4 noise impact assessment 4.1 introduction 4.2 … · 4.1 introduction 4.1.1 this chapter presents...

Drainage Services Department Agreement No. CE 41/2013 (EP)

Port Shelter Sewerage, Stage 3 – Sewerage Works at Po Toi O

Environmental Impact Assessment Studies - Investigation

Environmental Impact Assessment Report

IA13070/EIARpt v2.3 Cinotech 4-1

4 NOISE IMPACT ASSESSMENT

4.1 Introduction

4.1.1 This Chapter presents an assessment of the potential noise impact arising from the

construction and operation of the Project. Mitigation measures have been identified to

alleviate the impact and their effectiveness has been evaluated.

4.2 Environmental Legislation, Standards and Guidelines

Construction Noise

4.2.1 The Noise Control Ordinance (NCO) (Cap. 400) provides the statutory framework for

noise control in Hong Kong. Assessment procedures and standards are set out in the

respective Technical Memoranda (TM) promulgated under the NCO. The following

TMs are applicable to the assessment and control of construction noise.

Technical Memorandum on Noise from Construction Work other than

Percussive Piling (TM-GW);

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

Technical Memorandum on Noise on Construction Work in Designated

Areas (TM-DA)

Technical Memorandum on Noise from Places other than Domestic

Premises, Public Places or Construction Sites (TM-IND)

4.2.2 Both the percussive piling and construction work under restricted hours require a

construction noise permit (CNP) in order to carry out such work. As the issuance of a

CNP by the Noise Control Authority would depend on the compliance of percussive

piling noise impact or construction noise impact with the limits set out within the TM-

PP and TM-GW/TM-DA, the assessment of this type of noise would not be covered in

the EIA report.

4.2.3 For construction, there is no statutory limit on daytime construction noise under the

NCO and related TMs. Nevertheless, the “Technical Memorandum on Environmental

Impact Assessment Process” (EIAO-TM) stipulates noise standards for daytime

construction activities, as shown Table 4-1.






Table 4-1: Construction Noise Standards during Non-Restricted Hours

Uses

Noise Standards [1] , Leq (30 mins) dB(A)

0700 to 1900 hours

on any day not being a

Sunday or general

holiday

1900 to 0700 hours

or any time on Sundays or

general holiday

All domestic premises including

temporary housing

accommodation

75

(See Note 2) Hotels and hostels 75

Educational institutions including

kindergartens, nurseries and all

others where unaided voice

communication is required

70 65 (During

examinations)

Notes:

[1] The above standards apply to uses that rely on opened windows for ventilation.

[2] The criteria laid down in the relevant technical memoranda under the NCO for designated areas and

construction works other than percussive piling may be used for planning purpose. A Construction

Noise Permit (CNP) shall be required for the carrying out construction work during the period.

Construction Noise during Restricted Hours

4.2.4 The NCO provides statutory control on general construction works (excluding

percussive piling) conducted during restricted hours (i.e. 1900 to 0700 hours (of the

next day) from Monday to Saturday and at any time on Sundays or in public holidays).

A Construction Noise Permit (CNP) is required for carrying out of any general

construction activities involving the use of any Powered Mechanical Equipment (PME)

within restricted hours from the Authority under the NCO. The noise criteria and the

assessment procedures for issuing a CNP are specified in the TM-GW under the NCO.

4.2.5 The use of Specified PME (SPME) and/or the undertaking of Prescribed Construction

Work (PCW) within a Designated Area (DA) under the NCO during the restricted

hours are controlled by the TM-DA. The relevant technical details in Technical

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

NCO can be referred. The acceptable noise levels for construction during the restricted

hours are summarized in Table 4-2 below.

Table 4-2: Construction Noise Standards during Restricted Hours

Uses

Acceptable Noise Level for Area Sensitive Ratings, dB(A)

A B C

All weekdays during the evening

(1900 to 2300 hours), and general

holidays (including Sundays)

during the day and evening (0700 to

2300 hours)

60 65 70

All days during the night-time

(2300 to 0700 hours) 45 50 55






4.2.6 The Area Sensitive Rating depends on the type of area and the degree of impact that

Influencing Factors (IFs) have on the NSRs and is determined from Table 4-3 below.

Industrial area, major road or the area within the boundary of Hong Kong International

Airport shall be considered to be an IF.

Table 4-3: Area Sensitivity Ratings (ASRs)

Type of Area containing NSR Degree to which NSR is affected by IF

Not Affected

Indirectly Affected

Directly Affected

(i) Rural area, including country parks or village type

developments A B B

(ii) Low density residential area consisting of low-rise or

isolated high-rise developments A B C

(iii) Urban area B C C (iv) Area other than those above B B C

4.2.7 According to the preliminary construction programme, it is very likely that the

proposed construction works would be carried out during non-restricted hours only.

For carrying out any general construction activity involving the use of any Powered

Mechanical Equipment (PME) within restricted hours, a Construction Noise Permit

(CNP) is required from the authority under the NCO. The noise criteria and the

assessment procedures for issuing the CNP are specified in the TM-GW under the

NCO. 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 work within restricted hours as guided by the relevant TMs issued under

the NCO. It is the Contractor’s responsibility to ensure compliance with the NCO and

the relevant TMs in case of any construction activities during restricted hours.

