[Federal Register Volume 82, Number 182 (Thursday, September 21, 2017)]
[Proposed Rules]
[Pages 44254-44285]
[FR Doc No: 2017-19448]

Vol. 82

Thursday,

No. 182

September 21, 2017

Part II

Environmental Protection Agency

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40 CFR Part 63

 National Emission Standards for Hazardous Air Pollutants From the
Portland Cement Manufacturing Industry Residual Risk and Technology
Review; Proposed Rule

Federal Register / Vol. 82 , No. 182 / Thursday, September 21, 2017 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2016-0442; FRL-9967-61-OAR]
RIN 2060-AS92

National Emission Standards for Hazardous Air Pollutants From the
Portland Cement Manufacturing Industry Residual Risk and Technology
Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing
amendments to the National Emission Standards for Hazardous Air
Pollutants (NESHAP) From the Portland Cement Manufacturing Industry to
address the results of the residual risk and technology review (RTR)
the EPA is required to conduct in accordance with section 112 of the
Clean Air Act (CAA). We found risks due to emissions of air toxics to
be acceptable from this source category with an ample margin of safety,
and we identified no new cost-effective controls under the technology
review to achieve further emissions reductions. Therefore, we are
proposing no revisions to the numerical emission limits based on these
analyses. However, the EPA is proposing amendments to correct and
clarify rule requirements and provisions. While the proposed amendments
would not result in reductions in emissions of hazardous air pollutants
(HAP), this action, if finalized, would result in improved monitoring,
compliance, and implementation of the rule.

DATES:
    Comments. Comments must be received on or before November 6, 2017.
    Public Hearing. If a public hearing is requested by September 26,
2017, the EPA will hold a public hearing on October 6, 2017. The last
day to pre-register in advance to speak at the public hearing will be
October 4, 2017.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No.
EPA-HQ-OAR-2016-0442, at http://www.regulations.gov. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from Regulations.gov. The EPA may publish any
comment received to its public docket. Do not submit electronically any
information you consider to be Confidential Business Information (CBI)
or other information whose disclosure is restricted by statute.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the Web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.
    Public Hearing. If a hearing is requested, it will be held at the
EPA WJC East Building, 1201 Constitution Avenue NW., Washington, DC
20004. If a public hearing is requested, then we will provide details
about the public hearing on our Web site at https://www.epa.gov/stationary-sources-air-pollution/portland-cement-manufacturing-industry-national-emission-standards. The EPA does not intend to
publish any future notices in the Federal Register announcing any
updates on the request for public hearing. Please contact Aimee St.
Clair at<PHONE_NUMBER> or by email at<EMAIL_ADDRESS>to request
a public hearing, to register to speak at the public hearing, or to
inquire as to whether a public hearing will be held.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Mr. Brian Storey, 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 number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>For specific information
regarding the risk modeling methodology, contact Mr. James Hirtz,
Health and Environmental Impacts Division (C539-02), Office of Air
Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; telephone number: (919)
541-0881; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>For information about the applicability of the
NESHAP to a particular entity, contact Ms. Sara Ayres, Office of
Enforcement and Compliance Assurance, U.S. Environmental Protection
Agency, U.S. EPA Region 5 (E-19J), 77 West Jackson Boulevard, Chicago,
IL 60604; telephone number:<PHONE_NUMBER>; email address:
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2016-0442. All documents in the docket are
listed in the Regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy. Publicly available docket
materials are available either electronically in Regulations.gov or in
hard copy at the EPA Docket Center, Room 3334, EPA WJC West Building,
1301 Constitution Avenue NW., Washington, DC. The Public Reading Room
is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding
legal holidays. The telephone number for the Public Reading Room is
(202) 566-1744, and the telephone number for the EPA Docket Center is
(202) 566-1742.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2016-0442. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
online at http://www.regulations.gov, including any personal
information provided, unless the comment includes information claimed
to be CBI or other information whose disclosure is restricted by
statute. Do not submit information that you consider to be CBI or
otherwise protected through http://www.regulations.gov or email. The
http://www.regulations.gov Web site is an ``anonymous access'' system,
which means the EPA will not know your identity or contact information
unless you provide it in the body of your comment. If you send an email
comment directly to the EPA without going through http://www.regulations.gov, your email address will be automatically captured
and included as part of the comment that is placed in the public docket
and made available on the Internet. If you submit an electronic
comment, the EPA recommends that you include your name and other
contact information in the body of your comment and with any disk or
CD-ROM you submit. If the EPA cannot read your comment due to technical
difficulties and cannot contact you for clarification, the EPA may not
be able to consider your comment. Electronic files should not include
special characters or any form of encryption and be free of any defects
or

viruses. For additional information about the EPA's public docket,
visit the EPA Docket Center homepage at http://www.epa.gov/dockets.
    Preamble Acronyms and Abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines the following terms and acronyms here:

ACI activated carbon injection
AEGL acute exposure guideline levels
AERMOD air dispersion model used by the HEM-3 model
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
CISWI commercial and industrial solid waste incinerators
CO carbon monoxide
D/F dioxins and furans
EPA Environmental Protection Agency
ERP Emergency Response Planning
ERPG Emergency Response Planning Guidelines
ERT Electronic Reporting Tool
ESP electrostatic precipitators
FR Federal Register
GHGRP Greenhouse Gas Reporting Program
HAP hazardous air pollutants
HCl hydrochloric acid
HEM-3 Human Exposure Model
HF hydrogen fluoride
HI hazard index
HQ hazard quotient
IRIS Integrated Risk Information System
km kilometer
lb/hr pounds per hour
lb/ton pounds per ton
LOAEL lowest-observed-adverse-effect level
MACT maximum achievable control technology
mg/kg-day milligrams per kilogram per day
mg/m\3\ milligrams per cubic meter
mg/Nm\3\ milligrams per normal cubic meter
MIR maximum individual risk
NAAQS National Ambient Air Quality Standards
NAC National Advisory Committee
NAICS North American Industry Classification System
NAS National Academy of Sciences
NATA National Air Toxics Assessment
NEI National Emissions Inventory
NESHAP national emission standards for hazardous air pollutants
NOX nitrogen oxides
NOAA National Oceanic and Atmospheric Administration
NOAEL no-observed-adverse-effect level
NRC National Research Council
NRDC Natural Resources Defense Council
NSPS new source performance standards
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PCA Portland Cement Association
PEL probable effect level
PM particulate matter
POM polycyclic organic matter
ppm parts per million
ppmvd parts per million by volume, dry basis
PRA Paperwork Reduction Act
REL reference exposure level
RFA Regulatory Flexibility Act
RfC reference concentration
RfD reference dose
RTO regenerative thermal oxidizers
RTR residual risk and technology review
SAB Science Advisory Board
SCR selective catalytic reduction
SO2 sulfur dioxide
TEF toxicity equivalence factors
TEQ toxic equivalents
THC total hydrocarbons
TOSHI target organ-specific hazard index
tpy tons per year
TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and
Ecological Exposure model
UF uncertainty factor
[micro]g/m\3\ microgram per cubic meter
UISIS Universal Industrial Sectors Integrated Solutions
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
U.S.C. United States Code
WebFIRE Web Factor Information Retrieval System

    Organization of this Document. The information in this preamble is
organized as follows:

I. General Information
    A. Does this action apply to me?
    B. Where can I get a copy of this document and other related
information?
    C. What should I consider as I prepare my comments for the EPA?
II. Background
    A. What is the statutory authority for this action?
    B. What is this source category and how does the current NESHAP
regulate its HAP emissions?
    C. What data collection activities were conducted to support
this action?
    D. What other relevant background information and data are
available?
III. Analytical Procedures
    A. How did we estimate post-MACT risks posed by the source
category?
    B. How did we consider the risk results in making decisions for
this proposal?
    C. How did we perform the technology review?
IV. Analytical Results and Proposed Decisions
    A. What are the results of the risk assessment and analyses?
    B. What are our proposed decisions regarding risk acceptability,
ample margin of safety, and adverse environmental effects?
    C. What are the results and proposed decisions based on our
technology review?
    D. What other actions are we proposing?
    E. What compliance dates are we proposing?
V. Summary of Cost, Environmental, and Economic Impacts
    A. What are the impacts to affected sources?
    B. What are the air quality impacts?
    C. What are the cost impacts?
    D. What are the economic impacts?
    E. What are the benefits?
VI. Request for Comments
VII. Submitting Data Corrections
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Executive Order 13771: Reducing Regulations and Controlling
Regulatory Costs
    C. Paperwork Reduction Act (PRA)
    D. Regulatory Flexibility Act (RFA)
    E. Unfunded Mandates Reform Act (UMRA)
    F. Executive Order 13132: Federalism
    G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    H. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    I. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    J. National Technology Transfer and Advancement Act (NTTAA)
    K. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. Does this action apply to me?

    Table 1 of this preamble lists the NESHAP and associated regulated
industrial source category that is the subject of this proposal. Table
1 is not intended to be exhaustive, but rather provides a guide for
readers regarding the entities that this proposed action is likely to
affect. The proposed standards, once promulgated, will be directly
applicable to the affected sources. Federal, state, local, and tribal
government entities would not be affected by this proposed action. As
defined in the Initial List of Categories of Sources Under Section
112(c)(1) of the Clean Air Act Amendments of 1990 (see 57 FR 31576,
July 16, 1992), the Portland Cement Manufacturing Industry source
category is any facility engaged in manufacturing Portland cement by
either the wet or dry process. The category includes, but is not
limited to, the following process units: Kiln, clinker cooler, raw mill
system, finish mill system, raw mill dryer, raw material storage,
clinker storage, finished product storage, conveyor transfer points,
bagging, and bulk loading and unloading systems.

    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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Portland cement manufacturing  40 CFR part 63                    327310
 facilities.                    subpart LLL.
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\1\ North American Industry Classification System.

The source category does not include those kilns that burn hazardous
waste and are subject to and regulated under 40 CFR part 63, subpart
EEE, or kilns that burn solid waste and are subject to the Commercial
and Industrial Solid Waste Incinerator (CISWI) rule under 40 CFR part
60, subparts CCCC and DDDD.

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

    In addition to being available in the docket, an electronic copy of
this action is available on the Internet. Following signature by the
EPA Administrator, the EPA will post a copy of this proposed action at
https://www3.epa.gov/airquality/cement/actions.html. Following
publication in the Federal Register, the EPA will post the Federal
Register version of the proposal and key technical documents at this
same Web site. Information on the overall RTR program is available at
https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.

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

    Submitting CBI. Do not submit information containing CBI to the EPA
through http://www.regulations.gov or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
a disk or CD-ROM that you mail to the EPA, mark the outside of the disk
or CD-ROM as CBI and then identify electronically within the disk or
CD-ROM the specific information that is claimed as CBI. In addition to
one complete version of the comments that includes information claimed
as CBI, you must submit a copy of the comments that does not contain
the information claimed as CBI for inclusion in the public docket. If
you submit a CD-ROM or disk that does not contain CBI, mark the outside
of the disk or CD-ROM clearly that it does not contain CBI. Information
not marked as CBI will be included in the public docket and the EPA's
electronic public docket without prior notice. Information marked as
CBI will not be disclosed except in accordance with procedures set
forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver
information identified as CBI only to the following address: OAQPS
Document Control Officer (C404-02), OAQPS, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina 27711,
Attention Docket ID No. EPA-HQ-OAR-2016-0442.

