A noise impact assessment has been undertaken to define the nature and scale of potential environmental impacts associated with the Project specifically in terms of the effects in the vicinity of sensitive receivers. Both construction and operational phase impacts have been assessed and mitigation measures have been identified to determine whether any residual impacts can be reduced to acceptable levels.
The principal legislation for the control of construction noise is the Noise Control Ordinance (NCO) (Cap 400). Various Technical Memoranda (TMs), which stipulate control approaches and criteria, have been issued under the NCO and EIAO. For this project, the following TMs are relevant to the assessment of the construction noise impacts:-
· Technical Memorandum on Noise from Construction Work other than Percussive Piling (GW-TM);
· Technical Memorandum on Noise from Construction Work in Designated Areas (DA-TM); and
· Technical Memorandum on Environmental Impact Assessment Process (TMEIA).
Noise impacts arise from general construction works during normal working hours (i.e. 0700 to 1900 hours on any day not being a Sunday or public holiday) at the openable windows of noise sensitive buildings are to be assessed as per the guidelines contained in the TMEIA. The recommended noise standards are 75dB(A) for domestic premises, 70dB(A) for educational institutions, 65dB(A) during examinations.
The NCO provides statutory controls on general construction works during the restricted hours (i.e. 1900-0700 hours Monday to Saturday and at any time on Sundays and public holidays). The use of powered mechanical equipment (PME) for carrying out construction works during the restricted hours would require a CNP. The EPD is guided by the GW-TM when assessing such an application.
When assessing an application for the use of PME, the EPD will compare the ANLs, as promulgated in the GW-TM, and the CNLs (after accounting for factors such as barrier effects and reflections) associated with the proposed PME operations. A CNP will be issued if the CNL is equal to or less than the ANL. The ANLs are related to the noise sensitivity of the area in question and different Area Sensitivity Ratings (ASR) have been drawn up to reflect the background characteristics of different areas. The relevant ANLs are shown in Table 4.1 below.
Table 4.1 Acceptable Noise Levels (ANL, Leq, 5 min dB(A))
|
Time
Period |
Area Sensitivity
Rating |
||
|
A |
B |
C |
|
|
All days during the evening (1900-2300 hours) and
general holidays (including Sundays) during the day and evening (0700-2300
hours) |
60 |
65 |
70 |
|
All days during the night-time (2300-0700 hours) |
45 |
50 |
55 |
Regardless
of any description or assessment made in this EIA Report on construction noise
aspects, there is no guarantee that a CNP will be issued for construction of
the project. The Noise Control Authority
will consider a well-justified CNP application, once filed, for construction
works within restricted hours as guided by the relevant Technical Memoranda
issued under the Noise Control Ordinance. The Noise Control Authority will take
into account contemporary conditions / situations of adjoining land uses and
any previous complaints against construction activities at the site before
making his decision in granting a CNP. Nothing in this EIA Report shall bind
the Noise Control Authority in making his decision. If a CNP is to be issued, the Noise Control
Authority shall include in it any condition he thinks fit. Failure to comply with any such conditions
will lead to cancellation of the CNP and prosecution action under the NCO.
At
this moment, only construction works during non-restricted hours are assumed
and the feasibility of carrying out works during restricted hours has not been
assessed.
In
addition to the general controls on the use of PME during the restricted hours,
the EPD has implemented more stringent control mechanisms via the DA-TM. The DA-TM regulates the use of five types of
Specified Powered Mechanical Equipment (SPME) and three types of Prescribed
Construction Work (PCW), which are non-PME activities, in primarily densely
populated neighbourhoods called Designated Areas (DAs). The SPME and PCW are :
SPME :
· Hand-held breaker
· Bulldozer
· Concrete lorry mixer
· Dump truck
· Hand-held vibratory poker
PCW :
· Erection or dismantling of formwork or scaffolding
· Loading, unloading or handling or rubble, wooden boards, steel bars, wood or scaffolding material
· Hammering
In an attempt to provide environmental additional protection carrying out of PCW is generally banned inside a DA. As for the use of SPME, it would be necessary to comply with DA-TM noise level requirements that are 15 dB(A) more stringent than those listed in the GW-TM before a CNP would be issued. As some works areas of the project will be within DA, the requirements stated in the DA-TM apply to this study.
Noise
arising from general construction works during normal working hours is governed
by the TM-EIAO under the EIAO as shown in Table
4.1. TM for the Assessment of Noise
from Places other than Domestic Premises, Public Places or Construction Sites
(PL-TM) under the NCO stipulates that noise transmitted primarily through the
structural elements of building, or buildings, shall be 10 dB(A) less than the relevant ANLs.
Based
on the principle for groundborne noise criteria (i.e.
taking account of the minus 10dB(A) requirement under
the NCO PL-TM), groundborne construction noise levels
inside domestic premises and schools relying on open window for ventilation
will be limited to 65dB(A) and 60dB(A) respectively, with reference to the
daytime airborne noise criterion of 75dB(A) and 70 dB(A) in accordance with
TMEIA. In the evening (1900 – 2300hrs)
and during nighttime (2300 – 0700hrs), groundborne noise level will be limited to 10dB(A) below the respective ANLs
for the Area Sensitivity Rating category of “A, B and C” at the NSRs along the
proposed project. A summary of these
criteria is given in Table 4.2
below.
