7                        NOISE IMPACT

7.1                 Introduction

7.1.1           This section presents an assessment of potential noise impact pertinent to the construction and operation phase of the proposed upgrading work for the Tai Po Sewage Treatment Works (hereinafter referred to as “TPSTW”).  Appropriate mitigation measures have been recommended, where necessary, to alleviate the potential noise impacts to acceptable levels.

7.2                 Environmental Legislation, Policies, Plans, Standards and Criteria

7.2.1           Noise impacts were assessed in accordance with the criteria and methodology given in the Technical Memoranda made under the Noise Control Ordinance (NCO), and EIAO-TM.

7.2.2           The NCO provides the statutory framework for noise control.  This defines statutory limits applicable to equipment used during the construction and operation phases of the proposed works in the study area.  The NCO invokes four Technical Memoranda, which define the technical means for noise assessment:

·        Technical Memorandum on Noise from Places other than Domestic Premises, Public Places or Construction Sites (IND-TM);

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

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

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

7.2.3           The NCO and the accompanying Technical Memoranda provide a mechanism for assessing noise levels and provide the statutory power to control noise.

7.2.4           With regard to the assessment of the operational noise impacts, the NCO designates acceptable noise levels for Noise Sensitive Receivers (NSRs) on the basis of an Area Sensitivity Rating (ASR), based on the characteristics of the area within which they are located such as rural, village, low-density residential, or urban. Within these areas, the presence of "influencing factors" (such as the presence of industrial activities or major roads) can further affect the ASR and hence the acceptable noise level (see Table 7.1).






Table 7.1    Area Sensitivity Ratings

Type of Area Containing NSR

Degree to which NSR is affected by Influencing Factor

Not Affected

Indirectly Affected

Directly Affected

Rural Area




Urban Area




Low density residential area consisting of low-rise or isolated high-rise developments




Area other than those above




Construction Activities

7.2.5           Under the GW-TM, noise from construction activity is not restricted during the period 0700 - 1900 hours on weekdays, except Public Holidays. However, the EIAO-TM identifies a daytime general construction noise limit of 75 dB(A) Leq (30 minutes) for domestic premises.  This standard was used as the assessment criteria in the construction noise assessment.

7.2.6           Between 1900 and 0700 hours and all day on Sundays and public holidays, activities involving the use of powered mechanical equipment (PME) for the purpose of carrying out construction work are prohibited unless a Construction Noise Permit (CNP) has been obtained. A CNP may be granted provided that the Acceptable Noise Level (ANL) for the noise sensitive receivers (NSRs) can be complied with. ANLs are assigned depending upon the Area Sensitive Rating (ASRs). The corresponding basic noise levels (BNLs) for evening and night-time periods are given in Table 7.2.

 Table 7.2         Construction Noise Criteria for Activity other than Percussive Piling

Time Period

Basic Noise Level (BNLs) (dB(A))




Evening (1900 to 2300 hours) (1)




Night (2300 to 0700 hours)




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


7.2.7           As the study area for TPSTW is located inside Tai Po Industrial Estate as shown on Figure 7.1, the Area Sensitivity Rating (ASR) of “C” is determined. According to the Table 7.2, the construction noise criteria for the sensitive receiver would be 70 dB(A) in the evening and 55 dB(A) at night.










Operational Activities

7.2.8           Operational noise emitted from the TPSTW is controlled under the IND-TM.  According to the TM, the acceptable Noise Levels (ANLs) for different Area Sensitivity Ratings (ASRs) are given in Table 7.3.

7.2.9           The ANL is a function of the type of area within which the NSR is located, and the degree of the effect on the NSR of influencing factors such as major roads and industrial areas.  The ANLs for all ASRs are provided in Table 7.3.

