[Federal Register Volume 88, Number 202 (Friday, October 20, 2023)]
[Rules and Regulations]
[Pages 72372-72404]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-23247]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87, 1031, and 1068

[EPA-HQ-OAR-2022-0389; FRL-5934-02-OAR]
RIN 2060-AT10


Finding That Lead Emissions From Aircraft Engines That Operate on 
Leaded Fuel Cause or Contribute to Air Pollution That May Reasonably Be 
Anticipated To Endanger Public Health and Welfare

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final action.

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SUMMARY: In this action, the Administrator finds that lead air 
pollution may reasonably be anticipated to endanger the public health 
and welfare within the meaning of the Clean Air Act. The Administrator 
also finds that engine emissions of lead from certain aircraft cause or 
contribute to the lead air pollution that may reasonably be anticipated 
to endanger public health and welfare under the Clean Air Act.

DATES: These findings are effective on November 20, 2023.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OAR-2022-0389. All documents in the docket are 
listed in the https://www.regulations.gov website. Publicly available 
docket materials are available either electronically in https://www.regulations.gov or in hard copy at the EPA Air and Radiation Docket 
and Information Center, William Jefferson Clinton West Building, Room 
3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading 
Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, 
excluding legal holidays. The telephone number for the Public Reading 
Room is (202) 566-1744, and the telephone number for the Air Docket is 
(202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Ken Davidson, Office of Transportation 
and Air Quality, Assessment and Standards Division (ASD), Environmental 
Protection Agency; telephone number: (415) 972-3633; email address: 
[email protected].

SUPPLEMENTARY INFORMATION: 

A. General Information

Does this action apply to me?

    Regulated entities: These final findings do not themselves apply 
new requirements to entities other than the EPA and the FAA. With 
respect to requirements for the EPA and the FAA, as indicated in the 
proposal for this action, if the EPA issues final findings that 
emissions of lead from certain classes of engines used in certain 
aircraft cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health or welfare, the EPA then becomes 
subject to a duty to propose and promulgate emission standards pursuant 
to section 231 of the Clean Air Act. Upon EPA's issuance of 
regulations, the FAA shall prescribe regulations to ensure compliance 
with the EPA's emission standards pursuant to section 232 of the Clean 
Air Act. In contrast to the findings, those future standards would 
apply to and have an effect on other entities outside the Federal 
Government. In addition, pursuant to 49 U.S.C. 44714, the FAA has a 
statutory mandate to prescribe standards for the composition or 
chemical or physical properties of an aircraft fuel or fuel additive to 
control or eliminate aircraft emissions which the EPA has found 
endanger public health or welfare under section 231(a) of the Clean Air 
Act. In issuing these final findings, the EPA is making such a finding 
for emissions of lead from engines in covered aircraft.
    The classes of aircraft engines and of aircraft relevant to this 
final action are referred to as ``covered aircraft engines'' and as 
``covered aircraft,'' respectively throughout this document. Covered 
aircraft engines in this context means any aircraft engine that is 
capable of using leaded aviation gasoline. Covered aircraft in this 
context means all aircraft and ultralight vehicles \1\ equipped with 
covered engines. Covered aircraft would, for example, include smaller 
piston-engine aircraft such as the Cessna 172 (single-engine aircraft) 
and the Beechcraft Baron G58 (twin-engine aircraft), as well as the 
largest piston-engine aircraft such as the Curtiss C-46 and the Douglas 
DC-6. Other examples of covered aircraft would include rotorcraft,\2\ 
such as the Robinson R44 helicopter, light-sport aircraft, and 
ultralight vehicles equipped with piston engines. Because the majority 
of covered aircraft are piston-engine powered, this document focuses on 
those aircraft (in some contexts the EPA refers to these same engines 
as reciprocating engines). All such references and examples used in 
this document are covered aircraft as defined in this paragraph.
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    \1\ The FAA regulates ultralight vehicles under 14 CFR part 103.
    \2\ Rotorcraft encompass helicopters, gyroplanes, and any other 
heavier-than-air aircraft that depend principally for support in 
flight on the lift generated by one or more rotors.

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[[Page 72373]]

    Entities potentially interested in this final action include those 
that manufacture and sell covered aircraft engines and covered aircraft 
in the United States and those who own or operate covered aircraft. 
Categories that may be affected by a future regulatory action include, 
but are not limited to, those listed here:

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                                                                                       Examples of potentially
              Category                NAICS \a\ code          SIC \b\ code                affected entities
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Industry............................         3364412  3724........................  Manufacturers of new
                                                                                     aircraft engines.
Industry............................          336411  3721........................  Manufacturers of new
                                                                                     aircraft.
Industry............................          481219  4522........................  Aircraft charter services
                                                                                     (i.e., general purpose
                                                                                     aircraft used for a variety
                                                                                     of specialty air and flying
                                                                                     services). Aviation clubs
                                                                                     providing a variety of air
                                                                                     transportation activities
                                                                                     to the general public.
Industry............................          611512  8249 and 8299...............  Flight training.
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\a\ North American Industry Classification System (NAICS).
\b\ Standard Industrial Classification (SIC) code.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be interested in this 
final action. This table lists examples of the types of entities that 
the EPA is now aware of that could potentially have an interest in this 
final action. Other types of entities not listed in the table could 
also be interested and potentially affected by subsequent actions at 
some future time. If you have any questions regarding the scope of this 
final action, consult the person listed in the preceding FOR FURTHER 
INFORMATION CONTACT section of this document.

B. Children's Health

    Children are generally more vulnerable to environmental exposures 
and/or the associated health effects, and therefore more at risk than 
adults. These risks to children may arise because infants and children 
generally eat more food, drink more water and breathe more air than 
adults do, relative to their size, and consequently they may be exposed 
to relatively higher amounts of contaminants. In addition, normal 
childhood activity, such as putting hands in mouths or playing on the 
ground, can result in exposures to contaminants that adults do not 
typically have. Furthermore, environmental contaminants may pose health 
risks specific to children because children's bodies are still 
developing. For example, during periods of rapid growth such as fetal 
development, infancy and puberty, their developing systems and organs 
may be more easily harmed.\3\
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    \3\ EPA (2006) A Framework for Assessing Health Risks of 
Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-
05/093F, 2006.
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    Protecting children's health from environmental risks is 
fundamental to the EPA's mission. This action is subject to EPA's 
Policy on Children's Health because this action has considerations for 
human health.\4\ Consistent with this policy this document includes 
discussion and analysis that is focused particularly on children 
including early life exposure (the lifestages from conception, infancy, 
early childhood and through adolescence until 21 years of age) and 
lifelong health. For example, as described in section IV. of this 
document, the scientific evidence has long been established 
demonstrating that young children (due to rapid growth and development 
of the brain) are vulnerable to a range of neurological effects 
resulting from exposure to lead. Low levels of lead in young children's 
blood have been linked to adverse effects on intellect, concentration, 
and academic achievement, and as the EPA has previously noted ``there 
is no evidence of a threshold below which there are no harmful effects 
on cognition from [lead] exposure.'' \5\ Evidence suggests that while 
some neurocognitive effects of lead in children may be transient, some 
lead-related cognitive effects may be irreversible and persist into 
adulthood, potentially contributing to lower educational attainment and 
financial well-being.\6\ The 2013 Lead Integrated Science Assessment 
notes that in epidemiologic studies, postnatal (early childhood) blood 
lead levels are consistently associated with cognitive function 
decrements in children and adolescents.\7\ In addition, in section 
II.A.5. of this document, we describe the number of children living 
near and attending school near airports and provide a proximity 
analysis of the potential for greater representation of children in the 
near-airport environment compared with neighboring areas.
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    \4\ EPA. Memorandum: Issuance of EPA's 2021 Policy on Children's 
Health. October 5, 2021. Available at https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf. 
Children's environmental health includes conception, infancy, early 
childhood and through adolescence until 21 years of age.
    \5\ EPA (2013) ISA for Lead. Executive Summary ``Effects of Pb 
Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA/600/R-10/075F, 
2013. See also, National Toxicology Program (NTP) (2012) NTP 
Monograph: Health Effects of Low-Level Lead. Available at https://ntp.niehs.nih.gov/go/36443.
    \6\ EPA (2013) ISA for Lead. Executive Summary ``Effects of Pb 
Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA/600/R-10/075F, 
2013.
    \7\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and 
Neurodevelopmental Deficits in Children.'' p. I-75. EPA/600/R-10/
075F, 2013.
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Table of Contents

I. Executive Summary
II. Overview and Context for This Final Action
    A. Background Information Helpful To Understanding This Final 
Action
    1. Piston-Engine Aircraft and the Use of Leaded Aviation 
Gasoline
    2. Emissions of Lead From Piston-Engine Aircraft
    3. Concentrations of Lead in Air Attributable to Emissions From 
Piston-Engine Aircraft
    4. Fate and Transport of Emissions of Lead From Piston-Engine 
Aircraft
    5. Consideration of Environmental Justice and Children in 
Populations Residing Near Airports
    B. Federal Actions To Reduce Lead Exposure
    C. Lead Endangerment Petitions for Rulemaking and the EPA 
Responses
III. Legal Framework for This Action
    A. Statutory Text and Basis for This Action
    B. Considerations for the Endangerment and Cause or Contribute 
Analyses Under Section 231(a)(2)(A)
    C. Regulatory Authority for Emission Standards
    D. Response to Certain Comments on the Legal Framework for This 
Action
IV. The Final Endangerment Finding Under CAA Section 231
    A. Scientific Basis of the Endangerment Finding
    1. Lead Air Pollution
    2. Health Effects and Lead Air Pollution
    3. Welfare Effects and Lead Air Pollution
    B. Final Endangerment Finding
V. The Final Cause or Contribute Finding Under CAA Section 231
    A. Definition of the Air Pollutant
    B. The Data and Information Used To Evaluate the Final Cause or 
Contribute Finding
    C. Response to Certain Comments on the Cause or Contribute 
Finding
    D. Final Cause or Contribute Finding for Lead
VI. Statutory Authority and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive

[[Page 72374]]

Order 14094: Modernizing Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use
    I. National Technology Transfer and Advancement Act (NTTAA)
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations; Executive Order 14096: Revitalizing Our Nation's 
Commitment to Environmental Justice for All
    K. Congressional Review Act (CRA)
    L. Determination Under Section 307(d)
    M. Judicial Review
VII. Statutory Provisions and Legal Authority

I. Executive Summary

    Pursuant to section 231(a)(2)(A) of the Clean Air Act (CAA or Act), 
the Administrator finds that emissions of lead from covered aircraft 
engines cause or contribute to lead air pollution that may reasonably 
be anticipated to endanger public health and welfare. Covered aircraft 
include, for example, smaller piston-engine aircraft such as the Cessna 
172 (single-engine aircraft) and the Beechcraft Baron G58 (twin-engine 
aircraft), as well as the largest piston-engine aircraft such as the 
Curtiss C-46 and the Douglas DC-6. Other examples of covered aircraft 
include rotorcraft, such as the Robinson R44 helicopter, light-sport 
aircraft, and ultralight vehicles equipped with piston engines.
    For purposes of this action, the EPA defines the ``air pollution'' 
referred to in section 231(a)(2)(A) of the CAA as lead, which we also 
refer to as the lead air pollution in this document.\8\ In finding that 
the lead air pollution may reasonably be anticipated to endanger the 
public health and welfare, the EPA relies on the extensive scientific 
evidence critically assessed in the 2013 Integrated Science Assessment 
for Lead (2013 Lead ISA) and the previous Air Quality Criteria 
Documents (AQCDs) for Lead, which the EPA prepared to serve as the 
scientific foundation for periodic reviews of the National Ambient Air 
Quality Standards (NAAQS) for lead.9 10 11 12
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    \8\ As noted in section IV.A. of this document, the lead air 
pollution can occur as elemental lead or in lead-containing 
compounds.
    \9\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \10\ EPA (2006) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA/600/R-5/144aF, 2006.
    \11\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF, 1986.
    \12\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
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    Further, for purposes of this action, the EPA defines the ``air 
pollutant'' referred to in CAA section 231(a)(2)(A) as lead, which we 
also refer to as the lead air pollutant in this document.\13\ 
Accordingly, the Administrator finds that emissions of the lead air 
pollutant from covered aircraft engines cause or contribute to the lead 
air pollution that may reasonably be anticipated to endanger public 
health and welfare under CAA section 231(a)(2)(A).
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    \13\ As noted in section V.A. of this document, the lead air 
pollutant can occur as elemental lead or in lead-containing 
compounds.
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    This final action follows the Administrator's proposed findings 
\14\ and includes responses to public comments submitted to the EPA on 
that proposal. The proposal was posted on the EPA website on October 7, 
2022, and published in the Federal Register on October 17, 2022. The 
EPA held a virtual public hearing on November 1, 2022, and the public 
comment period closed on January 17, 2023. During the public comment 
period, we received more than 53,000 comments.\15\ The EPA received 
late comments, and to the extent feasible we have responded to those 
comments in the Response to Comments document for this action.
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    \14\ EPA (2022) Proposed Finding that Lead Emissions from 
Aircraft Engines that Operate on Leaded Fuel Cause or Contribute to 
Air Pollution that May Reasonably Be Anticipated to Endanger Public 
Health and Welfare 87 FR 62753 (October 17, 2022).
    \15\ Of these comments, more than 600 were unique letters, some 
of which provided data and other information for EPA to consider; 
the remaining comments were mass mailers sponsored by four different 
organizations, all of which urged the EPA to take action to finalize 
the findings and/or to take regulatory action to eliminate lead 
emissions from aircraft operating on leaded avgas.
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    A broad range of stakeholders provided comments, including state 
and local governments; non-governmental organizations; industry trade 
associations representing aircraft engine and airframe manufacturers, 
fuel producers, fuel distributors, fuel providers, the helicopter 
industry, and aircraft owners and operators; environmental 
organizations; environmental justice organizations; one Tribe; private 
citizens; and others. In this notice for this final action, we 
summarize and respond to certain issues raised by commenters, and we 
provide responses to the remainder of comments in the Response to 
Comments document that is available in the public docket for this 
action.\16\
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    \16\ U.S. EPA, ``Finding that Lead Emissions from Aircraft 
Engines that Operate on Leaded Fuel Cause or Contribute to Air 
Pollution that May Reasonably Be Anticipated to Endanger Public 
Health and Welfare--Response to Comments,'' Docket EPA-HQ-OAR-2022-
0389.
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    Section II. of this action includes an overview and background 
information that is helpful to understanding the source sector in the 
context of this action, a brief summary of some of the Federal actions 
focused on reducing lead exposures, and a brief summary of the 
petitions for rulemaking regarding lead emissions from aircraft 
engines. Section III. of this document provides the legal framework for 
this action, section IV. provides the EPA's final determination on the 
endangerment finding, section V. provides the EPA's final determination 
on the cause or contribute finding, and section VI. discusses various 
statutory authorities and executive orders.

II. Overview and Context for This Final Action

    We summarize here background information that provides additional 
context for this final action. This includes information on the 
population of aircraft that have piston engines, information on the use 
of leaded aviation gasoline (avgas) in covered aircraft, physical and 
chemical characteristics of lead emissions from engines used in covered 
aircraft, concentrations of lead in air from these engine emissions, 
and the fate and transport of lead emitted by engines used in such 
aircraft. We also include here an analysis of populations residing near 
and attending school near airports and an analysis of potential 
environmental justice implications with regard to residential proximity 
to runways where covered aircraft operate. This section ends with a 
description of a broad range of Federal actions to reduce lead exposure 
from a variety of environmental media and a brief summary of citizen 
petitions for rulemaking regarding lead emissions from covered aircraft 
and the EPA responses.

A. Background Information Helpful To Understanding This Final Action

    This final action draws extensively from the EPA's scientific 
assessments for lead, which are developed as part of the EPA's periodic 
reviews of the air quality criteria \17\ for lead and the lead

[[Page 72375]]

NAAQS.\18\ These scientific assessments provide a comprehensive review, 
synthesis, and evaluation of the most policy-relevant science that 
builds upon the conclusions of previous assessments. In the information 
that follows, we discuss and describe scientific evidence summarized in 
the most recent assessment for lead, the 2013 Lead ISA,19 20 
as well as information summarized in previous assessments, including 
the 1977, 1986, and 2006 AQCDs.21 22 23
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    \17\ Under section 108(a)(2) of the CAA, air quality criteria 
are intended to ``accurately reflect the latest scientific knowledge 
useful in indicating the kind and extent of all identifiable effects 
on public health or welfare which may be expected from the presence 
of [a] pollutant in the ambient air . . . .'' Section 109 of the CAA 
directs the Administrator to propose and promulgate ``primary'' and 
``secondary'' NAAQS for pollutants for which air quality criteria 
are issued. Under CAA section 109(d)(1), EPA must periodically 
complete a thorough review of the air quality criteria and the NAAQS 
and make such revisions as may be appropriate in accordance with 
sections 108 and 109(b) of the CAA. A fuller description of these 
legislative requirements can be found, for example, in the ISA (see 
2013 Lead ISA, p. lxix).
    \18\ Section 109(b)(1) defines a primary standard as one ``the 
attainment and maintenance of which in the judgment of the 
Administrator, based on such criteria and allowing an adequate 
margin of safety, are requisite to protect the public health.'' A 
secondary standard, as defined in section 109(b)(2), must ``specify 
a level of air quality the attainment and maintenance of which in 
the judgment of the Administrator, based on such criteria, is 
requisite to protect the public welfare from any known or 
anticipated adverse effects associated with the presence of [the] 
pollutant in the ambient air.''
    \19\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \20\ The EPA released the ISA for Lead External Review Draft as 
part of the Agency's current review of the science regarding health 
and welfare effects of lead. EPA/600/R-23/061. This draft assessment 
is undergoing peer review by the Clean Air Scientific Advisory 
Committee (CASAC) and public comment, and is available at: https://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=357282.
    \21\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
    \22\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \23\ EPA (2006) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA/600/R-5/144aF, 2006.
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    As described in the 2013 Lead ISA, lead emitted to ambient air is 
transported through the air and is distributed from air to other 
environmental media through deposition.\24\ Lead emitted in the past 
can remain available for environmental or human exposure for an 
extended time in some areas.\25\ Depending on the environment where it 
is deposited, it may to various extents be resuspended into the ambient 
air, integrated into the media on which it deposits, or transported in 
surface water runoff to other areas or nearby waterbodies.\26\ Lead in 
the environment today may have been airborne yesterday or emitted to 
the air long ago.\27\ Over time, lead that was initially emitted to air 
can become less available for environmental circulation by 
sequestration in soil, sediment and other reservoirs.\28\
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    \24\ EPA (2013) ISA for Lead. Section 3.1.1. ``Pathways for Pb 
Exposure.'' p. 3-1. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \25\ EPA (2013) ISA for Lead. Section 3.7.1. ``Exposure.'' p. 3-
144. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \26\ EPA (2013) ISA for Lead. Section 6.2. ``Fate and Transport 
of Pb in Ecosystems.'' p. 6-62. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \27\ EPA (2013) ISA for Lead. Section 2.3. ``Fate and Transport 
of Pb.'' p. 2-24. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \28\ EPA (2013) ISA for Lead. Section 1.2.1. ``Sources, Fate and 
Transport of Ambient Pb;'' p. 1-6. Section 2.3. ``Fate and Transport 
of Pb.'' p. 2-24. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
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    The multimedia distribution of lead emitted into ambient air 
creates multiple air-related pathways of human and ecosystem exposure. 
These pathways may involve media other than air, including indoor and 
outdoor dust, soil, surface water and sediments, vegetation and biota. 
The human exposure pathways for lead emitted into air include 
inhalation of ambient air or ingestion of food, water or other 
materials, including dust and soil, that have been contaminated through 
a pathway involving lead deposition from ambient air.\29\ Ambient air 
inhalation pathways include both inhalation of air outdoors and 
inhalation of ambient air that has infiltrated into indoor 
environments.\30\ The air-related ingestion pathways occur as a result 
of lead emissions to air being distributed to other environmental 
media, where humans can be exposed to it via contact with and ingestion 
of indoor and outdoor dusts, outdoor soil, food and drinking water.
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    \29\ EPA (2013) ISA for Lead. Section 3.1.1.''Pathways for Pb 
Exposure.'' p. 3-1. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \30\ EPA (2013) ISA for Lead. Sections 1.3. ``Exposure to 
Ambient Pb.'' p. 1-11. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
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    The scientific evidence documents exposure to many sources of lead 
emitted to the air that have resulted in higher blood lead levels, 
particularly for people living or working near sources, including 
stationary sources, such as mines and smelters, and mobile sources, 
such as cars and trucks when lead was a gasoline 
additive.31 32 33 34 35 36 Similarly, with regard to 
emissions from engines used in covered aircraft, there have been 
studies reporting positive associations of children's blood lead levels 
with proximity to airports and activity by covered 
aircraft,37 38 39 thus indicating potential for children's 
exposure to lead from covered aircraft engine emissions. A recent study 
evaluating cardiovascular mortality rates in adults 65 and older living 
within a few kilometers and downwind of runways, while not evaluating 
blood lead levels, found higher mortality rates in adults living near 
single-runway airports in years with more piston-engine air traffic, 
but not in adults living near multi-runway airports, suggesting the 
potential for adverse adult health effects near some airports.\40\
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    \31\ EPA (2013) ISA for Lead. Sections 3.4.1. ``Pb in Blood.'' 
p. 3-85; Section 5.4. ``Summary.'' p. 5-40. EPA, Washington, DC, 
EPA/600/R-10/075F, 2013.
    \32\ EPA (2006) Air Quality Criteria for Lead. Chapter 3. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
    \33\ EPA (1986) Air Quality Criteria for Lead. Section 1.11.3. 
EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \34\ EPA (1977) Air Quality Criteria for Lead. Section 12.3.1.1. 
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 
(NTIS PB280411), 1977.
    \35\ EPA (1977) Air Quality Criteria for Lead. Section 12.3.1.2. 
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 
(NTIS PB280411), 1977.
    \36\ EPA (1977) Air Quality Criteria for Lead. Section 12.3.1.1. 
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 
(NTIS PB280411), 1977.
    \37\ Miranda et al., 2011. A Geospatial Analysis of the Effects 
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental 
Health Perspectives. 119:1513-1516.
    \38\ Zahran et al., 2017. The Effect of Leaded Aviation Gasoline 
on Blood Lead in Children. Journal of the Association of 
Environmental and Resource Economists. 4(2):575-610.
    \39\ Zahran et al., 2022. Leaded Aviation Gasoline Exposure Risk 
and Child Blood Lead Levels. Proceedings of the National Academy of 
Sciences Nexus. 2:1-11.
    \40\ Klemick et al., 2022. Cardiovascular Mortality and Leaded 
Aviation Fuel: Evidence from Piston-Engine Air Traffic in North 
Carolina. International Journal of Environmental Research and Public 
Health. 19(10):5941.
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1. Piston-Engine Aircraft and the Use of Leaded Aviation Gasoline
    Aircraft operating in the U.S. are largely powered by either 
turbine engines or piston engines, although other propulsion systems 
are in use and in development. Turbine-engine powered aircraft and a 
small percentage of piston-engine aircraft (i.e., those with diesel 
engines) operate on fuel that does not contain a lead additive. Covered 
aircraft, which are predominantly piston-engine powered aircraft, 
operate on leaded avgas. Examples of covered aircraft include smaller 
piston-powered aircraft such as the Cessna 172 (single-engine aircraft) 
and the Beechcraft Baron G58 (twin-engine aircraft), as well as the 
largest piston-engine aircraft such as the Curtiss C-46 and the Douglas 
DC-6. Additionally, some rotorcraft, such as the Robinson R44 
helicopter, light-sport aircraft, and ultralight vehicles can have 
piston engines that operate using leaded avgas. In limited cases, some 
turbopropeller-powered aircraft (also