Table 4.2 Groundborne Noise Criteria (ANL, Leq, 5 min dB(A))
|
Time
Period |
Area
Sensitivity Rating |
||
|
A |
B |
C |
|
|
All days during the evening (1900-2300 hours) and
general holidays (including Sundays) during the day and evening (0700-2300
hours) |
50 |
55 |
60 |
|
All days during the night-time (2300-0700 hours) |
35 |
40 |
45 |
Area Sensitive Ratings (ASRs)
Determination of
the Area Sensitivity Ratings for the NSRs in this study has been made with
reference to relevant TMs. The study area comprises three intake and one
outfall structures. Each of which is
defined by different ASRs based on the type of area containing the NSR and
effect of influencing factors. For the
NSRs at Intake 1 and outfall 1, an Area Sensitivity Rating of “C” is assigned
as the area is classified as the ‘urban area’ and directly influenced by road
traffic noise from major roads (i.e.
A methodology for assessing construction noise other than percussive piling has followed the guidelines set out in the Technical Memorandum on Noise from Construction Work other than Percussive Piling (GW-TM). The methodology is as follows:
· identify the likely type, sequence and duration of principal noisy construction activities required for the implementation of the proposed project;
· identify a list of plant inventory likely to be required for each construction activity;
· calculate the maximum total sound power level (SWL) for each construction activity using the plant list and SWL data given for each plant in the technical memorandum.
· representative NSRs as defined by the EIA-TM have been identified, based on existing and committed landuses in the study area that may be affected by the worksite. For the purposes of this study, NSRs have been identified up to a distance of 300m from the alignment. However, the distance may be reduced, subject to the first layer of NSRs providing adequate acoustic shielding;
· calculate the distance attenuation and barrier corrections to NSRs from worksite notional noise source point; and
· predict construction noise levels at NSRs in the absence of any mitigation measures.
If the noise assessment criteria are exceeded at NSRs, mitigation measures must be considered. A re-evaluation of the total SWL for each construction activity will be made assuming the use of practical mitigation measure such as “quiet” equipment and movable noise barriers. If the criteria were still exceeded, further mitigation measures such as reduction in noisy plant working simultaneously would be considered.
For machines working in rock a preliminary estimate of vibration and ground borne noise can be made applying Miller and Bowers equations (ref.10)
V = 180x-1.3
Where V = upper bound PPV resultant (mm/s)
x = Distance between TBM source and receptor (m)
Introduction
The method used to predict construction groundborne noise is based on the U.S. Department of
Transportation “High-Speed Ground Transportation Noise and Vibration Impact
Assessment”, 1998 (ref.11). The
vibration level Lv,rms
at a distance R from the source is related to the vibration source level
at a reference distance Ro. The conversion from vibration
levels to groundborne noise levels is determined by
the following factors:
Cdist: Distance
attenuation
Cdamping: Soil
damping loss across the geological media
Cbuilding: Coupling
loss into building foundation
Cfloor: Coupling
loss per floor
Cnoise: Conversion
factor from floor vibration levels to noise levels
The predicted groundborne
noise level Lp
inside the noise sensitive rooms is given by the following equation.
Lp
= Lv,rms + Cdist + Cdamping
+ Cbuilding + Cfloor
+ Cnoise
The vibration
velocities of TBM were determined by measurements and some of these in Peak
Particle Velocity (PPV). In such cases,
a crest factor of four was applied to establish the rms level in accordance with the FTA Guidance
Manual (ref.12).
The
vibration measurements for the TBM were extracted from the in-situ measurements
during the bored tunnelling of Kwai Tsing Tunnel of the West Rail project. The geology consists of mainly granite, which
is considered similar to the geology along Tsuen Wan
Drainage. The measurements records are
considered the most appropriate available information for the purpose of
assessing TBM groundborne noise.
The geological
profiles along Tsuen Wan are mainly hardrock. No soil
damping loss is assumed.
Coupling Loss into Building
Structures
This represents the change in the incident
ground-surface vibration due to the presence of the piled building
foundation. The empirical values based
on the guidance set out in the Transportation Noise Reference Book (ref.13) are given in following Table.
Loss factor for coupling
into building foundation
|
Loss factor for coupling into building foundation, dB |
Octave Band Frequencies, Hz |
|||||
|
16 |
31.5 |
63 |
125 |
250 |
500 |
|
|
Large
building on Piles |
-7 |
-10 |
-12 |
-15 |
-17 |
-14 |
|
Single
residences |
-5 |
-6 |
-6 |
-5 |
-4 |
-3 |
Coupling Loss Per Floor
This represents the floor-to-floor vibration
transmission attenuation. In
multi-storey buildings, a common value for the attenuation of vibration from
floor-to-floor is approximately 1dB attenuation in the upper floor regions at
low frequencies and greater than 3dB attenuation at lower floors at high
frequencies. Coupling loss of –1 dB
reduction per floor is assumed for a conservative assessment.
