[Federal Register Volume 77, Number 30 (Tuesday, February 14, 2012)]
[Proposed Rules]
[Pages 8576-8629]
[FR Doc No: 2012-2874]

Vol. 77

Tuesday,

No. 30

February 14, 2012

Part V

Environmental Protection Agency

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40 CFR Part 63

National Emissions Standards for Hazardous Air Pollutants: Secondary
Aluminum Production; Proposed Rule

Federal Register / Vol. 77 , No. 30 / Tuesday, February 14, 2012 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2010-0544; FRL-9628-8]
RIN 2060-AQ40

National Emissions Standards for Hazardous Air Pollutants:
Secondary Aluminum Production

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing amendments to the national emissions
standards for hazardous air pollutants for Secondary Aluminum
Production to address the results of the residual risk and technology
review that the EPA is required to conduct by the Clean Air Act. In
addition, the EPA is proposing amendments to correct and clarify rule
requirements and provisions. These proposed amendments would require
emission sources to comply with the emission limits at all times
including periods of startup and shutdown; add a definition of
affirmative defense; add a requirement to report performance testing
through the Electronic Reporting Tool (ERT); add rule provisions
allowing owners and operators to change furnace classifications; add
rule requirements regarding testing of uncontrolled furnaces; add
compliance provisions for hydrogen fluoride (HF) for uncontrolled group
1 furnaces; add operating requirements such as monitoring of lime
injection rates; and make technical corrections and clarifications to
the applicability, definitions, operating, monitoring, and performance
testing requirements.

DATES: Comments must be received on or before March 30, 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 (OMB) receives a copy of your comments on or
before March 15, 2012.
    Public Hearing. If anyone contacts the EPA requesting to speak at a
public hearing by February 24, 2012, a public hearing will be held on
February 29, 2012.

ADDRESSES: Submit your comments, identified by Docket ID Number EPA-HQ-
OAR-2010-0544, by one of the following methods:
     http://www.regulations.gov: Follow the on-line
instructions for submitting comments.
     Email<EMAIL_ADDRESS>Attention Docket ID Number
EPA-HQ-OAR-2010-0544.
     Fax:<PHONE_NUMBER>, Attention Docket ID Number EPA-HQ-
OAR-2010-0544.
     Mail: U.S. Postal Service, send comments to: EPA Docket
Center, EPA West (Air Docket), Attention Docket ID Number EPA-HQ-OAR-
2010-0544, U.S. Environmental Protection Agency, Mailcode: 2822T, 1200
Pennsylvania Ave. NW., Washington, DC 20460. Please include a total of
two copies. In addition, please mail a copy of your comments on the
information collection provisions to the Office of Information and
Regulatory Affairs, Office of Management and Budget (OMB), Attn: Desk
Officer for EPA, 725 17th Street NW., Washington, DC 20503.
     Hand Delivery: U.S. Environmental Protection Agency, EPA
West (Air Docket), Room 3334, 1301 Constitution Ave. NW., Washington,
DC 20004, Attention Docket ID Number EPA-HQ-OAR-2010-0544. Such
deliveries are only accepted during the Docket's normal hours of
operation, and special arrangements should be made for deliveries of
boxed information.
    Instructions. Direct your comments to Docket ID Number EPA-HQ-OAR-
2010-0544. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
on-line at http://www.regulations.gov, including any personal
information provided, unless the comment includes information claimed
to be confidential business information (CBI) or other information
whose disclosure is restricted by statute. Do not submit information
that you consider to be CBI or otherwise protected through http://www.regulations.gov or email. The http://www.regulations.gov Web site
is an ``anonymous access'' system, which means the EPA will not know
your identity or contact information unless you provide it in the body
of your comment. If you send an email comment directly to the EPA
without going through http://www.regulations.gov, your email address
will be automatically captured and included as part of the comment that
is placed in the public docket and made available on the Internet. If
you submit an electronic comment, the EPA recommends that you include
your name and other contact information in the body of your comment and
with any disk or CD-ROM you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should avoid the use of special characters, any form of encryption, and
be free of any defects or viruses. For additional information about the
EPA's public docket, visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID Number EPA-HQ-OAR-2010-0544. The proposed rulemaking also
used material from Docket ID Number EPA-HQ-OAR-2010-0469 in the
development of this rule. 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., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy. Publicly available docket
materials are available either electronically in 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 February 29, 2012 and will be held at the EPA's 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. Virginia
Hunt, Office of Air Quality Planning and Standards, Sector Policies and
Programs Division, (D243-02), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; telephone number: (919)
541-0832.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Rochelle Boyd, Sector Policies and Programs
Division (D243-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, telephone<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; and email
address<EMAIL_ADDRESS>For specific information regarding the
risk modeling methodology, contact Dr. Michael Stewart, Office of Air
Quality Planning and Standards, Health and Environmental Impacts
Division, Air Toxics Assessment Group (C504-06), U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711;

telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; and email
address<EMAIL_ADDRESS>For information about the
applicability of the national emission standards for hazardous air
pollutants (NESHAP) to a particular entity, contact the appropriate
person listed in Table 1 of 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 Contact\2\
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Secondary Aluminum Production.  Scott Throwe, (202)  Rochelle Boyd,
                                 564-7013<PHONE_NUMBER>,
<EMAIL_ADDRESS> boyd.rochelle@epa.
                                 ov.                  gov
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\1\ EPA Office of Enforcement and Compliance Assurance.
\2\ EPA 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, for ease of reading of this
preamble and for reference purposes, the following terms and acronyms
are defined here:

ACGIH American Conference of Government Industrial Hygienists
ADAF age-dependent adjustment factors
AEGL acute exposure guideline levels
AERMOD air dispersion model used by the HEM-3 model
APCD air pollution control devices
AMOS ample margin of safety
ANPRM advance notice of proposed rulemaking
ATSDR Agency for Toxic Substances and Disease Registry
BACT best available control technology
CAA Clean Air Act
CBI confidential business information
CFR Code of Federal Regulations
D/F dioxins and furans
EJ environmental justice
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
ERT Electronic Reporting Tool
HAP hazardous air pollutants
HCl hydrogen chloride
HEM-3 Human Exposure Model, Version 3
HF hydrogen fluoride
HHRAP human health risk assessment protocols
HI hazard index
HQ hazard quotient
ICR information collection request
IRIS Integrated Risk Information System
km kilometer
LAER lowest achievable emissions rate
lb/yr pounds per year
MACT maximum achievable control technology
MACT Code code within the NEI used to identify processes included in
a source category
MDL method detection level
mg/acm milligrams per actual cubic meter
mg/dscm milligrams per dry standard cubic meter
mg/m\3\ milligrams per cubic meter
MIR maximum individual risk
MRL minimum risk level
NAC/AEGL Committee 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
NEI National Emissions Inventory
NESHAP National Emissions Standards for Hazardous Air Pollutants
NOAEL no observed adverse effects level
NRC National Research Council
NTTAA National Technology Transfer and Advancement Act
O&M operation and maintenance
OAQPS Office of Air Quality Planning and Standards
OECA Office of Enforcement and Compliance Assurance
OHEA Office of Health and Environmental Assessment
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PM particulate matter
ppmv parts per million by volume
RACT reasonably available control technology
RBLC RACT/BACT/LAER Clearinghouse
REL reference exposure level
RFA Regulatory Flexibility Act
RfC reference concentration
RfD reference dose
RIA regulatory impact analysis
RTR residual risk and technology review
SAB Science Advisory Board
SBA Small Business Administration
SCC source classification codes
SF3 2000 Census of Population and Housing Summary
SIP state implementation plan
SOP standard operating procedures
SSM startup, shutdown, and malfunction
TEF toxic equivalency factors
TEQ toxic equivalency quotient
THC total hydrocarbons
TOSHI target organ-specific hazard index
tpy tons per year
TRIM Total Risk Integrated Modeling System
TTN Technology Transfer Network
UBC used beverage containers
UF uncertainty factor
[mu]g/m\3\ microgram per cubic meter
UMRA Unfunded Mandates Reform Act
UPL upper predictive limit
URE unit risk estimate
VOC volatile organic compounds
VOHAP volatile organic hazardous air pollutants
WHO World Health Organization
WWW worldwide web

