6. NOISE IMPACT

6.1 Introduction

6.1.1 This section presents an assessment of the potential noise impacts associated with the construction and operation of the proposed SWC. Noise impacts during the construction phase are mainly associated with the construction activities and the use of powered mechanical equipment for construction works. For the operational phase, the noise impacts are primarily from the road traffic through the SWC.

6.2 Environmental Legislation, Policies, Plans, Standards and Criteria

Relevant Legislation in Hong Kong

Construction Noise

6.2.1 The principal legislation governing the control of construction noise is the Noise Control Ordinance (NCO) (Cap 400) and the Environmental Impact Assessment Ordinance (EIAO) (Cap 499). Guidelines concerning the assessment methodology and relevant criteria are provided in the supporting Technical Memoranda (TMs). The following TMs are applicable to the control of noise from construction activities:

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

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

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

· Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM)

Percussive Piling

6.2.2 Percussive Piling is prohibited at any time on Sundays and public holidays and during the weekday evening and night-time hours (1900-0700hrs, Monday through Saturday). A Construction Noise Permit (CNP) is required for such works during the weekday daytime hours (0700-1900hrs Monday through Saturday).

6.2.3 When assessing a CNP application for carrying out percussive piling, the Noise Control Authority is guided by the PP-TM. The Noise Control Authority will look at the difference between the Acceptable Noise Levels (ANLs), as promulgated in the PP-TM, and the Corrected Noise Levels (CNLs) that are associated with the proposed piling activities. Depending on the level of noise impact on nearby Noise Sensitive Receivers (NSRs), the Noise Control Authority would determine the time periods for percussive piling operation. The time periods are indicated in Table 6.1.

Table 6.1 Permitted Hours of Operation for Percussive Piling (not involving the use of diesel, pneumatic and/or steam hammers)

6.2.4 The Government is committed to phase out the use of diesel, pneumatic and steam hammer pile drivers, which are particularly noisy. There are more stringent requirements for the use of diesel, pneumatic and steam hammer after 1 October 1999.

General Construction Works

6.2.5 Noise generated by general construction works during normal working hours (i.e. 0700 to 1900 hours on any day not being a Sunday or public holiday) fall within the scope of the EIAO-TM. The recommended noise standards are presented in Table 6.2.

Table 6.2 EIAO-TM Daytime Construction Noise Limit

6.2.6 The NCO provides statutory controls on general construction works during the restricted hours (i.e. 1900 to 0700 hours Monday to Saturday and at any time on Sundays and public holidays). The use of powered mechanical equipment (PME) for the carrying out of construction works during the restricted hours would require a Construction Noise Permit (CNP). The Noise Control Authority is guided by the GW-TM when assessing such an application.

6.2.7 When assessing a CNP application for the use of PME, the Noise Control Authority will compare the ANL's as promulgated in the GW-TM, and the CNLs (after accounting for factors such as barrier effects and reflections) associated with the agreed PME operations. A CNP may be issued if the CNL is equal to or less than the ANL. The ANLs are related to the noise sensitivity of the area in question and the Noise Control Authority will judge these at the time of the CNP application. As conditions may vary between the time of the EIA for a project and the time of a CNP application, the assignment of any Area Sensitivity Ratings in the EIA is not binding upon the Noise Control Authority. The relevant ANLs are shown in Table 6.3 below, which are determined by Area Sensitive Ratings (ASRs). ASR is a function of the type of area within which the NSR is located and the degree of the effect on the NSR of particular Influencing Factors (IFs).

Table 6.3 Acceptable Noise Levels (ANL, Leq 5min dB(A))

6.2.8 Factors such as the assigning of Area Sensitivity Rating, ANLs etc could affect the assessment results of a CNP application. The Noise Control Authority would decide these at the time of assessment of such an application based on the contemporary situations/conditions. It should be noted that the situations/conditions around the sites may change from time to time.

6.2.9 Despite any description or assessment made in the subsequent paragraphs, the Noise Control Authority will be guided by the Technical Memorandum (Memoranda) in assessing an application, once filed, for a Construction Noise Permit (CNP). The Authority will consider all the factors affecting their decision taking contemporary situations/conditions into account. Nothing in this report shall bind the Authority in making their decision. There is no guarantee that a CNP will be issued. If a permit is to be issued, the Authority shall include any condition it thinks fit, and such conditions shall be followed while the works covered by the permit are being carried out. Failure to comply with any conditions could result in the cancellation of the permit and prosecution action under the NCO.

Operational Traffic Noise

6.2.10 The Road Traffic Noise Planning Criteria stated in EIAO apply to uses rely on opened windows for ventilation. The relevant criteria are shown in Table 6.5.

Table 6.5 Road Traffic Noise Planning Criteria

6.2.11 In cases where practicable direct mitigation measures alone would not be adequate in mitigating noise impacts, indirect technical remedies may be adopted for existing NSRs provided that the residual impacts satisfy all three criteria below:

(1) the predicted overall noise level from the new road together with other traffic in the vicinity must be above the specified noise level (e.g. 70 dB(A) for domestic premises and 65 dB(A) for education institutions, all in L10(1hr));

(2) the predicted overall noise level is at least 1.0 dB(A) more than the "prevailing traffic noise level", i.e. the total traffic noise level existing before the works to construct were commenced; and

(3) the contribution to the increase in the predicted overall noise level from the new road must be at least 1.0 dB(A).

