4.2 Environmental Legislation, Standards and Guidelines
4.3 Descriptions of Environment
4.4 Identification of Potential Noise Impact
4.6 Assessment Methodology, Prediction and Evaluation of
Environmental Impacts
4.7 Evaluation and Recommendation of Noise Mitigation
Measures
4.8 Evaluation of Residual Impacts
4.9 Environmental Monitoring and Audit Requirements
4
NOISE IMPACT ASSESSMENT
4.1.1
This
Chapter presents an assessment of the potential noise impact arising from the
construction and operation of the Project. Mitigation measures have been
identified to alleviate the impact and their effectiveness has been evaluated.
4.2
Environmental Legislation, Standards
and Guidelines
Construction Noise
4.2.1
The Noise Control Ordinance (NCO) (Cap. 400)
provides the statutory framework for noise control in Hong Kong. Assessment
procedures and standards are set out in the respective Technical Memoranda (TM)
promulgated under the NCO. The following
TMs are applicable to the assessment and control of construction noise.
·
Technical
Memorandum on Noise from Construction Work other than Percussive Piling
(TM-GW);
·
Technical Memorandum on Noise from Percussive
Piling (TM-PP); and
·
Technical Memorandum on Noise on Construction
Work in Designated Areas (TM-DA)
·
Technical
Memorandum on Noise from Places other than Domestic Premises, Public Places or
Construction Sites (TM-IND)
4.2.2
Both the percussive piling and construction
work under restricted hours require a construction noise permit (CNP) in order to carry out such work. As
the issuance of a CNP by the Noise Control Authority would depend on the compliance
of percussive piling noise impact or construction noise impact with the limits set out within
the TM-PP and TM-GW/TM-DA, the assessment of this type of noise would not be covered in the EIA
report.
4.2.3
For construction, there is no statutory limit on daytime construction
noise under the NCO and related TMs.
Nevertheless, the “Technical
Memorandum on Environmental Impact Assessment Process” (EIAO-TM) stipulates noise standards for
daytime construction activities, as shown Table 4-1.
Table
4-1: Construction Noise
Standards during Non-Restricted Hours
Uses |
Noise
Standards [1] , Leq (30 mins) dB(A) |
|
0700 to 1900 hours on any day not being a Sunday or general holiday |
1900 to 0700 hours or any time on Sundays or general holiday |
|
All domestic premises including
temporary housing accommodation |
75 |
(See Note 2) |
Hotels and hostels |
75 |
|
Educational institutions
including kindergartens, nurseries and all others where unaided voice
communication is required |
70 65 (During examinations) |
Notes:
[1] The above standards apply to uses that rely
on opened windows for ventilation.
[2] The criteria laid down in the relevant
technical memoranda under the NCO for designated areas and construction works
other than percussive piling may be used for planning purpose. A Construction
Noise Permit (CNP) shall be required for the carrying out construction work
during the period.
Construction Noise
during Restricted Hours
4.2.4
The NCO provides statutory control on
general construction works (excluding percussive piling) conducted during
restricted hours (i.e. 1900 to 0700 hours (of the next day) from Monday to
Saturday and at any time on Sundays or in public holidays). A Construction
Noise Permit (CNP) is required for carrying out of any general construction
activities involving the use of any Powered Mechanical Equipment (PME) within
restricted hours from the Authority under the NCO. The noise criteria and the
assessment procedures for issuing a CNP are specified in the TM-GW under the NCO.
4.2.5
The use of Specified PME (SPME) and/or the
undertaking of Prescribed Construction Work (PCW) within a Designated Area (DA)
under the NCO during the restricted hours are controlled by the TM-DA. The
relevant technical details in Technical Memorandum on Noise from Construction
Work in Designated Areas (TM-DA) under NCO can be referred. The acceptable
noise levels for construction during the restricted hours are summarized in Table 4-2 below.
Table 4-2: Construction Noise Standards during Restricted
Hours
Uses |
Acceptable Noise
Level for Area Sensitive Ratings, dB(A) |
||
A |
B |
C |
|
All weekdays
during the evening (1900 to 2300 hours), and general holidays (including
Sundays) during the day and evening (0700 to 2300 hours) |
60 |
65 |
70 |
All days during
the night-time (2300 to 0700 hours) |
45 |
50 |
55 |
4.2.6
The Area Sensitive Rating depends on the
type of area and the degree of impact that Influencing Factors (IFs) have on
the NSRs and is determined from Table 4-3 below. Industrial
area, major road or the area within the boundary of Hong Kong International
Airport shall be considered to be an IF.
Table 4-3: Area
Sensitivity Ratings (ASRs)
Type of Area containing NSR |
Degree to which NSR is affected by IF |
||
Not Affected |
Indirectly Affected |
Directly Affected |
|
(i)
Rural area, including country parks or village type developments |
A |
B |
B |
(ii)
Low density residential area consisting of low-rise or isolated high-rise
developments |
A |
B |
C |
(iii)
Urban area |
B |
C |
C |
(iv)
Area other than those above |
B |
B |
C |
4.2.7
According to the preliminary construction
programme, it is very likely that the proposed construction works would be
carried out during non-restricted hours only. For carrying out any general construction
activity involving the use of any Powered Mechanical Equipment (PME) within
restricted hours, a Construction Noise Permit (CNP) is required from the
authority under the NCO. The noise criteria and the assessment procedures for
issuing the CNP are specified in the TM-GW under the NCO. There is no guarantee that a CNP will be issued for the
project construction. The Noise Control Authority will consider a well
justified CNP application, once filed, for construction work within restricted
hours as guided by the relevant TMs issued under the NCO. It is
the Contractor’s responsibility to ensure compliance with the NCO and the
relevant TMs in case of any construction activities during restricted hours.
4.2.8 The Noise Control Ordinance (NCO) and Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) were followed for assessing the noise from powered mechanical equipment (PME) for different sensitive uses.
