Sound Resource Report Analysis of Sound Impacts on the...

South Fowl Lake Snowmobile Access Project

Final Environmental Impact Statement Appendix D

Appendix D

Sound Resource Report

Analysis of Sound Impacts on the

Boundary Waters Canoe Area Wilderness

from the Proposed McFarland Lake to

South Fowl Lake Snowmobile Trail


Final Environmental Impact Statement Appendix D


Final Environmental Impact Statement D-i Appendix D

Table of Contents

Executive Summary ........................................................................................................................ 1

I. Introduction ................................................................................................................................. 5

Background Information ............................................................................................................. 6

History of the Trail ...................................................................................................................... 6

Terminology ................................................................................................................................ 7

II. Affected Environment ................................................................................................................ 8

Vicinity ........................................................................................................................................ 8

Juxtaposition ................................................................................................................................ 9

Wilderness ............................................................................................................................... 9

Land and Resource Management Plan .................................................................................... 9

III. Framing the Study ................................................................................................................... 10

Understanding Sound Levels .................................................................................................... 10

Duration of Sound ................................................................................................................. 13

Methodology ............................................................................................................................. 13

Parameters to be measured .................................................................................................... 13

Data Collection ...................................................................................................................... 14

Analysis ..................................................................................................................................... 15

Analysis Area affected by sound levels ................................................................................. 15

IV. Results..................................................................................................................................... 18

Existing Condition (No Action) ................................................................................................ 18

A. Types of sounds heard within the BWCAW on Royal Lake and Royal River ................. 18

B. Sound Levels ..................................................................................................................... 19

C. Frequency of Snowmobile Use ......................................................................................... 22

D. Duration of Snowmobile Sound ....................................................................................... 22

Proposed Action Alternatives .................................................................................................... 23

A. Types of Sound ................................................................................................................. 23

B. Sound Levels, Audible Distance ....................................................................................... 23

C. Frequency .......................................................................................................................... 30

D. Duration ............................................................................................................................ 31


Final Environmental Impact Statement D-ii Appendix D

Impacts to Homeowners ............................................................................................................ 33

B. Sound Levels ..................................................................................................................... 33

C. Frequency .......................................................................................................................... 34

D. Duration ............................................................................................................................ 34

V. Effects to the BWCAW and Visitors ...................................................................................... 36

Methodologies ........................................................................................................................... 37

Effects on Wilderness Character “Opportunities for Solitude” ................................................ 38

Setting .................................................................................................................................... 38

Changes in sound levels ........................................................................................................ 38

Duration ................................................................................................................................. 39

Effects on Wilderness Visitors .................................................................................................. 39

VI. Conclusions............................................................................................................................. 41


Final Environmental Impact Statement D-1 Appendix D

Executive Summary

Introduction

A snowmobile trail known locally as the Tilbury Trail was discovered to be within the Boundary

Waters Canoe Area Wilderness and the District Ranger ordered the trail closed. Since an

alternate route that exists between McFarland Lake and South Fowl Lake is not safe, the District

Ranger assembled an interdisciplinary team to explore safe routes. The South Fowl Lake

Snowmobile Access Environmental Assessment (EA) was completed that compared the effects

of four alternate routes against No Action. In 2006 the EA was published along with the District

Ranger’s decision to implement Alternative 2 and possibly in the future, Alternative 4. The

decision was appealed and litigated. Upon litigation the Federal District Court remanded the

decision to the Forest Service with direction to analyze the impacts from snowmobile sound on

the Boundary Waters Canoe Area Wilderness.

The Court Order required an Environmental Impact Statement (EIS) on sound issues including

an analysis of four parameters to determine if there was:

A. A new type of sound,

B. Additional volume of snowmobile sound,

C. Additional frequency or how often the new sounds would be heard,

D. Additional duration of sound emitted by snowmobiles from the proposed routes.

Analysis Area and Affected Environment

The analysis area was determined to be the portion of the Wilderness near the alternative

snowmobile trails where snowmobile sounds are audible. It contains the eastern tip of the Vento

Unit of the Boundary Waters Canoe Area Wilderness (BWCAW), a community of cabins on

McFarland Lake and a series of lakes that form the border with Canada. The area is generally

forested but also contains bodies of water and hills including steep cliff faces. Snowmobile use

is common on McFarland Lake, the Fowl lakes, between McFarland and the border lakes and

along the border lakes to the west.

Alternatives:

1. No Action, or the condition that exists today,

2. Alternative 2, a route just outside the Wilderness or the northern route,

3. Alternative 3, a route heading south from McFarland with some new construction and

then follows a series of roads and trails to South Fowl Lake,



4. Alternative 4, also heads south from McFarland with some new construction up to the

Arrowhead Trail (County Road 16) where a trail would be constructed within the right of

way for the county road. Both Alternatives 3 and 4 would have the same general impacts

from sound and therefore were considered together.

5. Alternative 5 is being eliminated from further consideration in the EIS since it does not

meet the purpose and need for the project. It is not included in this study.

Framework for the Study

The works of the American Academy of Audiology, US Environmental Protection Agency

(EPA), Minnesota Pollution Control Agency (MPCA), Miller, Harrison and Rogers were

particularly informative when framing this study. We used them to explore the characteristics of

sound, the characteristics of remote areas, the effect that natural areas have on sound and

methodologies for conducting this study. From these works, we selected a combination of the

human ear, electronic instruments and modeling to measure the parameters outlined in the Court

Order. The more critical measurements were taken on site using the ear and instruments; then,

where reasonable, modeled results were used to complete the picture.

The study was implemented by nine technicians who were both familiar with the South Fowl

area and had been trained by the Superior National Forest Monitoring Coordinator on proper

techniques for the measurement of sound. Technicians placed test points within the BWCAW

along the Royal River and Royal Lake to measure sound from both sides of the Wilderness and

along the proposed route for Alternative 2. Alternative 2 was measured for sound above ambient

level in the BWCAW, while other action alternatives were too far distant to add noise above

ambient level in the wilderness. Measurements were taken on days with differing weather

conditions in 2009 and 2010.

Results

Technicians were able to discern the sounds that are present in the background. They measured

the distance snowmobile sound could be heard from an audible perspective. They also measured

the level of sound that was occurring without snowmobiles operating (natural ambient level) and

the distance that it took snowmobile sound to decay to the natural ambient level. Data collected

by the technicians is displayed graphically to demonstrate the area of the Wilderness that is

impacted by the alternatives including No Action. Data was also used to calculate the duration

that snowmobile sound would occur on each alternate route.

A. Type of Sounds: Snowmobile sounds are present within the project area; therefore

implementing any alternative would not create a new sound.

B. Additional Volume of Sound: Table D-1 below displays the area of impact by sound above

natural ambient (set at 34 dBA from data collected) by each alternative.



Table D-1: Area of Impact.

Alternative Area of BWCAW Above Natural

Ambient Change from Existing

Condition

No Action 763 acres

Alternative 2 799 acres 36 acres (0.5%)

Alternatives 3 & 4 763 acres No Change

Tilbury Trail 951 acres 188 acres (2.5%)

C. Additional Frequency of Snowmobile Use: Snowmobiles are currently traveling between

McFarland and South Fowl although under unsafe conditions. There is no data to suggest that

implementing any of the alternatives would change the number of snowmobiles in use.

D. Duration: Table D-2 below displays the percentage of the week that sound would be

generated for each trail for both audible and levels above natural ambient.

Table D-2: Duration of impact.

Alternative % of week

single sled use % of week

groups of two sleds

No Action, Audible Sound 11.0% 5.5%

Alt. 2, Audible Sound 11.8% 5.9%

Alt. 3 & 4, Audible 11.0% 5.5%

Tilbury Trail, Audible 11.8% 5.9%

No Action, Above N. A.* 0.0% 0.0%

Alt. 2, Above N. A. 2.2% 1.1%

Alt. 3 & 4 Above N.A. 0.0% 0.0%

Tilbury Trail, Above N.A. 7.1% 3.6% * Natural Ambient level

Discussion

The critical differences this study found between the alternatives is in sound levels and duration.

The types of sound and the frequency of snowmobile use were the same for all alternatives.

Sound levels for the ambient or background were highly variable. The quietest or lowest sound

level measured was when the temperatures were warmer (32 degrees in winter) and winds were

calm. Data in Appendix C-6 demonstrates that calm conditions occur only 7.7 percent of the

winter daytime hours. Average daily winter wind speeds are in the four to eight mile per hour

range. Wind often pushed our measured decibel levels above 50 and into 60 dBA.



Alternative 2 added 36 acres of wilderness that would be impacted by sound levels above natural

ambient. This addition is the primary difference between Alternatives 3, 4 and No Action and

which the deciding official should weigh into his decision.

While a much lower duration than the Tilbury Trail caused, Alternative 2 would have a longer

duration of sound above natural ambient compared to No Action or Alternatives 3 and 4 with the

increase being one to two percent of the week.

Conclusions

Two conditions are important to the final determination for this study in terms of impact from

sound. One is the location of the project area between two motorized travel routes. Second is

the Forest Plan desired conditions for opportunities for solitude within the Semi-primitive Non-

Motorized Management Area. The increase of 0.5 percent of the project area impacted and the

increase of one to two percent of the week being impacted by sounds above natural ambient

levels are rated as very minor. During those times when the wind is blowing out of the south, the

increase of five dBA into the Royal Lake area is rated as minor.

Our research has determined that measuring the impact to visitors is difficult. We chose the

criteria “level of annoyance” as a measure following Miller’s lead (2007) which is related to the

number of people hearing the sound. Within the Royal Lake area, our wilderness ranger patrols

have not noted any use by winter visitors on foot (non-snowmobilers). This correlates with

visitor permit data which indicates very low use levels in the area. Therefore the level of

annoyance is rated as very minor. It is noted that we have also added consideration of effect to

“opportunity for solitude” to section 3.2 of the FEIS since this is identified as a quality of

wilderness character.