6.2.12 The total number of existing dwellings, classrooms and other noise sensitive elements that may qualify for indirect technical remedies are then estimated.

6.2.13 For the purpose of this assessment, all roads were described as either:

(1) Existing roads: including existing roads that will remain either completely unchanged or that will undergo only very minor alterations; or

(2) New roads, Planned / Altered roads: including roads that will be new, planned or substantially altered.

6.3 Description of the Environment

Potential Noise Sources

6.3.1 The existing noise source is mainly from Deep Bay Road. It is a local road with one-lane two ways traffic. The traffic flow is low and the noise arising from Deep Bay Road is expected to be low. Noise is also generated from some workshops in the surrounding area. Generally, the background noise level near the landing point on the Hong Kong side is low.

6.3.2 The proposed Shenzhen Western Corridor is a dual-3 lane carriageway with hard shoulders linking the proposed DBL on the Hong Kong side to the section of SWC within the boundary of the Mainland. Potential noise sources include:

Construction Phase

· noise from construction activities

· noise from haul road traffic

· noise from the proposed barging point, concrete batching plant and fabrication yard at Lung Kwu Sheung Tan during construction phase of SWC

Operational Phase

· road traffic noise from the traffic carried by the proposed SWC

Cumulative Effects From Deep Bay Link

6.3.3 The demarcation line between the SWC project and DBL project illustrated in Figure 6.1 has been used as the basis for this SWC EIA. The DBL EIA has assessed the potential noise impact for the DBL portion and hence DBL is viewed as a "planned road" in this SWC EIA report. Relevant information is quoted in this SWC EIA for assessing the cumulative effects and the full picture. For management and administrative purpose, the work site area as shown in Figure 7.21 immediate south east of the demarcation line is proposed to be entrusted to SWC for design and construction ensuring the consistence in the design and construction of the bridge across the Deep Bay. This portion of work with relevant proposed mitigation measures is highlighted in this SWC EIA report for the future SWC Design and Construction Team reference.

6.3.4 All the land resumption works on the landside will be carried out by DBL project for simplification. Only the oyster bed and marine area clearance will be required under the SWC project.

6.3.5 Although both the DBL and SWC will be constructed concurrently, the proposed works area and haul roads are separated from both projects. Hence, construction works and traffic of both projects would not conflict with each other and therefore construction programme would not be affected.

6.3.6 This EIA has evaluated the cumulative construction phase noise impacts and operational phase noise impacts from SWC and DBL.
Cumulative Effects From Other Major Projects

6.3.7 The potential cumulative noise impacts from with other projects planned at, or in the vicinity of, the SWC have been considered in this EIA. These projects include:

Water Supply to Hung Shui Kiu, Kwu Tung North, Fanling North and Ping Che / Ta Kwu Ling New Development Areas (WSD)

6.3.8 WSD planned to supply salt water to the proposed New Development Areas (NDAs) in Northern New Territories, including Hung Shui Kiu NDA, Kwu Tung North NDA, Fanling North NDA, Ping Che/Ta Kwu Ling NDA etc. The proposed salt water inlet is located at Lung Kwu Sheung Tan where a sea water pumping station is situated. A 900mm diameter salt water main is proposed to be laid along the Deep Bay Road, passing through Fung Kong Tsuen Road to Hung Shui Kiu NDA and other areas. The project construction works are considered as minor works involving the laying of watermain as compared to SWC.

6.3.9 The tentative construction programme of this WSD project is scheduled to commence in around later 2005 and early 2006 for completion by 2009 that may overlap with the construction period of SWC in 2005. However, the SWC construction would be nearly completed in 2005 and the construction traffic would be very low. The noisy construction work for structures is expected to be mostly completed. The part of the watermain work near SWC/DBL would not likely commence in the same time in practical because the work site would still be used by SWC/DBL. Moreover, the construction traffic of the WSD project is anticipated low during the early stage of construction. The potential cumulative noise impact between this project and SWC is expected minimal.

Water Supply to Sludge Treatment Facility at Tuen Mun (WSD)

6.3.10 Fresh water main of 450mm diameter is proposed by WSD to be laid along Deep Bay Road, connecting with the proposed sludge treatment facility near WENT Landfill site, passing through Nim Wan Road, Lau Fau Shan Road, Tin Wah Road and Tin Ying Road, to an existing 600mm diameter fresh water main in Tin Shui Wai.

6.3.11 The fresh water main is scheduled to be constructed in 2005 for completion in 2008 that will overlap with SWC construction in 2005 but that is not the peak year of SWC construction and also the Deep Bay Road is not proposed as the haul road for SWC. The construction work for SWC/DBL structures is expected to be mostly completed. The part of the watermain work near SWC/DBL would not likely commence in the same time in practical since the work site would still be used by SWC/DBL. Thus, potential cumulative noise impacts are not expected.