Construction
Ground-Borne Noise
4.2.9 According to the TM-GW, the Area Sensitivity Rate of the area in which the identified NSRs are located is “A”. Moreover, the TM-IND under NCO mentioned that where the noise under investigation is transmitted primarily through the structural elements of the building or if the assessment point is at an internal location of a building, an adjustment of -10 dB(A) should be made to relevant acceptable noise levels (ANLs). The relevant noise limits for ground-borne noise are tabulated in Table 4-4.
Table 4-4 Ground-borne Construction Noise Limits
Time Period |
Uses |
Noise Standard (Leq, 30 min dB(A)) |
(1)Day-time |
Domestic Premises |
65 |
Educational institutions (normal periods) |
60 |
|
Educational institutions (during examination periods) |
55 |
|
(1)Evening-time |
All Noise Sensitive Uses |
50 |
(1)Night-time |
All Noise Sensitive Uses |
35 |
(1)
assessment point is at a
particular internal location
Operational
Noise
4.2.10 Noise from the proposed sewage treatment plant (STP) is considered as the only fixed noise source during the operation phase of the Project. Operational noise is controlled under the Noise Control Ordinance (NCO)’s Technical Memorandum on Noise from Places other than Domestic Premises, Public Places or Construction Sites (TM-IND).
4.2.11 According to the TM-IND, appropriate Area Sensitivity Ratings should be determined for the NSRs under consideration from Table 1 of the TM-IND. Then, the appropriate Acceptable Noise Level (ANL) for a given NSR and the time period under consideration could be read from Table 3 of TM-IND. According to the TM-IND, the ANLs for different Area Sensitivity Ratings (ASRs) of noise sensitive receivers (NSRs) are given in Table 4-5.
Table 4-5 Acceptable Noise Levels
Time Period |
ASR A |
ASR B |
ASR C |
All days during
the evening (1900 to 2300 hours), and general holidays (including Sundays) during
the day-time and evening (0700 to 2300 hours) |
60 |
65 |
70 |
All days during
the night-time (2300 to 0700 hours) |
50 |
55 |
65 |
4.2.12
More stringent criteria for fixed plant noise impacts recommended in
Table 1A of the EIAO-TM for planning purposes are as follow:
·
5 dB(A)
below the appropriate ANL set out in the TM-IND (the ANL–5 dB(A) criterion), or
·
The
prevailing background noise level where the prevailing background noise level
is 5 dB(A) below the appropriate ANL (although during the operation the NCO
will be the controlling legislation).
4.2.13 In this Project, the study area covering 300m from the proposed works boundary (as shown in Figure 4-1) is identified as rural area consisting village type developments without being affected by IF thus the NSRs are assigned an Area Sensitive Rating of “A”.
4.2.14 In order to determine the appropriate criteria for noise assessment, background noise survey was carried out during the course of the EIA process at two locations to determine the baseline noise levels. Noise monitoring was conducted for 14 consecutive days in November 2014. Locations of the monitoring stations are summarised in Table 4-6 and shown on Figure 4-1. For those sensitive receivers which were found to experience prevailing noise levels lower than the ANL-5dB(A) criterion, fixed plant noise impact were assessed against the prevailing background noise levels.
Table 4-6 Background
Noise Monitoring Results at Selected NSRs in Po Toi O
Time Period |
Measurement Parameter |
Noise Level (dB(A)) |
||||||
NM1 - Near Local Resident |
NM2 - Near Fairway Vista |
|||||||
Max. |
Min. |
Average |
Max. |
Min. |
Average |
|||
Daytime |
0700 -1900 |
Leq30min |
62 |
52 |
57 |
66 |
51 |
58 |
Evening Time |
1900 - 2300 |
Leq5min |
62 |
53 |
57 |
59 |
49 |
53 |
Night Time |
2300 - 0700 of next day |
Leq5min |
56 |
46 |
51 |
53 |
47 |
50 |
4.2.15
The lowest recorded background noise level during daytime/evening period
was 49 dB(A). Since the background noise level was 6 dB(A) lower than the ANL -5
dB(A), the noise criteria for daytime/evening time periods will adopt the prevailing background noise
level of 49 dB(A). As the lowest nighttime background
noise level was 1 dB(A) higher than the ANL-5dB(A), noise criterion of 45 dB(A)
is adopted for nighttime period. The operational phase noise criteria are
summarized in Table 4-7.
Table 4-7 Acceptable Noise Levels (ANLs) during
Operational Period
Time Period |
Acceptable Noise Levels
(ANLs), dB(A) |
(ANL -5) dB(A) |
Prevailing Background dB(A) |
*Noise Criteria dB(A) |
Day
(0700 to 1900 hours) |
60 |
55 |
49 |
49 |
Evening
(1900 to 2300 hours) |
||||
Night
(2300 to 0700 hours) |
50 |
45 |
46 |
45 |
* ANL – 5dB(A) or the prevailing background
noise levels (for quiet areas with level 5dB(A) below the ANL).
4.3
Descriptions of Environment
4.3.1 The village to be sewered is situated within a quiet rural area, with some of the surrounding open land used as a golf course, recreational areas and seafood restaurants. Noise levels in this village are generally very low with little noise influence from outside of the village.
4.4
Identification of Potential Noise
Impact
4.4.1
During
the construction phase, use of powered mechanical equipment (PME) will
inevitably generate construction noise and hence may cause noise nuisance to the nearby
residences. During the operational phase, equipment noise from the proposed sewage treatment plant will be the main noise source with potential noise impact on
the NSR.
4.5.1
The
Study Area covered 300m from the proposed works
boundary as shown in Figure 4-2.
