72372 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
1The FAA regulates ultralight vehicles under 14 
CFR part 103. 
2Rotorcraft 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. List of Subjects in 33 CFR Part 165 
Harbors, Marine safety, Navigation 
(water), Reporting and recordkeeping 
requirements, Security measures, Waterways. 
For the reasons discussed in the 
preamble, the Coast Guard amends 33 CFR part 165 as follows: 
PART 165—REGULATED NAVIGATION 
AREAS AND LIMITED ACCESS AREAS 
■1. The authority citation for part 165 
continues to read as follows: 
Authority: 46 U.S.C. 70034, 70051, 70124; 
33 CFR 1.05–1, 6.04–1, 6.04–6, and 160.5; 
Department of Homeland Security Delegation No. 00170.1, Revision No. 01.3. 
■2. Add § 165.T08–0797 to read as 
follows: 
§ 165.T08–0797 Safety Zone; Cumberland 
River, Nashville, TN. 
(a) Location. The following area is a 
safety zone: All navigable waters of the 
Cumberland River from Mile Marker 190 through 191, extending the entire width of the river. 
(b) Definitions. As used in this 
section, designated representative 
means a Coast Guard Patrol Commander, including a Coast Guard coxswain, petty officer, or other officer operating a Coast Guard vessel and a Federal, State, and local officer designated by or assisting the Captain of the Port Sector Ohio Valley (COTP) in the enforcement of the safety zone. 
(c) Regulations. (1) Under the general 
safety zone regulations in subpart C of this part, you may not enter the safety zone described in paragraph (a) of this section unless authorized by the COTP or the COTPs designated representative. 
(2) To seek permission to enter, 
contact the COTP or the COTP’s representative by 502–779–5422 or on VHR–FM channel 16. Those in the safety zone must comply with all lawful orders or directions given to them by the COTP or the COTP’s designated representative. 
(d) Enforcement period. This section 
will be enforced from 7 a.m. through 6 p.m. daily on October 21, 2023 through October 22, 2023. 
Dated: October 16, 2023. 
H.R. Mattern, 
Captain, U.S. Coast Guard, Captain of the 
Port Sector Ohio Valley. 
[FR Doc. 2023–23236 Filed 10–19–23; 8:45 am] 
BILLING CODE 9110–04–P ENVIRONMENTAL PROTECTION 
AGENCY 
40 CFR Parts 87, 1031, and 1068 
[EPA–HQ–OAR–2022–0389; FRL–5934–02– 
OAR] 
RIN 2060–AT10 
Finding That Lead Emissions From 
Aircraft Engines That Operate on Leaded Fuel Cause or Contribute to Air Pollution That May Reasonably Be Anticipated To Endanger Public Health and Welfare 
AGENCY : Environmental Protection 
Agency (EPA). 
ACTION : Final action. 
SUMMARY : In this action, the 
Administrator finds that lead air pollution may reasonably be anticipated to endanger the public health and welfare within the meaning of the Clean Air Act. The Administrator also finds that engine emissions of lead from certain aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare under the Clean Air Act. 
DATES : These findings are effective on 
November 20, 2023. 
ADDRESSES : The EPA has established a 
docket for this action under Docket ID No. EPA–HQ–OAR–2022–0389. All documents in the docket are listed in the https://www.regulations.gov 
website. Publicly available docket materials are available either electronically in https://www.regulations.gov or in hard copy at 
the EPA Air and Radiation Docket and Information Center, William Jefferson Clinton West Building, Room 3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566–1744, and the telephone number for the Air Docket is (202) 566–1742. 
FOR FURTHER INFORMATION CONTACT : Ken 
Davidson, Office of Transportation and Air Quality, Assessment and Standards Division (ASD), Environmental Protection Agency; telephone number: (415) 972–3633; email address: davidson.ken@epa.gov. 
SUPPLEMENTARY INFORMATION : 
A. General Information 
Does this action apply to me? 
Regulated entities: These final 
findings do not themselves apply new 
requirements to entities other than the EPA and the FAA. With respect to requirements for the EPA and the FAA, as indicated in the proposal for this action, if the EPA issues final findings that emissions of lead from certain classes of engines used in certain aircraft cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, the EPA then becomes subject to a duty to propose and promulgate emission standards pursuant to section 231 of the Clean Air Act. Upon EPA’s issuance of regulations, the FAA shall prescribe regulations to ensure compliance with the EPA’s emission standards pursuant to section 232 of the Clean Air Act. In contrast to the findings, those future standards would apply to and have an effect on other entities outside the Federal Government. In addition, pursuant to 49 U.S.C. 44714, the FAA has a statutory mandate to prescribe standards for the composition or chemical or physical properties of an aircraft fuel or fuel additive to control or eliminate aircraft emissions which the EPA has found endanger public health or welfare under section 231(a) of the Clean Air Act. In issuing these final findings, the EPA is making such a finding for emissions of lead from engines in covered aircraft. 
The classes of aircraft engines and of 
aircraft relevant to this final action are referred to as ‘‘covered aircraft engines’’ and as ‘‘covered aircraft,’’ respectively throughout this document. Covered aircraft engines in this context means any aircraft engine that is capable of using leaded aviation gasoline. Covered aircraft in this context means all aircraft and ultralight vehicles
1equipped with 
covered engines. Covered aircraft would, for example, include smaller piston-engine aircraft such as the Cessna 172 (single-engine aircraft) and the Beechcraft Baron G58 (twin-engine aircraft), as well as the largest piston- engine aircraft such as the Curtiss C–46 and the Douglas DC–6. Other examples of covered aircraft would include rotorcraft,
2such 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. 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00026 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172373 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
3EPA (2006) A Framework for Assessing Health 
Risks of Environmental Exposures to Children. 
EPA, Washington, DC, EPA/600/R–05/093F, 2006. 
4EPA. Memorandum: Issuance of EPA’s 2021 
Policy on Children’s Health. October 5, 2021. Available at https://www.epa.gov/system/files/ documents/2021-10/2021-policy-on-childrens- health.pdf. Children’s environmental health 
includes conception, infancy, early childhood and through adolescence until 21 years of age. 
5EPA (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. 
6EPA (2013) ISA for Lead. Executive Summary 
‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– lxxxviii. EPA/600/R–10/075F, 2013. 
7EPA (2013) ISA for Lead. Section 1.9.4. ‘‘Pb 
Exposure and Neurodevelopmental Deficits in Children.’’ p. I–75. EPA/600/R–10/075F, 2013. Entities potentially interested in this 
final action include those that 
manufacture and sell covered aircraft engines and covered aircraft in the United States and those who own or operate covered aircraft. Categories that may be affected by a future regulatory action include, but are not limited to, those listed here: 
Category NAICSacode SICbcode Examples of potentially affected entities 
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 vari-
ety 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. 
aNorth American Industry Classification System (NAICS). 
bStandard Industrial Classification (SIC) code. 
This table is not intended to be 
exhaustive, but rather provides a guide 
for readers regarding entities likely to be interested in this final action. This table lists examples of the types of entities that the EPA is now aware of that could potentially have an interest in this final action. Other types of entities not listed in the table could also be interested and potentially affected by subsequent actions at some future time. If you have any questions regarding the scope of this final action, consult the person listed in the preceding 
FOR FURTHER  
INFORMATION CONTACT section of this 
document. 
B. Children’s Health 
Children are generally more 
vulnerable to environmental exposures 
and/or the associated health effects, and therefore more at risk than adults. These risks to children may arise because infants and children generally eat more food, drink more water and breathe more air than adults do, relative to their size, and consequently they may be exposed to relatively higher amounts of contaminants. In addition, normal childhood activity, such as putting hands in mouths or playing on the ground, can result in exposures to contaminants that adults do not typically have. Furthermore, environmental contaminants may pose health risks specific to children because children’s bodies are still developing. For example, during periods of rapid growth such as fetal development, infancy and puberty, their developing systems and organs may be more easily harmed.
3 
Protecting children’s health from 
environmental risks is fundamental to the EPA’s mission. This action is subject to EPA’s Policy on Children’s Health because this action has considerations for human health.
4Consistent with this policy this document includes discussion and analysis that is focused particularly on children including early life exposure (the lifestages from conception, infancy, early childhood and through adolescence until 21 years of age) and lifelong health. For example, as described in section IV. of this document, the scientific evidence has long been established demonstrating that young children (due to rapid growth and development of the brain) are vulnerable to a range of neurological effects resulting from exposure to lead. Low levels of lead in young children’s blood have been linked to adverse effects on intellect, concentration, and academic achievement, and as the EPA has previously noted ‘‘there is no evidence of a threshold below which there are no harmful effects on cognition from [lead] exposure.’’
5Evidence 
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.
6The 2013 Lead 
Integrated Science Assessment notes that in epidemiologic studies, postnatal (early childhood) blood lead levels are consistently associated with cognitive function decrements in children and adolescents.
7In addition, in section 
II.A.5. of this document, we describe the number of children living near and attending school near airports and provide a proximity analysis of the potential for greater representation of children in the near-airport environment compared with neighboring areas. 
Table of Contents 
I. Executive Summary 
II. Overview and Context for This Final 
Action 
A. Background Information Helpful To 
Understanding This Final Action 
1. Piston-Engine Aircraft and the Use of 
Leaded Aviation Gasoline 
2. Emissions of Lead From Piston-Engine 
Aircraft 
3. Concentrations of Lead in Air 
Attributable to Emissions From Piston- Engine Aircraft 
4. Fate and Transport of Emissions of Lead 
From Piston-Engine Aircraft 
5. Consideration of Environmental Justice 
and Children in Populations Residing Near Airports 
B. Federal Actions To Reduce Lead 
Exposure 
C. Lead Endangerment Petitions for 
Rulemaking and the EPA Responses 
III. Legal Framework for This Action 
A. Statutory Text and Basis for This Action 
B. Considerations for the Endangerment 
and Cause or Contribute Analyses Under Section 231(a)(2)(A) 
C. Regulatory Authority for Emission 
Standards 
D. Response to Certain Comments on the 
Legal Framework for This Action 
IV. The Final Endangerment Finding Under 
CAA Section 231 
A. Scientific Basis of the Endangerment 
Finding 
1. Lead Air Pollution 2. Health Effects and Lead Air Pollution 3. Welfare Effects and Lead Air Pollution B. Final Endangerment Finding 
V. The Final Cause or Contribute Finding 
Under CAA Section 231 
A. Definition of the Air Pollutant B. The Data and Information Used To 
Evaluate the Final Cause or Contribute Finding 
C. Response to Certain Comments on the 
Cause or Contribute Finding 
D. Final Cause or Contribute Finding for 
Lead 
VI. Statutory Authority and Executive Order 
Reviews 
A. Executive Order 12866: Regulatory 
Planning and Review and Executive 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00027 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172374 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
8As noted in section IV.A. of this document, the 
lead air pollution can occur as elemental lead or in 
lead-containing compounds. 9EPA (2013) ISA for Lead. EPA, Washington, DC, 
EPA/600/R–10/075F, 2013. 
10EPA (2006) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA/600/R–5/144aF, 2006. 
11EPA (1986) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–83/028aF-dF, 1986. 
12EPA (1977) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–77–017 (NTIS PB280411), 1977. 
13As noted in section V.A. of this document, the 
lead air pollutant can occur as elemental lead or in lead-containing compounds. 
14EPA (2022) Proposed Finding that Lead 
Emissions from Aircraft Engines that Operate on Leaded Fuel Cause or Contribute to Air Pollution that May Reasonably Be Anticipated to Endanger Public Health and Welfare 87 FR 62753 (October 17, 2022). 
15Of these comments, more than 600 were unique 
letters, some of which provided data and other information for EPA to consider; the remaining comments were mass mailers sponsored by four different organizations, all of which urged the EPA to take action to finalize the findings and/or to take regulatory action to eliminate lead emissions from aircraft operating on leaded avgas. 16U.S. EPA, ‘‘Finding that Lead Emissions from 
Aircraft Engines that Operate on Leaded Fuel Cause or Contribute to Air Pollution that May Reasonably Be Anticipated to Endanger Public Health and Welfare—Response to Comments,’’ Docket EPA– HQ–OAR–2022–0389. 
17Under section 108(a)(2) of the CAA, air quality 
criteria are intended to ‘‘accurately reflect the latest Order 14094: Modernizing Regulatory 
Review 
B. Paperwork Reduction Act (PRA) C. Regulatory Flexibility Act (RFA) D. Unfunded Mandates Reform Act 
(UMRA) 
E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation 
and Coordination With Indian Tribal Governments 
G. Executive Order 13045: Protection of 
Children From Environmental Health Risks and Safety Risks 
H. Executive Order 13211: Actions 
Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use 
I. National Technology Transfer and 
Advancement Act (NTTAA) 
J. Executive Order 12898: Federal Actions 
To Address Environmental Justice in Minority Populations and Low-Income Populations; Executive Order 14096: Revitalizing Our Nation’s Commitment to Environmental Justice for All 
K. Congressional Review Act (CRA) L. Determination Under Section 307(d) M. Judicial Review 
VII. Statutory Provisions and Legal Authority 
I. Executive Summary 
Pursuant to section 231(a)(2)(A) of the 
Clean Air Act (CAA or Act), the 
Administrator finds that emissions of lead from covered aircraft engines cause or contribute to lead air pollution that may reasonably be anticipated to endanger public health and welfare. Covered aircraft include, for example, smaller piston-engine aircraft such as the Cessna 172 (single-engine aircraft) and the Beechcraft Baron G58 (twin- engine aircraft), as well as the largest piston-engine aircraft such as the Curtiss C–46 and the Douglas DC–6. Other examples of covered aircraft include rotorcraft, such as the Robinson R44 helicopter, light-sport aircraft, and ultralight vehicles equipped with piston engines. 
For purposes of this action, the EPA 
defines the ‘‘air pollution’’ referred to in section 231(a)(2)(A) of the CAA as lead, which we also refer to as the lead air pollution in this document.
8In finding 
that the lead air pollution may reasonably be anticipated to endanger the public health and welfare, the EPA relies on the extensive scientific evidence critically assessed in the 2013 Integrated Science Assessment for Lead (2013 Lead ISA) and the previous Air Quality Criteria Documents (AQCDs) for Lead, which the EPA prepared to serve as the scientific foundation for periodic reviews of the National Ambient Air Quality Standards (NAAQS) for 
lead.
91 01 11 2  
Further, for purposes of this action, 
the EPA defines the ‘‘air pollutant’’ referred to in CAA section 231(a)(2)(A) as lead, which we also refer to as the lead air pollutant in this document.
13 
Accordingly, the Administrator finds that emissions of the lead air pollutant from covered aircraft engines cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare 
under CAA section 231(a)(2)(A). 
This final action follows the 
Administrator’s proposed findings
14 
and includes responses to public comments submitted to the EPA on that proposal. The proposal was posted on the EPA website on October 7, 2022, and published in the Federal Register on October 17, 2022. The EPA held a virtual public hearing on November 1, 2022, and the public comment period closed on January 17, 2023. During the public comment period, we received more than 53,000 comments.
15The EPA 
received late comments, and to the extent feasible we have responded to those comments in the Response to Comments document for this action. 
A broad range of stakeholders 
provided comments, including state and local governments; non-governmental organizations; industry trade associations representing aircraft engine and airframe manufacturers, fuel producers, fuel distributors, fuel providers, the helicopter industry, and aircraft owners and operators; environmental organizations; environmental justice organizations; one Tribe; private citizens; and others. In this notice for this final action, we summarize and respond to certain issues raised by commenters, and we provide responses to the remainder of comments in the Response to Comments document that is available in the public docket for this action.
16 
Section II. of this action includes an 
overview and background information that is helpful to understanding the source sector in the context of this action, a brief summary of some of the Federal actions focused on reducing lead exposures, and a brief summary of the petitions for rulemaking regarding lead emissions from aircraft engines. Section III. of this document provides the legal framework for this action, section IV. provides the EPA’s final determination on the endangerment finding, section V. provides the EPA’s final determination on the cause or contribute finding, and section VI. discusses various statutory authorities and executive orders. 
II. Overview and Context for This Final 
Action 
We summarize here background 
information that provides additional context for this final action. This includes information on the population of aircraft that have piston engines, information on the use of leaded aviation gasoline (avgas) in covered aircraft, physical and chemical characteristics of lead emissions from engines used in covered aircraft, concentrations of lead in air from these engine emissions, and the fate and transport of lead emitted by engines used in such aircraft. We also include here an analysis of populations residing near and attending school near airports and an analysis of potential environmental justice implications with regard to residential proximity to runways where covered aircraft operate. This section ends with a description of a broad range of Federal actions to reduce lead exposure from a variety of environmental media and a brief summary of citizen petitions for rulemaking regarding lead emissions from covered aircraft and the EPA responses. 
A. Background Information Helpful To 
Understanding This Final Action 
This final action draws extensively 
from the EPA’s scientific assessments for lead, which are developed as part of the EPA’s periodic reviews of the air quality criteria
17for lead and the lead 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00028 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172375 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
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). 
18Section 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.’’ 
19EPA (2013) ISA for Lead. EPA, Washington, 
DC, EPA/600/R–10/075F, 2013. 
20The EPA released the ISA for Lead External 
Review Draft as part of the Agency’s current review of the science regarding health and welfare effects of lead. EPA/600/R–23/061. This draft assessment is undergoing peer review by the Clean Air Scientific Advisory Committee (CASAC) and public comment, and is available at: https://cfpub.epa.gov/ ncea/isa/recordisplay.cfm?deid=357282. 
21EPA (1977) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–77–017 (NTIS PB280411), 1977. 
22EPA (1986) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–83/028aF-dF (NTIS PB87142386), 1986. 
23EPA (2006) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA/600/R–5/144aF, 2006. 
24EPA (2013) ISA for Lead. Section 3.1.1. 
‘‘Pathways for Pb Exposure.’’ p. 3–1. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
25EPA (2013) ISA for Lead. Section 3.7.1. 
‘‘Exposure.’’ p. 3–144. EPA, Washington, DC, EPA/ 600/R–10/075F, 2013. 26EPA (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. 
27EPA (2013) ISA for Lead. Section 2.3. ‘‘Fate and 
Transport of Pb.’’ p. 2–24. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
28EPA (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. 
29EPA (2013) ISA for Lead. Section 
3.1.1.’’Pathways for Pb Exposure.’’ p. 3–1. EPA, 
Washington, DC, EPA/600/R–10/075F, 2013. 
30EPA (2013) ISA for Lead. Sections 1.3. 
‘‘Exposure to Ambient Pb.’’ p. 1–11. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
31EPA (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. 
32EPA (2006) Air Quality Criteria for Lead. 
Chapter 3. EPA, Washington, DC, EPA/600/R–5/ 144aF, 2006. 
33EPA (1986) Air Quality Criteria for Lead. 
Section 1.11.3. EPA, Washington, DC, EPA–600/8– 83/028aF–dF (NTIS PB87142386), 1986. 
34EPA (1977) Air Quality Criteria for Lead. 
Section 12.3.1.1. ‘‘Air Exposures.’’ p. 12–10. EPA, Washington, DC, EPA–600/8–77–017 (NTIS PB280411), 1977. 35EPA (1977) Air Quality Criteria for Lead. 
Section 12.3.1.2. ‘‘Air Exposures.’’ p. 12–10. EPA, 
Washington, DC, EPA–600/8–77–017 (NTIS PB280411), 1977. 
36EPA (1977) Air Quality Criteria for Lead. 
Section 12.3.1.1. ‘‘Air Exposures.’’ p. 12–10. EPA, Washington, DC, EPA–600/8–77–017 (NTIS PB280411), 1977. 
37Miranda et al., 2011. A Geospatial Analysis of 
the Effects of Aviation Gasoline on Childhood Blood Lead Levels. Environmental Health Perspectives. 119:1513–1516. 
38Zahran 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. 
