------------------------

    \25\ A more thorough discussion of these uncertainties is
included in the risk assessment documentation (Draft Residual Risk
Assessment for the Pulp and Paper Category) available in the docket
for this action.
---------------------------------------------------------------------------

a. Uncertainties in the Emissions Dataset
    Although the development of the RTR dataset involved QA/QC
processes, the accuracy of emissions values will vary depending on: (1)
The source of the data, (2) the degree to which data are incomplete or
missing, (3) the degree to which assumptions made to complete the
datasets are accurate, (4) whether and to what extent errors were made
in estimating emissions values, (5) whether the emissions were based on
or extrapolated from stack tests or estimates of fugitive emissions,
and (6) miscellaneous other factors.
    The annual HAP emissions estimates used in the risk assessment are
derived from data provided by mills in response to the Part II survey.
Many of these emissions estimates are based on emission factors,
developed from the most comprehensive dataset available for this
industry, provided by NCASI. The uncertainties associated with emission
factors include the uncertainties in the measurement of the data,
limitations in the size and quality of the dataset, the presence of
non-detects and outliers in the dataset, the emission factor
calculations used, etc. As noted in section III.A.1 of this preamble,
acrolein emissions were not modeled due to uncertainties in the
emissions estimates.\26\
---------------------------------------------------------------------------

    \26\ For more information, see the memorandum in the docket
titled, Inputs to the Pulp and Paper Industry October 2011 Residual
Risk Modeling.
---------------------------------------------------------------------------

b. Uncertainties in Dispersion Modeling
    Although the analysis employed the EPA's recommended regulatory
dispersion model, AERMOD, we recognize that there is uncertainty in
ambient concentration estimates associated with any model, including
AERMOD. In circumstances where we had to choose between various model
options, where possible, we selected model options (e.g., rural/urban,
plume depletion, chemistry) that provided an overestimate of ambient
concentrations of the HAP rather than an underestimate. However,
because of practicality and data limitation reasons, some factors
(e.g., building downwash) have the potential in some situations to
overestimate or underestimate ambient impacts. Despite these
uncertainties, we believe that at offsite locations and census block
centroids, the approach considered in the dispersion modeling analysis
should generally yield overestimates of ambient HAP concentrations.
c. Uncertainties in Inhalation Exposure
    The effects of human mobility on exposures were not included in the
assessment. Specifically, short-term mobility and long-term mobility
between census blocks in the modeling domain were not considered.\27\
The assumption of not considering short- or long-term population
mobility does not bias the estimate of the theoretical MIR, nor does it
affect the estimate of cancer incidence since 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 risk
levels.
---------------------------------------------------------------------------

    \27\ Short-term mobility is movement from one microenvironment
to another over the course of hours or days. Long-term mobility is
movement from one residence to another over the course of a
lifetime.
---------------------------------------------------------------------------

    In addition, the assessment predicted the chronic exposures at the
centroid of each populated census block as surrogates for the exposure
concentrations for all people living in that block. Using the census
block centroid to predict chronic exposures tends to over-predict
exposures for people in the census block who live

farther from the facility and under-predict exposures for people in the
census block who live closer to the facility. Thus, using the census
block centroid to predict chronic exposures may lead to a potential
understatement or overstatement of the true maximum impact for any one
individual but is an unbiased estimate of average risk and incidence.
    The assessments evaluate the projected cancer inhalation risks
associated with pollutant exposures over a 70-year period, which is the
assumed lifetime of an individual. In reality, both the length of time
that modeled emissions sources at facilities actually operate (i.e.,
more or less than 70 years), and the domestic growth or decline of the
modeled industry (i.e., the increase or decrease in the number or size
of United States 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 rare cases, where a facility
maintains or increases its emissions levels beyond 70 years, residents
live beyond 70 years at the same location and the residents spend most
of their days at that location, then the risks could potentially be
underestimated. Annual cancer incidence estimates from exposures to
emissions from these sources would not be affected by uncertainty in
the length of time emissions sources operate.
    The exposure estimates used in these analyses assume chronic
exposures to ambient 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, these
levels are typically lower. This factor has the potential to result in
an overstatement of 25 to 30 percent of exposures for some HAP.\28\
---------------------------------------------------------------------------

