5.
NOISE IMPACT ASSESSMENT
5.1.1 This chapter presents an assessment of noise impacts associated with the construction and operation of the proposed secondary drainage channel – KT13.
5.1.2 The main noise impacts are identified as follows:
(i) Construction Phase – the noise generated from construction activities and related powered mechanical equipment have the potential to pose adverse noise impacts to the surrounding sensitive receivers.
(ii) Operational Phase – the operation of the proposed secondary drainage channel – KT13 is not expected to pose any adverse noise impact on the surrounding environment. No noisy electrical or mechanical equipment will be operated. The maintenance access will be solely used by DSD only and will not be open for public use.
5.1.3 Appropriate mitigation measures are recommended, where necessary, to mitigate any adverse impacts.
Noise Assessment
Study Area
5.2.1 For the purpose of noise assessment, the Study Area covers essentially 300 m from the boundary of KT13 (Figure 5.1). The “study area” can be reduced if the first layer of the noise sensitive receivers, closer than 300m from the boundary, provides acoustic shielding to those receivers at further distance behind.
Description of
the Environment
5.2.2 The existing noise climate within the Study Area is dominated by the traffic on the major highway - Route 3 that is about 180 m west of the Study Area. Railway noise from West Rail that is about 200m east of the Study Area also contribute to the noise environment.
5.2.3 The major landuses in the vicinity of the Study Area is agriculture land with villages houses scattered around. There is no school in the immediate vicinity of the site. Also, no major industrial activities are found in the area.
Construction Noise Criteria
5.3.1 The principal legislation on the control of construction noise is the Noise Control Ordinance (NCO) (Cap. 400). In addition, there is provision in the Technical Memorandum on EIA Process for assessing noise from construction activities during daytime.
5.3.2 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) under the Technical Memorandum on EIA Process are given in Table 5.1.
Technical
Memorandum on EIA Process
Daytime
Construction Noise Standards
|
Uses |
Construction Noise
Standards, Leq (30 minutes) dB(A) |
|
Domestic
Premises |
75 |
|
Educational
institutions (normal periods) |
70 |
|
Educational
institutions (during examination periods) |
65 |
Note: These standards assume the use of open windows for ventilation. They are the maximum permissible noise levels assessed at 1 m from the NSR’s external facade.
5.3.3
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 with any regulations
made under the Ordinance, including restrictions placed on noise from
construction work and the requirements to seek Construction Noise Permit (CNP).
At present, construction works during restricted hours are not expected.
However, should works have to be carried out during restricted hours, a CNP
must be obtained from the relevant Noise Control Authority (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.
5.3.4 Despite the description or assessment made in the subsequent sections, EPD will be guided by the relevant Technical Memorandum (Memoranda) under the NCO in assessing an application, once filed, for a CNP. All factors affecting the decision will be considered including contemporary situations/conditions. Nothing in this report shall bind EPD in making its decision. There is no guarantee that a CNP will be issued. If a permit is to be issued, EPD will include any conditions considered appropriate and such conditions are to be followed while the works covered by the permit are being carried out. Failure to comply with the conditions stipulated will lead to cancellation of the permit and prosecution action under the NCO.
5.4
Representative Noise Sensitive Receivers
5.4.1 The Representative Noise Sensitive Receivers (RNSRs) chosen for construction noise assessment are shown in Figure 5.2. Based on site survey, there are no existing schools close to the works area. A description of the NSRs is tabulated in Table 5.2.