Given the proximity of the STP and associated sewerage works to the Po Toi O
village, noise sensitive receivers in the village are likely to
be affected by the Project during its construction and operation. Noise sensitive
receivers have been identified from the Approved Clear Water Bay Peninsula
South Outline Zoning Plan, S/SK-CWBS/2, and 1:1000 survey plans of the area. In
addition, site visits have been carried out to identify the NSR and
representative worst impact points of the identified NSR. In general, the
sewers are laid 2m away from and in parallel to NSRs. A list of the identified
NSR and their locations are depicted in Figure 4-2 and listed in Table 4-8 below. Photographic record can be found in Appendix 4.4.
Table
4-8 Representative Noise Sensitive Receivers
NSR |
Description |
Land
Use |
Ground
mPD |
Notional
Noise Distance (m) from NSR |
No.
of Storey |
||
Pipes |
Po
Toi O Chuen Road Sewer Pipe |
Sewage
Treatment Plant |
|||||
PTO_N1 |
Village
House in PTOCR 28 |
Village |
6 |
4 |
37.8 |
77.5 |
2 |
PTO_N2 |
Village
House in PTOCR 7A |
Village |
4.1 |
4.2 |
167.4 |
203.4 |
*3 |
PTO_N3 |
Temporary
Structure for living |
Village |
4.5 |
5.9 |
332.6 |
356.8 |
1 |
FV_N1 |
Fairway
Vista House 12 |
Village |
7.5 |
2 |
331.5 |
352.6 |
3 |
SC_N1 |
Seacrest
Villas in PTOCR No. 64 |
Village |
25.1 |
10.2 |
195.8 |
213.3 |
3 |
Noted: PTOCR = Po Toi O Chuen Road
* Ground floor of PTO_N2 is a seafood
restaurant. Only first and second floors are considered as NSR.
4.5.2
The village zone within or near the proposed sewerage
works covers the Po Toi O Village, Seacrest Villas and Fairway Vista. The land
on both sides of the proposed pipe alignment has already been fully occupied by
houses. No future addition of NSR is expected. Even if a house will be squeezed
into the already crowded land, it will only be of similar distance or further
away from the sewerage works when compared with the existing houses. This noise
assessment will be sufficient in assessing and evaluating the potential noise
impact.
4.6
Assessment Methodology, Prediction and Evaluation of Environmental Impacts
4.6.1
Noise impact assessment was conducted in accordance with the
requirements in EIAO-TM Annex 5 and 13.
Construction Noise
4.6.2
The Project comprises three main works including the construction of
sewage treatment plant (STP), underground sewers and rising mains, and the
submarine outfall.
4.6.3 Detailed construction method, sequence of works and the plant inventory in different work stages were proposed at the time of this EIA. Until a contractor is appointed, full details of the types and utilization of construction plants will not be known exactly. Typical types and number of powered mechanical equipment (PME) needed for various construction activities for the construction of STP and pipes installation have been assigned as shown in Tables 4-9 to 4-13 below. PME that will likely be used concurrently have been grouped within the same works stage. The project engineer has reviewed the currently proposed construction programme and methodology including list of PME items, percentage on-time assumptions, etc. such that they are considered practicable and appropriate for this project.
4.6.4 As not every item of PME would be operated all the time when it is on site, a typical percentage on time was assumed for each PME based on experience in actual site practice so that the noise prediction exercise would be a more realistic one. Accordingly, the effective sound power levels for each construction activity were quantified and are listed in the same table.
Construction of Sewage Treatment Plant
4.6.5
The construction of STP will include earthworks, trench support and ground compaction works, general
concrete building works, backfilling and surfacing works. Common construction plant including hydraulic breaker,
excavator/loader, concrete lorry mixer, vibratory poker, lorry and the like
will be used. Typical plant list
for STP construction is shown in Table
4-9.
Table 4-9: Typical PME to be used for Construction of Sewage
Treatment Plant
Activity |
Noise Source |
TM-GW Reference Number |
Nos. used |
SWL, dB(A) |
% on time |
Effective SWL in a 30 min period |
Overall SWL |
Stage I |
Earth Works |
||||||
1.1 |
Hydraulic breaker |
CNP 028 |
2 |
122 |
50% |
122 |
123 |
Excavator / loader |
CNP 081 |
2 |
112 |
80% |
114 |
||
Lorry |
CNP 141 |
2 |
112 |
30% |
110 |
||
|
|
|
|
|
|
|
|
Stage II |
Trench Support &
Ground Compaction |
||||||
2.1 |
Vibrating hammer (piling) |
CNP 172 |
2 |
115 |
80% |
117 |
118 |
Roller, vibratory |
CNP 186 |
2 |
108 |
80% |
110 |
||
|
|
|
|
|
|
|
|
Stage III |
|
||||||
3.1 |
Vibratory poker |
CNP 170 |
2 |
113 |
80% |
115 |
117 |
Concrete Lorry Mixer |
CNP 044 |
2 |
109 |
100% |
112 |
||
|
|
|
|
|
|
|
|
Stage IV |
Backfilling |
||||||
4.1 |
Backhoe |
CNP 081 |
1 |
112 |
80% |
111 |
112 |
Roller, vibratory |
CNP 186 |
1 |
108 |
60% |
106 |
||
|
|
|
|
|
|
|
|
Stage V |
Surfacing |
||||||
5.1 |
Vibratory poker |
CNP 170 |
1 |
113 |
80% |
112 |
114 |
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
100% |
109 |
||
|
|
|
|
|
|
|
|
Installation of Gravity Sewers and Rising Mains
4.6.6
Trenchless method is proposed for the laying of rising mains from the STP
to the footpath between village house no.23 and no.28 of Po Toi O Village,
which will be deep down to 10m underground. Since the launching site is located
at the STP, no additional power mechanical equipment is required for excavation
and backfilling work for the launching site. Pipe jacking machine (e.g.
hydraulic jack) would be applied underground. Therefore, the noise generated
for pipe laying under trenchless method is relatively small when compared to
other concurrent works and hence was not considered in the quantitative
construction noise assessment. The generator for powering the pipe jacking
machine will be located at the sewage treatment plant site over 77.5m away from
the nearest NSR. The noise from generator at NSR will be reduced to low level
that will have no major contribution to the overall construction noise level at
the NSR. This construction method is commonly applied in pipe laying in village
area. The ground compositions in the first few meters are soil and sand. No
significant groundborne noise impact is expected.