39Zahran et al., 2022. Leaded Aviation Gasoline 
Exposure Risk and Child Blood Lead Levels. Proceedings of the National Academy of Sciences Nexus. 2:1–11. 
40Klemick 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. NAAQS.18These scientific assessments 
provide a comprehensive review, 
synthesis, and evaluation of the most policy-relevant science that builds upon the conclusions of previous assessments. In the information that follows, we discuss and describe scientific evidence summarized in the most recent assessment for lead, the 2013 Lead ISA,
19 20as well as 
information summarized in previous assessments, including the 1977, 1986, and 2006 AQCDs.
21 22 23  
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.
24Lead emitted in the past 
can remain available for environmental or human exposure for an extended time in some areas.
25Depending on the 
environment where it is deposited, it may to various extents be resuspended into the ambient air, integrated into the media on which it deposits, or transported in surface water runoff to other areas or nearby waterbodies.
26 
Lead in the environment today may have been airborne yesterday or emitted to the air long ago.
27Over time, lead 
that was initially emitted to air can become less available for environmental circulation by sequestration in soil, sediment and other reservoirs.
28 
The multimedia distribution of lead 
emitted into ambient air creates multiple air-related pathways of human and ecosystem exposure. These pathways may involve media other than air, including indoor and outdoor dust, soil, surface water and sediments, vegetation and biota. The human exposure pathways for lead emitted into air include inhalation of ambient air or ingestion of food, water or other materials, including dust and soil, that have been contaminated through a pathway involving lead deposition from ambient air.
29Ambient air inhalation 
pathways include both inhalation of air outdoors and inhalation of ambient air that has infiltrated into indoor environments.
30The 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. 
The scientific evidence documents 
exposure to many sources of lead emitted to the air that have resulted in higher blood lead levels, particularly for people living or working near sources, including stationary sources, such as mines and smelters, and mobile sources, such as cars and trucks when lead was a gasoline additive.
31 32 33 34 35 36  Similarly, with regard to emissions from engines used in covered aircraft, there have been studies reporting positive associations of children’s blood lead levels with proximity to airports and activity by covered aircraft,
37 38 39 thus 
indicating potential for children’s exposure to lead from covered aircraft engine emissions. A recent study evaluating cardiovascular mortality rates in adults 65 and older living within a few kilometers and downwind of runways, while not evaluating blood lead levels, found higher mortality rates in adults living near single-runway airports in years with more piston- engine air traffic, but not in adults living near multi-runway airports, suggesting the potential for adverse adult health effects near some airports.
40 
1. Piston-Engine Aircraft and the Use of Leaded Aviation Gasoline 
Aircraft operating in the U.S. are 
largely powered by either turbine engines or piston engines, although other propulsion systems are in use and in development. Turbine-engine powered aircraft and a small percentage 
of piston-engine aircraft (i.e., those with 
diesel engines) operate on fuel that does not contain a lead additive. Covered aircraft, which are predominantly piston-engine powered aircraft, operate on leaded avgas. Examples of covered aircraft include smaller piston-powered aircraft such as the Cessna 172 (single- engine aircraft) and the Beechcraft Baron G58 (twin-engine aircraft), as well as the largest piston-engine aircraft such as the Curtiss C–46 and the Douglas DC– 6. Additionally, some rotorcraft, such as the Robinson R44 helicopter, light-sport aircraft, and ultralight vehicles can have piston engines that operate using leaded avgas. In limited cases, some turbopropeller-powered aircraft (also 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00029 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172376 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
41ASTM International (May 1, 2021) Standard 
Specification for Leaded Aviation Gasolines D910– 
21. 
42National Academies of Sciences, Engineering, 
and Medicine (NAS). 021. Options for Reducing Lead Emissions from Piston-Engine Aircraft. Washington, DC: The National Academies Press. https://doi.org/10.17226/26050. 
43Ogston 1981. A Short History of Aviation 
Gasoline Development, 1903–1980. Society of 
Automotive Engineers. p. 810848. 
44U.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. 
45U.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. 
46DOE. 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. 47Department of Transportation (DOT). FAA. 
Aviation Policy and Plans. FAA Aerospace Forecast Fiscal Years 2009–2025. p. 81. Retrieved on Mar. 22, 2022, from https://www.faa.gov/data_ research/ 
aviation/aerospace_ forecasts/2009-2025/media/
2009%20Forecast%20Doc.pdf. This document 
provides historical data for 2000–2008 as well as forecast data. 
48DOT. 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. 
49See FAA. NASR. Available at https://
www.faa.gov/air_ traffic/flight_ info/aeronav/aero_
data/eNASR_ Browser/. 
50FAA (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. 
51See FAA’s NASR. Available at https://
www.faa.gov/air_ traffic/flight_ info/aeronav/aero_
data/eNASR_ Browser/. 52FAA. 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/. 
53FAA. 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/. 
54General 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. 
55GAMA (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. 
56There 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. 
57See 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. 
58FAA 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. 
59FAA. U.S. Civil Airmen Statistics. 2021 Active 
Civil Airman Statistics. Retrieved from https:// referred to as turboprops), can use 
leaded avgas. 
Lead is added to avgas in the form of 
tetraethyl lead. Tetraethyl lead helps boost fuel octane, prevents engine knock, and prevents valve seat recession and subsequent loss of compression for engines without hardened valves. There are three main types of leaded avgas: 100 Octane, which can contain up to 4.24 grams of lead per gallon (1.12 grams of lead per liter), 100 Octane Low Lead (100LL), which can contain up to 2.12 grams of lead per gallon (0.56 grams of lead per liter), and 100 Octane Very Low Lead (100VLL), which can contain up to 0.71 grams of lead per gallon (0.45 grams of lead per liter).
41 
Currently, 100LL is the most commonly available and most commonly used type of avgas.
42Tetraethyl lead was first used 
in piston-engine aircraft in 1927.43 
Commercial and military aircraft in the U.S. operated on 100 Octane leaded avgas into the 1950s, but in subsequent years, the commercial and military aircraft fleet largely converted to turbine-engine powered aircraft which do not use leaded avgas.
44 45The 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. 
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.,
46and the FAA provides 
information on the volume of leaded avgas consumed in the U.S.47Over 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.
48As described later in this 
section, while the national consumption of leaded avgas is expected to decrease three percent from 2026 to 2041, the FAA projects increased activity at some airports and decreased activity at other airports out to 2045. 
The FAA’s National Airspace System 
Resource (NASR)
49provides 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.
50While less aircraft activity occurs 
at the remaining 16,300 airports, that activity is conducted predominantly by piston-engine aircraft. Approximately 
6,000 airports have been in operation since the early 1970s when the leaded fuel being used contained up to 4.24 grams of lead per gallon of avgas.
51The 
activity by piston-engine aircraft spans a range of purposes, as described further 
below. 
As of 2019, there were 171,934 piston- 
engine aircraft in the U.S.52This total 
includes 128,926 single-engine aircraft, 12,470 twin-engine aircraft, and 3,089 rotorcraft.
53The 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.
54In 
2019, 883 new piston-engine aircraft were manufactured in the U.S., some of which are exported.
55For the period 
from 2019 through 2041, the fleet of 
fixed-wing56piston-engine aircraft is 
projected to decrease at an annual average rate of 0.9 percent, and the hours flown by these aircraft are projected to decrease 0.9 percent per year from 2019 to 2041.
57An 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.
58There were 
approximately 664,565 pilots certified to fly general aviation aircraft in the U.S. in 2021.
59This included 197,665 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00030 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172377 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
www.faa.gov/data_ research/aviation_ data_
statistics/civil_ airmen_ statistics on May 20, 2022. 
60FAA. 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. 
61FAA. 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/. 
62FAA. 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/. 
63FAA. General Aviation and Part 135 Activity 
Surveys—CY 2019. Chapter 3: Primary and Actual Use. Table 5.1—General Aviation and Part 135 Total Fuel Consumed and Average Fuel Consumption Rate by Aircraft Type. Retrieved on Feb. 16, 2023 at https://www.faa.gov/data_ research/ 
aviation_ data_ statistics/general_ aviation/CY2019/. 
64FAA. 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/. 
65FAA. 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/. 
66In 2012, the FAA Aerospace Forecast projected 
a 0.03 percent increase in hours flown by the piston-engine aircraft fleet for the period 2012 through 2032. FAA Aerospace Forecast Fiscal Years 2012–2032. p. 53. Retrieved on Mar. 22, 2022 from https://www.faa.gov/data_ research/aviation/ 
aerospace_ forecasts/media/2012%
20FAA%20Aerospace%20Forecast.pdf. 
67See FAA’s Air Traffic Activity Data. Available 
at https://aspm.faa.gov/opsnet/sys/airport.asp. 68Geidosch. 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. 
69FAA’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. 
70The 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. student pilots and 466,900 non-student 
pilots. In addition, there were more than 301,000 FAA Non-Pilot Certificated mechanics.
60 
Piston-engine aircraft are used to 
conduct flights that are categorized as either general aviation or air taxi. General aviation flights are defined as all aviation other than military and those flights by scheduled commercial airlines. Air taxi flights are short duration flights made by small commercial aircraft on demand. The hours flown by aircraft in the general aviation fleet are comprised of personal and recreational transportation (67 percent), business (12 percent), instructional flying (8 percent), medical transportation (less than one percent), and the remainder includes hours spent in other applications such as aerial observation and aerial application.
61 
Aerial application for agricultural activity includes crop and timber production, which involve fertilizer and pesticide application and seeding 
cropland. In 2019, aerial application in agriculture represented 883,600 hours flown by general aviation aircraft, and approximately 17.5 percent of these total hours were flown by piston-engine aircraft.
62While the majority of leaded 
avgas is consumed by piston-engine aircraft, in 2019, 403,700 gallons (0.2 percent) of leaded avgas was consumed by turboprop aircraft.
63 
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.
64From the period 2012 through 2019, the total hours flown by 
piston-engine aircraft increased nine percent from 13.2 million hours in 2012 to 14.4 million hours in 2019.
65 66 
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).
67The 
ATADS reports three categories of airport operations that can be conducted by piston-engine aircraft: Itinerant General Aviation, Local Civil, and Itinerant Air Taxi. The sum of Itinerant General Aviation and Local Civil at a facility is referred to as general aviation operations. Piston-engine aircraft operations in these categories are not reported separately from operations conducted by aircraft using other propulsion systems (e.g., turboprop). 
Because piston-engine aircraft activity generally comprises the majority of general aviation activity at an airport, general aviation activity is often used as a surrogate measure for understanding piston-engine activity. 
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.
68The 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). 
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.
69For 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.
70The 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). 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00031 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172378 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
71EPA (1977) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–77–017 (NTIS 
PB280411), 1977. 
72EPA (1986) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–83/028aF–dF (NTIS PB87142386), 1986. 
73EPA (2013) ISA for Lead. Section 2.2.2.1 ‘‘Pb 
Emissions from Piston-engine Aircraft Operating on Leaded Aviation Gasoline and Other Non-road Sources.’’ pp. 2–7 through 2–10. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 74EPA (1986) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA–600/8–83/028aF–dF (NTIS PB87142386), 1986. 
75Griffith 2020. Electron microscopic 
characterization of exhaust particles containing lead dibromide beads expelled from aircraft burning leaded gasoline. Atmospheric Pollution Research 11:1481–1486. 
76EPA (1986) Air Quality Criteria for Lead. 
Volume 2: Chapters 5 & 6. EPA, Washington, DC, EPA–600/8–83/028aF–dF (NTIS PB87142386), 1986. 
77EPA (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. 
78EPA (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. 
79One commenter asserts that the information 
summarized in the 2013 Lead ISA regarding emission of alkyl lead from piston-engine aircraft is a supposition and should not inform this action. We respond to this comment in the Response to Comments document for this action. 
80Memorandum 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. 81Swiss FOCA (2007) Aircraft Piston Engine 
Emissions Summary Report. 33–05–003 Piston 
Engine Emissions_ Swiss FOCA_ Summary. Report_
070612_ rit. Available at https://
www.bazl.admin.ch/bazl/en/home/specialists/ regulations-and-guidelines/environment/pollutant- emissions/aircraft-engine-emissions/report-- appendices--database-and-data-sheets.html. Retrieved on June 15, 2022. 
82Swiss FOCA (2007) Aircraft Piston Engine 
Emissions Summary Report. 33–05–003 Piston Engine Emissions_ Swiss FOCA_ Summary. Report_
070612_ rit. Section 2.2.3.a. Available at https://
www.bazl.admin.ch/bazl/en/home/specialists/ regulations-and-guidelines/environment/pollutant-emissions/aircraft-engine-emissions/report-- appendices--database-and-data-sheets.html. Retrieved on June 15, 2022. 
83The 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. 
84EPA 2017 NEI. Available at https://
www.epa.gov/air-emissions-inventories/2017- national-emissions-inventory-nei-data. 2. Emissions of Lead From Piston- 
Engine Aircraft 
This section describes the physical 
and chemical characteristics of lead emitted by covered aircraft and the national, state, county and airport- specific annual inventories of these engine emissions of lead. Information regarding lead emissions from motor 
vehicle engines operating on leaded fuel is summarized in prior AQCDs for Lead, and the 2013 Lead ISA also includes information on lead emissions from piston-engine aircraft.
71 72 73 Lead is 
added to avgas in the form of tetraethyl lead along with ethylene dibromide, both of which were used in leaded gasoline for motor vehicles in the past. The piston engines in which leaded fuel was used in motor vehicles in the past have similarities to piston engines used in aircraft including the same combustion cycle and the absence of aftertreatment devices to limit pollutant emissions. Because the same chemical form of lead was used in these fuels and because of the similarity in the engines combusting these leaded fuels, the summary of the science regarding emissions of lead from motor vehicles presented in the 1997 and 1986 AQCDs for Lead is relevant to understanding some of the properties of lead emitted from piston-engine aircraft and the atmospheric chemistry these emissions are expected to undergo. Recent studies relevant to understanding lead emissions from piston-engine aircraft have also been published and are discussed here. 
a. Physical and Chemical Characteristics 
of Lead Emitted by Piston-Engine Aircraft 
As with motor vehicle engines, when 
leaded avgas is combusted in aircraft engines, the lead is oxidized to form lead oxide. In the absence of the ethylene dibromide lead scavenger in the fuel, lead oxide can collect on the valves and spark plugs, and if the deposits become thick enough, the engine can be damaged. Ethylene dibromide reacts with the lead oxide, converting it to brominated lead and lead oxybromides. These brominated forms of lead remain volatile at high combustion temperatures and are emitted from the engine along with the 
other combustion by-products.
74Upon 
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.
75In 
addition to lead bromides, ammonium salts of other lead halides were also emitted by motor vehicles, and therefore, ammonium salts of lead bromide compounds would be expected in the exhaust of piston-engine aircraft.
76 
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.
77Alkyl lead is the general term 
used for organic lead compounds and includes the lead additive tetraethyl lead. Summarizing the available data regarding emissions of alkyl lead from piston-engine aircraft, the 2013 Lead ISA notes that lead in the exhaust that might be in organic form may potentially be 20 percent (as an upper bound estimate).
78 79In addition, 
tetraethyl lead is a highly volatile compound, and therefore, a portion of tetraethyl lead in fuel exposed to air will partition into the vapor phase.
80 
Particles emitted by piston-engine 
aircraft are in the submicron size range (less than one micron in diameter). The Swiss Federal Office of Civil Aviation (FOCA) published a study of piston- engine aircraft emissions including measurements of lead.
81The Swiss 
FOCA reported the mean particle 
diameter of particulate matter emitted by one single-engine piston-powered aircraft operating on leaded fuel that ranged from 0.049 to 0.108 microns under different power conditions (lead particles would be expected to be present, but these particles were not separately identified in this study). The particle number concentration ranged from 5.7x10
6to 8.6x106particles per 
cm3. The authors noted that these 
particle emission rates are comparable to those from a typical diesel passenger car engine without a particle filter.
82 
Griffith (2020) collected exhaust particles from a piston-engine aircraft operating on leaded avgas and examined the particles using electron microscopy. Griffith reported that the mean diameter of particles collected in exhaust was 13 nanometers (0.013 microns) consisting of a 4 nanometer (0.004 micron) lead dibromide particle surrounded by hydrocarbons. 
b. Inventory of Lead Emitted by Piston- 
Engine Aircraft 
Lead emissions from covered aircraft 
are the largest single source of lead to air in the U.S., contributing over 50 percent of lead emissions to air starting in 2008 (Table 1).
83In 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.
84Lead 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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00032 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172379 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
85Advance Notice of Proposed Rulemaking on 
Lead Emissions from Piston-Engine Aircraft Using 
Leaded Aviation Gasoline. 75 FR 2440 (April 28, 2010). 
86Airport 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). 
87The 2017 NEI utilized 2014 aircraft activity 
data to develop airport-specific lead inventories. Details can be found on page 3–17 of the document located here: https://www.epa.gov/sites/default/ files/2021-02/documents/nei2017_ tsd_full_
jan2021.pdf#page=70&zoom=100,68,633. Because 
the 2020 inventory was impacted by the Covid–19 pandemic-related decrease in activity by aircraft in 2020, the EPA is focusing on the 2017 inventory in 
this final action. 
88Lead 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. 
89Airport lead annual emissions data cited were 
reported in the 2017 NEI. Available at https://
www.epa.gov/air-emissions-inventories/2017- national-emissions-inventory-nei-data. In addition 
to the triennial NEI, the EPA collects from state, local, and Tribal air agencies point source data for larger sources every year (see https://www.epa.gov/ air-emissions-inventories/air-emissions-reporting- requirements-aerr for specific emissions 
thresholds). While these data are not typically published as a new NEI, they are available publicly 
upon request and are also included in https://www.epa.gov/air-emissions-modeling/emissions- 
modeling-platforms that are created for years other 
than the triennial NEI years. County estimates of lead emissions from non-aircraft sources used in this action are from the 2019 inventory. There are 3,012 counties and statistical equivalent areas where EPA estimates engine emissions of lead occur. 
90See EPA lead inventory data available at 
https://www.epa.gov/air-emissions-modeling/ emissions-modeling-platforms. 
91EPA used the method described in EPA (2010) 
Calculating Piston-Engine Aircraft Airport Inventories for Lead for the 2008 NEI to estimate airport lead inventories in 2045. This document is available here: https://nepis.epa.gov/Exe/ZyPDF.cgi/P1009I13.PDF?Dockey=P1009I13.PDF. 
92Geidosch. 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. Aviation Gasoline85and in the 
document titled ‘‘Calculating Piston- 
Engine Aircraft Airport Inventories for Lead for the 2008 National Emissions Inventory.’’
86The EPA’s National Emissions Inventory (NEI) reports airport estimates of lead emissions as well as estimates of lead emitted in- flight, which are allocated to states based on the fraction of piston-engine aircraft activity estimated for each state. 
These inventory data are briefly summarized here at the state, county, and airport level.
87 
TABLE 1—P ISTON -ENGINE EMISSIONS OF LEAD TO AIR 
2008 2011 2014 2017 2020a 
Piston-engine emissions of lead to air, tons ........................................... 560 490 460 470 427 
Total U.S. lead emissions, tons ............................................................... 950 810 720 670 621 
Piston-engine emissions as a percent of the total U.S. lead inventory .. 59% 60% 64% 70% 69% 
aDue to the Covid-19 Pandemic, a substantial decrease in activity by aircraft occurred in 2020, impacting the total lead emissions for this year. 
The 2020 NEI is available at: https://www.epa.gov/air-emissions-inventories/2020-national-emissions-inventory-nei-data. 
At the state level, the EPA estimates 
of lead emissions from piston-engine 
aircraft range from 0.3 tons (Rhode Island) to 50.5 tons (California), 47 percent of which is emitted in the landing and takeoff cycle and 53 percent of which the EPA estimates is emitted in-flight, outside the landing and takeoff cycle.