Yuen Long and Kam Tin Sewerage and Sewage Disposal PWP Item No. 4215DS (DSD)

6.3.12 To the northeast of SWC near Tin Shui Wai, DSD is planning a sewage disposal project - " Yuen Long and Kam Tin Sewerage and Sewage Disposal" PWP Item No. 4215DS. Rising mains and gravity sewers are proposed to be placed at Tin Ying Road, Tin Wah Road and Lau Fau Shan Road. The project will not be physically clashed with SWC and cumulative noise impacts are not expected.

Upgrading & Expansion of San Wai Sewage Treatment Works and the Expansion of Ha Tsuen Pumping Station (DSD)

6.3.13 The construction work would commence in 2004. The only part of construction routes common to both projects may include Ting Ying Road, Hung Ting Road and the flyover above the junction of Tin Ying Road/Hung Tin Road/Ping Ha Road. It was estimated that the maximum two-way construction traffic would be approximately 10 pcu per hour (about 5 vehicles per hour). The cumulative construction traffic noise impact would be minimal. Furthermore, the site is too far away for the cumulative impacts of construction works other than construction traffic.

Hung Shui Kiu New Development Area (HSKNDA)

6.3.14 During the critical construction traffic period of SWC in 2004, the early stages of HSKNDA construction work would also take place. The construction traffic of each contract of HSKNDA accessing to various works areas would be via haul roads along Hung Tin Road, Ping Ha Road, Tin Ha Road and Yick Yuen Road from Castle Peak Road, whereas the construction traffic routes for SWC are Fung Kong Tsuen Road, Tin Wah Road, Tin Ying Road and Yuen Long Highway. In addition, the site limit of SWC is far away from the HSKNDA. Hence, there would not be any cumulative noise impacts.

6.3.15 Apart from the above, a fresh water service reservoir is also proposed in HSKNDA project for water supply to HSK New Town. The location is proposed at Fung Kong Tsuen near Fung Kong Tsuen Road adjacent to the WSD proposed alternative site (A-SR3) for salt water service reservoir. The construction of the reservoir would commence in around late 2005 and early 2006 for completion by 2008. Considering that SWC would be nearly completed by end 2005, construction works of the reservoir would not impose significant impact on the SWC construction traffic via Fung Kong Tsuen Road.

Conclusion

There would be no major cumulative noise effects from other planned projects considered above, which include two WSD's projects, on DSD's project and TDD's HSKNDA project.

6.4 Noise Sensitive Receivers

Hong Kong Side

6.4.1 With reference to Annex 13 of the EIAO-TM, noise sensitive receivers (NSRs) include residential uses (all domestic premises including temporary housing), institutional uses (educational institutions including kindergarten and nurseries, hospitals, medical clinics, homes for the aged, convalescent homes, places of worship, libraries, court of law, performing arts centres, auditoria and amphitheaters) and others. NSRs within a distance of 300 m from the either side of and along the full sketch of the project boundary (including the proposed road and the associate facilities) were identified for noise assessments.

6.4.2 Existing NSRs in the close vicinity to the landing point on the Hong Kong side are located at Ngau Hom Shek. They are scattered village houses generally in 1-storey high. Locations of existing NSRs are shown in Figure 6.1. Existing NSRs were identified by reference to topographic maps and field surveys.

6.4.3 Planned/committed NSRs in the future were identified by reference to relevant Outline Zoning Plans, Outline Development Plans, Layout Plans and other published plans in relation to the Planning and Development on Northwest New Territories. The planned landuses that are the nearest to SWC are the Hung Shui Kiu New Development Area (HSKNDA). However, such landuses are mainly OU (other use - container backup) in Ha Tsuen area. These uses are far away >300m and are not noise sensitive. Thus, no future NSRs in the HSKNDA within 300m assessment area from the landing point of SWC on the Hong Kong side is anticipated.

Mainland Side

6.4.4 As the landing point on the Mainland side would be on a future reclamation (see Figure 6.2), there are no NSRs identified within 300m of the alignment of SWC that would be affected by the noise sources within HKSAR. Adverse noise impact for Mainland side is therefore not expected.

6.5 Assessment Methodology

Construction Phase Noise

6.5.1 Construction noise impact was assessed by adopting the standard acoustic principles and the methodologies relevant to technical memoranda issue under the Noise Control Ordinance, primarily the TM on Noise from Construction Work other than Percussive Piling (GW-TM).

6.5.2 During daytime from 0700hr to 1900hr on weekdays other than general holidays, the assessment of construction noise excluding percussive piling was carried out in accordance with the methodology stipulated in paragraphs 5.3 and 5.4 of Annex 13 and the criteria in Table 1B of Annex 5 of the EIAO-TM.

6.5.3 The assessment also made reference to the British Standard BS 5228:Part 1:1984 Noise Control on Construction and Open Sites, Part 1: Code of Practice for Basic Information and Procedures for Noise Control. Sound power levels of equipment were referenced to these TMs and the BS5228, where applicable, and the emission levels in previous projects in Hong Kong were also be referenced.