[[Page 72376]]

referred to as turboprops), can use leaded avgas.
    Lead is added to avgas in the form of tetraethyl lead. Tetraethyl 
lead helps boost fuel octane, prevents engine knock, and prevents valve 
seat recession and subsequent loss of compression for engines without 
hardened valves. There are three main types of leaded avgas: 100 
Octane, which can contain up to 4.24 grams of lead per gallon (1.12 
grams of lead per liter), 100 Octane Low Lead (100LL), which can 
contain up to 2.12 grams of lead per gallon (0.56 grams of lead per 
liter), and 100 Octane Very Low Lead (100VLL), which can contain up to 
0.71 grams of lead per gallon (0.45 grams of lead per liter).\41\ 
Currently, 100LL is the most commonly available and most commonly used 
type of avgas.\42\ Tetraethyl lead was first used in piston-engine 
aircraft in 1927.\43\ Commercial and military aircraft in the U.S. 
operated on 100 Octane leaded avgas into the 1950s, but in subsequent 
years, the commercial and military aircraft fleet largely converted to 
turbine-engine powered aircraft which do not use leaded 
avgas.44 45 The use of avgas containing approximately 4 
grams of lead per gallon continued in piston-engine aircraft until the 
early 1970s when 100LL became the dominant leaded fuel in use.
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    \41\ ASTM International (May 1, 2021) Standard Specification for 
Leaded Aviation Gasolines D910-21.
    \42\ National Academies of Sciences, Engineering, and Medicine 
(NAS). 021. Options for Reducing Lead Emissions from Piston-Engine 
Aircraft. Washington, DC: The National Academies Press. https://doi.org/10.17226/26050.
    \43\ Ogston 1981. A Short History of Aviation Gasoline 
Development, 1903-1980. Society of Automotive Engineers. p. 810848.
    \44\ U.S. Department of Commerce Civil Aeronautics 
Administration. Statistical Handbook of Aviation (Years 1930-1959). 
https://babel.hathitrust.org/cgi/pt?id=mdp.39015027813032&view=1up&seq=899.
    \45\ U.S. Department of Commerce Civil Aeronautics 
Administration. Statistical Handbook of Aviation (Years 1960-1971). 
https://babel.hathitrust.org/cgi/pt?id=mdp.39015004520279&view=1up&seq=9&skin=2021.
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    There are two sources of data from the Federal Government that 
provide annual estimates of the volume of leaded avgas supplied and 
consumed in the U.S.: the Department of Energy, Energy Information 
Administration (DOE EIA) provides information on the volume of leaded 
avgas supplied in the U.S.,\46\ and the FAA provides information on the 
volume of leaded avgas consumed in the U.S.\47\ Over the ten-year 
period from 2011 through 2020, DOE estimates of the annual volume of 
leaded avgas supplied averaged 184 million gallons, with year-on-year 
fluctuations in fuel supplied ranging from a 25 percent increase to a 
29 percent decrease. Over the same period, from 2011 through 2020, the 
FAA estimates of the annual volume of leaded avgas consumed averaged 
196 million gallons, with year-on-year fluctuations in fuel consumed 
ranging from an eight percent increase to a 14 percent decrease. The 
FAA forecast for consumption of leaded avgas in the U.S. ranges from 
185 million gallons in 2026 to 179 million gallons in 2041, a decrease 
of three percent in that period.\48\ As described later in this 
section, while the national consumption of leaded avgas is expected to 
decrease three percent from 2026 to 2041, the FAA projects increased 
activity at some airports and decreased activity at other airports out 
to 2045.
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    \46\ DOE. EIA. Petroleum and Other Liquids; Supply and 
Disposition. Aviation Gasoline in Annual Thousand Barrels. Fuel 
production volume data obtained from https://www.eia.gov/dnav/pet/pet_sum_snd_a_eppv_mbbl_a_cur-1.htm and https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=C400000001&f=A on Dec. 30, 2021.
    \47\ Department of Transportation (DOT). FAA. Aviation Policy 
and Plans. FAA Aerospace Forecast Fiscal Years 2009-2025. p. 81. 
Retrieved on Mar. 22, 2022, from https://www.faa.gov/data_research/aviation/aerospace_forecasts/2009-2025/media/2009%20Forecast%20Doc.pdf. This document provides historical data 
for 2000-2008 as well as forecast data.
    \48\ DOT. FAA. Aviation Policy and Plans. Table 23. p. 111. FAA 
Aerospace Forecast Fiscal Years 2021-2041. Available at https://www.faa.gov/sites/faa.gov/files/data_research/aviation/aerospace_forecasts/FY2021-41_FAA_Aerospace_Forecast.pdf.
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    The FAA's National Airspace System Resource (NASR) \49\ provides a 
complete list of operational airport facilities in the U.S. Among the 
approximately 19,600 airports listed in the NASR, approximately 3,300 
are included in the National Plan of Integrated Airport Systems (NPIAS) 
and support the majority of piston-engine aircraft activity that occurs 
annually in the U.S.\50\ While less aircraft activity occurs at the 
remaining 16,300 airports, that activity is conducted predominantly by 
piston-engine aircraft. Approximately 6,000 airports have been in 
operation since the early 1970s when the leaded fuel being used 
contained up to 4.24 grams of lead per gallon of avgas.\51\ The 
activity by piston-engine aircraft spans a range of purposes, as 
described further below.
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    \49\ See FAA. NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
    \50\ FAA (2020) National Plan of Integrated Airport Systems 
(NPIAS) 2021-2025 Published by the Secretary of Transportation 
Pursuant to Title 49 U.S. Code, section 47103. Retrieved on Nov. 3, 
2021 from: https://www.faa.gov/airports/planning_capacity/npias/current/media/NPIAS-2021-2025-Narrative.pdf.
    \51\ See FAA's NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
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    As of 2019, there were 171,934 piston-engine aircraft in the 
U.S.\52\ This total includes 128,926 single-engine aircraft, 12,470 
twin-engine aircraft, and 3,089 rotorcraft.\53\ The average age of 
single-engine aircraft in 2018 was 46.8 years, and the average age of 
twin-engine aircraft in 2018 was 44.7 years old.\54\ In 2019, 883 new 
piston-engine aircraft were manufactured in the U.S., some of which are 
exported.\55\ For the period from 2019 through 2041, the fleet of 
fixed-wing \56\ piston-engine aircraft is projected to decrease at an 
annual average rate of 0.9 percent, and the hours flown by these 
aircraft are projected to decrease 0.9 percent per year from 2019 to 
2041.\57\ An annual average growth rate in the production of piston-
engine powered rotorcraft of 0.9 percent is forecast, with a 
commensurate 1.9 percent increase in hours flown in that period by 
piston-engine powered rotorcraft.\58\ There were approximately 664,565 
pilots certified to fly general aviation aircraft in the U.S. in 
2021.\59\ This included 197,665

[[Page 72377]]

student pilots and 466,900 non-student pilots. In addition, there were 
more than 301,000 FAA Non-Pilot Certificated mechanics.\60\
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    \52\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 1: Historical General Aviation and Air Taxi Measures. 
Table 1.1--General Aviation and Part 135 Number of Active Aircraft 
By Aircraft Type 2008-2019. Retrieved on Dec. 27, 2021 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/. Separately, FAA maintains a database of FAA registered 
aircraft and as of January 6, 2022 there were 222,592 piston engine 
aircraft registered with FAA. See: https://registry.faa.gov/aircraftinquiry/.
    \53\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 1: Historical General Aviation and Air Taxi Measures. 
Table 1.1--General Aviation and Part 135 Number of Active Aircraft 
By Aircraft Type 2008-2019. Retrieved on Dec. 27, 2021 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \54\ General Aviation Manufacturers Association (GAMA) (2019) 
General Aviation Statistical Databook and Industry Outlook, p. 27. 
Retrieved on October 7, 2021 from: https://gama.aero/wp-content/uploads/GAMA_2019Databook_Final-2020-03-20.pdf.
    \55\ GAMA (2019) General Aviation Statistical Databook and 
Industry Outlook, p. 16. Retrieved on October 7, 2021 from: https://gama.aero/wp-content/uploads/GAMA_2019Databook_Final-2020-03-20.pdf.
    \56\ There are both fixed-wing and rotary-wing aircraft; and 
airplane is an engine-driven, fixed-wing aircraft and a rotorcraft 
is an engine-driven rotary-wing aircraft.
    \57\ See FAA Aerospace Forecast Fiscal Years 2021-2041. p. 28. 
Available at https://www.faa.gov/sites/faa.gov/files/data_research/aviation/aerospace_forecasts/FY2021-41_FAA_Aerospace_Forecast.pdf.
    \58\ FAA Aerospace Forecast Fiscal Years 2021-2041. Table 28. p. 
116., and Table 29. p. 117. Available at https://www.faa.gov/sites/faa.gov/files/data_research/aviation/aerospace_forecasts/FY2021-41_FAA_Aerospace_Forecast.pdf.
    \59\ FAA. U.S. Civil Airmen Statistics. 2021 Active Civil Airman 
Statistics. Retrieved from https://www.faa.gov/data_research/aviation_data_statistics/civil_airmen_statistics on May 20, 2022.
    \60\ FAA. U.S. Civil Airmen Statistics. 2021 Active Civil Airman 
Statistics. Retrieved from https://www.faa.gov/data_research/aviation_data_statistics/civil_airmen_statistics on May 20, 2022.
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    Piston-engine aircraft are used to conduct flights that are 
categorized as either general aviation or air taxi. General aviation 
flights are defined as all aviation other than military and those 
flights by scheduled commercial airlines. Air taxi flights are short 
duration flights made by small commercial aircraft on demand. The hours 
flown by aircraft in the general aviation fleet are comprised of 
personal and recreational transportation (67 percent), business (12 
percent), instructional flying (8 percent), medical transportation 
(less than one percent), and the remainder includes hours spent in 
other applications such as aerial observation and aerial 
application.\61\ Aerial application for agricultural activity includes 
crop and timber production, which involve fertilizer and pesticide 
application and seeding cropland. In 2019, aerial application in 
agriculture represented 883,600 hours flown by general aviation 
aircraft, and approximately 17.5 percent of these total hours were 
flown by piston-engine aircraft.\62\ While the majority of leaded avgas 
is consumed by piston-engine aircraft, in 2019, 403,700 gallons (0.2 
percent) of leaded avgas was consumed by turboprop aircraft.\63\
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    \61\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 1: Historical General Aviation and Air Taxi Measures. 
Table 1.4--General Aviation and Part 135 Total Hours Flown By Actual 
Use 2008-2019 (Hours in Thousands). Retrieved on Dec. 27, 2021 at 
https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \62\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 3: Primary and Actual Use. Table 3.2--General Aviation 
and Part 135 Total Hours Flown by Actual Use 2008-2019 (Hours in 
Thousands). Retrieved on Mar., 22, 2022 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \63\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 3: Primary and Actual Use. Table 5.1--General Aviation 
and Part 135 Total Fuel Consumed and Average Fuel Consumption Rate 
by Aircraft Type. Retrieved on Feb. 16, 2023 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
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    Approximately 71 percent of the hours flown that are categorized as 
general aviation activity are conducted by piston-engine aircraft, and 
17 percent of the hours flown that are categorized as air taxi are 
conducted by piston-engine aircraft.\64\ From the period 2012 through 
2019, the total hours flown by piston-engine aircraft increased nine 
percent from 13.2 million hours in 2012 to 14.4 million hours in 
2019.\65\ \66\
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    \64\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 3: Primary and Actual Use. Table 3.2--General Aviation 
and Part 135 Total Hours Flown by Actual Use 2008-2019 (Hours in 
Thousands). Retrieved on Mar. 22, 2022 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \65\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 3: Primary and Actual Use. Table 1.3--General Aviation 
and Part 135 Total Hours Flown by Aircraft Type 2008-2019 (Hours in 
Thousands). Retrieved on Dec. 27, 2021 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \66\ In 2012, the FAA Aerospace Forecast projected a 0.03 
percent increase in hours flown by the piston-engine aircraft fleet 
for the period 2012 through 2032. FAA Aerospace Forecast Fiscal 
Years 2012-2032. p. 53. Retrieved on Mar. 22, 2022 from https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/2012%20FAA%20Aerospace%20Forecast.pdf.
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    As noted earlier, the U.S. has a dense network of airports where 
piston-engine aircraft operate, and a small subset of those airports 
have air traffic control towers which collect daily counts of aircraft 
operations at the facility (one takeoff or landing event is termed an 
``operation''). These daily operations are provided by the FAA in the 
Air Traffic Activity System (ATADS).\67\ The ATADS reports three 
categories of airport operations that can be conducted by piston-engine 
aircraft: Itinerant General Aviation, Local Civil, and Itinerant Air 
Taxi. The sum of Itinerant General Aviation and Local Civil at a 
facility is referred to as general aviation operations. Piston-engine 
aircraft operations in these categories are not reported separately 
from operations conducted by aircraft using other propulsion systems 
(e.g., turboprop). Because piston-engine aircraft activity generally 
comprises the majority of general aviation activity at an airport, 
general aviation activity is often used as a surrogate measure for 
understanding piston-engine activity.
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    \67\ See FAA's Air Traffic Activity Data. Available at https://aspm.faa.gov/opsnet/sys/airport.asp.
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    In order to understand the trend in airport-specific piston-engine 
activity in the past ten years, we evaluated the trend in general 
aviation activity. We calculated the average activity at each of the 
airports in ATADS over three-year periods for the years 2010 through 
2012 and for the years 2017 through 2019. We focused this trend 
analysis on the airports in ATADS because these data are collected 
daily at an airport-specific control tower (in contrast with annual 
activity estimates provided at airports without control towers). There 
were 513 airports in ATADS for which data were available to determine 
annual average activity for both the 2010-2012 period and the 2017-2019 
time period. The annual average operations by general aviation at each 
of these airports in the period 2010 through 2012 ranged from 31 to 
346,415, with a median of 34,368; the annual average operations by 
general aviation in the period from 2017 through 2019 ranged from 2,370 
to 396,554, with a median of 34,365. Of the 513 airports, 211 airports 
reported increased general aviation activity over the period 
evaluated.\68\ The increase in the average annual number of operations 
by general aviation aircraft at these 211 facilities ranged from 151 to 
136,872 (an increase of two percent and 52 percent, respectively).
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    \68\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past 
Trends and Future Projections in General Aviation Activity and 
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
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    While national consumption of leaded avgas is forecast to decrease 
three percent from 2026 to 2045, this change in fuel consumption is not 
expected to occur uniformly across airports in the U.S. The FAA 
produces the Terminal Area Forecast (TAF), which is the official 
forecast of aviation activity for the 3,300 U.S. airports that are in 
the NPIAS.\69\ For the 3,306 airports in the TAF, we compared the 
average activity by general aviation at each airport from 2017-2019 
with the FAA forecast for general aviation activity at those airports 
in 2045. The FAA forecasts that activity by general aviation will 
decrease at 234 of the airports in the TAF, remain the same at 1,960 
airports, and increase at 1,112 of the airports. To evaluate the 
magnitude of potential increases in activity for the same 513 airports 
for which we evaluated activity trends in the past ten years, we 
compared the 2017-2019 average general aviation activity at each of 
these airports with the forecasted activity for 2045 in the TAF.\70\ 
The annual operations estimated for the 513 airports in 2045 ranges 
from 2,914 to 427,821 with a median of 36,883. The TAF forecasts an 
increase in activity at 442 of the 513 airports out to 2045, with the 
increase in operations at those facilities ranging from 18 to 83,704 
operations annually (an increase of 0.2 percent and 24 percent, 
respectively).
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    \69\ FAA's TAF Fiscal Years 2020-2045 describes the forecast 
method, data sources, and review process for the TAF estimates. The 
documentation for the TAF is available at https://taf.faa.gov/Downloads/TAFSummaryFY2020-2045.pdf.
    \70\ The TAF is prepared to assist the FAA in meeting its 
planning, budgeting, and staffing requirements. In addition, state 
aviation authorities and other aviation planners use the TAF as a 
basis for planning airport improvements. The TAF is available on the 
internet. The TAF database can be accessed at: https://taf.faa.gov.

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[[Page 72378]]

2. Emissions of Lead From Piston-Engine Aircraft
    This section describes the physical and chemical characteristics of 
lead emitted by covered aircraft and the national, state, county and 
airport-specific annual inventories of these engine emissions of lead. 
Information regarding lead emissions from motor vehicle engines 
operating on leaded fuel is summarized in prior AQCDs for Lead, and the 
2013 Lead ISA also includes information on lead emissions from piston-
engine aircraft.\71\ \72\ \73\ Lead is added to avgas in the form of 
tetraethyl lead along with ethylene dibromide, both of which were used 
in leaded gasoline for motor vehicles in the past. The piston engines 
in which leaded fuel was used in motor vehicles in the past have 
similarities to piston engines used in aircraft including the same 
combustion cycle and the absence of aftertreatment devices to limit 
pollutant emissions. Because the same chemical form of lead was used in 
these fuels and because of the similarity in the engines combusting 
these leaded fuels, the summary of the science regarding emissions of 
lead from motor vehicles presented in the 1997 and 1986 AQCDs for Lead 
is relevant to understanding some of the properties of lead emitted 
from piston-engine aircraft and the atmospheric chemistry these 
emissions are expected to undergo. Recent studies relevant to 
understanding lead emissions from piston-engine aircraft have also been 
published and are discussed here.
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    \71\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
    \72\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \73\ EPA (2013) ISA for Lead. Section 2.2.2.1 ``Pb Emissions 
from Piston-engine Aircraft Operating on Leaded Aviation Gasoline 
and Other Non-road Sources.'' pp. 2-7 through 2-10. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
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a. Physical and Chemical Characteristics of Lead Emitted by Piston-
Engine Aircraft
    As with motor vehicle engines, when leaded avgas is combusted in 
aircraft engines, the lead is oxidized to form lead oxide. In the 
absence of the ethylene dibromide lead scavenger in the fuel, lead 
oxide can collect on the valves and spark plugs, and if the deposits 
become thick enough, the engine can be damaged. Ethylene dibromide 
reacts with the lead oxide, converting it to brominated lead and lead 
oxybromides. These brominated forms of lead remain volatile at high 
combustion temperatures and are emitted from the engine along with the 
other combustion by-products.\74\ Upon cooling to ambient temperatures 
these brominated lead compounds are converted to particulate matter. 
The presence of lead dibromide particles in the exhaust from a piston-
engine aircraft has been confirmed by Griffith (2020) and is the 
primary form of lead emitted by engines operating on leaded fuel.\75\ 
In addition to lead bromides, ammonium salts of other lead halides were 
also emitted by motor vehicles, and therefore, ammonium salts of lead 
bromide compounds would be expected in the exhaust of piston-engine 
aircraft.\76\
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    \74\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \75\ Griffith 2020. Electron microscopic characterization of 
exhaust particles containing lead dibromide beads expelled from 
aircraft burning leaded gasoline. Atmospheric Pollution Research 
11:1481-1486.
    \76\ EPA (1986) Air Quality Criteria for Lead. Volume 2: 
Chapters 5 & 6. EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS 
PB87142386), 1986.
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    Uncombusted alkyl lead was also measured in the exhaust of motor 
vehicles operating on leaded gasoline and is therefore likely to be 
present in the exhaust from piston-engine aircraft.\77\ Alkyl lead is 
the general term used for organic lead compounds and includes the lead 
additive tetraethyl lead. Summarizing the available data regarding 
emissions of alkyl lead from piston-engine aircraft, the 2013 Lead ISA 
notes that lead in the exhaust that might be in organic form may 
potentially be 20 percent (as an upper bound estimate).78 79 
In addition, tetraethyl lead is a highly volatile compound, and 
therefore, a portion of tetraethyl lead in fuel exposed to air will 
partition into the vapor phase.\80\
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    \77\ EPA (2013) ISA for Lead. Table 2-1. ``Pb Compounds Observed 
in the Environment.'' p. 2-8. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \78\ EPA (2013) ISA for Lead. Section 2.2.2.1 ``Pb Emissions 
from Piston-engine Aircraft Operating on Leaded-Aviation Gasoline 
and Other Non-road Sources.'' p. 2-10. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
    \79\ One commenter asserts that the information summarized in 
the 2013 Lead ISA regarding emission of alkyl lead from piston-
engine aircraft is a supposition and should not inform this action. 
We respond to this comment in the Response to Comments document for 
this action.
    \80\ Memorandum to Docket EPA-HQ-OAR-2022-0389. Potential 
Exposure to Non-exhaust Lead and Ethylene Dibromide. June 15, 2022. 
Docket ID EPA-HQ-2022-0389.
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    Particles emitted by piston-engine aircraft are in the submicron 
size range (less than one micron in diameter). The Swiss Federal Office 
of Civil Aviation (FOCA) published a study of piston-engine aircraft 
emissions including measurements of lead.\81\ The Swiss FOCA reported 
the mean particle diameter of particulate matter emitted by one single-
engine piston-powered aircraft operating on leaded fuel that ranged 
from 0.049 to 0.108 microns under different power conditions (lead 
particles would be expected to be present, but these particles were not 
separately identified in this study). The particle number concentration 
ranged from 5.7x10\6\ to 8.6x10\6\ particles per cm\3\. The authors 
noted that these particle emission rates are comparable to those from a 
typical diesel passenger car engine without a particle filter.\82\ 
Griffith (2020) collected exhaust particles from a piston-engine 
aircraft operating on leaded avgas and examined the particles using 
electron microscopy. Griffith reported that the mean diameter of 
particles collected in exhaust was 13 nanometers (0.013 microns) 
consisting of a 4 nanometer (0.004 micron) lead dibromide particle 
surrounded by hydrocarbons.
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    \81\ Swiss FOCA (2007) Aircraft Piston Engine Emissions Summary 
Report. 33-05-003 Piston Engine Emissions_Swiss FOCA_Summary. 
Report_070612_rit. Available at https://www.bazl.admin.ch/bazl/en/
home/specialists/regulations-and-guidelines/environment/pollutant-
emissions/aircraft-engine-emissions/report_appendices_database-
and-data-sheets.html. Retrieved on June 15, 2022.
    \82\ Swiss FOCA (2007) Aircraft Piston Engine Emissions Summary 
Report. 33-05-003 Piston Engine Emissions_Swiss FOCA_Summary. 
Report_070612_rit. Section 2.2.3.a. Available at https://
www.bazl.admin.ch/bazl/en/home/specialists/regulations-and-
guidelines/environment/pollutant-emissions/aircraft-engine-
emissions/report_appendices_database-and-data-sheets.html. 
Retrieved on June 15, 2022.
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b. Inventory of Lead Emitted by Piston-Engine Aircraft
    Lead emissions from covered aircraft are the largest single source 
of lead to air in the U.S., contributing over 50 percent of lead 
emissions to air starting in 2008 (Table 1).\83\ In 2017, approximately 
470 tons of lead were emitted by engines in piston-powered aircraft, 
which constituted 70 percent of the annual emissions of lead to air in 
that year.\84\ Lead is emitted at and near thousands of airports in the 
U.S. as described in section II.A.1. of this document. The EPA's method 
for developing airport-specific lead estimates is described in the 
EPA's Advance Notice of Proposed Rulemaking on Lead Emissions from 
Piston-Engine Aircraft Using Leaded

[[Page 72379]]

Aviation Gasoline \85\ and in the document titled ``Calculating Piston-
Engine Aircraft Airport Inventories for Lead for the 2008 National 
Emissions Inventory.'' \86\ The EPA's National Emissions Inventory 
(NEI) reports airport estimates of lead emissions as well as estimates 
of lead emitted in-flight, which are allocated to states based on the 
fraction of piston-engine aircraft activity estimated for each state. 
These inventory data are briefly summarized here at the state, county, 
and airport level.\87\
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    \83\ The lead inventories for 2008, 2011 and 2014 are provided 
in the U.S. EPA (2018b) Report on the Environment Exhibit 2. 
Anthropogenic lead emissions in the U.S. Available at https://cfpub.epa.gov/roe/indicator.cfm?i=13#2.
    \84\ EPA 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data.
    \85\ Advance Notice of Proposed Rulemaking on Lead Emissions 
from Piston-Engine Aircraft Using Leaded Aviation Gasoline. 75 FR 
2440 (April 28, 2010).
    \86\ Airport lead annual emissions data used were reported in 
the 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data. The methods 
used to develop these inventories are described in EPA (2010) 
Calculating Piston-Engine Aircraft Airport Inventories for Lead for 
the 2008 NEI. EPA, Washington, DC, EPA-420-B-10-044, 2010. (Also 
available in the docket for this action, EPA-HQ-OAR-2022-0389).
    \87\ The 2017 NEI utilized 2014 aircraft activity data to 
develop airport-specific lead inventories. Details can be found on 
page 3-17 of the document located here: https://www.epa.gov/sites/default/files/2021-02/documents/nei2017_tsd_full_jan2021.pdf#page=70&zoom=100,68,633. Because the 
2020 inventory was impacted by the Covid-19 pandemic-related 
decrease in activity by aircraft in 2020, the EPA is focusing on the 
2017 inventory in this final action.

                                 Table 1--Piston-Engine Emissions of Lead to Air
----------------------------------------------------------------------------------------------------------------
                                                     2008         2011         2014         2017       2020 \a\
----------------------------------------------------------------------------------------------------------------
Piston-engine emissions of lead to air, tons...          560          490          460          470          427
Total U.S. lead emissions, tons................          950          810          720          670          621
Piston-engine emissions as a percent of the              59%          60%          64%          70%          69%
 total U.S. lead inventory.....................
----------------------------------------------------------------------------------------------------------------
\a\ Due to the Covid-19 Pandemic, a substantial decrease in activity by aircraft occurred in 2020, impacting the
  total lead emissions for this year. The 2020 NEI is available at: https://www.epa.gov/air-emissions-inventories/2020-national-emissions-inventory-nei-data.

    At the state level, the EPA estimates of lead emissions from 
piston-engine aircraft range from 0.3 tons (Rhode Island) to 50.5 tons 
(California), 47 percent of which is emitted in the landing and takeoff 
cycle and 53 percent of which the EPA estimates is emitted in-flight, 
outside the landing and takeoff cycle.\88\ Among the counties in the 
U.S. where the EPA estimates engine emissions of lead from covered 
aircraft, these lead inventories range from 0.00005 tons per year to 
4.3 tons per year and constitute the only source of air-related lead in 
1,140 counties (the county estimates of lead emissions include the lead 
emitted during the landing and takeoff cycle and not lead emitted in-
flight).\89\ In the counties where engine emissions of lead from 
aircraft are the sole source of lead to these estimates, annual lead 
emissions from the landing and takeoff cycle ranged from 0.00015 to 
0.74 tons. Among the 1,872 counties in the U.S. with multiple sources 
of lead, including engine emissions from covered aircraft, the 
contribution of aircraft engine emissions ranges from 0.00005 to 4.3 
tons, comprising 0.15 to 98 percent of the county total, respectively.
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    \88\ Lead emitted in-flight is assigned to states based on their 
overall fraction of total piston-engine aircraft operations. The 
state-level estimates of engine emissions of lead include both lead 
emitted in the landing and takeoff cycle as well as lead emitted in-
flight. The method used to develop these estimates is described in 
EPA (2010) Calculating Piston-Engine Aircraft Airport Inventories 
for Lead for the 2008 NEI, available here: https://nepis.epa.gov/Exe/ZyPDF.cgi/P1009I13.PDF?Dockey=P1009I13.PDF.
    \89\ Airport lead annual emissions data cited were reported in 
the 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data. In addition 
to the triennial NEI, the EPA collects from state, local, and Tribal 
air agencies point source data for larger sources every year (see 
https://www.epa.gov/air-emissions-inventories/air-emissions-reporting-requirements-aerr for specific emissions thresholds). 
While these data are not typically published as a new NEI, they are 
available publicly upon request and are also included in https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms that 
are created for years other than the triennial NEI years. County 
estimates of lead emissions from non-aircraft sources used in this 
action are from the 2019 inventory. There are 3,012 counties and 
statistical equivalent areas where EPA estimates engine emissions of 
lead occur.
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    The EPA estimates that among the approximately 20,000 airports in 
the U.S., airport lead inventories range from 0.00005 tons per year to 
0.9 tons per year.\90\ In 2017, the EPA's NEI includes 638 airports 
where the EPA estimates engine emissions of lead from covered aircraft 
were 0.1 ton or more of lead annually. Using the FAA's forecasted 
activity in 2045 for the approximately 3,300 airports in the NPIAS (as 
described in section II.A.1. of this document), the EPA estimates 
airport-specific inventories may range from 0.00003 tons to 1.28 tons 
of lead (median of 0.03 tons), with 656 airports estimated to have 
inventories above 0.1 tons in 2045.\91\
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    \90\ See EPA lead inventory data available at https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms.
    \91\ EPA used the method described in EPA (2010) Calculating 
Piston-Engine Aircraft Airport Inventories for Lead for the 2008 NEI 
to estimate airport lead inventories in 2045. This document is 
available here: https://nepis.epa.gov/Exe/ZyPDF.cgi/P1009I13.PDF?Dockey=P1009I13.PDF.
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    We estimate that piston-engine aircraft have consumed approximately 
38.6 billion gallons of leaded avgas in the U.S. since 1930, excluding 
military aircraft use of this fuel, emitting approximately 113,000 tons 
of lead to the air.\92\
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    \92\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Lead 
Emissions from the use of Leaded Aviation Gasoline from 1930 through 
2020. June 1, 2022. Docket ID EPA-HQ-2022-0389.
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3. Concentrations of Lead in Air Attributable to Emissions From Piston-
Engine Aircraft
    In this section, we describe the concentrations of lead in air 
resulting from emissions of lead from covered aircraft. Air quality 
monitoring and modeling studies for lead at and near airports have 
identified elevated