Table 7.3     Acceptable Noise Levels (ANLs) (dB(A))

Time Period




Day (0700 to 1900 hours)




Evening (1900 to 2300 hours)

Night (2300 to 0700 hours)




7.2.10       The EIAO-TM states that all fixed noise sources should be so located and designed so that when assessed in accordance with the IND-TM, the level of the intruding noise at the facade of the nearest sensitive use should be at least 5 dB(A) below the appropriate ANL shown in Table 2 of the IND-TM or, in the case of the background being 5 dB(A) lower than the ANL, the predicted noise level should not exceed the background.

7.2.11       In any event, the ASR assumed in the EIA is for indicative assessment only.  It should be noted that fixed noise sources are controlled under section 13 of the NCO.    The Authority shall assess the noise impacts based on the contemporary conditions/situations.

7.2.12       As mentioned in Section 7.2.7, the study area is defined as ASR “C”, i.e. its planning criteria for NSRs would be 65 dB(A) for daytime operations and 55 dB(A) for night-time operations.

Noise Criteria arising from the New Proposed Equipment

7.2.13       A noise survey was undertaken in March 2003 to determine the background noise levels.  Results indicated that the measured average daytime & evening time noise level was 62.5 dB(A); and the measured average night-time noise level was 61.7 dB(A) at the selected station. As the background noise level for daytime & evening time is 7.5 dB(A) lower than the relevant ANL, the background noise level of 63 dB(A) (i.e. rounded to the nearest 1 dB(A)) would be adopted as the daytime & evening time assessment criterion. On the other hand, as the background noise level at night-time is higher than the relevant ANL, planning criteria of 55 dB(A) would be adopted as the night-time assessment criterion. The recommended assessment criteria for NSR are summarized in Table 7.4.







Table 7.4     Noise Criteria for Operational Noise Levels– New Proposed Equipment



Planning Criteria

Measured Background Noise Level

Recommended Noise Criteria

Day (0700 to 1900 hours)





Evening (1900 to 2300 hours)





Night (2300 to 0700 hours)






Cumulative Impact


7.2.14       Cumulative noise impacts arising from all items of equipment including new equipment and existing equipment were also calculated and compared against relevant ANL criteria. According to the Table 7.3, the ANL for the sensitive receiver would be 70 dB(A) in the daytime/evening and 60 dB(A) at night.


7.3                 Description of the Environment

7.3.1           The Project site is located at the south-eastern side of Tai Po Industrial Estate and away from the town centre of Tai Po, overlooking Tai Po Shuen Wan Golf Centre to the east and Tai Po Waterfront Park to the south.  The site is served by a local access road, Dai Kwai Street.

7.3.2           Baseline noise surveys were carried out at one selected location (Figure 7.2) within the study area on 2 and 3 March 2003.  The selected monitoring location is located near the TPSTW which is representative to reflect the prevailing background noise level. All the noise measurements were conducted in accordance with IND-TM.  The detailed methodology and results were presented in Appendix 7.1.  The measured noise levels at the selected location range from 60 to 66 Leq (30-min) dB(A).

7.4                 Assessment Methodology

Construction Phase

7.4.1           The assessment followed the procedures given in the GW-TM.  For the assessment of noise from PME, the distance attenuation was estimated using the standard formula:

Distance Attenuation in dB(A) = 20 log D + 8 [where D is the distance in metres]

7.4.2           Sound Power Levels of the equipment were taken from Table 3 of the GW-TM.  Where no SWL is supplied in the TM, reference was made to BS 5228, previous similar studies or information from the contractors. Groups of powered mechanical equipment (PME) likely to be employed for each construction task (i.e. site clearance and set up site office, piling work, excavation, demolition, concreting work and pipework or miscellaneous) are shown in Appendix 7.2. 

7.4.3           The construction noise assessment provided results for each month throughout the construction period.  As stated in paragraph 2.7.1, the Phase 1 of the Project is scheduled to commence in 20054 for completion in 2009 whilst the Phase 2 works, being subject to actual flow build-up, is scheduled to commission before 2016.  In order to assess the noise impacts, a construction programme as shown in Appendix 7.3, which assuming all works, including both Phase 1 and Phase 2, to be carried out continuously and completed by December 2010, is adopted for assessment.

