Environmental Impact Assessment Ordinance (Cap. 499), Technical
Memorandum on Environmental Impact Assessment Process (TM-EIAO)
5.1.1.4
The
TM-EIAO specifies the assessment methods and criteria for impact assessment.
This Study follows the TM-EIAO to assess the potential water quality impact
that may arise during both the construction and operational phases of the
Project. Sections in the TM-EIAO relevant to the water quality impact
assessment are:
·
Annex
6 - Criteria for Evaluating Water Pollution; and
·
Annex
14 - Guidelines for Assessment of Water Pollution.
Hong Kong Planning Standards and
Guidelines (HKPSG)
5.1.1.5
Chapter
9 of the HKPSG outlines environmental requirements that need to be considered
in land use planning. The recommended guidelines, standards and guidance cover the selection of suitable
locations for the developments and sensitive uses, provision of environmental
facilities, and design, layout, phasing and operational controls to minimise adverse environmental impacts. It also lists out environmental factors that
influence land use planning and recommends buffer distances for land uses.
Practice Note for Professional Persons on
Construction Site Drainage (ProPECC PN 1/94) “Construction Site Drainage”
5.1.1.6
The
ProPECC PN1/94 provides guidelines for the handling and disposal of
construction discharges. It is
applicable to this study for the control of site runoff and wastewater
generated during the construction phase.
The types of discharges from construction sites outlined in the ProPECC
PN1/94 include:
·
Surface
runoff;
·
Groundwater;
·
Boring
and drilling water;
·
Wastewater
from concrete batching plant;
·
Wheel
washing water;
·
Bentonite
slurries;
·
Water
for testing and sterilization of water retaining structures and water pipes;
·
Wastewater
from building construction and site facilities; and
·
Acid
cleaning, etching and pickling wastewater.
5.2.1.1
The
Project falls within the Mirs Bay WCZ according to the WPCO and is located
within the Geopark (Double Haven Geo-Area), Yan Chau Tong Marine Park and
Plover Cove Country Park. At about 120m to the south of the Project is the Lai
Chi Wo Beach Site of Special Scientific Interest (SSSI). Both seagrass bed and
mangrove stand fall within the SSSI. In addition, few coral colonies are found
at the pier head of the existing Lai Chi Wo pier and at about 290m to the north
of the Project near Kau Ma Shek.
5.2.1.2
Furthermore,
several land-based WSRs have been identified, including the two watercourses at
Lai Chi Wo and the conservation areas at Lai Chi Wo and Siu Tan. Ponds were
identified within the conservation area at Siu Tan in the ecological survey,
but they were not active for aquaculture. Lai Chi Wo Special Area is located at
the southwest of about 390m from the Project.
5.2.1.3
A
greater extend of Mirs Bay WCZ is also reviewed with respect to the potential
water quality impact from the Project. Fish Cultural Zones are found within the
Mirs Bay WCZ. The nearest one at Sai Lau Kong is located at about 2km from the
Project.
5.2.2
Baseline
Water and Sediment Quality Conditions
Environmental Protection Department (EPD)’s Marine Monitoring Stations
5.2.2.1
The
latest marine water quality monitoring data in 2018 and sediment quality
monitoring data in 2014-2018 were adopted to determine the ambient marine water
and sediment quality, which are presented in Table
5.3 and Table 5.4 respectively.
The locations of the monitoring stations are presented in Figure 5.1. According to the Annual Report of Marine Water
Quality in Hong Kong 2018, the Mirs Bay WCZ attained full compliance of WQOs in
2018.