II. Background

A. What is the statutory authority for this action?

    Section 112 of the CAA establishes a two-stage regulatory process
to address emissions of HAP from stationary sources. In the first
stage, after the EPA has identified categories of sources emitting one
or more of the HAP listed in CAA section 112(b), CAA section 112(d)
requires us to promulgate technology-based NESHAP for those sources.
``Major sources'' are those that emit or have the potential to emit 10
tons per year (tpy) or more of a single HAP or 25 tpy or more of any
combination of HAP. For major sources, the technology-based NESHAP must
reflect the maximum degree of emission reductions of HAP achievable
(after considering cost, energy requirements, and non-air quality
health and environmental impacts) and are commonly referred to as
maximum achievable control technology (MACT) standards.
    MACT standards must reflect the maximum degree of emissions
reduction achievable through the application of measures, processes,
methods, systems, or techniques, including, but not limited to,
measures that: (1) Reduce the volume of or eliminate pollutants through
process changes, substitution of materials, or other modifications; (2)
enclose systems or processes to eliminate emissions; (3) capture or
treat pollutants when released from a process, stack, storage, or
fugitive emissions point; (4) are design, equipment, work practice, or
operational standards (including requirements for operator training or
certification); or (5) are a combination of the above. CAA section
112(d)(2)(A)-(E). The MACT standards may take the form of design,
equipment, work practice, or operational standards where the EPA first
determines either that: (1) A pollutant cannot be emitted through a
conveyance designed and constructed to emit or capture the pollutant,
or that any requirement for, or use of, such a conveyance would be
inconsistent with law; or (2) the application of measurement
methodology to a particular class of sources is not practicable due to
technological and economic limitations. CAA section 112(h)(1)-(2).
    The MACT ``floor'' is the minimum control level allowed for MACT
standards promulgated under CAA section 112(d)(3) and may not be based
on cost considerations. For new sources, the MACT floor cannot be less
stringent than the emissions control that is achieved in practice by
the best-controlled similar source. The MACT floor for existing sources
can be less stringent than floors for new sources, but not less
stringent than the average emissions limitation achieved by the best-
performing 12 percent of existing sources in the category or
subcategory (or the best-performing five sources for categories or
subcategories with fewer than 30 sources). In developing MACT
standards, the EPA must also consider control options that are more
stringent than the floor. We may establish standards more stringent
than the floor based on considerations of the cost of achieving the
emission reductions, any non-air quality health and environmental
impacts, and energy requirements.
    The EPA is then required to review these technology-based standards
and revise them ``as necessary (taking into account developments in
practices, processes, and control technologies)'' no less frequently
than every 8 years. CAA section 112(d)(6). In conducting this review,
the EPA is not required to recalculate the MACT floor. Natural
Resources Defense Council (NRDC) v. EPA, 529 F.3d 1077, 1084 (D.C. Cir.
2008). Association of Battery Recyclers, Inc. v. EPA, 716 F.3d 667
(D.C. Cir. 2013).
    The second stage in standard-setting focuses on reducing any
remaining (i.e., ``residual'') risk according to CAA section 112(f).
Section 112(f)(1) of the CAA required that the EPA prepare a report to
Congress discussing (among other things) methods of calculating the
risks posed (or potentially posed) by sources after implementation of
the MACT standards, the public health significance of those risks, and
the EPA's recommendations as to legislation regarding such remaining
risk. The EPA prepared and submitted the Residual Risk Report to
Congress, EPA-453/R-99-001 (Risk Report) in March 1999.

Section 112(f)(2) of the CAA then provides that if Congress does not
act on any recommendation in the Risk Report, the EPA must analyze and
address residual risk for each category or subcategory of sources 8
years after promulgation of such standards pursuant to CAA section
112(d).
    Section 112(f)(2) of the CAA requires the EPA to determine for
source categories subject to MACT standards whether promulgation of
additional standards is needed to provide an ample margin of safety to
protect public health. Section 112(f)(2)(B) of the CAA expressly
preserves the EPA's use of the two-step process for developing
standards to address any residual risk and the Agency's interpretation
of ``ample margin of safety'' developed in the National Emissions
Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic
Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels,
Benzene Equipment Leaks, and Coke By-Product Recovery Plants (Benzene
NESHAP) (54 FR 38044, September 14, 1989). The EPA notified Congress in
the Risk Report that the Agency intended to use the Benzene NESHAP
approach in making CAA section 112(f) residual risk determinations
(EPA-453/R-99-001, p. ES-11). The EPA subsequently adopted this
approach in its residual risk determinations and in a challenge to the
risk review for the Synthetic Organic Chemical Manufacturing source
category, the United States Court of Appeals for the District of
Columbia Circuit (the Court) upheld as reasonable the EPA's
interpretation that CAA section 112(f)(2) incorporates the approach
established in the Benzene NESHAP. See NRDC v. EPA, 529 F.3d 1077, 1083
(D.C. Cir. 2008) (``[S]ubsection 112(f)(2)(B) expressly incorporates
the EPA's interpretation of the Clean Air Act from the Benzene
standard, complete with a citation to the Federal Register.''); see
also, A Legislative History of the Clean Air Act Amendments of 1990,
vol. 1, p. 877 (Senate debate on Conference Report).
    The first step in the process of evaluating residual risk is the
determination of acceptable risk. If risks are unacceptable, the EPA
cannot consider cost in identifying the emissions standards necessary
to bring risks to an acceptable level. The second step is the
determination of whether standards must be further revised in order to
provide an ample margin of safety to protect public health. The ample
margin of safety is the level at which the standards must be set,
unless an even more stringent standard is necessary to prevent, taking
into consideration costs, energy, safety, and other relevant factors,
an adverse environmental effect.
1. Step 1--Determination of Acceptability
    The Agency in the Benzene NESHAP concluded that ``the acceptability
of risk under section 112 is best judged on the basis of a broad set of
health risk measures and information'' and that the ``judgment on
acceptability cannot be reduced to any single factor.'' Benzene NESHAP
at 38046. The determination of what represents an ``acceptable'' risk
is based on a judgment of ``what risks are acceptable in the world in
which we live'' (Risk Report at 178, quoting NRDC v. EPA, 824 F. 2d
1146, 1165 (D.C. Cir. 1987) (en banc) (``Vinyl Chloride''), recognizing
that our world is not risk-free.
    In the Benzene NESHAP, we stated that ``EPA will generally presume
that if the risk to [the maximum exposed] individual is no higher than
approximately one in 10 thousand, that risk level is considered
acceptable.'' 54 FR at 38045, September 14, 1989. We discussed the
maximum individual lifetime cancer risk (or maximum individual risk
(MIR)) as being ``the estimated risk that a person living near a plant
would have if he or she were exposed to the maximum pollutant
concentrations for 70 years.'' Id. We explained that this measure of
risk ``is an estimate of the upper bound of risk based on conservative
assumptions, such as continuous exposure for 24 hours per day for 70
years.'' Id. We acknowledged that maximum individual lifetime cancer
risk ``does not necessarily reflect the true risk, but displays a
conservative risk level which is an upper-bound that is unlikely to be
exceeded.'' Id.
    Understanding that there are both benefits and limitations to using
the MIR as a metric for determining acceptability, we acknowledged in
the Benzene NESHAP that ``consideration of maximum individual risk * *
* must take into account the strengths and weaknesses of this measure
of risk.'' Id. Consequently, the presumptive risk level of 100-in-1
million (1-in-10 thousand) provides a benchmark for judging the
acceptability of maximum individual lifetime cancer risk, but does not
constitute a rigid line for making that determination. Further, in the
Benzene NESHAP, we noted that:

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

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

[i]n establishing a presumption for MIR, rather than a rigid line
for acceptability, the Agency intends to weigh it with a series of
other health measures and factors. These include the overall
incidence of cancer or other serious health effects within the
exposed population, the numbers of persons exposed within each
individual lifetime risk range and associated incidence within,
typically, a 50 km exposure radius around facilities, the science
policy assumptions and estimation uncertainties associated with the
risk measures, weight of the scientific evidence for human health
effects, other quantified or unquantified health effects, effects
due to co-location of facilities, and co-emission of pollutants.

Id. at 38045. In some cases, these health measures and factors taken
together may provide a more realistic description of the magnitude of
risk in the exposed population than that provided by maximum individual
lifetime cancer risk alone.
    As noted earlier, in NRDC v. EPA, the Court held that CAA section
112(f)(2) ``incorporates the EPA's interpretation of the Clean Air Act
from the Benzene Standard.'' The Court further held that Congress'
incorporation of the Benzene standard applies equally to carcinogens
and non-carcinogens. 529 F.3d at 1081-82. Accordingly, we also consider
non-cancer risk metrics in our determination of risk acceptability and
ample margin of safety.
2. Step 2--Determination of Ample Margin of Safety
    Section 112(f)(2) of the CAA requires the EPA to determine, for
source categories subject to MACT standards, whether those standards
provide an ample margin of safety to protect public health. As
explained in the Benzene NESHAP, ``the second step of the inquiry,
determining an `ample margin of safety,' again includes consideration
of all of the health factors, and whether to reduce the risks even
further * * *. Beyond that information, additional factors relating to
the appropriate level of control will also be considered, including
costs and economic impacts of controls, technological feasibility,
uncertainties, and any other relevant factors. Considering all of these
factors, the agency will establish the standard at

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

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

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

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

The Agency further stated that ``[t]he EPA also considers incidence
(the number of persons estimated to suffer cancer or other serious
health effects as a result of exposure to a pollutant) to be an
important measure of the health risk to the exposed population.
Incidence measures the extent of health risks to the exposed population
as a whole, by providing an estimate of the occurrence of cancer or
other serious health effects in the exposed population.'' Id. at 38045.
    In the ample margin of safety decision process, the Agency again
considers all of the health risks and other health information
considered in the first step, including the incremental risk reduction
associated with standards more stringent than the MACT standard or a
more stringent standard that the EPA has determined is necessary to
ensure risk is acceptable. In the ample margin of safety analysis, the
Agency considers additional factors, including costs and economic
impacts of controls, technological feasibility, uncertainties, and any
other relevant factors. Considering all of these factors, the Agency
will establish the standard at a level that provides an ample margin of
safety to protect the public health, as required by CAA section 112(f).
54 FR 38046, September 14, 1989.