This report presents the research, framework, methodology and results for the four parameters

outlined in the Court Order. We took each issue and analyzed it for all alternatives as weighed

against No Action. Then we put the parameters into the context of the site specific area and the

conditions outlined by the Forest Plan to provide perspective for the ratings. We have

determined that the small percentage of change created by any of the alternatives amounts to a

minor impact to this specific wilderness area.



I. Introduction

This report is completed to fulfill the requirements set out in the Court Order for Case 0:06-cv-

03357-JRT-RLE. Specifically the suit was brought by a coalition of groups challenging a range

of issues covered in the environmental assessment (EA) prepared for the proposed South Fowl

Lake Snowmobile Access Project (2005) on the Gunflint District, Superior National Forest. The

Court found that the potential impact of snowmobile sound emitted into the Boundary Waters

Canoe Area Wilderness (BWCAW) was not adequately analyzed in the EA. The Court ordered

that an Environmental Impact Statement (EIS) be prepared to assess “…the sound impact of each

of the proposed South Fowl Trail routes on the adjoining wilderness area…”

This report provides a brief history of the South Fowl Lake Snowmobile Access Project. It

outlines the concepts of the study, methodologies used, the results from the analysis, and then

displays the impacts that sound will have on wilderness character as well as the impacts to the

populations within the vicinity of the proposed trail alternatives.

The Court Order outlined four categories of sound for analyzing the impacts to wilderness

character and visitors.

A. New type of sound,

B. Additional volume of snowmobile sound,

C. Additional frequency or how often the new sounds would be heard,

D. Additional duration of sound emitted by snowmobiles from the proposed routes.

Each of these categories would evaluate snowmobile sounds against the current condition. From

the Court Order, the current condition includes the type of sounds in the background, the

frequency and the level of sound in the background.

Alternatives included in the EA and addressed in this report are:

Alternative 1, No Action (existing condition)

Alternative 2, The Northern Route

Alternative 3, a variation of a Southern Route

Alternative 4, another variation of the Southern Route

Alternative 5, has been dropped from further consideration in the EIS

See Figure D-1, the project area map which displays the location of each route.



Background Information

This report provides analytical information to be used in assessing the potential impacts of

snowmobile sounds that would come from snowmobiles traveling between McFarland Lake area

and the North and South Fowl Lakes. Results from this analysis will then be documented in the

South Fowl Lake Snowmobile Access Project EIS as a part of the decision process required

under the National Environmental Policy Act (NEPA). Three alternate routes (shown on Figure

D-1) plus Alternative 1 (the No Action Alternative) will be studied for both impacts to the

wilderness character of the BWCAW as well as impacts to humans in the area.

History of the Trail

The South Fowl Lake Snowmobile Access EA (USDA Forest Service 2005) identified that

snowmobile users were traveling between McFarland and the Fowls by the 1960s using a trail

that was established in part through a logging operation. This trail became known to Cook

County residents as the Tilbury Trail. In 1978 Congress passed PL 95-495 (BWCAW Act) that,

among other things, expanded the Wilderness boundaries to include a portion of National Forest

System land in the vicinity of Royal Lake (Figure D-1). In 2003 the Forest Service determined

that the Tilbury Trail was located within the BWCAW boundaries and that the trail needed to be

closed and relocated outside of the Wilderness (USDA Forest Service 2005 and 2006).

An environmental assessment was prepared to consider the effects of four alternate routes, in

addition with a No Action Alternative which was published in November, 2005. Based on that

Figure D-1: Location of Royal River and Royal Lake in relation to McFarland Lake on the west and South Fowl Lake on the east.



assessment, a Decision Notice was published in February 2006, approving Alternative 2 for

implementation, but also outlining circumstances for which Alternative 2 would be closed and

Alternative 4 would be constructed. An administrative appeal of the Decision Notice was filed

with the Reviewing Office and the Decision Notice was affirmed. A law suit was then filed in

the Federal District Court of Minnesota from which the Court Order remanded the issue of sound

(as it relates to affecting wilderness) to the Forest Service for analysis of impacts to be published

in an EIS.

Terminology

Sound: An alteration of pressure or vibration that propagates through an elastic medium such as

air that can be measured.

Decibel: A unit of relative loudness, electric voltage, or current equal to ten times the common

logarithm of the ratio of two readings, generally stated as dB. For sound, the decibel scale runs

from zero for the least perceptible sound to 130 for sound that causes pain.

dBA: A specific weighting method for decibel measure that most closely replicates what the

human ear can hear. Since this driver for this report is the human perceptions of sound in the

Wilderness, the A weighting is considered appropriate.

Background Sounds: For the purposes of this study, any sounds or noises present in the project

area that exist at the time of the study and regardless of the construction of a new route.

Ambient levels: For the purposes of this study, the loudest decibel level of combined

background sounds. For this study, there are locations where the sounds from current

snowmobile use are louder than the surrounding sounds of nature.

Natural Ambient: The loudest sound level if all human made noises were removed from the

environment. For this report, the natural ambient level is considered that level where the sounds

of nature are the loudest sounds present and are recorded on the decibel measuring device.

Human made sounds may be present in the background but are not the loudest sounds and

therefore are not those measured on the ExTech HD600 sound meter.

Audible: A sound that may be discerned by the human ear. A sound may be audible even if it has

a lower sound level than other sounds present in the environment.

OBSIL - Observer Based Source Identification Logging: Defined as “Observer of Silence”,

for the purposes of this report OBSIL is a methodology where a trained observer listens to and

records information on sounds. In general the observer records when the sound can be heard

(audible), what type of sound is being heard and what type of sound is being measured on the

sound meter.

Juxtaposition: The relative physical location of two or more things together, especially in order

to suggest a link between them or emphasize the contrast between them.

ROS - Recreational Opportunity Spectrum: A system of evaluating the nature of, or the

desired condition of, the combination of physical, biological, social, and managerial conditions



that give value to a place(Clark and Stankey, 1979). The “Spectrum” spans from primitive

(having very little human evidence) to Urban (very high evidence of human activity).

ExTech HD600: A sound meter /data logger that measures sound pressure levels in decibels.

Data is downloaded to computer software for graphing and correlation with observer listening

forms.

Models: A set of mathematical equations often calculated using computers where data is entered

into the equations and where the results suggest a condition or trend that helps in decision

making. Within this study, direct observed and measured data was used in consideration of

receptors within the Wilderness on Royal River and Lake. Modeled information was used to fill

in the complete picture, particularly where observations were too cumbersome or expensive to

obtain.

NEPA - National Environmental Policy Act: An act of Congress that outlines a process

Federal Agencies are to use to consider the environment when deciding to take action.

II. Affected Environment

Vicinity

The South Fowl Lake Snowmobile Access Project Area is located in the northeastern part of

Cook County Minnesota on the very eastern tip of the Boundary Waters Canoe Area Wilderness

and near the border with Canada. The setting is generally forested with several lakes, but with

also hills that at times have sharp cliff faces. One of the lakes, McFarland, includes a fairly large

component of private land, which has a community of seasonal homes or cabins around the lake.

Most are used as a second home meaning the dwelling is not the primary residence of the owner.

Figure D-2.

Vicinity Map.

Vento Unit (BWCAW)

South Fowl Lake

Snowmobile Access Project

Area

Hovland, MN



There are four cabins on South Fowl Lake and eighteen cabins on North Fowl Lake. Summer

travel to the cabins is predominantly by ATV to the South Fowl cabins and by motor boat to

North Fowl cabins and those sounds are fairly common. If the cabins are used in the winter,

access would be primarily by snowmobile; however the level of winter use is not known.

Snowmobiles are commonly used to travel into the Fowl lakes for recreational ice fishing.

Snowmobiling on McFarland, South Fowl and North Fowl Lakes and beyond to Moose and

other border lakes is legal and common (South Fowl DN 2006). Estimated snowmobile use is 25

to 30 sleds per day, on weekends with little use during the week. For the purposes of this

analysis three days were assumed to have snowmobile use, Friday, Saturday and Sunday, with 30

sleds each day. Other days were assumed at zero use.

Juxtaposition

Wilderness

The project area under analysis shown on Figure D-2 above includes a finger of the Vento Unit.

The Vento Unit is the smallest unit of the BWCAW that is disconnected from the main body of

the BWCAW, that dips southward and lies between McFarland Lake on west side and North and

South Fowl Lakes on the east side. There are several homes and cabins on McFarland Lake and

winter use is very important to the landowners (based on formal comments received through

preparation of the EA), which is verified through winter ranger observation and personal

communication with those landowners. This relative position between the McFarland and Fowl

Lakes and the eastern tip of the BWCAW creates a setting where motorized sounds are projected

toward the Wilderness from several directions (see Figure D-5).

Land and Resource Management Plan

To provide an understanding of expectations within the project area, the Superior National

Forest, Land and Resource Management Plan (Forest Plan, 2004) has divided the Forest into

Management Areas (MA). Each MA has outlined a theme, desired conditions, and has a

designation for the Recreational Opportunity Spectrum (ROS) where a particular management

area belongs. In some circumstances, the Management Area and Recreational Opportunity

Spectrum designations are the same.

The MA and ROS for the portion of BWCAW located between McFarland Lake and the Fowl

Lakes are both designated Semi-primitive Non-motorized and the visitor should expect to

encounter others and that solitude is not one of the their highest expectations. Some, but not a

high degree of challenge, risk and freedom is provided here (Forest Plan, p. 3-45; South Fowl

EA, p. 3).

McFarland, South and North Fowl Lakes are outside of the Wilderness and have a MA of

General Forest - Longer Rotation with an ROS of roaded natural. Visitors should expect to see

natural appearing environment with moderate evidence of the sights and sounds of man.

