4.                  NOISE

 

Introduction

 

4.1.            Construction noise was identified as a key issue in the study area due to the close proximity of the village houses to the construction sites.  As the sewer interceptor is proposed to run through the main street of the Sok Kwu Wan Village which is only a few metres wide, noise nuisance would be expected to occur at the adjacent village houses.  Since construction of the pumping stations would be near the village houses, noise exceedance is also likely to occur at the surrounding residential dwellings. 

 

4.2.            Operational noise arising from the proposed pumping stations and the STW were identified as another key issue for the Project.  However, since the proposed STW would be located far away from major residential settlement in the area, no adverse noise impacts arising from the operation of the STW is anticipated.

 

 

Environmental Legislation, Policies, Plans, Standards and Criteria

 

4.3.            Noise impacts were assessed in accordance with the criteria and methodology given in the Technical Memoranda made under the Noise Control Ordinance (NCO), and Technical Memoranda on Environmental Impact Assessment Process (EIAO-TM).

 

4.4.            The NCO provides the statutory framework for noise control. This defines statutory limits applicable to equipment used during the construction and operational 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).

 

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

 

4.6.            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 characterisation 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 therefore the acceptable noise level (see Table 4.1).

 

Table 4.1            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	A	B	B
Urban Area	B	C	C
Low density residential area consisting of low-rise or isolated high-rise developments	A	B	C

 

4.7.            The study area accommodates two types of area: rural and low-density residential.

 

4.8.            Influencing Factors (for the purposes of ASR classification) include the cement facility and the quarry on the northern side of Sok Kwu Wan. All potential NSRs were located more than 300m from the identified Influencing Factors and therefore would not be affected. As a result, ASR A was assumed in the assessment.  However, ratings at individual NSRs would likely be changed to reflect specific circumstances at the receiver.

 

Construction Activities

 

4.9.            Under the GW-TM, noise from construction activity is restricted during the period 1900 and 0700 hours and any time on a general holiday, including Sunday.  However, the EIAO-TM identifies a daytime general construction noise limit of 75 dB(A) _{Leq (30 mins)} for domestic premises and 70 dB(A) _{Leq (30 mins)} for educational institutions [65 dB(A) _{Leq (30 mins)} during examination periods]^[1], library and temple where unaided voice communication is required.  These standards were used as assessment criteria in the construction noise assessment.

 

4.10.        Between 1900 and 0700 hours and all day on Sundays and public holidays, activities involving the use of powered mechanical equipment (PME) for construction work are prohibited unless a construction noise permit (CNP) has been obtained. The noise Control Authority would consider a well-justified CNP application, once filed, for construction works within restricted hours as guided by the relevant technical memorandum issued under the Noise Control Ordinance (NCO).  The Noise Control Authority would take into account of contemporary conditions/situations of adjoining land uses and any previous complaints against construction activities at the site before making the decision to grant a CNP.  Nothing in this EIA Report shall bind the Noise Control Authority in making its decision.  If a CNP is to be issued, the Noise Control Authority shall include in the permit any condition he thinks fit.  Failure to comply with any such conditions would lead to cancellation of the CNP and prosecution action under the NCO.  A CNP could be granted provided that the Acceptable Noise Level (ANL) for the NSRs could be complied with. ANLs are assigned depending upon the ASR. The corresponding basic noise levels (BNLs) for evening and nighttime periods, together with daytime standard, are given in Table 4.2.

 

Table 4.2            Construction Noise Criteria for Activity other than Percussive Piling

 

Time Period	Basic Noise Level (BNLs) in dB(A)
	ASR A	ASR B	ASR C
Evening (1900 to 2300 hours) 1	60	65	70
Night (2300 to 0700 hours)	45	50	55

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

 

4.11.        Since night works would not be expected, only the daytime (0700 to 1900) criterion of 75 dB(A) would be applicable.

 

4.12.        Noise generated from the use of vibratory hammer for the piling work should be assessed with reference to the PP-TM. Activity involving percussive piling is prohibited unless a construction noise permit (CNP) is obtained.  A CNP would be granted provided that the Acceptable Noise Level (ANL) for the NSR could be complied with.

 

4.13.        Percussive piling works, if required, are excluded in the assessment since they are separately controlled under the NCO.

 

 

Operational Activities

 

4.14.        Operational noise emitted from the pumping stations and the STW is controlled under the IND-TM.  For this assessment, the sound power levels (SWL) of powered mechanical equipment (PME) were derived from the GW-TM.

 

4.15.        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 4.3.  In any event, the Area Sensitivity Rating assumed in this EIA Report is for indicative assessment only given that the building layout is only provisional.  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.

 

Table 4.3            Acceptable Noise Levels (ANLs) in dB(A)

 

Time Period	ASR A	ASR B	ASR C
Day (0700 to 1900 hours)	60	65	70
Evening (1900 to 2300 hours)
Night (2300 to 0700 hours)	50	55	60

 

4.16.        The EIAO-TM states that all fixed noise sources should be so located and designed 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 4.3 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 ^[2].

 

Description of the Environment

 

4.17.        The study area is located at the eastern side of the Lamma Island in an enclosed bay. The site is remote, undeveloped and isolated from major developments (e.g. the power station on the north-western side) and towns. The site has no road access and there are no major noise sources found at the site. The dominant noise source arises from the activities at the seafood restaurants in Sok Kwu Wan First Street and the marine traffic around Sok Kwu Wan.