[[Page 72380]]

concentrations of lead in air from piston-engine aircraft exhaust at, 
and downwind of, airports where these aircraft are 
active.93 94 95 96 97 98 99 This section provides a summary 
of the literature regarding the local-scale impact of aircraft 
emissions of lead on concentrations of lead at and near airports, with 
specific focus on the results of air monitoring for lead that the EPA 
required at a subset of airports and an analysis conducted by the EPA 
to estimate concentrations of lead at 13,000 airports in the U.S., 
titled ``Model-extrapolated Estimates of Airborne Lead Concentrations 
at U.S. Airports.'' 100 101
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    \93\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \94\ Feinberg et al., 2016. Modeling of Lead Concentrations and 
Hot Spots at General Aviation Airports. Journal of the 
Transportation Research Board, No. 2569, Transportation Research 
Board, Washington, DC, pp. 80-87. DOI: 10.3141/2569-09.
    \95\ Municipality of Anchorage (2012). Merrill Field Lead 
Monitoring Report. Municipality of Anchorage Department of Health 
and Human Services. Anchorage, Alaska. Available at https://www.muni.org/Departments/health/Admin/environment/AirQ/Documents/Merrill%20Field%20Lead%20Monitoring%20Study_2012/Merrill%20Field%20Lead%20Study%20Report%20-%20final.pdf.
    \96\ Environment Canada (2000) Airborne Particulate Matter, Lead 
and Manganese at Buttonville Airport. Toronto, Ontario, Canada: 
Conor Pacific Environmental Technologies for Environmental 
Protection Service, Ontario Region.
    \97\ Fine et al., 2010. General Aviation Airport Air Monitoring 
Study. South Coast Air Quality Management District. Available at 
https://www.aqmd.gov/docs/default-source/air-quality/air-quality-monitoring-studies/general-aviation-study/study-of-air-toxins-near-van-nuys-and-santa-monica-airport.pdf.
    \98\ Lead emitted from piston-engine aircraft in the particulate 
phase would also be measured in samples collected to evaluate total 
ambient PM2.5 concentrations.
    \99\ One commenter provided results from a monitoring and 
modeling study at a general aviation airport in Wisconsin that 
reports increased lead concentrations with increasing proximity to 
the airport. See attachments provided to the comments from the Town 
of Middleton (EPA-HQ-OAR-2022-0389-0178_attachment_2.pdf and EPA-HQ-
OAR-2022-0389-0178_attachment_3.pdf) available in the docket for 
this action EPA-HQ-OAR-2022-0389.
    \100\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020. Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf. EPA responses to peer review comments 
on the report are available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YIWD.pdf. These documents are also available in 
the docket for this action (Docket EPA-HQ-OAR-2022-0389).
    \101\ EPA (2022) Technical Support Document (TSD) for the EPA's 
Proposed Finding that Lead Emissions from Aircraft Engines that 
Operate on Leaded Fuel Cause or Contribute to Air Pollution that May 
Reasonably Be Anticipated to Endanger Public Health and Welfare. 
EPA, Washington, DC, EPA-420-R-22-025, 2022. Available in the docket 
for this action.
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    Gradient studies evaluate how lead concentrations change with 
distance from an airport where piston-engine aircraft operate. These 
studies indicate that concentrations of lead in air, averaged over 
periods of 18 hours to three months, are estimated to be one to two 
orders of magnitude higher at locations proximate to aircraft 
emissions, compared to nearby locations not impacted by a source of 
lead air emissions.102 103 104 105 106 The magnitude of lead 
concentrations at and near airports is highly influenced by the amount 
of aircraft activity (i.e., the number of take-off and landing 
operations, particularly if concentrated at one runway) and the time 
spent by aircraft in specific modes of operation. The most significant 
emissions in terms of ground-based activity, and therefore ground-level 
concentrations of lead in air, occur near the areas with greatest fuel 
consumption where the aircraft are stationary and 
running.107 108 109 For piston-engine aircraft these areas 
are most commonly locations in which pilots conduct engine tests during 
run-up operations prior to take-off (e.g., magneto checks during the 
run-up operation mode). Run-up operations are conducted while the 
brakes are engaged so the aircraft is stationary and are often 
conducted adjacent to the runway end from which the aircraft will take 
off. Additional modes of operation by piston-engine aircraft, such as 
taxiing or idling near the runway, may result in additional hotspots of 
elevated lead concentration (e.g., start-up and idle, maintenance run-
up).\110\
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    \102\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \103\ Heiken et al., 2014. Quantifying Aircraft Lead Emissions 
at Airports. ACRP Report 133. Available at https://www.nap.edu/catalog/22142/quantifying-aircraft-lead-emissions-at-airports.
    \104\ Hudda et al., 2022. Substantial Near-Field Air Quality 
Improvements at a General Aviation Airport Following a Runway 
Shortening. Environmental Science & Technology. DOI: 10.1021/
acs.est.1c06765.
    \105\ Fine et al., 2010. General Aviation Airport Air Monitoring 
Study. South Coast Air Quality Management District. Available at 
https://www.aqmd.gov/docs/default-source/air-quality/air-quality-monitoring-studies/general-aviation-study/study-of-air-toxins-near-van-nuys-and-santa-monica-airport.pdf.
    \106\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \107\ EPA (2010) Development and Evaluation of an Air Quality 
Modeling Approach for Lead Emissions from Piston-Engine Aircraft 
Operating on Leaded Aviation Gasoline. EPA, Washington, DC, EPA-420-
R-10-007, 2010. https://nepis.epa.gov/Exe/ZyPDF.cgi/P1007H4Q.PDF?Dockey=P1007H4Q.PDF.
    \108\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \109\ Feinberg et al., 2016. Modeling of Lead Concentrations and 
Hot Spots at General Aviation Airports. Journal of the 
Transportation Research Board, No. 2569, Transportation Research 
Board, Washington, DC, pp. 80-87. DOI: 10.3141/2569-09.
    \110\ Feinberg et al., 2016. Modeling of Lead Concentrations and 
Hot Spots at General Aviation Airports. Journal of the 
Transportation Research Board, No. 2569, Transportation Research 
Board, Washington, DC, pp. 80-87. DOI: 10.3141/2569-09.
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    The lead NAAQS was revised in 2008.\111\ The 2008 decision revised 
the level, averaging time and form of the standards to establish the 
current primary and secondary standards, which are both 0.15 micrograms 
per cubic meter of air, in terms of the average of three consecutive 
monthly averages of lead in total suspended particles within a three-
year period.\112\ In conjunction with strengthening the lead NAAQS in 
2008, the EPA enhanced the existing lead monitoring network by 
requiring monitors to be placed in areas with sources such as 
industrial facilities and airports with estimated lead emissions of 1.0 
ton or more per year. Lead monitoring was conducted at two airports 
following from these requirements (Deer Valley Airport, AZ, and the Van 
Nuys Airport, CA). In 2010, the EPA made further revisions to the 
monitoring requirements such that state and local air quality agencies 
are required to monitor near industrial facilities with estimated lead 
emissions of 0.50 tons or more per year and at airports with estimated 
emissions of 1.0 ton or more per year.\113\ As part of this 2010 
requirement to expand lead monitoring, the EPA also required a one-year 
monitoring study of 15 additional airports with estimated lead 
emissions between 0.50 and 1.0 ton per year in an effort to better 
understand how these emissions affect concentrations of lead in the air 
at and near airports. Further, to help evaluate airport characteristics 
that could lead to ambient lead concentrations that approach or exceed 
the lead NAAQS, airports for this one-year monitoring study were 
selected based on factors such as the level of piston-engine aircraft 
activity and the predominant use of one runway due to wind patterns.
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    \111\ 73 FR 66965 (Nov. 12, 2008).
    \112\ 40 CFR 50.16 (Nov. 12, 2008).
    \113\ 75 FR 81126 (Dec. 27, 2010).
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    As a result of these requirements, state and local air authorities 
collected and certified lead concentration data for at least one year 
at 17 airports with most monitors starting in 2012 and generally 
continuing through 2013. The data

[[Page 72381]]

presented in Table 2 are based on the certified data for these sites 
and represent the maximum concentration monitored in a rolling three-
month average for each location.114 115
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    \114\ EPA (2015) Program Overview: Airport Lead Monitoring. EPA, 
Washington, DC, EPA-420-F-15-003, 2015. Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi/P100LJDW.PDF?Dockey=P100LJDW.PDF.
    \115\ EPA (2022) Technical Support Document (TSD) for the EPA's 
Proposed Finding that Lead Emissions from Aircraft Engines that 
Operate on Leaded Fuel Cause or Contribute to Air Pollution that May 
Reasonably Be Anticipated to Endanger Public Health and Welfare. 
EPA, Washington, DC, EPA-420-R-22-025, 2022. Available in the docket 
for this action.
    \116\ A design value is a statistic that summarizes the air 
quality data for a given area in terms of the indicator, averaging 
time, and form of the standard. Design values can be compared to the 
level of the standard and are typically used to designate areas as 
meeting or not meeting the standard and assess progress towards 
meeting the NAAQS.

    Table 2--Lead Concentrations Monitored at 17 Airports in the U.S.
------------------------------------------------------------------------
                                                 Lead design value,\116\
                 Airport, State                         [mu]g/m\3\
------------------------------------------------------------------------
Auburn Municipal Airport, WA...................                     0.06
Brookhaven Airport, NY.........................                     0.03
Centennial Airport, CO.........................                     0.02
Deer Valley Airport, AZ........................                     0.04
Gillespie Field, CA............................                     0.07
Harvey Field, WA...............................                     0.02
McClellan-Palomar Airport, CA..................                     0.17
Merrill Field, AK..............................                     0.07
Nantucket Memorial Airport, MA.................                     0.01
Oakland County International Airport, MI.......                     0.02
Palo Alto Airport, CA..........................                     0.12
Pryor Field Regional Airport, AL...............                     0.01
Reid-Hillview Airport, CA......................                     0.10
Republic Airport, NY...........................                     0.01
San Carlos Airport, CA.........................                     0.33
Stinson Municipal, TX..........................                     0.03
Van Nuys Airport, CA...........................                     0.06
------------------------------------------------------------------------

    Monitored lead concentrations violated the lead NAAQS at two 
airports in 2012: the McClellan-Palomar Airport and the San Carlos 
Airport. At both of these airports, monitors were located in close 
proximity to the area at the end of the runway most frequently used for 
pre-flight safety checks (i.e., run-up). Alkyl lead emitted by piston-
engine aircraft would be expected to partition into the vapor phase and 
would not be collected by the monitoring conducted in this study, which 
is designed to quantitatively collect particulate forms of lead.\117\
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    \117\ As noted earlier, when summarizing the available data 
regarding emissions of alkyl lead from piston-engine aircraft, the 
2013 Lead ISA notes that an upper bound estimate of lead in the 
exhaust that might be in organic form may potentially be 20 percent 
(2013 Lead ISA, p. 2-10). Organic lead in engine exhaust would be 
expected to influence receptors within short distances of the point 
of emission from piston-engine aircraft. Airports with large flight 
schools and/or facilities with substantial delays for aircraft 
queued for takeoff could experience higher concentrations of alkyl 
lead in the vicinity of the aircraft exhaust.
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    Airport lead monitoring and modeling studies have identified the 
sharp decrease in lead concentrations with distance from the run-up 
area and therefore the importance of considering monitor placement 
relative to the run-up area when evaluating the maximum impact location 
attributable to lead emissions from piston-engine aircraft. The 
monitoring data in Table 2 reflect differences in monitor placement 
relative to the run-up area as well as other factors; this study also 
provided evidence that air lead concentrations at and downwind from 
airports could be influenced by factors such as the use of more than 
one run-up area, wind speed, and the number of operations conducted by 
single- versus twin-engine aircraft.\118\
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    \118\ The data in Table 2 represent concentrations measured at 
one location at each airport and monitors were not consistently 
placed in close proximity to the run-up areas. As described in 
section II.A.3., monitored concentrations of lead in air near 
airports are highly influenced by proximity of the monitor to the 
run-up area. In addition to monitor placement, there are individual 
airport factors that can influence lead concentrations (e.g., the 
use of multiple run-up areas at an airport, fleet composition, and 
wind speed). The monitoring data reported in Table 2 reflect a range 
of lead concentrations indicative of the location at which 
measurements were made and the specific operations at an airport.
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    The EPA recognized that the airport lead monitoring study provided 
a small sample of the potential locations where emissions of lead from 
piston-engine aircraft could potentially cause concentrations of lead 
in ambient air to exceed the lead NAAQS. Because we considered that 
additional airports and conditions could lead to exceedances of the 
lead NAAQS at and near airports where piston-engine aircraft operate, 
and in order to understand the range of lead concentrations at airports 
nationwide, we developed an analysis of 13,000 airports in the peer-
reviewed report titled, ``Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports.'' \119\ \120\ This report provides 
estimated ranges of lead concentrations that may occur at and near 
airports where leaded avgas is used. The study extrapolated modeling 
results from one airport to estimate air lead concentrations at the 
maximum impact area near the run-up location for over 13,000 U.S. 
airports.\121\ The model-extrapolated lead estimates in this study 
indicate that some additional U.S. airports may have air lead 
concentrations above the NAAQS at this area of maximum impact. The 
report also indicates that, at the levels of activity analyzed at the 
13,000 airports, estimated lead concentrations decrease to below the 
standard within 50 meters

[[Page 72382]]

from the location of highest concentration.
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    \119\ EPA (2020) Model-Extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \120\ EPA (2022) Technical Support Document (TSD) for the EPA's 
Proposed Finding that Lead Emissions from Aircraft Engines that 
Operate on Leaded Fuel Cause or Contribute to Air Pollution that May 
Reasonably Be Anticipated to Endanger Public Health and Welfare. 
EPA, Washington, DC, EPA-420-R-22-025, 2022. Available in the docket 
for this action.
    \121\ In this study, the EPA defined the maximum impact site as 
15 meters downwind of the tailpipe of an aircraft conducting run-up 
operations in the area designated for these operations at a runway 
end. The maximum impact area was defined as approximately 50 meters 
surrounding the maximum impact site.
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    To estimate the potential ranges of lead concentrations at and 
downwind of the anticipated area of highest concentration at airports 
in the U.S., the relationship between piston-engine aircraft activity 
and lead concentration at and downwind of the maximum impact site at 
one airport was applied to piston-engine aircraft activity estimates 
for each U.S. airport.\122\ This approach for conducting a nationwide 
analysis of airports was selected due to the impact of piston-engine 
aircraft run-up operations on ground-level lead concentrations, which 
creates a maximum impact area that is expected to be generally 
consistent across airports. Specifically, these aircraft consistently 
take off into the wind and typically conduct run-up operations 
immediately adjacent to the take-off runway end, and thus, modeling 
lead concentrations from this source is constrained by variation in a 
few key parameters. These parameters include (1) total amount of 
piston-engine aircraft activity, (2) the proportion of activity 
conducted at one runway end, (3) the proportion of activity conducted 
by multi-piston-engine aircraft, (4) the duration of run-up operations, 
(5) the concentration of lead in avgas, (6) wind speed at the model 
airport relative to the extrapolated airport, and (7) additional 
meteorological, dispersion model, or operational parameters. These 
parameters were evaluated through sensitivity analyses as well as 
quantitative or qualitative uncertainty analyses. To generate robust 
concentration estimates, the EPA evaluated these parameters, conducted 
wind-speed correction of extrapolated estimates, and used airport-
specific information regarding airport layout and prevailing wind 
directions for the 13,000 airports.\123\
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    \122\ Prior to this model extrapolation study, the EPA developed 
and evaluated an air quality modeling approach (this study is 
available here: https://nepis.epa.gov/Exe/ZyPDF.cgi/P1007H4Q.PDF?Dockey=P1007H4Q.PDF), and subsequently applied the 
approach to a second airport and again performed an evaluation of 
the model output using air monitoring data (this second study is 
available here: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf).
    \123\ EPA (2022) Technical Support Document (TSD) for the EPA's 
Proposed Finding that Lead Emissions from Aircraft Engines that 
Operate on Leaded Fuel Cause or Contribute to Air Pollution that May 
Reasonably Be Anticipated to Endanger Public Health and Welfare. 
EPA, Washington, DC, EPA-420-R-22-025, 2022. Available in the docket 
for this action.
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    Results of this national analysis show that model-extrapolated 
three-month average lead concentrations in the maximum impact area may 
potentially exceed the lead NAAQS at some airports with activity 
ranging from 3,616-26,816 Landing and Take-Off events (LTOs) in a 
three-month period.\124\ The lead concentration estimates from this 
model-extrapolation approach account for lead engine emissions from 
aircraft only, and do not include other sources of air-related lead. 
The broad range in LTOs that may lead to concentrations of lead 
exceeding the lead NAAQS is due to the piston-engine aircraft fleet mix 
at individual airports such that airports where the fleet is dominated 
by twin-engine aircraft would potentially reach concentrations of lead 
exceeding the lead NAAQS with fewer LTOs compared with airports where 
single-engine aircraft dominate the piston-engine fleet.\125\ Model-
extrapolated three-month average lead concentrations from aircraft 
engine emissions were estimated to be above background for a distance 
of at least 500 meters from the maximum impact area at airports with 
activity ranging from 1,275-4,302 LTOs in that three-month period.\126\ 
In a separate modeling analysis at an airport at which hundreds of 
take-off and landing events by piston-engine aircraft occur per day, 
the EPA found that modeled 24-hour concentrations of lead from aircraft 
engine emissions were estimated to be above background for almost 1,000 
meters downwind from the runway.\127\
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    \124\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. Table 6. p. 53. EPA, Washington, 
DC, EPA-420-R-20-003, 2020.
    \125\ See methods used in EPA (2020) Model-extrapolated 
Estimates of Airborne Lead Concentrations at U.S. Airports. Table 2. 
p.23. EPA, Washington, DC, EPA-420-R-20-003, 2020.
    \126\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports, Table 6. p.53. EPA, Washington, DC, 
EPA-420-R-20-003, 2020.
    \127\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment 45: 5795-5804.
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    Model-extrapolated estimates of lead concentrations in the EPA 
report ``Model-extrapolated Estimates of Airborne Lead Concentrations 
at U.S. Airports'' were compared with monitored values reported in 
Table 2 and show general agreement, suggesting that the extrapolation 
method presented in this report provides reasonable estimates of the 
range in concentrations of lead in air attributable to three-month 
activity periods of piston-engine aircraft at airports. The assessment 
included detailed evaluation of the potential impact of run-up 
duration, the concentration of lead in avgas, and the impact of 
meteorological parameters on model-extrapolated estimates of lead 
concentrations attributable to engine emissions of lead from piston-
powered aircraft. Additionally, this study included a range of 
sensitivity analyses as well as quantitative and qualitative 
uncertainty analyses.
    The EPA's model-extrapolation analysis of lead concentrations from 
engine emissions resulting from covered aircraft found that annual 
airport emissions of lead estimated to result in air lead 
concentrations potentially exceeding the NAAQS ranged from 0.1 to 0.6 
tons per year. There are key pieces of airport-specific data that are 
needed to fully evaluate the potential for piston-engine aircraft 
operating at an airport to cause concentrations of lead in the air to 
exceed the lead NAAQS, and the EPA's report ``Model-extrapolated 
Estimates of Airborne Lead Concentrations at U.S. Airports'' provides 
quantitative and qualitative analyses of these factors.\128\ The EPA's 
estimate for airports that have annual lead inventories of 0.1 ton or 
more are illustrative of and provide one approach for an initial 
screening evaluation of locations where engine emissions of lead from 
aircraft may increase localized lead concentrations in air. Airport-
specific assessments would be needed to determine the magnitude of the 
potential range in lead concentrations at and downwind of each 
facility.
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    \128\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. Table 6. p.53. EPA, Washington, DC, 
EPA-420-R-20-003, 2020.
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    As described in Section II.A.1 of this document, the FAA forecasts 
0.9 percent decreases in piston-engine aircraft activity out to 2041; 
however, these decreases are not projected to occur uniformly across 
airports. Among the more than 3,300 airports in the FAA TAF, the FAA 
forecasts both decreases and increases in general aviation, which is 
largely comprised of piston-engine aircraft. If the current conditions 
on which the forecast is based persist, then lead concentrations in the 
air may increase at the airports where general aviation activity is 
forecast to increase.
    In addition to airport-specific modeled estimates of lead 
concentrations, the EPA also provides annual estimates of lead 
concentrations for each census tract in the U.S. as part of the Air 
Toxics Screening Assessment (AirToxScreen).\129\ The census tract 
concentrations are averages of the area-weighted census block 
concentrations within the tract. Lead concentrations reported in the 
AirToxScreen are based on emissions estimates from

[[Page 72383]]

anthropogenic and natural sources of lead, including aircraft engine 
emissions.\130\ The 2019 AirToxScreen provides lead concentration 
estimates in air for 73,449 census tracts in the U.S.\131\ Lead 
concentrations associated with emissions from piston-engine aircraft 
comprised more than 50 percent of these census block area-weighted lead 
concentration estimates in over half of the census tracts, which 
included tracts in all 50 states, as well as Puerto Rico and the Virgin 
Islands.
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    \129\ See EPA's 2019 AirToxScreen. Available at https://www.epa.gov/AirToxScreen/2019-airtoxscreen.
    \130\ These concentration estimates are not used for comparison 
to the level of the Lead NAAQS due to different temporal averaging 
times and underlying assumptions in modeling. The AirToxScreen 
estimates are provided to help state, local and Tribal air agencies 
and the public identify which pollutants, emission sources and 
places they may wish to study further to better understand potential 
risks to public health from air toxics. There are uncertainties 
inherent in these estimates described by the EPA, some of which are 
relevant to these estimates of lead concentrations; however, these 
estimates provide perspective on the potential influence of piston-
engine emissions of lead on air quality. See https://www.epa.gov/AirToxScreen/airtoxscreen-limitations.
    \131\ As airports are generally in larger census blocks within a 
census tract, concentrations for airport blocks dominate the area-
weighted average in cases where an airport is the predominant lead 
emissions source in a census tract.
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4. Fate and Transport of Emissions of Lead From Piston-Engine Aircraft
    This section summarizes the chemical transformation that piston-
engine aircraft lead emissions are anticipated to undergo in the 
atmosphere and describes what is known about the deposition of piston-
engine aircraft lead and its potential impacts on soil, food, and 
aquatic environments.
a. Atmospheric Chemistry and Transport of Emissions of Lead From 
Piston-Engine Aircraft
    Lead emitted by piston-engine aircraft can have impacts in the 
local environment, and, due to their small size (i.e., typically less 
than one micron in diameter),132 133 lead-bearing particles 
emitted by piston engines may disperse widely in the environment. 
However, lead emitted during the landing and takeoff cycle, 
particularly during ground-based operations such as start-up, idle, 
preflight run-up checks, taxi and the take-off roll on the runway, may 
deposit to the local environment and/or infiltrate into 
buildings.134 135
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    \132\ Swiss FOCA (2007) Aircraft Piston Engine Emissions Summary 
Report. 33-05-003 Piston Engine Emissions_Swiss FOCA_Summary. 
Report_070612_rit. Available at https://www.bazl.admin.ch/bazl/en/
home/specialists/regulations-and-guidelines/environment/pollutant-
emissions/aircraft-engine-emissions/report-appendices_database_
and-data-sheets.html. Retrieved on June 15, 2022.
    \133\ Griffith 2020. Electron microscopic characterization of 
exhaust particles containing lead dibromide beads expelled from 
aircraft burning leaded gasoline. Atmospheric Pollution Research 
11:1481-1486.
    \134\ EPA (2013) ISA for Lead. Section 1.3. ``Exposure to 
Ambient Pb.'' p. 1-11. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \135\ The EPA received comments on the information provided in 
this section to which we respond in the Response to Comments 
document for this action.
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    The Lead AQCDs summarize the literature reporting on the 
atmospheric chemical transformation of lead compounds emitted by 
engines operating on leaded fuel. Briefly, lead halides emitted by 
motor vehicles operating on leaded fuel were reported to undergo 
compositional changes upon cooling and mixing with the ambient air as 
well as during transport, and we would anticipate lead bromides emitted 
by piston-engine aircraft to behave similarly in the atmosphere. The 
water solubility of these lead-bearing particles was reported to be 
higher for the smaller lead-bearing particles.\136\ Lead halides 
emitted in motor vehicle exhaust were reported to break down rapidly in 
the atmosphere via redox reactions in the presence of atmospheric 
acids.\137\ Depending on ambient conditions (e.g., ozone and hydroxyl 
concentrations in the atmosphere), alkyl lead may exist in the 
atmosphere for hours to days \138\ and may therefore be transported off 
airport property into nearby communities. Tetraethyl lead reacts with 
the hydroxyl radical in the gas phase to form a variety of products 
that include ionic trialkyl lead, dialkyl lead and metallic lead. 
Trialkyl lead is slow to react with the hydroxyl radical and is quite 
persistent in the atmosphere.\139\
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    \136\ EPA (1977) Air Quality Criteria for Lead. Section 6.2.2.1. 
EPA, Washington, DC, EPA-600/8-77-017, 1977.
    \137\ EPA (2006) Air Quality Criteria for Lead. Section E.6. 
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \138\ EPA (2006) Air Quality Criteria for Lead. Section E.6. p. 
2-5. EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \139\ EPA (2006) Air Quality Criteria for Lead. Section 2. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
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b. Deposition of Lead Emissions From Piston-Engine Aircraft and Soil 
Lead Concentrations to Which Piston-Engine Aircraft May Contribute
    Lead is removed from the atmosphere and deposited on soil, into 
aquatic systems and on other surfaces via wet or dry deposition.\140\ 
Meteorological factors (e.g., wind speed, convection, rain, humidity) 
influence local deposition rates. With regard to deposition of lead 
from aircraft engine emissions, the EPA modeled the deposition rate for 
aircraft lead emissions at one airport in a temperate climate in 
California with dry summer months. In this location, the average lead 
deposition rate from aircraft emissions of lead was 0.057 milligrams 
per square meter per year.\141\
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    \140\ EPA (2013) ISA for Lead. Section 1.2.1. ``Sources, Fate 
and Transport of Ambient Pb;'' p. 1-6; and Section 2.3. ``Fate and 
Transport of Pb.'' p. 2-24 through 2-25. EPA, Washington, DC, EPA/
600/R-10/075F, 2013.
    \141\ Memorandum to Docket EPA-HQ-OAR-2022-0389. Deposition of 
Lead Emitted by Piston-engine Aircraft. June 15, 2022. Docket ID 
EPA-HQ-2022-0389.
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    Studies summarized in the 2013 Lead ISA suggest that soil is a 
reservoir for contemporary and historical emissions of lead to 
air.\142\ Once deposited to soil, lead can be absorbed onto organic 
material, can undergo chemical and physical transformation depending on 
a number of factors (e.g., pH of the soil and the soil organic 
content), and can participate in further cycling through air or other 
media.\143\ The extent of atmospheric deposition of lead from aircraft 
engine emissions would be expected to depend on a number of factors 
including the size of the particles emitted (smaller particles, such as 
those in aircraft emissions, have lower settling velocity and may 
travel farther distances before being deposited compared with larger 
particles), the temperature of the exhaust (the high temperature of the 
exhaust creates plume buoyancy), as well as meteorological factors 
(e.g., wind speed, precipitation rates). As a result of the size of the 
lead particulate matter emitted from piston-engine aircraft and as a 
result of these emissions occurring at various altitudes, lead emitted 
from these aircraft may distribute widely through the environment.\144\ 
Murphy et al. (2008) reported weekend increases in ambient air lead 
concentrations monitored at remote locations in the U.S. that the 
authors hypothesized were related to weekend increases in piston-engine 
powered general aviation activity.\145\
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    \142\ EPA (2013) ISA for Lead. Section 2.6.1. ``Soils.'' p. 2-
118. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \143\ EPA (2013) ISA for Lead. Chapter 6. ``Ecological Effects 
of Pb.'' p. 6-57. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \144\ Murphy et al., 2008. Weekly patterns of aerosol in the 
United States. Atmospheric Chemistry and Physics. 8:2729-2739.
    \145\ Lead concentrations collected as part of the Interagency 
Monitoring of Protected Visual Environments (IMPROVE) network and 
the National Oceanic and Atmospheric Administration (NOAA) 
monitoring sites.
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    Heiken et al. (2014) assessed air lead concentrations potentially 
attributable to resuspended lead that previously deposited onto soil 
relative to air lead concentrations resulting directly from

