4. NOISE IMPACT

4.1 Introduction

4.1.1.1 This section presents an assessment of the potential noise impacts associated with the construction and operation of this project including the expansion and upgrading of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of emergency bypass culvert connecting the San Wai STW and the existing drainage channels for discharge of effluent to Deep Bay under maintenance and emergency situations. Noise impacts during the construction phase are mainly associated with the construction activities and the use of powered mechanical equipment for the construction works. For the operational phase, the noise impacts are primarily from plant noise of the expanded STW and pumping station.

4.2 Environmental Legislation, Policies, Plans, Standards and Criteria

4.2.1 Construction Noise

4.2.1.1 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

4.2.1.2 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).

4.2.1.3 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 4.1.

4.2.1.4 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

4.2.1.5 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 4.2 below.

4.2.1.6 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.

4.2.1.7 When assessing a CNP application for the use of PME, the Noise Control Authority will compare the ANLs 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 (see Table 4.3) in the EIA is not binding upon the Noise Control Authority. The relevant ANLs are shown in Table 4.4.

4.2.1.8 In addition to the general controls on the use of PME during the restricted hours, the Noise Control Authority has implemented a more stringent scheme via the DA-TM. The DA-TM regulates the use of five types of Specified Powered Mechanical Equipment (SPME) and three types of Prescribed Construction Work (PCW), which are non-PME activities, in primarily densely populated neighbourhoods called Designated Areas (DAs) during restricted hours. The SPME and PCW are shown in Table 4.5 below:

4.2.1.9 In the interest of offering additional protection to the population, the carrying out of PCW is generally banned inside a DA during restricted hours. As for the use of SPME, it would be necessary to comply with DA-TM noise level requirements that are 15 dB(A) less than those listed in the GW-TM before a CNP may be issued.

4.2.1.10 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.

4.2.1.11 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.

4.2.2 Operational Noise

4.2.2.1 Operational noise is controlled under the NCO's Technical Memorandum for the Assessment of Noise from Places other than Domestic Premises, Public Places or Construction Sites. Table 2 of the TM specifies the ANLs.

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

· 5 dB(A) below the appropriate ANLs shown in Table 2 of the Technical Memorandum for the Assessment of Noise from Places other than Domestic Premises, Public Places or Construction Sites (NCO-TM); or
· the prevailing background noise levels. (For quiet areas with 5 dB(A) below the ANL).

4.2.2.3 Table 4.6 compares the two criteria. 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 the above EIAO-TM criteria values and the background level, whichever is lower.

4.3 Description of the Environment

4.3.1.1 The vicinity of the western part of the study area is mostly rural in nature (and with some container storage areas) and become more urbanised in the eastern part. Existing noise environment in the area is mainly influenced by:
· Road network within and around the study area;
· Activities like container yards, open storage and workshops; and
· Construction activities within and around the study area.

4.3.1.2 With reference to the field surveys carried out in August 2001, it was observed that:

For San Wai STW,

i) The existing plant is mostly of open-design with equipment located outdoor. The operation of equipment is transient depending on sewage loading.
ii) The surrounding environment comprises of container yards, pig farm, fishponds and hill slopes.
iii) The container yards are potential influencing noise sources. The proposed Deep Bay Link would be a significant future noise source in the vicinity.

For Ha Tsuen Pumping Station,

i) The existing pumping station is an enclosed design with noisy equipment like pumps located in concrete plant rooms and below ground.
ii) Some noticeable minor sources of noise found are:
a. Ventilation exhausts and intakes, although there were acoustic lourves, some noise was generated perhaps due to the high flow rate;
b. Air-conditioning and ventilation equipment at the roof; and
c. Noise emission through the opened doors.However, the siting of these noisy points were away from sensitive receivers and were self-shielded by the building and other structures.
iii) The major noise sources seem to be the road traffic on Tin Ying Road, Hung Tin Road, Ping Ha Road and Ping Fuk Road, during daytime as observed.

4.4 Noise Sensitive Receivers

4.4.1.1 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.

