United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued April 11, 2002 Decided May 24, 2002
No. 01-1154
Grand Canyon Trust,
Petitioner
v.
Federal Aviation Administration,
Respondent
On Petition for Review of an Order of the
Federal Aviation Administration
Robin Cooley argued the cause and filed the briefs for
petitioner. Mary-Lynn Sferrazza entered an appearance.
Ellen J. Durkee, Attorney, U.S. Department of Justice,
argued the cause for respondent. With her on the brief was
Alice B. Thurston, Attorney.
Before: Edwards, Rogers and Tatel, Circuit Judges.
Opinion for the Court filed by Circuit Judge Rogers.
Rogers, Circuit Judge: The Grand Canyon Trust petitions
for review of the decision of the Federal Aviation Administra-
tion ("FAA") approving the federal actions necessary to allow
the city of St. George, Utah, to construct a replacement
airport near Zion National Park. The Trust challenges the
adequacy of the FAA's environmental assessment under
s 102(2)(C) of the National Environmental Policy Act of 1969
("NEPA"), 42 U.S.C. s 4332(C) (1970), and the FAA's conclu-
sion that there would be no significant environmental impacts
from the project necessitating preparation of an environmen-
tal impact statement under NEPA. Focusing on the noise
impacts on the Park, the Trust principally contends that the
FAA failed adequately to consider the cumulative impact on
the natural quiet of the Park and instead addressed only the
incremental impact of the replacement airport. We grant the
petition.
I.
In 1995, the FAA began working with the City of St.
George, Utah, to determine the feasibility of continuing use of
the existing airport as compared to development of a new
airport at a new site. A growing retirement community and
projected air-traffic demand was outstripping the capacity of
the existing airport, which could not be expanded due to
geographic constraints. Three sites in addition to a no-action
alternative were examined. In response to comments on a
draft environmental assessment, the FAA conducted a Sup-
plemental Noise Analysis on the potential noise impacts of the
replacement airport on Zion National Park ("the Park"). The
Park is located approximately 25 miles northeast of St.
George and is the preferred replacement airport alternative.
The FAA concluded that the noise impacts on the Park
from the replacement airport would be negligible and insignif-
icant. On January 30, 2001, the FAA approved the final
environmental assessment, concluding that an environmental
impact statement was unnecessary, and issued the record of
decision, setting forth actions, determinations, and approvals
that will allow St. George to construct the replacement air-
port. It is the determination underlying this record of deci-
sion, that the proposed action will not significantly affect the
environment of the Park, that the Trust challenges.
II.
The essential disagreement between the parties is whether
the FAA was required in its environmental assessment to
address more than the incremental impact of the replacement
airport as compared to the existing airport. NEPA requires
federal agencies to prepare an environmental impact state-
ment ("EIS") for "every ... major Federal action[ ] signifi-
cantly affecting the quality of the human environment." 42
U.S.C. s 4332(2)(C). An environmental assessment ("EA") is
made for the purpose of determining whether an EIS is
required. See 40 C.F.R. s 1508.9. "If any 'significant' envi-
ronmental impacts might result from the proposed agency
action then an EIS must be prepared before agency action is
taken." Sierra Club v. Peterson, 717 F.2d 1409, 1415 (D.C.
Cir. 1983) ("Peterson").
An agency decision that an EIS is not required may be
overturned "only if it was arbitrary, capricious or an abuse of
discretion." Sierra Club v. United States Dep't of Transpor-
tation, 753 F.2d 120, 126 (D.C. Cir. 1985) ("Transportation").
Under the long-established standard in this circuit, the court
reviews an agency's finding of no significant impact to deter-
mine whether:
First, the agency [has] accurately identified the relevant
environmental concern. Second, once the agency has
identified the problem it must have taken a 'hard look' at
the problem in preparing the EA. Third, if a finding of
no significant impact is made, the agency must be able to
make a convincing case for its finding. Last, if the
agency does find an impact of true significance, prepara-
tion of an EIS can be avoided only if the agency finds
that the changes or safeguards in the project sufficiently
reduce the impact to a minimum.
Id. at 127; see also Maryland-Nat'l Capital Park and Plan-
ning Comm'n v. U.S. Postal Serv., 487 F.2d 1029, 1040 (D.C.
Cir. 1973).
