Document ID: EPA-HQ-OAR-2022-0389-0001
Agency: epa
Document Type: Proposed Rule
Title: 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
Posted Date: 2022-10-17T04:00Z

[Federal Register Volume 87, Number 199 (Monday, October 17, 2022)]
[Proposed Rules]
[Pages 62753-62781]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-22223]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87, 1031, and 1068

[EPA-HQ-OAR-2022-0389; FRL-5934-01-OAR]
RIN 2060-AT10

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

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed action.

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SUMMARY: In this action, the Administrator is proposing to find that 
lead air pollution may reasonably be anticipated to endanger the public 
health and welfare within the meaning of section 231(a) of the Clean 
Air Act. The Administrator is also proposing 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 public 
health and welfare under section 231(a) of the Clean Air Act.

DATES: 
    Comments: Written comments must be received on or before January 
17, 2023.
    Public Hearing: The EPA plans to hold a virtual public hearing on 
November 1, 2022. See SUPPLEMENTARY INFORMATION for information on 
registering for a public hearing.

ADDRESSES: You may submit your comments, identified by Docket ID No. 
EPA-HQ-OAR-2022-0389, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov 
(our preferred method). Follow the online instructions for submitting 
comments.
     Email: [email protected]. Include Docket ID No. EPA-
HQ-OAR-

[[Page 62754]]

2022-0389 in the subject line of the message.
     Mail: U.S. Environmental Protection Agency, EPA Docket 
Center, OAR, Docket EPA-HQ-OAR-2022-0389. Mail Code 28221T, 1200 
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand Delivery or Courier (by scheduled appointment only): 
EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution 
Avenue NW, Washington, DC 20004. The Docket Center's hours of 
operations are 8:30 a.m.-4:30 p.m., Monday-Friday (except federal 
holidays).
    Instructions: All submissions received must include the Docket ID 
No. for this action. Comments received may be posted without change to 
https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the process for this action, see the ``Public 
Participation'' heading of the SUPPLEMENTARY INFORMATION section of 
this document.
    Public Hearing. EPA plans to hold a virtual public hearing for this 
action. Please refer to Participation in Virtual Public Hearing in the 
SUPPLEMENTARY INFORMATION section of this document for additional 
information.

FOR FURTHER INFORMATION CONTACT:  Marion Hoyer, Office of 
Transportation and Air Quality, Assessment and Standards Division 
(ASD), Environmental Protection Agency; Telephone number: (734) 214-
4513; Email address: [email protected].

SUPPLEMENTARY INFORMATION:

A. Public Participation

    Written Comments: Submit your comments, identified by Docket ID No. 
EPA-HQ-OAR-2022-0389, at https://www.regulations.gov (our preferred 
method), or the other methods identified in the ADDRESSES section of 
this document. Once submitted, comments cannot be edited or withdrawn 
from the docket. The EPA may publish any comment received to its public 
docket. Do not submit electronically any information you consider to be 
Confidential Business Information (CBI), Proprietary Business 
Information (PBI), or other information whose disclosure is restricted 
by statute. Multimedia submissions (audio, video, etc.) must be 
accompanied by a written comment. The written comment is considered the 
official comment and should include discussion of all points you wish 
to make. The EPA will generally not consider comments or comment 
contents located outside of the primary submission (including such 
content located on the web, cloud, or other file sharing system). For 
additional submission methods, the full EPA public comment policy, 
information about CBI, PBI, or multimedia submissions, and general 
guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    Documents to which the EPA refers in this proposed action are 
available online at https://www.regulations.gov/ in the docket for this 
action (Docket EPA-HQ-OAR-2022-0389). To access reference documents in-
person and for additional assistance, please refer to the following 
instructions.
    The EPA plans to hold a virtual hearing on November 1, 2022. This 
hearing will be held using Zoom. In order to attend the virtual public 
hearing, all attendees (including those who will not be presenting 
verbal testimony) must register in advance. Upon publication of this 
document in the Federal Register, the EPA will begin registering 
speakers for the hearing. To register to speak at the virtual hearing, 
please use the instructions at https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-lead-emissions-aircraft. If 
you have questions regarding registration, consult the person listed in 
the preceding FOR FURTHER INFORMATION CONTACT section of this document. 
The last day to register to speak at the hearing will be October 31, 
2022. Prior to the hearing, the EPA will post a general agenda that 
will list registered speakers in approximate order at: https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-lead-emissions-aircraft. The EPA will make every effort to follow the 
schedule as closely as possible on the day of the hearing; however, 
please plan for the hearings to run either ahead of schedule or behind 
schedule.
    The EPA anticipates that each commenter will have 5 minutes to 
provide oral testimony. The EPA recommends submitting the text of your 
oral testimony as written comments to the docket for this action. The 
EPA may ask clarifying questions during the oral presentations but will 
not respond to the presentations at that time. Written statements and 
supporting information submitted during the comment period will be 
considered with the same weight as oral testimony and supporting 
information presented at the public hearing.
    If you require the services of a translator or special 
accommodations such as audio description, please identify these needs 
when you register for the hearing no later than October 24, 2022. The 
EPA may not be able to arrange accommodations without advanced notice.

B. General Information

Does this action apply to me?

    Regulated Entities: In this action, the EPA is proposing to make 
endangerment and cause or contribute findings for the lead air 
pollution and engine emissions of lead from certain aircraft. The 
classes of aircraft engines and of aircraft relevant to this proposed 
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--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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    The proposed findings in this action, if finalized, would not 
themselves apply new requirements to entities other than the EPA and 
the Federal Aviation Administration (FAA). Specifically, if the EPA 
issues final findings that lead emissions from covered aircraft engines 
cause or contribute to air pollution which may reasonably be 
anticipated to endanger public health or welfare, then the EPA would, 
under section 231 of the Clean Air Act, promulgate aircraft engine 
emission standards for that air pollutant. In contrast to the findings, 
those standards would apply to and have an effect on other entities 
outside the federal government. Entities potentially interested in this 
proposed action include those that manufacture

[[Page 62755]]

and sell covered aircraft engines and covered aircraft in the United 
States and those who own or operate covered aircraft. Categories that 
may be regulated in a future regulatory action include, but are not 
limited to, those listed here:

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                                                                                Examples of potentially affected
                Category                    NAICS \a\ code      SIC \b\ code                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 potentially regulated entities likely to be 
interested in this proposed 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 proposed action. If the EPA issues final 
affirmative findings under section 231(a) of the Clean Air Act 
regarding lead, the EPA would then undertake a future notice and 
comment rulemaking to issue emission standards, and the FAA would be 
required to prescribe regulations to ensure compliance with these 
emissions standards pursuant to section 232 of the Clean Air Act. Such 
findings also would trigger the FAA's statutory mandate pursuant to 49 
U.S.C. 44714 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 EPA has decided endanger public 
health or welfare under section 231(a) of the Clean Air Act. 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 proposed action, consult 
the person listed in the preceding FOR FURTHER INFORMATION CONTACT 
section of this document.