4.4.1.2 Figures 4.1 and 4.2 show respectively the Assessment Area for noise impact assessment around the proposed expanded sites for San Wai STW and Ha Tsuen Pumping Station. Existing land uses within the Assessment Area of San Wai STW include mainly agricultural land, container storage areas, and scattered village houses. Whereas the existing land uses around the Ha Tsuen Pumping Station are mainly public and private residential housing estates with a number of schools.

4.4.1.3 Future NSRs around the proposed expanded and upgraded San Wai STW and Ha Tsuen Pumping Station include the planned sensitive land uses of the HSKNDA and HSK North NDA as shown in Figure 1.9. Immediately to the southwest of the proposed San Wai STW is the proposed Deep Bay Link. Among these future uses, those within 300m of the expanded San Wai STW is considered as noise sensitive.

4.4.1.4 The identified existing and future NSRs related to the works of San Wai STW and Ha Tsuen Pumping Station are summarised in Tables 4.7 and 4.8 and shown in Figures 4.1 and 4.2 respectively. The NSRs related to the works of the emergency bypass culvert are described in Section 4.5.

4.5 Enhancement Measures to Control Emergency Discharge

4.5.1.1 With reference to Section 1.2 of this report, in order to reduce the chance of discharging raw sewage into Tin Shui Wai Drainage Channel and hence Deep Bay, an emergency bypass culvert will be constructed in the form of box culvert from San Wai STW to nearby drainage channel as part of this project.

4.5.1.2 Four alternative alignments of the proposed emergency bypass culvert were considered and are shown in Figure 4.4. Figure 4.4 also indicates the extent of the construction works areas associated with the four alternative alignments. The potential noise impact of the proposed emergency bypass culvert is mainly related to the construction noise impact during the construction phase of the culvert.

4.5.1.3 In general, the construction works areas for the emergency bypass culverts would be a 10m wide strip along the culvert alignment from the expanded and upgraded San Wai STW up to the connection point with the existing Ting Shui Wai Drainage Channel for Alternatives 1, 2, and 3, and with the existing Lo Uk Tsuen Drainage Channel for Alternative 4. A summary of the length and the total construction works areas for the four alternatives is shown in Table 4.9. The identified NSRs related to the four alternatives of the emergency bypass culvert are shown in Figure 4.3 and listed in Table 4.10.

4.5.1.4 It is expected that the works related to the construction of the emergency bypass culvert would be carried out section by section. The construction noise generated from each section of the culvert construction works would be localised, and short-term. As shown in Figure 4.4, Alternative 4 of the emergency bypass culvert will only involve the construction of the culvert alignment from the expanded and upgraded San Wai STW to the existing Lo Uk Tsuen Drainage Channel with a total length of about 600m. By comparing the length and works area associated with the four alternatives as shown in Table 4.9, Alternative 4 would involve the shortest length and the smallest works area. Besides, Alternative 4 is also considered to have the least interfacing issues on project implementation. Alternative 4 is selected as the preferred alternative for this Project.

4.5.1.5 For the purpose of this assessment, the noise impact due to the construction of the preferred Alternative 4 of the proposed emergency bypass culvert was used to predict the worst-case cumulative noise impacts at the NSRs. The distance of the NSRs from Alternative 4 of the emeregency bypass culvert is shown in Table 4.10. Details of the construction noise calculation are presented in Appendix 4A.

4.6 Assessment Methodology

4.6.1 Construction Noise

4.6.1.1 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).

4.6.1.2 With reference to Section 1.3 of this report, apart from the construction of this project, there are a number of major projects planned in the vicinity of the study area which might cause cumulative construction phase impacts to the environment. These projects include Yuen Long and Kam Tin Sewerage and Sewage Disposal (YLKTSSD) Stage 1, YLKTSSD Stage 2, Deep Bay Link (DBL), and the Hung Shui Kiu New Development Area (HSKNDA). Concurrent construction activities identified within 300m from the NSRs and at the same angle of view from the San Wai STW and the Ha Tsuen Pumping Station are shown in Figures 4A.1 and 4A.2 in Appendix 4A. All these construction activities were included in the construction noise calculations to predict the worst-case cumulative noise impacts at the NSRs.

