5.                       NOISE IMPACT ASSESSMENT

 

5.1                   Introduction

 

5.1.1               This chapter addresses the potential noise impacts associated with construction and operation phases of the proposed Hong Kong West Drainage Tunnel.

 

5.1.2               The main noise impacts are identified as follows:

 

(i)         Construction Phase – the noise generated from construction activities in particular those requiring the use of powered mechanical equipment has the potential to pose adverse noise impacts to surrounding noise sensitive receivers (NSRs). The ground-borne noise / vibration impact may also pose noise impacts at the NSRs during the construction phases while the tunnel is excavated using a TBM (tunnel boring machine).

 

(ii)        Operation Phase – the operation impact is not expected to pose any adverse noise impact to the environment, as there will not be any noisy electrical or mechanical equipment to be operated during operation.

 

5.1.3               The scope of this noise impact assessment follows the requirement under Section 3.4.2 of the EIA Study Brief issued in May 2001.

 

5.2                   Construction Noise Assessment

 

Introduction

 

5.2.1               This section presents the methodology, representative sensitive receivers and relevant assessment criteria.

 

5.2.2               The Study Area is characterized by the suburbs of eastern and western mid-levels of Hong Kong Island, where district distributors interlace low-density or mid-density residential areas located at the edge of Country Parks. While the noise environment of these areas is dominated by traffic noise generated by relatively low traffic volume. Therefore, background noise is generally low. There are no major commercial or industrial premises in the Study Area, whereas some of the sensitive receivers are schools and educational institutions.

 

5.2.3               In this assessment, the worst case scenarios have been adopted to examine the noise impacts and where necessary appropriate mitigation measures have been recommended.

 

Construction Noise Assessment Criteria

 

5.2.4               Noise impacts were assessed in accordance with the criteria and methodology given in the Technical Memoranda made under the Noise Control Ordinance (NCO), and EIAO-TM.

 

5.2.5               The NCO provides the statutory framework for noise control.  This defines statutory limits applicable to equipment used during the construction and operation phases of the proposed works in the study area.  The NCO invokes four Technical Memoranda, which define the technical means for noise assessment:

 

              Technical Memorandum on Noise from Places other than Domestic Premises, Public Places or Construction Sites (IND-TM);

              Technical Memorandum on Noise from Construction Work in Designated Areas (DA-TM);

              Technical Memorandum on Noise from Construction Work other than Percussive Piling (GW-TM); and

              Technical Memorandum on Noise from Percussive Piling (PP-TM).

 

5.2.6               The NCO and the accompanying Technical Memoranda provide a mechanism for assessing noise levels and the statutory power to control noise.

 

5.2.7               With regard to the assessment of the operation noise impacts, the NCO designates acceptable noise levels for Noise Sensitive Receivers (NSRs) on the basis of an Area Sensitivity Rating (ASR), based on the characterisation of the area within which they are located such as rural, village, low-density residential, or urban.  Within these areas, the presence of "influencing factors" (such as the presence of industrial activities or major roads) can further affect the ASR and therefore the acceptable noise level (see Table 5.1).

 

Table 5.1 Area Sensitivity Ratings

 

Type of Area Containing NSR

Degree to which NSR is affected by Influencing Factor

Not Affected

Indirectly Affected

Directly Affected

Rural Area

A

B

B

Urban Area

B

C

C

Low density residential area consisting of low-rise or isolated high-rise developments

A

B

C

Area other than those above

B

B

C

 

Construction Activities

 

5.2.8               Under the GW-TM, noise from construction activity is not restricted during the period 0700 - 1900 hours on weekdays, except public holidays. However, the EIAO-TM identifies a daytime general construction noise limit of 75 dB(A) Leq (30 minutes) for domestic premises, 70 dB(A) Leq (30 minutes) for educational institutes and places where unaided voice communication is required and 65dB(A) Leq (30 minutes) is allowed for school during examination period. This standard was used as assessment criteria in the construction noise assessment.  The noise standards are present in Table 5.2.