Table 5.3 Summary of EPD’s Routine
Marine Water Quality Data for Mirs Bay WCZ in 2018
|
Parameters |
Mirs
Bay WCZ [1] [2] [3] [4] |
|||
|
MM2 |
MM3 |
MM7 |
||
|
Temperature (°C) |
24.0 |
23.6 |
23.8 |
|
|
Salinity (‰) |
32.0 |
32.2 |
32.1 |
|
|
Dissolved Oxygen (mg/L) |
Depth Average |
6.6 |
6.6 |
6.5 |
|
Bottom |
6.6 |
6.2 |
6.2 |
|
|
Dissolved Oxygen (% saturation) |
Depth Average |
93 |
92 |
92 |
|
Bottom |
92 |
87 |
87 |
|
|
pH |
7.9 |
7.9 |
7.9 |
|
|
Secchi Disc Depth (m) |
3.4 |
3.6 |
3.7 |
|
|
Turbidity (NTU) |
1.2 |
2.0 |
1.6 |
|
|
Suspended Solids (mg/L) |
5.9 |
6.1 |
5.3 |
|
|
5-day Biochemical Oxygen Demand
(mg/L) |
0.8 |
0.7 |
0.7 |
|
|
Ammonia Nitrogen (mg/L) |
0.027 |
0.022 |
0.030 |
|
|
Unionised Ammonia (mg/L) |
<0.001 |
<0.001 |
<0.001 |
|
|
Nitrite Nitrogen (mg/L) |
0.008 |
0.008 |
0.005 |
|
|
Nitrate Nitrogen (mg/L) |
0.016 |
0.012 |
0.011 |
|
|
Total Inorganic Nitrogen (mg/L) |
0.05 |
0.04 |
0.05 |
|
|
Total Kjeldahl Nitrogen (mg/L) |
0.39 |
0.37 |
0.34 |
|
|
Total Nitrogen (mg/L) |
0.42 |
0.39 |
0.35 |
|
|
Orthophosphate Phosphorus (mg/L) |
0.006 |
0.005 |
0.005 |
|
|
Total Phosphorus (mg/L) |
0.02 |
0.02 |
0.02 |
|
|
Silica (as SiO2) (mg/L) |
0.49 |
0.47 |
0.45 |
|
|
Chlorophy ll-a (µg/L) |
2.2 |
2.1 |
2.3 |
|
|
E.coli (cfu/100mL) |
1 |
1 |
1 |
|
|
Faecal Coliforms (cfu/100mL) |
2 |
1 |
1 |
|
Notes:
[1]
The table above is extracted from the Annual Report of Marine Water Quality in
Hong Kong in 2018.
[2]
Unless otherwise specified, data
presented are depth-averaged (A) values calculated by taking the means of three
depths: Surface (S), Mid-depth (M), Bottom (B).
[3]
Data
presented are annual arithmetic means of the depth-averaged results except for E. coli and faecal coliforms which are annual geometric means.
[4]
Data
in brackets indicate the ranges.
Table 5.4 Summary of EPD’s Routine
Marine Sediment Quality Data for Mirs Bay WCZ in 2014-2018
|
Parameters |
Mirs
Bay WCZ [1] [2] [3] |
||
|
MS2 |
MS3 |
MS7 |
|
|
Particle Size Fractionation
<63μm (%w/w) |
96 |
85 |
89 |
|
Electrochemical Potential (mV) |
-347 |
-289 |
-359 |
|
Total Solids (%w/w) |
33 |
43 |
31 |
|
Total Volatile Solids (%TS) |
9.5 |
8.0 |
11.4 |
|
Chemical Oxygen Demand (mg/kg) |
16100 |
13230 |
17400 |
|
Total Carbon (%w/w) |
0.6 |
0.7 |
0.8 |
|
Ammonical Nitrogen (mg/kg) |
10.57 |
9.00 |
9.99 |
|
Total Kjeldahl Nitrogen (mg/kg) |
640 |
510 |
680 |
|
Total Phosphorus (mg/kg) |
190 |
210 |
200 |
|
Total Sulphide (mg/kg) |
70.1 |
39 |
63.5 |
|
Total Cyanide (mg/kg) |
0.2 |
0.1 |
0.1 |
|
Arsenic (mg/kg) |
8.2 |
7.0 |
7.3 |
|
Cadmium (mg/kg) |
0.3 |
<0.1 |
0.4 |
|
Chromium (mg/kg) |
35 |
27 |
31 |
|
Copper (mg/kg) |
24 |
12 |
21 |
|
Lead (mg/kg) |
47 |
30 |
42 |
|
Mercury (mg/kg) |
0.06 |
0.05 |
0.07 |
|
Nickel (mg/kg) |
22 |
17 |
21 |
|
Silver (mg/kg) |
0.3 |
<0.2 |
0.2 |
|
Zinc (mg/kg) |
120 |
75 |
100 |
|
Total Polychlorinated Biphenyls
(PCBs) (µg/kg) [4] |
18 |
18 |
18 |
|
Low Molecular Weight Polycylic
Aromatic Hydrocarbons (PAHs) (µg/kg) [5] [7] |
160 |
120 |
150 |
|
High Molecular Weight Polycylic
Aromatic Hydrocarbons (PAHs) (µg/kg) [6] [7] |
51 |
40 |
82 |
Notes:
[1] The table above is extracted from the Annual
Report of Marine Water Quality in Hong Kong in 2018.
