airport-adjacent communities in multiairport regions from 1970 to
2010. Journal of the Transportation Research Board, 2626, 1-8.
    \183\ Rissman et al., 2013. Equity and health impacts of
aircraft emissions at the Hartfield-Jackson Atlanta International
Airport. Landscape and Urban Planning, 120: 234-247.
---------------------------------------------------------------------------

    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.'' \184\ In the second approach, we evaluated
people living near the NPIAS airports in the conterminous 48 states. As
noted in Section II.A.1 of this document, the NPIAS airports support
the majority of piston-engine aircraft activity that occurs in the U.S.
Among the NPIAS airports, we compared the demographic composition of
people living within one kilometer of runways with the demographic
composition of people living at a distance of one to five kilometers
from the same airports.
---------------------------------------------------------------------------

    \184\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020. EPA responses to peer review comments on the report are
available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YISM.pdf.
---------------------------------------------------------------------------

    The distances analyzed for those people living closest to airports
(i.e., distances of 500 meters and 1,000 meters) were chosen for
evaluation following from the air quality monitoring and modeling data
presented in Section II.A.3 of this document. Specifically, the EPA's
modeling and monitoring data indicate that concentrations of lead from
piston-engine aircraft emissions can be elevated above background
levels at distances of 500 meters over a rolling three-month period. On
individual days, concentrations of lead from piston-engine aircraft
emissions can be elevated above background levels at distances of 1,000
meters on individual days downwind of a runway, depending on aircraft
activity and prevailing wind direction.185 186 187
---------------------------------------------------------------------------

    \185\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \186\ Carr et. al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field impacts of lead
emissions from piston-engine aircraft operating on leaded aviation
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \187\ We do not assume or expect that all people living within
500m or 1,000m of a runway are exposed to lead from piston-engine
aircraft emissions, and the wide range of activity of piston-engine
aircraft at airports nationwide suggests that exposure to lead from
aircraft emissions is likely to vary widely.
---------------------------------------------------------------------------

    Because the U.S. has a dense network of airports, many of which
have neighboring communities, we first quantified the number of people
living and children attending school within 500 meters of the
approximately 20,000 airports in the U.S. The results of this analysis
are summarized at the national scale in the EPA's report titled
``National Analysis of the Populations Residing Near or Attending
School Near U.S. Airports.'' \188\ From this analysis, the EPA
estimates that approximately 5.2 million people live within 500 meters
of an airport runway, 363,000 of whom are children age five and under.
The EPA also estimates that 573 schools attended by 163,000 children in
kindergarten through twelfth grade are within 500 meters of an airport
runway.\189\
---------------------------------------------------------------------------

    \188\ In this analysis, we included populations living in census
blocks that intersected the 500-meter buffer around each runway in
the U.S. Potential uncertainties in this approach are described in
our report National Analysis of the Populations Residing Near or
Attending School Near U.S. Airports. EPA-420-R-20-001, available at
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf, and in the
EPA responses to peer review comments on the report, available here:
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YISM.pdf.
    \189\ EPA (2020) National Analysis of the Populations Residing
Near or Attending School Near U.S. Airports. EPA-420-R-20-001.
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf.
---------------------------------------------------------------------------

    In order to identify potential disparities in the near-airport
population, we first evaluated populations at the state level. Using
the U.S. Census population data for each State in the U.S., we compared
the percent of people by age, race and indigenous peoples (i.e.,
children five and under, Black, Asian, and Native American or Alaska
Native) living within 500 meters of an airport runway with the percent
by age, race, and indigenous peoples comprising the state
population.\190\ Using the methodology described in Clarke (2022), the
EPA identified states in which children, Black, Asian, and Native
American or Alaska Native populations represent a greater fraction of
the population compared with the percent of these groups in the state
population.\191\ Results of this analysis are presented in the
following tables.\192\ This state-level analysis presents summary
information for a subset of potentially relevant demographic
characteristics. We present data in this section regarding a wider
array of demographic characteristics when evaluating populations living
near NPIAS airports.
---------------------------------------------------------------------------

    \190\ Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389.
Estimation of Population Size and Demographic Characteristics among
People Living Near Airports by State in the United States. May 31,
2022. Docket ID EPA-HQ-2022-0389.
    \191\ Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389.
Estimation of Population Size and Demographic Characteristics among
People Living Near Airports by State in the United States. May 31,
2022. Docket ID EPA-HQ-2022-0389.
    \192\ These data are presented in tabular form for all states in
this memorandum located in the docket: Clarke. Memorandum to Docket
EPA-HQ-OAR-2022-0389. Estimation of Population Size and Demographic
Characteristics among People Living Near Airports by State in the
United States. May 31, 2022. Docket ID EPA-HQ-2022-0389.
---------------------------------------------------------------------------

    Among children five and under, there were three states (Nevada,
South Carolina, and South Dakota), in which the percent of children
five and under living within 500 meters of a runway represent a greater
fraction of the population by a difference of one percent or greater
compared with the percent of children five and under in the state
population (Table 3).

 Table 3--The Population of Children Five Years and Under Within 500 Meters of an Airport Runway Compared to the
                                State Population of Children Five Years and Under
----------------------------------------------------------------------------------------------------------------
                                                    Percent of      Percent of       Number of       Number of
                                                   children aged   children aged   children aged   children aged
                      State                       five years and  five years and  five years and  five years and
                                                   under within    under within    under within    under in the
                                                    500 meters       the state      500 meters         state
----------------------------------------------------------------------------------------------------------------
Nevada..........................................              10               8           1,000         224,200
South Carolina..................................               9               8             400         361,400
South Dakota....................................              11               9           3,000          71,300
----------------------------------------------------------------------------------------------------------------

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

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

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

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

    Among Native Americans and Alaska Natives, there were five states
(Alaska, Arizona, Delaware, South Dakota, and New Mexico) where the
near-airport population had greater representation by Native Americans
and Alaska Natives compared with the portion of the population they
comprise at the state level by a difference of one percent or greater.
In Alaska, as anticipated due to the critical nature of air travel for
the transportation infrastructure in that state, the disparity in
residential proximity to a runway was the largest; 16,000 Alaska
Natives were estimated to live within 500 meters of a runway,
representing 48 percent of the population within 500 meters of an
airport runway compared with 15 percent of the Alaska state population
(Table 6).

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

    In a separate analysis, the EPA focused on evaluating the potential
for disparities in populations residing near the NPIAS airports. The
EPA compared the demographic composition of people living within one
kilometer of runways at 2,022 of the approximately 3,300 NPIAS airports
with the demographic composition of people living at a distance of one
to five kilometers from the same airports.\193\ \194\ In this analysis,
over one-fourth of airports (i.e., 515) were identified at which
children under five were more highly represented in the zero to one
kilometer distance compared with the percent of children under five
living one to five kilometers away (Table 7). There were 666 airports
where people of color had a greater presence in the zero to one
kilometer area closest

to airport runways than in populations farther away. There were 761
airports where people living at less than two-times the Federal Poverty
Level represented a higher proportion of the overall population within
one kilometer of airport runways compared with the proportion of people
living at less than two-times the Federal Poverty Level among people
living one to five kilometers away.
---------------------------------------------------------------------------

    \193\ For this analysis, we evaluated the 2,022 airports with a
population of greater than 100 people inside the zero to one
kilometer distance to avoid low population counts distorting the
assessment of percent contributions of each group to the total
population within the zero to one kilometer distance.
    \194\ Kamal et.al., Memorandum to Docket EPA-HQ-OAR-2022-0389.
Analysis of Potential Disparity in Residential Proximity to Airports
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389. Methods used are described in this memo and include the
use of block group resolution data to evaluate the representation of
different demographic groups near-airport and for those living one
to five kilometers away.

