This Section presents the potential noise impacts associated with the construction and installation of the wind turbine and the operational noise impacts associated with maintenance and operation of the wind turbine.
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 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).
Apart from the above, 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.
Percussive piling is prohibited at any time on Sundays and public holidays and during the weekday evening and night-time hours (1900-0700 hours, Monday through Saturday). A Construction Noise Permit (CNP) is required for such works during weekday daytime hours (0700-1900 hours, Monday through Saturday).
When assessing a CNP application for carrying out percussive piling, the Environmental Protection Department (EPD) is guided by the PP-TM. The EPD will consider the difference between the Acceptable Noise Levels (ANLs), as promulgated in the PP-TM, and the Corrected Noise Levels (CNLs) in conjunction with the proposed piling activities. Depending on the level of noise impact on nearby Noise Sensitive Receivers (NSRs), the EPD may allow 3, 5 or 12 hours of daily piling time (see Table 4.1).
Table 4.1 Permitted Hours of Operation for Percussive Piling (Not Involving the Use of Diesel, Pneumatic and/or Steam Hammers)
|
Amount by which CNL exceeds ANL |
Permitted hours of operation on any day not being a
holiday |
|
more than 10 dB(A) |
0800 to 0900 and 1230 to 1330 and 1700 to 1800 |
|
between 0 dB(A) and 10 dB(A) |
0800 to 0930 and 1200 to 1400 and 1630 to 1800 |
|
no exceedance |
0700 to 1900 |
The issue of a CNP by the Noise Control Authority for percussive piling is governed by the procedures laid down in the PP-TM. However, as percussive piling is not required for this Study, the noise criteria stipulated under the PP-TM are not applicable in this Study.
Under the EIAO, noise impact arising from general construction works during normal working hours (i.e. 0700 to 1900 hours 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 as given in the EIAO-TM. The EIAO-TM noise standards are presented in Table 4.2.
Table 4.2 EIAO-TM Daytime Construction Noise Standard (Leq, 30 min dB(A))
|
Use |
Noise Standard |
|
Domestic Premises |
75 |
|
Educational Institutions (normal periods) Educational Institutions (during examination periods) |
70 65 |
When assessing a CNP application for the use of Powered Mechanical Equipment (PME) during restricted hours, the Noise Control Authority will compare the ANLs, as promulgated in GW-TM, and the CNLs (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 have been established to reflect the background characteristics of different areas. The relevant ANLs are shown in Table 4.3.
The Noise Control Authority will consider a well-justified Construction Noise Permit (CNP) application, once filed, 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 in granting a CNP. Nothing in this EIA Report shall bind the Noise Control Authority in making his 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.
Table 4.3 Acceptable Noise Levels (ANL, Leq, 5 min dB(A))
|
Time period |
Area Sensitivity Rating |
||
|
|
A |
B |
C |
|
All days during the evening (1900-2300 hours) and general holidays (including Sundays) during the day and evening (0700-2300 hours) |
60 |
65 |
70 |
|
All days during the night-time (2300-0700 hours) |
45 |
50 |
55 |
In addition to the general controls on the use of PME during restricted hours, the EPD has implemented a more stringent scheme via the DA-TM. The DA-TM regulates the use of five types of Specified Powered Mechanical Equipment (SPME) and three types of Prescribed Construction Work (PCW), which are non-PME activities, in primarily densely populated neighbourhoods called Designated Areas (DAs). The SPME and PCW are:
SPME:
· hand-held breaker;
· bulldozer;
· concrete lorry mixer;
· dump truck; and
· hand-held vibratory poker.
PCW:
· erection or dismantling of formwork or scaffolding;
· loading, unloading or handling of rubble, wooden boards, steel bars, wood or scaffolding material; and
· hammering.
A CNP will be required for works during the time between 1900 and 0700 hours and any time on a general holiday, including Sunday, and the noise criteria for evaluating noise impact laid down in relevant TM issued under the NCO must be met.