[[Page 72384]]

aircraft engine emissions.\146\ Based on comparisons of lead 
concentrations in total suspended particulate (TSP) and fine 
particulate matter (PM2.5) measured at the three airports, 
coarse particle lead was observed to account for about 20-30 percent of 
the lead found in TSP. The authors noted that based on analysis of lead 
isotopes present in the air samples collected at these airports, the 
original source of the lead found in the coarse particle range appeared 
to be from aircraft exhaust emissions of lead that previously deposited 
to soil and were resuspended by wind or aircraft-induced turbulence. 
Results from lead isotope analysis in soil samples collected at the 
same three airports led the authors to conclude that lead emitted from 
piston-engine aircraft was not the dominant source of lead in soil in 
the samples measured at the airports they studied. The authors note the 
complex history of topsoil can create challenges in understanding the 
extent to which aircraft lead emissions impact soil lead concentrations 
at and near airports (e.g., the source of topsoil can change as a 
result of site renovation, construction, landscaping, natural events 
such as wildfire and hurricanes, and other activities). Concentrations 
of lead in soil at and near airports servicing piston-engine aircraft 
have been measured using a range of 
approaches.147 148 149 150 151 152 Kavouras et al. (2013) 
collected soil samples at three airports and reported that construction 
at an airport involving removal and replacement of topsoil complicated 
interpretation of the findings at that airport and that the number of 
runways at an airport may influence resulting lead concentrations in 
soil (i.e., multiple runways may provide for more wide-spread dispersal 
of the lead over a larger area than that potentially affected at a 
single-runway airport).
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    \146\ Heiken et al., 2014. ACRP Web-Only Document 21: 
Quantifying Aircraft Lead Emissions at Airports. Contractor's Final 
Report for ACRP 02-34. Available at https://www.trb.org/Publications/Blurbs/172599.aspx.
    \147\ McCumber and Strevett 2017. A Geospatial Analysis of Soil 
Lead Concentrations Around Regional Oklahoma Airports. Chemosphere 
167:62-70.
    \148\ Kavouras et al., 2013. Bioavailable Lead in Topsoil 
Collected from General Aviation Airports. The Collegiate Aviation 
Review International 31(1):57-68. Available at https://doi.org/10.22488/okstate.18.100438.
    \149\ Heiken et al., 2014. ACRP Web-Only Document 21: 
Quantifying Aircraft Lead Emissions at Airports. Contractor's Final 
Report for ACRP 02-34. Available at https://www.trb.org/Publications/Blurbs/172599.aspx.
    \150\ EPA (2010) Development and Evaluation of an Air Quality 
Modeling Approach for Lead Emissions from Piston-Engine Aircraft 
Operating on Leaded Aviation Gasoline. EPA, Washington, DC, EPA-420-
R-10-007, 2010. https://nepis.epa.gov/Exe/ZyPDF.cgi/P1007H4Q.PDF?Dockey=P1007H4Q.PDF.
    \151\ Environment Canada (2000) Airborne Particulate Matter, 
Lead and Manganese at Buttonville Airport. Toronto, Ontario, Canada: 
Conor Pacific Environmental Technologies for Environmental 
Protection Service, Ontario Region.
    \152\ Lejano and Ericson 2005. Tragedy of the Temporal Commons: 
Soil-Bound Lead and the Anachronicity of Risk. Journal of 
Environmental Planning and Management. 48(2):301-320.
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c. Potential for Lead Emissions From Piston-Engine Aircraft To Impact 
Agricultural Products
    Studies conducted near stationary sources of lead emissions (e.g., 
smelters) have shown that atmospheric lead sources can lead to 
contamination of agricultural products, such as 
vegetables.153 154 In this way, air lead sources may 
contribute to dietary exposure pathways.\155\ As described in section 
II.A.1. of this document, piston-engine aircraft are used in the 
application of pesticides, fertilizers and seeding crops for human and 
animal consumption and, as such, provide a potential route of exposure 
for lead in food. To minimize drift of pesticides and other 
applications from the intended target, pilots are advised to maintain a 
height between eight and 12 feet above the target crop during 
application.\156\ An unintended consequence of this practice is that 
exhaust emissions of lead have a substantially increased potential for 
directly depositing on vegetation and surrounding soil. Lead halides, 
the primary form of lead emitted by engines operating on leaded 
fuel,\157\ are slightly water soluble and, therefore, may be more 
readily absorbed by plants than other forms of inorganic lead.
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    \153\ EPA (2013) ISA for Lead. Section 3.1.3.3. ``Dietary Pb 
Exposure.'' p. 3-20 through 3-24. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \154\ EPA (2006) Air Quality Criteria for Lead. Section 8.2.2. 
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \155\ EPA (2006) Air Quality Criteria for Lead. Section 8.2.2. 
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \156\ O'Connor-Marer. Aerial Applicator's Manual: A National 
Pesticide Applicator Certification Study Guide. p. 40. National 
Association of State Departments of Agriculture Research Foundation. 
Available at https://www.epa.gov/system/files/documents/2022-09/national-pesticide-applicator-cert-core-manual-2014.pdf.
    \157\ The additive used in the fuel to scavenge lead determines 
the chemical form of the lead halide emitted; because ethylene 
dibromide is added to leaded aviation gasoline used in piston-engine 
aircraft, the lead halide emitted is in the form of lead dibromide.
---------------------------------------------------------------------------

    The 2006 AQCD indicated that surface deposition of lead onto plants 
may be significant.\158\ Atmospheric deposition of lead provides a 
pathway for lead in vegetation as a result of contact with above-ground 
portions of the plant.159 160 161 Livestock may subsequently 
be exposed to lead in vegetation (e.g., grasses and silage) and in 
surface soils via incidental ingestion of soil while grazing.\162\
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    \158\ EPA (2006) Air Quality Criteria for Lead. pp. 7-9 and 
AXZ7-39 (citing U.S. studies of the 1990s). EPA, Washington, DC, 
EPA/600/R-5/144aF, 2006.
    \159\ EPA (2006) Air Quality Criteria for Lead. p. AXZ7-39. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
    \160\ EPA (1986) Air Quality Criteria for Lead. Sections 6.5.3. 
EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \161\ EPA (1986) Air Quality Criteria for Lead. Section 
7.2.2.2.1.EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS 
PB87142386), 1986.
    \162\ EPA (1986) Air Quality Criteria for Lead. Section 
7.2.2.2.2. EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS 
PB87142386), 1986.
---------------------------------------------------------------------------

d. Potential for Lead Emissions From Piston-Engine Aircraft To Impact 
Aquatic Ecosystems
    As discussed in section 6.4 of the 2013 Lead ISA, lead 
bioaccumulates in the tissues of aquatic organisms through ingestion of 
food and water or direct uptake from the environment (e.g., across 
membranes such as gills or skin).\163\ Alkyl lead, in particular, has 
been identified by the EPA as a Persistent, Bioaccumulative, and Toxic 
(PBT) pollutant.\164\ There are 527 seaport facilities in the U.S., and 
landing and take-off activity by seaplanes at these facilities provides 
a direct pathway for emission of organic and inorganic lead to the air 
near/above inland waters and ocean seaports where these aircraft 
operate.\165\ Inland airports may also provide a direct pathway for 
emission of organic and inorganic lead to the air near/above inland 
waters. Lead emissions from piston-engine aircraft operating at 
seaplane facilities as well as airports and heliports near water bodies 
can enter the aquatic ecosystem by either deposition from ambient air 
or runoff of lead deposited to surface soils.
---------------------------------------------------------------------------

    \163\ EPA (2013) ISA for Lead. Section 6.4.2. ``Biogeochemistry 
and Chemical Effects of Pb in Freshwater and Saltwater Systems.'' p. 
6-147. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \164\ EPA (2002) Persistent, Bioaccumulative, and Toxic 
Pollutants (PBT) Program. PBT National Action Plan for Alkyl-Pb. 
Washington, DC. June. 2002.
    \165\ See FAA's NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
---------------------------------------------------------------------------

    In addition to deposition of lead from engine emissions by piston-
powered aircraft, lead may enter aquatic systems from the pre-flight 
inspection of the fuel for contaminants that pilots conduct. While some 
pilots return the checked fuel to their fuel tank or dispose of it in a 
receptacle provided on the airfield, some pilots discard the fuel onto 
the tarmac, ground, or water, in the case of

[[Page 72385]]

a fuel check being conducted on a seaplane. Lead in the fuel discarded 
to the environment may evaporate to the air and may be taken up by the 
surface on which it is discarded. Lead on tarmac or soil surfaces is 
available for runoff to surface water. Tetraethyl lead in the avgas 
directly discarded to water will be available for uptake and 
bioaccumulation in aquatic life. The National Academy of Sciences 
Airport Cooperative Research Program (ACRP) conducted a survey study of 
pilots' fuel sampling and disposal practices. Among the 146 pilots 
responding to the survey, 36 percent indicated they discarded all fuel 
check samples to the ground regardless of contamination status, and 19 
percent of the pilots indicated they discarded only contaminated fuel 
to the ground.\166\ Leaded avgas discharged to the ground and water 
includes other hazardous fuel components such as ethylene 
dibromide.\167\
---------------------------------------------------------------------------

    \166\ National Academies of Sciences, Engineering, and Medicine 
2014. Best Practices for General Aviation Aircraft Fuel-Tank 
Sampling. Washington, DC: The National Academies Press. https://doi.org/10.17226/22343.
    \167\ Memorandum to Docket EPA-HQ-OAR-2022-0389. Potential 
Exposure to Non-exhaust Lead and Ethylene Dibromide. June 15, 2022. 
Docket ID EPA-HQ-2022-0389.
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5. Consideration of Environmental Justice and Children in Populations 
Residing Near Airports
    This section provides a description of how many people live in 
close proximity to airports where they may be exposed to airborne lead 
from aircraft engine emissions of lead (referred to here as the ``near-
airport'' population). This section also provides the demographic 
composition of the near-airport population, with attention to 
implications related to environmental justice (EJ) and the population 
of children in this near-source environment.\168\
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    \168\ As described in this section, the EPA evaluated 
environmental justice consistent with the EPA 2016 Technical 
Guidance. However, the final decisions in this action are based on 
EPA's consideration under CAA section 231(a)(2)(A) of potential 
risks to public health and welfare from the lead air pollution, as 
well as its evaluation of whether emissions of lead from engines in 
covered aircraft contribute to that air pollution. See section III. 
for further discussion of the statutory authority for this action 
and sections IV. and V. for further discussion of the basis for 
these findings.
---------------------------------------------------------------------------

    Executive Order 14096, ``Revitalizing Our Nation's Commitment to 
Environmental Justice for All,'' defines environmental justice as ``the 
just treatment and meaningful involvement of all people, regardless of 
income, race, color, national origin, Tribal affiliation, or 
disability, in agency decision-making and other Federal activities that 
affect human health and the environment so that people: (i) are fully 
protected from disproportionate and adverse human health and 
environmental effects (including risks) and hazards, including those 
related to climate change, the cumulative impacts of environmental and 
other burdens, and the legacy of racism or other structural or systemic 
barriers; and (ii) have equitable access to a healthy, sustainable, and 
resilient environment in which to live, play, work, learn, grow, 
worship, and engage in cultural and subsistence practices.'' \169\ 
Providing this information regarding potential EJ implications in the 
population living near airports is important for purposes of public 
information and awareness. Here, EPA finds that blood lead levels in 
children from low-income households remain higher than those in 
children from higher income households, and blood lead levels in Black 
children are higher than those in non-Hispanic White 
children.170 171 172
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    \169\ See, https://www.federalregister.gov/documents/2023/04/26/2023-08955/revitalizing-our-nations-commitment-to-environmental-justice-for-all. When the analysis discussed in this section was 
performed, EPA defined environmental justice as the fair treatment 
and meaningful involvement of all people regardless of race, color, 
national origin, or income, with respect to the development, 
implementation, and enforcement of environmental laws, regulations, 
and policies. Fair treatment means that ``no group of people should 
bear a disproportionate burden of environmental harms and risks, 
including those resulting from the negative environmental 
consequences of industrial, governmental and commercial operations 
or programs and policies.'' Meaningful involvement occurs when ``1) 
potentially affected populations have an appropriate opportunity to 
participate in decisions about a proposed activity [e.g., 
rulemaking] that will affect their environment and/or health; 2) the 
public's contribution can influence the regulatory Agency's 
decision; 3) the concerns of all participants involved will be 
considered in the decision-making process; and 4) [the EPA will] 
seek out and facilitate the involvement of those potentially 
affected.'' See, EPA's Guidance on Considering Environmental Justice 
During the Development of Regulatory Actions. Available at https://www.epa.gov/sites/default/files/2015-06/documents/considering-ej-in-rulemaking-guide-final.pdf. See also https://www.epa.gov/environmentaljustice.
    \170\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
40. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \171\ EPA. America's Children and the Environment. Summary of 
blood lead levels in children updated in 2022, available at https://www.epa.gov/americaschildrenenvironment/biomonitoring-lead. Data 
source: Centers for Disease Control and Prevention, National Report 
on Human Exposure to Environmental Chemicals. Blood Lead (2011-
2018). Updated March 2022. Available at https://www.cdc.gov/exposurereport/report/pdf/cgroup2_LBXBPB_2011-p.pdf.
    \172\ The relative contribution of lead emissions from covered 
aircraft engines to these disparities has not been determined and is 
not a goal of the evaluation described here.
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    The analysis described here provides information regarding whether 
some demographic groups are more highly represented in the near-airport 
environment compared with people who live farther from airports.\173\ 
Residential proximity to airports implies that there is an increased 
potential for exposure to lead from covered aircraft engine 
emissions.\174\ As described in section II.A.3. of this document, 
several studies have measured higher concentrations of lead in air near 
airports with piston-engine aircraft activity. Additionally, as noted 
in section II.A. of this document, three studies have reported 
increased blood lead levels in children with increasing proximity to 
airports.175 176 177
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    \173\ This analysis used the U.S. Census and demographic data 
from 2010 which was the most recent data available at the time of 
this assessment.
    \174\ Residential proximity to a source of a specific air 
pollutant(s) is a widely used surrogate measure to evaluate the 
potential for higher exposures to that pollutant (EPA 2016 Technical 
Guidance for Assessing Environmental Justice in Regulatory Analysis. 
Section 4.2.1). Data presented in section II.A.3. demonstrate that 
lead concentrations in air near the runup area can exceed the lead 
NAAQS and concentrations decrease sharply with distance from the 
ground-based aircraft exhaust and vary with the amount of aircraft 
activity at an airport. Not all people living within 500 meters of a 
runway are expected to be equally exposed to lead.
    \175\ Miranda et al., 2011. A Geospatial Analysis of the Effects 
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental 
Health Perspectives. 119:1513-1516.
    \176\ Zahran et al., 2017. The Effect of Leaded Aviation 
Gasoline on Blood Lead in Children. Journal of the Association of 
Environmental and Resource Economists. 4(2):575-610.
    \177\ Zahran et al., 2022. Leaded Aviation Gasoline Exposure 
Risk and Child Blood Lead Levels. Proceedings of the National 
Academy of Sciences Nexus. 2:1-11.
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    We first summarize here the literature on disparity among near-
airport populations. Then we describe the analyses the EPA conducted to 
evaluate potential disparity in the population groups living near 
runways where piston-engine aircraft operate compared to those living 
elsewhere.
    Numerous studies have found that environmental hazards such as air 
pollution are more prevalent in areas where people of color and low-
income populations represent a higher fraction

[[Page 72386]]

of the population compared with the general population, including near 
transportation sources.178 179 180 181 182 The literature 
includes studies that have reported on communities in close proximity 
to airports that are disproportionately represented by people of color 
and low-income populations. McNair (2020) described nineteen major 
airports that underwent capacity expansion projects between 2000 and 
2010, thirteen of which had a large concentration or presence of 
persons of color, foreign-born persons or low-income populations 
nearby.\183\ Woodburn (2017) reported on changes in communities near 
airports from 1970-2010, finding suggestive evidence that at many hub 
airports over time, the presence of marginalized groups residing in 
close proximity to airports increased.\184\ Rissman et al. (2013) 
reported that with increasing proximity to the Hartsfield-Jackson 
Atlanta International Airport, exposures to particulate matter were 
higher, and there were lower home values, income, education, and 
percentage of white residents.\185\
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    \178\ Rowangould 2013. A census of the near-roadway population: 
public health and environmental justice considerations. 
Transportation Research Part D 25:59-67. https://dx.doi.org/10.1016/j.trd.2013.08.003.
    \179\ Marshall et al., 2014. Prioritizing environmental justice 
and equality: diesel emissions in Southern California. Environmental 
Science & Technology 48: 4063-4068. https://doi.org/10.1021/es405167f.
    \180\ Marshall 2008. Environmental inequality: air pollution 
exposures in California's South Coast Air Basin. Atmospheric 
Environment 21:5499-5503. https://doi.org/10.1016/j.atmosenv.2008.02.005.
    \181\ Tessum et al., 2021. PM2.5 polluters 
disproportionately and systemically affect people of color in the 
United States. Science Advances 7:eabf4491.
    \182\ Mohai et al., 2009. Environmental justice. Annual Reviews 
34:405-430. Available at https://doi.org/10.1146/annurev-environ-082508-094348.
    \183\ McNair 2020. Investigation of environmental justice 
analysis in airport planning practice from 2000 to 2010. 
Transportation Research Part D 81:102286.
    \184\ Woodburn 2017. Investigating neighborhood change in 
airport-adjacent communities in multiairport regions from 1970 to 
2010. Journal of the Transportation Research Board, 2626, 1-8.
    \185\ Rissman et al., 2013. Equity and health impacts of 
aircraft emissions at the Hartfield-Jackson Atlanta International 
Airport. Landscape and Urban Planning, 120: 234-247.
---------------------------------------------------------------------------

    The EPA used two approaches to understand whether some members of 
the population (e.g., children five and under, people of color, 
indigenous populations, low-income populations) represent a larger 
share of the people living in proximity to airports where piston-engine 
aircraft operate compared with people who live farther away from these 
airports. In the first approach, we evaluated people living within, and 
children attending school within, 500 meters of all of the 
approximately 20,000 airports in the U.S., using methods described in 
the EPA's report titled ``National Analysis of the Populations Residing 
Near or Attending School Near U.S. Airports.'' \186\ In the second 
approach, we evaluated people living near the NPIAS airports in the 
conterminous 48 states. As noted in section II.A.1. of this document, 
the NPIAS airports support the majority of piston-engine aircraft 
activity that occurs in the U.S. Among the NPIAS airports, we compared 
the demographic composition of people living within one kilometer of 
runways with the demographic composition of people living at a distance 
of one to five kilometers from the same airports.
---------------------------------------------------------------------------

    \186\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
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    The distances analyzed for those people living closest to airports 
(i.e., distances of 500 meters and 1,000 meters) were chosen for 
evaluation following from the air quality monitoring and modeling data 
presented in section II.A.3. of this document. Specifically, the EPA's 
modeling and monitoring data indicate that concentrations of lead from 
piston-engine aircraft emissions can be elevated above background 
levels at distances of 500 meters over a rolling three-month period. On 
individual days, concentrations of lead from piston-engine aircraft 
emissions can be elevated above background levels at distances of 1,000 
meters downwind of a runway, depending on aircraft activity and 
prevailing wind direction.187 188 189
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    \187\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \188\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \189\ We do not assume or expect that all people living within 
500m or 1,000m of a runway are exposed to lead from piston-engine 
aircraft emissions, and the wide range of activity of piston-engine 
aircraft at airports nationwide suggests that exposure to lead from 
aircraft emissions is likely to vary widely.
---------------------------------------------------------------------------

    Because the U.S. has a dense network of airports, many of which 
have neighboring communities, we quantified the number of people living 
and children attending school within 500 meters of the approximately 
20,000 airports in the U.S.\190\ From this analysis, the EPA estimates 
that approximately 5.2 million people live within 500 meters of an 
airport runway, 363,000 of whom are children aged five and under. The 
EPA also estimates that 573 schools attended by 163,000 children in 
kindergarten through twelfth grade are within 500 meters of an airport 
runway.\191\
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    \190\ In this analysis, we included populations living in census 
blocks that intersected the 500-meter buffer around each runway in 
the U.S. Potential uncertainties in this approach are described in 
our report National Analysis of the Populations Residing Near or 
Attending School Near U.S. Airports. EPA-420-R-20-001, available at 
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf, and in the 
EPA responses to peer review comments on the report, available here: 
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YISM.pdf.
    \191\ EPA (2020) National Analysis of the Populations Residing 
Near or Attending School Near U.S. Airports. EPA-420-R-20-001. 
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf.
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    In order to identify potential disparities in the near-airport 
population, we also evaluated populations at the state level. Using the 
U.S. Census population data for each state in the U.S., we compared the 
percent of people by age, race and indigenous peoples (i.e., children 
five and under, Black, Asian, and Native American or Alaska Native) 
living within 500 meters of an airport runway with the percent by age, 
race, and indigenous peoples comprising the state population.\192\ 
Using the methodology described in Clarke (2022), the EPA identified 
states in which children, Black, Asian, and Native American or Alaska 
Native populations represent a greater fraction of the population 
living within 500 meters of a runway compared with the percent of these 
groups in the state population.\193\ Results of this analysis are 
presented in the following tables.\194\ This state-level analysis 
presents summary information for a subset of potentially relevant 
demographic characteristics. We present data in this section regarding 
a wider array of demographic characteristics when evaluating 
populations living near NPIAS airports.
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    \192\ Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389. 
Estimation of Population Size and Demographic Characteristics among 
People Living Near Airports by State in the United States. May 31, 
2022. Docket ID EPA-HQ-2022-0389.
    \193\ Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389. 
Estimation of Population Size and Demographic Characteristics among 
People Living Near Airports by State in the United States. May 31, 
2022. Docket ID EPA-HQ-2022-0389.
    \194\ These data are presented in tabular form for all states in 
this memorandum located in the docket: Clarke. Memorandum to Docket 
EPA-HQ-OAR-2022-0389. Estimation of Population Size and Demographic 
Characteristics among People Living Near Airports by State in the 
United States. May 31, 2022. Docket ID EPA-HQ-2022-0389.
---------------------------------------------------------------------------

    Among children five and under, there were three states (Nevada, 
South Carolina, and South Dakota) in which the percent of children five 
and under

[[Page 72387]]

living within 500 meters of a runway represents a greater fraction of 
the population by a difference of one percent or greater compared with 
the percent of children five and under in the state population (Table 
3).

 Table 3--The Population of Children Five Years and Under Within 500 Meters of an Airport Runway Compared to the
                                State Population of Children Five Years and Under
----------------------------------------------------------------------------------------------------------------
                                          Percent of         Percent of         Number of          Number of
                                        children aged      children aged      children aged      children aged
                State                   five years and     five years and     five years and     five years and
                                      under within  500  under within  the  under within  500    under in  the
                                            meters             state              meters             state
----------------------------------------------------------------------------------------------------------------
Nevada..............................                 10                  8               1000            224,200
South Carolina......................                  9                  8                400            361,400
South Dakota........................                 11                  9              3,000             71,300
----------------------------------------------------------------------------------------------------------------

    There were nine states in which the Black population represented a 
greater fraction of the population living in the near-airport 
environment by a difference of one percent or greater compared with the 
state as a whole. These states were California, Kansas, Kentucky, 
Louisiana, Mississippi, Nevada, South Carolina, West Virginia, and 
Wisconsin (Table 4).

     Table 4--The Black Population Within 500 Meters of an Airport Runway and the Black Population, by State
----------------------------------------------------------------------------------------------------------------
                                        Percent black      Percent black     Black population   Black population
                State                 within 500 meters   within the state  within 500 meters     in the state
----------------------------------------------------------------------------------------------------------------
California..........................                  8                  7             18,981          2,486,500
Kansas..............................                  8                  6              1,240            173,300
Kentucky............................                  9                  8              3,152            342,800
Louisiana...........................                 46                 32             14,669          1,463,000
Mississippi.........................                 46                 37              8,542          1,103,100
Nevada..............................                 12                  9              1,794            231,200
South Carolina......................                 31                 28             10,066          1,302,900
West Virginia.......................                 10                  3              1,452             63,900
Wisconsin...........................                  9                  6              4,869            367,000
----------------------------------------------------------------------------------------------------------------

    There were three states with a greater fraction of Asians in the 
near-airport environment compared with the state as a whole by a 
difference of one percent or greater: Indiana, Maine, and New Hampshire 
(Table 5).

     Table 5--The Asian Population Within 500 Meters of an Airport Runway and the Asian Population, by State
----------------------------------------------------------------------------------------------------------------
                                        Percent asian      Percent asian     Asian population   Asian population
                State                 within 500 meters   within the state  within 500 meters     in the state
----------------------------------------------------------------------------------------------------------------
Indiana.............................                  4                  2              1,681            105,500
Maine...............................                  2                  1                406             13,800
New Hampshire.......................                  4                  2                339             29,000
----------------------------------------------------------------------------------------------------------------

    There were five states (Alaska, Arizona, Delaware, South Dakota, 
and New Mexico) where the near-airport population had greater 
representation by Native Americans and Alaska Natives compared with the 
portion of the population they comprise at the state level by a 
difference of one percent or greater. In Alaska, the disparity in 
residential proximity to a runway was the largest: 16,020 Alaska 
Natives were estimated to live within 500 meters of a runway, 
representing 48 percent of the population within 500 meters of an 
airport runway. In contrast, Alaska Natives comprise 15 percent of the 
Alaska state population (Table 6).