    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 hazardous air pollutants (HAP) from stationary
sources. In the first stage, after the EPA has identified categories of
sources emitting one or more of the HAP listed in section 112(b) of the
CAA, section 112(d) of the CAA calls for us to promulgate national
emission standards for hazardous air pollutants (NESHAP) for those
sources. ``Major sources'' are those that emit or have the potential to
emit (PTE) 10 tons per year (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 emission reductions
of HAP achievable (after considering cost, energy requirements and non-
air quality health and environmental impacts) and are commonly referred
to as maximum achievable control technology (MACT) standards.
    MACT standards must require the maximum degree of emissions
reduction achievable through the application of measures, processes,
methods, systems or techniques including, but not limited to, measures
which (1) reduce the volume of or eliminate emissions of pollutants
through process changes, substitution of materials or other
modifications, (2) enclose systems or processes to eliminate emissions,
(3) capture or treat pollutants when released from a process, stack,
storage or fugitive emissions point, (4) are design, equipment, work
practice or operational standards (including requirements for operator
training or certification) or (5) are a combination of the above. CAA
section 112(d)(2)(A)-(E). The MACT standard may take the form of a
design, equipment, work practice or operational standard where the EPA
first determines that either (1) a pollutant cannot be emitted through
a conveyance designed and constructed to emit or capture the pollutant
or that any requirement for, or use of, such a conveyance would be
inconsistent with law, or (2) the application of measurement
methodology to a particular class of sources is not practicable due to
technological and economic limitations. CAA 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 emission 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 consideration of the cost of achieving the
emissions reductions and any non-air quality health and environmental
impacts and energy requirements.
    Under CAA section 112(d)(6), 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. In conducting
this review, the EPA is not obliged to completely recalculate the prior
MACT determination. 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 risk 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.
    CAA section 112(f)(2) requires us to determine, for source
categories subject to certain MACT standards, whether the emissions
standards provide an ample margin of safety to protect public health.
If the MACT standards for HAP ``classified as a known, probable, or
possible human carcinogen do not reduce lifetime excess cancer risks to
the individual most exposed to emissions from a source in the category
or subcategory to less than one in one million,'' the EPA must
promulgate residual risk standards for the source category (or
subcategory), as necessary, to provide an ample margin of safety to
protect public health. In doing so, the EPA may adopt standards equal
to existing MACT standards if the EPA determines that the existing
standards are sufficiently protective. NRDC v. EPA, 529 F.3d 1077, 1083
(DC Cir. 2008). (``If EPA determines that the existing technology-based
standards provide an `ample margin of safety,' then the agency is free
to readopt those standards during the residual risk rulemaking.'') The
EPA must also adopt more stringent standards, if necessary, to prevent
an adverse environmental effect \1\ but must consider cost, energy,
safety and other relevant factors in doing so.
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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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    Section 112(f)(2) of the CAA expressly preserves our use of a 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 necessary 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 United States Court of Appeals
for the District of Columbia

Circuit in NRDC v. EPA concluded that the EPA's interpretation of
subsection 112(f)(2) is a reasonable one. See NRDC v. EPA, 529 F.3d
1077 1083 (DC Cir. 2008) (``[S]ubsection 112(f)(2)(B) expressly
incorporates the EPA's interpretation of the Clean Air Act from the
Benzene standard, complete with a citation to the Federal Register'');
see also A Legislative History of the Clean Air Act Amendments of 1990,
volume 1, p. 877 (Senate debate on Conference Report). We 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, 54 FR at 38044-38045, we stated as an
overall objective:

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

    The agency stated that ``[t]he EPA also considers incidence (the
number of persons estimated to suffer cancer or other serious health
effects as a result of exposure to a pollutant) to be an important
measure of the health risk to the exposed population. Incidence
measures the extent of health risk 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.'' 54 FR at 38045. The
agency went on to conclude that ``estimated incidence would be weighed
along with other health risk information in judging acceptability.'' 54
FR at 38046. As explained more fully in our Residual Risk Report to
Congress, the EPA does not define ``rigid line[s] of acceptability,''
but considers rather 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 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 at 38045. We discussed the maximum individual
lifetime cancer risk (or maximum individual risk (MIR)) as being ``the
estimated risk that a person living near a plant would have if he or
she were exposed to the maximum pollutant concentrations for 70
years.'' Id. We explained that this measure of risk ``is an estimate of
the upper bound of risk based on conservative assumptions, such as
continuous exposure for 24 hours per day for 70 years.'' Id. We
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.
    The agency also explained in the 1989 Benzene NESHAP: ``[i]n
establishing a presumption for MIR, rather than a rigid line for
acceptability, the Agency intends to weigh it with a series of other
health measures and factors. These include the overall incidence of
cancer or other serious health effects within the exposed population,
the numbers of persons exposed within each individual lifetime risk
range and associated incidence within, typically, a 50 km [kilometer]
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 CAA section 112.'' 54 FR at 38046.
    As discussed above, we apply a two-step process for developing
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 limit on maximum individual lifetime [cancer]
risk (MIR) \2\ of approximately 1 in 10 thousand [i.e., 100 in 1
million].'' 54 FR at 38045. In the second step of the process, the EPA
sets the standard at a level that provides an ample margin of safety
``in consideration of all health information, including the number of
persons at risk levels higher than approximately 1 in 1 million, as
well as other relevant factors, including costs and economic impacts,
technological feasibility, and other factors relevant to each
particular decision.'' Id.
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    \2\ 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 to be exposed to the maximum
level of a pollutant for a lifetime.
---------------------------------------------------------------------------

    In past residual risk determinations, the EPA presented 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 hazard index (HI);
and the maximum acute noncancer hazard. In estimating risks, the EPA
considered source categories under review that are located near each
other and that affect the same population. The EPA estimates risk based
on the actual emissions from the source category under review as well
as based on the emissions allowed pursuant to the source category MACT
standard. The EPA also discussed and considered risk estimation
uncertainties. The EPA is providing this same type of information in
support of these actions.
    The agency acknowledges that the Benzene NESHAP provides
flexibility

regarding what factors the EPA might consider in making our
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: ``[t]he policy chosen by the Administrator permits
consideration of multiple measures of health risk. Not only can the MIR
figure be considered, but also incidence, the presence of noncancer
health effects, and the uncertainties of the risk estimates. In this
way, the effect on the most exposed individuals can be reviewed as well
as the impact on the general public. These factors can then be weighed
in each individual case. This approach complies with the Vinyl Chloride
mandate that the Administrator ascertain an acceptable level of risk to
the public by employing [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.
    For example, the level of the MIR is only one factor to be weighed
in determining acceptability of risks. The Benzene NESHAP explains ``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.'' 54 FR at 38045. Similarly, with
regard to the ample margin of safety analysis, the Benzene NESHAP
states 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.'' 54 FR
at 38061.

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. These standards, once finalized, will be directly
applicable to affected sources. Federal, State, local, and tribal
government entities are not affected by this proposed action. The EPA
defined the Secondary Aluminum source category in 1992 as any
establishment using clean charge, aluminum scrap, or dross from
aluminum production, as the raw material and performing one or more of
the following processes: Scrap shredding, scrap drying/delacquering/
decoating, thermal chip drying, furnace operations (i.e., melting,
holding, sweating, refining, fluxing, or alloying), recovery of
aluminum from dross, in-line fluxing, or dross cooling.

                Table 2--NESHAP and Industrial Source Categories Affected by This Proposed Action
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                                                                                NAICS     MACT
            Source category                                     NESHAP                        code \1\  code \2\
----------------------------------------------------------------------------------------------------------------
Secondary Aluminum Production..........  Secondary Aluminum Production......................    331314      0044
Primary aluminum production facilities.  ...................................................    331312
Aluminum sheet, plate, and foil          ...................................................    331315
 manufacturing facilities.
Aluminum extruded product manufacturing  ...................................................    331316
 facilities.
Other aluminum rolling and drawing       ...................................................    331319
 facilities.
Aluminum die casting facilities........  ...................................................    331521
Aluminum foundry facilities............  ...................................................    331524
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\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 World Wide Web (WWW)
through the EPA's Technology Transfer Network (TTN). 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 including the residual risk
and technology review (RTR) and 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-2010-0544.

