4. NOISE IMPACT

4.1 Legislation, Polices, Plans, Standards, and Criteria

Environmental Impact Assessment Ordinance

4.1.1 The general criteria and guidelines for evaluating and assessing noise impact are listed in Annexes 5 and 13 of the EIAO-TM and summarized here in Tables 4.1, and 4.2. The specific areas of noise impact are described in the sections that followed.

Notes:

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

The above standards should be viewed as the maximum permissible noise levels assessed at 1 m from the external façade.

The criteria laid down in the relevant technical memoranda under the Noise Control Ordinance 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 of the construction work during the period.

Construction Noise

4.1.2 The Noise Control Ordinance (NCO) (Cap. 400) provides the statutory framework for noise control in Hong Kong. Assessment procedures and standards have been set out in four Technical Memoranda (TM) promulgated under the NCO. The following three are applicable to the assessment and control of construction noise.

Notes:

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

The above standards should be viewed as the maximum permissible noise levels assessed at 1 m from the external façade.

4.1.4 For 1900 to 0700 hours or any time on Sundays or general holidays, construction noise (except percussive piling) is controlled by the NCO and the TM on Noise from Construction Work other than Percussive Piling. A Construction Noise Permit (CNP) from the Noise Control Authority is required for works carried out in these restricted periods. The TM also established permissible construction noise levels and described the methods for calculating noise levels. The control of noise from powered mechanical equipment (PME) is based on the Area Sensitivity Ratings (ASR) of where the noise sensitive receivers (NSRs) are located, rather than the measured background noise level. The ASRs, as shown in Table 4.3, take into account the types of dwelling present and the surrounding land uses.

4.1.5 Basic Noise Levels (BNL) are then ascribed according to the ASR, as shown in Table 4.4 Acceptable Noise Levels (ANL) for construction works are calculated from the BNL, following corrections for the duration of the CNP and for multiple site situations.

4.1.6 Despite any description or assessment made in this EIA Report on construction noise aspects, 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 works within restricted hours as guided by the relevant Technical Memoranda issued under the Noise Control Ordinance. The Noise Control Authority will take into account of contemporary conditions/situations of adjoining land uses and any previous complaints against construction activities at the site before making his decision in granting a CNP. Nothing in this EIA Report shall bind the Noise Control Authority in making his decision. If a CNP is to be issued, the Noise Control Authority shall include in it any condition he thinks fit. Failure to comply with any such conditions will lead to cancellation of the CNP and prosecution action under the NCO.

Table 4.3 Area Sensitivity Ratings (ASR)

4.1.7 Construction Noise Permits are also required for percussive piling (TM on Noise from Percussive Piling), which specify the permitted hours and other conditions of piling. Table 4.5 lists the acceptable percussive piling noise levels for various types of NSR buildings.

4.1.8 Percussive piling may be restricted to 12, 5 or 3 hours per day. It is prohibited during restricted periods unless specifically exempted. For NSRs that are particularly sensitive to noise, such as hospitals, medical clinics, educational institutions and courts of law, a further reduction of 10 dB(A) shall be applied to the above ANLs.

Operational Noise

4.1.9 Operational noise is controlled under the NCO's Technical Memorandum on Noise from Places other than Domestic Premises, Public Places or Construction Sites. Table 3 of the TM specifies the ANLs.

4.1.10 To plan for a better environment, the EIAO-TM specifies the following requirements:

5 dB(A) below the appropriate ANLs shown in Table 3 (reproduced in Table 4.6 below) of the Technical Memorandum on Noise from Places other than Domestic Premises, Public Places or Construction Sites; or

the prevailing background noise levels (for quiet areas with 5 dB(A) below the ANL).

4.1.11 Table 4.6 compares the two criteria. Details of the background noise measurements are given in Section 4.2.4. The EIAO-TM criteria were adopted for this study.

Note: According to the EIAO-TM, the level of the intruding noise should be lower than Part II values and the background level, whichever is lower.

