[Federal Register Volume 76, Number 227 (Friday, November 25, 2011)]
[Proposed Rules]
[Pages 72770-72819]
[FR Doc No: 2011-29454]

Vol. 76

Friday,

No. 227

November 25, 2011

Part II

Environmental Protection Agency

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40 CFR Part 63

 National Emissions Standards for Hazardous Air Pollutants: Mineral
Wool Production and Wool Fiberglass Manufacturing; Proposed Rule

Federal Register / Vol. 76 , No. 227 / Friday, November 25, 2011 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2010-1041, EPA-HQ-OAR-2010-1042; FRL-9491-9]
RIN 2060-AQ90

National Emissions Standards for Hazardous Air Pollutants:
Mineral Wool Production and Wool Fiberglass Manufacturing

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 Mineral Wool Production and
Wool Fiberglass Manufacturing to address the results of the residual
risk and technology review that the EPA is required to conduct by the
Clean Air Act. The proposed Mineral Wool Production amendments include
emissions limits for carbonyl sulfide, hydrogen fluoride and
hydrochloric acid for cupolas; add combined collection and curing
processes as new regulated sources; and include emissions limits for
formaldehyde, phenol and methanol for combined collection and curing
operations. Modifications to the testing and monitoring and related
notification, recordkeeping and reporting requirements are also
proposed.
    The proposed amendments for the Wool Fiberglass Manufacturing
source category include emissions limits for chromium compounds,
hydrogen fluoride, hydrochloric acid and particulate matter for glass-
melting furnaces at major sources; revised emissions limits for
formaldehyde, and the addition of emissions limits for phenol and
methanol for bonded product lines at major sources; and modifications
to testing and monitoring and related notification, recordkeeping and
reporting requirements.
    These proposed rules only apply to major sources, but we plan to
regulate wool fiberglass area sources in a future action.
    We are also proposing to revise provisions addressing periods of
startup, shutdown and malfunction to ensure that the rules are
consistent with a recent court decision.

DATES: Comments must be received on or before January 24, 2012. Under
the Paperwork Reduction Act, comments on the information collection
provisions are best assured of having full effect if the Office of
Management and Budget receives a copy of your comments on or before
December 27, 2011.
    Public Hearing. If anyone contacts the EPA requesting to speak at a
public hearing by December 5, 2011, a public hearing will be held on
December 12, 2011.

ADDRESSES: Submit your comments, identified by Docket ID Numbers EPA-
HQ-OAR-2010-1041 and EPA-HQ-OAR-2010-1042, 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-2010-1041 and EPA-HQ-OAR-2010-1042.
     Fax:<PHONE_NUMBER>, Attention Docket ID Number EPA-HQ-
OAR-2010-1041 or EPA-HQ-OAR-2010-1042.
     Mail: U.S. Postal Service, send comments to: EPA Docket
Center, EPA West (Air Docket), Attention Docket ID Number EPA-HQ-OAR-
2010-1041 or EPA-HQ-OAR-2010-1042, U.S. Environmental Protection
Agency, Mailcode: 2822T, 1200 Pennsylvania Ave. NW., Washington, DC
20460. Please include a total of two copies. In addition, please mail a
copy of your comments on the information collection provisions to the
Office of Information and Regulatory Affairs, Office of Management and
Budget, Attn: Desk Officer for EPA, 725 17th Street NW., Washington, DC
20503.
     Hand Delivery: U.S. Environmental Protection Agency, EPA
West (Air Docket), Room 3334, 1301 Constitution Ave. NW., Washington,
DC 20004, Attention Docket ID Number EPA-HQ-OAR-2010-1041 or EPA-HQ-
OAR-2010-1042. 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 on the Mineral Wool RTR to
Docket ID Number EPA-HQ-OAR-2010-1041 and direct your comments on the
Wool Fiberglass RTR to Docket ID Number EPA-HQ-OAR-2010-1042. 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 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 dockets for this rulemaking under
Docket ID Number EPA-HQ-OAR-2010-1041 (Mineral Wool Production) and
EPA-HQ-OAR-2010-1042 (Wool Fiberglass Manufacturing). 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>.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Susan Fairchild, Sector Policies and Programs
Division (D243-04), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, telephone<PHONE_NUMBER>; fax number: (919) 541-

3207; and email address<EMAIL_ADDRESS>For specific
information regarding the risk modeling methodology, contact Mr. Chris
Sarsony, Health and Environmental Impacts Division (C539-02), Office of
Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; telephone number:
(919) 541-4843; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>For information about the applicability of the
NESHAP to a particular entity, contact Scott Throwe, Office of
Enforcement and Compliance Assurance; U.S. EPA Headquarters Ariel Rios
Building; 1200 Pennsylvania Avenue NW. Mail Code: 2227A; Washington, DC
20460; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Organization of this Document. The information in this preamble is
organized as follows:

I. Preamble Acronyms and Abbreviations
II. General Information
    A. Does this action apply to me?
    B. Where can I get a copy of this document and other related
information?
    C. What should I consider as I prepare my comments for the EPA?
    D. When will a public hearing occur?
III. Background Information
    A. What are NESHAP?
    B. What litigation is related to this proposed action?
IV. Mineral Wool and Wool Fiberglass Source Categories
    A. Overview of the Mineral Wool Production Source Category and
MACT Standards
    B. Overview of the Wool Fiberglass Manufacturing Source Category
and 1999 MACT Rule
    C. What data collection activities were conducted to support
this action?
V. Analyses Performed
    A. How did we estimate risks posed by the source categories?
    B. How did we consider the risk results in making decisions for
this proposal?
    C. How did we perform the technology review?
    D. What other issues are we addressing in this proposal?
    E. What analyses were performed for the Mineral Wool Production
source category under the Regulatory Flexibility Act?
VI. Summary of Proposed Decisions and Actions
    A. What are the proposed decisions and actions related to the
Mineral Wool Production NESHAP?
    B. What are the proposed decisions and actions related to the
Wool Fiberglass Manufacturing NESHAP?
    C. What are the proposed decisions and actions related to
startup, shutdown and malfunction?
    D. What are the proposed decisions and actions related to
electronic reporting?
VII. Rationale for the Proposed Actions for the Mineral Wool
Production Source Category
    A. What data were used for the NESHAP analyses?
    B. What are the proposed decisions regarding surrogacy
relationships?
    C. What are the proposed decisions regarding certain unregulated
emissions sources?
    D. What are the proposed decisions regarding subcategorization?
    E. What are the results from the risk assessments performed and
the proposed decisions for the Mineral Wool Production source
category?
    F. What are our proposed decisions for the Mineral Wool
Production source category based on risk acceptability and ample
margin of safety?
    G. What are the results from the technology review and proposed
decisions?
VIII. Rationale for the Proposed Actions for the Wool Fiberglass
Manufacturing Source Category
    A. What data were used for the NESHAP analyses?
    B. What are the proposed decisions regarding surrogacy
relationships?
    C. What are the proposed decisions regarding certain unregulated
emissions sources?
    D. What are the results from the risk assessments and analyses
and the proposed decisions for the Wool Fiberglass Manufacturing
Source Category?
    E. What are our proposed decisions for the Wool Fiberglass
Manufacturing source category based on risk acceptability and ample
margin of safety?
    F. What are the results from the technology review and proposed
decisions?
IX. Summary of Cost, Environmental, and Economic Impacts for the
Mineral Wool Source Category
    A. What are the affected sources in the Mineral Wool Production
source category?
    B. How are the impacts for this proposal evaluated?
    C. What are the air quality impacts for the Mineral Wool
Production source category?
    D. What are the water quality and solid waste impacts?
    E. What are the secondary impacts?
    F. What are the energy impacts?
    G. What are the cost impacts for the Mineral Wool Production
source category?
    H. What are the economic impacts for the Mineral Wool Production
source category?
    I. What are the benefits for the Mineral Wool Production source
category?
    J. What demographic groups might benefit the most from this
regulation?
X. Summary of Cost, Environmental, and Economic Impacts for the Wool
Fiberglass Manufacturing Source Category
    A. What are the affected sources in the Wool Fiberglass
Manufacturing source category?
    B. How are the impacts for this proposal evaluated?
    C. What are the air quality impacts?
    D. What are the water quality and solid waste impacts?
    E. What are the secondary impacts?
    F. What are the energy impacts?
    G. What are the cost impacts?
    H. What are the economic impacts?
    I. What are the benefits?
    J. What demographic groups might benefit the most from this
regulation?
XI. Request for Comments
XII. Submitting Data Corrections
XIII. 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. Preamble Acronyms and Abbreviations

    Several acronyms and terms used to describe industrial processes,
data inventories, and risk modeling are included in this preamble.
While this may not be an exhaustive list, to ease the reading of this
preamble and for reference purposes, the following terms and acronyms
are defined here:

ACGIH American Conference of Governmental Industrial Hygienists
AEGL acute exposure guideline levels
AERMOD air dispersion model used by the HEM-3 model
ATSDR Agency for Toxic Substances and Disease Registry
BACT best available control technology
BLDS bag leak detection systems
BTF beyond the floor
CAA Clean Air Act
CalEPA California EPA
CA-REL California reference exposure level
CBI Confidential Business Information
CFR Code of Federal Regulations
CIIT Chemical Industry Institute of Toxicology
CO carbon monoxide
COS Carbonyl sulfide
EJ environmental justice
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
ERT Electronic Reporting Tool
ESP electrostatic precipitators