88Among the counties in the U.S. 
where the EPA estimates engine emissions of lead from covered aircraft, these lead inventories range from 0.00005 tons per year to 4.3 tons per year and constitute the only source of air-related lead in 1,140 counties (the county estimates of lead emissions include the lead emitted during the landing and takeoff cycle and not lead emitted in-flight).
89In the counties 
where engine emissions of lead from aircraft are the sole source of lead to these estimates, annual lead emissions from the landing and takeoff cycle ranged from 0.00015 to 0.74 tons. Among the 1,872 counties in the U.S. with multiple sources of lead, including engine emissions from covered aircraft, the contribution of aircraft engine emissions ranges from 0.00005 to 4.3 tons, comprising 0.15 to 98 percent of the county total, respectively. 
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.
90In 2017, the EPA’s NEI includes 
638 airports where the EPA estimates engine emissions of lead from covered aircraft were 0.1 ton or more of lead annually. Using the FAA’s forecasted activity in 2045 for the approximately 3,300 airports in the NPIAS (as described in section II.A.1. of this document), the EPA estimates airport- specific inventories may range from 0.00003 tons to 1.28 tons of lead (median of 0.03 tons), with 656 airports estimated to have inventories above 0.1 tons in 2045.
91 
We estimate that piston-engine 
aircraft have consumed approximately 38.6 billion gallons of leaded avgas in the U.S. since 1930, excluding military aircraft use of this fuel, emitting approximately 113,000 tons of lead to the air.
92 
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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00033 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172380 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
93Carr 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. 
94Feinberg 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. 
95Municipality 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%20
Lead%20Study%20Report%20-%20final.pdf. 
96Environment Canada (2000) Airborne 
Particulate Matter, Lead and Manganese at 
Buttonville Airport. Toronto, Ontario, Canada: Conor Pacific Environmental Technologies for Environmental Protection Service, Ontario Region. 
97Fine 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. 
98Lead emitted from piston-engine aircraft in the 
particulate phase would also be measured in samples collected to evaluate total ambient PM
2.5 
concentrations. 
99One commenter provided results from a 
monitoring and modeling study at a general aviation airport in Wisconsin that reports increased lead concentrations with increasing proximity to the airport. See attachments provided to the comments from the Town of Middleton (EPA–HQ– OAR–2022–0389–0178 _attachment_ 2.pdf and EPA– 
HQ–OAR–2022–0389–0178 _attachment_ 3.pdf) 
available in the docket for this action EPA–HQ–OAR–2022–0389. 
100EPA (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). 
101EPA (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. 
102Carr 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. 
103Heiken 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. 
104Hudda 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. 
105Fine 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. 
106EPA (2020) Model-extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA–420–R–20–003, 2020. 
107EPA (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. 
108EPA (2020) Model-extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA–420–R–20–003, 2020. 
109Feinberg 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. 110Feinberg 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. 
11173 FR 66965 (Nov. 12, 2008). 
11240 CFR 50.16 (Nov. 12, 2008). 
11375 FR 81126 (Dec. 27, 2010). concentrations of lead in air from 
piston-engine aircraft exhaust at, and downwind of, airports where these aircraft are active.
93 94 95 96 97 98 99 This 
section provides a summary of the literature regarding the local-scale impact of aircraft emissions of lead on concentrations of lead at and near airports, with specific focus on the results of air monitoring for lead that the EPA required at a subset of airports and an analysis conducted by the EPA to estimate concentrations of lead at 13,000 airports in the U.S., titled ‘‘Model-extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports.’’
100 101  Gradient studies evaluate how lead 
concentrations change with distance from an airport where piston-engine aircraft operate. These studies indicate that concentrations of lead in air, averaged over periods of 18 hours to three months, are estimated to be one to two orders of magnitude higher at locations proximate to aircraft emissions, compared to nearby locations not impacted by a source of lead air emissions.
102 103 104 105 106 The magnitude 
of lead concentrations at and near airports is highly influenced by the amount of aircraft activity (i.e., the 
number of take-off and landing operations, particularly if concentrated at one runway) and the time spent by aircraft in specific modes of operation. The most significant emissions in terms of ground-based activity, and therefore ground-level concentrations of lead in air, occur near the areas with greatest fuel consumption where the aircraft are stationary and running.
107 108 109 For 
piston-engine aircraft these areas are most commonly locations in which pilots conduct engine tests during run- up operations prior to take-off (e.g., magneto checks during the run-up operation mode). Run-up operations are conducted while the brakes are engaged so the aircraft is stationary and are often conducted adjacent to the runway end from which the aircraft will take off. Additional modes of operation by piston-engine aircraft, such as taxiing or idling near the runway, may result in additional hotspots of elevated lead concentration (e.g., start-up and idle, 
maintenance run-up).
110 
The lead NAAQS was revised in 
2008.111The 2008 decision revised the 
level, averaging time and form of the standards to establish the current primary and secondary standards, which are both 0.15 micrograms per cubic meter of air, in terms of the average of three consecutive monthly averages of lead in total suspended particles within a three-year period.
112 
In conjunction with strengthening the lead NAAQS in 2008, the EPA enhanced the existing lead monitoring network by requiring monitors to be placed in areas with sources such as industrial facilities and airports with estimated lead emissions of 1.0 ton or more per year. Lead monitoring was conducted at two airports following from these requirements (Deer Valley Airport, AZ, and the Van Nuys Airport, CA). In 2010, the EPA made further revisions to the monitoring requirements such that state and local air quality agencies are required to monitor near industrial facilities with estimated lead emissions of 0.50 tons or more per year and at airports with estimated emissions of 1.0 ton or more per year.
113As 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. 
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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00034 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172381 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
114EPA (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. 
115EPA (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. 
116A 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. 
117As 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. 
118The 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. 
119EPA (2020) Model-Extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA–420–R–20–003, 2020. 
120EPA (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. 
121In 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. presented in Table 2 are based on the 
certified data for these sites and represent the maximum concentration monitored in a rolling three-month 
average for each location.
114 115  
TABLE 2—L EADCONCENTRATIONS MONITORED AT 17 A IRPORTS IN THE U.S. 
Airport, State Lead design value,116 
μg/m3 
Auburn Municipal Airport, WA ................................................................................................... .......................................... 0.06 
Brookhaven Airport, NY ......................................................................................................... .............................................. 0.03 
Centennial Airport, CO ......................................................................................................... ............................................... 0.02 
Deer Valley Airport, AZ ........................................................................................................ ................................................ 0.04 
Gillespie Field, CA ............................................................................................................ ................................................... 0.07 
Harvey Field, WA ............................................................................................................... .................................................. 0.02 
McClellan-Palomar Airport, CA .................................................................................................. .......................................... 0.17 
Merrill Field, AK ................................................................................................................................................................... 0.07 
Nantucket Memorial Airport, MA ................................................................................................. ........................................ 0.01 
Oakland County International Airport, MI ....................................................................................... ..................................... 0.02 
Palo Alto Airport, CA .......................................................................................................... ................................................. 0.12 
Pryor Field Regional Airport, AL ............................................................................................... ........................................... 0.01 
Reid-Hillview Airport, CA ...................................................................................................... ............................................... 0.10 
Republic Airport, NY ........................................................................................................... ................................................. 0.01 
San Carlos Airport, CA ......................................................................................................... ............................................... 0.33 
Stinson Municipal, TX .......................................................................................................... ................................................ 0.03 
Van Nuys Airport, CA ........................................................................................................... ............................................... 0.06 
Monitored lead concentrations 
violated the lead NAAQS at two airports 
in 2012: the McClellan-Palomar Airport and the San Carlos Airport. At both of these airports, monitors were located in close proximity to the area at the end of the runway most frequently used for pre-flight safety checks (i.e., run-up). 
Alkyl lead emitted by piston-engine aircraft would be expected to partition into the vapor phase and would not be 
collected by the monitoring conducted in this study, which is designed to quantitatively collect particulate forms of lead.
117 
Airport lead monitoring and modeling 
studies have identified the sharp decrease in lead concentrations with distance from the run-up area and therefore the importance of considering monitor placement relative to the run- up area when evaluating the maximum impact location attributable to lead emissions from piston-engine aircraft. 
The monitoring data in Table 2 reflect differences in monitor placement relative to the run-up area as well as other factors; this study also provided evidence that air lead concentrations at and downwind from airports could be influenced by factors such as the use of more than one run-up area, wind speed, and the number of operations conducted by single- versus twin-engine aircraft.
118 
The EPA recognized that the airport 
lead monitoring study provided a small 
sample of the potential locations where emissions of lead from piston-engine aircraft could potentially cause concentrations of lead in ambient air to exceed the lead NAAQS. Because we considered that additional airports and conditions could lead to exceedances of the lead NAAQS at and near airports where piston-engine aircraft operate, and in order to understand the range of lead concentrations at airports 
nationwide, we developed an analysis of 13,000 airports in the peer-reviewed report titled, ‘‘Model-extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports.’’
119 120  
This report provides estimated ranges of lead concentrations that may occur at and near airports where leaded avgas is used. The study extrapolated modeling results from one airport to estimate air lead concentrations at the maximum impact area near the run-up location for over 13,000 U.S. airports.
121The 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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00035 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172382 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
122Prior 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). 
123EPA (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. 124EPA (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. 
125See 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. 
126EPA (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. 
127Carr 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. 128EPA (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. 
129See EPA’s 2019 AirToxScreen. Available at 
https://www.epa.gov/AirToxScreen/2019- airtoxscreen. from the location of highest 
concentration. 
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.
122This approach 
for conducting a nationwide analysis of airports was selected due to the impact of piston-engine aircraft run-up operations on ground-level lead concentrations, which creates a maximum impact area that is expected to be generally consistent across airports. Specifically, these aircraft consistently take off into the wind and typically conduct run-up operations immediately adjacent to the take-off runway end, and thus, modeling lead concentrations from this source is constrained by variation in a few key parameters. These parameters include (1) total amount of piston-engine aircraft activity, (2) the proportion of activity conducted at one runway end, (3) the proportion of activity conducted by 
multi-piston-engine aircraft, (4) the duration of run-up operations, (5) the concentration of lead in avgas, (6) wind speed at the model airport relative to the extrapolated airport, and (7) additional meteorological, dispersion model, or operational parameters. These parameters were evaluated through sensitivity analyses as well as quantitative or qualitative uncertainty analyses. To generate robust concentration estimates, the EPA evaluated these parameters, conducted wind-speed correction of extrapolated estimates, and used airport-specific information regarding airport layout and prevailing wind directions for the 13,000 airports.
123 
Results of this national analysis show 
that model-extrapolated three-month average lead concentrations in the maximum impact area may potentially exceed the lead NAAQS at some 
airports with activity ranging from 3,616–26,816 Landing and Take-Off events (LTOs) in a three-month period.
124The 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.
125Model- 
extrapolated three-month average lead concentrations from aircraft engine emissions were estimated to be above background for a distance of at least 500 meters from the maximum impact area at airports with activity ranging from 1,275–4,302 LTOs in that three-month period.
126In a separate modeling 
analysis at an airport at which hundreds of take-off and landing events by piston- engine aircraft occur per day, the EPA found that modeled 24-hour concentrations of lead from aircraft engine emissions were estimated to be above background for almost 1,000 meters downwind from the runway.
127 
Model-extrapolated estimates of lead 
concentrations in the EPA report ‘‘Model-extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports’’ were compared with monitored values reported in Table 2 and show general agreement, suggesting that the extrapolation method presented in this report provides reasonable estimates of the range in concentrations of lead in air attributable to three-month activity periods of piston-engine aircraft at airports. The assessment included detailed evaluation of the potential impact of run-up duration, the concentration of lead in avgas, and the impact of meteorological parameters on model-extrapolated estimates of lead concentrations attributable to engine emissions of lead from piston-powered aircraft. Additionally, this study included a range of sensitivity analyses as well as quantitative and qualitative uncertainty analyses. 
The EPA’s model-extrapolation 
analysis of lead concentrations from engine emissions resulting from covered aircraft found that annual airport emissions of lead estimated to result in air lead concentrations potentially exceeding the NAAQS ranged from 0.1 to 0.6 tons per year. There are key pieces of airport-specific data that are needed to fully evaluate the potential for piston-engine aircraft operating at an airport to cause concentrations of lead in the air to exceed the lead NAAQS, and the EPA’s report ‘‘Model- extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports’’ provides quantitative and qualitative analyses of these factors.
128The EPA’s 
estimate for airports that have annual lead inventories of 0.1 ton or more are illustrative of and provide one approach for an initial screening evaluation of locations where engine emissions of lead from aircraft may increase localized lead concentrations in air. Airport- specific assessments would be needed to determine the magnitude of the potential range in lead concentrations at and downwind of each facility. 
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).
129The 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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00036 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172383 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
130These 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. 
131As 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. 
132Swiss FOCA (2007) Aircraft Piston Engine 
Emissions Summary Report. 33–05–003 Piston Engine Emissions_ Swiss FOCA_ Summary. Report_
070612_ rit. Available at https://
www.bazl.admin.ch/bazl/en/home/specialists/ regulations-and-guidelines/environment/pollutant- emissions/aircraft-engine-emissions/report- appendices--database--and-data-sheets.html. Retrieved on June 15, 2022. 
133Griffith 2020. Electron microscopic 
characterization of exhaust particles containing lead dibromide beads expelled from aircraft burning leaded gasoline. Atmospheric Pollution Research 11:1481–1486. 134EPA (2013) ISA for Lead. Section 1.3. 
‘‘Exposure to Ambient Pb.’’ p. 1–11. EPA, 
Washington, DC, EPA/600/R–10/075F, 2013. 
135The EPA received comments on the 
information provided in this section to which we 
respond in the Response to Comments document for this action. 
136EPA (1977) Air Quality Criteria for Lead. 
Section 6.2.2.1. EPA, Washington, DC, EPA–600/8– 
77–017, 1977. 
137EPA (2006) Air Quality Criteria for Lead. 
Section E.6. EPA, Washington, DC, EPA/600/R–5/ 144aF, 2006. 
138EPA (2006) Air Quality Criteria for Lead. 
Section E.6. p. 2–5. EPA, Washington, DC, EPA/ 600/R–5/144aF, 2006. 
139EPA (2006) Air Quality Criteria for Lead. 
Section 2. EPA, Washington, DC, EPA/600/R–5/ 144aF, 2006. 
140EPA (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. 141Memorandum to Docket EPA–HQ–OAR– 
2022–0389. Deposition of Lead Emitted by Piston- engine Aircraft. June 15, 2022. Docket ID EPA–HQ– 2022–0389. 
142EPA (2013) ISA for Lead. Section 2.6.1. 
‘‘Soils.’’ p. 2–118. EPA, Washington, DC, EPA/600/ R–10/075F, 2013. 
143EPA (2013) ISA for Lead. Chapter 6. 
‘‘Ecological Effects of Pb.’’ p. 6–57. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
144Murphy et al., 2008. Weekly patterns of 
aerosol in the United States. Atmospheric Chemistry and Physics. 8:2729–2739. 
145Lead concentrations collected as part of the 
Interagency Monitoring of Protected Visual Environments (IMPROVE) network and the National Oceanic and Atmospheric Administration (NOAA) monitoring sites. anthropogenic and natural sources of 
lead, including aircraft engine emissions.
130The 2019 AirToxScreen 
provides lead concentration estimates in air for 73,449 census tracts in the U.S.
131Lead concentrations associated 
with emissions from piston-engine aircraft comprised more than 50 percent of these census block area-weighted lead concentration estimates in over half of the census tracts, which included tracts in all 50 states, as well as Puerto Rico and the Virgin Islands. 
4. Fate and Transport of Emissions of 
Lead From Piston-Engine Aircraft 
This section summarizes the chemical 
transformation that piston-engine aircraft lead emissions are anticipated to undergo in the atmosphere and describes what is known about the deposition of piston-engine aircraft lead and its potential impacts on soil, food, and aquatic environments. 
a. Atmospheric Chemistry and 
Transport of Emissions of Lead From Piston-Engine Aircraft 
Lead emitted by piston-engine aircraft 
can have impacts in the local environment, and, due to their small size (i.e., typically less than one micron 
in diameter),
132 133 lead-bearing particles 
emitted by piston engines may disperse widely in the environment. However, lead emitted during the landing and takeoff cycle, particularly during ground-based operations such as start- up, idle, preflight run-up checks, taxi and the take-off roll on the runway, may 
deposit to the local environment and/or infiltrate into buildings.
134 135  
The Lead AQCDs summarize the 
literature reporting on the atmospheric chemical transformation of lead compounds emitted by engines operating on leaded fuel. Briefly, lead halides emitted by motor vehicles operating on leaded fuel were reported to undergo compositional changes upon cooling and mixing with the ambient air as well as during transport, and we would anticipate lead bromides emitted by piston-engine aircraft to behave similarly in the atmosphere. The water solubility of these lead-bearing particles was reported to be higher for the smaller lead-bearing particles.
136Lead halides 
emitted in motor vehicle exhaust were reported to break down rapidly in the atmosphere via redox reactions in the presence of atmospheric acids.
137 
Depending on ambient conditions (e.g., ozone and hydroxyl concentrations in the atmosphere), alkyl lead may exist in the atmosphere for hours to days
138and 
may therefore be transported off airport property into nearby communities. Tetraethyl lead reacts with the hydroxyl radical in the gas phase to form a variety of products that include ionic trialkyl lead, dialkyl lead and metallic lead. Trialkyl lead is slow to react with the hydroxyl radical and is quite persistent in the atmosphere.
139 
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.
140Meteorological 
factors (e.g., wind speed, convection, 
rain, humidity) influence local deposition rates. With regard to deposition of lead from aircraft engine 
emissions, the EPA modeled the deposition rate for aircraft lead emissions at one airport in a temperate climate in California with dry summer months. In this location, the average lead deposition rate from aircraft emissions of lead was 0.057 milligrams per square meter per year.
141 
Studies summarized in the 2013 Lead 
ISA suggest that soil is a reservoir for contemporary and historical emissions of lead to air.
142Once 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.
143The 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.
144Murphy et al. (2008) 
reported weekend increases in ambient air lead concentrations monitored at remote locations in the U.S. that the authors hypothesized were related to weekend increases in piston-engine powered general aviation activity.
145 
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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00037 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172384 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
146Heiken 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. 
147McCumber and Strevett 2017. A Geospatial 
Analysis of Soil Lead Concentrations Around Regional Oklahoma Airports. Chemosphere 167:62– 
70. 
148Kavouras 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. 
149Heiken 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. 
150EPA (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. 
151Environment Canada (2000) Airborne 
Particulate Matter, Lead and Manganese at Buttonville Airport. Toronto, Ontario, Canada: Conor Pacific Environmental Technologies for Environmental Protection Service, Ontario Region. 
152Lejano 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. 153EPA (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. 
154EPA (2006) Air Quality Criteria for Lead. 
Section 8.2.2. EPA, Washington, DC, EPA/600/R–5/ 144aF, 2006. 
155EPA (2006) Air Quality Criteria for Lead. 
Section 8.2.2. EPA, Washington, DC, EPA/600/R–5/ 144aF, 2006. 
156O’Connor-Marer. Aerial Applicator’s Manual: 
A National Pesticide Applicator Certification Study Guide. p. 40. National Association of State Departments of Agriculture Research Foundation. Available at https://www.epa.gov/system/files/ documents/2022-09/national-pesticide-applicator- cert-core-manual-2014.pdf. 
157The 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. 
158EPA (2006) Air Quality Criteria for Lead. pp. 
7–9 and AXZ7–39 (citing U.S. studies of the 1990s). EPA, Washington, DC, EPA/600/R–5/144aF, 2006. 159EPA (2006) Air Quality Criteria for Lead. p. 
AXZ7–39. EPA, Washington, DC, EPA/600/R–5/ 
144aF, 2006. 
