8.
CONSTRUCTION
NOISE IMPACT ASSESSMENT
8.1.1
This Chapter presents an assessment
of noise impacts associated with the construction of the proposed Project.
8.1.2
Noise generated during the
construction phase by works activities and powered mechanical equipment will
impose potential impacts on nearby Noise Sensitive Receivers (NSRs). Appropriate
mitigation measures are recommended where necessary.
8.1.3
No noise impact is expected during
operation phase of this Project.
Construction Noise
8.2.1
There are currently no statutory
criteria for noise generated from construction work other than percussive
piling during the daytime hours of
8.2.2
The noise standards for general
construction works during normal working hours (i.e. 0700 to 1900 hours on any
day not being a Sunday or public holiday) stipulated in
Table 1B of Annex 5 of the
EIAO-TM are given
in Table
8.1.
EIAO-TM Daytime
Construction Noise Standards
|
Uses |
Daytime Construction Noise Standards, Leq
(30 minutes) dB(A) |
|
Domestic
Premises |
75 |
|
Educational
institutions (normal periods) |
70 |
|
Educational institutions
(during examination periods) |
65 |
Notes:
These standards assume the use of open windows for
ventilation. They are the maximum permissible noise levels assessed at 1 m from
the receiver’s external façade.
8.2.3
The principal legislation on the control
of construction noise during restricted hours is the Noise Control Ordinance
(NCO) (Cap.400) and its associated Technical Memoranda (TM). The NCO provides
statutory controls on general construction works during the restricted hours
(i.e. 1900 to 0700 hours Monday to Saturday and at any time on Sundays and
public holidays). The Contractor shall comply with the NCO and all relevant
regulations under this Ordinance, including restrictions placed on noise from
construction work and the requirements to seek Construction Noise Permit (CNP).
8.2.4
At present, construction works
during restricted hours are not expected. However, should works have to be
carried out during restricted hours, the Contractor must obtain a CNP from the
relevant Noise Control Authority (i.e. EPD) before the works are allowed to
take place. Percussive piling works are also subjected to CNP licensing under
the NCO. The Contractor is also required to display these permits
appropriately.
8.2.5
Despite the description or
assessment made in the subsequent sections, there is no guarantee that a CNP
will be issued for the project construction. The Noise Control Authority will
consider a well-justified CNP application, once filed, for construction works
within restricted hours as guided by the by the relevant Technical Memorandum
(Memoranda) issued under the NCO. The Noise Control Authority will take into
account of contemporary situations/conditions of adjoining land uses and any
previous complaints against construction activities at the site before making
his decision in granting a CNP. Nothing in this Report shall bind the Noise
Control Authority in making his decision. If a CNP is to be issued, the Noise
Control Authority shall include in it any conditions that are considered
appropriate and such conditions are to be followed while the works covered by
the permit are being carried out. Failure to comply with any such conditions
will lead to cancellation of the CNP and prosecution action under the NCO.
Noise
Assessment Study Area
8.3.1
For the purpose of noise
assessment, the Study Area covers essentially 300 m from the boundary of each
of the work sites of the Project. This Study Area can be reduced if the first
layer of the noise sensitive receivers, closer than 300 m from the boundary,
provides acoustic shielding to those receivers at further distance behind.
Description
of the Existing
Noise Environment
Cheung
Chau
8.3.2
The major land use in the vicinity
of the Project area at Cheung Chau is village
and marine environs. Cheung Chau enjoys a car-free environment with only
a limited number of village vehicles and emergency vehicles. The Project area
in Cheung Chau is generally quiet with the dominant noise mainly from village
vehicles travelling along
8.3.3
Commercial activities are mainly
centred near the ferry pier and
Lantau (Chi Ma Wan
8.3.4
The major land use in the Project
area at Lantau is natural coastline and the
8.4
Representative
Noise Sensitive Receivers
8.4.1
The Representative Noise Sensitive
Receivers (NSRs) chosen for noise assessment are shown in Figure 8.1. Photographs
showing these NSRs are shown in Figure 1 of Appendix 8.1. These Representative NSRs are selected in
accordance with the criteria in Annex 13 of the EIAO-TM. Reference has been
made to the land uses annotated under the following latest approved Cheung Chau
Outline Zoning Plan (OZP): S/I-CC/4.
8.4.2
Based on
the available information at the time of assessment, there are no planning
applications of sensitive uses within the Study Area. There are no NSRs found
within 500 m of the Project area at Lantau. There are also no educational
institutions within the Study Area of the Project. A
description of the Representative NSRs
is tabulated in Table 8.2.
