4
Noise
This Section assesses the
potential noise impacts associated with the construction and operation of the
Project.
4.2
Relevant
Legislation and Guidelines
4.2.1
Construction Noise
The principal legislation relating to the control of construction noise
is the Noise Control Ordinance (Cap. 400)
(NCO). Various Technical
Memoranda (TMs), which stipulate control approaches
and criteria, have been issued under the NCO. The following TMs
are applicable to the control of noise impacts from construction activities:
·
Technical Memorandum on Noise from
Percussive Piling (PP-TM);
·
Technical Memorandum on Noise from
Construction Work other than Percussive Piling (GW-TM); and
·
Technical Memorandum on Noise from
Construction Work in Designated Areas (DA-TM).
The Environmental
Impact Assessment Ordinance (EIAO)
(Cap. 499) also provides means to
assess construction noise impacts. The Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM),
issued under the EIAO, provides
guidelines and noise criteria for evaluating construction noise impacts.
General Construction Works
Under the EIAO,
potential noise impact arising from general construction works during normal
working hours (ie 07:00 to 19:00 hrs on any day not
being a Sunday or public holiday) at the openable
windows of buildings is to be assessed in accordance with the noise criteria
specified in the EIAO-TM. The EIAO-TM
noise standards are presented in Table
4.2a.
Table 4.2a EIAO-TM
Day-time Construction Noise Standard (Leq,
30 min dB(A))
When assessing a Construction Noise Permit
(CNP) application for the use of Powered Mechanical Equipment (PME) during the
restricted hours, the Noise Control Authority will compare the Acceptable Noise
Levels (ANLs), as promulgated in GW-TM, and
the Corrected Noise Levels (CNLs) (ie after accounting for factors such as barrier effects and
reflections) associated with the proposed PME operations. The ANLs are related
to the noise sensitivity of the area in question and different Area Sensitivity
Ratings (ASR) have been established to reflect the
background characteristics of different areas.
The appropriate ASR for the Noise Sensitive Receiver (NSR) is determined
with reference to Table 4.2b.
Table 4.2b Area
Sensitivity Ratings
The relevant ANLs are shown in Table 4.2c.
Table 4.2c Acceptable Noise Levels (ANL, Leq, 5 min
dB(A))
As the Project Site is located in a rural area and no
influencing factors affect the NSRs, an ASR of “A”
has been assigned.
The Noise Control Authority will consider a well-justified CNP
application, for
construction works within restricted hours as guided by the relevant Technical
Memorandum issued under the NCO.
The Noise Control Authority will take into account adjoining land uses
and any previous complaints against construction activities at the site before
making a decision. Nothing in this EIA
Report shall bind the Noise Control Authority in making its decision. The Noise Control Authority may include any
conditions in a CNP that it considers appropriate. Failure to comply with any such conditions
may lead to cancellation of the CNP and prosecution action under the NCO.
4.2.2
Operational Noise
The EIAO-TM and Technical Memorandum on
Noise From Places Other than Domestic Premises, Public
Places or Construction Sites (IND-TM) specifies the applicable ANLs for the operation of the Project. The ANLs are dependent
on the ASR and the time of the day and are presented in Table 4.2d.
Table 4.2d ANLs to be used as Operation Noise Criteria
Fixed Plant Noise
Fixed plant noise is controlled under Section 13 of
the NCO and the predictions will be undertaken in accordance with the IND-TM. The noise criteria for planning and design of
Designated Projects are set out in the EIAO-TM as follows:
·
the noise level at the facade of the nearest NSR is at least 5 dB(A)
lower than the appropriate ANL (as shown in Table 4.2d) as specified in
the IND-TM; or,
·
the prevailing background noise level (for quiet areas
with a noise level 5 dB(A) below the appropriate ANL).
The noise criteria stipulated in the IND-TM are
also dependent on the ASR of the NSR, as shown in Table 4.2d.
