Could EPA better describe various options that could be considered if
emissions standards or other remedies are considered, including
incentives or other flexible mechanisms?  Consider for example that
approximately 60% of Forest Service aircraft are piston aircraft using
leaded aviation fuel, including a several floatplanes. Many of these are
firefighting aircraft that are critical to the protection of lives and
property.  A primary concern with this proposal is that many of the
aircraft that we own or operate are so old that they no longer have a
manufacturer to support engine modifications to meet any new standard or
conversions to unleaded fuel. Consequently, this burden would most
likely fall on the current owners, and could reduce the current fleet of
firefighting aircraft. Hence, the Forest Service would like the EPA and
FAA to consider alternative options or additional incentives for owners
and operators to replace piston aircraft with turbine powered aircraft.
This could result in the same benefits of reduced lead emissions without
the research and development costs of converting piston engines to
unleaded fuel. 

Response:  We are not yet at the stage, for this action, of discussing
scenarios.  We thus have a broad outline of potential options regarding
engine emission standards in the section VI.C.  This type of information
is very useful and is the type of input we are hoping to elicit through
the request for comment on the ANPR.

The exposure section should have references for all relevant statements
and assertions.  The exposure section seems to use quite a few
characterizations that are not supported by referenced literature, such
as the descriptions of land use near airports (ex: “Airports are often
surrounded by …recreational sport facilities…”), “airports are
especially attractive to young children…” and “programs .. provide
outdoor observation facilities and picnic facilities for families..”. 
“Personal gardens, community gardens…” etc are all
characterizations that are not referenced.  Perhaps there is a
background document EPA could cite?

Response:  We collected this information from visiting approximately 100
of the most active GA airport websites and/or Google Earth images of
these airports.  We avoided citations in this section because it would
single out individual airports.  We have looked for, and not found,
national databases for this information.  We are adding the following
additional sentence to page 73:  “EPA is requesting information
regarding national databases that provide information regarding
recreational fields and community gardens in close proximity to
airports.”

In the count of schools within 1km of an airport, could EPA break out
preschools, elementary schools, middle schools, high schools and
colleges?  This is relevant because vulnerable populations are typically
very young (pre-school and elementary / grammer school).

Response:  The data we used for this analysis will be in the docket for
this rule.  For each airport facility that has a school within 1 km, the
file will list the airport and its location information as well as each
school(s) within 1 km and its location and site information, demographic
data, school lunch program eligibility, and total enrollment data.  For
the purposes of discussing a relevant exposed population in this ANPR,
we are including all children in this analysis.  The Lead Criteria
Document notes effects in children older than pre-school and elementary
school age.  We will consider the analysis of school class for our
future action.   

Could EPA provide references to support the statement on p 11 and
Section VI “The data described in Section VI of this ANPR indicate
that lead levels in ambient air on and near airports servicing
piston-fired aircraft are higher than lead levels in areas not directly
influenced by a lead source”.  This statement seems to characterize
all airports relative to all other areas, and implies we have a great
deal of information about lead levels and airports and other areas.  If
so, that information should be discussed more fully as it is important
for the entire document. 

Response:  This summary statement is a characterization of the studies
referenced in Section IV.

We recommend that the language on p 14 in the “Background on Leaded
Aviation Gasoline” section be deleted or moved, because it describes
airports not Gasoline.  If the language is necessary, perhaps move it
into a section about airports?  (“Over 3,000 of the 20,000 airport
facilities … if this fuel was all 100LL, it would account for
approximately 34,00 tons of lead emitted into the air.”)

Response:  This information is relevant for the reader in the context of
background on leaded avgas because of the persistence of this pollutant
in the environment.  This issue of airports and avgas use are
inextricably linked.

The draft ANPRM should try to focus on referenced materials and
published studies.  For example, “If this fuel was all 100LL, it would
account for approximately 34,00 tons of lead emitted into the air.” 
EPA has other estimates, such as NEI, to represent source contribution.

Response:  We have found no published data on the annual consumption of
leaded avgas.  The NEI would not provide a cumulative total relevant to
the time period when leaded avgas has been used.  

Is the endangerment finding based on current conditions, or possible
forecasted conditions?  EPA mentions on p 15: “As described in III.B
of this ANPR, the is a slight growth in the activity of general aviation
aircraft projected to 2025.”  Also, on p 59, there is a section on
Projections for Future Growth.  Should readers infer that an
endangerment finding is based on forecasted conditions, not current
conditions, or is this statement irrelevant?  

Response:  This action is not an endangerment finding.  For future
analyses the EPA will consider both current and projected conditions.

If forecasts are relevant and retained in the text, forecast
uncertainties should be clearly discussed and comment taken on forecast
estimates.

Response:  We will add a request for comment on the forecast information
and the uncertainty in these projections.

Could EPA provide a citation on p 60 for “…prior AQCDs for Lead.”

Response:  Yes, we have added those citations (they were provided
earlier in the document but repeating that here is fine).

What flexibility does EPA have to wait to promulgate this ANPRM until
the information is available that EPA discusses?  EPA seems to be
relying on only 1 study (Santa Monica Airport) to understand emissions
of lead from piston-engine aircraft, and that study is not yet complete.
 Furthermore, monitoring for airports have been proposed but is not yet
finalized by EPA, and in fact EPA may not have finished reviewing public
comments on the monitoring reconsideration.

Response:  The ANPR is not making a finding based on the information
presented in this action.  We discuss the results of the Santa Monica
study conducted by the South Coast Air Quality Management District along
with studies at four other airports.  One reason we are issuing an ANPR
rather than an NPRM is because we need to respond to the petition now,
and information will be forthcoming that will inform our future action. 