4.2 Description of Environment

4.2.1 The aim of the Project is to provide sewage collection system infrastructure to serve the entire Ngong Ping area on Lantau Island to meet the demands of both the existing and future developments in the catchment. The key elements of the Project are:

1. the construction of a sewage collection system at Ngong Ping;
2. the construction of a sewage treatment works (STW) to provide biological and tertiary treatment with disinfection;
3. the provision of sludge treatment and disposal facilities;
4. the construction of an effluent pipeline to convey the treated effluent from the STW to Tai O for discharge

4.2.2 Noise sensitive receivers (NSRs) were identified with reference to Annex 13 of the EIAO-TM for which included all existing ones and all planned or committed noise sensitive developments and uses. The noise impact assessment included all areas within 300m from the project boundary (Drawings No. 23400/EN/006-007). Subject to the agreement of the Director, the assessment area could be reduced accordingly if the first layer of noise sensitive receivers, closer than 300m from the project boundary, provides acoustic shielding to those receivers located further away. Table 4.7 and Drawings No. 23400/EN/009-015 present the summary of identified noise sensitive receivers and their likely impact.

Note: N/A Not Applicable.

4.2.3 The planned cable car terminal immediately northeast to the proposed STW site and it is considered not a noise sensitive receiver with reference to the EIAO-TM.

4.2.4 The background noise level was relatively low in the vicinity of Ngong Ping area and comprises of rural noise. Background noise measurement was conducted from 11 May 2002 to 15 May 2002 at Lin Chi Monastery and a village house at Ngong Ping Road near the bus terminal respectively. For noise measurement taken at Lin Chi Monastery, the noise levels (Leq) ranged from 48 dB(A) to 62 dB(A) during daytime/evening while the noise levels (Leq) ranged from 45 dB(A) to 54 dB(A) during nighttime noise measurement. For noise measurement taken at a village house at Ngong Ping Road, the noise levels (Leq) ranged from 50 dB(A) to 58 dB(A) during daytime/evening while the noise levels (Leq) ranged from 49 dB(A) to 54 dB(A) during nighttime. Traffic noise from Ngong Ping Road would be the dominant noise sources as background noise. As observed during site visit, the announcement broadcasted by Po Lin Monastery through loudspeakers would be another significant noise source. Details of noise measurement results are presented in Appendix 4C.

4.2.5 Given the setting of the area, an ASR of "A" is assumed here for the purpose of this EIA study (see Table 4.3). According to the noise survey conducted, the lowest background noise level during night-time is 45 dB(A), which is 5 dB(A) below the relevant ANL for this area. For planning purpose, all fixed noise sources would be designed to meet this requirement. As these sources are assumed to operate at the same loading round the clock, there should not be any problem in meeting the daytime ANL provided that the night-time limit is being met. In any event, the Area Sensitivity Rating assumed in this EIA Report is for indicative assessment only. It should be noted that fixed noise sources are controlled under section 13 of the NCO. At the time of investigation, the Noise Control Authority shall determine noise impact from concerned fixed noise sources on the basis of prevailing legislation and practices being in force, and taking account of contemporary conditions / situations of adjoining land uses. Nothing in this EIA Report shall bind the Noise Control Authority in the context of law enforcement against all the fixed noise sources being assessed.

4.3 Assessment Methodology

4.3.1 Key noise generating activities involved are likely to be:

1. the construction and operation of the proposed sewage treatment work;
2. the construction of effluent pipeline from STW to Tai O and;
3. the construction of sewage collection system at Ngong Ping.

4.3.2 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).

4.3.3 An inventory of powered mechanical equipment was developed for the purpose of assessing the potential construction noise impacts (see Appendix 4A). DSD/CM confirmed that the inventory used for this assessment is practicable and reasonable for the completion of the project within the scheduled construction programme based on the information at this stage. The construction noise assessment took into account the construction programme, construction work packages, construction noise levels from work tasks, existing noise sensitive receivers and the development phasing of planned noise sensitive receivers. Practicable direct mitigation measures including movable barriers, enclosures, quieter alternative methods, re-scheduling and restricting hours of operation of noisy task were investigated. At this stage, the project works can be divided into 3 packages as follows:

Package 1 - Ngong Ping STW
Package 2 - Ngong Ping main trunk sewer and effluent export pipeline
Package 3 - Ngong Ping village sewerage system

4.3.4 Details of the three packages of the project are as follows:

1. Package 1 – Ngong Ping Sewage Treatment Work

2. Package 2 –Ngong Ping Main Trunk Sewer and Effluent Export Pipeline

3. Package 3 – Ngong Ping sewerage

Construction of a new sewage collection network at Ngong Ping to serve the remaining area within this region, including local food stalls, village houses, Po Lin Monastery and the committed developments in the area. Works of the proposed sewerage system includes connections and diversions of public sewers to the new trunk sewers, connections of sewer systems of public toilets to the new trunk sewers, and tapping sewers from the new trunk sewers to adjacent private land lot boundaries. Approximately 3 km of foul sewers and two local pump chambers at Ngong Ping will be constructed.

4.3.5 The construction works of Package 1 and Package 2 will be carried out in two separate contracts. The tender phase for Package 2 work can be completed early to meet the road operating requirements.

4.3.6 For Package 3, it will be implemented as a separate contract at a later stage as it depends on the progress of land resumption process. Also the village sewerage work is not dependent on the Cable Car Project.

4.3.7 Construction work during restricted hours is not expected under current programme. Please refer to sections 4.1.4 to 4.1.6 for construction works during restricted hours.

4.3.8 Fixed Noise sources include the activities related to the operations of Ngong Ping STW and 2 local pump chambers at Ngong Ping. Noise predication was based on assumed plant inventories and utilisation schedule for the worst-case scenario. Assessments were based on standard acoustic principle with reference to the Technical Memorandum on Noise from places other than Domestic Premises, Public Places or Construction Sites, issued under the Noise Control Ordinance.

4.3.9 It was observed that the background noise was basically rural noise with low ambient noise level, especially during nighttime. There was also intermittent noise from vehicles (particularly buses) passing-by and announcement through loudspeakers from the Po Lin Monastery.

4.3.10 A noise measurement exercise which consisted of monitoring of background noise levels during daytime, evening and night-time was carried out to evaluate and compare the background noise level with the noise criteria for ASR A under EIAO-TM.

4.4 Identification, Prediction and Evaluation of Potential Impacts

4.4.1 Noise from construction activities is closely related to the three work packages. The details of the construction work are described as follows.

Site Formation and Foundation Works

4.4.2 The site formation works would commence first. The site area for the STW would be approximately 180 m x 90 m. Construction traffic would be able to access the site directly via Ngong Ping Road.

4.4.3 The peak construction traffic would be generated during the site formation works and also the excavation of the sub-structures especially the Emergency Storage Tanks. A peak of about 32 trips/day or 4 trips/hr. in each direction of dump trucks would be required during this period to transport a total of approximate 47,600m3 of excavated materials and about 14,000m³ of imported filling materials. In addition, 10 car/small van trips/day in each direction would be made by the personnel on site.

4.4.4 The proposed STW is to be designed on minipile foundation. Minipiles are to be 4 no. T50 hot-rolled high strength steelbars in non-shrink cement grout. All piles would be socketted into grade III or better rock with a certain bearing capacity to be determined in detail design. A hole of minimum diameter 235mm would be drilled from ground level to rockhead level. Drilling equipment would be needed. Say 2 nos. of 36T mobile cranes would be operated on site during that stage. Number of workforce including supervisory personnel at this stage was estimated to be in the range of 30 to 50.

4.4.5 The construction traffic related to the construction of the STW would be based on an in-situ concreting method. Contractor will be instructed to regulate the arrival of their concrete mixer trucks such that there would be only one concrete mixer truck involved in the concreting while a second truck is on stand-by. Based on this regulated operation during concreting and a concreting rate of 15-20 minutes for each concrete mixer truck, the trip generation/attraction at Ngong Ping Road during each concrete pour would be 4 vehs/hr. This arrival rate of concrete mixer trucks would be sufficient to support the concreting activities at the worksite. Number of workforce including supervisory personnel at this stage was estimated to be in the range of 50 to 100.