The Trust does not dispute that the FAA properly defined
the relevant environmental concern of noise impacts from
aircraft on the Park. Rather, the Trust contends that the
FAA cannot be said to have taken a "hard look" at the
problem when it considered only the incremental impacts of
the replacement airport and not the total noise impact that
will result from the relocated airport. The Trust notes that
the EA does not address the cumulative impact in light of
other air flights over the Park, air tours in or near the Park,
and reasonably foreseeable future aircraft activity and airport
expansions that will contribute to the cumulative noise impact
on the Park. Indeed, the EA's statement on cumulative
impact is, in full: "There are no known factors that could
result in cumulative impacts as a result of the proposed St.
George Replacement Airport." Further, the Trust notes, the
FAA's Supplemental Noise Analysis disregards cumulative
impacts. The FAA responds that it adequately considered
the cumulative impact when it compared noise impacts associ-
ated with the replacement airport with the no-action alterna-
tive of continued use of the existing airport. It rejects the
Trust's position that it was required in an EA to compare the
project to an environmental baseline of natural quiet and to
consider the total impact of aircraft noise on the Park.
The issue dividing the parties is settled by regulations
promulgated by the Council on Environmental Quality
("CEQ") to implement NEPA and by case law applying those
regulations.* "The CEQ regulations, which ... are entitled
to substantial deference, impose a duty on all federal agen-
cies." Marsh v. Oregon Natural Res. Council, 490 U.S. 360,
372 (1989) (citations omitted); see also Citizens Against
Burlington, Inc. v. Busey, 938 F.2d 190, 200 (D.C. Cir. 1991).
The CEQ regulations define each term within NEPA's re-
quirement of an EIS for "every ... major Federal action[ ]
significantly affecting the quality of the human environment."
__________
* Neither party challenges the regulatory authority of the CEQ,
and hence we have no occasion to question the binding effect of the
regulations on the FAA. See City of Alexandria v. Slater, 198 F.3d
862, 866 n.3 (D.C. Cir. 1999).
42 U.S.C. s 4332(2)(C); 40 C.F.R. s 1502.3. The term "sig-
nificantly" is defined as those actions "with individually insig-
nificant but cumulatively significant impacts. Significance
exists if it is reasonable to anticipate a cumulatively signifi-
cant impact on the environment." 40 C.F.R. s 1508.27(b)(7).
"Cumulative impact," in turn, is defined as:
the impact on the environment which results from the
incremental impact of the action when added to other
past, present, and reasonably foreseeable future actions
regardless of what agency (Federal or non-Federal) or
person undertakes such other actions. Cumulative im-
pacts can result from individually minor but collectively
significant actions taking place over a period of time.
40 C.F.R. s 1508.7. Although federal agencies have discre-
tion to decide whether a proposed action "is significant
enough to warrant preparation of an EIS," the court owes no
deference to the FAA's interpretation of NEPA or the CEQ
regulations because NEPA is addressed to all federal agen-
cies and Congress did not entrust administration of NEPA to
the FAA alone. Citizens Against Rails-to-Trails v. Surface
Transportation Board, 267 F.3d 1144, 1150 (D.C. Cir 2001);
see Amfac Resorts, LLC v. United States Dep't. of Interior,
282 F.3d 818, 835 (D.C. Cir. 2002); cf. Al-Fayed v. CIA, 254
F.3d 300, 307 (D.C. Cir. 2001).
The courts, in reviewing whether a federal agency has
acted arbitrarily and capriciously in finding no significant
environmental impact, have given effect to the plain language
of the regulations. While the factual settings differ in some
respects from the instant case, the consistent position in the
case law is that, depending on the environmental concern at
issue, the agency's EA must give a realistic evaluation of the
total impacts and cannot isolate a proposed project, viewing it
in a vacuum. For example, in Coalition on Sensible Trans-
portation v. Dole, 826 F.2d 60 (D.C. Cir. 1987) ("Dole"), this
court stated that the CEQ regulations on cumulative impact
"provide a distinct meaning to the concept" separate and
apart from the notion of improper segmentation of agency
action. Id. at 70. Noting that the regulatory definition of
cumulative impact specifies that the " 'incremental impact of
the action' [at issue]" must be considered " 'when added to
other past, present, and reasonably foreseeable future ac-
tions,' " id. (quoting 40 C.F.R. s 1508.7), the court observed
that, consistent with the regulation and purpose of NEPA,
"[i]t makes sense to consider the 'incremental impact' of a
project for possible cumulative effects by incorporating the
effects of other projects into the background 'data base' of the
project at issue." Id. at 70-71. The point, the court stated,
was to provide in the EA "sufficient [information] to alert
interested members of the public to any arguable cumulative
impacts involving [ ] other projects." Id. at 71. Further, the
court concluded that insofar as Kleppe v. Sierra Club, 427
U.S. 390 (1976), "may bear on an agency's duty to consider
impacts in a context that realistically includes other pending
projects, the [agency] fully complied by planning on the basis
of ... ultimate completion of the related projects." Id.