     Table 7--Number of Airports (Among the 2,022 Airports Evaluated) With Disparity for Certain Demographic
 Populations Within One Kilometer of an Airport Runway in Relation to the Comparison Population Between One and
                                     Five Kilometers From an Airport Runway
----------------------------------------------------------------------------------------------------------------
                                                       Number of airports with disparity \a\
                                 -------------------------------------------------------------------------------
        Demographic group         Total airports                   Disparity 5-    Disparity 10-
                                  with disparity  Disparity 1-5%        10%             20%       Disparity 20%+
----------------------------------------------------------------------------------------------------------------
Children under five years of age             515             507               7               1               0
People with income less than                 761             307             223             180              51
 twice the Federal Poverty Level
People of Color (all races,                  666             377             126             123              40
 ethnicities and indigenous
 peoples).......................
Non-Hispanic Black..............             405             240              77              67              21
Hispanic........................             551             402              85              47              17
Non-Hispanic Asian..............             268             243              18               4               3
Non-Hispanic Native American or              144             130               6               7               1
 Alaska Native \195\............
Non-Hispanic Hawaiian or Pacific              18              17               1               0               0
 Islander.......................
Non-Hispanic Other Race.........              11              11               0               0               0
Non-Hispanic Two or More Races..             226             226               0               0               0
----------------------------------------------------------------------------------------------------------------

    To understand the extent of the potential disparity among the 2,022
NPIAS airports, Table 7 provides information about the distribution in
the percent differences in the proportion of children, individuals with
incomes below two-times the Federal Poverty Level, and people of color
living within one kilometer of a runway compared with those living one
to five kilometers away. For children, Table 7 indicates that for the
vast majority of these airports where there is a higher percentage of
children represented in the near-airport population, differences are
relatively small (e.g., less than five percent). For the airports where
disparity is evident on the basis of poverty, race and ethnicity, the
disparities are potentially large, ranging up to 42 percent for those
with incomes below two-times the Federal Poverty Level, and up to 45
percent for people of color.\196\
---------------------------------------------------------------------------

    \195\ This analysis of 2,022 NPIAS airports did not include
airports in Alaska.
    \196\ Kamal et.al., Memorandum to Docket EPA-HQ-OAR-2022-0389.
Analysis of Potential Disparity in Residential Proximity to Airports
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389.
---------------------------------------------------------------------------

    There are uncertainties in the results provided here inherent to
the proximity-based approach used. These uncertainties include the use
of block group data to provide population numbers for each demographic
group analyzed, and uncertainties in the Census data, including from
the use of data from different analysis years (e.g., 2010 Census Data
and 2018 income data). These uncertainties are described, and their
implications discussed in Kamal et.al. (2022).\197\
---------------------------------------------------------------------------

    \197\ Kamal et.al., Memorandum to Docket EPA-HQ-OAR-2022-0389.
Analysis of Potential Disparity in Residential Proximity to Airports
in the Conterminous United States. May 24, 2022. Docket ID EPA-HQ-
2022-0389.
---------------------------------------------------------------------------

    The data summarized here indicate that there is a greater
prevalence of children under five years of age, an at-risk population
for lead effects, within 500 meters or one kilometer of some airports
compared to more distant locations. This information also indicates
that there is a greater prevalence of people of color and of low-income
populations within 500 meters or one kilometer of some airports
compared with people living more distant. If such differences were to
contribute to disproportionate and adverse impacts on people of color
and low-income populations, they could indicate a potential EJ concern.
Given the number of children in close proximity to runways, including
those in EJ populations, there is a potential for substantial
implications for children's health. The EPA invites comment on the
potential EJ impacts of aircraft lead emissions from aircraft engines
and on the potential impacts on children in close proximity to runways
where piston-engine aircraft operate.

B. Federal Actions To Reduce Lead Exposure

    The federal government has a longstanding commitment to programs to
reduce exposure to lead, particularly for children. In December 2018,
the President's Task Force on Environmental Health Risks and Safety
Risks to Children released the Federal Lead Action Plan, detailing the
federal government's commitments and actions to reduce lead exposure in
children, some of which are described in this section.\198\ In this
section, we describe some of the EPA's actions to reduce lead exposures
from air, water, lead-based paint, and contaminated sites.
---------------------------------------------------------------------------

    \198\ Federal Lead Action Plan to Reduce Childhood Lead
Exposures and Associated Health Impacts. (2018) President's Task
Force on Environmental Health Risks and Safety Risks to Children.
Available at https://www.epa.gov/sites/default/files/2018-12/documents/fedactionplan_lead_final.pdf.
---------------------------------------------------------------------------

    In 1976, the EPA listed lead under CAA section 108, making it what
is called a ``criteria air pollutant.'' \199\ Once lead was listed, the
EPA issued primary and secondary NAAQS under sections 109(b)(1) and
(2), respectively. The EPA issued the first NAAQS for lead in 1978 and
revised the lead NAAQS in 2008 by reducing the level of the standard
from 1.5 micrograms per cubic meter to 0.15 micrograms per cubic meter,
and revising the averaging time and form to an average over a
consecutive three-month period, as described in 40 CFR 50.16.\200\ The
EPA's 2016 Federal Register notice describes the Agency's decision to
retain the existing Lead

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

    \199\ 41 FR 14921 (April 8, 1976). See also, e.g., 81 FR at
71910 (Oct. 18, 2016) for a description of the history of the
listing decision for lead under CAA section 108.
    \200\ 73 FR 66965 (Nov. 12, 2008).
    \201\ 81 FR 71912-71913 (Oct. 18, 2016).
    \202\ Documents pertaining to the current review of the NAAQS
for Lead can be found here: https://www.epa.gov/naaqs/lead-pb-air-quality-standards.
---------------------------------------------------------------------------

    States are primarily responsible for ensuring attainment and
maintenance of the NAAQS. Under section 110 of the Act and related
provisions, states are to submit, for EPA review and, if appropriate,
approval, state implementation plans that provide for the attainment
and maintenance of such standards through control programs directed to
sources of the pollutants involved. The states, in conjunction with the
EPA, also administer the Prevention of Significant Deterioration
program for these pollutants.
    Additional EPA programs to address lead in the environment include
the Federal Motor Vehicle Control program under Title II of the Act,
which involves controls for motor vehicles and nonroad engines and
equipment; the new source performance standards under section 111 of
the Act; and emissions standards for solid waste incineration units and
the national emission standards for hazardous air pollutants (NESHAP)
under sections 129 and 112 of the Act, respectively.
    The EPA has taken a number of actions associated with these air
pollution control programs, including completion of several regulations
requiring reductions in lead emissions from stationary sources
regulated under the CAA sections 112 and 129. For example, in January
2012, the EPA updated the NESHAP for the secondary lead smelting source
category.\203\ These amendments to the original maximum achievable
control technology standards apply to facilities nationwide that use
furnaces to recover lead from lead-bearing scrap, mainly from
automobile batteries. Regulations completed in 2013 for commercial and
industrial solid waste incineration units also require reductions in
lead emissions.\204\
---------------------------------------------------------------------------

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

    A broad range of Federal programs beyond those that focus on air
pollution control provide for nationwide reductions in environmental
releases and human exposures to lead. For example, pursuant to section
1417 of the Safe Drinking Water Act (SDWA), any pipe, pipe or plumbing
fitting or fixture, solder, or flux for potable water applications may
not be used in new installations or repairs or introduced into commerce
unless it is considered ``lead free'' as defined by that Act.\205\ Also
under section 1412 of the SDWA, the EPA's 1991 Lead and Copper Rule
\206\ regulates lead in public drinking water systems through corrosion
control and other utility actions which work together to minimize lead
levels at the tap.\207\ On January 15, 2021, the agency published the
Lead and Copper Rule Revisions (LCRR) \208\ and subsequently reviewed
the rule in accordance with Executive Order 13990.\209\ While the LCRR
took effect in December 2021, the agency concluded that there are
significant opportunities to improve the LCRR.\210\ The EPA is
developing a new proposed rule, the Lead and Copper Rule Improvements
(LCRI),\211\ that would further strengthen the lead drinking water
regulations. The EPA identified priority improvements for the LCRI:
proactive and equitable lead service line replacement (LSLR),
strengthening compliance tap sampling to better identify communities
most at risk of lead in drinking water and to compel lead reduction
actions, and reducing the complexity of the regulation through
improvement of ``methods to identify and trigger action in communities
that are most at risk of elevated drinking water levels.'' \212\ The
EPA intends to propose the LCRI and take final action on it prior to
October 16, 2024.
---------------------------------------------------------------------------

    \205\ Effective in Jan. 2014, the amount of lead permitted in
pipes, fittings, and fixtures was lowered. See, Section 1417 of the
Safe Drinking Water Act: Prohibition on Use of Lead Pipes, Solder,
and Flux at https://www.epa.gov/sdwa/use-lead-free-pipes-fittings-fixtures-solder-and-flux-drinking-water.
    \206\ 40 CFR 141 Subpart I (June 7, 1991).
    \207\ 40 CFR 141 Subpart I (June 7, 1991).
    \208\ 86 FR 4198. (Jan. 15, 2021).
    \209\ E.O. 13990. Protecting Public Health and the Environment
and Restoring Science to Tackle the Climate Crisis. 86 FR 7037 (Jan.
20, 2021).
    \210\ 86 FR 31939. (Dec. 17, 2021).
    \211\ See https://www.epa.gov/ground-water-and-drinking-water/review-national-primary-drinking-water-regulation-lead-and-copper.
Accessed on Nov. 30, 2021.
    \212\ 86 FR 31939 (Dec. 17, 2021).
---------------------------------------------------------------------------