C. Children's Health

    Executive Order 13045 \3\ requires agencies to identify and assess 
health and safety risks that may disproportionately affect children and 
ensure that activities address disproportionate risks to children. 
Children may be 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 relative 
to their size than adults do, and consequently 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.\4\
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    \3\ E.O. 13045. Protection of Children From Environmental Health 
Risks and Safety Risks. 62 FR 19885 (April 23, 1997).
    \4\ 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. Since the inception of Executive 
Order 13045, the understanding of children's environmental health has 
broadened to include conception, infancy, early childhood and through 
adolescence until 21 years of age.\5\ Because behavioral and 
physiological characteristics can affect children's environmental 
health risks, childhood and children's health is viewed with an 
understanding of the concept of ``lifestages,'' which recognize unique 
growth and developmental periods through which all humans pass.\6\
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    \5\ 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.
    \6\ EPA. ``Childhood Lifestages relating to Children's 
Environmental Health.'' Oct. 25, 2021. Retrieved from https://www.epa.gov/children/childhood-lifestages-relating-childrens-environmental-health on Nov. 22, 2021.
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    This document includes discussion and analysis that is focused 
particularly on children. For example, as described in Sections III.A 
and V 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.'' \7\ 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.\8\ The 2013 Lead ISA 
notes that in epidemiologic studies, postnatal (early childhood) blood 
lead levels are consistently associated with cognitive function 
decrements in children and adolescents.\9\ 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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    \7\ 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.
    \8\ EPA (2013) ISA for Lead. Executive Summary ``Effects of Pb 
Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA/600/R-10/075F, 
2013.
    \9\ 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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D. Environmental Justice

    Executive Order 12898 establishes federal executive policy on 
environmental justice. It directs federal agencies, to the greatest 
extent practicable and permitted by law, to make achieving 
environmental justice part of their mission by identifying and 
addressing, as appropriate, disproportionately high and adverse human 
health or environmental effects

[[Page 62756]]

of their programs, policies, and activities on people of color 
populations and low-income populations in the United States.\10\ The 
EPA defines 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.\11\
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    \10\ 59 FR 7629 (Feb. 16, 1994).
    \11\ 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.'' A potential EJ concern is defined as ``the actual or 
potential lack of fair treatment or meaningful involvement of 
minority populations, low-income populations, Tribes, and indigenous 
peoples in the development, implementation and enforcement of 
environmental laws, regulations and policies.'' See, EPA's 
Environmental Justice During the Development of an Action. 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.
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    Executive Order 14008 also calls on federal agencies to make 
achieving environmental justice part of their missions ``by developing 
programs, policies, and activities to address the disproportionately 
high and adverse human health, environmental, climate-related and other 
cumulative impacts on disadvantaged communities, as well as the 
accompanying economic challenges of such impacts.'' \12\ It also 
declares a policy ``to secure environmental justice and spur economic 
opportunity for disadvantaged communities that have been historically 
marginalized and overburdened by pollution and under-investment in 
housing, transportation, water and wastewater infrastructure and health 
care.'' Under Executive Order 13563, federal agencies may consider 
equity, human dignity, fairness, and distributional considerations, 
where appropriate and permitted by law.\13\
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    \12\ 86 FR 7619 (Feb. 1, 2021).
    \13\ 76 FR 3821 (Jan. 18, 2011).
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    The United States has made substantial progress in reducing lead 
exposure, but disparities remain along racial, ethnic, and 
socioeconomic lines. For example, blood lead levels in children from 
low-income households remain higher than those in children from higher 
income households, and the most exposed Black children still have 
higher blood lead levels than the most exposed non-Hispanic White 
children.\14\ \15\ Depending on the levels and associated risk, such 
blood lead levels may lead to lifelong health effects and barriers to 
social and economic well-being.\16\
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    \14\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' pp. 5-40 
through 5-42. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \15\ EPA (2022) ``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.
    \16\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68; Section 1.9.5. ``Reversibility and 
Persistence of Neurotoxic Effects of Pb.'' p. 1-76. EPA, Washington, 
DC, EPA/600/R-10/075F, 2013.
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    In this action, the EPA is undertaking an evaluation, under section 
231(a)(2)(A) of the Clean Air Act, of whether 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, and 
therefore, our consideration of environmental justice is focused on 
describing populations living near airports in the United States. 
Section II.A.5 of this document, and the Technical Support Document 
\17\ for this action describe the scientific evidence and analyses 
conducted by the EPA that provide information about the disparity in 
residential location for some low-income populations, people of color 
and some indigenous peoples in the United States, particularly Alaska 
Natives, with regard to their proximity to some airports where covered 
aircraft operate. The information presented in Section II.A.5 of this 
document 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 people of color and low-income populations, they could indicate a 
potential environmental justice concern.
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    \17\ 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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Table of Contents

I. Executive Summary
II. Overview and Context for This Proposal
    A. Background Information Helpful to Understanding This Proposal
    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. History of Lead Endangerment Petitions for Rulemaking and the 
EPA Responses
III. Legal Framework for This Action
    A. Statutory Text and Basis for This Proposal
    B. Considerations for the Endangerment and Cause or Contribute 
Analyses Under Section 231(a)(2)(A)
    C. Regulatory Authority for Emission Standards
IV. The Proposed 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. Proposed Endangerment Finding
V. The Proposed Cause or Contribute Finding Under CAA Section 231
    A. Proposed Definition of the Air Pollutant
    B. The Data Used To Evaluate the Proposed Cause or Contribute 
Finding
    C. Proposed Cause or Contribution Finding for Lead
VI. Statutory Authority and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (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
    K. Determination Under Section 307(d)
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 proposes to find that

[[Page 62757]]

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 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--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.
    For purposes of this action, the EPA is proposing to define 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.\18\ In proposing to find 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.\19\ 
\20\ \21\ \22\ 
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    \18\ As noted in Section IV.A of this notice, the lead air 
pollution that we are considering in this proposed finding can occur 
as elemental lead or in lead-containing compounds.
    \19\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \20\ EPA (2006) AQC for Lead. EPA, Washington, DC, EPA/600/R-5/
144aF, 2006.
    \21\ EPA (1986) AQC for Lead. EPA, Washington, DC, EPA-600/8-83/
028aF-dF, 1986.
    \22\ EPA (1977) AQC 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 is proposing to 
define 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.\23\ Accordingly, the Administrator is proposing to find 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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    \23\ As noted in Section V.A of this notice, the lead air 
pollutant we are considering in this proposed finding can occur as 
elemental lead or in lead-containing compounds.
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    In addition to the proposed findings and the science on which they 
are based, this document includes an overview and background context 
helpful to understanding the source sector in the context of this 
proposal, a brief summary of some of the federal actions focused on 
reducing lead exposures, and the legal framework for this action.

II. Overview and Context for This Proposal

    We summarize here background information that provides additional 
context for this proposed 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 summary of citizen 
petitions for rulemaking regarding lead emissions from covered aircraft 
and the EPA responses.

A. Background Information Helpful to Understanding This Proposal

    This proposal 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 \24\ for lead and the lead 
NAAQS.\25\ 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, the 2013 Lead ISA \26\ as well as 
information summarized in previous assessments, including the 1977, 
1986, and 2006 AQCDs.\27\ \28\ \29\
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    \24\ 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).
    \25\ 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.''
    \26\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \27\ EPA (1977) AQC for Lead. EPA, Washington, DC, EPA-600/8-77-
017 (NTIS PB280411), 1977.
    \28\ EPA (1986) AQC for Lead. EPA, Washington, DC, EPA-600/8-83/
028aF-dF (NTIS PB87142386), 1986.
    \29\ EPA (2006) AQC 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.\30\ Lead emitted in the past 
can remain available for environmental or human exposure for extended 
time in some areas.\31\ 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.\32\ Lead in 
the environment today may have been airborne yesterday or emitted to 
the air long ago.\33\ Over time, lead that was initially emitted to air 
can become less available for environmental circulation by 
sequestration in soil, sediment and other reservoirs.\34\
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    \30\ 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.
    \31\ EPA (2013) ISA for Lead. Section 3.7.1. ``Exposure.'' p. 3-
144. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \32\ 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.
    \33\ 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.
    \34\ 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