The EIAO-TM and Technical Memorandum on Noise From Places
Other than Domestic Premises, Public Places or Construction Sites (IND-TM)
specifies the applicable Acceptable Noise Levels (ANLs) for operational noise
of the wind turbine system. The
ANLs are dependent on the Area Sensitivity Rating (ASR) and the time of the day
and are presented in Table 4.4.
Table 4.4 ANLs to be used as Operation Noise Criteria
|
Time Period |
LAeq
30min (dB(A)) |
||
|
ASR
“A” |
ASR
“B” |
ASR
“C” |
|
|
Daytime 0700-1900 |
60 |
65 |
70 |
|
Evening 1900-2300 |
60 |
65 |
70 |
|
Night-time 2300-0700 |
50 |
55 |
60 |
Fixed plant noise is controlled under Section 13 of the NCO
and the predictions will be undertaken in accordance with the IND-TM. The criteria noise limits are set out
in the EIAO-TM as follows:
·
the total fixed
source noise level at the facade of the nearest NSR is at least 5 dB(A) lower
than the appropriate ANL (as shown in Table 4.4) as specified in the Technical
Memorandum on Noise from Places other than Domestic Premises, Public Places or
Construction Sites (IND-TM);
or,
·
where the
prevailing noise level in the area is 5 dB(A) or more below the appropriate
ANL, the total fixed source noise level must not exceed this noise level.
The criteria noise limits stipulated in the IND-TM are dependent on the Area Sensitivity Rating (ASR) of the NSRs as shown in Table 4.4.
As the site is located in a rural area and no influencing factors affect
the NSRs, an ASR “A” has been assumed for the NSRs located within 300 m of
study boundary. Background noise
measurements have been conducted by HEC during 2004 to investigate the
prevailing noise level in the study area.
The 48-hour continuous measurements of prevailing free field noise
levels in the vicinity of No. 1 Tai Ling Tsuen are in the range of 45 – 80
dB(A) LAeq, 30min. With
the inclusion of façade correction, the measured prevailing noise level will be
higher than the (ANL-5) criterion, and therefore the (ANL – 5) criterion, i.e.
45 dB(A) LAeq, 30min for night-time period will be considered as the
stipulated noise limit for the assessment of operational noise impact. Detail of the noise measurement will be
further discussed in Section 4.3.2.
In any event, the Area Sensitive Rating assumed in this Report is for
indicative assessment only given that there are currently no influencing
factors assumed in the vicinity of the NSRs. It should be noted that fixed noise sources are controlled
under Section 13 of the NCO.
At the time of investigation, the Noise Control Authority shall
determine noise impact from concerned fixed noise sources on the basis of
prevailing legislation and practices being in force, and taking account of
contemporary conditions / situations of adjoining land uses. Nothing in this Report shall bind the
Noise Control Authority in the context of law enforcement against all the fixed
noise sources being assessment.
The proposed wind turbine system is located on the north-eastern side of Lamma Island. The Study Area is rural in nature and is characterised by predominantly low-rise/village type houses. Background noise is generally low and there are no private vehicles or industrial facilities within the Study Area. The major noise source is identified as the community noise from the residents.
To investigate the prevailing noise levels at the NSRs, a continuous 48-hour noise measurement has been conducted from 1200 hours on 25 May 2004 to 1200 hours on 27 May 2004. As there were problems in gaining access to the nearest NSR (N1), free-field noise measurement has been made at a close proximity to N1. In addition, as the measurements are conducted off-site from the nearest NSR N1, potential community noise associated with the residents will not be included in the measurement. Therefore, the measured levels are considered to represent the lowest ambient noise levels.