[[Page 72388]]



 Table 6--The Native American and Alaska Native Population Within 500 Meters of an Airport Runway and the Native
                                 American and Alaska Native Population, by State
----------------------------------------------------------------------------------------------------------------
                                                                             Native American
                                        Percent Native     Percent Native       and Alaska      Native American
                State                    American and       American and    Native population      and Alaska
                                        Alaska Native      Alaska Native        within 500     Native population
                                      within 500 meters   within the state        meters          in the state
----------------------------------------------------------------------------------------------------------------
Alaska..............................                 48                 15             16,020            106,300
Arizona.............................                 18                  5              5,017            335,300
Delaware............................                  2                  1                112              5,900
New Mexico..........................                 21                 10              2,265            208,900
South Dakota........................                 22                  9              1,606             72,800
----------------------------------------------------------------------------------------------------------------

    In a separate analysis, the EPA focused on evaluating the potential 
for disparities in populations residing near the NPIAS airports. The 
EPA compared the demographic composition of people living within one 
kilometer of runways at 2,022 of the approximately 3,300 NPIAS airports 
with the demographic composition of people living at a distance of one 
to five kilometers from the same airports.195 196 In this 
analysis, over one-fourth of airports (i.e., 515) were identified at 
which children under five were more highly represented in the zero to 
one kilometer distance compared with the percent of children under five 
living one to five kilometers away (Table 7). There were 666 airports 
where people of color had a greater presence in the zero to one 
kilometer area closest to airport runways than in populations farther 
away. There were 761 airports where people living at less than two-
times the Federal Poverty Level represented a higher proportion of the 
overall population within one kilometer of airport runways compared 
with the proportion of people living at less than two times the Federal 
Poverty Level among people living one to five kilometers away.
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    \195\ For this analysis, we evaluated the 2,022 airports with a 
population of greater than 100 people inside the zero to one 
kilometer distance to avoid low population counts distorting the 
assessment of percent contributions of each group to the total 
population within the zero to one kilometer distance.
    \196\ Kamal et al., Memorandum to Docket EPA-HQ-OAR-2022-0389. 
Analysis of Potential Disparity in Residential Proximity to Airports 
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389. Methods used are described in this memo and include the 
use of block group resolution data to evaluate the representation of 
different demographic groups near-airport and for those living one 
to five kilometers away.

     Table 7--Number of Airports (Among the 2,022 Airports Evaluated) With Disparity for Certain Demographic
 Populations Within One Kilometer of an Airport Runway in Relation to the Comparison Population Between One and
                                     Five Kilometers From an Airport Runway
----------------------------------------------------------------------------------------------------------------
                                                        Number of airports with disparity
                                --------------------------------------------------------------------------------
       Demographic group          Total airports                   Disparity 5-    Disparity 10-
                                  with disparity  Disparity 1-5%        10%             20%       Disparity 20%+
----------------------------------------------------------------------------------------------------------------
Children under five years of                 515             507               7               1               0
 age...........................
People with income less than                 761             307             223             180              51
 twice the Federal Poverty
 Level.........................
People of Color (all non-White               666             377             126             123              40
 races, ethnicities and
 indigenous peoples)...........
Non-Hispanic Black.............              405             240              77              67              21
Hispanic.......................              551             402              85              47              17
Non-Hispanic Asian.............              268             243              18               4               3
Non-Hispanic Native American or              144             130               6               7               1
 Alaska Native \197\...........
Non-Hispanic Hawaiian or                      18              17               1               0               0
 Pacific Islander..............
Non-Hispanic Other Race........               11              11               0               0               0
Non-Hispanic Two or More Races.              226             226               0               0               0
----------------------------------------------------------------------------------------------------------------

    To understand the extent of the potential disparity among the 2,022 
NPIAS airports, Table 7 provides information about the distribution in 
the percent differences in the proportion of children, individuals with 
incomes below two times the Federal Poverty Level, and people of color 
living within one kilometer of a runway compared with those living one 
to five kilometers away. For children, Table 7 indicates that for the 
vast majority of these airports where there is a higher percentage of 
children represented in the near-airport population, differences are 
relatively small (e.g., less than five percent). For the airports where 
disparity is evident on the basis of poverty, race and ethnicity, the 
disparities are potentially large, ranging up to 42 percent for those 
with incomes below two times the Federal Poverty Level, and up to 45 
percent for people of color.\198\
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    \197\ This analysis of 2,022 NPIAS airports did not include 
airports in Alaska.
    \198\ Kamal et al., Memorandum to Docket EPA-HQ-OAR-2022-0389. 
Analysis of Potential Disparity in Residential Proximity to Airports 
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389.
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    There are uncertainties in the results provided here inherent to 
the proximity-based approach used. These uncertainties include the use 
of block group data to provide population numbers for each demographic 
group analyzed, and uncertainties in the Census data, including from 
the use of data from different analysis years (e.g., 2010 Census Data 
and 2018 income data). These uncertainties are described

[[Page 72389]]

and their implications discussed in Kamal et al. (2022).\199\
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    \199\ Kamal et al., Memorandum to Docket EPA-HQ-OAR-2022-0389. 
Analysis of Potential Disparity in Residential Proximity to Airports 
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389.
---------------------------------------------------------------------------

    The data summarized in this section indicate that there is a 
greater prevalence of children under five years of age, an at-risk 
population for lead effects, within 500 meters or one kilometer of some 
airports compared to more distant locations. This information also 
indicates that there is a greater prevalence of people of color and of 
low-income populations within 500 meters or one kilometer of some 
airports compared with people living more distant. If such differences 
were to contribute to disproportionate and adverse impacts on 
particular communities, they could indicate an EJ concern. Given the 
number of children in close proximity to runways, including those in 
communities with EJ concerns, there is a potential for substantial 
implications for children's health, depending on lead exposure levels 
and associated risk.
    Some commenters on the proposed findings expressed concern that 
communities in close proximity to general aviation airports are often 
low-income communities and communities of color who are 
disproportionately burdened by lead exposure.\200\ Some commenters also 
noted that children who attend school near airports may experience 
higher levels of exposure compared with children who attend school more 
distant from an airport, and they cite recent research reporting higher 
blood lead levels in children who attend school near one highly active 
general aviation airport.\201\ The EPA responds to these comments in 
the Response to Comments document for this action.
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    \200\ During the public comment period on the proposed findings 
for this action, commenters provided an additional evaluation of 
populations living near airports that they conclude to indicate that 
disparity by race and income is larger and occurs more frequently at 
airports that have the highest lead emissions and the highest 
residential population density compared with airports where less 
lead is emitted and population density is lower. This comment is 
available in the docket at regulations.gov: EPA-HQ-OAR-2022-0389-
0238.
    \201\ Zahran et al., 2022. Leaded Aviation Gasoline Exposure 
Risk and Child Blood Lead Levels. Proceedings of the National 
Academy of Sciences Nexus. 2:1-11.
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B. Federal Actions To Reduce Lead Exposure

    The Federal Government has a longstanding commitment to programs to 
reduce exposure to lead, particularly for children. In December 2018, 
the President's Task Force on Environmental Health Risks and Safety 
Risks to Children released the Federal Action Plan to Reduce Childhood 
Lead Exposures and Associated Health Impacts (Federal Lead Action 
Plan), detailing the Federal Government's commitments and actions to 
reduce lead exposure in children, some of which are described in this 
section.\202\ Building on the 2018 Federal Lead Action Plan, in October 
2022, the EPA finalized its Strategy to Reduce Lead Exposures and 
Disparities in U.S. Communities (Lead Strategy).\203\ The Lead Strategy 
describes the EPA-wide and government-wide approaches to strengthen 
public health protections, address legacy lead contamination for 
communities with the greatest exposures, and promote environmental 
justice. In this section, we describe some of the EPA's actions to 
reduce lead exposures from air, water, lead-based paint, and 
contaminated sites.
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    \202\ Federal Lead Action Plan to Reduce Childhood Lead 
Exposures and Associated Health Impacts. (2018) President's Task 
Force on Environmental Health Risks and Safety Risks to Children. 
Available at https://www.epa.gov/sites/default/files/2018-12/documents/fedactionplan_lead_final.pdf.
    \203\ EPA (2022) EPA Strategy to Reduce Lead Exposures and 
Disparities in U.S. Communities. EPA 540R22006. Available at https://www.epa.gov/system/files/documents/2022-11/Lead%20Strategy_1.pdf.
---------------------------------------------------------------------------

    In 1976, the EPA listed lead under CAA section 108, making it what 
is called a ``criteria air pollutant.'' \204\ Once lead was listed, the 
EPA issued primary and secondary NAAQS under sections 109(b)(1) and 
(2), respectively. The EPA issued the first NAAQS for lead in 1978 and 
revised the lead NAAQS in 2008 by reducing the level of the standard 
from 1.5 micrograms per cubic meter to 0.15 micrograms per cubic meter 
and revising the averaging time and form to an average over a 
consecutive three-month period, as described in 40 CFR 50.16.\205\ The 
EPA's 2016 Federal Register document describes the Agency's decision to 
retain the existing Lead NAAQS.\206\ The Lead NAAQS is currently 
undergoing review.\207\ \208\
---------------------------------------------------------------------------

    \204\ 41 FR 14921 (April 8, 1976). See also, e.g., 81 FR 71910 
(Oct. 18, 2016) for a description of the history of the listing 
decision for lead under CAA section 108.
    \205\ 73 FR 66965 (Nov. 12, 2008).
    \206\ 81 FR 71912-71913 (Oct. 18, 2016).
    \207\ Documents pertaining to the current review of the NAAQS 
for Lead can be found here: https://www.epa.gov/naaqs/lead-pb-air-quality-standards.
    \208\ The EPA released the ISA for Lead, External Review Draft, 
as part of the Agency's current review of the science regarding 
health and welfare effects of lead. EPA/600/R-23/061. This draft 
assessment is undergoing peer review by the Clean Air Scientific 
Advisory Committee (CASAC) and public comment, and is available at: 
https://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=357282.
---------------------------------------------------------------------------

    States are primarily responsible for ensuring attainment and 
maintenance of the NAAQS. Under section 110 of the Act and related 
provisions, states are to submit, for the EPA's review and, if 
appropriate, approval, state implementation plans that provide for the 
attainment and maintenance of such standards through control programs 
directed to sources of the pollutants involved.
    Additional EPA programs to address lead in the environment include 
the prohibition on gasoline containing lead or lead additives for 
highway use under section 211 of the Act; the new source performance 
standards under section 111 of the Act; and emissions standards for 
solid waste incineration units and the national emission standards for 
hazardous air pollutants (NESHAP) under sections 129 and 112 of the 
Act, respectively.
    The EPA has taken a number of actions associated with these air 
pollution control programs, including completion of several regulations 
requiring reductions in lead emissions from stationary sources 
regulated under the CAA sections 111, 112 and 129. For example, in 
January 2012, the EPA updated the NESHAP for the secondary lead 
smelting source category.\209\ These amendments to the original maximum 
achievable control technology standards apply to facilities nationwide 
that use furnaces to recover lead from lead-bearing scrap, mainly from 
automobile batteries. Regulations completed in 2013 for commercial and 
industrial solid waste incineration units also require reductions in 
lead emissions.\210\ In February 2023, the EPA finalized amendments to 
the NSPS (as a new subpart) and the Area Source NESHAP for the Lead 
Acid Battery Manufacturing source category.\211\ The amendments to the 
standards for affected processes including grid casting, lead 
reclamation, and paste mixing operations at lead acid battery 
facilities will result in reductions in lead emissions and improvements 
in compliance assurance measures.
---------------------------------------------------------------------------

    \209\ 77 FR 555 (Jan. 5, 2012).
    \210\ 78 FR 9112 (Feb. 7, 2013).
    \211\ 88 FR 11556 (Feb. 23, 2023).
---------------------------------------------------------------------------

    A broad range of Federal programs beyond those that focus on air 
pollution control provide for nationwide reductions in environmental 
releases and human exposures to lead. For example, pursuant to section 
1417 of the Safe Drinking Water Act (SDWA), any pipe, pipe or plumbing 
fitting or fixture, solder, or flux may not be used in new 
installations or repairs of any public water system or plumbing in a

[[Page 72390]]

residential or non-residential facility providing water for human 
consumption or introduced into commerce (except uses for manufacturing 
or industrial purposes) unless it is considered ``lead free'' as 
defined by that Act.\212\ The EPA's Lead and Copper Rule,\213\ first 
promulgated in 1991, regulates lead in public drinking water systems 
through a treatment technique that requires water systems to monitor 
drinking water at customer taps and, if an action level is exceeded, 
undertake a number of actions including those to control corrosion to 
minimize lead exposure.\214\ On January 15, 2021, the agency published 
the most recent revisions, the Lead and Copper Rule Revisions 
(LCRR),\215\ and subsequently reviewed the rule in accordance with 
Executive Order 13990.\216\ While the LCRR took effect in December 
2021, the agency concluded that there are significant opportunities to 
improve the LCRR.\217\ The EPA is developing a new proposed rule, the 
Lead and Copper Rule Improvements (LCRI),\218\ to further strengthen 
the lead drinking water regulations. The EPA identified priority 
improvements for the LCRI: proactive and equitable lead service line 
replacement (LSLR), strengthening compliance tap sampling to better 
identify communities most at risk of lead in drinking water and to 
compel lead reduction actions, and reducing the complexity of the 
regulation through improvement of the action and trigger level 
construct.\219\ The EPA intends to propose and promulgate the LCRI 
prior to October 16, 2024.
---------------------------------------------------------------------------

    \212\ Effective in Jan. 2014, the amount of lead permitted in 
pipes, fittings, and fixtures was lowered. See, section 1417 of the 
Safe Drinking Water Act: Prohibition on Use of Lead Pipes, Solder, 
and Flux at https://www.epa.gov/sdwa/use-lead-free-pipes-fittings-fixtures-solder-and-flux-drinking-water.
    \213\ 40 CFR part 141, subpart I (June 7, 1991).
    \214\ 40 CFR part 141, subpart I (June 7, 1991).
    \215\ 86 FR 4198. (Jan. 15, 2021).
    \216\ E.O. 13990. Protecting Public Health and the Environment 
and Restoring Science to Tackle the Climate Crisis. 86 FR 7037 (Jan. 
20, 2021).
    \217\ 86 FR 31939 (Dec. 17, 2021).
    \218\ See https://www.epa.gov/ground-water-and-drinking-water/review-national-primary-drinking-water-regulation-lead-and-copper. 
Accessed on Nov. 30, 2021.
    \219\ 86 FR 31939 (Dec. 17, 2021).
---------------------------------------------------------------------------

    While the EPA continues to improve regulatory actions to reduce 
lead exposure in drinking water, the EPA recognizes that directly 
assisting states and communities and providing dedicated funding 
provided in the Bipartisan Infrastructure Law for lead service line 
identification and replacement of full lead service lines (LSLs) is 
also important in safeguarding public health. The EPA is providing $15 
billion through the Drinking Water State Revolving Fund (DWSRF) 
dedicated exclusively to lead service line identification and 
replacement. In addition, $11.7 billion in DWSRF general supplemental 
funding, provided by the Bipartisan Infrastructure Law, is going to 
projects to improve drinking water quality, including those to reduce 
lead in drinking water. For this funding, states are required to 
provide 49% as additional subsidization in the form of principal 
forgiveness and/or grants. States must provide additional subsidization 
to water systems that meet the state's disadvantaged community criteria 
as described in section 1452(d) of SDWA, furthering the objectives of 
the Justice40 Initiative. In October 2022, the EPA announced projects 
selected to receive over $30 million in grant funding that will help 
communities and schools address lead in drinking water and remove lead 
pipes across the country in underserved and other disadvantaged 
communities through the Water Infrastructure Improvements for the 
Nation Act's Reducing Lead in Drinking Water grant program. The EPA 
recently announced the Lead Service Line Replacement Accelerators 
initiative which will provide targeted technical assistance to 
communities in Connecticut, Pennsylvania, New Jersey, and Wisconsin to 
support expanded access to funding and to accelerate lead pipe 
replacement. While the EPA is focusing initial efforts in four states, 
the Agency anticipates this work will serve as a roadmap for additional 
lead service line replacement efforts across the nation in the future.
    Federal programs to reduce exposure to lead in paint, dust, and 
soil are specified under the comprehensive Federal regulatory framework 
developed under the Residential Lead-Based Paint Hazard Reduction Act 
(Title X). Under Title X (codified, in part, as Title IV of the Toxic 
Substances Control Act [TSCA]), the EPA has established regulations and 
associated programs in six categories: (1) Training, certification and 
work practice requirements for persons engaged in lead-based paint 
activities (abatement, inspection and risk assessment); accreditation 
of training providers; and authorization of state and Tribal lead-based 
paint programs; (2) training, certification, and work practice 
requirements for persons engaged in home renovation, repair and 
painting (RRP) activities; accreditation of RRP training providers; and 
authorization of state and Tribal RRP programs; (3) ensuring that, for 
most housing constructed before 1978, information about lead-based 
paint and lead-based paint hazards flows from sellers to purchasers, 
from landlords to tenants, and from renovators to owners and occupants; 
(4) establishing standards for identifying dangerous levels of lead in 
paint, dust and soil; (5) providing grant funding to establish and 
maintain state and Tribal lead-based paint programs; and (6) providing 
information on lead hazards to the public, including steps that people 
can take to protect themselves and their families from lead-based paint 
hazards.
    The most recent rules issued under Title IV of TSCA revised the 
dust-lead hazard standards (DLHS) and dust-lead clearance levels (DLCL) 
which were established in a 2001 final rule entitled ``Identification 
of Dangerous Levels of Lead.'' \220\ The DLHS are incorporated into the 
requirements and risk assessment work practice standards in the EPA's 
Lead-Based Paint Activities Rule, codified at 40 CFR part 745, subpart 
L. They provide the basis for risk assessors to determine whether dust-
lead hazards are present in target housing (i.e., most pre-1978 
housing) and child-occupied facilities (pre-1978 nonresidential 
properties where children 6 years of age or under spend a significant 
amount of time such as daycare centers and kindergartens). If dust-lead 
hazards are present, the risk assessor will identify acceptable options 
for controlling the hazards in the respective property, which may 
include abatements and/or interim controls. In July 2019, the EPA 
published a final rule revising the DLHS from 40 micrograms per square 
foot and 250 micrograms per square foot to 10 micrograms per square 
foot and 100 micrograms per square foot of lead in dust on floors and 
windowsills, respectively.\221\ The DLCL are used to evaluate the 
effectiveness of a cleaning following an abatement. If the dust-lead 
levels are not below the clearance levels, the components (i.e., 
floors, windowsills, troughs) represented by the failed sample(s) shall 
be recleaned and retested. In January 2021, the EPA published a final 
rule revising the DLCL to match the DLHS, lowering them from 40 
micrograms per square foot and 250 micrograms per square foot to 10 
micrograms per square foot and 100 micrograms per square foot on floors 
and windowsills, respectively.\222\ The EPA is now reconsidering the 
2019 and 2021 rules in accordance with Executive Order 13990 \223\ and 
in response to a

[[Page 72391]]

May 2021 decision by U.S. Court of Appeals for the Ninth Circuit. In 
August 2023, EPA proposed updating the DLHS and DLCL again.\224\ If 
finalized as proposed, the DLHS for floors and window sills would be 
any reportable level greater than zero, as analyzed by any laboratory 
recognized by EPA's National Lead Laboratory Accreditation Program. The 
new DLCL would be 3 micrograms per square foot ([mu]g/ft\2\) for 
floors, 20 [mu]g/ft\2\ for window sills and 25 [mu]g/ft\2\ for window 
troughs.
---------------------------------------------------------------------------

    \220\ 66 FR 1206 (Jan. 5, 2001).
    \221\ 84 FR 32632 (July 9, 2019).
    \222\ 86 FR 983 (Jan. 7, 2021).
    \223\ 86 FR 7037 (Jan. 20, 2021).
    \224\ 88 FR 50444 (August 1, 2023).
---------------------------------------------------------------------------

    Programs associated with the Comprehensive Environmental Response, 
Compensation, and Liability Act (CERCLA or Superfund) \225\ and 
Resource Conservation Recovery Act (RCRA) \226\ also implement removal 
and remedial response programs that reduce or abate exposures to 
releases or threatened releases of lead and other hazardous substances. 
Furthermore, CERCLA section 104(a)(1) authorizes the EPA and other 
Federal agencies to respond to releases or threatened releases of 
pollutants or contaminants when the release, or potential release, may 
present an imminent and substantial danger to the public health or 
welfare. In addition, CERCLA section 104(a)(1) and the National Oil and 
Hazardous Substances Pollution Contingency Plan (NCP) authorize 
remedial investigations (e.g., monitoring, testing, information 
collection) and removal actions for hazardous substances, pollutants, 
or contaminants.
---------------------------------------------------------------------------

    \225\ For more information about the EPA's CERCLA program, see 
https://www.epa.gov/superfund.
    \226\ For more information about the EPA's RCRA program, see 
https://www.epa.gov/rcra.
---------------------------------------------------------------------------

    The EPA develops and implements protective levels for lead in soil 
(and other media when appropriate) at Superfund sites and, together 
with states, at RCRA corrective action facilities. The Office of Land 
and Emergency Management develops policy and guidance for addressing 
multimedia lead contamination and determining appropriate response 
actions at lead-contaminated sites. Federal programs, including those 
implementing RCRA, provide for management of hazardous substances such 
as lead in hazardous and municipal solid waste (e.g., 50 FR 28702, July 
15, 1985; 52 FR 45788, December 1, 1987).

C. Lead Endangerment Petitions for Rulemaking and the EPA Responses

    The Administrator's final findings further respond to several 
citizen petitions on this subject, including the following: petition 
for rulemaking submitted by Friends of the Earth in 2006, petition for 
rulemaking submitted by Friends of the Earth, Oregon Aviation Watch and 
Physicians for Social Responsibility in 2012, petition for 
reconsideration submitted by Friends of the Earth, Oregon Aviation 
Watch, and Physicians for Social Responsibility in 2014, and petition 
for rulemaking from Alaska Community Action on Toxics, Center for 
Environmental Health, Friends of the Earth, Montgomery-Gibbs 
Environmental Coalition, Oregon Aviation Watch, the County of Santa 
Clara, CA, and the Town of Middleton, WI, in 2021. These petitions and 
the EPA's responses are described more fully in the proposal for this 
action.227 228
---------------------------------------------------------------------------

    \227\ See https://www.epa.gov/regulations-emissions-vehicles-and-engines/petitions-and-epa-response-memorandums-related-lead.
    \228\ 87 FR 62772 (Oct. 17, 2022).
---------------------------------------------------------------------------

    In the most recent of these petitions, submitted in 2021, Alaska 
Community Action on Toxics, Center for Environmental Health, Friends of 
the Earth, Montgomery-Gibbs Environmental Coalition, Oregon Aviation 
Watch, the County of Santa Clara, CA, and the Town of Middleton, WI, 
again petitioned the EPA to conduct a proceeding under CAA section 231 
regarding whether lead emissions from piston-engine aircraft cause or 
contribute to air pollution that may reasonably be anticipated to 
endanger public health or welfare.\229\ The EPA responded in 2022 
noting our intent to develop a proposal under CAA section 231(a)(2)(A) 
regarding whether lead emissions from piston-engine aircraft cause or 
contribute to air pollution that may reasonably be anticipated to 
endanger public health or welfare, and, after evaluating public 
comments on the proposal, issue any final determination in 2023, as the 
Agency is doing in this action.\230\
---------------------------------------------------------------------------

    \229\ The 2021 petition is available at https://www.epa.gov/system/files/documents/2022-01/aviation-leaded-avgas-petition-exhibits-final-2021-10-12.pdf.
    \230\ EPA's response to the 2021 petition is available at 
https://www.epa.gov/system/files/documents/2022-01/ltr-response-aircraft-lead-petitions-aug-oct-2022-01-12.pdf.
---------------------------------------------------------------------------

III. Legal Framework for This Action

    In this action, the EPA is finalizing two separate determinations--
an endangerment finding and a cause or contribute finding--under 
section 231(a)(2)(A) of the Clean Air Act. The EPA has, most recently, 
finalized such findings under CAA section 231 for greenhouse gases 
(GHGs) in 2016 (2016 Findings), and in that action the EPA provided a 
detailed explanation of the legal framework for making such findings 
and the statutory interpretations and caselaw supporting its 
approach.\231\ In this final action, the Administrator used the same 
approach of applying a two-part test under section 231(a)(2)(A) as 
described in the 2016 Findings and relied on the same interpretations 
supporting that approach, which are briefly described in this section, 
and set forth in greater detail in the 2016 Findings.\232\ This is also 
the same approach that the EPA used in making endangerment and cause or 
contribute findings for GHGs under section 202(a) of the CAA in 2009 
(2009 Findings),\233\ which was affirmed by the U.S. Court of Appeals 
for the D.C. Circuit in 2012.\234\ As explained further in the 2016 
Findings, the text of the CAA section 231(a)(2)(A), which concerns 
aircraft emissions, mirrors the text of CAA section 202(a), which 
concerns motor vehicle emissions and which was the basis for the 2009 
Findings.235 236 Accordingly, for the same reasons as 
discussed in the 2016 Findings, the EPA believes it is reasonable to 
use the same approach under section 231(a)(2)(A)'s similar text as was 
used under section 202(a) for the 2009 Findings, and it is acting 
consistently with that framework for purposes of these final findings 
under section 231.\237\ As this approach has

[[Page 72392]]

been previously discussed at length in the 2016 Findings, as well as in 
the 2009 Findings, the EPA provides only a brief description in this 
final action.
---------------------------------------------------------------------------

    \231\ 81 FR 54422-54475 (Aug. 15, 2016).
    \232\ See e.g., 81 FR 55434-54440 (Aug. 15, 2016).
    \233\ 74 FR 66505-66510 (Dec. 15, 2009).
    \234\ Coalition for Responsible Regulation, Inc. v. EPA, 684 
F.3d 102 (D.C. Cir. 2012) (CRR) (rev'd in part on other grounds sub 
nom. Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014)). As 
discussed in greater detail in the 2016 Findings, the Supreme Court 
granted some of the petitions for certiorari that were filed on CRR, 
while denying others, but agreed to decide only the question: 
``Whether EPA permissibly determined that its regulation of 
greenhouse gas emissions from new motor vehicles triggered 
permitting requirements under the Clean Air Act for stationary 
sources that emit greenhouse gases.'' 81 FR 54422, 54442 (Aug. 15, 
2016). Thus, the Supreme Court did not disturb the D.C. Circuit's 
holding in CRR that affirmed the 2009 Endangerment Finding.
    \235\ For example, the text in CAA section 202(a) that was the 
basis for the 2009 Findings addresses ``the emission of any air 
pollutant from any class or classes of new motor vehicles or new 
motor vehicle engines, which in [the Administrator's] judgment 
cause, or contribute to, air pollution which may reasonably be 
anticipated to endanger public health or welfare.'' Similarly, 
section 231(a)(2)(A) concerns ``the emission of any air pollutant 
from any class or classes of aircraft engines which in [the 
Administrator's] judgment causes, or contributes to, air pollution 
which may reasonably be anticipated to endanger public health or 
welfare.'' Additional discussion of the parallels in the statutory 
text and legislative history between CAA section 202(a) and 
231(a)(2)(A) can be found in the 2016 Findings. See 81 FR 55434--
55437 (Aug. 15, 2016).
    \236\ 81 FR 55434 (Aug. 15, 2016).
    \237\ 81 FR 55434 (Aug. 15, 2016).
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A. Statutory Text and Basis for This Action