Evaluation of Impacts

4.4.6 Potential construction noise impact was predicted for the construction activities of Ngong Ping STW. NSRs are generally located far away from the proposed Ngong Ping STW. Three nearest NSRs namely Lin Chi Monastery, village house along Ngong Ping Road near bus terminal and Tin Tan Buddha Statue were identified and used in this assessment. They are about 441m away, 240m away and 276m away respectively.

4.4.7 The predicted construction noise levels as shown in Table 4.8. For the NSR Tin Tan Buddha Statue and Lin Chi Monastery, the construction noise was within the limit of 75dB(A) for the unmitigated scenario. However, the predicted noise level was found above the 70 dB(A) guideline for village house along Ngong Ping Road near bus terminal. With the adoption of quiet construction plant, the predicted noise level was within the 70 dB(A). No adverse impacts are therefore expected. Details of calculations of construction noise are presented in Appendix 4A.

Table 4.8 Construction Noise Impact due to the Construction of Ngong Ping STW 

Note:

Mitigation Level 1 Use of quiet plant

Mitigation Level 2 Use of quiet plant and use of movable and temporary noise barriers

Package 3 - Ngong Ping Village Sewerage Construction

4.4.12 The construction of sewer laying in Ngong Ping Village will be carried out by traditional open trench method. The pipe size of the sewer would be ranging from 150 dia. to 400mm dia. Ductile iron pipe will be used to minimise the risk of leakage due to the high environmental sensitivity of the area. Construction traffic might not be able to access to locations of sewers to be laid on narrow footpaths. The sewer generally runs at a depth of 2 to 2.5m below ground. The number of work force was estimated to be 3 - 4 workers per working team. There might be 2 to 3 teams working in the village at the same time depending on the contractor's planning. To minimize the noise impacts, powered mechanical equipment will only be used for breaking up the concrete surface. Excavation and handling of the heavy ductile iron pipes as well as the reinstatement of pavement within the village will be carried out using manual construction methods (i.e. use of hand tools).

4.4.13 It is noted that the construction work of Package 3 would include construction of manhole with tapping pipes for future connection to the village house. No house-to-house connection works are included under the Package 3 works. The construction work might be carried out in the vicinity of premises or close to premises. Prediction of potential construction noise impact due to the breaking of concrete surface was carried out at 3 representative NSRs, namely v60, v27 and v129 (Drawing No. 23400/EN/084), with a distance of 12.5m, 1m and 6.8m from the proposed sewers respectively. The predicted construction noise levels are given in Table 4.9a. Details of calculations of construction noise can be found in Appendix 4A.

Table 4.9a Construction Noise Impact due to the Construction of Village Sewerage

Note:

Mitigation Level 2 Use of quiet plant and use of movable and temporary noise barriers

4.4.14 With mitigation level 2 in place, the predicted noise level at NSR v60 could be brought down to within the limit. The prediction demonstrated that the impact from using PME could be mitigated by level 2 measures. However, the predicted noise levels at NSRs v129 and v27, which is much closer to the proposed sewer, exceeded the noise limit of 75dB(A) with level 2 mitigation measures.

4.4.15 It can be seen that, from Table 4.9a above, even with Mitigation Level 2 in place, there would be residual impact of 21 dB(A) at receiver v27. Since all practicable mitigation measures on PME have been exhausted, it is recommended to adopt Level 3 mitigation measures (i.e. manual construction methods) in those works areas which are within 5m from the nearest NSR, so as to minimize the noise impacts as it is not practicable to adopt Level 2 mitigation measures (i.e. use of noise barriers) in limited space like narrow alleys. In other words, a total of 25 village houses will have the residual impact reduced down to a maximum of 7 dB(A). It is considered undesirable to extend the use of Level 3 mitigation measures for works areas which are more than 5 m away from the NSR to further reduce the residual impacts as this would have great implication on the project program. It should be noted that use of manual construction methods for sewerage construction is very time consuming. The residual impacts of 7 d(B) (maximum) would last for only a few hours for individual NSRs depending on the actual site conditions. These unavoidable noise impacts would be transient and localized originated from breaking of footpath surface.