The chirps of the insect “cicadas” were identified as the dominant noise sources during the noise measurement. Although the chirps are seasonal in nature, the cicadas only chirps in early morning and day-time, such that the measured noise levels during night-time would not be affected by the chirps. Therefore the background noise measurement would represent the typical acoustic environment in the vicinity of the NSRs. The noise measurement report is presented in Annex B1 and the measurement results are summarised in Table 4.5. Since the measurement is a free field measurement, an appropriate façade correction of 3dB(A) has been applied to the noise measurement results. A timeline chart showing the prevailing noise levels is presented in Figure 4.1.
Table 4.5 Measured Prevailing Free-field Noise Level (with Façade Correction)
|
Period |
|
LAeq, 30min dB(A)
|
|
|
|
Minimum |
Average |
Maximum |
|
0700 – 2300 hours |
49.8 |
65.8 |
81.9 |
|
2300 – 0700 hours |
47.6 |
60.8 |
82.5 |
All NSRs, as defined by EIAO-TM, have been identified within an area of 300 m of the Study Area boundary. For NSRs outside the 300m Study Area boundary, such as Tai Wan Kau Tsuen and Lo Tik Wan are also identified. The locations of the NSRs are shown in Figure 4.2. No planned NSRs are identified in the study boundary.
Table 4.6 Identified Noise Sensitive Receivers
|
NSR |
Location |
Type of Uses |
|
N1 |
No. 1 Tai Ling Tsuen |
Residential (2-Storey) |
|
N2 |
No. 2 Tai Ling Tsuen |
Residential (1-Storey) |
|
N3 |
No. 3 Tai Ling Tsuen |
Residential (1-Storey) |
|
N4 |
Tai Wan Kau Tsuen |
Residential (3-Storey) |
|
N5 |
Lo Tik Wan |
Residential (1-Storey) |
The main construction activities associated with the Project that may cause noise impacts to the nearby NSRs are:
· Site formation - excavation by cutting and filling to form a site platform; construction of retaining wall around site perimeter; and construction of concrete footing for wind turbine foundation;
· E & M Erection - erection of wind turbine and high voltage distribution pillar; and
· Landscaping works - planting of trees and shrubs.
The construction works for Site Formation, E&M Erection and Landscape work will be carried out in phases without overlapping according to planned project programme, i.e. E&M works will be carried out after completion of site preparation and foundation work; and landscaping work will follow the completion of E&M erection.
The use of PME during the construction phase will be the main source of noise impact. For excavation activities associated with the site formation, the use of PMEs such as crane lorry, excavator, hand-held breaker, concrete lorry mixer, and vibratory poker have been considered in the noise impact assessment.
For the erection of wind turbine and high voltage distribution pillars, the use of PMEs such as heavy duty tracked crane, mobile crane and truck have been considered in the noise impact assessment.
Annex B2 presents a detailed list of PMEs, which are provided by the Project Proponent, assumed for each construction activity considered in the noise impact assessment. Project Proponent has confirmed that the plant inventory is practicable for the construction of wind turbine.
The normal working hours of the contractor will be between 0700 and 1900 hours from Monday to Saturday (except public holidays) and construction activities during restricted hours are not expected. Should evening and night works between 1900 and 0700 hours or on public holidays (including Sunday) be required, the contractor should submit a CNP application and will be assessed by the Noise Control Authority. Conditions stipulated in CNPs should be strictly followed.
The sources of noise emitted from the operating wind turbine include the rotation of mechanical and electrical equipment and aerodynamic noise originating from the flow of air around the blade. The mechanical and electrical equipment that may have potential noise producing effects are gearbox, transformer and generator.
Aerodynamic noise is produced by the flow of air over the blades, and it generally increases with rotor speed. Aerodynamic broadband noise is typically the largest source of wind turbine noise. The mechanisms of aerodynamic noise can be divided in the following:
· Low frequency noise - It is generated when rotating blade encounters localized flow deficiencies due to the flow around a tower and wind speed changes;
· Inflow turbulence noise - It depends on the amount of atmospheric turbulence. The atmospheric turbulence results in local force or local pressure fluctuations around the blade; and
· Airfoil self noise - It includes the noise generated by the air flow right along the surface of the airfoil.