Table 4-10: Typical PME to be
used for Installation of Rising Mains (Trenchless Method)
Activity |
Noise
Source |
TM-GW
Reference Number |
Nos.
used |
SWL,
dB(A) |
%
on time |
Effective
SWL in a 30 min period |
Overall
SWL |
- |
Generator, portable |
CNP 107 |
1 |
100 |
100% |
100 |
100 |
|
|
|
|
|
|
|
|
Table
4-11: Typical PME to be used for Installation of Gravity Sewers and Rising Mains (Open Cut Method)
Activity |
Noise
Source |
TM-GW
Reference Number |
Nos.
used |
SWL,
dB(A) |
%
on time |
Effective
SWL in a 30 min period |
Overall
SWL |
|||||||
Stage I |
Excavation |
|||||||||||||
1.1 |
Breaker, hand held |
CNP 026 |
1 |
114 |
60% |
112 |
112 |
|||||||
Generator, portable |
CNP 107 |
1 |
100 |
60% |
98 |
|||||||||
|
|
|
|
|
|
|
|
|||||||
Stage II |
Trench Support &
Ground Compaction |
|||||||||||||
No PME would be needed. Manual working
for construction would be adopted. |
||||||||||||||
|
|
|
|
|
|
|
|
|||||||
Stage III |
Pipe-laying |
|||||||||||||
No PME would be needed. Manual working
for construction would be adopted. |
||||||||||||||
|
|
|
|
|
|
|
|
|||||||
Stage IV |
Backfilling |
|||||||||||||
No PME would be needed. Manual working
for construction would be adopted. |
||||||||||||||
|
|
|
|
|
|
|
|
|||||||
Stage V |
Surfacing |
|||||||||||||
5.1 |
Vibratory poker |
CNP 170 |
1 |
113 |
80% |
112 |
112 |
|||||||
|
|
|
|
|
|
|
|
|||||||
4.6.8
For the laying of gravity sewer on Po Toi O Chuen Road, larger scale of PMEs
are required for excavation and surfacing work. The plant list for open trench
method for pipe laying on Po Toi O Chuen is shown in Table 4-12.
Table 4-12: Typical PME to be used for Installation of Gravity Sewers on Po
Toi O Chuen Road (Open Cut Method)
Activity |
Noise Source |
TM-GW Reference Number |
Nos. used |
SWL, dB(A) |
% on time |
Effective SWL in a 30 min period |
Overall SWL |
|
Stage I |
Earth Works |
|||||||
1.1 |
Hydraulic breaker |
CNP 028 |
1 |
122 |
50% |
119 |
120 |
|
Excavator / loader |
CNP 081 |
1 |
112 |
80% |
111 |
|||
Lorry |
CNP 141 |
1 |
112 |
30% |
107 |
|||
|
|
|
|
|
|
|
|
|
Stage II |
Trench Support &
Ground Compaction |
|||||||
2.1 |
Vibrating hammer (piling) |
CNP 172 |
1 |
115 |
80% |
114 |
115 |
|
Roller, vibratory |
CNP 186 |
1 |
108 |
80% |
107 |
|||
|
|
|
|
|
|
|
|
|
Stage III |
Pipe-laying |
|||||||
No PME would be needed. Manual working
for construction would be adopted. |
||||||||
Stage IV |
Backfilling |
|||||||
4.1 |
Backhoe |
CNP 081 |
1 |
112 |
80% |
111 |
112 |
|
Roller, vibratory |
CNP 186 |
1 |
108 |
60% |
106 |
|||
|
|
|
|
|
|
|
|
|
Stage V |
Surfacing |
|||||||
5.1 |
Vibratory poker |
CNP 170 |
1 |
113 |
80% |
112 |
114 |
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
100% |
109 |
|||
|
|
|
|
|
|
|
|
|
Construction of Submarine Outfall
4.6.9 The submarine outfall will be constructed by horizontal directional drilling (HDD). An entry pit will be excavated within sheet piles at the rocky shore for insertion of the drill head. The drill head will drill into the rock layer below seabed and the tunnel will be enlarged by pre-reaming. After that, the rising mains will be pulled from the diffuser installation point back to the entry site. The plant equipment for HDD will be placed on the rocky shore, which is about 13.2m from the nearest sensitive receiver (a house). The plant list for HDD method for construction of submarine outfall is shown in Table 4-13. According to the Ground Investigation results, the rock layer is 10m below ground. As drilling depth at the launching site is shallower where soft marine deposits and alluvium are located, no significant groundborne noise is expected from HDD works.
Table 4-13: Typical
PME to be used for Construction of Submarine Outfall (Land-based Works)
Activity |
Noise
Source |
TM-GW
Reference Number |
Nos.