4.4.16 With mitigation level 3 in place, it is predicted that roughly 30% (45 out of 151) of the identified village houses would experience short-term noise exceedances (max. 1 day) due to the breaking up of concrete surface. The levels of residual impacts would range from 5 to 7 dB(A) for 7% (11 out of 151) of the village houses and from 1 to 5 dB(A) for 23% (34 out of 151) of the village houses. Table 4A.5 of Appendix 4A gives the distances between each of identified village houses and its nearest sewer. Table 4A.6 of Appendix 4A gives the durations and levels of residual impacts for individual NSRs.

4.4.17  Two local pump chambers will also be constructed. One is adjacent to Lin Chi Monastery and the other is near the proposed cable car terminal. Construction noise impacts were assessed for the proposed pump chamber adjacent to Lin Chi Monastery. The results as shown in Table 4.10 below indicated that the prediction noise levels were within 70 dB(A) limit with the implementation of mitigation level 2 measures (quiet plant + temporary movable noise barrier).

4.5.8 The proposed mitigation measures for construction noise are arranged in an increasing level of efforts. Since the actual activities in the construction sites may vary at local site level, the level of mitigation measures adopted should also be determined with reference to the findings of the EM&A programme. The following are mitigation levels:
Mitigation Level 1 Use of quiet plant and working methods.
Mitigation Level 2 Use of quiet plant and working methods and use of movable and temporary noise barriers.

Mitigation Level 3 Use of manual construction methods in very limited space within Ngong Ping Village like narrow alleys

Adopt administrative measures to inform and, if necessary, liaise with the village residents on the construction schedule and work locations before the start of any construction work within the village.

4.5.9 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.

4.5.10 For construction activities of Ngong Ping STW, mitigation level 1 with the use of quiet plant is recommended. For construction of effluent export pipeline, village sewerage and the two local pump chambers, mitigation level 2 with the use of quiet plant and use of movable temporary noise barrier is recommended. For construction of village sewerage, mitigation level 3 with the use of manual construction methods are recommended in those narrow alleys which are less than 4 m away from the nearest NSR where it may not be practical to use noise barriers. It is also recommended that the contractor should inform and, if necessary, liaise with the residents in Ngong Ping village on the construction schedule and work locations before the start of any construction work within the village.

4.5.11 The project proponent (i.e. DSD/CM) confirmed that the mitigation measures for construction noise were considered practicable.

4.5.12 In order to meet both the daytime/evening and night-time noise limits, mitigation measures as suggested in Scenario 2 as shown in Table 4.11 should be applied. The proposed mitigation measures are further elaborated as follows:

1. Building Envelope/Enclosure

The building envelope holding noisy equipment should be made of suitable materials (e.g. concrete) and design capable of achieving a reduction of 20 dB(A). It should be a complete enclosure with minimal openings for which these openings should not be facing any NSRs in the east or south. The building materials should be of surface density of 25kg/m² or higher. Ventilation should not be overlooked as most equipment, such as motors, requires an adequate air supply either to prevent overheating or to enable them to function efficiently. A silenced ventilation system incorporating silencers at the air intakes and discharge openings should be employed.

2. Layout of Building Structures

It would be beneficial if building structures e.g. plant office capable of screening noisy components could be located in the east side of the site to act as noise screening structures.

4.5.13 Two pump chambers will be located in Ngong Ping village. One of these pump chambers will be located in close proximity to Lin Chi Monastery (Drawing No. 23400/R/VS/002) and the noise requirements for 24 hrs’ operation would be stringent (45 dB(A)). For compliance with the standard, it is required that the two pump chambers to be fully enclosed as underground facilities.

4.5.14 Ventilation should not be overlooked as most equipment, such as motors, requires an adequate air supply either to prevent overheating or to enable them to function efficiently. A silenced ventilation system incorporating silencers at the air intakes and discharge openings should be employed for both the STW and local pump chambers.