With reference to the recent study([1]) , it is anticipated that vibration introduced by the modern 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. In fact, wind turbine manufactures nowadays use computer aided model in wind turbine design and fabrication to ensure that the vibration of different components do not interact to amplify noise.
It is now a standard practice for the wind turbine manufacturers to incorporate the low-noise design into their standard products. Sound insulation materials will be used in the nacelle to totally enclose the generator, shaft and gearbox so as to minimize medium and high frequency noise. Airfoil blades are purposely designed to reduce aerodynamic noise generated during wind turbine operation. Commercial products of wind turbine available in the market are already standard products of low-noise design.
For the proposed wind turbine, the transformer will be installed inside the tower; while the gearbox and generator will be located inside the nacelle and the switchgear and power conditioning devices will be installed in stainless steel huts with 20-30 mm thickness. It is envisaged that the noise from the mechanical and electrical equipment will be comparatively lower than the aerodynamic noise.
Some wind turbines, usually older models with higher rotational speed, may have tonal characteristics and can produce thumping noise. This can be caused by mechanical components or usual wind currents interacting with turbine blades. Pure tone have generally been eradicated in modern wind turbine design
Different wind turbine suppliers offer products of slightly
different noise data depending on their equipment specifications and site specific
requirements. The
proposed wind turbine system has a capacity of 600 – 850kW, with a design
maximum blade rotating speed of 31 rpm (refer to Table 3.1). This design limits the noise
generation, and hence it will also limit the noise impact to the nearby
NSRs. In addition, modern wind
turbines have already incorporated many designs to reduce the noise emissions.
The information sourced from wind turbine
suppliers reveals that the typical maximum sound power levels of 600 – 850kW
wind turbine fall approximately in the range of 98 to 104 dB(A) inclusive of the
rotation of mechanical parts, sound of electrical components and aerodynamic
noise. There has been at least one no. of the
prospective suppliers providing Type Approval ([2])
confirming their 600 - 850kW class wind turbines can be designed to a
maximum sound power level of 100dB(A).
The maximum sound power level of wind
turbines covers full range of operation including start-up, shut-down, cut-in,
cut-out, braking and yawing and full range of wind speeds. The standard design features of modern wind
turbines for lowing noise emission levels are described below:
·
Designing for Low Mechanical Noise from Wind Turbines
Mechanical noise is induced from the metal components moving or knocking against each other may originate in the gearbox, in the drive train (the shafts), and in the generator of a wind turbine. The better engineering practices described below can reduce the mechanical noise.
(i) Quieting Wind
Turbine Gearboxes
Gearboxes for wind turbines are no longer standard industrial gearboxes, but they have been adapted specifically for quiet operation of wind turbines. One way of achieving this is to ensure that the steel wheels of the gearbox have a semi-soft, flexible core, but a hard surface to ensure strength and long time wear.
The gear wheels
are heated up after their teeth have been ground, and then cool off slowly
while they are packed in a special high carbon-content powder. The carbon will then migrate into the
surface of the metal. This ensures
a high carbon content and high durability in the surface of the metal, while
the steel alloy in the interior remains softer and more flexible.
(ii) Structural Dynamics Analysis
An important
consideration, which enters into the turbine design process, is the fact that
the rotor blades may act as membranes that may retransmit noise vibrations from
the nacelle and tower. Wind turbine manufactures nowadays
use computer aided model in wind turbine design and fabrication to ensure that
the vibration of different components do not interact to amplify noise.
In addition, holes are drilled into the chassis frame so as to ensure that the frame will not vibrate in step with the other components in the turbine.