Conversion from Floor
Vibration to Noise Levels
Conversion from floor vibration levels to
indoor reverberant noise levels is based on standard acoustic principles. The conversion factor is dependent on the
surface area S of the room in m2, the radiation efficiency (,
the volume of the room V in m3 and the room reverberation time RT in
seconds. Analyses were carried out for
residential units, school and temple. Results are summarised in following
Table.
Conversion factors from
floor vibration levels to indoor reverberant noise levels
|
NSR Description |
Conversion Cnoise (dB re 1x10-6 mm/s) |
|
Residential Unit |
–27 |
|
|
–27 |
|
School |
–24 |
The construction noise resulting from the proposed project will be present at the three intake structures, I-1, I-2 and I-3 and outlet structure. The existing ambient noise within Study Area is generally urban with road traffic with the exception of Intake I-3 which is located within the area proposed in future to be an ecological park (although no plans have been put in place yet).
· Intake I-1 is within 60m of Cheung Pei Shan Road; and a number of smaller roads including Wo Yi Hop Road (20m), Shing Mun Road (adjoining) and Wo Yi Hop Lane (20m).
·
Intake I-2 adjoins
· Intake I-3 is located 150m from at Route Twisk.
·
Outlet O-1 adjoins
Representative Noise Sensitive Receivers (NSRs) within 300m of the Project limit have been identified according to the criteria set out in the TMEIA and through site inspections and a review of land use plans. NSRs and their horizontal distance to the nearest emission source have been identified and are summarized in Table 4.3. Locations of the NSRs are shown in Figure 4.1 (Intake I-1), Figure 4.2 (Intake I-2), Figure 4.3 (Intake I-3) and Figure 4.4 (Outfall O-1).
Table 4.3 Noise Sensitive Receivers
|
ID No. |
NSR No. |
Locat. |
Description |
Noise Criteria |
Distance to the nearest Emission Source (m) |
No. of floors |
|
1 |
NSR1* |
I1 |
|
70 |
60 |
6 |
|
2 |
NSR2* |
|
Kwai Shue House |
75 |
90 |
25 |
|
3 |
|
|
Chuk Shue House |
75 |
120 |
N.A |
|
4 |
|
|
Sheng Kung Hui Li Ping Secondary School |
70 |
130 |
N.A |
|
5 |
|
|
Lei Muk Shui Estate (Block 6) |
75 |
140 |
N.A |
|
6 |
|
|
Lei Muk Shui Estate Chung Shue House |
75 |
140 |
N.A |
|
7 |
|
|
Leu Muk
Shui Estate (Block 5) |
75 |
190 |
N.A |
|
8 |
|
|
Ho Shun Primary School |
70 |
210 |
N.A |
|
9 |
|
|
|
70 |
260 |
N.A |
|
|
|
|
|
|
|
|
|
10 |
NSR3* |
I2 |
|
75 |
24(1) |
1 |
|
11 |
NSR4* |
|
Yuen Yuen Care and Attention Home for the Aged |
75 |
55 |
6 |
|
12 |
NSR5* |
|
Western Monastery |
75 |
70 |
1 |
|
13 |
|
|
Yuen Yuen Home for the Aged |
75 |
70 |
N.A |
|
14 |
|
|
Yuen Yuen Institute ( |
75 |
100 |
N.A |
|
|
|
|
|
|
|
|
|
15 |
NSR6* |
I3 |
Squatters |
75 |
50 |
1 |
|
16 |
NSR7* |
|
Route Twisk Villa (Block 7-8) |
75 |
160 |
6 |
|
|
|
|
|
|
|
|
|
17 |
NSR8* |
O1 |
|
75 |
70 |
30 |
|
18 |
NSR9* |
|
Greenview Terrace (Block 1) |
75 |
60 |
30 |
|
19 |
|
|
|
75 |
130 |
N.A |
|
20 |
|
|
Fung Chik Sen Villa |
75 |
95 |
N.A |
|
21 |
|
|
|
75 |
120 |
N.A |
|
22 |
|
|
Blossom Terrace (Block 10) |
75 |
130 |
N.A |
|
|
|
|
|
|
|
|
Note: * Noise Sensitive Receivers are representative and will be used in prediction calculations.
Noise Criteria/ Standards are based on Noise resulting from Daytime Construction Activities listed in the TMEIA.
(1) Distance to the notional source position
N.A. Not Applicable
Potential impacts that could arise from this Project include noise generated from site clearance and site preparation, machinery operation (site foundation and excavation, concreting and formwork and reinforcement); and vehicle movements. Tunnelling works are expected to be undertaken over a 24 hour period. The depth of the tunnel ranges from 7m to 200m below ground level. With regard to 24-hour working, a Construction Noise Permit (CNP) will be necessary for the construction during restricted period as the main tunnel will be driven by TBM (Working 24 hours). For the sake of provision for optimal programming and use of resources 24-hour working for tunnel construction is assumed to be normal practice. The allowance in the programme for the TBM drive is 22 months. Assuming a practical driven rate of 20m/day for 24 hrs working, the tunnelling works could be completed in 8 to 9 months for the 5.13km tunnel. This leaves plenty of float in the programme for the tunnelling works to be undertaken.