4.6 Influence from Other Projects

4.6.1 The Tung Chung - Ngong Ping Cable Car Project is scheduled to be commissioned in August 2005. Hence, the construction of the sewerage and sewage treatment project will be in progress at the same time as construction of the cable car terminal. Also, WSD has proposed a project for the provision of water supply to Ngong Ping. A large section of the proposed water pipe alignment at Ngong Ping runs in parallel with the proposed village sewer alignment. Construction of the entire water pipeline alignment is also scheduled to be completed before July 2005. The cumulative noise impacts will need to be considered based on the available information. Drawing No. 23400/EN/018 shows the locations of Ngong Ping Sewerage System, the Tung Chung Cable Car System and the Project 'Provision of Water Supply at Ngong Ping'.
Tung Chung - Ngong Ping Cable Car Project

4.6.2 The Cable Car project had completed the Final Feasibility Study Report in March 1999 under the MTR Corporation's Consultancy Agreement NEX/034 Tung Chung Cable Car Feasibility Study (TCCCFS). The study identified compliance with noise criteria would be able to be achieved for construction phase impact given the discrete location for construction works for the proposed cable car system. Construction noise mitigation measures were suggested. Based on the detailed noise assessment conducted for this EIA, with the adoption of quiet construction plant, the predicted construction noise levels generated from the proposed STW site were within the 70 dB(A) at the nearest NSR which are well within the noise limit of 75dB(A). It is therefore anticipated that the cumulative construction noise is unlikely to be a major issue as both projects are far away from the NSRs. It is also important that the future EIA for the cable car project could address the cumulative noise issue based on the findings of this noise assessment.

4.6.3 Operational noise from the cable car system was identified to be originated from the mechanical equipment at the end terminal stations and when the cable car passing through pylon sites. While no detailed assessments were conducted in the study, a site survey was carried out at Ocean Park on 30 September 1998 purposed to estimate the noise from the existing cable car system. The survey found that the typical noise levels 10m outside the terminal were around 55-67 dB(A). The power motors were identified as the major source of noise. The cable car terminal in Ocean Park was with neither the terminal nor motors were enclosed or sound insulated. Measurement results showed that the noise impact from the operation of a cable car system would generate acceptable noise levels (in the order of around 55 dB) and further improvement could be made by housing the motors inside concrete building.

4.6.4 Considering the cumulative impacts, the main concern for both the operation of the proposed Ngong Ping STW and the proposed cable car system would be daytime/evening noise levels, since the proposed cable car system would not operate during night-time (11pm to 7am). The Ngong Ping STW is to be designed to cope the more stringent standard of 45dB(A) compared to daytime/evening standard of 55dB(A). The noise levels for Scenario 3 mitigation proposed under the TCCCFS (i.e. with enclosure of plant room) are around 44-45dB(A). This would not cause significant increase (>1 dB) in noise level.

4.6.5 This project is about the increase of fresh water supply by constructing the water transfer system from Tung Chung Service Reservoir to Ngong Ping to cater for the increase in water demand. The tentative completion date of the entire water pipe is July 2005 which overlap the project period of this project. Work entrustment for part of the village sewer pipe laying work may be possible. Close liaison with Water Supplies Department (WSD) is required to avoid any potential interfacing problems and duplicating of construction work. Potential construction impacts and disturbance to villagers are to be minimised.

4.7 Definition of Adverse Impacts

4.7.1 Construction phase noise impact could be controlled within acceptable levels for Package 1 Construction of Ngong Ping STW and Package 2 Ngong Ping main trunk sewer and effluent export pipeline under the proposed mitigation measures.

4.7.2 For Package 3 Ngong Ping sewerage, noise exceeding the compliance limit of 75dB(A) may be expected at some village houses even after the mitigation measures are in place due to the close proximity to the construction work. These unavoidable noise impacts would be transient and localized originated from breaking of footpath surface and small-scale excavation of soil. It would take about 2 to 3 days to complete for individual NSRs.

4.7.3 Operation phase would require the proposed mitigation measures to be in place in order to bring the noise level to the acceptable limits. No further residual impacts were identified.