    Section 231(a)(2)(A) of the CAA provides that the ``Administrator 
shall, from time to time, issue proposed emission standards applicable 
to the emission of any air pollutant from any class or classes of 
aircraft engines which in his judgment causes, or contributes to, air 
pollution which may reasonably be anticipated to endanger public health 
or welfare.'' \238\ In this action, the EPA is addressing the predicate 
for regulatory action under CAA section 231 through a two-part test, 
which as noted previously, is the same as the test used in the 2016 
Findings under section 231 and in the 2009 Findings under section 202 
of the CAA.
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    \238\ Regarding ``welfare,'' the CAA states that ``[a]ll 
language referring to effects on welfare includes, but is not 
limited to, effects on soils, water, crops, vegetation, manmade 
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, whether caused by transformation, 
conversion, or combination with other air pollutants.'' CAA section 
302(h). Regarding ``public health,'' there is no definition of 
``public health'' in the Clean Air Act. The Supreme Court has 
discussed the concept of ``public health'' in the context of whether 
costs can be considered when setting NAAQS. Whitman v. American 
Trucking Ass'n, 531 U.S. 457 (2001). In Whitman, the Court imbued 
the term with its most natural meaning: ``the health of the 
public.'' Id. at 466.
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    As the first step of the two-part test, the Administrator must 
decide whether, in his judgment, the air pollution under consideration 
may reasonably be anticipated to endanger public health or welfare. As 
the second step, the Administrator must decide whether, in his 
judgment, emissions of an air pollutant from certain classes of 
aircraft engines cause or contribute to this air pollution. If the 
Administrator answers both questions in the affirmative, he will issue 
standards under section 231.\239\
---------------------------------------------------------------------------

    \239\ See Massachusetts v. EPA, 549 U.S. 497, 533 (2007) 
(interpreting an analogous provision in CAA section 202).
---------------------------------------------------------------------------

    In accordance with the EPA's interpretation of the text of section 
231(a)(2)(A), as described in the 2016 Findings, the phrase ``may 
reasonably be anticipated'' and the term ``endanger'' in section 
231(a)(2)(A) authorize, if not require, the Administrator to act to 
prevent harm and to act in conditions of uncertainty.\240\ They do not 
limit him to merely reacting to harm or to acting only when certainty 
has been achieved; indeed, the references to anticipation and to 
endangerment imply that the failure to look to the future or to less 
than certain risks would be to abjure the Administrator's statutory 
responsibilities. As the D.C. Circuit explained, the language ``may 
reasonably be anticipated to endanger public health or welfare'' in CAA 
section 202(a) requires a ``precautionary, forward-looking scientific 
judgment about the risks of a particular air pollutant, consistent with 
the CAA's precautionary and preventive orientation.'' \241\ The court 
determined that ``[r]equiring that the EPA find `certain' endangerment 
of public health or welfare before regulating greenhouse gases would 
effectively prevent the EPA from doing the job that Congress gave it in 
[section] 202(a)--utilizing emission standards to prevent reasonably 
anticipated endangerment from maturing into concrete harm.'' \242\ The 
same language appears in section 231(a)(2)(A), and the same 
interpretation applies in that context.
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    \240\ See 81 FR 54435 (Aug. 15, 2016).
    \241\ CRR, 684 F.3d at 122 (internal citations omitted) (June 
26, 2012).
    \242\ CRR, 684 F.3d at 122 (internal citations omitted) (June 
26, 2012).
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    Moreover, by instructing the Administrator to consider whether 
emissions of an air pollutant cause or contribute to air pollution in 
the second part of the two-part test, the Act makes clear that he need 
not find that emissions from any one sector or class of sources are the 
sole or even the major part of the air pollution considered. This is 
clearly indicated by the use of the term ``contribute.'' Further, the 
phrase ``in his judgment'' authorizes the Administrator to weigh risks 
and to consider projections of future possibilities, while also 
recognizing uncertainties and extrapolating from existing data.
    Finally, when exercising his judgment in making both the 
endangerment and cause-or-contribute findings, the Administrator 
balances the likelihood and severity of effects. Notably, the phrase 
``in his judgment'' modifies both ``may reasonably be anticipated'' and 
``cause or contribute.''
    Often, past endangerment and cause or contribute findings have been 
proposed concurrently with proposed standards under various sections of 
the CAA, including section 231.\243\ Comment has been taken on these 
proposed findings as part of the notice and comment process for the 
emission standards.\244\ However, there is no requirement that the 
Administrator propose or finalize the endangerment and cause or 
contribute findings concurrently with proposed standards and, most 
recently under section 231, the EPA made endangerment and cause or 
contribute findings for GHGs separate from, and prior to, proceeding to 
set standards.
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    \243\ 81 FR 54425 (Aug. 15, 2016).
    \244\ See, e.g., Rulemaking for non-road compression-ignition 
engines under section 213(a)(4) of the CAA, Proposed Rule at 58 FR 
28809, 28813-14 (May 17, 1993), Final Rule at 59 FR 31306, 31318 
(June 17, 1994); Rulemaking for highway heavy-duty diesel engines 
and diesel sulfur fuel under sections 202(a) and 211(c) of the CAA, 
Proposed Rule at 65 FR 35430 (June 2, 2000), and Final Rule at 66 FR 
5002 (Jan. 18, 2001).
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    As noted in the proposal,\245\ the Administrator is applying the 
procedural provisions of CAA section 307(d) to this action, pursuant to 
CAA section 307(d)(1)(V), which provides that the provisions of 307(d) 
apply to ``such other actions as the Administrator may determine.'' 
\246\ Any subsequent standard-setting rulemaking under CAA section 231 
would also be subject to the procedures under CAA section 307(d), as 
provided in CAA section 307(d)(1)(F) (applying the provisions of CAA 
section 307(d) to the promulgation or revision of any aircraft emission 
standard under CAA section 231). Thus, these final findings are subject 
to the same procedural requirements that would apply if the final 
findings were part of a standard-setting rulemaking.
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    \245\ 87 FR 62773-62774 (Oct. 17, 2022).
    \246\ As the Administrator is applying the provisions of CAA 
section 307(d) to this action under section 307(d)(1)(V), we need 
not determine whether those provisions would apply to this action 
under section 307(d)(1)(F).
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B. Considerations for the Endangerment and Cause or Contribute Analyses 
Under Section 231(a)(2)(A)

    In the context of this final action, the EPA understands section 
231(a)(2)(A) of the CAA to call for the Administrator to exercise his 
judgment and make two separate determinations: first, whether the 
relevant kind of air pollution (here, lead air pollution) may 
reasonably be anticipated to endanger public health or welfare, and 
second, whether emissions of any air pollutant from classes of the 
sources in question (here, any aircraft engine that is capable of using 
leaded aviation gasoline), cause or contribute to this air 
pollution.\247\
---------------------------------------------------------------------------

    \247\ See CRR, 684 F.3d at 117 (explaining two-part analysis 
under section 202(a)) (June 26, 2012).
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    This analysis entails a scientific judgment by the Administrator 
about the potential risks posed by lead emissions to public health and 
welfare. In this final action, the EPA used the same approach in making 
scientific judgments regarding endangerment as it has previously 
described in the 2016

[[Page 72393]]

Findings, and its analysis was guided by the same five principles that 
guided the Administrator's analysis in those Findings.\248\
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    \248\ See, e.g., 81 FR 54434-55435 (Aug. 15, 2016).
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    Similarly, the EPA took the same approach to the cause or 
contribute analysis as was previously explained in the 2016 
Findings.\249\ For example, as previously noted, section 231(a)(2)(A)'s 
instruction to consider whether emissions of an air pollutant cause or 
contribute to air pollution makes clear that the Administrator need not 
find that emissions from any one sector or class of sources are the 
sole or even the major part of an air pollution problem.\250\ Moreover, 
like the language in CAA section 202(a) that governed the 2009 
Findings, the statutory language in section 231(a)(2)(A) does not 
contain a modifier on its use of the term ``contribute.'' \251\ Unlike 
other CAA provisions, it does not require ``significant'' contribution. 
Compare, e.g., CAA sections 111(b); 213(a)(2), (4). Congress made it 
clear that the Administrator is to exercise his judgment in determining 
contribution, and authorized regulatory controls to address air 
pollution even if the air pollution problem results from a wide variety 
of sources.\252\ While the endangerment test looks at the air pollution 
being considered as a whole and the risks it poses, the cause or 
contribute test is designed to authorize the EPA to identify and then 
address what may well be many different sectors, classes, or groups of 
sources that are each part of the problem.\253\
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    \249\ See, e.g., 81 FR 54437-54438 (Aug. 15, 2016).
    \250\ See, e.g., 81 FR 54437-54438 (Aug. 15, 2016).
    \251\ See, e.g., 81 FR 54437-54438 (Aug. 15, 2016).
    \252\ See 81 FR 54437-54438 (Aug. 15, 2016).
    \253\ See 81 FR 54437-54438 (Aug. 15, 2016).
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    Moreover, as the EPA has previously explained, the Administrator 
has ample discretion in exercising his reasonable judgment and 
determining whether, under the circumstances presented, the cause or 
contribute criterion has been met.\254\ As noted in the 2016 Findings, 
in addressing provisions in section 202(a), the D.C. Circuit has 
explained that the Act at the endangerment finding step did not require 
the EPA to identify a precise numerical value or ``a minimum threshold 
of risk or harm before determining whether an air pollutant 
endangers.'' \255\ Accordingly, the EPA ``may base an endangerment 
finding on `a lesser risk of greater harm . . . or a greater risk of 
lesser harm' or any combination in between.'' \256\ As the language in 
section 231(a)(2)(A) is analogous to that in section 202(a), it is 
reasonable to apply this interpretation to the endangerment 
determination under section 231(a)(2)(A).\257\ Moreover, the logic 
underlying this interpretation supports the general principle that 
under CAA section 231 the EPA is not required to identify a specific 
minimum threshold of contribution from potentially subject source 
categories in determining whether their emissions ``cause or 
contribute'' to the endangering air pollution.\258\ The reasonableness 
of this principle is further supported by the fact that section 231 
does not impose on the EPA a requirement to find that such contribution 
is ``significant,'' let alone the sole or major cause of the 
endangering air pollution.\259\
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    \254\ See 81 FR 54437-54438 (Aug. 15, 2016).
    \255\ CRR, 684 F.3d at 122-123 (June 26, 2012).
    \256\ CRR, 684 F.3d at 122-123. (quoting Ethyl Corp., 541 F.2d 
at 18) (June 26, 2012).
    \257\ 81 FR 54438 (Aug. 15, 2016).
    \258\ 81 FR 54438 (Aug. 15, 2016).
    \259\ 81 FR 54438 (Aug. 15, 2016).
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    Finally, as also described in the 2016 Findings, there are a number 
of possible ways of assessing whether air pollutants cause or 
contribute to the air pollution which may reasonably be anticipated to 
endanger public health and welfare, and no single approach is required 
or has been used exclusively in previous cause or contribute 
determinations under title II of the CAA.\260\
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    \260\ See 81 FR 54462 (Aug. 15, 2016).
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C. Regulatory Authority for Emission Standards

    Though the EPA is not proposing standards in this final action, in 
issuing these final findings, the EPA becomes subject to a duty under 
CAA section 231 regarding emission standards applicable to emissions of 
lead from aircraft engines. As noted in section III.A. of this 
document, section 231(a)(2)(A) of the CAA directs the Administrator of 
the EPA to propose and promulgate emission standards applicable to the 
emission of any air pollutant from classes of aircraft engines which in 
his or her judgment causes or contributes to air pollution that may 
reasonably be anticipated to endanger public health or welfare.
    CAA section 231(a)(2)(B) further directs the EPA to consult with 
the Administrator of the FAA on such standards, and it prohibits the 
EPA from changing aircraft emission standards if such a change would 
significantly increase noise and adversely affect safety. CAA section 
231(a)(3) provides that after we provide an opportunity for a public 
hearing on standards, the Administrator shall issue standards ``with 
such modifications as he deems appropriate.'' In addition, under CAA 
section 231(b), the effective date of any standards shall provide the 
necessary time to permit the development and application of the 
requisite technology, giving appropriate consideration to the cost of 
compliance, as determined by the EPA in consultation with the U.S. 
Department of Transportation (DOT).
    Once the EPA adopts standards, CAA section 232 then directs the 
Secretary of DOT to prescribe regulations to ensure compliance with the 
EPA's standards. Finally, section 233 of the CAA vests the authority to 
promulgate emission standards for aircraft or aircraft engines only in 
the Federal Government. States are preempted from adopting or enforcing 
any standard respecting aircraft or aircraft engine emissions unless 
such standard is identical to the EPA's standards.\261\
---------------------------------------------------------------------------

    \261\ CAA section 233.
---------------------------------------------------------------------------

D. Response to Certain Comments on the Legal Framework for This Action

    In commenting on the legal framework for this action, some 
commenters assert that the EPA does have authority under CAA section 
231(a)(2)(A) to both find that lead air pollution may reasonably be 
anticipated to endanger the public health and welfare and to find that 
engine emissions of lead from certain aircraft cause or contribute to 
the lead air pollution that may reasonably be anticipated to endanger 
the public health and welfare. We agree with these comments.
    Other commenters assert that the EPA does not have the legal 
authority to proceed with this proposal or regulate aviation fuel. 
These commenters state that Congress excluded aircraft from the CAA of 
1970, that the EPA does not have authority to regulate aircraft fuel 
(citing a regulatory definition of ``transportation fuel'' in 40 CFR 
80.1401) and that aircraft are not motor vehicles (citing a regulatory 
definition of ``motor vehicles'' in 40 CFR 85.1703). These commenters 
say that the definitions of transportation fuel and motor vehicles were 
not changed through 1977 or 1990 amendments to the CAA. Additionally, 
commenters assert that the ``EPA points to findings for Green House 
Gases (GHGs) under section 202(a) supportive of its proposed 
authority,'' quoting that section and emphasizing the terms ``new motor 
vehicles'' and ``new motor vehicle engines'' which are used in it.
    In response, the EPA notes that these commenters have fundamentally 
misunderstood the nature of this action and the legal authority upon 
which it relies. These final findings do not

[[Page 72394]]

establish regulatory standards for leaded avgas, nor are they related 
in any way to the regulatory definitions of transportation fuels in 40 
CFR 80.1401 or of motor vehicles in 40 CFR 85.1703, which implement EPA 
programs under Part A of Title II of the CAA and do not apply to 
aircraft that are governed by Part B of Title II. EPA's regulatory 
provisions implementing Title II Part B and related to air pollution 
from aircraft are found in 40 CFR parts 87, 1030, and 1031. The EPA's 
authority for this action is not based on its authority to regulate 
fuels under CAA section 211 or its authority to regulate motor vehicles 
or motor vehicle engines under CAA section 202(a). Rather, the EPA's 
authority for this action comes from CAA section 231(a)(2). Further, 
this action is focused on the threshold endangerment and cause or 
contribute criteria, which are being undertaken in proceedings that are 
separate and distinct from any follow-on regulatory action; no 
regulatory provisions were proposed and none are being finalized in 
this action.
    In response to the claims that aircraft are excluded from the CAA 
and that the EPA does not have authority to conduct this endangerment 
and cause or contribute finding, we disagree. As described in the 
proposal, the EPA is acting under the express authority prescribed by 
Congress in section 231(a)(2)(A) of the CAA, which, as amended, 
provides that the Administrator ``shall, from time to time, issue 
proposed emission standards applicable to the emission of any air 
pollutant from any class or classes of aircraft engines which in his 
judgment causes, or contributes to, air pollution which may reasonably 
be anticipated to endanger public health or welfare.'' The D.C. Circuit 
recognized EPA's authority to promulgate emission standards applicable 
to air pollutants from aircraft engines under CAA section 231 in 
National Association of Clean Air Agencies v. EPA, 489 F.3d 1221 (D.C. 
Cir. 2007) (``NACAA''). Similarly, in the 1970 amendments to the CAA, 
section 231(a)(2) provided that the Administrator ``shall issue 
proposed emission standards applicable to emissions of any air 
pollutant from any class or classes of aircraft or aircraft engines 
which in his judgment cause or contribute to or are likely to cause or 
contribute to air pollution which endangers the public health or 
welfare.'' Public Law 91-604. Thus, the statement in the comment that 
the 1970 CAA excluded aircraft is incorrect.\262\ Further, the EPA has 
previously made endangerment and cause or contribute findings related 
to emissions from aircraft engines under section 231 of the CAA.
---------------------------------------------------------------------------

    \262\ The change to the current language in section 231(a)(2) 
occurred in 1977, see Clean Air Act Amendments of 1977, Public Law 
95-95, 91 Stat. 685, 791 (1977).
---------------------------------------------------------------------------

    As explained in the proposal, and in section III. above, in this 
action the Administrator is using the same approach of applying a two-
part test under section 231(a)(2)(A) as described in the finalized 
endangerment and cause or contribute findings under CAA section 231 for 
greenhouse gases (GHGs) emissions from aircraft in 2016.\263\ We 
further explained that this approach is the same approach that the EPA 
used in making endangerment and cause and contribute findings for GHGs 
under section 202(a) of the CAA in 2009 (2009 Findings), which is 
reasonable in light of the parallels of the language and structure 
between sections 231(a)(2)(A) and 202(a)(1) of the CAA.\264\ Some 
comments misconstrued EPA's discussion of section 202(a) in the 
proposal to infer that EPA was relying on its authority under section 
202(a) in this action. That is not the case. While using the same 
approach as in the 2009 Findings, the EPA is not acting under the 
authority of section 202(a) in making these final findings, but rather, 
is relying on the authority under section 231(a)(2)(A) as described 
herein, which expressly authorizes regulation of emissions of air 
pollutants from aircraft engines which the Administrator judges to 
cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health or welfare.
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    \263\ See e.g., 81 FR 55434-54440 (Aug. 15, 2016).
    \264\ 74 FR 66496, 66505-10 (Dec. 15, 2009); see also Coalition 
for Responsible Regulation, Inc. v. EPA, 684 F.3d 102 (D.C. Cir. 
2012) (CRR) (subsequent history omitted) (affirming EPA's approach 
in the 2009 Findings).
---------------------------------------------------------------------------

    Additional commenters state that they are opposed to any rulemaking 
that could lead to the elimination of leaded avgas before a 
comparatively priced substitute fuel is available for widespread use. 
As an initial matter, the EPA notes that, as described in section 
III.A. of this document, in this action, the EPA is addressing the 
predicate to regulatory action under CAA section 231 through a two-part 
test. In the first step of the two-part test, the Administrator must 
decide whether, in his judgment, the air pollution under consideration 
may reasonably be anticipated to endanger public health or welfare. As 
the second step, the Administrator must decide whether, in his 
judgment, emissions of an air pollutant from certain classes of 
aircraft engines cause or contribute to this air pollution. If the 
Administrator answers both questions in the affirmative, as he is doing 
here, the EPA becomes subject to a duty to propose and promulgate 
standards under section 231, but the EPA is not proposing or 
promulgating any standards in this action. These commenters have 
concerns regarding the cost and availability of unleaded fuels that 
might be required to meet a future emission standard for lead. To 
reiterate, the EPA is not proposing or promulgating any standards in 
this action, nor is the EPA reaching any conclusions about the possible 
elimination of leaded avgas or the cost or availability of 
comparatively priced substitute fuels; those issues will be addressed, 
if at all, only in a future standard-setting rulemaking. As for future 
standards, the delegation of authority in CAA section 231 to the EPA 
``is both explicit and extraordinarily broad,'' NACAA, 489 F.3d at 
1229, and ``confer[s] broad discretion to the [EPA] Administrator to 
weigh various factors in arriving at appropriate standards,'' id. at 
1230. However, as described in section III.C. of this document, CAA 
section 231(a)(2)(B) directs the EPA to consult with the Administrator 
of the FAA on such standards, and it prohibits the EPA from changing 
aircraft emission standards if such a change would significantly 
increase noise and adversely affect safety. Further, under CAA section 
231(b), the effective date of any standards shall provide the necessary 
time to permit the development and application of the requisite 
technology, giving appropriate consideration to the cost of compliance, 
as determined by the EPA in consultation with the U.S. Department of 
Transportation (DOT).

IV. The Final Endangerment Finding Under CAA Section 231

    In this action, the Administrator finds that lead air pollution may 
reasonably be anticipated to endanger the public health and welfare 
within the meaning of CAA section 231(a)(2)(A). This section discusses 
both the public health and welfare aspects of the endangerment finding 
and describes the scientific evidence that informs the Administrator's 
final determination. The vast majority of comments supported the EPA's 
proposal and agreed with the EPA's description of the health and 
welfare effects of lead air pollution. The Agency's responses to public 
comments on the proposed endangerment finding, including those opposing 
finalizing the finding, can be

[[Page 72395]]

found in the Response to Comments document for this action. After 
consideration of the comments on this topic, the EPA concludes that the 
scientific evidence supports finalizing the finding as proposed.

A. Scientific Basis of the Endangerment Finding

1. Lead Air Pollution
    Lead is emitted and exists in the atmosphere in a variety of forms 
and compounds and is emitted by a wide range of sources.\265\ Lead is 
persistent in the environment. Atmospheric transport distances of 
airborne lead vary depending on its form and particle size, as 
discussed in section II.A. of this document, with coarse lead-bearing 
particles deposited to a greater extent near the source, while fine 
lead-bearing particles can be transported long distances before being 
deposited. Through atmospheric deposition, lead is distributed to other 
environmental media, including soils and surface water bodies.\266\ 
Lead is retained in soils and sediments, where it provides a historical 
record and, depending on several factors, can remain available in some 
areas for extended periods for environmental or human exposure, with 
any associated potential public health and public welfare impacts.
---------------------------------------------------------------------------

    \265\ EPA (2013) ISA for Lead. Section 2.2. ``Sources of 
Atmospheric Pb.'' p. 2-1. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
    \266\ EPA (2013) ISA for Lead. Executive Summary. ``Sources, 
Fate and Transport of Lead in the Environment, and the Resulting 
Human Exposure and Dose.'' pp. lxxviii-lxxix. EPA, Washington, DC, 
EPA/600/R-10/075F, 2013.
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    For purposes of this action, the EPA defines the ``air pollution'' 
referred to in section 231(a)(2)(A) of the CAA as lead, which we also 
refer to as lead air pollution in this document.\267\
---------------------------------------------------------------------------

    \267\ The lead air pollution can occur as elemental lead or in 
lead-containing compounds, and this definition of the air pollution 
recognizes that lead in air (whatever form it is found in, including 
in inorganic and organic compounds containing lead) has the 
potential to elicit public health and welfare effects. We note, for 
example, that the 2013 Lead ISA and 2008 AQCD described the 
toxicokinetics of inorganic and organic forms of lead and studies 
evaluating lead-related health effects commonly measure total lead 
level (i.e., all forms of lead in various biomarker tissues such as 
blood).
---------------------------------------------------------------------------

2. Health Effects and Lead Air Pollution
    In 2013, the EPA completed the Integrated Science Assessment for 
Lead which built on the findings of previous AQCDs for Lead. These 
documents critically assess and integrate relevant scientific 
information regarding the health and welfare effects of lead and have 
undergone extensive critical review by the EPA, the Clean Air 
Scientific Advisory Committee (CASAC), and the public. As such, these 
assessments provide the primary scientific and technical basis for the 
Administrator's finding that lead air pollution is reasonably 
anticipated to endanger public health and welfare.268 269
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    \268\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-
10/075F, 2013.
    \269\ EPA (2006) Air Quality Criteria for Lead. EPA, Washington, 
DC, EPA/600/R-5/144aF, 2006.
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    As summarized in section II.A. of this document, human exposure to 
lead that is emitted into the air can occur by multiple pathways. 
Inhalation pathways include both ambient air outdoors and ambient air 
that has infiltrated into indoor environments. Additional exposure 
pathways may involve media other than air, including indoor and outdoor 
dust, soil, surface water and sediments, vegetation and biota. The 
bioavailability of air-related lead is modified by several factors in 
the environment (e.g., the chemical form of lead, environmental fate of 
lead emitted to air). That notwithstanding, as described in section 
II.A. of this document, it is well-documented that exposures to lead 
emitted into the air can result in increased blood lead levels, 
particularly for children living near air lead sources, due to their 
proximity to these sources of exposure.\270\
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    \270\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
40. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    As described in the EPA's 2013 Lead ISA and in prior AQCDs, lead 
has been demonstrated to exert a broad array of deleterious effects on 
multiple organ systems. The 2013 Lead ISA characterizes the causal 
nature of relationships between lead exposure and health effects using 
a weight-of-evidence approach.\271\ We summarize here those health 
effects for which the EPA in the 2013 Lead ISA has concluded that the 
evidence supports a determination of either a ``causal relationship,'' 
``likely to be causal relationship,'' or ``suggestive of a causal 
relationship'' between lead exposure and a health effect.\272\ In the 
discussion that follows, we summarize findings regarding effects 
observed in children, effects observed in adults, and additional 
effects observed that are not specific to an age group.
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    \271\ The causal framework draws upon the assessment and 
integration of evidence from across scientific disciplines, spanning 
atmospheric chemistry, exposure, dosimetry and health effects 
studies (i.e., epidemiologic, controlled human exposure, and animal 
toxicological studies), and assessment of the related uncertainties 
and limitations that ultimately influence our understanding of the 
evidence. This framework employs a five-level hierarchy that 
classifies the overall weight of evidence with respect to the causal 
nature of relationships between criteria pollutant exposures and 
health and welfare effects using the following categorizations: 
causal relationship; likely to be causal relationship; suggestive 
of, but not sufficient to infer, a causal relationship; inadequate 
to infer the presence or absence of a causal relationship; and not 
likely to be a causal relationship. EPA (2013) ISA for Lead. 
Preamble section. p. xliv. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
    \272\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal 
determinations for the relationship between exposure to Pb and 
health effects.'' pp. lxxxiii-lxxxvii. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
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    The EPA has concluded that there is a ``causal relationship'' 
between lead exposure during childhood (pre and postnatal) and a range 
of health effects in children, including the following: cognitive 
function decrements; the group of externalizing behaviors comprising 
attention, increased impulsivity, and hyperactivity; and developmental 
effects (i.e., delayed pubertal onset).\273\ In addition, the EPA has 
concluded that the evidence supports a conclusion that there is a 
``likely to be causal relationship'' between lead exposure and conduct 
disorders in children and young adults, internalizing behaviors such as 
depression, anxiety and withdrawn behavior, auditory function 
decrements, and fine and gross motor function decrements.\274\
---------------------------------------------------------------------------