7.4.4           Generally, the construction activities of the Project would be carried out in non-restricted hours (0700-1900 hours) with the exception of pipework/miscellaneous work which may be carried out in restricted hours. In the event that the construction activities are undertaken during restricted hours, it would be the responsibility of the Contractor to ensure compliance with the NCO and the relevant TMs. In such cases, the Contractor will be required to submit CNP application to the Noise Control Authority and abide by any conditions stated in the CNP, should one be issued. Therefore, the potential noise impacts of construction works within restricted hours are not formally assessed in this EIA Report. In order to facilitate the efforts of the project proponent to avoid any potentially adverse noise impact, an indicative assessment for representative NSR has been undertaken and is presented in Section 7.9below.

7.4.5           As the E&M works are mainly installation work, limited number of PME would be used. Also most of the E&M works would be carried out indoors. Thus, it is considered that E&M works would not contribute to the cumulative impact at the NSR and are excluded from this study.

7.4.6           Based on the construction programme and the assigned PME groups, the construction noise levels from both individual and all concurrent construction activities of the civil works which are considered to be significant at the NSR have been assessed.

7.4.7           Noise impact was assessed on the basis of the following three conservative assumptions:

·         All PME items required for a particular construction activity would be located at the notional source position, which is at a position mid-way between the appropriate geographical centre of the construction site and its boundary nearest to the NSR.

·         A +3 dB(A) façade correction was added to the predicted noise levels to account for the façade effect at each NSR.

·         Noise impacts at the nearest sensitive façades of the residential buildings to the source positions were assessed.

7.4.8           Within 300m from the project boundary, there are no other construction activities identified to be undertaken concurrently with construction of this Project during the construction period.  Therefore, cumulative construction noise impact is not expected.






Operational Phase

7.4.9           The assessment followed the procedures given in the GW-TM.  For the assessment of noise from equipment, the distance attenuation was estimated using the standard formula as mentioned in Section 7.4.1.

7.4.10       To provide more accurate and realistic prediction, on-site noise measurement was carried out for some equipment (i.e. mechanically raked bar screen and screw type grit classifier). However, on-site noise measurement for other equipment (such as air blower, pumps and ventilation fans etc) could not be carried out due to site constraint and high background noise levels  from other noisy equipment nearby. On-site noise measurement would also affect the normal operation of TPSTW if turning off the equipment. To avoid overestimation/underestimation on the SWL of these equipment, the SWL of pump and ventilation fans were derived from the Good Practices on Pumping System Noise Control (GP-PS) and Good Practices on Ventilation System Noise Control (GP-VS). The estimated SWLs of other equipment were made reference to the specifications of similar items of equipment provided by contractor/plant supplier and other similar projects.

7.4.11       Noise impact was assessed on the basis of the following three conservative assumptions:

·            All items of operational plant required for operation of the TPSTW / proposed facilities would be located at the actual source position. 

·            A +3 dB(A) façade correction was added to the predicted noise levels to account for the façade effect at each NSR.

·            Noise impacts at the nearest sensitive façades of the residential buildings to the source positions were assessed.

7.5                 Identification of Environmental Impacts

Potential Noise Impacts

7.5.1           Major potential noise impacts arising from the Project would be:

·      Construction noise

·      Operation noise.

Noise Sensitive Receivers (NSRs)

7.5.2           Noise sensitive receivers (NSRs) were identified according to the criteria set out in the EIAO-TM and through site inspection. In accordance with Section 3 of Annex 13 of EIAO-TM, one NSR (Staff Quarters at TPSTW) has been identified and is shown in Figure 7.3.

7.5.3           Apart from the Staff Quarters of TPSTW, the nearest existing noise sensitive receivers (i.e. Marino Casa, Richwood Park, Tycoon Place, Fortune Garden and Ha Hang) are located more than 600m away from the boundary of TPSTW. With reference to the Outline Zoning Plan (Plan No. S/TP/14) issued in July 2002, no planned noise sensitive uses are identified within 300m of the TPSTW. The area in the close vicinity of TPSTW has been zoned for Other Specified Uses  (“OU”).