Interactions between users may be moderate to high with evidence of other user prevalent (Forest



Plan, Glossary-22). McFarland Lake has a considerable amount of private land where the Forest

Plan does not determine the ROS class; however this area trends toward, but may not fully reach

the “Rural” classification where visitors expect to see an environment which has been

substantially modified by the development of structures, vegetative manipulation or pastoral

agricultural development. Sights and sounds of humans are readily evident and the interaction

between users is often moderate to high (Forest Plan, Glossary-23).

These adjacent MAs with differing ROS classes that are separated only by the Wilderness

boundary, help explain the background sounds that are present in this project area.

Landscape Qualities

This area has several natural features that can affect or reduce the level of sound as it travels.

Sound “decays” or there is a reduction in the volume (decibel level) as the distance from the

source increases (also called attenuation). The decay rates are affected by factors such as

topography (Aylor, unknown date), vegetation, in our case trees (Sumara 2007), and weather

conditions like wind, temperature and humidity (Bonn 1988). Figure D-1 provides a three

dimensional view of the general area showing the topography. Areas of water or non-forested

wetlands would affect sound decay generally only by the air. Areas of land that are generally

forested would reduce the impacts of sound. The hills including cliff faces could either increase

or decrease the level of sound depending on where the sound originated and what hills were in

the line of travel for the sound.

III. Framing the Study

The introduction to this report outlined that we look at the existing sounds as compared to any

new or additional sound from snowmobiles. A review of background literature was completed to

better inform the study and address some of the unique challenges faced here. Considering the

South Fowl Access, there are a closed route, an existing route and three potential routes. Sound

that was present on the Tilbury Trail does not exist now and the sound that would be generated

through use of the potential alternatives does not exist now. Those facts do not allow a direct

measurement of actual snowmobile use. Also complicating this study is the mixture of

recreational settings from roaded natural on one side of the BWCAW line to Semi-primitive

Non-motorized on the other side. We needed to address the challenges of evaluating

snowmobile sound from the alternative routes. Several sources were reviewed to understand the

qualities of sound and how the impacts of sound relate to the setting for the South Fowl Lake

Snowmobile Access Project.

Understanding Sound Levels

The American Academy of Audiology provides a picture (Figure D-3) of the general levels of

sound in a variety of settings, however similar results are also found in MPCA (2008), Nave

(1999), San Ramon (2010), EPA (1973), etc.



Rogers et al (2006) provides the following notes on the response that humans would typically

have to sounds measured in decibels.

Except under laboratory conditions, a change in sound level of 1 dB cannot be perceived.

Doubling the energy of a sound source corresponds to a 3 dB increase.

Outside the laboratory, a 3 dB change in sound level is considered a barely discernible

difference.

A change in sound level of 5 dB will typically result

in a noticeable community response.

A 6 dB increase is equivalent to moving half the

distance towards a sound source.

A 10 dB increase is subjectively heard as an

approximate doubling in loudness

The threshold of pain is an SPL of 140 dB

There is no way to perfectly measure subjective

experience of noise

Individual’s tolerance for noise varies. Humans hear

certain pitches more than others, so a sound filter

referred to as “A weighting” or dBA has been created

to approximate the response of the human ear to

sounds and their pitches.

Methods of Measuring Sound Levels

In determining the approach to use that would provide

appropriate information to the deciding official, several

reports were reviewed and their methods considered.

Within urban areas where there are sounds from a variety

of sources, sound engineers may use complex

instruments that will measure and separate the various

sounds into their group of frequencies (spectral analysis)

and then measure the decibel levels of those frequencies.

It is the combination of frequencies that allow listeners to

discern one type of sound from another even though the

sounds are received at the same or similar decibel levels.

Methodologies may then include use of complex models

used to estimate the impacts of sound that take into

account distance from the source, effects on sound

Figure D-3. Graphic scale of relative Sound Pressure levels. The American Academy of Audiology has provided their interpretations associated with the level of sound from Faint to Painful and Dangerous.



caused by screening which can either be hardscape or vegetation. Often the goal is to reduce the

impact of sounds from highways, airports, etc. However, the analysis approach used in urban

areas does not necessarily provide the best fit for our rural/wilderness setting.

A review of the US National Park Service (NPS) management plans for both Grand Canyon and

Yellowstone National Parks (NPS 1999 & 2008, Miller 2007) provides a look at methodologies

used in more remote areas. The goal in both studies was to reduce the current levels of

motorized sounds, particularly the sound levels in less developed areas of the parks. Instruments

were used to determine existing levels of sound, but then the human ear also played a role in

some circumstances. Miller (2007) outlined a method sometimes used in more remote areas

called Observer Based Source Identification Logging (OBSIL) which uses the human ear to

discern whether a sound is audible and to determine the type of sound being heard. Miller and

the NPS used a combination of measured sound along motor routes, the human ear for some

observations and used models to display the impacts across Yellowstone National Park.

Yellowstone planning processes mapped the park into soundscapes using current sound levels

and proximity to a type of sound source. When interpreting those zones within their studies and

planning processes, the Park Service considered the concept of ROS where each soundscape was

correlated to one of the ROS classes, ranging from Urban to Primitive. Of note in Yellowstone

was that ROS classes were assigned to the study primarily based on current human use patterns

and corresponding sound levels. Next for each of those soundscapes, they determined acceptable

levels of sound in terms of how loud the sounds of snowmobiles would be and what percent of

the day those sounds could be heard. Maps were constructed of zone with decibel levels

portrayed and zones of audibility (including the concept of duration of sound). A final step was

to set standards for upper decibel levels and duration for each acoustical zone.

South Fowl has many similar qualities to Yellowstone and therefore consideration was given to

National Park Service methods. As was done for the Yellowstone study, we used a combination

of measured and calculated sounds of snowmobiles and with that data mapped the areas of

impact from existing motorized routes. Then we used the visitor expectations outlined in ROS

and evaluated the changes in sound levels relative to those expectations.

South Fowl is different from Yellowstone because at least a portion of each trail and the entire

proposed trail in Alternative 2 does not exist and therefore measuring actual snowmobile use was

not possible. However, sound was projected through electronic devices that adequately

simulated snowmobile sound.

Whenever feasible, the researchers in this study measured actual sound of running snowmobiles

or played back sound, rather than relying on models. We chose to use actual measurements in

response to public concerns about the cliff south of Royal Lake causing an amplifying effect to



snowmobile sound in Alternative 2. Actual measurements accounted for existing features rather

than relying on modeled results. Data from the measurements was then mapped to show the

areas where snowmobile sound would be audible and where the sound would be above the

natural ambient level. Modeling was used where actual measurements were not feasible and

where data from models adequately demonstrated the results.

The results displayed in FEIS Appendix D were checked with additional modeling with the

SPreAD-GIS model. See FEIS Appendix G for methods and results of this modeling.

Duration of Sound

When addressing the issue of sound duration, we considered three important receptors: the

BWCAW as an entity, people within the Wilderness who might hear the sound, and homeowners

on the south side of McFarland Lake. Factors being considered for this analysis are duration of

audible sound and duration of sound that is above ambient natural level of dBA. It is important

to remember that this analysis is designed to present the difference of impacts between

alternatives. Since none of the alternatives have been implemented, the analysis uses some

estimates to make the assessment of potential impacts.

This study focuses on the time or duration a snowmobile would be ridden on each of the

potential routes between McFarland Lake and South Fowl Lake. Analysts did not measure the

duration of all snowmobile sound or the various background sounds. Snowmobiles currently

ride on McFarland and the Fowl Lakes and the duration of snowmobile operation on these lakes

are considered the same for all alternatives and therefore are not included in the calculations.

Total snowmobile use (numbers of sleds) is not expected to change regardless of alternative.

Snowmobiling has and is occurring between McFarland and South Fowl Lakes and ice fishing is

still popular on South Fowl and other border lakes even though the route is unsafe. There is no

data that suggests there were more snowmobiles operating between McFarland and South Fowl

Lakes when the Tilbury Trail was in use versus now since that trail has been closed. Similarly

there is no data to suggest that constructing a safe route would increase the number of

snowmobiles from present use regardless of alternative. The difference would be in the route

taken to approach and leave South Fowl Lake.

Methodology

Parameters to be measured

Four parameters were used to determine the impacts of sound emanating from snowmobiles;

The types of sounds audible within the project area,

The area where snowmobile sound level was audible to the human ear,

The area where snowmobile sound level was measured above natural ambient levels and



The duration snowmobile sound was measured at both audible and natural above ambient

levels while being operated on the various proposed routes.

Data Collection

A group of nine technicians were trained on data requirements, instruments to be used, the

design of the study, and the limitations of the methods. They went into the BWCAW on Royal

River and Royal Lake and measured snowmobile sounds during winter conditions. They noted

the type of sounds in the background, measured ambient levels of sound and measured

snowmobile sounds on alternative routes.

Technicians used an EXTECH HD600 decibel meter to measure the loudest levels of sound,

including both natural ambient levels and snowmobiles sound when it exceeded the natural

ambient level. Appendix C-2 displays the graphic recordings from the EXTECH plus notes for

the sounds on those graphs.

The human ear (OBSIL) was used by the technicians to note the types of sounds picked up by

both the EXTECH, the types of sound in the background and the distance a sound was audible

from its source. Distances that sounds were recorded or observed were measured using Global

Positioning Satellite (GPS) systems with accuracy of two to five meters.