·
Designing for Low Aerodynamic Noise from Wind Turbines
(i) Rotor
Blade Sound Emission
Rotor blades must
brake the wind to transfer energy to the rotor. In the process they will cause some emission of white
noise. If the surfaces of the
rotor blades are very smooth (which indeed they must be for aerodynamic reasons),
the surfaces will emit a minor part of the noise. Most of the noise will originate from the trailing (back)
edge of the blades. Careful design
of trailing edges and very careful handling of rotor blades while they are
mounted, have become routine practice in the industry for noise control. In addition, most modern wind turbine
systems are pitch controlled, ensuring continuous and optimal adjustment of the
angles of the blades in relation to the prevailing wind, so as to maximize the
power output yet maintaining low noise levels.
(ii) Rotor
Blade Tip Design
Since the tip of the
blade moves substantially faster than the root of the blade, great care is
taken in the design of the rotor tip.
Research has been undertaken for performance reasons, since most of the
torque (rotational moment) of the rotor comes from the outer part of the blades. In addition, the airflows around the
tip of rotor blades are extremely complex, compared to the airflow over the
rest of the rotor blade. Specific
rotor blade tip design may be conducted in order to fulfill the site specific
requirement.
In conclusion, it is technically feasible and
practicable to limit the sound power level for wind turbine to 100 dB(A) by applying the
above standard
plant
design
features. The noise data presented represents a
typical noise spectrum of a 600 - 850kW class wind turbine which is technically
achievable.
For the tonal quality, there are now standard
accepted conditions which are imposed on wind turbine supplier which ensure the
absence of tonal content in the wind turbine noise spectra. These conditions are set out in
warranty agreements with wind turbine and tonal character is controlled by the
compliance level imposed on the wind turbine system. There has been at least one prospective supplier providing certificates
confirming their 750kW wind turbine is of pure tone free design. Moreover, the Danish Wind Industry
Association and American Wind Energy Association have
indicated that pure tones have generally been eradicated completely for modern
wind turbines manufactured by a number of the major suppliers.
The Project Proponent has committed to adopt
a wind turbine with an overall sound power level of not more than 100 dB(A) and
free of pure tones, which will be included as part of their tender
specification of wind turbine. The Project
Proponent will be requesting all the potential tenderers to confirm the noise
performance of their wind turbines before deciding on the wind turbine to be
used in the project. The maximum overall noise levels
and free of pure tones will be guaranteed by the plant supplier and verified on
site during commissioning and testing of the plant in accordance to
international standard procedures such as IEC 61400-11.
An overall sound
power level of 100 dB(A) with no tonal correction has been assumed in this
noise assessment.
When the wind speeds are below and above
the cut-in and cut-out wind speed, the wind turbine will become stationary and
therefore no noise impacts are expected below or above the cut-in and cut-out
wind speed.
Normally the rotor
speed of proposed wind turbine will vary from 14 to 31 rpm in the range of
effective wind speed, i.e. 2.5 to 25 m/s. The rotors will reach the maximum speed
when wind speed reaches about 9 – 10 m/s and keep steady up to 25 m/s.
Exceeding wind speed of 25 m/s, the wind turbine will cut-off, i.e. the
rotating parts of wind turbine including rotor, blades and shaft will all stop,
and hence the wind turbine will not cause for the increase in noise level. It should also be noted that in high wind speeds
exceeding 10 m/s, the background noise generated by tree, shrub, terrain and wind itself will gradually exceed
and mask the
wind turbine noise.
Based on the information from various wind
turbine suppliers, the sound power levels of wind turbines will reach the
maximum when the wind speed is at about 9 m/s, where rotor speed reaches the
maximum. The sound power levels in
octave bands are presented in Annex B3, which present the maximum noise
emission of the wind turbine operating at 9 m/s.
Based on the wind monitoring data, the
proposed wind turbine site will have high wind speeds exceeding 9 m/s for less than 10% of time per
year. In view of the low
percentage of time in high wind speed, it is anticipated that the wind turbine would be operating for
about 90% of the time below 100dB(A).
