5.                   COnSTRuction NOISE IMPACT

Introduction

5.1               This section presents the potential noise impacts arising from the proposed Project during construction phase. It is expected that construction noise impact will arise from the proposed Project as well as the nearby concurrent project (i.e. Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction). Cumulative daytime construction noise impacts are assessed in this study.

Environmental Legislation, Policies, Plans, Standards and Criteria

General

5.2               Noise impacts generated by the construction of this Project have been assessed in accordance with the criteria and methodology given in the Technical Memoranda (TMs) under the Noise Control Ordinance (NCO), and the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM).

5.3               The NCO and EIAO provide the statutory framework for noise control. Applicable assessment procedures and standards are set out in three TMs listed below:

·            EIAO-TM

·            TM on Noise from Construction Work other than Percussive Piling (GW-TM)

·            TM on Noise from Construction Work in Designated Areas (DA-TM)

Construction Noise – General Construction Works

5.4               The NCO provides the statutory framework for noise control of construction work, other than percussive piling, using powered mechanical equipment (PME) between the hours of 1900 and 0700 hours or at any time on Sundays and general holiday (that is, restricted hours). Noise control on construction activities taking place at other times is subject to the Criteria for Evaluating Noise Impact stated in Table 1A of Annex 5 in the EIAO-TM. The noise limit is Leq (30 minutes) 75 dB(A) at the façades of dwellings and 70 dB(A) at the façade of schools (65 dB(A) during examinations). The EIAO-TM construction noise criteria are summarised in Table 5.1.

 

Table 5.1      Daytime Construction Noise Criteria

Use

Noise Level in Leq(30-minutes), dB(A)

Residential

75

Educational Institution

70

Educational Institution (during examination)

65

 

5.5               Between 1900 and 0700 hours and all day on Sundays and public holidays, activities involving the use of PME for the purpose of carrying out construction work is prohibited unless a construction noise permit (CNP) has been obtained. A CNP may be granted provided that the Acceptable Noise Level (ANL) for the noise sensitive receivers can be complied with. ANLs are assigned depending upon the area sensitive rating (ASR). The corresponding ANLs for evening and night time periods are given in Table 5.2.

 

 

Table 5.2      Acceptable Noise Levels

Time Period

Acceptable Noise Level in Leq(5-minutes), dB(A)

ASR A

ASR B

ASR C

Evening (1900 to 2300 hours) (1)

60

65

70

Night (2300 to 0700 hours)

45

50

55

Note: (1) Includes Sundays and Public Holidays during daytime and evening

 

5.6               Despite any description or assessment made in this EIA Report on construction noise aspects, there is no guarantee that a Construction Noise Permit (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 relevant Technical Memoranda issued under the Noise Control Ordinance. The Noise Control Authority will take into account of contemporary conditions / situations 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 EIA Report shall bind the Noise Control Authority in making his decision. Failure to comply with any such conditions will lead to cancellation of the CNP and prosecution action under the NCO.

5.7               Under the DA-TM, the use of five types of Specified Powered Mechanical Equipment (SPME) and three types of Prescribed Construction Work (PCW) within a designated area during restricted hours would require a valid CNP. The SPME includes hand-held breaker, bulldozer, concrete lorry mixer, dump truck and hand-held vibratory poker. The PCW are:

·            erecting or dismantling of formwork or scaffolding

·            loading, unloading or handling of rubble, wooden boards, steel bars, wood or scaffolding material

·            hammering

5.8               In general, it should not be presumed that a CNP would be granted for carrying out PCW within a designated area during the restricted hours. The CNP may be granted for the execution of construction works during restricted hours involving the use of PME and / or SPME if the relevant Acceptable Noise Levels and criteria stipulated in the GW-TM and DA-TM can be met.

5.9               It is envisaged that no construction works will be conducted during restricted hours (i.e. time between 1900 and 0700 hours and any time on a general holiday, including Sunday) according to the preliminary construction programme.

Noise Sensitive Receivers

5.10            Based on the criteria set out in the EIAO-TM, representative noise sensitive receivers (NSRs) have been identified close to the Project site. Table 5.3 presents descriptions of these selected NSRs. Locations of NSRs and the proposed works areas are illustrated in Figure 5.1.