[[Page 62758]]

ambient air.\35\ Ambient air inhalation pathways include both 
inhalation of air outdoors and inhalation of ambient air that has 
infiltrated into indoor environments.\36\ 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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    \35\ 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.
    \36\ 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.37 38 39 40 41 42 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,43 44 
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.\45\
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    \37\ 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.
    \38\ EPA (2006) AQC for Lead. Chapter 3. EPA, Washington, DC, 
EPA/600/R-5/144aF, 2006.
    \39\ EPA (1986) AQC for Lead. Section 1.11.3. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \40\ EPA (1977) AQC for Lead. Section 12.3.1.1. ``Air 
Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 (NTIS 
PB280411), 1977.
    \41\ EPA (1977) AQC for Lead. Section 12.3.1.2. ``Air 
Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 (NTIS 
PB280411), 1977.
    \42\ EPA (1977) AQC for Lead. Section 12.3.1.1. ``Air 
Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017 (NTIS 
PB280411), 1977.
    \43\ Miranda et al., 2011. A Geospatial Analysis of the Effects 
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental 
Health Perspectives. 119:1513-1516.
    \44\ 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.
    \45\ 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--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.
    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).\46\ 
Currently, 100LL is the most commonly available and most commonly used 
type of avgas.\47\ Tetraethyl lead was first used in piston-engine 
aircraft in 1927.\48\ 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.49 50 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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    \46\ ASTM International (May 1, 2021) Standard Specification for 
Leaded Aviation Gasolines D910-21.
    \47\ National Academies of Sciences, Engineering, and Medicine 
(NAS). 2021. Options for Reducing Lead Emissions from Piston-Engine 
Aircraft. Washington, DC: The National Academies Press. https://doi.org/10.17226/26050.
    \48\ Ogston 1981. A Short History of Aviation Gasoline 
Development, 1903-1980.Society of Automotive Engineers. p. 810848.
    \49\ 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.
    \50\ 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.,\51\ and the FAA provides information on the 
volume of leaded avgas consumed in the U.S.\52\ 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.\53\ As described later in this 
section, while the consumption of leaded avgas is expected to decrease 
three percent from 2026 to 2041, FAA projects increased activity at 
some airports and decreased activity at other airports out to 2045.
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    \51\ 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.
    \52\ Department of Transportation (DOT). FAA. Aviation Policy 
and Plans. FAA Aerospace Forecast Fiscal Years 2009-2025. p. 81. 
Available at http://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.
    \53\ 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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[[Page 62759]]

    The FAA's National Airspace System Resource (NASR) \54\ 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.\55\ While less aircraft activity occurs at the 
remaining 15,336 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.\56\ The 
activity by piston-engine aircraft spans a range of purposes, as 
described further below. In Alaska this fleet of aircraft currently 
play a critical role in the transportation infrastructure.
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    \54\ See FAA. NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
    \55\ 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.
    \56\ 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.\57\ This total includes 128,926 single-engine aircraft, 12,470 
twin-engine aircraft, and 3,089 rotorcraft.\58\ 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.\59\ In 2019, 883 new 
piston-engine aircraft were manufactured in the U.S. some of which are 
exported.\60\ For the period from 2019 through 2041, the fleet of fixed 
wing \61\ piston-engine aircraft is projected to decrease at an annual 
average rate of 0.9 percent, and the hours flown by these aircraft is 
projected to decrease 0.9 percent per year from 2019 to 2041.\62\ 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.\63\ There were approximately 664,565 pilots certified to 
fly general aviation aircraft in the U.S. in 2021.\64\ This included 
197,665 student pilots and 466,900 non-student pilots. In addition, 
there were more than 301,000 FAA Non-Pilot Certificated mechanics.\65\
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    \57\ 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/.
    \58\ 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/.
    \59\ 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.
    \60\ 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.
    \61\ 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.
    \62\ 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.
    \63\ 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.
    \64\ 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.
    \65\ 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.\66\ 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.\67\
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    \66\ 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/.
    \67\ 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/.
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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.\68\ 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 
2019.69 70
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    \68\ 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/.
    \69\ 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/.
    \70\ 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. Available at 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).\71\ 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,

[[Page 62760]]

general aviation activity is often used as a surrogate measure for 
understanding piston-engine activity.
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    \71\ 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.\72\ 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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    \72\ 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.\73\ 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.\74\ 
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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    \73\ 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.
    \74\ 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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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.75 76 77 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. Therefore, 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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    \75\ EPA (1977) AQC for Lead. EPA, Washington, DC, EPA-600/8-77-
017 (NTIS PB280411), 1977.
    \76\ EPA (1986) AQC for Lead. EPA, Washington, DC, EPA-600/8-83/
028aF-dF (NTIS PB87142386), 1986.
    \77\ 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.
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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, 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.\78\ 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.\79\ In addition to lead 
bromides, ammonium salts of other lead halides were also emitted by 
motor vehicles and would be expected in the exhaust of piston-engine 
aircraft.\80\
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    \78\ EPA (1986) AQC for Lead. EPA, Washington, DC, EPA-600/8-83/
028aF-dF (NTIS PB87142386), 1986.
    \79\ Griffith 2020. Electron microscopic characterization of 
exhaust particles containing lead dibromide beads expelled from 
aircraft burning leaded gasoline. Atmospheric Pollution Research 
11:1481-1486.
    \80\ EPA (1986) AQC 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.\81\ 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).\82\ 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.\83\
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    \81\ 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.
    \82\ 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.
    \83\ 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

[[Page 62761]]

measurements of lead.\84\ The Swiss FOCA reported the mean particle 
diameter of particulate matter emitted by one single-engine piston-
powered aircraft 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.\85\ 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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    \84\ 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.
    \85\ 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.
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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. in recent years, contributing over 50 
percent of lead emissions to air starting in 2008 (Table 1).\86\ 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.\87\ 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 
Aviation Gasoline \88\ and in the document titled ``Calculating Piston-
Engine Aircraft Airport Inventories for Lead for the 2008 National 
Emissions Inventory.'' \89\ 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.\90\
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    \86\ 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.
    \87\ EPA 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data.
    \88\ Advance Notice of Proposed Rulemaking on Lead Emissions 
from Piston-Engine Aircraft Using Leaded Aviation Gasoline. 75 FR 
2440 (April 28, 2010).
    \89\ 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).
    \90\ 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.

                                 Table 1--Piston-Engine Emissions of Lead to Air
----------------------------------------------------------------------------------------------------------------
                                                       2008            2011            2014            2017
----------------------------------------------------------------------------------------------------------------
Piston-engine emissions of lead to air, tons....             560             490             460             470
Total U.S. lead emissions, tons.................             950             810             720             670
Piston-engine emissions as a percent of the                  59%             60%             64%             70%
 total U.S. lead inventory......................
----------------------------------------------------------------------------------------------------------------

    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.\91\ Among the counties in the 
U.S. where the EPA estimates engine emissions of lead from covered 
aircraft, lead inventories range from 0.00005 tons per year to 4.1 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).\92\ 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 emission from covered aircraft, the 
contribution of aircraft engine emissions ranges from 0.0006 to 0.26 
tons, comprising 0.0065 to 99.98 percent of the county total, 
respectively.
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    \91\ 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.
    \92\ 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 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.\93\ 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

[[Page 62762]]

estimated to have inventories above 0.1 tons in 2045.\94\
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    \93\ See EPA lead inventory data available at https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms.
    \94\ EPA used the method describe 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.\95\
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    \95\ 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 concentrations of lead in air from piston-engine 
aircraft exhaust at, and downwind of, airports where these aircraft are 
active.96 97 98 99 
100 101 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.'' 102 103
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    \96\ 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.
    \97\ 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.
    \98\ 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.
    \99\ 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.
    \100\ 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.
    \101\ Lead emitted from piston-engine aircraft in the 
particulate phase would also be measured in samples collected to 
evaluate total ambient PM2.5 concentrations.
    \102\ 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).
    \103\ 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.
---------------------------------------------------------------------------

    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 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 (concentrations for periods of 
approximately 18 hours to three-month averages).104 
105 106 107 108 
109 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.110 111 
112 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).\113\
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    \104\ These studies report monitored or modeled data for 
averaging times ranging from approximately 18 hours to three-month 
averages.
    \105\ 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.
    \106\ 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.
    \107\ 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.
    \108\ 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.
    \109\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \110\ 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.
    \111\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020. EPA responses to peer review comments on the report are 
available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YIWD.pdf.
    \112\ 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.
    \113\ 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.
---------------------------------------------------------------------------

    The lead NAAQS was revised in 2008.\114\ 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 consecutive three-month average of 
lead in total suspended particles.\115\ 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 now 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

[[Page 62763]]

ton or more per year.\116\ 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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    \114\ 73 FR 66965 (Nov. 12, 2008).
    \115\ 40 CFR 50.16 (Nov. 12, 2008).
    \116\ 75 FR 81226 (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 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. 
117 118
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    \117\ 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.
    \118\ 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.

