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From: Panel RBT2 / Commission RBT2 (CEAA/ACEE)To: Panel RBT2 /
Commission RBT2 (CEAA/ACEE)Subject: Technical Data Report - Effects
of Meteorological Conditions on Sound Propagation from Roberts Bank
TerminalsDate: June 27, 2017 2:24:59 PMAttachments: Technical Data
Report - Effects of Meteorological Conditions on Sound Propagation
from Roberts Bank
Terminals.pdf
Dear Panel Members,
As requested, please find attached the Upland Noise and
Vibration Technical Data Report entitled
“Effects of Meteorological Conditions on Sound Propagation from
Roberts Bank Terminals” as
referenced in Table 9.3-1 of the Environmental Impact Statement.
The document will be posted to the
Registry shortly.
Review Panel Secretariat, Roberts Bank Terminal 2 Project |
Secrétariat de la commission
d'examen, Projet du Terminal 2 à Roberts Bank
c/o Canadian Environmental Assessment Agency | a/s de l’Agence
canadienne d'évaluation
environnementale
22nd Floor, 160 Elgin St. Ottawa ON K1A 0H3 | 160, rue Elgin,
22ième étage, Ottawa ON K1A 0H3
[email protected] / [email protected]
Tel: 613-957-0626 / toll free 1-866-582-1884 | Tél. :
613-957-0626 / sans frais: 1-866-582-1884
mailto:/O=EC/OU=NCR/CN=RECIPIENTS/CN=PANELRBT2_COMMISSIONmailto:[email protected]:[email protected]:[email protected]
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ROBERTS BANK TERMINAL 2
TECHNICAL DATA REPORT
Upland Noise and Vibration
Effects of Meteorological Conditions
on Sound Propagation from Roberts Bank Terminals Prepared for:
Port Metro Vancouver 100 The Pointe, 999 Canada Place Vancouver, BC
V6C 3T4 Prepared by: Wakefield Acoustics Ltd. 310-2250 Oak bay
Avenue Victoria, BC V8R 1G5 File: 302-042.02 March 2014
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation March 2014
Technical Report/Technical Data Report Disclaimer
The Canadian Environmental Assessment Agency determined the
scope of the proposed Roberts Bank
Terminal 2 Project (RBT2 or the Project) and the scope of the
assessment in the Final Environmental
Impact Statement Guidelines (EISG) issued January 7, 2014. The
scope of the Project includes the
project components and physical activities to be considered in
the environmental assessment. The scope
of the assessment includes the factors to be considered and the
scope of those factors. The
Environmental Impact Statement (EIS) has been prepared in
accordance with the scope of the Project
and the scope of the assessment specified in the EISG. For each
component of the natural or human
environment considered in the EIS, the geographic scope of the
assessment depends on the extent of
potential effects.
At the time supporting technical studies were initiated in 2011,
with the objective of ensuring adequate
information would be available to inform the environmental
assessment of the Project, neither the scope
of the Project nor the scope of the assessment had been
determined.
Therefore, the scope of supporting studies may include physical
activities that are not included in the
scope of the Project as determined by the Agency. Similarly, the
scope of supporting studies may also
include spatial areas that are not expected to be affected by
the Project.
This out-of-scope information is included in the Technical
Report (TR)/Technical Data Report (TDR) for
each study, but may not be considered in the assessment of
potential effects of the Project unless
relevant for understanding the context of those effects or to
assessing potential cumulative effects.
https://www.ceaa-acee.gc.ca/050/documents/p80054/97463E.pdf
https://www.ceaa-acee.gc.ca/050/documents/p80054/97463E.pdf
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - i - March 2014
EXECUTIVE SUMMARY
This Technical Data Report describes the outcomes of an
investigation into the effects of meteorological
conditions on the propagation of sound from the existing Roberts
Bank terminals. The investigation
included a review of the current knowledge of long range sound
propagation, particularly over water, and
employed that knowledge to illustrate the potential effects of
variations in meteorological conditions on the
levels of Port-related noise reaching the adjacent residential
areas to the east, along the Tsawwassen
Bluffs and on Tsawwassen First Nation land. The investigation
also included the use of commercial sound
propagation software to model the effects of variations in key
meteorological conditions on these
noise levels.
Distances from the eastern edge of the Deltaport Terminal to the
shoreline are in the range of 3.5 to
4.5 km. Over such distances, atmospheric absorption removes
virtually all higher-frequency sound energy
so that the noise reaching distant receivers has only middle and
low-frequency content, regardless of air
temperature and humidity. Lower to mid-frequency noise levels in
the closest residential areas are
determined in part by the noise levels being emitted by Port
operations, and in part by weather conditions,
namely wind direction, wind speed gradients and air temperature
gradients.
Results of the literature review indicate that sound travelling
long distances over open water may undergo
modest (2 to 3 decibel (dB)) amplification effects, compared to
noise levels experienced under neutral
atmospheric conditions, when the wind blows in the direction of
sound travel (downwind propagation), or
when positive air temperature gradients (temperature inversions)
are present. Sound levels at distant
receivers may be subjected to reductions of up to 10 to 20 dB
when the wind blows against the direction
of sound travel, or when strong negative air temperature
gradients (temperature lapses) exist, thereby
placing the receivers in a “sound shadow”. Finally, under
certain wind conditions, referred to as low level
jets, is it possible for substantial (10 to 15 dB) amplification
of sound to occur at large distances from a
water-based noise source, due to the confinement of sound waves
within a relatively narrow “channel” or
layer above the water surface.
The effects of upwind and downwind sound propagation in the
context of the Roberts Bank terminals
were modelled using three different meteorological algorithms
within the CadnaA sound propagation
software. This exercise yielded overall variations in received
noise levels between nominal worst-case
and best-case propagation conditions of between 8.7 and 11.7
dB.
Multi-day noise level histories recorded at two locations on the
Tsawwassen Bluffs by Wakefield
Acoustics Ltd. (WAL) in June and July of 2013, and at one
location by BKL Consultants Ltd. in July and
August of 2011, were reviewed and compared with wind direction
and other meteorological data collected
in the local area. The primary findings were that, while the
background noise levels from Roberts Bank
terminals operations at residences near the shoreline can show
hour by hour variations of 5 to 10 dB,
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - ii - March 2014
the daily average levels are quite consistent day to day. More
importantly, there is very little clear
correlation between background or average noise levels and
either wind direction or the CONCAWE
atmospheric stability class utilised by BKL as an indicator of
anticipated sound propagation efficiency.
The clearest evidence of such correlation was found in noise
data collected between June 4 and 6, 2013,
at Fred Gingell Park. In this case 12 hours of continuous
southeast winds (which would tend to support a
sound shadow) were followed by 25 hours of northwest winds
(under which any sound shadow would be
expected to disappear and perhaps be replaced by modest sound
amplification). The difference in
average background noise levels measured over these two extended
time periods, however, was only
3.3 A-weighted decibels (dBA), appearing to indicate that a
sound shadow had not existed during upwind
propagation.
This investigation has then revealed apparent meteorological
effects on the Roberts Bank terminals
sound levels experienced at the residential communities to the
east which, at 3.3 dBA, were not of
sufficient magnitude to be readily perceptible from one hour, or
one day, to the next. The ability to
uncover such effects, however, is confounded to some degree by
the fact that Port-related noise
emissions are themselves not entirely constant, so that
additional sources of variability may mask the
effects of meteorology on observed sound levels. In addition,
and particularly during the daytime, other
non-Port-related noise sources in the community can influence
the average noise levels measured. Any
correlation between Port-related noise and meteorological
conditions will then be most easily identifiable
during the nighttime hours. Finally, residences located at
greater distances (400 to 600 m or more inland)
from the Tsawwassen shoreline may experience larger variations
in noise levels from sources at the
Roberts Bank terminals (although likely at lower absolute noise
levels), due to the effects of the
intervening land forms on sound propagation.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - iii - March 2014
TABLE OF CONTENTS
EXECUTIVE SUMMARY
...............................................................................................................................
I
1.0 INTRODUCTION
..............................................................................................................................
1
1.1 PROJECT BACKGROUND
........................................................................................................
1
1.2 EFFECTS OF METEOROLOGY ON SOUND PROPAGATION - OVERVIEW
....................................... 1
2.0 REVIEW OF EXISTING LITERATURE AND DATA
.......................................................................
3
2.1 OUTDOOR SOUND PROPAGATION
...........................................................................................
3
2.1.1 Overview
................................................................................................................
3
2.1.2 Geometric Spreading
.............................................................................................
3
2.1.3 Atmospheric Absorption
.........................................................................................
4
2.1.4 Upward Refraction – Sound Shadows
...................................................................