5.11            As shown in Figure 5.1, Pok Fu Lam Country Park lies to the south of the Project site and would be regarded as NSRs according to the EIAO-TM. Visitors to the country park would potentially be impacted by the proposed construction works.

 

Table 5.3      Summary of Representative Existing Noise Sensitive Receivers

NSR

Location

Horizontal Separation from Closest Works Area Boundary (m)

Land Use

N1

Block A, Po Shan Mansions

7

Residential

N2

Block A, Po Shan Mansions

35

Residential

N3

Hamilton Court

145

Residential

N4

Piccadilly Mansion

165

Residential

N5

No. 21 Po Shan Road

45

Residential

N6

No. 53 Conduit Road

55

Residential

N7

Pok Fu Lam Country Park

(1)

Country Park

Note: (1) The landslide preventive works fall partially within the Pok Fu Lam Country Park

Assessment Methodology

5.12            The proposed works are scheduled to complete within 10 months. The preliminary construction activities involved in the Project is shown in Table 5.4.

 

Table 5.4      Construction Activities Involved

Item

Activity

1

Site clearance and set up

2

Soil nail installation

3

Soil nail head construction

4

Rock slope stabilization works

5

Raking drain installation

6

Landscaping works

7

Site reinstatement works

 

5.13            The construction plant inventory for all construction activities and planned works areas relevant to this Project are given in Table 5.5.

 

Table 5.5      Proposed Construction Plant Inventory

PME

Number

To be used in activity

Works Area (1)

Dump truck

1

Site clearance and set up

B

Air compressor

4

Soil nail installation, soil nail head construction, rock slope stabilization and raking drain installation

2 in A and 2 in G

Drill rig

6

E and F

Grouting machine

3

1 in A and 2 in G

Generator

2

1 in A and 1 in G

Concrete mixer

3

1 in A and 2 in G

Note: (1) Refer to Figure 5.1

 

5.14            In accordance with the EIAO, the methodology outlined in the GW-TM has been used for the assessment of construction noise (excluding percussive piling). Sound Power Levels (SWLs) of the equipment were taken from Table 3 of this TM. Where no SWL was supplied in the GW-TM, reference was made to BS 5228, previous similar studies or from measurements taken at other sites in Hong Kong. Schedule of powered mechanical equipment (PME) for the different construction tasks during normal daytime working hours is presented in Appendix 5.1.

5.15            It was assumed that air compressors, grouting machines, generators and concrete mixers would be located at particular locations as far as possible from NSRs at construction site. The assessment is based on the cumulative SWL of PME likely to be used for each location, taking into account the construction period in the vicinity of the receiver location. To predict the noise level, PME was divided into groups required for each discrete construction task. The objective was to identify the worst case scenario representing those items of PME that would be in use concurrently at any given time. The sound pressure level of each construction task was calculated, depending on the number of plant and distance from receivers. The noise levels at NSRs were then predicted by adding up the SWLs of all concurrent construction tasks.

5.16            A positive 3 dB(A) façade correction was added to the predicted noise levels in order to account for the facade effect at each NSR.

Identification of Environmental Impacts

5.17            The scope of this Project includes the installation about 700 numbers of soil nails and about 60 numbers of ranking drains on the natural terrain within the concerned areas as shown in Figure 1.4. The length of the soil is about 20m with spacing of 2m horizontally and 3m vertically; the length of ranking drains is about 10m with spacing of 5m horizontally and 15m vertically. Potential construction impacts of the Project may arise from the following activities:

·            Transportation on access road by dump truck for site clearance;

·            Air compressor, drill rig, grouting machine, generator and concrete mixer for soil nail installation, soil head construction, rock slope stabilization and ranking drain installation.

5.18            The Project (Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction) would also contribute to the cumulative construction noise impacts.

Prediction and Evaluation of Environmental Impacts

5.19            For normal daytime working hours, exceedences of the construction noise criteria i.e. Leq (30 minutes) 75 dB(A) for residential uses are predicted at representative NSRs in the absence of mitigation measures.