During restricted hours the construction activities will
be contained within the tunnel. All
material excavated during restricted hours will be stockpiled within the tunnel
or at the tunnel portal and will be removed only during normal working hours (
Various construction methods have been reviewed in the Options Selection Report from which it was concluded that TBM or drill and blast would be applicable to the deep tunnel option to be constructed below bedrock level (Grade III rock or better). For the construction method of the intake shafts, drill and blast at I-2 and I-3 is more feasible for the relatively short lengths and varying diameters based on the current proposed differing shaft diameters. The proposed shaft diameters for I-2 and I-3 are 7.8m and 5.25m respectively.
The noise assessment has used the premise that the most noisy construction task (e.g. Site Formation and Excavation) is representative of the worst case situation. No percussive piling is required for this construction. The plant inventory list has been established and the details are contained in Table 4.4.
Table 4.4 Plant Inventory (for Tunnel Construction and for Intakes 1, 2, 3 and Outfall 1) (No Mitigation Measures)
|
|
Activities |
PME |
TM ID Code |
Unit |
SWL dB(A) |
|
Powered Mechanical
Equipment Used for Tunnel Construction |
|
|
|||
|
A |
General |
Loader |
CNP 081 |
1 |
112 |
|
|
|
Backhoe / Muck Car |
CNP 081 |
1 |
112 |
|
|
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
|
|
|
Mobile Crane |
CNP 048 |
1 |
112 |
|
|
|
Dump Truck |
CNP 067 |
1 |
117 |
|
|
|
Concrete Pump |
CNP 047 |
1 |
109 |
|
|
|
Mobile Generator |
CNP 101 |
1 |
108 |
|
|
|
Compressor |
CNP 002 |
1 |
102 |
|
|
|
Water Pump |
CNP 281 |
1 |
88 |
|
|
|
Ventilation Fan |
CNP 241 |
1 |
108 |
|
|
|
|
Total SWL |
121 |
|
|
B |
Site Formation |
Rock Drill
(Hydraulic) |
CNP 182 |
1 |
123 |
|
|
|
Shotcrete Vehicle |
CNP 047 |
1 |
109 |
|
|
|
Explosive Delivery
Vehicle |
CNP 141 |
1 |
112 |
|
|
|
Total SWL |
123 |
||
|
C |
TBM Tunnel
Construction |
Tunnel Boring Machine |
- |
1 |
88 |
|
|
|
Conveyor Belt System |
CNP 041 |
1 |
90 |
|
|
|
(thorough the tunnel
and at |
|
|
|
|
|
|
the Outfall for spoil
disposal) |
|
|
|
|
|
|
|
Total SWL |
92 |
|
|
D |
Concreting Works |
Concrete Delivery
Truck |
CNP 141 |
1 |
112 |
|
|
|
Pumping Plant |
CNP 047 |
1 |
109 |
|
|
|
|
Total SWL |
114 |
|
|
|
|
||||
|
A |
General |
Mobile Crane |
CNP 048 |
1 |
112 |
|
|
|
Dump Truck |
CNP 067 |
2 |
112 |
|
|
|
Mobile Generator |
CNP 101 |
2 |
108 |
|
|
|
Compressor |
CNP 002 |
2 |
102 |
|
|
|
Water Pump |
CNP 281 |
2 |
88 |
|
Total SWL |
118 |
||||
|
B |
Site Formation and Excavation |
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Dump Truck |
CNP 067 |
1 |
117 |
|
Total SWL |
119 |
||||
|
C |
Concreting |
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
|
|
|
Compactor, vibratory |
CNP 050 |
1 |
105 |
|
Total SWL |
114 |
||||
|
D |
Piling |
Piling, large diameter bored, oscillator |
CNP 165 |
1 |
115 |
|
|
|
Piling, large diameter bored, reverse circulation drill |
CNP 166 |
1 |
100 |
|
Total SWL |
116 |
||||
|
E |
Slope work |
Drill, percussive, hand-held (electric) |
CNP 064 |
2 |
103 |
|
|
|
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Roller, vibratory |
CNP 186 |
1 |
108 |
|
Total SWL |
116 |
||||
|
F |
Formwork and Reinforcement |
Bar bender and cutter (electric) |
CNP 021 |
2 |
90 |
|
|
|
Generator, standard |
CNP 101 |
1 |
108 |
|
|
|
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Saw, circular, wood |
CNP 201 |
1 |
108 |
|
|
|
Lorry |
CNP 141 |
1 |
112 |
|
Total SWL |
116 |
||||
|
Powered Mechanical Equipment Used for Construction of I-2 |
|
|
|||
|
A |
General |
Mobile Crane |
CNP 048 |
1 |
112 |
|
|
|
Dump Trucks |
CNP 067 |
2 |
117 |
|
|
|
Mobile generator |
CNP 101 |
2 |
108 |
|
|
|
Compressor |
CNP 002 |
2 |
102 |
|
|
|
Water Pump |
CNP 281 |
2 |
88 |
|
Total SWL |
121 |
||||
|
B |
Site Formation and Excavation |
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Dump Trucks |