160EPA (1986) Air Quality Criteria for Lead. 
Sections 6.5.3. EPA, Washington, DC, EPA–600/8– 83/028aF–dF (NTIS PB87142386), 1986. 
161EPA (1986) Air Quality Criteria for Lead. 
Section 7.2.2.2.1.EPA, Washington, DC, EPA–600/ 8–83/028aF–dF (NTIS PB87142386), 1986. 
162EPA (1986) Air Quality Criteria for Lead. 
Section 7.2.2.2.2. EPA, Washington, DC, EPA–600/ 8–83/028aF–dF (NTIS PB87142386), 1986. 
163EPA (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. 
164EPA (2002) Persistent, Bioaccumulative, and 
Toxic Pollutants (PBT) Program. PBT National Action Plan for Alkyl-Pb. Washington, DC. June. 2002. 
165See FAA’s NASR. Available at https://
www.faa.gov/air_ traffic/flight_ info/aeronav/aero_
data/eNASR_ Browser/. aircraft engine emissions.146Based on 
comparisons of lead concentrations in 
total suspended particulate (TSP) and fine particulate matter (PM
2.5) measured 
at the three airports, coarse particle lead was observed to account for about 20– 30 percent of the lead found in TSP. The authors noted that based on analysis of lead isotopes present in the air samples collected at these airports, the original source of the lead found in the coarse particle range appeared to be from aircraft exhaust emissions of lead that previously deposited to soil and were resuspended by wind or aircraft- induced turbulence. Results from lead isotope analysis in soil samples collected at the same three airports led the authors to conclude that lead emitted from piston-engine aircraft was not the dominant source of lead in soil in the samples measured at the airports they studied. The authors note the complex history of topsoil can create challenges in understanding the extent to which aircraft lead emissions impact soil lead concentrations at and near airports (e.g., the source of topsoil can 
change as a result of site renovation, construction, landscaping, natural events such as wildfire and hurricanes, and other activities). Concentrations of lead in soil at and near airports servicing piston-engine aircraft have been measured using a range of approaches.
147 148 149 150 151 152 Kavouras 
et al. (2013) collected soil samples at three airports and reported that construction at an airport involving removal and replacement of topsoil complicated interpretation of the findings at that airport and that the number of runways at an airport may influence resulting lead concentrations in soil (i.e., multiple runways may 
provide for more wide-spread dispersal of the lead over a larger area than that potentially affected at a single-runway airport). 
c. Potential for Lead Emissions From 
Piston-Engine Aircraft To Impact Agricultural Products 
Studies conducted near stationary 
sources of lead emissions (e.g., smelters) 
have shown that atmospheric lead sources can lead to contamination of agricultural products, such as vegetables.
153 154 In this way, air lead 
sources may contribute to dietary 
exposure pathways.155As 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.
156An 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,
157are slightly 
water soluble and, therefore, may be more readily absorbed by plants than other forms of inorganic lead. 
The 2006 AQCD indicated that 
surface deposition of lead onto plants may be significant.
158Atmospheric deposition of lead provides a pathway 
for lead in vegetation as a result of contact with above-ground portions of the plant.
159 160 161 Livestock may 
subsequently be exposed to lead in vegetation (e.g., grasses and silage) and 
in surface soils via incidental ingestion of soil while grazing.
162 
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).
163Alkyl lead, in particular, has 
been identified by the EPA as a Persistent, Bioaccumulative, and Toxic (PBT) pollutant.
164There 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.
165Inland 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. 
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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00038 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172385 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
166National 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. 
167Memorandum 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. 
168As described in this section, the EPA 
evaluated environmental justice consistent with the EPA 2016 Technical Guidance. However, the final decisions in this action are based on EPA’s consideration under CAA section 231(a)(2)(A) of potential risks to public health and welfare from the lead air pollution, as well as its evaluation of whether emissions of lead from engines in covered aircraft contribute to that air pollution. See section III. for further discussion of the statutory authority for this action and sections IV. and V. for further discussion of the basis for these findings. 169See, https://www.federalregister.gov/ 
documents/2023/04/26/2023-08955/revitalizing- 
our-nations-commitment-to-environmental-justice- for-all. When the analysis discussed in this section 
was performed, EPA defined environmental justice as the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. Fair treatment means that ‘‘no group of people should bear a disproportionate burden of environmental harms and risks, including those resulting from the negative environmental consequences of industrial, governmental and commercial operations or programs and policies.’’ Meaningful involvement occurs when ‘‘1) potentially affected populations have an appropriate opportunity to participate in decisions about a proposed activity [e.g., rulemaking] that will affect their environment and/ or health; 2) the public’s contribution can influence the regulatory Agency’s decision; 3) the concerns of all participants involved will be considered in the decision-making process; and 4) [the EPA will] seek out and facilitate the involvement of those potentially affected.’’ See, EPA’s Guidance on Considering Environmental Justice During the Development of Regulatory Actions. Available at https://www.epa.gov/sites/default/files/2015-06/ documents/considering-ej-in-rulemaking-guide- final.pdf. See also https://www.epa.gov/ 
environmentaljustice. 
170EPA (2013) ISA for Lead. Section 5.4. 
‘‘Summary.’’ p. 5–40. EPA, Washington, DC, EPA/ 600/R–10/075F, 2013. 
171EPA. 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. 
172The 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. 
173This analysis used the U.S. Census and 
demographic data from 2010 which was the most recent data available at the time of this assessment. 
174Residential proximity to a source of a specific 
air pollutant(s) is a widely used surrogate measure to evaluate the potential for higher exposures to that pollutant (EPA 2016 Technical Guidance for Assessing Environmental Justice in Regulatory Analysis. Section 4.2.1). Data presented in section II.A.3. demonstrate that lead concentrations in air near the runup area can exceed the lead NAAQS and concentrations decrease sharply with distance from the ground-based aircraft exhaust and vary with the amount of aircraft activity at an airport. Not all people living within 500 meters of a runway are expected to be equally exposed to lead. 
175Miranda et al., 2011. A Geospatial Analysis of 
the Effects of Aviation Gasoline on Childhood Blood Lead Levels. Environmental Health Perspectives. 119:1513–1516. 
176Zahran 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. 
177Zahran et al., 2022. Leaded Aviation Gasoline 
Exposure Risk and Child Blood Lead Levels. Proceedings of the National Academy of Sciences Nexus. 2:1–11. 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.
166Leaded avgas discharged to 
the ground and water includes other hazardous fuel components such as ethylene dibromide.
167 
5. Consideration of Environmental Justice and Children in Populations Residing Near Airports 
This section provides a description of 
how many people live in close proximity to airports where they may be exposed to airborne lead from aircraft engine emissions of lead (referred to here as the ‘‘near-airport’’ population). This section also provides the demographic composition of the near- airport population, with attention to implications related to environmental justice (EJ) and the population of children in this near-source environment.
168 
Executive Order 14096, ‘‘Revitalizing 
Our Nation’s Commitment to 
Environmental Justice for All,’’ defines environmental justice as ‘‘the just treatment and meaningful involvement of all people, regardless of income, race, 
color, national origin, Tribal affiliation, or disability, in agency decision-making and other Federal activities that affect human health and the environment so that people: (i) are fully protected from disproportionate and adverse human health and environmental effects (including risks) and hazards, including those related to climate change, the cumulative impacts of environmental and other burdens, and the legacy of racism or other structural or systemic barriers; and (ii) have equitable access to a healthy, sustainable, and resilient environment in which to live, play, work, learn, grow, worship, and engage in cultural and subsistence practices.’’
169Providing this 
information regarding potential EJ implications in the population living near airports is important for purposes of public information and awareness. Here, EPA finds that blood lead levels in children from low-income households remain higher than those in children from higher income households, and blood lead levels in Black children are higher than those in non-Hispanic White children.
170 171 172  The analysis described here provides 
information regarding whether some 
demographic groups are more highly represented in the near-airport environment compared with people who live farther from airports.
173 
Residential proximity to airports implies that there is an increased 
potential for exposure to lead from covered aircraft engine emissions.
174As 
described in section II.A.3. of this document, several studies have measured higher concentrations of lead in air near airports with piston-engine aircraft activity. Additionally, as noted in section II.A. of this document, three studies have reported increased blood lead levels in children with increasing proximity to airports.
175 176 177  
We first summarize here the literature 
on disparity among near-airport populations. Then we describe the analyses the EPA conducted to evaluate potential disparity in the population groups living near runways where piston-engine aircraft operate compared to those living elsewhere. 
Numerous studies have found that 
environmental hazards such as air pollution are more prevalent in areas where people of color and low-income populations represent a higher fraction 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00039 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172386 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
178Rowangould 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. 
179Marshall 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. 
180Marshall 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. 
181Tessum et al., 2021. PM 2.5polluters 
disproportionately and systemically affect people of color in the United States. Science Advances 7:eabf4491. 
182Mohai et al., 2009. Environmental justice. 
Annual Reviews 34:405–430. Available at https://doi.org/10.1146/annurev-environ-082508-094348. 
183McNair 2020. Investigation of environmental 
justice analysis in airport planning practice from 2000 to 2010. Transportation Research Part D 81:102286. 
184Woodburn 2017. Investigating neighborhood 
change in airport-adjacent communities in multiairport regions from 1970 to 2010. Journal of the Transportation Research Board, 2626, 1–8. 
185Rissman et al., 2013. Equity and health 
impacts of aircraft emissions at the Hartfield- Jackson Atlanta International Airport. Landscape and Urban Planning, 120: 234–247. 186EPA (2020) Model-extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA–420–R–20–003, 2020. 
187EPA (2020) Model-extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA–420–R–20–003, 2020. 
188Carr 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. 
189We 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. 
190In 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. 
191EPA (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. 
192Clarke. 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. 
193Clarke. 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. 
194These 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. of the population compared with the 
general population, including near transportation sources.
178 179 180 181 182  
The literature includes studies that have reported on communities in close proximity to airports that are disproportionately represented by people of color and low-income populations. McNair (2020) described nineteen major airports that underwent capacity expansion projects between 2000 and 2010, thirteen of which had a large concentration or presence of persons of color, foreign-born persons or low-income populations nearby.
183 
Woodburn (2017) reported on changes in communities near airports from 1970–2010, finding suggestive evidence that at many hub airports over time, the presence of marginalized groups residing in close proximity to airports increased.
184Rissman et al. (2013) 
reported that with increasing proximity to the Hartsfield-Jackson Atlanta International Airport, exposures to particulate matter were higher, and there were lower home values, income, education, and percentage of white residents.
185 
The EPA used two approaches to 
understand whether some members of the population (e.g., children five and 
under, people of color, indigenous populations, low-income populations) represent a larger share of the people living in proximity to airports where piston-engine aircraft operate compared with people who live farther away from these airports. In the first approach, we evaluated people living within, and children attending school within, 500 
meters of all of the approximately 20,000 airports in the U.S., using methods described in the EPA’s report titled ‘‘National Analysis of the Populations Residing Near or Attending School Near U.S. Airports.’’
186In 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. 
The distances analyzed for those 
people living closest to airports (i.e., distances of 500 meters and 1,000 meters) were chosen for evaluation following from the air quality monitoring and modeling data presented in section II.A.3. of this document. Specifically, the EPA’s modeling and monitoring data indicate that concentrations of lead from piston- engine aircraft emissions can be elevated above background levels at distances of 500 meters over a rolling three-month period. On individual days, concentrations of lead from piston- engine aircraft emissions can be elevated above background levels at distances of 1,000 meters downwind of a runway, depending on aircraft activity and prevailing wind direction.
187 188 189  
Because the U.S. has a dense network 
of airports, many of which have neighboring communities, we quantified the number of people living and children attending school within 500 meters of the approximately 20,000 airports in the U.S.
190From this analysis, the EPA estimates that 
approximately 5.2 million people live within 500 meters of an airport runway, 363,000 of whom are children aged five and under. The EPA also estimates that 573 schools attended by 163,000 children in kindergarten through twelfth grade are within 500 meters of an airport runway.
191 
In order to identify potential 
disparities in the near-airport population, we also evaluated populations at the state level. Using the U.S. Census population data for each state in the U.S., we compared the percent of people by age, race and indigenous peoples (i.e., children five 
and under, Black, Asian, and Native American or Alaska Native) living within 500 meters of an airport runway with the percent by age, race, and indigenous peoples comprising the state population.
192Using the methodology 
described in Clarke (2022), the EPA identified states in which children, Black, Asian, and Native American or Alaska Native populations represent a greater fraction of the population living within 500 meters of a runway compared with the percent of these groups in the state population.
193 
Results of this analysis are presented in the following tables.
194This 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. 
Among children five and under, there 
were three states (Nevada, South 
Carolina, and South Dakota) in which the percent of children five and under 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00040 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172387 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
living within 500 meters of a runway 
represents a greater fraction of the population by a difference of one percent or greater compared with the percent of children five and under in the state population (Table 3). 
TABLE 3—T HEPOPULATION OF CHILDREN FIVEYEARS AND UNDER WITHIN 500 M ETERS OF AN AIRPORT RUNWAY  
COMPARED TO THE STATE POPULATION OF CHILDREN FIVEYEARS AND UNDER  
State Percent of 
children aged 
five years and 
under within 
500 meters Percent of 
children aged 
five years and 
under within 
the state Number of 
children aged 
five years and 
under within 
500 meters Number of 
children aged 
five years and 
under in 
the state 
Nevada ..................................................................................... 10 8 1000 224,200 
South Carolina ......................................................................... 9 8 400 361,400 
South Dakota ........................................................................... 11 9 3,000 71,300 
There were nine states in which the 
Black population represented a greater fraction of the population living in the near-airport environment by a difference of one percent or greater compared with the state as a whole. These states were California, Kansas, Kentucky, Louisiana, Mississippi, Nevada, South Carolina, West Virginia, and Wisconsin (Table 4). 
TABLE 4—T HEBLACK POPULATION WITHIN 500 M ETERS OF AN AIRPORT RUNWAY AND THE BLACK POPULATION , BY 
STATE 
State Percent black 
within 500 meters Percent black 
within the state Black population 
within 500 meters Black population 
in the state 
California .................................................................................. 8 7 18,981 2,486,500 
Kansas ..................................................................................... 8 6 1,240 173,300 
Kentucky .................................................................................. 9 8 3,152 342,800 
Louisiana .................................................................................. 46 32 14,669 1,463,000 
Mississippi ................................................................................ 46 37 8,542 1,103,100 
Nevada ..................................................................................... 12 9 1,794 231,200 
South Carolina ......................................................................... 31 28 10,066 1,302,900 
West Virginia ............................................................................ 10 3 1,452 63,900 
Wisconsin ................................................................................. 9 6 4,869 367,000 
There were three states with a greater 
fraction of Asians in the near-airport environment compared with the state as a whole by a difference of one percent or greater: Indiana, Maine, and New Hampshire (Table 5). 
TABLE 5—T HEASIAN POPULATION WITHIN 500 M ETERS OF AN AIRPORT RUNWAY AND THE ASIAN POPULATION , BYSTATE 
State Percent asian 
within 500 meters Percent asian 
within the state Asian population 
within 500 meters Asian population 
in the state 
Indiana ..................................................................................... 4 2 1,681 105,500 
Maine ....................................................................................... 2 1 406 13,800 
New Hampshire ....................................................................... 4 2 339 29,000 
There were five states (Alaska, 
Arizona, Delaware, South Dakota, and New Mexico) where the near-airport population had greater representation by Native Americans and Alaska Natives compared with the portion of the population they comprise at the state level by a difference of one percent or greater. In Alaska, the disparity in residential proximity to a runway was the largest: 16,020 Alaska Natives were estimated to live within 500 meters of a runway, representing 48 percent of the 
population within 500 meters of an 
airport runway. In contrast, Alaska Natives comprise 15 percent of the Alaska state population (Table 6). 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00041 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172388 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
195For 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. 
196Kamal 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. 197This analysis of 2,022 NPIAS airports did not 
include airports in Alaska. 
198Kamal 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. TABLE 6—T HENATIVE AMERICAN AND ALASKA NATIVE POPULATION WITHIN 500 M ETERS OF AN AIRPORT RUNWAY AND  
THENATIVE AMERICAN AND ALASKA NATIVE POPULATION , BYSTATE 
State Percent Native 
American and 
Alaska Native 
within 500 meters Percent Native 
American and 
Alaska Native 
within the state Native American 
and Alaska 
Native population 
within 500 meters Native American 
and Alaska 
Native population 
in the state 
Alaska ...................................................................................... 48 15 16,020 106,300 
Arizona ..................................................................................... 18 5 5,017 335,300 
Delaware .................................................................................. 2 1 112 5,900 
New Mexico ............................................................................. 21 10 2,265 208,900 
South Dakota ........................................................................... 22 9 1,606 72,800 
In a separate analysis, the EPA 
focused on evaluating the potential for 
disparities in populations residing near the NPIAS airports. The EPA compared the demographic composition of people living within one kilometer of runways at 2,022 of the approximately 3,300 NPIAS airports with the demographic composition of people living at a distance of one to five kilometers from the same airports.
195 196 In this analysis, over one-fourth of airports (i.e., 515) 
were identified at which children under five were more highly represented in the zero to one kilometer distance compared with the percent of children under five living one to five kilometers away (Table 7). There were 666 airports where people of color had a greater presence in the zero to one kilometer area closest to airport runways than in populations farther away. There were 761 airports where people living at less than two- 
times the Federal Poverty Level represented a higher proportion of the overall population within one kilometer of airport runways compared with the proportion of people living at less than two times the Federal Poverty Level among people living one to five kilometers away. 
TABLE 7—N UMBER OF AIRPORTS (AMONG THE 2,022 A IRPORTS EVALUATED ) WITHDISPARITY FOR CERTAIN DEMO-
GRAPHIC POPULATIONS WITHIN ONEKILOMETER OF AN AIRPORT RUNWAY IN RELATION TO THE COMPARISON POPU-
LATION BETWEEN ONE AND FIVEKILOMETERS FROM AN AIRPORT RUNWAY  
Demographic group Number of airports with disparity 
Total airports 
with disparity Disparity 
1–5% Disparity 
5–10% Disparity 
10–20% Disparity 
20%+ 
Children under five years of age ....................................... 515 507 7 1 0 
People with income less than twice the Federal Poverty 
Level ............................................................................... 761 307 223 180 51 
People of Color (all non-White races, ethnicities and in-
digenous peoples) .......................................................... 666 377 126 123 40 
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 Alaska Native197......... 144 130 6 7 1 
Non-Hispanic Hawaiian or Pacific Islander ....................... 18 17 1 0 0 
Non-Hispanic Other Race .................................................. 11 11 0 0 0 
Non-Hispanic Two or More Races .................................... 226 226 0 0 0 
To understand the extent of the 
potential disparity among the 2,022 NPIAS airports, Table 7 provides information about the distribution in the percent differences in the proportion of children, individuals with incomes below two times the Federal Poverty Level, and people of color living within one kilometer of a runway compared with those living one to five kilometers away. For children, Table 7 indicates that for the vast majority of these airports where there is a higher percentage of children represented in the near-airport population, differences are relatively small (e.g., less than five 
percent). For the airports where disparity is evident on the basis of poverty, race and ethnicity, the disparities are potentially large, ranging up to 42 percent for those with incomes below two times the Federal Poverty Level, and up to 45 percent for people of color.
198 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 
VerDate Sep<11>2014 19:08 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00042 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172389 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
199Kamal 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. 
200During the public comment period on the 
proposed findings for this action, commenters provided an additional evaluation of populations living near airports that they conclude to indicate that disparity by race and income is larger and occurs more frequently at airports that have the highest lead emissions and the highest residential population density compared with airports where less lead is emitted and population density is lower. This comment is available in the docket at regulations.gov: EPA–HQ–OAR–2022–0389–0238. 