4.2.8 The Noise Control Ordinance (NCO) and Technical Memorandum on Environmental

Impact Assessment Process (EIAO-TM) were followed for assessing the noise from

powered mechanical equipment (PME) for different sensitive uses.

Construction Ground-Borne Noise

4.2.9 According to the TM-GW, the Area Sensitivity Rate of the area in which the identified

NSRs are located is “A”. Moreover, the TM-IND under NCO mentioned that where

the noise under investigation is transmitted primarily through the structural elements

of the building or if the assessment point is at an internal location of a building, an

adjustment of -10 dB(A) should be made to relevant acceptable noise levels (ANLs).

The relevant noise limits for ground-borne noise are tabulated in Table 4-4.






Table 4-4 Ground-borne Construction Noise Limits

Time Period Uses Noise Standard

(Leq, 30 min dB(A))

(1)Day-time

Domestic Premises 65

Educational institutions (normal

periods) 60

Educational institutions (during

examination periods) 55

(1)Evening-time All Noise Sensitive Uses 50

(1)Night-time All Noise Sensitive Uses 35

(1) assessment point is at a particular internal location

Operational Noise

4.2.10 Noise from the proposed sewage treatment plant (STP) is considered as the only fixed

noise source during the operation phase of the Project. Operational noise is controlled

under the Noise Control Ordinance (NCO)’s Technical Memorandum on Noise from

Places other than Domestic Premises, Public Places or Construction Sites (TM-IND).

4.2.11 According to the TM-IND, appropriate Area Sensitivity Ratings should be determined

for the NSRs under consideration from Table 1 of the TM-IND. Then, the appropriate

Acceptable Noise Level (ANL) for a given NSR and the time period under

consideration could be read from Table 3 of TM-IND. According to the TM-IND, the

ANLs for different Area Sensitivity Ratings (ASRs) of noise sensitive receivers

(NSRs) are given in Table 4-5.

Table 4-5 Acceptable Noise Levels

Time Period ASR A ASR B ASR C

All days during the evening (1900 to 2300 hours), and

general holidays (including Sundays) during the day-

time and evening (0700 to 2300 hours)

60 65 70

All days during the night-time (2300 to 0700 hours) 50 55 65

4.2.12 More stringent criteria for fixed plant noise impacts recommended in Table 1A of the

EIAO-TM for planning purposes are as follow:

5 dB(A) below the appropriate ANL set out in the TM-IND (the ANL–5 dB(A)

criterion), or

The prevailing background noise level where the prevailing background noise

level is 5 dB(A) below the appropriate ANL (although during the operation the

NCO will be the controlling legislation).






4.2.13 In this Project, the study area covering 300m from the proposed works boundary (as

shown in Figure 4-1) is identified as rural area consisting village type developments

without being affected by IF thus the NSRs are assigned an Area Sensitive Rating of

“A”.

4.2.14 In order to determine the appropriate criteria for noise assessment, background noise

survey was carried out during the course of the EIA process at two locations to

determine the baseline noise levels. Noise monitoring was conducted for 14

consecutive days in November 2014. Locations of the monitoring stations are

summarised in Table 4-6 and shown on Figure 4-1. For those sensitive receivers

which were found to experience prevailing noise levels lower than the ANL-5dB(A)

criterion, fixed plant noise impact were assessed against the prevailing background

noise levels.

Table 4-6 Background Noise Monitoring Results at Selected NSRs in Po Toi O

Time Period Measurement

Parameter

Noise Level (dB(A))

NM1 - Near Local

Resident

NM2 - Near Fairway

Vista

Max. Min. Average Max. Min. Average

Daytime 0700 -1900 Leq30min 62 52 57 66 51 58

Evening

Time 1900 - 2300 Leq5min 62 53 57 59 49 53

Night

Time

2300 - 0700

of next day Leq5min 56 46 51 53 47 50

4.2.15 The lowest recorded background noise level during daytime/evening period was 49

dB(A). Since the background noise level was 6 dB(A) lower than the ANL -5 dB(A),

the noise criteria for daytime/evening time periods will adopt the prevailing

background noise level of 49 dB(A). As the lowest nighttime background noise level

was 1 dB(A) higher than the ANL-5dB(A), noise criterion of 45 dB(A) is adopted for

nighttime period. The operational phase noise criteria are summarized in Table 4-7.

Table 4-7 Acceptable Noise Levels (ANLs) during Operational Period

Time Period

Acceptable

Noise Levels

(ANLs),

dB(A)

(ANL -5)

dB(A)

Prevailing

Background

dB(A)

*Noise

Criteria

dB(A)

Day (0700 to 1900 hours) 60 55 49 49

Evening (1900 to 2300 hours)

Night (2300 to 0700 hours) 50 45 46 45

* ANL – 5dB(A) or the prevailing background noise levels (for quiet areas with level 5dB(A) below the

ANL).






4.3 Descriptions of Environment

4.3.1 The village to be sewered is situated within a quiet rural area, with some of the

surrounding open land used as a golf course, recreational areas and seafood

restaurants. Noise levels in this village are generally very low with little noise

influence from outside of the village.