used |
SWL,
dB(A) |
%
on time |
Overall
SWL |
Stage I |
Plant Setup
and Entry Pit Setup |
|||||
1.1 |
Vibrating hammer (piling) |
CNP165 |
1 |
115 |
60% |
112.8 |
Excavator / loader |
CNP081 |
1 |
112 |
60% |
109.8 |
|
Concrete Mixer (petrol) |
CNP046 |
1 |
96 |
50% |
93.0 |
|
Generator, silenced |
CNP102 |
1 |
100 |
100% |
100.0 |
|
Welding and cuting set |
-- |
1 |
89 |
30% |
83.8 |
|
Stage II |
Pilot
Drilling |
|||||
2.1 |
Generator, silenced |
CNP102 |
1 |
100 |
100% |
100.0 |
HDD Drill Rig |
-- |
1 |
88 |
80% |
87.0 |
|
Crane |
CNP049 |
1 |
95 |
40% |
91.0 |
|
Mud pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Agitator |
CNP005 |
1 |
90 |
80% |
89.0 |
|
Drilling fluid mixer |
CNP105 |
1 |
90 |
80% |
89.0 |
|
Drilling Fluid pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Bentonite filtering plant |
CNP162 |
1 |
105 |
100% |
105.0 |
|
Mud Tanks and recycling
unit (pump) |
-- |
1 |
104 |
70% |
102.5 |
|
Water / mud pump
(electric) |
CNP281 |
1 |
88 |
80% |
87.0 |
|
Generator (for drilling
rig) |
CNP102 |
1 |
100 |
100% |
100.0 |
|
Air compressor |
CNP001 |
1 |
100 |
70% |
98.5 |
|
Hydraulic power pack |
CNP174 |
1 |
100 |
100% |
100.0 |
|
Stage III |
Pre-Reaming
& Cofferdam at Diffuser |
|||||
3.1 |
Generator, silenced |
CNP102 |
2 |
100 |
100% |
103.0 |
HDD Drill Rig |
-- |
1 |
88 |
80% |
87.0 |
|
Crane |
CNP049 |
2 |
95 |
40% |
94.0 |
|
Mud pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Agitator |
CNP005 |
1 |
90 |
80% |
89.0 |
|
Drilling fluid mixer |
CNP105 |
1 |
90 |
80% |
89.0 |
|
Drilling Fluid pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Bentonite filtering plant |
CNP162 |
1 |
105 |
100% |
105.0 |
|
Mud Tanks and recycling
unit (pump) |
-- |
1 |
104 |
70% |
102.5 |
|
Water / mud pump
(electric) |
CNP281 |
1 |
88 |
80% |
87.0 |
|
Generator (for drilling
rig) |
CNP102 |
1 |
100 |
100% |
100.0 |
|
Air compressor |
CNP001 |
1 |
100 |
70% |
98.5 |
|
Hydraulic power pack |
CNP174 |
1 |
100 |
100% |
100.0 |
|
Welding and cuting set |
-- |
1 |
89 |
30% |
83.8 |
|
Stage IV |
Pipe
Installation & Installation of Diffuser & Removal of Cofferdam |
|||||
4.1 |
Generator, silenced |
CNP102 |
2 |
100 |
100% |
103.0 |
HDD Drill Rig |
-- |
1 |
88 |
80% |
87.0 |
|
Crane |
CNP049 |
2 |
95 |
40% |
94.0 |
|
Mud pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Agitator |
CNP005 |
1 |
90 |
80% |
89.0 |
|
Drilling fluid mixer |
CNP105 |
1 |
90 |
80% |
89.0 |
|
Drilling Fluid pump |
CNP106 |
1 |
105 |
80% |
104.0 |
|
Bentonite filtering plant |
CNP162 |
1 |
105 |
100% |
105.0 |
|
Mud Tanks and recycling
unit (pump) |
-- |
1 |
104 |
70% |
102.5 |
|
Water / mud pump
(electric) |
CNP281 |
1 |
88 |
80% |
87.0 |
|
Generator (for drilling
rig) |
CNP102 |
1 |
100 |
100% |
100.0 |
|
Air compressor |
CNP001 |
1 |
100 |
70% |
98.5 |
|
Hydraulic power pack |
CNP174 |
1 |
100 |
100% |
100.0 |
4.6.10 Phases of construction of the works were identified and unmitigated and mitigated scenarios were assessed for noise impact at the identified NSR.
Prediction of Unmitigated Construction Noise Impact
4.6.11 The impact of construction noise on the identified NSRs was assessed in accordance with the procedures laid down in Technical Memorandum on Noise from Construction Work Other Than Percussive Piling. A +3 dB (A) façade correction was added to the predicted noise levels to account for the façade effect at each NSR. In general, the noise impact will be the highest when works are being carried out close to the NSRs and, as the works areas gradually shift away, the noise would tend to diminish.
4.6.12 As a conservative approach to assessing the worst-case construction noise impacts, it was assumed that all the proposed PMEs for each construction work stage were operating concurrently. The predicted cumulative worst-case construction noise levels at the NSRs due to construction of STP, laying of gravity sewer and rising mains on Po Toi O Chuen Road and in the village, and construction of submarine outfall are summarized in Table 4-14. Detailed calculations are provided in Appendix 4.1.
Table
4-14: Predicted Worst-case Cumulative Construction Noise Levels at
Representative NSRs - Unmitigated Scenario
NSR |
Description of NSR |
Predicted Worst-case Construction Noise Level dB(A) |
||
Unmitigated Results |
Noise Criteria |
Exceedance |
||
PTO1_N1 |
Village House in
PTOCR 28 |
95 |
75 |
20 |
PTO_N2 |
Village House in
PTOCR 7A |
95 |
75 |
20 |
PTO_N3 |
Temporary Structure
for Living |
92 |
75 |
17 |
FV_N1 |
Fairway Vista
House 12 |
101 |
75 |
26 |
SC_N1 |
Seacrest Villas
in PTOCR No. 64 |
90 |
75 |
15 |
4.6.13 Based on the effective sound power level of the PMEs and the distance of work site to the noise sensitive receivers, unmitigated construction noise level for some work stages were predicted to exceed the EIAO-TM of 75dB(A) guideline level by 15 to 26 dB(A). About 130 residential dwellings and 1 temple will be affected. Various mitigation options have been considered in accordance with the guidelines laid down in the Environmental Impact Assessment Ordinance, Guidance Note No. 9/2010 “Preparation of Construction Noise Impact Assessment under the Environmental Impact Assessment Ordinance” (GN 9/2010) as discussed in Section 4.7.