201Zahran et al., 2022. Leaded Aviation Gasoline 
Exposure Risk and Child Blood Lead Levels. Proceedings of the National Academy of Sciences Nexus. 2:1–11. 202Federal 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. 
203EPA (2022) EPA Strategy to Reduce Lead 
Exposures and Disparities in U.S. Communities. EPA 540R22006. Available at https://www.epa.gov/ system/files/documents/2022-11/Lead%20Strategy_1.pdf. 
20441 FR 14921 (April 8, 1976). See also, e.g., 81 
FR 71910 (Oct. 18, 2016) for a description of the history of the listing decision for lead under CAA section 108. 
20573 FR 66965 (Nov. 12, 2008). 
20681 FR 71912–71913 (Oct. 18, 2016). 
207Documents pertaining to the current review of 
the NAAQS for Lead can be found here: https://www.epa.gov/naaqs/lead-pb-air-quality-standards. 
208The EPA released the ISA for Lead, External 
Review Draft, as part of the Agency’s current review of the science regarding health and welfare effects of lead. EPA/600/R–23/061. This draft assessment is undergoing peer review by the Clean Air 
Scientific Advisory Committee (CASAC) and public comment, and is available at: https://cfpub.epa.gov/ ncea/isa/recordisplay.cfm?deid=357282. 
20977 FR 555 (Jan. 5, 2012). 
21078 FR 9112 (Feb. 7, 2013). 
21188 FR 11556 (Feb. 23, 2023). and their implications discussed in 
Kamal et al. (2022).199 
The data summarized in this section 
indicate that there is a greater prevalence of children under five years of age, an at-risk population for lead effects, within 500 meters or one kilometer of some airports compared to more distant locations. This information also indicates that there is a greater prevalence of people of color and of low-income populations within 500 meters or one kilometer of some airports compared with people living more distant. If such differences were to contribute to disproportionate and adverse impacts on particular communities, they could indicate an EJ concern. Given the number of children in close proximity to runways, including those in communities with EJ concerns, there is a potential for substantial implications for children’s health, depending on lead exposure levels and associated risk. 
Some commenters on the proposed 
findings expressed concern that communities in close proximity to general aviation airports are often low- income communities and communities of color who are disproportionately burdened by lead exposure.
200Some 
commenters also noted that children who attend school near airports may experience higher levels of exposure compared with children who attend school more distant from an airport, and they cite recent research reporting higher blood lead levels in children who attend school near one highly active general aviation airport.
201The EPA 
responds to these comments in the Response to Comments document for this action. 
B. Federal Actions To Reduce Lead 
Exposure 
The Federal Government has a 
longstanding commitment to programs to reduce exposure to lead, particularly for children. In December 2018, the President’s Task Force on 
Environmental Health Risks and Safety Risks to Children released the Federal Action Plan to Reduce Childhood Lead Exposures and Associated Health Impacts (Federal Lead Action Plan), detailing the Federal Government’s commitments and actions to reduce lead exposure in children, some of which are described in this section.
202Building on 
the 2018 Federal Lead Action Plan, in October 2022, the EPA finalized its Strategy to Reduce Lead Exposures and Disparities in U.S. Communities (Lead Strategy).
203The Lead Strategy 
describes the EPA-wide and government-wide approaches to strengthen public health protections, address legacy lead contamination for communities with the greatest exposures, and promote environmental justice. In this section, we describe some of the EPA’s actions to reduce lead exposures from air, water, lead-based paint, and contaminated sites. 
In 1976, the EPA listed lead under 
CAA section 108, making it what is called a ‘‘criteria air pollutant.’’
204Once 
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.
205The EPA’s 2016 Federal 
Register document describes the 
Agency’s decision to retain the existing Lead NAAQS.
206The Lead NAAQS is 
currently undergoing review.207 208  States are primarily responsible for 
ensuring attainment and maintenance of the NAAQS. Under section 110 of the Act and related provisions, states are to submit, for the EPA’s review and, if appropriate, approval, state implementation plans that provide for the attainment and maintenance of such standards through control programs directed to sources of the pollutants involved. 
Additional EPA programs to address 
lead in the environment include the prohibition on gasoline containing lead or lead additives for highway use under section 211 of the Act; the new source performance standards under section 111 of the Act; and emissions standards for solid waste incineration units and the national emission standards for hazardous air pollutants (NESHAP) under sections 129 and 112 of the Act, respectively. 
The EPA has taken a number of 
actions associated with these air pollution control programs, including completion of several regulations requiring reductions in lead emissions from stationary sources regulated under the CAA sections 111, 112 and 129. For example, in January 2012, the EPA updated the NESHAP for the secondary lead smelting source category.
209These 
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.
210In 
February 2023, the EPA finalized amendments to the NSPS (as a new subpart) and the Area Source NESHAP for the Lead Acid Battery Manufacturing source category.
211The amendments to 
the standards for affected processes including grid casting, lead reclamation, and paste mixing operations at lead acid battery facilities will result in reductions in lead emissions and improvements in compliance assurance measures. 
A broad range of Federal programs 
beyond those that focus on air pollution control provide for nationwide reductions in environmental releases and human exposures to lead. For example, pursuant to section 1417 of the Safe Drinking Water Act (SDWA), any pipe, pipe or plumbing fitting or fixture, solder, or flux may not be used in new installations or repairs of any public water system or plumbing in a 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00043 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172390 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
212Effective 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. 
21340 CFR part 141, subpart I (June 7, 1991). 
21440 CFR part 141, subpart I (June 7, 1991). 
21586 FR 4198. (Jan. 15, 2021). 
216E.O. 13990. Protecting Public Health and the 
Environment and Restoring Science to Tackle the 
Climate Crisis. 86 FR 7037 (Jan. 20, 2021). 
21786 FR 31939 (Dec. 17, 2021). 
218See https://www.epa.gov/ground-water-and- 
drinking-water/review-national-primary-drinking- water-regulation-lead-and-copper. Accessed on 
Nov. 30, 2021. 
21986 FR 31939 (Dec. 17, 2021). 22066 FR 1206 (Jan. 5, 2001). 
22184 FR 32632 (July 9, 2019). 
22286 FR 983 (Jan. 7, 2021). 
22386 FR 7037 (Jan. 20, 2021). residential or non-residential facility 
providing water for human consumption or introduced into commerce (except uses for manufacturing or industrial purposes) unless it is considered ‘‘lead free’’ as defined by that Act.
212The EPA’s Lead 
and Copper Rule,213first promulgated 
in 1991, regulates lead in public drinking water systems through a treatment technique that requires water systems to monitor drinking water at customer taps and, if an action level is exceeded, undertake a number of actions including those to control corrosion to minimize lead exposure.
214 
On January 15, 2021, the agency published the most recent revisions, the Lead and Copper Rule Revisions (LCRR),
215and subsequently reviewed 
the rule in accordance with Executive Order 13990.
216While the LCRR took 
effect in December 2021, the agency concluded that there are significant opportunities to improve the LCRR.
217 
The EPA is developing a new proposed rule, the Lead and Copper Rule Improvements (LCRI),
218to further 
strengthen the lead drinking water regulations. The EPA identified priority improvements for the LCRI: proactive and equitable lead service line replacement (LSLR), strengthening compliance tap sampling to better identify communities most at risk of lead in drinking water and to compel lead reduction actions, and reducing the complexity of the regulation through improvement of the action and trigger level construct.
219The EPA intends to 
propose and promulgate the LCRI prior to October 16, 2024. 
While the EPA continues to improve 
regulatory actions to reduce lead exposure in drinking water, the EPA recognizes that directly assisting states and communities and providing dedicated funding provided in the Bipartisan Infrastructure Law for lead service line identification and replacement of full lead service lines (LSLs) is also important in safeguarding public health. The EPA is providing $15 
billion through the Drinking Water State Revolving Fund (DWSRF) dedicated exclusively to lead service line identification and replacement. In addition, $11.7 billion in DWSRF general supplemental funding, provided by the Bipartisan Infrastructure Law, is going to projects to improve drinking water quality, including those to reduce lead in drinking water. For this funding, states are required to provide 49% as additional subsidization in the form of principal forgiveness and/or grants. States must provide additional subsidization to water systems that meet the state’s disadvantaged community criteria as described in section 1452(d) of SDWA, furthering the objectives of the Justice40 Initiative. In October 2022, the EPA announced projects selected to receive over $30 million in grant funding that will help communities and schools address lead in drinking water and remove lead pipes across the country in underserved and other disadvantaged communities through the Water Infrastructure Improvements for the Nation Act’s Reducing Lead in Drinking Water grant program. The EPA recently announced the Lead Service Line Replacement Accelerators initiative which will provide targeted technical assistance to communities in Connecticut, Pennsylvania, New Jersey, and Wisconsin to support expanded access to funding and to accelerate lead pipe replacement. While the EPA is focusing initial efforts in four states, the Agency anticipates this work will serve as a roadmap for additional lead service line replacement efforts across the nation in the future. 
Federal programs to reduce exposure 
to lead in paint, dust, and soil are specified under the comprehensive Federal regulatory framework developed under the Residential Lead-Based Paint Hazard Reduction Act (Title X). Under Title X (codified, in part, as Title IV of the Toxic Substances Control Act [TSCA]), the EPA has established regulations and associated programs in six categories: (1) Training, certification and work practice requirements for persons engaged in lead-based paint activities (abatement, inspection and risk assessment); accreditation of training providers; and authorization of state and Tribal lead-based paint programs; (2) training, certification, and work practice requirements for persons engaged in home renovation, repair and painting (RRP) activities; accreditation of RRP training providers; and authorization of state and Tribal RRP programs; (3) ensuring that, for most housing constructed before 1978, information about lead-based paint and 
lead-based paint hazards flows from sellers to purchasers, from landlords to tenants, and from renovators to owners and occupants; (4) establishing standards for identifying dangerous levels of lead in paint, dust and soil; (5) providing grant funding to establish and maintain state and Tribal lead-based paint programs; and (6) providing information on lead hazards to the public, including steps that people can take to protect themselves and their families from lead-based paint hazards. 
The most recent rules issued under 
Title IV of TSCA revised the dust-lead hazard standards (DLHS) and dust-lead clearance levels (DLCL) which were established in a 2001 final rule entitled ‘‘Identification of Dangerous Levels of Lead.’’
220The 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.
221The DLCL are used to 
evaluate the effectiveness of a cleaning following an abatement. If the dust-lead levels are not below the clearance levels, the components (i.e., floors, 
windowsills, troughs) represented by the failed sample(s) shall be recleaned and retested. In January 2021, the EPA published a final rule revising the DLCL to match the DLHS, lowering them from 40 micrograms per square foot and 250 micrograms per square foot to 10 micrograms per square foot and 100 micrograms per square foot on floors and windowsills, respectively.
222The 
EPA is now reconsidering the 2019 and 2021 rules in accordance with Executive Order 13990
223and in response to a 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00044 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172391 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
22488 FR 50444 (August 1, 2023). 
225For more information about the EPA’s 
CERCLA program, see https://www.epa.gov/ 
superfund. 
226For more information about the EPA’s RCRA 
program, see https://www.epa.gov/rcra. 227See https://www.epa.gov/regulations- 
emissions-vehicles-and-engines/petitions-and-epa- 
response-memorandums-related-lead. 
22887 FR 62772 (Oct. 17, 2022). 
229The 2021 petition is available at https://
www.epa.gov/system/files/documents/2022-01/ 
aviation-leaded-avgas-petition-exhibits-final-2021- 10-12.pdf. 
230EPA’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. 23181 FR 54422–54475 (Aug. 15, 2016). 
232See e.g., 81 FR 55434–54440 (Aug. 15, 2016). 
23374 FR 66505–66510 (Dec. 15, 2009). 
234Coalition for Responsible Regulation, Inc. v. 
EPA, 684 F.3d 102 (D.C. Cir. 2012) (CRR) (rev’d in 
part on other grounds sub nom. Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014)). As 
discussed in greater detail in the 2016 Findings, the Supreme Court granted some of the petitions for certiorari that were filed on CRR, while denying 
others, but agreed to decide only the question: ‘‘Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases.’’ 81 FR 54422, 54442 (Aug. 15, 2016). Thus, the Supreme Court did not disturb the D.C. Circuit’s holding in CRR that affirmed the 
2009 Endangerment Finding. 
235For example, the text in CAA section 202(a) 
that was the basis for the 2009 Findings addresses ‘‘the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in [the Administrator’s] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.’’ Similarly, section 231(a)(2)(A) concerns ‘‘the emission of any air pollutant from any class or classes of aircraft engines which in [the Administrator’s] judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare.’’ Additional discussion of the parallels in the statutory text and legislative history between CAA section 202(a) and 231(a)(2)(A) can be found in the 2016 Findings. See 81 FR 55434—55437 
(Aug. 15, 2016). 
23681 FR 55434 (Aug. 15, 2016). 
23781 FR 55434 (Aug. 15, 2016). May 2021 decision by U.S. Court of 
Appeals for the Ninth Circuit. In August 2023, EPA proposed updating the DLHS and DLCL again.
224If finalized as 
proposed, the DLHS for floors and window sills would be any reportable level greater than zero, as analyzed by any laboratory recognized by EPA’s National Lead Laboratory Accreditation Program. The new DLCL would be 3 micrograms per square foot (mg/ft
2) for 
floors, 20 mg/ft2for window sills and 25 
mg/ft2for window troughs. 
Programs associated with the 
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund)
225and 
Resource Conservation Recovery Act (RCRA)
226also implement removal and 
remedial response programs that reduce or abate exposures to releases or threatened releases of lead and other hazardous substances. Furthermore, CERCLA section 104(a)(1) authorizes the EPA and other Federal agencies to respond to releases or threatened releases of pollutants or contaminants when the release, or potential release, may present an imminent and substantial danger to the public health or welfare. In addition, CERCLA section 104(a)(1) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) authorize remedial investigations (e.g., monitoring, testing, information collection) and removal actions for hazardous substances, pollutants, or contaminants. 
The EPA develops and implements 
protective levels for lead in soil (and other media when appropriate) at Superfund sites and, together with states, at RCRA corrective action facilities. The Office of Land and Emergency Management develops policy and guidance for addressing multimedia lead contamination and determining appropriate response actions at lead-contaminated sites. Federal programs, including those implementing RCRA, provide for management of hazardous substances such as lead in hazardous and municipal solid waste (e.g., 50 FR 
28702, July 15, 1985; 52 FR 45788, December 1, 1987). 
C. Lead Endangerment Petitions for 
Rulemaking and the EPA Responses 
The Administrator’s final findings 
further respond to several citizen petitions on this subject, including the following: petition for rulemaking submitted by Friends of the Earth in 2006, petition for rulemaking submitted by Friends of the Earth, Oregon Aviation Watch and Physicians for Social Responsibility in 2012, petition for reconsideration submitted by Friends of the Earth, Oregon Aviation Watch, and Physicians for Social Responsibility in 2014, and petition for rulemaking from Alaska Community Action on Toxics, Center for Environmental Health, Friends of the Earth, Montgomery-Gibbs Environmental Coalition, Oregon Aviation Watch, the County of Santa Clara, CA, and the Town of Middleton, WI, in 2021. These petitions and the EPA’s responses are described more fully in the proposal for this action.
227 228  
In the most recent of these petitions, 
submitted in 2021, Alaska Community Action on Toxics, Center for Environmental Health, Friends of the Earth, Montgomery-Gibbs Environmental Coalition, Oregon Aviation Watch, the County of Santa Clara, CA, and the Town of Middleton, WI, again petitioned the EPA to conduct a proceeding under CAA section 231 regarding whether lead emissions from piston-engine aircraft cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare.
229The EPA 
responded in 2022 noting our intent to develop a proposal under CAA section 231(a)(2)(A) regarding whether lead emissions from piston-engine aircraft cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare, and, after evaluating public comments on the proposal, issue any final determination in 2023, as the Agency is doing in this action.
230 
III. Legal Framework for This Action 
In this action, the EPA is finalizing 
two separate determinations—an endangerment finding and a cause or contribute finding—under section 231(a)(2)(A) of the Clean Air Act. The EPA has, most recently, finalized such findings under CAA section 231 for greenhouse gases (GHGs) in 2016 (2016 Findings), and in that action the EPA provided a detailed explanation of the legal framework for making such 
findings and the statutory interpretations and caselaw supporting its approach.
231In this final action, the 
Administrator used the same approach of applying a two-part test under section 231(a)(2)(A) as described in the 2016 Findings and relied on the same interpretations supporting that approach, which are briefly described in this section, and set forth in greater 
detail in the 2016 Findings.
232This is 
also the same approach that the EPA used in making endangerment and cause or contribute findings for GHGs under section 202(a) of the CAA in 2009 (2009 Findings),
233which was affirmed 
by the U.S. Court of Appeals for the D.C. Circuit in 2012.
234As explained further 
in the 2016 Findings, the text of the CAA section 231(a)(2)(A), which concerns aircraft emissions, mirrors the text of CAA section 202(a), which concerns motor vehicle emissions and which was the basis for the 2009 Findings.
235 236 Accordingly, for the 
same reasons as discussed in the 2016 Findings, the EPA believes it is reasonable to use the same approach under section 231(a)(2)(A)’s similar text as was used under section 202(a) for the 2009 Findings, and it is acting consistently with that framework for purposes of these final findings under section 231.
237As this approach has 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00045 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172392 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
238Regarding ‘‘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. 
239See Massachusetts v. EPA, 549 U.S. 497, 533 
(2007) (interpreting an analogous provision in CAA section 202). 
240See 81 FR 54435 (Aug. 15, 2016). 241CRR, 684 F.3d at 122 (internal citations 
omitted) (June 26, 2012). 
242CRR, 684 F.3d at 122 (internal citations 
omitted) (June 26, 2012). 
24381 FR 54425 (Aug. 15, 2016). 
244See, 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). 
24587 FR 62773–62774 (Oct. 17, 2022). 
246As 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). 
247See CRR, 684 F.3d at 117 (explaining two-part 
analysis under section 202(a)) (June 26, 2012). been previously discussed at length in 
the 2016 Findings, as well as in the 2009 Findings, the EPA provides only a brief description in this final action. 
A. Statutory Text and Basis for This 
Action 
Section 231(a)(2)(A) of the CAA 
provides that the ‘‘Administrator shall, from time to time, issue proposed emission standards applicable to the emission of any air pollutant from any class or classes of aircraft engines which in his judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare.’’
238In this action, the EPA 
is addressing the predicate for regulatory action under CAA section 231 through a two-part test, which as noted previously, is the same as the test used in the 2016 Findings under section 231 and in the 2009 Findings under 
section 202 of the CAA. 
As the first step of the two-part test, 
the Administrator must decide whether, in his judgment, the air pollution under consideration may reasonably be anticipated to endanger public health or welfare. As the second step, the Administrator must decide whether, in his judgment, emissions of an air pollutant from certain classes of aircraft engines cause or contribute to this air pollution. If the Administrator answers both questions in the affirmative, he will issue standards under section 231.
239 
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.
240They 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.’’
241The 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.’’
242The 
same language appears in section 231(a)(2)(A), and the same interpretation applies in that context. 
Moreover, by instructing the 
Administrator to consider whether emissions of an air pollutant cause or contribute to air pollution in the second part of the two-part test, the Act makes clear that he need not find that emissions from any one sector or class of sources are the sole or even the major part of the air pollution considered. This is clearly indicated by the use of the term ‘‘contribute.’’ Further, the phrase ‘‘in his judgment’’ authorizes the Administrator to weigh risks and to consider projections of future possibilities, while also recognizing uncertainties and extrapolating from existing data. 
Finally, when exercising his judgment 
in making both the endangerment and cause-or-contribute findings, the Administrator balances the likelihood and severity of effects. Notably, the phrase ‘‘in his judgment’’ modifies both ‘‘may reasonably be anticipated’’ and ‘‘cause or contribute.’’ 
