4 NOISE impact

4.2 Environmental Legislation and Standards

4.2.1 Noise impacts were assessed in accordance with the criteria and methodology given in the Technical Memoranda (TM) under the Noise Control Ordinance (NCO) and the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) under the Environmental Impact Assessment Ordinance (EIAO).

4.2.2 The NCO provides the statutory framework for noise control. This defines statutory limits applicable to equipment used during the construction phase of the proposed works in the study area. The NCO invokes four Technical Memoranda, which defines 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).

4.2.3 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 and Leq(30min) 70dB(A) for schools during normal hours (65dB(A) during examination) and all other sensitive areas where unaided voice communication is required. This standard was used as assessment criteria in the construction noise assessment during daytime.

4.2.4 Between 1900 and 0700 hours and all day on Sundays and public holidays, activities involving the use of powered mechanical equipment (PME) for the purpose of carrying out construction work are prohibited unless a Construction Noise Permit (CNP) has been obtained. A CNP may be granted provided that the Acceptable Noise Level (ANL) for the noise sensitive receivers (NSRs) can be complied with. ANLs are assigned depending upon the Area Sensitive Rating (ASRs). The corresponding basic noise levels (BNLs) for evening and night-time periods are given in Table 4.1.

Table 4.1 Construction Noise Criteria for Activity other than Percussive Piling

Time Period	Basic Noise Level (BNLs) (dB(A))
Time Period	ASR A	ASR B	ASR C
Evening (1900 to 2300 hours) ⁽¹⁾	60	65	70
Night (2300 to 0700 hours)	45	50	55

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

4.2.5 According to the preliminary construction programme, all the proposed construction works would be carried out during non-restricted hours. In case of any construction activities during restricted hours, it would be the Contractor’s responsibility to ensure compliance with the NCO and the relevant TM. The Contractor will be required to submit CNP application to the Noise Control Authority and abide by any conditions stated in the CNP, should one be issued.

4.2.6 Based on the preliminary design information, percussive piling would not be adopted for the proposed Project. Therefore, noise criteria as stipulated in the PP-TM would not be applicable to this Project.

4.2.7 In this regard, noise impacts associated with the construction of the proposed Project would primarily be assessed against the noise criteria set out in Table 1B of Annex 5 of the EIAO-TM.

4.3 Description of the Environment

4.3.1 The sites for the proposed drainage improvement works at Pak Ngau Heung River, Tai Tei Tong River, Luk Tei Tong River and Luk Tei Tong By-pass Channel are located in Mui Wo, South Lantau. The sites are generally rural in nature, and mainly comprises village houses and agricultural land. Village establishments including Tai Tei Tong, Ma Po Tsuen, Ling Tsui Tau Tsuen, Luk Tei Tong and Ha Tsuen Long Luk Tei Tong were identified in the vicinity of the work areas.

4.3.2 Based on the survey maps and site visits conducted in December 2003, there was no major noise source found within or in the vicinity of the sites. The dominant noise sources arise from human activities and road traffic along some local access roads.

4.4 Noise Sensitive Receivers

4.4.1 In accordance with the Mui Wo Fringe Outline Zoning Plan (OZP) No. S/I-MWF/3, the land uses to the surrounding areas of the Project were zoned as Residential Group D (“R(D)”), Open Space(“O”), Village (“V”), Government/ Institution /Community (“G/IC”), Recreation (“REC”) and Agriculture (“AGR”). At the time of this EIA study, no information about the development schedule and details of the areas zoned as “R(D)” and “V” was available. Hence, no futher/planned NSR within these areas was identified for the construction noise assessment.

4.4.2 To represent the worst-case scenario, a number of existing NSRs in the vicinity of the proposed drainage works, have been designated for the assessment. Table 4.2 summarizes the representative NSRs for the noise impact assessment. Locations of the representative NSRs are shown in Figure 4.1.