As the Project Site is located in a rural area and no
influencing factors affect the NSRs, an ASR of “A”
has been assigned. Background noise
measurement has been conducted to investigate the prevailing noise level in the
Study Area. A 24-hour continuous
measurement of prevailing free field noise levels in the vicinity of Hei Ling Chau
Correctional Institution (N1) gave levels in the range 42 to 56 dB(A) LAeq, 30min. With the inclusion of façade correction, the
measured prevailing noise level will be equal to the (ANL – 5) criterion, and
therefore the (ANL – 5) criterion, ie 45 dB(A) LAeq, 30min for night-time period
will be considered as the stipulated noise limit for the assessment of
operational noise impact. Details of the
background noise measurements are provided in Section 4.3.3.
4.3
Baseline
Environmental Conditions and Noise Sensitive Receivers
4.3.1
Baseline Environmental
Conditions
The proposed wind turbine will be located at the southern side of Hei Ling Chau. An associated temporary steel platform and
bridge will be located at the south-western part of the island. The Study Area is rural in nature and is
characterised by the low-rise buildings of the Correctional Institution and
Addiction Treatment Centre. Background
noise levels are typical of a general rural environment and there are limited
numbers of vehicles or noisy plant items within the Study Area. The major noise sources are identified as the
noise from the Correctional Institution and Addiction Treatment Centre, the
traffic noise within the island and noise from passing marine vessels.
4.3.2
Noise Sensitive Receivers
The nearest NSRs are the Hei Ling Chau
Correctional Institution (N1) and Hei Ling Chau
Addiction Treatment Centre (Annex) (N2),
which are located
at about 740m and 380m away from the Project Site, respectively (see Figure 4.3a). The nearest NSR that may be affected by the
enabling works along the long access route has been identified as the Staff
Quarters (N3) ([1]) (see Figure 4.3a). For other locations along the long access
route, there is either no NSR within a 300m radius or those that are presented
are screened by non-sensitive air-conditioned administration buildings. The natural terrain between the NSRs (N1 and N2) and the Project Site will act as a barrier
and reduce the potential construction and operational noise impacts. Terrain profiles between the NSRs (N1 and N2) and the Project Site are presented in Annex A1. The separation distances between the NSRs and the Project Site are summarised in Table
4.3a. No planned NSR is identified
within 2 km of the Project Site.
Table 4.3a Identified
Noise Sensitive Receivers
4.3.3
Baseline Noise Measurement
To investigate the prevailing noise levels at Hei
Ling Chau, noise measurements were made from 6 to 7
June 2006 at the boundary of Hei Ling Chau Correctional Institution (N1). The noise measurements were conducted using a
SVAN 949 Sound Level Meter (Type 1), calibrated using a SVAN Sound Level
Calibrator Type 4231 with a calibration signal of 94.0 dB(A) at 1kHz. The measurements were conducted with
reference to the calibration and measurement procedures stated in the IND-TM.
As the background noise at Hei Ling Chau is generally low, the baseline noise measurement represents
the typical acoustic environment in the vicinity of the NSRs. The measurement results are summarised in Table
4.3b. Since the microphone was set
in the free field measurement mode, an appropriate façade correction of 3dB(A)
has been applied to the noise measurement results. The timeline chart showing the prevailing
noise levels at N1 is presented in Figure
4.3b.
Table 4.3b Measured
Prevailing Noise Levels (with 3dB(A) Façade
Correction)
The measured noise levels at NSR N2 are in the range
of 51 – 54dB(A) Leq, 30min
during daytime, which are similar to the noise levels measured at NSR N1. It is anticipated that the background noise
levels at NSR N2 during night-time will be similar to that measured at NSR N1
due to the similar environment on the island.
4.4
Potential Sources
of Impact
4.4.1
Construction Phase
The main construction activities associated with the Project with the
potential to cause noise impacts to the identified NSRs
are as follows:
·
Construction
of the temporary steel platform and bridge at the short access route – transportation of plant and equipment,
rock breaking, micro-piling, excavation, soil nailing, concreting, erection of
the temporary bridge and transportation of wind turbine components;
·
Enabling
works along the long access route – minor road widening and slope works at some sections of the existing
road; and
·
Construction
works at wind turbine site
– site formation and erection of wind turbine.