4
2.1.5 Downward Refraction – Sound Amplification
......................................................... 5
2.1.6 Ground Effect Attenuation
......................................................................................
6
2.2 LONG RANGE SOUND PROPAGATION OVER WATER
................................................................
7
2.2.1 Overview
................................................................................................................
7
2.2.2 Low Level Jets
.......................................................................................................
7
3.0 METHODS
.....................................................................................................................................
10
3.1 STUDY AREA
.......................................................................................................................
10
3.2 TEMPORAL
SCOPE...............................................................................................................
10
3.3 STUDY METHODS
................................................................................................................
10
3.4 DATA ANALYSIS
...................................................................................................................
10
4.0 RESULTS
......................................................................................................................................
11
4.1 METEOROLOGICAL CONDITIONS IN THE STUDY AREA – OVERVIEW
......................................... 11
4.1.1 Prevailing Winds
..................................................................................................
11
4.1.2 Temperature Inversions Over
Water....................................................................
11
4.1.3 Occurrence of Low Level Jets
..............................................................................
12
4.2 WIND CONDITIONS DURING SPECIFIC PERIODS OF BASELINE NOISE
MONITORING .................. 12
4.2.1 WAL Baseline Noise Monitoring of July 22 to 24, 2013
....................................... 12
4.2.2 WAL Noise Monitoring of June 4 to 6, 2013
........................................................ 13
4.3 MODELLING THE EFFECTS OF METEOROLOGY ON SOUND PROPAGATION
............................... 13
4.3.1 CadnaA Sound Propagation Software
.................................................................
13
4.3.2 Approaches to Modelling Meterological Effects
................................................... 13
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - iv - March 2014
4.3.3 Modelling the Roberts Bank Study Area
..............................................................
14
4.4 OBSERVED EFFECTS OF METEOROLOGICAL CONDITIONS ON COMMUNITY
NOISE EXPOSURES 14
4.4.1 Fred Gingell Park, June 4 to 6, 2013
...................................................................
14
4.4.2 1043 Pacific Drive, July 22 to 24, 2013
...............................................................
15
4.4.3 476 Tsawwassen Beach Road, July 28 to August 11, 2011
............................... 15
5.0 DISCUSSION
.................................................................................................................................
17
5.1 KEY FINDINGS
.....................................................................................................................
17
5.1.1 Potential Effects of Meteorology on Sound Propagation
..................................... 17
5.1.2 Observed Effects of Meteorology on Noise Levels at
Tsawwassen Residences 18
5.2 DATA GAPS AND LIMITATIONS
..............................................................................................
18
6.0 CLOSURE
......................................................................................................................................
20
7.0 REFERENCES
...............................................................................................................................
21
8.0 STATEMENT OF LIMITATIONS
...................................................................................................
22
List of Tables
Table 1-1 Effects of Meteorology on Sound Propagation Study
Components and Objectives .......... 2
List of Appendices
Appendix A Figures
Appendix B Tables
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 1 - March 2014
1.0 INTRODUCTION
1.1 PROJECT BACKGROUND
The Roberts Bank Terminal 2 Project (RBT2) is a proposed new
three-berth marine terminal at Roberts
Bank in Delta, B.C. that could provide 2.4 million TEUs
(twenty-foot equivalent unit containers) of
additional container capacity annually. The project is part of
Port Metro Vancouver’s Container Capacity
Improvement Program, a long-term strategy to deliver projects to
meet anticipated growth in demand for
container capacity to 2030.
Port Metro Vancouver (PMV) has retained Hemmera to undertake
environmental studies related to the
Project. This Technical Data Report (TDR) has been prepared by
Wakefield Acoustics Ltd. (WAL), in its
role as a sub-consultant to Hemmera. This TDR describes the
results of an investigation into the effects
of meteorological conditions on the long-range propagation of
sound (noise) from the existing Roberts
Bank terminals to the neighbouring residential communities
located on the Tsawwassen Bluffs to the
southeast and Tsawwassen First Nation land to the east of the
terminals.
1.2 EFFECTS OF METEOROLOGY ON SOUND PROPAGATION - OVERVIEW
Due to the highly acoustically-reflective nature of water
surfaces, sound waves can generally propagate
more efficiently, with less loss of intensity with distance,
over bodies of water than over most land
surfaces. Residents of the Tsawwassen Bluffs and Tsawwassen
First Nation land are located
approximately 4 to 6 km from the existing Roberts Bank
terminals. Despite these relatively large
propagation distances, some residents report being disturbed by
noises created by Port-related sources
such as: ship engines; ship generators; train locomotives and
other diesel-powered equipment; and
various materials handling activities (bumps and bangs) at the
terminals (Municipality of Delta 2012, Port
Metro Vancouver 2012). Residents have also reported experiencing
substantial variations in the levels of
terminal-related noise that reach their residences. Some of
these reports have come from residents living
near sea level along Tsawwassen Beach Road and on Tsawwassen
First Nation land, while others have
come from residents located well above sea level on the bluffs
overlooking the BC Ferries and Roberts
Bank terminals. Residents living as far as 800 m from the bluffs
have reported being disturbed by such
noises (particularly intermittent/impulsive noises) (Economic
Planning Group 2013).
Noise monitoring has been conducted within the residential areas
around Roberts Bank on several
occasions (BKL Consultants Ltd. 2004, 2012) over the past decade
in relation to former and planned
future expansions to the Roberts Bank terminals. The most
extensive of these monitoring programs in
terms of duration was conducted by BKL Consultants Ltd. in July
and August of 2011. This program
included two weeks of continuous noise monitoring at three
community locations conducted in relation to
the Deltaport Terminal Road and Rail Improvement Project. (one
at the Tsawwassen Bluffs, one at the
Tsawwassen First Nation longhouse and one near the Roberts Bank
Rail Corridor). However, since none
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 2 - March 2014
of the past noise monitoring programs have been truly
“long-term” in that they have not extended over an
entire year or even an entire month, it is possible that noise
monitoring programs may not yet have
included periods when meteorological conditions were conducive
to the exposure of adjacent
communities to Port-related noise at, or near, its highest
levels. To address this potential monitoring gap,
the current study has explored the effects of variations in
meteorological conditions on sound propagation
from the existing Roberts Bank terminals to the Tsawwassen
Bluffs and Tsawwassen First Nation land.
The proposed scope of work for the Uplands Noise and Vibration
Impact Assessment component of the
RBT2 environmental studies included a field measurement-based
evaluation of the effects of
meteorological conditions on sound propagation in the study
area. However, there was concern about the
ability to access the terminal on an ongoing basis in order to
create an intense, highly-reproducible sound
that would permit the controlled assessment of sound level
variations within the community under a range
of meteorological conditions. There was also concern regarding
the likelihood of a suitably wide range of
weather conditions being experienced during the monitoring
period. Meteorological effects have
therefore been investigated through application of current
theoretical understanding of long-range sound
propagation over water as well as through computer modeling.
Table 1-1 below lists the main
components of this study, describes their objectives and
provides brief overviews of each.
Table 1-1 Effects of Meteorology on Sound Propagation Study
Components and Objectives
Component Objective Overview
Review of existing literature
Determine extent of existing scientific knowledge of long range
sound propagation over water.
Review literature regarding long-range sound propagation, in
particular the effects of meteorology on sound propagation over
water.
Scale of meteorological effects
Establish potential scale of meteorological effects from current
theoretical knowledge.
Basic principles of sound attenuation with distance, as well as
more unique phenomena that can occur near ocean shores, were
employed to establish scale of meteorological effects.
Establish potential scale of meteorological effects using
commercial sound propagation software.
Commercial sound propagation modelling and plotting software
(CadnaA, Version 4.4, by DataKustiks), was used in conjunction with
outdoor sound propagation algorithms contained in ISO 9613-2 (6) to
explore variations in community noise levels under various weather
conditions.
Examine historical baseline noise and weather data
Establish correlation between weather conditions and
Port-related noise levels.
Examine baseline noise monitoring data collected in the study
area since 2011 and corresponding weather data to determine to what
extent community noise exposures appear to correlate with wind
direction and speed records.
Study limitations List factors which may limit the accuracy of
study findings.
Factors, other than weather, which may contribute to noise level
variability in the neighbouring communities, are discussed.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 3 - March 2014
2.0 REVIEW OF EXISTING LITERATURE AND DATA
2.1 OUTDOOR SOUND PROPAGATION
2.1.1 Overview
There are four principal phenomena that influence the rate of
attenuation of sound levels with increasing
distance from the sound source, and ultimately the level (or
intensity) of sound reaching receptor points a
substantial distance (here 4 to 6 km) away (Embleton 1996,
Crocker 1998). These are:
Geometric spreading.
Atmospheric absorption.
Refraction effects due to wind and air temperature
gradients.