Table 4.2 Summary of Representative Noise Sensitive Receivers

NSR	Location	Use	No of Storeys	Distance (m)*
Pak Ngau Heung River
PNH1	No. 22 Village House, Tai Tei Tong	Residential	3	4
PNH2	No. 1 Village House adjacent to Pak Ngau Heung River	Residential	2	5
PNH3	No. 10 Village House adjacent to Pak Ngau Heung River	Residential	2	4
PNH4	Village House, Ling Tsui Tau Tsuen	Residential	1	4
PNH5	No. 6 Village House adjacent to Pak Ngau Heung Outlet	Residential	3	6
PNH6	Village House, Ling Tsui Tau Tsuen	Residential	2	2
LT1	Village House, Ling Tsui Tau Tsuen	Residential	2	17
LT2	No. 75 Village House, Ling Tsui Tau Tsuen	Residential	1	1
Tai Tei Tong River
TTT1	No. 25 Village House, Ma Po Tsuen	Residential	2	27
TTT2	No. 27 Village House, Ma Po Tsuen	Residential	2	45
TTT3	No. 23 Village House adjacent to Tai Tei Tong River	Residential	3	4
TTT4	No. 10 Village House adjacent to Tai Tei Tong River Outlet	Residential	2	5
SCH	Mui Wo Shcool	Education	1	17
Luk Tei Tong River and Luk Tei Tong By-pass Channel
LTT1	No. 135 Village House, Luk Tei Tong	Residential	3	1
LTT2	No. 19 Village House, Luk Tei Tong	Residential	2	15
LTT3	No. 36 Village House, Luk Tei Tong	Residential	3	32
LTT4	No. 4 Village House adjacent to Luk Tei Tong River Outlet	Residential	3	1

Note: * Horizontal Separation from nearest site boundary (m)

4.5 Assessment Methodology

4.5.1 Noise impact associated with the construction activities of the Project was assessed using the standard acoustic principles and the methodology outlined in the GW-TM issued under the NCO as well as the guideline given in Annex 13 of the EIAO-TM.

4.5.2 Prior to the appointment of the Contractor, exact number and type of construction plant to be adopted for the construction activities are not available. For the purpose of the assessment, a preliminary equipment inventory (Appendix 4.1) has been assumed based on typical construction activities of similar projects.

4.5.3 Sound power levels (SWLs) of the PME in Appendix 4.1 were taken from Table 3 of the GW-TM. Where no sound power level (SWL) was given in the GW-TM, reference was made to BS 5228: Part 1:1997 Noise and Vibration Control on Construction and Open Sites.

4.5.4 In order to provide more realistic calculations of the construction noise levels, reasonable on-time percentage of each PME (the time when the PME is in operation within a 30 minutes time slot) was made. Table 4.3 summarizes the on-time percentage of the PME.

Table 4.3 On-time Percentage Assumptions of PME

PME	Assumed on–time %
Assumed On-time Percentage for All Construction Tasks Except Construction of Retaining Wall at Pak Ngan Heung Outlet (CH250-300) and Luk Tei Tong River Outlet (CH195-225)
Generator, Drainage Pump and Mini-Excavator	100%
Systemised Piling Machinery	80%
Excavator/Loader, Roller, Concrete Lorry Mixer, Vibratory Poker, Bar and Bender/Cutter, Crane, Osciallator, Power Rammer, Compactor Rammer, Grout Mixer and Grout Pump	70%
Dump truck, Hydraulic Breaker	50%
Assumed On-time Percentage for Construction of Retaining Wall at Pak Ngan Heung Outlet (CH250-300) and Luk Tei Tong River Outlet (CH195-225)
Generator and Drainage Pump	100%
Concrete Lorry Mixer, Vibratory Poker, Bar and Bender/Cutter, Crane,	70%
Power Rammer	50%

4.5.5 The assumed construction plant inventory for unmitigated and mitigated scenarios of various construction activities and the percentage on-time were confirmed by the project proponent as practicable and reasonable for completing the project within the scheduled construction programme based on the information available at this stage.

4.5.6 All items of PME were assumed to be located at a notional or probable source position of the segment where each activity would be undertaken. Notional noise sources for different construction areas were assumed in accordance with the GW-TM. According to Section 2.11 of the GW-TM, a positive correction of 3 dB(A) for acoustic reflection has been applied to the predicted noise levels in order to account for the façade effect at each representative NSR.

4.5.7 The assessment was based on the cumulative SWL of PME likely to be used for each location, taking into account the construction period in the vicinity of the receiver location. To predict the noise level, PME was divided into groups required for each discrete construction activity. The objective was to identify the worst-case scenario representing those items of PME that would be in use concurrently at any given time. The sound pressure level (SPL) of each construction task at NSRs was calculated, depending on the number of plants, their frequency of operation, and their distance from receivers. The noise levels at NSRs were then predicted by adding up the sound pressure level of all concurrent construction tasks.

4.5.8 Construction activities, within 300m of a given NSR at the same period, were considered to contribute to the cumulative impact at that NSR. Noise sources from the areas greater than this distance were excluded from the assessment.