[2] Data presented are arithmetic means;
data in brackets indicate ranges.
[3] All data are based on the analyses
of bulk (unsieved) sediment and are reported on a dry weight basis unless
stated otherwise.
[4] Total PCBs results are derived from
the summation of 18 congeners. If the concentration of a congener is below
report limit (RL), the result will be taken as 0.5xRL in the calculation.
[5] Low molecular weight poly aromatic
hydrocarbons (PAHs) include 6 congeners of molecular weight below 200, namely:
Acenaphthene, Acenaphthylene, Anthracene, Flourene, Naphthalene and
Phenanthrene.
[6] High molecular weight poly aromatic
hydrocarbons (PAHs) include 10 congeners of molecular weight above 200, namely:
Fluoranthene, Pyrene, Benzo(a)anthracene, Chrysene, Benzo(b)f luoranthene, Benzo(k)fluoranthene,
Benzo(a)pyrene, Dibenzo(a,h)anthracene, Benzo(g,h,i)perylene and
Indeno(1,2,3-cd)pyrene.
[7] Low and high molecular weight PAHs
results are derived from the summation of the corresponding congeners. If the
concentration of a congener is below report limit (RL), the result will be
taken as 0.5xRL in the calculation.
5.2.3
Marine
Park Water Quality Monitoring
5.2.3.1
In
addition, water quality monitoring in Yan Chau Tong Marine Park is carried out
quarterly by AFCD. The water quality monitoring at Yan Chau Tong Marine Park is
taken at three sites at Yan Chau Tong, Lai Chi Wo and Kau Ma Shek within the
marine park. This data will be adopted in establishing the water quality
baseline conditions for the Project. The monitoring results in 2019 are shown
in Table 5.5.
Table 5.5 Water Quality of Yan Chau Tong Marine Park in Year 2019
|
Parameters |
Yan
Chau Tong |
Lai Chi
Wo |
Kau Ma
Shek |
|||
|
Water Depth Surface |
Surface |
Bottom |
Surface |
Bottom |
Surface |
Bottom |
|
Air Temperature (°C) |
25.65 |
25.70 |
25.53 |
|||
|
Temperature (°C) |
25.59 |
24.51 |
25.68 |
24.40 |
25.43 |
24.51 |
|
Salinity (‰) |
32.11 |
32.53 |
30.85 |
32.47 |
32.26 |
32.50 |
|
Dissolved Oxygen (mg/L) |
7.66 |
6.17 |
7.49 |
6.03 |
7.50 |
5.96 |
|
pH |
8.14 |
8.19 |
8.14 |
8.16 |
8.21 |
8.20 |
|
Secchi Disc Depth (m) |
2.8 |
2.5 |
2.5 |
|||
|
Turbidity (NTU) |
<1 |
<1 |
1.00 |
1.00 |
1.25 |
1.25 |
|
Suspended Solids (mg/L) |
3.00 |
3.00 |
3.50 |
2.75 |
3.25 |
3.00 |
|
5-Day Biochemical Oxygen Demand (mg/L) |
2.63 |
3.25 |
2.75 |
2.25 |
2.13 |
2.25 |
|
Ammoniacal Nitrogen (mg/L) |
0.03 |
0.02 |
0.02 |
0.02 |
0.01 |
0.02 |
|
Unionized Ammonia (mg/L) |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
|
Nitrite Nitrogen (mg/L) |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
|
Nitrate Nitrogen (mg/L) |
0.03 |
0.03 |
0.03 |
0.03 |
0.03 |
0.03 |
|
Total Inorganic Nitrogen (mg/L) |
0.05 |
0.04 |
0.05 |
0.05 |
0.05 |
0.05 |
|