Details of the Existing NSRs
close to KT13
|
RNSR |
General Description |
No. of Floors |
Horizontal Distance from Construction Activities
(Notional Point Source) (m) |
|
13a |
Village house in Ma On Kong Village |
3 |
50 |
|
13b |
Village house in North of Ma On Kong Village |
3 |
25 |
|
13c |
Village house in Ma On Kong Village |
3 |
28 |
|
13d |
Village house in Ho Pui Village |
1 |
14 |
|
13e |
Village house in Ho Pui Village |
3 |
25 |
|
13f |
Village house in Ma On Kong Village |
3 |
12 |
5.5
Construction Noise Assessment and Mitigation
Potential
Sources of Impacts
5.5.1 The construction activities of KT13 mainly include the site clearance, excavation of channel, construction of formwork and concreting works. It will be carried out one after another without overlapping periods. Any concrete to be used will be transported to the work site. No on-site concrete batching plant will be erected. When construction tenders/contracts are prepared, these documents will clearly specify that the Contractor shall not erect and operate on-site concrete batching plant.
Construction
Equipment
5.5.2 The type and quantity of Powered Mechanical Equipment (PME) likely to be used in each construction works described above and their Sound Power Level (SWL) are listed in Appendix F. It should be noted that this is an assumption of the most likely equipment to be used. The actual construction equipment will be determined by the Contractor performing the works.
5.5.3
The equipment list was reviewed
by the design engineers and was considered to be reasonable in terms of the
types and numbers based on the tentative construction program. A copy of DSD’s
memo [Ref. (19) in DSD PM 8/4092 CD/17 (V)] dated
Construction
Schedule and Program
5.5.4
The
construction duration for KT13 is expected to last for about 36 months, from mid
2007 to mid 2010. Based on the
current programme, work during restricted hours is not anticipated.
Assessment
Methodology and Assumptions
5.5.5
The construction noise
assessment has been conducted based on standard acoustic principles, the methodology
stated in the Technical Memorandum on Noise from Construction Works Other Than
Percussive Piling and Sections 5.3 & 5.4 of Annex 13 of the Technical
Memorandum on EIA Process. The assessment also makes reference to the BS 5228:
Part 1: 1997 Noise and Vibration Control on Construction and Open Sites, Part
1: Code of Practice for Basic Information and Procedures for Noise and
Vibration Control (BS5228).
5.5.6
In general terms, the methodology used involves the
following steps:
(i) identification of
the most likely worst case scenario from the construction program;
(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 criteria.
5.5.7 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 Technical Memorandum on Noise from Construction Works Other Than Percussive Piling) and is operating at the same time. Shielding effect from existing building structures, topographic features and/or neighbouring construction sites 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.
5.5.8 Construction works that are more than 1000 m away from the RNSRs have not been considered in the calculations as the distance attenuation will result in 68 dB(A) noise reduction, thereby rendering the noise contribution from distant construction works being very minor.
5.5.9 Details of the construction activities and the noise levels are presented in Appendix F.
Assessment Results
5.5.10 The unmitigated PNL at the NSRs of various construction activities are summarised below in Table 5.3. Detailed calculations are presented in Appendix F.
Predicted (Unmitigated)
Construction Noise Levels
|
RNSR |
Predicted (Unmitigated) Construction Noise Level,
dB(A) |
|||
|
Construction Activities |
Site Clearance |
Excavation of Channel |
Construction of Formwork |
Concreting Works |
|
13a |
76 |
76 |
75 |
78 |
|
13b |
82 |
82 |
81 |
84 |
|
13c |
81 |
81 |
80 |
83 |
|
13d |
87 |
87 |
86 |
89 |
|
13e |
82 |
82 |
81 |
84 |
|
13f |
88 |
88 |
87 |
90 |
Notes:
BOLD denotes exceedance of daytime
noise criteria 75 dB(A) for residential premises.
5.5.11 Table 5.3 shows that the results of the unmitigated construction noise level would exceed the Technical Memorandum on EIA Process daytime noise standard at most of the RNSRs of up to 15 dB(A), as the construction works will be carried out at a short distance of less than 12 m from the NSR. Among the construction activities, the worst construction noise impact is predicted to be that associated with the concreting works. Since gabion is proposed as the channel base and lining, the volume of concrete required is expected to be substantially reduced. The likely exceedance with respect to each receiver is expected to be temporary and intermittent. Suitable mitigation measures are proposed. The recommended mitigation measures for the construction works are discussed in the following section.