The first Royal River Sound Test was completed in January and February of 2009 with a follow

up test in March 2010. The results can be found in Appendix C-2. You’ll note that the Extech

HD600 used in the sound test could only record the loudest sound levels present (rated from 30

to 130 dB) which were displayed on the graphs. It is noted that additional ambient sound level

data was collected in March 2011 with a Larson Davis 831 sound meter, which can detect lower

sound levels. See FEIS Appendix G for data collected with the Larson Davis 831 meter. Based

on these measurements, the average natural ambient sound level in the Royal Lake and Royal

River area of the BWCAW was estimated to be 34 dBA.

Data collected included:

the types of sounds within the background,

point samples along Royal Lake and Royal River of ambient levels for background

sounds, with and without snowmobiles operating on existing routes,

audible distance of current snowmobile sounds,

point samples from Royal Lake and Royal River where snowmobile sound would be

above natural ambient sound level.



Analysis

Analysis Area affected by sound levels

The first task was to define the “analysis area” from which the acreage will be used for the

calculations in this report. The question addressed for this report was “What area would be or is

currently affected by snowmobile sound in the Wilderness between McFarland and the Fowl

Lakes. The analysis area for all calculations was set as the area affected by current audible

snowmobile sound to the point where audible sounds from each side of the project area

overlapped. Note on Figure D-7 where the audible zone around McFarland Lake begins

separating from the audible zone along the border. Snowmobiles can continue to run along the

border beyond that point meaning the audible zone continues. The analysis area is set where

those two audible zones overlap (the area that is both cross hatched and blue on Figure D-7)

which is the area a visitor cannot escape motorized sound. A BWCAW visitor traveling west of

this area may find wilderness that is not affected by snowmobile sound but not along the border.

Sound levels

This study uses sound levels (L) measured in two minute points of time. Values for ambient

background sounds were averaged over a two minute period (L2min) however the spikes can also

be seen on the graphs. Sounds that caused peak values (Lmax) were noted and those peaks for

snowmobile sound were used in the analysis.

Figure D-4. Example of two minute sound test recording. Alternative 2 sound projection was recorded by sound meter. Large spike was caused by a sniffle.

Sound point 7 Trail Recording. 02/05/2009 11:13. Average dBA: 41.5



Figure D-4 demonstrates the L2min is 41.5 dBA and the sniffle caused an Lmax of 73 dBA (not

used in calculations).

Commonly sound levels are recorded and displayed as the percentage of time for the loudest

sounds, displayed as L10, L50 and L90; L10 being the 10% of the loudest sounds over a given time

period, L50 = 50% of the loudest sounds, L90 = 90% of the loudest sounds). The difficulty with

using this protocol is that it is generally measured for existing sounds that are somewhat

routinely heard. The time period used to measure L10, 50 or 90 values is quite often one hour, but

sometimes a 24 hour period. Considering South Fowl, there may be no snowmobiles operated

on some days, but then operated much more often on weekends. Plus, since Alternative 2 does

not exist, the L10 value would have to be estimated.

Decibel levels and distance from the data collected were entered into a Geographical Information

Systems (GIS) to spatially locate and analyze the sound impact zones and determine affected

areas for existing conditions as well as proposed trail routes. This included a zone for audible

sound and a zone demonstrating the area that motorized sound would be above ambient (Figures

D-6 to D-12).

Duration of effect

The length of each trail that sound would be audible or above natural ambient was determined

using sound level distance measurement. Then those distances were used with estimated

snowmobile speeds and the average number of snowmobiles per day to determine the duration of

time snowmobile use would be heard (calculations are shown in Appendix C-5 and results are in

Table D-4).

Limitations

A trail for the proposed Alternative 2 route does not exist and therefore it was not possible to

have a snowmobile in use from which sound could be measured. The sound test methodology

included using a device that recorded a snowmobile traveling at the design speed of the trail.

That device was then connected to a bullhorn type speaker to project the sound of a snowmobile

from Alternative 2. The sound level of the recording was played back at the same level as it was

recorded (102 dBA) but it is not known that the speaker system reproduced the exact quality of

snowmobile sound. Technicians conducting the test could not differentiate the recording from a

“live” snowmobile and the volumes were correct so the results were considered adequate.

Data points were not collected for every possible location. Snowmobile drivers riding on lakes

could travel at various speeds, hence the broadcast levels of dBA could be greater or lesser than

figures used in calculations for sound decay. The sound level for a snowmobile was held



constant (74 dBA at 50 feet equivalent to 105 dBA measured at one foot1). Another factor would

be the actual route of the snowmobile. When considering travel to be on roads, the location is

fairly accurate, however when the snowmobilers are on lakes, obviously they could travel on

many paths. This analysis assumes the snowmobiles were driving along the lakeshore. The

decision to use lakeshore was based on photographic evidence (Appendix C-3) that snowmobiles

often ride within a few feet of the lakeshore.

Rates of decay would be different in open air versus through the forest. Note that the only areas

where sound would not be affected by trees would essentially be the lakes. The technicians

conducting the sound test took specific measurements of decay to no audible sound and decay to

natural ambient where the receptor location was the Royal River and Royal Lake and the points

of origin of snowmobile sound was from the surrounding lakes or the Alternative 2 route

location. These measurements served us well for the analysis of rates of decay through open air.

However for the rate of decay through the forest, the analysis used calculated measurements for

decay distances. There are several miles of wilderness boundary where snowmobile sound is

immediately adjacent and projected into the Wilderness. The forest likely has some variability

where sound decay could also vary to a small degree. Work done by Sumara and Tsitsoni (2007)

and Harrison (1980) suggests that vegetation variability would not measurably affect sound

decay. Therefore the calculated measurements used for decay rates where a forest was present

were considered adequate. See Appendix C-5 for calculations that take vegetation into account.

Sound levels were calculated for the impact to homeowners. The terrain is flat on the lake with

no vegetation between the sleds and the homes so the model was presumed adequate.

Alternative 3 and 4 as they would ascend the hill from the lakes do not exist and the technicians

did not have permission from the home owners to set up the test equipment on their land.

Models when compared to actual tests for the Alternative 2 route underestimated the sound level,

therefore we conclude that sound levels received at the home sites is not overestimated. For

purposes of comparison, the modeled sound levels were considered adequate.

Sound levels for use on the Arrowhead Trail were calculated. Using a snowmobile on this road

is unsafe and therefore modeled information was used.

MPCA (1999) states that doubling the number of sound sources (from one to two snowmobiles

in this case) would add 3 dBA to the total measured levels. This would be true background

sounds as well for each of the alternatives. While a 3 dBA increase doubles the sound pressure,

1 Snowmobiles produced since February 1, 1975 and certified by the Snowmobile Safety and Certification

Committee's independent testing company emit no more than 78 dB(A) from a distance of 50 feet while traveling at

full throttle when tested under the Society of Automotive Engineers (SAE) J192 procedures. Additionally, those

produced after June 30, 1976 and certified by the Snowmobile Safety and Certification Committee's independent

testing company emit no more than 73 dB(A) at 50 feet while traveling at 15 mph when tested under SAE J1161

procedures.



MPCA also notes that 3 dBA is the human ear’s threshold for perceiving a change in sound

levels. Assuming the total number of snowmobile riders does not change, and they rode in

groups of two, the perceived level of sound would only change slightly. For example, if you

were walking down a road and a car approaches you from behind, you may or may not be able to

tell that two cars are coming at you. However the time that snowmobile sound was present

would be roughly half the time. Again, as if you were walking down the road and two cars

passed you separately, you’d experience twice the duration of sound as two cars passing at once.

For the purposes of this analysis one snowmobile is assumed to be the source of sound with the

exception of the calculations for duration as displayed in Table D-4.

IV. Results

Existing Condition (No Action)

40 CFR 1052.14 requires that the impacts that would be caused by a proposed action, and

alternatives to the proposed action, be compared to No Action in an EIS. In other words, what is

the difference from leaving things as they are? When reading this report, the existing condition

can be considered synonymous with the No Action Alternative.

Tilbury Trail: At the time this project originated, the Tilbury was being closed and a

replacement trail located outside the Wilderness was being considered and therefore the scope of

this analysis might have been proper to consider the change caused by each alternative compared

to use on the Tilbury Trail. Public comments on the EA suggest this comparison. Since this

project has been delayed from a process standpoint, there is a new “existing” condition, that

being where snowmobiles use Arrowhead Road to South Fowl Road, to the trail that leads down

into South Fowl Lake. This more recent current condition will be assessed as the No Action

Alternative since the Tilbury Trail is closed. For the purposes of this report, a comparison is

made to both time frames so that the reader can fully understand the scope of this project.

Therefore this analysis compares the sounds that would be emitted from these alternatives to the

sounds when the Tilbury Trail was being used and it compares to the sounds of the No Action

Alternative.

Background Sounds

A. Types of sounds heard within the BWCAW on Royal Lake and Royal River

The four seasons will bring differing sounds within the background. This report focuses on those

that are present in the winter when snowmobiles are in operation. Technicians report in the

Sound Test (Appendix C-2) common sounds within the background including snowmobiles,

regular vehicle traffic, snow removal equipment around and near McFarland Lake, wind and in

at least one location rapidly moving water in Royal River.



Sources of Background Sounds

Figure D-5 displays the locations around the project area that are known sources of motorized

sounds. The lines are drawn near the edges of the lake due to evidence from the photo that

snowmobiles often operate near the shoreline, however it is understood that snowmobiles can run

nearly anywhere on the lakes. Farther into this analysis these routes will be referred to as

Motorized Travel Routes or simply travel routes.

B. Sound Levels

Ambient Levels

During our research we found that a forested area under very calm conditions may have an

ambient decibel level more toward 30 dBA (EPA, 1974), but the conditions for the analysis were

tested on an ice covered lake and river. The measured background levels for the Royal River and

Royal Lake areas averaged between 33 and 42 dBA with no wind (Sound Test, Appendix C-2).