Total Kjeldahl Nitrogen (mg/L) |
0.45 |
0.56 |
0.34 |
0.29 |
0.61 |
0.36 |
|
Total Nitrogen (mg/L) |
0.46 |
0.58 |
0.51 |
0.41 |
0.63 |
0.39 |
|
Orthophosphate Phosphorus (mg/L) |
<0.01 |
<0.01 |
<0.01 |
0.01 |
0.01 |
0.02 |
|
Total Phosphorus (mg/L) |
<0.1 |
<0.1 |
<0.1 |
<0.1 |
<0.1 |
<0.1 |
|
Chlorophyll-a (μg/L) |
3.21 |
2.34 |
2.08 |
2.33 |
2.09 |
2.13 |
|
E. coli
(cfu/100 mL) |
7 |
5 |
0 |
22 |
0 |
16 |
|
Faecal Coliforms (cfu/100 mL) |
60 |
26 |
7 |
29 |
11 |
27 |
5.3
Assessment
Area and Water Sensitive Receivers
5.3.1
Assessment
Area
5.3.1.1
The
assessment area for the water quality impact assessment is stated in Clause
3.4.6.2 of EIA Study Brief (ESB-305/2017). It includes areas within 500m from
the boundary of the Project and the works of the Project, and covers the Mirs
Bay Water Control Zone as designated under the Water Pollution Control
Ordinance (Cap. 358), and the water sensitive receivers outside the 500m
boundary but in the vicinity of the Project. The assessment area for this
Project includes Yan Chau Tong Marine Park near Lai Chi Wo and extends to
include Fish Culture Zone at Sai Lau Kong. Figure
5.1 shows the water quality assessment area for this Project.
5.3.2
Water
Sensitive Receivers
5.3.2.1
Representative Water Sensitive Receivers (WSRs) are
identified within the assessment area and indicated in Figure 5.1. They include Marine Park, Country Park, SSSI, Conservation
Areas, Fish Culture Zones,
ponds, watercourses and coral colonies as summarised in Table 5.6.
Table
5.6 WSRs within assessment
area
|
Description |
Type |
Approximate
distance from the Project (m) |
|
|
LCW-W1 |
Yan Chau Tong
Marine Park |
Marine Park |
Project within
the Marine Park |
|
LCW-W2 |
Plover Cove
Country Park |
Country Park |
Project within
the Country Park |
|
LCW-W3 |
Lai Chi Wo Beach
SSSI |
SSSI |
120 |
|
LCW-W4 |
Coral Colonies
near Kau Ma Shek |
Coral Colonies |
290 |
|
LCW-W5 |
Watercourse at
Lai Chi Wo |
Inland Natural
Watercourse |
210 |
|
LCW-W6 |
Watercourse at
Lai Chi Wo |
Inland Natural
Watercourse |
220 |
|
LCW-W7 |
Conservation Area
at Lai Chi Wo |
Conservation Area |
160 |
|
LCW-W8 |
Conservation Area
at Siu Tan (Including ponds within) |
Conservation Area
and Ponds |
370 |
|
LCW-W9 |
Lai Chi Wo
Special Area |
Special Area |
390 |
|
LCW-W10 |
Fish culture zone
at Sai Lau Kong |
Fish Culture Zone |
2,000 |
|
LCW-W11 |
Spawning grounds
of commercial fisheries resources |
Fisheries
resources |
Project within
the area |
|
LCW-W12 |
Nursery grounds
of commercial fisheries resources |
Fisheries
resources |
Project within the
area |
Note:
[1] Few coral colonies with very low coverage are
located at the pier head of the existing LCW Pier. They are unavoidably lost by
the Project and is not considered as a WSR.