Often, past endangerment and cause 
or contribute findings have been proposed concurrently with proposed standards under various sections of the CAA, including section 231.
243 
Comment has been taken on these proposed findings as part of the notice 
and comment process for the emission standards.
244However, there is no requirement that the Administrator propose or finalize the endangerment and cause or contribute findings concurrently with proposed standards and, most recently under section 231, the EPA made endangerment and cause or contribute findings for GHGs separate from, and prior to, proceeding to set standards. 
As noted in the proposal,
245the 
Administrator is applying the procedural provisions of CAA section 307(d) to this action, pursuant to CAA section 307(d)(1)(V), which provides that the provisions of 307(d) apply to ‘‘such other actions as the Administrator may determine.’’
246Any subsequent 
standard-setting rulemaking under CAA section 231 would also be subject to the procedures under CAA section 307(d), as provided in CAA section 307(d)(1)(F) (applying the provisions of CAA section 307(d) to the promulgation or revision of any aircraft emission standard under CAA section 231). Thus, these final findings are subject to the same procedural requirements that would apply if the final findings were part of a standard-setting rulemaking. 
B. Considerations for the Endangerment 
and Cause or Contribute Analyses Under Section 231(a)(2)(A) 
In the context of this final action, the 
EPA understands section 231(a)(2)(A) of the CAA to call for the Administrator to exercise his judgment and make two separate determinations: first, whether the relevant kind of air pollution (here, lead air pollution) may reasonably be anticipated to endanger public health or welfare, and second, whether emissions of any air pollutant from classes of the sources in question (here, any aircraft engine that is capable of using leaded aviation gasoline), cause or contribute to this air pollution.
247 
This analysis entails a scientific 
judgment by the Administrator about the potential risks posed by lead emissions to public health and welfare. In this final action, the EPA used the same approach in making scientific judgments regarding endangerment as it has previously described in the 2016 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00046 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172393 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
248See, e.g., 81 FR 54434–55435 (Aug. 15, 2016). 
249See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 
250See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 
251See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 
252See 81 FR 54437–54438 (Aug. 15, 2016). 
253See 81 FR 54437–54438 (Aug. 15, 2016). 
254See 81 FR 54437–54438 (Aug. 15, 2016). 
255CRR, 684 F.3d at 122–123 (June 26, 2012). 
256CRR, 684 F.3d at 122–123. (quoting Ethyl 
Corp., 541 F.2d at 18) (June 26, 2012). 25781 FR 54438 (Aug. 15, 2016). 
25881 FR 54438 (Aug. 15, 2016). 
25981 FR 54438 (Aug. 15, 2016). 
260See 81 FR 54462 (Aug. 15, 2016). 261CAA section 233. Findings, and its analysis was guided by 
the same five principles that guided the Administrator’s analysis in those Findings.
248 
Similarly, the EPA took the same 
approach to the cause or contribute analysis as was previously explained in the 2016 Findings.
249For 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.
250Moreover, like the language 
in CAA section 202(a) that governed the 2009 Findings, the statutory language in section 231(a)(2)(A) does not contain a modifier on its use of the term ‘‘contribute.’’
251Unlike 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.
252While the 
endangerment test looks at the air pollution being considered as a whole and the risks it poses, the cause or contribute test is designed to authorize the EPA to identify and then address what may well be many different sectors, classes, or groups of sources that are each part of the problem.
253 
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.
254As 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.’’
255Accordingly, 
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.’’
256As 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).
257Moreover, 
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.
258The 
reasonableness of this principle is further supported by the fact that section 231 does not impose on the EPA a requirement to find that such contribution is ‘‘significant,’’ let alone the sole or major cause of the endangering air pollution.
259 
Finally, as also described in the 2016 
Findings, there are a number of possible ways of assessing whether air pollutants cause or contribute to the air pollution which may reasonably be anticipated to endanger public health and welfare, and no single approach is required or has been used exclusively in previous cause or contribute determinations under title II of the CAA.
260 
C. Regulatory Authority for Emission Standards 
Though the EPA is not proposing 
standards in this final action, in issuing these final findings, the EPA becomes subject to a duty under CAA section 231 regarding emission standards applicable to emissions of lead from aircraft engines. As noted in section III.A. of this document, section 231(a)(2)(A) of the CAA directs the Administrator of the EPA to propose and promulgate emission standards applicable to the emission of any air pollutant from classes of aircraft engines which in his or her judgment causes or contributes to air pollution that may reasonably be anticipated to endanger public health or welfare. 
CAA section 231(a)(2)(B) further 
directs the EPA to consult with the Administrator of the FAA on such standards, and it prohibits the EPA from changing aircraft emission standards if such a change would significantly increase noise and adversely affect safety. CAA section 231(a)(3) provides that after we provide an opportunity for a public hearing on standards, the Administrator shall issue standards ‘‘with such modifications as he deems appropriate.’’ In addition, under CAA section 231(b), the effective date of any 
standards shall provide the necessary time to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance, as determined by the EPA in consultation with the U.S. Department of Transportation (DOT). 
Once the EPA adopts standards, CAA 
section 232 then directs the Secretary of DOT to prescribe regulations to ensure compliance with the EPA’s standards. Finally, section 233 of the CAA vests the authority to promulgate emission standards for aircraft or aircraft engines only in the Federal Government. States are preempted from adopting or enforcing any standard respecting aircraft or aircraft engine emissions unless such standard is identical to the EPA’s standards.
261 
D. Response to Certain Comments on the Legal Framework for This Action 
In commenting on the legal 
framework for this action, some commenters assert that the EPA does have authority under CAA section 231(a)(2)(A) to both find that lead air pollution may reasonably be anticipated to endanger the public health and welfare and to find that engine emissions of lead from certain aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger the public 
health and welfare. We agree with these comments. 
Other commenters assert that the EPA 
does not have the legal authority to proceed with this proposal or regulate aviation fuel. These commenters state that Congress excluded aircraft from the CAA of 1970, that the EPA does not have authority to regulate aircraft fuel (citing a regulatory definition of ‘‘transportation fuel’’ in 40 CFR 80.1401) and that aircraft are not motor vehicles (citing a regulatory definition of ‘‘motor vehicles’’ in 40 CFR 85.1703). These commenters say that the definitions of transportation fuel and motor vehicles were not changed through 1977 or 1990 amendments to the CAA. Additionally, commenters assert that the ‘‘EPA points to findings for Green House Gases (GHGs) under section 202(a) supportive of its proposed authority,’’ quoting that section and emphasizing the terms ‘‘new motor vehicles’’ and ‘‘new motor vehicle engines’’ which are used in it. 
In response, the EPA notes that these 
commenters have fundamentally misunderstood the nature of this action and the legal authority upon which it relies. These final findings do not 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00047 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172394 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
262The change to the current language in section 
231(a)(2) occurred in 1977, see Clean Air Act Amendments of 1977, Public Law 95–95, 91 Stat. 
685, 791 (1977). 
263See e.g., 81 FR 55434–54440 (Aug. 15, 2016). 
26474 FR 66496, 66505–10 (Dec. 15, 2009); see 
also Coalition for Responsible Regulation, Inc. v. EPA, 684 F.3d 102 (D.C. Cir. 2012) (CRR) 
(subsequent history omitted) (affirming EPA’s approach in the 2009 Findings). establish regulatory standards for leaded 
avgas, nor are they related in any way to the regulatory definitions of transportation fuels in 40 CFR 80.1401 or of motor vehicles in 40 CFR 85.1703, which implement EPA programs under Part A of Title II of the CAA and do not apply to aircraft that are governed by Part B of Title II. EPA’s regulatory provisions implementing Title II Part B and related to air pollution from aircraft are found in 40 CFR parts 87, 1030, and 1031. The EPA’s authority for this action is not based on its authority to regulate fuels under CAA section 211 or its authority to regulate motor vehicles or motor vehicle engines under CAA section 202(a). Rather, the EPA’s authority for this action comes from CAA section 231(a)(2). Further, this action is focused on the threshold endangerment and cause or contribute criteria, which are being undertaken in proceedings that are separate and distinct from any follow-on regulatory action; no regulatory provisions were proposed and none are being finalized in this action. 
In response to the claims that aircraft 
are excluded from the CAA and that the EPA does not have authority to conduct this endangerment and cause or contribute finding, we disagree. As described in the proposal, the EPA is acting under the express authority prescribed by Congress in section 231(a)(2)(A) of the CAA, which, as amended, provides that the Administrator ‘‘shall, from time to time, issue proposed emission standards applicable to the emission of any air pollutant from any class or classes of aircraft engines which in his judgment causes, or contributes to, air pollution 
which may reasonably be anticipated to endanger public health or welfare.’’ The D.C. Circuit recognized EPA’s authority to promulgate emission standards applicable to air pollutants from aircraft engines under CAA section 231 in National Association of Clean Air Agencies v. EPA, 489 F.3d 1221 (D.C. 
Cir. 2007) (‘‘NACAA’’). Similarly, in the 1970 amendments to the CAA, section 231(a)(2) provided that the Administrator ‘‘shall issue proposed emission standards applicable to emissions of any air pollutant from any class or classes of aircraft or aircraft engines which in his judgment cause or contribute to or are likely to cause or contribute to air pollution which endangers the public health or welfare.’’ Public Law 91–604. Thus, the statement in the comment that the 1970 CAA excluded aircraft is incorrect.
262 Further, the EPA has previously made 
endangerment and cause or contribute findings related to emissions from aircraft engines under section 231 of the CAA. 
As explained in the proposal, and in 
section III. above, in this action the Administrator is using the same approach of applying a two-part test under section 231(a)(2)(A) as described in the finalized endangerment and cause or contribute findings under CAA section 231 for greenhouse gases (GHGs) emissions from aircraft in 2016.
263We 
further explained that this approach is the same approach that the EPA used in making endangerment and cause and contribute findings for GHGs under section 202(a) of the CAA in 2009 (2009 Findings), which is reasonable in light of the parallels of the language and structure between sections 231(a)(2)(A) and 202(a)(1) of the CAA.
264Some 
comments misconstrued EPA’s discussion of section 202(a) in the proposal to infer that EPA was relying on its authority under section 202(a) in this action. That is not the case. While using the same approach as in the 2009 Findings, the EPA is not acting under the authority of section 202(a) in making these final findings, but rather, is relying on the authority under section 231(a)(2)(A) as described herein, which expressly authorizes regulation of emissions of air pollutants from aircraft engines which the Administrator judges to cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. 
Additional commenters state that they 
are opposed to any rulemaking that 
could lead to the elimination of leaded avgas before a comparatively priced substitute fuel is available for widespread use. As an initial matter, the EPA notes that, as described in section III.A. of this document, in this action, the EPA is addressing the predicate to regulatory action under CAA section 231 through a two-part test. In the first step of the two-part test, the Administrator must decide whether, in his judgment, the air pollution under consideration may reasonably be anticipated to endanger public health or welfare. As the second step, the Administrator must decide whether, in his judgment, emissions of an air pollutant from certain classes of aircraft engines cause or contribute to this air pollution. If the Administrator answers 
both questions in the affirmative, as he is doing here, the EPA becomes subject to a duty to propose and promulgate standards under section 231, but the 
EPA is not proposing or promulgating any standards in this action. These commenters have concerns regarding the cost and availability of unleaded fuels that might be required to meet a future emission standard for lead. To reiterate, the EPA is not proposing or promulgating any standards in this action, nor is the EPA reaching any conclusions about the possible elimination of leaded avgas or the cost or availability of comparatively priced substitute fuels; those issues will be addressed, if at all, only in a future standard-setting rulemaking. As for future standards, the delegation of authority in CAA section 231 to the EPA ‘‘is both explicit and extraordinarily broad,’’ NACAA, 489 F.3d at 1229, and 
‘‘confer[s] broad discretion to the [EPA] Administrator to weigh various factors in arriving at appropriate standards,’’ id. at 1230. However, as described in section III.C. of this document, CAA section 231(a)(2)(B) directs the EPA to consult with the Administrator of the FAA on such standards, and it prohibits the EPA from changing aircraft emission standards if such a change would significantly increase noise and adversely affect safety. Further, under CAA section 231(b), the effective date of any standards shall provide the necessary time to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance, as determined by the EPA in consultation with the U.S. Department of Transportation (DOT). 
IV. The Final Endangerment Finding 
Under CAA Section 231 
In this action, the Administrator finds 
that lead air pollution may reasonably be anticipated to endanger the public health and welfare within the meaning of CAA section 231(a)(2)(A). This section discusses both the public health and welfare aspects of the endangerment finding and describes the scientific evidence that informs the Administrator’s final determination. The vast majority of comments supported the EPA’s proposal and agreed with the EPA’s description of the health and welfare effects of lead air pollution. The Agency’s responses to public comments on the proposed endangerment finding, including those opposing finalizing the finding, can be 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00048 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172395 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
265EPA (2013) ISA for Lead. Section 2.2. 
‘‘Sources of Atmospheric Pb.’’ p. 2–1. EPA, 
Washington, DC, EPA/600/R–10/075F, 2013. 
266EPA (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. 
267The lead air pollution can occur as elemental 
lead or in lead-containing compounds, and this definition of the air pollution recognizes that lead in air (whatever form it is found in, including in inorganic and organic compounds containing lead) has the potential to elicit public health and welfare effects. We note, for example, that the 2013 Lead ISA and 2008 AQCD described the toxicokinetics of inorganic and organic forms of lead and studies evaluating lead-related health effects commonly measure total lead level (i.e., all forms of lead in 
various biomarker tissues such as blood). 268EPA (2013) ISA for Lead. EPA, Washington, 
DC, EPA/600/R–10/075F, 2013. 
269EPA (2006) Air Quality Criteria for Lead. EPA, 
Washington, DC, EPA/600/R–5/144aF, 2006. 
270EPA (2013) ISA for Lead. Section 5.4. 
‘‘Summary.’’ p. 5–40. EPA, Washington, DC, EPA/ 
600/R–10/075F, 2013. 
271The 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. 272EPA (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. 
273EPA (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. 
274EPA (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. 
275EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– lxxxviii. EPA, Washington, DC, EPA/600/R–10/ 075F, 2013. found in the Response to Comments 
document for this action. After consideration of the comments on this topic, the EPA concludes that the scientific evidence supports finalizing the finding as proposed. 
A. Scientific Basis of the Endangerment 
Finding 
1. Lead Air Pollution 
Lead is emitted and exists in the 
atmosphere in a variety of forms and 
compounds and is emitted by a wide range of sources.
265Lead 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.
266Lead 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. 
For purposes of this action, the EPA 
defines the ‘‘air pollution’’ referred to in section 231(a)(2)(A) of the CAA as lead, which we also refer to as lead air pollution in this document.
267 
2. Health Effects and Lead Air Pollution 
In 2013, the EPA completed the 
Integrated Science Assessment for Lead which built on the findings of previous AQCDs for Lead. These documents critically assess and integrate relevant scientific information regarding the health and welfare effects of lead and have undergone extensive critical review by the EPA, the Clean Air Scientific Advisory Committee (CASAC), and the public. As such, these 
assessments provide the primary scientific and technical basis for the Administrator’s finding that lead air pollution is reasonably anticipated to endanger public health and welfare.
268 269  
As summarized in section II.A. of this 
document, human exposure to lead that is emitted into the air can occur by multiple pathways. Inhalation pathways include both ambient air outdoors and ambient air that has infiltrated into indoor environments. Additional exposure pathways may involve media other than air, including indoor and outdoor dust, soil, surface water and sediments, vegetation and biota. The bioavailability of air-related lead is modified by several factors in the environment (e.g., the chemical form of 
lead, environmental fate of lead emitted to air). That notwithstanding, as described in section II.A. of this document, it is well-documented that exposures to lead emitted into the air can result in increased blood lead levels, particularly for children living near air lead sources, due to their proximity to these sources of exposure.
270 
As described in the EPA’s 2013 Lead 
ISA and in prior AQCDs, lead has been demonstrated to exert a broad array of deleterious effects on multiple organ systems. The 2013 Lead ISA characterizes the causal nature of relationships between lead exposure and health effects using a weight-of- evidence approach.
271We summarize 
here those health effects for which the EPA in the 2013 Lead ISA has concluded that the evidence supports a determination of either a ‘‘causal relationship,’’ ‘‘likely to be causal relationship,’’ or ‘‘suggestive of a causal 
relationship’’ between lead exposure and a health effect.
272In 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. 
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).
273In addition, the EPA 
has concluded that the evidence supports a conclusion that there is a ‘‘likely to be causal relationship’’ between lead exposure and conduct disorders in children and young adults, internalizing behaviors such as depression, anxiety and withdrawn behavior, auditory function decrements, and fine and gross motor function decrements.
274 
Multiple epidemiologic studies 
conducted in diverse populations of children consistently demonstrate the harmful effects of lead exposure on cognitive function (as measured by decrements in intelligence quotient [IQ], decreased academic performance, and poorer performance on tests of executive function). These findings are supported by extensively documented toxicological evidence substantiating the plausibility of these findings in the epidemiological literature and provide information on the likely mechanisms underlying these neurotoxic effects.
275 
Intelligence quotient is a well- 
established, and among the most rigorously standardized, cognitive function measure that has been used extensively as a measure of the negative 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00049 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172396 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
276EPA (2013) ISA for Lead. Section 4.3.2. 
‘‘Cognitive Function.’’ p. 4–59. EPA, Washington, 
DC, EPA/600/R–10/075F, 2013. 
277EPA (2006) Air Quality Criteria for Lead. 
Sections 6.2.2 and 8.4.2. EPA, Washington, DC, EPA/600/R–5/144aF, 2006. 
278EPA (2013) ISA for Lead. Section 4.3.2. 
‘‘Cognitive Function.’’ p. 4–59. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
279In this statement, the term ‘‘concurrent’’ is 
referring to blood lead measurements that were taken concurrently with the neurocognitive testing. 
280EPA (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. 
281EPA (2013) ISA for Lead. Section 1.9.4. ‘‘Pb 
Exposure and Neurodevelopmental Deficits in Children.’’ p. 1–76. EPA/600/R–10/075F, 2013. 
282EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– lxxxviii. EPA, Washington, DC, EPA/600/R–10/ 075F, 2013. 283EPA (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. 
284EPA (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. 
285EPA (2013) ISA for Lead. Section 1.9.1. 
‘‘Public Health Significance.’’ p. 1–68. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
286EPA (2013) ISA for Lead. Executive Summary. 
‘‘Public Health Significance.’’ p. xciii. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
287EPA (2013) ISA for Lead. Section 1.9.1. 
‘‘Public Health Significance.’’ p. 1–68. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
288EPA (2013) ISA for Lead. Section 1.9.1. 
‘‘Public Health Significance.’’ p. 1–68. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 289EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. EPA/600/R–10/075F, 2013. 
290EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. EPA/600/R–10/075F, 2013. 
291EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. EPA/600/R–10/075F, 2013. 
292EPA (2013) ISA for Lead. Executive Summary. 
‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. EPA/600/R–10/075F, 2013. 
293EPA (2013) ISA for Lead. Executive Summary. 
‘‘Public Health Significance.’’ p. xciii. EPA, Washington, DC, EPA/600/R–10/075F, 2013. 
294EPA (2013) ISA for Lead. Table ES–1. 
‘‘Summary of causal determinations for the relationship between exposure to Pb and health effects of exposure to lead.276 277  
Examples of other measures of cognitive 
function negatively associated with lead exposure include measures of intelligence and cognitive development and cognitive abilities, such as learning, memory, and executive functions, as well as academic performance and achievement.
278 
In summarizing the evidence relating 
neurocognitive effects to lead exposure metrics, the 2013 Lead ISA notes that ‘‘in individual studies, postnatal (early childhood and concurrent) blood [lead] levels are also consistently associated with cognitive function decrements in children and adolescents.’’