6.5.4 Practicable direct mitigation measures including movable barriers, enclosures, quieter alternative methods, re-scheduling and restricting hours of operation of noisy task were considered if exceedance of relevant criteria was predicted. In case where the mitigated noise levels still exceeded the relevant criteria, the duration of the noise exceedance would be given.

6.5.5 Assessment points (APs) were selected to represent identified NSRs for quantitative noise assessments. Only the nearest APs were selected as they reflect the worst impact received during construction. The construction noise impacts on the respective APs were calculated. Details of the selected APs are presented in Appendix 6A2.

Operational Phase Traffic Noise

6.5.6 The computer programme, HFANoise, was used to model traffic noise on the road networks. It adopts methodology of the UK Department of Transport's Calculation of Road Traffic Noise (CRTN) which has been accepted for the assessment of road traffic noise impact in the Annex 13 of the EIAO-TM. The road traffic noise was presented in terms of noise levels exceeded for 10% of the one-hour period for the hour having the peak traffic flow [L10(1hr) dB(A)].

6.5.7 Considering the scope of this Project, road sections were classified as the following categories for purpose of road traffic noise assessment:

(i) New roads / Planned roads:

· SWC alignment - new road

· Deep Bay Link alignment - planned road

(ii) Existing roads

· All existing roads if any

6.5.8 Calculations of future road traffic noise were based on the peak hourly flow in respect of the maximum traffic projected within a 15 years period upon commencement of operation i.e. afternoon peak hour traffic flow in year 2021. DBL and SWC were predicted to have maximum traffic flows in year 2021 during the period 2006 to 2021, which represented the worst case.

6.5.9 The traffic forecasts in this WP were based on the Traffic Review (Final) Report under the Agreement No. CE109/98 Deep Bay Link Investigation and Preliminary Design Co-location Option issued in February 2002. TD's has endorsed the traffic flow forecasts for 2021 for DBL EIA for which it is basically the same road at Ngau Hom Shek. The forecast traffic flow is shown in the extracted Figure 2.10 Co-location Option 2021 PM Peak Traffic Forecasts for EIA in Appendix 6B3. The proposed speed limit offshore at SWC is 100 km/hr and for DBL is 80km/hr as shown in Figure 6.1.

6.5.10 Assessment points (APs) at noise sensitive façade were selected to represent identified NSRs for quantitative noise assessments. Locations of the APs are shown in Figure 6.1 and details of the APs are presented in Table 6B1.1 of Appendix 6B1. Traffic noise levels at the APs in respect of each road section and the overall noise levels from the combined road sections (both new and existing) were calculated.

6.6 Identification of Environmental Impacts

Construction Phase

SWC Alignment

6.6.1 The construction of SWC alignment from Ngau Hom Shek, the landing point, to Shekou in the Mainland is scheduled to commence in August 2003 and completed by end of 2005, a total anticipated construction period of about 28 months.

6.6.2 The road connecting the SWC on the Hong Kong side is the DBL alignment. The construction schedule would be from mid-2003 to 2005/2006. As it is anticipated that the construction schedule of DBL would likely coincide with that of SWC, cumulative impacts due to construction activities were assessed based on the construction schedule that had been concurrent with SWC. The concerned construction activities in the vicinity of Ngau Hom Shek area for both SWC and DBL are identified in Table 6.7.

Table 6.7 Major Construction Activities Affecting NSRs of SWC Project

6.6.3 Construction of alignment segment at local level would be a more important concern that the overall construction programme. Sensitive receivers are mainly affected by the construction of road alignment, which in turn operates in a sequential manner. After completion of a particular task, the construction activities and equipment move to the next location. Receivers are only affected temporarily and intermittently.

6.6.4 It is assumed that all the powered mechanical equipment (PME) would be located at the relevant notional noise source (NNS) points which are established in accordance with GW-TM. The details of the assessment are given in Appendix 6A3.

6.6.5 In this EIA, the project proponent is planned to have construction works during restricted hours such as all days during the evening (1900 to 2300 hrs), and general holidays (including Sundays) during the day time and evening (0700 to 2300hrs), and all days during night-time (2300 to 0700 hrs). A separate construction noise assessment is given in Section 6.7.

6.6.6 Only a tentative construction schedule is available in this preliminary design stage as shown in Table 6A1.1 of Appendix 6A1. Due to the complicated land resumption requirements and limited geotechnical data, a detailed construction programme could not be derived at this stage.

6.6.7 The project proponent had confirmed that the construction equipment inventory and construction schedule were reasonable and practicable for the completion of the construction work within the scheduled construction programme at this stage.

Proposed Barging Point, Concrete Batching Plant and Fabrication Yard at Lung Kwu Sheung Tan

6.6.8 During construction stage, it would be necessary to provide a barging point for barges to transport the construction materials (e.g. concrete for in-situ construction, precast viaduct segments, dump waste (e.g. dredged materials) and workers etc. to and from the site through marine route. A concrete batching plant and a fabrication yard are also proposed at the same location.

