Table of contents

4 Noise Impact Assessment.. 4-1

4.1 Introduction. 4-1

4.2 Environmental Legislation, Standards and Guidelines. 4-1

4.3 Descriptions of Environment 4-6

4.4 Identification of Potential Noise Impact 4-6

4.5 Noise Sensitive Receivers. 4-6

4.6 Assessment Methodology, Prediction and Evaluation of Environmental Impacts. 4-7

4.7 Evaluation and Recommendation of Noise Mitigation Measures. 4-16

4.8 Evaluation of Residual Impacts. 4-20

4.9 Environmental Monitoring and Audit Requirements. 4-21

4.10 Conclusion. 4-21

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
PTO_N2	Village House in 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	Vibratory poker	CNP 170	1	113	80%	112	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)

Activity	Noise Source	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)

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	Excavation
1.1	Breaker, hand held	CNP 026	1	114	60%	112	112
	Generator, portable	CNP 107	1	100	60%	98
Stage II	Trench Support & Ground Compaction
No PME would be needed. Manual working for construction would be adopted.
Stage III	Pipe-laying
No PME would be needed. Manual working for construction would be adopted.
Stage IV	Backfilling
No PME would be needed. Manual working for construction would be adopted.
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)

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	1	122	50%	119	120
	Excavator / loader		CNP 081	1	112	80%	111
	Lorry		CNP 141	1	112	30%	107
Stage II	Trench Support & Ground Compaction
2.1	Vibrating hammer (piling)		CNP 172	1	115	80%	114	115
	Roller, vibratory		CNP 186	1	108	80%	107
Stage III		Pipe-laying
No PME would be needed. Manual working for construction would be adopted.
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	Vibratory poker		CNP 170	1	113	80%	112	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)

Activity	Noise Source	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	Generator, silenced	CNP102	1	100	100%	100.0
	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	Generator, silenced	CNP102	2	100	100%	103.0
	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
	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
	Welding and cuting set	--	1	89	30%	83.8
Stage IV	Pipe Installation & Installation of Diffuser & Removal of Cofferdam
4.1	Generator, silenced	CNP102	2	100	100%	103.0
	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
	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

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
PTO_N2	Village House in PTOCR 7A	95	75	20
PTO_N3	Temporary Structure for Living	92	75	17
FV_N1	Fairway Vista House 12	101	75	26
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
	Deodourizing fan (Ref. 4)	2	85	88.0
	Exhaust fan (Ref. 2)	1	79	79.0
Sludge Treatment Unit	Submersible pump (Ref. 1)	2	85	88.0
	Deodourizing fan (Ref. 4)	2	85	88.0
	Exhaust fan (Ref. 2)	1	79	79.0
Air Blower Room	Blower (Ref. 6)	1	85	85.0
	Exhaust fan (Ref. 2)	1	79	79.0
Outfall Pumping Station and Header Tank	Mechanical pump (Ref. 5)	4	92	98.0
	Deodourizing fan (Ref. 4)	2	85	88.0
	Exhaust fan (Ref. 2)	2	79	82.0

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
	Exhaust fan (Ref. 2)	--	0
Air Blower Room	Blower (Ref. 6)	Enclosed Inside Building Structure	-20
	Exhaust fan (Ref. 2)	--	0
Existing Outfall Pumping Station and Header Tank	Mechanical pump (Ref. 5)	Enclosed Inside Building Structure	-20
	Deodourizing fan (Ref. 4)		-20
	Exhaust fan (Ref. 2)	--	0

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)
PTO_N1	Village House in PTOCR 28	45	49	45
PTO_N2	Village House in PTOCR 7A	37	49	45
PTO_N3	Temporary Structure for living	32	49	45
FV_N1	Fairway Vista House 12	32	49	45
SC_N1	Seacrest Villas in 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_ind=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.

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	Predicted Worst-case Construction Noise Level dB(A)
		Mitigated Results	Noise Criteria	Exceedance
PTO1_N1	Village House in PTOCR 28	75	75	-
PTO_N2	Village House in PTOCR 7A	75	75	-
PTO_N3	Temporary Structure for living	74	75	-
FV_N1	Fairway Vista House 12	75	75	-
SC_N1	Seacrest Villas in 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.