 

4.18.        Existing marine traffic in Sok Kwu Wan includes ocean going and barge traffic to the cement facility on the northern side of Sok Kwu Wan, barges to the quarry, which is also on the northern side of the bay, ferry services between Central and the Sok Kwu Wan ferry pier, ferry services to Aberdeen, small craft involved in the fish culture operations in the bay and pleasure craft to the seafood restaurants. Vehicular traffic is minimal, only in terms of small moped trucks and village vehicles.

 

4.19.        Baseline Noise Surveys were carried out at six selected locations (Figure 4.1) within the study area on 28 and 29 November 1999.  The measured noise levels in terms of L_eq (30-mins) are summarised in Table 4.4.  The measured noise levels at the selected locations range from 52 to 60 _{Leq (30-min)} dB(A). The results indicate that the noise environment for the project site was representative of quiet rural areas due to its remote locations and lack of large scale industrial and transport infrastructure developments. Therefore, the site was sensitive to any increase in noise levels. 

 

Table 4.4            Background Noise Levels in the Study Area

 

Location ID	Description	Measured Noise Level, Leq (30-mins) dB(A)
M1	Chung Mei Village No.30	59* (46-66)
M2	Chung Mei Village No. 1	54* (47-60)
M3	Village house nearby Tin Hau Temple	52* (40-58)
M4	Leisure and Cultural Services Department Sok Kwu Wan Office	60* (52-65)
M5	Peach Garden Seafood Restaurant	54* (51-57)
M6	Ta Shui Wan	56* (53-58)

Note:

*                Arithmetic average

( )       Range

 

Description of Assessment Methodologies

 

4.20.        The assessment followed the procedures given in the GW-TM. For the assessment of noise from Powered Mechanical Equipment (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]

 

4.21.        In accordance with the EIAO, the methodology outlined in the GW-TM was used for the assessment of construction noise other than noise from percussive piling.  The fixed noise during operation phase was calculated using the above formula. 

 

4.22.        Sound Power Levels (SWLs) 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 ^[3], previous similar studies or from measurements taken at other sites in Hong Kong. Equipment likely to be employed for the various identified construction activities and the operation of the three pumping stations and the STW are shown in Appendices 4.1 – 4.4.  It is noted that the plant inventory lists for both unmitigated and mitigated scenarios of various construction activities have been confirmed with Project Proponent as being practicable in completing the works within scheduled timeframe. 

 

4.23.        The noise impact was assessed on the basis of the following assumptions:

 

·           All PME items required for a particular construction activity would be located at the notional or probable source position of the segment where such activity would be performed.

 

·           A +3 dB(A) façade correction was added to the predicted noise levels in order 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.

 

4.24.        Given the openness of the immediate locality of the construction site and the NSRs under consideration, correction for acoustic reflection would not apply to the assessment.

 

 

Identification of Environmental Impacts

 

Potential Noise Impacts

 

4.25.        Major potential noise impacts arising from the Project would be:

 

·        Construction of the pumping stations;

·        Construction of the STW;

·        Construction of the sewers, and

·        Operation of the pumping stations and the STW.

 

Noise Sensitive Receivers (NSRs)

 

4.26.        For the construction activity of the sewerage infrastructure and operation of the pumping stations and the STW, there were four distinct zones of sensitive use, which would likely be affected by construction and operational noise.

 

1)            Chung Mei Village

 

Chung Mei Village is located immediately to the western end of the study area. Some of the residential dwellings in this area would have a direct line of sight to the Pumping Station P1a and P1b, and pipeline construction activities in the vicinity. These dwellings would represent some of the closest NSRs to the construction sites and would be highly susceptible to the noise impact.

 

2)            Sok Kwu Wan Village

 

The village houses along the existing Sok Kwu Wan First Street would be most affected by the construction of the sewers.  Short distance of the receivers from the proposed routing of sewer is likely to cause noise exceedance at these receivers.

 

3)            Isolated Receivers along the Coast of Ta Shui Wan

 

Village houses are scattered between the proposed Pumping Station P2 and the STW. These houses were built at a level lower than the existing footpath where the sewers would be buried underground.

 

4)            Mo Tat Wan

 

The village is located to the eastern end of the study area. The receivers in this village would be located more than 300 m from the major construction activities. However, the construction of the submarine outfall would likely have cause noise nuisance to a few isolated houses, which would be close to the outfall alignment.

 

4.27.        A number of representative NSRs were selected for the assessment and are described in Table 4.5.  The locations of the representative NSRs are shown in Figure 4.2.

 

 

Table 4.5            Summary of Representative Noise Sensitive Receivers

 

Receiver	Name	Type
1) Chung Mei Village
CMV1	27, Chung Mei Village	R
CMV2	30, Chung Mei Village	R
CMV3	4, Chung Mei Village	R
CMV4	1, Chung Mei Village	R
CMV5	Village house, Chung Mei Village	R
CMV6	Village house, Chung Mei Village	R
2) Sok Kwu Wan Village
THT	Tin Hau Temple	T
SKW1	29, Sok Kwu Wan	R
SKW2	25, Sok Kwu Wan	R
SKW3	20, Sok Kwu Wan	R
SKW4	13, Sok Kwu Wan	R
SKW5	6, Sok Kwu Wan	R
SKW6	1B, Sok Kwu Wan (northern façade)	R
SKW7	28, Sok Kwu Wan	R
SKW8	21, Sok Kwu Wan	R
SKW9	15, Sok Kwu Wan	R
SKW10	2, Sok Kwu Wan	R
SKW11	1B, Sok Kwu Wan (eastern façade)	R
SKW 12	Public library	L
3) Isolated Receivers along the Coast of Ta Shui Wan
TSW1	2-storey village house at Ta Shui Wan	R
TSW2	3A, Ta Shui Wan	R
TSW3	3E, Ta Shui Wan	R
TSW4	1, Ta Shui Wan	R
4) Mo Tat Wan
MTW1	18, Mo Tat Wan	R
MTW2	17A, Mo Tat Wan	R