II. Background

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

    The Secondary Aluminum Production source category includes
facilities that produce aluminum from scrap aluminum material and
consists of the following operations: (1) Preprocessing of scrap
aluminum, including size reduction and removal of oils, coatings, and
other contaminants; (2) Furnace operations including melting, in-
furnace refining, fluxing, and tapping; (3) Additional refining, by
means of in-line fluxing; and (4) Cooling of dross. The following
sections include descriptions of the affected sources in the secondary
aluminum production source category, the origin of HAP emissions from
these affected sources, and factors affecting the emissions.
    Scrap aluminum is often preprocessed prior to melting.
Preprocessing steps may include shredding to reduce the size of
aluminum scrap; drying of oily scrap such as machine turnings and
borings; and/or heating in a scrap dryer, delacquering kiln or
decoating kiln to remove coatings or other contaminants that may be
present on the scrap. Heating of high iron content scrap in a sweat
furnace to reclaim the aluminum content is also a preprocessing
operation.
    Crushing, shredding and grinding operations are used to reduce the
size of scrap aluminum. Particulate matter (PM) and HAP metals
emissions are generated as dust from coatings and other contaminants
contained in the scrap aluminum as they are processed.
    A chip dryer is used to evaporate oil and/or moisture from uncoated
aluminum chips and borings. Chip dryers typically operate at
temperatures ranging between 150 [deg]C to 400 [deg]C (300 [deg]F to
750 [deg]F). An uncontrolled chip dryer may emit dioxins and furans (D/
F) and total hydrocarbons (THC), of which some fraction is organic HAP.
    Painted and/or coated materials are processed in a scrap dryer/
delacquering kiln/decoating kiln to remove coatings and other
contaminants that may be present in the scrap prior to melting.
Coatings, oils, grease, and lubricants represent up to 20 percent of
the total weight of these materials. Organic HAP, D/F, and inorganic
HAPs including particulate metal HAP are emitted during the drying/
delacquering/decoating process.
    Used beverage containers (UBC) comprise a major portion of the
recycled aluminum scrap used as feedstock by the industry. In scrap
drying/delacquering/decoating operations, UBC and other post-consumer,
coated products (e.g., aluminum siding) are heated to an exit
temperature of up to 540 [deg]C (1,000 [deg]F) to volatilize and remove
various organic contaminants such as paints, oils, lacquers, rubber,
and plastic laminates prior to melting. An uncontrolled scrap dryer/
delacquering kiln/decoating kiln emits PM (of which some fraction is
particulate metal HAP), HCl, THC (of which some fraction is organic
HAP), and D/F.
    A sweat furnace is typically used to reclaim (or ``sweat'') the
aluminum from scrap with high levels of iron. These furnaces operate in
batch mode at a temperature that is high enough to melt the aluminum
but not high enough to melt the iron. The aluminum melts and flows out
of the furnace while the iron remains in the furnace in solid form. The
molten aluminum can be cast into sows, ingots, or T-bars that are used
as feedstock for aluminum melting and refining furnaces. Alternately,
molten aluminum can be fed directly to a melting or refining furnace.
An uncontrolled sweat furnace may emit D/F.
    Process (i.e. melting, holding or refining) furnaces are
refractory-lined metal vessels heated by an oil or gas burner to
achieve a metal temperature of about 760 [deg]C (1,400 [deg]F). The
melting process begins with the charging of scrap into the furnace. A
gaseous (typically, chlorine) or salt flux may be added to remove
impurities and reduce aluminum oxidation. Once molten, the chemistry of
the bath is adjusted by adding selected scrap or alloying agents, such
as silicon. Salt and other fluxes contain chloride and fluoride
compounds that may be released when introduced to the bath. HCl may
also be released when chlorine-containing contaminants (such as
polyvinyl chloride coatings) present in some types of scrap are
introduced to the bath. Argon and nitrogen fluxes are not reactive and
do not produce HAPs. In a sidewell melting furnace, fluxing is
performed in the sidewell and fluxing emissions from the sidewell are
controlled. In this type of furnace, fluxing is not typically done in
the hearth and hearth emissions (which include products of combustion
from the oil and gas fired furnaces) are typically uncontrolled.
    Process furnaces may process contaminated scrap which can result in
HAP emissions. In addition, fluxing agents may contain HAPs, some
fraction of which is emitted from the furnace. Process furnaces are
significant sources of HAP emissions in the secondary aluminum
industry. An uncontrolled melting furnace which processes contaminated
scrap and uses reactive fluxes emits PM (of which some fraction is
particulate metal HAP), HCl, and D/F.
    Process furnaces are divided into group 1 and group 2 furnaces.
Group 1 furnaces are unrestricted in the type of scrap they process and
the type of fluxes they can use. Group 2 furnaces process only clean
charge and conduct no reactive fluxing.
    Dross-only furnaces are furnaces dedicated to reclamation of
aluminum from drosses formed during the melting/holding/alloying
operations carried out in other furnaces. Exposure to the atmosphere
causes the molten aluminum to oxidize, and the flotation of the
impurities to the surface along with any salt flux creates ``dross.''
Prior to tapping, the dross is periodically skimmed from the surface of
the aluminum bath and cooled. Dross-only furnaces are typically rotary
barrel furnaces (also known as salt furnaces). A dross-only furnace
without controls emits PM (of which some fraction is particulate metal
HAP).
    Rotary dross coolers are devices used to cool dross in a rotating,
water-cooled drum. A rotary dross cooler without controls emits PM (of
which some fraction is particulate metal HAP).
    In-line fluxers are devices used for aluminum refining, including
degassing, outside the furnace. The process involves the injection of
chlorine, argon, nitrogen or other gases to achieve the desired metal
purity. Argon and nitrogen are not reactive and do not produce HAPs.
In-line fluxers are found primarily at facilities that manufacture very
high quality aluminum or in facilities with no other means of
degassing. An in-line fluxer operating without emission controls emits
HCl and PM.
    The Secondary Aluminum Production NESHAP was promulgated on March
23, 2000, (65 FR 15690) and codified as 40 CFR part 63, subpart RRR.
The rule was amended at 67 FR 79808, December 30, 2002; 69 FR 53980,
September 3, 2004; 70 FR 57513, October 3, 2005 and 70 FR 75320,
December 19, 2005. The existing subpart RRR NESHAP regulates HAP
emissions from secondary aluminum production facilities that are major
sources of HAP that operate aluminum scrap shredders, thermal chip
dryers, scrap dryers/delacquering kilns/decoating kilns, group 1
furnaces, group 2 furnaces, sweat furnaces, dross only furnaces, rotary
dross coolers, and secondary aluminum processing units (SAPUs). The
SAPUs include group 1 furnaces and in-line fluxers. The subpart RRR
NESHAP regulates HAP

emissions from secondary aluminum production facilities that are area
sources of HAP only with respect to emissions of dioxins/furans (D/F)
from thermal chip dryers, scrap dryers/delacquering kilns/decoating
kilns, group 1 furnaces, sweat furnaces, and SAPUs.
    The secondary aluminum industry consists of approximately 161
secondary aluminum production facilities, of which the EPA estimates 53
to be major sources of HAP. Several of the secondary aluminum
facilities are co-located with primary aluminum, coil coating, and
possibly other source category facilities. Natural gas boilers or
process heaters may also be co-located at a few secondary aluminum
facilities.
    The HAP emitted by these facilities are metals, organic HAP, D/F,
hydrogen chloride (HCl), and hydrogen fluoride (HF).
    The standards promulgated in 2000 established emission limits for
particulate matter (PM) as a surrogate for metal HAP, total
hydrocarbons (THC) as a surrogate for organic HAP other than D/F, D/F
expressed as toxicity equivalents, and HCl as a surrogate for acid
gases including HF, chlorine and fluorine. HAP are emitted from the
following affected sources: aluminum scrap shredders (subject to PM
standards), thermal chip dryers (subject to standards for THC and D/F),
scrap dryers/delacquering kilns/decoating kilns (subject to standards
for PM, D/F, HCl and THC), sweat furnaces (subject to D/F standards),
dross-only furnaces (subject to PM standards), rotary dross coolers
(subject to PM standards), group 1 furnaces (subject to standards for
PM, HCl and D/F), and in-line fluxers (subject to standards for PM and
HCl). Group 2 furnaces and certain in-line fluxers are subject to work
practice standards. Table 3 provides a summary of the current MACT
emissions limits for existing and new sources under the 2000 NESAHP and
the 2005 amendments.

[GRAPHIC] [TIFF OMITTED] TP14FE12.031

[GRAPHIC] [TIFF OMITTED] TP14FE12.032

[GRAPHIC] [TIFF OMITTED] TP14FE12.033

    Control devices currently in use to reduce emissions from affected
sources subject to the subpart RRR NESHAP include fabric filters for
control of PM from aluminum scrap shredders; afterburners for control
of THC and D/F from thermal chip dryers; afterburners plus lime-
injected fabric filters for control of PM, HCl, THC, and D/F from scrap
dryers/delacquering kilns/decoating kilns; afterburners for control of
D/F from sweat furnaces; fabric filters for control of PM from dross-
only furnaces and rotary dross coolers; lime-injected fabric filters
for control of PM and HCl from in-line fluxers; and lime-injected
fabric filters for control of PM, HCl and D/F from group 1 furnaces.
All affected sources with add-on controls are also subject to design
requirements and operating limits to limit fugitive emissions.
    Compliance with the emission limits in the current rule is
demonstrated by an initial performance test for each affected source.
Repeat performance tests are required every 5 years. Area sources are
only subject to one-time performance tests for D/F. After the
compliance tests, facilities are required to monitor various control
parameters or conduct other types of monitoring to ensure continuous
compliance with the MACT standards. Owners or operators of sweat
furnaces that operate an afterburner that meets temperature and
residence time requirements are not required to conduct performance
tests.