B. What is this source category and how does the current NESHAP
regulate its HAP emissions?

    The EPA initially promulgated the Portland Cement Manufacturing
Industry NESHAP on June 14, 1999 (64 FR 31898), under title 40, part
63, subpart LLL of the CFR (40 CFR part 63, subpart LLL). The rule was
amended on April 5, 2002 (67 FR 16614); July 5, 2002 (67 FR 44766);
December 6, 2002 (67 FR 72580); December 20, 2006 (71 FR 76518);
September 9, 2010 (75 FR 54970); January 18, 2011 (76 FR 2832);
February 12, 2013 (78 FR 10006); July 27, 2015 (80 FR 44772); September
11, 2015 (80 FR 54728); and July 25, 2016 (81 FR 48356). The amendments
further defined affected cement kilns as those used to manufacture
Portland cement, except for kilns that burn hazardous waste, and are
subject to and regulated under 40 CFR part 63, subpart EEE, and kilns
that burn solid waste, which are subject to the CISWI rule under 40 CFR
part 60, subparts CCCC and DDDD. Additionally, onsite sources that are
subject to standards for nonmetallic mineral processing plants in 40
CFR part 60, subpart OOO are not subject to 40 CFR part 63, subpart
LLL. Crushers are not covered by 40 CFR part 63, subpart LLL regardless
of their location. Subpart LLL NESHAP regulates HAP emissions from new
and existing Portland cement production facilities that are major or
area sources of HAP, with one exception. Kilns located at facilities
that are area sources, are not regulated for hydrochloric acid (HCl)
emissions.
    Portland cement manufacturing is an energy-intensive process in
which cement is made by grinding and heating a mixture of raw materials
such as limestone, clay, sand, and iron ore in a rotary kiln. The kiln
is a large furnace that is fueled by coal, oil, gas, coke, and/or
various waste materials. The product (known as clinker) from the kiln
is cooled, ground, and then mixed with a small amount of gypsum to
produce Portland cement.
    The main source of air toxics emissions from a Portland cement
plant is the kiln. Emissions originate from the burning of fuels and
heating of feed materials. Air toxics are also emitted from the
grinding, cooling, and materials handling steps in the manufacturing
process. Pollutants regulated under the subpart LLL NESHAP are
particulate matter (PM) as a surrogate for non-mercury HAP metals,
total hydrocarbons (THC) as a surrogate for organic HAP other than
dioxins and furans (D/F), organic HAP as an alternative to the limit
for THC, mercury, HCl (from major sources only), and D/F expressed as
toxic equivalents (TEQ). The kiln is regulated for all HAP and raw
material dryers are regulated for THC or the alternative organic HAP.
Clinker coolers are regulated for PM. Finish mills and raw mills are
regulated for opacity. During periods of startup and shutdown, the
kiln, clinker cooler, and raw material dryer are regulated by work
practices. Open clinker storage piles are regulated by work practices.
The emission standards for the affected sources are summarized in Table
2.

         Table 2--Emission Limits for Kilns, Clinker Coolers, Raw Material Dryers, Raw and Finish Mills
----------------------------------------------------------------------------------------------------------------
                                                                                And the units
                                   And the         And it is      Your emissions       of the        The oxygen
  If your source is a (an):     operating mode   located at a:     limits are:    emissions limit    correction
                                     is:                                                are:         factor is:
----------------------------------------------------------------------------------------------------------------
1. Existing kiln.............  Normal           Major or area    PM \1\ 0.07....  Pounds (lb)/ton  NA.
                                operation.       source.                           clinker.

                                                                 D/F \2\ 0.2....  Nanograms/dry    7 percent.
                                                                                standard cubic
                                                                                meters (ng/
                                                                                dscm) (TEQ).
                                                                 Mercury 55.....  lb/million (MM)  NA.
                                                                                tons clinker.
                                                                 THC \3\ \4\ 24.  Parts per        7 percent.
                                                                                million,
                                                                                volumetric dry
                                                                                (ppmvd).
2. Existing kiln.............  Normal           Major source...  HCl 3..........  ppmvd..........  7 percent.
                                operation.
3. Existing kiln.............  Startup and      Major or area    Work practices.  NA.............  NA.
                                shutdown.        source.         (63.1346(g))...
4. New kiln..................  Normal           Major or area    PM \1\ 0.02....  lb/ton clinker.  NA.
                                operation.       source.
                                                                 D/F \2\ 0.2....  ng/dscm (TEQ)..  7 percent.
                                                                 Mercury 21.....  lb/MM tons       NA.
                                                                                clinker.
                                                                 THC \3\ \4\ 24.  ppmvd..........  7 percent.
5. New kiln..................  Normal           Major source...  HCl 3..........  ppmvd..........  7 percent.
                                operation.
6. New kiln..................  Startup and      Major or area    Work practices.  NA.............  NA.
                                shutdown.        source.         (63.1346(g))...
7. Existing clinker cooler...  Normal           Major or area    PM 0.07........  lb/ton clinker.  NA.
                                operation.       source.
8. Existing clinker cooler...  Startup and      Major or area    Work practices   NA.............  NA.
                                shutdown.        source.          (63.1348(b)(9)
                                                                  ).
9. New clinker cooler........  Normal           Major or area    PM 0.02........  lb/ton clinker.  NA.
                                operation.       source.
10. New clinker cooler.......  Startup and      Major or area    Work practices   NA.............  NA.
                                shutdown.        source.          (63.1348(b)(9)
                                                                  ).
11. Existing or new raw        Normal           Major or area    THC \3\ \4\ 24.  ppmvd..........  NA.
 material dryer.                operation.       source.
12. Existing or new raw        Startup and      Major or area    Work practices   NA.............  NA.
 material dryer.                shutdown.        source.          (63.1348(b)(9)
                                                                  ).
13. Existing or new raw or     All operating    Major source...  Opacity 10.....  percent........  NA.
 finish mill.                   modes.
----------------------------------------------------------------------------------------------------------------
\1\ The initial and subsequent PM performance tests are performed using Method 5 or 5I and consist of three test
  runs.
\2\ If the average temperature at the inlet to the first PM control device (fabric filter or electrostatic
  precipitator) during the D/F performance test is 400 [deg]F or less, this limit is changed to 0.40 ng/dscm
  (TEQ).
\3\ Measured as propane.
\4\ Any source subject to the 24 ppmvd THC limit may elect to meet an alternative limit of 12 ppmvd for total
  organic HAP.

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

    For the Portland Cement Manufacturing Industry source category, we
did not submit data collection requests to the industry or request
emissions testing by the industry for the information used in this
analysis. The data and data sources used to support this action are
described in section II.D below.

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

    For the Portland Cement Manufacturing Industry source category, a
comprehensive list of facilities and kilns was compiled using
information from the EPA's Greenhouse Gas Reporting Program (GHGRP)
(https://www.epa.gov/ghgreporting). All manufacturers of Portland
cement are required to report annually their greenhouse gas emissions
to the EPA (40 CFR part 98, subpart H). In reporting year 2015, 95
Portland cement facilities reported under the GHGRP. As explained above
in section II.B, kilns that are fueled by hazardous waste are subject
to the hazardous waste regulations in 40 CFR part 63, subpart EEE and,
therefore, are not subject to 40 CFR part 63, subpart LLL. Kilns that
are fueled by solid waste are subject to regulations in 40 CFR part 60,
subpart CCCC or DDDD and are also not subject to subpart LLL. To assist
in the identification of which sources are subject to subpart LLL, the
comprehensive list of Portland cement manufacturing facilities was
submitted to the Portland Cement Association (PCA) for review. The PCA
is an organization that represents the manufacturers of cement. The PCA
provided information on the status of each kiln and clinker cooler,
whether or not they were subject to subpart LLL regulations, and
identified other sources at facilities, such as raw material dryers,
that were also subject to subpart LLL.
    The risk modeling dataset was developed in a two-step process.
Initially, a draft dataset was developed using available information on
emissions, stack parameters, and emission source locations. In step
two, the draft dataset for each Portland cement manufacturing facility
was submitted to the facility or its parent company to review for
accuracy. Based on the review by each company and the submittal of
documentation supporting the changes, the risk modeling dataset was
revised. Copies of the datasets sent to the companies for review and
the revised datasets and supporting documentation submitted by each
company are contained in the docket to this rulemaking (Docket ID No.
EPA-HQ-OAR-2016-0442).
    The initial draft dataset was developed using emission test data to
the extent possible. Under 40 CFR part 63, subpart LLL, the EPA
requires that performance test results be submitted to the EPA via the
Compliance and Emissions Data Reporting Interface (CEDRI), which can be
accessed through the EPA's Central Data Exchange (CDX). Emissions data
are publicly available through the EPA's Web Factor Information
Retrieval System (WebFIRE) using the EPA's electronic reporting tool
(ERT) as listed on the EPA's ERT Web site (https://www.epa.gov/electronic-reporting-air-emissions/electronic-reporting-tool-ert). To
estimate actual emissions, available emissions data were extracted from
each facility's submitted ERT file. When emissions data were not
available in ERT, the subpart LLL emissions limit was substituted as a
placeholder for actual emissions until the data set could be reviewed
and revised by industry.

III. Analytical Procedures

    In this section, we describe the analyses performed to support the
proposed decisions for the RTR and other issues addressed in this
proposal.

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

    The EPA conducted a risk assessment that provides estimates of the
MIR posed by the HAP emissions from each source in the source category,
the hazard index (HI) for chronic exposures to HAP with the potential
to cause non-cancer health effects, and the hazard quotient (HQ) for
acute exposures to HAP with the potential to cause non-cancer health
effects. The assessment also provides estimates of the distribution of
cancer risks within the exposed populations, cancer incidence, and an
evaluation of the potential for adverse environmental effects. The
eight sections that follow this paragraph describe how we estimated
emissions and conducted the risk assessment. The docket for this
rulemaking contains the following document which provides more
information on the risk assessment inputs and models: Residual Risk
Assessment for the Portland Cement Manufacturing Industry Source
Category in Support of the Risk and Technology Review September, 2017
Proposed Rule. The methods used to assess risks (as described in the
eight primary steps below) are consistent with those peer-reviewed by a
panel of the EPA's Science Advisory Board (SAB) in 2009 and described
in their peer review report issued in 2010;\2\ they are also consistent
with the key recommendations contained in that report.
---------------------------------------------------------------------------