Note:                R – Residential                            T – Temple                   L - Library

 

 

Prediction and Evaluation of Environmental Impacts

 

Construction Phase

 

Pumping Station

 

4.28.        The construction of the pumping stations  would include excavation, formwork, reinforcement and fixing, concreting and backfilling.  PME will be required for these construction activities.  The sound power levels (SWLs) of typical equipment that will be adopted for the construction of the pumping stations are provided in Appendix 4.1. Unmitigated noise levels at the representative NSRs listed in Table 4.5 during the construction of the pumping stations were calculated.  The results are presented in Appendix 4.5. 

 

4.29.        The unmitigated noise levels during the construction of the pumping stations would be in the range of 38 to 89dB(A).  No exceedance of the noise criteria would be predicted with the exception of NSRs CMV1-6, THT, SKW12 and TSW1-2.  Owing to the close proximity of these NSR to the pumping station, 1-14dB(A) exceedances were predicted. Hence, mitigation measures would be required.

 

Sewage Treatment Plant (STW)

 

4.30.        The proposed STW would be constructed at the disused quarry located more than 200m away from the Refuse Transfer Station (Figure 4.2).  Since there was no NSR located within 300m from the construction site of the proposed STW, the noise impact arising from the construction activities of the STW would be not expected to be significant.  Hence, quantitative noise impact assessment for the construction of the STW was not included.

 

Sewer Alignment

 

4.31.        Construction of the sewer alignment would involve works, including pavement breaking, excavation, installation of pipes and bedding, backfilling and reinstatement of road surface.   The SWLs of the equipment assumed for the sewer construction are given in Appendix 4.2.  Unmitigated noise impacts from the sewers construction at the representative NSRs were calculated and are presented in Appendix 4.6.

 

4.32.        As shown in Appendix 4.6, the unmitigated noise levels at the NSRs were predicted to be in the range of 51 to 106 dB(A).  The majority of the NSRs would exceed noise levels by up to 31dB(A).  In view of the substantially exceedances of the noise criteria, mitigation measures would be required during the construction of the sewers.

 

Submarine Outfall

 

4.33.        Horizontal Directional Drilling (HDD) technique would be employed to construct the proposed submarine outfall pipeline.  The key activities of the HDD technique comprise erection of steel working platform, drilling and installation of HDPE pipeline, and installation of diffuser section by dredging. Details of the HDD technique are given in Appendix 2.1.  The SWLs of equipment for the HDD technique are provided in Appendix 4.3.  The erection of steel working platform would consist of three stages, including (i) setting up steel working platform, (ii) grouting and (iii) installation of steel casing in rock.  It is expected that the three stages would be carried out stage by stage and no concurrent operation of these activities is expected.  Hence, the SWL for setting up steel working platform (the highest SWL amongst the three stages) has been used for the prediction of the noise impact from the erection of steel working platform as a worst-case scenario.  Potential noise impact arising from the submarine outfall construction using the HDD technique were predicted and are provided in Appendix 4.7.

 

4.34.        The proposed submarine outfall would be located to the west of Mo Tat Wan Village.  The closest NSRs to the work site of the submarine outfall would be NSRs MTW1 and MTW2, which would be located more than 190m away from the work site.  The results show that the noise levels at NSRs MTW1 and MTW2 would be well below the 75dB(A) noise criterion.

 

Cumulative Impact

 

4.35.        As indicated in the preliminary construction programme (Appendix 4.1a), the pumping stations, sewer alignment and the submarine outfall will likely be constructed concurrently.  Cumulative noise impact from the construction of the pumping stations, sewer alignment and the submarine outfall was assessed.  The maximum noise levels predicted for each construction work were used to predict the cumulative noise impact as a worst-case scenario.  The unmitigated cumulative noise levels are presented in Table 4.6 below.

 

Table 4.6Cumulative Construction Noise Levels at Representative NSRs (Without Mitigation)

 

NSRs	Maximum Noise Level, dB(A)					Cumulative Noise Levels, dB(A)
	P1a	P1b	P2	Sewer	Submarine Outfall
CMV1	81.4	64.7	--	102.0	--	102
CMV2	89.4	77.7	--	99.5	--	100
CMV3	70.6	76.7	--	91.5	--	92
CMV4	82.7	82.7	--	89.9	--	91
CMV5	83.7	77.7	--	95.9	--	96
CMV6	87.5	77.4	--	95.9	--	97
THT	70.8	74.9	--	95.9	--	96
SKW1	69.4	72.4	--	99.5	--	100
SKW2	68.5	61.8	58	99.5	--	100
SKW3	--	59.9	59	102.0	--	102
SKW4	--	58.3	60	102.0	--	102
SKW5	--	--	62	85.5	--	86
SKW6	--	--	65	79.9	--	80
SKW7	59.0	72.2	--	79.9	--	81
SKW8	57.5	70.1	59	79.9	--	80
SKW9	--	68.6	60	79.9	--	80
SKW10	--	--	74	105.5	--	106
SKW11	--	--	75	95.9	--	96
SKW12	--	--	77	102.0		102
TSW1	--	--	84	95.9	--	96
TSW2	--	--	76	91.5	--	92
TSW3	--	--	74	95.9	--	96
TSW4	--	--	72	99.5	--	99
MTW1	--	--	--	65.9	67.1	70
MTW2	--	--	--	63.9	65.1	68

Note:

3 dB(A) facade effect was added in the calculation

--      The noise level at this particular NSR was negligible as it would be more than 300m away from the construction activity.

