Change in Noise Evaluation Methodology for Air Tour Operations Over Grand Canyon National Park

DEPARTMENT OF THE INTERIOR

National Park Service

Change in Noise Evaluation Methodology for Air Tour Operations

Over Grand Canyon National Park

AGENCY: National Park Service, Interior.

ACTION: Public notice.

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SUMMARY: As part of its implementation actions to achieve the

objectives of Public Law 100-91 regarding the substantial restoration

of natural quiet at Grand Canyon National Park (GCNP), including

current rulemaking [and environmental assessment actions], the National

Park Service (NPS) is working cooperatively with the Federal Aviation

Administration (FAA) on further actions to aid that restoration as well

as planning for the development of a comprehensive noise management

plan for air tour operations over GCNP. NPS previously determined that

in order to substantially restore natural quiet to GCNP, at least 50

percent of the park must achieve ``natural quiet'' (i.e., no aircraft

audible) for 75 to 100 percent of the day. The reasonableness and

validity of this standard was upheld by the United States Court of

Appeals for the District of Columbia in 1998.

In previous environmental assessments related to GCNP

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rulemaking since 1996, a single threshold of the average natural

ambient sound level plus 3 decibels was applied through the FAA

Integrated Noise Model to estimate the percent of time that air tour

aircraft would be noticeable under each action alternative. In light of

its experience and additional information, NPS is now refining its

methodology used to evaluate the achievement of its natural quiet

restoration standard.

Particularly, the NPS refinements contemplate a two-zone system for

evaluating achievement of the natural quiet standard. The zones reflect

more accurately the differences in geography, facilities development,

and regulatory restraints of specific geographic areas of GCNP and

allow noise thresholds to be tailored to the circumstances of each

zone. The refinements apply only to evaluation methodology; the

standard for substantial restoration of natural quiet remains

unchanged.

This notice seeks public comment on the refinements to NPS's

evaluation methodology, i.e., the two-zone system and the noise

thresholds to be applied to the zones. Additional matters concerning

the GCNP comprehensive noise management plan for air tour operations

will be addressed in subsequent public notices, including, but not

limited to, a model validation study and a noise monitoring strategy.

DATES: Comments must be received on or before March 20, 1999.

ADDRESSES: Comments may be delivered or mailed, in triplicate, to, the

National Park Service, attention: Tom Hale, National Park Service,

Grand Canyon Science Center, P.O. Box 129, Grand Canyon, Arizona 86023.

FOR FURTHER INFORMATION CONTACT: Tom Hale (520-556-7219).

SUPPLEMENTARY INFORMATION

Background

Section 3 of Public Law 100-91 (Overflights Act) states that noise

associated with aircraft overflights at Grand Canyon National Park

(GCNP) is causing a significant adverse effect on the natural quiet and

the experience of GCNP. The statute directed the Secretary of the

Interior (Secretary) to make recommendations to the Administrator of

the FAA for the development of a plan for management of air traffic in

the air space above GCNP for the purposes, among other matters, of

providing substantial restoration to the natural quiet and experience

of the park and protection of public health and safety from adverse

effects associated with aircraft overflight. The FAA is charged with

implementing these recommendations without change unless it determines

that they would adversely affect aviation safety.

A plan intended to achieve these purposes was established by FAA in

1988 with the adoption of Special Federal Aviation Regulation (SFAR)

No. 50-2. SFAR 50-2 established minimum altitudes, four flight free

zones, and special routes for commercial air-tour operators over the

park.

In 1994, as required by the Overflights Act, the Secretary

submitted to the Congress a report, developed by NPS, regarding

overflights over units of the national park system in general. The

``Report on the Effects of Aircraft Overflights on the National Park

System'' (Report), reviewed the effectiveness of SFAR 50-2 and offered

a new set of recommendations for further regulatory action by FAA. The

Report concluded that SFAR 50-2 had not succeeded in substantially

restoring natural quiet to GCNP noting, particularly, that the level of

commercial air-tour operations (and consequent aircraft noise) at GCNP

had increased since 1988 and was likely to continue to increase under

SFAR 50-2. The Report recommended simplification of the existing

commercial air-tour route structure, expansion of flight free zones,

phased implementation of quieter aircraft technology, consideration of

limits on aircraft operations or noise, and the imposition of temporal

curfews on commercial air-tour overflights.

In addition, the Report determined the threshold value for the

substantial restoration of natural quiet: 50% or more of the park must

achieve ``natural quiet'' (i.e., no aircraft audible) for 75-100

percent of the day. ``Natural quiet'' is a park resource defined as the

natural ambient sound conditions found in national park units. It

describes the natural sound conditions found in national parks when

people with normal hearing can perceive nothing but the sounds produced

by the natural and cultural components of the parks.

On April 22, 1996, in an Executive Memorandum, the President

required the Secretary of Transportation, in consultation with the

Secretary of the Interior and the National Park Service, to issue

regulations ``to place appropriate limits on sightseeing aircraft over

the Grand Canyon National Park to reduce the noise immediately and make

further substantial progress toward restoration of natural quiet, as

defined by the Secretary of the Interior, while maintaining aviation

safety in accordance with the Overflights Act (Pub. L. 100-91).''