Representative Noise Sensitive Receivers (NSRs)
|
Representative
NSR |
General
Description |
No.
of Floors |
Approximate
Horizontal Distance from Construction Activities (Notional Point Source) |
|
|
Launching Site |
Land-based |
|||
|
NSR 1 |
Village
house at No. 10 Siu Kwai Wan |
2 |
88
m |
90
m |
|
NSR 2 |
Village
house at No. 1A Tai Kwai Wan San Tsuen |
1 |
58
m |
20
m |
|
NSR 3 |
Village
house at Tai Kwai Wan San Tsuen |
2 |
165
m |
50
m |
|
NSR 4 |
Villa
at Block 1B, |
3 |
190
m |
75
m |
Note:
The location of the NSRs is
shown in Figure 8.1.
8.5
Construction
Noise Impact Assessment
Potential
Sources of Impacts
8.5.1
The main construction works will include laying of the submarine
portion of the water main across Adamasta Channel using Horizontal Directional
Drilling (HDD) technique and laying of the land-based water main using
traditional open cut method. Details of the construction activities and
sequencing of works are presented in Chapter 2.
8.5.2
In general, the main staging area
(launching site) will be located in Cheung Chau side. With the proposed
construction method of forward reaming and pushing the pipe from Cheung Chau
side, very minimum construction works will be required at Lantau side.
Likewise, land-based main at Lantau will be constructed and connected to the
nearby existing exposed main. No excavation is necessary at Lantau side, except
for a small exit pit for the drill string and reamers.
8.5.3
For the HDD works at Cheung Chau,
the main construction activities include site clearance / formation and
mobilisation of equipment, drilling, pipe installation / connections, and
demobilisation / site reinstatement works. For the land-based main laying at
Cheung Chau, the 500 mm diameter main will be laid along
8.5.4
Majority of the potential
construction noise impact will therefore occur at the launching site in Cheung
Chau.
Construction
Equipment
8.5.5
The type and quantity of Powered
Mechanical Equipment (
8.5.6
The equipment used in the noise
calculation was based on site experience and was reviewed by the design
engineers. It was considered reasonable in terms of the types and numbers to be
used by the Contractor for satisfactory completion of the Project based on the
tentative construction programme, though there may be variation in the actual
construction stage. A copy of WSD’s memo acknowledging the proposed
construction equipment is attached in Appendix
8.1.
Construction Schedule and Programme
8.5.7
The
construction duration for this Project is expected to last for about 24 months
within the tentative construction timeframe of early 2012 to early 2014.
Currently, construction work during restricted
hours is not anticipated.
Assessment Methodology and Assumptions
8.5.8
The construction noise assessment
has been conducted based on standard acoustic principles. The methodology has
made reference to the following:
·
Sections 5.3 & 5.4 of
Annex 13 of the EIAO-TM;
·
Technical Memorandum on Noise from
Construction Work other than Percussive Piling (TM-GW);
·
BS 5228-1:2009 – Code of Practice
for Noise and Vibration Control on Construction and Open Sites – Part 1: Noise (BS5228); and
·
EIAO Guidance Note No. 9/2004 –
“Preparation of Construction Noise Impact
Assessment under the Environmental Impact Assessment Ordinance”.
8.5.9
In general
terms, the methodology used involves the following steps:
(i)
identification
of the most likely worst case scenario from the construction programme;
(ii)
identification
of the nearest representative NSRs to the work site;
(iii)
calculation
of the total Sound Power Level (SWL) of equipment to be used;
(iv)
calculation of
distance attenuation to NSRs from work site notional noise source point; and
(v)
comparison of
the Predicted Noise Levels (PNLs) with the relevant noise standards.
8.5.10
The assessment has been undertaken
on the basis of the assumption that all construction equipment will be located
on a notional noise source point (in accordance with the TM-GW) and is
operating at the same time. The various construction activities are not
expected to be carried out concurrently. Likewise, the land-based main will
commence construction only after the submarine main has been installed.
Shielding effect from existing building structures, and/or topographic features
have not been considered to simulate worst-case effect. A façade correction of
+3 dB(A) is added to account for the sound reflection from the building’s
surface of a NSR.
Assessment Results
8.5.11
The unmitigated PNL at the Representative NSRs are
summarised below in Table 8.3. Detailed calculations are presented in Appendix 8.1.