Measurements taken in 2009 where air temperatures were near zero degrees Fahrenheit

registered ambient levels from 37 dBA to 42 dBA. Those measurements taken in 2010 where

the air temperatures were near 32 degrees Fahrenheit showed the ambient level at 33 dBA.

Subsequent measurements in March 2011 with the more sensitive Larson Davis 831 meter

showed that daytime natural ambient sound levels to be a median level of 34 dBA (see Appendix

G for data). The daytime median level is used because this is when snowmobiles are likely to be

operated. The level used for this report will be the 34 dBA.

Figure D-5. Potential source locations of ambient sound audible into the BWCAW. Appendix C-3 contains photo points of winter use on these source locations.



Natural Ambient

While motorized sounds were present in the background, their sound levels were not the loudest

and hence were not those recorded on the sound meter. The measured levels of averages of 33-

42 dBA are also the levels for natural ambient. Wind gusts often caused spikes in the decibel

meter above 50 and sometimes above 60 dBA.

Audible Distances

Figure D-6 displays the sound test points (from Appendix C-2) with a yellow arrow drawn from

the snowmobile location as it was being operated on Little John Lake to the point it was barely

audible at the entrance of Royal Lake. This distance used the human ear for detection and GPS

for distance measurement, and accounts for the topography and forest between the source and the

detection point. The distance for the yellow arrow is the audible distance which was measured at

approximately 2,030 meters or 6,650 feet. According to the models in Appendix C-4, the

calculated decibel level at that distance should be around 22 dBA (a whisper is considered 20

dBA –MPCA, 1999). Site conditions of topography and vegetation, plus competing background

sounds reduced the audibility of the test snowmobile. The distance measured for the yellow line

on Figure D-6 is considered a realistic estimate of audible distance that takes into account site

conditions.

Figure D-6: Distance that a snowmobile could be heard or audible (from Appendix B Sound Test). Yellow arrow indicates distance of higher speed snowmobile traveling on a lake, which measured in a straight line, was 2,030 meters (using GIS technology). Red arrow indicates distance of slower speed snowmobile projected from Alternative 2 route, which measured 1,340 meters. Both distances were determined by the human ear in the sound test.



Area affected by current snowmobile use

For the purposes of this report the distance measured between the source on Little John and the

detection location was used as the distance a source could be heard if a person were in the

Wilderness, either on typical travel routes or if they found their way into the forest. This (yellow

arrow) was the distance used to determine the depth that background noise would travel and was

used to develop Figure D-7, Zone of audibility.

Once the distance a snowmobile could be heard or was audible was determined, then the area

within the Wilderness where snowmobiles that were operated where currently legal was

calculated. A map (Figure D-7) was created that used the 2,030 meter distance and plotted it

along the routes and locations that currently are legal and are known to have motorized use. This

demonstrates the area within the BWCAW that motorized sound can be heard2 (audible) under

existing conditions (including No Action). As can be seen, this zone covers the entire Royal

River and Royal Lake area. The area of this audible zone that is within the BWCAW was also

used as the analysis area to calculate effects to the Wilderness.

2 Snowmobiles can legally ride on the Canadien side of the international border continuing from North Fowl Lake to

Moose Lake and beyond. Therefore the zone of effect from snowmobile sounds could be carried along the border

several miles to the west. However as the zone began leaving to the area near the alternative routes, it was

determine to use the area shown as the analysis area for calculations.

Figure D-7: Zone of audibility for each alternative, and existing/ongoing snowmobile sounds.



Background Sound above Natural Ambient

The purpose of this section is to determine the distance it would take for the sound level to

reduce to the ambient of 34 dBA (roughly the mode natural ambient level). Motorized sound is

both audible and measurable above the “natural3” sound and therefore often is a part of the

background. Sound Points 1 and 10 measured levels of 55 dBA from Little John and North Fowl

Lakes respectively.

As mentioned earlier the decibel level of a snowmobile operated at recreational speeds on the

lakes including McFarland, North and South Fowl and Little John could be as high as 110 dBA,

however a more conservative 105 dBA was used in the formulas to develop Figure D-8. This

lower number was used to reduce the zone of impact under the existing condition which then

allowed for a greater contrast between sounds present under the existing condition and sounds

generated by the alternatives.

The effect that trees have on the distance sound will travel before decaying to ambient is roughly

half the distance of that where sound travels only through air. The area of wilderness affected by

current use of snowmobiles is 763 acres and is shown in Figure D-8 below. This distance

through vegetation was calculated using basic sound decay models as adjusted by related

research findings. If extrapolated the distance the 74 dBA snowmobile sound (measured from 50

feet; equivalent to 105 dBA at one foot) would travel through trees, until it was reduced to

ambient, would be approximately 270 meters. Through open air, sound would travel 540 meters

to reach natural ambient levels (based on the model in Appendix C-4). A summary of

calculations accounting for vegetation is included in Appendix C-5.

C. Frequency of Snowmobile Use

The numbers of snowmobiles traveling from McFarland to the Fowls was outlined in the 2005

EA as 25 to 30. For the purposes of conservative estimates of impact from the trails, 30 was

used as the number of sleds per day for three days per week.

D. Duration of Snowmobile Sound

At present, a snowmobile has to travel from McFarland to South Fowl Lake along a set of roads

and trails. Snowmobile sound may not be audible for the entire time the sled is operated on that

route, so only the portions of that route where the sound could be heard on Royal Lake was

measured for that parameter. That length of time for audible sound was 12.1 minutes of time for

one sled to make the trip. This results in 14 percent of the week having audible snowmobile

sounds from the existing McFarland to South Fowl route (Appendix C-5). Assuming two sleds

3 Natural sound conditions are when people with normal hearing can perceive nothing but the sounds produce by the

natural and cultural components (National Park Service, 1999)



per group the exposure would be 12.2 minutes per trip and would add to seven percent of the

week, including nights and weekends (see Table D-4 for comparison of routes).

Proposed Action Alternatives

A. Types of Sound

Alternatives 2, 3 and 4

Snowmobile use is common in the project area and therefore no new sounds would be produced

by this project.

B. Sound Levels, Audible Distance

Alternative 2

Figure D-6 displays the sound test points (from Appendix C-2) with yellow and red arrows that

show audible distances. These measurements used the human ear, not a decibel meter or a

model. These were the distances used to determine the depth that background noise would travel

and was used to develop Figure D-7, Zone of audibility.

Figure D-8: Zone of decay to ambient under existing conditions. The shaded areas show where the sound of a snowmobile could be measured above the natural ambient decibel levels (shown only within the Wilderness).



The red arrow was the distance, 1,340 meters, that the sound (102 dBA, measured at one foot)

broadcast from proposed Alternative 2 was audible. The test used recorded sound emitted from a

speaker at the given dBA levels to simulate the snowmobile sound level from a sled operated on

the proposed Alternative 2. Beyond that distance the sound of a snowmobile operated at trail

speed could not be heard. Since the sound was projected from the point closest to the Wilderness

boundary and where density of tree cover was at its least, plus there was very little tree cover

between the site of projection and the receptor site, this was considered a conservative estimate.

These parameters were measured under differing weather conditions from 2009 to 2010 but the

actual distance was measured to be the same regardless of weather conditions (Appendix C-2).

Alternative 3 & 4

When considering the audible distance of snowmobiles, Alternatives 3 and 4 would be the same

as No Action. This is due to the fact that the route locations are the same for No Action,

Alternatives 3 and 4. The distance for the yellow arrow measured was approximately 2,030

meters or 6,650 feet. It should be noted that the test snowmobile, operated on Little John Lake

outside the Wilderness, was driven at speeds from 15 to 25 miles per hour. Those speeds would

produce a lower operating dBA than a typical recreational rider would use.

Tilbury Trail

Audible distances for the Tilbury Trail are not displayed in this report. Snowmobile riders using

the former trail would have operated at speeds similar to Alternative 2 until they reached Royal

Lake and then speeds would have been similar to Alternatives 3 and 4. Therefore the audible

distances for the Tilbury Trail would have been estimated at 1,340 meters while in the wooded

section and 2,030 meters while on Royal Lake and Royal River. Since the trail coursed through

the area shown on Figure D-6, the zone of audibility would overlap with the No Action,

Alternatives 2, 3 and 4.

Audible area affected by current snowmobile use

Alternatives 2, 3, & 4

As can be seen, there would be no increase in the area of wilderness where a snowmobile could

be heard if Alternative 2 where in place. Figure D-7 is repeated here to show that the area of

audible snowmobile sound does not change from the current condition regardless of alternative.

Audible distance for No Action was measured at 2,030 meters which would be the same for

Alternatives 3 and 4. Alternative 2 audible distance was measured at 1,340 meters (Sound Test,

Appendix C-2). Using the 1,340 meter distance, a second zone was then overlayed onto the map

in Figure D-6 to outline where the audible sound that would be heard if Alternative 2 were in

use.



Area of Impact above Natural Ambient

Alternative 2

The sound test measured actual decibel levels at several points and noted the test points where

the sound projected from the proposed Alternative 2 trail were measurable on the EXTECH

HD600 decibel meter. The location where the sound was broadcast from was the point where

the proposed trail would be closest to the Wilderness boundary and where the vegetation would

provide the least reducing impact on the sound.

This test determined that point number 5 (see Figure D-9 below) was the furthest from the source

that the sound broadcasted could be measured above the ambient and it was measured at 44 dBA

on the first test and 43 dBA on the second test.

These 400 meters (1,310 feet) was the distance it would take sound from a snowmobile driven at

10 mph speeds along Alternative 2 route to decay to the ambient level. Calculating the decay

rate for the projected sound using the formula in Appendix C-4 results in a distance much less

than was measured. Main (2009) presents information on the differing effects of weather

Figure D-7. Zone of audibility for each alternative, and existing/ongoing snowmobile sounds.