Operational Noise
4.6.14 During the operational phase, equipment noise from the proposed sewage treatment plant will be the main noise source with potential noise impact on the NSRs.
4.6.15 The equipment inventory of the Po Toi O STP will be similar to those for small sewage treatment plants in Hong Kong, and this would include sewage pumps, ventilation fans, deodourizing fans, mechanically raked fine screen and blower. A typical equipment inventory based on the design at the time of preparation of this EIA, is provided in Table 4-15. The inventory and operation modes were confirmed with the project engineer. The typical Sound Power Levels (SWL) associated with these equipment items are also provided.
Table 4-15: Typical Noisy Equipment for the
Proposed Po Toi O Sewage Treatment Plant
Location |
Equipment |
No. of Units |
Typical SWL, dB(A) |
Sub-total SWL, dB(A) |
Preliminary Treatment
Units |
Submersible pump (Ref.
1) |
2 |
85 |
88.0 |
Mechanically raked fine
screen (Ref. 3) |
2 |
89 |
92.0 |
|
Deodourizing fan (Ref.
4) |
2 |
85 |
88.0 |
|
Exhaust fan (Ref. 2) |
1 |
79 |
79.0 |
|
MBR Equipment Unit |
Mechanically pump (Ref. 5) |
3 |
92 |
96.8 |
Deodourizing fan (Ref. 4) |
2 |
85 |
88.0 |
|
Exhaust fan (Ref. 2) |
1 |
79 |
79.0 |
|
Sludge Treatment Unit |
Submersible pump (Ref. 1) |
2 |
85 |
88.0 |
Deodourizing fan (Ref. 4) |
2 |
85 |
88.0 |
|
Exhaust fan (Ref. 2) |
1 |
79 |
79.0 |
|
Air Blower Room |
Blower (Ref. 6) |
1 |
85 |
85.0 |
Exhaust fan (Ref. 2) |
1 |
79 |
79.0 |
|
Outfall Pumping Station and Header Tank |
Mechanical pump (Ref. 5) |
4 |
92 |
98.0 |
Deodourizing fan (Ref. 4) |
2 |
85 |
88.0 |
|
Exhaust fan (Ref. 2) |
2 |
79 |
82.0 |
Remark: -
SWL – Sound Power Level
Only noisy equipment is included in
the table. Other equipment which do not
have significant noise emissions are excluded.
(Ref. 1) SWL referenced to CNP283.
(Ref. 2) SWL referenced to approved
EIA of Harbour Area Treatment Scheme (HATS) Stage 2A (EIA-148/2008) and Good
Practices on Ventilation System Noise Control based on the flow rate of 1,300m3/hr.
(Ref. 3) SWL referenced to the
approved EIA Report on Tai Po Sewage Treatment Works Stage V (EIA-097/2004).
(Ref 4) SWL of plant refers to Good
Practices on Ventilation System Noise Control based on the flow rate of 17,000
m3/hr and 125 Pa.
(Ref 5) SWL of plant refer to Good
Practices on Pumping System Noise Control based on the horsepower of pumpset 20
hp at 1800 rpm.
(Ref 6) SWL of plant refers to the
tender specification for Shatin STW Stage 3 Upgrading and approved EIA of
Harbour Area Treatment Scheme (HATS) Stage 2A (EIA-148/2008).
4.6.16
Standby equipment would only be used in case of failure or maintenance of
duty units. Therefore, concurrent operation of both duty and standby equipment
will not occur under the normal operation.
As
a reasonable worst case scenario assessment, the maximum sound power levels during
operation would be under the full operation of all duty equipment which is given in Table 4-15.
4.6.17
The impact of operational
noise on the identified NSRs was assessed in accordance with the procedures laid down in Technical Memorandum
on Noise from Places other than Domestic Premises,
Public Places or Construction Sites. A +3
dB (A) façade correction was added to the predicted noise levels to account for the façade
effect at each NSR.
4.6.18
All identified noisy equipment items of the STP would
be confined inside the building structure except exhaustion fans. A reduction of 20 dB(A) can be
achieved if the building enclosure is built using suitable material such as concrete with surface density of 25
kg/m2. Equipment items to be confined within the building structure of PTOSTW
with noise reduction consideration are summarized in Table 4-16.
Table
4-16: Proposed Design Measures For Operation of Po Toi O Sewage Treatment Plant
Location |
Equipment |
Mitigation Measures |
Noise Reduction dB(A) |
Preliminary Treatment Units |
Submersible pump |
Enclosed Inside Building Structure |
-20 |
Mechanically raked fine screen |
-20 |
||
Deodourizing fan |
-20 |
||
Exhaust fan |
-- |
0 |
|
MBR Equipment Unit |
Mechanically pump (Ref. 5) |
Enclosed Inside Building Structure |
-20 |
Deodourizing fan (Ref. 4) |
-20 |
||
Exhaust fan (Ref. 2) |
-- |
0 |
|
Sludge Treatment Unit |
Submersible pump (Ref. 1) |
Enclosed Inside Building Structure |
-20 |
Deodourizing fan (Ref. 4) |
-20 |
||
Exhaust fan (Ref. 2) |
-- |
0 |
|
Air Blower Room |
Blower (Ref. 6) |
Enclosed Inside Building Structure |
-20 |
Exhaust fan
(Ref. 2) |
-- |
0 |
|
Existing
Outfall Pumping Station and Header Tank |
Mechanical pump
(Ref. 5) |
Enclosed Inside Building Structure |
-20 |
Deodourizing
fan (Ref. 4) |
-20 |
||
Exhaust fan
(Ref. 2) |
-- |
0 |
4.6.19
The predicted worst-case noise levels at identified NSRs due to the
operation of STP would
comply with the noise criteria at all time.
The predicted noise levels at representative NSRs are summarized in Table 4-17 and detailed in Appendix 4.2.