Predicted
Noise Level during Construction at Cheung Chau - Unmitigated
|
Construction Activities |
Unmitigated Construction
Noise Level, dB(A) |
|||
|
NSR
1 |
NSR
2 |
NSR
3 |
NSR
4 |
|
|
Horizontal Directional Drilling works at Cheung Chau
|
||||
|
Site clearance / formation & equipment
mobilization |
74 |
77 |
69 |
68 |
|
Drilling (pilot bore and forward reaming) |
74 |
78 |
69 |
68 |
|
Pipe installation and connections |
74 |
78 |
69 |
68 |
|
Testing and commissioning |
70 |
74 |
65 |
64 |
|
Demobilization and site reinstatement |
73 |
76 |
67 |
66 |
|
Construction of land-based water main at Cheung Chau |
||||
|
Road breaking |
70 |
82 |
75 |
72 |
|
Trench excavation |
68 |
80 |
74 |
70 |
|
Pipe laying |
68 |
80 |
74 |
70 |
|
Backfilling |
69 |
81 |
74 |
71 |
|
Road reinstatement |
57 |
70 |
63 |
60 |
Notes:
Numbers in BOLD denote exceedance of
daytime noise standard: 75 dB(A) for residential premises.
8.5.12 Table 8.3 shows that unmitigated construction noise levels would exceed the daytime noise standards only at NSR 2. The predicted exceedance is due to the close proximity of the construction works to the NSR. Mitigation measures will be required. The recommended mitigation measures for the construction works are discussed in the subsequent section.
8.6.1 The predicted noise levels showed that construction works would give rise to daytime noise impacts to NSR 2 only. The following types of mitigation measures are recommended.
Level 1
Mitigation – Use of Quiet Plant
8.6.2
The use of quiet plant (also
referred as silenced equipment) can provide significant reduction in noise
level. Quiet plant is defined as PME whose actual sound power level is less
than the value specified in the TM-GW for the same piece of equipment. The common
source of these information is from international standard / certification,
e.g. BS 5228. To allow the Contractor some flexibility to select equipment to
suit actual needs, it is considered too restrictive to specify which specified silenced
equipment to be used for the construction works. Hence, it is preferable and
practical to specify the noise performance specification of the plant on site
in terms of the sound power level so that the Contractor is allowed some
flexibility. It should be noted that various types of silenced equipment can be
found in
8.6.3 The use of quiet plant is considered to be the most effective way of alleviating construction noise impact. The Contractor should use quiet plant with sound power level lower than that stipulated in the TM-GW as the Level 1 mitigation for construction noise.
8.6.4 The use of mini or lower power rating equipment (e.g. mini excavator) should also be considered where practical. This technique would be feasible and practical at some locations given the limited space available for using large size construction equipment and the small scale works involved such as the land-based water main in Cheung Chau.
8.6.5 The Contractor should take note of ETWB TCW No. 19/2005 – “Environmental Management on Construction Sites” which sets out the policy and procedures requiring contractors to, among others, adopt Quality Powered Mechanical Equipment (QPME).
*QPME are
construction plant and equipment that are notably quieter, more environmentally
friendly and efficient. EPD has developed a system for the registration of QPME
that are used in
8.6.6 A list of quiet powered mechanical equipment (PME) recommended for use during construction phase is tabulated below in Table 8.4.
Quiet Powered Mechanical
Equipment Recommended for Use during Construction Phase
|
Powered
Mechanical Equipment |
Power
Rating / Size, Weight |
Reference |
Sound
Power Level, dB(A) |
|
Excavator, loader |
107 kW / 22t |
BS5228 C.4-64 |
103 |
|
Crane |
390 kW / 600t |
BS5228 C.4-50 |
99 |
|
Power rammer |
3 kW |
BS5228 D.3-119 |
105 |
|
Hand-held breaker |
-- |
-- |
107 |
8.6.7 With the use of quiet plant, noise levels at NSR 2 will still exceed the daytime construction noise standard (from construction activities at the launching site) and will still require further mitigation measures (see Table 8.5).