  

Table 5.2 EIAO-TM Daytime Construction Noise Standards

 

Uses

Noise Standard

(Leq, 30 min dB(A))

Domestic Premises

75

Educational Institutions (normal periods)

70

Educational Institutions (during examination periods)

65

 

5.2.9               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 use of powered mechanical equipment (PME) for carrying out of construction works during the restricted hours will require a CNP.  The Noise Control Authority is guided by the GW-TM when assessing such an application.  A CNP may be issued if the CNL is equal to or less than the ANL.  The ANLs are related to the noise sensitivity of the area in question and the Noise Control Authority will judge these at the time of the CNP application.  As conditions may vary between the time of the EIA for a project and the time of a CNP application, the assignment of any Area Sensitivity Ratings in the EIA is not binding upon the Noise Control Authority.  The relevant ANLs are shown in Table 5.3, which are determined by Area Sensitive Ratings (ASRs).

 

Table 5.3 Acceptable Noise Levels (ANL, Leq, 5min 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

 

5.3                   Representative Noise Sensitive Receivers

 

5.3.1               A site survey and desk study of government survey maps were conducted to determine the location of existing noise sensitive receivers within 300m from the boundary of the Study Area. There are a number of residences in the vicinity of the work areas; the most representative of these are chosen as Representative Noise Sensitive Receivers (RNSRs). RNSRs were selected to represent both existing and future land uses based on the consideration of their respective distances from construction activities.

 

5.3.2               For assessment of construction noise, RNSRs are selected near the tunnel portals and intake shafts where Powered Mechanical Equipment (PME) will be used during construction. The choice of the locations for the tunnel portals and intake shafts are given in Chapter 2 of this report.  RNSRs are not selected along tunnel sections where PME is used underground. Ground-borne noise during construction tunnel has been taken into account during the construction phase.

 

5.3.3               Figures 5.1-5.32 present the locations of the selected RNSRs. Table 5.4 gives the details of each of these RNSRs and the type of land use they represent.

 

Table 5.4 Details of Representative Noise Sensitive Receivers

 

NSR No.

Figure no.

Descriptions

Status

No. of Floors

No. of stories of non-sensitive structure

Shortest distance to RNSR (m)

Eastern Portal

5.1

 

 

 

 

 

EP/1

 

Blk B Lai Sing Court

Residential

22

 

61

EP/2

 

Future Residential Development (Tower 1, The Legend)

Residential

40

6 floors of Car Park

48

EP/3

 

True Light Middle School of Hong Kong

School

5

 

40

Western Portal

5.2

 

 

 

 

 

WP/1

 

Point Breeze

Residential

2

 

175

WP/2

 

Aegean Terrace

Residential

3

 

140

Intake shafts B2(P)

5.3

 

 

 

 

 

B2(P)/1

 

Borrett Mansions

Residential

21

 

37

B2(P)/2

 

Carmel School

School

4

 

95

B2(P)/3

 

Glory Mansion

Residential

10

 

45

B2(P)/4

 

Grand House

Residential

10

 

45

Intake shafts BR3(P)

5.4

 

 

 

 

 

BR3(P)/1

 

Greenville Garden Block D

Residential

23

5 floors of Car Park

85

Intake shafts BR4(P)

5.5

 

 

 

 

 

BR4(P)/1

 

Kennedy Court

Residential

5

 

110

BR4(P)/2

 

St. James' Primary School

School

4

1 floor of Hall

141

BR4(P)/3

 

Grandview Tower

Residential

29

 

120

Intake shafts BR5(P)

5.6

 

 

 

 

 

BR5(P)/1

 

Sakura Court

Residential

 

12

1 floor of Car Park

90

BR5(P)/2

 

Camelot Height

Residential

20

 

96

BR5(P)/3

 

HK Tang King Po College

School

6

 

160

Intake shafts BR6(P)

5.7

 

 

 

 

 

BR6(P)/1

 