FA flame attenuation
GP General Provisions
GHG Greenhouse Gases
HAP hazardous air pollutants
HCl Hydrogen chloride
HEM Human Exposure Model
HEM-3 Human Exposure Model, Version 3
HF Hydrogen fluoride
HI Hazard Index
HQ Hazard Quotient
IRFA Initial Regulatory Flexibility Analysis
IRIS Integrated Risk Information System
kg/MG kilogram/megawatt
km kilometer
LAER lowest achievable emissions rate
lb/ton pounds per ton
lb/yr pounds per year
MACT maximum achievable control technology
mg/L milligrams per liter
mg/m3 milligrams per cubic meter
MIR maximum individual risk
NAAQS National Ambient Air Quality Standard
NAICS North American Industry Classification System
NaOH sodium hydroxide
NAS National Academy of Sciences
NATA National Air Toxics Assessment
NESHAP National Emissions Standards for Hazardous Air Pollutants
NIOSH National Institutes for Occupational Safety and Health
NRC National Research Council
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PM particulate matter
RACT reasonably available control technology
RBLC RACT/BACT/LAER Clearinghouse
RCRA Resource Conservation and Recovery Conservation
REL reference exposure level
RFA Regulatory Flexibility Act
RfC reference concentrations
RfD reference dose
RS rotary spin
RTO regenerative thermal oxidizers
RTR residual risk and technology review
SAB Science Advisory Board
SBA Small Business Administration
SBAR Small Business Advocacy Review
SCC Source Classification Codes
SER Small Entity Representatives
SO2 sulfur dioxide
SSM startup, shutdown, and malfunction
TC Toxicity Characteristics
TCLP Toxicity Characteristic Leaching Procedure
TLV threshold limit value
TOSHI target organ-specific hazard index
tpy tons per year
TRIM Total Risk Integrated Modeling System
TTN Technology Transfer Network
UF uncertainty factors
[micro]g/m3 microgram per cubic meter
UMRA Unfunded Mandates Reform Act
UPL upper predictive limit
URE unit risk estimate
WHO World Health Organization
WWW worldwide web

II. General Information

A. Does this action apply to me?

    The regulated industrial source categories that are the subject of
this proposed rule are listed in Table 1 of this preamble. Table 1 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.
    In 1992 the EPA defined the Mineral Wool Production source category
as any facility engaged in producing mineral wool fiber from slag or
rock. Mineral wool is a material used mainly for thermal and acoustical
insulation. This category includes, but is not limited to, the
following process units: a cupola furnace for melting the mineral
charge; a blow chamber in which air and, in some cases, a binder is
drawn over the fibers, forming them to a screen; a curing oven to bond
the fibers; and a cooling compartment.
    In 1992 the EPA defined the Wool Fiberglass Manufacturing source
category as any facility engaged in producing wool fiberglass from
sand, feldspar, sodium sulfate, anhydrous borax, boric acid or any
other materials. In the wool fiberglass manufacturing process, molten
glass is formed into fibers that are bonded with an organic resin to
create a wool-like material that is used as thermal or acoustical
insulation. The category includes, but is not limited to the following
processes: glass-melting furnace, marble forming, refining, fiber
forming, binder application, curing and cooling.

    Table 1--NESHAP and Industrial Source Categories Affected by This
                             Proposed Action
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       Source category                   NESHAP           NAICS code \1\
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Mineral Wool Production......  Mineral Wool Production..          327993
Wool Fiberglass Manufacturing  Wool Fiberglass                    327993
                                Manufacturing.
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\1\ North American Industry Classification System.

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

    In addition to being available in the docket, an electronic copy of
this proposal will also be available on the WWW through the EPA's 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. In addition, a copy of each rule
showing specific changes proposed under this action is available in
their respective dockets. The TTN provides information and technology
exchange in various areas of air pollution control.

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

    Submitting CBI. Do not submit information containing CBI to the EPA
through http://www.regulations.gov or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
a disk or CD-ROM that you mail to the EPA, mark the outside of the disk
or CD-ROM as CBI and then identify electronically within the disk or
CD-ROM the specific information that is claimed as CBI. In addition to
one complete version of the 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 indicating 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-2010-1041 (Mineral Wool RTR) or Attention Docket ID
Number EPA-HQ-OAR-2010-1042 (Wool Fiberglass RTR).

D. When will a public hearing occur?

    If a public hearing is held, it will begin at 10 a.m. on December
12, 2011 and will be held at a location to be determined. Persons
interested in presenting oral testimony or inquiring as to whether a
public hearing is to be held should contact Ms. Pamela Garrett, Office
of Air Quality Planning and Standards, Sector Policies and Programs
Division, (D243-01), U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; telephone number:<PHONE_NUMBER>;
email address<EMAIL_ADDRESS>
III. Background Information

A. What are NESHAP?

1. What is the statutory authority for NESHAP?
    Section 112 of the CAA establishes a two-stage regulatory process
to address emissions of HAP from stationary sources. In the first
stage, after the EPA has identified categories of sources emitting one
or more of the HAP listed in CAA section 112(b), CAA section 112(d)
calls for us to promulgate NESHAP for those sources. ``Major sources''
are those that emit or have the potential to emit 10 tpy or more of a
single HAP or 25 tpy or more of any combination of HAP. For major
sources, these technology-based standards must reflect the maximum
degree of emissions reductions of HAP achievable (after considering
cost, energy requirements, and non-air quality health and environmental
impacts) and are commonly referred to as MACT standards. Area sources
are those that emit less than major amounts of HAP.
    MACT standards must require the maximum degree of emissions
reduction through the application of measures, processes, methods,
systems, or techniques, including, but not limited to, measures that
(A) reduce the volume of or eliminate pollutants through process
changes, substitution of materials or other modifications; (B) enclose
systems or processes to eliminate emissions; (C) capture or treat
pollutants when released from a process, stack, storage or fugitive
emissions point; (D) are design, equipment, work practice or
operational standards (including requirements for operator training or
certification); or (E) are a combination of the above (CAA section
112(d)(2)(A)-(E)). The MACT standards may take the form of design,
equipment, work practice or operational standards where the EPA first
determines either that, (A) a pollutant cannot be emitted through a
conveyance designed and constructed to emit or capture the pollutants,
or that any requirement for, or use of, such a conveyance would be
inconsistent with law; or (B) the application of measurement
methodology to a particular class of sources is not practicable due to
technological and economic limitations (CAA sections 112(h)(1)-(2)).
    The MACT ``floor'' is the minimum control level allowed for MACT
standards promulgated under CAA section 112(d)(3) and may not be based
on cost considerations. For new sources, the MACT floor cannot be less
stringent than the emissions control that is achieved in practice by
the best-controlled similar source. The MACT floors for existing
sources can be less stringent than floors for new sources, but they
cannot be less stringent than the average emissions limitation achieved
by the best-performing 12 percent of existing sources in the category
or subcategory (or the best-performing 5 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 considerations of the cost of achieving the
emissions reductions, any non-air quality health and environmental
impacts, and energy requirements.
    The EPA is then required to review these technology-based standards
and revise them ``as necessary (taking into account developments in
practices, processes, and control technologies)'' no less frequently
than every 8 years, under CAA section 112(d)(6). In conducting this
review, the EPA is not obliged to completely recalculate the prior MACT
determination, and, in particular, is not obligated to recalculate the
MACT floors. NRDC v. EPA, 529 F.3d 1077, 1084 (DC Cir., 2008).
    The second stage in standard-setting focuses on reducing any
remaining ``residual'' risk according to CAA section 112(f). This
provision requires, first, that the EPA prepare a Report to Congress
discussing (among other things) methods of calculating the risks posed
(or potentially posed) by sources after implementation of the MACT
standards, the public health significance of those risks, and the EPA's
recommendations as to legislation regarding such remaining risk. The
EPA prepared and submitted this report (Residual Risk Report to
Congress, EPA-453/R-99-001) in March 1999. Congress did not act in
response to the report, thereby triggering the EPA's obligation under
CAA section 112(f)(2) to analyze and address residual risk.
    Section 112(f)(2) of the CAA requires us to determine, for source
categories subject to certain MACT standards, whether those emissions
standards provide an ample margin of safety to protect public health.
If the MACT standards that apply to a source category emitting a HAP
that is ``classified as a known, probable, or possible human carcinogen
do not reduce lifetime excess cancer risks to the individual most
exposed to emissions from a source in the category or subcategory to
less than one-in-one million,'' the EPA must promulgate residual risk
standards for the source category (or subcategory) as necessary to
provide an ample margin of safety to protect public health (CAA section
112(f)(2)(A)). This requirement is procedural. It mandates that the EPA
establish CAA section 112(f) residual risk standards if certain risk
thresholds are not satisfied, but does not determine the level of those
standards (NRDC v. EPA, 529 F. 3d at 1083). The second sentence of CAA
section 112(f)(2) sets out the substantive requirements for residual
risk standards: Protection of public health with an ample margin of
safety based on the EPA's interpretation of this standard in effect at
the time of the CAA amendments. Id. This refers to the National
Emissions Standards for Hazardous Air Pollutants: Benzene Emissions
from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene
Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery
Plants (Benzene NESHAP), (54 FR 38044, September 14, 1989), described
in the next paragraph.
    The EPA may adopt residual risk standards equal to existing MACT
standards if the EPA determines that the existing standards are
sufficiently protective, even if (for example) excess cancer risks to a
most exposed individual are not reduced to less than one-in-one
million. Id. at 1083 (``If the EPA determines that the existing
technology-based standards provide an `ample margin of safety,' then
the agency is free to readopt those standards during the residual risk
rulemaking''). Section 112(f)(2) of the CAA further authorizes the EPA
to adopt more stringent standards, if necessary ``to prevent, taking
into consideration costs, energy, safety, and other relevant

factors, an adverse environmental effect.'' \1\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    CAA section 112(f)(2) expressly preserves our use of the two-step
process for developing standards to address any residual risk and our
interpretation of ``ample margin of safety'' developed in the Benzene
NESHAP. The first step in this process is the determination of
acceptable risk. This determination ``considers all health information,
including risk estimation uncertainty, and includes a presumptive limit
on MRI [cancer] \2\ of approximately 1-in-10 thousand [i.e., 100-in-1
million]'' (54 FR 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.)
---------------------------------------------------------------------------