The construction works for the temporary
steel platform and bridge at the short access route and at the Project Site will be carried out
in phases without overlapping in accordance with the proposed construction work
programme. As
per the proposed construction programme, there will
be about 1 to 2 vehicles passing through the long and short access routes per
hour.
The construction noise assessment was undertaken based
on the proposed construction
work programme and plant inventory presented in Annex A2 and Figures 3.1b, 3.3a to 3.3g. The
plant inventory has been reviewed by the Design Engineer and is confirmed to be
suitable for completing the Project within the scheduled timeframe.
The normal working hours of the contractor will be between 07:00 and
19:00 hours from Monday to Saturday (except public holidays). Construction activities during restricted
hours are not expected. Should evening
and night works between 19:00 and 07:00 hours or on public holidays (including
Sundays) be required, the contractor will submit a CNP application which will
be assessed by the Noise Control Authority.
Conditions stipulated in CNP will be strictly followed.
4.4.2
Operational Phase
Sources of Wind Turbine Noise
The sources of noise emitted from the operating the wind turbine include
the rotation of mechanical and electrical equipment and aerodynamic noise
originating from the flow of air around the blades. The mechanical and electrical equipment that
may have potential noise producing effects are the gearbox, transformer and
generator. The aerodynamic noise generally
increases with increases in rotor speed.
With reference to a published study ([2]), it is anticipated that vibration
introduced by the wind turbine will not be a concern as the components of the
wind turbine are attached in such a way that vibrations are either not transmitted or are damped. Wind turbine manufactures use computer aided
models for wind turbine design and fabrication to ensure that the vibration of
different components does not interact to amplify noise.
It is now
a standard practice for the wind turbine manufacturers to
incorporate low-noise features into their standard products. Sound
insulation materials will be used in the nacelle to enclose the generator,
shaft and gearbox so as to reduce the medium and high frequency noises. The airfoil blades are
purposely designed to reduce aerodynamic noise generated during wind turbine
operation.
For the proposed wind turbine, the use of a synchronous generator makes
it possible to transfer the revolution of the wind turbine directly to the
power generator without using a multiplying gear, which contributes to the
elimination of noise caused by the gear and saving the labour needed for its maintenance.
Wind Turbine Noise Source Term
The proposed wind turbine has a capacity of 800kW to 1.3MW, with a
design maximum blade rotating speed of about 31 rpm (refer to Table 3.2a). This design limits the noise generation, and
hence it will also limit the noise impacts to the identified NSRs. In addition,
modern wind turbines have already incorporated many design features to reduce
noise emissions.
Information sourced from
wind turbine suppliers indicates that the typical sound power level of a wind
turbine with a capacity of 800kW
to 1.3MW can be designed to 104
dB(A), inclusive of the rotation of mechanical parts,
sound of electrical components and aerodynamic noise.
The sound power level of
the proposed wind turbines covers the full range of operation, including
start-up, shut-down, cut-in, cut-out, braking and yawing and the full range of
wind speeds. It is technically feasible
and practicable to limit the operational noise level for a wind turbine to 104
dB(A) and with no tone, impulse and intermittency characteristics by applying
standard plant design features (see Annex
3). The tender specification of the
Project will specify that the wind turbine will have a typical operational
noise level of 104 dB(A) with no tonality, impulsiveness and intermittency
characteristics.
In view of the above, an
overall sound power level of 104 dB(A) with no tonal, impulse and intermittency
characteristics has been assumed in the noise impact assessment.