    \2\ U.S. EPA SAB. Risk and Technology Review (RTR) Risk
Assessment Methodologies: For Review by the EPA's Science Advisory
Board with Case Studies--MACT I Petroleum Refining Sources and
Portland Cement Manufacturing, May 2010.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions
release characteristics?
    The pollutants regulated under 40 CFR part 63, subpart LLL are PM,
HCl, THC, mercury, and D/F. The emission standards apply to Portland
cement plants that are major or area sources, with one exception. Kilns
that are located at a facility that is an area source are not subject
to the emission limits for HCl. Sources subject to the emissions limit
for THC may elect to meet an alternative limit for total organic HAP.
For purposes of subpart LLL, total organic HAP is the sum of the
concentrations of compounds of formaldehyde, benzene, toluene, styrene,
m-xylene, p-xylene, o-xylene, acetaldehyde, and naphthalene as measured
by EPA Test Method 320 or Method 18 of appendix A to 40 CFR part 63 or
ASTM D6348-03 or a combination of these methods, as appropriate. The
affected sources at Portland cement plants that were accounted for in
the risk modeling dataset include the kiln, as well as any alkali
bypass or inline raw mill or inline coal mill, clinker coolers, and raw
material dryers. Kilns fueled with hazardous waste or solid waste and
not subject to subpart LLL were excluded from the dataset. All affected
sources in the risk modeling dataset emit through stacks. As mentioned
in section II.D above, the risk modeling dataset used for estimating
actual emissions was developed in a two-step process. Initially, the
dataset was developed using available information and is described
below. The dataset for each Portland cement manufacturing facility was
then submitted to the facility, or its parent company, to review for
accuracy. Based on the review by each company, and the submittal of
documentation supporting the changes, the risk modeling dataset was
then revised. Copies of the datasets sent to the companies for review
and the revised datasets submitted by each company are contained in the
docket to this rulemaking (Docket ID No. EPA-HQ-OAR-2016-0442).
    As described in section II.D above, available emissions data were
extracted from each facility's submitted ERT file. To ensure that the
emissions data reflect process and control device changes made at each
Portland cement plant to comply with the 2013 final amendments to 40
CFR part 63, subpart LLL (February 12, 2013, 78 FR 10006), emissions
data from mid-2015 and later were used as inputs into the emissions
modeling file.
    Emissions data are reported in ERT in units of pounds per hour (lb/
hr), which were multiplied by a facility's reported annual hours of
operation to calculate emissions in tpy. If hours of operation were not
reported, the default of 8,760 hours per year was used. When emissions
data were not available in ERT, the 40 CFR part 63, subpart LLL
emissions limit was substituted as a placeholder for actual emissions
until the data set could be reviewed and revised by industry.
    Subpart LLL of 40 CFR part 63 uses PM as a surrogate for non-
mercury metallic HAP and THC as a surrogate for organic HAP. The
specific non-mercury metallic HAP that went into the modeling file are
antimony, arsenic, beryllium, cadmium, chromium, cobalt, lead,
manganese, mercury, nickel, and selenium. As an alternative to
measuring THC, subpart LLL allows sources to measure directly their
emissions of the nine organic HAP listed in subpart LLL. The specific
organic HAP that went into the modeling file are acetaldehyde,
formaldehyde, naphthalene, styrene, toluene, m-xylene, o-xylene, p-
xylene, and benzene. Because subpart LLL compliance testing is
typically performed for the surrogates PM and THC, there are limited
test data available for compound-specific non-mercury metallic and
organic HAP emissions. To generate compound-specific metallic HAP and
organic HAP emissions estimates, recent emissions tests were identified
in which testing was done for compound-specific metallic and organic
HAP emissions. To account for recent changes in emission controls and
production processes that have been implemented by facilities to comply
with the subpart LLL MACT standards, emissions testing that occurred in
2015 and later were used to develop compound-specific estimates for
metallic HAP and organic HAP emissions. In the case of D/F, the subpart
LLL emission limits for D/F were unchanged in the 2013 final rule.
Thus, older D/F test data could be used along with more recent test
data.
    The approach used to develop the final risk modeling dataset
assures the quality of the data at various steps in the process of
developing the dataset. The initial step in developing the dataset was
to compile a list of affected facilities. A comprehensive list of
cement manufacturing facilities and kilns was derived from the EPA's
GHGRP, which requires reporting by all cement manufacturing facilities.
Not all Portland cement kilns are subject to 40 CFR part 63, subpart
LLL. Kilns that burn commercial and industrial solid waste are subject
to 40 CFR part 60, subpart CCCC and DDDD. Kilns that burn hazardous
waste are subject to 40 CFR part 63, subpart EEE. To help identify the
cement kilns that are subject to subpart LLL regulations, the list of
facilities and kilns was submitted to the PCA for review. In their
review, they provided useful information on which cement manufacturing
facilities were or were not subject to subpart LLL, whether kilns and
clinker coolers used separate or combined stacks, the presence of
additional affected sources not on the initial list, and the presence
of kilns that were not currently operating. For those kilns identified
as not currently operating, the appropriate state permitting agency was
contacted to determine whether the kiln was currently permitted to
operate. If the kiln was not operating, but retained their title V
permit, they were kept in the dataset. In other instances, company
representatives were contacted to verify that kilns at their facilities
were or were

not subject to subpart LLL regulations. In developing the emissions
data, operating hours, stack parameters (i.e., stack height,
temperature, diameter, velocity, and flowrate), and stack locations
(i.e., latitude and longitude), the use of the EPA's ERT provides a
single source of electronic test data and replaces the manual
collection and evaluation of test data. The regulated facility owner or
operator submits their summary report semiannually to the EPA via the
CEDRI, which is accessed through the EPA's CDX (www.epa.gov/cdx). This
electronic submission of data helps to ensure that information and
procedures required by test methods are documented, provides consistent
criteria to quantitatively characterize the quality of the data
collected during the emissions test, and standardizes the reporting of
results. Information on stack parameters and stack locations were also
derived from ERT. For facilities that had not yet submitted their test
information to ERT, the emission limits were used as placeholders until
industry could review the information. When operating hours were not in
ERT, a placeholder of 8,760 hours was used until industry could review
the information. When stack parameters and stack locations were not in
ERT, other sources of information such as the 2013 Universal Industrial
Sectors Integrated Solutions (UISIS) modeling file created by the EPA
and the 2011 National Emissions Inventory (NEI) were used. As a check
on the emissions data, operating hours, stack parameters, and stack
locations compiled for each facility, a draft of the dataset consisting
of the data for all the facilities under a single company was sent to a
representative at the appropriate company for review. Instructions for
reviewing and making changes to the dataset required that any revisions
be supported with appropriate documentation. In addition, example
calculations for emissions estimates and default stack parameters were
provided. Revisions made to the data for each facility were
incorporated into a master final dataset. The master final dataset was
subjected to further quality evaluation. For example, exhaust gas
flowrates were checked using information on stack diameters and gas
velocities. Stack diameters and stack velocities are checked for
outliers. Stack locations were also checked using Google Earth[supreg]
to ensure that stack locations were correctly located at the cement
manufacturing facility.
    The derivation of actual emission estimates is discussed in more
detail in the document, Development of the RTR Risk Modeling Dataset
for the Portland Cement Manufacturing Industry Source Category, which
is available in the docket for this proposed rulemaking.
2. How did we estimate MACT-allowable emissions?
    The available emissions data in the RTR emissions dataset include
estimates of the mass of HAP emitted during the specified annual time
period. In some cases, these ``actual'' emission levels are lower than
the emission levels required to comply with the current MACT standards.
The emissions level allowed to be emitted by the MACT standards is
referred to as the ``MACT-allowable'' emissions level. We discussed the
use of both MACT-allowable and actual emissions in the final Coke Oven
Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed
and final Hazardous Organic NESHAP RTRs (71 FR 34428, June 14, 2006,
and 71 FR 76609, December 21, 2006, respectively). In those actions, we
noted that assessing the risks at the MACT-allowable level is
inherently reasonable since these risks reflect the maximum level
facilities could emit and still comply with national emission
standards. We also explained that it is reasonable to consider actual
emissions, where such data are available, in both steps of the risk
analysis, in accordance with the Benzene NESHAP approach (54 FR 38044,
September 14, 1989).
    Allowable emissions are calculated using the emission limits in the
rule for existing sources along with the emission factors for metallic
HAP, organic HAP, and D/F congeners, the annual production capacity,
and, when the emission limit is a concentration-based limit, the annual
hours of operation reported by each source. We note that these are
conservative estimates of allowable emissions. It is unlikely that
emissions would be at the maximum limit at all times because sources
cannot emit HAP at a level that is exactly equal to the limit and
remain in compliance with the standard due to day-to-day variability in
process operations and emissions. On average, facilities must emit at
some level below the MACT limit to ensure that they are always in
compliance. The derivation of allowable emissions is discussed in more
detail in the document, Development of the RTR Risk Modeling Dataset
for the Portland Cement Manufacturing Industry Source Category, which
is available in the docket for this proposed rulemaking.
3. How did we conduct dispersion modeling, determine inhalation
exposures, and estimate individual and population inhalation risks?
    Both long-term and short-term inhalation exposure concentrations
and health risks from the source category addressed in this proposal
were estimated using the Human Exposure Model (Community and Sector
HEM-3). The HEM-3 performs three primary risk assessment activities:
(1) conducting dispersion modeling to estimate the concentrations of
HAP in ambient air, (2) estimating long-term and short-term inhalation
exposures to individuals residing within 50 kilometers (km) of the
modeled sources,\3\ and (3) estimating individual and population-level
inhalation risks using the exposure estimates and quantitative dose-
response information.
---------------------------------------------------------------------------

    \3\ This metric comes from the Benzene NESHAP. See 54 FR 38046,
September 14, 1989.
---------------------------------------------------------------------------

    The air dispersion model used by the HEM-3 model (AERMOD) is one of
the EPA's preferred models for assessing pollutant concentrations from
industrial facilities.\4\ To perform the dispersion modeling and to
develop the preliminary risk estimates, HEM-3 draws on three data
libraries. The first is a library of meteorological data, which is used
for dispersion calculations. This library includes 1 year (2016) of
hourly surface and upper air observations for more than 800
meteorological stations, selected to provide coverage of the U.S. and
Puerto Rico. A second library of U.S. Census Bureau census block \5\
internal point locations and populations provides the basis of human
exposure calculations (U.S. Census, 2010). In addition, for each census
block, the census library includes the elevation and controlling hill
height, which are also used in dispersion calculations. A third library
of pollutant unit risk factors and other health benchmarks is used to
estimate health risks. These risk factors and health benchmarks are the
latest values recommended by the EPA for HAP and other toxic air
pollutants. These values are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants and are discussed in more detail later in this
section.
---------------------------------------------------------------------------

    \4\ U.S. EPA. Revision to the Guideline on Air Quality Models:
Adoption of a Preferred General Purpose (Flat and Complex Terrain)
Dispersion Model and Other Revisions (70 FR 68218, November 9,
2005).
    \5\ A census block is the smallest geographic area for which
census statistics are tabulated.
---------------------------------------------------------------------------

    In developing the risk assessment for chronic exposures, we used
the

estimated annual average ambient air concentrations of each HAP emitted
by each source for which we have emissions data in the source category.
The air concentrations at each nearby census block centroid were used
as a surrogate for the chronic inhalation exposure concentration for
all the people who reside in that census block. We calculated the MIR
for each facility as the cancer risk associated with a continuous
lifetime (24 hours per day, 7 days per week, and 52 weeks per year for
a 70-year period) exposure to the maximum concentration at the centroid
of inhabited census blocks. Individual cancer risks were calculated by
multiplying the estimated lifetime exposure to the ambient
concentration of each of the HAP (in micrograms per cubic meter ([mu]g/
m\3\)) by its unit risk estimate (URE). The URE is an upper bound
estimate of an individual's probability of contracting cancer over a
lifetime of exposure to a concentration of 1 microgram of the pollutant
per cubic meter of air. For residual risk assessments, we generally use
URE values from the EPA's Integrated Risk Information System (IRIS).
For carcinogenic pollutants without IRIS values, we look to other
reputable sources of cancer dose-response values, often using
California EPA (CalEPA) URE values, where available. In cases where
new, scientifically credible dose response values have been developed
in a manner consistent with the EPA guidelines and have undergone a
peer review process similar to that used by the EPA, we may use such
dose-response values in place of, or in addition to, other values, if
appropriate.
    The EPA estimated incremental individual lifetime cancer risks
associated with emissions from the facilities in the source category as
the sum of the risks for each of the carcinogenic HAP (including those
classified as carcinogenic to humans, likely to be carcinogenic to
humans, and suggestive evidence of carcinogenic potential \6\) emitted
by the modeled sources. Cancer incidence and the distribution of
individual cancer risks for the population within 50 km of the sources
were also estimated for the source category as part of this assessment
by summing individual risks. A distance of 50 km is consistent with
both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044,
September 14, 1989) and the limitations of Gaussian dispersion models,
including AERMOD.
---------------------------------------------------------------------------

    \6\ These classifications also coincide with the terms ``known
carcinogen, probable carcinogen, and possible carcinogen,''
respectively, which are the terms advocated in the EPA's previous
Guidelines for Carcinogen Risk Assessment, published in 1986 (51 FR
33992, September 24, 1986). In August 2000, the document,
Supplemental Guidance for Conducting Health Risk Assessment of
Chemical Mixtures (EPA/630/R-00/002) was published as a supplement
to the 1986 document. Copies of both documents can be obtained from
https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944. 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 the EPA's National Air Toxics Assessment
(NATA) titled, NATA--Evaluating the National-scale Air Toxics
Assessment 1996 Data--an SAB Advisory, available at http://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
---------------------------------------------------------------------------