Given that there is not a monitoring network at airports now, how do
monitoring studies show “…an increase in lead levels in ambient
air…” as described in the first line on p 65?  Or should this read
“higher levels at airports with piston aircraft than at airports
without piston aircraft”?

Response:  The sentence on the first line on p. 65 is summarizing the
lead airport monitoring studies presented in Section IV.  

Please provide information on the study design for the Santa Monica
Study, for example why monitors were placed in certain locations, how
that would help identify lead gradient, and why only two short time
periods were adopted for the study.

Response:  This study was conducted by the South Coast Air Quality
Management District.  They are in the process of finalizing the report
on this study that will provide this information.  The document
referenced in the ANPR notes the key questions and objectives that the
monitoring design was intended to address.

Could EPA explain why“..analogies to gradients in ultrafine PM are
relevant” (p66).  PM is both formed from precursors (unlike lead) and
emitted from motor vehicles that are typically restricted to roads,
whereas aircraft are not restricted to roads.

Response:  The analogy referred to on page 66 is in part in regard to
lead which is emitted as a gas in the form of lead dibromide and quickly
condenses to particulate matter (see p. 61).  Aircraft also emit
ultrafine PM and the study referenced on p.66 describes a gradient in
ultrafine PM not dissimilar to the gradient in lead monitored by the
South Coast Air Quality Management District. 

Is the model referenced on p70 available for public review, or is it in
the docket?

Response:  If the question is in regard to NATA, please see:   HYPERLINK
"http://www.epa.gov/nata/"  http://www.epa.gov/nata/ .  For local-scale
analysis of lead, EPA is using AERMOD, which is available at:  
HYPERLINK "http://www.epa.gov/scram001/dispersion_prefrec.htm#aermod" 
http://www.epa.gov/scram001/dispersion_prefrec.htm#aermod .  

Please confirm on p70 that EPA plans to use the study of one airport to
characterize that airport, and not to generalize to other airports which
may have dramatically different conditions.

Response:  EPA is evaluating model performance at one airport and we
will apply the modeling framework to other airports using
airport-specific inputs.

EPA might intend to say that use of leaded avgas in piston-fired
aircraft is one of the larger sources of current emissions instead of
“The continued use of lead in avgas by piston-engine aircraft is a
significant source of lead to the environment.”  On p71.

Response: Leaded avgas is the largest remaining source for lead
emissions to air and is therefore a significant source. 

Does higher ambient concentration of lead result from concentrated
emissions (airports) or from the fact that emissions occur at various
altitudes?  P71 (and agin on p72) reads: “Piston-engine aircraft
emissions of lead occur at ground level as well as at flying altitude. 
Consequently, lead from this source is concentrated near airports but is
also deposited over a large geographic area potentially contributing to
higher ambient concentrations in many communities.”

Response:  The data presented in Section IV indicate that lead is
elevated near airports.  The sentence quoted is intended to note that
lead emitted at altitude can contribute to higher background
concentrations of lead.

Could EPA define the term “fresh emissions”.  Does this mean
“current emissions”, or refer to something else? 

Response:  We are using the term “fresh emissions” to refer to
emissions immediately upon exit from the exhaust system.

Could EPA provide references for the background documents or analysis
that supports the characterization of land use around airports.  (for
Example: “Airports are often surrounded by a variety of land uses
including recreational sport facilities, ….”o p 72-73)

Response:  See the response to question 2.

Could EPA explain the statement on p74:  “The limited ambient lead
monitoring data near airports presented in Section IV of this ANPR
suggests that for some airports this analysis will underestimate the
actual number of people potentially exposed to elevated levels of
ambient lead from piston-engine powered aircraft.”

Response:  As we explain starting on p.73, for airports with a large
footprint, there will be people within 1 km of an airport who will not
be included in this analysis. 

Could EPA provide analysis of Slow, Medium and Busy airports and the
number of residences, schools, etc located within 1km.  We suggest
deciling the airports by LTO, then counting the residences, schools, and
parks located with 1km of the airports in each decile.  This analysis
will help explain how representative are the airports in the limited
studies available and other airports in the US.

Response:  This is not an analysis we are conducting for the ANPR but is
one approach for evaluating potential impacts for the NPRM.

Could EPA provide more information on which airports are located very
close to community gardens or other crop production sites.

Response:  Please see the response to question 2.  We are looking for
national or regional databases that would support further analysis of
this issue.

The Section “Bioaccumulation of Lead” should clarify that it refers
only to the environment, not to human tissue.

Response:  Lead accumulates in human and animal tissues.  



Please consider replacing the phrase “EPA is concerned about” with
“EPA requests comment on”.

Response:  We are requesting comment on the issues for which we note
Agency concern.

When will the Santa Monica study be available?

Response:  This study was recently finalized and is now available at
www.epa.gov/otaq/aviation.htm.

Has monitoring begun at airports listed on p95?

Response:  Yes, monitoring has begun at two airports.

On p96, please clarify which information will be available in 2010 and
which will be available in 2011 or later.

Response:  Information regarding areas currently out of attainment or
designated as maintenance with the 1978 Lead NAAQS and areas out of
attainment with the 2008 lead NAAQS will be available later this year. 
Information from new lead monitors will be available in 2011.

Please describe the limitations and uncertainties associated with the
modeling EPA outlines on p98.

Response:   When we conduct the modeling analyses, we will include a
full description of the modeling limitations and uncertainties. 

Summary of interagency working comments on draft rule under EO 12866.  

These comments do not necessarily represent the views of OMB and are
subject to further policy review.