    Table 2--Lead Concentrations Monitored at 17 Airports in the U.S.
------------------------------------------------------------------------
                                                             Lead design
                       Airport, State                        value,\119\
                                                              [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.\120\
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    \119\ 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.
    \120\ 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.\121\
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    \121\ 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.
---------------------------------------------------------------------------

    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 anticipated 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.'' \122 123\ 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.\124\ 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 from the location of highest concentration.
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    \122\ EPA (2020) Model-Extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \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.
    \124\ 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.
---------------------------------------------------------------------------

    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.\125\ This approach for conducting a nationwide 
analysis of airports was selected due to the impact of piston-engine 
aircraft run-up

[[Page 62764]]

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.\126\
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    \125\ 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).
    \126\ 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.
---------------------------------------------------------------------------

    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 airports with activity ranging 
from 3,616-26,816 Landing and Take-Off events (LTOs) in a three-month 
period.\127\ 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.\128\ Model-extrapolated 
three-month average lead concentrations from aircraft engine emissions 
were estimated to extend to 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.\129\ 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 were estimated above background extending 
almost 1,000 meters downwind from the runway.\130\
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    \127\ 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.
    \128\ 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.
    \129\ 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.
    \130\ 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.
---------------------------------------------------------------------------

    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 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 
invites comment on the approach used in this model-extrapolation 
analysis.
    The EPA's model-extrapolation analysis of lead concentrations from 
engine emissions resulting from covered aircraft found that the lowest 
annual airport emissions of lead estimated to result in air lead 
concentrations approaching or potentially exceeding the NAAQS was 0.1 
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.\131\ The EPA's 
estimate of 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 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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    \131\ 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. EPA responses to peer review comments on the 
report are available here: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YIWD.pdf.
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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).\132\ 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 anthropogenic and 
natural sources, including aircraft engine emissions.\133\ The 2017 
AirToxScreen provides lead concentration estimates in air for 73,449

[[Page 62765]]

census tracts in the U.S.\134\ Lead emissions from piston-engine 
aircraft comprised more than 50 percent of these census block area-
weighted lead concentrations 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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    \132\ See EPA's 2017 AirToxScreen. Available at https://www.epa.gov/AirToxScreen.
    \133\ 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.
    \134\ 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 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),\135 136\ 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.\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.
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    \135\ 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.
    \136\ Griffith 2020. Electron microscopic characterization of 
exhaust particles containing lead dibromide beads expelled from 
aircraft burning leaded gasoline. Atmospheric Pollution Research 
11:1481-1486.
    \137\ EPA (2013) ISA for Lead. Section 1.3. ``Exposure to 
Ambient Pb.'' p. 1-11. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \138\ EPA (2006) AQC for Lead. Section E.6. p. 2-5. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
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    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.\139\ 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.\140\ Tetraethyl lead has an 
atmospheric residence time ranging from a few hours to a few days. 
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.\141\
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    \139\ EPA (1977) AQC for Lead. Section 6.2.2.1. EPA, Washington, 
DC, EPA-600/8-77-017, 1977.
    \140\ EPA (2006) AQC for Lead. Section E.6. EPA, Washington, DC, 
EPA/600/R-5/144aF, 2006.
    \141\ EPA (2006) AQC 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.\142\ 
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.\143\
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    \142\ 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.
    \143\ 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.\144\ 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.\145\ 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.\146\ 
Murphy et al. (2008) reported weekend increases in ambient lead 
monitored at remote locations in the U.S. that the authors attributed 
to weekend increases in piston-engine powered general aviation 
activity.\147\
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    \144\ EPA (2013) ISA for Lead. Section 2.6.1. ``Soils.'' p. 2-
118. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \145\ EPA (2013) ISA for Lead. Chapter 6. ``Ecological Effects 
of Pb.'' p. 6-57. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \146\ Murphy et al., 2008. Weekly patterns of aerosol in the 
United States. Atmospheric Chemistry and Physics. 8:2729-2739.
    \147\ 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 aircraft 
engine emissions.\148\ 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

[[Page 62766]]

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.149 150 151 152 153 154 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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    \148\ 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.
    \149\ McCumber and Strevett 2017. A Geospatial Analysis of Soil 
Lead Concentrations Around Regional Oklahoma Airports. Chemosphere 
167:62-70.
    \150\ 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.
    \151\ 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.
    \152\ 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.
    \153\ 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.
    \154\ 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.155 156 In this way, air lead sources may 
contribute to dietary exposure pathways.\157\ 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.\158\ The low flying height is needed to minimize the drift 
of the fertilizer and pesticide particles away from their intended 
target. 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,\159\ 
are slightly water soluble and, therefore, may be more readily absorbed 
by plants than other forms of inorganic lead.
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    \155\ 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.
    \156\ EPA (2006) AQC for Lead. Section 8.2.2. EPA, Washington, 
DC, EPA/600/R-5/144aF, 2006.
    \157\ EPA (2006) AQC for Lead. Section 8.2.2. EPA, Washington, 
DC, EPA/600/R-5/144aF, 2006.
    \158\ 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.agaviation.org/Files/RelatedEntities/Aerial_Applicators_Manual.pdf.
    \159\ 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.
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    The 2006 AQCD indicated that surface deposition of lead onto plants 
may be significant.\160\ Atmospheric deposition of lead provides a 
pathway for lead in vegetation as a result of contact with above-ground 
portions of the plant.161 162 163 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.\164\
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    \160\ EPA (2006) AQC for Lead. pp. 7-9 and AXZ7-39. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
    \161\ EPA (2006) AQC for Lead. p. AXZ7-39. EPA, Washington, DC, 
EPA/600/R-5/144aF, 2006.
    \162\ EPA (1986) AQC for Lead. Sections 6.5.3. EPA, Washington, 
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \163\ EPA (1986) AQC for Lead. Section 7.2.2.2.1.EPA, 
Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \164\ EPA (1986) AQC for Lead. Section 7.2.2.2.2. EPA, 
Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
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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).\165\ Alkyl lead, in particular, has 
been identified by the EPA as a Persistent, Bioaccumulative, and Toxic 
(PBT) pollutant.\166\ 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.\167\ 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.
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    \165\ 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.
    \166\ EPA (2002) Persistent, Bioaccumulative, and Toxic 
Pollutants (PBT) Program. PBT National Action Plan for Alkyl-Pb. 
Washington, DC. June. 2002.
    \167\ See FAA's NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
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    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 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.\168\ 
Leaded avgas discharged to the ground and water includes other

[[Page 62767]]

hazardous fuel components such as ethylene dibromide.\169\
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    \168\ 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.
    \169\ 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. Consideration of EJ 
implications in the population living near airports is important 
because blood lead levels in children from low-income households remain 
higher than those in children from higher income households, and the 
most exposed Black children still have higher blood lead levels than 
the most exposed non-Hispanic White children.\170\ \171\ \172\
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    \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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    Executive Orders 12898 (59 FR 7629, February 16, 1994) and 14008 
(86 FR 7619, February 1, 2021) direct Federal agencies, to the greatest 
extent practicable and permitted by law, to make achieving EJ part of 
their mission by identifying and addressing, as appropriate, 
disproportionately high and adverse human health or environmental 
effects of their programs, policies, and activities on people of color 
populations and low-income populations in the United States. The EPA 
defines 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.
    For the reasons described in Supplementary Information Section D, 
our consideration of EJ implications here is focused on describing 
conditions relevant to the most recent year for which demographic data 
are available. 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. Residential proximity to airports implies that there is 
an increased potential for exposure to lead from covered aircraft 
engine emissions.\173\ 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, two studies have reported increased 
blood lead levels in children with increasing proximity to 
airports.\174\ \175\
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    \173\ 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 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.
    \174\ Miranda et al., 2011. A Geospatial Analysis of the Effects 
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental 
Health Perspectives. 119:1513-1516.
    \175\ 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.
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    We first summarize here the literature on disparity with regard to 
those who live in proximity to airports. Then we describe the analyses 
the EPA has 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 of the population 
compared with the general population, including near transportation 
sources.\176\ \177\ \178\ \179\ \180\ 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.\181\ 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.\182\ 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.\183\
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    \176\ 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.
    \177\ 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.
    \178\ 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.
    \179\ Tessum et al., 2021. PM2.5 polluters 
disproportionately and systemically affect people of color in the 
United States. Science Advances 7:eabf4491.
    \180\ Mohai et al., 2009. Environmental justice. Annual Reviews 
34:405-430. Available at https://doi.org/10.1146/annurev-environ-082508-094348.
    \181\ McNair 2020. Investigation of environmental justice 
analysis in airport planning practice from 2000 to 2010. 
Transportation Research Part D 81:102286.
    \182\ 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.
    \183\ 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.
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    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