(temperature, relative humidity, inversions, wind direction and speed, etc.) that can alter sound

travel, all of which explain why measured results are different than calculated. In addition, the

cliff face likely increased sound levels above the calculated value which are accounted for in the

measured value.

The GIS calculated area of wilderness that is above natural ambient level would be 799 acres.

Alternative 2 affects 36 more acres when compared to the No Action. Figure D-10 was

developed with an analysis similar to that which was done for Figure D-7. It displays the area

within the BWCAW that would be affected by sound levels above natural ambient. Figure D-

10presents the critical difference between Alternative 2 and No Action or Alternatives 3 and 4.

The deciding official will need to consider these 36 acres for this decision.

Figure D-9: Distance that a snowmobile could be measured above ambient level (from Appendix B Sound Test). Blue arrow indicates distance a snowmobile traveling Alternative 2, which measured in a straight line, was 400 meters (using GIS technology). This measurement was determined using a combination of the decibel meter for dB and a GPS unit for distance.



Alternative 3 & 4

The GIS calculated area of wilderness that is above natural ambient level would be 763 acres.

When compared to the No Action Alternative, Alternatives 3 and 4 would have no increase.

Figure D-11 was developed with an analysis similar to that which was done for Figure D-8. It

displays the area within the BWCAW that would be affected by sound levels above natural

ambient. In essence this is the same area affected by No Action since the routes that are in use

now would affect the same areas of wilderness as Alternatives 3 and 4.

Tilbury Trail

The GIS calculated area of wilderness that is above natural ambient level was 951 acres.

Constructing Alternative 2 would be a 152 acre reduction in impact. Constructing Alternative 3

or 4 would be a 188 acre reduction in impact. Figure D-12 was developed with an analysis

similar to that which was done for Figure D-8. It displays the area within the BWCAW that

would be affected by sound levels above natural ambient.

Figure D-10. Zone for decay to ambient for proposed Alternative 2. Similar to the existing condition, the shaded areas show where the sound of a snowmobile could be measured above the ambient decibel levels.



Figure D-12. Zone for decay to ambient from the former Tilbury Trail. For purposes of comparison, this map shows the effects from the former trail that has been closed as a part of the project.

Figure D-11. Zone of decay to ambient for Alternatives 3 and 4. The shaded areas show where the sound of a snowmobile could be measured above the natural ambient decibel levels (shown only within the Wilderness).



Summary on Area of Impact

No Action results in a minimum wilderness area of 763 acres that are impacted with snowmobile

sound that is measureable above natural ambient levels. A comparison of the totals for all

alternatives is presented in the Table D-3 below.

To understand Table D-3 you must consider all the locations that a legal motorized piece of

equipment could operate. For this particular analysis a snowmobile was considered the source of

the motorized sound being emitted. If you mapped the total area within the BWCAW (as part of

the project area) that snowmobile sound could be heard at decibel levels above ambient for each

of the routes under analysis, those areas are displayed in Figures D-10, D-11 and D-12 with the

corresponding acreages shown in Table D-3 (second column). The third column “Portion of the

Project Area Impacted by Sound” demonstrates the changes brought about by closing that trail.

The column on the right “Change from 2009” shows that Alternative 2 would expose 36 more

acres to sound levels above ambient than would No Action or Alternatives 3 & 4 (0.5 percent of

the project area). The 36 acres or 0.5 percent change in area of impact is the critical difference

between alternatives to be considered by the deciding official for the South Fowl Lakes

Snowmobile Access Project.

C. Frequency

The South Fowl Lakes Snowmobile Access EA and Decision Notice presented information that

the numbers of snowmobiles would not change based on the alternative selected. Total

snowmobile use (numbers of sleds) is not expected to change regardless of alternative.

Snowmobiling has and is occurring between McFarland and South Fowl Lakes and ice fishing is

still popular on South Fowl and other border lakes (though the route is unsafe). Monitoring

indicates that there has not been an increase in the number of snowmobiles operating between

McFarland and South Fowl Lakes when the Tilbury Trail was in use verses now since the that

trail has been closed. Similarly there is no data to suggest that constructing a safe route would

Table D-3. Impacts to Boundary Waters Canoe Area Wilderness from Sound Levels above Ambient.

Trail Status Calculation of acres

of Wilderness Impacted

Portion of Project Area Impacted by

Sound

Change from 2009 Level

Tilbury Trail 951 Acres impacted by sound

above natural ambient 12.8 % of the project

area

2.5% More acres

impacted

No Action,

Alternative

3 or 4

763 Acres impacted by sound

above natural ambient

10.3% fewer acres

impacted than Tilbury 2009 Condition

Proposed

Alternative 2

799 acres impacted by sound

above natural ambient

10.8% fewer acres

impacted than Tilbury

0.5% more acres

impacted.



increase the number of snowmobiles from present use regardless of alternative. The difference

would be in the route taken to approach and leave South Fowl Lake.

The Forest Plan indicates that the Superior National Forest may see an overall increase in

snowmobile use and that may occur in the South Fowl area, however that is not related to the

alternatives and there is no difference expected from any alternative.

D. Duration

Alternative 2

Snowmobiles operated on the route proposed in Alternative 2 would be audible within the

Wilderness for the entire length of the trail. The duration for audible sound was calculated for

the length of the entire trail at the speed of 10 mph for a time of 13.2 minutes per sled or 13.3

minutes for groups of two.

For Alternative 2 it was assumed that a snowmobile would travel at 10 mph and the distance the

sled would travel where the sound, as perceived on Royal Lake would be above natural ambient

was measured to be approximately 2,000 feet (Sound Test, March 2010). This is variable since

the trail would run parallel to the Wilderness border and these distances are measured from a

point where the sled would be close enough to create a decibel level above ambient level on

Royal Lake. Since the measurement of 2,000 feet was measured in the field with the sound

recordings, it takes into account all of the variables that affect sound travel such as vegetation

and topography4. Assuming 2,000 feet of distance traveled that would have sound levels above

ambient; the time one sled would be perceived above ambient would be 2.3 minutes. From the

South Fowl Lake Snowmobile Access EA, the number of snowmobiles traveling the route on

one day might be as high as 30 sleds, which means the duration of sound above ambient

(assuming the snowmobiles traveled as single sleds and not in groups) would be 69 minutes or

1.2 hours per day (30 sleds times 2.3 minutes per sled).

This time period would be reduced if the case were that sleds were grouped. If the sleds were

grouped in twos (data for visitor monitoring in the area suggests that sleds are most often

grouped in two or more, however there is not enough data to suggest an average number of sleds

per group, therefore an assumption is made of two sleds per group), the duration of impact would

be half or 36 minutes or 0.6 hours during one day.

Alternative 3 & 4

Alternatives 3 and 4 have differing lengths of trail at their beginning points as the trails depart

from McFarland Lake, however the length of trail where snowmobile sound may be audible

would be the same. Therefore these two alternatives are considered as having the same impacts

for sound duration. The audible distance measured with the sound test was applied to the

4 Measurements were made using GPS units taking simultaneous point samples as sound was broadcast from the

proposed trail to the Extech HD600 receiver.



Arrowhead Trail (County Road 16) where snowmobiles would travel away from McFarland

Lake and then to the trail from South Fowl Road coming down the hill toward South Fowl Lake.

Average speeds were applied to snowmobile use of the roads and trail to determine the length of

time snowmobile sound would be audible within the Wilderness. The calculated time for one

sled would be 12.1 minutes and for groups of two sleds would be 12.2 minutes.

The duration that snowmobile sound would be above ambient would be the same as No Action.

In other words, the proposed trail routes would not add any time above ambient levels.

Tilbury Trail

Duration of snowmobile sound that was audible while Tilbury Trail was used would be very

similar to Alternative 2, 13.2 minutes per sled.

The distance a sled would be operated and the sound would be above natural ambient would

have been 7.9 minutes per single sled or 8 minutes per group of two.

Summary for Duration Impacts

Table D-4. Comparisons of Time Sound Emissions would be Audible or above Ambient Levels as would be heard from Royal Lake.

Duration above Natural Ambient

Time in minutes

Total minutes per day

Total hours per day

Total Hour per week

Percent of Week

Alternative 2, 2,000 feet of trail Single Sled

2.3 min/sled 69 minutes 1.2 hours 3.6 hours 2.2%

Alternative 2, 2,000 feet of trail Two Sleds/group

2.4 /group * 36 minutes 0.6 hours 1.8 hours 1.1%

Alternative 3 or 4 No increase No increase

Tilbury Trail Single Sled


Tilbury Trail Two Sled/group

8.0 120 minutes 2.0 hours 6.0 hours 3.6%

Duration Audible**

Alternative 2; 2.2 miles** Single Sled


Alternative 2; 2.2 miles** Two Sled/group

13.3/group 199.5 minutes 3.3 hours 10.0 hours 5.9%

Alternative 3 or 4, No Action Single Sled


Alternative 3 or 4, No Action Two sleds/group

12.2/group 186 minutes 3.1 hours 9.2 hours 5.5%

*Assumes the snowmobiles are 6 seconds apart in travel.

** Duration would be same for Tilbury Trail



Impacts to Homeowners Through the public involvement process, we have become aware that home or cabin owners on

the south side of McFarland Lake are very concerned over the potential sound levels they would

experience if the trail were located along Alternative 3 or 4.

B. Sound Levels

No Action

The existing condition is where snowmobilers ride the Arrowhead Trail south to the South Fowl

Road and into South Fowl Lake. This alternative directs snowmobiles toward the private homes

on the south side. The closest distance to the homes of those commenting would be

approximately 760 feet which would project a calculated sound level of 41 dBA.