4.4 Identification of Potential Noise Impact

4.4.1 During the construction phase, use of powered mechanical equipment (PME) will

inevitably generate construction noise and hence may cause noise nuisance to the

nearby residences. During the operational phase, equipment noise from the proposed

sewage treatment plant will be the main noise source with potential noise impact on

the NSR.

4.5 Noise Sensitive Receivers

4.5.1 The Study Area covered 300m from the proposed works boundary as shown in Figure

4-2. Given the proximity of the STP and associated sewerage works to the Po Toi O

village, noise sensitive receivers in the village are likely to be affected by the Project

during its construction and operation. Noise sensitive receivers have been identified

from the Approved Clear Water Bay Peninsula South Outline Zoning Plan, S/SK-

CWBS/2, and 1:1000 survey plans of the area. In addition, site visits have been carried

out to identify the NSR and representative worst impact points of the identified NSR.

In general, the sewers are laid 2m away from and in parallel to NSRs. A list of the

identified NSR and their locations are depicted in Figure 4-2 and listed in Table 4-8

below. Photographic record can be found in Appendix 4.4.

Table 4-8 Representative Noise Sensitive Receivers

NSR Description Land

Use

Ground

mPD

Notional Noise Distance (m) from

NSR No. of

Storey Pipes

Po Toi O

Chuen Road

Sewer Pipe

Sewage

Treatment

Plant

PTO_N1 Village House in

PTOCR 28 Village 6 4 37.8 77.5 2


PTOCR 7A Village 4.1 4.2 167.4 203.4 *3

PTO_N3

Temporary

Structure for

living

Village 4.5 5.9 332.6 356.8 1

FV_N1 Fairway Vista

House 12 Village 7.5 2 331.5 352.6 3

SC_N1

Seacrest Villas

in PTOCR No.

64

Village 25.1 10.2 195.8 213.3 3

Noted: PTOCR = Po Toi O Chuen Road

* Ground floor of PTO_N2 is a seafood restaurant. Only first and second floors are considered as NSR.






4.5.2 The village zone within or near the proposed sewerage works covers the Po Toi O

Village, Seacrest Villas and Fairway Vista. The land on both sides of the proposed

pipe alignment has already been fully occupied by houses. No future addition of NSR

is expected. Even if a house will be squeezed into the already crowded land, it will

only be of similar distance or further away from the sewerage works when compared

with the existing houses. This noise assessment will be sufficient in assessing and

evaluating the potential noise impact.

4.6 Assessment Methodology, Prediction and Evaluation of Environmental Impacts

4.6.1 Noise impact assessment was conducted in accordance with the requirements in

EIAO-TM Annex 5 and 13.

Construction Noise

4.6.2 The Project comprises three main works including the construction of sewage

treatment plant (STP), underground sewers and rising mains, and the submarine outfall.

4.6.3 Detailed construction method, sequence of works and the plant inventory in different

work stages were proposed at the time of this EIA. Until a contractor is appointed, full

details of the types and utilization of construction plants will not be known exactly.

Typical types and number of powered mechanical equipment (PME) needed for

various construction activities for the construction of STP and pipes installation have

been assigned as shown in Tables 4-9 to 4-13 below. PME that will likely be used

concurrently have been grouped within the same works stage. The project engineer has

reviewed the currently proposed construction programme and methodology including

list of PME items, percentage on-time assumptions, etc. such that they are considered

practicable and appropriate for this project.

4.6.4 As not every item of PME would be operated all the time when it is on site, a typical

percentage on time was assumed for each PME based on experience in actual site

practice so that the noise prediction exercise would be a more realistic one.

Accordingly, the effective sound power levels for each construction activity were

quantified and are listed in the same table.

Construction of Sewage Treatment Plant

4.6.5 The construction of STP will include earthworks, trench support and ground

compaction works, general concrete building works, backfilling and surfacing works.

Common construction plant including hydraulic breaker, excavator/loader, concrete

lorry mixer, vibratory poker, lorry and the like will be used. Typical plant list for STP

construction is shown in Table 4-9.






Table 4-9: Typical PME to be used for Construction of Sewage Treatment Plant

Activity Noise Source

TM-GW

Reference

Number

Nos.

used

SWL,

dB(A)

% on

time

Effective SWL in

a 30 min period

Overall

SWL

Stage I Earth Works

1.1

Hydraulic breaker CNP 028 2 122 50% 122

123 Excavator / loader CNP 081 2 112 80% 114

Lorry CNP 141 2 112 30% 110

Stage II Trench Support & Ground Compaction

2.1

Vibrating hammer

(piling) CNP 172 2 115 80% 117

118

Roller, vibratory CNP 186 2 108 80% 110

Stage III Concrete Building Works

3.1

Vibratory poker CNP 170 2 113 80% 115

117 Concrete Lorry

Mixer CNP 044 2 109 100% 112

Stage IV Backfilling

4.1 Backhoe CNP 081 1 112 80% 111

112 Roller, vibratory CNP 186 1 108 60% 106

Stage V Surfacing

5.1


114 Concrete Lorry

Mixer CNP 044 1 109 100% 109

Installation of Gravity Sewers and Rising Mains

4.6.6 Trenchless method is proposed for the laying of rising mains from the STP to the

footpath between village house no.23 and no.28 of Po Toi O Village, which will be