Table
4-17: Predicted Worst-case Operation Noise Levels
at Representative NSRs - Unmitigated Scenario
NSR |
NSR Description |
Predicted Unmitigated
Noise Level, dB(A) |
Day-time Noise
Criterion, dB(A) |
Night-time Noise
Criterion, dB(A) |
PTO_N1 |
Village House in
PTOCR 28 |
45 |
49 |
45 |
PTO_N2 |
Village House in
PTOCR 7A |
37 |
49 |
45 |
PTO_N3 |
Temporary
Structure for living |
32 |
49 |
45 |
FV_N1 |
Fairway Vista
House 12 |
32 |
49 |
45 |
SC_N1 |
Seacrest Villas
in PTOCR No. 64 |
37 |
49 |
45 |
4.6.20
In fact, typical concrete wall has better noise
insulation performance. The assumption of 20 dB(A) reduction has been
conservative. Also, with some of the equipment stored underground, the noise
impact will be further reduced. Furthermore, the acoustic louvres are designed
to face the slope but not the village, avoiding direct view of the noise source
from NSR. The maximum allowable sound power levels of equipment items would be
specified in the tender specification to ensure the operational noise impact complying
with relevant noise criteria.
4.6.21
Most of the noisy equipment items in the sewage
treatment plant are fully enclosed underground or enclosed by concrete
structure. With noise reduction due to distance between the STP and the nearest
NSR, no operational noise impact is anticipated and therefore no mitigation is
required.
4.7
Evaluation and Recommendation of Noise
Mitigation Measures
Construction Noise
4.7.1
Mitigation
at source or path should be the most effective way to reduce the impact. There
are 4 ways in doing that viz. : -
·
by
use of quiet plants and working methods to mitigate at source;
·
by
use of mobile noise barriers/enclosures along the path of noise propagation;
·
by
adopting good site practice to limit noise emissions at source;
·
by
scheduling of work to minimize work scale and duration of impact.
Use of Quiet Plants and Working Methods
4.7.2
Silenced
plants or quality powered mechanical equipment (QPME) are quieter than those
noise levels given in TM-GW for the equivalent type of equipment. These
silenced equipment items are known to be available in Hong Kong and hence
should be adopted as far as practical. Table
4-18 shows the
possible alternative quieter PME which are taken from BS:5228: Part 1:2009 or
available noise label. These quieter PMEs
are available in the market and have been successfully applied to other
projects and have achieved noticeable noise reductions. The quieter PMEs to be used for the works
shall meet the following SWLs, or lower:
Table
4-18 Quiet PME and Associated Sound Power Level
Proposed for the Project
Description of PME |
Equivalent Quiet PME |
SWL, dB(A) |
Hydraulic
breaker |
BS5228 Tab.
D8-12 |
106 |
Excavator /
loader |
EPD-00081 |
99 |
Lorry |
BS5228 Tab.
D8-25 |
96 |
Vibrating
hammer (piling) |
BS5228 Tab.
D4-12 |
94 |
Roller,
vibratory |
BS5228 Tab.
D3-115 |
102 |
Vibratory poker |
BS5228 Tab.
D6-40 |
98 |
Backhoe |
BS5228 Tab.
D3-108 |
97 |
Breaker, hand
held |
Noise Label
NB-0022-13-001 |
100 |
Ref:
·
BS 5228-1:2009. BSI British Standards. Code of practice
for noise and vibration control on construction and open sites – Part 1: Noise
·
EPD Issued Noise Emission Label: https://epic.epd.gov.hk/eForm/lic_epd119/lrrf031_list.jsp?epic_lic_no=002030606&a119_or_119_ind=A&lang=eng
4.7.3
In
addition to use of breaker for breaking up road surface in the village area,
drilling with chemical agent will be considered as far as practicable in the construction
phase according to local situation.
Use of Mobile Noise Barriers/Enclosures
4.7.4
Mobile
noise barriers can be effective in screening noise from reaching sensitive
receivers, particularly for the low-rise houses in this case.
4.7.5
Some
sections of gravity sewers and rising mains construction would be aligned close
to the village houses. As the handheld breaker is the noisy PME for
excavation work, it shall be
fitted with mufflers to minimize noise emission. A movable enclosure made up of plywood is proposed to surround both worker and breaker during breaking process. The internal wall of the enclosure should be
laid with sound absorbent such as mineral wool. Without direct view of the noisy part of
the breaker from NSR, this design can achieve 15dB(A) reduction, which has already taken into account sound
leakage through the gaps. A typical
drawing of the enclosure can be found in Appendix
4-5.
4.7.6
For construction of submarine outfall using HDD, the work area is large
enough to accommodate semi-enclosure. It should enclose the stationary plant
equipment on three sides with cover. Only the side facing the sea shall be
opened for heat exhaustion.
Schedule of Work
4.7.7
As
the footpath between village houses is very narrow, pipe laying in close
proximity of the NSRs cannot be avoided. Construction work will be divided into
short sections (10m) to reduce the duration of localized work (about one month
per workfront). Three workfronts will progress at the same time. Each workfront
should be separated from each other by at least 100m to minimize cumulative
effect.
4.7.8
During
laying of gravity sewers and rising mains near NSRs PTO_N1 and PTO_N3, major
concurrent noisy activities are laying of Po Toi O Chuen Road sewer and
horizontal directional drilling (HDD) respectively. The 10m workfront of
gravity sewers and rising mains installation near the two NSRs shall be
scheduled at different times from these noisy activities to minimize cumulative
noise impact.
4.7.9
As
the prevailing noise level in restricted hours is lower than daytime (averaged
50 – 51 dB(A) vs 57 - 59 dB(A) based on baseline monitoring), construction
works will be carried out in daytime to avoid nuisance during evening and night
time.