    \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 exposed to the maximum level
of a pollutant for a lifetime.
---------------------------------------------------------------------------

    The terms ``individual most exposed'', ``acceptable level'', and
``ample margin of safety'' are not specifically defined in the CAA.
However, CAA section 112(f)(2)(B) preserves the EPA's interpretation
set out in the Benzene NESHAP, and the Court in NRDC v. EPA concluded
that the EPA's interpretation of CAA section 112(f)(2) is a reasonable
one. See NRDC v. EPA, 529 F.3d at 1083 (DC Cir. 2008), which says
``[S]ubsection 112(f)(2)(B) expressly incorporates the EPA's
interpretation of the CAA from the Benzene standard, complete with a
citation to the Federal Register.'' See also, A Legislative History of
the Clean Air Act Amendments of 1990, volume 1, p. 877 (Senate debate
on Conference Report). We also notified Congress in the Residual Risk
Report to Congress that we intended to use the Benzene NESHAP approach
in making CAA section 112(f) residual risk determinations (EPA-453/R-
99-001, p. ES-11).
    In the Benzene NESHAP, we stated as an overall objective: * * * in
protecting public health with an ample margin of safety, we strive to
provide maximum feasible protection against risks to health from
hazardous air pollutants by (1) Protecting the greatest number of
persons possible to an individual lifetime risk level no higher than
approximately 1-in-1 million; and (2) limiting to no higher than
approximately 1-in-10 thousand [i.e., 100-in-1 million] the estimated
risk that a person living near a facility would have if he or she were
exposed to the maximum pollutant concentrations for 70 years.
    The agency also stated that, ``The EPA also considers incidence
(the number of persons estimated to suffer cancer or other serious
health effects as a result of exposure to a pollutant) to be an
important measure of the health risk to the exposed population.
Incidence measures the extent of health risks to the exposed population
as a whole, by providing an estimate of the occurrence of cancer or
other serious health effects in the exposed population.'' The agency
went on to conclude that ``estimated incidence would be weighed along
with other health risk information in judging acceptability.'' As
explained more fully in our Residual Risk Report to Congress, the EPA
does not define ``rigid line[s] of acceptability,'' but rather
considers broad objectives to be weighed with a series of other health
measures and factors (EPA-453/R-99-001, p. ES-11). The determination of
what represents an ``acceptable'' risk is based on a judgment of ``what
risks are acceptable in the world in which we live'' (Residual Risk
Report to Congress, p. 178, quoting the DC Circuit's en banc Vinyl
Chloride decision at 824 F.2d 1165) recognizing that our world is not
risk-free.
    In the Benzene NESHAP, we stated that ``the EPA will generally
presume that if the risk to [the maximum exposed] individual is no
higher than approximately 1-in-10 thousand, that risk level is
considered acceptable.'' 54 FR 38045. We discussed the maximum
individual lifetime cancer risk as being ``the estimated risk that a
person living near a plant would have if he or she were exposed to the
maximum pollutant concentrations for 70 years.'' Id. We explained that
this measure of risk ``is an estimate of the upper bound of risk based
on conservative assumptions, such as continuous exposure for 24 hours
per day for 70 years.'' Id. We acknowledge that maximum individual
lifetime cancer risk ``does not necessarily reflect the true risk, but
displays a conservative risk level which is an upper-bound that is
unlikely to be exceeded.'' Id.
    Understanding that there are both benefits and limitations to using
maximum individual lifetime cancer risk as a metric for determining
acceptability, we acknowledged in the 1989 Benzene NESHAP that
``consideration of maximum individual risk * * * must take into account
the strengths and weaknesses of this measure of risk.'' Id.
Consequently, the presumptive risk level of 100-in-1 million (1-in-10
thousand) provides a benchmark for judging the acceptability of maximum
individual lifetime cancer risk, but does not constitute a rigid line
for making that determination.
    The agency also explained in the 1989 Benzene NESHAP the following:
``In establishing a presumption for MIR [maximum individual cancer
risk], rather than a rigid line for acceptability, the agency intends
to weigh it with a series of other health measures and factors. These
include the overall incidence of cancer or other serious health effects
within the exposed population, the numbers of persons exposed within
each individual lifetime risk range and associated incidence within,
typically, a 50- km exposure radius around facilities, the science
policy assumptions and estimation uncertainties associated with the
risk measures, weight of the scientific evidence for human health
effects, other quantified or unquantified health effects, effects due
to co-location of facilities, and co-emissions 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.'' In the ample margin of safety decision process, the agency
again considers all of the health risks and other health information
considered in the first step. Beyond that information, additional
factors relating to the appropriate level of control will also be
considered, including costs and economic impacts of controls,
technological feasibility, uncertainties and any other relevant
factors. Considering all of these factors, the agency will establish
the standard at a level that provides an ample margin of safety to
protect the public health and prevent adverse environmental effects,
taking into consideration costs, energy, safety, and other relevant
factors, as

required by CAA section 112(f) (54 FR 38046).
2. How do we consider the risk results in making decisions?
    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 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 provided estimates of the
expected difference in actual emissions from the source category under
review and 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: ``The policy chosen by the Administrator permits
consideration of multiple measures of health risk. Not only can the MIR
figure be considered, but also incidence, the presence of noncancer
health effects, and the uncertainties of the risk estimates. In this
way, the effect on the most exposed individuals can be reviewed as well
as the impact on the general public. These factors can then be weighed
in each individual case. This approach complies with the Vinyl Chloride
mandate that the Administrator ascertain an acceptable level of risk to
the public by employing [her] expertise to assess available data. It
also complies with the Congressional intent behind the CAA, which did
not exclude the use of any particular measure of public health risk
from the EPA's consideration with respect to CAA section 112
regulations, and, thereby, implicitly permits consideration of all
measures of health risk which the Administrator, in [her] judgment,
believes are appropriate to determining what will `protect the public
health.' ''
    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 an MIR
less than the presumptively acceptable level is unacceptable in the
light of other health risk factors.'' Similarly, with regard to the
ample margin of safety analysis, the Benzene NESHAP states 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.''

B. What litigation is related to this proposed action?

    In 2007, the DC Circuit (Court) found that the EPA had erred in
establishing emissions standards for sources of HAP in the NESHAP for
Brick and Structural Clay Products Manufacturing and Clay Ceramics
Manufacturing, 67 FR 26,690 (May 16, 2003), and consequently vacated
the rule.\3\ These errors included incorrectly calculated MACT emission
limits, instances where EPA failed to set emission limits, and
instances where EPA failed to regulate processes that emitted HAP. We
are taking action to correct errors in both the Mineral Wool and Wool
Fiberglass NESHAP for HAP that are not regulated. Some pollutants were
represented in the 1999 MACT rules by surrogates; other pollutants were
not regulated at all in the rule. In both these cases, we are
establishing pollutant-specific emission limits. With the exception of
PM as a surrogate for all HAP metals, where surrogacy relationships
exist, we are proposing to remove that surrogacy. We are also
correcting one unregulated HAP-emitting process in the Mineral Wool
NESHAP.
---------------------------------------------------------------------------

    \3\ Sierra Club v. EPA, 479 F. 3d 875 (DC Cir. March 13, 2007).
---------------------------------------------------------------------------

    In two earlier court decisions 4 5 the court found EPA
had erred in not setting MACT standards for every HAP emitted from a
source. Therefore, with the exception of PM as a surrogate for HAP
metals, in this action we are proposing emission limits for all HAP
emitted from Mineral Wool and Wool Fiberglass. We note that we have
established through previous analyses upheld by the court \6\ that PM
is an appropriate surrogate for HAP metals, therefore, we retain that
surrogacy relationship in these proposed rules.
---------------------------------------------------------------------------

    \4\ Cement Kiln Recycling Coalition v. EPA, 255 F.3d 855 (DC
Cir. 2001) (per curiam).
    \5\ National Lime Ass'n v. EPA, 233 F.3d 625 (DC Cir. 2000).
    \6\ Sierra Club v. EPA, 353 F. 3d 976 (DC Cir. 2004).
---------------------------------------------------------------------------

    In separate litigation, the Court vacated portions of two
provisions in EPA's CAA section 112 regulations that govern emissions
of HAP during periods of SSM.\7\ Specifically, the Court vacated the
SSM exemption contained in 40 CFR 63.6(f)(1) and 63.6(h)(1) that are
part of regulations commonly referred to as the GP rule. When
incorporated into section 112(d) regulations for specific source
categories, these two provisions exempt sources from the requirement to
comply with otherwise applicable MACT standards during periods of SSM.
Because both of the Mineral Wool and Wool Fiberglass NESHAP relied on
the GP rule for startup and shutdown provisions (40 CFR 63.1194 and
63.1386(c)), we are also proposing to revise these provisions for both
of the Mineral Wool and Wool Fiberglass source categories.
---------------------------------------------------------------------------

    \7\ Sierra Club v. EPA, 551 F. 3d 1019 (DC Cir. 2008), cert.
denied, 130 S. Ct 1735 (2010).
---------------------------------------------------------------------------

    Recent litigation \8\ led to a consent decree under which we must
propose these amendments no later than October 31, 2011; and promulgate
no later than June 29, 2012.
---------------------------------------------------------------------------

    \8\ Consent Decree, Sierra Club v. Jackson (No. 09-cv-00152SBA,
N.D. Cal., Sept. 27, 2010).
---------------------------------------------------------------------------