Mitigation Measures
5.5.12 The predicted noise levels showed that construction works would give rise to adverse daytime noise impacts to most of the RNSRs. The following types of mitigation measures are recommended.
Use of Quiet Plant
5.5.13
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 Technical Memorandum on Noise from Construction Works
Other Than Percussive Piling for the same piece of equipment. To allow the
Contractor some flexibility to select equipment to suit his needs, it is
considered too restrictive to specify which specific items of silenced
equipment to be used for the construction operations. It should be noted that
various types of silenced equipment can be found in
5.5.14 The quiet plant used in the construction noise calculation is shown in Appendix F.
Use of Movable and Temporary Barriers
5.5.15 Movable (mobile) barriers can be used to screen NSRs from particular items of plant or noisy operations. Movable barriers of 3 to 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, compressor) and within about 5 m or more of a mobile equipment (e.g. excavator, mobile crane), such that the line of sight to the NSR is blocked by the barriers. It would be possible for the Contractor to provide mobile noise barriers or screens constructed of appropriate material with a minimum superficial density of 10 kg/m2 located close to operating equipment. Certain types of stationary equipment, such as generators and compressors, can be completely screened by construction barriers giving a total noise reduction of 10 dB(A) or more.
5.5.16 For this assessment, it was estimated that movable noise barriers can achieve a 10 dB(A) reduction for the construction equipment.
Use of Noise Screening Structures or Purpose-built
Noise Barriers along the Site Boundary
5.5.17 Since most of the NSRs within the Study Area are typically low-rise village houses, 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 10 kg/m2. Merely using plywood would not be effective. It is noted that under the WBTC No. 19/2001, all construction sites are required to use metallic site hoarding to reduce the amount of timber. This metallic hoarding can be slightly modified (such as the addition of steel backings) into purpose-built noise barriers. The noise barrier should have a vertical height of at least 3 m or a height ensuring that the operating equipment can be shielded from the view of the NSRs. It should have no gaps or opening at joints. The Contractor should regularly inspect and maintain the noise barrier to ensure its effectiveness.
5.5.18 Similar to the movable barrier, a 10 dB(A) reduction is expected for construction plant.
Proper Site Practices
5.5.19 In general, potential construction noise impact can be minimized or avoided by imposing a combination of the following proper 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) Stationary equipment should be located within the channel when weather conditions permit (e.g. dry season).
(g) 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.
(h) 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.
5.5.20 The implementation of the above proper 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.
Proposed
Construction Noise Mitigation Measures
5.5.21 The Contractor is required to adopt Levels 1 and 2 site specific direct technical measures as specified below during construction phase. The Contractor is also required to implement the proper site practices described above.
Level 1
Mitigation Measure
5.5.22 The use of quiet plant is considered to be one of the most effective ways of alleviating construction noise impacts. The use of equipment with sound power level lower than that stipulated in the Technical Memorandum on Noise from Construction Works Other Than Percussive Piling is recommended as the first level mitigation (Level 1 mitigation) for all construction works for KT13.
Level 2 Mitigation Measure
5.5.23 In addition to the use of quiet plant, mitigation in the form of purpose built site hoarding as noise barrier (Level 2 mitigation) are proposed where several construction works would be undertaken close to the existing villages, such as Ho Pui Village and village houses in and to the north of Ma On Kong Village (Figure 5.3). Temporary noise barrier of minimum 3m in height should be erected along the site boundary of the construction work which is closest to the NSRs. Notwithstanding the minimum height required, these barriers shall be constructed in a way such that no construction works and PME can be visible from the low rise noise sensitive receivers they protect. This is considered achievable, as some of the construction equipment/activities would be located within the channel, the base of which is about 2 m below the surrounding ground level. The temporary noise barrier should be gap free apart from necessary entrance/exits. Minimum density of the construction material for the temporary barrier shall be 10 kg/m².