    \28\ U.S. EPA. National-Scale Air Toxics Assessment for 1996.
EPA 453/R-01-003; January 2001; page 85.
---------------------------------------------------------------------------

    In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that should
be highlighted. The accuracy of an acute inhalation exposure assessment
depends on the simultaneous occurrence of independent factors that may
vary greatly, such as hourly emissions rates, meteorology and human
activity patterns. In this assessment, we assume that individuals
remain for 1 hour at the point of maximum ambient concentration as
determined by the co-occurrence of peak emissions and worst-case
meteorological conditions. These assumptions would tend to be worst-
case actual exposures since it is unlikely that a person would be
located at the point of maximum exposure during the time of worst-case
impact.
d. Uncertainties in Dose-Response Relationships
    There are uncertainties inherent in the development of the dose-
response values used in our risk assessments for cancer effects from
chronic exposures and noncancer 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 residual risk documentation which is available in the docket for
this action.
    Cancer URE values used in our risk assessments are those that have
been developed to generally provide an upper bound estimate of risk.
That is, they represent a ``plausible upper limit to the true value of
a quantity'' (although this is usually not a true statistical
confidence limit).\29\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances the risk could be
greater.\30\ 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).
---------------------------------------------------------------------------

    \29\ IRIS glossary (http://www.epa.gov/NCEA/iris/help_gloss.htm).
    \30\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible and which is based on maximum
likelihood estimates.
---------------------------------------------------------------------------

    Chronic noncancer reference (RfC and 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 UF approach (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,\31\ e.g., factors of 10 or 3, used in the absence of compound-
specific data; where data are available, UF may also be developed using
compound-specific information. When data are limited, more assumptions
are needed and more UF are used. Thus, there may be a greater tendency
to overestimate risk in the sense that further study might support
development of reference values that are higher (i.e., less potent)
because fewer default assumptions are needed. However, for some
pollutants, it is possible that risks may be underestimated. While
collectively termed ``UF,'' these factors account for a number of
different quantitative considerations when using observed animal
(usually rodent) or human toxicity data in the development of the RfC.
The UF are intended to account for:

(1) Variation in susceptibility among the members of the human
population (i.e., inter-individual variability); (2) uncertainty in
extrapolating from experimental animal data to humans (i.e.,
interspecies differences); (3) uncertainty in extrapolating from data
obtained in a study with less-than-lifetime exposure (i.e.,
extrapolating from sub-chronic to chronic exposure); (4) uncertainty in
extrapolating the observed data to obtain an estimate of the exposure
associated with no adverse effects; and (5) uncertainty when the
database is incomplete or there are problems with the applicability of
available studies. Many of the UF used to account for variability and
uncertainty in the development of acute reference values are quite
similar to those developed for chronic durations, but they more often
use individual UF values that may be less than 10. Uncertainty factors
are applied based on chemical-specific or health effect-specific
information (e.g., simple irritation effects do not vary appreciably
between human individuals, hence a value of 3 is typically used), or
based on the purpose for the reference value (see the following
paragraph). The UF applied in acute reference value derivation include:
(1) Heterogeneity among humans; (2) uncertainty in extrapolating from
animals to humans; (3) uncertainty in lowest observed adverse effect
(exposure) level to no observed adverse effect (exposure) level
adjustments; and (4) uncertainty in accounting for an incomplete
database on toxic effects of potential concern. Additional adjustments
are often applied to account for uncertainty in extrapolation from
observations at one exposure duration (e.g., 4 hours) to derive an
acute reference value at another exposure duration (e.g., 1 hour).
---------------------------------------------------------------------------

    \31\ According to the NRC report, Science and Judgment in Risk
Assessment (NRC, 1994) ``[Default] options are generic approaches,
based on general scientific knowledge and policy judgment, that are
applied to various elements of the risk assessment process when the
correct scientific model is unknown or uncertain.'' The 1983 NRC
report, Risk Assessment in the Federal Government: Managing the
Process, defined default option as ``the option chosen on the basis
of risk assessment policy that appears to be the best choice in the
absence of data to the contrary'' (NRC, 1983a, p. 63). Therefore,
default options are not rules that bind the agency; rather, the
agency may depart from them in evaluating the risks posed by a
specific substance when it believes this to be appropriate. In
keeping with the EPA's goal of protecting public health and the
environment, default assumptions are used to ensure that risk to
chemicals is not underestimated (although defaults are not intended
to overtly overestimate risk). See EPA, 2004, An Examination of EPA
Risk Assessment Principles and Practices, EPA/100/B-04/001 available
at: http://www.epa.gov/osa/pdfs/ratf-final.pdf.
---------------------------------------------------------------------------