    To assess the risk of non-cancer health effects from chronic
exposures, we summed the HQ for each of the HAP that affects a common
target organ system to obtain the HI for that target organ system (or
target organ-specific HI, TOSHI). The HQ is the estimated exposure
divided by the chronic reference value, which is a value selected from
one of several sources. First, the chronic reference level can be the
EPA reference concentration (RfC) (https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary), defined as ``an estimate
(with uncertainty spanning perhaps an order of magnitude) of a
continuous inhalation exposure to the human population (including
sensitive subgroups) that is likely to be without an appreciable risk
of deleterious effects during a lifetime.'' Alternatively, in cases
where an RfC from the EPA's IRIS database is not available or where the
EPA determines that using a value other than the RfC is appropriate,
the chronic reference level can be a value from the following
prioritized sources: (1) The Agency for Toxic Substances and Disease
Registry (ATSDR) Minimal Risk Level (MRL) (http://www.atsdr.cdc.gov/mrls/index.asp), which is defined as ``an estimate of daily human
exposure to a hazardous substance that is likely to be without an
appreciable risk of adverse non-cancer health effects (other than
cancer) over a specified duration of exposure''; (2) the CalEPA Chronic
Reference Exposure Level (REL) (http://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0), which is defined as ``the concentration level (that is
expressed in units of [mu]g/m\3\ for inhalation exposure and in a dose
expressed in units of milligram per kilogram-day (mg/kg-day) for oral
exposures), at or below which no adverse health effects are anticipated
for a specified exposure duration''; or (3), as noted above, a
scientifically credible dose-response value that has been developed in
a manner consistent with the EPA guidelines and has undergone a peer
review process similar to that used by the EPA, in place of or in
concert with other values.
    As mentioned above, in order to characterize non-cancer chronic
effects, and in response to key recommendations from the SAB, the EPA
selects dose-response values that reflect the best available science
for all HAP included in RTR risk assessments.\7\ More specifically, for
a given HAP, the EPA examines the availability of inhalation reference
values from the sources included in our tiered approach (e.g., IRIS
first, ATSDR second, CalEPA third) and determines which inhalation
reference value represents the best available science. Thus, as new
inhalation reference values become available, the EPA will typically
evaluate them and determine whether they should be given preference
over those currently being used in RTR risk assessments.
---------------------------------------------------------------------------

    \7\ Recommendations from the SAB's review of RTR Risk Assessment
Methodologies and the review materials are available at http://
yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf
and at https://cfpub.epa.gov/si/si_publiclowbar;record_report.cfm?dirEntryID=238928, respectively.
---------------------------------------------------------------------------

    The EPA also evaluated screening estimates of acute exposures and
risks for each of the HAP (for which appropriate acute dose-response
values are available) at the point of highest potential off-site
exposure for each facility. To do this, the EPA estimated the risks
when both the peak hourly emissions rate and worst-case dispersion
conditions occur. We also assume that a person is located at the point
of highest impact during that same time. In accordance with our mandate
in section 112 of the CAA, we use the point of highest off-site
exposure to assess the potential risk to the maximally exposed
individual. The acute HQ is the estimated acute exposure divided by the
acute dose-response value. In each case, the EPA calculated acute HQ
values using best available, short-term dose-response values. These
acute dose-response values, which are described below, include the
acute REL, acute exposure guideline levels (AEGL) and Emergency
Response Planning Guidelines (ERPG) for 1-hour exposure durations. As
discussed below, we used conservative assumptions for emissions rates,
meteorology, and exposure location.
    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://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary) is defined as ``the concentration level at
or below which no adverse health effects are anticipated for a
specified exposure duration.'' Id. at page 2. Acute REL values are
based on the most sensitive, relevant, adverse health effect reported
in the peer-reviewed medical and toxicological literature. Acute REL
values are designed to protect the most sensitive individuals in the
population through the inclusion of margins of safety. Because margins
of safety are incorporated to address data gaps and uncertainties,
exceeding the REL does not automatically indicate an adverse health
impact.
    AEGL values were derived in response to recommendations from the
National Research Council (NRC). The National Advisory Committee (NAC)
for the Development of Acute Exposure Guideline Levels for Hazardous
Substances, usually referred to as the AEGL Committee or the NAC/AEGL
committee, developed AEGL values for at least 273 of the 329 chemicals
on the AEGL priority chemical list. The last meeting of the NAC/AEGL
Committee was in April 2010, and its charter expired in October 2011.
The NAC/AEGL Committee ended in October 2011, but the AEGL program
continues to operate at the EPA and works with the National Academies
to publish final AEGLs (https://www.epa.gov/aegl).
    As described in Standing Operating Procedures (SOP) of the National
Advisory Committee on Acute Exposure Guideline Levels for Hazardous
Chemicals (https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf),\8\ ``the
NRC's previous name for acute exposure levels--community emergency
exposure levels--was replaced by the term AEGL to reflect the broad
application of these values to planning, response, and prevention in
the community, the workplace, transportation, the military, and the
remediation of Superfund sites.'' Id. at 2. This document also states
that AEGL values ``represent threshold exposure limits for the general
public and are applicable to emergency exposures ranging from 10
minutes to eight hours.'' Id. at 2.
---------------------------------------------------------------------------

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

    The document lays out the purpose and objectives of AEGL by stating
that ``the primary purpose of the AEGL program and the National
Advisory Committee for Acute Exposure Guideline Levels for Hazardous
Substances is to develop guideline levels for once-in-a-lifetime,
short-term exposures to airborne concentrations of acutely toxic, high-
priority chemicals.'' Id. at 21. In detailing the intended application
of AEGL values, the document states that ``[i]t is anticipated that the
AEGL values will be used for regulatory and nonregulatory purposes by
U.S. Federal and state agencies and possibly the international
community in conjunction with chemical emergency response, planning,
and prevention programs. More specifically, the AEGL values will be
used for conducting various risk assessments to aid in the development
of emergency preparedness and prevention plans, as well as real-time
emergency response actions, for accidental chemical releases at fixed
facilities and from transport carriers.'' Id. at 31.
    The AEGL-1 value is then specifically defined as ``the airborne
concentration (expressed as ppm (parts per million) or mg/m\3\
(milligrams per cubic meter)) of a substance above which it is
predicted that the general population, including susceptible
individuals, could experience notable discomfort, irritation, or
certain asymptomatic nonsensory effects. However, the effects are not
disabling and are transient and reversible upon cessation of
exposure.'' Id. at 3. The document also notes that, ``Airborne
concentrations below AEGL-1 represent exposure levels that can produce
mild and progressively increasing but transient and nondisabling odor,
taste, and sensory irritation or certain asymptomatic, nonsensory
effects.'' Id. Similarly, the document defines AEGL-2 values as ``the
airborne concentration (expressed as parts per million or milligrams
per cubic meter) of a substance above which it is predicted that the
general population, including susceptible individuals, could experience
irreversible or other serious, long-lasting adverse health effects or
an impaired ability to escape.'' Id.
    ERPG values are derived for use in emergency response, as described
in the American Industrial Hygiene Association's Emergency Response
Planning (ERP) Committee document titled, ERPGS Procedures and
Responsibilities (https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf), which
states that, ``Emergency Response Planning Guidelines were developed
for emergency planning and are intended as health based guideline
concentrations for single exposures to chemicals.'' \9\ Id. at 1. The
ERPG-1 value is defined as ``the maximum airborne concentration below
which it is believed that nearly all individuals could be exposed for
up to 1 hour without experiencing other than mild transient adverse
health effects or without perceiving a clearly defined, objectionable
odor.'' Id. at 2. Similarly, the ERPG-2 value is defined as ``the
maximum airborne concentration below which it is believed that nearly
all individuals could be exposed for up to one hour without
experiencing or developing irreversible or other serious health effects
or symptoms which could impair an individual's ability to take
protective action.'' Id. at 1.
---------------------------------------------------------------------------

    \9\ ERP Committee Procedures and Responsibilities. March 2014.
American Industrial Hygiene Association.
---------------------------------------------------------------------------

    As can be seen from the definitions above, the AEGL and ERPG values
include the similarly-defined severity levels 1 and 2. For many
chemicals, a severity level 1 value AEGL or ERPG has not been developed
because the types of effects for these chemicals are not consistent
with the AEGL-1/ERPG-1 definitions; in these instances, we compare
higher severity level AEGL-2 or ERPG-2 values to our modeled exposure
levels to screen for potential acute concerns. When AEGL-1/ERPG-1
values are available, they are used in our acute risk assessments.
    Acute REL values for 1-hour exposure durations are typically lower
than their corresponding AEGL-1 and ERPG-1 values. Even though their
definitions are slightly different, AEGL-1 values are often the same as
the corresponding ERPG-1 values, and AEGL-2 values are often equal to
ERPG-2 values. Maximum HQ values from our acute screening risk
assessments typically result when basing them on the acute REL value
for a particular pollutant. In cases where our maximum acute HQ value
exceeds 1, we also report the HQ value based on the next highest acute
dose-response value (usually the AEGL-1 and/or the ERPG-1 value).
    To develop screening estimates of acute exposures in the absence of
hourly emissions data, generally we first develop estimates of maximum
hourly emissions rates by multiplying the

average actual annual hourly emissions rates by a default factor to
cover routinely variable emissions. We choose the factor to use
partially based on process knowledge and engineering judgment. The
factor chosen also reflects a Texas study of short-term emissions
variability, which showed that most peak emission events in a heavily-
industrialized four-county area (Harris, Galveston, Chambers, and
Brazoria Counties, Texas) were less than twice the annual average
hourly emissions rate. The highest peak emissions event was 74 times
the annual average hourly emissions rate, and the 99th percentile ratio
of peak hourly emissions rate to the annual average hourly emissions
rate was 9.\10\ Considering this analysis, to account for more than 99
percent of the peak hourly emissions, we apply a conservative screening
multiplication factor of 10 to the average annual hourly emissions rate
in our acute exposure screening assessments as our default approach. A
further discussion of why this factor was chosen can be found in the
memorandum, Emissions Data and Acute Risk Factor Used in Residual Risk
Modeling: Portland Cement Manufacturing Industry, available in the
docket for this rulemaking.
---------------------------------------------------------------------------

    \10\ Allen, et al., 2004. Variable Industrial VOC Emissions and
their impact on ozone formation in the Houston Galveston Area. Texas
Environmental Research Consortium. https://www.researchgate.net/publication/237593060_Variable_Industrial_VOC_Emissions
and_their_Impact_on_Ozone_Formation_in_the_Houston_Galveston_Area.
---------------------------------------------------------------------------