    Federal programs to reduce exposure to lead in paint, dust, and
soil are specified under the comprehensive federal regulatory framework
developed under the Residential Lead-Based Paint Hazard Reduction Act
(Title X). Under Title X (codified, in part, as Title IV of the Toxic
Substances Control Act [TSCA]), the EPA has established regulations and
associated programs in six categories: (1) Training, certification and
work practice requirements for persons engaged in lead-based paint
activities (abatement, inspection and risk assessment); accreditation
of training providers; and authorization of state and Tribal lead-based
paint programs; (2) training, certification, and work practice
requirements for persons engaged in home renovation, repair and
painting (RRP) activities; accreditation of RRP training providers; and
authorization of state and Tribal RRP programs; (3) ensuring that, for
most housing constructed before 1978, information about lead-based
paint and lead-based paint hazards flows from sellers to purchasers,
from landlords to tenants, and from renovators to owners and occupants;
(4) establishing standards for identifying dangerous levels of lead in
paint, dust and soil; (5) providing grant funding to establish and
maintain state and Tribal lead-based paint programs; and (6) providing
information on lead hazards to the public, including steps that people
can take to protect themselves and their families from lead-based paint
hazards.
    The most recent rules issued under Title IV of TSCA revised the
dust-lead hazard standards (DLHS) and dust-lead clearance levels (DLCL)
which were established in a 2001 final rule entitled ``Identification
of Dangerous Levels of Lead.'' \213\ The DLHS are incorporated into the
requirements and risk assessment work practice standards in the EPA's
Lead-Based Paint Activities Rule, codified at 40 CFR part 745, subpart
L. They provide the basis for risk assessors to determine whether dust-
lead hazards are present in target housing (i.e., most pre-1978
housing) and child-occupied facilities (pre-1978 nonresidential
properties where children 6 years of age or under spend a significant
amount of time such as daycare centers and kindergartens). If dust-lead
hazards are present, the risk assessor will identify acceptable options
for controlling the hazards in the respective property, which may
include abatements and/or interim controls. In July 2019, the EPA
published a final rule revising the DLHS from 40 micrograms per square
foot and 250 micrograms per square foot to 10 micrograms per square
foot and 100 micrograms per square foot of lead in dust on floors and
windowsills, respectively.\214\ The DLCL are used to evaluate the
effectiveness of a cleaning following an abatement. If the dust-lead
levels are not below the clearance levels, the components (i.e.,
floors, windowsills, troughs) represented by the failed sample(s) shall
be recleaned and retested. In January 2021, the EPA published a final
rule revising the DLCL to match the DLHS, lowering them from 40
micrograms per square foot and 250 micrograms per square foot to 10
micrograms per square foot and 100 micrograms per square foot on floors

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

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

    Programs associated with the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA or Superfund) \217\ and
Resource Conservation Recovery Act (RCRA) \218\ also implement removal
and remedial response programs that reduce exposures to the release or
threat of a release of lead and other hazardous substances. The EPA
develops and implements protective levels for lead in soil at Superfund
sites and, together with states, at RCRA corrective action facilities.
The Office of Land and Emergency Management develops policy and
guidance for addressing multimedia lead contamination and determining
appropriate response actions at lead sites. Federal programs, including
those implementing RCRA, provide for management of hazardous substances
in hazardous and municipal solid waste (e.g., 66 FR 58258, November 20,
2001).
---------------------------------------------------------------------------

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

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

    The Administrator's proposed findings further respond to several
citizen petitions on this subject including the following: petition for
rulemaking submitted by Friends of the Earth in 2006, petition for
rulemaking submitted by Friends of the Earth, Oregon Aviation Watch and
Physicians for Social Responsibility in 2012, petition for
reconsideration submitted by Friends of the Earth, Oregon Aviation
Watch, and Physicians for Social Responsibility in 2014, and petition
for rulemaking from Alaska Community Action on Toxics, Center for
Environmental Health, Friends of the Earth, Montgomery-Gibbs
Environmental Coalition, Oregon Aviation Watch, the County of Santa
Clara, CA, and the Town of Middleton, WI in 2021. These petitions and
the EPA's responses are described here.\219\
---------------------------------------------------------------------------

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

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

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

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

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

    In 2012, Friends of the Earth, Physicians for Social
Responsibility, and Oregon Aviation Watch filed a new petition claiming
that, among other things, the EPA had unreasonably delayed in
responding to the 2006 petition from Friends of the Earth because it
had failed to determine whether emissions of lead from general aviation
aircraft engines cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare.\223\
The EPA responded to the 2012 petition with our plan for collecting the
necessary information and conducting a proceeding under CAA section 231
regarding whether lead emissions from piston-engine aircraft cause or
contribute to air pollution that may reasonably be anticipated to
endanger public health or welfare. Friends of the Earth, Physicians for
Social Responsibility, and Oregon Aviation Watch submitted a petition
for reconsideration in 2014 \224\ to which the EPA responded in
2015.\225\
---------------------------------------------------------------------------

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

    In 2021, Alaska Community Action on Toxics, Center for
Environmental Health, Friends of the Earth, Montgomery-Gibbs
Environmental Coalition, Oregon Aviation Watch, the County of Santa
Clara, CA, and the Town of Middleton, WI, again petitioned the EPA to
conduct a proceeding under CAA section 231 regarding whether lead
emissions from piston-engine aircraft cause or contribute to air
pollution that may reasonably be anticipated to endanger public health
or welfare.\226\ The EPA responded in 2022 noting our intent to develop
this proposal regarding whether lead emissions from piston-engine
aircraft cause or contribute to air pollution that may reasonably be
anticipated to endanger public health or welfare.\227\
---------------------------------------------------------------------------

    \226\ The 2021 petition is available at https://www.epa.gov/system/files/documents/2022-01/aviation-leaded-avgas-petition-exhibits-final-2021-10-12.pdf.
    \227\ EPA's response to the 2021 petition is available at
https://www.epa.gov/system/files/documents/2022-01/ltr-response-aircraft-lead-petitions-aug-oct-2022-01-12.pdf.
---------------------------------------------------------------------------

III. Legal Framework for This Action

    In this action, the EPA is proposing to make two separate
determinations--an endangerment finding and a cause or contribute
finding--under section 231(a)(2)(A) of the Clean Air Act. The EPA has,
most recently, finalized such findings under CAA section 231 for
greenhouse gases (GHGs) in 2016 (2016 Findings), and in that action the
EPA

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

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

A. Statutory Text and Basis for This Proposal

    Section 231(a)(2)(A) of the CAA provides that the ``The
Administrator shall, from time to time, issue proposed emission
standards applicable to the emission of any air pollutant from any
class or classes of aircraft engines which in his judgment causes, or
contributes to, air pollution which may reasonably be anticipated to
endanger public health or welfare.'' \234\ In this proposal, the EPA is
addressing the predicate for regulatory action under CAA section 231
through a two-part test, which as noted previously, is the same as the
test used in the 2016 Findings and in the 2009 Findings.
---------------------------------------------------------------------------

    \234\ Regarding ``welfare,'' the CAA states that ``[a]ll
language referring to effects on welfare includes, but is not
limited to, effects on soils, water, crops, vegetation, manmade
materials, animals, wildlife, weather, visibility, and climate,
damage to and deterioration of property, and hazards to
transportation, as well as effects on economic values and on
personal comfort and well-being, whether caused by transformation,
conversion, or combination with other air pollutants.'' CAA section
302(h). Regarding ``public health,'' there is no definition of
``public health'' in the Clean Air Act. The Supreme Court has
discussed the concept of ``public health'' in the context of whether
costs can be considered when setting NAAQS. Whitman v. American
Trucking Ass'n, 531 U.S. 457 (2001). In Whitman, the Court imbued
the term with its most natural meaning: ``the health of the
public.'' Id. at 466.
---------------------------------------------------------------------------

    As the first step of the two-part test, the Administrator must
decide whether, in his judgment, the air pollution under consideration
may reasonably be anticipated to endanger public health or welfare. As
the second step, the Administrator must decide whether, in his
judgment, emissions of an air pollutant from certain classes of
aircraft engines cause or contribute to this air pollution. If the
Administrator answers both questions in the affirmative, he will issue
standards under section 231.\235\
---------------------------------------------------------------------------

    \235\ See Massachusetts v. EPA, 549 U.S. 497,533 (2007)
(interpreting an analogous provision in CAA section 202).
---------------------------------------------------------------------------

    In accordance with the EPA's interpretation of the text of section
231(a)(2)(A), as described in the 2016 Findings, the phrase ``may
reasonably be anticipated'' and the term ``endanger'' in section
231(a)(2)(A) authorize, if not require, the Administrator to act to
prevent harm and to act in conditions of uncertainty.\236\ They do not
limit him to merely reacting to harm or to acting only when certainty
has been achieved; indeed, the references to anticipation and to
endangerment imply that the failure to look to the future or to less
than certain risks would be to abjure the Administrator's statutory
responsibilities. As the D.C. Circuit explained, the language ``may
reasonably be anticipated to endanger public health or welfare'' in CAA
section 202(a) requires a ``precautionary, forward-looking scientific
judgment about the risks of a particular air pollutant, consistent with
the CAA's precautionary and preventive orientation.'' \237\ The court
determined that ``[r]equiring that the EPA find `certain' endangerment
of public health or welfare before regulating greenhouse gases would
effectively prevent the EPA from doing the job that Congress gave it in
[section] 202(a)--utilizing emission standards to prevent reasonably
anticipated endangerment from maturing into concrete harm.'' \238\ The
same language appears in section 231(a)(2)(A), and the same
interpretation applies in that context.
---------------------------------------------------------------------------