5.20            Based on the proposed plant inventory as shown in Table 5.5, construction noise impacts from various construction activities were predicted. It was assumed that drill rigs were located closest to the NSRs in Works Area C as a worst case scenario for prediction. Due to engineering consideration, the drill rigs have to be located 15m apart from each other.

5.21            Details of construction noise calculations and results are presented in Appendix 5.2. Results show that the predicted noise levels at NSRs N1 to N6 are in the range of 52 to 82 dB(A). A summary of the unmitigated construction noise levels of the representative NSRs during normal daytime working hours within the construction period of the Project is listed in Table 5.6. Noise mitigation measures would therefore be required to reduce noise levels to the stipulated standard.

 

Table 5.6      Unmitigated Construction Noise Levels

NSR

Predicted Noise Levels, dB(A)

Daytime Construction Noise Criteria, dB(A)

N1

62 – 82

75

N2

61 – 79

75

N3

53 – 69

75

N4

52 – 68

75

N5

64 – 72

75

N6

60 – 72

75

 

5.22            Visitors to the Country Park (NSR N7) would potentially be impacted by the proposed construction works. Taking into account the transient nature of visitors to the Country Park, insurmountable construction noise impact on the NSR N7 would not be envisaged.

 

Mitigation of Adverse Environmental Impacts

5.23            In order to reduce the excessive noise impacts at the affected NSRs N1 and N2 during normal daytime working hours, mitigation measures such as adopting quiet powered mechanical equipment, movable noise barrier, noise enclosure and noise insulating fabric for drill rigs are recommended. The above mitigation measures have been vetted and confirmed by the Engineer as being practicable in completing the works within scheduled timeframe.

5.24            Construction plants located in Works Area A are in close proximity to the NSRs. Noise mitigation measures have to be implemented for plants operating in Works Area A in order to comply with the noise criteria. Movable noise barrier is proposed to mitigate the noise generated from concrete mixer. Noise enclosure is proposed to mitigate the noise generated from air compressor, grouting machine and generator. It is assumed that the proposed noise barrier could give a noise attenuation of at least 5 dB(A) and the noise enclosure could give a noise attenuation of at least 10 dB(A).

5.25            The typical section of the proposed moveable noise barrier is shown in Figure 5.2 (Sheet 1) (Sheet 2). The typical section of the proposed noise enclosure is shown in Figure 5.3.

5.26            In order to ensure the compliance of the noise criteria, two operation modes had been derived as follows:

(i)                   During the construction period, no more than 2 drill rigs could be operated in Works Area E. The rest of the operating drills must be operated in Works Area F. Mitigation measures in terms of noise insulting fabric have to be in place for drill rigs operating in Works Area E.

(ii)                 No more than 6 drill rigs could be operated at the same time in Works Area F. Mitigation measures in terms of noise insulating fabric is not required. However, no drill rig could be operated in Works Area E.

5.27            These two operation modes have been confirmed by the Engineer as being practicable in completing the works within scheduled timeframe. It is assumed that the noise insulating fabric could give a noise attenuation of at least 5 dB(A). The configuration of the proposed noise insulating fabric is shown in Figure 5.4.

5.28            Operation Mode (i) is considered as the worst scenario as drill rigs would be operated in Works Area E which is closer to the existing NSRs than Works Area F. It is assumed that 2 drill rigs in Works Area E and 4 drill rigs in Works Area F were operating at the same time would be the worst case scenario for Operation Mode (i), with the six drill rigs located closest to the NSRs with about 15m horizontally apart from each other.

5.29            The mitigated noise levels for Operation Mode (i) with worst case scenario were estimated as shown in Appendix 5.3. A summary of the mitigated construction noise levels of the representative NSRs during normal daytime working hours within the construction period of the Project is shown in Table 5.7.