Interactions with the surface of the ground (ground effect) or
of water.
These effects will be briefly described below.
2.1.2 Geometric Spreading
Geometric spreading refers to the steady expansion of the total
area of a sound wave front over which its
energy is distributed as the wave propagates farther and farther
from its source (like the dimming of light
as one moves away from a lamp, or the expanding wavelets on a
pond when a stone is tossed in). As the
area of the wave front expands, the intensity of the sound
diminishes proportionately. For a small,
localised noise source (such as a gun muzzle or a truck or
locomotive exhaust), wave fronts spread
outwards in the form of spheres with ever-increasing radii (or
hemispheres, in the common case where
the sound source is located close to the ground surface). Since
the surface area of a sphere is given by
4π r2, (where r is the radius of the sphere), the rate of sound
attenuation with each doubling of distance
(DD) from such a point source is given by:
Spherical Spreading attenuation rate = 10 log [4π (2r)2/4π r
2] = 10 log [4 r
2/ r
2] = 10 log (4) = 6 dB/DD.
Similarly, with a “line” source of sound (like a busy highway,
or very long train), wave fronts spread
outwards in the form of cylinders of ever increasing radii.
Since the area of a cylinder is given by 2π r L,
where r is the radius and L the length of the cylinder, the rate
of sound level attenuation with each
doubling of distance from a line source of sound is given
by:
Cylindrical Spreading attenuation rate = 10 log (2π x 2r L / 2π
r L) = 10 log (2) = 3 dB/DD.
Therefore, for the noise sources that will be considered in the
analysis of sound propagation from the
existing Roberts Bank terminals and from the proposed RBT2, the
rate of sound attenuation with distance
due to geometric spreading alone will generally be between 3 and
6 dB per doubling of distance.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 4 - March 2014
2.1.3 Atmospheric Absorption
As sound waves pass through the atmosphere, energy is steadily
extracted from the waves by various
processes. Sound waves (which manifest themselves locally as
oscillations in the relatively static air
molecules) cause molecules of oxygen and nitrogen, as well as
water vapour, to vibrate and rotate –
effects which are referred to collectively as molecular
relaxation. The viscosity of the air also consumes
sound wave energy. The rate of atmospheric absorption varies
substantially with the frequency of sound
(being much larger at high frequencies than at low and middle
frequencies) and also depends on air
temperature, pressure and relative humidity. Global average
values for atmospheric absorption
(International Standards Organization (ISO). 1996. Standard
9613-2) range from 0.11 decibels per
kilometer (dB/km) at 63 Hertz (Hz.), to 0.4 dB/km at 125 Hz., to
2.4 dB/km at 500 Hz., to 18.8 dB/km
at 2,000 Hz., and to 129 dB/km at 8,000 Hz. After a sound wave
has travelled a long distance, very little
mid to high frequency sound energy remains. Therefore, most
Port-related sound heard at residences
4 to 6 km away from the Roberts Bank terminals will be in the
low to mid-frequency range.
While atmospheric attenuation rates clearly vary with
meteorological conditions, these variations are
much smaller for low-frequency sound. The primary focus of this
investigation, therefore, is not on the
effects of variations in atmospheric absorption rates, but
rather on the potentially much larger effects of
air temperature and wind gradients on sound propagation, as will
be discussed in the next sections.
2.1.4 Upward Refraction – Sound Shadows
Refraction in the noise context refers to the bending of sound
waves due to the presence of sound speed
gradients in the atmosphere near the ground. Such sound speed
gradients are in turn caused by
gradients in air temperature and/or wind speed with elevation
above the ground or water surface. Since
the speed of sound (which is 343 m/sec in dry air at 20 degrees
Celsius) increases as air temperature
increases, sound (which, in this context, can be considered to
behave like a ray) rarely travels in a
perfectly straight line.
Under calm daytime conditions, when the earth’s surface is
warmed by the sun, the air is warmer nearer
the ground than at higher elevations. Under such “temperature
lapse” conditions, the speed of sound is
greater near the ground than above it and, as a result, sound
waves are refracted, or bent, upwards and
away from the ground. Under temperature lapse conditions, a
“sound shadow” zone may develop, into
which relatively little acoustic energy can enter. Sound shadow
zones due to temperature lapses can
develop beyond a certain distance from, and in all directions
from, the noise source. Such conditions can
then lead to significantly reduced sound levels at large
distances from the source, compared to “neutral”
atmospheric conditions (i.e., with little or no wind speed or
air temperature gradients) under which sound
waves would follow a more or less straight path.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 5 - March 2014
Sound shadows can also occur when the wind is blowing in the
direction opposite to that in which sound
is propagating (i.e., winds from the noise receiver location
towards the source location) so that the speed
of sound relative to the earth is higher near the ground than
above it, causing sound waves to be
refracted upwards. In this case however, a sound shadow will be
experienced only by receivers located
upwind of the sound source. At receiver locations downwind of
the source, sound levels will either be
similar to, or higher than, those experienced under neutral
conditions. The formation of a sound shadow
due to wind and temperature gradients is illustrated in Appendix
A: Figure 1.
Refraction-created sound shadows as described above can
theoretically produce excess attenuations of
up to 30 to 40 dB compared to sound levels that would be
experienced under neutral atmospheric
conditions. However, other effects, such as atmospheric
turbulence and diffraction (which scatter sound
into the shadow zone) and surface, or creeping waves, which are
coupled to, and can propagate along
the surface of soft ground and into the shadow zone, impose a
practical limit of 15 to 20 dB on such
effects (NPL U.K. 2007).
2.1.5 Downward Refraction – Sound Amplification
There are two mechanisms by which the downwardly-refracted sound
waves associated with positive
(increasing with height) wind speed gradients or air temperature
gradients (i.e., temperature inversions)
can result in amplified sound levels at large distances. These
are discussed in this section and in
Section 2.2.2. The first and more familiar mechanism involves
sound waves being bent downwards to the
earth’s surface and then, upon reflection, bent downwards again
so that they eventually combine with the
direct but also downward bending wave. Because these direct and
reflected sound waves (it is helpful to
think of them as “sound rays” in this situation) follow quite
different paths in arriving at the receiver
position, their phases are sufficiently randomised by
atmospheric turbulence that they combine
energetically. According to ray theory (Johansson 2003), at most
four such reflected rays are possible
between any unique source and receiver locations. Therefore,
compared to the neutral atmosphere
situation where a maximum of two sound paths are possible (one
direct and one reflected), the maximum
amplification of sound levels that can occur under such downward
refraction conditions is given by –
10 log (4 paths/2 paths) = 10 log (2) = 3 dB.
This upper value can only be approached when the intervening
surface is hard ground, water or ice. Such
amplification effects under soft ground conditions are smaller
as energy is lost from the sound waves
when they encounter such surfaces.
When a wind speed gradient is the cause of such downward bending
of sound waves, the zone of sound
amplification occurs only in the downwind direction from the
source. However, if the downward bending
is caused by an air temperature inversion, then the sound
amplification occurs in all directions around
the source.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 6 - March 2014
2.1.6 Ground Effect Attenuation
If sound is considered to behave as “rays” spreading out
uniformly in all directions from a source, then it
can be imagined that under neutral atmospheric condition, there
will be one sound ray that travels
directly, in a straight line, from this source to a receiver
located some distance away and a modest
distance above the intervening ground. There will be another
ray, emitted at an angle slightly below the
horizontal, that will encounter the ground at a point roughly
midway between source and receiver and
be reflected upwards so as to arrive at the receiver point very
slightly after the direct ray (Appendix A:
Figure 2). This small time delay is a result of the slightly
greater path length that the reflected ray follows.
If the intervening ground is hard and acoustically reflective,
such as concrete, hard-packed earth, ice or
water, then the reflected sound will arrive at the receiver
having suffered little or no loss of energy, and
only a minor phase shift. Therefore, in the hard ground case,
the direct and reflected waves combine
constructively, producing a small (less than 3 dB) increase in
sound level at the receiver, compared to the
level that would be experienced if the source and receiver were
both located far above ground and no
significant reflected sound wave existed. Machinery is commonly
operated on acoustically reflective
surfaces; therefore, ground-reflected sound energy is often
included in the reference noise emissions for
such equipment.