CNP 067 |
1 |
117 |
|
Total SWL |
119 |
||||
|
C |
Concreting |
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
|
|
|
Compactor, vibratory |
CNP 050 |
1 |
105 |
|
Total SWL |
114 |
||||
|
D |
Hand Digging for Intake Shaft |
Breaker, hand-held, mass>35kg |
CNP026 |
1 |
114 |
|
|
(for the first 8m below ground) |
Excavator/loader, wheeled/tracked |
CNP081 |
1 |
112 |
|
Total SWL |
116 |
||||
|
E |
Drill & Blast for Intake Shaft |
Rock Drill (Hydraulic) |
CNP 182 |
1 |
123 |
|
|
|
Shotcrete Vehicle |
CNP 047 |
1 |
109 |
|
|
|
Explosive Delivery Vehicle |
CNP 141 |
1 |
112 |
|
Total SWL |
123 |
||||
|
F |
Diaphragm walling |
Piling, diaphragm wall, bentonite filtering
plant |
CNP 162 |
1 |
105 |
|
|
|
Piling, diaphragm wall, hydraulic extractor |
CNP 163 |
1 |
90 |
|
Total SWL |
105 |
||||
|
G |
Formwork and Reinforcement |
Bar bender and cutter (electric) |
CNP 021 |
2 |
90 |
|
|
|
Generator, standard |
CNP 101 |
1 |
108 |
|
|
|
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Saw, circular, wood |
CNP 201 |
1 |
108 |
|
|
|
Lorry |
CNP 141 |
1 |
112 |
|
Total SWL |
116 |
||||
|
Powered Mechanical Equipment Used for Construction of I-3 |
|
|
|||
|
A |
General |
Mobile Crane |
CNP 048 |
1 |
112 |
|
|
|
Dump Trucks |
CNP 067 |
2 |
117 |
|
|
|
Mobile Generator |
CNP 101 |
2 |
108 |
|
|
|
Compressor |
CNP 002 |
2 |
102 |
|
|
|
Water Pump |
CNP 281 |
2 |
88 |
|
Total SWL |
121 |
||||
|
B |
Site Formation and Excavation |
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Dump Trucks |
CNP 067 |
1 |
117 |
|
Total SWL |
119 |
||||
|
C |
Concreting |
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
|
|
|
Compactor, vibratory |
CNP 050 |
1 |
105 |
|
Total SWL |
114 |
||||
|
D |
Drill & Blast for Intake Shaft |
Rock Drill (Hydraulic) |
CNP 182 |
1 |
123 |
|
|
|
Shotcrete Vehicle |
CNP 047 |
1 |
109 |
|
|
|
Explosive Delivery Vehicle |
CNP 141 |
1 |
112 |
|
Total SWL |
123 |
||||
|
E |
Diaphragm walling |
Piling, diaphragm wall, bentonite filtering
plant |
CNP 162 |
1 |
105 |
|
|
|
Piling, diaphragm wall, hydraulic extractor |
CNP 163 |
1 |
90 |
|
Total SWL |
105 |
||||
|
F |
Slope work |
Drill, percussive, hand-held (electric) |
CNP 064 |
2 |
103 |
|
|
|
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Roller, vibratory |
CNP 186 |
1 |
108 |
|
Total SWL |
116 |
||||
|
G |
Formwork and Reinforcement |
Bar bender and cutter (electric) |
CNP 021 |
2 |
90 |
|
|
|
Generator, standard |
CNP 101 |
1 |
108 |
|
|
|
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Saw, circular, wood |
CNP 201 |
1 |
108 |
|
|
|
Lorry |
CNP 141 |
1 |
112 |
|
Total SWL |
116 |
||||
|
Powered Mechanical Equipment Used for Construction of O-1 |
|
|
|||
|
A |
General |
Mobile Crane |
CNP 048 |
1 |
112 |
|
|
|
Dump Trucks |
CNP 067 |
2 |
117 |
|
|
|
Mobile Generator |
CNP 101 |
2 |
108 |
|
|
|
Compressor |
CNP 002 |
2 |
102 |
|
|
|
Water Pump |
CNP 281 |
2 |
88 |
|
Total SWL |
121 |
||||
|
B |
Site Formation and Excavation |
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Dump Truck |
CNP 067 |
1 |
117 |
|
Total SWL |
119 |
||||
|
C |
Concreting |
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Concrete Lorry Mixer |
CNP 044 |
1 |
109 |
|
|
|
Compactor, vibratory |
CNP 050 |
1 |
105 |
|
|
|
Explosive Delivery Vehicle |
CNP 141 |
1 |
112 |
|
Total SWL |
116 |
||||
|
D |
Piling |
Piling, large diameter bored, oscillator |
CNP 165 |
2 |
115 |
|
|
|
Piling, large diameter bored, reverse circulation drill |
CNP 166 |
1 |
100 |
|
Total SWL |
118 |
||||
|
E |
Slope work |
Drill, percussive, hand-held (electric) |
CNP 064 |
2 |
103 |
|
|
|
Excavator |
CNP 081 |
2 |
112 |
|
|
|
Roller, vibratory |
CNP 186 |
1 |
108 |
|
Total SWL |
116 |
||||
|
F |
Formwork and Reinforcement |
Bar bender and cutter (electric) |
CNP 021 |
2 |
90 |
|
|
|
Generator, standard |
CNP 101 |
1 |
108 |
|
|
|
Crane, mobile |
CNP 048 |
1 |
112 |
|
|
|
Saw, circular, wood |
CNP 201 |
1 |
108 |
|
|
|
Lorry |
CNP 141 |
1 |
112 |
|
Total SWL |
116 |
||||
|
G |
Rap-rip |
Derrick barge |