    \236\ See 81 FR at 54435 (Aug. 19, 2016).
    \237\ CRR, 684 F.3d at 122 (internal citations omitted) (June
26, 2012).
    \238\ CRR, 684 F.3d at 122 (internal citations omitted) (June
26, 2012).
---------------------------------------------------------------------------

    Moreover, by instructing the Administrator to consider whether
emissions of an air pollutant cause or contribute to air pollution in
the second part of the two-part test, the Act makes clear that he need
not find that emissions from any one sector or class of sources are the
sole or even the major part of the air pollution considered. This is
clearly indicated by the use of the term ``contribute.'' Further, the
phrase ``in his judgment'' authorizes the Administrator to weigh risks
and to consider projections of future possibilities, while also
recognizing uncertainties and extrapolating from existing data.
    Finally, when exercising his judgment in making both the
endangerment and cause-or-contribute findings, the Administrator
balances the likelihood and severity of effects. Notably, the phrase
``in his judgment'' modifies both ``may reasonably be anticipated'' and
``cause or contribute.''
    Often, past endangerment and cause or contribute findings have been
proposed concurrently with proposed standards under various sections of
the CAA, including section 231.\239\ Comment has been taken on these
proposed findings as part of the notice and comment process for the
emission standards.\240\ However, there is no requirement that the
Administrator propose the endangerment and cause or contribute findings
concurrently with proposed standards and, most recently under section
231, the EPA made separate endangerment and cause or contribute
findings for GHGs before proceeding to set standards.
---------------------------------------------------------------------------

    \239\ 81 FR at 54425 (Aug. 19, 2016).
    \240\ See, e.g., Rulemaking for non-road compression-ignition
engines under section 213(a)(4) of the CAA, Proposed Rule at 58 FR
28809, 28813-14 (May 17, 1993), Final Rule at 59 FR 31306, 31318
(June 17, 1994); Rulemaking for highway heavy-duty diesel engines
and diesel sulfur fuel under sections 202(a) and 211(c) of the CAA,
Proposed Rule at 65 FR 35430 (June 2, 2000), and Final Rule at 66 FR
5002 (Jan. 18, 2001).
---------------------------------------------------------------------------

    The Administrator is applying the rulemaking provisions of CAA
section 307(d) to this action, pursuant to CAA section 307(d)(1)(V),
which provides that the provisions of 307(d) apply to ``such other
actions as the Administrator may determine.'' \241\ Any subsequent

standard setting rulemaking under CAA section 231 will also be subject
to the notice and comment rulemaking procedures under CAA section
307(d), as provided in CAA section 307(d)(1)(F) (applying the
provisions of CAA section 307(d) to the promulgation or revision of any
aircraft emission standard under CAA section 231). Thus, these proposed
findings will be subject to the same procedural requirements that would
apply if the proposed findings were part of a standard-setting
rulemaking.
---------------------------------------------------------------------------

    \241\ As the Administrator is applying the provisions of CAA
section 307(d) to this action under section 307(d)(1)(V), we need
not determine whether those provisions would apply to this action
under section 307(d)(1)(F).
---------------------------------------------------------------------------

B. Considerations for the Endangerment and Cause or Contribute Analyses
Under Section 231(a)(2)(A)

    In the context of this proposal, the EPA understands section
231(a)(2)(A) of the CAA to call for the Administrator to exercise his
judgment and make two separate determinations: first, whether the
relevant kind of air pollution (here, lead air pollution) may
reasonably be anticipated to endanger public health or welfare, and
second, whether emissions of any air pollutant from classes of the
sources in question (here, any aircraft engine that is capable of using
leaded aviation gasoline), cause or contribute to this air
pollution.\242\
---------------------------------------------------------------------------

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

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

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

    Similarly, the EPA is taking the same approach to the cause or
contribute analysis as was previously explained in the 2016
Findings.\244\ For example, as previously noted, section 231(a)(2)(A)'s
instruction to consider whether emissions of an air pollutant cause or
contribute to air pollution makes clear that the Administrator need not
find that emissions from any one sector or class of sources are the
sole or even the major part of an air pollution problem.\245\ Moreover,
like the CAA section 202(a) language that governed the 2009 Findings,
the statutory language in section 231(a)(2)(A) does not contain a
modifier on its use of the term ``contribute.'' \246\ Unlike other CAA
provisions, it does not require ``significant'' contribution. Compare,
e.g., CAA sections 111(b); 213(a)(2), (4). Congress made it clear that
the Administrator is to exercise his judgment in determining
contribution, and authorized regulatory controls to address air
pollution even if the air pollution problem results from a wide variety
of sources.\247\ While the endangerment test looks at the air pollution
being considered as a whole and the risks it poses, the cause or
contribute test is designed to authorize the EPA to identify and then
address what may well be many different sectors, classes, or groups of
sources that are each part of the problem.\248\
---------------------------------------------------------------------------

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

    Moreover, as the EPA has previously explained, the Administrator
has ample discretion in exercising his reasonable judgment and
determining whether, under the circumstances presented, the cause or
contribute criterion has been met.\249\ As noted in the 2016 Findings,
in addressing provisions in section 202(a), the D.C. Circuit has
explained that the Act at the endangerment finding step did not require
the EPA to identify a precise numerical value or ``a minimum threshold
of risk or harm before determining whether an air pollutant
endangers.'' \250\ Accordingly, the EPA ``may base an endangerment
finding on `a lesser risk of greater harm . . . or a greater risk of
lesser harm' or any combination in between.'' \251\ As the language in
section 231(a)(2)(A) is analogous to that in section 202(a), it is
reasonable to apply this interpretation to the endangerment
determination under section 231(a)(2)(A).\252\ Moreover, the logic
underlying this interpretation supports the general principle that
under CAA section 231 the EPA is not required to identify a specific
minimum threshold of contribution from potentially subject source
categories in determining whether their emissions ``cause or
contribute'' to the endangering air pollution.\253\ The reasonableness
of this principle is further supported by the fact that section 231
does not impose on the EPA a requirement to find that such contribution
is ``significant,'' let alone the sole or major cause of the
endangering air pollution.\254\
---------------------------------------------------------------------------

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

    Finally, as also described in the 2016 Findings, there are a number
of possible ways of assessing whether air pollutants cause or
contribute to the air pollution which may reasonably be anticipated to
endanger public health and welfare, and no single approach is required
or has been used exclusively in previous cause or contribute
determinations under title II of the CAA.\255\
---------------------------------------------------------------------------

    \255\ See 81 FR at 54462 (Aug. 15, 2016).
---------------------------------------------------------------------------

C. Regulatory Authority for Emission Standards

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

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

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

IV. The Proposed Endangerment Finding Under CAA Section 231

A. Scientific Basis of the Endangerment Finding

1. Lead Air Pollution
    Lead is emitted and exists in the atmosphere in a variety of forms
and compounds and is emitted by a wide range of sources.\257\ Lead is
persistent in the environment. Atmospheric transport distances of
airborne lead vary depending on its form and particle size, as
discussed in Section II.A of this document, with coarse lead-bearing
particles deposited to a greater extent near the source, while fine
lead-bearing particles can be transported long distances before being
deposited. Through atmospheric deposition, lead is distributed to other
environmental media, including soils and surface water bodies.\258\
Lead is retained in soils and sediments, where it provides a historical
record and, depending on several factors, can remain available in some
areas for extended periods for environmental or human exposure, with
any associated potential public health and public welfare impacts.
---------------------------------------------------------------------------

    \257\ EPA (2013) ISA for Lead. Section 2.2. ``Sources of
Atmospheric Pb.'' p. 2-1. EPA, Washington, DC, EPA/600/R-10/075F,
2013.
    \258\ EPA (2013) ISA for Lead. Executive Summary. ``Sources,
Fate and Transport of Lead in the Environment, and the Resulting
Human Exposure and Dose.'' pp. lxxviii-lxxix. EPA, Washington, DC,
EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    For purposes of this action, the EPA is proposing to define the
``air pollution'' referred to in section 231(a)(2)(A) of the CAA as
lead, which we also refer to as the lead air pollution in this
document.\259\
---------------------------------------------------------------------------

    \259\ The lead air pollution that we are considering in this
proposed finding can occur as elemental lead or in lead-containing
compounds, and this proposed definition of the air pollution
recognizes that lead in air (whatever form it is found in, including
in inorganic and organic compounds containing lead) has the
potential to elicit public health and welfare effects. We note, for
example, that the 2013 Lead ISA and 2008 AQCD described the
toxicokinetics of inorganic and organic forms of lead and studies
evaluating lead-related health effects commonly measure total lead
level (i.e., all forms of lead in various biomarker tissues such as
blood).
---------------------------------------------------------------------------