5.4
Construction
Phase Assessment
5.4.1
Identification
of Environmental Impacts
5.4.1.1
The Project comprises the following works which may potentially give rise to water
quality impacts during the construction phase. No specific
activity during the operational phase is anticipated to bear water quality
impacts. Detailed description of the works and tentative construction programme
are presented in Section 2.
·
Carrying
out site investigation works for detailed design;
·
Provision
of plants, equipment and materials on working barge(s) for implementation of
the Project;
·
Provision
of temporary berthing and mooring facilities (temporary pier) using floating
pontoon and/or steel structures supported by piles to maintain access to Lai
Chi Wo throughout the construction stage;
·
Installation
of piles for the new pier and as guide piles for floating pontoon;
·
Modification
of the existing pier and construction of new pier structures (e.g. installation
of precast elements of the pier structure etc.);
·
Construction
of associated facilities on the pier; and;
·
Removal
of temporary pier after completion of the improvement works on the existing
pier.
·
Marine-based
site investigation works;
·
Marine-based
foundation works;
·
Above-water
construction works;
·
Demolition
works;
·
Hydrodynamic
impact;
·
Site
run-off from general site operation;
·
Accidental
spillage of chemicals; and
·
Sewage
from workforce.
5.4.2
Prediction
and Evaluation of Environmental Impacts
Marine-based Site Investigation Works
5.4.2.2
Before the commencement of rotary drilling works, all
drill rig, circulation tank and equipment shall be thoroughly cleaned off-site.
An outer casing shall be first placed on the seabed level to avoid the spillage
of drilling fluid during drilling works. Throughout the drilling process,
seawater shall be used as drilling fluid for lubricating the drill bit, and no
lubricants or other additives shall be introduced. The drilling fluid shall be
circulated within the system through the circulation tank, where the recycled
fluid with small amount of sediment will be settled and collected in the tank.
The inner casing shall be advanced to the rockhead by rotary core drilling and
shall be cleaned by the recirculated flushing water before extraction.
Thereafter, the inner and outer casings shall then be extracted slowly to the
barge deck. Final disposal of the drilling fluid would be discharged offsite
with a valid discharge license under the WPCO with the provision of silt
removal facilities, or to the facilities of the Contractor. The discharge
requirements shall comply with TM-WPCO as specified in Table 5.2. No
sediment within the borehole will be made in direct contact with the open sea
water and sediment disposal under the site investigation works is not
anticipated.
Marine-based Foundation Works (for Temporary Pier and Proposed Pier)
5.4.2.4
The
pre-drilling works of foundation for proposed LCW Pier would be in the similar
fashion as the site investigation work as described in Section 5.4.2.1 to 5.4.2.3.
Pile Installation Works
5.4.2.5
The
foundations of the proposed LCW Pier and the temporary pier will be composed of
in-situ bored piles or similar pile types (e.g. rock socketed Steel H-pile). A
working platform in form of a working barge and/or temporary steel structure
supported by mini-piles (~219 or 273mm dia.) will be adopted to facilitate the
pier construction works. Working barge will be fixed in a position by anchoring
onto the seabed while the mini-piles used to support the temporary steel
structure would follow the pile casing and silt curtain method as discussed in Section
2.6.3.2 to Section 2.6.3.3 in order to
control the water quality and
ecological impacts. Minimal
disturbance of existing seabed level during positioning of anchors and
mini-pile installation would be resulted but significant dispersion of
suspended solids is not expected.
