3. NOISE

3.1 Introduction

3.1.1.1 This section stipulates the EM&A requirements for construction noise during the construction phase of the Project, whereas during the operation phase of Project, the EIA findings confirmed that proper design of San Wai STW and Ha Tsuen PS would control the potential noise impacts at noise sensitive receivers within acceptable levels.

3.2 Noise Parameters

3.2.1.1 Monitoring and audit of noise levels should be carried out by the ET to ensure that any unacceptable noise impacts could be readily detected and timely and appropriate action be undertaken to rectify the situation.

3.2.1.2 The construction noise level should be measured in terms of the A-weighted equivalent continuous sound pressure level (Leq). Leq(30 min) should be used as the monitoring parameter for the time period between 0700-1900 hours on normal weekdays. For all other time periods, Leq(5 min) should be employed for comparison with the NCO criteria.

3.2.1.3 As supplementary information for data auditing, statistical results such as L10 and L90 should also be obtained for reference. A sample data record sheet is shown in Appendix B for reference.

3.3 Monitoring Equipment

3.3.1.1 As referred to in the Technical Memorandum (TM) issued under the Noise Control Ordinance (NCO), sound level meters in compliance with the International Electrotechnical Commission Publications 651: 1979 (Type 1) and 804: 1985 (Type 1) specifications should be used for carrying out the noise monitoring. Immediately prior to and following each noise measurement the accuracy of the sound level meter should be checked using an acoustic calibrator generating a known sound pressure level at a known frequency. Measurements may be accepted as valid only if the calibration level from before and after the noise measurement agree to within 1.0 dB.

3.3.1.2 Noise measurements should not be made in the presence of fog, rain, wind with a steady speed exceeding 5 m/s or wind with gusts exceeding 10 m/s. The wind speed should be checked with a portable wind speed meter capable of measuring the wind speed in m/s.

3.3.1.3 The ET Leader should be responsible for the provision of the monitoring equipment. He/she should ensure that sufficient noise measuring equipment and associated instrumentation are available for carrying out the baseline monitoring, regular impact monitoring and ad hoc monitoring. All the equipment and associated instrumentation should be clearly labelled. The equipment installation location should be proposed by the ET Leader and agreed with the ER and EPD in consultation with the IEC.

3.4 Monitoring Locations

3.4.1.1 Four noise monitoring stations, two for San Wai STW and another two for Ha Tsuen PS, are proposed to set up at locations shown in Figures 3.1 and 3.2 during construction phase.

3.4.1.2 The status and locations of noise sensitive receivers (NSRs) may change after issuing this Manual. If such cases exist, the ET Leader should propose updated monitoring locations and seek approval from ER and agreement from the IEC and EPD of the proposal.

3.4.1.3 When alternative noise monitoring locations are proposed, the monitoring locations should be chosen based on the following criteria:
a. At locations close to the major site activities which are likely to have noise impacts, with proper position/siting and orientation of the monitoring equipment ensured;
b. Close to the noise sensitive receivers (any domestic premises, hotel, hostel, temporary housing accommodation, hospital, medical clinic, educational institution, place of public worship, library, court of law, performing art centre should be considered as noise sensitive receiver); and
c. For monitoring locations located in the vicinity of the sensitive receivers, care should be taken to cause minimal disturbance to the occupants during monitoring.

3.4.1.4 The monitoring station should normally be at a point 1m from the exterior of the sensitive receivers building facade and be at a position 1.2m above the ground. If there is problem with access to the normal monitoring position, an alternative position may be chosen, and a correction to the measurements should be made. For reference, a correction of +3dB(A) should be made to the free field measurements. The ET Leader should agree with the IEC on the monitoring position and the corrections adopted. Once the positions for the monitoring stations are chosen, the baseline monitoring and the impact monitoring should be carried out at the same positions.

3.5 Baseline Monitoring

3.5.1.1 The ET Leader should carry out baseline noise monitoring prior to the commencement of the construction works. The baseline monitoring should be carried out daily for a period of at least two weeks. A schedule on the baseline monitoring should be submitted to the ER for approval before the monitoring starts.

3.5.1.2 During the baseline monitoring, there should not be any construction activities in the vicinity of the monitoring stations.

3.5.1.3 In exceptional cases, when insufficient baseline monitoring data or questionable results are obtained, the ET Leader should liaise with EPD and in consultation with ER to agree on an appropriate set of data to be used as a baseline reference.

3.6 Impact Monitoring

3.6.1.1 Noise monitoring should be carried out at all the designated monitoring stations for the construction phase. Given that the operating hours during the construction phase of the Project will be restricted and no noise-generating activities would be expected during 1900 to 0700 hours all days or any time on Sundays or general holidays, noise monitoring will only be carried out during 0700 to 1900 hours on normal weekdays.

3.6.1.2 One set of measurements between 0700 to 1900 hours on normal weekdays should be carried out for each station on a per week basis when noise-generating activities are underway. One set of measurements should at least include 6 consecutive Leq(5 min) results (i.e. a minimum of 30 minutes).

3.7 Event and Action Plan for Construction Noise

3.7.1.1 Since the monitoring would be carried out near site boundary, the ET should predict the noise levels at the nearest NSRs using standard acoustic principles on the basis of the measured noise levels from monitoring. The predicted noise levels should then be compared with the action and limit levels in Tables 3.1.

3.7.1.2 The Action and Limit levels for noise are defined in Table 3.1. Should non-compliance of the criteria occur, action in accordance with the Action Plan in Table 3.2 should be carried out.

Table 3.2 Event/Action Plan for Construction Noise

3.8 Mitigation Measures for Construction Noise Control

3.8.1.1 The EIA Report has recommended construction noise control and mitigation measures. The Contractor should be responsible for the design and implementation of these measures under the supervision of the ER and the ET.

3.8.1.2 Noise emissions from construction sites during construction phase could be minimised by adopting good site practice, selecting quiet plant, using quiet working methods and installing temporary barriers.

3.8.1.3 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.

Proposed Construction Phase Mitigation Measures

3.8.1.4 During construction of San Wai STW expansion and emergency bypass culvert, mitigation in the form of quiet plants should be used in order to reduce the noise impacts to protect the nearby NSRs. The list of recommended quiet plant should refer to Appendix 4A of the EIA Report. 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 of the EIA Report.

3.8.1.5 During construction of Ha Tsuen Pumping Station expansion, mitigation in the form of quiet plants and temporary noise barriers should be used in order to reduce the noise impacts emanating from the construction sites on nearby NSRs. The list of the recommended quite plant should refer to Appendix 4A of the EIA Report. The locations of temporary noise barriers are shown in Figure A4.4 in Appendix 4A of the EIA Report. 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.

3.8.1.6 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

3.8.1.7 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.

3.8.1.8 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

3.8.1.9 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

3.8.1.10 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

3.8.1.11 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.

3.9 Mitigation Measures for Operational Noise Control

3.9.1.1 The EIA Report has recommended operational noise control and mitigation measures. The Contractor should be responsible for the design and implementation of these measures under the supervision of the ER and the ET.

3.9.1.2 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. 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. The Guidelines Good Practices on Ventilation System Noise Control and Good Practices on Pumping System Noise Control should be followed.