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

    For the Secondary Aluminum Production source category, we compiled
a dataset from two primary sources: (1) An all-company information
collection request (ICR) sent to companies in February 2011, and (2) a
nine-company testing ICR, sent in May 2010.
    Responses to the all-company ICR contained data on stack release
characteristics such as height, volumetric flow rate, temperature, and
location (latitude/longitude) coordinates. Responses to the all-company
ICR also contained data on maximum production capacity and actual
production in tpy and testing results for pollutants regulated under
subpart RRR.
    As mentioned above, the pollutants regulated under subpart RRR are
PM, HCl, THC and D/F. PM is a surrogate for metal HAP and THC is a
surrogate for organic HAP. Since subpart RRR compliance testing is
performed for the surrogates PM and THC, there are limited test data
available for speciated metal HAP and organic HAP emissions. Therefore,
responses to the nine-company testing ICR were used to extrapolate the
PM and THC testing results reported in the all-company ICR to specific
metal and organic HAP emissions. In the nine-company testing ICR,
companies were asked to provide speciated metal HAP concentrations
(e.g. arsenic, cadmium, cobalt, lead, nickel, etc.) in the particulate
collected by fabric filters. For more information on the selection of
these facilities, see the Draft Technical Support Document for the
Secondary Aluminum Production Source Category located in the docket.
These data were then used to estimate speciated metal HAP emissions,
based on the PM emissions reported in the all-company ICR. For example,
if a response to the all-company ICR indicated a particular piece of
equipment at a specific secondary aluminum facility had 10 tpy of PM
emissions, and based on an analysis of the results of the nine-company
testing ICR the EPA determined that the cobalt concentration in the
fabric filter particulate matter catch was 20 parts-per-million (ppm),
the estimated emissions of cobalt would be 0.0002 tpy. In the nine-
company testing ICR, companies were also required to conduct speciated
organic HAP and THC emission testing for the two types of equipment
that have THC limits under subpart RRR, scrap dryer/delacquering/
decoating kilns and thermal chip dryers. The speciated organic HAPs for
which data were provided included volatile HAPs (e.g., benzene,
chloroprene, toluene, etc.) and semi-volatile HAPs (anthracene,
chrysene, naphthalene, etc.).
    Using the reported amount of charge or production for the most
recent year and the reported test results (in lb per ton of charge)
from the all-company ICR, emissions were calculated. Where test results
from the all-company ICR responses were expressed in terms of PM and
THC surrogates, emissions were

converted to speciated metal and organic HAP emissions using the nine-
company test results, as described above. Allowable and actual
emissions were calculated for each piece of equipment. The derivation
of allowable emissions estimates is described in Section III of this
preamble.
    The emissions data, calculations and risk assessment inputs for the
Secondary Aluminum Production source category are described further in
the memorandum Draft Development of the RTR Risk Modeling Dataset for
the Secondary Aluminum Production Source Category which is available in
the docket for this proposed rulemaking.

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 provide estimates of the
MIR posed by the HAP emissions for each source in the category, the HI
for chronic exposures to HAP with the potential to cause noncancer
health effects, and the hazard quotient (HQ) for acute exposures to HAP
with the potential to cause noncancer health effects. The assessments
also provided estimates of the distribution of cancer risks within the
exposed populations, cancer incidence and an evaluation of the
potential for adverse environmental effects for the source category.
The risk assessments consisted of seven primary steps, as discussed
below. The docket for this rulemaking contains the following document
which provides more information on the risk assessment inputs and
models: Draft Residual Risk Assessment for the Secondary Aluminum
Production Source Category. The methods used to assess risks (as
described in the six primary steps below) are consistent with those
peer-reviewed by a panel of the EPA's Science Advisory Board (SAB) in
2009 and described in their peer review report issued in 2010;\3\ they
are also consistent with the key recommendations contained in that
report.
---------------------------------------------------------------------------

    \3\ U.S. EPA SAB. Risk and Technology Review (RTR) Risk
Assessment Methodologies: For Review by the EPA's Science Advisory
Board with Case Studies--MACT I Petroleum Refining Sources and
Portland Cement Manufacturing, May 2010.
---------------------------------------------------------------------------

1. 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 a dataset
based on the estimated actual and allowable emissions as the basis for
the risk assessment. This dataset was based on responses to an
Information Collection Request (ICR) sent to approximately 425
facilities potentially subject to the subpart RRR NESHAP. Approximately
161 sources subject to the NESHAP responded, approximately 166
facilities confirmed that they were not subject to the NESHAP and no
responses were received to approximately 51 ICRs. In addition to these
responses, as described in section II.B, an earlier ICR was sent to 9
companies requiring them to provide speciated metal and organic HAP
concentrations for purposes of calculating speciated HAP emissions
based on reported emissions of the surrogate pollutants, THC and PM. As
part of our quality assurance (QA) process, we checked the coordinates
of every facility in the dataset using tools such as Google Earth. We
corrected coordinates that were found to be incorrect. We also
performed QA of the emissions data and release characteristics to
identify outliers and then confirmed or corrected the data.
2. Establishing the Relationship Between Actual Emissions and MACT-
Allowable Emissions Levels
    The available emissions data in the MACT dataset include estimates
of the mass of HAP actually emitted during the specified annual time
period. These ``actual'' emission levels are often lower than the
emission levels that a facility might be allowed to emit and still
comply with the MACT standards. The emissions level allowed to be
emitted by the MACT standards is referred to as the ``MACT-allowable''
emissions level. This represents the highest emissions level that could
be emitted by 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 Hazardous Organic NESHAP
residual risk rules (71 FR 34428, June 14, 2006, and 71 FR 76609,
December 21, 2006, respectively). In those previous actions, we noted
that assessing the risks at the MACT-allowable level is inherently
reasonable since these risks reflect the maximum level sources could
emit and still comply with national emission standards. But 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.)
    As discussed above, allowable and actual emissions were calculated
for each piece of equipment. The estimates of actual emissions are
described in Section II of this preamble.
    Allowable emissions for this source category were calculated by
assuming emissions were at the maximum level allowed by the MACT
standard (i.e., we assume emissions would be emitted at a level equal
to the MACT emission limit). Nevertheless, we note that these are
conservative estimates of allowable emissions. It is unlikely that
emissions would be at the maximum limit at all times because sources
cannot emit HAP at a level that is exactly equal to the limit at all
times and remain in compliance with the standard due to day-to-day
variability in process operations and emissions. On average, facilities
must emit at some level below the MACT limit to ensure that they are
always in compliance.
    The derivation of actual and allowable emissions estimates are
discussed in more detail in the document Draft Development of the RTR
Emissions Dataset for the Secondary Aluminum Production Source Category
which is available in the docket for this proposed rulemaking.
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 each facility in the source category were
estimated using the Human Exposure Model (HEM) (Community and Sector
HEM-3 version 1.1.0). The HEM-3 performs three primary risk assessment
activities: (1) Conducting dispersion modeling to estimate the
concentrations of HAP in ambient air, (2) estimating long-term and
short-term inhalation exposures to individuals residing within 50 km of
the modeled sources 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.\4\ To perform the dispersion modeling and to develop the
preliminary risk estimates, HEM-3 draws on three data libraries. The
first is a library of meteorological data, which is used for dispersion
calculations. This library includes 1 year (1991) of hourly surface and
upper air observations for more than 158 meteorological stations,
selected to provide coverage of the United States and Puerto Rico. A
second library of United States Census Bureau census block \5\ internal
point locations and populations provides the basis of human exposure
calculations (Census, 2000). 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.
---------------------------------------------------------------------------