4.6.1.3 An inventory of powered mechanical equipment was developed for the purpose of assessing the potential construction noise impacts from each of the three key project items namely the expansion and upgrading of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of the emergency bypass culvert, as well as the other concurrent construction activities in the area. The construction noise assessment has taken into account the construction programme, the construction noise levels from work tasks, and 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.

4.6.1.4 The inventories of powered mechanical equipment together with the tentative construction programs taken in this assessment are included in Appendix 4A.
4.6.1.5 The construction plant inventory assumed for this assessment was confirmed by the project proponent namely Drainage Services Department as practicable and reasonable for the completion of the project within the scheduled construction programme based on the information available at this stage.

4.6.2 Operational Noise

4.6.2.1 Fixed noise sources during the operational phase of this project include the activities related to the operations of expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station. Noise prediction was based on the assumed plant inventories and utilisation schedule for the worst-case scenario. Assessments were undertaken based on standard acoustic principle with reference to the Technical Memorandum for the Assessment of Noise from Places other than Domestic Premises, Public Places or Construction Sites, issued under the Noise Control Ordinance.

4.7 Identification of Environmental Impacts

4.7.1.1 This project includes the upgrading and expansion of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of the emergency bypass culvert. Potential sources of noise include:

Construction Phase

· construction activities associated with the expansion and upgrading works of San Wai STW;
· construction activities associated with the expansion works of Ha Tsuen Pumping Station;
· construction activities of emergency bypass culvert from San Wai STW to existing drainage channels; and
· cumulative construction noise impacts arising from concurrent construction activities of other major projects namely YLKTSSD Stage 1, YLKTSSD Stage 2, Deep Bay Link, and the HSKNDA.

Operational Phase

· operational activities of the expanded and upgraded San Wai STW, which include the operation of pumps, motors, ventilation equipment and others; and
· operational activities of the expanded Ha Tsuen Pumping Station, which include the operation of pumps, ventilation equipment and others.

4.8 Prediction and Evaluation of Environmental Impacts

4.8.1 Construction Phase Impact

4.8.1.1 The predicted construction noise impacts associated with the expansion and upgrading of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of the emergency bypass culvert are discussed below. Details of the construction noise impact assessment together with the inventories of powered mechanical equipment and the tentative construction programs for these three key project items are included in Appendix 4A.

4.8.1.2 It is anticipated that there will be no construction work carried out during the restricted hours (i.e. between 7pm and 7am and any time during general holidays including Sunday) under the scheduled construction programme.

Area Near San Wai STW

4.8.1.3 Potential construction noise impact was predicted for the construction activities associated with the expansion and upgrading of the existing San Wai STW. With reference to Table 4.7 and Figure 4.1, NSRs are located far away from the proposed expanded San Wai STW. The nearest NSR is an existing village house in San Wai located at 190m from the boundary of the expanded STW.

4.8.1.4 The predicted construction noise levels at the identified NSRs within 300m from the boundary of the expanded STW site and the construction site of the preferred Alternative 4 of the proposed emergency bypass culvert are shown in Table 4.11. All the predictions are based on the worst-case scenario when there are concurrent construction activities for both the expansion and upgrading of San Wai STW and the construction of Deep Bay Link at the southwestern side of the expansion site.

4.8.1.5 As shown in Table 4.11, the predicted cumulative construction noise levels at the NSRs exceeded the construction noise limit of 75dB(A) for the unmitigated scenario. Nevertheless, with the implementation of noise mitigation measures by using quiet plant and/or temporary barrier, the predicted cumulative construction noise levels at the NSRs are all within the limit and no adverse impacts are therefore expected.

Note: Mitigated Level 1 : Use of quiet plant

Mitigated Level 2 : Use of quiet plant + Temporary noise barrier

Area Near Ha Tsuen Pumping Station

4.8.1.6 Potential construction noise impact was predicted for the construction activities associated with the expansion of the existing Ha Tsuen Pumping Station. With reference to Table 4.8 and Figure 4.2, NSRs are located at considerable distance from the proposed expanded Ha Tsuen Pumping Station. The nearest NSR is an existing residential block of Ting Shing Court in Tin Shui Wai located at about 100m from the boundary of the expanded pumping station.