6.6.9 The proposed location for three facilities is located at Lung Kwu Sheung Tan to the south of WENT Landfill along Yung Long Road. As shown in Figure 6.3, road access is provided by Yung Long Road connecting Lung Kwu Tan Road, which then leads to Tuen Mun Road to other places. The roads are currently used as access for the power station in Lung Kwu Tan, thus upgrading is generally not necessary.

6.6.10 The number of vehicles for loading and unloading in barging points is expected to be small, likely around 2 nos. per hour at maximum. The likely mechanical equipment involved are one barge, the crane of the barge or probably a mobile crane.

6.6.11 The batching plant would have about 1000 tons silo capacity required under the current estimate. The fabrication yard would be for precasting deck segments.

6.6.12 No existing NSRs were identified within 300m from this proposed location and hence there would be no adverse impact expected.

Operational Phase

6.6.13 The SWC alignment nearest to the landing point of Ngau Hom Shek is elevated and is on bridge structures. Figure 6.5 shows the bridge structure for landside alignment. Surrounding the NSRs are squatter houses or temporary houses, which are 1-storey high. Since the alignment is elevated, noise from traffic is screened by the bridge structure itself and the impact on low-rise NSRs is to a lesser extent.

6.7 Prediction and Evaluation of Environmental Impacts

Construction Phase

Potential Impacts for Unmitigated Scenario

6.7.1 At local level, the noisy construction activities are likely to be the construction of bridge foundation particularly pile cap and column construction for the both SWC and DBL road sections. Due to the close proximity to existing village houses, exceedances were found at NSRs located within 90m under unmitigated scenario with the cumulative impacts from DBL. The predicted cumulative noise impacts from all the construction activities are presented in Appendix 6A7. Cumulative construction noise levels at the representative APs 8004, 8010, 8016 and 8025 under worst-case scenario are Leq 69-76 dB(A), 74-83 dB(A), 76-85 dB(A) and 70-77 dB(A) respectively exceeding the limit of 75 dB(A) for the worst periods.

6.7.2 The haul roads to construction sites were also assessed. The proposed haul road is indicated in the Figure 6.6. There would be an upgrading of existing track leading to Ngau Hom Shek. This section of track is located in the remote hill site with most of the section with bare soil or heavy weather. The construction noise would generally affect NSRs within 32m (as shown in Table 6A4.5 CA5 in Appendix 6A4). There were no existing NSRs identified within 32m and the adverse impact due to construction of haul road is not expected.

6.7.3 Since there would be no large-scale cut and fill, or site formation activities, the peak haul road traffic would likely be around 80 veh/hr in total for both to-and-from directions. Noise due to haul road traffic was estimated and the details of the prediction are presented in Appendix 6A6 Table 6A6.1. The results show that at distances 3m, 5m, and 10m from the centre of the haul road the noise levels would be 73 dB(A), 71 dB(A) and 68 dB(A) respectively. Hence, the potential noise impacts to nearby NSRs would not be adverse and be within the acceptable standard of 75 dB(A).
6.7.4 Details of construction noise activities and assessments are all contained in Appendix 6A.

Construction Work During Restricted Hours

6.7.5 The current target completion date of SWC section on the Mainland side is 2005. In connection with the Mainland section, the SWC section on Hong Kong side is targeted by end-2005. With the estimated earliest tentative commencement of construction in about August 2003, there are only 28 months of construction period. Also, about 6 months of advance works at Ngau Hom Shek is to be allowed for rescue excavation of archaeological deposits as a part of the cultural heritage protection. The potential water quality impact and ecological impact to intertidal mudflat may also limit the possible number of simultaneous working units.

6.7.6 Based on the preliminary implementation programme, two scenarios with and without night-time work were compared. For the scenario without night-time work, the road opening for the SWC would be in May 2006. This could not meet the programme for this fast-track project. For the case with night-time work, the road opening for the SWC would be by end of Dec 2005 and this could meet the targeted opening day for SWC. In this section, night-time noise assessment is therefore included to determine the feasibility of including night-time work in the SWC construction programme. It also gives an review of the construction noise impact due to construction work during restricted hours and explores the potential capacity for carrying out certain limited amount of construction work within the noise limits under the NCO.

6.7.7 However, it should be noted that the assessment provided here are for indicative purpose only and as a reference for the future design & construction stage. Whether a Construction Noise Permit (CNP) could be issued would be subject to the discretion of the Authority taking into account of the details and information provided and the circumstance when the CNP application is filed. The actual amount of construction work and the resultant noise levels would be compiled with the requirement of CNP.

6.7.8 NSRs in Ngau Hom Shek Area was assumed belonging to (i) Rural Area, including country parks or village type development and "not affected" (means that the NSR is at such a location that noise generated by the influencing factors (IF) is not noticeable at the NSR) under the TM on Noise from Construction Work Other than Percussive Piling. The noise limits for the Area Sensitivity Rating (ASR) of "A" are 60 dB(A) for all days during the evening (1900-2300 hours) and general holidays (including Sundays) during the day and evening (0700-2300 hours), and 45 dB(A) for all days during the night-time (2300-0700 hours).

6.7.9 The amount of construction work performed would be restricted by the stringent noise limits of 60 dB(A) and 45 dB(A) as compared to the normal day time limit of 75 dB(A). The construction work during restricted hours is under the control of the Noise Control Ordinance.