5.5.24 Where the affected sensitive receivers are very close to the construction works so that they cannot be adequately screened by the proposed temporary noise barrier as depicted on Figure 5.3, the Contractor is required to fully or partially modified the design of the temporary noise barrier, such as adding a cantilever portion or the use of mobile barrier, to screen the construction works from the line of sight of the affected sensitive receivers. A typical cross section view of the construction site and proposed noise barriers is shown in Figure F1 of Appendix F.
5.5.25 Tables 5.4a-d show the predicted noise level with the implementation of the proposed mitigation measures.
Predicted
(Mitigated) Construction Noise Level for Site Clearance
|
RNSR |
Unmitigated Construction
Noise Level, dB(A) |
Mitigated Construction
Noise Level, dB(A) |
|
|
Level 1 Mitigation: Use of
Quiet Plant |
Level 2 Mitigation: Use of
Quiet Plant + Noise Barrier |
||
|
13a |
76 |
71 |
N/A |
|
13b |
82 |
78 |
68 |
|
13c |
81 |
77 |
67 |
|
13d |
87 |
83 |
73 |
|
13e |
82 |
78 |
68 |
|
13f |
88 |
84 |
74 |
Notes:
NA = not applicable or not required
BOLD denotes
exceedance of daytime noise criteria: 75 dB(A) for residential premises.
Predicted
(Mitigated) Construction Noise Level for Excavation of Channel
|
RNSR |
Unmitigated Construction
Noise Level, dB(A) |
Mitigated Construction
Noise Level, dB(A) |
|
|
Level 1 Mitigation: Use of
Quiet Plant |
Level 2 Mitigation: Use of
Quiet Plant + Noise Barrier |
||
|
13a |
76 |
71 |
N/A |
|
13b |
82 |
78 |
68 |
|
13c |
81 |
77 |
67 |
|
13d |
87 |
83 |
73 |
|
13e |
82 |
78 |
68 |
|
13f |
88 |
84 |
74 |
Notes:
NA = not applicable or not required
BOLD denotes
exceedance of daytime noise criteria: 75 dB(A) for residential premises.
Predicted
(Mitigated) Construction Noise Level for Formwork Construction
|
RNSR |
Unmitigated Construction
Noise Level, dB(A) |
Mitigated Construction
Noise Level, dB(A) |
|
|
Level 1 Mitigation: Use of
Quiet Plant |
Level 2 Mitigation: Use of
Quiet Plant + Noise Barrier |
||
|
13a |
75 |
N/A |
N/A |
|
13b |
81 |
76 |
66 |
|
13c |
80 |
75 |
N/A |
|
13d |
86 |
81 |
71 |
|
13e |
81 |
76 |
66 |
|
13f |
87 |
82 |
72 |
Notes:
NA = not applicable or not required
BOLD denotes
exceedance of daytime noise criteria: 75 dB(A) for residential premises,
Predicted
(Mitigated) Construction Noise Level for Concreting Work
|
RNSR |
Unmitigated Construction
Noise Level, dB(A) |
Mitigated Construction
Noise Level, dB(A) |
|
|
Level 1 Mitigation: Use of
Quiet Plant |
Level 2 Mitigation: Use of
Quiet Plant + Noise Barrier |
||
|
13a |
78 |
67 |
N/A |
|
13b |
84 |
73 |
N/A |
|
13c |
83 |
72 |
N/A |
|
13d |
89 |
78 |
68 |
|
13e |
84 |
73 |
N/A |
|
13f |
90 |
79 |
69 |
Notes:
NA = not applicable or not required
BOLD denotes
exceedance of daytime noise criteria: 75 dB(A) for residential premises,
5.5.26 Table 5.5 summarizes the mitigation measures proposed for the construction works. All the proposed construction noise mitigation measures should be implemented by the Contractor during the construction stage of the works. The locations of the temporary noise barriers should be further reviewed during the detailed design stage by the detailed design engineer or by the Engineer / Environmental Team (ET) Leader during the construction stage based on the latest construction programme and contemporary site conditions, including any changes with respect to NSRs. The Contractor should design, construct, operate and maintain the mitigation measures throughout the construction stage 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 ET Leader and verified by the Independent Environmental Checker (IEC) to ensure the intended noise reduction effectiveness can be achieved.