CNP 061 |
1 |
104 |
|
|
|
Dump Truck |
CNP 067 |
1 |
117 |
|
Total SWL |
117 |
||||
The predicted noise impacts are shown in Table 4.5 (no mitigation measures), Table 4.6 (mitigation measures - quiet plant), and Table 4.7 (mitigation measures - noise barrier), the detailed calculations are shown in Appendix D which gives the construction activities involved at each intake and outfall location. Typically, the activities required for the construction of I-2 and I-3 included drill and blast shaft construction, hand dug method (for I-2 only), site formation and excavation, slope work and concreting. For I-1 and O-1, all aforesaid construction activities are required except hand digging and drill and blast shaft construction. Based on the construction programme of Tsuen Wan Drainage Tunnel given as Appendix A, there is a potential interfacing project named the Construction and Improvement of Tuen Mun Road. In order to predict the noise level in worse case scenario, the cumulative effect of construction activities at outfall location of Tsuen Wan Drainage Tunnel and at Yau Kom Tau section of Tuen Mun Road are assumed to be undertaken concurrently and shown in Table 4.5 below.
Table 4.5 Cumulative Noise Impacts (No mitigation Measures) - (Leq, 30min dB(A))
|
No. |
Location |
Description |
Noise Criteria |
Noise Impacts from the Project /dB(A) |
|
NSR1 |
Intake 1 |
|
70 |
79 |
|
NSR2 |
|
Kwai Shue House |
75 |
75 |
|
|
|
|
|
|
|
NSR3 |
Intake 2 |
|
75 |
91 |
|
NSR4 |
|
Yuen Yuen Care and Attention Home for the Aged |
75 |
84 |
|
NSR5 |
|
Western Monastery |
75 |
82 |
|
|
|
|
|
|
|
NSR6 |
Intake 3 |
Squatters |
75 |
85 |
|
NSR7 |
|
Route Twisk Villa |
75 |
74 |
|
|
|
|
|
|
|
NSR8 |
Outfall 1 |
|
75 |
82 |
|
NSR9 |
|
Greenview Terrace (Block 1) |
75 |
84 |
|
|
|
|
|
|
Notes: Bold figures indicates that the noise criteria is exceeded.
The noise assessment is based on the construction stage with the highest total SWL.
Table 4.5 shows that the cumulative construction noise impact of unmitigated construction activities associated with construction of tunnel, intakes and outfall together with the potential interfacing project would cause exceedence of daytime construction noise criterion at majority of the NSRs, up to 91dB(A) at NSR3, Hong Hoi Chee Hong Temple located close to the proposed intake I-2 location. Mitigation measures are therefore required for these NSRs in order to alleviate the noise impacts generated from the construction works.
1st Level of
Mitigation Measures
Table 4.6 Cumulative Noise Impacts (Mitigation Measures – Quiet Plant)
|
NSR No. |
Location |
Description |
Noise Criteria |
Noise Impacts from the Project /dB(A)(1) |
|
NSR1 |
Intake 1 |
|
70 |
75 |
|
NSR2 |
|
Kwai Shue House |
75 |
72 |
|
|
|
|
|
|
|
NSR3 |
Intake 2 |
|
75 |
91 |
|
NSR4 |
|
Yuen Yuen Care and Attention Home for the Aged |
75 |
83 |
|
NSR5 |
|
Western Monastery |
75 |
81 |
|
|
|
|
|
|
|
NSR6 |
Intake 3 |
Squatters |
75 |
84 |
|
NSR7 |
|
Route Twisk Villa |
75 |
74 |
|
|
|
|
|
|
|
NSR8 |
Outfall 1 |
|
75 |
81 |
|
NSR9 |
|
Greenview Terrace (Block 1) |
75 |
83 |
Notes: Bold figures indicates that the noise criteria is exceeded.
The noise assessment is based on the construction stage with the highest total SWL.
With the use of quiet plant, the cumulative noise impact would still exceed the daytime noise criterion (i.e. 75dB(A) for residential use and 70dB(A) for institutional use) by up to 16dB(A) and 5dB(A) respectively as shown in Table 4.6. Due to the close proximity to the construction works, the Hong Hoi Tsz Chee Hong Temple (NSR3) would be adversely affected and the predicted noise levels would exceed the daytime noise criterion (i.e. 75dB(A) for residential) by 16dB(A) and the Sik Sik Yuen Ho Fung College (NSR1) would exceed the criterion (i.e. 70dB(A) for schools) by 5dB(A). Details of the calculation are provided in Table D-3 and D-4 of Appendix D. Additional mitigation measures are therefore required to further reduce noise to acceptable levels.