IV. Mineral Wool and Wool Fiberglass Source Categories

A. Overview of the Mineral Wool Production Source Category and MACT
Standards

    The NESHAP (or MACT rule) for the Mineral Wool Production source
category was promulgated on June 1, 1999 (64 FR 29490), and codified at
40 CFR part 63, subpart DDD. As promulgated in 1999, the NESHAP applies
to affected sources of HAP emissions at mineral wool production
facilities. As defined in the 1992 EPA report, ``Documentation for
Developing the Initial Source Category List'' (EPA-450/3/91/030, July
1992), a ``mineral wool facility'' is ``any facility engaged in
producing mineral wool fiber from slag, rock or other materials,
excluding sand or glass.''
    The MACT rule for the Mineral Wool Production source category does
not apply to facilities that manufacture wool fiberglass from sand,
feldspar, sodium sulfate, anhydrous borax, boric acid or other similar
materials.\9\ Although there

are some similarities among rock that may be used for both mineral wool
and wool fiberglass production, the two industries are distinct.
Mineral wool is used in cases in which fireproofing, structural
strength and sound attenuation are needed, such as in high occupancy
commercial and industrial buildings. Wool fiberglass is used primarily
for insulation, in residential and small commercial buildings. Some
wool fiberglass facilities also operate a ceiling tile or pipe product
manufacturing line. The manufacturing of ceiling tile is not regulated
under the Wool Fiberglass Manufacturing MACT Standard.
---------------------------------------------------------------------------

    \9\ Wool fiberglass produced from sand, feldspar, sodium
sulfate, anhydrous borax, boric acid, etc. are a part of the wool
fiberglass source category, which is also addressed in this action.
---------------------------------------------------------------------------

    Today, there are seven mineral wool facilities that are subject to
the MACT rule. No new mineral wool facilities have been built in the
last 21 years and the agency does not anticipate new mineral wool
facilities will be built in the foreseeable future. According to the
size definition applied to this industry by the U.S. SBA (750 company
employees or less), 5 of the 7 firms, employing 540 employees
altogether, are classified as a small business.
    Mineral wool is a fibrous, glassy substance consisting of silicate
fibers typically 4 to 7 micrometers in diameter, made from natural rock
(such as basalt, granite and other rock), blast furnace slag, glass
cullet, coke and other similar materials. Products made from mineral
wool are widely used in thermal and acoustical insulation and other
products where mineral wool fiber is added to impart structural
strength or fire resistance. In the mineral wool manufacturing process,
raw materials (e.g., rock and slag) are melted in a cupola using coke
as fuel; the molten material is then formed into fiber. In the
production of mineral wool products that do not require high rigidity,
oil is typically applied to suppress dust and add some strength to the
fiber; the fiber is then sized and bagged or baled. This is known as a
``nonbonded'' product which is manufactured on a ``nonbonded''
production line.
    For mineral wool products requiring a higher structural rigidity,
typically a phenol/formaldehyde binder may be applied to the fiber. The
binder-laden fiber mat is then thermoset in a curing oven and cooled.
This is known as a ``bonded'' product which is made on a ``bonded
product'' line. The major differences between the ``nonbonded'' and
``bonded'' production lines are the application of binder during fiber
collection and the use of a curing oven. Four facilities only
manufacture nonbonded products, while the other three facilities
operate both bonded and nonbonded production lines. A total of 11
cupolas and 3 curing ovens are operated by the facilities in this
source category.
    HAP emission sources at mineral wool production facilities include
the cupola where the mineral charge is melted; a collection chamber, in
which air and a binder are drawn over the fibers, forming them into a
mat against a screen; and a curing oven that bonds the fibers (for
bonded products). HAP are emitted from the cupolas, curing ovens and
collection operations when collection occurs with curing. Collection at
nonbonded product lines does not emit HAP. COS accounts for the
majority of the HAP emissions from these facilities (approximately 224
tpy and 51 percent of the total HAP emissions by mass). The majority of
HAP emissions (approximately 58 percent of the total HAP by mass,
including HF and HCl are from the cupolas. The remainder of the HAP are
from bonded lines, including phenol, formaldehyde, and methanol.
Although the majority of HAP are emitted from the cupola, the emissions
(primarily formaldehyde and phenol) that were significant in evaluating
risk are from the collection chambers on the bonded lines. Formaldehyde
and phenol are emitted only from bonded mineral wool production lines;
these lines include emissions from the application of the binder during
collection and curing.
    The current NESHAP requires control of PM emissions, as a surrogate
for HAP metals, from the cupolas and formaldehyde emissions from the
curing ovens. Fabric filters are the control devices used by this
industry to reduce both PM and HAP metal emissions from cupolas.
Emissions from collection operations are not regulated under the
current NESHAP, but collection and curing ovens are generally
controlled using RTOs and fabric filters.
    The existing MACT rule applies to each existing, new and
reconstructed cupola or curing oven in a mineral wool production
facility. All mineral wool production facilities that are major sources
are subject to the standards. For all cupolas, the 1999 MACT rule
specifies a numerical emission limit for PM, as a surrogate for metal
HAP. For new and reconstructed cupolas, emissions limits are specified
for CO, as a surrogate for COS. Emissions limits for formaldehyde are
also specified (as a surrogate for phenol emissions) for each existing,
new, and reconstructed curing oven. Under the 1999 MACT rule, a mineral
wool production facility may elect to comply with a numerical
formaldehyde or CO emission limit expressed in mass of emissions per
unit of production (kg/MG of melt or lb/ton of melt) or a percent
reduction standard. PM emissions from existing, new, and reconstructed
cupolas are limited to an outlet concentration of 0.05 kg/Mg (0.10 lb/
ton) of melt, 40 CFR 63.1178(a). CO emissions limits from new and
reconstructed cupolas are limited to an outlet concentration of 0.05
kg/Mg (0.10 lb/ton) of melt or 99 percent CO removal, 40 CFR
63.1178(a). Formaldehyde emissions limits from existing, new, and
reconstructed curing ovens are limited to an outlet concentration of
0.03 kg/Mg (0.06 lb/ton) of melt or 80 percent formaldehyde removal, 40
CFR 63.1179(a).

B. Overview of the Wool Fiberglass Manufacturing Source Category and
1999 MACT Rule

    The NESHAP (or MACT rule) for the Wool Fiberglass Manufacturing
source category was promulgated on June 14, 1999 (62 FR 31695), and
codified at 40 CFR part 63, subpart NNN. As promulgated in 1999, the
MACT rule applies to affected sources of HAP emissions at wool
fiberglass manufacturing facilities. Although the source category
definition includes all manufacturers of wool fiberglass, the 1999 MACT
rule (40 CFR 63.1381) defines a ``wool fiberglass manufacturing
facility'' as ``any facility manufacturing wool fiberglass on a RS
manufacturing line producing bonded building insulation or on a FA
manufacturing line producing bonded pipe insulation and bonded heavy-
density products.'' The MACT rule for the Wool Fiberglass Manufacturing
source category does not apply to facilities that manufacture mineral
wool from rock, slag, and other similar materials. In addition, RS and
FA manufacturing lines that produce nonbonded products (in which no
phenol-formaldehyde binder is applied) are not subject to the current
standards.
    Wool fiberglass products are primarily used as thermal and
acoustical insulation for buildings, automobiles, aircraft, appliances,
ductwork and pipes. Other uses include liquid and air filtration.
Approximately 90 percent of the wool fiberglass currently produced is
used for residential and commercial building insulation products.
Today, wool fiberglass is currently manufactured in the United States
by 5 companies operating 29 facilities across 16 states. According to
the size definition applied to this industry by the U.S. SBA (750
company employees or less), none of these companies are classified as a
small business. One new wool fiberglass facility was recently built in
2007 and one wool fiberglass facility closed in 2010. Because several

furnaces have been idled across the industry, current production of
wool fiberglass is below production levels from previous years, and
several months of stockpiled products exist at wool fiberglass
companies, we do not expect new wool fiberglass facilities to be built
in the near future.
    Wool fiberglass is manufactured in a process that forms thin fibers
from molten glass. Over 90 percent of the wool fiberglass industry
produces insulation; two plants also operate a pipe product line and
one plant operates a ceiling tile line (although the production of
ceiling tile is not part of this MACT standard). A typical wool
fiberglass manufacturing line consists of the following processes: (1)
Heating of raw materials and/or cullet in a furnace to a molten state,
(2) preparation of molten glass for fiberization, (3) formation of
fibers into a wool fiberglass mat or pipe insulation product, (4)
curing the binder-coated fiberglass mat, (5) cooling the mat (this
process is not always present), and (6) backing, cutting, and
packaging.
    The primary component of most types of wool fiberglass is silica
sand, but wool fiberglass also includes varying quantities of feldspar,
sodium sulfate, anhydrous borax, boric acid, and may be made entirely
of glass cullet, crushed recycled glass. Wool fiberglass manufacturing
plants typically operate one or more manufacturing lines. Refined raw
materials for the glass batch are weighed, mixed, and conveyed to the
glass-melting furnace, which may be gas-fired, electric, oxygen-
enriched or a combination of gas and electric.
    Two methods of forming fibers are used by the industry, RS and FA.
In the RS process, centrifugal force causes molten glass to flow
through small holes in the wall of a rapidly rotating cylinder. In the
FA process, molten glass flows by gravity from a small furnace, or pot,
to form threads that are then attenuated (stretched to the point of
breaking) with air and/or flame.
    After the fibers are formed, they are sprayed with a binder to hold
the fibers together. These bonded fibers are then collected as a mat on
a conveyor. Binder compositions vary with product type. At the time of
development of the MACT standard, wool fiberglass mat was typically
made using a phenol-formaldehyde resin based binder. According to the
trade organization, only a few insulation products are currently made
using a formaldehyde-based binder because new formaldehyde- and HAP-
free binder formulations have been developed in recent years.\10\ Most
new binder formulations are now HAP-free. According to the information
collected through a survey by the industry, a few pipe insulation
products made from wool fiberglass are still made at two facilities
using a phenol-formaldehyde based binder.
---------------------------------------------------------------------------