16 Caronia

Residential

2

 

30

BR6(P)/2

 

Man Yuen Garden

Residential

12

 

45

BR6(P)/3

 

15 Carionia

Residential

2

 

90

Intake shafts BR7(P)

5.7

 

 

 

 

 

BR7(P)/1

 

16 Caronia

Residential

4

 

23

BR7(P)/2

 

15 Caronia

Residential

2

 

28

BR7(P)/3

 

12 B Bowen Road

Residential

5

 

70

BR7(P)/4

 

Monticello

Residential

20

 

61

BR7(P)/5

 

Man Yuen Garden

Residential

12

 

75

Intake shafts DG1(P)

5.8

 

 

 

 

 

DG1(P)/1

 

Rosaryhill School

School

6

2 floors of Hall

62

DG1(P)/2

 

Blk C Villa Monte Rosa

Residential

20

1 floor of Car Park

34

DG1(P)/3

 

Evergreen Villa

Residential

16

3 floors of Cark Park

75

Intake shafts E5(A)(P)

5.9

 

 

 

 

 

E5(A)(P)/1

 

Buddist Li Ka Shing Care & Attention Home for the Elderly

Elderly Home

9

2 floors of Car Park

15

E5(A)(P)/2

 

Blk 10, 135 Tai Hang Road

Residential

20

2 floors of Car Park

23

Intake shafts E5(B)(P)

5.9

 

 

 

 

 

E5(B)(P)/1

 

Blk 9 Aurizon

Residential

20

2 floors of Car Park

32

E5(B)(P)/2

 

Blk 1 Cavendish Heights

Residential

32

4 floors of Car Park

27

E5(B)(P)/3

 

Blk 10, 135 Tai Hang Road

Residential

20

2 floors of Car Park

37

Intake shafts E7(P)

5.10

 

 

 

 

 

E7(P)/1

 

Marymount Secondary School

School (School hall)

7

 

19

E7(P)/2

 

French International School

School (School hall)

6

 

87

E7(P)/3

 

117 Blue Pool Road

Residential

3

1 floor of Car Park

20

E7(P)/4

 

Blk J Villa Dorada

Residential

2

 

51

E7(P)/5

 

Blk 1 Green Lane Court

Residential

3

1 floor of Car Park

52

Intake shafts GL1(P)

5.11

 

 

 

 

 

GL1(P)/1

 

Green Lane Hall

Residential

15

 

29

Intake shafts HKU(P)

5.12

 

 

 

 

 

HKU1(P)/1

 

WSD Staff Quarters

Residential

2

 

44

Intake shafts HR1

5.13

 

 

 

 

 

HR1/1

 

Shuk Yuen Terrace

Residential

3

 

52

HR1/2

 

16-20 Broom Road

Residential

4

 

33

Intake shafts M3(P)

5.14

 

 

 

 

 

M3(P)/1

 

May Fair

Residential

 

29

9 floors of Car Park /Hall

65

Intake shafts MA13(P)&MA14(P) 

5.15

 

 

 

 

 

MA13(P) & MA14(P)/1

 

The Harbour View

Residential

25

4 floors of Club/ Car Park

31

MA13(P) & MA14(P)/2

 

Magazine Gap Towers

Residential

12

 

31

MA13(P) & MA14(P)/3

 

Magazine Heights

Residential

13

4 floors of Platform

75

Intake shafts MA15(P)

5.15

 

 

 

 

 

MA15(P)/1

 

The Harbour View

Residential

25

6 floors of Club/ Car Park

35

MA15(P)/2

 

Magazine Gap Towers

Residential

12

 

105

MA15(P)/3

 

Rose Gardens

Residential

12

 

56

MA15(P)/4

 

Magazine Court

Residential

12

1 floor of Car Park

85

Intake shafts MA17(P)

5.16

 

 

 

 

 

MA17(P)/1

 

Blk A Grenville House

Residential

12

1 floor of Car Park

51

MA17(P)/2

 