    Not all acute reference values are developed for the same purpose,
and care must be taken when interpreting the results of an acute
assessment of human health effects relative to the reference value or
values being exceeded. Where relevant to the estimated exposures, the
lack of short-term dose-response values at different levels of severity
should be factored into the risk characterization as potential
uncertainties.
    Although every effort is made to identify peer-reviewed reference
values for cancer and noncancer effects for all pollutants emitted by
the sources included in this assessment, some HAP continue to have no
reference values for cancer or chronic noncancer or acute effects.
Since exposures to these pollutants cannot be included in a
quantitative risk estimate, an understatement of risk for these
pollutants at environmental exposure levels is possible. For a group of
compounds that are either unspeciated or do not have reference values
for every individual compound (e.g., glycol ethers), we conservatively
use the most protective reference value to estimate risk from
individual compounds in the group of compounds.
    Additionally, chronic reference values for several of the compounds
included in this assessment are currently under the EPA IRIS review
(e.g., formaldehyde), and revised assessments may determine that these
pollutants are more or less potent than the current value. We may re-
evaluate residual risks for the final rulemaking if these reviews are
completed prior to our taking final action for this source category and
if a dose-response metric changes enough to indicate that the risk
assessment supporting this notice may significantly understate human
health risk.
e. Uncertainties in the Multipathway and Environmental Effects
Screening
    We generally assume that when exposure levels are not anticipated
to adversely affect human health, they also are not anticipated to
adversely affect the environment. For each source category, we
generally rely on the site-specific levels of PB-HAP emissions to
determine whether a full assessment of the multipathway and
environmental effects is necessary. Our screening methods use worst-
case scenarios to determine whether multipathway impacts might be
important. The results of such a process are biased high for the
purpose of screening out potential impacts. Thus, when individual
pollutants or facilities screen out, we are confident that the
potential for multipathway impacts is negligible. On the other hand,
when individual pollutants or facilities do not screen out, it does not
mean that multipollutant impacts are significant, only that we cannot
rule out that possibility. The site-specific PB-HAP emission levels
were almost all far below levels which would trigger a refined
assessment of multipathway impacts. The only PB-HAP to exceed the
screening threshold was POM with emissions exceeding the screening
threshold by a factor of 2. Thus, we are confident that these types of
impacts are insignificant for the facilities in this source category.

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

    As discussed in the previous section of this preamble, we apply a
two-step process for determining whether to develop standards to
address residual risk. In the first step, the EPA determines whether
risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive level on maximum individual lifetime [cancer] risk (MIR)
\32\ of approximately one in 10 thousand [i.e., 100 in 1 million].'' 54
FR 38045. In the second step of the process, the EPA determines what
level of the standard is needed to provide an ample margin of safety
``in consideration of all health information, including the number of
persons at risk levels higher than approximately one in one million, as
well as other relevant factors, including costs and economic impacts,
technological feasibility, and other factors relevant to each
particular decision.'' Id.
---------------------------------------------------------------------------

    \32\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk were an individual exposed to the maximum level
of a pollutant for a lifetime.
---------------------------------------------------------------------------

    In past residual risk actions, the EPA presented and considered a
number of human health risk metrics associated with emissions from the
category under review, including: the MIR; the numbers of persons in
various risk ranges; cancer incidence; the maximum noncancer HI; and
the maximum acute noncancer hazard. See, e.g., 75 FR 65068, 65072-74
(October 21, 2010) and 76 FR 22566, 22575 (April 21, 2011). In
estimating risks, the EPA considered sources under review that are
located near each other and that affect the same population. The EPA
developed risk estimates based on the actual emissions from the source
category under review as well as based on the maximum emissions allowed
pursuant to the source category MACT standards. The EPA also discussed
and considered risk estimation uncertainties. The EPA is providing this
same type of information in support of this action.
    The agency is considering all available health information to
inform our determinations of risk acceptability and ample margin of
safety under CAA section 112(f). Specifically, as explained in the
Benzene NESHAP, ``the first step judgment on acceptability cannot be
reduced to any single factor'' and thus ``[t]he Administrator believes
that the acceptability of risk under [previous] section 112 is best
judged on the basis of a broad set of health risk measures and
information'' (54 FR 38046). Similarly, with regard to making the ample
margin of safety determination, as stated in the Benzene NESHAP, ``[in
the ample margin decision, the agency again considers all of the health
risk and other health information considered in the first step. Beyond
that information,