When the intervening ground between source and receiver is
“acoustically soft”, such as lawns,
grassland, farmlands, forests and snow, the reflected sound will
be partially absorbed and significantly
phase-delayed, so that when the direct and reflected waves
combine at the receiver, they do so
destructively. That is, when the acoustic pressures associated
with the two waves arrive at the receiver,
they are largely “out-of-phase” (i.e., one is positive – an
“over-pressure”, while the other is negative – an
“under-pressure” or rarefaction) and, as a result, largely
cancel one another at the receiver location. The
sound energy is not actually dissipated (destroyed) in this
process, but it is locally cancelled, much in the
manner that sound cancellation headphones and other active noise
control technologies create local
zones of quiet by generating “out-of phase” sound waves to
cancel the sound waves generated by the
actual noise source. In outdoor sound propagation, this sound
wave cancellation phenomenon is known
as “ground effect”. This effect is frequency dependent, with the
sound frequencies experiencing the
largest cancellation depending on the specific nature (acoustic
impedance) of the soft ground surface
involved. Ground effect tends to be largest in the low-mid (200
to 1,000 Hz.) frequency range within which
it can range from 10 to 20 dB, or more. The magnitude of the
ground effect increases as the elevations of
the sound source and/or receiver relative to the ground
decrease.
Under high tide conditions, the intervening surface between the
Roberts Bank terminals and the
residential areas along the shoreline to the east is water, and
therefore acoustically hard. During an ebb
tide, it is expected that the sediment surface across the tidal
flat would still be relatively hard acoustically,
particularly in areas where the sediments remain saturated very
near the sediment-air interface.
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Ground effect tends to occur most prominently under neutral,
calm wind conditions when both direct and
reflected sound waves follow paths close to the ground, and
hence travel through similar portions of the
atmosphere so that introduced phase differences due to
atmospheric turbulence are minimized. Ground
effect can be essentially lost under downwind sound propagation
or temperature inversion conditions,
both of which create downward bending sound waves due to their
positive (increasing with height) wind
speed or temperature gradients. Under such conditions, sound
waves tend to follow downward arching
paths relatively high above the earth in reaching distant
receivers, thereby largely avoiding the
cancelation effects experienced by waves traveling close to soft
ground. The existence of ground effect,
and its loss under the above conditions, together with upwind
sound shadow effects, are largely
responsible for the variations experienced in noise levels
received from distant noise sources over soft
ground. However, since ground effect does not occur over highly
sound-reflective surfaces like water, it is
not expected to influence the reported variations in Roberts
Bank terminals activity noise levels, as
received at residences near the waterfront within
Tsawwassen.
2.2 LONG RANGE SOUND PROPAGATION OVER WATER
2.2.1 Overview
In the past decade, considerable investigation has been
conducted into long-range sound propagation
over water, primarily in relation to the exposure of coastal
communities to the noise of offshore wind
turbine farms (Johansson 2003, Boue 2007, Bolin 2009). This
research has been directed at developing
best practices for monitoring noise from such wind farms and
accurate models for predicting the noise
levels to be expected at distant receivers under various
meteorological conditions. All of the sound
attenuation and amplification phenomena described in Section
2.1, with the important exception of
ground effect, can be experienced during the propagation of
sound over open water. However, there is an
additional phenomenon, referred to as a Low Level Jet, that has
been identified and discussed as part of
these wind farm noise studies which, to some degree, is unique
to coastal regions and hence relevant
both to noise from offshore wind farms and marine terminals such
as those at Roberts Bank. Low Level
Jets are described in Section 2.2.2.
2.2.2 Low Level Jets
Low level jets (Johansson 2003, Boue 2007, Bolin 2009) are
strong winds blowing at relatively low
altitudes, and are typically observed over large flat areas such
as oceans, seas and deserts. They can
arise under at least two conditions, known as ‘internal
oscillations’ and ‘land sea breezes’.
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Low level jets may arise in conjunction with inertial
oscillations, which occur when warm inland air flows
out over a cold water surface. Because of the inherent
atmospheric stability that develops when a cold
layer of air near the water surface is overtopped by a warmer
layer (here encroaching from the land),
there is little or no thermal mixing so that turbulence tends to
die away in the layer of air nearest the
water. Without turbulence, shear stress between layers of air
near the surface approaches zero and wind
speed is able to increase dramatically with height. Appendix A:
Figure 4 shows an example of the type
of vertical wind profiles that can exist under such conditions.
It is seen that wind speed increases
rapidly with height until, at about 200 m above the water, it
begins to decrease again over approximately
the next 800 m.
The second possible cause of low level jets are the more
familiar land-sea breezes. During the daytime,
the sun warms the land and the warmer, lighter air near the land
begins to rise. As the warm air over the
land rises and spills out over the adjacent ocean, cooler air
from near the ocean surface begins to flow
inland to replace the rising warm air, giving rise to a
‘sea-breeze’. During the nighttime the reverse can
occur - air over the land cools and sinks and flows out over the
sea surface giving rise to a ’land breeze‘,
while at higher altitudes, warmer air flows in from the sea and
over the land. A sea breeze-related wind
speed profile is shown in Appendix A: Figure 5.
Wind speed profiles associated with low level jets, (as seen in
Appendix A: Figures 4 and 5), have the
following effects on sound propagation:
Near the ocean surface, wind speed increases rapidly with height
so that sound waves travelling
in the downwind direction are refracted strongly downwards
towards the ocean surface.
Above a certain elevation the wind gradient reverses, so that
wind speeds begin to decrease with
increasing height and sound waves begin to be refracted upwards
away from the ocean.
The effect of such a bifurcated wind speed profile is to create
an acoustic “shadow zone” well
above the earth in the downwind direction and, at lower
elevations, to constrain the expanding
sound waves to an atmospheric layer of limited height. As a
result, beyond a certain distance
from the source, these constrained sound waves begin to
experience geometric spreading that is
more cylindrical in nature than spherical.
The key effect of low level jets is that they reduce the rate of
attenuation of sound levels with distance
from the source. The distance beyond which the expanding sound
wave front begins to look more like a
section of cylinder, or annulus, than a sphere depends upon
local weather conditions and the strength of
the low level jet, but it has variously been indicated as being
from 200 to 700 m (Boue 2007). Beyond this
distance, the nominal sound attenuation rate due to geometric
spreading alone will decrease from 6 to
3 dB/DD. The following expression (Johansson 2003) can be used
to estimate the total decrease in
sound levels (at any distance beyond the spherical/cylindrical
spreading transition) due to geometric
spreading under low level jet conditions.
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Lp = Lw – 20 log (r) – 8 - ∆La - 10 log (r/rtrans) dB.
Where: r = source receiver distance (m);
Lp = sound pressure level at distance r;
Lw = sound power level of source;
8 dB is a constant = 10 log 2π;
∆La = attenuation over distance r due to atmospheric absorption;
and
rtrans = distance from source to point of transition from
spherical to cylindrical spreading.
It may then be seen that if r is 4,000 m and rtrans is taken as
700 m, the sound level under such a low level
jet condition may be estimated as:
Lp = Lw – 20 log (4000) – 8 - ∆La - 10 log (4000/700) dB
= Lw – 72 – 8 - ∆La – 7.5 dB
= Lw – ∆La – 87.5 dB
In order to estimate the effect of such a low level jet on sound
levels at a receiver 4 km away, we may
then calculate the sound level that would exist at the same
distance r, in the absence of a low level jet.
Lp = Lw – 20 log (4000) – 8 - ∆La
= Lw – 72 – 8 – ∆La dB
= Lw – ∆La – 80 dB
Under the above conditions, the low level jet effect is then
predicted to be 87.5 – 80 = 7.5 dB. If by
comparison, rtrans is taken to be 200 m and the source receiver
distance is 5 km, then the low level jet
effect would theoretically be much larger, more specifically 10
log (5,000/200) = 14 dB.
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3.0 METHODS
3.1 STUDY AREA
The area encompassed by this investigation into long range sound
propagation from the Roberts Bank
terminals includes the terminals themselves, the intervening
ocean and the lands surfaces within Delta
and the Tsawwassen Bluffs to the northeast, east and southeast
of the terminal that are within a radius of
approximate 6 km from the centre of the terminal. (See Appendix
A: Figure 9).
3.2 TEMPORAL SCOPE
The analyses provided herein apply to current conditions at
Roberts Bank terminals with regard to Port-
related noise transmission. Since the overall objective is to
provide a strong theoretical and pragmatic
understanding of the influence of meteorological conditions on
especially landward noise propagation, the
interpretations and conclusions are expected to be applicable
into the foreseeable future.
This investigation does not consider possible changes in
climatic conditions and the associated
meteorological influences on noise propagation between the
present and future (e.g. 2030).
3.3 STUDY METHODS
The study methods involved the completion of the following
tasks:
Review literature regarding long range, outdoor sound
propagation, particularly over water.
Apply knowledge acquired from literature review to estimate the
potential magnitude of
meteorological effect on sound propagation within the study
area.
Analyse meteorological data collected at two weather stations in
the study area to determine
prevailing wind patterns in relation to Roberts Bank terminals
and the communities to the east.
Utilise commercial sound propagation software (CadnaA by
DataKustiks) to model the range of
sound levels to be expected in residential communities under
various meteorological conditions,
as forecast using three different meteorological effects
algorithms.