    \10\ Letter from the North American Insulation Manufacturers
Association (NAIMA). June 8, 2011 Letter.
---------------------------------------------------------------------------

    After application of the binder and formation of the mat, the
conveyor carries the newly formed mat through an oven to cure the
thermosetting resin and then through a cooling section. Some products,
such as those made on FA manufacturing lines, do not require curing
and/or cooling.
    Process emissions sources include the furnace where the charge is
melted; the collection process, in which air carrying a binder is drawn
over the fibers, forming them into a mat; and the curing oven that
bonds the fibers (for bonded products only).
    HAP, including chromium compounds, are emitted from glass-melting
furnaces. Glass-melting furnaces are constructed using refractory
bricks or blocks (commonly called refractories), that provide thermal
insulation and corrosion protection. The refractory bricks re-direct
the heat of the furnace back into the melt. Refractories are produced
to withstand the extreme corrosive thermal conditions of a furnace and
may contain a variety of mineral materials, including chromium, and
more specifically chromic oxide.\11\
---------------------------------------------------------------------------

    \11\ Chromium in Refractories. Sept. 2000. Dr. Mariano Velez,
Ceramic Engineering Dept., Univ. Missouri-Rolla.
---------------------------------------------------------------------------

    In a wool fiberglass glass-melting furnace, sufficient temperatures
are reached to drive the transformation of chromium from the trivalent
to the hexavalent valence state. Because of the corrosive properties of
the molten glass and the fining agents (salts added to the top of the
molten glass layer which act to draw the gas bubbles out of the molten
glass), the refractory of the inner furnace walls are eroded and fresh
refractory is continually exposed along the metal/glass line within the
furnace. As a result, when the glass-melting furnace is constructed
using refractories containing high percentages of chromium, the
emission levels of chromium compounds continuously increase over the
life of the furnace according to the increasingly exposed refractory
surface area.12 13 14
---------------------------------------------------------------------------

    \12\ Notes of April 14, 2011 telephone discussion between Carlos
Davis, Environmental Manager, Certainteed, Kansas City, KS; and
Susan Fairchild, project lead, USEPA/OAQPS/SPPD.
    \13\ Region 7 Certainteed, Kansas City, KS; meeting and site
visit notes.
    \14\ Emissions Test Results from Certainteed, Kansas City, KS.
2005 and 2008.
---------------------------------------------------------------------------

    In addition, organic HAP (formaldehyde, phenol, and methanol) may
be released from RS forming and curing processes and FA forming and
curing processes.
    The 1999 MACT rule applies to process emissions from each of the
following existing, newly constructed, and reconstructed sources:
Glass-melting furnaces located at a wool fiberglass manufacturing
plant, RS manufacturing lines that produce building insulation, and FA
manufacturing lines producing pipe insulation. The MACT rule also
applies to FA manufacturing lines producing heavy-density products.
    The 1999 MACT rule requires control of PM emissions from the glass-
melting furnaces and formaldehyde emissions from the RS and FA lines.
Typical control devices to reduce PM and HAP emissions from furnaces
include both wet and dry ESP and fabric filters. Low and high-
temperature thermal oxidizers are used to control phenol, formaldehyde,
and methanol from curing operations on bonded lines.
    The 1999 MACT rule limits PM emissions to an outlet concentration
of 0.50 lb of PM per ton of glass pulled for both existing and new
furnaces, 40 CFR 63.1382. Emissions of formaldehyde from RS
manufacturing lines are limited to an outlet concentration of 1.2 lb/
ton of glass pulled for existing sources and 0.80 lb/ton of glass
pulled for new sources. Emissions of formaldehyde from FA manufacturing
lines producing pipe insulation are limited to an outlet concentration
of 6.8 lb/ton of glass pulled from both existing and new sources, 40
CFR 63.1382. Emissions of formaldehyde from FA manufacturing lines
producing heavy-density products are limited to an outlet concentration
of 7.8 lb/ton of glass pulled for new sources; no emission limit is
specified for existing FA manufacturing lines producing heavy-density
products, 40 CFR 63.1382. A surrogate approach, where PM serves as a
surrogate for HAP metals and formaldehyde serves as a surrogate for
organic HAP, was used in the 1999 MACT rule to allow for easier and
less expensive testing and monitoring requirements.
    The industry trade association has advised us that because the wool

fiberglass industry has voluntarily phased out most uses of phenol-
formaldehyde based binders, there may now be only two wool fiberglass
facilities that are subject to the current MACT rule. If this is
accurate, 27 of the 29 facilities manufacturing wool fiberglass may not
be considered major sources due to the phaseout of phenol-formaldehyde
based binders. We are soliciting comment on our understanding that
there will be no major sources in the wool fiberglass insulation source
category (other than pipe insulation products) by the end of the 2012
calendar year.

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

    In June 2010, the industry conducted a voluntary survey among all
companies that own and operate mineral wool production and wool
fiberglass manufacturing facilities. The survey sought test data for
PM, CO and HAP emissions and information on the process equipment,
control devices, point and fugitive emissions, practices used to
control point and fugitive emissions, and other aspects of facility
operations. Facilities were asked to seek and obtain prior EPA approval
where new test data for a subset of processes, control devices and
operations would be submitted as representative of an untested subset
of processes, control devices and operations. In addition, facilities
were allowed, in lieu of conducting new testing and with prior EPA
approval, to submit existing and well-documented test data that were
representative of current operations using the recommended test methods
in the industry survey. Furthermore, the EPA requested, and industry
agreed, that a subset of the facilities that were thought to be
representative of emission sources from both the mineral wool and wool
fiberglass industries would conduct additional emissions testing for
certain HAP from specific processes. The bases for representativeness
included design type and size of process units or equipment; fuel type;
operating temperatures; control devices; and raw material content.
Facilities completed and submitted responses to the industry survey in
the spring of 2011.
    In summary, the EPA received existing emissions test data from all
7 mineral wool facilities and 26 of the 29 wool fiberglass facilities,
with some facilities submitting data for multiple years. Mineral wool
facilities provided existing test data on cupolas, curing ovens, and
collection operations. Wool fiberglass facilities provided existing
test data on one or more of the following emission sources: Glass-
melting furnaces, curing ovens, forming, and collection operations.
Emissions test data provided by facilities in both source categories,
including the emission unit and pollutant tested, varied widely by
facility.
    The mineral wool industry included testing for most HAP metals, CO,
PM and certain organic HAP (formaldehyde, phenol, methanol and COS).
Pollutants tested for by the wool fiberglass manufacturing source
category included most HAP metals, including chromium and hexavalent
chromium, PM, formaldehyde, phenol and methanol. The EPA completed the
dataset by assigning emission estimates from tested processes and their
known production rates to the similar represented processes based on
production rates at the untested processes. A copy of the dataset can
be found in the docket to this proposed rule.
    The results of these emission tests were compiled into a database
for each source category, which is available in the docket for this
action.

V. Analyses Performed

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

    The EPA conducted a risk assessment that provided estimates of (1)
The MIR posed by the HAP emissions from the 7 mineral wool facilities
and 29 wool fiberglass manufacturing facilities in the source
categories, (2) the distribution of cancer risks within the exposed
populations, (3) the total cancer incidence, (4) estimates of the
maximum TOSHI for chronic exposures to HAP with the potential to cause
chronic non-cancer health effects, (5) worst-case screening estimates
of HQ for acute exposures to HAP with the potential to cause non-cancer
health effects, and (6) an evaluation of the potential for adverse
environmental effects. In June of 2009, the EPA's SAB conducted a
formal peer review of the risk assessment methodologies used in its
review of the document entitled, ``Risk and Technology Review
Assessment Methodologies.'' \15\ We received the final SAB report on
this review in May of 2010.\16\ Where appropriate, we have responded to
the key messages from this review in developing the current risk
assessment; we will be continuing our efforts to improve our
assessments by incorporating updates based on the SAB recommendations
as they are developed and become available. The risk assessment
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 Mineral Wool Production and Wool Fiberglass
Manufacturing Source Categories.
---------------------------------------------------------------------------

    \15\ U.S. EPA, 2009. 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. EPA-452/R-09-006. Available at http://www.epa.gov/ttn/atw/rrisk/rtrpg.html.
    \16\ U.S. EPA, 2010. SAB's Response to EPA's RTR Risk Assessment
Methodologies. Available at: http://yosemite.epa.gov/sab/
sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-
007-unsigned.pdf.
---------------------------------------------------------------------------