    As part of our acute risk assessment process, for cases where acute
HQ values from the screening step are less than or equal to 1 (even
under the conservative assumptions of the screening analysis), acute
impacts are deemed negligible and no further analysis is performed for
these HAP. In cases where an acute HQ from the screening step is
greater than 1, additional site-specific data are considered to develop
a more refined estimate of the potential for acute impacts of concern.
For this source category, since no HQ was greater than 1, no further
analysis was performed.
    Ideally, we would prefer to have continuous measurements over time
to see how the emissions vary by each hour over an entire year. Having
a frequency distribution of hourly emissions rates over a year would
allow us to perform a probabilistic analysis to estimate potential
threshold exceedances and their frequency of occurrence. Such an
evaluation could include a more complete statistical treatment of the
key parameters and elements adopted in this screening analysis.
Recognizing that this level of data is rarely available, we instead
rely on the multiplier approach.
    To better characterize the potential health risks associated with
estimated acute exposures to HAP, and in response to a key
recommendation from the SAB's 2010 peer review of the EPA's RTR risk
assessment methodologies,\11\ we generally examine a wider range of
available acute health metrics (e.g., RELs, AEGLs) than we do for our
chronic risk assessments. This is in response to the SAB's
acknowledgement that there are generally more data gaps and
inconsistencies in acute reference values than there are in chronic
reference values. In some cases, when Reference Value Arrays \12\ for
HAP have been developed, we consider additional acute values (i.e.,
occupational and international values) to provide a more complete risk
characterization.
---------------------------------------------------------------------------

    \11\ The SAB peer review of RTR Risk Assessment Methodologies is
available at http://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
    \12\ U.S. EPA. 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, 2009, and available online at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003.
---------------------------------------------------------------------------

4. How did we conduct the multipathway exposure and risk screening?
    The EPA conducted a screening analysis examining the potential for
significant human health risks due to exposures via routes other than
inhalation (i.e., ingestion). We first determined whether any sources
in the source category emitted any HAP known to be persistent and
bioaccumulative in the environment (PB-HAP). The PB-HAP compounds or
compound classes are identified for the screening from the EPA's Air
Toxics Risk Assessment Library (available at http://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Portland Cement Manufacturing Industry source category, we
identified emissions of lead compounds, cadmium compounds, mercury
compounds, arsenic compounds, and D/F. Because one or more of these PB-
HAP are emitted by at least one facility in the Portland Cement
Manufacturing Industry source category, we proceeded to the next step
of the evaluation. In this step, we determined whether the facility-
specific emission rates of the emitted PB-HAP were large enough to
create the potential for significant non-inhalation human health risks
under reasonable worst-case conditions. To facilitate this step, we
developed screening threshold emission rates for several PB-HAP using a
hypothetical upper-end screening exposure scenario developed for use in
conjunction with the EPA's Total Risk Integrated Methodology.Fate,
Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with
screening threshold emission rates are: Cadmium compounds, mercury
compounds, arsenic compounds, and D/F and polycyclic organic matter
(POM). We conducted a sensitivity analysis on the screening scenario to
ensure that its key design parameters would represent the upper end of
the range of possible values, such that it would represent a
conservative, but not impossible scenario. The facility-specific PB-HAP
emission rates were compared to their respective screening threshold
emission rate to assess the potential for significant human health
risks via non-inhalation pathways. We call this application of the
TRIM.FaTE model the Tier 1 TRIM-screen or Tier 1 screen.
    For the purpose of developing emission rates for the Tier 1 TRIM-
screen, we derived emission levels for these PB-HAP (other than lead
compounds) at which the maximum excess lifetime cancer risk would be 1-
in-1 million (i.e., D/F, arsenic compounds, and POM) or, for HAP that
cause non-cancer health effects (i.e., cadmium compounds and mercury
compounds), the maximum HQ would be 1. If the emission rate of any PB-
HAP included in the Tier 1 screen exceeds the Tier 1 screening
threshold emission rates for any facility, we conduct a second screen,
which we call the Tier 2 TRIM-screen or Tier 2 screen.
    In the Tier 2 screen, the location of each facility that exceeds
the Tier 1 screening threshold emission rates is used to refine the
assumptions associated with the environmental scenario while
maintaining the exposure scenario assumptions. A key assumption that is
part of the Tier 1 screen is that a lake is located near the facility;
we confirm the existence of lakes near the facility as part of the Tier
2 screen. We also examine the differences between local meteorology
near the facility and the meteorology used in the Tier 1 screen. We
then adjust the risk-based Tier 1 screening threshold emission rates
for each PB-HAP for each facility based on an understanding of how
exposure concentrations estimated for the screening scenario change
with meteorology and environmental

assumptions. PB-HAP emissions that do not exceed these new Tier 2
screening threshold emission rates are considered to be below a level
of concern. If the PB-HAP emissions for a facility exceed the Tier 2
screening threshold emission rates and data are available, we may
decide to conduct a more refined Tier 3 multipathway assessment or
proceed to a site-specific assessment. There are several analyses that
can be included in a Tier 3 screen depending upon the extent of
refinement warranted, including validating that the lakes are fishable,
considering plume-rise to estimate emissions lost above the mixing
layer, and considering hourly effects of meteorology and plume rise on
chemical fate and transport. For this source category a Tier 3 screen
was conducted for 1 facility that had dioxin emissions exceeding the
Tier 2 threshold emission rates up to a value of 100-in-1 million. If
the Tier 3 screen is exceeded, the EPA may conduct a refined site-
specific assessment.
    When tiered screening values for any facility indicate a potential
health risk to the public, we may conduct a more refined multipathway
assessment. A refined assessment was conducted for mercury in lieu of
conducting a Tier 3 screen. To select the candidate facilities for the
site-specific assessment, we analyzed the facilities with the maximum
exceedances of the Tier 2 screening values as well as the combined
effect from multiple facilities on lakes within the same watershed. In
addition to looking at the Tier 2 screen value for each lake, the
location and number of lakes or farms impacted for each watershed was
evaluated to assess elevation/topography influences. A review of the
source category identified 3 facilities located in Midlothian, Texas,
as the best candidates for mercury impacts. These candidate sites were
selected because of their exceedances of the Tier 2 mercury screening
value and based upon the above considerations.
    In evaluating the potential multipathway risk from emissions of
lead compounds, rather than developing a screening threshold emission
rate for them, we compared maximum estimated 1-hour acute inhalation
exposures with the level of the current National Ambient Air Quality
Standard (NAAQS) for lead.\13\ Values below the level of the Primary
(health-based) Lead NAAQS were considered to have a low potential for
multipathway risk.
---------------------------------------------------------------------------

    \13\ In doing so, the EPA notes that the legal standard for a
primary NAAQS--that a standard is requisite to protect public health
and provide an adequate margin of safety (CAA section 109(b))--
differs from the CAA section 112(f) standard (requiring, among other
things, that the standard provide an ``ample margin of safety'').
However, the Primary Lead NAAQS is a reasonable measure of
determining risk acceptability (i.e., the first step of the Benzene
NESHAP analysis) since it is designed to protect the most
susceptible group in the human population--children, including
children living near major lead emitting sources. 73 FR 67002/3; 73
FR 67000/3; 73 FR 67005/1. In addition, applying the level of the
Primary Lead NAAQS at the risk acceptability step is conservative,
since that Primary Lead NAAQS reflects an adequate margin of safety.
---------------------------------------------------------------------------

    For further information on the multipathway analysis approach, see
the Residual Risk Assessment for the Portland Cement Manufacturing
Industry Source Category in Support of the Risk and Technology Review
September 2017 Proposed Rule, which is available in the docket for this
action.
5. How did we assess risks considering emissions control options?
    In addition to assessing baseline inhalation risks and screening
for potential multipathway risks, we also estimated risks considering
the potential emission reductions that would be achieved by the control
options under consideration. In these cases, the expected emission
reductions were applied to the specific HAP and emission points in the
RTR emissions dataset to develop corresponding estimates of risk and
incremental risk reductions.
6. How did we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect
    The EPA conducts a screening assessment to examine the potential
for adverse environmental effects as required under section
112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines ``adverse
environmental effect'' as ``any significant and widespread adverse
effect, which may reasonably be anticipated, to wildlife, aquatic life,
or other natural resources, including adverse impacts on populations of
endangered or threatened species or significant degradation of
environmental quality over broad areas.''
b. Environmental HAP
    The EPA focuses on eight HAP, which we refer to as ``environmental
HAP,'' in its screening analysis: Six PB-HAP and two acid gases. The
six PB-HAP are cadmium compounds, D/F, arsenic compounds, POM, mercury
compounds (both inorganic mercury and methyl mercury), and lead
compounds. The two acid gases are HCl and hydrogen fluoride (HF). The
rationale for including these eight HAP in the environmental risk
screening analysis is presented below.
    HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment, and water. The
PB-HAP are taken up, through sediment, soil, water, and/or ingestion of
other organisms, by plants or animals (e.g., small fish) at the bottom
of the food chain. As larger and larger predators consume these
organisms, concentrations of the PB-HAP in the animal tissues increases
as does the potential for adverse effects. The six PB-HAP we evaluate
as part of our screening analysis account for 99.8 percent of all PB-
HAP emissions nationally from stationary sources (on a mass basis from
the 2005 EPA NEI).
    In addition to accounting for almost all of the mass of PB-HAP
emitted, we note that the TRIM.FaTE model that we use to evaluate
multipathway risk allows us to estimate concentrations of cadmium
compounds, D/F, arsenic compounds, POM, and mercury compounds in soil,
sediment, and water. For lead compounds, we currently do not have the
ability to calculate these concentrations using the TRIM.FaTE model.
Therefore, to evaluate the potential for adverse environmental effects
from lead compounds, we compare the estimated HEM-modeled exposures
from the source category emissions of lead with the level of the
Secondary Lead NAAQS.\14\ We consider values below the level of the
Secondary Lead NAAQS to be unlikely to cause adverse environmental
effects.
---------------------------------------------------------------------------

    \14\ The Secondary Lead NAAQS is a reasonable measure of
determining whether there is an adverse environmental effect since
it was established considering ``effects on soils, water, crops,
vegetation, man-made materials, animals, wildlife, weather,
visibility and climate, damage to and deterioration of property, and
hazards to transportation, as well as effects on economic values and
on personal comfort and well-being.''
---------------------------------------------------------------------------

    Due to their well-documented potential to cause direct damage to
terrestrial plants, we include two acid gases, HCl and HF, in the
environmental screening analysis. According to the 2005 NEI, HCl and HF
account for about 99 percent (on a mass basis) of the total acid gas
HAP emitted by stationary sources in the U.S. In addition to the
potential to cause direct damage to plants, high concentrations of HF
in the air have been linked to fluorosis in livestock. Air
concentrations of these HAP are already calculated as part of the human
multipathway exposure and risk screening analysis using the HEM3-AERMOD
air dispersion model, and we are able to use the air dispersion
modeling results to estimate the