Review noise level histories recorded in the study area since
2011 to reveal degree of correlation
between wind conditions and noise exposures in the Tsawwassen
Bluffs area.
3.4 DATA ANALYSIS
Data analysis for this study was limited to the generation of
statistical distributions of wind directions
versus time as collected at the Westshore meteorological station
located at the west end of the BC
Ferries terminal and at the Sand Heads Light House, located at
the mouth of the South Arm of the Fraser
River. Wind data were scrutinised for the periods during which
WAL conducted baseline noise monitoring
in June and July, 2013. These data were visually examined in
conjunction with the noise level histories to
determine whether or not there is a correlation between wind
conditions and background or average
noise levels at receiver/monitoring sites in the Tsawwassen
Bluffs.
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4.0 RESULTS
4.1 METEOROLOGICAL CONDITIONS IN THE STUDY AREA – OVERVIEW
4.1.1 Prevailing Winds
Appendix A: Figure 6 shows wind roses generated from wind
direction and speed data collected
throughout 2010 at the meteorological station located near Berth
5 at the west end on BC Ferries
terminal. The prevailing winds were from the southeast and
east-southeast, with opposing winds blowing
somewhat less frequently from the northwest and west-northwest.
These are the assumed typical
prevailing winds direction for locations along the shores of
Georgia Strait (Salish Sea), where winds most
commonly blow up and down the straight. The most southerly
Portions of the Tsawwassen Bluffs area
(approaching the U.S. border) are frequently either directly
upwind of, or downwind from, the existing
Roberts Bank terminals.
Residences at the northern end of the Tsawwassen Bluffs (near
the BC Ferries causeway) are located
roughly 45º offset from the prevailing wind direction, and their
locations are only infrequently in a direct
upwind or downwind direction from the Roberts Bank terminals.
Tsawwassen First Nation residences
(which are largely east-northeast of the terminals), are roughly
90º off the prevailing wind direction and so
are frequently in a crosswind direction with respect to the
terminals. Also note from Appendix A:
Figure 6 that the observed “Frequency of Calms” during 2010 was
very low (1.3%).
Based on the 2010 wind rose, terminal noise as perceived by
residents of the mid and southern portions
of Tsawwassen Bluffs may be subject to some degree of sound
shadow attenuation approximately 40%
of the time. Sound from the Roberts Bank terminals must then
travel against the prevailing southeasterly
winds to reach these areas. Conversely, for about 20% of the
time, sound from the terminals must travel
downwind in reaching the Tsawwassen Bluffs, so that modest
amplification of terminal noise (compared
to the levels observed under neutral atmospheric conditions) may
occur. On this basis, substantial
variation in Roberts Bank terminals noise levels reaching
Tsawwassen Bluffs under upwind (SE) and
downwind (NW) conditions could be expected (with an upper limit
of 15 to 20 dBA), depending largely on
the strengths of the sound shadows that are generated to the
southeast of the terminals.
4.1.2 Temperature Inversions Over Water
Data showing the prevalence of air temperature inversions over
the ocean around the Roberts Bank
terminals were not available. For most of the year, however, the
ocean water would be colder than the air
above, so that during periods of little or no wind, a stable
temperature inversion could be created in the
layer of air adjacent to the water surface. Such an inversion
would then have the effect of amplifying
terminal noise levels by up to 3 dB in all directions from the
source and beyond a distance of several
hundred meters.
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4.1.3 Occurrence of Low Level Jets
As discussed in Section 2.2.2, low level jets (associated with
either sea breezes or inertial oscillations
leading to strong positive wind speed gradients near the surface
of open water) can increase the noise
levels from sources well out to sea as perceived by receivers on
the shoreline. It is not known
whether such wind conditions actually develop in the study area.
The following lines of evidence are
relevant, however:
Should sea breezes develop along the shores of Tsawwassen during
the warmer months, they
would blow more or less directly onshore and could then result
in enhanced propagation of
terminal noise towards both the Tsawwassen Bluffs and Tsawwassen
First Nation land. Based on
the 2010 wind rose shown in Appendix A: Figure 6, winds blew
from directions which could be
considered “onshore” (i.e., WNW, W, WSW and SW) for a total of
19% of the time. However,
without a detailed analysis of wind patterns hour by hour and
the associated wind speed profiles,
it is not known whether these winds were truly sea-breezes or
simply westerly winds. In either
case, some increase in terminal noise levels, compared to those
occurring under neutral
conditions, would be expected at residences near the shoreline
under these conditions.
Low levels jets associated with inertial oscillations could
conceivably occur in the study area, with
warm air from the flat lands of Delta to north of the Tsawwassen
Bluffs flowing out over the much
cooler ocean water. However, if a low level jet was to be
created in this way, it would tend to blow
from the noise receiver areas on land towards the noise source
areas offshore. As a result,
it would be expected to contribute to the formation of a sound
shadow at receivers on
Tsawwassen First Nation land rather than noise amplification due
to a transition from spherical to
cylindrical wave spreading.
4.2 WIND CONDITIONS DURING SPECIFIC PERIODS OF BASELINE NOISE
MONITORING
4.2.1 WAL Baseline Noise Monitoring of July 22 to 24, 2013
In July of 2013 WAL conducted baseline noise monitoring at
several locations in the Tsawwassen Bluffs
and on Tsawwassen First Nation land. During the 48-hour
monitoring period from July 22 to 24 2013,
five ships came and went from Deltaport. One of these, the
Hanover Express, was reported by residents
to be particularly noisy. This was the reason for monitoring on
these dates. Meteorological data collected
at the Canadian Government’s Sand Heads Light House (located off
the mouth of the Fraser River’s
south arm, approximately 6 km north of Deltaport) were used to
establish the wind direction distributions
that existed during this specific noise monitoring period. The
wind direction distribution for the 48-hour
period from 11:00 AM July 22 to 11:00 AM, July 24, 2013 over
which WAL conducted baseline noise
monitoring is shown in Appendix A: Figure 7. During
approximately 29 of the 48 hours (60% of the time),
winds were generally from the southeast and there were no hours
during which the prevailing wind
direction was from the northwest. Such a wind distribution would
then be expected to have supported the
creation of an acoustic shadow zone in the Tsawwassen Bluffs
area.
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For a total of seven of these 48 hours (15% of time), winds blew
from the SSW and south. During these
hours, sound travelling from the terminals to Tsawwassen Bluffs
could be considered to be in a crosswind
situation, during which terminal noise would not be expected to
have been either amplified or diminished
due to wind effects. Finally, for five hours (10% of time) the
prevailing winds were from the WSW so that
terminal noise could be considered to be traveling downwind
towards receivers on Tsawwassen First
Nation land and, as such, could be subject to a minor
amplification effect.
4.2.2 WAL Noise Monitoring of June 4 to 6, 2013
In June 2013, WAL conducted continuous noise monitoring over
48-hour periods at four locations in
adjacent communities (three of which are shown in Appendix A;
Figure 9) to assist Port Metro
Vancouver in identifying optimal locations for permanent noise
monitoring stations in the vicinity of the
Roberts Bank terminals. From approximately 11:00 AM, June 4 to
11:00 AM, June 6, 2013, wind direction
data collected at the Sand Heads Light House (Appendix A: Figure
8) showed that for 28 of the
48 hours (56% of the time), winds blew generally from the
northwest (placing the Tsawwassen Bluffs in a
downwind condition associated with a minor sound amplification),
while for 8 of the 48 hours (17% of the
time) they blew generally from the southeast (upwind conditions
potentially associated with sound
shadow formation). This wind distribution was essentially the
opposite of that which was observed during
the baseline noise monitoring of July 22 to 24, 2013.
4.3 MODELLING THE EFFECTS OF METEOROLOGY ON SOUND
PROPAGATION
4.3.1 CadnaA Sound Propagation Software
Sound propagation over long distances can be predicted using
specialised modelling and contour plotting
software such as CadnaA. Within CadnaA, sound propagation
effects are modelled using ISO 9613-2.
This software allows the inputting of various sound source
characteristics, source and receiver locations,
intervening terrain characteristics and meteorological
conditions in order to generate sound level contours
over the desired study area.
4.3.2 Approaches to Modelling Meterological Effects
In utilising ISO 9613-2 within CadnaA, users may select between
three different approaches that have
been developed to account for the effects of meteorological
conditions on outdoor sound propagation.