Level 2
Mitigation – Use of Temporary Noise Barriers
8.6.8 Since NSR 2 (as with most of the NSRs within the Project area) are typically low-rise village houses of not more than 3 storeys (NSR 2 is one storey), it would be effective to have noise screening structures or temporary noise barriers purposely-built along the site boundary to provide additional protection to NSRs close to the construction site boundary. This could be in the form of purposely-built site hoarding constructed from appropriate materials with a minimum superficial density of 7 kg/m2. The noise barrier should have a vertical height of at least 4 m with a small cantilevered upper portion if necessary ensuring that the operating equipment can be shielded from the view of the NSRs. The temporary noise barrier should have no gaps or opening at joints. The Contractor should regularly inspect and maintain the noise barrier to ensure its effectiveness.
8.6.9 For the construction works which have the potential to exceed the noise standards on nearby NSR and whose line of sight cannot be effectively blocked by the temporary noise barrier, movable (mobile) barriers should be provided. This may also be applicable in situation where construction of a temporary noise barrier may not be possible due to site / space constraints, for example blocking village or emergency vehicle access. Movable barriers of at least 2.5 m height with a small cantilevered upper portion and skid footing can be located within a few meters of stationary plant (e.g. generator) and within about 5 m or more of a mobile equipment (e.g. excavator), such that the line of sight to the NSR is blocked by the barriers.
8.6.10 With the shielding effect provided by the proposed temporary noise barriers, noise reduction of 10 dB(A) and 5 dB(A) is expected for stationary equipment and mobile equipment respectively.
8.6.11 The proposed noise barrier for the NSR 2 is shown in Figure 8.2. A typical cross section view of the barrier showing line of sight could be shielded by the proposed barrier is included in Appendix 8.1.
Good Site Practices
8.6.12 In general, potential construction noise impact can be minimised or avoided by imposing a combination of the following good site practices as mitigation measures:
(a)
Only
well-maintained plant should be operated on-site and plant should be serviced
regularly during the construction period.
(b) Construction plant should be sited away from NSRs.
(c) Machines and plant that may be in intermittent use should be shut down between works periods or should be throttled down to a minimum.
(d) Equipment known to emit sound strongly in one direction should be orientated such that the noise is directed away from nearby NSRs.
(e) Material stockpiles and other structures (such as site offices) should be effectively utilised to shield on-site construction activities.
(f) The Contractor shall devise, arrange methods of working and carrying out the works in such manner as to minimise noise impacts on the surrounding environment, and shall provide experienced personnel with suitable training to ensure that these measures are implemented properly.
(g) In the event that new schools are built near the works area, the Contractor should minimise construction noise exposure to the schools (especially during examination periods). The Contractor should liaise with the school and the Examination Authority to ascertain the exact dates and times of all examination periods during the course of the contract and to avoid noisy activities during these periods.
8.6.13 The implementation of the above good site practices could be readily applied to construction sites and can, in theory, provide additional reduction in construction noise levels. However, such noise reduction is difficult to quantify and is therefore not considered in the calculations.
Public
Relations Strategy
8.6.14 Having good public relations with the local communities during the construction phase is indispensable for the smooth implementation of the Project. Prior to commencement of the construction, visits to the affected villages, local communities and property owners should be carried out. The purpose of the visits is to advise the public the following information in relation to the Project:
· the implementation programme of the works;
· the planned construction activities that will be involved;
· the possible impacts arising from the works;
· the measures to avoid or mitigate any adverse impacts;
· the monitoring programme to check the efficiency of the measures; and
· the communication channels between the local communities and the project office.
8.6.15 To maintain an effective communication channel with the public, a 24-hour hotline system should be established by the project office for the Contractor to receive any enquiry and complaint lodged by the public in respect of the Project. Upon receipt of enquiry / complaint, the Contractor (or its Environmental Team) should investigate the causes of the incident and take the appropriate action to rectify the situation. Periodic newsletters, information leaflets, notices or other means of communication should be provided to the affected villages, communities, and residents advising them the current progress, the schedule of works in future, the potential environmental impacts arising from the works and the corresponding mitigation measures. It is considered that such a close relation between the local communities and the project site office could ensure speedy resolution of any environmental non-compliance and maintain an environmental standard acceptable to the local communities during construction.
8.6.16 Table 8.5 shows the predicted noise levels with the implementation of Level 1 mitigation measures (use of quiet plant).