In response, on December 31, 1996, the FAA published a Final Rule

amending part 93 of Federal Aviation Regulations by adding a new

subpart (Subpart U) to codify the provisions of Special Federal

Aviation Regulation (SFAR) 50-2, Special Flight Rules in the Vicinity

of GCNP (61 FR No. 252, pages 69302-69333) modifying the dimensions of

the GCNP Special Flight Rules Area; establishing new and modifying

existing flight corridors and flight free zones; establishing reporting

requirements for commercial sightseeing companies operating in the

Special Flight Rules Area; restricting flights in Zuni and Dragon

Corridors during certain time periods (curfews); and limiting the

number of aircraft that can be used for commercial sightseeing

operations in the GCNP Special Flight Rules Area (cap). Subsequently,

it became necessary to delay implementation of several of the rule's

provisions to continue consultation with Indian tribes on routes and

address problems with the cap on sightseeing operations. As a result,

the reporting requirements, curfews, and cap on aircraft numbers are in

effect, but modification of the Special Flight Rules Area and the

flight free zones will not be completed until decisions on air tour

routes can be finalized.

In addition, on December 31, 1996, FAA published a notice of a

proposed rulemaking regarding additional noise limitations for aircraft

operations in the vicinity of GCNP (61 FR No. 252, pages 69334-69355).

Then, on December 31, 1996, FAA issued proposed air-tour routes for

GCNP (61 FR No. 252, pages 69356-69357). These latter actions have not

been finalized. The FAA has initiated other actions since that time,

notably delaying implementation of certain sections of the final rule

to allow the FAA and the Department of Interior to consider comments

and suggestions to improve the proposed route structure. Complete

background information on these and other actions taken by the FAA may

be found in the Federal Register Vol. 63, No. 234, pages 67544-67546.

The preamble to Subpart U, in addition to discussing the need for

the rule, states that FAA and NPS are committed to the development of a

noise management plan for GCNP related to air tour operations. This

plan is intended to provide for a more adaptive management approach,

full resolution of all monitoring and modeling issues, additional

public input, and the provision of improved incentives to invest in

noise efficient aircraft. The GCNP noise management plan is intended to

ensure development of a flexible and adaptive approach to noise

mitigation and management, and,

[[Page 3971]]

among other matters, will address validation and documentation of the

most effective way(s) to monitor and model aircraft noise in GCNP.

Discussion

As part of its preparation for developing the GCNP air tour noise

management plan, the NPS has reexamined the current methodology for

evaluating the substantial restoration of natural quiet in GCNP.

As previously noted, the NPS determined in 1994 that the threshold

for substantially restoring natural quiet to GCNP required that 50% or

more of the park must achieve natural quiet (i.e., no audible

aircraft), for 75-100% of the day.

The methodology previously used to evaluate the achievement of the

substantial restoration of natural quiet under this standard treated

the entirety of GCNP as one area and applied a single noise threshold

to the entire area. The threshold used was the average natural ambient

(multiple levels based on vegetative cover from the best available

acoustic data set) plus 3 decibels, otherwise known as noticeability.

Noticeability is defined as the level at which visitors engaged in

activities other than contemplation of the national park are likely to

hear aircraft noise. This threshold was used in calculating the

percentage of the day and the percentage of GCNP that aircraft noise

would be noticeable. And the threshold was used irrespective of

differences in geography, development circumstances, or regulatory

restraints of particular areas of the park, and, irrespective of the

fact that it might be appropriate to apply different noise thresholds

to different parts of GCNP to reflect such differing circumstances.

Based on further review and the experience of NPS and FAA in

applying the current aircraft noise evaluation methodology, the NPS

believes the current methodology should be refined to take into account

the characteristics of specific areas of GCNP and to utilize different

noise thresholds where appropriate.

Particularly, NPS is refining the current evaluation methodology by

incorporating a two-zone geographic system with different noise

thresholds applicable to the circumstances of each of the two zones.

In this connection, NPS, acting for the Secretary, is charged with

the management of areas of the National Park System. It is the

responsibility of NPS to preserve park areas and to provide for their

enjoyment in a manner that will leave them unimpaired for the enjoyment

of future generations. Preserving and maintaining natural and cultural

``soundscapes'' in areas of the national park system is a component of

this responsibility. A concern for the achievement of the ``substantial

restoration of natural quiet'' in GCNP is analogous to concerns

regarding the preservation of wildlife, historic structures or

ecosystems that are significant features of parks. As part of its

mandate, the NPS seeks to make available the opportunity to experience

the natural features of park areas with as little evidence of human

activity, visible or audible, as possible.

All of the larger natural area parks are zoned by NPS for differing

uses and differing levels of resource protection based upon park

purpose and other mandates, and differing levels of development to

serve visitors. In general, a park's frontcountry has facilities,

roads, parking lots and commercial services to provide necessary and

appropriate visitor needs, while the backcountry, whether a wilderness

area or not, has only trails for use by visitors.