Magazine Court

Residential

12

7 floors of Platform

65

MA17(P)/3

 

Rose Gardens

Residential

12

 

95

Intake shafts MB16(P)

5.17

 

 

 

 

 

MB16/1

 

Clement Court

Residential

3

1 floors of Platform

37

MB16/2

 

81 Perkins Road

Residential

2

 

28

MB16/3

 

83 Perkins Road

Residential

2

 

27

Intake shafts MBD2

5.18

 

 

 

 

 

MBD2/1

 

Amber Lodge

Residential

2

1 floor of Ground Story

40

Intake shafts P5(P)

5.19

 

 

 

 

 

P5(P)/1

 

24 Po Shan Road

Residential

1

1 floor of Car Park

20

P5(P)/2

 

23 Po Shan Road

Residential

10

1 floor of Car Park

45

P5(P)/3

 

Haddon Court

Residential

4

 

57

Intake shafts PFLR(P)

5.20

 

 

 

 

 

PFLR(P)/1

 

Honey Court

Residential

9

1 floor of Car Park

28

PFLR(P)/2

 

Pokfulam Heights

Residential

4

1 floor of Car Park

29

Intake shafts RR1(P)

5.21

 

 

 

 

 

RR1(P)/1

 

Primrose Court

Residential

28

1 floor of Hall

27

RR1(P)/2

 

Scenic Heights

Residential

24

8 floors of Car Park/ Hall

33

RR1(P)/3

 

Ying Wa Girl's School

School

6

1 floor of Car Park

77

RR1(P)/4

 

Peaksville Court

Residential

14

2 floors of Car Park

35

Intake shafts THR2(P)

5.22

 

 

 

 

 

THR2(P)/1

 

Hong Chi Lions Morninghill School

School (School hall)

2

 

45

THR2(P)/2

 

Hong Kong Japanese School

School

5

1 floor of Hall

41

THR2(P)/3

 

Wan Chui Chuen

Residential

5

 

30

THR2(P)/4

 

Marymount Primary School

School

5

 

97

Intake shafts TP4(P)

5.23

 

 

 

 

 

TP4(P)/1

 

Tregunter Tower 1

Residential

34

1 floor of Hall

41

TP4(P)/2

 

Tregunter Tower 2

Residential

32

1 floor of Hall

40

Intake shafts TP5(P)

5.23

 

 

 

 

 

TP5(P)/1

 

Tavistock II

Residential

34

1 floor of Hall

61

Intake shafts TP789(P)

5.24

 

 

 

 

 

TP789(P)/1

 

Tavistock

Residential

13

1 floor of Hall

48

TP789(P)/2

 

Branksome

Residential

23

 

64

Intake shafts WO(P)

5.25

 

 

 

 

 

WO(P)/1

 

Sir Ellis Kadoorie Secondary School (Edward Hall)

School (School hall)

4

 

36

WO(P)/2

 

Goodview Garden

Residential

2

2 floors of Car Park

51

WO(P)/3

 

Kui Yuen

Residential

3

 

72

Intake shafts W1(P)

5.26

 

 

 

 

 

W1(P)/1

 

74 Bamboo Grove

Residential

33

1 floor of Hall

81

W1(P)/2

 

Blk B Merry Garden

Residential

12

1 floor of Hall

76

W1(P)/3

 

St James's Primary School

School

4

1 floor of Hall

122

W1(P)/4

 

Caine Terrace

Residential

4

1 floor of Hall

72

Intake shafts W3(P)

5.27

 

 

 

 

 

W3(P)/1

 

Regent on the Park

Residential

36

1 floor of Hall

75

W3(P)/2

 

Carmel School

School

3

 

174

W3(P)/3

 

Green Villa

Residential

4

 

128

Intake shafts W5(P)

5.28

 

 

 

 

 

W5(P)/1

 

Raimondi College

School

7

3 floors of Platform

13

W5(P)/2

 

Raimondi Primary School

School

10

3 floors of Platform

12

W5(P)/3

 