The methodology for the noise impact assessment is in accordance with the procedures outlined in the GW-TM, which is issued under the NCO and the EIAO-TM. In general, the methodology is as follows:
· locate representative NSRs that may be affected by the works;
· determine the plant teams for corresponding activities, based on agreed plant inventories;
· 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 activity was based on an assumed plant inventory, agreed with the Project Proponent. The notional source position of the work site was established in accordance with the procedures stated in the GW-TM. Noise impacts at NSRs were subsequently evaluated by comparing the predicted noise levels with the EIAO-TM daytime construction noise limits (Leq, 30min dB(A)), as outlined in Section 4.2.1.
The methodology
for the noise impact assessment is 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 will take into account
the distance attenuation, atmospheric absorption and corrections of tonality,
impulsiveness and intermittency, if any, in accordance with the IND-TM.
To assess the worst-case noise impact from the wind turbine, maximum noise emission of the wind turbine has been taken in the assessment.
Based on the notional source position as identified in accordance
with the procedures stated in the GW-TM, the source-to-NSR distances are
presented in Table 4.7.
Table 4.7 Noise Sensitive Receivers
|
NSR |
Location |
Approx. Horizontal Distance to Source (m) |
|
N1 |
No. 1 Tai Ling Tsuen |
260 |
|
N2 |
No. 2 Tai Ling Tsuen |
313 |
|
N3 |
No. 3 Tai Ling Tsuen |
357 |
|
N4 |
Tai Wan Kau Tsuen |
450 |
|
N5 |
Lo Tik Wan |
460 |
Based on existing topography, none of the NSRs will have direct line of sight to the construction site (Annex B5). Therefore, with reference to the GM-TM, a negative correction of 10 dB(A) has been included in the construction noise assessment.
Without the use of mitigation measures, predicted construction noise levels at all NSRs in all stages comply with the stipulated criterion. Details of the calculations are presented in Annex B2. A summary of the construction noise levels is presented in Table 4.8. As confirmed by the Project Proponent, there will not be overlapping periods between each construction activities. Hence cumulative noise impact during the construction period will not be a concern. Given that the predicted construction noise levels are well within the stipulated noise criterion, mitigation measures are not required to alleviate the noise impacts.
Table 4.8 Construction Noise Levels - Unmitigated (Leq, 30 min dB(A))
|
|
Construction Noise
Levels at Different Stages, Leq,
30 min dB(A) |
||
|
NSRs |
Site Formation |
Electrical &
Mechanical erection |
Landscaping |
|
N1 |
61 |
54 |
49 |
|
N2 |
59 |
52 |
47 |
|
N3 |
58 |
51 |
46 |
As NSRs N4 and N5 are located further away from the construction site, it is anticipated that the NSRs located in Tai Wan Kau Tsuen and Lo Tik Wan would not be affected by the construction noise.
Based on the maximum sound power level of 100 dB(A) for a typical wind turbine system, the facade noise levels at the identified NSRs are predicted and summarised in Table 4.9. Results indicate that the nearest NSR will be subject to noise level of 45 dB(A), therefore N4 and N5, which are located further away and are shielded by the existing topography, will be subject to even lower noise level than N1. N4 and N5 are therefore not expected to be affected by the operation of wind turbine.
A 5 dB(A) screening effect is taken into account for the N2 and N3 due to topography shielding and no direct line of sight to the whole swept area of the rotors of the wind turbine (see Annex B5). The terrain profiles presented in Annex B5 are derived by Digital Elevation Model (DEM) basing on the Land Information Centre (LIC) data from the Lands Department. Details of the calculations are presented in Annex B4.
Table 4.9 Predicted
Facade Noise Levels at NSRs
|
NSRs |
Description |
Predicted Facade Noise Level, dB(A) |
|
N1 |
No. 1 Tai Ling Tsuen |
45 |
|
N2 |
No. 2 Tai Ling Tsuen |
38 |
|
N3 |
No. 3 Tai Ling Tsuen |
37 |
Results indicated that the predicted facade noise levels will comply with the night-time (ANL-5) noise criterion at all NSRs.