Alternative 2

Alternative 2 would direct snowmobilers toward the north side of McFarland which puts them

2,500 feet away if the snowmobiles ride the lake and 4,480 feet if they ride the roads from the

homes on the north side to the proposed trail head. At that distance the snowmobiles would

create a calculated sound level would reach the homes at a level of 26 to 31 dBA.

Alternatives 3 & 4

These alternatives direct snowmobiles to routes that are located between the private homes.

These routes exit McFarland Lake on a parcel of land that was acquired as a result of PL 95-495

with the purchase of what was known as Wilderness Retreat. This parcel is located between the

landowners who have concerns with sound levels, with the distance from the proposed trail to

their homes/cabins being approximately 150 feet. Experience shows that snowmobiles traveling

on the lake and exiting to the trail would be moving at a higher rate of speed while on the lake

and likely slowing as they ascend the driveway hill. However the power needed to ascend the

hill would likely cause increased engine speed and therefore noise levels. For the purposes of

this analysis, lower dBA were used for slower speeds. Anticipated decibel levels from

snowmobiles traveling at the higher speeds would be near or over 100-110 dBA assuming the 50

foot measurement would be a maximum of 78 dBA (Davis and Marietta, 2004). Calculated

sound levels (from Appendix C-5) that would reach the homes/cabins would be 55 dBA.

Homeowners outside their cabins would experience sound levels at this approximate level,

however when inside their cabins the walls of the cabin would reduce that level.

EPA (1973) discusses how the reducing effect of buildings is highly variable but an assumed rate

of reduction for homes built in winter climates with the windows closed would be 27 dBA.

Using that average, the homeowner while inside during the winter, would experience 14 dBA for

No Action, 0-4 dBA for Alternative 2 and 28 dBA for Alternatives 3 and 4.



Table D-5. Potential Sound Impacts to Homeowners.

Alternative Calculated Sound Impacts

Outside of Home Impact While Inside

No Action 41 dBA 14 dBA

Alterative 2 26 – 31 dBA 0 – 4 dBA

Alternatives 3 & 4 55 dBA 28 dBA

C. Frequency

No measurements for frequency of impact to the homeowners were completed. Snowmobiles

travel on McFarland regularly on weekends and the total numbers are not known. However

Alternative 2 would direct snowmobiles traveling to South Fowl on a route away from homes

and therefore would have a lower total number of contacts. Alternatives 3 and 4 would direct

snowmobiles on a route between the homes and therefore would increase the total number of

contacts.

D. Duration

No Action

The highest decibel level experienced from snowmobile use on the Arrowhead Trail is calculated

to be 41 dBA. That above the median natural ambient level of 34 dBA. The speed of

snowmobiles operating on Arrowhead Trail is not known, but it is expected that there would only

be a few seconds where the sound levels could be measured above natural ambient.

Measurements were not taken for duration of audible; however sound levels would start at 41

dBA and fade as the sleds traveled toward the south. Speed on the road would likely be higher

relative to Alternatives 2, 3 and 4 resulting in less audible time.

Alternative 2

At levels above natural ambient or background levels with snowmobile sound, there would be a

decrease in duration from No Action. All snowmobile sound levels would be below natural

ambient. Measurements were not taken for duration for audible; however sound levels would

start at 31 dBA and fade as the sled traveled toward South Fowl Lake. Speeds on Alternative 2

would be about 10 mph which are the slowest of any alternatives.

Alternatives 3 & 4

Snowmobiles would travel toward the homes with a decreasing speed as they reached the

shoreline. Sound would be elevated above ambient as they approached and then again as they

proceeded up the proposed route. Assuming an average speed of 30 mph as a sled comes from

the lake and 10 mph as it ascends the hill away from the lake, would compute to about 1.25

minutes of time the sound would be above natural ambient taking into account the effect of trees

that cover the hill going to the south. This would result in 37.5 minutes per weekend day of

sound above ambient if single sleds were encountered or 18 minutes if grouped in twos.

Measurements were not taken for duration of audible; however sound levels would start at 55



dBA and fade as the sleds traveled toward the south. Speeds are variable with some sections

near the homes being at 10 mph but higher on McFarland and on the Arrowhead Trail.

Summary of Sound Analysis

Using the District Court Judge’s criteria, the following conclusions can be made about the

impacts from sound caused by the proposed snowmobile routes from McFarland Lake to South

Fowl Lake.

Type or quality of sounds present in the background:

People conducting sound tests within the Boundary Waters Canoe Area Wilderness,

on the Royal River/Royal Lake, heard sounds of motorized equipment being used

around McFarland Lake including regular vehicles, snow plows, trucks and graders,

and snowmobiles.

Volume of sound present in the background:

When audible, the decibel levels of those sounds were less than the ambient dBA

levels.

Natural Ambient sound was recorded at a range from 33 to 41 dBA (and assumed to

be 34 dBA in the daytime).

Legal snowmobile use just outside the Wilderness border would likely have operating

level of 105 dBA (measured at one foot) which would decay with distance into the

BWCAW.

The volume of sound emitted from the proposed routes:

Snowmobile sound is present within the entire project area; therefore the proposed

action and alternatives would not add a new quality of sound.

The current level of sound above ambient level that is emitted into the BWCAW

effects approximately 2.5 percent fewer acres than when the Tilbury Trail was being

used.

Alternatives 3 and 4 would affect the same number of acres of the BWCAW of sound

above ambient as the current level.

Alternative 2 would affect two percent less area of the BWCAW with sound above

ambient compared to the Tilbury Trail and 0.5 percent more than the current level or

those projected for Alternatives 3 and 4.

Measured decibel levels from Alternative 2 when the wind was blowing from the

source toward the receptor would be 5 dBA above ambient as experienced on Royal

Lake. With no wind the dBA recording was 1-2 dBA above ambient.

Alternatives 3 and 4 would emit higher decibel levels toward the homes on

McFarland Lake compared to both the current level and Alternatives 3 and 4

(estimated to be 55 dBA).



The frequency of snowmobile sounds:

The number of snowmobiles is not expected to be different between alternatives,

including No Action.

Duration

There is a small difference in duration of the audible sound between Alternatives 2

and Alternatives 3 and 4 (including No Action) with Alternatives 3, 4 and No Action

being slightly shorter. This does not include audible sounds emitted into the

Wilderness and toward the homes on the south side of McFarland Lake while

machines are not using the trails or South and North Fowl Lake, it considers only trail

use.

Alternatives 3 and 4 do not increase the duration of sound above natural ambient

relative to No Action. The duration of sound above natural ambient that would be

projected through use of Alternative 2 would be up to 2.3 minutes per snowmobile

and up to 1.2 hours per weekend day. Actual experienced duration of sound level

above ambient levels would more likely be 0.6 hours (36 minutes) or much less per

weekend day.

Duration of sound above ambient that would be projected toward the homes on the

south side of McFarland would be 1.25 minutes per snowmobile or 0.63 hours per

day. Actual experienced duration of sound level above ambient levels would likely

be 0.34 hours or less per weekend day.

V. Effects to the BWCAW and Visitors

In this section of the report, information from the section IV Results is applied to the site

specific location of the Boundary Waters Canoe Area Wilderness to determine effects on the

wilderness. The starting point for this analysis is that snowmobile sounds are present and

audible throughout the project area. No change in the frequency of snowmobiles in the project

area is expected as a result of this project. Further, the snowmobile sounds from adjacent areas

outside the wilderness are audible within the wilderness above the natural ambient sound levels

as outlined in Figure D-8. Therefore there are no criteria for the quality (type) or frequency of

snowmobiles of sound since the issue is snowmobile sound and it already exists. The focus of

this section is directed at the impacts of volume or sound level including the area of the

wilderness affected by that sound level plus duration of sound as the key measures.

Direction from Wilderness Law

Our first concern was to determine what the inherent characteristics of wilderness are and how

would snowmobile sound affect those characteristics. Our first references were the two

wilderness laws. First is the original Wilderness Act that was passed in 1964 which provides



guidance for all Federal wilderness areas. Second is the BWCA Wilderness Act that was passed

in 1978 that applied only to the Boundary Waters Canoe Area Wilderness.

PL 88-577 or the 1964 Wilderness Act outlines characteristics of “wilderness” within Section 2

“Purpose”:

A wilderness, in contrast with those areas where man and his works dominate the

landscape, is hereby recognized as an area where the earth and its community of life are

untrammeled by man, where man himself is a visitor who does not remain. An area of

wilderness is further defined to mean in this Act an area of undeveloped Federal land

retaining its primeval character and influence, without permanent improvements or

human habitation, which is protected and managed so as to preserve its natural

conditions and which (1) generally appears to have been affected primarily by the forces

of nature, with the imprint of man's work substantially unnoticeable; (2) has outstanding

opportunities for solitude or a primitive and unconfined type of recreation; (3) has at

least five thousand acres of land or is of sufficient size as to make practicable its

preservation and use in an unimpaired condition; and (4) may also contain ecological,

geological, or other features of scientific, educational, scenic, or historical value.

“…Outstanding opportunities for solitude…” is the characteristic that the sound of machinery

from outside the Wilderness might affect and therefore is the characteristic that is analyzed with

this report.

A review of PL 95-495 or the 1978 BWCAW Act includes additional purposes for this

wilderness, but provides no further direction on wilderness characteristics to be analyzed during

the decision process.

Methodologies

Our second concern was to determine how to relate the impacts of sound to the opportunities for

solitude. There are no direct criteria established in law, policy or the Superior National Forest

Land and Resource Management Plan to determine the impacts sound could have on wilderness.

Therefore a look across other land management agencies, having a similar concern for solitude,

was done to provide some foundation for this assessment and determination.