[[Page 62768]]

School Near U.S. Airports.'' \184\ 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.
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    \184\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020. EPA responses to peer review comments on the report are 
available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YISM.pdf.
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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 on individual days downwind of a runway, depending on aircraft 
activity and prevailing wind direction.185 186 187
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    \185\ EPA (2020) Model-extrapolated Estimates of Airborne Lead 
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \186\ 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.
    \187\ 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.
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    Because the U.S. has a dense network of airports, many of which 
have neighboring communities, we first quantified the number of people 
living and children attending school within 500 meters of the 
approximately 20,000 airports in the U.S. The results of this analysis 
are summarized at the national scale in the EPA's report titled 
``National Analysis of the Populations Residing Near or Attending 
School Near U.S. Airports.'' \188\ 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 age 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.\189\
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    \188\ 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.
    \189\ 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.
---------------------------------------------------------------------------

    In order to identify potential disparities in the near-airport 
population, we first 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.\190\ 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 compared with the percent of these groups in the state 
population.\191\ Results of this analysis are presented in the 
following tables.\192\ 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.
---------------------------------------------------------------------------

    \190\ 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.
    \191\ 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.
    \192\ 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 living within 500 meters of a runway represent 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    under within    under within    under in the
                                                    500 meters       the state      500 meters         state
----------------------------------------------------------------------------------------------------------------
Nevada..........................................              10               8           1,000         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).

[[Page 62769]]

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

    Among Native Americans and Alaska Natives, 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, as anticipated due to the critical nature of air travel for 
the transportation infrastructure in that state, the disparity in 
residential proximity to a runway was the largest; 16,000 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 compared with 15 percent of the Alaska state population 
(Table 6).

 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
                                                  Percent Native  Percent Native   American and       Native
                                                   American and    American and    Alaska Native   American and
                      State                        Alaska Native   Alaska Native    population     Alaska Native
                                                    within 500      within the      within 500     population in
                                                      meters           state          meters         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.\193\ \194\ 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

[[Page 62770]]

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.
---------------------------------------------------------------------------

    \193\ 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.
    \194\ 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 \a\
                                 -------------------------------------------------------------------------------
        Demographic group         Total airports                   Disparity 5-    Disparity 10-
                                  with disparity  Disparity 1-5%        10%             20%       Disparity 20%+
----------------------------------------------------------------------------------------------------------------
Children under five years of age             515             507               7               1               0
People with income less than                 761             307             223             180              51
 twice the Federal Poverty Level
People of Color (all races,                  666             377             126             123              40
 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 \195\............
Non-Hispanic Hawaiian or Pacific              18              17               1               0               0
 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.\196\
---------------------------------------------------------------------------

    \195\ This analysis of 2,022 NPIAS airports did not include 
airports in Alaska.
    \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.
---------------------------------------------------------------------------

    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, and their 
implications discussed in Kamal et.al. (2022).\197\
---------------------------------------------------------------------------

    \197\ 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 here 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 people of color 
and low-income populations, they could indicate a potential EJ concern. 
Given the number of children in close proximity to runways, including 
those in EJ populations, there is a potential for substantial 
implications for children's health. The EPA invites comment on the 
potential EJ impacts of aircraft lead emissions from aircraft engines 
and on the potential impacts on children in close proximity to runways 
where piston-engine aircraft operate.

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 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.\198\ In this 
section, we describe some of the EPA's actions to reduce lead exposures 
from air, water, lead-based paint, and contaminated sites.
---------------------------------------------------------------------------

    \198\ 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.
---------------------------------------------------------------------------

    In 1976, the EPA listed lead under CAA section 108, making it what 
is called a ``criteria air pollutant.'' \199\ 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.\200\ The 
EPA's 2016 Federal Register notice describes the Agency's decision to 
retain the existing Lead

[[Page 62771]]

NAAQS.\201\ The Lead NAAQS is currently undergoing review.\202\
---------------------------------------------------------------------------

    \199\ 41 FR 14921 (April 8, 1976). See also, e.g., 81 FR at 
71910 (Oct. 18, 2016) for a description of the history of the 
listing decision for lead under CAA section 108.
    \200\ 73 FR 66965 (Nov. 12, 2008).
    \201\ 81 FR 71912-71913 (Oct. 18, 2016).
    \202\ 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.
---------------------------------------------------------------------------

    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 EPA 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. The states, in conjunction with the 
EPA, also administer the Prevention of Significant Deterioration 
program for these pollutants.
    Additional EPA programs to address lead in the environment include 
the Federal Motor Vehicle Control program under Title II of the Act, 
which involves controls for motor vehicles and nonroad engines and 
equipment; 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 112 and 129. For example, in January 
2012, the EPA updated the NESHAP for the secondary lead smelting source 
category.\203\ 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.\204\
---------------------------------------------------------------------------

    \203\ 77 FR 555 (Jan. 5, 2012).
    \204\ 78 FR 9112 (Feb. 7, 2013).
---------------------------------------------------------------------------

    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 for potable water applications may 
not be used in new installations or repairs or introduced into commerce 
unless it is considered ``lead free'' as defined by that Act.\205\ Also 
under section 1412 of the SDWA, the EPA's 1991 Lead and Copper Rule 
\206\ regulates lead in public drinking water systems through corrosion 
control and other utility actions which work together to minimize lead 
levels at the tap.\207\ On January 15, 2021, the agency published the 
Lead and Copper Rule Revisions (LCRR) \208\ and subsequently reviewed 
the rule in accordance with Executive Order 13990.\209\ While the LCRR 
took effect in December 2021, the agency concluded that there are 
significant opportunities to improve the LCRR.\210\ The EPA is 
developing a new proposed rule, the Lead and Copper Rule Improvements 
(LCRI),\211\ that would 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 ``methods to identify and trigger action in communities 
that are most at risk of elevated drinking water levels.'' \212\ The 
EPA intends to propose the LCRI and take final action on it prior to 
October 16, 2024.
---------------------------------------------------------------------------

    \205\ 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.
    \206\ 40 CFR 141 Subpart I (June 7, 1991).
    \207\ 40 CFR 141 Subpart I (June 7, 1991).
    \208\ 86 FR 4198. (Jan. 15, 2021).
    \209\ E.O. 13990. Protecting Public Health and the Environment 
and Restoring Science to Tackle the Climate Crisis. 86 FR 7037 (Jan. 
20, 2021).
    \210\ 86 FR 31939. (Dec. 17, 2021).
    \211\ See https://www.epa.gov/ground-water-and-drinking-water/review-national-primary-drinking-water-regulation-lead-and-copper. 
Accessed on Nov. 30, 2021.
    \212\ 86 FR 31939 (Dec. 17, 2021).
---------------------------------------------------------------------------

    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.'' \213\ 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.\214\ 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

[[Page 62772]]

and windowsills, respectively.\215\ The EPA is now reconsidering the 
2019 and 2021 rules in accordance with Executive Order 13990 \216\ and 
in response to a May 2021 decision by U.S. Court of Appeals for the 
Ninth Circuit.
---------------------------------------------------------------------------