Boldface indicates an exceedance of the noise criteria of 75dB(A) for residential uses and 70dB(A) for Temple and library.

 

4.36.        The above table indicates that the cumulative noise levels at all NSRs would exceed the noise criteria, except NSRs MTW 1 and MTW2.  All the exceedances would be mainly attributable to the construction of the sewer alignment. 

 

Operational Phase

 

Pumping Stations

 

4.37.        Each pumping station would contain one duty and one standby submersible pumps situated below ground level in a wet well and under a cover, while the deodouriser would be installed at ground level as a separate unit.  The major sources during the operational noise from the pumping stations would be mainly contributed from the pump and the ventilation exhaust fan of the deodouriser.  A ventilation exhaust fan with 1700m³/hr at pressure of 125pa was assumed for the deodouriser.  Only one of the pumps would be in operation at any one time. Since the submersible pump would be enclosed in a reinforced concrete structure underground with removable covers, 10 dB(A) noise reduction was assumed.  The concrete walls would have a minimum thickness of 400mm.  The SWLs for the equipment used in the operation of the pumping stations are provided in Appendix 4.4.  The plant inventory list (including the assumed ventilation exhaust fan) has been confirmed with Project Proponent as being practicable for the operation of the pumping stations.

 

4.38.        Single operational noise impacts from each pumping station and cumulative operational noise impacts from the three pumping stations were predicted and are presented in Table 4.7.  The results indicate the noise levels during the operation of the Pumping Stations P1b and P2 would not exceed both daytime (55dB(A)) and nighttime (45dB(A)) noise criteria due to sufficient separation between the NSRs and the pumping stations.  Nevertheless, 1-3 dB(A) exceedance of the nighttime noise criterion at NSRs CMV2 and CMV6 were predicted due to the operation of Pumping Station P1a.  Hence, mitigation measures for the operation of Pumping Station P1a would be required.

 

Table 4.7Cumulative Operational Noise Levels at Representative NSRs (Without Mitigation)

 

Sensitive receiver	Distance between Noise Source and NSR, m			Single Noise Level, dB(A)			Cumulative Noise Level, dB(A)
	P1a	P1b	P2	P1a	P1b	P2
CMV1	60	130	--	39.9	33.2	--	41
CMV2	24	92	--	47.9	36.2	--	48
CMV3	66	104	--	39.1	35.2	--	41
CMV4	52	52	--	41.2	41.2	--	44
CMV5	46	92	--	42.2	36.2	--	43
CMV6	30	96	--	46.0	35.9		46
THT	204	128	--	29.3	33.4	--	35
SKW1	240	170	--	27.9	30.9	--	33
SKW2	266	182	288	27.0	30.3	26.3	33
SKW3	--	226	256	--	28.4	27.3	31
SKW4	--	272	212	--	26.8	29.0	31
SKW5	--	--	168	--	--	31.0	31
SKW6	--	--	130	--	--	33.2	33
SKW7	250	174	--	27.5	30.7	--	32
SKW8	300	222	260	26.0	28.6	27.2	32
SKW9	--	262	223	--	27.1	28.5	31
SKW10	--	--	140	--	--	32.6	33
SKW11	--	--	120	--	--	33.9	34
SKW12	--	--	103	--	--	35.2	35
TSW1	--	--	44	--	--	42.6	43
TSW2	--	--	118	--	--	34.1	34
TSW3	--	--	138	--	--	32.7	33
TSW4	--	--	188	--	--	30.0	30
MTW1	--	--	--	--	--	--	--
MTW2	--	--	--	--	--	--	--

Note:

Criteria: 55dB(A) (0700-2300 hrs); 45dB(A) (2300-0700 hrs)

3 dB(A) facade effect was added in the calculation

‘--'  Not applicable because NSR would be over 300m from the construction activities, unoccupied or unaffected Boldface indicate an exceedance of the noise criterion of 45dB(A)

 

STW

 

4.39.        As mentioned in Section 4.3 there would be no NSR located within 300m from the proposed STW.  The nearest NSR (TSW4) would be located at about 330m from the STW site and would be screened topographically.  Hence, no significant operational noise from the STW would be anticipated.  Quantitative noise impact assessment for the operation of the STW was not included.

 

 

Mitigation of Adverse Environmental Impacts

 

Construction Phase

 

4.40.        This assessment has considered normally adopted plant without assuming the use of special noise attenuating characteristics.  Source mitigation is an efficient and attractive method of mitigation.  This type of mitigation can be implemented at a site by the presentation of performance specifications for equipment in Contract Documentation.

 

Pumping stations

 

Use of Quiet PME

 

4.41.        As mentioned in Section 4.29, exceedance of the noise criterion was predicted at some NSRs during the concreting workconstruction of the pumping stations.  In order to reduce the construction noise impact, the use of quiet equipment for this construction activity was recommended.  The recommended quiet equipment for the concreting work at the pumping stations which is commercially available in Hong Kong are presented below:

 

Equipment	Reference	SWL, dB(A)
Hydraulic Breaker, excavator mounted	BS5228, Table C.8, item 13	110
Air Compressor	BS5228, Table C.7, item 24	95
Vibratory Poker, hand-held (Electric)	BS 5228, Table C.6, item 32	100

 

4.42.        With the adoption of the above quiet equipment, the total SWLs for the construction of the pumping stations are provided in Appendix 4.8.  The mitigated noise levels at the NSRs are presented in Appendix 4.9.  The results indicate that the mitigated noise levels at all NSRs would meet the noise criteria during the construction of the Pumping Stations P1b and P2, whereas exceedances at NSRs CMV2 and CMV6 would be expected during the construction of Pumping Station P1a.  Hence, further mitigation measures would be required.