279 280 The 
2013 Lead ISA additionally notes that the findings from experimental animal studies indicate that lead exposures during multiple early lifestages and periods are observed to induce impairments in learning, and that these findings ‘‘are consistent with the understanding that the nervous system continues to develop (i.e., synaptogenesis and synaptic pruning remains active) throughout childhood and into adolescence.’’
281The 2013 
Lead ISA further notes that ‘‘it is clear that [lead] exposure in childhood presents a risk; further, there is no evidence of a threshold below which there are no harmful effects on cognition from [lead] exposure,’’ and additionally recognizes uncertainty about the patterns of [lead] exposure that contribute to the blood [lead] levels analyzed in epidemiologic studies (uncertainties which are greater in studies of older children and adults than in studies of younger children who do not have lengthy exposure histories).
282Evidence 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,
283potentially affecting lower 
educational attainment and financial well-being.
284 
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.
285For 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.’’
286Specifically, if lead- 
related decrements are manifested uniformly across the range of IQ scores in a population, ‘‘a small shift in the population mean IQ may be significant from a public health perspective because such a shift could yield a larger proportion of individuals functioning in the low range of the IQ distribution, which is associated with increased risk of educational, vocational, and social failure’’ as well as a decrease in the proportion with high IQ scores.
287 
With regard to lead effects identified 
for the adult population, the 2013 Lead ISA concluded that there is a ‘‘causal relationship’’ between lead exposure and hypertension and coronary heart disease in adults. The 2013 Lead ISA concluded that cardiovascular effects in adults were those of greatest public health concern for adults because the evidence indicated that these effects occurred at the lowest blood lead levels, compared to other health effects, although it further noted that the role of past versus recent exposures to lead is unclear.
288 
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.’’
289In 
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.’’
290The 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.
291The 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.’’
292In 
summarizing the public health significance of lead on the adult population, the 2013 Lead ISA notes that ‘‘small [lead]-associated increases in the population mean blood pressure could result in an increase in the proportion of the population with hypertension that is significant from a public health perspective.’’
293 
In addition to the effects summarized 
here, the EPA has concluded there is a ‘‘likely to be causal relationship’’ between lead exposure and both cognitive function decrements and psychopathological effects in adults. The 2013 Lead ISA also concludes that there is a ‘‘causal relationship’’ between lead exposure and decreased red blood cell survival and function, altered heme synthesis, and male reproductive function. The EPA has also concluded there is a ‘‘likely to be causal relationship’’ between lead exposure and decreased host resistance, resulting in increased susceptibility to bacterial infection and suppressed delayed type hypersensitivity, and cancer.
294 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00050 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172397 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
effects.’’ pp. lxxxiv–lxxxvii. EPA, Washington, DC, 
EPA/600/R–10/075F, 2013. 
295EPA (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. 
296EPA (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. 
297EPA (2013) ISA for Lead. Section 5.4. 
‘‘Summary.’’ p. 5–44. EPA, Washington, DC, EPA/ 600/R–10/075F, 2013. 
298Causal 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. 299EPA (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. 
300EPA (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. 
301EPA (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. 
302EPA (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. 
303EPA (2013) ISA for Lead. ‘‘Summary.’’ p. xcvi. 
EPA, Washington, DC, EPA/600/R–10/075F, 2013. Additionally, in 2013 EPA concluded 
that the evidence is ‘‘suggestive of a 
causal relationship’’ between lead exposure and some additional effects. These include auditory function decrements in adults and subclinical atherosclerosis, reduced kidney function, birth outcomes (e.g., low birth 
weight, spontaneous abortion), and 
female reproductive function.
295 
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.
296The 2013 
Lead ISA concludes that ‘‘there is adequate evidence that several factors— childhood, race/ethnicity, nutrition, residential factors, and proximity to [lead] sources—confer increased risk of lead-related health effects.’’
297 
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.
298We 
summarize here the welfare effects for which the EPA has concluded that the evidence supports a determination of either a ‘‘causal relationship,’’ or a ‘‘likely to be causal relationship,’’ with exposure to lead, or that the evidence is ‘‘suggestive of a causal relationship’’ with lead exposure. The discussion that follows is organized to first provide a 
summary of the effects of lead in the terrestrial environment, followed by a summary of effects of lead in freshwater and saltwater ecosystems. The 2013 Lead ISA further describes the scales or levels at which these determinations between lead exposure and effects on plants, invertebrates, and vertebrates were made (i.e., community-level, 
ecosystem-level, population-level, organism-level or sub-organism level).
299 
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.
300The 
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. 
In freshwater environments, the EPA 
found that ‘‘causal relationships’’ exist between lead exposure and reproductive and developmental effects in vertebrates and invertebrates, growth in invertebrates, survival for vertebrates and invertebrates, and hematological effects in vertebrates. The EPA also determined that there were ‘‘likely to be causal relationships’’ between lead exposure and community and ecosystem effects, growth in plants, neurobehavioral effects in invertebrates and vertebrates, hematological effects in invertebrates, and physiological stress in plants, invertebrates, and vertebrates.
301 
The EPA also determined that the 
evidence for saltwater ecosystems was ‘‘suggestive of a causal relationship’’ between lead exposure and reproductive and developmental effects in invertebrates, hematological effects in vertebrates, and physiological stress in invertebrates.
302 The 2013 Lead ISA concludes, ‘‘With 
regard to the ecological effects of [lead], uptake of [lead] into fauna and subsequent effects on reproduction, growth and survival are established and are further supported by more recent evidence. These may lead to effects at the population, community, and ecosystem level of biological organization. In both terrestrial and aquatic organisms, gradients in response are observed with increasing concentration of [lead] and some studies report effects within the range of [lead] detected in environmental media over the past several decades. Specifically, effects on reproduction, growth, and survival in sensitive freshwater invertebrates are well-characterized from controlled studies at concentrations at or near [lead] concentrations occasionally encountered in U.S. fresh surface waters. Hematological and stress related responses in some terrestrial and aquatic species were also associated with elevated [lead] levels in polluted areas. However, in natural environments, modifying factors affect [lead] bioavailability and toxicity and there are considerable uncertainties associated with generalizing effects observed in controlled studies to effects at higher levels of biological organization. Furthermore, available studies on community and ecosystem- level effects are usually from contaminated areas where [lead] concentrations are much higher than typically encountered in the environment. The contribution of atmospheric [lead] to specific sites is not clear and the connection between air concentration of [lead] and ecosystem exposure continues to be poorly characterized.’’
303 
B. Final Endangerment Finding 
The Administrator finds, for purposes 
of CAA section 231(a)(2)(A), that lead air pollution may reasonably be anticipated to endanger the public health and welfare. This finding is based on consideration of the extensive scientific evidence, described in this section, that has been amassed over decades and rigorously peer reviewed by CASAC, as well as consideration of public comments on the proposal. 
V. The Final Cause or Contribute 
Finding Under CAA Section 231 
In this action, the Administrator finds 
that engine emissions of lead from 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00051 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172398 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
304The lead air pollutant can occur as elemental 
lead or in lead-containing compounds, and this 
definition of the air pollutant recognizes the range of chemical forms of lead emitted by engines in covered aircraft. 305The 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. 
306As described in section II.A.2., the EPA 
estimates 427 tons of lead were emitted by aircraft engines operating on leaded fuel in 2020. Due to the Covid–19 pandemic, a substantial decrease in activity by aircraft occurred in 2020, impacting the total lead emissions for this year. The 2020 NEI is available at: https://www.epa.gov/air-emissions- inventories/2020-national-emissions-inventory-nei- data. 307Airport 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. 
308FAA. 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/. 
309Geidosch. 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. 
310Geidosch. 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. 
311FAA 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. certain aircraft cause or contribute to the 
lead air pollution that may reasonably be anticipated to endanger public health and welfare under section 231(a)(2)(A) of the Clean Air Act. This section describes the definition of the air pollutant and the data and information supporting the Administrator’s final determination. Public comments on the cause or contribute finding were largely supportive of the EPA’s proposal, though some commenters opposed finalizing the finding. After consideration of the comments on this topic, the EPA concludes that the scientific evidence supports finalizing the finding as proposed. The Agency’s responses to certain public comments on the cause or contribute finding can be found in section V.C. of this document, and responses to additional comments on the cause or contribute finding can be found in the Response to Comments document for this action. 
A. Definition of the Air Pollutant 
Under section 231, the Administrator 
is to determine whether emissions of 
any air pollutant from any class or classes of aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. As in the 2016 Findings that the EPA made under section 231 for greenhouse gases, in making this cause or contribute finding under section 231(a)(2), the Administrator first defines the air pollutant being evaluated. The Administrator has reasonably and logically considered the relationship between the lead air pollution and the air pollutant when considering emissions of lead from engines used in covered aircraft. The Administrator defines the air pollutant to match the definition of the air pollution, such that the air pollutant analyzed for contribution mirrors the air pollution considered in the endangerment finding. Accordingly, for purposes of this action, the Administrator defines the ‘‘air pollutant’’ referred to in section 231(a)(2)(A) as lead, which we also refer to as the lead air pollutant in this document.
304As 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. 
B. The Data and Information Used To 
Evaluate the Final Cause or Contribute Finding 
The Administrator’s assessment of 
whether emissions from the engines used in covered aircraft cause or contribute to lead air pollution was informed by estimates of lead emissions from the covered aircraft, lead concentrations in air at and near airports that are attributable to lead emissions from piston engines used in covered aircraft, and projected future conditions. 
As used in this final action, the term 
‘‘covered aircraft’’ refers to all aircraft and ultralight vehicles equipped with covered engines which, in this context, means any aircraft engine that is capable of using leaded avgas. Examples of covered aircraft would include smaller piston-powered aircraft such as the Cessna 172 (single-engine aircraft) and the Beechcraft Baron G58 (twin-engine aircraft), as well as the largest piston- engine aircraft such as the Curtiss C–46 and the Douglas DC–6. Other examples of covered aircraft would include rotorcraft, such as the Robinson R44 helicopter, light-sport aircraft, and ultralight vehicles equipped with piston 
engines. The vast majority of covered aircraft are piston-engine powered. 
In recent years, covered aircraft are 
estimated to be the largest single source of lead to air in the U.S. Since 2008, as described in section II.A.2.b. of this document, lead emissions from covered aircraft are estimated to have contributed over 50 percent of all lead emitted to the air nationally. The EPA estimates 470 tons of lead were emitted by covered aircraft in 2017, comprising 70 percent of lead emitted to air nationally that year.
305 306 In 
approximately 1,000 counties in the U.S., the EPA’s emissions inventory identifies covered aircraft as the sole source of lead emissions. Among the 1,872 counties in the U.S. for which the inventory identifies multiple sources of lead emissions, including engine 
emissions from covered aircraft, the contribution of aircraft engine emissions ranges from 0.00005 to 4.3 tons per year, comprising 0.15 to 98 percent (respectively) of total lead emissions to air in those counties.
307 
Covered aircraft activity, as measured 
by the number of hours flown nationwide, increased nine percent in the period from 2012 through 2019.
308 
General aviation activity, largely conducted by covered aircraft, increased up to 52 percent at airports that are among the busiest in the U.S.
309In 
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.
310Although there is some 
uncertainty in these projections, they indicate that lead emissions from covered aircraft may increase at some airports in the future.
311 
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 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00052 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172399 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
312Carr 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. 
313EPA (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. 
314Carr 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. 
315Heiken 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. 316Hudda 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. 
31773 FR 66965 (Nov. 12, 2008). 
31875 FR 81126 (Dec. 27, 2010). 319EPA (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. 
320EPA’s 2019 AirToxScreen is available at 
https://www.epa.gov/AirToxScreen/2019- airtoxscreen. 
321South 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. 
322EPA provides updated information regarding 
nonattainment areas at this website: https://
www.epa.gov/green-book/green-book-lead-2008- area-information. the environment. Therefore, because 
lead is a persistent pollutant in the environment, we anticipate current and future emissions of lead from covered aircraft engines may contribute to exposures and uptake by humans and biota into the future. 
In evaluating the contributions of 
engine emissions from covered aircraft to the lead air pollution, as defined in section IV.A. of this document, the EPA also considered three types of information about lead concentrations in the ambient air: monitored concentrations, modeled concentrations, and model-extrapolated estimates of lead concentrations. Lead concentrations monitored in the ambient air typically quantify lead compounds collected as suspended particulate matter. The information gained from air monitoring and air quality modeling provides insight into how lead emissions from piston engines used in covered aircraft can affect lead concentrations in air. 
As described in section II.A.3. of this 
document, the EPA has conducted air quality modeling at two airports and extrapolated modeled estimates of lead concentrations to 13,000 airports with piston-engine aircraft activity. These studies indicate that over a three-month averaging time (the averaging time for the Lead NAAQS), the engine emissions of lead from covered aircraft are estimated to contribute to air lead concentrations to a distance of at least 500 meters downwind from a runway.
312 313 Additional studies have 
reported that lead emissions from covered aircraft may have increased concentrations of lead in air by one to two orders of magnitude at locations proximate to aircraft emissions compared to nearby locations not impacted by a source of lead air emissions.
314 315 316  In 2008 and 2010, the EPA enhanced 
the lead monitoring network by 
requiring monitors to be placed in areas with sources such as industrial facilities and airports, as described further in section II.A.3. of this document.
317 318  
As part of this 2010 requirement to expand lead monitoring nationally, the EPA required a 1-year monitoring study of 15 additional airports with estimated lead emissions between 0.50 and 1.0 ton per year in an effort to better understand how these emissions affect concentrations of lead in the air at and near airports. Further, to help evaluate airport characteristics that could lead to ambient lead concentrations that approach or exceed the lead NAAQS, airports for this 1-year monitoring study were selected based on factors such as the level of activity of covered aircraft and the predominant use of one runway due to wind patterns. Monitored lead concentrations in ambient air are highly sensitive to monitor location relative to the location of the run-up areas for piston-engine aircraft and other localized areas of elevated lead concentrations relative to the air monitor locations. 
The lead monitoring study at airports 
began in 2011. In 2012, air monitors were placed in close proximity to the run-up areas at the San Carlos Airport (measurements started on March 10, 2012) and the McClellan-Palomar Airport (measurements started on March 16, 2012). The concentrations of lead measured at both of these airports in 2012 were above the level of the lead NAAQS, with the highest measured levels of lead in total suspended particles over a rolling three-month average of 0.33 micrograms per cubic meter of air at the San Carlos Airport and 0.17 micrograms per cubic meter of air at the McClellan-Palomar Airport. These concentrations violate the primary and secondary lead NAAQS, which are set at a level of 0.15 micrograms per cubic meter of air measured in total suspended particles, as an average of three consecutive monthly concentrations. 
In recognition of the potential for lead 
concentrations to exceed the lead NAAQS in ambient air near the area of maximum concentration at airports, the EPA further conducted an assessment of airports nationwide, titled ‘‘Model- extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports’’ and described in section II.A.3. of this 
document.
319The 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. 
Additional information regarding the 
contribution of engine emissions of lead from covered aircraft to lead air pollution is provided by the EPA’s Air Toxics Screening Assessment. As described and summarized in section II.A.3. of this document, the EPA’s Air Toxics Screening Assessment estimates that piston engines used in aircraft contribute more than 50 percent of the estimated lead concentrations in over half of the census tracts in the U.S.
320 
The EPA also notes that lead is 
emitted from engines in covered aircraft in three of the ten areas in the U.S. currently designated as nonattainment for the 2008 lead NAAQS. These areas are Arecibo, PR, and Hayden, AZ, each of which include one airport servicing covered aircraft, and the Los Angeles County-South Coast Air Basin, CA, which contains at least 22 airports within its nonattainment area boundary.
321 322 Although the lead 
emissions from aircraft are not the predominant source of airborne lead in these areas, the emissions from covered aircraft may increase ambient air lead concentrations in these areas. 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00053 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172400 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
C. Response to Certain Comments on 
the Cause or Contribute Finding 
The EPA received comments related 
to the contribution of lead emissions from engines in covered aircraft to lead air pollution. Commenters provided both support for and opposition to the EPA’s proposed cause or contribute finding, with specific comments regarding the amount of lead emitted by aircraft operating on leaded fuel and the contribution of aircraft engine emissions to lead concentrations in the air. 
Numerous commenters state their 
support for the proposed cause or contribute finding, in some cases noting that ample evidence supports this finding and highlighting the important role that lead emissions from covered aircraft engines have in local environments in many areas of the U.S. Additional commenters express concern regarding monitored lead concentrations that exceed the NAAQS at some airports. The comments expressing support for the proposed cause or contribute finding and EPA’s responses are described in greater detail in the Response to Comment document for this action. We acknowledge these comments and the support expressed for the EPA’s cause or contribute finding, and we agree with the commenters that lead emissions from engines in covered aircraft contribute to lead air pollution. 
Commenters stating opposition to the 
cause or contribute finding based on the amount of lead emitted by aircraft operating on leaded fuel, assert that lead emissions today are 425 times less than lead emissions of the 1970s or that the emissions of lead from aircraft are less than one quarter of one percent of the emissions from cars in the 1970s. Some commenters also state that it only stands to reason that covered aircraft engine emissions of lead represent a high percentage of current lead emissions because lead is no longer being emitted by motor vehicles. At least one additional commenter states that given the number of hours flown by covered aircraft, they do not contribute enough lead to affect air pollution. 
Commenters stating opposition to the 
cause or contribute finding based on the concentrations of lead in air from engine emissions by covered aircraft state that concentrations of lead exceeding the lead NAAQS are rare, representing two of 17 airports studied. One commenter also notes that Table 2 (in section II.A.3. of this document) does not address the localized conditions of the airports studied and that the airports where lead concentrations violated the lead NAAQS may have unique conditions that resulted in the concentrations measured. Additionally, some 
commenters state that there is no evidence that engine emissions of lead are creating a hazard, and that the lead emitted is not toxic in the small amount emitted by aircraft engines. 
In response to commenters comparing 
emissions of lead from covered aircraft to lead emitted by motor vehicles in the 1970s, the EPA acknowledges that more lead was emitted by motor vehicles in the 1970s than is emitted by covered aircraft engines currently. This cause or contribute finding is focused on emissions of lead from covered aircraft engines, a different category of mobile sources from motor vehicles, and the commenters do not explain why the fact that historical emissions were higher from a different source category means that current emissions from covered aircraft engines are not contributing to the existing lead air pollution. Similarly, the historical contributions of lead emitted by motor vehicles is not germane to the present-day analysis of the contribution of lead emissions from covered aircraft engines to the total lead released to the air annually in the U.S. Indeed, nothing in CAA section 231(a) precludes EPA from making a cause or contribute finding for emissions from aircraft engines where such a finding is warranted, even if emissions from other sources regulated elsewhere in the CAA or under other Federal programs may also contribute to that air pollution or have historically contributed to it. See Massachusetts v. E.P.A., 549 U.S. 497, 
533 (2007) (the alleged efficacy of other ‘‘Executive Branch programs’’ in addressing the air pollution problem is not a valid reason for declining to make an endangerment finding). As noted previously, in making a cause or contribute finding, CAA section 231 does not require the EPA to find that the contribution from the relevant source category is ‘‘significant,’’ let alone the sole or major cause of the endangering air pollution. As described in section V.B., the lead emissions from engines used in covered aircraft clearly contribute to the endangering lead air pollution, as these emissions contributed over 50 percent of lead emissions to air starting in 2008, when approximately 560 tons of lead were emitted by engines in covered aircraft, and more recently, in 2017, when approximately 470 tons of lead were emitted by engines in covered aircraft. In the EPA’s view, both the quantity and percentage of lead emitted by covered aircraft engines amply demonstrate that this source contributes to lead air 
pollution in the U.S. 
In response to commenters stating 
that the number of hours flown by covered aircraft do not contribute 
enough lead to affect air pollution, the EPA notes that the commenters made a conclusory allegation and did not provide data or analysis supporting their claim. The EPA disagrees with this comment, and we present data in section V.B. of this document demonstrating that the activity by covered aircraft, which includes the number of hours flown, contributes to lead air pollution as described in the preceding paragraph. 