(citing Kleppe, 427 U.S. at 415 n.26). Similarly, the court in
Peterson, without regard to any particular NEPA regulation,
reversed a finding of no significant impact and a decision to
issue certain oil and gas leases in national forests without
preparing an EIS, remanding the case because the agency
had failed, as NEPA requires, to "fully assess[ ] the possible
environmental consequences" of activities "which have the
potential for disturbing the environment." 717 F.2d at 1415.
NRDC v. Hodel, 865 F.2d 288 (D.C. Cir. 1988), is to the same
effect. There, the agency had failed to consider the cumula-
tive impact, as defined in the CEQ regulations, of simulta-
neous development in the region on "species, particularly
whales and salmon, that migrate through the different plan-
ning areas" when it considered only the effect on those
species "within the Planning Area" rather than "the inter-
regional effects." Id. at 297-99. Other circuits take a similar
approach in applying the regulations. See, e.g., Fritiofson v.
Alexander, 772 F.2d 1225 (5th Cir. 1985), rev'd on other
grounds, Sabine River Auth. v. Dep't of the Interior, 951 F.2d
669 (5th Cir. 1992). Although the FAA would distinguish
Hanly v. Kleindienst, 471 F.2d 823 (2d Cir. 1972), on which
the Trust relies, on the ground that it preceded the regula-
tions, the court was addressing the requirements of NEPA,
and the FAA can point to nothing in the regulations that
would suggest the court erred in holding that NEPA requires
review of a proposed action in light of
the cumulative harm that results from [the action's]
contribution to existing adverse conditions or uses in the
area.... [E]ven a slight increase in adverse conditions
that form an existing environmental milieu may some-
times threaten harm that is significant. One more facto-
ry ... may represent the straw that breaks the back of
the environmental camel.
Id. at 831.
The FAA, in finding that the St. George replacement
airport would have no significant impact on the environment
of the Park, concluded that "there is little discernable in-
creased noise intrusion to the Park" from the proposed
replacement airport as compared to the existing airport, and
that "the increase in noise levels that would result from the
development of a replacement airport is negligible [because]
aircraft traffic will increase even if the replacement airport is
not constructed." The FAA's analysis appears principally in
a Supplemental Noise Analysis attached to the EA, and
proceeds on the basis of a comparison of the noise impacts
from predicted air traffic at the existing airport and predicted
air traffic at the larger replacement airport. At the existing
airport, the FAA predicted that flight activity would increase
due to normal traffic growth from 46,193 flights in 1998 to
59,640 flights in 2008 (more than 80 departures and 80
arrivals every day), and to 78,490 in 2018 (more than 100
departures and 100 arrivals each day). At the replacement
airport, traffic would increase to 63,290 flights in 2008 (more
than 85 departures and 85 arrivals every day), and to 79,220
flights in 2018 (more than 105 departures and 105 arrivals
each day). Comparing the predicted noise impact on the
Park from the existing and replacement airports, the FAA
found that Day-Night Noise Level ("DNL")1 would increase
"due to the implementation of the replacement airport over
__________
1 Day-Night Noise Level ("DNL") is a 24-hour, time-weighted
energy average noise level based on the A-weighted decibel. It is a
measure of the overall noise experienced during an entire day.
"Time-weighted" refers to the fact that noise occurring during
the use of the existing airport" by no more than 3.5 dBA2 in
2008 and 3.2 dBA in 2018, which the FAA characterized as
"extremely low" increases. The FAA concluded that "there
will be little difference associated with the replacement air-
port, as compared with the existing airport, in the long-term
based on the DNL metric."