4.8.1.7 The predicted cumulative construction noise levels at the NSRs within 300m from the boundary of the expanded pumping station are shown in Table 4.12. As shown in Table 4.12, the predicted cumulative construction noise levels at the NSRs exceeded the construction noise limit of 75dB(A) for domestic premises and 70dB(A) for schools under the unmitigated scenario. Nevertheless, with the implementation of noise mitigation measures by using quiet plant and temporary noise barrier, the predicted cumulative construction noise levels at the NSRs are all within the respective limits. However, for NSR N1 namely Ho Ming Primary School, the predicted cumulative construction noise level with the use of quiet plant and site hoarding exceeded the noise limit of 65 dB(A) for school during examination periods. The dominant source of noise is contributed from the installation of sewer lines of YLKTSSD Stage 2. The construction work should be programmed such that the noisier construction activities would not be coincided with the examination periods of NSR N1. With the implementation of these mitigation measures, no adverse impacts are expected.

Note: Mitigated Level 2 : Use of quiet plant + Temporary noise barrier

* 65 dB(A) for school during examination periods.

4.8.2 Operational Phase Impact

4.8.2.1 The predicted operational noise impacts associated with the expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station are discussed below. Details of the plant inventory and operational noise impact assessment are included in Appendix 4B.

Expansion and Upgrading of San Wai STW

4.8.2.2 Potential operational noise impact was predicted for the noisy equipment associated with the operation of the expanded and upgraded San Wai STW. With reference to Table 4.7 and Figure 4.1, NSRs are located far away from the proposed expanded and upgraded San Wai STW. The nearest NSR is an existing village house in San Wai located at more than 190m from the boundary of the expanded STW.

4.8.2.3 Background noise monitoring in the proximity of San Wai STW has been undertaken during 22-26 August 2002. The results are tabulated in Table 4.13.

4.8.2.4 Based on the type of area (rural area) and considered that there is no influencing factor in the area, the Area Sensitive Rating for all the NSRs within the study boundary of San Wai STW could be classified as "A". In any event, however, the ASR assumed here is for indicative assessment only. It should be noted that fixed noise sources are controlled under section 13 of the NCO. Nothing in this report should bind the Noise Control Authority in assessing noise from these sources upon the receipt of complaints. The Authority should assess the noise impacts based on the contemporary conditions/situations.

4.8.2.5 Based on the noise measurement results, the prevailing background noise levels are taken as 50 dB(A) during daytime and 47 dB(A) during nighttime. Since the prevailing background daytime noise level was more than 5dB(A) below the ANL, the noise criteria adopted for this assessment for daytime and nighttime is 50dB(A) and 45 dB(A) respectively.

4.8.2.6 Under the unmitigated scenario, the predicted operational noise levels at the NSRs within 300m from the boundary of the expanded STW are shown in Table 4.14. The prediction assumed all noisy equipment are located outdoor as the worst-case. The predicted operational noise level at the NSRs exceeds the EIAO-TM criteria for both daytime and nighttime. Mitigation measures are required and are formulated in this EIA.

4.8.2.7 With the implementation of suitable mitigation measures as in Section 4.9.2, in particular, housing all the noisy equipment of the expanded and upgraded San Wai STW underground or within concrete building structures, the noise levels due to the proposed expanded and upgraded San Wai STW would be lower. Predicted noise levels under the mitigated scenario for the expanded and upgraded San Wai STW are shown in Table 4.15. All predicted noise levels at NSRs are found within the TM noise limits.

Expansion of Ha Tsuen Pumping Station

4.8.2.8 Potential operational noise impact was predicted for the noisy equipment associated with the operation of the expanded Ha Tsuen Pumping Station. With reference to Table 4.8 and Figure 4.2, NSRs are located at considerable distance from the proposed expanded Ha Tsuen Pumping Station except the future residential area under the HSK North NDA development which is located about 30 to 50m to the south of the Ha Tsuen Pumping Station.