2. Health Effects and Lead Air Pollution
    As noted in Section II.A of this document, in 2013, the EPA
completed the Integrated Science Assessment for Lead which built on the
findings of previous AQCDs for Lead. These documents critically assess
and integrate relevant scientific information regarding the health and
welfare effects of lead and have undergone extensive critical review by
the EPA, the Clean Air Scientific Advisory Committee (CASAC), and the
public. As such, these assessments provide the primary scientific and
technical basis on which the Administrator is proposing to find that
lead air pollution is reasonably anticipated to endanger public health
and welfare.\260 261\
---------------------------------------------------------------------------

    \260\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-
10/075F, 2013.
    \261\ EPA (2006) AQC for Lead. EPA, Washington, DC, EPA/600/R-5/
144aF, 2006.
---------------------------------------------------------------------------

    As summarized in Section II.A of this document, human exposure to
lead that is emitted into the air can occur by multiple pathways.
Ambient air inhalation pathways include both inhalation of air outdoors
and inhalation of ambient air that has infiltrated into indoor
environments. Additional exposure pathways may involve media other than
air, including indoor and outdoor dust, soil, surface water and
sediments, vegetation and biota. While the bioavailability of air-
related lead is modified by several factors in the environment (e.g.,
the chemical form of lead, environmental fate of lead emitted to air),
as described in Section II.A of this document, it is well-documented
that exposures to air-related lead can result in increased blood lead
levels, particularly for children living near air lead sources, who may
have increased blood lead levels due to their proximity to these
sources of exposure.\262\
---------------------------------------------------------------------------

    \262\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
40. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    As described in the EPA's 2013 Lead ISA and in prior Criteria
Documents, lead has been demonstrated to exert a broad array of
deleterious effects on multiple organ systems. The 2013 Lead ISA
characterizes the causal nature of relationships between lead exposure
and health effects using a weight-of-evidence approach.\263\ We
summarize here those health effects for which the EPA in the 2013 Lead
ISA has concluded that the evidence supports a determination of either
a ``causal relationship,'' or a ``likely to be causal relationship,''
or for which the evidence is ``suggestive of a causal relationship''
between lead exposure and a health effect.\264\ In the discussion that
follows, we summarize findings regarding effects observed in children,
effects observed in adults, and additional effects observed that are
not specific to an age group.
---------------------------------------------------------------------------

    \263\ The causal framework draws upon the assessment and
integration of evidence from across scientific disciplines, spanning
atmospheric chemistry, exposure, dosimetry and health effects
studies (i.e., epidemiologic, controlled human exposure, and animal
toxicological studies), and assessment of the related uncertainties
and limitations that ultimately influence our understanding of the
evidence. This framework employs a five-level hierarchy that
classifies the overall weight-of-evidence with respect to the causal
nature of relationships between criteria pollutant exposures and
health and welfare effects using the following categorizations:
causal relationship; likely to be causal relationship; suggestive
of, but not sufficient to infer, a causal relationship; inadequate
to infer the presence or absence of a causal relationship; and not
likely to be a causal relationship. EPA (2013) ISA for Lead.
Preamble Section. p. xliv. EPA, Washington, DC, EPA/600/R-10/075F,
2013.
    \264\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal
determinations for the relationship between exposure to Pb and
health effects.'' pp. lxxxiii-lxxxvii. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
---------------------------------------------------------------------------

    The EPA has concluded that there is a ``causal relationship''
between lead exposure during childhood (pre and postnatal) and a range
of health effects in children, including the following: Cognitive
function decrements; the group of externalizing behaviors comprising
attention, increased impulsivity, and hyperactivity; and developmental
effects (i.e., delayed pubertal onset).\265\ In addition, the EPA has
concluded that the evidence supports a conclusion that there is a
``likely to be causal relationship'' between lead exposure and conduct
disorders in children and young adults, internalizing behaviors such as
depression, anxiety and withdrawn behavior, auditory function
decrements, and fine and gross motor function decrements.\266\
---------------------------------------------------------------------------

    \265\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal
determinations for the relationship between exposure to Pb and
health effects.'' p. lxxxiii and p. lxxxvi. EPA, Washington, DC,
EPA/600/R-10/075F, 2013.
    \266\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal
determinations for the relationship between exposure to Pb and
health effects.'' pp. lxxxiii-lxxxiv. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
---------------------------------------------------------------------------

    Multiple epidemiologic studies conducted in diverse populations of
children consistently demonstrate the harmful effects of lead exposure
on cognitive function (as measured by decrements in intelligence
quotient [IQ], decreased academic performance, and poorer performance
on tests of executive function). These findings are supported by
extensively documented toxicological evidence substantiating the
plausibility of these findings in the epidemiological literature and
provide information on the likely mechanisms underlying these
neurotoxic effects.\267\
---------------------------------------------------------------------------

    \267\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of
Pb Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

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

used extensively as a measure of the negative effects of exposure to
lead.268 269 Examples of other measures of cognitive
function negatively associated with lead exposure include measures of
intelligence and cognitive development and cognitive abilities, such as
learning, memory, and executive functions, as well as academic
performance and achievement.\270\
---------------------------------------------------------------------------

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

    In summarizing the evidence related to neurocognitive impacts of
lead at different childhood lifestages, the 2013 Lead ISA notes that
``in individual studies, postnatal (early childhood and concurrent
[with IQ testing]) blood lead levels are also consistently associated
with cognitive function decrements in children and adolescents.'' \271\
The 2013 Lead ISA additionally notes that the findings from
experimental animal studies indicate that lead exposures during
multiple early lifestages and periods are observed to induce
impairments in learning, and that these findings ``are consistent with
the understanding that the nervous system continues to develop (i.e.,
synaptogenesis and synaptic pruning remains active) throughout
childhood and into adolescence.'' \272\ The 2013 Lead ISA further notes
that ``it is clear that lead exposure in childhood presents a risk;
further, there is no evidence of a threshold below which there are no
harmful effects on cognition from lead exposure,'' and additionally
recognizes uncertainty about the lead exposures that are part of the
effects and blood lead levels observed in epidemiologic studies
(uncertainties which are greater in studies of older children and
adults than in studies of younger children).\273\ Evidence suggests
that while some neurocognitive effects of lead in children may be
transient, some lead-related cognitive effects may be irreversible and
persist into adulthood,\274\ potentially affecting lower educational
attainment and financial well-being.\275\
---------------------------------------------------------------------------

    \271\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and
Neurodevelopmental Deficits in Children.'' p. 1-76. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
    \272\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and
Neurodevelopmental Deficits in Children.'' p. 1-76. EPA/600/R-10/
075F, 2013.
    \273\ EPA (2013) ISA for Lead. Executive Summary. ``Effects of
Pb Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
    \274\ EPA (2013) ISA for Lead. Section 1.9.5. ``Reversibility
and Persistence of Neurotoxic Effects of Pb.'' p. 1-76. EPA,
Washington, DC, EPA/600/R-10/075F, 2013.
    \275\ EPA (2013) ISA for Lead. Section 4.3.14. ``Public Health
Significance of Associations between Pb Biomarkers and
Neurodevelopmental Effects.'' p. 4-279. EPA, Washington, DC, EPA/
600/R-10/075F, 2013.
---------------------------------------------------------------------------

    The 2013 Lead ISA concluded that neurodevelopmental effects in
children were among the effects best substantiated as occurring at the
lowest blood lead levels, and that these categories of effects were
clearly of the greatest concern with regard to potential public health
impact.\276\ For example, in considering population risk, the 2013 Lead
ISA notes that ``[s]mall shifts in the population mean IQ can be highly
significant from a public health perspective''.\277\ Specifically, if
lead-related decrements are manifested uniformly across the range of IQ
scores in a population, ``a small shift in the population mean IQ may
be significant from a public health perspective because such a shift
could yield a larger proportion of individuals functioning in the low
range of the IQ distribution, which is associated with increased risk
of educational, vocational, and social failure'' as well as a decrease
in the proportion with high IQ scores.\278\
---------------------------------------------------------------------------

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

    With regard to lead effects identified for the adult population,
the 2013 Lead ISA concluded that there is a ``causal relationship''
between lead exposure and hypertension and coronary heart disease in
adults. The 2013 Lead ISA concluded that cardiovascular effects in
adults were those of greatest public health concern for adults because
the evidence indicated that these effects occurred at the lowest blood
lead levels, compared to other health effects, although the role of
past versus current exposures to lead is unclear.\279\
---------------------------------------------------------------------------

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

    With regard to evidence of cardiovascular effects and other effects
of lead on adults, the 2013 Lead ISA notes that ``[a] large body of
evidence from both epidemiologic studies of adults and experimental
studies in animals demonstrates the effect of long-term lead exposure
on increased blood pressure and hypertension.'' \280\ In addition to
its effect on blood pressure, ``lead exposure can also lead to coronary
heart disease and death from cardiovascular causes and is associated
with cognitive function decrements, symptoms of depression and anxiety,
and immune effects in adult humans.'' \281\ The extent to which the
effects of lead on the cardiovascular system are reversible is not
well-characterized. Additionally, the frequency, timing, level, and
duration of lead exposure causing the effects observed in adults has
not been pinpointed, and higher exposures earlier in life may play a
role in the development of health effects measured later in life.\282\
The 2013 Lead ISA states that ``[i]t is clear however, that lead
exposure can result in harm to the cardiovascular system that is
evident in adulthood and may also affect a broad array of organ
systems.'' \283\ In summarizing the public health significance of lead
on the adult population, the 2013 Lead ISA notes that ``small lead-
associated increases in the population mean blood pressure could result
in an increase in the proportion of the population with hypertension
that is significant from a public health perspective.'' \284\
---------------------------------------------------------------------------