additional factors relating to the appropriate level of control will
also be considered, including cost and economic impacts of controls,
technological feasibility, uncertainties, and any other relevant
factors.'' Id.
    The agency acknowledges that the Benzene NESHAP provides
flexibility regarding what factors the EPA might consider in making
determinations and how they might be weighed for each source category.
In responding to comment on our policy under the Benzene NESHAP, the
EPA explained that: ``The policy chosen by the Administrator permits
consideration of multiple measures of health risk. Not only can the MIR
figure be considered, but also incidence, the presence of noncancer
health effects, and the uncertainties of the risk estimates. In this
way, the effect on the most exposed individuals can be reviewed as well
as the impact on the general public. These factors can then be weighed
in each individual case. This approach complies with the Vinyl Chloride
mandate that the Administrator ascertain an acceptable level of risk to
the public by employing [her] expertise to assess available data. It
also complies with the Congressional intent behind the CAA, which did
not exclude the use of any particular measure of public health risk
from the EPA's consideration with respect to CAA section 112
regulations, and, thereby, implicitly permits consideration of any and
all measures of health risk which the Administrator, in [her] judgment,
believes are appropriate to determining what will `protect the public
health.''' (54 FR at 38057).
    Thus, the level of the MIR is only one factor to be weighed in
determining acceptability of risks. The Benzene NESHAP explained that
``an MIR of approximately 1 in 10 thousand should ordinarily be the
upper end of the range of acceptability. As risks increase above this
benchmark, they become presumptively less acceptable under CAA section
112, and would be weighed with the other health risk measures and
information in making an overall judgment on acceptability. Or, the
agency may find, in a particular case, that a risk that includes MIR
less than the presumptively acceptable level is unacceptable in the
light of other health risk factors'' (Id. at 38045). Similarly, with
regard to the ample margin of safety analysis, the EPA stated in the
Benzene NESHAP that: ``* * * EPA believes the relative weight of the
many factors that can be considered in selecting an ample margin of
safety can only be determined for each specific source category. This
occurs mainly because technological and economic factors (along with
the health-related factors) vary from source category to source
category'' (Id. at 38061).