potential for an adverse environmental effect.
    The EPA acknowledges that other HAP beyond the eight HAP discussed
above may have the potential to cause adverse environmental effects.
Therefore, the EPA may include other relevant HAP in its environmental
risk screening in the future, as modeling science and resources allow.
The EPA invites comment on the extent to which other HAP emitted by the
source category may cause adverse environmental effects. Such
information should include references to peer-reviewed ecological
effects benchmarks that are of sufficient quality for making regulatory
decisions, as well as information on the presence of organisms located
near facilities within the source category that such benchmarks
indicate could be adversely affected.
c. Ecological Assessment Endpoints and Benchmarks for PB-HAP
    An important consideration in the development of the EPA's
screening methodology is the selection of ecological assessment
endpoints and benchmarks. Ecological assessment endpoints are defined
by the ecological entity (e.g., aquatic communities, including fish and
plankton) and its attributes (e.g., frequency of mortality). Ecological
assessment endpoints can be established for organisms, populations,
communities or assemblages, and ecosystems.
    For PB-HAP (other than lead compounds), we evaluated the following
community-level ecological assessment endpoints to screen for organisms
directly exposed to HAP in soils, sediment, and water:
     Local terrestrial communities (i.e., soil invertebrates,
plants) and populations of small birds and mammals that consume soil
invertebrates exposed to PB-HAP in the surface soil;
     Local benthic (i.e., bottom sediment dwelling insects,
amphipods, isopods, and crayfish) communities exposed to PB-HAP in
sediment in nearby water bodies; and
     Local aquatic (water-column) communities (including fish
and plankton) exposed to PB-HAP in nearby surface waters.
    For PB-HAP (other than lead compounds), we also evaluated the
following population-level ecological assessment endpoint to screen for
indirect HAP exposures of top consumers via the bioaccumulation of HAP
in food chains:
     Piscivorous (i.e., fish-eating) wildlife consuming PB-HAP-
contaminated fish from nearby water bodies.
    For cadmium compounds, D/F, arsenic compounds, POM, and mercury
compounds, we identified the available ecological benchmarks for each
assessment endpoint. An ecological benchmark represents a concentration
of HAP (e.g., 0.77 [micro]g of HAP per liter of water) that has been
linked to a particular environmental effect level through scientific
study. For PB-HAP we identified, where possible, ecological benchmarks
at the following effect levels:
     Probable effect levels (PEL): Level above which adverse
effects are expected to occur frequently;
     Lowest-observed-adverse-effect level (LOAEL): The lowest
exposure level tested at which there are biologically significant
increases in frequency or severity of adverse effects; and
     No-observed-adverse-effect levels (NOAEL): The highest
exposure level tested at which there are no biologically significant
increases in the frequency or severity of adverse effect.
    We established a hierarchy of preferred benchmark sources to allow
selection of benchmarks for each environmental HAP at each ecological
assessment endpoint. In general, the EPA sources that are used at a
programmatic level (e.g., Office of Water, Superfund Program) were used
in the analysis, if available. If not, the EPA benchmarks used in
Regional programs (e.g., Superfund) were used. If benchmarks were not
available at a programmatic or Regional level, we used benchmarks
developed by other federal agencies (e.g., National Oceanic and
Atmospheric Administration (NOAA)) or state agencies.
    Benchmarks for all effect levels are not available for all PB-HAP
and assessment endpoints. In cases where multiple effect levels were
available for a particular PB-HAP and assessment endpoint, we use all
of the available effect levels to help us to determine whether
ecological risks exist and, if so, whether the risks could be
considered significant and widespread.
d. Ecological Assessment Endpoints and Benchmarks for Acid Gases
    The environmental screening analysis also evaluated potential
damage and reduced productivity of plants due to direct exposure to
acid gases in the air. For acid gases, we evaluated the following
ecological assessment endpoint:
     Local terrestrial plant communities with foliage exposed
to acidic gaseous HAP in the air.
    The selection of ecological benchmarks for the effects of acid
gases on plants followed the same approach as for PB-HAP (i.e., we
examine all of the available chronic benchmarks). For HCl, the EPA
identified chronic benchmark concentrations. We note that the benchmark
for chronic HCl exposure to plants is greater than the reference
concentration for chronic inhalation exposure for human health. This
means that where the EPA includes regulatory requirements to prevent an
exceedance of the reference concentration for human health, additional
analyses for adverse environmental effects of HCl would not be
necessary.
    For HF, the EPA identified chronic benchmark concentrations for
plants and evaluated chronic exposures to plants in the screening
analysis. High concentrations of HF in the air have also been linked to
fluorosis in livestock. However, the HF concentrations at which
fluorosis in livestock occur are higher than those at which plant
damage begins. Therefore, the benchmarks for plants are protective of
both plants and livestock.
e. Screening Methodology
    For the environmental risk screening analysis, the EPA first
determined whether any facilities in the Portland Cement Manufacturing
Industry sources emitted any of the eight environmental HAP. For the
Portland Cement Manufacturing Industry source category, we identified
emissions of lead compounds, cadmium compounds, mercury compounds,
arsenic compounds, D/F, and HCl.
    Because one or more of the eight environmental HAP evaluated are
emitted by at least one facility in the source category, we proceeded
to the second step of the evaluation.
f. PB-HAP Methodology
    For cadmium compounds, arsenic compounds, mercury compounds, POM,
and D/F, the environmental screening analysis consists of two tiers,
while lead compounds are analyzed differently as discussed earlier. In
the first tier, we determined whether the maximum facility-specific
emission rates of each of the emitted environmental HAP were large
enough to create the potential for adverse environmental effects under
reasonable worst-case environmental conditions. These are the same
environmental conditions used in the human multipathway exposure and
risk screening analysis.
    To facilitate this step, TRIM.FaTE was run for each PB-HAP under
hypothetical environmental conditions designed to provide
conservatively high

HAP concentrations. The model was set to maximize runoff from
terrestrial parcels into the modeled lake, which in turn, maximized the
chemical concentrations in the water, the sediments, and the fish. The
resulting media concentrations were then used to back-calculate a
screening level emission rate that corresponded to the relevant
exposure benchmark concentration value for each assessment endpoint. To
assess emissions from a facility, the reported emission rate for each
PB-HAP was compared to the screening level emission rate for that PB-
HAP for each assessment endpoint. If emissions from a facility do not
exceed the Tier 1 screening level, the facility ``passes'' the screen,
and, therefore, is not evaluated further under the screening approach.
If emissions from a facility exceed the Tier 1 screening level, we
evaluate the facility further in Tier 2.
    In Tier 2 of the environmental screening analysis, the emission
rate screening levels are adjusted to account for local meteorology and
the actual location of lakes in the vicinity of facilities that did not
pass the Tier 1 screen. The modeling domain for each facility in the
Tier 2 analysis consists of 8 octants. Each octant contains 5 modeled
soil concentrations at various distances from the facility (5 soil
concentrations x 8 octants = total of 40 soil concentrations per
facility) and one lake with modeled concentrations for water, sediment,
and fish tissue. In the Tier 2 environmental risk screening analysis,
the 40 soil concentration points are averaged to obtain an average soil
concentration for each facility for each PB-HAP. For the water,
sediment, and fish tissue concentrations, the highest value for each
facility for each pollutant is used. If emission concentrations from a
facility do not exceed the Tier 2 screening level, the facility passes
the screen, and typically is not evaluated further. If emissions from a
facility exceed the Tier 2 screening level, the facility does not pass
the screen and, therefore, may have the potential to cause adverse
environmental effects. Such facilities are evaluated further to
investigate factors such as the magnitude and characteristics of the
area of exceedance.
g. Acid Gas Methodology
    The environmental screening analysis evaluates the potential
phytotoxicity and reduced productivity of plants due to chronic
exposure to acid gases. The environmental risk screening methodology
for acid gases is a single-tier screen that compares the average off-
site ambient air concentration over the modeling domain to ecological
benchmarks for each of the acid gases. Because air concentrations are
compared directly to the ecological benchmarks, emission-based
screening levels are not calculated for acid gases.
    For purposes of ecological risk screening, the EPA identifies a
potential for adverse environmental effects to plant communities from
exposure to acid gases when the average concentration of the HAP around
a facility exceeds the LOAEL ecological benchmark. In such cases, we
further investigate factors such as the magnitude and characteristics
of the area of exceedance (e.g., land use of exceedance area, size of
exceedance area) to determine if there is an adverse environmental
effect.
    For further information on the environmental screening analysis
approach, see the Residual Risk Assessment for the Portland Cement
Manufacturing Industry Source Category in Support of the Risk and
Technology Review September 2017 Proposed Rule, which is available in
the docket for this action.
7. How did we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine
the risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
For this source category, we conducted the facility-wide assessment
using the 2014 NEI. We analyzed risks due to the inhalation of HAP that
are emitted ``facility-wide'' for the populations residing within 50 km
of each facility, consistent with the methods used for the source
category analysis described above. For these facility-wide risk
analyses, the modeled source category risks were compared to the
facility-wide risks to determine the portion of facility-wide risks
that could be attributed to the source category addressed in this
proposal. We specifically examined the facility that was associated
with the highest estimate of risk and determined the percentage of that
risk attributable to the source category of interest. The Residual Risk
Assessment for the Portland Cement Manufacturing Industry Source
Category in Support of the Risk and Technology Review September 2017
Proposed Rule, available through the docket for this action, provides
the methodology and results of the facility-wide analyses, including
all facility-wide risks and the percentage of source category
contribution to facility-wide risks.
8. How did we consider uncertainties in risk assessment?
    In the Benzene NESHAP, we concluded that risk estimation
uncertainty should be considered in our decision-making under the ample
margin of safety framework. Uncertainty and the potential for bias are
inherent in all risk assessments, including those performed for this
proposal. Although uncertainty exists, we believe that our approach,
which used conservative tools and assumptions, ensures that our
decisions are health protective and environmentally protective. A brief
discussion of the uncertainties in the RTR emissions dataset,
dispersion modeling, inhalation exposure estimates, and dose-response
relationships follows below. A more thorough discussion of these
uncertainties is included in the Residual Risk Assessment for the
Portland Cement Manufacturing Industry Source Category in Support of
the Risk and Technology Review September 2017 Proposed Rule, which is
available in the docket for this action.
a. Uncertainties in the RTR Emissions Dataset
    Although the development of the RTR emissions dataset involved
quality assurance/quality control processes, the accuracy of emissions
values will vary depending on the source of the data, the degree to
which data are incomplete or missing, the degree to which assumptions
made to complete the datasets are accurate, errors in emission
estimates, and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years, and they do not
reflect short-term fluctuations during the course of a year or
variations from year to year. The estimates of peak hourly emission
rates for the acute effects screening assessment were based on an
emission adjustment factor applied to the average annual hourly
emission rates, which are intended to account for emission fluctuations
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including the EPA's recommended
regulatory dispersion model, AERMOD. In using a model to estimate
ambient pollutant concentrations, the user chooses certain options to
apply. For RTR assessments,