2nd Level of
Mitigation Measures
Table 4.7 Cumulative Noise Impacts (Mitigation Measures – Noise Barrier)
|
NSR No. |
Location |
Description |
Noise Criteria |
Noise Impacts from the Project /dB(A)(1) |
|
NSR1 |
Intake 1 |
|
70 |
70 |
|
NSR2 |
|
Kwai Shue House |
75 |
66 |
|
|
|
|
|
|
|
NSR3 |
Intake 2 |
|
75 |
75 |
|
NSR4 |
|
Yuen Yuen Care and Attention Home for the Aged |
75 |
68 |
|
NSR5 |
|
Western Monastery |
75 |
66 |
|
|
|
|
|
|
|
NSR6 |
Intake 3 |
Squatters |
75 |
74 |
|
NSR7 |
|
Route Twisk Villa |
75 |
74 |
|
|
|
|
|
|
|
NSR8 |
Outfall 1 |
|
75 |
74 |
|
NSR9 |
|
Greenview Terrace (Block 1) |
75 |
75 |
|
|
|
|
|
|
Notes: Bold figures indicates that the noise criteria is exceeded.
The noise assessment is based on the construction stage with the highest total SWL.
In addition to the above
mitigation measures, a temporary vertical barrier (1)
which would provide sufficient screening effect ranged from 5 to 10 dB(A) reduction is proposed to be erected at the tunnel
portal area (i.e. Outfall 1) and intake locations (i.e. intakes 1, 2 and 3) in
order to alleviate the construction noise impact by blocking the line of view
from the nearby receivers. Indicative
locations and details of the barrier are demonstrated on Figure 4.6. Especially for the
construction of vertical shaft at Intake I-2, as the first 8m of the shaft will
be carried out by hand dug method, using vertical noise barrier will be able to
reduce the noise level to within acceptable level. When the shaft excavation
reaches 8m below ground, rock drilling will be required. However, the shielding effect offered by the
shaft above could achieve further
Table 4.7 demonstrated that with incorporation of quiet plant and the use of movable barrier, the cumulative noise impact at all NSRs would comply with the daytime construction noise criterion. Details of the calculation are provided in Table D-5 and D-6 of Appendix D.
Both TBM and Drill and Blast activities will be used to excavate rock. The interaction between the operation of equipment and the rock will induce ground borne noise and vibration (to varying extent depending on the geological conditions and equipment used). A preliminary assessment was carried out and presented in the following paragraphs.
As explained in Section 4.5.1, drill and blast (D&B) techniques are considered more feasible and thus envisaged for the rock excavations for the shaft constructions of Intakes I-2, and I-3. A separate Blasting Assessment Report will be produced in accordance with Practice Note for Authorized Persons (PNAP) 178 and submitted to Building Department in early 2005 for approval (not part of the EIA submission). Figure 4.5 is produced to highlight the locations of the proposed blasting, the nearest noise sensitive receivers, and the anticipated dominant vibration constraints. Discussions on each intake shafts are provided below.
The noise sensitive receiver identified in the proximity
is the
The noise sensitive receiver identified in the proximity is the squatters 50m south. Preliminary assessment indicates the use of explosives could be constrained by an existing registered feature (cut slope) immediate east of the shaft and the above mentioned squatters. The maximum charge weight is expected to be less than 0.4 kg/delay.
For the Yau Kom
Tau water treatment work, the preliminary assessment
indicates that the vibration level at this receiver would be 1.5mm/s which will
below the PPV limit of water retaining structure (i.e. 13mm/s).
Preliminary TBM
Assessment
As TBM would be used for tunnel excavation, the preliminary noise assessment due to the operation of TBM was conducted and the discussions on each intakes are provided below. Similar to the drill and blast, the contract will require the D & C contractor to carry out a detailed assessment to ascertain the possible noise impact on properties adjacent to the rock sections of tunnelling.
Intake I-1 and
Outfall
The noise sensitive receivers identified in the proximity at Intake I-1 and Outfall are Ho Fung College and Greenview Terrace respectively. Preliminary assessment indicates that the noise level at those receivers would be ranged from 24 dB(A) to 36 dB(A) which complied with the noise criteria during non-restricted period (i.e. 1900 to 0700). The detailed calculation is shown in Appendix D.
Intake I-2 and I-3
The noise sensitive receiver identified in the proximity
at Intake I-2 and I-3 are
The assessment as shown in this section previously carried
out only indicates marginal/non-compliance with the night-time criteria at 2300
– 0700 so it is suggested that at these locations the TBM would only operate
between
Referring to the foregoing section, the impacts due to ground borne noise and vibration were assessed throughout the tunnelling operation. The results revealed that the levels were well below normal human perception levels. To conclude, the transmission of structure borne noise due to the TBM and Drill and Blast operation is unlikely to cause impacts to the nearby residents or worshippers at the temple.