Summary of Proposed Construction Noise Mitigation
Measures
|
Proposed Mitigation
Measures |
Application to Construction
Sites / Works |
|
Use of quiet
equipment (Level 1 mitigation) |
Applicable
to all construction sites / works |
|
Use of
purpose-built minimum 3m tall boundary wall / site hoarding along
construction site boundary and/or movable (mobile) noise barrier (Level 2
mitigation). The barriers should be located at the location of the works to
enable shielding of the NSRs from the construction works. Where the affected NSRs cannot be
adequately screened by the noise barriers, it should be modified by adding a
cantilever portion to screen off direct line of sight to the construction
site. |
Applicable
to the construction sites / works close to NSRs such as Ho Pui Village, Ma On
Kong Village and North of Ma On Kong Village |
|
Proper site
practice |
Applicable
to all construction sites / works |
Note:
All the proposed construction
noise mitigation measures are to be implemented by the Construction
Contractor(s) during the construction stage of the works.
5.6.1 Residual construction impact is not expected after implementation of both Level 1 and Level 2 site specific measures as well as the general mitigation measures specified above.
5.7
Cumulative Construction Noise Impact
5.7.1 Most known major civil works projects such as West Rail and Kam Tin River Main Drainage Channel have been completed. No cumulative noise impacts with such projects is likely.
5.7.2 Other secondary drainage channels might be constructed within the same timeframe as KT13. All are spread out across the Kam Tin area. The nearest of which (KT12) is at least 350 m east of KT13. The other nearby projects included the secondary drainage channels KT14 and KT15 which is approximately 650m and 1300m away from KT13. This large buffer distance would greatly reduce the noise impact generated by each construction activities. Despite the two years construction period, the cumulative noise impacts as a result of concurrent channel works within the Kam Tin areas are not expected to be significant provided that the recommended noise mitigation measures are implemented.
5.8
Monitoring and Audit Requirements
5.8.1 Noise monitoring should be carried out at selected representative NSR during the construction period to monitor compliance with permissible noise levels for the construction activities being undertaken for the drainage improvement work. Monitoring is also required to check the effectiveness of the recommended mitigation measures. Ad-hoc monitoring and audit should also be carried out at other NSRs in case of complaints, and measures taken to ensure acceptable noise levels are met as far as possible.
5.8.2 It is recommended that the following representative NSRs be monitored during construction stage of the drainage improvement work. These NSRs are selected to represent a particular area likely to be worst affected by the construction works and where applicable to monitor potential cumulative noise impacts from concurrent projects.
· NSR 13b : North of Ma On Kong Village (N1) – closest to Section A
·
NSR 13d :
·
NSR 13f :
5.8.3 The details of EM&A requirements are presented in Chapter 11 of this Report.
5.9.1 The use of powered mechanical equipment during the construction phase of KT13 is expected to create construction noise nuisance due to the close proximity between the works area and the sensitive receivers. Mitigation measures are available to reduce the construction noise impacts to acceptable levels. The recommended mitigation measures include use of quiet plant, the use of noise barriers and proper site practices. Provided the Contractor implements the recommended mitigation measures, the construction noise levels can be kept to reasonable levels at all times.
5.9.2
Noise monitoring is recommended
at selected representative NSRs during the construction period to monitor
compliance with daytime construction noise levels for the construction
activities being undertaken for the drainage improvement.
5.9.3
It is expected that the
operation of the channelized KT13 will not pose any adverse noise impact to the
surrounding environment.