    \273\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal 
determinations for the relationship between exposure to Pb and 
health effects.'' p. lxxxiii and p. lxxxvi. EPA, Washington, DC, 
EPA/600/R-10/075F, 2013.
    \274\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal 
determinations for the relationship between exposure to Pb and 
health effects.'' pp. lxxxiii-lxxxiv. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
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    Multiple epidemiologic studies conducted in diverse populations of 
children consistently demonstrate the harmful effects of lead exposure 
on cognitive function (as measured by decrements in intelligence 
quotient [IQ], decreased academic performance, and poorer performance 
on tests of executive function). These findings are supported by 
extensively documented toxicological evidence substantiating the 
plausibility of these findings in the epidemiological literature and 
provide information on the likely mechanisms underlying these 
neurotoxic effects.\275\
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    \275\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
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    Intelligence quotient is a well-established, and among the most 
rigorously standardized, cognitive function measure that has been used 
extensively as a measure of the negative

[[Page 72396]]

effects of exposure to lead.276 277 Examples of other 
measures of cognitive function negatively associated with lead exposure 
include measures of intelligence and cognitive development and 
cognitive abilities, such as learning, memory, and executive functions, 
as well as academic performance and achievement.\278\
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    \276\ EPA (2013) ISA for Lead. Section 4.3.2. ``Cognitive 
Function.'' p. 4-59. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \277\ EPA (2006) Air Quality Criteria for Lead. Sections 6.2.2 
and 8.4.2. EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \278\ EPA (2013) ISA for Lead. Section 4.3.2. ``Cognitive 
Function.'' p. 4-59. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
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    In summarizing the evidence relating neurocognitive effects to lead 
exposure metrics, the 2013 Lead ISA notes that ``in individual studies, 
postnatal (early childhood and concurrent) blood [lead] levels are also 
consistently associated with cognitive function decrements in children 
and adolescents.'' 279 280 The 2013 Lead ISA additionally 
notes that the findings from experimental animal studies indicate that 
lead exposures during multiple early lifestages and periods are 
observed to induce impairments in learning, and that these findings 
``are consistent with the understanding that the nervous system 
continues to develop (i.e., synaptogenesis and synaptic pruning remains 
active) throughout childhood and into adolescence.'' \281\ The 2013 
Lead ISA further notes that ``it is clear that [lead] exposure in 
childhood presents a risk; further, there is no evidence of a threshold 
below which there are no harmful effects on cognition from [lead] 
exposure,'' and additionally recognizes uncertainty about the patterns 
of [lead] exposure that contribute to the blood [lead] levels analyzed 
in epidemiologic studies (uncertainties which are greater in studies of 
older children and adults than in studies of younger children who do 
not have lengthy exposure histories).\282\ Evidence suggests that while 
some neurocognitive effects of lead in children may be transient, some 
lead-related cognitive effects may be irreversible and persist into 
adulthood,\283\ potentially affecting lower educational attainment and 
financial well-being.\284\
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    \279\ In this statement, the term ``concurrent'' is referring to 
blood lead measurements that were taken concurrently with the 
neurocognitive testing.
    \280\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and 
Neurodevelopmental Deficits in Children.'' p. 1-76. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
    \281\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and 
Neurodevelopmental Deficits in Children.'' p. 1-76. EPA/600/R-10/
075F, 2013.
    \282\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
    \283\ EPA (2013) ISA for Lead. Section 1.9.5. ``Reversibility 
and Persistence of Neurotoxic Effects of Pb.'' p. 1-76. EPA, 
Washington, DC, EPA/600/R-10/075F, 2013.
    \284\ EPA (2013) ISA for Lead. Section 4.3.14. ``Public Health 
Significance of Associations between Pb Biomarkers and 
Neurodevelopmental Effects.'' p. 4-279. EPA, Washington, DC, EPA/
600/R-10/075F, 2013.
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    The 2013 Lead ISA concluded that neurodevelopmental effects in 
children were among the effects best substantiated as occurring at the 
lowest blood lead levels, and that these categories of effects were 
clearly of the greatest concern with regard to potential public health 
impact.\285\ For example, in considering population risk, the 2013 Lead 
ISA notes that ``[s]mall shifts in the population mean IQ can be highly 
significant from a public health perspective.'' \286\ Specifically, if 
lead-related decrements are manifested uniformly across the range of IQ 
scores in a population, ``a small shift in the population mean IQ may 
be significant from a public health perspective because such a shift 
could yield a larger proportion of individuals functioning in the low 
range of the IQ distribution, which is associated with increased risk 
of educational, vocational, and social failure'' as well as a decrease 
in the proportion with high IQ scores.\287\
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    \285\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
    \286\ EPA (2013) ISA for Lead. Executive Summary. ``Public 
Health Significance.'' p. xciii. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \287\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
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    With regard to lead effects identified for the adult population, 
the 2013 Lead ISA concluded that there is a ``causal relationship'' 
between lead exposure and hypertension and coronary heart disease in 
adults. The 2013 Lead ISA concluded that cardiovascular effects in 
adults were those of greatest public health concern for adults because 
the evidence indicated that these effects occurred at the lowest blood 
lead levels, compared to other health effects, although it further 
noted that the role of past versus recent exposures to lead is 
unclear.\288\
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    \288\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
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    With regard to evidence of cardiovascular effects and other effects 
of lead on adults, the 2013 Lead ISA notes that ``[a] large body of 
evidence from both epidemiologic studies of adults and experimental 
studies in animals demonstrates the effect of long-term [lead] exposure 
on increased blood pressure and hypertension.'' \289\ In addition to 
its effect on blood pressure, ``[lead] exposure can also lead to 
coronary heart disease and death from cardiovascular causes and is 
associated with cognitive function decrements, symptoms of depression 
and anxiety, and immune effects in adult humans.'' \290\ The extent to 
which the effects of lead on the cardiovascular system are reversible 
is not well characterized. Additionally, the frequency, timing, level, 
and duration of lead exposure causing the effects observed in adults 
has not been pinpointed, and higher exposures earlier in life may play 
a role in the development of health effects measured later in 
life.\291\ The 2013 Lead ISA states that ``[i]t is clear however, that 
[lead] exposure can result in harm to the cardiovascular system that is 
evident in adulthood and may also affect a broad array of organ 
systems.'' \292\ In summarizing the public health significance of lead 
on the adult population, the 2013 Lead ISA notes that ``small [lead]-
associated increases in the population mean blood pressure could result 
in an increase in the proportion of the population with hypertension 
that is significant from a public health perspective.'' \293\
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    \289\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \290\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \291\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \292\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \293\ EPA (2013) ISA for Lead. Executive Summary. ``Public 
Health Significance.'' p. xciii. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
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    In addition to the effects summarized here, the EPA has concluded 
there is a ``likely to be causal relationship'' between lead exposure 
and both cognitive function decrements and psychopathological effects 
in adults. The 2013 Lead ISA also concludes that there is a ``causal 
relationship'' between lead exposure and decreased red blood cell 
survival and function, altered heme synthesis, and male reproductive 
function. The EPA has also concluded there is a ``likely to be causal 
relationship'' between lead exposure and decreased host resistance, 
resulting in increased susceptibility to bacterial infection and 
suppressed delayed type hypersensitivity, and cancer.\294\
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    \294\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal 
determinations for the relationship between exposure to Pb and 
health effects.'' pp. lxxxiv-lxxxvii. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.

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[[Page 72397]]

    Additionally, in 2013 EPA concluded that the evidence is 
``suggestive of a causal relationship'' between lead exposure and some 
additional effects. These include auditory function decrements in 
adults and subclinical atherosclerosis, reduced kidney function, birth 
outcomes (e.g., low birth weight, spontaneous abortion), and female 
reproductive function.\295\
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    \295\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal 
determinations for the relationship between exposure to Pb and 
health effects.'' pp. lxxxiv-lxxxvi. EPA, Washington, DC, EPA/600/R-
10/075F, 2013.
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    The EPA has identified factors that may increase the risk of health 
effects of lead exposure due to susceptibility and/or vulnerability; 
these are termed ``at-risk'' factors. The 2013 Lead ISA describes the 
systematic approach the EPA uses to evaluate the coherence of evidence 
to determine the biological plausibility of associations between at-
risk factors and increased vulnerability and/or susceptibility. An 
overall weight of evidence is used to determine whether a specific 
factor results in a population being at increased risk of lead-related 
health effects.\296\ The 2013 Lead ISA concludes that ``there is 
adequate evidence that several factors--childhood, race/ethnicity, 
nutrition, residential factors, and proximity to [lead] sources--confer 
increased risk of lead-related health effects.'' \297\
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    \296\ EPA (2013) ISA for Lead. Chapter 5. ``Approach to 
Classifying Potential At-Risk Factors.'' p. 5-2. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
    \297\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
44. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
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3. Welfare Effects and Lead Air Pollution
    The 2013 Lead ISA characterizes the causal nature of relationships 
between lead exposure and welfare effects using a five-level hierarchy 
that classifies the overall weight of evidence.\298\ We summarize here 
the welfare effects for which the EPA has concluded that the evidence 
supports a determination of either a ``causal relationship,'' or a 
``likely to be causal relationship,'' with exposure to lead, or that 
the evidence is ``suggestive of a causal relationship'' with lead 
exposure. The discussion that follows is organized to first provide a 
summary of the effects of lead in the terrestrial environment, followed 
by a summary of effects of lead in freshwater and saltwater ecosystems. 
The 2013 Lead ISA further describes the scales or levels at which these 
determinations between lead exposure and effects on plants, 
invertebrates, and vertebrates were made (i.e., community-level, 
ecosystem-level, population-level, organism-level or sub-organism 
level).\299\
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    \298\ Causal determinations for ecological effects were based on 
integration of information on biogeochemistry, bioavailability, 
biological effects, and exposure-response relationships of lead in 
terrestrial, freshwater, and saltwater environments. This framework 
employs a five-level hierarchy that classifies the overall weight of 
evidence with respect to the causal nature of relationships between 
criteria pollutant exposures and health and welfare effects using 
the categorizations described in the 2013 Lead NAAQS.
    \299\ EPA (2013) ISA for Lead. Table ES-2. ``Schematic 
representation of the relationships between the various MOAs by 
which Pb exerts its effects.'' p. lxxxii. EPA, Washington, DC, EPA/
600/R-10/075F, 2013.
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    In terrestrial environments, the EPA determined that ``causal 
relationships'' exist between lead exposure and reproductive and 
developmental effects in vertebrates and invertebrates, growth in 
plants, survival for invertebrates, hematological effects in 
vertebrates, and physiological stress in plants.\300\ The EPA also 
determined that there were ``likely to be causal relationships'' 
between lead exposure and community and ecosystem effects, growth in 
invertebrates, survival in vertebrates, neurobehavioral effects in 
invertebrates and vertebrates, and physiological stress in 
invertebrates and vertebrates.
---------------------------------------------------------------------------

    \300\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal 
determinations for the relationship between Pb exposure and effects 
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    In freshwater environments, the EPA found that ``causal 
relationships'' exist between lead exposure and reproductive and 
developmental effects in vertebrates and invertebrates, growth in 
invertebrates, survival for vertebrates and invertebrates, and 
hematological effects in vertebrates. The EPA also determined that 
there were ``likely to be causal relationships'' between lead exposure 
and community and ecosystem effects, growth in plants, neurobehavioral 
effects in invertebrates and vertebrates, hematological effects in 
invertebrates, and physiological stress in plants, invertebrates, and 
vertebrates.\301\
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    \301\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal 
determinations for the relationship between Pb exposure and effects 
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    The EPA also determined that the evidence for saltwater ecosystems 
was ``suggestive of a causal relationship'' between lead exposure and 
reproductive and developmental effects in invertebrates, hematological 
effects in vertebrates, and physiological stress in invertebrates.\302\
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    \302\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal 
determinations for the relationship between Pb exposure and effects 
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    The 2013 Lead ISA concludes, ``With regard to the ecological 
effects of [lead], uptake of [lead] into fauna and subsequent effects 
on reproduction, growth and survival are established and are further 
supported by more recent evidence. These may lead to effects at the 
population, community, and ecosystem level of biological organization. 
In both terrestrial and aquatic organisms, gradients in response are 
observed with increasing concentration of [lead] and some studies 
report effects within the range of [lead] detected in environmental 
media over the past several decades. Specifically, effects on 
reproduction, growth, and survival in sensitive freshwater 
invertebrates are well-characterized from controlled studies at 
concentrations at or near [lead] concentrations occasionally 
encountered in U.S. fresh surface waters. Hematological and stress 
related responses in some terrestrial and aquatic species were also 
associated with elevated [lead] levels in polluted areas. However, in 
natural environments, modifying factors affect [lead] bioavailability 
and toxicity and there are considerable uncertainties associated with 
generalizing effects observed in controlled studies to effects at 
higher levels of biological organization. Furthermore, available 
studies on community and ecosystem-level effects are usually from 
contaminated areas where [lead] concentrations are much higher than 
typically encountered in the environment. The contribution of 
atmospheric [lead] to specific sites is not clear and the connection 
between air concentration of [lead] and ecosystem exposure continues to 
be poorly characterized.'' \303\
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    \303\ EPA (2013) ISA for Lead. ``Summary.'' p. xcvi. EPA, 
Washington, DC, EPA/600/R-10/075F, 2013.
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B. Final Endangerment Finding

    The Administrator finds, for purposes of CAA section 231(a)(2)(A), 
that lead air pollution may reasonably be anticipated to endanger the 
public health and welfare. This finding is based on consideration of 
the extensive scientific evidence, described in this section, that has 
been amassed over decades and rigorously peer reviewed by CASAC, as 
well as consideration of public comments on the proposal.

V. The Final Cause or Contribute Finding Under CAA Section 231

    In this action, the Administrator finds that engine emissions of 
lead from

[[Page 72398]]

certain aircraft cause or contribute to the lead air pollution that may 
reasonably be anticipated to endanger public health and welfare under 
section 231(a)(2)(A) of the Clean Air Act. This section describes the 
definition of the air pollutant and the data and information supporting 
the Administrator's final determination. Public comments on the cause 
or contribute finding were largely supportive of the EPA's proposal, 
though some commenters opposed finalizing the finding. After 
consideration of the comments on this topic, the EPA concludes that the 
scientific evidence supports finalizing the finding as proposed. The 
Agency's responses to certain public comments on the cause or 
contribute finding can be found in section V.C. of this document, and 
responses to additional comments on the cause or contribute finding can 
be found in the Response to Comments document for this action.

A. Definition of the Air Pollutant

    Under section 231, the Administrator is to determine whether 
emissions of any air pollutant from any class or classes of aircraft 
engines cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health or welfare. As in the 2016 
Findings that the EPA made under section 231 for greenhouse gases, in 
making this cause or contribute finding under section 231(a)(2), the 
Administrator first defines the air pollutant being evaluated. The 
Administrator has reasonably and logically considered the relationship 
between the lead air pollution and the air pollutant when considering 
emissions of lead from engines used in covered aircraft. The 
Administrator defines the air pollutant to match the definition of the 
air pollution, such that the air pollutant analyzed for contribution 
mirrors the air pollution considered in the endangerment finding. 
Accordingly, for purposes of this action, the Administrator defines the 
``air pollutant'' referred to in section 231(a)(2)(A) as lead, which we 
also refer to as the lead air pollutant in this document.\304\ As noted 
in section II.A.2. of this document, lead emitted to the air from 
covered aircraft engines is predominantly in particulate form as lead 
dibromide; however, some chemical compounds of lead that are expected 
in the exhaust from these engines, including alkyl lead compounds, 
would occur in the air in gaseous form.
---------------------------------------------------------------------------

    \304\ The lead air pollutant can occur as elemental lead or in 
lead-containing compounds, and this definition of the air pollutant 
recognizes the range of chemical forms of lead emitted by engines in 
covered aircraft.
---------------------------------------------------------------------------

B. The Data and Information Used To Evaluate the Final Cause or 
Contribute Finding

    The Administrator's assessment of whether emissions from the 
engines used in covered aircraft cause or contribute to lead air 
pollution was informed by estimates of lead emissions from the covered 
aircraft, lead concentrations in air at and near airports that are 
attributable to lead emissions from piston engines used in covered 
aircraft, and projected future conditions.
    As used in this final action, the term ``covered aircraft'' refers 
to all aircraft and ultralight vehicles equipped with covered engines 
which, in this context, means any aircraft engine that is capable of 
using leaded avgas. Examples of covered aircraft would include smaller 
piston-powered aircraft such as the Cessna 172 (single-engine aircraft) 
and the Beechcraft Baron G58 (twin-engine aircraft), as well as the 
largest piston-engine aircraft such as the Curtiss C-46 and the Douglas 
DC-6. Other examples of covered aircraft would include rotorcraft, such 
as the Robinson R44 helicopter, light-sport aircraft, and ultralight 
vehicles equipped with piston engines. The vast majority of covered 
aircraft are piston-engine powered.
    In recent years, covered aircraft are estimated to be the largest 
single source of lead to air in the U.S. Since 2008, as described in 
section II.A.2.b. of this document, lead emissions from covered 
aircraft are estimated to have contributed over 50 percent of all lead 
emitted to the air nationally. The EPA estimates 470 tons of lead were 
emitted by covered aircraft in 2017, comprising 70 percent of lead 
emitted to air nationally that year.\305\ \306\ In approximately 1,000 
counties in the U.S., the EPA's emissions inventory identifies covered 
aircraft as the sole source of lead emissions. Among the 1,872 counties 
in the U.S. for which the inventory identifies multiple sources of lead 
emissions, including engine emissions from covered aircraft, the 
contribution of aircraft engine emissions ranges from 0.00005 to 4.3 
tons per year, comprising 0.15 to 98 percent (respectively) of total 
lead emissions to air in those counties.\307\
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    \305\ The lead inventories for 2008, 2011 and 2014 are provided 
in the EPA (2018b) Report on the Environment Exhibit 2. 
Anthropogenic lead emissions in the U.S. Available at https://cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead inventories for 
2017 are available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data#dataq.
    \306\ As described in section II.A.2., the EPA estimates 427 
tons of lead were emitted by aircraft engines operating on leaded 
fuel in 2020. Due to the Covid-19 pandemic, a substantial decrease 
in activity by aircraft occurred in 2020, impacting the total lead 
emissions for this year. The 2020 NEI is available at: https://www.epa.gov/air-emissions-inventories/2020-national-emissions-inventory-nei-data.
    \307\ Airport lead annual emissions data used were reported in 
the 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data. In addition 
to the triennial NEI, the EPA collects from state, local, and Tribal 
air agencies point source data for larger sources every year (see 
https://www.epa.gov/air-emissions-inventories/air-emissions-reporting-requirements-aerr for specific emissions thresholds). 
While these data are not typically published as a new NEI, they are 
available publicly upon request and are also included in https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms, 
which are created for years other than the triennial NEI years. 
County estimates of lead emissions from non-aircraft sources used in 
this action are from the 2019 inventory. There are 3,012 counties 
and statistical equivalent areas where EPA estimates engine 
emissions of lead occur.
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    Covered aircraft activity, as measured by the number of hours flown 
nationwide, increased nine percent in the period from 2012 through 
2019.\308\ General aviation activity, largely conducted by covered 
aircraft, increased up to 52 percent at airports that are among the 
busiest in the U.S.\309\ In future years, while piston-engine aircraft 
activity overall is projected to decrease slightly, this change in 
activity is not projected to occur uniformly across airports in the 
U.S.; some airports are forecast to have increased activity by general 
aviation aircraft, the majority of which is conducted by piston-engine 
aircraft.\310\ Although there is some uncertainty in these projections, 
they indicate that lead emissions from covered aircraft may increase at 
some airports in the future.\311\
---------------------------------------------------------------------------

    \308\ FAA. General Aviation and Part 135 Activity Surveys--CY 
2019. Chapter 3: Primary and Actual Use. Table 1.3--General Aviation 
and Part 135 Total Hours Flown by Aircraft Type 2008-2019 (Hours in 
Thousands). Retrieved on Dec., 27, 2021 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \309\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past 
Trends and Future Projections in General Aviation Activity and 
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
    \310\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past 
Trends and Future Projections in General Aviation Activity and 
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
    \311\ FAA TAF Fiscal Years 2020-2045 describes the forecast 
method, data sources, and review process for the TAF estimates. The 
documentation for the TAF is available at https://taf.faa.gov/Downloads/TAFSummaryFY2020-2045.pdf.
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    Additionally, engine emissions of lead from covered aircraft may 
deposit in the local environment and, due to the small size of the 
lead-bearing particles emitted by engines in covered aircraft, these 
particles may disperse widely in

[[Page 72399]]

the environment. Therefore, because lead is a persistent pollutant in 
the environment, we anticipate current and future emissions of lead 
from covered aircraft engines may contribute to exposures and uptake by 
humans and biota into the future.
    In evaluating the contributions of engine emissions from covered 
aircraft to the lead air pollution, as defined in section IV.A. of this 
document, the EPA also considered three types of information about lead 
concentrations in the ambient air: monitored concentrations, modeled 
concentrations, and model-extrapolated estimates of lead 
concentrations. Lead concentrations monitored in the ambient air 
typically quantify lead compounds collected as suspended particulate 
matter. The information gained from air monitoring and air quality 
modeling provides insight into how lead emissions from piston engines 
used in covered aircraft can affect lead concentrations in air.
    As described in section II.A.3. of this document, the EPA has 
conducted air quality modeling at two airports and extrapolated modeled 
estimates of lead concentrations to 13,000 airports with piston-engine 
aircraft activity. These studies indicate that over a three-month 
averaging time (the averaging time for the Lead NAAQS), the engine 
emissions of lead from covered aircraft are estimated to contribute to 
air lead concentrations to a distance of at least 500 meters downwind 
from a runway.\312\ \313\ Additional studies have reported that lead 
emissions from covered aircraft may have increased concentrations of 
lead in air by one to two orders of magnitude at locations proximate to 
aircraft emissions compared to nearby locations not impacted by a 
source of lead air emissions.\314\ \315\ \316\
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    \312\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \313\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. Table 6. EPA-420-R-20-003, 2020. 
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
    \314\ Carr et al., 2011. Development and evaluation of an air 
quality modeling approach to assess near-field impacts of lead 
emissions from piston-engine aircraft operating on leaded aviation 
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \315\ Heiken et al., 2014. Quantifying Aircraft Lead Emissions 
at Airports. ACRP Report 133. Available at https://www.nap.edu/catalog/22142/quantifying-aircraft-lead-emissions-at-airports.
    \316\ Hudda et al., 2022. Substantial Near-Field Air Quality 
Improvements at a General Aviation Airport Following a Runway 
Shortening. Environmental Science & Technology. DOI: 10.1021/
acs.est.1c06765.
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    In 2008 and 2010, the EPA enhanced the lead monitoring network by 
requiring monitors to be placed in areas with sources such as 
industrial facilities and airports, as described further in section 
II.A.3. of this document.\317\ \318\ As part of this 2010 requirement 
to expand lead monitoring nationally, the EPA required a 1-year 
monitoring study of 15 additional airports with estimated lead 
emissions between 0.50 and 1.0 ton per year in an effort to better 
understand how these emissions affect concentrations of lead in the air 
at and near airports. Further, to help evaluate airport characteristics 
that could lead to ambient lead concentrations that approach or exceed 
the lead NAAQS, airports for this 1-year monitoring study were selected 
based on factors such as the level of activity of covered aircraft and 
the predominant use of one runway due to wind patterns. Monitored lead 
concentrations in ambient air are highly sensitive to monitor location 
relative to the location of the run-up areas for piston-engine aircraft 
and other localized areas of elevated lead concentrations relative to 
the air monitor locations.
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    \317\ 73 FR 66965 (Nov. 12, 2008).
    \318\ 75 FR 81126 (Dec. 27, 2010).
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    The lead monitoring study at airports began in 2011. In 2012, air 
monitors were placed in close proximity to the run-up areas at the San 
Carlos Airport (measurements started on March 10, 2012) and the 
McClellan-Palomar Airport (measurements started on March 16, 2012). The 
concentrations of lead measured at both of these airports in 2012 were 
above the level of the lead NAAQS, with the highest measured levels of 
lead in total suspended particles over a rolling three-month average of 
0.33 micrograms per cubic meter of air at the San Carlos Airport and 
0.17 micrograms per cubic meter of air at the McClellan-Palomar 
Airport. These concentrations violate the primary and secondary lead 
NAAQS, which are set at a level of 0.15 micrograms per cubic meter of 
air measured in total suspended particles, as an average of three 
consecutive monthly concentrations.
    In recognition of the potential for lead concentrations to exceed 
the lead NAAQS in ambient air near the area of maximum concentration at 
airports, the EPA further conducted an assessment of airports 
nationwide, titled ``Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports'' and described in section II.A.3. of 
this document.\319\ The model-extrapolated lead concentrations 
estimated in this study are attributable solely to emissions from 
engines in covered aircraft operating at the airports evaluated and did 
not include other sources of lead emissions to air. The EPA identified 
four airports with the potential for lead concentrations above the lead 
NAAQS due to lead emissions from engines used in covered aircraft.
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    \319\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports Table 6. EPA-420-R-20-003, 2020. 
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
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    Additional information regarding the contribution of engine 
emissions of lead from covered aircraft to lead air pollution is 
provided by the EPA's Air Toxics Screening Assessment. As described and 
summarized in section II.A.3. of this document, the EPA's Air Toxics 
Screening Assessment estimates that piston engines used in aircraft 
contribute more than 50 percent of the estimated lead concentrations in 
over half of the census tracts in the U.S.\320\
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    \320\ EPA's 2019 AirToxScreen is available at https://www.epa.gov/AirToxScreen/2019-airtoxscreen.
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    The EPA also notes that lead is emitted from engines in covered 
aircraft in three of the ten areas in the U.S. currently designated as 
nonattainment for the 2008 lead NAAQS. These areas are Arecibo, PR, and 
Hayden, AZ, each of which include one airport servicing covered 
aircraft, and the Los Angeles County-South Coast Air Basin, CA, which 
contains at least 22 airports within its nonattainment area 
boundary.\321\ \322\ Although the lead emissions from aircraft are not 
the predominant source of airborne lead in these areas, the emissions 
from covered aircraft may increase ambient air lead concentrations in 
these areas.
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    \321\ South Coast Air Quality Management District (2012) 
Adoption of 2012 Lead SIP Los Angeles County by South Coast 
Governing Board, p.3-11, Table 3-3. Available at https://www.aqmd.gov/home/air-quality/clean-air-plans/lead-state-implementation-plan. The South Coast Air Quality Management District 
identified 22 airports in the Los Angeles County-South Coast Air 
Basin nonattainment area; the Whiteman Airport is among those in the 
nonattainment area and the EPA estimated activity at this airport 
may increase lead concentrations to levels above the lead NAAQS in 
the report, Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. Table 7. EPA, Washington, DC, EPA-
420-R-20-003, 2020. Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
    \322\ EPA provides updated information regarding nonattainment 
areas at this website: https://www.epa.gov/green-book/green-book-lead-2008-area-information.