7.6                 Prediction and Evaluation of Environmental Impacts

Construction Phase

7.6.1           As illustrated in the construction programme, various construction activities would be carried out concurrently during certain periods. Cumulative noise impacts arising from different construction activities have been predicted and are shown in Appendix 7.4. As indicated in Appendix 7.2, the major noisy construction tasks would be site clearance and excavation with total SWL of 124 dB(A).

7.6.2           The predicted noise levels at NSR TP1 were in the range 64 to 79 dB(A). The cumulative noise level at the NSR TP1 would exceed the noise criteria of 75 dB(A) during certain periods. As a result, noise mitigation measures would be required.


Operation Phase

7.6.3           The plant inventory and the SWL of the TPSTW are summarised in Appendix 7.5. As confirmed by the Project Proponent, the plant inventory used for prediction of operation noise impact is practical and realistic. To represent the worst case scenario, all items of equipment were assumed to operate concurrently 24 hours a day and the directivity was not included in the calculation.

7.6.4           Facilities that would be housed / enclosed in a concrete structure were assumed to have a 20 dB(A) reduction of noise emitted from the sources due to transmission loss of the wall.  Some items of equipment would be screened from the line-of-sight of NSRs by building or the structures within the site.  This allowed a reduction in the SWL of 10 dB(A) in accordance with the relevant Technical Memorandum.  Due to the facade effect, a positive 3 dB(A) has been added to predict noise levels at the NSRs.  For determining the distance correction factors, the distances between the probable source positions and the NSRs were considered.


Noise Impact Arising from The New Equipment


7.6.5           According to the plant inventory of the new proposed equipment as shown in Appendix 7.5, the predicted noise levels at the NSR TP1 is 54 dB(A), which would meet both the daytime and night-time criteria of 63 dB(A) and 55 dB(A) respectively. Thus, no mitigation measures would be required for the new equipment.  Details of the calculation are presented in Appendix 7.6.






Cumulative Impact

7.6.6           Assessment was also carried out based on the SWLs of existing plant as well as new and replacement plant likely to be installed under the works of the Project. Appendix 7.6 presents the results of the cumulative operational noise impacts of TPSTW.

7.6.7           According to Appendix 7.6, the predicted cumulative operational noise levels at the NSR TP1 would be 60 dB(A) , which would meet both the daytime and night-time criteria of 70 dB(A) and 60 dB(A) respectively. Thus, no mitigation measures would be required.  


Table 7.5     The Predicted Noise Levels at Representative NSR –Tai Po Sewage Treatment Plant Staff Quarters (TP1)


Predicted Unmitigated Noise Levels, dB(A)


New Proposed Equipment





Noise Criteria

Daytime -63

Nighttime -55



7.7                 Mitigation of Adverse Environmental Impacts

Construction Phase


Use of Quiet PME

7.7.1           To reduce construction noise impacts on the affected NSRs, silenced types of PME, which are in accordance with BS 5228: Part 1, 1997, are recommended.  The total Sound Power Level (SWL) of PME for each construction activity were calculated and are summarised in Appendix 7.7.

7.7.2           With the use of quiet PME, a noise reduction of up to 7 dB(A) could be achieved. A detailed calculation of construction noise impact for the mitigated scenario is presented in Appendix 7.8.  The results indicate that the cumulative construction noise levels predicted at NSR TP1 would comply with the daytime noise criteria of 75 dB(A).


Good Site Practice

7.7.3           In addition to quiet PME, good site practices listed below should be adopted to further abate any residual impacts during the construction phase of the Project and should be included in the contract :

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

·          Silencers or mufflers on construction equipment should be utilised and should be properly maintained during the construction program.

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

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

·          Plant known to emit noise strongly in one direction should, wherever possible, be orientated so that the noise is directed away from the nearby NSRs.