The FAA also examined in the Supplemental Noise Analy-
sis the peak hour Equivalent Noise Level ("LEQ")3 based on
a threshold of 45 dBA, when aircraft would be clearly audible
and noticeable in the Park. The FAA assumed that typical
background noise levels in the Park would be 20 dBA during
quiet times and locations and in the low 30 dBA in less quiet
times and locations. Based on its own data and on research
sponsored by the National Park Service ("NPS"), the FAA
found that only one flight path from the replacement airport
would present noise greater than 45 dBA for more than one
minute an hour in 2008, which represented only a 0.7%
increase over the predicted traffic at the existing airport. In
2018, three of eleven flight paths from the replacement
airport would present noise greater than 45 dBA for more
than one minute per hour, a change of no more than 0.9%
from the predicted traffic at the existing airport. Using a
lower noise annoyance threshold of 35 dBA, the FAA predict-
ed that no flight path would have noise above 35 dBA for
__________
certain sensitive time periods is penalized for occurring at these
times.
2 The standard unit of measurement of sound is the decibel
("dB"). Because the human ear is not equally sensitive to all
frequencies, with some frequencies judged to be louder for a given
signal than others, the most common method of frequency weight-
ing is the A-weighted noise curve ("dBA"). The A-weighted decibel
scale discriminates between frequencies in a manner approximating
the sensitivity of the human ear. In the A-weighted decibel scale,
everyday sounds normally range from 30 dBA (very quiet) to 100
dBA (very loud).
3 Equivalent Noise Level ("LEQ") measures the energy aver-
age noise level resulting from the sound level corresponding to a
steady-state A-weighted sound level containing the same total ener-
gy as a time-varying signal over a given sample period.
more than 7 minutes per hour in 2008 and 7.7 minutes each
hour in 2018. Based on this data, the FAA found that while
2% to 7% of Park visitors would experience moderate to
extreme annoyance due to aircraft noise from the existing St.
George Airport, the number would only increase to 2% to 8%
with the replacement airport using the 45 dBA threshold.
Using a 35 dBA threshold, the FAA interpreted the data to
mean that between 3% and 15% of Park visitors would be
annoyed by aircraft noise from the existing airport, compared
to 4% to 15% of visitors who would be annoyed by aircraft
from the replacement airport, with a 3% increase (from 11%
to 14%) of Park visitors experiencing moderate to extreme
annoyance from the aircraft noise on the loudest flight path.
The FAA concluded that "there will be little difference in
noise between the existing and replacement airport."
In a section of the EA entitled "Impacts to Natural Quiet of
the Park," the FAA did acknowledge the existence of "over-
flights" that pass over the Park. Noting that NPS had
completed ambient noise monitoring in Zion National Park,
the FAA stated that the results showed that "the background
or ambient noise levels vary, but are often in the low 20
dBA." Finding that the typical peak or maximum noise
levels from aircraft from either the existing or proposed St.
George airport sites ranged from 45 to 65 dBA when passing
directly overhead, the FAA concluded that, because "these
aircraft are at or near cruise altitude, or in the case of jets
[are] above 20,000 feet, the peak or maximum noise levels will
remain the same for either airport site." While recognizing
that these overflights constitute noise events that are higher
than background natural quiet during periods when ambient
noise levels are low, the FAA focused on the incremental
impact, stating that it was "important to illustrate that the
development of the St. George replacement airport has little
effect on the overall aircraft noise levels in the Park." The
FAA referred to the 250 overflights following established
flight paths near or over the Park4 that are not associated
__________
4 Instrument flight rules ("IFR") designate flights using estab-
lished flight paths, as distinct from aircraft operating under visual
flight rules ("VFR").
with St. George Airport in concluding that "the replacement
airport has very little contribution to the cumulative number
of aircraft over flights over Zion National Park." The FAA
observed that St. George Airport contributed only 31 flights
using instrument flight rules over Zion, a number that was
expected to increase to 48 in 2008 at the existing airport and
54 at the replacement airport, and to 67 in 2018 at the
existing airport and 69 at the replacement airport. The FAA
then found that the replacement airport would add only six
additional flights using instrument flight rules per day in 2008
and only two additional such flights in 2018. In addition, the
FAA predicted that less than four aircraft per day would fly
over Zion using visual-flight-rules routes, a number the FAA
predicted would remain the same for either the existing or
the replacement site. The FAA concluded that the existing
St. George airport would contribute only 11% of all existing
flights using instrument flight rules over or near the Park,
and that the increased flights from the replacement airport
would represent only approximately 2% of the total aircraft
flights using instrument flight rules over or near the Park.