1. Establishing the Nature and Magnitude of Actual Emissions and
Identifying the Emissions Release Characteristics
    For each facility in the Mineral Wool Production and Wool
Fiberglass Manufacturing source categories, we developed and compiled
an emissions profile (including emissions estimates, stack parameters,
and location data) based on the information provided by the industry
survey, the emissions test data, and various calculations. We used the
production rates of tested processes to assign emissions to untested
but similar processes based on known production rates at the untested
processes. The site-specific emissions profiles include annual
estimates of process emissions for the 2010 timeframe, as well as
emissions release characteristics such as emissions release height,
temperature, velocity, and location coordinates. We are requesting
comment on the assumptions used to complete the dataset, including
assumptions we made to assign emission rates.
    The primary risk assessment is based on estimates of the actual
emissions (though we also analyzed allowable emissions and the
potential risks due to allowable emissions). We received a substantial
amount of emissions test data and other information from the industry
survey that enabled us to derive estimates of stack emissions of
certain HAP for all of the facilities in both source categories. The
wool fiberglass industry provided emission testing on all known
pollutants, including total chromium and hexavalent chromium, PM, and
other metals at furnaces they considered to be representative of other
furnaces operated by the company. Where different furnace types were
used to melt fiberglass, industry usually tested representative
furnaces for each furnace type. The representative furnaces were chosen
by industry according to production rates and furnace type. For
untested furnaces, industry provided

the normal operating rate in terms of tons of glass produced per hour.
We estimated emissions at untested furnaces by using data from the
representative tested furnaces. To do this, we used test data from
representative furnaces that provided emissions rates of all tested
pollutants on a pound per hour basis. We applied this pound per hour
basis to the untested furnaces with the known production rates of those
furnaces to estimate pounds per hour of pollutants. We considered
furnace type and company when making these assignments.
    We consider these estimates to be very good because they are based
upon known emission test methods, have test reports that verify the
results, were signed as being true and accurate by authorized company
representatives, and also signed as being accurate by the testing
company. In addition, one testing company was used by the industry to
conduct all the emissions testing using approved EPA methods. We are
requesting comment on our use of the available test data to assign
emission estimates to untested emission points.
2. Establishing the Relationship Between Actual Emissions and MACT-
Allowable Emissions Levels
    The emissions data in our data set consists of actual stack
emissions and, where we did not have actual emissions data, estimates
of emissions based on a subset of operations that were representative
of such emission points. In the EPA's experience, with most source
categories, we generally have found that ``actual'' emissions levels
are lower than the emissions levels that a facility is allowed to emit
under the MACT standards. The emissions levels allowed to be emitted by
the MACT standards are referred to as the ``MACT-allowable'' emissions
levels. This represents the highest emissions level that could be
emitted by facilities without violating the MACT standards.
    As we discussed in prior residual risk and technology review rules,
assessing the risks at the MACT-allowable level is reasonable since
these risks reflect the maximum level at which sources could emit while
still complying with the MACT standards. However, we also explained
that it is reasonable to consider actual emissions, where such data are
available, in both steps of the risk analysis, in accordance with the
Benzene NESHAP (54 FR 38044, September 14, 1989). Considering actual
emissions is reasonable because source categories typically seek to
perform better than required by emissions standards to provide an
operational cushion and to accommodate the variability in manufacturing
processes and control device performance. Facilities' actual emissions
may also be significantly lower than MACT-allowable emissions for other
reasons such as State requirements, improvements in performance of
control devices since by the MACT standards, or reduced production. In
this case, we are reducing the allowable emissions limits to the levels
of actual emissions. For this reason, for the pollutants emitted, we
are using only actual emissions in our risk analysis.
    For both the Mineral Wool Production and Wool Fiberglass
Manufacturing source categories, we evaluated actual and allowable
stack emissions. Appendices 1a and 1b of the Draft Residual Risk
Assessment for the Mineral Wool Production and Wool Fiberglass
Manufacturing Source Categories, available in the docket, further
describe the estimates of MACT-allowable emissions and the estimates of
risks due to allowable emissions.
    a. Actual and allowable emissions for the Mineral Wool Production
source category.
    The analysis of allowable emissions for the Mineral Wool Production
source category was largely focused on formaldehyde emissions, which we
considered the most important HAP emitted from this source category
based on our screening level risk assessment and the HAP for which we
had the most data. However, we also considered allowable emissions for
other HAP, including HAP metals and COS. To estimate the difference
between the actual and allowable emissions, we averaged the actual
formaldehyde emission rates of manufacturing lines provided by
facilities and compared those values to the maximum level allowed by
the existing MACT standard (i.e., 0.06 pounds of formaldehyde per ton
of melt) from all curing ovens.
    We realize that these estimates of allowable emissions are
theoretical high-end estimates as facilities must maintain average
emissions levels at some level below the MACT limit to ensure
compliance with the standard at all times because of the day-to-day
variability in emissions. Nevertheless, these high-end estimates of
allowable emissions were adequate for us to estimate the magnitude of
allowable emissions and the differences between the estimates of actual
emissions and the MACT allowable emissions.
    Based on this analysis, we conclude that all facilities in the
mineral wool source category are emitting formaldehyde at levels lower
than allowable and that the differences between actual and allowable
emissions are significant. For the facilities producing bonded product,
the estimated actual emissions were up to three times lower than
allowable emissions. That is, MACT-allowable emissions were determined
to be three times the actual emissions for all pollutants in the
Mineral Wool Production category. Therefore, we multiplied the actual
stack emissions from each facility by a factor of 3 to derive estimates
of allowable emissions for modeling (whether these emissions were
measured by testing or calculated based on representative emission
tests).
    b. Analysis of allowable and actual emissions for the Wool
Fiberglass Manufacturing source category.
    The analysis of allowable emissions for the Wool Fiberglass
Manufacturing source category was largely focused on emissions of
chromium compounds and formaldehyde because these are the only
pollutants emitted with significant health risks. To estimate the
difference between the actual and allowable emissions, we averaged the
actual formaldehyde emission rates of manufacturing lines provided by
facilities and compared those values to the maximum level allowed by
the existing MACT standard (i.e., 1.2 or 0.8 lb/ton of glass pulled for
formaldehyde).
    We realize that these estimates of allowable emissions are
theoretical high-end estimates as facilities must maintain average
emissions levels at some level below the MACT limit to ensure
compliance with the standard at all times because of the day-to-day
variability in emissions. Nevertheless, these high-end estimates of
allowable emissions were adequate for us to estimate the magnitude of
allowable emissions and the differences between the estimates of actual
emissions and the MACT allowable emissions. Based on this analysis, we
conclude that allowable emissions are estimated to be three times
higher than actual emissions. Therefore, to develop the MACT-allowable
emissions, the actual stack emissions for formaldehyde, phenol and
methanol were multiplied by a factor of 3. The range of differences
between actual and allowable formaldehyde emission levels is
significant, that is, for some sources there was little difference
between actual and allowable emission levels, other times, allowable
emissions were up to 5 times greater than actual emissions. MACT-
allowable emissions for chromium compounds were determined to be equal
to actual emissions since there is currently no

emissions limit for chromium compounds.
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 source in both the source categories
addressed in this proposal were estimated using the HEM (Community and
Sector HEM-3 version 2.1 Beta). 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.\17\ HEM-3 draws on three data libraries to
perform the dispersion modeling and to develop the preliminary risk
estimates. The first is a library of meteorological data, which is used
for dispersion calculations. This library includes 1 year of hourly
surface and upper air observations for more than 200 meteorological
stations, selected to provide coverage of the United States and Puerto
Rico. A second library of United States Census Bureau census block \18\
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 used in dispersion calculations. A third library of
pollutant unit risk factors and other health benchmarks is used to
estimate health risks. These risk factors and health benchmarks are the
latest values recommended by the EPA for HAP and other toxic air
pollutants. These values are available at http://www.epa.gov/ttn/atw/toxsource/summary.html and are discussed in more detail later in this
section.
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    \17\ 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).
    \18\ 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 exposure (24 hours per day, 7 days per week, and
52 weeks per year for a 70-year period) to the maximum concentration at
the centroid of an inhabited census block. Individual cancer risks were
calculated by multiplying the estimated lifetime exposure to the
ambient concentration of each of the HAP (in micrograms per cubic
meter) by its URE, which is an upper bound estimate of an individual's
probability of contracting cancer over a lifetime of exposure to a
concentration of 1 microgram of the pollutant per cubic meter of air.
For residual risk assessments, we generally use URE values from the
EPA's Integrated Risk Information System (IRIS). For carcinogenic
pollutants without an EPA IRIS value, we look to other reputable
sources of cancer dose-response values, often using CalEPA URE values,
where available. We may use dose-response values in place of or in
addition to other values, if appropriate, 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.
    With regard to formaldehyde, the EPA determined in 2004 that the
CIIT cancer dose-response value for formaldehyde (5.5 x
10-\9\ per [mu]g/m\3\) was based on better science than the
IRIS cancer dose-response value (1.3 x 10-\5\ per [mu]g/
m\3\) and we switched from using the IRIS value to the CIIT value in
risk assessments supporting regulatory actions. Based on subsequent
published research, however, EPA changed its determination regarding
the CIIT model and in 2010 the EPA returned to using the 1991 IRIS
value. The EPA has been working on revising the formaldehyde IRIS
assessment and the NAS completed its review of the EPA's draft in May
of 2011. The EPA is reviewing the public comments and the NAS
independent scientific peer review. The EPA will follow the NAS Report
recommendations and will present results obtained by implementing the
biologically based dose-response (BBDR) model for formaldehyde. The EPA
will compare these estimates with those currently presented in the
External Review draft of the assessment and will discuss their
strengths and weaknesses. As recommended by the NAS committee,
appropriate sensitivity and uncertainty analyses will be an integral
component of implementing the BBDR model. The draft IRIS assessment
will be revised in response to the NAS peer review and public comments
and the final assessment will be posted on the IRIS database. In the
interim, we will present findings using the 1991 IRIS value as a
primary estimate, and may also consider other information as the
science evolves. As described in the risk assessment, the IRIS URE for
formaldehyde is 1.3 x 10-\5\ [mu]g/m\3\, whereas, the CIIT
URE for formaldehyde is 5.5 x 10-\9\ [mu]g/m\3\.
    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 \19\) 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.
---------------------------------------------------------------------------