we select some model options that have the potential to overestimate
ambient air concentrations (e.g., not including plume depletion or
pollutant transformation). We select other model options that have the
potential to underestimate ambient impacts (e.g., not including
building downwash). Other options that we select have the potential to
either under- or overestimate ambient levels (e.g., meteorology and
receptor locations). On balance, considering the directional nature of
the uncertainties commonly present in ambient concentrations estimated
by dispersion models, the approach we apply in the RTR assessments
should yield unbiased estimates of ambient HAP concentrations.
c. Uncertainties in Inhalation Exposure
    The EPA did not include the effects of human mobility on exposures
in the assessment. Specifically, short-term mobility and long-term
mobility between census blocks in the modeling domain were not
considered.\15\ The approach of not considering short or long-term
population mobility does not bias the estimate of the theoretical MIR
(by definition), nor does it affect the estimate of cancer incidence
because the total population number remains the same. It does, however,
affect the shape of the distribution of individual risks across the
affected population, shifting it toward higher estimated individual
risks at the upper end and reducing the number of people estimated to
be at lower risks, thereby increasing the estimated number of people at
specific high risk levels (e.g., 1-in-10 thousand or 1-in-1 million).
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    \15\ 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 farther from the
facility and under-predict exposures for people in the census block who
live closer to the facility. Thus, using the census block centroid to
predict chronic exposures may lead to a potential understatement or
overstatement of the true maximum impact, but is an unbiased estimate
of average risk and incidence. We reduce this uncertainty by analyzing
large census blocks near facilities using aerial imagery and adjusting
the location of the block centroid to better represent the population
in the block, as well as adding additional receptor locations where the
block population is not well represented by a single location.
    The assessment evaluates the cancer inhalation risks associated
with pollutant exposures over a 70-year period, which is the assumed
lifetime of an individual. In reality, both the length of time that
modeled emission sources at facilities actually operate (i.e., more or
less than 70 years) and the domestic growth or decline of the modeled
industry (i.e., the increase or decrease in the number or size of
domestic facilities) will influence the future risks posed by a given
source or source category. Depending on the characteristics of the
industry, these factors will, in most cases, result in an overestimate
both in individual risk levels and in the total estimated number of
cancer cases. However, in the unlikely scenario where a facility
maintains, or even increases, its emissions levels over a period of
more than 70 years, residents live beyond 70 years at the same
location, and the residents spend most of their days at that location,
then the cancer inhalation risks could potentially be underestimated.
However, annual cancer incidence estimates from exposures to emissions
from these sources would not be affected by the length of time an
emissions source operates.
    The exposure estimates used in these analyses assume chronic
exposures to ambient (outdoor) levels of pollutants. Because most
people spend the majority of their time indoors, actual exposures may
not be as high, depending on the characteristics of the pollutants
modeled. For many of the HAP, indoor levels are roughly equivalent to
ambient levels, but for very reactive pollutants or larger particles,
indoor levels are typically lower. This factor has the potential to
result in an overestimate of 25 to 30 percent of exposures.\16\
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    \16\ 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 the EPA
conducts as part of the risk review under section 112 of the CAA 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 the presence of humans at the location of the maximum
concentration. In the acute screening assessment that we conduct under
the RTR program, we assume that peak emissions from the source category
and worst-case meteorological conditions co-occur, thus, resulting in
maximum ambient concentrations. These two events are unlikely to occur
at the same time, making these assumptions conservative. We then
include the additional assumption that a person is located at this
point during this same time period. For this source category, these
assumptions would tend to be worst-case actual exposures as it is
unlikely that a person would be located at the point of maximum
exposure during the time when peak emissions and worst-case
meteorological conditions occur simultaneously.
d. Uncertainties in Dose-Response Relationships
    There are uncertainties inherent in the development of the dose-
response values used in our risk assessments for cancer effects from
chronic exposures and non-cancer effects from both chronic and acute
exposures. Some uncertainties may be considered quantitatively, and
others generally are expressed in qualitative terms. We note as a
preface to this discussion a point on dose-response uncertainty that is
brought out in the EPA's 2005 Cancer Guidelines; namely, that ``the
primary goal of EPA actions is protection of human health; accordingly,
as an Agency policy, risk assessment procedures, including default
options that are used in the absence of scientific data to the
contrary, should be health protective'' (EPA's 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 Assessment for the Portland Cement Manufacturing
Industry Source Category in Support of the Risk and Technology Review
September 2017 Proposed Rule, 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).\17\ In some circumstances, the true risk could be as

low as zero; however, in other circumstances, the risk could be
greater.\18\ 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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    \17\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \18\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible, and which is based on maximum
likelihood estimates.
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    Chronic non-cancer RfC and reference dose (RfD) values represent
chronic exposure levels that are intended to be health-protective
levels. Specifically, these values provide an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure (RfC) or a daily oral exposure (RfD) to the human
population (including sensitive subgroups) that is likely to be without
an appreciable risk of deleterious effects during a lifetime. To derive
values that are intended to be ``without appreciable risk,'' the
methodology relies upon an uncertainty factor (UF) approach (U.S. EPA,
1993 and 1994) which considers uncertainty, variability, and gaps in
the available data. The UF are applied to derive reference values that
are intended to protect against appreciable risk of deleterious
effects. The UF are commonly default values,\19\ (e.g., factors of 10
or 3), used in the absence of compound-specific data; where data are
available, a 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.
---------------------------------------------------------------------------

    \19\ According to the NRC report, Science and Judgment in Risk
Assessment (NRC, 1994) ``[Default] options are generic approaches,
based on general scientific knowledge and policy judgment, that are
applied to various elements of the risk assessment process when the
correct scientific model is unknown or uncertain.'' The 1983 NRC
report, Risk Assessment in the Federal Government: Managing the
Process, defined default option as ``the option chosen on the basis
of risk assessment policy that appears to be the best choice in the
absence of data to the contrary'' (NRC, 1983a, p. 63). Therefore,
default options are not rules that bind the Agency; rather, the
Agency may depart from them in evaluating the risks posed by a
specific substance when it believes this to be appropriate. In
keeping with the EPA's goal of protecting public health and the
environment, default assumptions are used to ensure that risk to
chemicals is not underestimated (although defaults are not intended
to overtly overestimate risk). See EPA, An Examination of EPA Risk
Assessment Principles and Practices, EPA/100/B-04/001, 2004,
available at https://nctc.fws.gov/resources/course-resources/pesticides/Risk%20Assessment/Risk%20Assessment%20Principles%20and%20Practices.pdf.
---------------------------------------------------------------------------

    While collectively termed ``UF,'' these factors account for a
number of different quantitative considerations when using observed
animal (usually rodent) or human toxicity data in the development of
the RfC. The UF are intended to account for: (1) Variation in
susceptibility among the members of the human population (i.e., inter-
individual variability); (2) uncertainty in extrapolating from
experimental animal data to humans (i.e., interspecies differences);
(3) uncertainty in extrapolating from data obtained in a study with
less-than-lifetime exposure (i.e., extrapolating from sub-chronic to
chronic exposure); (4) uncertainty in extrapolating the observed data
to obtain an estimate of the exposure associated with no adverse
effects; and (5) uncertainty when the database is incomplete or there
are problems with the applicability of available studies.
    Many of the UF used to account for variability and uncertainty in
the development of acute reference values are quite similar to those
developed for chronic durations, but they more often use individual UF
values that may be less than 10. The UF are applied based on chemical-
specific or health effect-specific information (e.g., simple irritation
effects do not vary appreciably between human individuals, hence a
value of 3 is typically used), or based on the purpose for the
reference value (see the following paragraph). The UF applied in acute
reference value derivation include: (1) Heterogeneity among humans; (2)
uncertainty in extrapolating from animals to humans; (3) uncertainty in
lowest observed adverse effect (exposure) level to no observed adverse
effect (exposure) level adjustments; and (4) uncertainty in accounting
for an incomplete database on toxic effects of potential concern.
Additional adjustments are often applied to account for uncertainty in
extrapolation from observations at one exposure duration (e.g., 4
hours) to derive an acute reference value at another exposure duration
(e.g., 1 hour).
    Not all acute reference values are developed for the same purpose,
and care must be taken when interpreting the results of an acute
assessment of human health effects relative to the reference value or
values being exceeded. Where relevant to the estimated exposures, the
lack of short-term dose-response values at different levels of severity
should be factored into the risk characterization as potential
uncertainties.
    Although every effort is made to identify appropriate human health
effect dose-response assessment values for all pollutants emitted by
the sources in this risk assessment, some HAP emitted by this source
category are lacking dose-response assessments. Accordingly, these
pollutants cannot be included in the quantitative risk assessment,
which could result in quantitative estimates understating HAP risk. To
help to alleviate this potential underestimate, where we conclude
similarity with a HAP for which a dose-response assessment value is
available, we use that value as a surrogate for the assessment of the
HAP for which no value is available. To the extent use of surrogates
indicates appreciable risk, we may identify a need to increase priority
for new IRIS assessment of that substance. We additionally note that,
generally speaking, HAP of greatest concern due to environmental
exposures and hazard are those for which dose-response assessments have
been performed, reducing the likelihood of understating risk. Further,
HAP not included in the quantitative assessment are assessed
qualitatively and considered in the risk characterization that informs
the risk management decisions, including with regard to consideration
of HAP reductions achieved by various control options.
    For a group of compounds that are unspeciated (e.g., glycol
ethers), we conservatively use the most protective reference value of
an individual compound in that group to estimate risk. Similarly, for
an individual compound in a group (e.g., ethylene glycol diethyl ether)
that does not have a specified reference value, we also apply the most
protective reference value from the other compounds in the group to
estimate risk.
e. Uncertainties in the Multipathway Assessment
    For each source category, we generally rely on site-specific levels
of PB-HAP emissions to determine whether a refined assessment of the
impacts from multipathway exposures is necessary. This determination is
based on the results of a three-tiered screening analysis that relies
on the outputs from models that estimate environmental pollutant
concentrations and human exposures for five PB-HAP. Two important types
of uncertainty

associated with the use of these models in RTR risk assessments and
inherent to any assessment that relies on environmental modeling are
model uncertainty and input uncertainty.\20\
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    \20\ In the context of this discussion, the term ``uncertainty''
as it pertains to exposure and risk encompasses both variability in
the range of expected inputs and screening results due to existing
spatial, temporal, and other factors, as well as uncertainty in
being able to accurately estimate the true result.
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    Model uncertainty concerns whether the selected models are
appropriate for the assessment being conducted and whether they
adequately represent the actual processes that might occur for that
situation. An example of model uncertainty is the question of whether
the model adequately describes the movement of a pollutant through the
soil. This type of uncertainty is difficult to quantify. However, based
on feedback received from previous EPA SAB reviews and other reviews,
we are confident that the models used in the screen are appropriate and
state-of-the-art for the multipathway risk assessments conducted in
support of RTR.
    Input uncertainty is concerned with how accurately the models have
been configured and parameterized for the assessment at hand. For Tier
1 of the multipathway screen, we configured the models to avoid
underestimating exposure and risk. This was accomplished by selecting
upper-end values from nationally-representative datasets for the more
influential parameters in the environmental model, including selection
and spatial configuration of the area of interest, lake location and
size, meteorology, surface water and soil characteristics, and
structure of the aquatic food web. We also assume an ingestion exposure
scenario and values for human exposure factors that represent
reasonable maximum exposures.
    In Tier 2 of the multipathway assessment, we refine the model
inputs to account for meteorological patterns in the vicinity of the
facility versus using upper-end national values, and we identify the
actual location of lakes near the facility rather than the default lake
location that we apply in Tier 1. By refining the screening approach in
Tier 2 to account for local geographical and meteorological data, we
decrease the likelihood that concentrations in environmental media are
overestimated, thereby increasing the usefulness of the screen. The
assumptions and the associated uncertainties regarding the selected
ingestion exposure scenario are the same for Tier 1 and Tier 2.
    For both Tiers 1 and 2 of the multipathway assessment, our approach
to addressing model input uncertainty is generally cautious. We choose
model inputs from the upper end of the range of possible values for the
influential parameters used in the models, and we assume that the
exposed individual exhibits ingestion behavior that would lead to a
high total exposure. This approach reduces the likelihood of not
identifying high risks for adverse impacts.
    Despite the uncertainties, when individual pollutants or facilities
do screen out, we are confident that the potential for adverse
multipathway impacts on human health is very low. On the other hand,
when individual pollutants or facilities do not screen out, it does not
mean that multipathway impacts are significant, only that we cannot
rule out that possibility and that a refined multipathway analysis for
the site might be necessary to obtain a more accurate risk
characterization for the source category. The site-specific
multipathway assessment improves upon the screens by utilizing AERMOD
to estimate dispersion and deposition impacts upon delineated
watersheds and farms. This refinement also provides improved soil and
water run-off calculations for effected watershed(s) and adjacent
parcels in estimating media concentrations for each PB-HAP modeled.
    For further information on uncertainties and the Tier 1 and 2