4.6 Identification of Environmental Impacts

4.6.1 The potential source of noise impact during the construction phase of the Project would be the use of PME for various construction activities. As indicated in the preliminary construction programme (Appendix 2.2 refers), the construction of the proposed Project would last from June 2006 to June 2009. The major construction activities for the proposed drainage works include:

· Site clearance

· Excavation

· Retaining wall

· Backfilling/Channel lining

· Box culvert

· Low flow diversion pipes and bund

· U-channel construction

4.6.2 The proposed drainage works would mostly be carried out within a linear construction site. Construction equipment and activities would be moving along the channel sections as the construction proceeds. Since some of the identified sensitive receivers are in close proximity to the proposed work sites, adverse construction noise impacts would be expected at these receivers if no noise control measures are implemented.

4.6.3 As indicated in Section 2.10, construction of the Project would likely interface with the following projects:

Projects in the Vicinity	Anticipated Construction Programme
Outlying Sewerage Stage 2 – Mui Wo Village Sewerage (Package 1A)	Late 05 to Mid 07
Construction of Emergency Vehicular Access (EVA) and Sewerage Works at Luk Tei Tong, Mui Wo	Late 04 to Late 06

4.6.4 As indicated above, the construction of EVA and sewerage works at Luk Tei Tong would likely coincide with this Project during the period of mid to late 2006. However, it is expected that, the major construction works of the EVA and sewerage works at Luk Tei Tong would have been finished substantially prior to the start of the proposed drainage improvement works under the Project and only minor construction works would remain during the coincidence period. As such, adverse cumulative noise impact from the construction works of this concurrent project would not be anticipated.

4.6.5 The proposed sewerage works under the Mui Wo Village Sewerage would take place in the vicinity of the Pak Ngan Heung River and would likely coincide with the proposed drainage improvement works under the Project from mid 2006 to mid 2007. In order to investigate the potential cumulative noise impact associated with the construction activities of this concurrent project, a cumulative noise assessment was carried out based on the latest available information (Section 4.9).

4.7 Prediction and Evaluation of Impacts

4.7.1 As illustrated in the preliminary construction programme, various construction activities of the Project would be carried out concurrently during a particular period.

4.7.2 Based on the preliminary construction programme and the plant inventory (Appendix 4.1), unmitigated cumulative noise impact arising from different construction activities of the Project on the representative NSRs have been predicted.

4.7.3 The predicted construction noise levels for the unmitigated scenario at the representative NSRs are given in Appendix 4.2 A and Table 4.4 below. A sample calculation of construction noise level for the unmitigated scenario is provided in Appendix 4.2.

Table 4.4 Summary of Unmitigated Construction Noise Levels During Normal Daytime Working Hours

	Predicted Noise Levels, dB(A)			EIAO-TM Normal Daytime Construction Noise Criteria, dB(A)
Pak Ngau Heung River
PNH1	69	-	92	75
PNH2	74	-	93	75
PNH3	71	-	93	75
PNH4	71	-	100	75
PNH5	69	-	97	75
PNH6	68	-	90	75
LT1	71	-	88	75
LT2	68	-	100	75
Tai Tei Tong River
TTT1	62	-	79	75
TTT2	62	-	77	75
TTT3	62	-	88	75
TTT4	67	-	85	75
SCH	66	-	79	70 (School during normal hours) 65 (School during examination hours)
Luk Tei Tong River and Luk Tei Tong By-pass Channel
LTT1	62	-	90	75
LTT2	62	-	86	75
LTT3	63	-	83	75
LTT4	65	-	96	75

4.7.4 The assessment results showed that the predicted cumulative noise levels at the representative NSRs would range from 62 to 100 dB(A), exceeding the noise criteria by 1 - 25 dB(A) without mitigation measures. Mitigation measures would therefore be required to abate the construction noise impacts.

4.8 Mitigation Measures

Good Site Practices

4.8.1 Although the noise mitigation effects are not quantifiable and the benefits may vary with site conditions and operation conditions, good site practices and noise management measures are easy to implement and do not impact upon the work schedule. The following site practices should be followed during the construction phase:

· Only well-maintained plant should be operated on-site and plant should be serviced regularly during the construction programme;

· Silencers or mufflers on construction equipment should be utilized and should be properly maintained during the construction programme;

· Mobile plant, if any, should be sited as far from NSRs as possible;

· Machines and plant (such as trucks) that may be in intermittent use should be shut down between work periods or should be throttled down to a minimum;

· 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; and

· Material stockpiles and other structures should be effectively utilised, wherever practicable, in screening noise from on-site construction activities.