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

Operation Phase

7.7.4           The assessment results indicated that during the operation phase of the Project, the predicted noise levels at NSR TP1 would satisfy the requirements of the IND-TM and hence mitigation measures would not be required.

7.8                 Evaluation of Residual Impacts

7.8.1           No adverse construction noise impact from the Project is expected with the use of silenced PME and implementation of good site practices.

7.8.2           The assessment results indicated that the relevant noise criteria would not be exceeded during the operation of the TPSTW. The noise contribution from the operation of the new proposed equipment for TPSTW would not increase the background noise levels (60-66 dB(A)) recorded in the baseline noise survey) by more than 1 dB(A). The noise impact from the operation of the TPSTW would therefore be negligible to the existing environment.

7.9                 Construction Activities during Restricted Hours

7.9.1           As most of the temporary flow diversion works could only be carried out at night-time (during low flow conditions), the pipework/miscellaneous work would be carried out during restricted hours (1900-2300 and 2300-0700) at some working areas and therefore would be under the control of the GW-TM. The locations of the works area, namely Area A and Area B, are shown on Figure 7.4.

7.9.2           An indicative assessment was undertaken to investigate the potential noise impact likely to arise from the construction works. The construction criteria of 70 dB(A) in the evening and 55 dB(A) at night were adopted in this assessment.

7.9.3           As indicated in Appendix 7.10, the predicted noise levels at NSR TP1 with adoption of Quiet PME are predicted to range from 56 to 60 dB(A), which would comply with the evening noise criteria of 70 dB(A).

7.9.4           In order to reduce the construction noise impact during the night-time period (2300-0700), use of quiet PME, movable noise barrier and reduction in percentage on-time have been proposed for particular plant. According to GW-TM, a movable noise barrier with a cantilevered upper portion located above the noise generating part of the PME could reduce noise by 5 dB(A) and 10 dB(A), depending on the line of sight that could be blocked by the barrier when viewed from the NSR. The results are summarised in Appendix 7.9.

7.9.5           With adoption of the above mitigation measures, it is expected that the mitigated noise levels at NSR TP1 would comply with the night-time noise criterion of 55 dB(A). Details of calculation are presented in Appendix 7.10.

7.9.6           It should be noted that construction noise impact assessment during restricted hours are carried out for indicative purpose only. The Noise Control Authority will process any CNP application, based on the NCO and the relevant TMs, in addition to considering the contemporary situations/conditions.

7.10             Environmental Monitoring and Audit

7.10.1       It is recommended to establish an Environmental Monitoring and Audit (EM&A) programme for control of construction noise. The recommended mitigation measures should be incorporated into the EM&A programme for implementation during construction period.  Operational noise monitoring is not required.  Details of the programme are provided in a stand-alone EM&A Manual.

7.11             Conclusions

Construction Phase

7.11.1       The potential noise impact arising from construction activities on the representative NSR located in the vicinity of the work sites were assessed. With the adoption of quiet PME and good site practices, the predicted construction noise levels at representative NSR would not exceed the relevant noise criteria.

7.11.2       An indicative assessment was undertaken for pipework/miscellaneous work of the TPSTW during restricted hours (1900 to 0700). With the adoption of quiet plant, the mitigated noise level at the representative NSR TP1 would comply with the evening noise criterion but exceedance of the night-time noise criterion was still predicted. 

7.11.3       With adoption of the quiet PME, movable noise barrier and reduction in percentage on-time for particular plant, the mitigated noise levels at NSR TP1 would comply with the night-time noise criterion of 55dB(A).  It should be noted that the results of the construction noise impact assessment for restricted hours (1900 to 0700) are for indicative purpose; the Noise Control Authority will process any CNP application, based on the NCO and the relevant technical memoranda in addition to considering the contemporary situations / conditions.


Operation Phase

7.11.4       The noise impacts associated with the operation of the Project were also assessed. The assessment result indicated that the unmitigated operation noise levels predicted at representative NSR TP1 would comply with both the daytime and nighttime criteria. Thus, no adverse noise impact arising from the Project would be expected.