deep down to 10m underground. Since the launching site is located at the STP, no

additional power mechanical equipment is required for excavation and backfilling

work for the launching site. Pipe jacking machine (e.g. hydraulic jack) would be

applied underground. Therefore, the noise generated for pipe laying under trenchless

method is relatively small when compared to other concurrent works and hence was

not considered in the quantitative construction noise assessment. The generator for

powering the pipe jacking machine will be located at the sewage treatment plant site

over 77.5m away from the nearest NSR. The noise from generator at NSR will be

reduced to low level that will have no major contribution to the overall construction

noise level at the NSR. This construction method is commonly applied in pipe laying

in village area. The ground compositions in the first few meters are soil and sand. No

significant groundborne noise impact is expected.






Table 4-10: Typical PME to be used for Installation of Rising Mains (Trenchless

Method)


TM-GW

Reference

Number

Nos.

used

SWL,

dB(A)

% on

time

Effective SWL in

a 30 min period

Overall

SWL

- Generator,

portable CNP 107 1 100 100% 100 100

4.6.7 Gravity sewers and rising mains will be laid within the first 3m below ground in the

village area. As there are different existing underground utilities located along

footpath in Po Toi O, trenchless method is considered risky for pipe laying in shallow

ground layer. Open trench method (cut and cover) will be adopted, in which

construction works generally take place in successive sequences as excavation, trench

support and ground compaction, pipe laying, backfilling, and surfacing. Construction

of pipelines in areas with restricted access in narrow alleys and pathways will mainly

use manual method or semi-PME method in order to reduce noise impact on the quiet

village. A typical plant list for construction of gravity sewers and rising mains in the

village area is provided in Table 4-11.

Table 4-11: Typical PME to be used for Installation of Gravity Sewers and Rising

Mains (Open Cut Method)


TM-GW

Reference

Number

Nos.

used

SWL,

dB(A)

% on

time

Effective SWL in

a 30 min period

Overall

SWL

Stage I Excavation

1.1

Breaker, hand

held CNP 026 1 114 60% 112

112 Generator,

portable CNP 107 1 100 60% 98


No PME would be needed. Manual working for construction would be adopted.

Stage III Pipe-laying




Stage V Surfacing

5.1 Vibratory poker CNP 170 1 113 80% 112 112

4.6.8 For the laying of gravity sewer on Po Toi O Chuen Road, larger scale of PMEs are

required for excavation and surfacing work. The plant list for open trench method for

pipe laying on Po Toi O Chuen is shown in Table 4-12.






Table 4-12: Typical PME to be used for Installation of Gravity Sewers on Po Toi O

Chuen Road (Open Cut Method)


TM-GW

Reference

Number

Nos.

used

SWL,

dB(A)

% on

time

Effective SWL in

a 30 min period

Overall

SWL

Stage I Earth Works

1.1

Hydraulic breaker CNP 028 1 122 50% 119

120 Excavator / loader CNP 081 1 112 80% 111

Lorry CNP 141 1 112 30% 107


2.1

Vibrating hammer

(piling) CNP 172 1 115 80% 114

115

Roller, vibratory CNP 186 1 108 80% 107

Stage III Pipe-laying



4.1 Backhoe CNP 081 1 112 80% 111

112 Roller, vibratory CNP 186 1 108 60% 106

Stage V Surfacing

5.1


114 Concrete Lorry

Mixer CNP 044 1 109 100% 109

Construction of Submarine Outfall

4.6.9 The submarine outfall will be constructed by horizontal directional drilling (HDD). An

entry pit will be excavated within sheet piles at the rocky shore for insertion of the

drill head. The drill head will drill into the rock layer below seabed and the tunnel will

be enlarged by pre-reaming. After that, the rising mains will be pulled from the

diffuser installation point back to the entry site. The plant equipment for HDD will be

placed on the rocky shore, which is about 13.2m from the nearest sensitive receiver (a

house). The plant list for HDD method for construction of submarine outfall is shown

in Table 4-13. According to the Ground Investigation results, the rock layer is 10m

below ground. As drilling depth at the launching site is shallower where soft marine

deposits and alluvium are located, no significant groundborne noise is expected from

HDD works.






Table 4-13: Typical PME to be used for Construction of Submarine Outfall (Land-

based Works)


TM-GW

Reference

Number

Nos.