Adoption of Quiet Plant

4.8.2 The use of quiet PME was considered to be a practicable means to abate the potential construction noise impact. The Contractor would be able to obtain particular models of plant that are quieter than the PME given in GW-TM. The noise reduction achieved in this way will depend on the Contractor’s chosen construction methods and it is considered that specifying particular plant models would be too restrictive to Contractor’s preferred construction methods. Hence, it is preferable and practical to specify the overall noise performance specification of all plant on site in terms of the total SWL so that the Contractor is allowed some flexibility to select plant to suit his needs.

4.8.3 In this assessment, the recommended silenced PME are taken from the BS5228: Part 1:1997, which are known to be used in Hong Kong. It should be noted that various types of quiet PME are commercially available in Hong Kong and have been used in other designated projects. The SWL for the quiet PME adopted are summarized in Table 4.5 below.

Table 4.5 Sound Power Levels for Quiet PME

Quiet PME adopted	SWL, dB(A)	Reference
Excavator/Loader	105	BS 5228 Table C3, item 97
Dump truck	103	BS 5228 Table C9, item 39
Vibratory roller	96	BS 5228 Table C8, item 25
Concrete lorry mixer	100	BS 5228 Table C6, item 23
Vibratory poker	98	BS 5228 Table C6, item 40
Crane	101	BS 5228 Table C7, item 114
Hydraulic Breaker	110 /106	BS 5228 Table C8, item 13 and item 12
Generator	95	CNP103

4.8.4 Noise reduction is anticipated with the use of the quiet PME (Appendix 4.3). However, the predicted construction noise levels at some NSRs during certain construction stages would not comply with the EIAO-TM noise criteria. Therefore, further noise mitigation measures would be required for those affected NSRs.

Use of Movable Noise Barrier and Temporary Noise Barrier

4.8.5 The use of noise barriers would be an effective means to alleviate the noise impact arising from the construction works, particularly for low-rise NSRs. Based on the site survey, all the NSRs within the Assessment Area are low-rise in nature with 1-3 storeys. In addition, the majority of the channel construction works would be undertaken below the ground levels of the NSRs. As such, a 2.4m high purpose-built site hoarding (with a superficial density of at least 7kg/m², and free from gaps/openings) could screen their sensitive façade from viewing the ground-level construction equipment within the site. However, it should be noted that the practicality of using temporary noise barriers would depend on whether there would be sufficient space available. Owing to site constraints, the use of temporary noise barrier would not be practicable for all areas. In view of the site conditions, only the works areas near NSRs PNH 4, PNH5 and LTT4 are considered feasible to erect temporary noise barriers (Figure 4.2). Based on the assessment result, the noise exceedances are attributable to the construction of retaining wall located less than 15m from these NSRs. The proposed temporary noise barriers as shown in Figure 4.2 would be designed to have sufficient length to shield the line of site of the NSRs PNH 4, PNH5 and LTT4 from the construction of retaining wall within 15m. With the implementation of the temporary noise barrier, a 10 dB(A) noise reduction was assumed.

4.8.6 For the works areas where it would not be feasible to erect temporary noise barriers, movable noise barriers are recommended. According to the GW-TM, a movable noise barrier with a cantilevered upper portion located above the noise generating part of the PME could reduce noise by 5 dB(A) or up to 10 dB(A), depending on the line of sight that could be blocked by the barriers when viewed from the NSR. Depending on the size of the PME, the dimension of the movable noise barrier will be designed by the Contractor with a view to blocking the line of sight. Barrier material of surface mass in excess of 7 kg/m² is recommended to achieve the maximum screening effect. The design of the movable barriers should be certified by the Environmental Team (ET) Leader and verified by the Independent Environmental Checker (IEC) to ensure the intended noise reduction effectiveness can be achieved. Table 4.6 summarises the use of movable noise barrier and noise reduction for certain items of PME. Appendix 4.4 provides the total SWL for various construction noise activities with the adoption of quiet PME and movable noise barriers.