The first two, namely LfU Bayer and LUA NRW, are European
algorithms which account only for the
effects of wind direction and hence may be applied to sound
propagation over water or land. The third,
approach, CONCAWE, accounts for vector wind speed as well as the
stability of the atmosphere in the
local area. Atmospheric stability itself depends on wind speed
as well as cloud cover conditions. The
CONCAWE system utilises three atmospheric Pasquill Stability
Categories (Unstable, Normal and Stable)
in combination with six vector wind speed ranges to define six
Meteorological Categories. Category 1 is
the least favourable to sound propagation (i.e., lowest noise
levels at distant receivers), Category 4 is
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neutral, having no effects on propagation, and Category 6 is
most favourable to propagation (i.e., highest
noise levels at distant receivers). However, because the CONCAWE
approach is based on empirical
sound propagation data collected exclusively over land, and
because the Pasquill Stability Catagories
were similarly developed in relation to ground, not water,
surfaces, the CONCAWE approach has not
been applied here.
4.3.3 Modelling the Roberts Bank Study Area
A CadnaA model of the study area was developed and all three of
the above meteorological effects
approaches have been examined. In each case, the CadnaA model
was calibrated so as to generate the
same representative level of Roberts Bank terminals noise,
specifically L90 42.8 dBA, at the same
receiver location, 1043 Pacific Drive (see site plan in Appendix
A: Figure 9). This noise level is
representative of background levels observed during nighttime
hours in the Tsawwassen Bluffs due to
ongoing terminal operations and was generated using average
meteorological conditions as defined by
the 2010 wind rose (Appendix A: Figure 6). Parameter values
corresponding to “most-favourable” and
“least-favourable” propagation conditions were then inputted
into the model for each of the three
meteorological effect approaches.
The results of this exercise are summarised in Appendix B: Table
1. The total variation in Roberts Bank
terminals background sound levels at the Tsawwassen Bluffs
between most favourable and least
favourable sound propagation conditions, as computed using the
LfU Bayer and LUA NRW
meteorological effects approaches, ranged from 8.7 dBA for the
LUA NRW approach to 9.8 dBA for the
LfU Bayer approach.
4.4 OBSERVED EFFECTS OF METEOROLOGICAL CONDITIONS ON COMMUNITY
NOISE EXPOSURES
4.4.1 Fred Gingell Park, June 4 to 6, 2013
Based on the variations in wind conditions observed during the
June 4 to 6, 2013 baseline monitoring
period described in Section 4.2.2, it might be expected that the
background noise levels generated at the
Tsawwassen Bluffs by ongoing Roberts Bank terminals operations
would exhibit pronounced variations
correlated with the observed variations in wind direction. Some
evidence of this is provided by the noise
level histories recorded from June 4 to 6 at Fred Gingell Park.
Fred Gingell Park (Appendix A: Figure 9)
is located just west of English Bluff Road between 2nd
and 3rd
Avenues and lies along an east-by-
southeast bearing from the Roberts Bank terminals. The noise
level histories recorded at Fred Gingell
Park from 11:00 AM, June 4 to 11:00 AM, June 6 are shown in
Appendix A: Figures 10 and 11.
The background noise levels, as represented by the L90, (i.e.,
that sound level which, during the
monitoring period of interest, was exceeded for 90% of the time)
measured from June 4 to 6 do show
some correlation with the wind patterns recorded at Sand Heads
during that period. More specifically,
during the 12 hours between 9:00 PM on June 4 and 9:00 AM on
June 5, winds blew generally from the
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southeast. The average background noise level at Fred Gingell
Park during these, largely nighttime,
hours was L90 38.4 dBA. At about 10:00 AM on June 5, the winds
reversed and then blew consistently
from the northwest for the next 25 hours, ending at 1:00 PM on
June 6. The average background noise
level over this 25 hour period was L90 41.7 dBA. Assuming that
the background noise levels at Fred
Gingell Park were controlled by Roberts Bank terminals
operations and that the noise emissions from
these operations were essentially constant, then the average
effect of the reversal of prevailing winds
(i.e., first upwind and then downwind sound propagation) on
Port-related noise levels over these periods
was 3.3 dBA.
4.4.2 1043 Pacific Drive, July 22 to 24, 2013
Sand Heads Light House wind records for July 22 to 24, 2013 may
be compared with noise level histories
(Appendix A: Figures 12 and 13) measured over this period at
1043 Pacific Drive located on the
Tsawwassen Bluffs almost due east of the Roberts Bank terminals.
With the exception of two brief
periods around 2:00 PM on July 22 and 1:00 AM on July 24,
background noise levels (L90’s) were quite
steady. This is expected since, in reaching this monitoring
location, terminal noise must travel in a
direction roughly perpendicular to the prevailing winds, so that
neither upward nor downward sound
refraction will tend to occur with any regularity. However for a
few brief periods (9:00 PM on July 22,
8:00 PM on July 23, and 8:00 AM on July 24), the wind blew from
the east, while for approximately one
hour around 4 PM on July 23, it blew from the west. Therefore
during the former three periods, the
1043 Pacific Drive monitoring site was directly upwind of the
terminals, while during the later single
period, it was directly downwind. However, from Appendix A:
Figures 12 and 13, it is seen that
background noise levels (L90’s) during the corresponding hours
reveal no co-variation with these periods
of easterly and westerly winds.
4.4.3 476 Tsawwassen Beach Road, July 28 to August 11, 2011
The two noise monitoring sites discussed in Section 4.6 and 4.7
were both located on the top of the
Tsawwassen Bluffs, 45 to 55 m above sea level. It is possible
that upwind sound shadow effects and
downwind sound amplification effects were not clearly evident at
these locations because, given their
elevations above the ocean and the Port-related noise sources,
wind gradient-related sound refraction
effects were not fully developed. It is therefore of interest to
examine the noise level histories collected by
BKL Consultants Ltd. (BKL 2012) in relation to the Deltaport
Terminal Road and Rail Improvement Project
(DTRRIP) which included a site much closer to sea level. BKL
collected noise level histories at three
locations over a two week period from July 28 to August 12,
2011. BKL’s Site 1 was located on the roof of
the residence at 476 Tsawwassen Beach Road and, as such, was 5
to 10 m above sea level. Based on
data collected with a portable weather station located 3.5 m
above ground, the CONCAWE
Meteorological Categories that existed throughout the noise
monitoring period were calculated and
plotted alongside the noise level histories obtained.
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Overall, there was no consistent correlation between average
noise levels and CONCAWE
Meteorological Categories. In fact, the recurring pattern was
for the lowest average noise levels (typically
around 40 dBA) to occur during the nighttime hours (generally
between 10:00 PM and 5:00 AM) when
Meteorological Category 5 (moderately favourable sound
propagation conditions) prevailed. There was
some evidence that noise levels increased during the few brief
periods when Category 6 (most favourable
sound propagation conditions) occurred. In the first instance,
Category 6 occurred over three midday
hours on August 1. Average noise levels were 48 to 54 dBA during
this period; however, they continued
in this elevated range for several more afternoon and evening
hours during which Categories 3, 4 and 5
were prevalent. Another hour of Category 6 conditions occurred
at midday on August 6, during which
average noise levels were in the 49 to 53 dBA range. However,
noise levels were also in this range
during the previous hour when Category 3 prevailed.
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5.0 DISCUSSION
The following sections present the key findings of this
investigation into the effects of meteorology on the
propagation of sound from the Roberts Bank terminals to adjacent
residential areas and also discuss the
data gaps and limitations of the study.
5.1 KEY FINDINGS
Based on the well-established principals of outdoor sound
propagation over land and on more recently
acquired understanding of unique sound propagation phenomena
that can occur along coastlines, it might
be expected that pronounced variations in Roberts Bank terminals
noise levels would be observed at
residential locations along Tsawwassen shoreline to the east of
the terminals. However, based on the
review of noise histories and corresponding local wind logs,
only modest (3 to 4 dBA) variations in
average background noise levels were observed and even these
were not consistent over time
and space.
5.1.1 Potential Effects of Meteorology on Sound Propagation
The meteorological conditions that would be expected to most
influence the levels of Port-related noise
received at the Tsawwassen Bluffs and on the adjacent Tsawwassen
First Nation land are wind direction
and speed and/or air temperature gradients in the atmospheric
layer directly above the intervening ocean
surface.
On the infrequent occasions that neither wind speed nor air
temperature gradients exist above the ocean
surface, “neutral” atmospheric conditions are considered to
exist, and sound levels at distant residences
are neither amplified nor attenuated due to the refraction, or
“bending” of sound waves downwards
towards or upwards away from the surface. Under such conditions,
the levels of Port-related noise
reaching residences 4 to 6 km away depend predominantly upon
Port emission levels and source-
receiver distance (spherical spreading of sound waves with
increasing distance).
When either a wind speed or temperature gradient exists in the
atmospheric layer near the ocean
surface, then current understanding suggests that Roberts Bank
terminals noise levels at the residential
shoreline may be somewhat higher (up to 3 dB) or substantially
lower (10 to 20 dB) than the noise levels
experienced under neutral atmospheric conditions. The direction
and magnitude of these effects will
depend on wind direction and the strength of wind and/or
temperature gradients.