C. How did we perform the technology review?

    Our technology review focused on the identification and evaluation
of developments in practices, processes and control technologies that
have occurred since the 1998 NESHAP was promulgated. In cases where the
technology review identified such developments, we conducted an
analysis of the technical feasibility of applying these developments,
along with the estimated impacts (costs, emissions reductions, risk
reductions, etc.) of applying these developments. We then made
decisions on whether it is necessary and appropriate to propose
amendments to the regulation to require any of the identified
developments.
    Based on specific knowledge of the source category, we began by
identifying known developments in practices, processes and control
technologies. For the purpose of this exercise, we considered any of
the following to be a ``development'':
     Any add-on control technology or other equipment that was
not identified and considered during development of the 1998 NESHAP;
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the 1998 NESHAP) that could result in significant additional emissions
reductions;
     Any work practice or operational procedure that was not
identified or considered during development of the 1998 NESHAP; and
     Any process change or pollution prevention alternative
that could be broadly applied to the industry and that was not
identified or considered during development of the 1998 NESHAP.
    In addition to reviewing the practices, processes or control
technologies that were not considered at the time we developed the 1998
NESHAP, we reviewed a variety of data sources in our evaluation of
whether there were additional practices, processes or controls to
consider for the pulp and paper industry. To aid in our evaluation of
whether there were additional practices, processes or controls to
consider, one of these sources of data was subsequent air toxics rules.
Since the promulgation of the MACT standards for the source category
addressed in this proposal, the EPA has developed air toxics
regulations for a number of additional source categories. In these
subsequent air toxic regulatory actions, we consistently evaluated any
new practices, processes and control technologies. We reviewed the
regulatory requirements and/or technical analyses associated with these
subsequent regulatory actions to identify any practices, processes and
control technologies considered in these efforts that could possibly be
applied to emission sources in the source category under this current
RTR review.
    We also consulted the EPA's RBLC to identify potential technology
advances.\33\ Control technologies, classified as RACT, BACT or LAER
apply to stationary sources depending on whether the sources are
existing or new, and on the size, age and location of the facility.
Best available control technology and LAER (and sometimes RACT) are
determined on a case-by-case basis, usually by state or local
permitting agencies. The EPA established the RBLC to provide a central
database of air pollution technology information (including
technologies required in source-specific permits) to promote the
sharing of information among permitting agencies and to aid in
identifying future possible control technology options that might apply
broadly to numerous sources within a category or apply only on a
source-by-source basis. The RBLC contains over 5,000 air pollution
control permit determinations that can help identify appropriate
technologies to mitigate many air pollutant emission streams. We
searched this database to determine whether it contained any practices,
processes or control technologies for the types of processes covered by
the pulp and paper source category. We also further analyzed a number
of BACT determinations listed in the RBLC to obtain further
information.
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    \33\ See the memorandum in the docket titled, Summary of RBLC
and Other Findings to Support Section 112(d)(6) Technology Review
for Pulp and Paper NESHAP.
---------------------------------------------------------------------------

    Additionally, we conducted a general search of the Internet and
other sources for information on control technologies applicable to
pulp and paper production. Finally, we conducted a search of the
database containing the responses received from the Part I survey to
obtain information on process and emission controls currently in use in
pulp and paper production.
    Each of the evaluations listed above considered and reviewed the
technologies suitable to demonstrate compliance with the requirements
listed in Sec. Sec.  63.440 through 63.449 (subpart S).\34\
---------------------------------------------------------------------------

    \34\ See the memoranda titled, Section 112(d)(6) Technology
Review for Pulping and Papermaking Processes and Summary of Pulp
Bleaching Technology Review, in the docket for this rulemaking.

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D. What other issues are we addressing in this proposal?

    In addition to the analyses described above, we also reviewed other
aspects of the MACT standards for possible revision as appropriate and
necessary. Based on this review, we have identified aspects of the MACT
standards that we believe need revision.
    This includes proposing revisions to the SSM provisions of the MACT
rule in order to ensure that they are consistent with the court
decision in Sierra Club v. EPA, 551 F. 3d 1019 (DC Cir. 2008). In
addition, we are proposing various changes based on our review of the
rule for testing and monitoring sufficiency, including a requirement
for 5-year repeat air emissions testing for selected equipment and
additional test methods for measuring methanol. We are also proposing
minor changes with regards to editorial errors. The analyses and
proposed decisions for these actions are presented in section IV of
this preamble.

IV. Analytical Results and Proposed Decisions

    This section of the preamble provides the results of our RTR for
the pulp and paper source category and our proposed decisions
concerning changes to the 1998 NESHAP.

A. What are the results of the risk assessments?

    For the pulp and paper source category, we conducted an inhalation
risk assessment based upon actual and allowable emissions for all HAP
emitted, as well as a multipathway analysis. This assessment also
included a whole-facility analysis to estimate inhalation risks from
all source categories for the pulp and paper industry.
1. Inhalation Risk Assessment Results
    Table 3 provides an overall summary of the results of the
inhalation risk assessment from the 171 modeled mills subject to this
source category. We also conducted an assessment of facilitywide risk.
Details of the risk assessments and analyses can be found in the
residual risk documentation referenced in section IV.A of this
preamble, which is available in the docket for this action.