In response to commenters asserting 
that concentrations of lead exceeding the lead NAAQS are rare, representing two of 17 airports studied, as an initial matter, the EPA notes that nothing in section 231(a) of the CAA premises the cause or contribute finding on emissions from the relevant classes of aircraft engines contributing to such exceedances in a minimum number of air quality regions. More importantly, the EPA notes that the purpose of this airport monitoring study was not to determine the frequency with which potential violations of the lead NAAQS occur at or near airports, but to understand the potential range in lead concentrations at a small sample of airports and the factors that influence those concentrations. As described in section II.A.3. of this document, the concentrations of lead monitored at and near highly active general aviation airports is largely determined by the placement of the monitor relative to the run-up area, and monitor placement relative to the run-up area was not uniform across the airports studied. The EPA fully explains the basis on which the Administrator finds that emissions of lead from covered aircraft engine emissions cause or contribute to lead air pollution. The data that support this finding are presented in section V.B. and, as articulated in section V.D., where, among other data, the Administrator takes into account the fact that in some situations lead emissions from covered aircraft have contributed and may continue to contribute to air concentrations that exceed the lead NAAQS. Given that the lead NAAQS are established to provide requisite protection of public health and welfare, the Administrator expresses particular concern with contributions to concentrations that exceed the lead NAAQS, and those contributions are part of the support for the conclusion that lead emissions from engines in covered aircraft cause or contribute to the endangering air pollution. 
In response to the comment regarding 
the assertion that the two airports where 
lead concentrations violated the lead NAAQS may have unique conditions 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00054 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172401 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
323The 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. 
324EPA (2020) Model-extrapolated Estimates of 
Airborne Lead Concentrations at U.S. Airports Appendix B, Table B–2. EPA–420–R–20–003, 2020. Available at https://nepis.epa.gov/Exe/ ZyPDF.cgi?Dockey=P100YG52.pdf. 325While the comment does not clearly explain 
what it is referring to with the phrase ‘‘creating a 
hazard,’’ we understand that phrase to align with the ‘‘cause’’ portion of the cause or contribute findings. 326The 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. 
327EPA (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. that resulted in the concentrations 
measured, the EPA notes that the commenter did not specify or explain what localized conditions might lead to this result; nor did they provide supporting evidence for localized conditions occurring in these areas that could explain these lead concentrations presented in Table 2 of this document. The EPA describes in section II.A.3. of this document that at both of these airports, monitors were located in close proximity to the area at the end of the runway most frequently used for pre- flight safety checks (i.e., run-up), and 
monitor placement relative to the run- up area is a key factor in evaluating the maximum impact location attributable to lead emissions from piston-engine aircraft. Additionally, as described in section II.A.3. of this document, air lead concentrations at and downwind from airports can be influenced by factors such as the use of more than one run- up area, wind speed, and the number of operations conducted by single- versus twin-engine aircraft.
323At the two 
airports at which concentrations of lead violated the lead NAAQS, the EPA observed a similar fleet composition of single- versus twin-engine aircraft compared with other airports where on- site measurements were taken; wind speeds, which are inversely proportional to lead concentration, were not lower at the airports with lead concentrations violating the lead NAAQS compared with other airports; and these airports were not unique in that the activity by piston-engine aircraft was in the range of activity by these aircraft at the majority of airports where monitors were located.
324The 
EPA thus concludes that these two airports do not have unique conditions responsible for the concentrations of lead that violated the lead NAAQS. 
In response to the comments that 
there is no evidence that engine emissions of lead are creating a hazard,
325and that the lead emitted is 
not toxic in the small amount emitted 
by aircraft engines, we note that these comments conflate the endangerment and cause or contribute steps of the analysis. The text in section 231(a)(2) provides for the EPA to make a finding based on a determination that emissions of the air pollutant from the covered aircraft engine ‘‘causes, or contributes to’’ the air pollution. In making a cause or contribute finding, the EPA need not additionally and separately make a determination as to whether the emissions from covered aircraft engines alone cause endangerment. In section IV. of this document, the EPA explained why the Administrator is finding that the lead air pollution endangers public health and welfare. The only remaining issue at the second step of the analysis is whether emissions from the analyzed class or classes of aircraft engines cause or contribute to the air pollution that may reasonably be anticipated to endanger public health and welfare. For the reasons described in section V. of this document, in the Administrator’s judgment, emissions of the lead air pollutant from engines in the covered aircraft cause or contribute to the lead air pollution. 
Additional comments were submitted 
to the EPA regarding the emissions, deposition, transport, and fate of lead emitted by covered aircraft engines. The EPA responds to these comments in the Response to Comments Document for this action. 
D. Final Cause or Contribute Finding for 
Lead 
Taking into consideration the data 
and information summarized in section V. of this document, and the public comments received on the proposed finding, the Administrator finds that engine emissions of the lead air pollutant from covered aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare. In reaching this conclusion, the Administrator noted that piston-engine aircraft operate on leaded avgas. That operation emits lead-containing compounds into the air, contributing to lead air pollution in the environment. As explained in section II.A. of this document, once emitted from covered aircraft, lead may be transported and distributed to other environmental media, where it presents the potential for human exposure through air and non-air pathways before the lead is removed to deeper soils or waterbody sediments. In reaching this final finding, the Administrator takes into consideration different air quality scenarios in which emissions of the lead air pollutant from engines in covered aircraft may cause or contribute to lead air pollution. Among these considerations, he places weight on the fact that current lead emissions from covered aircraft are an important source of air-related lead in the environment and that engine emissions of lead from covered aircraft are the largest single source of lead to air in the U.S. in recent years. In this regard, he notes that these emissions contributed over 50 percent of lead emissions to air starting in 2008, when approximately 560 tons of lead was emitted by engines in covered aircraft (of the total 950 tons of lead) and, more recently, in 2017, when approximately 470 tons of lead was emitted by engines in covered aircraft (of the total 670 tons of lead).
326 
Additionally, he takes into account 
the fact that in some situations lead emissions from covered aircraft have contributed and may continue to contribute to air concentrations that exceed the lead NAAQS. The NAAQS are standards that have been set to protect public health, including the health of sensitive groups, with an adequate margin of safety and to protect public welfare from any known or anticipated adverse effects associated with the presence of the pollutant in the 
ambient air. For example, the EPA’s monitoring data show that lead concentrations at two airports, McClellan-Palomar and San Carlos, violated the lead NAAQS. The EPA’s model-extrapolated estimates of lead also indicate that some U.S. airports may have air lead concentrations above the NAAQS in the area of maximum impact from operation of covered aircraft.
327Given that the lead NAAQS 
are established to protect public health and welfare, contributions to concentrations that exceed the lead NAAQS are of particular concern to the Administrator and are persuasive support for the conclusion that lead emissions from engines in covered 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00055 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172402 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
328FAA Terminal Area Forecast provides 
projections of aircraft activity at airports. The 
forecast is available at https://taf.faa.gov and the 
FAA Terminal Area Forecast for Fiscal Years 2020– 2045 describes the forecast method, data sources, and review process for the TAF estimates, available at: https://taf.faa.gov/Downloads/ 
TAFSummaryFY2020-2045.pdf. 
329Geidosch. 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. 330See 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. aircraft cause or contribute to the 
endangering air pollution. 
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.
328For 
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.
329Although 
there is some uncertainty in these projections, they indicate that lead emissions from covered aircraft may increase at some airports in the future. Thus, even assuming that consumption of leaded avgas and general aviation activity decrease somewhat overall, as projected, the Administrator anticipates that current concerns about these sources of air-related lead will continue into the future, without controls. Accordingly, the Administrator is considering both current levels of emissions and anticipated future levels of emissions from covered aircraft. In doing so, the Administrator finds that current levels cause or contribute to pollution that may reasonably be anticipated to endanger public health and welfare. He also is taking into consideration the projections that some airports may see increases in activity while others see decreases, as well as the uncertainties in these predictions. The Administrator therefore considers all this information and data collectively to inform his judgment on whether lead emissions from covered aircraft cause or contribute to endangering air pollution. 
Accordingly, for all the reasons 
described, the Administrator concludes that emissions of the lead air pollutant from engines in covered aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare. 
VI. Statutory Authority and Executive 
Order Reviews 
Additional information about these 
statutes and Executive Orders can be found at https://www2.epa.gov/laws- regulations/laws-and-executive-orders. 
A. Executive Order 12866: Regulatory 
Planning and Review and Executive Order 14094: Modernizing Regulatory Review 
This action is a ‘‘significant regulatory 
action’’ as defined in Executive Order 12866, as amended by Executive Order 14094. Accordingly, EPA submitted this action to the Office of Management and Budget (OMB) for Executive Order 12866 review. Documentation of any changes made in response to the Executive Order 12866 review is available in the docket. This action finalizes a finding that emissions of the lead air pollutant from engines in covered aircraft cause or contribute to the lead air pollution that may be reasonably anticipated to endanger public health and welfare. 
B. Paperwork Reduction Act (PRA) 
This action does not impose an 
information collection burden under the 
PRA. The final endangerment and cause or contribute findings under CAA section 231(a)(2)(A) do not contain any information collection activities. 
C. Regulatory Flexibility Act (RFA) 
I certify that this action will not have 
a significant economic impact on a 
substantial number of small entities under the RFA. This action will not impose any requirements on small entities. The final endangerment and cause or contribute findings under CAA section 231(a)(2)(A) do not in-and-of- themselves impose any new requirements on any regulated entities but rather set forth the Administrator’s finding that emissions of the lead air pollutant from engines in covered aircraft cause or contribute to lead air pollution that may be reasonably anticipated to endanger public health and welfare. 
D. Unfunded Mandates Reform Act 
(UMRA) 
This action does not contain any 
unfunded mandate as described in UMRA, 2 U.S.C. 1531–1538 and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any state, local or Tribal governments or the private sector. E. Executive Order 13132: Federalism 
This action does not have federalism 
implications. It will not have substantial 
direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government. 
F. Executive Order 13175: Consultation 
and Coordination With Indian Tribal Governments 
This action does not have Tribal 
implications as specified in Executive Order 13175. The final endangerment and cause or contribute findings under CAA section 231(a)(2)(A) do not in-and- of-themselves impose any new requirements but rather set forth the Administrator’s final finding that emissions of the lead air pollutant from engines in covered aircraft cause or contribute to lead air pollution that may 
be reasonably anticipated to endanger public health and welfare. Thus, Executive Order 13175 does not apply to this action. 
Tribes have previously submitted 
comments to the EPA noting their concerns regarding potential impacts of lead emitted by piston-engine aircraft operating on leaded avgas at airports on, and near, their Reservation Land.
330The 
EPA plans to continue engaging with Tribal stakeholders on this issue and will offer a government-to-government consultation upon request. 
G. Executive Order 13045: Protection of 
Children From Environmental Health Risks and Safety Risks 
Executive Order 13045 (62 FR 19885, 
April 23, 1997) directs Federal agencies to include an evaluation of the health and safety effects on children of a planned regulation in setting Federal health and safety standards. This action is not subject to Executive Order 13045 because it does not propose to establish an environmental standard intended to mitigate health or safety risks. Although the Administrator considered health and safety risks as part of the endangerment and cause or contribute findings under CAA section 231(a)(2)(A), the findings themselves do not impose a standard intended to mitigate those risks. However, the EPA’s Policy on Children’s Health applies to this action. Consistent with this policy, 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00056 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172403 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
331Sierra Club v. EPA, 47 F.4th 738, 745 (D.C. Cir. 
2022) (‘‘EPA’s decision whether to make and 
publish a finding of nationwide scope or effect is committed to the agency’s discretion and thus is unreviewable’’); Texas v. EPA, 983 F.3d 826, 834– 
35 (5th Cir. 2020). 
33281 FR 54422 (Aug. 15, 2016) (2016 Findings); 
74 FR 66496 (2009 Findings). 
333Coalition for Responsible Regulation, Inc. v. 
EPA, 684 F.3d 102 (D.C. Cir. 2012) (subsequent 
history omitted) (affirming 2009 Findings); Biogenic CO2 Coalition v. EPA (Doc. No. 1932392, No. 16– 
1358, D.C. Cir., January 26, 2022) (granting petitioner’s motion to voluntarily dismiss petition for review of 2016 Findings). 
334In deciding whether to invoke the exception 
by making and publishing a finding that an action is based on a determination of nationwide scope or effect, the Administrator takes into account a number of policy considerations, including his judgment balancing the benefit of obtaining the D.C. Circuit’s authoritative centralized review versus allowing development of the issue in other contexts and the best use of agency resources. the Administrator considered lead 
exposure risks to children as part of this final endangerment finding under CAA section 231(a)(2)(A). Information on how the Policy was applied is available under ‘‘Children’s Environmental Health’’ in the 
SUPPLEMENTARY  
INFORMATION section B. of this 
document. A copy of the documents pertaining to the impacts on children’s health from emissions of lead from piston-engine aircraft that the EPA references in this action have been placed in the public docket for this action (Docket EPA–HQ–OAR–2022– 0389). 
H. Executive Order 13211: Actions 
Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use 
This action is not a ‘‘significant 
energy action’’ because it is not likely to have a significant adverse effect on the 
supply, distribution or use of energy. Further, we have concluded that this action is not likely to have any adverse energy effects because the final endangerment and cause or contribute findings under section 231(a)(2)(A) do not in-and-of themselves impose any new requirements but rather set forth the Administrator’s finding that emissions of the lead air pollutant from engines in covered aircraft cause or contribute to lead air pollution that may be reasonably anticipated to endanger public health and welfare. 
I. National Technology Transfer and 
Advancement Act (NTTAA) 
This action does not involve technical 
standards. 
J. Executive Order 12898: Federal 
Actions To Address Environmental Justice in Minority Populations and Low-Income Populations; Executive Order 14096: Revitalizing Our Nation’s Commitment to Environmental Justice for All 
The EPA believes that the human 
health or environmental conditions that exist prior to this action result in or have the potential to result in disproportionate and adverse human health or environmental effects on communities with environmental justice concerns. The EPA conducted an analysis of people living within 500 meters or one kilometer of airports and found that there is a greater prevalence of people of color and of low-income populations within 500 meters or one kilometer of some airports compared with people living more distant. The EPA provides a summary of the evidence for potentially disproportionate and adverse effects among people of color and low-income populations residing near airports in section II.A.5. of this document. A copy of the documents pertaining to the EPA’s analysis of potential environmental justice concerns regarding populations who live in close proximity to airports has been placed in the public docket for this action (Docket EPA–HQ–OAR–2022–0389). 
The EPA believes that this action will 
not change existing disproportionate and adverse effects on communities with environmental justice concerns. In this action, the EPA finds, under section 231(a)(2)(A) of the Clean Air Act, that emissions of lead from engines in covered aircraft may cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare. We are not proposing emission standards at this time. 
The EPA additionally promoted fair 
treatment and meaningful involvement for the public, including for communities with environmental justice concerns, in this action by briefing Tribal members on this action and providing information on our website in both Spanish and English, as well as providing access to Spanish translation during the public hearing. 
K. Congressional Review Act (CRA) 
The EPA will submit a rule report to 
each House of the Congress and to the 
Comptroller General of the United States. This action is not a ‘‘major rule’’ as defined by 5 U.S.C. 804(2). 
L. Determination Under Section 307(d) 
Section 307(d)(1)(V) of the CAA 
provides that the provisions of section 
307(d) apply to ‘‘such other actions as the administrator may determine.’’ Pursuant to section 307(d)(1)(V), the Administrator determines that this action is subject to the provisions of section 307(d). 
M. Judicial Review 
Section 307(b)(1) of the CAA governs 
judicial review of final actions by the 
EPA. This section provides, in part, that petitions for review must be filed in the D.C. Circuit: (i) when the agency action consists of ‘‘nationally applicable regulations promulgated, or final actions taken, by the Administrator,’’ or (ii) when such action is locally or regionally applicable, but ‘‘such action is based on a determination of nationwide scope or effect and if in taking such action the Administrator finds and publishes that such action is based on such a determination.’’ For locally or regionally applicable final actions, the CAA reserves to the EPA complete discretion whether to invoke the exception in (ii) 
described in the preceding sentence.
331 
This action is ‘‘nationally applicable’’ 
within the meaning of CAA section 307(b)(1) because in issuing these final findings, the EPA becomes subject to a statutory duty to propose and promulgate aircraft engine emission standards under CAA section 231(a), which are nationally applicable regulations for which judicial review is available only in the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) pursuant to CAA section 307(b)(1). Further, these emission standards would apply to covered aircraft, wherever in the nation they are located. We note also that similar actions, including the 2016 Endangerment and Cause or Contribute Findings under CAA section 231 for greenhouse gases and the 2009 Endangerment and Cause or Contribute Findings under CAA section 202(a) for greenhouse gases, were also nationally applicable
332and were challenged in 
the D.C. Circuit.333 
In the alternative, to the extent a court 
finds this final action to be locally or regionally applicable, the Administrator is exercising the complete discretion afforded to him under the CAA to make 
and publish a finding that this action is based on a determination of ‘‘nationwide scope or effect’’ within the meaning of CAA section 307(b)(1).
334In 
issuing these final findings, the EPA becomes subject to a statutory duty to propose and promulgate emissions standards under CAA section 231(a), which would apply nationwide to covered aircraft that travel and operate within multiple judicial circuits. As described in section III. of this document, in making these findings, the EPA is applying the same analytical framework that the Agency applied in the 2016 Endangerment and Cause or 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00057 Fmt 4700 Sfmt 4700 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES172404 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 
Contribute Findings under CAA section 
231 for greenhouse gases and the 2009 Endangerment and Cause or Contribute Findings under CAA section 202(a) for greenhouse gases, both of which were challenged in the D.C. Circuit, as noted above. 
The Administrator finds that this is a 
matter on which national uniformity in judicial resolution of any petitions for review is desirable, to take advantage of the D.C. Circuit’s administrative law expertise, and to facilitate the orderly development of the law under the Act. The Administrator also finds that consolidated review of this action in the D.C. Circuit will avoid piecemeal litigation in the regional circuits, further judicial economy, and eliminate the risk of inconsistent results, and that a nationally consistent approach to the CAA’s provisions related to making endangerment and cause or contribute 
findings under section 231 of the CAA, including for lead air pollution and 
emissions of lead from engines in covered aircraft as here, constitutes the best use of agency resources. 
For these reasons, this final action is 
nationally applicable or, alternatively, the Administrator is exercising the complete discretion afforded to him by the CAA and finds that this final action is based on a determination of nationwide scope or effect for purposes of CAA section 307(b)(1) and is publishing that finding in the Federal Register. Under section 307(b)(1) of the CAA, petitions for judicial review of this action must be filed in the United States Court of Appeals for the District of Columbia Circuit by December 19, 2023. 
VII. Statutory Provisions and Legal 
Authority 
Statutory authority for this action 
comes from 42 U.S.C. 7571, 7601 and 
7607. List of Subjects 
40 CFR Parts 87 and 1031 
Environmental protection, Air 
pollution control, Aircraft, Aircraft 
engines. 
40 CFR Part 1068 
Environmental protection, 
Administrative practice and procedure, 
Confidential business information, Imports, Motor vehicle pollution, Penalties, Reporting and recordkeeping requirements, Warranties. 
Michael S. Regan, 
Administrator. 
[FR Doc. 2023–23247 Filed 10–19–23; 8:45 am] 
BILLING CODE 6560–50–P 
VerDate Sep<11>2014 17:07 Oct 19, 2023 Jkt 262001 PO 00000 Frm 00058 Fmt 4700 Sfmt 9990 E:\FR\FM\20OCR1.SGM 20OCR1ddrumheller on DSK120RN23PROD with RULES1