 

Use of Temporary and Movable Noise Barriers

 

4.43.        In view of the site conditions of Pumping Station P1a, the use of temporary noise barrier in the form of site hoarding (with superficial density of at least 7 kg/m², with no substantial gaps), along the site boundary is considered to be practicable.  Considering the low-rise nature of the nearby NSRs, a 2.42.4 m high purpose-built site hoarding could screen their sensitive facades from viewing the ground-level construction equipment within the site of Pumping Station P1a.  With the implementation of the temporary noise barrier, a 5 dB(A) noise reduction was assumed.  Appendix 4.9a provides the mitigated noise levels with the implementation of the quiet equipment and temporary noise barrier.  The results indicate that no exceedance of the noise criteria was predicted.  Hence, no further mitigation measures would be required.   

 

Sewer Alignment

 

4.44.        To reduce construction noise impacts from the sewer construction, the following mitigation measures were recommended:

 

·        Good site practices.

·        Use of quiet PME or method; and

·        Restriction on the number plant.

 

Good Site Practices

 

·        Good site practices and noise management can provide considerable benefits in noise reduction.  The following site practices should be followed during the sewer construction.

 

-       Only well-maintained plant should be operated on-site and plant should be serviced regularly 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.

 

Use of Quiet PME

 

4.45.        The following quiet PMEs were recommended for the construction work of the sewer alignment.

 

Equipment	Reference	SWL, dB(A)
Air Compressor	BS5228, C.7, item 17	90
Vibratory Poker, hand-held (Electric)	BS 5228, Table C.6, item 40	98

 

4.46.        Apart from the above quiet equipment, the kick ripper (saw and lift) method was also recommended to replace the breaker for pavement removal.  Appendix 4.10 provides the total SWL for each construction activity with the adoption of the above quiet PME and the kick ripper method. 

 

4.47.        Based on the total SWLs in Appendix 4.10, mitigated noise levels at the representative NSRs for sewer construction were calculated and are provided in Appendix 4.11.  The results indicate that the majority of NSRs would still be exposed to noise levels in exceedance of the noise criteria during all construction activities of the sewer alignment.  Thus, additional mitigation measures would be required.

 

Restriction on Number of Plant Operating

 

4.48.        In combination with the adoption of quiet equipment, the total SWLs for various construction activities for sewer construction would be further reduced through restricting the number of plant to be used concurrently on-site.  A reduced plant inventory for the sewer construction was derived in Appendix 4.12.  With the mitigation applied, the noise impacts at the representative NSRs from the sewer construction were predicted and are presented in Appendix 4.13.  The results show that noise exceedances was still predicted at most of the NSRs.  

 

4.49.        Mitigated cumulative noise impact from the construction of the pumping stations, sewer alignment and the submarine outfall was also calculated based on the maximum noise levels predicted for each construction activity.  Table 4.8 presents the cumulative noise impact with the adoption of the recommended mitigation measures.  The results show that the majority of the NSRs would still experience residual impacts of up to 23 dB(A) even with the mitigation measures in place.  In order to further reduce the noise impact from the sewer construction, other possible mitigation measures were are considered in the following sections.

Table 4.8Cumulative Construction Noise Levels at Representative NSRs (With Mitigation)

 

NSRs	Maximum Noise Level, dB(A)					Cumulative Noise Levels, dB(A)
	P1a	P1b	P2	Sewer	Submarine Outfall
CMV1	65.1	53.4	--	94.1	--	94
CMV2	73.1	66.4	--	91.6	--	92
CMV3	6454.3	65.4	--	83.6	--	84
CMV4	66.4	71.4	--	82.0	--	82
CMV5	67.4	66.4	--	88.0	--	88
CMV6	71.2	66.1	--	88.0	--	88
THT	54.5	63.6	--	88.0	--	88
SKW1	53.1	61.1	--	91.6	--	92
SKW2	52.2	50.5	46.5	91.6	--	92
SKW3	--	48.6	47.5	94.1	--	94
SKW4	--	47.0	49.2	94.1	--	94
SKW5	--	--	51.2	77.6	--	78
SKW6	--	--	53.4	72.0	--	72
SKW7	42.7	60.9	--	72.0	--	72
SKW8	41.2	58.8	47.4	72.0	--	72
SKW9	--	57.3	48.7	72.0	--	72
SKW10	--	--	62.8	97.6	--	98
SKW11	--	--	64.1	88.0	--	88
SKW12	--	--	65.4	94.1	--	94
TSW1	--	--	72.8	88.0	--	88
TSW2	--	--	64.3	83.6	--	84
TSW3	--	--	62.9	88.0	--	88
TSW4	--	--	60.2	91.6	--	92

Note:

3 dB(A) facade effect was added in the calculation

--      The noise level at this particular NSR was negligible as it would be more than 300m away from the construction activity.

Boldface indicates an exceedance of the noise criteria of 75dB(A) for residential uses and 70dB(A) for temple and library.

 

Other Possible Mitigation Measures

 

4.50.        The possible mitigation measures to further reduced the noise impacts could include:

 

Other Possible Mitigation Measures

 

4.1.The possible mitigation measures to further reduced the noise impacts could include:

4.1. 