used

SWL,

dB(A) % on time

Overall

SWL

Stage I Plant Setup and Entry Pit Setup

1.1

Vibrating hammer (piling) CNP165 1 115 60% 112.8

Excavator / loader CNP081 1 112 60% 109.8

Concrete Mixer (petrol) CNP046 1 96 50% 93.0

Generator, silenced CNP102 1 100 100% 100.0

Welding and cuting set -- 1 89 30% 83.8

Stage II Pilot Drilling

2.1


HDD Drill Rig -- 1 88 80% 87.0

Crane CNP049 1 95 40% 91.0

Mud pump CNP106 1 105 80% 104.0

Agitator CNP005 1 90 80% 89.0

Drilling fluid mixer CNP105 1 90 80% 89.0

Drilling Fluid pump CNP106 1 105 80% 104.0

Bentonite filtering plant CNP162 1 105 100% 105.0

Mud Tanks and recycling unit

(pump) -- 1 104 70% 102.5

Water / mud pump (electric) CNP281 1 88 80% 87.0

Generator (for drilling rig) CNP102 1 100 100% 100.0

Air compressor CNP001 1 100 70% 98.5

Hydraulic power pack CNP174 1 100 100% 100.0

Stage III Pre-Reaming & Cofferdam at Diffuser

3.1


HDD Drill Rig -- 1 88 80% 87.0

Crane CNP049 2 95 40% 94.0

Mud pump CNP106 1 105 80% 104.0

Agitator CNP005 1 90 80% 89.0





(pump) -- 1 104 70% 102.5





Welding and cuting set -- 1 89 30% 83.8

Stage IV Pipe Installation & Installation of Diffuser & Removal of Cofferdam

4.1


HDD Drill Rig -- 1 88 80% 87.0

Crane CNP049 2 95 40% 94.0

Mud pump CNP106 1 105 80% 104.0

Agitator CNP005 1 90 80% 89.0







TM-GW

Reference

Number

Nos.

used

SWL,

dB(A) % on time

Overall

SWL





(pump) -- 1 104 70% 102.5





4.6.10 Phases of construction of the works were identified and unmitigated and mitigated

scenarios were assessed for noise impact at the identified NSR.

Prediction of Unmitigated Construction Noise Impact

4.6.11 The impact of construction noise on the identified NSRs was assessed in accordance

with the procedures laid down in Technical Memorandum on Noise from Construction

Work Other Than Percussive Piling. A +3 dB (A) façade correction was added to the

predicted noise levels to account for the façade effect at each NSR. In general, the

noise impact will be the highest when works are being carried out close to the NSRs

and, as the works areas gradually shift away, the noise would tend to diminish.

4.6.12 As a conservative approach to assessing the worst-case construction noise impacts, it

was assumed that all the proposed PMEs for each construction work stage were

operating concurrently. The predicted cumulative worst-case construction noise levels

at the NSRs due to construction of STP, laying of gravity sewer and rising mains on

Po Toi O Chuen Road and in the village, and construction of submarine outfall are

summarized in Table 4-14. Detailed calculations are provided in Appendix 4.1.

Table 4-14: Predicted Worst-case Cumulative Construction Noise Levels at

Representative NSRs - Unmitigated Scenario

NSR Description of NSR

Predicted Worst-case Construction Noise

Level dB(A)

Unmitigated

Results

Noise

Criteria Exceedance

PTO1_N1 Village House in

PTOCR 28 95 75 20


PTOCR 7A 95 75 20

PTO_N3 Temporary Structure

for Living 92 75 17

FV_N1 Fairway Vista House

12 101 75 26

http://www.epd.gov.hk/epd/english/environmentinhk/noise/guide_ref/tm_nonpp.html







NSR Description of NSR


Level dB(A)

Unmitigated

Results

Noise

Criteria Exceedance

SC_N1 Seacrest Villas in

PTOCR No. 64 90 75 15

4.6.13 Based on the effective sound power level of the PMEs and the distance of work site to

the noise sensitive receivers, unmitigated construction noise level for some work

stages were predicted to exceed the EIAO-TM of 75dB(A) guideline level by 15 to 26

dB(A). About 130 residential dwellings and 1 temple will be affected. Various

mitigation options have been considered in accordance with the guidelines laid down

in the Environmental Impact Assessment Ordinance, Guidance Note No. 9/2010

“Preparation of Construction Noise Impact Assessment under the Environmental

Impact Assessment Ordinance” (GN 9/2010) as discussed in Section 4.7.

Operational Noise

4.6.14 During the operational phase, equipment noise from the proposed sewage treatment

plant will be the main noise source with potential noise impact on the NSRs.

4.6.15 The equipment inventory of the Po Toi O STP will be similar to those for small

sewage treatment plants in Hong Kong, and this would include sewage pumps,

ventilation fans, deodourizing fans, mechanically raked fine screen and blower. A

typical equipment inventory based on the design at the time of preparation of this EIA,

is provided in Table 4-15. The inventory and operation modes were confirmed with

the project engineer. The typical Sound Power Levels (SWL) associated with these

equipment items are also provided.

Table 4-15: Typical Noisy Equipment for the Proposed Po Toi O Sewage

Treatment Plant

Location Equipment No. of

Units

Typical

SWL,

dB(A)

Sub-total

SWL,

dB(A)

Preliminary

Treatment Units

Submersible pump (Ref. 1) 2 85 88.0

Mechanically raked fine screen

(Ref. 3) 2 89 92.0

Deodourizing fan (Ref. 4) 2 85 88.0

Exhaust fan (Ref. 2) 1 79 79.0

MBR Equipment

Unit

Mechanically pump (Ref. 5) 3 92 96.8



Sludge

Treatment Unit

Submersible pump (Ref. 1) 2 85 88.0







Location Equipment No. of

Units

Typical

SWL,

dB(A)

Sub-total

SWL,

dB(A)


Air Blower

Room

Blower (Ref. 6) 1 85 85.0


Outfall Pumping

Station and

Header Tank

Mechanical pump (Ref. 5) 4 92 98.0



Remark: -

SWL – Sound Power Level

Only noisy equipment is included in the table. Other equipment which do not have significant noise

emissions are excluded.