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

    In addition to the effects summarized here, the EPA has concluded
there is a ``likely to be causal relationship'' between lead exposure
and both cognitive function decrements and psychopathological effects
in adults. The 2013 Lead ISA also concludes that there is a ``causal
relationship'' between lead exposure and decreased red blood cell
survival and function, altered heme synthesis, and male reproductive
function. The EPA has also concluded there is a ``likely to be causal
relationship'' between lead exposure and decreased host resistance,
resulting in increased susceptibility to bacterial infection and
suppressed delayed type hypersensitivity, and cancer.\285\
---------------------------------------------------------------------------

    \285\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal
determinations for the relationship between exposure to Pb and
health effects.'' pp. lxxxiv-lxxxvii. EPA, Washington, DC, EPA/600/
R-10/075F, 2013.
---------------------------------------------------------------------------

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

subclinical atherosclerosis, reduced kidney function, birth outcomes
(e.g., low birth weight, spontaneous abortion), and female reproductive
function.\286\
---------------------------------------------------------------------------

    \286\ EPA (2013) ISA for Lead. Table ES-1. ``Summary of causal
determinations for the relationship between exposure to Pb and
health effects.'' pp. lxxxiv-lxxxvi. EPA, Washington, DC, EPA/600/R-
10/075F, 2013.
---------------------------------------------------------------------------

    The EPA has identified factors that may increase the risk of health
effects of lead exposure due to susceptibility and/or vulnerability;
these are termed ``at-risk'' factors. The 2013 Lead ISA describes the
systematic approach the EPA uses to evaluate the coherence of evidence
to determine the biological plausibility of associations between at-
risk factors and increased vulnerability and/or susceptibility. An
overall weight of evidence is used to determine whether a specific
factor results in a population being at increased risk of lead-related
health effects.\287\ The 2013 Lead ISA concludes that ``there is
adequate evidence that several factors--childhood, race/ethnicity,
nutrition, residential factors, and proximity to lead sources--confer
increased risk of lead-related health effects.'' \288\
---------------------------------------------------------------------------

    \287\ EPA (2013) ISA for Lead. Chapter 5. ``Approach to
Classifying Potential At-Risk Factors.'' p. 5-2. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
    \288\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
44. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

3. Welfare Effects and Lead Air Pollution
    The 2013 Lead ISA characterizes the causal nature of relationships
between lead exposure and welfare effects using a five-level hierarchy
that classifies the overall weight-of-evidence.\289\ We summarize here
the welfare effects for which the EPA has concluded that the evidence
supports a determination of either a ``causal relationship,'' or a
``likely to be causal relationship,'' with exposure to lead, or that
the evidence is ``suggestive of a causal relationship'' with lead
exposure. The discussion that follows is organized to first provide a
summary of the effects of lead in the terrestrial environment, followed
by a summary of effects of lead in freshwater and saltwater ecosystems.
The 2013 Lead ISA further describes the scales or levels at which these
determinations between lead exposure and effects on plants,
invertebrates, and vertebrates were made (i.e., community-level,
ecosystem-level, population-level, organism-level or sub-organism
level).\290\
---------------------------------------------------------------------------

    \289\ Causal determinations for ecological effects were based on
integration of information on biogeochemistry, bioavailability,
biological effects, and exposure-response relationships of lead in
terrestrial, freshwater, and saltwater environments. This framework
employs a five-level hierarchy that classifies the overall weight-
of-evidence with respect to the causal nature of relationships
between criteria pollutant exposures and health and welfare effects
using the categorizations described in the 2013 Lead NAAQS.
    \290\ EPA (2013) ISA for Lead. Table ES-2. ``Schematic
representation of the relationships between the various MOAs by
which Pb exerts its effects.'' p. lxxxii. EPA, Washington, DC, EPA/
600/R-10/075F, 2013.
---------------------------------------------------------------------------

    In terrestrial environments, the EPA determined that ``causal
relationships'' exist between lead exposure and reproductive and
developmental effects in vertebrates and invertebrates, growth in
plants, survival for invertebrates, hematological effects in
vertebrates, and physiological stress in plants.\291\ The EPA also
determined that there were ``likely to be causal relationships''
between lead exposure and community and ecosystem effects, growth in
invertebrates, survival in vertebrates, neurobehavioral effects in
invertebrates and vertebrates, and physiological stress in
invertebrates and vertebrates.
---------------------------------------------------------------------------

    \291\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal
determinations for the relationship between Pb exposure and effects
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    In freshwater environments, the EPA found that ``causal
relationships'' exist between lead exposure and reproductive and
developmental effects in vertebrates and invertebrates, growth in
invertebrates, survival for vertebrates and invertebrates, and
hematological effects in vertebrates. The EPA also determined that
there were ``likely to be causal relationships'' between lead exposure
and community and ecosystem effects, growth in plants, neurobehavioral
effects in invertebrates and vertebrates, hematological effects in
invertebrates, and physiological stress in plants, invertebrates, and
vertebrates.\292\
---------------------------------------------------------------------------

    \292\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal
determinations for the relationship between Pb exposure and effects
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    The EPA also determined that the evidence for saltwater ecosystems
was ``suggestive of a causal relationship'' between lead exposure and
reproductive and developmental effects in invertebrates, hematological
effects in vertebrates, and physiological stress in invertebrates.\293\
---------------------------------------------------------------------------

    \293\ EPA (2013) ISA for Lead. Table ES-2. ``Summary of causal
determinations for the relationship between Pb exposure and effects
on plants, invertebrates, and vertebrates.'' p. xc. EPA, Washington,
DC, EPA/600/R-10/075F, 2013.
---------------------------------------------------------------------------

    The 2013 Lead ISA concludes, ``With regard to the ecological
effects of lead, uptake of lead into fauna and subsequent effects on
reproduction, growth and survival are established and are further
supported by more recent evidence. These may lead to effects at the
population, community, and ecosystem level of biological organization.
In both terrestrial and aquatic organisms, gradients in response are
observed with increasing concentration of lead and some studies report
effects within the range of lead detected in environmental media over
the past several decades. Specifically, effects on reproduction,
growth, and survival in sensitive freshwater invertebrates are well-
characterized from controlled studies at concentrations at or near lead
concentrations occasionally encountered in U.S. fresh surface waters.
Hematological and stress related responses in some terrestrial and
aquatic species were also associated with elevated lead levels in
polluted areas. However, in natural environments, modifying factors
affect lead bioavailability and toxicity and there are considerable
uncertainties associated with generalizing effects observed in
controlled studies to effects at higher levels of biological
organization. Furthermore, available studies on community and
ecosystem-level effects are usually from contaminated areas where lead
concentrations are much higher than typically encountered in the
environment. The contribution of atmospheric lead to specific sites is
not clear and the connection between air concentration of lead and
ecosystem exposure continues to be poorly characterized.'' \294\
---------------------------------------------------------------------------

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

B. Proposed Endangerment Finding

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

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

A. Proposed Definition of the Air Pollutant

    Under section 231, the Administrator is to determine whether
emissions of any air pollutant from any class or classes of aircraft
engines cause or contribute to air pollution which may reasonably be
anticipated to endanger public health or welfare. As in the 2016
Findings that the EPA made under

section 231 for greenhouse gases, in making this proposed cause or
contribute finding under section 231(a)(2), the Administrator first
defines the air pollutant being evaluated. The Administrator has
reasonably and logically considered the relationship between the lead
air pollution and the air pollutant when considering emissions of lead
from engines used in covered aircraft. The Administrator proposes to
define the air pollutant to match the proposed definition of the air
pollution, such that the air pollutant analyzed for contribution would
mirror the air pollution considered in the endangerment finding.
Accordingly, for purposes of this action, the Administrator is
proposing to define the ``air pollutant'' referred to in section
231(a)(2)(A) as lead, which we also refer to as the lead air pollutant
in this document.\295\ As noted in Section II.A.2 of this document,
lead emitted to the air from covered aircraft engines is predominantly
in particulate form as lead dibromide; however, some chemical compounds
of lead that are expected in the exhaust from these engines, including
alkyl lead compounds, would occur in the air in gaseous form.
---------------------------------------------------------------------------

    \295\ The lead air pollutant we are considering in this proposed
finding can occur as elemental lead or in lead-containing compounds,
and this definition of the air pollutant recognizes the range of
chemical forms of lead emitted by engines in covered aircraft.
---------------------------------------------------------------------------