Use of Noise Screening Structures

 

·          Owing to the severity of noise exceedances, the use of noise screening structures such as temporary/movable noise barrier or acoustic enclosure/shed for the sewer construction has been considered.  According to the GW-TM, a 10dB(A) noise reduction could be achieved when all items of PME to be used on site are totally screened by a substantial barrier.  In accordance with the EPD’s A Practical Guide for the Reduction of Noise from Construction Works, an acoustic enclosures with inside lined with sound absorbing material can achieve a noise reduction of up to 20dB(A).  The proposed sewers would be aligned along the existing footpaths from Chung Mei Village through Sok Kwu Wan First Street, Second Street, Side Streets and Mo Tat Road to the proposed STW.  The majority of the footpath and streets within the villageswere only a few metres in width and sometimes with structures such as air conditioners and canopies protruding.  Considering of the site constraints, the use of noise screening structures would maynot be practicablein most areas large sized PME, such as excavator, lorry and mobile crane.

 

·            

·            

·           For the section of sewer construction along the footpath or streets outside the villages, the use of movable noise barriers is considered more feasible owing to the provision of more space for erecting the noise screening structure and without the air conditioners and canopies protruding.  Considering the low rise nature of the NSRs (2-3 storeys village houses), a noise screening structure (with a superficial density of at least 7 kg/m², with no substantial gaps) located close to the noise generating part of a PME could produce at least 10 dB(A) screening for stationary plant such as poker vibratorhand-held breaker and 5 dB(A) for mobile plant such as excavator, mobile cranekick ripper and compactor, provided it blocked the direct line of sight between the PME and the NSR.  Figure 4.3 shows a typical design of the noise screening structures.

 

 

·           During pavement breaking, rock removal in the course of trench excavation and concreting work of manhole, the use of PME such as kick ripper, hand-held breaker and vibratory poker would likely be necessary.  As mentioned above, due to the space constraints and protruding structures, the use of noise screening structures within the alleyways of villages would not be feasible in most areas.  Up to 23 dB(A) noise exceedances were predicted at some NSRs due to the physical constraints of the work area that the acoustic shed could not be employed and the close proximity of the NSRs to the work sites.  Considering the substantial noise exceedances from the operation of these equipment, noise screening structure in the form of acoustic shed as shown in Figure 4.3 should be adopted wherever practicable in an area with sufficient clearance and headroom and this should be determined by the Contractor on site.  It is assumed that 10 dB(A) noise reduction could be achieved for hand-held breaker and 5 dB(A) reduction for kick ripper (Appendix 4.14a) with the use of the acoustic shed.  As indicated in Appendix 4.14b, around 2-14 dB(A) noise exceedances would be expected with the implementation of the acoustic shed.  Since individual section of the sewer construction work would be carried out in a linear fashion, any given sensitive receiver experiencing worst-case noise impact would last for only a short period.  In general, for every 20 m length of sewer, it would take about ½ day for breaking pavement and 7 days for trenching.  It is noted that the trenching work would continue intermittently over the period of a day but would also be on-going for only 1-2 hours in one go.  In addition, the use of breaker would only be applied for rock removal in the course of trench excavation.  Hence, the residual impact would be infrequent and transient.

 

·        During concreting work of manhole, it is considered feasible to use a small acoustic shed as shown in Figure 4.4 to screen noise from the operation of the vibratory poker.  It is considered that 10 dB(A) noise reduction could be achieved with the use of the acoustic shed (with a superficial density of at least 7 kg/m²).  Given the distance between the NSR and manhole is 3 m and the vibratory poker (hand-held, electric) with SWL of 98dB(A), the noise level at the NSRs was predicted to be about 73dB(A), complying with the EIAO-TM noise criterion.  Nevertheless, 2-8 dB(A) exceedances would likely occur at receivers located less than 3m from a manhole.  Since the use of vibratory poker for the concreting work of a manhole would be very short and infrequent and works in any one location could be completed less than an hour, the residual impact if occur would be transient and localized. 

 

 

Manual working for Sewer Construction

 

·        For area where noise exceedances were predicted, the use of manual working (i.e. use of hand tools) has been considered.  Adoption of manual working for sewer construction could eliminate noise impact arising from the use of PME.  However, this method would be slower and require more manpower in comparison with the method using PME and its practicability would depend on the nature of the works.  A longer construction period would cause greater inconvenience to the residents, visitors and in particular, the restaurants.  The use of the manual working would be subject to the construction programme, manpower constraints and the nature of works.  Notwithstanding, in view of the substantial exceedances of the criterion, it is recommended that manual working should be adopted wherever practicable and feasible in areas where the worksites of the proposed sewer alignment are located less than 20 m from the residential NSRs and less than 30 m from the temple (THT) and the public library. 

For area where the use of noise screening structures could not be applied and/or exceedances were predicted, the use of manual working (i.e. use of hand tools) has been considered.  Adoption of manual working for sewer construction (breaking up pavement, excavation of trench, installation of pipes and bedding, backfilling and reinstatement)could eliminate noise impact arising from the use of PME.  However, this method would be slower and require more manpower in comparison with the method using PME and its practicability would depend on the nature of the works.  A longer construction period would cause greater inconvenience to the residents, visitors and in particular, the restaurants.  The use of the manual working would be subject to the construction programme, manpower constraints and the nature of works.  Notwithstanding, in view of the substantial exceedances of the criterion, it is recommended that manual working should be adopted wherever practicable and feasible in areas where the worksites of the proposed sewer alignment are located less than 20 m from the residential NSRs and less than 30 m from the temple (THT) and the public library.  Figure 4.4 shows the areas (including Chung Mei Village, Sok Kwu Wan Village and Ta Shui Wan) where the use of PME should not be adopted wherever possible.