The National Park Service when preparing management plans for Yellowstone National Park

(2008) and Grand Canyon National Park (1999) considered acoustical zones. Areas of the parks

where the levels of sound that would be within acceptable limits as related to the expected

experience of the visitor. Grand Canyon considered two zones. Zone one, or frontcountry,

where “…greater amount of human activity and consequently more limited expectation of

natural quiet…” “…while backcountry, whether wilderness area or not, has only foot trails for

use by visitors.”



In Yellowstone the National Park Service evaluated four management zones; Developed Area

which they equated to an ROS setting of Rural and Urban, Road Corridor which they equated to

and ROS setting of Roaded Natural, Transition Zone which was related to both Roaded Natural

and Semi-Primitive Non-Motorized ROS and finally Backcountry which was equated to

Primitive ROS (Winter Use Plan EA, 2008).

It should be noted that for both Grand Canyon and Yellowstone, the National Park Service was

creating a management plan that would provide guidance to the park managers. South Fowl EIS

is a site specific plan that does not set management direction but simply analyzes the effects of

alternative methods to implement a project. However Yellowstone sets a concept of measuring

sound levels as they relate to visitor expectations within each of their management zones. This

concept provides a method that can be used with the Forest Plan management areas. Following

the Court Order, we have assessed the changes in sound levels and duration of sound as related

to the visitor expectations outlined in the Forest Plan Wilderness Management Areas.

Effects on Wilderness Character “Opportunities for Solitude”

Setting

As outlined in the section on “Juxtaposition” the management area for this portion of wilderness

is Semi-primitive Non-motorized with the surrounding ROS outside the Wilderness being

Roaded Natural. From the Forest Plan the characteristics for Semi-primitive Non-motorized are

outlined as:

Desired Future… (5) Social Conditions: “Moderate to low opportunities for isolation

and solitude”… “Frequency of encountering others in the area: Moderate…” (Forest

Plan, Table BWC-1 Limits of Acceptable Change (LAC) Standards 3-66, 67)

“The Semi-primitive Non-motorized Wilderness MA is generally located along the main

wilderness travel routes, where a visitor can expect to encounter others and solitude is

not one of their highest expectations. Some, but not a high degree of challenge, risk and

freedom is provided here”. (Forest Plan, Page 3-45).

Changes in sound levels

No Action

Figures D-7 and D-8 display the locations of the Wilderness where a visitor would experience

motorized sounds both audible and above ambient from existing sources, regardless of the

alternative selected.

Alternative 2



During January 2009 measurements when conditions were calm but temperatures were near zero

Fahrenheit, there was a 1 dBA change from ambient caused by sound emitted from the proposed

trail. When a 6 mph wind was blowing from the source to the receptor on Royal Lake, there was

a 5 dBA increase. Tests in 2010 when temperatures were toward 32 degrees Fahrenheit the

increase was 2 dBA.

MPCA (1999) reports that generally a 3 dBA change is the threshold for perceiving a change in

sound. Therefore, a change of 3 dBA or less is rated as a negligible impact on solitude within

the Semi-primitive Non-motorized Management Area. MPCA reports that a 5 dBA change is

clearly noticeable. A 5 dBA change within the Semi-primitive Non-motorized Management

Area is rated as a minor impact on solitude. Therefore the impact of the change in sound levels

from Alternative 2 is rated as negligible to minor.

Alternatives 3-4

These alternatives use the same or similar travel corridors as No Action so there would be no

change in sound level under these alternatives.

Duration

Alternative 2

Alternative 2 audible sound duration of trail use would be less than No Action which could be

considered a positive change (decrease). However the duration of sound above natural ambient

(relative to No Action) is 2.1 percent for the most conservative case. Given a less conservative

and more probable case, the increase was 1.1 percent. Considering the area is Semi-primitive

Non-motorized and the site specific location, this change of one to two percent in duration of

sound would be considered negligible.

Alternatives 3 or 4

Alternatives 3 or 4 would have a slightly longer duration for audible time relative to Alternative

2 but the same as No Action and therefore there is no change. Similarly there would be no

change in the duration of sound relative to No Action and therefore this is no change.

Effects on Wilderness Visitors

The difficulty in determining the effects on people is that personal preferences play a strong role

in whether an experience is favorable or unfavorable. Miller (2007) discusses metrics and goals

for sound measurements, then concluded that “Noise metrics do not always relate well to human

experience.” Further Miller indicated through cognitive interviews with visitors to National

Parks, that their observations per hour and the sound levels of their observation related to their

level of “annoyance” caused by sound.



Figure D-13 (Miller 2007) demonstrates the correlation that the more noticeable the sound or

change in sound level is, the more annoyed the visitor became. In this study, we estimate that for

a wilderness visitor seeking solitude, the greater the sound level from snowmobiles would equate

to a greater level of annoyance. However, not all people that heard the sound considered it to be

annoying.

No Action

Visitors in the BWCAW near McFarland Lake and South and North Fowl Lakes then continuing

along the US/Canadian border (visitors within the blue shaded area of Figure D-7) would

experience snowmobile sound. Visitors within the shaded areas of Figure D-8 would experience

sound above the natural ambient level. However none of the alternatives would cause a change

from the existing condition for any of the alternatives. A person seeking solitude or escape from

motorized sounds would not find that place within the project area and the closer they were to ice

covered lakes, it is likely they would experience a greater level of annoyance.

Figure D-13: Visitors

“Annoyance” Miller sampled visitors in 39 National Parks to determine what percentage of visitors heard overflights of aircraft and what their level of annoyance was.



Alternative 2

The difference between this alternative and No Action would be for the visitor on Royal Lake.

Figure D-10 shows 36 more acres where sound would be above ambient and if a person were

visiting Royal Lake they would be in those 36 acres. Further, if a wilderness visitor was

camping on Royal Lake on a weekend, they may experience a higher level of annoyance by

snowmobile use of Alternative 2.

Alternative 3 or 4

If either of these were constructed, a wilderness visitor would hear the same sound levels and

experience the same level of annoyance as in No Action.

Conclusions on Effects to Wilderness Users

The data indicates there are insufficient winter wilderness visitors to Royal Lake to conduct a

valid survey. The EA indicated that the average number of permits for the John Lake Entry

Point within the winter is eight (more recent data suggests 15) for the entire winter. As noted in

the sound test, travel toward Royal River and Royal Lake is reasonably impeded by open water

and difficult walking conditions. Winter monitoring has not indicated that there has been any

fishing on Royal Lake and has noted the lack of tracks from human travel on foot, snowshoe, ski

or dogsled. Cross referencing the visitor use in this area with Millers graph (Figure D-13), the

very low number of people hearing the sound, equates to a level of annoyance that is very minor.

VI. Conclusions

This report has taken the direction from the Court Order and provided an analysis of the impacts

of sound in the Royal Lake area both that exist and the potential sounds from alternative

snowmobiles routes. From various points within the Wilderness, technicians measured the

sounds of operating snowmobiles on the east and west sides of Royal River and Royal Lake, plus

the recorded sound of a snowmobile from the hillside where Alternative 2 would be located.

Their measured sound levels take into account all the natural features present in the Royal River-

Royal Lake area and provide accurate results.

A. Type or Quality of Sound

Technicians working on Royal Lake and Royal River were able to discern that snowmobile and

other motorized sounds exist and are audible throughout the project area. Therefore construction

of any alternative would not add a new or different sound to the project area.

B. Sound levels

The natural ambient level of sound was measured at a range of 33 to 41 dBA, and a natural

daytime ambient level of sound was assumed to be 34 dBA based on measurements with a

Larson Davis 831 meter (other than sound point 2 where the sound of running water in the river



was recorded at 44 dBA). Snowmobile sounds from current sources outside the Wilderness (No

Action) are measured at levels above natural ambient. Sound Points 1 and 10 measured levels of

up to 44-55 dBA (9-17 dBA above the natural ambient at those points) from outside the

Wilderness. Sound projected from Alternative 2 route was measured 5 dBA above the natural

ambient level. The sound levels of snowmobiles from any alternative are not out of the range

that this area of wilderness is currently experiencing from snowmobile use.

C. Frequency

Snowmobiles are currently operated on McFarland and the border lakes (South, North Fowl

Lakes and beyond). Snowmobiles have historically traveled between McFarland and the border

lakes and the final designated route is not expected to change the frequency of travel between

those lakes.

D. Duration of sound

Alternative 2 would have a longer duration of sound level above natural ambient, while

Alternatives 3 and 4 would have longer durations of audible sound. The time snowmobiles are

on any trail between McFarland and the Fowls is calculated to be a small part of the week,

generally on weekends. Neither the audible time nor the duration of sound above ambient is out

of the range of existing snowmobile sounds for the project area.

Impacts from snowmobile sound: The research indicates this is a difficult impact to measure, it

is a personal perception. Comments on the South Fowl Lakes Snowmobile Access EA show that

people are sharply divided on the proposed routes. Current winter users of the area seemingly

are all snowmobilers and they indicate they are not negatively affected by sound. However,

wilderness users indicate they would be negatively affected just knowing the trail exists. Miller

sampled people to determine how annoyed they were with the sounds of motorized use (aircraft

for his work) and there was a correlation between the number of people who heard the sound to

their level of being annoyed. Alternative 2 does not exist so there is no sample of snowmobile

related annoyance was available to measure. Further, during the several trips to Royal Lake,

wilderness rangers did not record any foot traffic and therefore a sample of wilderness users was

not available. With virtually no wilderness users within this project area the impacts from sound

were not measureable.

The opportunities for solitude that exist within the project area contain the sounds of motorized

equipment, including snowmobiles. The changes brought about by any of the alternatives do not

exceed the expectations outlined by the Forest Plan Management Area for this project area.

Each of the impacts from the potential changes brought about by construction on a snowmobile

route was rated as very minor with the exception of the sound level coming from Alternative 2

toward Royal Lake. That impact was rated as minor when the wind was blowing from the trail

location toward Royal Lake.

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