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.

1) 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.

2) 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.”

3) 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. 

4) 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 
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.

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.

5) 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.

6) 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. 

7) 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.

8) 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.

9) 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).

10) 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. 

11) 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 
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.

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. 

12) 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.

13) 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. 

14) 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: http://www.epa.gov/nata/. For 

local-scale analysis of lead, EPA is using AERMOD, which is available at: 

http://www.epa.gov/scram001/dispersion_prefrec.htm#aermod. 

15) 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.

16) 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. 

17) 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: “Pistonengine 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.

18) Could EPA define the term “fresh emissions”. Does this mean “current emissions”, or refer to 

something else? 
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.

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

from the exhaust system.

19) 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.

20) 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. 

21) 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.

22) 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.

23) 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. 
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.

24) 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.

25) 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.

26) Has monitoring begun at airports listed on p95?

Response: Yes, monitoring has begun at two airports.

27) 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.

28) 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.