(Ref. 1) SWL referenced to CNP283.

(Ref. 2) SWL referenced to approved EIA of Harbour Area Treatment Scheme (HATS) Stage 2A (EIA-

148/2008) and Good Practices on Ventilation System Noise Control based on the flow rate of

1,300m3/hr.

(Ref. 3) SWL referenced to the approved EIA Report on Tai Po Sewage Treatment Works Stage V

(EIA-097/2004).

(Ref 4) SWL of plant refers to Good Practices on Ventilation System Noise Control based on the flow

rate of 17,000 m3/hr and 125 Pa.

(Ref 5) SWL of plant refer to Good Practices on Pumping System Noise Control based on the

horsepower of pumpset 20 hp at 1800 rpm.

(Ref 6) SWL of plant refers to the tender specification for Shatin STW Stage 3 Upgrading and approved

EIA of Harbour Area Treatment Scheme (HATS) Stage 2A (EIA-148/2008).

4.6.16 Standby equipment would only be used in case of failure or maintenance of duty units.

Therefore, concurrent operation of both duty and standby equipment will not occur

under the normal operation. As a reasonable worst case scenario assessment, the

maximum sound power levels during operation would be under the full operation of

all duty equipment which is given in Table 4-15.

4.6.17 The impact of operational noise on the identified NSRs was assessed in accordance

with the procedures laid down in Technical Memorandum on Noise from Places other

than Domestic Premises, Public Places or Construction Sites. A +3 dB (A) façade

correction was added to the predicted noise levels to account for the façade effect at

each NSR.

4.6.18 All identified noisy equipment items of the STP would be confined inside the building

structure except exhaustion fans. A reduction of 20 dB(A) can be achieved if the

building enclosure is built using suitable material such as concrete with surface density

of 25 kg/m2. Equipment items to be confined within the building structure of

PTOSTW with noise reduction consideration are summarized in Table 4-16.








Table 4-16: Proposed Design Measures For Operation of Po Toi O Sewage

Treatment Plant

Location Equipment Mitigation

Measures

Noise

Reduction

dB(A)

Preliminary

Treatment

Units

Submersible pump Enclosed Inside

Building Structure

-20

Mechanically raked

fine screen

-20

Deodourizing fan -20

Exhaust fan -- 0

MBR

Equipment Unit

Mechanically pump

(Ref. 5)

Enclosed Inside

Building Structure

-20

Deodourizing fan

(Ref. 4)

-20

Exhaust fan (Ref. 2) -- 0

Sludge

Treatment Unit

Submersible pump

(Ref. 1)

Enclosed Inside

Building Structure

-20

Deodourizing fan

(Ref. 4)

-20


Air Blower

Room

Blower (Ref. 6) Enclosed Inside

Building Structure

-20


Existing Outfall

Pumping

Station and

Header Tank

Mechanical pump

(Ref. 5)

Enclosed Inside

Building Structure

-20

Deodourizing fan

(Ref. 4)

-20


4.6.19 The predicted worst-case noise levels at identified NSRs due to the operation of STP

would comply with the noise criteria at all time. The predicted noise levels at

representative NSRs are summarized in Table 4-17 and detailed in Appendix 4.2.






Table 4-17: Predicted Worst-case Operation Noise Levels at Representative NSRs

- Unmitigated Scenario

NSR NSR Description Predicted

Unmitigated

Noise Level,

dB(A)

Day-time

Noise

Criterion,

dB(A)

Night-time

Noise

Criterion,

dB(A)


PTOCR 28 45 49 45


PTOCR 7A 37 49 45

PTO_N3 Temporary Structure

for living 32 49 45

FV_N1 Fairway Vista House

12 32 49 45


PTOCR No. 64 37 49 45

4.6.20 In fact, typical concrete wall has better noise insulation performance. The assumption

of 20 dB(A) reduction has been conservative. Also, with some of the equipment stored

underground, the noise impact will be further reduced. Furthermore, the acoustic

louvres are designed to face the slope but not the village, avoiding direct view of the

noise source from NSR. The maximum allowable sound power levels of equipment

items would be specified in the tender specification to ensure the operational noise

impact complying with relevant noise criteria.

4.6.21 Most of the noisy equipment items in the sewage treatment plant are fully enclosed

underground or enclosed by concrete structure. With noise reduction due to distance

between the STP and the nearest NSR, no operational noise impact is anticipated and

therefore no mitigation is required.

4.7 Evaluation and Recommendation of Noise Mitigation Measures

Construction Noise

4.7.1 Mitigation at source or path should be the most effective way to reduce the impact.

There are 4 ways in doing that viz. : -

by use of quiet plants and working methods to mitigate at source;

by use of mobile noise barriers/enclosures along the path of noise propagation;

by adopting good site practice to limit noise emissions at source;

by scheduling of work to minimize work scale and duration of impact.