    \4\ U.S. EPA. Revision to the Guideline on Air Quality Models:
Adoption of a Preferred General Purpose (Flat and Complex Terrain)
Dispersion Model and Other Revisions (70 FR 68218, November 9,
2005).
    \5\ A census block is 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 used as a surrogate for the chronic inhalation exposure
concentration for all the people who reside in that census block. We
calculated the MIR for each facility as the cancer risk associated with
a continuous lifetime (24 hours per day, 7 days per week, and 52 weeks
per year for a 70-year period) exposure to the maximum concentration at
the centroid of 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 unit risk estimate (URE), which is an upper bound
estimate of an individual's probability of contracting cancer over a
lifetime of exposure to a concentration of 1 microgram of the pollutant
per cubic meter of air. For residual risk assessments, we generally use
URE values from the EPA's Integrated Risk Information System (IRIS).
For carcinogenic pollutants without the EPA IRIS values, we look to
other reputable sources of cancer dose-response values, often using
California EPA (CalEPA) URE values, where available. In cases where
new, scientifically credible dose-response values have been developed
in a manner consistent with the EPA guidelines and have undergone a
peer review process similar to that used by the EPA, we may use such
dose-response values in place of, or in addition to, other values, if
appropriate.
    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 \6\) emitted by the
modeled source. Cancer incidence and the distribution of individual
cancer risks for the population within 50 km of any 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.
---------------------------------------------------------------------------

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

    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 target organ-
specific HI, TOSHI). The HQ for chronic exposures is the estimated
chronic exposure divided by the chronic reference level, which is
either the EPA reference concentration (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 an RfC
from the EPA's IRIS database is not available, a value from the
following prioritized sources: (1) The agency for Toxic Substances and
Disease Registry Minimum Risk Level, which is defined as ``an estimate
of daily human exposure to a substance that is likely to be without an
appreciable risk of adverse effects (other than cancer) over a
specified duration of exposure''; (2) the CalEPA Chronic Reference
Exposure Level (REL), which is defined as ``the concentration level at
or below which no adverse health effects are anticipated for a
specified exposure duration;'' or (3) as noted above, a scientifically
credible dose-response value that has been developed in a manner
consistent with the EPA guidelines and has undergone a peer review
process similar to that used by the EPA, in place of or in concert with
other values.
    Screening estimates of acute exposures and risks were also
evaluated for each of the HAP at the point of highest off-site exposure
for each facility (i.e., not just the census block centroids), assuming
that a person is located at this spot at a time when both the peak
(hourly) emission rates from each emission point at the facility and
worst-case dispersion conditions occur. The acute HQ is the estimated
acute exposure divided by the acute dose-response value. In each case,
acute HQ values were calculated using best available, short-term dose-
response values. These acute dose-response values, which are described
below, include the acute REL, acute exposure guideline levels (AEGL)
and emergency response planning guidelines (ERPG) for 1-hour exposure
durations. As discussed below, we used conservative assumptions for
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.'' Acute REL values are
based on the most sensitive, relevant, adverse health effect reported
in the medical and toxicological literature. Acute REL values are
designed to protect the most sensitive sub-populations (e.g.,
asthmatics) by the inclusion of margins of safety. Since margins of
safety are incorporated to address data gaps and uncertainties,
exceeding the acute REL does not automatically indicate an adverse
health impact.

    AEGL values were derived in response to recommendations from the
National Research Council (NRC). As described in Standing Operating
Procedures (SOP) of the National Advisory Committee on Acute Exposure
Guideline Levels for Hazardous Substances (http://www.epa.gov/opptintr/aegl/pubs/sop.pdf),\7\ ``the NRC's previous name for acute exposure
levels--community emergency exposure levels--was replaced by the term
AEGL to reflect the broad application of these values to planning,
response, and prevention in the community, the workplace,
transportation, the military, and the remediation of Superfund sites.''
This document also states that AEGL values ``represent threshold
exposure limits for the general public and are applicable to emergency
exposures ranging from 10 minutes to eight hours.'' The document lays
out the purpose and objectives of AEGL by stating (page 21) that ``the
primary purpose of the AEGL program and the National Advisory Committee
for Acute Exposure Guideline Levels for Hazardous Substances is to
develop guideline levels for once-in-a-lifetime, short-term exposures
to airborne concentrations of acutely toxic, high-priority chemicals.''
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 U.S. Federal and
state agencies and possibly the international community in conjunction
with chemical emergency response, planning, and prevention programs.
More specifically, the AEGL values will be used for conducting various
risk assessments to aid in the development of emergency preparedness
and prevention plans, as well as real-time emergency response actions,
for accidental chemical releases at fixed facilities and from transport
carriers.''
---------------------------------------------------------------------------

    \7\ 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.''
    ERPG values are derived for use in emergency response, as described
in the American Industrial Hygiene Association's document entitled,
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.'' \8\ 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.''
---------------------------------------------------------------------------

    \8\ 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 assess potential
for 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 similar to
the corresponding ERPG-1 values, and AEGL-2 values are often similar to
ERPG-2 values. Maximum HQ values from our acute screening risk
assessments typically result when basing them on the acute REL value
for a particular pollutant. In cases where our maximum acute HQ value
exceeds 1, we also report the HQ value based on the next highest acute
dose-response value (usually the AEGL-1 and/or the ERPG-1 value).
    To develop screening estimates of acute exposures, we developed
estimates of maximum hourly emission rates by multiplying the average
actual annual hourly emission rates by a factor to cover routinely
variable emissions. We chose the factor to use based on process
knowledge and engineering judgment and with awareness of a Texas study
of short-term emissions variability, which showed that most peak
emissions events, in a heavily-industrialized 4-county area (Harris,
Galveston, Chambers, and Brazoria Counties, Texas) were less than twice
the annual average hourly emissions rate. The highest peak emissions
event was 74 times the annual average hourly emissions rate, and the
99th percentile ratio of peak hourly emissions rate to the annual
average hourly emissions rate was 9.\9\ This analysis is provided in
Appendix 4 of the Draft Residual Risk Assessment for Secondary Aluminum
Production which is available in the docket for this action.
Considering this analysis, unless specific process knowledge or data
are available to provide an alternate value, to account for more than
99 percent of the peak hourly emissions, we generally apply the
assumption to most source categories that the maximum one-hour
emissions rate from any source other than those resulting in fugitive
dust emissions are 10 times the average annual hourly emissions rate
for that source. We use a factor other than 10 in some cases if we have
information that indicates that a different factor is appropriate for a
particular source category. For this source category however, there was
no such information available and the default factor of 10 was used in
the acute screening process.
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    \9\ See http://www.tceq.state.tx.us/compliance/field_ops/eer/index.html or docket to access the source of these data.
---------------------------------------------------------------------------

    When worst-case HQ values from the initial acute screen step were
less than 1, acute impacts were deemed negligible and no further
analysis was performed. In the cases where any worst-case 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. However, for this source category no acute
values were greater than 1 and therefore, further refinement was not
performed.
    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, hence our use of the multiplier
approach.
    To better characterize the potential health risks associated with
estimated acute exposures to HAP, and in response to a key
recommendation from the SAB's peer review of the EPA's RTR risk
assessment methodologies,\10\ we generally examine a wider range of
available acute health metrics than we do for our chronic risk
assessments. This is in response to the SAB's acknowledgement that
there are generally more data gaps and inconsistencies in acute
reference values than there are in chronic reference values.
---------------------------------------------------------------------------