Caritas House

Residential

9

 

30

W5(P)/4

 

Canossa Hospital

Hospital

6

 

76

Intake shafts W8(P)

5.29

 

 

 

 

 

W8/1

 

Blk1, 80 Robinson Road

Residential

28

11 floors of Platform

11

W8/2

 

Bonham Court

Residential

27

1 floor of Hall

17

W8/3

 

Hong Kong Institute of Technology

School

6

2 floors including G/F

5

Intake shafts W10(P)

5.30

 

 

 

 

 

W10/1

 

Future Residential Development

Residential

12

 

24

W10/2

 

Blk 2 Po Shan Rd

Residential

10

7 floors of Platform

29

W10/3

 

University Lodge

School

1

 

60

W10/4

 

Blk A-B University Heights

Residential

12

1 floor of Hall

56

Intake shafts W11(P)

5.31

 

 

 

 

 

W11(P)/1

 

17 Hatton Road

Residential

3

1 floor of Car Park

48

W11/(P)/2

 

Block B  Hatton Place

Residential

10

1 floor of Car Park

74

Intake shafts W12(P)

5.32

 

 

 

 

 

W12(P)/1

 

Sylvanbrook

Residential

4

1 floor of Car Park

10

W12(P)/2

 

94A Pok Fu Lam Road

Residential

3

1 floor of Car Park

11

W12(P)/3

 

Blk A La Clare Mansion

Residential

12

3 floors of Platform

43

 

5.4                   Airborne Construction Noise Assessment

 

Potential Sources of Impacts

 

5.4.1               The major construction activities that are anticipated at tunnel portals and intake are summarised in Table 5.5.  All proposed intakes and portals locations are outside Country Parks.  The proposed intakes locations and alternative have been considered and discussed in Chapter 2.

 

Table 5.5 Construction activities at portals and intakes

 

Eastern/Western Portals

Intakes (35 in total)

Remarks

Site clearance and surface breaking

Site clearance and surface breaking

use of earthmoving machinery and vehicles

Drilling

Initial Excavation

use of excavators, loaders, dump trucks, rock drill

Loading

Rock drilling for manhole construction

Site formation

Excavation

TBM supporting activities

-

Conveyor belt, gantry, dump truck, muck train

Finalized stage – General works

Finalized stage – General works

Dump trucks, conveyor belts

Finalized stage – Concreting works

Finalized stage – Concreting

Concrete lorry mixer, poker

Finalized stage – Marine Transport

-

Barge, Tug boat

 

5.4.2               All concrete to be used will be transported to the work sites. Therefore, there will be no concrete batching plant on-site. All sites except Western Portal will be accessed mainly via existing roads.

 

Construction Equipment

5.4.3               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 Tables 5.6a-b. 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.

 

Table 5.6a Equipment List for each Construction Activity for Eastern and Western Portals

 

Activity / Equipment

Date

Duration

TM Code

SWL,
dB(A)

Quantity

Summation
of SWL, dB(A)

Total SWL dB(A), Eastern Portal

Total SWL dB(A), Western portal

Site clearance

May 2007 to Jun 2008

56 weeks

 

 

 

 

 

 

Bulldozer

030

115

1

115

115

115

Surface breaking

 

 

 

 

 

 

Breaker, excavator mounted

028

122

1

122

122

122

Drilling

 

 

 

 

 

 

Rock drill, hand-held (pneumatic)

183

116

1

116

116

116

Air compressor

003

104

1

104

 

 

Loading

 

 

 

 

 

 

Wheeled Loader

081

112

1

112

118

118

Dump Truck

067

117

1

117

 

 

Site formation

 

 

Excavator

081

112

1

112

118

118

Dump Truck

067

117

1

117

 

 

TBM Supporting Activities

Jun 2008 to Jun 2011

Eastern Portal -

208 weeks

Western Portal  - 212 weeks

 

 

Gantry

122

95

1

95

118

119

Ventilation fan

241

108

1

108

 