Description of Wind Turbine
Operation
Normally the rotor speed of proposed wind turbine will vary from 14 to
31 rpm in the range of effective wind speed, ie 3 to
25 m s-1. The rotors will reach the maximum speed when
wind speed reaches about 10 to 15 m s-1 and thereafter remain at the same speed up to 25 m s-1. With
reference to a wind turbine model that is a suitable size for the Hei Ling Chau site, the noise
level reaches maximum noise level of 104dB(A) at about 15 m s-1 (see
Annex A3.3). When the wind speed exceeds 25 m s-1, the wind turbine will cut-off, ie the rotating parts of the wind turbine including rotor,
blades and shaft will all stop, and hence the wind turbine will not cause any
mechanical noise. With reference to the
hourly wind speed data obtained from the Hong Kong Observatory at Cheung Chau Station for Year 2004, about 96% of the data were
below 15 m s-1, in which 93% were below 10 m s-1. It should also be noted
that in high wind speeds exceeding 10 m s-1, the background
noise generated by trees, shrubs, terrain and wind itself would gradually
exceed and mask the wind turbine noise. Therefore, an overall sound power level of 104 dB(A) has
been adopted as the reasonable worst-case.
The anticipated sound power
levels of the wind turbine in 1/3 octave bands are presented in Annex A3.1.
4.5.1
Construction Phase
The construction noise impact assessment was
undertaken in accordance with the procedures outlined in the GW-TM, which is issued under the NCO and the EIAO-TM. The assessment
methodology is summarised below.
·
Locate
representative NSRs that may be affected by the
Project;
·
Determine
the plant teams for corresponding activities, based on the agreed plant
inventory;
·
Assign
sound power levels (SWLs) to the PME proposed based
on the GW-TM or other sources;
·
Calculate
the correction factors based on the distance between the NSRs
and the notional noise source position of the work sites;
·
Apply
corrections in the calculations, such as potential screening effects and
acoustic reflection, if any; and
·
Predict
the construction noise levels at NSRs in the absence
of any mitigation measures.
The total SWL associated with each construction
activity was based on an assumed plant inventory. All
4.5.2
Operational Phase
The operational noise impact assessment was undertaken in accordance
with the procedures outlined in the ISO 9613 ([3]) and IND-TM,
which is issued under the NCO and the EIAO-TM. The
assessment took into account the distance attenuation, atmospheric absorption
and corrections of tonality, impulsiveness and intermittency, if any, in
accordance with the IND-TM.
4.6.1
Construction Phase
The source-to-NSR distances are presented
in Table 4.6a.
Table 4.6a Noise
Sensitive Receivers and Horizontal Distance to Major Noise Sources
Based on existing topography, NSR N1 will not have direct line of sight
to the Project Site. Therefore, with
reference to the GM-TM, a negative correction of 10 dB(A) has been
included in the construction noise assessment.
There will be some enabling works along some sections of the long access
route, including slope cutting, erection of temporary platform and
backfilling. The nearest NSR (N3) that
may be affected is located next to one of the enabling work areas along the
route (see Figure 3.3c). Due to the close proximity to the work area,
practicable mitigation measures, including limiting the concurrent use of
construction equipment, using quiet construction plant and noise barriers, are
recommended to be implemented when works are undertaken near NSR N3. Since the works area is very close to this
NSR, it would be possible for the contractor to provide noise barrier in the
form of site hoardings to achieve the screening effect, provided that the
barriers have no openings or gaps ([4]).
The proposed barriers should be at least 3m high with a superficial
surface density of at least 10 
. This would provide a minimum 10 dB(A)
attenuation. The contractor will ensure
that the conditions of the hoardings are properly maintained throughout the
construction period.
As NSR N3 is located at more than 1.5km and 2km from the temporary steel
platform and bridge at the short access route and the Project Site,
respectively, it is anticipated that the construction works at these locations
will have negligible noise impacts to NSR N3.
Similarly, the enabling works along the long access route will have negligible
noise impacts to NSRs N1 and N2.
The predicted noise levels at NSRs N1 and N2
due to the construction works at the temporary steel platform and bridge and
the Project Site comply with the stipulated criterion. The predicted noise levels at NSR N3 (after
the implementation of the recommended mitigation measures) due to the enabling
works along the long access route range from 79 to 83 dB(A), which exceed the
noise criterion by 4 to 8 dB(A).