    \10\ 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.
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    Comparisons of the estimated maximum off-site 1-hour exposure
levels are not typically made to occupational levels for the purpose of
characterizing public health risks in RTR assessments. This is because
they are developed for working age adults and are not generally
considered protective for the general public. We note that occupational
ceiling values are, for most chemicals, set at levels higher than a 1-
hour AEGL-1.
4. Conducting 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 two-
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 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. Since three of these PB-HAP (cadmium
compounds, POM and chlorinated D/F) are emitted by at least one
facility in this source category, we proceeded to the second step of
the evaluation. In this step, we determined whether the facility-
specific emission rates of each of the emitted PB-HAP were large enough
to create the potential for significant non-inhalation human or
environmental risks under, worst-case conditions. To facilitate this
step, we developed emission rate thresholds for each PB-HAP using a
hypothetical worst-case screening exposure scenario developed for use
in conjunction with the EPA's 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 were compared to
the TRIM-Screen emission threshold values for each of the PB-HAP
identified in the source category datasets to assess the potential for
significant human health risks or environmental risks via non-
inhalation pathways. See Section IV for results of this screening
analysis.
5. Conducting Other Risk-Related Analyses: Facilitywide Assessments
    To put the source category risks in context, for our residual risk
reviews, we also typically examine the risks from the entire
``facility,'' where the facility includes all HAP-emitting operations
within a contiguous area and under common control. In these
facilitywide assessments 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. For the secondary aluminum source
category, a facilitywide assessment was performed for all major
sources.
    A facilitywide assessment was not conducted for area sources. By
definition, no major sources of HAP (e.g., primary aluminum production
or coil coating operations) are collocated with any of the secondary
aluminum area sources. Further, at many area sources, equipment subject
to the Secondary Aluminum NESHAP is the only HAP-emitting equipment.
Therefore, the most significant HAP emissions from area sources were
already being considered under the area source risk assessment, and low
levels of HAP emissions from equipment not subject to the Secondary
Aluminum NESHAP at these facilities would not contribute appreciably to
the risk profile. The results of the facilitywide assessment for major
sources are provided in Section IV.
6. Considering Uncertainties in Risk Assessment
    Uncertainty and the potential for bias are inherent in all risk
assessments, including those performed for the Secondary Aluminum
source category addressed in this proposal. Although uncertainty
exists, we believe that our approach, which used conservative tools and
assumptions, ensures that our decisions are health-protective. A brief
discussion of the uncertainties in the emissions datasets, dispersion
modeling, inhalation exposure estimates and dose-response relationships
follows below. A more thorough discussion of these uncertainties is
included in the risk assessment documentation (referenced earlier)
available in the docket for this action.
a. Uncertainties in the Emissions Datasets
    Although the development of the MACT dataset involved QA/quality
control processes, the accuracy of emissions values will vary depending
on the source of the data, the degree to which data are incomplete or
missing, the degree to which assumptions made to complete the datasets
are accurate, errors in estimating emissions values and other factors.
The emission estimates considered in this analysis were generally
developed from one-time or periodic performance tests that do not
reflect short-term fluctuations during the course of a year or
variations from year to year.
    The estimates of peak hourly emission rates for the acute effects
screening assessment were based on a default factor of 10 applied to
the average annual hourly emission rate, which is intended to account
for emission fluctuations due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    While 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, model
options (e.g., rural/urban, plume depletion, chemistry) were selected
to provide an overestimate of ambient air concentrations of the HAP
rather than underestimates. However, because of practicality and data
limitation reasons, some factors (e.g., meteorology, building downwash)
have the potential in some situations to overestimate or underestimate
ambient impacts. For example, meteorological data were taken from a
single year (1991), and facility locations can be a significant
distance from the sites where these data were taken. Despite these
uncertainties, we believe that at off-site 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.\11\
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.
---------------------------------------------------------------------------

    \11\ Short-term mobility is movement from one micro-environment
to another over the course of hours or days. Long-term mobility is
movement from one residence to another over the course of a
lifetime.
---------------------------------------------------------------------------

    In addition, the assessment predicted the chronic exposures at the
centroid of each populated census block as surrogates for the exposure
concentrations for all people living in that block. Using the census
block centroid to predict chronic exposures tends to over-predict
exposures for people in the census block who live further from the
facility, and under-predict exposures for people in the census block
who live closer to the facility. Thus, using the census block centroid
to predict chronic exposures may lead to a potential understatement or
overstatement of the true maximum impact, but it is an unbiased
estimate of average risk and incidence.
    The assessments evaluate the cancer inhalation risks associated
with continuous 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 risks posed by a given
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 emission 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.\12\
---------------------------------------------------------------------------

    \12\ 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 other factors specific to the acute exposure assessment. 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 overestimate 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 2005 Cancer Guidelines; namely, that ``the
primary goal of the 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).\13\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances, the risk could also be
greater.\14\ 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).
---------------------------------------------------------------------------

    \13\ IRIS glossary (http://www.epa.gov/NCEA/iris/help_gloss.htm).
    \14\ 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 reference dose (RfD)) values
represent chronic exposure levels that are intended to be health-
protective levels. Specifically, these values provide an

estimate (with uncertainty spanning perhaps an order of magnitude) of
daily oral exposure (RfD) or of a continuous inhalation exposure (RfC)
to the human population (including sensitive subgroups) that is likely
to be without an appreciable risk of deleterious effects during a
lifetime. To derive values that are intended to be ``without
appreciable risk,'' the methodology relies upon an uncertainty factor
(UF) approach (U.S. EPA, 1993, 1994) which includes consideration of
both uncertainty and variability. When there are gaps in the available
information, UF are applied to derive reference values that are
intended to protect against appreciable risk of deleterious effects.
The UF are commonly default values,\15\ 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 ``uncertainty factor,'' 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 more often they use individual UF
values that may be less than 10. UF are applied based on chemical-
specific or health effect-specific information (e.g., simple irritation
effects do not vary appreciably between human individuals, hence a
value of 3 is typically used), or based on the purpose for the
reference value (see the following paragraph). The UF applied in acute
reference value derivation include: (1) Heterogeneity among humans; (2)
uncertainty in extrapolating from animals to humans; (3) uncertainty in
lowest observed adverse effect (exposure) level to no observed adverse
effect (exposure) level adjustments; and (4) uncertainty in accounting
for an incomplete database on toxic effects of potential concern.
Additional adjustments are often applied to account for uncertainty in
extrapolation from observations at one exposure duration (e.g., 4
hours) to derive an acute reference value at another exposure duration
(e.g., 1 hour).
---------------------------------------------------------------------------

    \15\ According to the NRC report, Science and Judgment in Risk
Assessment (NRC, 1994) ``[Default] options are generic approaches,
based on general scientific knowledge and policy judgment, that are
applied to various elements of the risk assessment process when the
correct scientific model is unknown or uncertain.'' The 1983 NRC
report, Risk Assessment in the Federal Government: Managing the
Process, defined default option as ``the option chosen on the basis
of risk assessment policy that appears to be the best choice in the
absence of data to the contrary'' (NRC, 1983a, p. 63). Therefore,
default options are not rules that bind the Agency; rather, the
Agency may depart from them in evaluating the risks posed by a
specific substance when it believes this to be appropriate. In
keeping with EPA's goal of protecting public health and the
environment, default assumptions are used to ensure that risk to
chemicals is not underestimated (although defaults are not intended
to overtly overestimate risk). See EPA, 2004, An Examination of EPA
Risk Assessment Principles and Practices, EPA/100/B-04/001 available
at: http://www.epa.gov/osa/pdfs/ratf-final.pdf.
---------------------------------------------------------------------------

    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 (see
table 3.1-1 of the risk assessment document available in the docket for
this proposed rulemaking). 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., POM), 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,
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 a dose-response metric
changes enough to indicate that the risk assessment supporting this
notice may significantly understate human health risk. More information
regarding the dose-response values used in this assessment is provided
in the Draft Residual Risk Assessment for the Secondary Aluminum
Production Source Category, which is available in the docket.
e. Uncertainties in the Multipathway and Environmental Effects
Screening Assessment
    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. For this source category, we only performed
a worst-case multipathway screening assessment for PB-HAP. Thus, it is
important to note that potential PB-HAP multipathway risks are biased
high.

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

    In evaluating and developing standards under section 112(f)(2), as
discussed in Section I.A of this preamble, we apply a two-step process
to address residual risk. In the first step, the EPA determines whether
risks are acceptable. This determination

``considers all health information, including risk estimation
uncertainty, and includes a presumptive limit on maximum individual
lifetime [cancer] risk (MIR) \16\ of approximately 1 in 10 thousand
[i.e., 100 in 1 million]'' (54 FR at 38045). In the second step of the
process, the EPA sets the standard at a level that provides 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.
---------------------------------------------------------------------------