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

B. The Data Used To Evaluate the Proposed Cause or Contribute Finding

    The Administrator's assessment of whether emissions from the
engines used in covered aircraft cause or contribute to lead air
pollution is informed by estimates of lead emissions from the covered
aircraft, lead concentrations in air at and near airports that are
attributable to lead emissions from piston engines used in covered
aircraft, and potential future conditions.
    As used in this proposal, the term, ``covered aircraft'' refers to
all aircraft and ultralight vehicles equipped with covered engines
which, in this context, means any aircraft engine that is capable of
using leaded avgas. Examples of covered aircraft would include smaller
piston-powered aircraft such as the Cessna 172 (single-engine aircraft)
and the Beechcraft Baron G58 (twin-engine aircraft), as well as the
largest piston-engine aircraft--the Curtiss C-46 and the Douglas DC-6.
Other examples of covered aircraft would include rotorcraft, such as
the Robinson R44 helicopter, light-sport aircraft, and ultralight
vehicles equipped with piston engines. The vast majority of covered
aircraft are piston-engine powered.
    In recent years, covered aircraft are estimated to be the largest
single source of lead to air in the U.S. Since 2008, as described in
Section II.A.2.b of this document, lead emissions from covered aircraft
are estimated to have contributed over 50 percent of all lead emitted
to the air nationally. The EPA estimates 470 tons of lead were emitted
by covered aircraft in 2017, comprising 70 percent of lead emitted to
air nationally that year.\296\ In approximately 1,000 counties in the
U.S., the EPA's emissions inventory identifies covered aircraft as the
sole source of lead emissions. Among the 1,872 counties in the U.S. for
which the inventory identifies multiple sources of lead emissions,
including engine emissions from covered aircraft, the contribution of
aircraft engine emissions ranges from 0.0006 to 0.26 tons per year,
comprising 0.0065 to 99.98 percent (respectively) of total lead
emissions to air in those counties from covered aircraft.\297\
---------------------------------------------------------------------------

    \296\ The lead inventories for 2008, 2011 and 2014 are provided
in the EPA (2018b) Report on the Environment Exhibit 2.
Anthropogenic lead emissions in the U.S. Available at https://cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead inventories for
2017 are available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data#dataq.
    \297\ Airport lead annual emissions data used were reported in
the 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data. In addition
to the triennial NEI, the EPA collects from state, local, and Tribal
air agencies point source data for larger sources every year (see
https://www.epa.gov/air-emissions-inventories/air-emissions-reporting-requirements-aerr for specific emissions thresholds).
While these data are not typically published as a new NEI, they are
available publicly upon request and are also included in https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms,
which are created for years other than the triennial NEI years.
County estimates of lead emissions from non-aircraft sources used in
this action are from the 2019 inventory. There are 3,012 counties
and statistical equivalent areas where EPA estimates engine
emissions of lead occur.
---------------------------------------------------------------------------

    Covered aircraft activity, as measured by the number of hours flown
nationwide, increased nine percent in the period from 2012 through
2019.\298\ General aviation activity, largely conducted by covered
aircraft, increased up to 52 percent at airports that are among the
busiest in the U.S.\299\ In future years, while piston-engine aircraft
activity overall is projected to decrease slightly, this change in
activity is not projected to occur uniformly across airports in the
U.S.; some airports are forecast to have increased activity by general
aviation aircraft, the majority of which is conducted by piston-engine
aircraft.\300\ Although there is some uncertainty in these projections,
they indicate that lead emissions from covered aircraft may increase at
some airports in the future.\301\
---------------------------------------------------------------------------

    \298\ FAA. General Aviation and Part 135 Activity Surveys--CY
2019. Chapter 3: Primary and Actual Use. Table 1.3--General Aviation
and Part 135 Total Hours Flown by Aircraft Type 2008-2019 (Hours in
Thousands). Retrieved on Dec., 27, 2021 at https://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2019/.
    \299\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past
Trends and Future Projections in General Aviation Activity and
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
    \300\ Geidosch. Memorandum to Docket EPA-HQ-OAR-2022-0389. Past
Trends and Future Projections in General Aviation Activity and
Emissions. June 1, 2022. Docket ID EPA-HQ-2022-0389.
    \301\ FAA TAF Fiscal Years 2020-2045 describes the forecast
method, data sources, and review process for the TAF estimates. The
documentation for the TAF is available at https://taf.faa.gov/Downloads/TAFSummaryFY2020-2045.pdf.
---------------------------------------------------------------------------

    Additionally, engine emissions of lead from covered aircraft may
deposit in the local environment and, due to the small size of the
lead-bearing particles emitted by engines in covered aircraft, these
particles may disperse widely in the environment. Therefore, because
lead is a persistent pollutant in the environment, we anticipate
current and future emissions of lead from covered aircraft engines may
contribute to exposures and uptake by humans and biota into the future.
    In evaluating the contributions of engine emissions from covered
aircraft

to lead air pollution, as defined in Section V.A of this document, the
EPA also considers lead concentrations in the ambient air--monitored
concentrations, modeled concentrations, and model-extrapolated
estimates of lead concentrations. Lead concentrations monitored in the
ambient air typically quantify lead compounds collected as suspended
particulate matter. The information gained from air monitoring and air
quality modeling provides insight into how lead emissions from piston
engines used in covered aircraft can affect lead concentrations in air.
    As described in Section II.A.3 of this document, the EPA has
conducted air quality modeling at two airports and extrapolated modeled
estimates of lead concentrations to 13,000 airports with piston-engine
aircraft activity. These studies indicate that over a three-month
averaging time (the averaging time for the Lead NAAQS), the engine
emissions of lead from covered aircraft are estimated to contribute to
air lead concentrations to a distance of at least 500 meters downwind
from a runway.302 303 Additional studies have reported that
lead emissions from covered aircraft may have increased concentrations
of lead in air by one to two orders of magnitude at locations proximate
to aircraft emissions compared to nearby locations not impacted by a
source of lead air emissions.304 305 306
---------------------------------------------------------------------------

    \302\ Carr et. al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field impacts of lead
emissions from piston-engine aircraft operating on leaded aviation
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \303\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. Table 6. EPA-420-R-20-003, 2020.
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
    \304\ Carr et al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field impacts of lead
emissions from piston-engine aircraft operating on leaded aviation
gasoline. Atmospheric Environment, 45 (32), 5795-5804. DOI: https://dx.doi.org/10.1016/j.atmosenv.2011.07.017.
    \305\ Heiken et al., 2014. Quantifying Aircraft Lead Emissions
at Airports. ACRP Report 133. Available at https://www.nap.edu/catalog/22142/quantifying-aircraft-lead-emissions-at-airports.
    \306\ Hudda et al., 2022. Substantial Near-Field Air Quality
Improvements at a General Aviation Airport Following a Runway
Shortening. Environmental Science & Technology. DOI: 10.1021/
acs.est.1c06765.
---------------------------------------------------------------------------

    In 2008 and 2010, the EPA enhanced the lead monitoring network by
requiring monitors to be placed in areas with sources such as
industrial facilities and airports, as described further in Section
II.A.3 of this document.307 308 As part of this 2010
requirement to expand lead monitoring nationally, the EPA required a 1-
year monitoring study of 15 additional airports with estimated lead
emissions between 0.50 and 1.0 ton per year in an effort to better
understand how these emissions affect concentrations of lead in the air
at and near airports. Further, to help evaluate airport characteristics
that could lead to ambient lead concentrations that approach or exceed
the lead NAAQS, airports for this 1-year monitoring study were selected
based on factors such as the level of activity of covered aircraft and
the predominant use of one runway due to wind patterns. Monitored lead
concentrations in ambient air are highly sensitive to monitor location
relative to the location of the run-up areas for piston-engine aircraft
and other localized areas of elevated lead concentrations relative to
the air monitor locations.
---------------------------------------------------------------------------

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

    The lead monitoring study at airports began in 2011. In 2012, air
monitors were placed in close proximity to the run-up areas at the San
Carlos Airport (starting on March 10, 2012) and the McClellan-Palomar
Airport (starting on March 16, 2012). The concentrations of lead
measured at both of these airports in 2012 were above the level of the
lead NAAQS, with the highest measured levels of lead in total suspended
particles over a rolling three-month average of 0.33 micrograms per
cubic meter of air at the San Carlos Airport and 0.17 micrograms per
cubic meter of air at the McClellan-Palomar Airport. These
concentrations violate the primary and secondary lead NAAQS, which are
set at a level of 0.15 micrograms per cubic meter of air measured in
total suspended particles, as an average of three consecutive monthly
concentrations.
    In recognition of the potential for lead concentrations to exceed
the lead NAAQS in ambient air near the area of maximum concentration at
airports, the EPA further conducted an assessment of airports
nationwide, titled ``Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports'' and described in Section II.A.3 of
this document.\309\ The model-extrapolated lead concentrations
estimated in this study are attributable solely to emissions from
engines in covered aircraft operating at the airports evaluated and did
not include other sources of lead emissions to air. The EPA identified
four airports with the potential for lead concentrations above the lead
NAAQS due to lead emissions from engines used in covered aircraft.
---------------------------------------------------------------------------