Table 4.6 Movable Noise Barrier for Certain Items of PME

Construction Task		PME for which Movable Barrier is Adopted	Barrier Correction, dB(A)
Site Clearance		Excavator	5
Excavation		Excavator	5
Excavation		Hydraulic Breaker, Generator and Drainage Pump	10
Backfilling/Channel lining		Excavator and Concrete Lorry Mixer	5
		Vibratory Poker	10
Box Culvert	Piling	Oscillator	10
	Earthworks	Excavator	5
		Hydraulic Breaker, Generator and Drainage Pump	10
	Reinforcement Fixing / Concrete operations	Crane and Concrete Lorry Mixer	5
		Vibratory Poker and Bar Bender/Cutter	10
	Backfilling	Excavator	5
Low Flow Diversion Pipes and bund		Crane and Concrete Lorry Mixer	5
		Vibratory Poker and Bar Bender/Cutter	10
U-Channel Construction		Excavator and Mini-Excavator	5
		Hydraulic Breaker and Compactor Rammer	10
Gabion Channel		Excavator	5
		Vibratory Roller, Generator and Drainage Pump	10
Widening of Bottleneck		Excavator	5
		Generator and Drainage Pump	10
Retaining Wall-L/T Shape		Crane and Concrete Lorry Mixer	5
		Power Rammer, Vibratory Poker, Bar Bender/Cutter, Generator and Drainage Pump	10
Retaining Wall-Mini Bored Pile Wall	Installation of Temporary Works	Crane	5
		Systemised Pilling Machinery, Generator, Drainage Pump, Grout Mixer, Grout Pump and Vibratory Poker,	10
	Earth Wall	Excavator	5
		Hydraulic Breaker, Generator and Drainage Pump	10
	Reinforcement Fixing/Concrete Operations	Concrete Lorry Mixer	5
		Generator, Drainage Pump Vibratory Poker and Bar Bender/Cutter	10

4.8.7 With the adoption of the quiet PME and temporary/movable noise barriers, the mitigated noise levels have been predicted and are summarised in Appendix 4.5 A and Table 4.7. A sample calculation of construction noise levels for mitigated scenario is presented in Appendix 4.5.

Table 4.7 Summary of Mitigated Construction Noise Levels During Normal Daytime Working Hours (Use of Quiet PME and Temporary/Movable Noise Barriers)

NSR	Predicted Noise Levels, dB(A)			EIAO-TM Normal Daytime Construction Noise Criteria, dB(A)	Mitigation Measures Proposed
Pak Ngau Heung River
PNH1	52	-	75	75	Use of Quiet PME and Movable Barrier
PNH2	57	-	75	75	Use of Quiet PME and Movable Barrier
PNH3	55	-	75	75	Use of Quiet PME and Movable Barrier
PNH4	49	-	78	75	Use of Quiet PME and Temporary Noise Barrier
PNH5	48	-	75	75	Use of Quiet PME and Temporary Noise Barrier
PNH6	50	-	74	75	Use of Quiet PME and Movable Barrier
LT1	54	-	71	75	Use of Quiet PME and Movable Barrier
LT2	51	-	74	75	Use of Quiet PME and Movable Barrier
Tai Tei Tong River
TTT1	46	-	65	75	Use of Quiet PME and Movable Barrier
TTT2	49	-	63	75	Use of Quiet PME and Movable Barrier
TTT3	47	-	74	75	Use of Quiet PME and Movable Barrier
TTT4	50	-	72	75	Use of Quiet PME and Movable Barrier
SCH	52	-	65	70 (during normal hours) 65 (during examination)	Use of Quiet PME and Movable Barrier
Luk Tei Tong River and Luk Tei Tong By-pass Channel
LTT1	49	-	75	75	Use of Quiet PME and Movable Barrier
LTT2	46	-	72	75	Use of Quiet PME and Movable Barrier
LTT3	47	-	68	75	Use of Quiet PME and Movable Barrier
LTT4	47	-	75	75	Use of Quiet PME and Temporary Noise Barrier

4.8.8 The results indicate that due to the very close proximity to the work sites, NSR PNH4 would be exposed to noise levels in exceedance of the noise criterion even with the implementation of all the recommended mitigation measures.

4.8.9 Based on the results, the exceedance is due to the close proximity of NSR PNH4 (around 5 m) to the worksite of the retaining wall located at the Pak Ngau Heung River outlet. In order to further alleviate the noise impacts from the proposed drainage improvement works, the use of other possible mitigation measures have been considered and are discussed in the following sections.