6.7.10 It is recommended to divide the construction work into different work groups by the different distances to the NSRs along the shore of Ngau Hom Shek. The distances are 250m, 500m, 1000m, 1500m and 2000m offshore for respective work groups. For each work group, there may be several work units for which each work unit is made up of a pair of working piers. Construction noise was analysed based on these settings and two scenarios were worked out for considerations:

Scenario 1 - No restrictions on the type of work at each work unit

· There is no restriction on the type of work performed by a work unit, it was assumed that all work unit would be performing the noisiest task i.e.Road Construction and Paving which would had a sound power level (SWL) of 121 dB(A) for one work unit.

Scenario 2 - Restricted work tasks for restricted hours at each work unit

· It was assumed that construction tasks other than the Construction of Temporary Access Bridge, Construction of Bridge Deck, Construction of Bridge Column and Road Construction and Paving could be performed at each work unit i.e. a pair of piers. The worst-case SWL in this case would be 117 dB(A) for one work unit.

6.7.11 The results for the two scenarios with different number of work units assumed for each work group are shown in Table 6.8 and detailed in Appendix 6A8 Construction Noise Assessment for Restricted Hours. Each test case represents a combination of the number of work units to be carried out simultaneously at different locations. The predicted noise level is compared with the evening and holiday standard and the nighttime standard for checking the compliance.

Table 6.8 Study on the Construction Work during Restricted Hours

6.7.12 The results show that certain amount of construction work could be carried out under the two noise limits which specify for 60 dB(A) for all days during the evening (1900-2300 hours) and general holidays (including Sundays) during the day and evening (0700-2300 hours), and 45 dB(A) for all days during the night-time (2300-0700 hours).

6.7.13 For Scenario 1, Case 1 shows that it would exceed the 60 dB limit by 14 dB when 3 typical work units are at each work group. Cases 2 to 4 indicate that it would exceed the 60 dB limit if work units are present in 250m and 500m offshore and the possible way to meet the 60 dB limit is to have 4 work unit at 1000m and 1 unit at 1500m and 5 units at 2000m. To meet the stringent nighttime limit of 45 dB, only one work unit at 2000m would be possible as demonstrated in Cases 6 and 7.

6.7.14 For Scenario 2, Case 1 shows that when 3 typical work units are at each work group it would exceed the 60 dB limit by 10 dB. Case 9 indicate that it would exceed the 60 dB limit if work units are present in 250m offshore. The best way to meet the 60 dB limit is to have 1 work unit at 500m and 4 units at 1000m, 5 units at 1500m and 4 units at 2000m as shown in Cases 10 to 13. To meet the stringent nighttime limit of 45 dB, only 3 work units at 2000m or 1 unit at 1500m plus 1 unit at 2000m could be possible as demonstrated in Cases 14 and 12 respectively.

6.7.15 The details of construction work programme for restricted hours should be worked out during the design and construction stage based on the findings in this assessment. It is noted that this assessment will not exempt the requirements for a Construction Noise Permit (CNP) for carrying out works during the restricted hours. The future contractor has to apply for a CNP under NCO for carrying construction work during restricted hours.

Operational Phase

6.7.16 Predicted cumulative traffic noise levels at NSRs were around L10 65 to 70dB(A) for peak hour traffic. All NSRs, residential units at Ngau Hom Shek, showed compliance with the EIAO-TM noise criteria of 70 dB(A).

6.7.17 Table 6.9 presents the summary of traffic noise predictions and the details of assessments are given in Appendix 6B2.

Table 6.9 Summary of Traffic Noise Impacts for Unmitigated Scenario

Note: * Noise level dominant by SWC

6.8 Mitigation of Adverse Environmental Impacts

Construction Phase

6.8.1 The predicted cumulative noise levels showed that construction noise activities are likely to give rise to adverse daytime noise impacts at some of the identified NSRs. The range of noise exceedance is around 1 to 8 dB(A) for individual construction activity. For cumulative noise impact under worst-case, the range of noise exceedance is 1 to 10 dB(A). Mitigation measures are therefore required and the following forms of mitigation have been considered:

Use of Quiet Plant and Working Methods

6.8.2 The use of quiet plant was identified to be a feasible solution to tackle the adverse impacts associated with construction works. The Contractor should obtain particular models of plant that are quieter than standard types given in the GW-TM. The benefits achievable in this way would depend on the details of the Contractor's chosen methods of working, and it would be too restrictive to specify that a Contractor has to use specific items of plant for the construction operations. It is therefore both preferable and practical to specify an overall plant noise performance specification to apply to the total SWL of all plants on the site so that the Contractor is allowed some flexibility to select plant items to suit his needs. It should be noted that various types of silenced equipment could be found in Hong Kong. However, the Authority, when processing a CNP application, will apply the noise levels contained in the relevant statutory TMs unless the noise emission of a particular piece of equipment can be validated by a certificate or through a demonstration.

6.8.3 Quiet PME is defined as PME whose actual SWL is less than the value specified in the GW-TM for the same item of plant. Reference can be made to the British Standard BS5228: Part 1:1997 Control on Construction and Open Sites.