Amplification of Port-related noise levels at shoreline
residences by more than a few decibels above their
neutral atmosphere values appears only to be possible in the
presence of a “low level jet”, which through
its associated strong downward refraction of sound waves near
the ocean surface and upward refraction
of sound at greater elevations, can “trap” sound waves near the
water, thereby reducing the rate at which
sound is attenuated with distance due to geometrical spreading
and potentially increasing noise levels by
as much as 10 to 15 dBA. While it is possible that low level
jets leading to sound amplification (most likely
daytime sea-breezes) could occur along the Tsawwassen shoreline,
evidence of this is not available.
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The effects of upwind and downwind sound propagation in the
context of the Roberts Bank terminals
were modelled using three different meteorological algorithms
within the CadnaA sound propagation
software. This exercise yielded overall variations in received
noise levels between nominal worst-case
and best-case propagation conditions of between 8.7 and 11.7
dB.
5.1.2 Observed Effects of Meteorology on Noise Levels at
Tsawwassen Residences
Review of local wind logs from 2010 and 2013 has shown that
prevailing wind directions in the study area
are from the southeast and northwest (up and down the Georgia
Straight) so that residences along the
Tsawwassen Bluffs (particularly the southern portion) are, for
much of the time, either upwind or
downwind of the Roberts Bank terminals.
Comparison of local weather station wind logs with the noise
level histories obtained through continuous
noise monitoring conducted by WAL in June and July, 2013, and by
BKL Consultants Ltd. in July and
August, 2011, has revealed some limited examples of correlation
between wind direction and Roberts
Bank terminals noise levels. However, this correlation has been
neither strong nor consistent.
The clearest evidence of such correlation was seen in noise data
collected between June 4 and 6, 2013
at Fred Gingell Park overlooking Tsawwassen beach. In this
instance 12 hours of continuous southeast
winds were followed by 25 hours of northwest winds. The
difference between the average background
noise levels measured over these two extended time periods was
3.3 dBA. A noise level variation of this
magnitude is consistent with the minor sound amplification
associated with downwind sound propagation
or a temperature inversion over water, but not with the loss of
a fully-developed sound shadow that might
be expected to accompany a reversal in wind direction from
southeast to northwest. Changes in noise
levels of this magnitude (3.3 dBA) are not readily perceptible
if they occur from one hour, or one day,
to the next.
5.2 DATA GAPS AND LIMITATIONS
The following sections present issues and factors which may
limit the accuracy and/or general
applicability of the results and observations made in the above
sections.
Due to the variety of noise sources (fixed and mobile equipment,
ships, etc.) active at the Roberts Bank
terminal (including BC Ferries) at any given time, the levels of
quasi-continuous noise (as opposed to
intermittent, often impulsive, noises from material handling
activities) emitted from the terminals tend to be
fairly steady over time. However, they are not entirely steady,
so that any variations in the collective
noise emissions from these terminals (hour to hour, daytime to
nighttime, etc.) may confound and
obscure background noise level(s) variations observed at the
residences that might be attributable to
meteorological effects.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 19 - March 2014
Particularly during the daytime, other noise sources not related
to Port facilities contribute to the overall
noise environment in the waterfront residential areas, thereby
potentially obscuring variations in Port-
related noise levels that may be attributable to meteorological
effects.
No prolonged noise monitoring has been done during winter months
when meteorological effects on
sound propagation may be different than during summer
months.
It is possible that, at residential locations much farther
inland than the monitoring sites discussed herein,
the effects of meteorology on the levels of Port-related noise
may be more pronounced. In the case of
Tsawwassen First Nation land, it is possible that some ground
effect attenuation could occur at locations
far enough from the shoreline to permit sound waves reflected
from the soft ground surface to interfere
destructively with sound waves arriving directly from the
Roberts Bank terminals. This would, however, be
a sound-reducing, rather than sound-amplifying effect. Sound
levels would then “appear” to be amplified
under conditions, such as downwind propagation under westerly
winds, which would cause this ground
effect to be partially or entirely lost. It is also possible
that, at residences located more than about 400 m
east of the Tsawwassen Bluffs, terrain shielding effects created
by the ridge running parallel to, and
inland from, the shoreline may reduce exposures to Port-related
noise under most weather conditions. It
is possible that under westerly wind conditions, this terrain
shielding could be partially or entirely lost,
resulting in higher Port-related noise levels at these
residences. Again this would not truly be a sound
amplification effect, but rather the loss of excess attenuation
due to terrain shielding.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 20 - March 2014
6.0 CLOSURE
Major authors and reviewers of this technical data report are
listed below, along with their signatures.
Report prepared by: Wakefield Acoustics Ltd.
Clair W. Wakefield, M.A.Sc., P.Eng. President Report peer
reviewed by: Wakefield Acoustics Ltd.
Andrew P. Williamson, P.Eng. Project Engineer
-
Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 21 - March 2014
7.0 REFERENCES
BKL Consultants Ltd. 2004. Roberts Bank Container Expansion
Project Environmental Noise
Assessment. Prepared for Port Metro Vancovuer, Vancouver,
B.C,
BKL Consultants Ltd. 2012. Deltaport Terminal Road and Rail
Improvement Project Environmental Noise
and Vibration Assessment, Final Draft Report, File No. 2720-11B.
Prepared for Port Metro
Vancovuer, Vancouver, B.C.
Bolin, K. 2009. Wind Turbine Noise and Natural Sounds – Masking,
Propagation and Modeling.
Boue, M. 2007. Long-Range Sound Propagation Over the Sea with
Application to Wind Turbine Noise.
Final Report to the Swedish Energy Agency Project 21597-3.
Crocker, M. J., editor. 1998. Handbook of Acoustics, Chapter 28,
Atmospheric Sound Propagation.
Economic Planning Group. 2013. Roberts Bank Terminal 2: Survey
of Area Residents Regarding Noise
and Vibration Issues. Prepared for Port Metro Vancovuer,
Vancouver, B.C.
Embleton. T. F. 1996. Tutorial on Sound Propagation Outdoors.
Journal of Acoustical Society of
America, Volume 100 (1). July, 1996.
International Standards Organization (ISO). 1996. ISO Standard
9613-2, “Acoustics- Attenuation of
sound during propagation outdoors”, Part 2 – General Method of
Calculation.
Johansson, L. 2003. Sound Propagation around Off-shore Wind
Turbines. Licentiate Thesis,
Department of Civil and Architectural Engineering, Div. of
Building Technology, Stockholm,
Sweden.
Municipality of Delta. 2012. Community Complaints Log.
National Physical Laboratory (NPL), U.K. 2007. Guide to
Predictive Modelling of Environmental
Noise, Appendix A – Sound Propagation theory and Methodologies.
Acoustics Group, National
Measurement Systems Acoustics Programme, 2004 – 2007.
Port Metro Vancouver. December 2012. Complaints Log (January 1
to December 6, 2012).
Sondergaard, B. and B. Plovsing. 2005. Noise from Offshore Wind
Turbines. Danish Ministry of
the Environment, Environmental Protection Branch, Environmental
Project No. 1016.
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Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation - 22 - March 2014
8.0 STATEMENT OF LIMITATIONS
This report was prepared by Wakefield Acoustics Ltd., based on
research and fieldwork conducted by
Wakefield Acoustic Ltd., for the sole benefit and exclusive use
of Port Metro Vancouver. The material in it
reflects Wakefield Acoustics Ltd.’s best judgment in light of
the information available to it at the time of
preparing this Report. Any use that a third party makes of this
Report, or any reliance on or decision
made based on it, is the responsibility of such third parties.
Wakefield Acoustics Ltd. accepts no
responsibility for damages, if any, suffered by any third party
as a result of decisions made or actions
taken based on this Report.
Wakefield Acoustics Ltd. has performed the work as described
above and made the findings and
conclusions set out in this Report in a manner consistent with
the level of care and skill normally
exercised by members of the consulting engineering profession
practicing under similar conditions at the
time the work was performed.
This Report represents a reasonable review of the information
available to Wakefield Acoustics Ltd. within
the established Scope, work schedule and budgetary
constraints.
In preparing this Report, Wakefield Acoustics Ltd. has relied in
good faith on information provided by
others as noted in this Report, and has assumed that the
information provided by those individuals is both
factual and accurate. Wakefield Acoustics Ltd. accepts no
responsibility for any deficiency, misstatement
or inaccuracy in this Report resulting from the information
provided by those individuals.