Other Possible Mitigation Measures

4.8.10 The possible mitigation measures to further reduce the noise impacts may include:

Use of Acoustic Enclosure

4.8.11 In accordance with the EPD’s “A Practical Guide for the Reduction of Noise from Construction Works”, an acoustic enclosure with the inside lined with sound absorbing material can achieve a noise reduction of up to 20 dB(A). Nevertheless, it should be noted that the viability of using acoustic enclosure would largely depends on whether there would be sufficient space available and size of the PME. Since the work area of construction of retaining wall at the Pak Ngau Heung River outlet would be very close (about 5m) to NSR PHN4 and the use of large PME such as hydraulic breaker, erection of acoustic enclosure/shed was considered not feasible. Instead, a temporary noise barrier has been proposed to be erected in front of NSR PHN4 (Section 4.5.8 refers).

Manual Working

4.8.12 For areas where noise exceedances were predicted, the use of manual working (i.e. use of hand tools) has been considered. Adoption of manual working could eliminate noise impact arising from the use of PME. However, this method would be slow and require more manpower in comparison with the method using PME and its practicability would depend on the nature of the works. In view of the work nature, manual working was considered not feasible for the construction of retaining wall, which would inevitably require the use of PME such as hydraulic breaker, pilling machine and excavator.

Re-scheduling of Works

4.8.13 Re-scheduling of works has been considered to ameliorate the residual impact. However, based on the results, the noise exceedance is only due to construction of retaining wall at Pak Ngau Heung River outlet. Therefore, rescheduling of work was considered not applicable.

4.8.14 It is considered that all practicable mitigation measures have been exhausted and this unavoidable noise impact would be short-term (around four weeks) and localized.

4.9 Cumulative Construction Noise Impact from Concurrent Project

4.9.1 As mentioned in Section 4.6.5, the construction of the proposed sewerage work under the Mui Wo Village Sewerage would be between late 2005 and mid 2007. Cumulative noise impacts from the construction works of this concurrent project and this project is therefore expected between mid 2006 to mid 2007. Worst affected NSRs located in the vicinity of the work sites of the Mui Wo Village Sewerage, i.e. PNH4, PNH5, PNH6 and LTT4 were selected to check the cumulative construction noise impacts.

4.9.2 It should be noted that the implementation of this concurrent project would be subject to the on-going review by relevant project proponent and details of construction programme and plant inventory were not available at this stage. The cumulative noise assessment was therefore conducted based on the following assumptions:

· The sewerage works of the concurrent project would be divided into three areas (Areas A, B and C) as shown in Drawing No. Appendix 4.6.

· Sewerage works in Areas A, B and C would be constructed from October 2005 to May 2006, June 2006 to December 2006 and January 2007 to July 2007, respectively. Hence, only the works in Areas B and C would overlap with the Project.

· Maximum SWL for the concurrent project was estimated by the assumption that the nearest residential NSRs to the worksites of the sewerage works would comply with the noise criterion of 75 dB(A).

4.9.3 Based on the above assumptions, the cumulative construction noise levels from this Project and the Mui Wo Village Sewerage were calculated and are presented in Appendix 4.6.

4.9.4 The results indicate that the cumulative construction noise levels from the Mui Wo Village Sewerage and the Project at all NSRs would comply with the noise criteria of 75 dB(A) throughout the overlapping period, except NSR PNH4. The exceedances at NSR PNH4 are attributable to the construction of the retaining wall at Pak Ngau Heung River outlet under the Project. Based on the calculation, no adverse cumulative construction noise impact from the Mui Wo Village Sewerage would be anticipated.

4.10 Residual Environmental Impact

4.10.1 No residual noise impacts would be expected, except the short-term residual impacts at NSR PNH4 during the construction of the retaining wall at Pak Ngau Heung River outlet. Residual impacts of about 3dB(A) were predicted at NSR PNH4 even with the implementation of all practicable noise mitigation measures. It should be noted that the construction noise assessment results presented in Appendix 4.5A were based on the worst case scenario where the notional noise sources were assumed. It is therefore envisaged that the actual exceedances would be limited only to time period when the construction work is being carried out adjacent to the NSR PNH4 (within a radius of about 15m). As estimated by the Engineer, the residual impact would last for around four weeks. In sum, the residual noise impacts are short-term and localised, and are considered minimised compared with the overall benefits of the drainage improvements to the area.

4.11 Environmental Monitoring and Audit Requirements

4.11.1 An Environmental Monitoring and Audit (EM&A) programme is recommended to be established according to the predicted occurrence of noisy activities. All the recommended mitigation measures should be incorporated into the EM&A programme for implementation during the construction phase. Details of the EM&A programme are provided in a stand-alone EM&A Manual.