Adoption of Good Site
Practice
4.7.10
Good
site practice and noise management can significantly reduce the impact of a
construction site’s activities on nearby NSRs. Although the reduction in noise
level is not readily predictable and quantified, the following measures should
be useful during each phase of construction:
·
Only
well-maintained plant should be operated on-site and plant should be serviced
regularly during the construction programme;
·
Machines
that may be in intermittent use should be shut down between work periods or
should be throttled down to a minimum;
·
Silencer
and mufflers on construction equipment should be utilised and should be
properly maintained during the construction programme;
·
Noisy
activities can be scheduled to minimise exposure of nearby NSRs to high levels
of construction noise. For example, noisy activities can be scheduled for
midday. Avoid carrying out noisy activities at the same time;
·
For
the installation of gravity sewers and rising mains near residence, hand-held breaker may be used to break the hard
concrete layer. The manual equipment should be used as far as practicable to
avoid using the PME. If found necessary, the percentage on time should be
limited to reduce continuous contributions;
·
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;
·
Mobile
plant should be sited as far away from NSRs as possible; and
·
Material
stockpiles and other structures should be effectively utilised, wherever
practicable, in screening noise from on-site construction activities.
4.7.11
During
excavation works for gravity sewers and rising mains installation, generator
and breaker will be operated at the same time. Generator should be placed at a
fixed location and screened by noise barrier. It should be at least 5-6m away
from the NSRs whenever excavation work has to be carried out at their front
doors (calculations in Appendix 4.3
refers). These measures can minimize the noise contribution from the generator
and the total sound power level at NSRs.
4.7.12
Only
one vibratory poker is proposed for surfacing work after pipe laying. To
further minimize noise nuisance, vibratory poker will only be operated 4m away
from NSR and with noise barrier properly erected. This can reduce the construction
noise level at the NSR to 75B(A) as shown in Appendix
4.3 (NSRs PTO_N1 & FV_N1). Surfacing work within 4m from
NSR will be carried out by manual method.
4.7.13
“Recommended Pollution Control Clauses for
Construction Contracts” is available on EPD website. It contains the
recommended noise pollution control measures to be implemented by the
contractor during the construction stage. The predicted noise levels are summarized in Table 4-19. Detailed calculations are provided in Appendix 4.3.
Table
4-19: Predicted Cumulative Construction Noise
Levels at Representative NSRs - Mitigated Scenario
NSR |
Description of NSR |
Predicted Worst-case Construction Noise Level dB(A) |
||
Mitigated Results |
Noise Criteria |
Exceedance |
||
PTO1_N1 |
Village House in
PTOCR 28 |
75 |
75 |
- |
PTO_N2 |
Village House in
PTOCR 7A |
75 |
75 |
- |
PTO_N3 |
Temporary
Structure for living |
74 |
75 |
- |
FV_N1 |
Fairway Vista
House 12 |
75 |
75 |
- |
SC_N1 |
Seacrest Villas
in PTOCR No. 64 |
71 |
75 |
- |
4.7.14
With the adoption of quiet PMEs and temporary barrier/enclosure/semi-enclosure, no construction noise exceedance is expected. When the works areas
gradually shifted away, the noise would tend to diminish.
Cumulative Noise Impact Due to Concurrent Project
4.7.15
The
following discusses the potential cumulative interface issues between
concurrent projects as indicated in Chapter
2 – Project Description. There may be two potential concurrent projects in
the area, i.e.
·
Roundabout
near the minibus stop
·
Fish
culture zone (FCZ) dredging and relocation
4.7.16
During
the course of the study, CEDD has confirmed that there was no programme for the
fish culture zone dredging and relocation. There was also no information on
when the roundabout would be constructed. Therefore, no cumulative noise
impact is expected.
4.7.17
Should
there be concurrent project in the vicinity, continuous discussion between
contractors shall be conducted to plan the location and programme of
construction work to minimize cumulative impact.
4.8
Evaluation of Residual Impacts
4.8.1 After implementation of mitigation measures as mentioned in Section 4.7, construction noise impact on NSRs would comply with the daytime noise guideline 75dB(A). Upon completion of the sewage treatment plant, noisy plant equipment will be operated within the building structure or underground. The fixed equipment noise will comply with the daytime/evening time and nighttime noise criteria. Therefore, no residual noise impact is expected in both construction and operational phases.
4.9
Environmental Monitoring and Audit
Requirements
4.9.1
With the
implementation of proposed construction noise mitigation measures such as use
of quality powered mechanical equipment (QPME), use of mobile noise barriers,
enclosure and semi-enclosure, good site practice and management, and
construction noise monitoring and audit programme, construction noise impact
could be reduced down to acceptable levels. Regular monitoring of noise level should
be carried out at noise monitoring stations near representative sensitive
receivers before and throughout construction work to ensure that relevant noise
standard can be met.
4.9.2
Since the
noisy equipment items in the sewage treatment plant are fully enclosed
underground or enclosed by concrete structure, operational noise impact is
expected to be acceptable. Operational noise monitoring is considered
unnecessary.
4.9.3
General
EM&A requirements were presented in Chapter
12.
4.10.1
Construction
noise arising from typical types and numbers of powered mechanical equipment
items (PME) for the construction of sewage treatment plant, rising mains/sewer
installation and submarine outfall have been assessed. Based on the effective
sound power levels of the PMEs and the notional noise distances to the noise
sensitive receivers, unmitigated construction noise levels would exceed the
75dB(A) guideline level for the non-restricted hours for all NSRs. At source
mitigation measures have been proposed including the use of quality plants, use
of mobile noise barriers, semi-enclosure, enclosure, strategic work scheduling
and good site practice. With the proposed mitigation measures, no construction
noise exceedance is expected.
4.10.2
Most of
the noisy equipment items in the sewage treatment plant would be fully
underground or enclosed by concrete structure. With noise reduction due to
distance between the STP and the nearest NSR, operational noise impact is
anticipated to be acceptable.