    \16\ 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 has 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 non-cancer hazard
index (HI); and the maximum acute non-cancer hazard (72 FR 25138, May
3, 2007; 71 FR 42724, July 27, 2006). In more recent proposals the EPA
also presented and considered additional measures of health
information, such as estimates of the risks associated with the maximum
level of emissions which might be allowed by the current MACT standards
(see, e.g., 76 FR 72770, November 25, 2011, 76 FR 72508, November 23,
2011, 75 FR 65068, October 21, 2010, and 75 FR 80220, December 21,
2010). The EPA also discussed and considered risk estimation
uncertainties. The EPA is providing this same type of information in
support of the proposed determinations described in this Federal
Register notice.
    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 at 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 these factors 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 non-cancer health effects, and the uncertainties of the
risk estimates. In this way, the effect on the most exposed individuals
can be reviewed as well as the impact on the general public. These
factors can then be weighed in each individual case. This approach
complies with the Vinyl Chloride mandate that the Administrator
ascertain an acceptable level of risk to the public by employing [her]
expertise to assess available data. It also complies with the
Congressional intent behind the CAA, which did not exclude the use of
any particular measure of public health risk from the EPA's
consideration with respect to CAA section 112 regulations, and,
thereby, implicitly permits consideration of any and all measures of
health risk which the Administrator, in [her] judgment, believes are
appropriate to determining what will `protect the public health' '' (54
FR at 38057).
    For example, 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'' (54 FR at 38045). Similarly, with
regard to the ample margin of safety analysis, the EPA stated in the
Benzene NESHAP that: ``the EPA believes the relative weight of the many
factors that can be considered in selecting an ample margin of safety
can only be determined for each specific source category. This occurs
mainly because technological and economic factors (along with the
health-related factors) vary from source category to source category''
(54 FR at 38061).
    The EPA wishes to point out that certain health information has not
been considered to date in making residual risk determinations. In
assessing risks to populations in the vicinity of the facilities in
each category, we present estimates of risk associated with HAP
emissions from the source category alone (source category risk
estimates) and HAP emissions from the entire facility at which the
covered source category is located (facilitywide risk estimates). We do
not attempt to characterize the risks associated with all HAP emissions
impacting the populations living near the sources in these categories.
That is, at this time, we do not attempt to quantify those HAP risks
that may be associated with emissions from other facilities that do not
include the source category in question, mobile source emissions,
natural source emissions, persistent environmental pollution, or
atmospheric transformation in the vicinity of the sources in these
categories.
    The agency understands the potential importance of considering an
individual's total exposure to HAP in addition to considering exposure
to HAP emissions from the source category and facility. This is
particularly important when assessing non-cancer risks, where
pollutant-specific exposure health reference levels (e.g., Reference
Concentrations (RfCs)) are based on the assumption that thresholds
exist for adverse health effects. For example, the agency recognizes
that, although exposures attributable to emissions from a source
category or facility alone may not indicate the potential for increased
risk of adverse non-cancer health effects in a population, the
exposures resulting from emissions from the facility in combination
with emissions from all of the other sources (e.g., other facilities)
to which an individual is exposed may be sufficient to result in
increased risk of adverse non-cancer health effects. In May 2010, the
Science Advisory Board (SAB) advised us ``* * * that RTR assessments
will be most useful to decision makers and communities if results are
presented in the broader context of aggregate and cumulative risks,
including background concentrations and contributions from other
sources in the area.'' \17\
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    \17\ The EPA's responses to this and all other key
recommendations of the SAB's advisory on RTR risk assessment
methodologies (which is available at: http://yosemite.epa.gov/sab/
sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-
007-unsigned.pdf) are outlined in a memo to this rulemaking docket
from David Guinnup, UESPA/OAQPS entitled, EPA's Actions in Response
to the Key Recommendations of the SAB Review of RTR Risk Assessment
Methodologies.

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    While we are interested in placing source category and facilitywide
HAP risks in the context of total HAP risks from all sources combined
in the vicinity of each source, we are concerned about the
uncertainties of doing so. At this point, we believe that such
estimates of total HAP risks will have significantly greater associated
uncertainties than for the source category or facilitywide estimates
hence compounding the uncertainty in any such comparison. This is
because we have not conducted a detailed technical review of HAP
emissions data for source categories and facilities that have not
previously undergone an RTR review or are not currently undergoing such
review. We are requesting comment on whether and how best to estimate
and evaluate total HAP exposure in our assessments and, in particular,
on whether and how it might be appropriate to use information from
EPA's National Air Toxics Assessment (NATA) to support such estimates.
We are also seeking comment on how best to consider various types and
scales of risk estimates when making our acceptability and ample margin
of safety determinations under CAA section 112(f).

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 Secondary Aluminum Production 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 appropriate or
necessary to propose amendments to the 2000 NESHAP to require any of
the identified developments.
    Based on our analyses of the data and information collected from
industry and the trade organization representing facilities subject to
the NESHAP, our general understanding of the industry, and other
available information in the literature on potential controls for this
industry, we identified several new 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 2000 Secondary
Aluminum Production NESHAP.
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the 2000 Secondary Aluminum Production NESHAP) that could result in
significant additional emissions reduction.
     Any work practice or operational procedure that was not
identified or considered during development of the 2000 Secondary
Aluminum Production NESHAP.
     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 2000 Secondary
Aluminum Production NESHAP.
    In addition to reviewing the practices, processes, or control
technologies that were not considered at the time we developed the 2000
NESHAP, we reviewed a variety of data sources in our evaluation of
whether there were additional practices, processes, or controls to
consider for the Secondary Aluminum Production industry. Among the data
sources we reviewed were the NESHAP for various industries that were
promulgated after the 2000 NESHAP. We reviewed the regulatory
requirements and/or technical analyses associated with these regulatory
actions to identify any practices, processes, and control technologies
considered in these efforts that could possibly be applied to emissions
sources in the Secondary Aluminum Production source category, as well
as the costs, non-air impacts, and energy implications associated with
the use of these technologies.
    Additionally, we requested information from facilities regarding
developments in practices, processes, or control technology. Finally,
we reviewed other information sources, such as State or local
permitting agency databases and industry-supported databases. In
particular, we consulted the EPA's RACT/BACT/LAER Clearinghouse (RBLC)
to identify potential technology advances. Control technologies
classified as RACT (Reasonably Available Control Technology), BACT
(Best Available Control Technology), or LAER (Lowest Achievable
Emissions Rate) apply to stationary sources depending on whether the
sources are existing or new and on the size, age, and location of the
facility. BACT 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
emissions streams. We searched this database to determine whether it
contained any practices, processes or control technologies for the
types of processes covered by the Secondary Aluminum Production NESHAP.
No such practices, processes or control technologies were identified in
this database.

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 startup, shutdown and
malfunction (SSM) provisions of the MACT rule in order to ensure that
they are consistent with the court decision in Sierra Club v. EPA, 551
F. 3d 1019 (D.C. Cir. 2008).
    We are also proposing changes to the rule related to affirmative
defense for violation of an emission limit during a malfunction. We are
proposing other changes to address HF emissions, fugitive emissions
during testing and numerous clarifications and corrections related to
the existing provisions in the rule. Descriptions of each issue and the
proposed revision to address the issue 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 Secondary Aluminum Production source category and our proposed
decisions concerning changes to the Secondary Aluminum Production
NESHAP.

A. What are the results of the risk assessments?

    For major sources in the Secondary Aluminum source category, we

conducted an inhalation risk assessment for all HAP emitted. In
addition, we performed a facilitywide risk assessment for the major
sources in the secondary aluminum source category. For area sources, we
conducted an inhalation risk assessment for D/F since this is the only
HAP covered by the subpart RRR MACT standards at area sources. For all
sources, we conducted multipathway screening analyses for PB-HAP
emitted (e.g., D/F). Although there are 53 major sources and 108 area
sources covered by the subpart RRR MACT standards, 52 major sources and
103 area sources were modeled due to the other sources' lack of
equipment subject to the applicable emission standards. Results of the
risk assessment are presented briefly below and in more detail in the
residual risk documentation referenced in Section III of this preamble,
which is available in the docket for this action.
    Table 4 of this preamble provides an overall summary of the results
of the inhalation risk assessment.

                                        Table 4--Secondary Aluminum Production Inhalation Risk Assessment Results
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                 Maximum individual cancer risk                                    Maximum chronic non-cancer
                                       (in 1 million) \1\           Estimated       Estimated               TOSHI \2\
                               ---------------------------------  population at   annual cancer --------------------------------    Worst-case maximum
     Category & number of                           Based on     increased risk     incidence       Based on        Based on     refined screening acute
      facilities modeled        Based on actual     allowable    of cancer >= 1    (cases per        actual         allowable       non-cancer HQ \3\
                                emissions level     emissions     in 1 million      year) \4\       emissions       emissions
                                                      level            \4\                            level           level
--------------------------------------------------------------------------------------------------------------------------------------------------------
Major Source (52).............              1                20               2          0.0006          0.05             1      HQREL 0.7 (HCl)
Area Source (103).............              0.4               6               0          0.0006          0.0003           0.005  .......................
Facility-wide Major Source....             20    ..............          62,000          0.006           0.4     ..............  .......................
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Estimated maximum individual excess lifetime cancer risk due to HAP emissions from the source category. We did not have allowable emissions
  information at the facilitywide level, therefore, risk estimates based on facilitywide allowable emissions were not calculated.
\2\ Maximum TOSHI. The target organ with the highest TOSHI for the secondary aluminum source category is the respiratory system.
\3\ There is no acute dose-response value for dioxins, thus an acute HQ value for area sources was not calculated. See Section III.B of this preamble
  for explanations of acute dose-response values.
\4\ These estimates are based on actual emissions.