    \19\ 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 TOSHI). The HQ
for chronic exposures is the estimated chronic exposure divided by the
chronic reference level, which is either the EPA RfC, defined as ``an
estimate (with uncertainty spanning perhaps an order of magnitude) of a
continuous inhalation exposure to the human population (including
sensitive subgroups) that is likely to be without an appreciable risk
of deleterious effects

during a lifetime,'' or, in cases where an RfC from the EPA's IRIS
database is not available, the EPA will utilize the following
prioritized sources for our chronic dose-response values: (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 REL, which is defined as ``the concentration
level at or below which no adverse health effects are anticipated for a
specified exposure duration''; and (3), as noted above, in cases where
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 those dose-
response values 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 rate and worst-case dispersion conditions (1991
calendar year data) 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, AEGL and ERPG for 1-hour exposure durations. As
discussed below, we used conservative assumptions for emission rates,
meteorology and exposure location for our acute analysis.
    As described in the CalEPA's Air Toxics Hot Spots Program Risk
Assessment Guidelines, Part I, The Determination of Acute Reference
Exposure Levels for Airborne Toxicants, an acute REL value (http://www.oehha.ca.gov/air/pdf/acuterel.pdf) is defined as ``the
concentration level at or below which no adverse health effects are
anticipated for a specified exposure duration.'' 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 individuals in the population by
the inclusion of margins of safety. Since margins of safety are
incorporated to address data gaps and uncertainties, exceeding the
acute REL does not automatically indicate an adverse health impact.
    AEGL values were derived in response to recommendations from the
NRC. As described in Standing Operating Procedures of the National
Advisory Committee on Acute Exposure Guideline Levels for Hazardous
Substances (http://www.epa.gov/opptintr/aegl/pubs/sop.pdf),\20\ ``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 8
hours.'' The document lays out the purpose and objectives of AEGL by
stating (page 21) that ``the primary purpose of the AEGL program and
the 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.''
---------------------------------------------------------------------------

    \20\ 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.'' \21\ 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.''
---------------------------------------------------------------------------

    \21\ ERP Committee Procedures and Responsibilities. November 1,
2006. American Industrial Hygiene Association.
---------------------------------------------------------------------------

    As can be seen from the definitions above, the AEGL and ERPG values
include the similarly-defined severity levels 1 and 2. For many
chemicals, a severity level 1 value AEGL or ERPG has not been
developed; in these instances, higher severity level AEGL-2 or ERPG-2
values are compared to our modeled exposure levels to screen for
potential acute concerns.
    Acute REL values for 1-hour exposure durations are typically lower
than their corresponding AEGL-1 and ERPG-1 values. Even though their
definitions are slightly different, AEGL-1 values are often the same as
the corresponding ERPG-1 values, and AEGL-2 values are often equal to
ERPG-2 values. Maximum HQ values from our acute screening risk
assessments typically result when basing them on the acute

REL value for a particular pollutant. In cases where our maximum acute
HQ value exceeds 1, we also report the HQ value based on the next
highest acute 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 based on process knowledge and
engineering judgment and with awareness of a Texas study of short-term
emissions variability, which showed that most peak emission events, in
a heavily-industrialized four county area (Harris, Galveston, Chambers
and Brazoria Counties, Texas) were less than twice the annual average
hourly emission rate. The highest peak emission event was 74 times the
annual average hourly emission rate, and the 99th percentile ratio of
peak hourly emission rate to the annual average hourly emission rate
was 9.\22\ This analysis is provided in Appendix 4 of the Draft
Residual Risk Assessment for the Mineral Wool Production and Wool
Fiberglass Manufacturing Source Categories, 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
apply a conservative screening multiplication factor of 10 to the
average annual hourly emission rate in these acute exposure screening
assessments. The factor of 10 was used for the Wool Fiberglass
Manufacturing source category, but we determined that a factor of 3 is
more appropriate for the Mineral Wool Production source category (for
more details see the Acute Effects Factor for Mineral Wool
Manufacturing Operations document in the docket for this rulemaking).
---------------------------------------------------------------------------

    \22\ See http://www.tceq.state.tx.us/compliance/field_ops/eer/index.html or docket to access the source of these data.
---------------------------------------------------------------------------

    For the mineral wool source category, we used data from the highest
formaldehyde emitting source among the mineral wool producers. That
company also presented the highest risk due to formaldehyde emissions.
This company provided the agency with 10 years of measurements of
binder formulation, formaldehyde content in binders, binder application
rates, and binder retention rates. Because the industry must
manufacture their product for use in fireproofing, they must keep
meticulous records of production specifics. These data are used to show
compliance with Underwriters Laboratories and other building
construction safety standards. From this specific 10-year data set, the
EPA determined that, on a worst-case possible basis, formaldehyde could
be emitted at levels no more than three times the actual rate. The
worst-case scenario is possible if the binder contained the maximum
amount of resin possible, the resin contained the maximum amount of
formaldehyde possible, was sprayed at the maximum rate possible, and
retained in the product at the minimum level possible. These data were
used to in the risk assessment to determine the acute health effects
hazard index. For Mineral Wool Production, the plant-specific acute
factors were calculated and ranged from 1.0 to 1.6. Based on these
results, and to allow for additional uncertainty in emissions, we used
an acute factor of 3.0. The calculation we used to determine this acute
factor is available in the docket to this rule.\23\
---------------------------------------------------------------------------

    \23\ Acute Factor Memo. Cindy Hancy and David Reeves, RTI; to
Susan Fairchild, USEPA/OAQPS/SPPD; EPA Project Lead. August 30,
2011.
---------------------------------------------------------------------------

    In cases where acute HQ values from the screening step were less
than or equal to 1, acute impacts were deemed negligible and no further
analysis was performed. In cases where an acute HQ from the screening
step was greater than 1, additional site-specific data were considered
to develop a more refined estimate of the potential for acute impacts
of concern. The data refinements employed for these source categories
consisted of using the site-specific facility layout to distinguish
facility property from an area where the public could be exposed. These
refinements are discussed in the draft risk assessment document, which
is available in the docket for each of these source categories.
Ideally, we would prefer to have continuous measurements over time to
see how the emissions vary 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 worst-case acute exposures to HAP, and in response to a key
recommendation from the SAB's peer review of EPA's RTR risk assessment
methodologies,\24\ we examine a wider range of available acute health
metrics than we do for our chronic risk assessments. This is in
response to the acknowledgement that there are generally more data gaps
and inconsistencies in acute reference values than there are in chronic
reference values. By definition, the acute CA-REL represents a health-
protective level of exposure, with no risk anticipated below those
levels, even for repeated exposures; however, the health risk from
higher-level exposures is unknown. Therefore, when a CA-REL is exceeded
and an AEGL-1 or ERPG-1 level is available (i.e., levels at which mild
effects are anticipated in the general public for a single exposure),
we have used them as a second comparative measure. Historically,
comparisons of the estimated maximum off-site one-hour exposure levels
have not been typically made to occupational levels for the purpose of
characterizing public health risks in RTR assessments. This is because
occupational ceiling values are not generally considered protective for
the general public since they are designed to protect the worker
population (presumed healthy adults) for short duration (< 15 minute)
increases in exposure.\25\ As a result, for most chemicals, the 15-
minute occupational ceiling values are set at levels higher than a one-
hour AEGL-1, making comparisons to them irrelevant unless the AEGL-1 or
ERPG-1 levels are exceeded (U.S. EPA 2009). Such is not the case when
comparing the available acute inhalation health effect reference values
for formaldehyde (U.S. EPA 2009).
---------------------------------------------------------------------------

    \24\ The SAB Peer review of RTR Risk Assessment Methodoligies is
available at: http://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
    \25\ U.S. EPA. (2009) Chapter 2.9 Chemical Specific Reference
Values for Formaldehyde in Graphical Arrays of Chemical-Specific
Health Effect Reference Values for Inhalation Exposures (Final
Report). U.S. Environmental Protection Agency, Washington, DC, EPA/
600/R-09/061, and available on-line at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003.
---------------------------------------------------------------------------

    The worst-case maximum estimated 1-hour exposure to formaldehyde
outside the facility fence line for the mineral wool source category is
0.47 mg/m\3\. This estimated worst-case exposure exceeds the 1-hour REL
by a factor of 8 (HQREL = 8) and is below the 1-hour AEGL-1
(HQAEGL-1 = 0.4). This exposure estimate does not exceed the
AEGL-1, or exceed the workplace ceiling level guideline for the
formaldehyde value developed by the

NIOSH \26\ ``for any 15 minute period in a work day'' (NIOSH REL-
ceiling value of 0.12 mg/m\3\; HQNIOSH = 4). The estimate is
at the value developed by the ACGIH as ``not to be exceeded at any
time'' (ACGIH TLV-ceiling value of 0.37 mg/m\3\; HQACGIH =
1). Additionally, the estimated maximum acute exposure exceeds the Air
Quality Guideline value that was developed by the World Health
Organization \27\ for 30-minute exposures (0.1 mg/m\3\;
HQWHO = 5).
---------------------------------------------------------------------------

    \26\ National Institutes for Occupational Saffety and Health
(NIOSH). Occupational Safety and Health Guideline for Formaldehyde;
http://www.cdc.gov/niosh/docs/81-123/pdfs/0293.pdf.
    \27\ WHO (2000). Chapter 5.8 Formaldehyde, in Air Quality
Guidelines for Europe, second edition. World Health Organization
Regional Publications, European Series, No. 91. Copenhagen, Denmark.
Available on-line at http://www.euro.who.int/_data/assets/pdf_file/0005/74732/E71922.pdf.
---------------------------------------------------------------------------

    For the wool fiberglass manufacturing source category, the worst-
case maximum estimated 1-hour exposure to formaldehyde outside the
facility fence line is 1.92 mg/m\3\. This estimated worst-case exposure
exceeds the 1-hour REL by a factor of 30 (HQREL = 30) and
the 1-hour AEGL-1 (HQAEGL-1 = 2). This exposure estimate
also exceeds multiple workplace ceiling level guidelines for
formaldehyde, including the value developed by the American Conference
of Governmental Industrial Hygienists (ACGIH) as ``not to be exceeded
at any time'' (ACGIH TLV-ceiling value of 0.37 mg/m\3\;
HQACGIH = 5), and the value developed by the National
Institutes for Occupational Safety and Health (NIOSH) ``for any 15
minute period in a work day'' (NIOSH REL-ceiling value of 0.12 mg/m\3\;
HQNIOSH = 16). Additionally, the estimated maximum acute
exposure exceeds the Air Quality Guideline value that was developed by
the World Health Organization \28\ for 30-minute exposures (0.1 mg/
m\3\; HQWHO = 19). Id.
---------------------------------------------------------------------------