4.8.2.9 The Ha Tsuen Pumping Station is bounded by the Tin Shui Wai Drainage Channel to the west, and Ping Ha Road and Hung Tin Road on other two sides. According to the Annual Traffic Census 2000 issued by the Transport Department, the annual average daily traffic (AADT) for Hung Tin Road that is a district distributor road in the year 2000 is 32,370. According to the Technical Memorandum for the Assessment of Noise from Places other than Domestic Premises, Public Places or Construction Sites, those NSRs with direct view and in close proximity to Hung Tin Road namely N3, N5 and N50 are considered as under the direct influence of a "major road". For the other NSRs, they are considered not affected by any influencing factor.

4.8.2.10 The type of area for all NSRs are taken as "Urban Area" except NSRs N11 and N12 which are located at "Rural Area". Based on the type of area and the influencing factor discussed above, the Area Sensitive Rating (ASR) for NSRs N3, N5 and N50 is rated as "C", the ASR for NSRs N1, N2, N6, N7, N8, N43, N44, N45, N46, N47, N48 and N49 is rated as "B", and the ASR for NSRs N11 and N12 is rated as "A".

4.8.2.11 Background noise monitoring in the proximity of Ha Tsuen Pumping Station has been undertaken during 22-26 August 2002. The results are tabulated in Table 4.16.

4.8.2.12 Since the prevailing background noise level is within 5dB(A) of the ANL, the TM noise limit could be adopted accordingly.
4.8.2.13 Under the unmitigated scenario, the predicted operational noise levels at the NSRs within 300m from the boundary of the expanded pumping station are shown in Table 4.17. The predicted operational noise level at the NSRs exceeds the EIAO-TM criteria for both daytime and nighttime. Mitigation measures were adopted.

Note: For school sites, assessment for nighttime is not applicable.

4.8.2.14 With the implementation of suitable mitigation measures as in Section 4.9.2, in particular, housing all the noisy equipment of the expanded Ha Tseun Pumping Station underground or within concrete building structures, the noise levels due to the proposed expanded Ha Tsuen Pumping Station would be lower. Predicted noise levels under the mitigated scenario for the expanded Ha Tsuen Pumping Station are shown in Table 4.18. All predicted noise levels at NSRs are found within the TM noise limits.

Table 4.18 Predicted Noise Impacts during Operational Phase of the Expanded Ha Tsuen Pumping Station for Mitigated Scenario

Note: For school sites, assessment for nighttime is not applicable.

4.9 Mitigation of Adverse Environmental Impacts

4.9.1 Construction Phase

4.9.1.1 During construction of San Wai STW expansion and emergency bypass culvert, mitigation in the form of quiet plants, i.e. Mitigation Level 1, should be used in order to reduce the noise impacts to protect the nearby NSRs. For NSR N40, which is a village house in close proximity to the emergency bypass culvert, additional mitigation measures in the form of temporary noise barriers are required besides using of quiet plants. The locations of temporary noise barriers are shown in Figure A4.3 in Appendix 4A. The number of plants operating close to the NSR should be reduced as far as practical in order to reduce the level of noise impact.

4.9.1.2 During construction of Ha Tsuen Pumping Station expansion, mitigation in the form of quiet plants and temporary noise barriers, i.e. Mitigation Level 2, should be used in order to reduce the noise impacts emanating from the construction sites on nearby NSRs. The location of the temporary noise barriers would be along the site boundary of the Ha Tsuen Pumping Station and is shown in Figure A4.4 in Appendix 4A. The construction work should also be well programmed such that the noisier construction activities would not be coincided with the examination periods of the school at NSR N1.

4.9.1.3 Besides the above specific measures, the measures discussed below should be adopted as far as practicable to further reduce the construction noise impacts from the project.

Use of Quiet Plant

4.9.1.4 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 given 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.

4.9.1.5 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.

4.9.1.6 The list of quiet PME that has been taken into account in the construction noise assessment is summarized in Table 4.19 below.