 

Conveyor belt

041

90

1

90

 

 

Muck train

#

105

1

105

 

 

Dump Truck

067

117

1

117

 

 

Air compressor

003

104

1

104

 

 

Tug Boat (Western portal only)

221

110

1

110

 

 

Crane, barge mounted (Western portal only)

048

112

1

112

 

 

Finalized stage - General Works

Apr 2011 to Nov 2011

 

Eastern Portal -

12 weeks

Western Portal -18 weeks

 

 

 

Excavator

081

112

1

112

118

117

Dump Truck

067

117

1

117

 

 

Finalized stage - Concreting

 

 

 

 

 

 

Concrete lorry mixer

044

109

1

109

114

114

Poker, vibratory, hand-held

170

113

1

113

 

 

Finalized stage - Marine Transport

 

 

 

 

 

 

Tug Boat (Western portal only)

221

110

1

110

 

114

Crane, barge mounted (Western portal only)

048

112

1

112

 

 

 

SWL – Sound Power Level; # - Information from supplier

 

Table 5.6b Equipment List for each Construction Activity for Intakes

 

Activity / Equipment

Date

Duration per intake

TM Code

SWL,
dB(A)

Quantity

Summation
of SWL, dB(A)

Total SWL dB(A),

Site clearance

Aug 2008   to      Jun 2011

2 weeks

 

Excavator

081

112

1

112

112

Surface breaking

 

Breaker, excavator mounted

028

122

1

122

122

Initial Excavation

4

months

 

Excavator

081

112

1

112

112

Water pump, submersible (electric)

283

85

1

85

 

Generator, silenced

102

100

1

100

 

Rock drill for manhole

1 month

 

Breaker, excavator mounted

028

122

1

122

122

Excavation method I

5   months

 

Raise boring machine

166

100

1

100

103

Hydraulic power pack

102

100

1

100

 

Excavation method II*

 

 

 

 

 

Reverse circulation drill (50% on time)

166

100

1

97

110

Water pump, submersible (electric)

283

85

1

85

 

Generator, silenced

102

100

1

100

 

Lorry with grab (50% on time)

141

112

1

109

 

Finalized stage - General Works

1.5 months

 

 

 

 

 

Lorry with crane

141

112

1

112

112

Finalized stage - Concreting

 

 

 

 

 

Concrete lorry mixer

044

109

1

109

114

Poker, vibratory, hand-held

170

113

1

113

 

 

SWL – Sound Power Level

For raise boring SWL, it is assumed the sound power level for raise boring machine is close to reverse circulation drill.   Most of intakes shafts will be constructed by Excavated Method I (raise boring) except W8, W5, RR1, THR2, WO and HR1 (Excavated method II – reverse circulation drill).  The Method I is only applicable for site with high rock level while Method II is applicable for site with thick soil stratum.

 

5.4.4               The equipment list was reviewed by the Project Proponent and was considered reasonable in terms of the types and numbers based on the tentative construction programme.

 

Construction Schedule and Program

 

5.4.5               Only a tentative construction programme is available at the time of assessment. Work is schedule to commence in May 2007 and will be completed in Nov 2011.

 

Construction Works during Restricted Hours

 

5.4.6               Construction of intakes will not be carried out during restricted hours.  For the underground adits and tunnel, it will be carried out during restricted hours subject to CNP applications. 

 

5.4.7               No movement of spoil off-site will be carried out during restricted hours at both portals. Spoil arising from the tunneling activities will be moved to muck pit for overnight stock piling using a conveyor system. Full enclosure should be provided at muck pit area enclosing air compressor, muck train, conveyor belt system and ventilation fan during the TBM support construction stage at the Eastern portal.

 

5.4.8               Construction works within restricted hours will be under the control of the statutory conditions of the CNP. The assessment of these works is outside the current scope of the EIA brief. The contractor shall have responsibility of meeting the requirements from the Noise Control Ordinance.  They will have the responsibility for applying for the necessary CNPs and demonstrating the predicted noise impacts for their proposed construction activities during the restricted hours and the effectiveness of the proposed mitigation, if any.