                    Table 3--Pulp and Paper Production Inhalation Risk Assessment Results \1\
----------------------------------------------------------------------------------------------------------------
Maximum individual cancer risk                                     Maximum chronic noncancer
      (in 1 million) \2\           Estimated       Estimated               TOSHI \3\
-------------------------------  population at   annual cancer --------------------------------    Worst-case
   Based on        Based on     increased risk     incidence       Based on        Based on      maximum refined
    actual         allowable    of cancer >= 1    (cases per        actual         allowable     screening acute
   emissions       emissions     in 1 Million        year)         emissions       emissions    noncancer HQ \4\
     level           level                                           level           level
----------------------------------------------------------------------------------------------------------------
            10              10          76,000            0.01             0.4             0.6  HQREL = 20
                                                                                HQERPG	1 = 0.4
                                                                                (acetaldehyde)
                ..............  ..............  ..............  ..............  ..............   HQREL = 6.
                                                                                HQERPG	1 = 0.004
                                                                                (chloroform).
                ..............  ..............  ..............  ..............  ..............   HQREL = 5.
                                                                                HQAEGL	1 = 0.2
                                                                                (formaldehyde)
                ..............  ..............  ..............  ..............  ..............   HQREL = 2.
                                                                                HQERPG	1 = 0.2
                                                                                (methanol)
----------------------------------------------------------------------------------------------------------------
\1\ As noted in section III.A.1 of this preamble, acrolein emissions were not modeled due to uncertainties in
  the emissions estimates.
\2\ Estimated maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\3\ Maximum TOSHI. The target organ with the highest TOSHI for the pulp and paper source category is the
  respiratory system.
\4\ See section III.B of this preamble for explanation of acute dose-response values.

    As shown in Table 3, the results of the inhalation risk assessment
performed using actual emissions data indicate the maximum lifetime
individual cancer risk could be up to 10 in 1 million, primarily due to
hexachloroethane emissions; the maximum chronic noncancer TOSHI value
could be up to 0.4, primarily due to acetaldehyde emissions; and the
maximum offsite worst-case acute HQ value could be up to 20, based on
the REL value for acetaldehyde. The HQ of 20 represents an upper-bound
risk estimate and is located in an uninhabited location with limited
public access or an offsite area that is owned by the facility. An
acute noncancer HQ of 3 reflects the risk where people are living with
access to a public road. This would then result in the next highest HQ
of 6 for this source category based on the acute REL dose-response
value for chloroform. One hundred sixty-two of the 171 facilities in
this source category had an estimated worst-case HQ less than or equal
to 1; the remaining 9 facilities had an estimated worst-case HQ less
than or equal to 6.\35\
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    \35\ The acute refined HQ values for this source category can be
found in Appendix 6, Table 1 of the Risk Assessment report. A
summary of the refined acute 1-hour HQ values that were greater than
1 for this source category are as follows: 20,6,5,5,4,3,2,2,2,2,2.
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    To better characterize the potential health risks associated with
estimated worst-case acute exposures to HAP, and in response to a key
recommendation from the SAB's peer review of EPA's RTR risk assessment
methodologies,\36\ we examine a wider range of available acute health
metrics than we do for our chronic risk assessments. This is in
response to the acknowledgement that there are generally more data gaps
and inconsistencies in acute reference values than there are in chronic
reference values. By definition, the acute CalEPA REL represents a
health-protective level of exposure, with no risk anticipated below
those levels, even for repeated exposures; however, the health risk
from higher-level exposures is unknown. Therefore, when a CalEPA REL is
exceeded and an AEGL-1 or ERPG-1 level is available (i.e., levels at
which mild effects are anticipated in the general public for a single
exposure), we have used them as a second comparative measure.
Historically, comparisons of the estimated maximum offsite 1-hour
exposure levels have not been typically made to occupational levels for
the purpose of characterizing public health risks in RTR assessments.
This is because occupational ceiling values are not generally
considered protective for the general public since they are

designed to protect the worker population (presumed healthy adults) for
short-duration (less than 15-minute) increases in exposure.\37\ As a
result, for most chemicals, the 15-minute occupational ceiling values
are set at levels higher than a 1-hour AEGL-1, making comparisons to
them irrelevant unless the AEGL-1 or ERPG-1 levels are exceeded. Such
is not the case when comparing the available acute inhalation health
effect reference values for formaldehyde.
---------------------------------------------------------------------------

    \36\ 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.
    \37\ 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.
---------------------------------------------------------------------------