 

 

Table 5.7      Mitigated Construction Noise Levels - Operation Mode (i)

NSR

Predicted Noise Levels, dB(A)

Daytime Construction Noise Criteria, dB(A)

N1

57 – 74

75

N2

56 – 72

75

N3

47 – 64

75

N4

46 – 64

75

N5

59 – 67

75

N6

55 – 66

75

 

5.30            For Operation Mode (ii), drill rigs would be allowed to operate only in Works Area F. Due to the long distance from this Works Area to the NSRs (more than 110m to the closest NSRs N1 and N2), it is considered that no noise insulating fabric would be required as mitigation measures. The worst scenario of this operation mode is that all six drill rigs operated in Works Area F located closest to the existing NSRs, with 15m horizontally apart from each other. The mitigated noise levels for Operation Mode (ii) with worst case scenario were estimated as shown in Appendix 5.4. A summary of the mitigated construction noise levels of the representative NSRs during normal daytime working hours within the construction period of the Project is shown in Table 5.8.

 

Table 5.8      Mitigated Construction Noise Levels - Operation Mode (ii)

NSR

Predicted Noise Levels, dB(A)

Daytime Construction Noise Criteria, dB(A)

N1

57 – 73

75

N2

56 – 70

75

N3

47 – 64

75

N4

46 – 64

75

N5

59 – 68

75

N6

55 – 66

75

 

5.31            It is found that the maximum construction noise levels of Operation Mode (ii) at all the representative NSRs are equal to or less than that of Operation Mode (i), except NSR N5. The maximum predicted construction noise level at N5 is 1 dB(A) higher in Operation Mode (ii) i.e. 68 dB(A). The estimated construction noise impacts of the two operation modes at all the representative NSRs with implementation of mitigation measures would comply with the stipulated noise criteria.

Cumulative Noise Impacts

5.32            There are interactions with another designated project “Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction” (under Environmental Permit EP-235/2005/A) on-going during the construction period of the Project (hereafter the “Concurrent Project”). Cumulative noise impact at the NSRs would be expected.

5.33            According to the latest information available from the Contractor at the time when preparing this EIA Report, construction programme of the Concurrent Project presented in Appendix 5.5 is the most updated one. It is found that the work tasks “Tunnel No.2 excavation” and “Installation of vertical drains” of the Concurrent Project to be carried out after November 2007 would be overlapped with the works of this Project (see Appendix 2.1).

5.34            To predict the cumulative noise impact, the predicted maximum construction noise levels at the NSRs from this Project and that of the Concurrent Project were combined to obtain the overall noise levels of the worst case scenario. The cumulative construction noise impacts at the NSRs were predicted as shown in Appendix 5.6. A summary of the cumulative construction noise levels at the representative NSRs during daytime hours with mitigation measures in place are listed in Table 5.9.

 

Table 5.9      Cumulative Construction Noise Levels

NSR

Maximum Predicted Noise Levels, dB(A)

Daytime Construction Noise Criteria, dB(A)

N1

75

75

N2

72

75

N3

66

75

N4

65

75

N5

70

75

N6

70

75

 

5.35            As shown in Table 5.9, the predicted cumulative construction noise levels at NSRs N1 to N6 would comply with the stipulated noise criteria with recommended mitigation measures in place.

5.36            Hence it is concluded that the estimated cumulative construction noise levels at all NSRs would comply with the stipulated noise criteria.

Project-induced Traffic Noise

5.37            The construction of the Project would induce additional traffic to the existing Po Shan Road. However, it is envisaged that only about two construction vehicles per day (on average) would be induced by the proposed Project. No insurmountable noise impact due to project-induced traffic during construction phase would be expected.

Environmental Monitoring and Audit

5.38            An EM&A programme is recommended to be established according to the predicted occurrence of noisy activities. All the recommended mitigation measures for daytime normal working activities should be incorporated into the EM&A programme for implementation during construction. Details of the programme are provided in the stand-alone EM&A Manual.

Conclusion

5.39            This assessment has predicted the construction noise impacts of the Project during normal daytime working hours, taking into account the concurrent project, namely the “Agreement No.CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction”. With the use of quiet PME and insulating fabric for drill rigs for construction tasks under the Project, the noise levels at all representative residential NSRs would comply with the EIAO-TM construction noise criteria.