    \213\ 66 FR 1206 (Jan. 5, 2001).
    \214\ 84 FR 32632 (July 9, 2019).
    \215\ 86 FR 983 (Jan. 7, 2021).
    \216\ 86 FR 7037 (Jan. 20, 2021).
---------------------------------------------------------------------------

    Programs associated with the Comprehensive Environmental Response, 
Compensation, and Liability Act (CERCLA or Superfund) \217\ and 
Resource Conservation Recovery Act (RCRA) \218\ also implement removal 
and remedial response programs that reduce exposures to the release or 
threat of a release of lead and other hazardous substances. The EPA 
develops and implements protective levels for lead in soil 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 sites. Federal programs, including 
those implementing RCRA, provide for management of hazardous substances 
in hazardous and municipal solid waste (e.g., 66 FR 58258, November 20, 
2001).
---------------------------------------------------------------------------

    \217\ For more information about the EPA's CERCLA program, see 
www.epa.gov/superfund.
    \218\ For more information about the EPA's RCRA program, see 
https://www.epa.gov/rcra.
---------------------------------------------------------------------------

C. History of Lead Endangerment Petitions for Rulemaking and the EPA 
Responses

    The Administrator's proposed 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 here.\219\
---------------------------------------------------------------------------

    \219\ See https://www.epa.gov/regulations-emissions-vehicles-and-engines/petitions-and-epa-response-memorandums-related-lead. 
Accessed on Dec. 12, 2021.
---------------------------------------------------------------------------

    In a 2003 letter to the EPA, Friends of the Earth initially raised 
the issue of the potential for lead emissions from the use of leaded 
avgas in general aviation aircraft using piston engines to cause or 
contribute to endangerment of public health or welfare.\220\ In 2006, 
Friends of the Earth filed a petition with the EPA requesting that the 
Administrator find endangerment or, if there was insufficient 
information to find endangerment, commence a study of lead emissions 
from piston-engine aircraft. In 2007, the EPA issued a Federal Register 
notice on the petition requesting comments and information related to a 
wide range of issues regarding the use of leaded avgas and potential 
public health and welfare exposure issues.\221\ The EPA did not receive 
new information to inform the evaluation of whether lead emissions from 
aircraft engines using leaded avgas cause or contribute to air 
pollution which may reasonably be anticipated to endanger public health 
or welfare.
---------------------------------------------------------------------------

    \220\ Friends of the Earth (formerly Bluewater Network) comment 
dated Dec. 12, 2003, submitted to EPA's 68 FR 56226, published Sept. 
30, 2003.
    \221\ See 72 FR 64570 (Nov. 16, 2007).
---------------------------------------------------------------------------

    In 2010, the EPA further responded to the 2006 petition from 
Friends of the Earth by issuing an Advance Notice of Proposed 
Rulemaking on Lead Emissions from Piston-Engine Aircraft Using Leaded 
Aviation Gasoline (ANPR).\222\ In the ANPR, the EPA described 
information currently available and information being collected that 
would be used by the Administrator to issue a subsequent proposal 
regarding whether, in the Administrator's judgment, aircraft lead 
emissions from aircraft using leaded avgas cause or contribute to air 
pollution which may reasonably be anticipated to endanger public health 
or welfare. After issuing the ANPR, the EPA continued the data 
collection and evaluation of information that is described in Sections 
II.A, IV and V of this action.
---------------------------------------------------------------------------

    \222\ 75 FR 22440-68 (Apr. 28, 2010).
---------------------------------------------------------------------------

    In 2012, Friends of the Earth, Physicians for Social 
Responsibility, and Oregon Aviation Watch filed a new petition claiming 
that, among other things, the EPA had unreasonably delayed in 
responding to the 2006 petition from Friends of the Earth because it 
had failed to determine whether emissions of lead from general aviation 
aircraft engines cause or contribute to air pollution which may 
reasonably be anticipated to endanger public health or welfare.\223\ 
The EPA responded to the 2012 petition with our plan for collecting the 
necessary information and conducting 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. Friends of the Earth, Physicians for 
Social Responsibility, and Oregon Aviation Watch submitted a petition 
for reconsideration in 2014 \224\ to which the EPA responded in 
2015.\225\
---------------------------------------------------------------------------

    \223\ Petitioners filed a complaint in district court seeking to 
compel EPA to respond to their 2006 petition for rulemaking and to 
issue an endangerment finding and promulgate regulations. The EPA 
then issued its response to the petition, mooting that claim of the 
complaint. In response to EPA's motion for summary judgment on the 
remaining claims, the court concluded that making the endangerment 
determination is not a nondiscretionary act or duty and thus that it 
lacked jurisdiction to grant the relief requested by plaintiffs. 
Friends of the Earth v. EPA, 934 F. Supp. 2d 40, 55 (D.D.C. 2013).
    \224\ The petition for reconsideration submitted to EPA by 
Friends of the Earth, Physicians for Social Responsibility, and 
Oregon Aviation Watch is available at https://www.epa.gov/sites/default/files/2016-09/documents/avgas-petition-reconsider-04-21-14.pdf.
    \225\ The 2015 EPA response to the 2014 petition for 
reconsideration is available at https://www.epa.gov/sites/default/files/2016-09/documents/ltr-response-av-ld-foe-psr-oaw-2015-1-23.pdf.
---------------------------------------------------------------------------

    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.\226\ The EPA responded in 2022 noting our intent to develop 
this proposal 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.\227\
---------------------------------------------------------------------------

    \226\ 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.
    \227\ 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 proposing to make 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

[[Page 62773]]

provided a detailed explanation of the legal framework for making such 
findings and the statutory interpretations and caselaw supporting its 
approach.\228\ In this proposal, the Administrator is using the same 
approach of applying a two-part test under section 231(a)(2)(A) as 
described in the 2016 Findings and is relying on the same 
interpretations supporting that approach, which are briefly described 
in this Section, and set forth in greater detail in the 2016 
Findings.\229\ This is also 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),\230\ which was 
affirmed by the U.S. Court of Appeals for the D.C. Circuit in 
2012.\231\ As explained further in the 2016 Findings, the text of the 
CAA section concerning aircraft emissions in section 231(a)(2)(A) 
mirrors the text of CAA section 202(a) that was the basis for the 2009 
Findings.\232\ 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 proposing to act 
consistently with that framework for purposes of these proposed section 
231 findings.\233\ As this approach has been previously discussed at 
length in the 2016 and 2009 Findings, the EPA provides only a brief 
description in this proposal.
---------------------------------------------------------------------------

    \228\ FR 54422-54475 (Aug. 15, 2016).
    \229\ See e.g., 81 FR at 55434-54440 (Aug. 19, 2016).
    \230\ 74 FR 66496, 66505-10 (Dec. 15, 2009).
    \231\ Coalition for Responsible Regulation, Inc. v. EPA, 684 
F.3d 102 (D.C. Cir. 2012) (CRR) (subsequent history omitted).
    \232\ 81 FR at 55434 (Aug. 19, 2016).
    \233\ 81 FR at 55434 (Aug. 19, 2016).
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A. Statutory Text and Basis for This Proposal

    Section 231(a)(2)(A) of the CAA provides that the ``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.'' \234\ In this proposal, 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 and in the 2009 Findings.
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    \234\ 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.
---------------------------------------------------------------------------

    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.\235\
---------------------------------------------------------------------------

    \235\ 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.\236\ 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.'' \237\ 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.'' \238\ The 
same language appears in section 231(a)(2)(A), and the same 
interpretation applies in that context.
---------------------------------------------------------------------------

    \236\ See 81 FR at 54435 (Aug. 19, 2016).
    \237\ CRR, 684 F.3d at 122 (internal citations omitted) (June 
26, 2012).
    \238\ 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.\239\ Comment has been taken on these 
proposed findings as part of the notice and comment process for the 
emission standards.\240\ However, there is no requirement that the 
Administrator propose the endangerment and cause or contribute findings 
concurrently with proposed standards and, most recently under section 
231, the EPA made separate endangerment and cause or contribute 
findings for GHGs before proceeding to set standards.
---------------------------------------------------------------------------