    The worst-case maximum estimated 1-hour exposure to formaldehyde
outside the facility fence line for the pulp and paper source category
is 0.25 mg/m\3\. This estimated worst-case exposure exceeds the 1-hour
REL by a factor of 5 (HQREL=5) and is below the 1-hour AEGL-
1 (HQAEGL-1=0.2). This exposure estimate is below the AEGL-
1, and exceeds the workplace ceiling level guideline for the
formaldehyde value developed by NIOSH \38\ ``for any 15 minute period
in a work day'' (NIOSH REL-ceiling value of 0.12 mg/m\3\;
HQNIOSH=2). The estimate is at the value developed by the
ACGIH \39\ as ``not to be exceeded at any time'' (ACGIH TLV-ceiling
value of 0.37 mg/m\3\; HQACGIH=1). Additionally, the
estimated maximum acute exposure exceeds the Air Quality Guideline
value that was developed by the World Health Organization \40\ for 30-
minute exposures (0.1 mg/m\3\; HQWHO=2.5).
---------------------------------------------------------------------------

    \38\ National Institutes for Occupational Safety and Health
(NIOSH). Occupational Safety and Health Guideline for Formaldehyde;
http://www.cdc.gov/niosh/docs/81-123/pdfs/0293.pdf.
    \39\ ACGIH (2001) Formaldehyde. In Documentation of the
TLVs[reg] and BEIs[reg] with Other Worldwide Occupational Exposure
Values. ACGIH, 1300 Kemper Meadow Drive, Cincinnati, OH 45240 (ISBN:
978-1-882417-74-2) and available on-line at http://www.acgih.org.
    \40\ WHO (2000). Chapter 5.8 Formaldehyde, in Air Quality
Guidelines for Europe, second edition. World Health Organization
Regional Publications, European Series, No. 91. Copenhagen, Denmark.
Available on-line at http://www.euro.who.int/_data/assets/pdf_file/0005/74732/E71922.pdf.
---------------------------------------------------------------------------

    All other HAP and facilities modeled had worst-case acute HQ values
less than 1, indicating that they carry no potential to pose acute
concerns. The maximum HQ based on an ERPG-1 dose-response value is 0.4
for acetaldehyde. In characterizing the potential for acute noncancer
impacts of concern, it is important to remember the upward bias of
these exposure estimates (e.g., worst-case meteorology coinciding with
a person located at the point of maximum concentration during the hour)
and to consider the results along with the uncertainties related to the
emissions estimates and the screening methodology. However, it is
acknowledged that the acute emission multipliers ranged from 1.4 to 3
and approached the annual hourly average emission rate for the
facilities within the source category.
    The total estimated cancer incidence from these facilities based on
actual emissions levels is 0.01 excess cancer cases per year, or 1 case
in every 100 years. The cancer incidence is primarily driven by
emissions of acetaldehyde and formaldehyde from papermaking and kraft
wastewater operations.\41\
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    \41\ We note that the MIR for this source category would not
change if the CIIT URE for formaldehyde had been used in the
assessment; however, the total cancer incidence would decrease by
about 36 percent. There is an ongoing IRIS reassessment for
formaldehyde and future RTR risk assessments will use the cancer
potency for formaldehyde that results from that reassessment. As a
result, the current results many not match those of future
assessments.
---------------------------------------------------------------------------

    There are 68 facilities with maximum individual cancer risks of 1
in 1 million or greater and two facilities with maximum individual
cancer risks of 10 in a million that represented the highest cancer
risks for the source category. The MIR of 10 in a million for the
source category was driven by emissions of hexachloroethane.
    As explained above, our analysis of potential differences between
actual emissions levels and emissions allowable under the pulp and
paper MACT standards indicate that MACT-allowable emission levels are
roughly equal to the actual emission levels.\42\ The risk results from
the inhalation risk assessment indicate the maximum lifetime individual
cancer risks are the same at 20 in a million, and the maximum chronic
noncancer TOSHI value could be up to 0.6 at the MACT-allowable
emissions level.
---------------------------------------------------------------------------

    \42\ For more information, see the memorandum in the docket
titled Inputs to the Pulp and Paper Industry October 2011 Residual
Risk Modeling.
---------------------------------------------------------------------------

2. Multipathway Risk Screening Results
    The results of a multipathway screening analysis showed that
emissions of POM, cadmium and mercury were almost all below their
respective screening emission rates, thereby indicating a negligible
risk of adverse health effects associated with multipathway exposures.
The only PB-HAP to exceed the screening threshold was POM, with
emissions exceeding the screening threshold by a factor of 2.
3. Facilitywide Risk Assessment Results
    A facilitywide risk analysis was also conducted based on actual
emissions levels. Table 4 displays the results of the facilitywide risk
assessment.\43\
---------------------------------------------------------------------------

    \43\ For detailed facilityspecific results, see Appendix 6 of
the Draft Residual Risk Assessment for Pulp and Paper in the docket
for this rulemaking.