    The results of the chronic inhalation cancer risk assessment for
major sources indicate that the maximum lifetime individual cancer
risk, considering actual emissions, could be up to 1 in 1 million,
driven by dioxin emissions. The maximum cancer risks for this source
category exceeded a cancer risk of 1 in 1 million at 1 of 52
facilities. The total estimated cancer incidence from this source
category based on actual emission levels is 0.0006 excess cancer cases
per year, or one excess case in every 1,666 years. No people were
estimated to have cancer risks above 10 in a million and approximately
2 people were estimated to have cancer risks above 1 in 1 million
considering all major source facilities in this source category. Based
on MACT-allowable emissions for the major sources in this category, the
MIR could be up to 20 in 1 million.
    With respect to chronic inhalation noncancer risk from major
sources, we estimate a maximum TOSHI value of 0.05 for the Secondary
Aluminum source category, primarily from hydrochloric acid from Group 1
furnaces. Considering MACT-allowable emissions, this maximum TOSHI
value is estimated to be 1. Moreover, our worst-case highest acute
screening value for major sources was 0.7 based on the REL for HCL.
    Considering facility wide emissions at the 52 major sources, the
MIR is estimated to be up to 20 in 1 million, the estimated annual
incidence is 0.006 cases per year, and the chronic non-cancer TOSHI
value is calculated to be 0.4.
    In addition, we estimated risks associated with dioxin emissions at
the 103 area sources in the Secondary Aluminum Production source
category. The results of the chronic inhalation cancer risk assessment
indicate that the maximum lifetime individual cancer risk could be up
to 0.4 in 1 million and an estimated annual incidence of 0.0006 cases
per year. Considering MACT-allowable emissions, the MIR could be up to
6 in 1 million. With respect to chronic inhalation noncancer risk from
D/F emissions at area sources, we estimate a maximum TOSHI value of
0.0003. Considering MACT-allowable emissions, this maximum TOSHI value
is estimated to be 0.005 for area sources.
    In addition to the analyses presented above, to screen for
potential multipathway effects from emissions of PB-HAP (such as
cadmium, dioxins and PAHs) we compared actual emission rates from major
source facilities in this source category to the screening values for
these PB HAP described above (see Section III(A)(4)). For dioxins, we
also screened for potential multipathway effects from emissions of D/F
from area sources by comparing the estimated actual emission rates from
these area sources to the screening value for D/F described above. (see
Risk Assessment Document Appendix 4 for a more detailed discussion of
screening emission rates). Results of this worst-case screen estimate
that actual POM emissions from 10 of the 52 major source facilities
exceed the POM screening emission rate. With respect to D/F, of the 46
major sources that emitted dioxins, 39 exceeded our screening emission
rate. Similarly, 76 out of 103 area sources exceeded our D/F screening
rate. These exceedances of the worst-case multipathway screening level
for POM and dioxins indicate that there may be potential multipathway
impacts of concern due to emissions of POM and dioxins. In general,
emission rates below the worst-case multipathway screening level
indicate no significant potential for multipathway-related health or
environmental effects; whereas emission levels above this worst-case
screening level only indicate the potential for multipathway-related
health or environmental risks of concern based on a worst-case
scenario. Thus, we note that these screening values are biased high for
purposes of screening and are subject to significant uncertainties. As
such, they do not represent refined estimates of risk and thus, do not
necessarily indicate that potential multipathway risks from the source
category may be a concern; we can only say that we cannot rule them
out.
    With respect to the potential for adverse environmental effects
from non PB-HAP, we note that for both major

and area sources all chronic non-cancer HQ values for all pollutants
considering actual emissions are well below 1 using human health
reference values. Thus, we believe that it is unlikely that adverse
environmental effects would occur at the actual HAP concentrations
estimated in our human health risk assessment.

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

1. Risk Acceptability
    As noted in Section III.C of this preamble, we weigh all health
risk factors in our risk acceptability determination, including the
MIR, the numbers of persons in various risk ranges, cancer incidence,
the maximum noncancer HI, the maximum acute noncancer hazard, the
extent of noncancer risks, the potential for adverse environmental
effects, distribution of risks in the exposed population, and risk
estimation uncertainties (54 FR 38044, September 14, 1989).
    For the Secondary Aluminum Production source category, the risk
analysis indicates that the cancer risks to the individual most exposed
could be up to 1 in 1 million due to actual emissions and up to 20 in 1
million due to MACT-allowable emissions. These risks are considerably
less than 100 in 1 million, which is the presumptive upper limit of
acceptable risk. The risk analysis also shows very low cancer incidence
(0.0006 cases per year), as well as no potential for adverse chronic or
acute non-cancer health effects. In addition, the risk assessment
indicates no significant potential for adverse environmental effects.
    In addition to the analyses presented above, to screen for
potential multipathway effects from emissions of D/F and POM, we
compared the estimated actual emission rates from facilities in this
source category to the multipathway screening levels described in
section III.B. With respect to POM and dioxins, both major and area
sources in the category exceeded our worst-case screening levels.
However, we note that this is a worst-case conservative screening level
analysis, therefore these results are biased high for purposes of
screening and are subject to significant uncertainties. Moreover, we
note that due to data limitations we were unable to further refine this
worst-case screening scenario. As such, they do not necessarily
indicate that significant multipathway risks actually exist at
secondary aluminum facilities, only that we cannot rule them out as a
possibility. With regard to facilitywide multipathway risk, based on
the low level of risk identified for the source category, a
facilitywide multipathway risk analysis was not conducted for this
source category.
    Considering all of the health risk information and factors
discussed above, including the uncertainties discussed in section
IV.A.7 of this preamble, we propose that the risks from the Secondary
Aluminum Production source category are acceptable.
2. Ample Margin of Safety Analysis
    We next considered whether the existing MACT standard provides an
ample margin of safety to protect public health. Under the ample margin
of safety analysis, we evaluated the cost and feasibility of available
control technologies and other measures (including the controls,
measures and costs reviewed under the technology review) that could be
applied in this source category to further reduce the risks (or
potential risks) due to emissions of HAP identified in our risk
assessment, along with all of the health risks and other health
information considered in the risk acceptability determination
described above. In this analysis we considered the results of the
technology review, risk assessment and other aspects of our MACT rule
review to determine whether there are any cost-effective controls or
other measures that would reduce emissions further to provide an ample
margin of safety with respect to the risks associated with these
emissions.
    For POM, THC and metal HAP emissions, our risk analysis indicated
very low potential for risk from the facilities in the source category.
Our technology review did not identify any new practices, controls or
process options that are being used in this industry or in other
industries that would be cost-effective for further reduction of these
emissions. Based on the estimated low risk levels and absence of new
practices or control options, we conclude that the provisions of the
current MACT provide for an ample margin of safety for public health
with respect to emissions of POM, THC and metal HAP.
    Our multipathway screening analysis results indicated exceedances
of the worst-case screening levels which do not necessarily indicate
any risks, however, they do suggest a potential for risks that cannot
be ruled out. To evaluate the potential to reduce D/F emissions to
ensure an ample margin of safety, our analysis for D/F focused on two
options: (1) Lowering the existing D/F limit from 15 to 10 [mu]g TEQ/Mg
feed for Group 1 furnaces processing other than clean charge at all
facilities; and (2) lowering the existing D/F limit for Group 1
furnaces processing other than clean charge, after applying a
subcategorization based on facility production capacity. The lower D/F
limits potentially could be met by using an activated carbon injection
(ACI) system. With regard to the option of lowering the emission limit
to 10 [mu]g TEQ/Mg feed for Group 1 furnaces handling other than clean
charge, we estimate that about 11 facilities would need to reduce their
D/F emissions and that the costs would be about $5.9 million in total
capital costs with total annualized costs of about $2.7 million. This
option would achieve an estimated 1.66 grams TEQ reduction of D/F
emissions with an overall cost-effectiveness of about $1.61 million per
gram D/F TEQ. The second option of lowering the emission limit based on
a subcategorization according to facility production capacity yielded
cost-effectiveness estimates of greater than $1 million per gram D/F
TEQ reduced. Furthermore, our analysis indicates that these options
would not result in significant emissions reductions and would not,
therefore, result in significant changes to the potential risk levels.
After considering the costs and the small reductions that would be
achieved, we have decided not to propose any of these options. For more
information, please refer to the Draft Technical Document for the
Secondary Aluminum Production Source Category that is available in the
public docket for this proposed rulemaking.
    We also evaluated possible options based on work practices to