-
APPENDIX A
Figures
-
Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 1 - March 2014
Figure 1 Illustrations of the Formation of Sound Shadows under
Upwind Propagation or Temperature Lapse Conditions
Figure 2 Illustration of the Situation in which Ground Effect
Attenuation can Occur due to the Destructive Interference of Direct
and Ground-Reflected Sound Waves when both Travel Close to Soft
Ground
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 2 - March 2014
Figure 3 Illustrations of the Downward Refraction of Sound Waves
Downwind Propagation or Temperature Lapse Conditions
Figure 4a Sound Propagation Simulation Result for 80 Hz., Low
Level Jet Conditions (12) Left - Wind Speed Profile of Low Level
Jet (LLJ) Centre – Relative Sound Level Distribution under LLJ
Right – Relative Sound Level Legend/Palette
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 3 - March 2014
Figure 4b Wind Speed & Direction Profiles of Low Level Jet
caused by Inertial Oscillation (8)
Figure 5 Wind Speed & Direction Profiles Associated with Low
Level Jet caused by a Sea Breeze (9)
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 4 - March 2014
Figure 6 2010 Wind Rose from Weather Station (located at west
end of BC Ferries terminal)
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 5 - March 2014
Figure 7 Wind Direction Histogram (Sand Heads) for July 22 to
24, 2013
0
2
4
6
8
10
12
10 30 50 70 90 110 130 150 170 190 210 230 250 270 290 310 330
350
Nu
mb
er
of
Ho
urs
Wind Direction (0/360 = North, 90 = East, 180 = South, 270 =
West)
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 6 - March 2014
Figure 8 Wind Direction Histogram (Sand Heads) for June 4 to 6,
2013
-
Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 7 - March 2014
Figure 9 Noise Monitoring Site Plan. Extent of 6 km (from centre
of Deltaport) sound propagation study zone indicated by red
line
-
Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 8 - March 2014
Figure 10 Noise Level History Measured by WAL June 4 to 5, 2013
at Fred Gingell Park, Tsawwassen
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
11:30 AM 2:00 PM 4:30 PM 7:00 PM 9:30 PM 12:00 AM 2:30 AM 5:00
AM 7:30 AM 10:00 AM
So
un
d P
ressu
re L
evel
(dB
A)
Time
DNMN - Prelim Monitoring Site 4; Fred Gingell Park, Tsawwassen,
June 4-5, 2013
noise levels in 15 minute intervals
Leq(15 min) Lmax L90
Ldn = 52.1 dBA
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 9 - March 2014
Figure 11 Noise Level History Measured by WAL June 5 to 6, 2013
at Fred Gingell Park, Tsawwassen
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 10 - March 2014
Figure 12 Noise Level History Measured by WAL July 22 to 23,
2013 at 1043 Pacific Drive, Tsawwassen
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
10:30 AM 1:00 PM 3:30 PM 6:00 PM 8:30 PM 11:00 PM 1:30 AM 4:00
AM 6:30 AM 9:00 AM
So
un
d P
ressu
re L
evel
(dB
A)
Time
RBT2 - Baseline Noise Monitoring Site 3; 1043 Pacific Drive,
Tsawassen, July 22-23, 2013
noise levels in 15 minute intervals
Leq(15 min) Lmax L90
Ldn = 54.3 dBA
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Port Metro Vancouver APPENDIX A Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 11 - March 2014
Figure 13 Noise Level History Measured by WAL July 23 to 24,
2013 at 1043 Pacific Drive, Tsawwassen
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
10:45 AM 1:15 PM 3:45 PM 6:15 PM 8:45 PM 11:15 PM 1:45 AM 4:15
AM 6:45 AM 9:15 AM
So
un
d P
ressu
re L
evel
(dB
A)
Time
RBT2 - Baseline Noise Monitoring Site 3; 1043 Pacific Drive,
Tsawwassen, July 23-24, 2013
noise levels in 15 minute intervals
Leq(15 min) Lmax L90
Ldn = 54.1 dBA
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APPENDIX B
Tables
-
Port Metro Vancouver APPENDIX B Wakefield Acoustics Ltd. RBT2 –
Effects of Meteorology on Sound Propagation - 1 - March 2014
Table 1 Modelled Variations in Roberts Bank Terminals Sound
Levels at Tsawwassen Bluffs (1043 Pacific Drive) due to Variations
in Meteorological Conditions (Wind Direction)
Meteorology
Standard
Site 3 – Average Port-related Sound Level
L90 (dBA)
Variation in L90 Relative to Average Conditions (dBA)
Total Variation in
L90 (dBA)
(Upwind vs. Downwind)
Average Wind
Conditions
Downwind
Conditions
Upwind Conditions
Downwind Conditions
Upwind Conditions
FfU Bayerr 45.0 47.6 37.8 2.5 - 7.4 9.8
LUA NRW 45.0 47.6 38.9 2.4 - 6.3 8.7
ROBERTS BANK TERMINAL 2 TECHNICAL DATA REPORT: Upland Noise and
Vibration Effects of Meteorological Conditionson Sound Propagation
from Roberts Bank Terminals
Technical Report/Technical Data Report Disclaimer
Executive Summary
Table of Contents
1.0 Introduction
1.1 Project Background
1.2 Effects of Meteorology on Sound Propagation - Overview
2.0 Review of Existing Literature and Data
2.1 Outdoor Sound Propagation
2.1.1 Overview
2.1.2 Geometric Spreading
2.1.3 Atmospheric Absorption
2.1.4 Upward Refraction – Sound Shadows
2.1.5 Downward Refraction – Sound Amplification
2.1.6 Ground Effect Attenuation
2.2 Long Range Sound Propagation Over Water
2.2.1 Overview
2.2.2 Low Level Jets
3.0 Methods
3.1 Study Area
3.2 Temporal Scope
3.3 Study Methods
3.4 Data Analysis
4.0 Results
4.1 Meteorological Conditions in the Study Area – Overview
4.1.1 Prevailing Winds
4.1.2 Temperature Inversions Over Water
4.1.3 Occurrence of Low Level Jets
4.2 Wind Conditions during Specific Periods of Baseline Noise
Monitoring
4.2.1 WAL Baseline Noise Monitoring of July 22 to 24, 2013
4.2.2 WAL Noise Monitoring of June 4 to 6, 2013
4.3 Modelling the Effects of Meteorology on Sound
Propagation
4.3.1 CadnaA Sound Propagation Software
4.3.2 Approaches to Modelling Meterological Effects
4.3.3 Modelling the Roberts Bank Study Area
4.4 Observed Effects of Meteorological Conditions on Community
Noise Exposures
4.4.1 Fred Gingell Park, June 4 to 6, 2013
4.4.2 1043 Pacific Drive, July 22 to 24, 2013
4.4.3 476 Tsawwassen Beach Road, July 28 to August 11, 2011
5.0 Discussion
5.1 Key Findings
5.1.1 Potential Effects of Meteorology on Sound Propagation
5.1.2 Observed Effects of Meteorology on Noise Levels at
Tsawwassen Residences
5.2 Data Gaps and Limitations
6.0 Closure
7.0 References
8.0 Statement of Limitations
APPENDICES
APPENDIX A: Figures
APPENDIX B: Tables
-
ROBERTS BANK TERMINAL 2
TECHNICAL DATA REPORT
Upland Noise and Vibration
Effects of Meteorological Conditions
on Sound Propagation from Roberts Bank Terminals Prepared for:
Port Metro Vancouver 100 The Pointe, 999 Canada Place Vancouver, BC
V6C 3T4 Prepared by: Wakefield Acoustics Ltd. 310-2250 Oak bay
Avenue Victoria, BC V8R 1G5 File: 302-042.02 March 2014
-
Port Metro Vancouver Wakefield Acoustics Ltd. RBT2 – Effects of
Meteorology on Sound Propagation March 2014
Technical Report/Technical Data Report Disclaimer
The Canadian Environmental Assessment Agency determined the
scope of the proposed Roberts Bank
Terminal 2 Project (RBT2 or the Project) and the scope of the
assessment in the Final Environmental
Impact Statement Guidelines (EISG) issued January 7, 2014. The
scope of the Project includes the
project components and physical activities to be considered in
the environmental assessment. The scope
of the assessment includes the factors to be considered and the
scope of those factors. The
Environmental Impact Statement (EIS) has been prepared in
accordance with the scope of the Project
and the scope of the assessment specified in the EISG. For each
component of the natural or human
environment considered in the EIS, the geographic scope of the
assessment depends on the extent of
potential effects.
At the time supporting technical studies were initiated in 2011,
with the objective of ensuring adequate
information would be available to inform the environmental
assessment of the Project, neither the scope
of the Project nor the scope of the assessment had been
determined.
Therefore, the scope of supporting studies may include physical
activities that are not included in the
scope of the Project as determined by the Agency. Similarly, the
scope of supporting studies may also
include spatial areas that are not expected to