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[[Page 72400]]

C. Response to Certain Comments on the Cause or Contribute Finding

    The EPA received comments related to the contribution of lead 
emissions from engines in covered aircraft to lead air pollution. 
Commenters provided both support for and opposition to the EPA's 
proposed cause or contribute finding, with specific comments regarding 
the amount of lead emitted by aircraft operating on leaded fuel and the 
contribution of aircraft engine emissions to lead concentrations in the 
air.
    Numerous commenters state their support for the proposed cause or 
contribute finding, in some cases noting that ample evidence supports 
this finding and highlighting the important role that lead emissions 
from covered aircraft engines have in local environments in many areas 
of the U.S. Additional commenters express concern regarding monitored 
lead concentrations that exceed the NAAQS at some airports. The 
comments expressing support for the proposed cause or contribute 
finding and EPA's responses are described in greater detail in the 
Response to Comment document for this action. We acknowledge these 
comments and the support expressed for the EPA's cause or contribute 
finding, and we agree with the commenters that lead emissions from 
engines in covered aircraft contribute to lead air pollution.
    Commenters stating opposition to the cause or contribute finding 
based on the amount of lead emitted by aircraft operating on leaded 
fuel, assert that lead emissions today are 425 times less than lead 
emissions of the 1970s or that the emissions of lead from aircraft are 
less than one quarter of one percent of the emissions from cars in the 
1970s. Some commenters also state that it only stands to reason that 
covered aircraft engine emissions of lead represent a high percentage 
of current lead emissions because lead is no longer being emitted by 
motor vehicles. At least one additional commenter states that given the 
number of hours flown by covered aircraft, they do not contribute 
enough lead to affect air pollution.
    Commenters stating opposition to the cause or contribute finding 
based on the concentrations of lead in air from engine emissions by 
covered aircraft state that concentrations of lead exceeding the lead 
NAAQS are rare, representing two of 17 airports studied. One commenter 
also notes that Table 2 (in section II.A.3. of this document) does not 
address the localized conditions of the airports studied and that the 
airports where lead concentrations violated the lead NAAQS may have 
unique conditions that resulted in the concentrations measured. 
Additionally, some commenters state that there is no evidence that 
engine emissions of lead are creating a hazard, and that the lead 
emitted is not toxic in the small amount emitted by aircraft engines.
    In response to commenters comparing emissions of lead from covered 
aircraft to lead emitted by motor vehicles in the 1970s, the EPA 
acknowledges that more lead was emitted by motor vehicles in the 1970s 
than is emitted by covered aircraft engines currently. This cause or 
contribute finding is focused on emissions of lead from covered 
aircraft engines, a different category of mobile sources from motor 
vehicles, and the commenters do not explain why the fact that 
historical emissions were higher from a different source category means 
that current emissions from covered aircraft engines are not 
contributing to the existing lead air pollution. Similarly, the 
historical contributions of lead emitted by motor vehicles is not 
germane to the present-day analysis of the contribution of lead 
emissions from covered aircraft engines to the total lead released to 
the air annually in the U.S. Indeed, nothing in CAA section 231(a) 
precludes EPA from making a cause or contribute finding for emissions 
from aircraft engines where such a finding is warranted, even if 
emissions from other sources regulated elsewhere in the CAA or under 
other Federal programs may also contribute to that air pollution or 
have historically contributed to it. See Massachusetts v. E.P.A., 549 
U.S. 497, 533 (2007) (the alleged efficacy of other ``Executive Branch 
programs'' in addressing the air pollution problem is not a valid 
reason for declining to make an endangerment finding). As noted 
previously, in making a cause or contribute finding, CAA section 231 
does not require the EPA to find that the contribution from the 
relevant source category is ``significant,'' let alone the sole or 
major cause of the endangering air pollution. As described in section 
V.B., the lead emissions from engines used in covered aircraft clearly 
contribute to the endangering lead air pollution, as these emissions 
contributed over 50 percent of lead emissions to air starting in 2008, 
when approximately 560 tons of lead were emitted by engines in covered 
aircraft, and more recently, in 2017, when approximately 470 tons of 
lead were emitted by engines in covered aircraft. In the EPA's view, 
both the quantity and percentage of lead emitted by covered aircraft 
engines amply demonstrate that this source contributes to lead air 
pollution in the U.S.
    In response to commenters stating that the number of hours flown by 
covered aircraft do not contribute enough lead to affect air pollution, 
the EPA notes that the commenters made a conclusory allegation and did 
not provide data or analysis supporting their claim. The EPA disagrees 
with this comment, and we present data in section V.B. of this document 
demonstrating that the activity by covered aircraft, which includes the 
number of hours flown, contributes to lead air pollution as described 
in the preceding paragraph.
    In response to commenters asserting that concentrations of lead 
exceeding the lead NAAQS are rare, representing two of 17 airports 
studied, as an initial matter, the EPA notes that nothing in section 
231(a) of the CAA premises the cause or contribute finding on emissions 
from the relevant classes of aircraft engines contributing to such 
exceedances in a minimum number of air quality regions. More 
importantly, the EPA notes that the purpose of this airport monitoring 
study was not to determine the frequency with which potential 
violations of the lead NAAQS occur at or near airports, but to 
understand the potential range in lead concentrations at a small sample 
of airports and the factors that influence those concentrations. As 
described in section II.A.3. of this document, the concentrations of 
lead monitored at and near highly active general aviation airports is 
largely determined by the placement of the monitor relative to the run-
up area, and monitor placement relative to the run-up area was not 
uniform across the airports studied. The EPA fully explains the basis 
on which the Administrator finds that emissions of lead from covered 
aircraft engine emissions cause or contribute to lead air pollution. 
The data that support this finding are presented in section V.B. and, 
as articulated in section V.D., where, among other data, the 
Administrator takes into account the fact that in some situations lead 
emissions from covered aircraft have contributed and may continue to 
contribute to air concentrations that exceed the lead NAAQS. Given that 
the lead NAAQS are established to provide requisite protection of 
public health and welfare, the Administrator expresses particular 
concern with contributions to concentrations that exceed the lead 
NAAQS, and those contributions are part of the support for the 
conclusion that lead emissions from engines in covered aircraft cause 
or contribute to the endangering air pollution.
    In response to the comment regarding the assertion that the two 
airports where lead concentrations violated the lead NAAQS may have 
unique conditions

[[Page 72401]]

that resulted in the concentrations measured, the EPA notes that the 
commenter did not specify or explain what localized conditions might 
lead to this result; nor did they provide supporting evidence for 
localized conditions occurring in these areas that could explain these 
lead concentrations presented in Table 2 of this document. The EPA 
describes in section II.A.3. of this document that at both of these 
airports, monitors were located in close proximity to the area at the 
end of the runway most frequently used for pre-flight safety checks 
(i.e., run-up), and monitor placement relative to the run-up area is a 
key factor in evaluating the maximum impact location attributable to 
lead emissions from piston-engine aircraft. Additionally, as described 
in section II.A.3. of this document, air lead concentrations at and 
downwind from airports can be influenced by factors such as the use of 
more than one run-up area, wind speed, and the number of operations 
conducted by single- versus twin-engine aircraft.\323\ At the two 
airports at which concentrations of lead violated the lead NAAQS, the 
EPA observed a similar fleet composition of single- versus twin-engine 
aircraft compared with other airports where on-site measurements were 
taken; wind speeds, which are inversely proportional to lead 
concentration, were not lower at the airports with lead concentrations 
violating the lead NAAQS compared with other airports; and these 
airports were not unique in that the activity by piston-engine aircraft 
was in the range of activity by these aircraft at the majority of 
airports where monitors were located.\324\ The EPA thus concludes that 
these two airports do not have unique conditions responsible for the 
concentrations of lead that violated the lead NAAQS.
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    \323\ The data in Table 2 represent concentrations measured at 
one location at each airport and monitors were not consistently 
placed in close proximity to the run-up areas. As described in 
section II.A.3., monitored concentrations of lead in air near 
airports are highly influenced by proximity of the monitor to the 
run-up area. In addition to monitor placement, there are individual 
airport factors that can influence lead concentrations (e.g., the 
use of multiple run-up areas at an airport, fleet composition, and 
wind speed). The monitoring data reported in Table 2 reflect a range 
of lead concentrations indicative of the location at which 
measurements were made and the specific operations at an airport.
    \324\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports Appendix B, Table B-2. EPA-420-R-20-
003, 2020. Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
---------------------------------------------------------------------------

    In response to the comments that there is no evidence that engine 
emissions of lead are creating a hazard,\325\ and that the lead emitted 
is not toxic in the small amount emitted by aircraft engines, we note 
that these comments conflate the endangerment and cause or contribute 
steps of the analysis. The text in section 231(a)(2) provides for the 
EPA to make a finding based on a determination that emissions of the 
air pollutant from the covered aircraft engine ``causes, or contributes 
to'' the air pollution. In making a cause or contribute finding, the 
EPA need not additionally and separately make a determination as to 
whether the emissions from covered aircraft engines alone cause 
endangerment. In section IV. of this document, the EPA explained why 
the Administrator is finding that the lead air pollution endangers 
public health and welfare. The only remaining issue at the second step 
of the analysis is whether emissions from the analyzed class or classes 
of aircraft engines cause or contribute to the air pollution that may 
reasonably be anticipated to endanger public health and welfare. For 
the reasons described in section V. of this document, in the 
Administrator's judgment, emissions of the lead air pollutant from 
engines in the covered aircraft cause or contribute to the lead air 
pollution.
---------------------------------------------------------------------------

    \325\ While the comment does not clearly explain what it is 
referring to with the phrase ``creating a hazard,'' we understand 
that phrase to align with the ``cause'' portion of the cause or 
contribute findings.
---------------------------------------------------------------------------

    Additional comments were submitted to the EPA regarding the 
emissions, deposition, transport, and fate of lead emitted by covered 
aircraft engines. The EPA responds to these comments in the Response to 
Comments Document for this action.

D. Final Cause or Contribute Finding for Lead

    Taking into consideration the data and information summarized in 
section V. of this document, and the public comments received on the 
proposed finding, the Administrator finds that engine emissions of the 
lead air pollutant from covered aircraft cause or contribute to the 
lead air pollution that may reasonably be anticipated to endanger 
public health and welfare. In reaching this conclusion, the 
Administrator noted that piston-engine aircraft operate on leaded 
avgas. That operation emits lead-containing compounds into the air, 
contributing to lead air pollution in the environment. As explained in 
section II.A. of this document, once emitted from covered aircraft, 
lead may be transported and distributed to other environmental media, 
where it presents the potential for human exposure through air and non-
air pathways before the lead is removed to deeper soils or waterbody 
sediments. In reaching this final finding, the Administrator takes into 
consideration different air quality scenarios in which emissions of the 
lead air pollutant from engines in covered aircraft may cause or 
contribute to lead air pollution. Among these considerations, he places 
weight on the fact that current lead emissions from covered aircraft 
are an important source of air-related lead in the environment and that 
engine emissions of lead from covered aircraft are the largest single 
source of lead to air in the U.S. in recent years. In this regard, he 
notes that these emissions contributed over 50 percent of lead 
emissions to air starting in 2008, when approximately 560 tons of lead 
was emitted by engines in covered aircraft (of the total 950 tons of 
lead) and, more recently, in 2017, when approximately 470 tons of lead 
was emitted by engines in covered aircraft (of the total 670 tons of 
lead).\326\
---------------------------------------------------------------------------

    \326\ The lead inventories for 2008, 2011 and 2014 are provided 
in the U.S. EPA (2018b) Report on the Environment Exhibit 2. 
Anthropogenic lead emissions in the U.S. Available at https://cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead inventories for 
2017 are available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data#dataq.
---------------------------------------------------------------------------

    Additionally, he takes into account the fact that in some 
situations lead emissions from covered aircraft have contributed and 
may continue to contribute to air concentrations that exceed the lead 
NAAQS. The NAAQS are standards that have been set to protect public 
health, including the health of sensitive groups, with an adequate 
margin of safety and to protect public welfare from any known or 
anticipated adverse effects associated with the presence of the 
pollutant in the ambient air. For example, the EPA's monitoring data 
show that lead concentrations at two airports, McClellan-Palomar and 
San Carlos, violated the lead NAAQS. The EPA's model-extrapolated 
estimates of lead also indicate that some U.S. airports may have air 
lead concentrations above the NAAQS in the area of maximum impact from 
operation of covered aircraft.\327\ Given that the lead NAAQS are 
established to protect public health and welfare, contributions to 
concentrations that exceed the lead NAAQS are of particular concern to 
the Administrator and are persuasive support for the conclusion that 
lead emissions from engines in covered

[[Page 72402]]

aircraft cause or contribute to the endangering air pollution.
---------------------------------------------------------------------------

    \327\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports Table 7. EPA-420-R-20-003, 2020. 
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
---------------------------------------------------------------------------

    The Administrator is also concerned about the likelihood for these 
emissions to continue to be an important source of air-related lead in 
the environment in the future, if uncontrolled. While recognizing that 
national consumption of leaded avgas is forecast to decrease slightly 
from 2026 to 2041 commensurate with overall piston-engine aircraft 
activity, the Administrator also notes that these changes are not 
expected to occur uniformly across the U.S.\328\ For example, he takes 
note of the FAA forecasts for airport-specific aircraft activity out to 
2045 that project decreases in activity by general aviation at some 
airports, while projecting increases at other airports.\329\ Although 
there is some uncertainty in these projections, they indicate that lead 
emissions from covered aircraft may increase at some airports in the 
future. Thus, even assuming that consumption of leaded avgas and 
general aviation activity decrease somewhat overall, as projected, the 
Administrator anticipates that current concerns about these sources of 
air-related lead will continue into the future, without controls. 
Accordingly, the Administrator is considering both current levels of 
emissions and anticipated future levels of emissions from covered 
aircraft. In doing so, the Administrator finds that current levels 
cause or contribute to pollution that may reasonably be anticipated to 
endanger public health and welfare. He also is taking into 
consideration the projections that some airports may see increases in 
activity while others see decreases, as well as the uncertainties in 
these predictions. The Administrator therefore considers all this 
information and data collectively to inform his judgment on whether 
lead emissions from covered aircraft cause or contribute to endangering 
air pollution.
---------------------------------------------------------------------------

    \328\ FAA Terminal Area Forecast provides projections of 
aircraft activity at airports. The forecast is available at https://taf.faa.gov and the FAA Terminal Area Forecast for Fiscal Years 
2020-2045 describes the forecast method, data sources, and review 
process for the TAF estimates, available at: https://taf.faa.gov/Downloads/TAFSummaryFY2020-2045.pdf.
    \329\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past 
Trends and Future Projections in General Aviation Activity and 
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
---------------------------------------------------------------------------

    Accordingly, for all the reasons described, the Administrator 
concludes that emissions of the lead air pollutant from engines in 
covered aircraft cause or contribute to the lead air pollution that may 
reasonably be anticipated to endanger public health and welfare.

VI. Statutory Authority and Executive Order Reviews

    Additional information about these statutes and Executive Orders 
can be found at https://www2.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 14094: Modernizing Regulatory Review

    This action is a ``significant regulatory action'' as defined in 
Executive Order 12866, as amended by Executive Order 14094. 
Accordingly, EPA submitted this action to the Office of Management and 
Budget (OMB) for Executive Order 12866 review. Documentation of any 
changes made in response to the Executive Order 12866 review is 
available in the docket. This action finalizes a finding that emissions 
of the lead air pollutant from engines in covered aircraft cause or 
contribute to the lead air pollution that may be reasonably anticipated 
to endanger public health and welfare.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. The final endangerment and cause or contribute findings under 
CAA section 231(a)(2)(A) do not contain any information collection 
activities.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. The final 
endangerment and cause or contribute findings under CAA section 
231(a)(2)(A) do not in-and-of-themselves impose any new requirements on 
any regulated entities but rather set forth the Administrator's finding 
that emissions of the lead air pollutant from engines in covered 
aircraft cause or contribute to lead air pollution that may be 
reasonably anticipated to endanger public health and welfare.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in 
UMRA, 2 U.S.C. 1531-1538 and does not significantly or uniquely affect 
small governments. The action imposes no enforceable duty on any state, 
local or Tribal governments or the private sector.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This action does not have Tribal implications as specified in 
Executive Order 13175. The final endangerment and cause or contribute 
findings under CAA section 231(a)(2)(A) do not in-and-of-themselves 
impose any new requirements but rather set forth the Administrator's 
final finding that emissions of the lead air pollutant from engines in 
covered aircraft cause or contribute to lead air pollution that may be 
reasonably anticipated to endanger public health and welfare. Thus, 
Executive Order 13175 does not apply to this action.
    Tribes have previously submitted comments to the EPA noting their 
concerns regarding potential impacts of lead emitted by piston-engine 
aircraft operating on leaded avgas at airports on, and near, their 
Reservation Land.\330\ The EPA plans to continue engaging with Tribal 
stakeholders on this issue and will offer a government-to-government 
consultation upon request.
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    \330\ See Docket ID Number EPA-HQ-OAR-2006-0735. The Tribes that 
submitted comments were: The Bad River Band of Lake Superior Tribe 
of Chippewa Indians, The Quapaw Tribe of Oklahoma, The Leech Lake 
Band of Ojibwe, The Lone Pine Paiute-Shoshone Reservation, The Fond 
du Lac Band of Lake Superior Chippewa, and The Mille Lacs Band of 
Ojibwe.
---------------------------------------------------------------------------

G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    Executive Order 13045 (62 FR 19885, April 23, 1997) directs Federal 
agencies to include an evaluation of the health and safety effects on 
children of a planned regulation in setting Federal health and safety 
standards. This action is not subject to Executive Order 13045 because 
it does not propose to establish an environmental standard intended to 
mitigate health or safety risks. Although the Administrator considered 
health and safety risks as part of the endangerment and cause or 
contribute findings under CAA section 231(a)(2)(A), the findings 
themselves do not impose a standard intended to mitigate those risks. 
However, the EPA's Policy on Children's Health applies to this action. 
Consistent with this policy,

[[Page 72403]]

the Administrator considered lead exposure risks to children as part of 
this final endangerment finding under CAA section 231(a)(2)(A). 
Information on how the Policy was applied is available under 
``Children's Environmental Health'' in the SUPPLEMENTARY INFORMATION 
section B. of this document. A copy of the documents pertaining to the 
impacts on children's health from emissions of lead from piston-engine 
aircraft that the EPA references in this action have been placed in the 
public docket for this action (Docket EPA-HQ-OAR-2022-0389).

H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. Further, we have concluded that this 
action is not likely to have any adverse energy effects because the 
final endangerment and cause or contribute findings under section 
231(a)(2)(A) do not in-and-of themselves impose any new requirements 
but rather set forth the Administrator's finding that emissions of the 
lead air pollutant from engines in covered aircraft cause or contribute 
to lead air pollution that may be reasonably anticipated to endanger 
public health and welfare.

I. National Technology Transfer and Advancement Act (NTTAA)

    This action does not involve technical standards.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations; Executive 
Order 14096: Revitalizing Our Nation's Commitment to Environmental 
Justice for All

    The EPA believes that the human health or environmental conditions 
that exist prior to this action result in or have the potential to 
result in disproportionate and adverse human health or environmental 
effects on communities with environmental justice concerns. The EPA 
conducted an analysis of people living within 500 meters or one 
kilometer of airports and found that there is a greater prevalence of 
people of color and of low-income populations within 500 meters or one 
kilometer of some airports compared with people living more distant. 
The EPA provides a summary of the evidence for potentially 
disproportionate and adverse effects among people of color and low-
income populations residing near airports in section II.A.5. of this 
document. A copy of the documents pertaining to the EPA's analysis of 
potential environmental justice concerns regarding populations who live 
in close proximity to airports has been placed in the public docket for 
this action (Docket EPA-HQ-OAR-2022-0389).
    The EPA believes that this action will not change existing 
disproportionate and adverse effects on communities with environmental 
justice concerns. In this action, the EPA finds, under section 
231(a)(2)(A) of the Clean Air Act, that emissions of lead from engines 
in covered aircraft may cause or contribute to air pollution that may 
reasonably be anticipated to endanger public health or welfare. We are 
not proposing emission standards at this time.
    The EPA additionally promoted fair treatment and meaningful 
involvement for the public, including for communities with 
environmental justice concerns, in this action by briefing Tribal 
members on this action and providing information on our website in both 
Spanish and English, as well as providing access to Spanish translation 
during the public hearing.

K. Congressional Review Act (CRA)

    The EPA will submit a rule report to each House of the Congress and 
to the Comptroller General of the United States. This action is not a 
``major rule'' as defined by 5 U.S.C. 804(2).

L. Determination Under Section 307(d)

    Section 307(d)(1)(V) of the CAA provides that the provisions of 
section 307(d) apply to ``such other actions as the administrator may 
determine.'' Pursuant to section 307(d)(1)(V), the Administrator 
determines that this action is subject to the provisions of section 
307(d).

M. Judicial Review

    Section 307(b)(1) of the CAA governs judicial review of final 
actions by the EPA. This section provides, in part, that petitions for 
review must be filed in the D.C. Circuit: (i) when the agency action 
consists of ``nationally applicable regulations promulgated, or final 
actions taken, by the Administrator,'' or (ii) when such action is 
locally or regionally applicable, but ``such action is based on a 
determination of nationwide scope or effect and if in taking such 
action the Administrator finds and publishes that such action is based 
on such a determination.'' For locally or regionally applicable final 
actions, the CAA reserves to the EPA complete discretion whether to 
invoke the exception in (ii) described in the preceding sentence.\331\
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    \331\ Sierra Club v. EPA, 47 F.4th 738, 745 (D.C. Cir. 2022) 
(``EPA's decision whether to make and publish a finding of 
nationwide scope or effect is committed to the agency's discretion 
and thus is unreviewable''); Texas v. EPA, 983 F.3d 826, 834-35 (5th 
Cir. 2020).
---------------------------------------------------------------------------

    This action is ``nationally applicable'' within the meaning of CAA 
section 307(b)(1) because in issuing these final findings, the EPA 
becomes subject to a statutory duty to propose and promulgate aircraft 
engine emission standards under CAA section 231(a), which are 
nationally applicable regulations for which judicial review is 
available only in the U.S. Court of Appeals for the District of 
Columbia Circuit (D.C. Circuit) pursuant to CAA section 307(b)(1). 
Further, these emission standards would apply to covered aircraft, 
wherever in the nation they are located. We note also that similar 
actions, including the 2016 Endangerment and Cause or Contribute 
Findings under CAA section 231 for greenhouse gases and the 2009 
Endangerment and Cause or Contribute Findings under CAA section 202(a) 
for greenhouse gases, were also nationally applicable \332\ and were 
challenged in the D.C. Circuit.\333\
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    \332\ 81 FR 54422 (Aug. 15, 2016) (2016 Findings); 74 FR 66496 
(2009 Findings).
    \333\ Coalition for Responsible Regulation, Inc. v. EPA, 684 
F.3d 102 (D.C. Cir. 2012) (subsequent history omitted) (affirming 
2009 Findings); Biogenic CO2 Coalition v. EPA (Doc. No. 1932392, No. 
16-1358, D.C. Cir., January 26, 2022) (granting petitioner's motion 
to voluntarily dismiss petition for review of 2016 Findings).
---------------------------------------------------------------------------

    In the alternative, to the extent a court finds this final action 
to be locally or regionally applicable, the Administrator is exercising 
the complete discretion afforded to him under the CAA to make and 
publish a finding that this action is based on a determination of 
``nationwide scope or effect'' within the meaning of CAA section 
307(b)(1).\334\ In issuing these final findings, the EPA becomes 
subject to a statutory duty to propose and promulgate emissions 
standards under CAA section 231(a), which would apply nationwide to 
covered aircraft that travel and operate within multiple judicial 
circuits. As described in section III. of this document, in making 
these findings, the EPA is applying the same analytical framework that 
the Agency applied in the 2016 Endangerment and Cause or

[[Page 72404]]

Contribute Findings under CAA section 231 for greenhouse gases and the 
2009 Endangerment and Cause or Contribute Findings under CAA section 
202(a) for greenhouse gases, both of which were challenged in the D.C. 
Circuit, as noted above.
---------------------------------------------------------------------------

    \334\ In deciding whether to invoke the exception by making and 
publishing a finding that an action is based on a determination of 
nationwide scope or effect, the Administrator takes into account a 
number of policy considerations, including his judgment balancing 
the benefit of obtaining the D.C. Circuit's authoritative 
centralized review versus allowing development of the issue in other 
contexts and the best use of agency resources.
---------------------------------------------------------------------------

    The Administrator finds that this is a matter on which national 
uniformity in judicial resolution of any petitions for review is 
desirable, to take advantage of the D.C. Circuit's administrative law 
expertise, and to facilitate the orderly development of the law under 
the Act. The Administrator also finds that consolidated review of this 
action in the D.C. Circuit will avoid piecemeal litigation in the 
regional circuits, further judicial economy, and eliminate the risk of 
inconsistent results, and that a nationally consistent approach to the 
CAA's provisions related to making endangerment and cause or contribute 
findings under section 231 of the CAA, including for lead air pollution 
and emissions of lead from engines in covered aircraft as here, 
constitutes the best use of agency resources.
    For these reasons, this final action is nationally applicable or, 
alternatively, the Administrator is exercising the complete discretion 
afforded to him by the CAA and finds that this final action is based on 
a determination of nationwide scope or effect for purposes of CAA 
section 307(b)(1) and is publishing that finding in the Federal 
Register. Under section 307(b)(1) of the CAA, petitions for judicial 
review of this action must be filed in the United States Court of 
Appeals for the District of Columbia Circuit by December 19, 2023.

VII. Statutory Provisions and Legal Authority

    Statutory authority for this action comes from 42 U.S.C. 7571, 7601 
and 7607.

List of Subjects

40 CFR Parts 87 and 1031

    Environmental protection, Air pollution control, Aircraft, Aircraft 
engines.

40 CFR Part 1068

    Environmental protection, Administrative practice and procedure, 
Confidential business information, Imports, Motor vehicle pollution, 
Penalties, Reporting and recordkeeping requirements, Warranties.

Michael S. Regan,
Administrator.
[FR Doc. 2023-23247 Filed 10-19-23; 8:45 am]
BILLING CODE 6560-50-P