Details of the noise calculations are presented in Annex A2. A summary of the construction noise levels is
presented in Table 4.6b. As per
the proposed construction programme, there will not be overlapping periods
between construction activities.
Table 4.6b Predicted
Construction Noise Levels at NSRs
The assessment indicates that the predicted noise levels will exceed the
day-time construction noise criterion after the implementation of the
recommended mitigation measures due to the close proximity of the NSR N3 to the
works area. Details of the residual
construction noise impact associated with the enabling works along the long
access route are summarised in Table 4.6c. Erection of a full enclosure is considered
not practicable due to the space constraints.
Table 4.6c Predicted
Residual Noise Impacts at N3 (After Mitigation)
Due to the construction sequence, it is not possible that all the
construction plant and equipment to be delivered or transported to the Project
Site using the short access route (see Section
2). Although
residual impacts from the enabling works along the route are predicted, the period of exceedance
is very short. The works near the
staff quarters will last for about a week only and the affected time is very short
when compared with the overall construction programme of about 12 months.
As confirmed on site, air-conditioners are provided for the
NSR N3 and the quarter is not currently occupied. CSD agreed not to arrange staff to stay at
this quarter as far as possible when construction works are undertaken in the
area. CAPCO will inform CSD prior to the
commencement of the construction works.
The noise impacts to the NSR N3 would be considered as low and
acceptable in terms of the magnitude and the effects on health. No long-term adverse impact is anticipated.
It should be noted that the construction noise assessment
presented above is based on a worst case scenario in which the construction
plant are assumed to be operated continuously and simultaneously during each
construction stage. In reality, this
scenario is unlikely to occur.
As per the proposed construction programme, there will not be
overlapping periods between each construction activities. Therefore, cumulative noise impacts during
the construction period will not be a concern.
Given that there will be residual impacts from the enabling works in the
area of the long access route, mitigation measures as recommended in Section 4.7 should be implemented.
4.6.2
Operational Phase
Based on the typical sound power level of 104 dB(A),
the facade noise levels at the identified NSRs are
predicted and summarised in Table
4.6d. The predicted noise levels
comply with both of the stipulated (ANL-5) daytime and night-time noise
criteria of 55 dB(A) and 45 dB(A). A 10 dB(A) screening effect has been
taken into account for NSR N1 due to topography shielding and no direct line of
sight to the whole swept area of the rotors (see Annex A1.1). Some buildings in NSR N2 may have line of sight to
a small part of the swept area of the blades but most part of the wind turbine
will be screened off (see Annex
A1.2). Therefore, a 5 dB(A)
attenuation was included in the calculation.
The terrain profiles presented in Annex A1 are derived from a Digital
Elevation Model (DEM) based on the Land Information Centre (LIC) data obtained
from the Lands Department. Details of
the noise calculations are presented in Annex A4.
Table 4.6d Predicted
Facade Noise Levels at NSRs
It should be noted that the assessment is conservative as a
hemispherical propagation model has been assumed. If spherical propagation is adopted, which is
considered a feasible approach for a project with one wind turbine surrounded
by soft ground, the noise level at the NSRs will be
further reduced by 3 dB(A). Also, based
on the methodology outlined
in the ISO 9613, the predicted noise levels are the maximum worst-case
as the assessment has assumed 100% downwind propagation ([5]). Graphical
representations of the wind direction and wind speed prepared based on the
hourly wind data obtained from the Hong Kong Observatory at Cheung Chau Station in Year 2004, and the wind monitoring data
obtained from the on-site wind monitoring station are presented in Annex A5. It is indicated that the prevailing wind
propagation are from north and east. In
reality, NSRs N1 and N2 are not located along the
downwind propagation paths as they are located to the north and north-west of
the wind turbine, respectively.
Therefore, the
actual noise levels perceived at the NSRs are
expected to be lower than those shown in Table
4.6d.