 

4.51.        With the adoption of the movable noise barrier and the manual working, the noise impacts at the NSRs from the sewer construction were predicted and are presented in Appendices 4.14 15aand 4.1515b.  The results indicate that no exceedance of the noise criteria at all NSRs was predicted during the sewer construction. 

 

4.52.        Mitigated cumulative noise impact from the construction of the sewer alignment and pumping stations was also calculated based on the maximum noise levels predicted for each construction activity.  Table 4.8a below presents the mitigated cumulative noise impact if manual working could be applied. 

 

Table 4.8aCumulative Construction Noise Levels at Representative NSRs (With the Adoption of Quiet Equipment, Restriction on Number of Plant Operating, Use of Noise Screening Structures and Manual Working)

 

NSRs	Maximum Noise Level, dB(A)					Cumulative Noise Levels, dB(A)
	P1a	P1b	P2	Sewer	Submarine Outfall
CMV1	65.1	53.4	--	71.169.8	--	7271
CMV2	73.1	66.4	--	71.169.8	--	7675
CMV3	6454.3	65.4	--	71.169.8	--	7272
CMV4	66.4	71.4	--	71.169.8	--	7574
CMV5	67.4	66.4	--	71.169.8	--	7473
CMV6	71.2	66.1	--	71.169.8	--	7574
THT	54.5	63.6	--	67.666.3	--	6968
SKW1	53.1	61.1	--	71.169.8	--	7270
SKW2	52.2	50.5	46.5	71.169.8	--	7170
SKW3	--	48.6	47.5	71.169.8	--	7170
SKW4	--	47.0	49.2	71.169.8	--	7170
SKW5	--	--	51.2	71.169.8	--	7170
SKW6	--	--	53.4	61.159.8	--	6261
SKW7	42.7	60.9	--	61.159.8	--	6463
SKW8	41.2	58.8	47.4	61.159.8	--	6362
SKW9	--	57.3	48.7	61.159.8	--	6362
SKW10	--	--	62.8	71.169.8	--	7271
SKW11	--	--	64.1	71.169.8	--	7271
SKW12	--	--	65.4	67.666.3	--	7069
TSW1	--	--	72.8	71.169.8	--	7575
TSW2	--	--	64.3	71.169.8	--	7271
TSW3	--	--	62.9	71.169.8	--	7271
TSW4	--	--	60.2	71.169.8	--	7170

Note:

3 dB(A) facade effect was added in the calculation

--      The noise level at this particular NSR was negligible as it would be more than 300m away from the construction activity.

Boldface indicates an exceedance of the noise criteria of 75dB(A) for residential uses and 70dB(A) for temple and library.

 

4.53.        As indicated in the above table, all NSRs would comply with the noise criteria, except at NSR CMV2.  The exceedances at this receiver would be mainly due to the cumulative effect from the construction of Pumping Station P1a and the section of sewer between the NSR and the pumping station.  In order to reduce the cumulative noise impact at this NSR, the use of PME for the construction of this section of sewer should not be allowed during the excavation work of Pumping Station P1a.As indicated in the above table, all NSRs would comply with the noise criteria with the implementation of the above mitigation measures.

 

4.1.        It is noted that the use of PME could not be totally excluded during sewer construction due to the nature of the works and site conditions.  During concrete breaking, trenching if come across rock and construction of sewer will include the construction ofconcreting work of manhole, the use of PME such as kick ripper, hand-held breaker and vibratory poker would be unavoidable. 

4.1.         

4.1.        To minimize the potential impacts from concrete breaking and trenching, quiet equipment and restriction on the number of PME as recommended in Sections 4.44-49 would be adopted.  Owing to the small sized of the hand-held breaker and kick ripper, it is considered thatnoise screening structure in the form of acoustic shed as shown in Figure 4.3 is practicable to be appliedduring the sewer construction.  It is assumed that 10 dB(A) noise reduction could be achieved for hand-held breaker and 5 dB(A) reduction for kick ripper.  During the concreting work of manhole, the use of vibratory poker is considered necessary and hence the use of PME could not be totally excluded within the areas specified in Figure 4.4.  As indicated in Appendix 4.15a, around 2-12 dB(A) noise exceedances would still be expected with the implementation of these mitigation measures.  Since individual section of the sewer construction work would be carried out in a linear fashion, any given sensitive receiver experiencing worst-case noise impact would last for only a short period.  In general, for every 20 m length of sewer, it would take about ½ day for breaking pavement and 7 days for trenching.  It is noted that the use the breaker for trenching would be only applied if hand-dig is not feasible, e.g. the present of rockshort-term. 

4.1.        During concreting work of manhole, it is considered feasible to use a small acoustic shed as shown in Figure 4.5 to screen noise from the operation of the vibratory poker.  It is considered that 10 dB(A) noise reduction could be achieved with the use of the acoustic shed (with a superficial density of at least 7 kg/m²).  Given the distance between the NSR and manhole is 3 m and the vibratory poker (hand-held, electric) with SWL of 98dB(A), the noise level at the NSRs was predicted to be about 73dB(A), complying with the EIAO-TM noise criterion.  Nevertheless, 2-8 dB(A) exceedances would likely occur at receivers located less than 3m from a manhole.  Since the use of vibratory poker for the concreting work of a manhole would be very short and infrequent and works in any one location could be completed less than an hour, the residual impact if occur would be transient and localized. 