    \309\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports Table 6. EPA-420-R-20-003, 2020.
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
---------------------------------------------------------------------------

    Additional information regarding the contribution of engine
emissions of lead from covered aircraft to lead air pollution is
provided by the EPA's Air Toxics Screening Assessment. As described and
summarized in Section II.A.3 of this document, the EPA's Air Toxics
Screening Assessment estimates that piston engines used in aircraft
contribute more than 50 percent of the lead concentration in over half
of the census tracts in the U.S.\310\
---------------------------------------------------------------------------

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

    The EPA also notes that lead emissions from engines in covered
aircraft are present in three of the ten areas in the U.S. currently
designated as nonattainment for the 2008 lead NAAQS. These areas are
Arecibo, PR, and Hayden, AZ, each of which include one airport
servicing covered aircraft, and the Los Angeles County-South Coast Air
Basin, CA, which contains at least 22 airports within its nonattainment
area boundary.311 312 Although the lead emissions from
aircraft are not the predominant source of airborne lead in these
areas, the emissions from covered aircraft may increase ambient air
lead concentrations in these areas.
---------------------------------------------------------------------------

    \311\ South Coast Air Quality Management District (2012)
Adoption of 2012 Lead SIP Los Angeles County by South Coast
Governing Board, p.3-11, Table 3-3. Available at https://www.aqmd.gov/home/air-quality/clean-air-plans/lead-state-implementation-plan. The South Coast Air Quality Management District
identified 22 airports in the Los Angeles County-South Coast Air
Basin nonattainment area; the Whiteman Airport is among those in the
nonattainment area and the EPA estimated activity at this airport
may increase lead concentrations to levels above the lead NAAQS in
the report, Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. Table 7. EPA, Washington, DC, EPA-
420-R-20-003, 2020. Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
    \312\ EPA provides updated information regarding nonattainment
areas at this website: https://www.epa.gov/green-book/green-book-lead-2008-area-information.
---------------------------------------------------------------------------

C. Proposed Cause or Contribution Finding for Lead

    Taking into consideration the data and information summarized in
Section V of this document, the Administrator proposes to find that
engine emissions of the lead air pollutant from covered aircraft cause
or contribute to the lead air pollution that may reasonably be
anticipated to endanger public health and welfare. In reaching this
proposed conclusion, the Administrator notes that piston-engine
aircraft operate on leaded avgas. That operation emits lead-

containing compounds into the air, contributing to lead air pollution
in the environment. As explained in Section II.A of this document, once
emitted from covered aircraft, lead may be transported and distributed
to other environmental media, and present the potential for human
exposure through air and non-air pathways before the lead is removed to
deeper soils or waterbody sediments. In reaching this proposed finding,
the Administrator takes into consideration different air quality
scenarios in which emissions of the lead air pollutant from engines in
covered aircraft may cause or contribute to lead air pollution. Among
these considerations, he places weight on the fact that current lead
emissions from covered aircraft are an important source of air-related
lead in the environment and that engine emissions of lead from covered
aircraft are the largest single source of lead to air in the U.S. in
recent years. In this regard, he notes that these emissions contributed
over 50 percent of lead emissions to air starting in 2008, when
approximately 560 tons of lead was emitted by engines in covered
aircraft, and more recently, in 2017, when approximately 470 tons of
lead was emitted by engines in covered aircraft.\313\
---------------------------------------------------------------------------

    \313\ The lead inventories for 2008, 2011 and 2014 are provided
in the U.S. EPA (2018b) Report on the Environment Exhibit 2.
Anthropogenic lead emissions in the U.S. Available at https://cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead inventories for
2017 are available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data#dataq.
---------------------------------------------------------------------------

    Additionally, he takes into account the fact that in some
situations lead emissions from covered aircraft have contributed and
may continue to contribute to air quality that exceeds the lead NAAQS.
The NAAQS are standards that have been set to protect public health,
including the health of sensitive groups, with an adequate margin of
safety, and to protect public welfare from any known or anticipated
adverse effects associated with the presence of the pollutant in the
ambient air. For example, the EPA's monitoring data show that lead
concentrations at two airports, McClellan-Palomar and San Carlos,
violated the lead NAAQS. The EPA's model-extrapolated estimates of lead
also indicate that some U.S. airports may have air lead concentrations
above the NAAQS in the area of maximum impact from operation of covered
aircraft.\314\ Given that the lead NAAQS are established to protect
public health and welfare, contributions to concentrations that exceed
the lead NAAQS are of particular concern to the Administrator and add
support for the proposed conclusion that lead emissions from engines in
covered aircraft cause or contribute to the endangering air pollution.
---------------------------------------------------------------------------

    \314\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports Table 7. EPA-420-R-20-003, 2020.
Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG52.pdf.
---------------------------------------------------------------------------

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

VI. Statutory Authority and Executive Order Reviews

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

A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review

    This action is a ``significant regulatory action'' because of the
cross-agency nature of this issue. Accordingly, it was submitted to the
Office of Management and Budget (OMB) for review under Executive Order
12866. This action proposes a finding that emissions of the lead air
pollutant from engines in covered aircraft cause or contribute to the
lead air pollution that may be reasonably anticipated to endanger
public health and welfare. Any changes made in response to OMB
recommendations have been documented in the docket.

B. Paperwork Reduction Act (PRA)

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

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities. The proposed
endangerment and cause or contribute findings under CAA section
231(a)(2)(A) do not in-and-of-themselves impose any new requirements
but rather set forth the Administrator's proposed finding that
emissions of the lead air pollutant from engines in covered aircraft
cause or contribute to lead air pollution that may be reasonably
anticipated to endanger public health and welfare. Accordingly, this
action affords no opportunity for the EPA to fashion for small entities
less burdensome compliance or reporting requirements or timetables or
exemptions from all or part of the proposal.

D. Unfunded Mandates Reform Act (UMRA)

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

E. Executive Order 13132: Federalism

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

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

    This action does not have Tribal implications as specified in
Executive Order 13175. The proposed endangerment and cause or
contribute findings under CAA section 231(a)(2)(A) do not in-and-of-
themselves impose any new requirements but rather set forth the
Administrator's proposed finding that emissions of the lead air
pollutant from engines in covered aircraft cause or contribute to lead
air pollution that may be reasonably anticipated to endanger public
health and welfare. Thus, Executive Order 13175 does not apply to this
action.
    Tribes have previously submitted comments to the EPA noting their
concerns regarding potential impacts of lead emitted by piston-engine
aircraft operating on leaded avgas at airports on, and near, their
Reservation Land.\315\ The EPA plans to continue engaging with Tribal
stakeholders on this issue and will offer a government-to-government
consultation upon request.
---------------------------------------------------------------------------

    \315\ See Docket ID Number EPA-HQ-OAR-2006-0735. The Tribes that
submitted comments were: The Bad River Band of Lake Superior Tribe
of Chippewa Indians, The Quapaw Tribe of Oklahoma, The Leech Lake
Band of Ojibwe, The Lone Pine Paiute-Shoshone Reservation, The Fond
du Lac Band of Lake Superior Chippewa, and The Mille Lacs Band of
Ojibwe.
---------------------------------------------------------------------------

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

    The EPA interprets E.O. 13045 (62 FR 19885, April 23, 1997) as
applying only to those regulatory actions that concern health or safety
risks, such that the analysis required under section 5-501 of the E.O.
has the potential to influence the regulation. This action is not
subject to E.O. 13045 because it does not propose to establish an
environmental standard intended to mitigate health or safety risks.
Although the Administrator considered health and safety risks as part
of the proposed endangerment and cause or contribute findings under CAA
section 231(a)(2)(A), the proposed findings themselves, if finalized,
would not impose a standard intended to mitigate those risks. While
this action is not subject to Executive Order 13045 in this scenario,
the Agency's Policy on Children's Health \316\ still applies. The
Administrator considered lead exposure risks to children as part of
this proposed endangerment finding under CAA section 231(a)(2)(A). This
action's discussion of the impacts of lead exposure on public health
and welfare is found in Section IV of this document, and specific
discussion with regard to children are contained in Supplemental
Information Section C, as well as Sections II.A.5, and IV of this
document. A copy of the documents pertaining to the impacts on
children's health from emissions of lead from piston-engine aircraft
that the EPA references in this action have been placed in the public
docket for this action (Docket EPA-HQ-OAR-2022-0389).
---------------------------------------------------------------------------

    \316\ EPA (2021) EPA Policy on Children's Health. Available at
https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf.
---------------------------------------------------------------------------

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

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

I. National Technology Transfer and Advancement Act (NTTAA)

    This action does not involve technical standards.

J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations

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

K. Determination Under Section 307(d)

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

VII. Statutory Provisions and Legal Authority

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

List of Subjects

40 CFR Parts 87 and 1031

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

40 CFR Part 1068

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

Michael S. Regan,
Administrator.
[FR Doc. 2022-22223 Filed 10-14-22; 8:45 am]
BILLING CODE 6560-50-P