The FAA's noise analysis in the EA, including the Supple-
mental Noise Analysis, may, in fact, be a splendid incremental
analysis, but it fails to address what is crucial if the EA is to
serve its function. While, as the FAA stresses, the EA is not
intended to be a lengthy document, see 40 C.F.R.
s 1508.9(a)(1), it must at a minimum address the consider-
ations relevant to determining whether an EIS is required.
NEPA regulations require that an agency consider cumula-
tive impacts and the FAA's EA fails to address the total noise
impact that will result from the replacement airport. Indeed,
the FAA's own NEPA policy calls for consideration of cumu-
lative impact, parroting the language of the NEPA regula-
tions to include proposed projects and past, present, and
reasonably foreseeable future actions. See Policies and Pro-
cedures for Considering Environmental Impacts, FAA Order
1050.1D. Comments on the draft EA called the FAA's
attention to the need to consider mitigation measures in view
of the results of the study of noise-annoyance to persons in
the Park; the EA does not respond and provides no analysis
of the 2% to 9% or the 4% to 15% level of annoyance shown in
the NPS study. Yet, as the FAA was aware, the NPS had
identified Zion National Park as among the nine national
parks of "highest priority" for attention to noise impact on
their natural quiet from overflights. See U.S. Department of
the Interior/National Park Service, Report on Effects of
Aircraft Overflights on the National Park System: Report to
Congress (July, 1995). Comments also expressed concern
about the total impacts of noise on the Park and on Park
visitors, yet the EA contains no analysis of the impact of 54
daily flights in 2008 and 69 in 2018 associated with St. George.
The Trust maintains that each flight may be responsible for
a noise level of 45 to 65 dBA and points to expert testimony
that an increase of 10 dBA correlates to a doubling of
loudness such that a commercial jet overflight at the Park
may be 4 to 23 times as loud as the natural soundscape.
Even in the absence of the regulatory definitions it would be
difficult to understand how an agency could determine that an
EIS is not required if it had not evaluated existing noise
impacts as well as those planned impacts that will exist by the
time the new facility is constructed and in operation. As the
Trust gleans from case law:
a meaningful cumulative impact analysis must identify (1)
the area in which the effects of the proposed project will
be felt; (2) the impacts that are expected in that area
from the proposed project; (3) other actions--past, pres-
ent, and proposed, and reasonably foreseeable--that
have had or are expected to have impacts in the same
area; (4) the impacts or expected impacts from these
other actions; and (5) the overall impact that can be
expected if the individual impacts are allowed to accumu-
late.
Petitioner's Reply Br. at 3, citing Fritiofson, 772 F.2d at 1245
(citing Cabinet Mountains Wilderness/Scotchman's Peak
Grizzly Bears v. Peterson, 685 F.2d 678, 683-84 (D.C. Cir.
1982)); see also Hodel, 865 F.2d at 297-99; City of Carmel-
by-the-Sea v. DOT, 123 F.3d 1142, 1160 (9th Cir. 1997).
The analysis in the EA, in other words, cannot treat the
identified environmental concern in a vacuum, as an incre-
mental approach attempts. Although the replacement airport
may contribute only a 2% increase to the amount of over-
flights near or over the Park, there is no way to determine
from the FAA's analysis in the EA whether, deferring to the
FAA's expert calculations, a 2% increase, in addition to other
noise impacts on the Park, will "significantly affect[ ]" the
quality of the human environment in the Park. At no point
does the FAA's EA aggregate the noise impacts on the Park.
The analysis in the EA does not address the accumulated, or
total, incremental impacts of various man-made noises, such
as the 250 daily aircraft flights near or over the Park that
originate at, or have as their destination, airports other than
that in St. George. Neither does the EA consider in any
manner the air tours near and over the Park originating from
the St. George airport. Nor does the EA address the impact,
much less the cumulative impact, of noise in the Park as a
result of other activities, such as the planned expansions of
other regional airports that have flights near or over the
Park. Without analyzing the total noise impact on the Park
as a result of the construction of the replacement airport, the
FAA is not in a position to determine whether the additional
noise that is projected to come from the expansion of the St.
George airport facility at a new location would cause a
significant environmental impact on the Park and, thus, to
require preparation of an EIS.
In defense of its incremental approach in the EA, the FAA
make three arguments. First, it relies on several phrases in
the NEPA regulations. The FAA points to the phrase "in-
cremental impacts" in 40 C.F.R. s 1508.7 to contend that it is
obligated to consider only the incremental impact of any
project. The difficulty with this position is that it ignores the
rest of the sentence in s 1508.7 directing an agency to
consider that incremental impact "when added to other past,
present, and reasonably foreseeable future actions regardless
of what agency ... or person undertakes such other actions."