    \239\ 81 FR at 54425 (Aug. 19, 2016).
    \240\ 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).
---------------------------------------------------------------------------

    The Administrator is applying the rulemaking 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.'' \241\ Any subsequent

[[Page 62774]]

standard setting rulemaking under CAA section 231 will also be subject 
to the notice and comment rulemaking 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 proposed 
findings will be subject to the same procedural requirements that would 
apply if the proposed findings were part of a standard-setting 
rulemaking.
---------------------------------------------------------------------------

    \241\ 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 proposal, 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.\242\
---------------------------------------------------------------------------

    \242\ See CRR, 684 F.3d at 117 (explaining two-part analysis 
under section 202(a)) (June 26, 2012).
---------------------------------------------------------------------------

    This analysis entails a scientific judgment by the Administrator 
about the potential risks posed by lead emissions to public health and 
welfare. In this proposed action, the EPA is using the same approach in 
making scientific judgments regarding endangerment as it has previously 
described in the 2016 Findings, and its analysis is guided by the same 
five principles that guided the Administrator's analysis in those 
Findings.\243\
---------------------------------------------------------------------------

    \243\ See, e.g., 81 FR 54422, 54434-55435 (Aug. 15, 2016).
---------------------------------------------------------------------------

    Similarly, the EPA is taking the same approach to the cause or 
contribute analysis as was previously explained in the 2016 
Findings.\244\ 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.\245\ Moreover, 
like the CAA section 202(a) language 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.'' \246\ 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.\247\ 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.\248\
---------------------------------------------------------------------------

    \244\ See, e.g., 81 FR at 54437-54438 (September 4, 2013).
    \245\ See, e.g., 81 FR at 54437-54438 (Aug. 15, 2016).
    \246\ See, e.g., 81 FR at 54437-54438 (Aug. 15, 2016).
    \247\ See 81 FR at 54437-54438 (Aug. 15, 2016).
    \248\ See 81 FR at 54437-54438 (Aug. 15, 2016).
---------------------------------------------------------------------------

    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.\249\ 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.'' \250\ 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.'' \251\ 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).\252\ 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.\253\ 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.\254\
---------------------------------------------------------------------------

    \249\ See 81 FR at 54437-54438 (Aug. 15, 2016).
    \250\ CRR, 684 F.3d at 122-123 (June 26, 2012).
    \251\ CRR, 684 F.3d at 122-123. (quoting Ethyl Corp., 541 F.2d 
at 18) (June 26, 2012).
    \252\ 81 FR at 54438 (Aug. 15, 2016).
    \253\ 81 FR at 54438 (Aug. 15, 2016).
    \254\ 81 FR at 54438 (Aug. 15, 2016).
---------------------------------------------------------------------------

    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.\255\
---------------------------------------------------------------------------

    \255\ See 81 FR at 54462 (Aug. 15, 2016).
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C. Regulatory Authority for Emission Standards

    Though the EPA is not proposing standards in this action, should 
the EPA finalize these findings, the EPA would then proceed to propose 
emission standards under CAA section 231. As noted in Section III.A of 
this document, section 231(a)(2)(A) of the CAA directs the 
Administrator of the EPA to, from time to time, propose aircraft engine 
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 notice and an opportunity for 
a public hearing on standards, the Administrator shall issue such 
standards ``with such modifications as he deems appropriate.'' In 
addition, under CAA section 231(b), the EPA determines, in consultation 
with the U.S. Department of Transportation (DOT), that the effective 
date of any standard provides the necessary time to permit the 
development and application of the requisite technology, giving 
appropriate consideration to the cost of compliance.
    Once the EPA adopts standards, CAA section 232 then directs the 
Secretary of Transportation 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

[[Page 62775]]

emissions unless such standard is identical to the EPA's 
standards.\256\
---------------------------------------------------------------------------

    \256\ CAA Section 233 (Dec. 31, 1970).
---------------------------------------------------------------------------

IV. The Proposed Endangerment Finding Under CAA Section 231

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.\257\ 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.\258\ 
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.
---------------------------------------------------------------------------

    \257\ EPA (2013) ISA for Lead. Section 2.2. ``Sources of 
Atmospheric Pb.'' p. 2-1. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
    \258\ 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.
---------------------------------------------------------------------------

    For purposes of this action, the EPA is proposing to define 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.\259\
---------------------------------------------------------------------------

    \259\ The lead air pollution that we are considering in this 
proposed finding can occur as elemental lead or in lead-containing 
compounds, and this proposed 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
    As noted in Section II.A of this document, 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 on which the Administrator is proposing to find that 
lead air pollution is reasonably anticipated to endanger public health 
and welfare.\260 261\
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    \260\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-
10/075F, 2013.
    \261\ EPA (2006) AQC for Lead. EPA, Washington, DC, EPA/600/R-5/
144aF, 2006.
---------------------------------------------------------------------------

    As summarized in Section II.A of this document, human exposure to 
lead that is emitted into the air can occur by multiple pathways. 
Ambient air inhalation pathways include both inhalation of air outdoors 
and inhalation of 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. While 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), 
as described in Section II.A of this document, it is well-documented 
that exposures to air-related lead can result in increased blood lead 
levels, particularly for children living near air lead sources, who may 
have increased blood lead levels due to their proximity to these 
sources of exposure.\262\
---------------------------------------------------------------------------

    \262\ 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 Criteria 
Documents, 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.\263\ 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,'' or a ``likely to be causal relationship,'' 
or for which the evidence is ``suggestive of a causal relationship'' 
between lead exposure and a health effect.\264\ 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.
---------------------------------------------------------------------------

    \263\ 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.
    \264\ 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.
---------------------------------------------------------------------------

    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).\265\ 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.\266\
---------------------------------------------------------------------------

    \265\ 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.
    \266\ 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.
---------------------------------------------------------------------------

    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.\267\
---------------------------------------------------------------------------

    \267\ 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.
---------------------------------------------------------------------------

    Intelligence quotient is a well-established, widely recognized and 
rigorously standardized measure of neurocognitive function which has 
been

[[Page 62776]]

used extensively as a measure of the negative effects of exposure to 
lead.268 269 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.\270\
---------------------------------------------------------------------------

    \268\ EPA (2013) ISA for Lead. Section 4.3.2. ``Cognitive 
Function.'' p. 4-59. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \269\ EPA (2006) AQC for Lead. Sections 6.2.2 and 8.4.2. EPA, 
Washington, DC, EPA/600/R-5/144aF, 2006.
    \270\ EPA (2013) ISA for Lead. Section 4.3.2. ``Cognitive 
Function.'' p. 4-59. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    In summarizing the evidence related to neurocognitive impacts of 
lead at different childhood lifestages, the 2013 Lead ISA notes that 
``in individual studies, postnatal (early childhood and concurrent 
[with IQ testing]) blood lead levels are also consistently associated 
with cognitive function decrements in children and adolescents.'' \271\ 
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.'' \272\ 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 lead exposures that are part of the 
effects and blood lead levels observed in epidemiologic studies 
(uncertainties which are greater in studies of older children and 
adults than in studies of younger children).\273\ 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,\274\ potentially affecting lower educational 
attainment and financial well-being.\275\
---------------------------------------------------------------------------

    \271\ 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.
    \272\ 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.
    \273\ 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.
    \274\ 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.
    \275\ 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.
---------------------------------------------------------------------------

    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.\276\ 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''.\277\ 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.\278\
---------------------------------------------------------------------------

    \276\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
    \277\ EPA (2013) ISA for Lead. Executive Summary. ``Public 
Health Significance.'' p. xciii. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \278\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
---------------------------------------------------------------------------

    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 the role of 
past versus current exposures to lead is unclear.\279\
---------------------------------------------------------------------------

    \279\ EPA (2013) ISA for Lead. Section 1.9.1. ``Public Health 
Significance.'' p. 1-68. EPA, Washington, DC, EPA/600/R-10/075F, 
2013.
---------------------------------------------------------------------------