It should be noted
that the assessment are on a conservative side as hemispherical propagation
model has been assumed in the assessment.
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. In reality, NSRs N1 to N3 are not located along the
favourable propagation path as Lamma Island is dominant by easterly wind and
NSRs N1 to N3 are located to the south-west of the wind turbine. In addition,
although the wind turbine will be partially screened by the topography (as
shown in Annex B5) when viewed from N1, the potential noise screening
effect has not been taken into account in the assessment as a conservative approach.
Moreover, the assessment are based on the worst-case scenario whereby
the wind turbine is operating at a worst-case wind speed with a maximum sound
power levels of 100 dB(A) is assumed.
With reference to the wind monitoring data, this worst-case will only
happen for less than 10% of time per year. It should also be noted that in this assessment, the
worst-case noise directivity effect associated with the wind turbine have been
assumed in the direction of the NSRs N1 to N3.
In view of the above, the noise assessment, in
particular to NSR N1, is considered to be on the conservative side.
The Project
Proponent has committed to adopt a wind turbine with an overall sound power
level of not more than 100 dB(A) and free of pure tones, which will be included
as part of their tender specification of wind turbine. The maximum noise level shall cover
full range of operation including start-up, shut-down, cut-in, cut-out, braking
and yawing; and full range of wind speeds. The supplier shall guarantee this noise level by providing
certificate of measurement and verify the overall noise level during
commissioning and testing in accordance to international standard procedures
such as IEC 61400-11. Whenever necessary, the supplier shall
apply attenuation measures to achieve the guaranteed noise level during detailed
design stage.
Though the predicted construction noise levels comply with the stipulated noise criterion, good site practice and noise management is recommended for minimising the construction noise impact on nearby NSRs.
It is difficult to quantify the reduction in noise impact that can be expected by adhering to good site practice, however the following measures are recommended to be followed during construction phase to reduce noise impacts:
· Only well-maintained plant should be operated on-site and plant should be serviced regularly during the construction works;
· Machines and plant that may be use intermittently, such as vibratory poker, should be shut down between work periods or should be throttled down to a minimum;
· Plant known to emit noise strongly in one direction, should, where possible, be orientated to direct noise away from nearby NSRs; and
· Mobile plant should be sited as far away from NSRs as possible.
The noise assessment indicated that, based on a worst-case scenario, with a maximum sound power level of 100 dB(A) and a tone free wind turbine, the predicted facade noise levels will comply with the night-time noise criterion at all NSRs. Hence, no further mitigation measures are required.
Given the compliance with the stipulated noise criterion, noise monitoring is not required during the construction stage. Though site audit will be conducted to ensure that the plant inventory used on site are consistent with the assumptions used in the EIA report.
During the operational phase, noise monitoring is recommended to ensure the compliance with the stipulated noise criterion at the nearby NSRs. A noise monitoring location is proposed at No. 1 Tai Ling Tsuen (N1). It is proposed noise monitoring shall be carried out during the night-time period at the agreed monitoring location once every fourteen days for a period of six consecutive months. Details of monitoring schedule and plan are presented in the separate EM&A Manual.
Unmitigated construction activities associated with the Project will not cause adverse noise impact to the nearby NSRs with the predicted construction noise levels in the range of 46 – 61 dB(A), which comply with the stipulated noise criterion. The mitigation measure of adopting good site practices is proposed to further minimise the construction noise impact to the environment. Regular site audits will be conducted during construction to ensure the plant inventory used on site is consistent with the assumptions in the EIA report.
With the adoption of a maximum sound power level of 100 dB(A) and a pure tone free wind turbine, the predicted facade noise levels will comply with the night-time noise criterion at all NSRs. The Project Proponent has committed to adopt a wind turbine with an overall sound power level of not more than 100 dB(A) and free of pure tones, which will be included as part of their tender specification of wind turbine. Noise monitoring during the operational phase is recommended so as to ensure the compliance with the stipulated noise criterion at the nearby NSRs.