The FAA also relies on the phrase "related to" in the
definition of "significantly" in 40 C.F.R. s 1508.28(b)(7) to
contend that it need not consider either the overflights not
associated with St. George or the proposed expansion at Las
Vegas Airport and the proposals for new airports at Mesquite
and Cedar City because they are "not related" to the St.
George's airport expansion. Again, the FAA ignores other
language in the regulation that "[s]ignificance exists if it is
reasonable to anticipate a cumulatively significant impact on
the environment." 40 C.F.R. s 1508.28(b)(7).
Second, the FAA points to 40 C.F.R. s 1508.25(a) and
Kleppe, 427 U.S. at 409-10 & n.20, to contend that it need
consider only other projects that are "inextricably inter-
twined" and not those that are "substantially independent."
Both the regulation and the opinion address the proper scope
of an EIS, not an EA, but to the extent the former influences
the latter, nothing in Kleppe suggests that the FAA could
ignore the total noise impact in the area of identified environ-
mental concern. See Dole, 826 F.2d at 71.
Third, the FAA, quoting CEQ guidance on preparation of
an EIS, contends that the no-action alternative is properly
viewed as a "benchmark against which decisionmakers may
compare the magnitude of environmental effects" of actions.
See 46 Fed. Reg. 18,026, 18,027 (March 23, 1981). Neither
the guidance nor the cases cited by the FAA relieve it of the
duty to consider cumulative impact in the EA. Although the
court stated in Allison v. DOT, 908 F.2d 1024 (D.C. Cir.
1990), that 40 C.F.R. s 1508.25(a) did not require the FAA to
consider unconnected single actions that are neither related
to nor dependent on the proposed new airport for Denver,
Colorado, the court was not addressing the requirements of
40 C.F.R. s 1508.7 on cumulative impact. Id. at 1030. In
contrast, here, the FAA responded to comments that baseline
data and cumulative impact was lacking in the draft EA by
stating, on the basis of its incremental analysis, that "The
current noise levels in Zion National Park will not be adverse-
ly affected by either the existing or future noise levels
associated with aircraft." Because there is no analysis of
cumulative noise impact on the Park against which the addi-
tional noise impact of the replacement airport can be evaluat-
ed, the FAA's error in ignoring cumulative impact of man-
made noise is not harmless, see Allison, 908 F.2d at 1029, for
the FAA has impermissibly taken "a foreshortened view of
the impacts which could result from the act" of constructing
the replacement airport. Peterson, 717 F.2d at 1413.
Accordingly, we grant the petition without reaching the
Trust's contention that an EIS is required because the pro-
ject is "highly controversial," 40 C.F.R. s 1508.27(b)(4);
Fund for Animals v. Frizzell, 530 F.2d 982, 988 n.15 (D.C.
Cir. 1976). We remand the case because the record is
insufficient for the court to determine whether an EIS is
required. On remand, the FAA must evaluate the cumulative
impact of noise pollution on the Park as a result of construc-
tion of the proposed replacement airport in light of air traffic
near and over the Park, from whatever airport, air tours near
or in the Park, and the acoustical data collected by NPS in
the Park in 1995 and 1998 mentioned in comments on the
draft EA. See 42 U.S.C. s 4332(2)(C); Marsh, 490 U.S. at
371; Transportation, 753 F.2d at 129 (citing Committee for
Nuclear Responsibility, Inc. v. Seaborg, 463 F.2d 783, 787
(D.C. Cir. 1971)). Other data may also prove relevant. Al-
though the FAA explained in responding to comments that it
does not use "natural ambient noise levels," because they
exclude human sounds and are therefore not a true reflection
of the existing noise environment, and rejected the "L90"
methodology5 used by NPS to calculate natural ambient noise
levels, because 90% of sounds in the Park would be consid-
ered noisier than the "natural" ambient level, the FAA in fact
did consider NPS data in its Supplemental Noise Analysis
and fails to demonstrate that this information is not relevant
to the cumulative impact analysis to be prepared for the EA.
See Allison, 908 F.2d at 1029; Transportation, 753 F.2d at
129.
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5 Under the "L90" methodology, the natural ambient level is
based on the quietest 10% of noise data statistically derived from
noise monitoring.