    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.'' \280\ 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.'' \281\ 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.\282\ 
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.'' \283\ 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.'' \284\
---------------------------------------------------------------------------

    \280\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \281\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \282\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \283\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of 
Pb Exposure in Adults.'' p. lxxxviii. EPA/600/R-10/075F, 2013.
    \284\ 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.\285\
---------------------------------------------------------------------------

    \285\ 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.
---------------------------------------------------------------------------

    Additionally, the evidence is suggestive of lead exposure and some 
additional effects. These include auditory function decrements and

[[Page 62777]]

subclinical atherosclerosis, reduced kidney function, birth outcomes 
(e.g., low birth weight, spontaneous abortion), and female reproductive 
function.\286\
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    \286\ 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.\287\ 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.'' \288\
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    \287\ 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.
    \288\ 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.\289\ 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).\290\
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    \289\ 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.
    \290\ 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.\291\ 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.
---------------------------------------------------------------------------

    \291\ 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.\292\
---------------------------------------------------------------------------

    \292\ 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.\293\
---------------------------------------------------------------------------

    \293\ 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.'' \294\
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    \294\ EPA (2013) ISA for Lead. ``Summary.'' p. xcvi. EPA, 
Washington, DC, EPA/600/R-10/075F, 2013.
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B. Proposed Endangerment Finding

    The Administrator proposes to find, 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 proposal 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.

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

A. Proposed 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

[[Page 62778]]

section 231 for greenhouse gases, in making this proposed 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 proposes to 
define the air pollutant to match the proposed definition of the air 
pollution, such that the air pollutant analyzed for contribution would 
mirror the air pollution considered in the endangerment finding. 
Accordingly, for purposes of this action, the Administrator is 
proposing to define 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.\295\ 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.
---------------------------------------------------------------------------

    \295\ The lead air pollutant we are considering in this proposed 
finding 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.
---------------------------------------------------------------------------

    Under section 231(a), the Administrator is required to set 
``emission standards applicable to the emission of any air pollutant'' 
from classes of aircraft engines that the Administrator determines 
causes or contributes to air pollution that may reasonably be 
anticipated to endanger public health or welfare. If the Administrator 
makes a final determination under section 231 that the emissions of the 
lead air pollutant from certain classes of aircraft engines cause or 
contribute to air pollution that may reasonably be anticipated to 
endanger public health and welfare, then he is called on to set 
standards applicable to the emission of this air pollutant. The term 
``standards applicable to the emission of any air pollutant'' is not 
defined, and the Administrator has the discretion to interpret it in a 
reasonable manner to effectuate the purposes of section 231. We 
anticipate that the Administrator would consider a variety of factors 
in determining what approach to take in setting the standard or 
standards, and the EPA would provide notice and an opportunity to 
comment on the proposed standards before finalizing them.

B. The Data Used To Evaluate the Proposed 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 is 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 potential future conditions.
    As used in this proposal, 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--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.\296\ 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 0.0006 to 0.26 tons per year, 
comprising 0.0065 to 99.98 percent (respectively) of total lead 
emissions to air in those counties from covered aircraft.\297\
---------------------------------------------------------------------------

    \296\ 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.
    \297\ 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.\298\ General aviation activity, largely conducted by covered 
aircraft, increased up to 52 percent at airports that are among the 
busiest in the U.S.\299\ 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.\300\ Although there is some uncertainty in these projections, 
they indicate that lead emissions from covered aircraft may increase at 
some airports in the future.\301\
---------------------------------------------------------------------------

    \298\ 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/.
    \299\ 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.
    \300\ 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.
    \301\ 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 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

[[Page 62779]]

to lead air pollution, as defined in Section V.A of this document, the 
EPA also considers 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.302 303 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.304 305 306
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    \302\ 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.
    \303\ 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.
    \304\ 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.
    \305\ 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.
    \306\ 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.
---------------------------------------------------------------------------

    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.307 308 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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    \307\ 73 FR 66965 (Nov. 12, 2008).
    \308\ 75 FR 81226 (Dec. 27, 2010).
---------------------------------------------------------------------------

    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 (starting on March 10, 2012) and the McClellan-Palomar 
Airport (starting 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.\309\ 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.
---------------------------------------------------------------------------

    \309\ 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 lead concentration in over half 
of the census tracts in the U.S.\310\
---------------------------------------------------------------------------

    \310\ EPA's 2017 AirToxScreen is available at https://www.epa.gov/AirToxScreen.
---------------------------------------------------------------------------

    The EPA also notes that lead emissions from engines in covered 
aircraft are present 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.311 312 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.
---------------------------------------------------------------------------

    \311\ 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.
    \312\ 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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C. Proposed Cause or Contribution Finding for Lead

    Taking into consideration the data and information summarized in 
Section V of this document, the Administrator proposes to find 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 
proposed conclusion, the Administrator notes that piston-engine 
aircraft operate on leaded avgas. That operation emits lead-

[[Page 62780]]

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, and present 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 proposed 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, and more recently, in 2017, when approximately 470 tons of 
lead was emitted by engines in covered aircraft.\313\
---------------------------------------------------------------------------

    \313\ 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 quality that exceeds 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.\314\ 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 add 
support for the proposed conclusion that lead emissions from engines in 
covered aircraft cause or contribute to the endangering air pollution.
---------------------------------------------------------------------------

    \314\ 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. 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. 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 is proposing to find 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.
    Accordingly, for all the reasons described, the Administrator 
proposes to conclude 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 13563: Improving Regulation and Regulatory Review

    This action is a ``significant regulatory action'' because of the 
cross-agency nature of this issue. Accordingly, it was submitted to the 
Office of Management and Budget (OMB) for review under Executive Order 
12866. This action proposes 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. Any changes made in response to OMB 
recommendations have been documented in the docket.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. The proposed 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 proposed 
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 proposed 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. Accordingly, this 
action affords no opportunity for the EPA to fashion for small entities 
less burdensome compliance or reporting requirements or timetables or 
exemptions from all or part of the proposal.

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.

[[Page 62781]]

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 proposed 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 proposed 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.\315\ 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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    \315\ 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.
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G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    The EPA interprets E.O. 13045 (62 FR 19885, April 23, 1997) as 
applying only to those regulatory actions that concern health or safety 
risks, such that the analysis required under section 5-501 of the E.O. 
has the potential to influence the regulation. This action is not 
subject to E.O. 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 proposed endangerment and cause or contribute findings under CAA 
section 231(a)(2)(A), the proposed findings themselves, if finalized, 
would not impose a standard intended to mitigate those risks. While 
this action is not subject to Executive Order 13045 in this scenario, 
the Agency's Policy on Children's Health \316\ still applies. The 
Administrator considered lead exposure risks to children as part of 
this proposed endangerment finding under CAA section 231(a)(2)(A). This 
action's discussion of the impacts of lead exposure on public health 
and welfare is found in Section IV of this document, and specific 
discussion with regard to children are contained in Supplemental 
Information Section C, as well as Sections II.A.5, and IV 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).
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    \316\ EPA (2021) EPA Policy on Children's Health. Available at 
https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf.
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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 
proposed 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 proposed 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

    The EPA believes this action will not have potentially 
disproportionately high and adverse human health or environmental 
effects on people of color, low-income, or indigenous populations 
because this action does not affect the level of protection provided to 
human health or the environment. The Administrator considered the 
potential for lead exposure risks to people of color, low-income, and 
indigenous populations as part of this proposed endangerment finding 
under CAA section 231(a)(2)(A). This action's discussion of lead 
exposure impacts on public health and welfare is found in Section IV of 
this document. Specific discussion focused on environmental justice 
with regard to people of color, low-income, and indigenous populations 
are found in Supplemental Information Section D, as well as Sections 
II.A.5, and Section IV of this document. A copy of the documents 
pertaining to the EPA's analysis of potential environmental justice 
concerns related to this action have been placed in the public docket 
for this action (Docket EPA-HQ-OAR-2022-0389).

K. 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).

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. 2022-22223 Filed 10-14-22; 8:45 am]
BILLING CODE 6560-50-P