Using Temporary and Movable Noise Barriers

6.8.4 Movable barriers that can be located close to noisy plant can be very effective at screening NSRs from particular items of plant or noisy operations. Movable barriers of 3 to 5 m height with a small cantilevered upper portion and skid footing can be located within a few metres of stationary plant and within about 5 m or more of mobile equipment such as an excavator and mobile crane etc., such that the line of slight to the NSR is blocked by the barriers. It would be possible for the Contractor to provide purpose-built noise barriers or screens constructed of appropriate material (minimum superficial density of 15 kg/m2) located close to operating PME, in order to reduce the noise impact to the surrounding sensitive uses. Certain types of PME, such as generators and compressors, can be completely screened by portable barriers giving a total noise reduction of 10 dB(A) or more.

6.8.5 For this assessment, it was estimated that movable noise barriers can achieve a 10 dB(A) noise reduction for stationary plant and 5 dB(A) for movable plant. Considering the nature of SWC alignment, noise barriers may not be applicable for construction work at sea.
Reducing the Numbers of Plants Operating in Critical Areas Close to NSRs

6.8.6 In general the number of plant should be left to the choice of the Contractor so that in combination with the selection of quiet plant, any further reduction in the total plant noise level, or the site specific maximum sound power levels, as described above, can be achieved. It would be appropriate to restrict the number of operating PME within certain parts of the site that are very close to the NSRs in order to reduce the level of noise impacts. This method could be more effective for activities associated with foundation work, pile construction and excavation activities in which a large number of PME are anticipated, but not all of them would be utilised at the same time.

Using Noise Screening Structures or Purpose-built Noise Barriers along the Site Boundary

6.8.7 Considering the low-lying nature of surrounding NSRs (typically village houses or temporary houses), it would be effective to have noise screening structures along the site boundary to protect NSRs close to the construction site boundary. The following measures could be applied to reduce the construction noise:

· Site buildings such as office and stores could be grouped together to form a substantial barrier separating site operations and nearby noise sensitive premises. This may be applicable for road alignment sites.

· Stacks of certain materials such as bricks, aggregate, timber or top soil can be strategically placed to form a barrier. This may be applicable for construction of road alignment.

· For adverse cases, purpose-built noise barriers or screens could be placed along the site boundary. This may be applicable for road alignment sites.

6.8.8 An estimate of about 10 dB(A) reduction could be achieved for substantial structures or purpose-built noise barrier/screen. Higher reduction and benefit could also be achieved for NSRs close to the site. This measures have been considered in the DBL EIA for the landside alignment construction.

Good Site Practice

6.8.9 The following good site practice should be adopted during the construction phase:

· The contractor should site noisy equipment and activities as far from sensitive receivers as practical. Also, temporary site offices (and other similar structures) should be located, as far as is possible, such that sensitive receivers are screened by these structures from the line of sight of the construction areas.

· Intermittent noisy activities should be scheduled to minimize exposure of nearby NSRs to high levels of construction noise. For example, noisy activities could be scheduled at times coinciding with periods when the schools are likely to be unoccupied. Prolonged operation of noisy equipment close to the schools should be avoided.

· Idle equipment should be turned off or throttled down. Noisy equipment should be properly maintained and used no more often than is necessary.

· Construction activities should be planned so that parallel operation of several sets of equipment close to a given receiver is avoided.

· Where possible, the numbers of concurrently operating items of plant should be reduced through sensitive programming.

· Construction plant should be properly maintained and operated. Construction equipment often has silencing measures built in or added on, e.g. compressor panels, and mufflers. Silencing measures should be properly maintained and utilized.

Proposed Construction Noise Mitigation Measures for SWC

6.8.10 Upon review of the construction noise contribution, most of the NSRs at Ngau Hom Shek are found affected mainly from the construction work of the DBL. Relative minor construction is from SWC construction work where it is located offshore. Mitigation measures have been proposed in DBL EIA to reduce the potential cumulative impact to the acceptable noise levels.

6.8.11 The proposed mitigation measures for SWC construction noise is the use of quiet construction equipment which aim to mitigate at source. It is because most of the work sites of SWC are at sea and there is no much room for using mitigation at the noise propagation pathway such temporary noise barriers.

6.8.12 The number of PME used on site should be reviewed from time to time to avoid excessive or dummy PME located too close to NSRs. Good site practice should be followed through the construction phase.

DBL EIA Recommended Measures Applicable to the Future Entrusted Design and Construction Area for SWC D&C Project Team

6.8.13 This part of mitigation measures are extracted from DBL EIA which will be applicable to the proposed part of the DBL entrusted to SWC Design and Construction Project Team in the next stage for design and construction.

6.8.14 To minimise the potential of adverse impact, the following measures are specifically recommended to be adopted for DBL landside alignment:

(1) a construction site boundary wall or hoarding is constructed in such a way to act as an acoustic screen/noise barrier for active carriageway construction work proximity to NSRs in locations shown in Figure 6.7. The indicative setting is demonstrated in Figure 6.8. The screening effect is expected for ground level equipment. The boundary wall or hoarding should:

· have a mass per unit of surface area in excess of 7 kg/m2 to prevent sound transmitted through the screen;

· have no gaps or openings at joints in the screen material; and

· have a vertical height of 3m.