Using Temporary and Movable Noise Barriers

4.9.1.7 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 sight 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 7 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.
Reducing the Numbers of Plants Operating in Critical Areas Close to NSRs

4.9.1.8 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.

Good Site Practice

4.9.1.9 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 minimise 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 utilised.

4.9.2 Operational Phase

4.9.2.1 All the noisy equipment of the expanded and upgraded San Wai STW and Ha Tsuen Pumping Station should be housed underground or within building structures made of suitable materials (e.g. concrete). It should be a complete enclosure with minimal openings for which these openings should not be facing any NSRs. The building materials should provide a sound transmission loss of 30dB(A) or better (e.g. concrete with thickness of 300mm). 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 with noise reduction of not less than 10 dB(A) at the air intakes and discharge openings should be employed. The Guidelines Good Practices on Ventilation System Noise Control and Good Practices on Pumping System Noise Control should be followed.

4.10 Evaluation of Residual Impacts

4.10.1.1 In view of the large distance between the NSRs and the construction site of the San Wai STW, the predicted construction noise levels at the NSRs are all within the construction noise criteria with the use of quiet plant. Similar predictions are obtained for the construction of Ha Tsuen Pumping Station and the construction noise levels at the NSRs are also within the construction noise criteria with the use of both quiet plant and temporary noise barriers. No residual noise impacts are therefore expected during the construction phase of San Wai STW and Ha Tsuen Pumping Station. For the construction of the emergency bypass culvert, no adverse noise impact is expected by employing mitigation measures in the form of quiet plant and temporary noise barriers when construction work is carried out in close proximity to NSRs. Residual noise impact is not expected.

4.10.1.2 While there are other major projects in the vicinity such as DBL, HSKNDA, and YLKTSSD Stage 1 and 2 would also undergo construction during the construction phase of San Wai STW, Ha Tsuen Pumping Station and emergency bypass culvert, cumulative noise impact has also been assessed. The predicted noise levels at the NSRs are all within the construction noise criteria with the use of quiet plant and temporary noise barrier. Adverse cumulative noise impact is not expected and no residual noise impact is expected.

4.10.1.3 The major operational noise impacts would be associated with the mechanical equipment operation of San Wai STW and Ha Tsuen Pumping Station. Provided that all the noisy equipment would be housed within building structure made of material with a sound transmission loss of 30 dB(A) or better (e.g. concrete with thickness of 300mm). All NSRs would be with acceptable noise levels and EIAO-TM for both daytime and nighttime, therefore residual noise impacts at the NSRs are not expected.

4.11 Environmental Monitoring and Audit

4.11.1.1 The detailed environmental monitoring and audit requirements for noise during the construction phase of the project are prepared in accordance with the requirements stipulated in Annex 21 of the TM on EIAO Process. Together with the implementation schedule for noise mitigation measures, all the material are included in the EM&A Manual.

4.12 Conclusions

4.12.1.1 The construction noise impacts of this project will be associated with the expansion and upgrading of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of the emergency bypass culvert. The identified NSRs are all located at considerable distance from the construction site of the San Wai STW and Ha Tsuen Pumping Station. The predicted construction noise levels at the NSRs are all within the construction noise criteria with the use of quiet plant and temporary barrier. No residual noise impacts are therefore expected during the construction phase of San Wai STW and Ha Tsuen Pumping Station.

4.12.1.2 With mitigation measures in the form of quiet plant and temporary noise barrier in place, the predicted cumulative noise impacts at the identified NSRs during the construction phase near San Wai STW under the worst-case scenario are 68 to 75 dB(A), which are all within the construction noise criteria. Whereas the predicted cumulative noise impacts at the identified NSRs during the construction phase near Ha Tsuen Pumping Station under the worst-case scenario are 60 to 74 dB(A), which are all within the construction noise criteria except at NSR N1 during the examination periods of school.

4.12.1.3 During the operational phase of the expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station, provided that all the indoor noisy equipment would be housed underground or within building structure made of suitable material and with effective silencers for the ventilation system, residual noise impacts at the nearest NSRs are not expected.