A similar planning methodology is now proposed to be adopted by NPS

with respect to the substantial restoration of ``natural quiet'' at

GCNP. Under this methodology for Grand Canyon, Zone One would be

composed of (1) the developed areas of GCNP as identified in GCNP's

1995 General Management Plan, encompassing, on the South Rim, the area

from approximately Desert View to Hermits Rest, and, on the North Rim,

the developed area on Bright Angel Point; (2) the Sanup Flight Free

Zone; and (3), the Marble Canyon Sector. Zone One comprises

approximately one-third of the area of GCNP.

The developed areas included in Zone One for this purpose are

generally those delineated as ``Developed Areas'' on the Management

Zones map in the 1995 GCNP General Management Plan. Exceptions include

(a) Tuweep and Phantom Ranch which are excluded from Zone One because

they are managed to more primitive standards than the other developed

areas; and (b) the North Rim paved roads because they are surrounded by

proposed wilderness areas and because the roads and utility corridors

are too narrow (approximately 600 feet) for practical noise and impact

modeling on the scales involved. Only the Bright Angel Point developed

area is included in Zone One on the North Rim. For Zone One on the

South Rim, the system of developed areas, roads, and utility corridors

is blocked into a single contiguous unit. This unit extends from the

rim to the southern boundary of GCNP and from Hermit's Rest to Desert

View.

The North and South Rim developed areas as described above are

included in Zone One in recognition of the greater amount of human

activity and consequent more limited expectations of natural quiet in

these areas as opposed to undeveloped areas of the park. The area west

Whitmore Rapid is included in Zone One because the relatively low

designated aircraft ceiling of the Sanup Flight-free Zone (7999 feet,

MSL), needed for safe transit of the area by general aviation, limits

the ability of the flight-free zone to provide acoustic protection to

this area.

The Marble Canyon Sector is included in Zone One because the

narrowness of Marble Canyon and the SFRA boundary effectively preclude

acoustic protection of the canyon floor and river area, and because it

is not feasible to establish a flight-free zone while still providing

for safe transit of the area by general aviation traffic.

Zone Two would encompass, in a large contiguous area in the center

of GCNP, approximately two-thirds of the park's area. The two zones are

shown on the map accompanying this notice.

Under this proposal, the noise threshold for Zone One is set at 3

decibels above the average natural ambient sound levels (A-weighted)

found to exist in these areas of the park as determined by previous

scientific acoustic measurement studies. This is the same as the single

standard used in previous evaluations (i.e., noticeability).

The threshold for Zone Two is proposed to be different because data

collected at GCNP indicates that technicians monitoring the sound

environment identified aircraft noise levels at levels significantly

below A-weighted natural ambient levels. These technicians, tested to

have normal hearing, were listening actively to note the source of

noise levels as the source changed over time, noting, for example,

whether the noise source was the natural ambient environment or one or

more of a variety of human sources such as aircraft or vehicles. The

level at which an attentive listener, such as these technicians, can

begin to hear a noise source is the only objective point from which the

amount of time the source is audible can be measured; it incorporates

the masking level natural ambient environment, including wind. Park

visitors, sitting quietly but actively seeking to experience the

natural quiet and solitude of the park, were key people that NPS

decision-makers had in mind concerning the phrase ``no aircraft

audible'' in the natural quiet standard. However, with a noise

threshold of 3

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decibels above average natural ambient sound levels, the NPS learned

that such persons could potentially hear aircraft as much as 100% of

the time at levels lower than that threshold. The NPS considers this

standard to be inappropriate for the whole park.

The technicians identified aircraft noise at A-weighted levels of

8-12 decibels below the average A-weighted natural ambient sound

levels, depending upon aircraft type. Therefore, the threshold for Zone

Two is set at 8 decibels below the average ambient sound levels, a

threshold which reflects the point at which aviation noise can be heard

(i.e., audible) by ground visitors seeking to experience the natural

and cultural soundscapes of national parks.

The legislative history of Public Law 100-91 confirms that the

purpose of flight-free zones is to provide a location where visitors

can experience the park essentially free from aircraft sound

intrusions. The aerial extent of these zones will also be adequate to

ensure that sound from aircraft flying adjacent is not detectable from

most locations within the zones. It is within these flight-free zones

that substantial restoration of natural quiet is expected to be

achieved.

NPS considers that adoption of these changes to its noise

evaluation methodology for GCNP will result in more accurate and

realistic means to evaluate the substantial restoration of natural

quiet in GCNP consistent with the NPS Report to Congress. The Report

defined the substantial restoration of natural quiet using a noise

evaluation standard based upon the sound level at which a person with

normal hearing can hear aircraft noise.

The NPS and the FAA will use this refined methodology in future

evaluations of the substantial restoration of natural quiet at GCNP,

unless science or public planning processes provides better approaches.

These refinements of the evaluation methodology may make more

challenging the efforts to achieve the substantial restoration of

natural quiet in GCNP. However, the use of the two noise thresholds and

two geographic zones will better achieve the preservation of the GCNP

resources and visitor experiences the NPS is charged to protect.

Jaqueline Lowie,

Deputy Director.

[GRAPHIC] [TIFF OMITTED] TN26JA99.000

[FR Doc. 99-1685 Filed 1-25-99; 8:45 am]

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