4.7.1
Construction Phase
The contractor is required to adopt site specific direct
technical measures as specified below for the enabling works along the long
access route near NSR N3.
·
Avoid
or reduce concurrent operation of construction equipment;
·
Use of quiet
construction plant;
·
Use
of site hoarding barriers with a minimum height of 3m. In general, this would provide a minimum 10
dB(A) attenuation for the low-rise receivers.
The barriers should not have openings or gaps and have a superficial
surface density of at least 10 kgm-2. The location and extent of the proposed
barrier are shown in Figure 4.7a;
·
As a
last resort, indirect mitigation measures in the form of window insulation and
air-conditioning (air-conditioners have been provided for the staff quarters)
are recommended to mitigate the residual noise impact. In general, this would provide a minimum 10 dB(A)
attenuation for the receivers.
·
After
consultation with CSD, agreed mitigation measures would be implemented (eg the use of air-conditioners and avoidance of use of the
affected staff quarter during the period when works are undertaking in the
area). The Contractor will closely
liaise with the CSD to programme the noisy construction works such that the
noise impact to the CSD staff will be avoided or reduced. Prior to commencement of the construction,
CSD will be notified with the programme of the works, the planned construction
activities, the potential impacts to the Staff Quarters, the measures to
mitigate the impacts, the monitoring programme to check the efficiency of the
measures, and the communication channels between CSD and the Site Engineer.
4.7.2
Operation Phase
Noise reduction methods for wind turbines include special finishing of
gear teeth, using low speed cooling fans and adding baffles and acoustic
insulation to the nacelle. The detailed
methods to be employed vary from supplier to supplier. It is practicable and achievable to reduce the wind turbine with typical
sound power level to 104 dB(A) during the detailed design stage of the wind
turbine.
The noise assessment indicates that under the worst-case scenario (covering
a full range of operation including start-up, shut-down, cut-in, cut-out,
braking and yawing; and the full range of wind speeds), with a wind turbine with typical sound power level
of 104 dB(A) and with no tone, impulse and intermittence characteristics, the
predicted facade noise levels at the identified NSRs
will comply with the day-time and night-time noise limits at all NSRs.
4.8
Environmental
Monitoring and Audit
4.8.1
Construction Phase
Noise monitoring is recommended during the construction phase to ensure
the compliance to acceptable noise levels at
the identified NSRs.
Noise monitoring will be undertaken at two locations, Hei Ling Chau Addiction Treatment Centre
(Annex) (N2) and Staff
Quarters (N3) ([6]), and at a frequency of once a week. Regular site audits (ie
once a month) will be conducted to ensure that the proposed mitigation
measures are implemented properly and that the plant inventory used on site is consistent with the
assumptions used in the EIA Report.
4.8.2
Operation Phase
During the operation phase, noise monitoring will be undertaken at the
nearest NSR (ie Hei Ling Chau Addiction Treatment Centre (Annex) (N2)) during the night-time period at the agreed
monitoring location to ensure the compliance with the stipulated noise
criterion. As wind speed will vary
throughout the year and hence the potential noise impacts, it is recommended to
monitor noise levels at monthly intervals for the first 12 months of the
operation of the wind turbine. The
monitoring frequency will increase to biweekly intervals during the higher wind
speed months (ie winter months - from December to
January), and storm season – (July) within the first 12-month monitoring
period.
No adverse construction phase noise impacts are predicted at
NSRs N1 and N2.
The mitigated construction noise activities for the enabling works along
the long access route near the CSD’s Staff Quarters
(N3) would cause a temporary exceedance of the
day-time construction noise criterion.
Mitigation measures have been recommended.
The tender specification of the Project will specify that the wind turbine will have a typical sound power level of 104 dB(A) with no tonality, impulsiveness and intermittency characteristics. For a wind turbine with a typical sound power level of 104 dB(A), the consequent predicted facade noise levels will comply with the day-time and night-time noise limits at all NSRs. Noise monitoring for the first 12 months of operation of the wind turbine is recommended to ensure compliance with the stipulated noise limits.