Assessment Methodology and Assumptions

5.4.9               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 British Standards (BS) 5228: Part 1.

5.4.10           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.

 

5.4.11           All PME are assumed to be stationary while performing the noisiest activity, such as loading/off-loading, lifting and ground breaking at different Notional Noise Sources (NNS) attributed to various construction activities.

 

5.4.12           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 neighboring 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.

 

5.4.13           For the construction of intake shafts along the proposed tunnel, the construction activities will take place sequentially. For the construction of the two tunnel portals and the stilling basin, some of the construction activities may take place at the same time. The total predicted sound power levels attributed to each construction activity and the scenarios for assessing concurrent construction noise impact are analysed.

 

Assessment Results

 

5.4.14           Predicted noise levels at the closest identified NSRs without mitigation measures are given in Tables 5.7a-b for Eastern/Western Portals and Intakes respectively.  The results show that the construction noise will exceed the daytime noise criteria at most of the RNSRs in view of their close proximity to the site. Suitable mitigation measures are thus required. The recommended mitigation measures for the construction works are discussed in the following section.

 

Table 5.7a Predicted Noise Level (Unmitigated) at RNSRs for

Eastern Portals and Western Portals

 

 

Site clearance

Surface Breaking

Drilling

Loading

Site Formation

TBM Support

Finalized Stage - General Works

Finalized Stage- Concreting

Finalized Stage - Marine Transport

Approximate Duration  (weeks)

2

2

8

208

8

212

18

18

18

Educational institutions

EP/3

78

85

79

81

81

81

81

77

 

Domestic premises/hotels/hostels

EP/1

75

81

76

77

77

77

77

74

 

EP/2

76

83

77

79

79

79

79

75

 

WP/1

64

71

66

68

68

69

68

64

64

WP/2

66

73

67

69

69

71

69

66

65

Remarks:

> 70 dB (Educational Institution)

> 75 dB (Domestic premises/hotels/hostels)

 

Table 5.7b Predicted Noise Level (Unmitigated) at RNSRs for Intakes

 

 

Site clearance

Surface breaking

Initial Excavation

Rock Drilling for Manhole

Excavation

Finalized stage - General Works

Finalized stage - Concreting

Approximate Duration

1 week

1 week

4 months

1 month

< 5 months

1 month

2 weeks

Educational institutions

B2(P)/2

67

77

67

77

58

67

70

BR4(P)/2

64

74

64

74

55

64

66

BR5(P)/3

63

73

63

73

54

63

65

DG1(P)/1

71

81

71

81

62

71

74

E7(P)/1

80

90

80

90

71

80

83

E7(P)/2

67

77

67

77

58

67

69

RR1(P)/3

69

79

69

79

67

69

72

THR2(P)/1

64

74

64

74

62

64

66

THR2(P)/2

64

74

64

74

62

64

66

THR2(P)/4

67

77

68

77

65

67

70

WO(P)/1

76

86

76

86

73

76

78

W1(P)/3

65

75

66

75

56

65

68

W3(P)/2

61

71

61

71

52

61

64

W5(P)/1

83

93

83

93

80

83

85

W5(P)/2

83

93

83

93

81

83

86

W8/3

88

98

88

98

86

88

91

Domestic premises/hotels/hostels

B2(P)/1

74

84

75

84

65

74

77

B2(P)/3

74

84

74

84

65

74

76

B2(P)/4

74

84

74

84

65

74

76

BR3(P)/1

68

78

69

78

59

68

71

BR4(P)/1

66

76

66

76

57

66

69

BR4(P)/3

65

75

66

75

56

65

56

BR5(P)/1

68

78

68

78

59

68

70

BR5(P)/2

67

77

68

77

58

67

70

BR6(P)/1

77

87

77

87

68

77

79

BR6(P)/2