Maintenance may include the use of vehicles to remove debris from inside the tunnel and general maintenance surrounding the intake and outlet structures such as ensuring access is not encroached by vegetation, desilting of boulder/sand traps at intakes and outfall and repairing concrete surface. Details of the plant inventory for maintenance are listed as follows:
Activity Plant
General Lorry
Ventilation fan
Loader
Desilting Excavator
Grab
Water Jet
Concrete repairing Concrete chipper
Concrete pump
Compactor/vibratory
The main noise will
come from the cascade at the outfall structure. The tunnel will only be in
operation when rainfall intensities exceed 30m/hr. Under such conditions, the
noise of the rainfall itself in the vicinity of the noise sensitive receiver is
expected to exceed those from the cascade.
However, as mentioned, the event would only occur in very short duration
under rare occasion.
Also, the outfall structure is in the form of cascade at
which the level difference between tunnel portal and sea level is divided by 18
steps. The level drop at each stop is
only about 1.8m. It implied that the
noise level due to outfall structure in the form of cascade would be lowered
due to the energy dissipation being spread out. The noise level at receiver would be further
masked by the noise from major road traffic in the vicinity such as Tuen Mun Road and Castle Peak
Road i.e. 60 to 70 dB(A).
Consequently,
outfall noise is belonging to the categories of ‘white noise’, which is a
combination of all of the different frequencies of sound,
that aids sleeping, relaxation and provides sound masking for
distracting unwanted noise.
Hence, based on
the above-mentioned points, it can be concluded that the noise impact from
outfall would be insignificant.
Noise levels during maintenance activities are anticipated to be acceptable as the impacts are likely to be very short in duration (two times per year), will be conducted during normal working hours and will not require the simultaneous use of a number of PME.
Appropriate mitigation measures such as the use of quiet equipment and movable barriers will be developed to ensure that noise can be reduced to acceptable levels without causing programme delays.
Good site practice and noise management can significantly reduce the impact of construction site activities on nearby NSRs. The following package of measures should be followed during construction:
· only well-maintained plant should be operated on-site and plant should be serviced regularly during the construction works;
· machines and plant 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, where possible, be orientated to direct noise away from the NSRs;
· mobile plant should be sited as far away from NSRs as possible; and
· material stockpiles and other structures should be effectively utilised, where practicable, to screen noise from on-site construction activities.
For Drill and Blast Works
· Charge mass per delay should be decreased by minimising the number of blastholes firing on each delay.
· Smaller blasthole patterns and longer delays should be used between dependent charges
· Times of blasting should be established to suit the situation and firing blasts when neighbours are busy with their daily tasks (and at a regular time such as lunch time).
For TBM Tunnelling
· For the tunnel excavation, it is anticipated that beyond the initial length (say within 30m), excavation will be carried out well within the tunnel and door should be provided to further minimize the noise nuisance to the nearby receivers.
Good site practice and noise management can significantly reduce the impact of maintenance activities on nearby NSRs. The following package of measures should be followed during construction:
· only well-maintained plant should be operated on-site;
· machines and plant that may be in intermittent use should be shut down between work periods or should be throttled down to a minimum; and
· plant known to emit noise strongly in one direction, should, where possible, be orientated to direct noise away from the NSRs.
No residual impacts are predicted for the construction or operation of the Project.
Full compliance with the noise criteria will be achieved at all NSRs with the implementation of mitigation measures. Environmental monitoring and audit is recommended to ensure that the noise levels do not exceed the criteria during the construction phase as discussed in the EM&A Manual.
The construction of the Project may lead to noise generation if noise mitigation measures are not undertaken. It is predicted that various construction activities associated with the earthworks, excavation and construction may cause temporary impacts without mitigation. “Best practice measures”, Quiet plant and mobile noise barriers are recommended to suppress noise emissions from construction activities where noise exceedance is anticipated.
1) Noise Control Ordinance.
2) Professional Persons Environmental Consultative Committee (ProPECC) (1993) Practice Note 2/93 Noise from Construction Activities – Non-statutory Controls.
3) Planning Department
(2003)
4) Environmental Protection Department (Updated 2003) Guidelines On Design of Noise Barriers.
5) http://www.epd.gov.hk/epd/textonly/english/environmentinhk/noise/guide_ref/design_
barriers_content1.html
6) Technical Memorandum on Environmental Impact Assessment Process.
7) Technical Memorandum on Noise from Construction Work other than Percussive Piling.
8) U.K. Li, S.Y. Ng,
Prediction of blast vibration and current Practice of measurement in
9) Australian Standards
Association, Australian Standard AS2187.2 Part 2, 1993
10) Hiller, D.M. & Bowers
K.H. Groundborne vibration from mechanized tunnelling
works. Transport Research Laboratory,
11)
12)
13) Transportation Noise Reference Book
(1) Noise barriers should be located as close as possible to either the noise source or receiver. Gaps and openings t joints in the barrier material should be avoided where possible. Barrier material of surface mass in excess of 7 kg/m2 is desirable to achieve the maximum screening effect. The length of a barrier should generally be at least five times greater than its height and the minimum height of a barrier should be such that no part of the noise source will be visible from the noise sensitive receiver being protected.