The exact location of purpose-built construction site hoarding would be subject to local site conditions and to be reviewed during the construction stage. Temporary noise barriers should be placed close to the noisy mechanical equipment in case the purpose-built site hoarding could not effectively screen the NSRs.

(2) Quiet plant/power mechanical equipment of sound power level lowered than those listed in Table 3 of the GW-TM shall be used for all DBL construction sites.

Summary of Cumulative Construction Noise Impacts after Mitigation

6.8.15 Table 6.11 presents the summary of results for cumulative construction noise impacts. With proposed mitigation measures in place, the predicted noise levels at the representative assessment points will be in full compliance with noise limit of 75 dB(A). The predicted noise level would be 51 to 72 dB(A) for individual construction activity. For cumulative noise impact under worst-case, the predicted noise level would be 68 to 75 dB(A).

6.8.16 Provided that the general and specific construction noise mitigation was in place, there would not be any residual impacts expected and noise levels at NSRs would be complied with EIAO-TM standard.

Table 6.11 Summary of Potential Construction Noise Impacts

Note:
Cumulative impact with different construction activities were predicted based on the construction schedule of each activity.

Operational Phase

Road Traffic Noise

6.8.17 Low noise surfacing for the alignment would be adequate to mitigate the noise impact into acceptable levels. It is a standard provision for the roads with vehicle speed limit greater than 70km/hr under the current policy. All low noise surfacing should be designed according to the design guidelines/practice notes issued by HyD Guidance Note No. RD/GN/011B Guidance Notes on Noise Reducing Road Surfacing. The traffic noise assessment has assumed that low noise road surfacing materials would be provided to SWC and DBL for sections affecting the NSRs in Ngau Hom Shek. As review in the design, the friction course (low noise surface) would be applied on the approach bridge from the start of the cable-stayed bridge within HK waters. The total length of road section with friction course is about 2.7km.

6.8.18 As shown in the unmitigated scenario in Table 6.8, the predicted traffic noise levels at NSRs are around 65-70dB(A) without additional mitigation measures. All of the dwellings would achieve full compliance with the EIAO-TM noise criteria of 70 dB(A).

6.9 Evaluation of Residual Impacts

Construction Phase

6.9.1 With proposed mitigation measures in place, noise reduction could be achieved in the range of 1- to 10 dB(A) under worst-case cumulative noise impacts. Residual impact exceeding the applicable criteria is not expected with the implementation of the proposed mitigation scheme. The predicted worst noise levels at selected NSRs are from Leq 68 to 75 dB(A).
Operational Phase

6.9.2 No residual impact exceeding the EIAO standard was predicted due to this Project with the implementation of the proposed design scheme. The predicted worst noise levels at selected NSRs are from L10 65 to 70 dB(A) for peak hour traffic in year 2021.

6.10 Environmental Monitoring and Audit

6.10.1 Due to the potential construction noise impact to the nearby residential developments, it is recommended that EM&A for construction noise be carried out throughout the construction period of the project. Monitoring at the operational phase is also suggested to review the traffic noise prediction. Details of the EM&A program are given in the EM&A Manual.

6.11 Conclusions

Review of Existing Condition

6.11.1 Generally, the background noise level near the landing point for SWC on the Hong Kong side is low. Rural noise arising from Deep Bay Road is expected to be minimal. Parts of the SWC would be constructed on existing rural land lots in the Ngau Hom Shek areas. Under this circumstance, some of the existing noise sensitive receivers would be located close to the SWC alignment and affected by the construction noise and operational noise to a different extent.

Construction Phase

6.11.2 Construction noise assessments were conducted based on the preliminary construction schedule in this preliminary design stage. Due to the close proximity of some of the existing NSRs and the cumulative impacts from SWC and DBL, noise levels exceeding EIAO-TM criteria were predicted for the unmitigated scenario.

6.11.3 In order to reduce the likely impacts, different forms of mitigation measures were examined including the use of quiet plant and working methods, the use of movable and temporary noise barriers, provision of noise screening structures and purpose-built noise barriers. All NSRs were adequately protected by the proposed mitigation schemes which involve the use of quiet construction equipment together with the mitigation measures for DBL construction sites under DBL EIA. The predicted noise levels are ranged from Leq 68 to 75 dB(A) which is in compliance with construction noise limit of 75 dB(A). Residual noise impacts are not expected when the proposed mitigation schemes are applied.

Operational Phase

6.11.4 Noise from road traffic was assessed based on the traffic forecast for year 2021 i.e. the worst case within 15 years after the completion of SWC and the linking of DBL. The predicted noise levels at NSRs were found to be all within acceptable standard. It is ranged from L10 65 to 70 dB(A) for peak hour traffic which is in compliance with traffic noise limit of 70 dB(A). All of the dwellings would be protected from adverse impacts. No residual impacts were identified for the operational phase of the SWC project.