      Table 4--Pulp and Paper Facilitywide Risk Assessment Results
------------------------------------------------------------------------

------------------------------------------------------------------------
Number of facilities analyzed..............................          171
Cancer Risk:
    Estimated maximum facilitywide individual cancer risk             30
     (in 1 million)........................................
    Number of facilities with estimated facilitywide                   7
     individual cancer risk of 10 in 1 million or more.....
    Number of pulp and papermaking operations contributing             2
     50 percent or more to facilitywide individual cancer
     risk of 10 in 1 million or more.......................
    Number of facilities with facilitywide individual                 99
     cancer risk of 1 in 1 million or more.................
    Number of pulp and papermaking operations contributing            57
     50 percent or more to facilitywide individual cancer
     risk of 1 in 1 million or more........................
Chronic Noncancer Risk:
    Maximum facilitywide chronic noncancer TOSHI...........            2
    Number of facilities with facilitywide maximum                     4
     noncancer TOSHI of 1 or more..........................
    Number of pulp and papermaking operations contributing             0
     50 percent or more to facilitywide maximum noncancer
     TOSHI of 1 or more....................................
------------------------------------------------------------------------

    The maximum individual cancer whole-facility risk from all HAP
emissions at any mill is estimated to be 30 in 1 million based on
actual emissions. Of the 171 mills included in this analysis, seven
have facilitywide maximum individual cancer risks of 10 in 1 million or
greater. At these mills, pulp and papermaking operations account for 30
percent of the total facilitywide risk. There are 99 facilities with
facilitywide maximum individual cancer risks of 1 in 1 million or
greater. Of these 99 mills, 57 have pulp and papermaking operations
that contribute greater than 50 percent to the facilitywide risks. The
facilitywide cancer risks at these 57 mills, and at the 7 mills with
risks of 10 in a million or more, are primarily driven by emissions of
arsenic compounds, chromium compounds and nickel compounds from boiler
and lime kiln operations. However, we note that there are uncertainties
in the amount and form of chromium emitted from these mills. For many
of the mills, the emissions inventory used for the risk assessment
included estimates for the two main forms of chromium (i.e., hexavalent
and trivalent chromium). However, for other mills, we only had
estimates of total chromium emitted. For those mills, we applied a
hexavalent chromium speciation factor assigned by SCC for this source
category.\44\ Although, hexavalent chromium is toxic and is a known
human carcinogen, trivalent chromium is less toxic and is currently
``not classified as to its human carcinogenicity.'' \45\ Therefore, the
relative emissions of these two forms can have a significant effect on
the cancer risk estimates.
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    \44\ See the memorandum in the docket titled, Inputs to the Pulp
and Paper Industry October 2011 Residual Risk Modeling.
    \45\ EPA's IRIS Weight-of-Evidence Characterization for
trivalent chromium http://www.epa.gov/iris/subst/0028.htm#refinhal.
---------------------------------------------------------------------------

    The facilitywide maximum individual chronic noncancer TOSHI is
estimated to be 2 based on actual emissions. Of the 171 mills included
in this analysis, only four mills have a HI value greater than 1, with
all mills having an HI value less than or equal to 2. The chronic
noncancer risks at these mills are primarily driven by acrolein
emissions from industrial boilers and antimony emissions from smelt
dissolving tank kraft process units, which are not regulated under the
Pulp and paper source category.

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

1. Risk Acceptability
    As noted in section III.B of this preamble, we weigh all health
risk factors and measures in our risk acceptability determination,
including the MIR; the number of persons in various cancer and
noncancer risk ranges; cancer incidence; the maximum noncancer HI; the