Use of Quiet Plants and Working Methods

4.7.2 Silenced plants or quality powered mechanical equipment (QPME) are quieter than

those noise levels given in TM-GW for the equivalent type of equipment. These

silenced equipment items are known to be available in Hong Kong and hence should

be adopted as far as practical. Table 4-18 shows the possible alternative quieter PME

which are taken from BS:5228: Part 1:2009 or available noise label. These quieter

PMEs are available in the market and have been successfully applied to other projects

and have achieved noticeable noise reductions. The quieter PMEs to be used for the

works shall meet the following SWLs, or lower:

Table 4-18 Quiet PME and Associated Sound Power Level Proposed for the

Project

Description of PME Equivalent Quiet PME SWL, dB(A)

Hydraulic breaker BS5228 Tab. D8-12 106

Excavator / loader EPD-00081 99

Lorry BS5228 Tab. D8-25 96

Vibrating hammer (piling) BS5228 Tab. D4-12 94

Roller, vibratory BS5228 Tab. D3-115 102

Vibratory poker BS5228 Tab. D6-40 98

Backhoe BS5228 Tab. D3-108 97

Breaker, hand held Noise Label NB-0022-13-001 100

Ref:

BS 5228-1:2009. BSI British Standards. Code of practice for noise and vibration control on

construction and open sites – Part 1: Noise

EPD Issued Noise Emission Label:

https://epic.epd.gov.hk/eForm/lic_epd119/lrrf031_list.jsp?epic_lic_no=002030606&a119_or_119_i

nd=A&lang=eng

4.7.3 In addition to use of breaker for breaking up road surface in the village area, drilling

with chemical agent will be considered as far as practicable in the construction phase

according to local situation.

Use of Mobile Noise Barriers/Enclosures

4.7.4 Mobile noise barriers can be effective in screening noise from reaching sensitive

receivers, particularly for the low-rise houses in this case. 3m high mobile barriers

with skid footing and a small cantilevered upper portion can be located within a few

metres of stationary plants and within about 5m of more mobile plant such as

hydraulic breaker. All these PMEs are slow moving or usually stationary when they

are operating and hence the position of the mobile barriers will not need to be

frequently adjusted.

https://epic.epd.gov.hk/eForm/lic_epd119/lrrf031_list.jsp?epic_lic_no=002030606&a119_or_119_ind=A&lang=eng

https://epic.epd.gov.hk/eForm/lic_epd119/lrrf031_list.jsp?epic_lic_no=002030606&a119_or_119_ind=A&lang=eng






4.7.5 Some sections of gravity sewers and rising mains construction would be aligned close

to the village houses. As the handheld breaker is the noisy PME for excavation work,

it shall be fitted with mufflers to minimize noise emission. A movable enclosure made

up of plywood is proposed to surround both worker and breaker during breaking

process. The internal wall of the enclosure should be laid with sound absorbent such as

mineral wool. Without direct view of the noisy part of the breaker from NSR, this

design can achieve 15dB(A) reduction, which has already taken into account sound

leakage through the gaps. A typical drawing of the enclosure can be found in

Appendix 4-5.

4.7.6 For construction of submarine outfall using HDD, the work area is large enough to

accommodate semi-enclosure. It should enclose the stationary plant equipment on

three sides with cover. Only the side facing the sea shall be opened for heat

exhaustion.

Schedule of Work

4.7.7 As the footpath between village houses is very narrow, pipe laying in close proximity

of the NSRs cannot be avoided. Construction work will be divided into short sections

(10m) to reduce the duration of localized work (about one month per workfront).

Three workfronts will progress at the same time. Each workfront should be separated

from each other by at least 100m to minimize cumulative effect.

4.7.8 During laying of gravity sewers and rising mains near NSRs PTO_N1 and PTO_N3,

major concurrent noisy activities are laying of Po Toi O Chuen Road sewer and

horizontal directional drilling (HDD) respectively. The 10m workfront of gravity

sewers and rising mains installation near the two NSRs shall be scheduled at different

times from these noisy activities to minimize cumulative noise impact.

4.7.9 As the prevailing noise level in restricted hours is lower than daytime (averaged 50 –

51 dB(A) vs 57 - 59 dB(A) based on baseline monitoring), construction works will be

carried out in daytime to avoid nuisance during evening and night time.

Adoption of Good Site Practice

4.7.10 Good site practice and noise management can significantly reduce the impact of a

construction site’s activities on nearby NSRs. Although the reduction in noise level is

not readily predictable and quantified, the following measures should be useful during

each phase of construction:

Only well-maintained plant should be operated on-site and plant should be

serviced regularly during the construction programme;

Machines that may be in intermittent use should be shut down between work

periods or should be throttled down to a minimum;

Silencer and mufflers on construction equipment should be utilised and should

be properly maintained during the construction programme;






Noisy activities can be scheduled to minimise exposure of nearby NSRs to

high levels of construction noise. For example, noisy activities can be

scheduled for midday. Avoid carrying out noisy activities at the same time;

For the installation of gravity sewers and rising mains near residence, hand-

held breaker may be used to break the hard concrete layer. The manual

equipment should be used as far as practicable to avoid using the PME. If

found necessary, the percentage on time should be limited to reduce continuous

contributions;

Plant known to emit noise strongly in one direction should, wherever possible,

be orientated so that the noise is directed away from the nearby NSRs;

Mobile plant should be sited as far away from NSRs as possible; and

Material stockpiles and other structures should be effectively utilised, wherever

practicable, in screening noise from on-site construction activities.