4.1.         

4.1.        With the adoption of the recommended mitigation measures, no exceedance of the EIAO-TM noise criteria would be expected, except short short-term exceedances during the sewer construction.  ISince it is considered that all practicable mitigation measures have been exhaustedly deployed.  , no further mitigation measure is considered. 

4.1.         

4.54.        The purpose of the Project is to improve the water quality at the Picnic Bay by eliminating the untreated or partially treated wastewater directly discharged to the inner Picnic Bay.  The construction of the sewer alignment is an integral element of the Projects and cannot be avoided.  Owing to the close proximity of the NSRs, site constraints and nature of works, residual impacts from the sewer construction works are expected.  However, considering the short duration of these impacts, the residual impacts, they are considered acceptable in light of the overall environmental benefits of the Project.

 

 

4.1.According to the consultation with Islands District Council, Lamma Area Committee and South Lamma Rural Committee, the Project was generally supported and they expressed their concerns on the construction sequence of sewer laying works along Sok Kuw Wan First Street where restaurants are located.  They requested that the following restrictions be applied when laying sewers along the Sok Kwu Wan First Street:

 

·No works should be carried out during the summer months, weekends and the public holidays

·Works be completed before dinner time on each working day with works area clear of obstruction and trenches covered;and

·Ground breaking activities be confined to limited hours before lunch.

 

4.1.In response of their concerns, the above suggestions would be taken into consideration during the detailed design of the Project in order to miminimse the nuisances and inconvenience from the construction of the proposed sewer alignment. 

 

Operational Phase

 

4.55.        Exceedances of the nighttime noise criterion at NSRs CMV2 and CMV6 were predicted during the operation of Pumping Station P1a.  To mitigate the operational noise impact, it was recommended to install a silencer at the air discharge point of the deodouriser at Pumping Station P1a.  The installation of silencer is to be carried out by the E&M Contractor.  To ensure that the noise impact from the pumping station would comply with the nighttime noise criterion, the silencer recommended for the deodouriser should be capable of achieving at least 8dB(A) noise reduction.  Appendix 4.16 provides the total SWL for the operation of Pumping Station P1a with the adoption of the silencer.

 

4.56.        Based on the total SWL in Appendix 4.16, the operational noise impacts from the Pumping Station P1a were predicted and are shown in Table 4.9 below. The results indicate that the operational noise levels from the Pumping Station P1a at all NSRs would meet the night-time noise criterion of 45dB(A).

 

Table 4.9Cumulative Operational Noise Levels at Representative NSRs (With the Installation of Silencer)

 

Sensitive receiver	Distance between Noise Source and NSR, m			Single Noise Level, dB(A)			Cumulative Noise Level, dB(A)
	P1a	P1b	P2	P1a	P1b	P2
CMV1	60	130	--	35.9	33.2	--	38
CMV2	24	92	--	43.9	36.2	--	45
CMV3	66	104	--	35.1	35.2	--	38
CMV4	52	52	--	37.2	41.2	--	43
CMV5	46	92	--	38.2	36.2	--	40
CMV6	30	96	--	42.0	35.9		43
THT	204	128	--	25.3	33.4	--	34
SKW1	240	170	--	23.9	30.9	--	32
SKW2	266	182	288	23.0	30.3	26.3	32
SKW3	--	226	256	--	28.4	27.3	31
SKW4	--	272	212	--	26.8	29.0	31
SKW5	--	--	168	--	--	31.0	31
SKW6	--	--	130	--	--	33.2	33
SKW7	250	174	--	23.5	30.7	--	31
SKW8	300	222	260	22.0	28.6	27.2	31
SKW9	--	262	223	--	27.1	28.5	31
SKW10	--	--	140	--	--	32.6	33
SKW11	--	--	120	--	--	33.9	34
SKW12	--	--	103	--	--	35.2	35
TSW1	--	--	44	--	--	42.6	43
TSW2	--	--	118	--	--	34.1	34
TSW3	--	--	138	--	--	32.7	33
TSW4	--	--	188	--	--	30.0	30

Note:

Criteria: 55dB(A) (0700-2300 hrs); 45dB(A) (2300-0700 hrs)

3 dB(A) facade effect was added in the calculation

‘--'  Not applicable because NSR would be over 300m from the construction activities, unoccupied or unaffected Boldface indicate an exceedance of the noise criterion of 45dB(A)

 

4.57.        The above table also shows the cumulative noise impacts from the operation of P1a (with silencer), P1b, and P2.  It indicates that the cumulative noise levels from the operation of the three pumping stations would be within the daytime and nighttime noise criteria.  Hence, further mitigation measures would not be required.

 

Definition and Evaluation of Residual Environmental Impacts

 

4.58.        No residual noise impacts would be expected, except short term residual impacts during the concreting sewer construction.  However, it is considered that all practicable mitigation measures have been exhausted and this unavoidable noise impact would be transient and localized.  Having considered that the construction of the sewer alignment is unavoidable as it is an integral element of the Project and the short duration of the sensitive receiver experiencing the impacts, these short-term residual impacts were considered acceptable.

 

4.59.        No residual noise impacts would be anticipated during the operation of the Project.

 

Environmental Monitoring and Audit

 

4.60.        An Environmental Monitoring and Audit (EM&A) programme was recommended according to the predicted occurrence of noisy activities.  All the recommended mitigation measures should be incorporated into the EM&A programme for the implementation during construction.  Details of the programme are provided in a stand-alone EM&A Manual.