Predicted
Noise Level during Construction at Cheung Chau – Mitigated (Level 1
Mitigation: Use of Quiet Plant)
|
Construction Activities |
Mitigated Construction
Noise Level, dB(A) |
|||
|
NSR
1 |
NSR
2 |
NSR
3 |
NSR
4 |
|
|
Horizontal Directional Drilling works at Cheung Chau
|
||||
|
Site clearance / formation & equipment
mobilization |
69 |
73 |
64 |
63 |
|
Drilling (pilot bore and forward reaming) |
73 |
77 |
68 |
67 |
|
Pipe installation and connections |
73 |
77 |
68 |
67 |
|
Testing and commissioning |
67 |
71 |
62 |
61 |
|
Demobilization and site reinstatement |
69 |
72 |
64 |
62 |
|
Construction of land-based water main at Cheung Chau |
||||
|
Road breaking |
63 |
75 |
69 |
65 |
|
Trench excavation |
62 |
74 |
67 |
64 |
|
Pipe laying |
63 |
75 |
69 |
65 |
|
Backfilling |
62 |
74 |
68 |
65 |
|
Road reinstatement |
57 |
70 |
63 |
60 |
Note:
Numbers in BOLD denote exceedance of
daytime noise standard: 75 dB(A) for residential premises.
8.6.17 Table 8.6 shows the predicted noise levels for NSR 2 with the implementation of the proposed Level 2 mitigation measures (use of quiet plant + temporary noise barrier).
Predicted
Noise Level during Construction at Cheung Chau – Mitigated (Level 2
Mitigation: Use of Quiet Plant + Temporary Noise Barrier)
|
Construction Activities |
Mitigated Construction
Noise Level, dB(A) |
|
NSR
2 |
|
|
Horizontal Directional Drilling works at Cheung Chau
|
|
|
Site clearance / formation & equipment
mobilization |
71 |
|
Drilling (pilot bore and forward reaming) |
67 |
|
Pipe installation and connections |
67 |
|
Testing and commissioning |
62 |
|
Demobilization and site reinstatement |
71 |
Note:
Numbers in BOLD denote exceedance of
daytime noise standard: 75 dB(A) for residential premises.
8.6.18 All the above construction noise mitigation measures should be implemented by the Contractor during the construction phase of the works. The location of the temporary noise barriers (including any mobile barriers) should be further reviewed by the Contractor during the construction stage based on the latest construction programme and contemporary conditions, including any changes with respect to NSRs. The Contractor should design, construct, operate and maintain the mitigation measures throughout the construction phase and as required by the Engineer. Before commencement of the works, the Contractor should submit to the Engineer for approval (as part of their method statement) details of the mitigation measures to be employed under the works. The Contractor’s proposed mitigation measures should also be certified by the Environmental Team (ET) Leader and verified by the Independent Environmental Checker (IEC) to ensure the intended noise reduction effectiveness can be achieved.
8.7.1 With the implementation of proposed mitigation measures, adverse residual noise impact would not be expected from the construction works.
8.8.1 As indicated in Chapter 2, there is a potential concurrent project within the Study Area. Based on the best available information, this project involves the construction of village sewer at Tai Kwai Wan San Tsuen. Close liaison will be carried out to ensure concurrent works are avoided as far as possible. By avoiding concurrent works and given the small scale works involved, adverse cumulative noise impact is not expected during construction.
8.9
Monitoring
and Audit Requirements
8.9.1 Further information regarding construction noise monitoring and audit are broadly described in Chapter 9 of this EIA report. Key points are summarised in the following sections. Details of the monitoring and audit of the construction noise will be presented in the separate EM&A Manual.
8.9.2 Noise monitoring should be carried out at selected representative NSRs during the construction period to check for compliance with permissible noise standards, and to verify the effectiveness of the recommended mitigation measures. Ad-hoc monitoring and audit should also be carried out at other NSRs if complaints are received. Measures should be taken by the Contractor to ensure compliance with the noise standards.
8.9.3 It is recommended that NSR 2 should be monitored during the construction phase. This representative sensitive receiver has been selected for monitoring to represent a particular area likely to be most affected by the construction works of this Project.
8.10.1 The use of powered mechanical equipment during the construction phase of this Project is expected to create noise nuisance, due to the close proximity between the works areas and noise sensitive receivers. Assessment indicates that such noise impacts can be mitigated to acceptable levels by appropriate measures, such as the use of quiet plant, temporary noise barriers and the implementation of good site practices. The Contractor will be required to implement these measures when powered mechanical equipment is used during the construction phase. With these measures in place, residual noise impact would not be expected from the construction works and will comply with the EIAO-TM daytime construction noise standard.
8.10.2
Noise monitoring is recommended
at selected noise sensitive receivers during the construction period to check
for compliance with permissible noise levels and effectiveness of the proposed
mitigation measures.