4.7.11 During excavation works for gravity sewers and rising mains installation, generator

and breaker will be operated at the same time. Generator should be placed at a fixed

location and screened by noise barrier. It should be at least 5-6m away from the NSRs

whenever excavation work has to be carried out at their front doors (calculations in

Appendix 4.3 refers). These measures can minimize the noise contribution from the

generator and the total sound power level at NSRs.

4.7.12 Only one vibratory poker is proposed for surfacing work after pipe laying. To further

minimize noise nuisance, vibratory poker will only be operated 4m away from NSR

and with noise barrier properly erected. This can reduce the construction noise level at

the NSR to 75B(A) as shown in Appendix 4.3 (NSRs PTO_N1 & FV_N1). Surfacing

work within 4m from NSR will be carried out by manual method.

4.7.13 “Recommended Pollution Control Clauses for Construction Contracts” is available on

EPD website. It contains the recommended noise pollution control measures to be

implemented by the contractor during the construction stage. The predicted noise

levels are summarized in Table 4-19. Detailed calculations are provided in Appendix

4.3.

Table 4-19: Predicted Cumulative Construction Noise Levels at Representative

NSRs - Mitigated Scenario

NSR Description of

NSR


Level dB(A)

Mitigated

Results

Noise

Criteria Exceedance

PTO1_N1 Village House in

PTOCR 28 75 75 -


PTOCR 7A 75 75 -

PTO_N3 Temporary

Structure for living 74 75 -






NSR Description of

NSR


Level dB(A)

Mitigated

Results

Noise

Criteria Exceedance

FV_N1 Fairway Vista

House 12 75 75 -


PTOCR No. 64 71 75 -

4.7.14 With the adoption of quiet PMEs and temporary barrier/enclosure/semi-enclosure, no

construction noise exceedance is expected. When the works areas gradually shifted

away, the noise would tend to diminish.

Cumulative Noise Impact Due to Concurrent Project

4.7.15 The following discusses the potential cumulative interface issues between concurrent

projects as indicated in Chapter 2 – Project Description. There may be two potential

concurrent projects in the area, i.e.

Roundabout near the minibus stop

Fish culture zone (FCZ) dredging and relocation

4.7.16 During the course of the study, CEDD has confirmed that there was no programme for

the fish culture zone dredging and relocation. There was also no information on when

the roundabout would be constructed. Therefore, no cumulative noise impact is

expected.

4.7.17 Should there be concurrent project in the vicinity, continuous discussion between

contractors shall be conducted to plan the location and programme of construction

work to minimize cumulative impact.

4.8 Evaluation of Residual Impacts

4.8.1 After implementation of mitigation measures as mentioned in Section 4.7,

construction noise impact on NSRs would comply with the daytime noise guideline

75dB(A). Upon completion of the sewage treatment plant, noisy plant equipment will

be operated within the building structure or underground. The fixed equipment noise

will comply with the daytime/evening time and nighttime noise criteria. Therefore, no

residual noise impact is expected in both construction and operational phases.






4.9 Environmental Monitoring and Audit Requirements

4.9.1 With the implementation of proposed construction noise mitigation measures such as

use of quality powered mechanical equipment (QPME), use of mobile noise barriers,

enclosure and semi-enclosure, good site practice and management, and construction

noise monitoring and audit programme, construction noise impact could be reduced

down to acceptable levels. Regular monitoring of noise level should be carried out at

noise monitoring stations near representative sensitive receivers before and throughout

construction work to ensure that relevant noise standard can be met.

4.9.2 Since the noisy equipment items in the sewage treatment plant are fully enclosed

underground or enclosed by concrete structure, operational noise impact is expected to

be acceptable. Operational noise monitoring is considered unnecessary.

4.9.3 General EM&A requirements were presented in Chapter 12.

4.10 Conclusion

4.10.1 Construction noise arising from typical types and numbers of powered mechanical

equipment items (PME) for the construction of sewage treatment plant, rising

mains/sewer installation and submarine outfall have been assessed. Based on the

effective sound power levels of the PMEs and the notional noise distances to the noise

sensitive receivers, unmitigated construction noise levels would exceed the 75dB(A)

guideline level for the non-restricted hours for all NSRs. At source mitigation

measures have been proposed including the use of quality plants, use of mobile noise

barriers, semi-enclosure, enclosure, strategic work scheduling and good site practice.

With the proposed mitigation measures, no construction noise exceedance is expected.

4.10.2 Most of the noisy equipment items in the sewage treatment plant would be fully

underground or enclosed by concrete structure. With noise reduction due to distance

between the STP and the nearest NSR, operational noise impact is anticipated to be

acceptable.

4 noise impact assessment 4.1 introduction 4.2 … · 4.1 introduction 4.1.1 this chapter presents...

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