    \28\ WHO (2000). Chapter 5.8 Formaldehyde, In Air Quality
Guidelinies for Europe, second edition. World Health Organization
Regional Publications, European Series, No. 91. Copenhagen, Denmark.
Available on-line at http://www.euro.who.int_data/assets/pdf_file/0005/74732/E71922.pdf.
---------------------------------------------------------------------------

    We solicit comment on the use of the occupational values described
above in the interpretation of these worst-case acute screening
exposure estimates for both the Mineral Wool Production and Wool
Fiberglass Manufacturing source categories.
4. Conducting Multipathway Exposure and Risk Modeling
    The potential for significant human health risks due to exposures
via routes other than inhalation (i.e., multi-pathway exposures) and
the potential for adverse environmental impacts were evaluated in a
three-step process. In the first step, we determined whether any
facilities emitted any PB-HAP in the environment. There are 14 PB-HAP
compounds or compound classes identified for this screening in the
EPA's Air Toxics Risk Assessment Library (available at http://www.epa.gov/ttn/fera/risk_atra_vol1.html). They are cadmium
compounds, chlordane, chlorinated dibenzodioxins and furans,
dichlorodiphenyldichloroethylene, heptachlor, hexachlorobenzene,
hexachlorocyclohexane, lead compounds, mercury compounds, methoxychlor,
polychlorinated biphenyls, polycyclic organic matter, toxaphene and
trifluralin.
    Since three of these PB-HAP (lead, cadmium, and mercury compounds)
are emitted by at least one facility in both source categories, 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
reasonable 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 in each source
category 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.
    None of the facilities in the Mineral Wool Production and Wool
Fiberglass Manufacturing source categories reported emissions of PB-HAP
that were greater than the de minimis threshold levels, indicating no
potential for significant multi-pathway risks from these facilities.
Therefore, multi-pathway exposures and environmental risks were deemed
negligible and no further analysis was performed. This analysis is
provided in the Draft Residual Risk Assessment for the Mineral Wool
Production and Wool Fiberglass Manufacturing Source Categories, which
is available in the docket for this action.
5. Assessing Risks After Control Options
    In addition to assessing baseline inhalation risks and screening
for potential multi-pathway risks, where appropriate, we also estimated
risks considering the potential emission reductions that would be
achieved by the particular control options under consideration. In
these cases, the expected emissions reductions were applied to the
specific HAP and emissions sources in the source category dataset to
develop corresponding estimates of risk reductions. More information on
the risks remaining after controls are in place to meet the emissions
limits is available in the Draft Residual Risk Assessment for the
Mineral Wool Production and Wool fiberglass Manufacturing Source
Categories, which is available in the docket for this action.
6. Conducting Facility Wide Risk Assessments
    To put the source category risks in context, we also examine the
risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, for each facility that includes one or more
sources from one of the source categories under review, we examine the
HAP emissions not only from the source category of interest, but also
from all other emission sources at the facility. For both source
categories, all significant HAP sources have been included in the
source category risk analysis and there are no other significant HAP
emissions sources present. Therefore, we conclude that the facility
wide risk is essentially the same as the source category risk for both
the mineral wool and wool fiberglass source categories and that no
separate facility wide analysis is necessary.
7. Considering Uncertainties in Risk Assessment
    Uncertainty and the potential for bias are inherent in all risk
assessments, including those performed for the source categories
addressed in this proposal. Although uncertainty exists, we believe
that our approach, which uses 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 draft risk assessment
documentation (referenced earlier) available in the docket for this
action.
a. Uncertainties in the Emissions Datasets
    Although the development of the MACT datasets involved quality
assurance/quality control processes, the accuracy of emissions values
will vary depending on the source of the data, the degree to which data
are incomplete or missing, the degree to which assumptions made to
complete the datasets are inaccurate, errors in estimating emissions
values and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years 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 multiplication 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 site where
these data were taken. Despite these uncertainties, we believe that the
approach considered in the dispersion modeling analysis for off-site
locations and census block centroids 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.\29\
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.
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    \29\ 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.
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    In addition, the assessment predicted the chronic exposures at the
centroid of each populated census block as surrogates for the exposure
concentrations for all people living in that block. Using the census
block centroid to predict chronic exposures tends to over-predict
exposures for people in the census block who live further from the
facility, and under-predict exposures for people in the census block
who live closer to the facility. Thus, using the census block centroid
to predict chronic exposures may lead to a potential understatement or
overstatement of the true maximum impact, but is an unbiased estimate
of average risk and incidence.
    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.\30\
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    \30\ U.S. EPA. National-Scale Air Toxics Assessment for 1996.
(EPA 453/R-01-003; January 2001; page 85.)
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    In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that should
be highlighted. The accuracy of an acute inhalation exposure assessment
depends on the simultaneous occurrence of independent factors that may
vary greatly, such as hourly emissions rates, meteorology, and human
activity patterns. In this assessment, we assume that individuals
remain for 1 hour at the point of maximum ambient concentration as
determined by the co-occurrence of peak emissions and worst-case
meteorological conditions. These assumptions would tend to 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).\31\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances, the risk could also be
greater.\32\ When developing an upper bound estimate of risk and to
provide risk values that do not underestimate risk, health-protective
default approaches are generally used. To err on the side of ensuring
adequate health-protection, the EPA typically uses the upper bound
estimates rather than lower bound or central tendency estimates in our
risk assessments, an approach that may have limitations for other uses
(e.g., priority-setting or expected benefits analysis).
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    \31\ IRIS glossary (http://www.epa.gov/NCEA/iris/help_gloss.htm).
    \32\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible and which is based on maximum
likelihood estimates.
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    Chronic noncancer reference (RfC and RfD) values represent chronic
exposure levels that are intended to be health-protective levels.
Specifically, these values provide an estimate (with uncertainty
spanning perhaps an order of magnitude) of 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 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,\33\ 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 they more often 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).
---------------------------------------------------------------------------

    \33\ 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 underestimate risk). See EPA, 2004, An Examination
of EPA Rick Assessment Principles and Practices, EPA/100/B-001
available at: http://www.epa.gov/osa/pdfs/ratf-final.pdf.
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    Not all acute reference values are developed for the same purpose
and care must be taken when interpreting the results of an acute
assessment of human health effects relative to the reference value or
values being exceeded. Where relevant to the estimated exposures, the
lack of short-term dose-response values at different levels of severity
should be factored into the risk characterization as potential
uncertainties.
    Although every effort is made to identify peer-reviewed reference
values for cancer and noncancer effects for all pollutants emitted by
the sources included in this assessment, some HAP continue to have no
reference values for cancer or chronic noncancer or acute effects.
Since exposures to these pollutants cannot be included in a
quantitative risk estimate, an understatement of risk for these
pollutants at environmental exposure levels is possible. For a group of
compounds that are either unspeciated, or do not have reference values
for every individual compound (e.g., glycol ethers), we conservatively
use the most protective reference value to estimate risk from
individual compounds in the group of compounds.
    Additionally, chronic reference values for several of the compounds
included in this assessment are currently under the EPA IRIS review 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 these source categories and if dose-response
metric changes enough to indicate that the risk assessment supporting
this notice may significantly understate human health risk.
    When we identify acute impacts which exceed their relevant
benchmarks, we pursue refining our acute screening estimates. For the
Mineral Wool Production source category, we used a refined emissions
multiplier of 3 to estimate the peak hourly emission rates from the
average rates. For a detailed description of how the refined emissions
multiplier was developed for the Mineral Wool Production source
category see the memo on the Acute Effects Factor for Mineral Wool
Manufacturing

Operations, which is in the docket for this action. For the Wool
Fiberglass Manufacturing source category, data were not available to
develop a refined emissions multiplier; therefore, the default
emissions multiplier of 10 was used.
e. Uncertainties in the Multi-Pathway and Environmental Effects
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 multi-pathway and
environmental effects is necessary. As discussed above, we conclude
that the potential for these types of impacts is low for these source
categories.
f. Uncertainties in the Facility Wide Risk Assessment
    Given that the same general analytical approach and the same models
were used to generate facility wide risk results as were used to
generate the source category risk results, the same types of
uncertainties discussed above for our source category risk assessments
apply to the facility wide risk assessments. Because the source
category processes are the only processes at each facility, there is no
greater uncertainty for facility wide emissions.

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

    Based on our risk assessment we are proposing that risks due to
hexavalent chromium and formaldehyde are acceptable, with a maximum
individual cancer risk for the source category at 40-in-one million.
Emissions testing at the facility presenting this risk indicated that
92 percent of the total chromium compounds were hexavalent chromium. In
the second step of the process, the EPA sets the standard at a level
that provides an ample margin of safety.
    We found from our risk assessment that risks due to hexavalent
chromium were acceptable at 40-in-one million. In the second step of
our risk assessment, we considered whether any cost-effective measures,
technologies or practices are available to reduce risks further to an
``ample margin of safety''. We found two methods whereby hexavalent
chromium emissions can be reduced at wool fiberglass facilities and we
are proposing in this action emission limits for hexavalent chromium
from wool fiberglass facilities that will provide an ample margin of
safety to protect the public health and prevent adverse environmental
effects. We discuss these methods further in Sections V.A., VIII. D and
VIII. E of this preamble.
    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 HI;
and the maximum acute non-cancer hazard (72 FR 25138, May 3, 2007; 71
FR 42724, July 27, 2006). In our most recent proposals (75 FR 65068,
October 21, 2010 and 75 FR 80220, December 21, 2010), 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., 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 actions 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). The agency acknowledges that the