5.4.2.6
A
pile casing of approximately 0.8-1m in diameter will be slowly drilled through
the seabed and would disturb small areas of seabed, only limited spillage of
sediment is expected. Once the pile casing passed through the surface of
seabed, all excavation work would be carried out inside the pile casing to
avoid spillage of sediment and water containing suspended solids (SS) during
piling work. The pile casing will be installed into the seabed by a hydraulic
oscillator from the working platform. Pile shaft excavation by using hammer
grab will be carried out within the casing. Grab excavator will be used to
minimise leakage of materials collected during the grab process. The grabbed
materials will then be conveyed to the circulation tank on the working barge
where the suspended solids will be settled and collected in the tank. No grabbed
materials will be in direct contact with the open sea water. An illustrative
figure of the tentative set-up of the marine-based foundation work is shown in Image 5.1.
Image 5.1 Tentative Set-up of Marine-based
Foundation Work
5.4.2.7
As
a precautionary measure, the proposed temporary pier and permanent pier will be
surrounding by silt curtains during their construction. According to the
Contaminated Spoil Management Study [1], the installation of silt curtain
would reduce dispersion of suspended solids by around 75%. Commonly used silt
curtains include woven polypropylene geotextile, reinforced poly-vinyl chloride
or similar geotextile materials which have been widely adopted in different
marine-based construction projects in Hong Kong and well proven for their
effectiveness to minimise dispersion of suspended solids. The water depth of
the Project site is approximately 2m to 3m, where the water depth is sufficient
for the deployment of silt curtain. Considering that the Project is located
within the inshore of Crooked Harbour, where the waters is relatively calm,
deployment of silt curtain would be suitable to mitigate the potential water
quality, even though the water depth of the Project site is relatively shallow.
5.4.2.8
Silt
curtains will be deployed before driving of casings into the seabed, and will
only be removed after the removal of the casings. Deployment locations at
different construction stages are illustrated in Appendix 5.2. Water
quality impacts due to the installation and removal of the casings are
therefore not anticipated with the deployment of silt curtain. In addition,
regular inspection should be undertaken in the course of deployment of the silt
curtain to ensure the intact of silt curtain and its proper function. With the mitigation
measures in place, no adverse water quality impact is anticipated during the
insertion of pile casings.
5.4.2.9
The
steel casing will then be jacked down into the ground by the oscillator again
and will continue the next grabbing process until reaching bedrock. Reverse
Circulation Drill (RCD) will be deployed to drill through the bedrock and hard
material encountered until reaching the required founding level.
5.4.2.10
The
grabbed materials collected in the circulation tank will be transported by
barge or marine vessel to the public fill reception facilities (e.g. Tseung
Kwan O Area 137 Fill Bank which receives public fill only) or the Outlying
Island Transfer Facilities (which receive both public fill and non-inert
C&D materials).
5.4.2.11
Upon
completion of excavation and removal of the drill bit, air-lifting will be
carried out to remove debris inside the casing. Drilling fluid in the pile
casing will be continuously pumped out to the circulation tank on the barge to
avoid muddy water overflown from the casing to the sea directly. The drilling
fluid will be stored on barge where the recycled fluid with small amount of
sediment will be settled and collected in the tank. The recycled fluid will be used
for the subsequent piling works. No drilling fluid and sediment will be
discharged on site or within the boundary of Yan Chau Tong Marine Park, Plover
Cove Country Park, Lai Chi Wo Beach SSSI and the other identified WSRs.
5.4.2.12
Final
disposal of the drilling fluid would be discharged offsite with a valid
discharge license under the WPCO with the provision of silt removal facilities,
or to the facilities of the Contractor. The discharge requirements shall comply
with TM-WPCO as specified in Table 5.2.
Thus, water quality and ecological impacts are not anticipated from the
marine-based foundation works on the identified WSRs.
Above-water Construction
Works
5.4.2.13
The proposed deck of the
temporary pier would be a steel structure with working barge of about 70m long
and 3m wide above the sea. Prefabricated elements of steel
structure will be shipped to and installed on site. No adverse water quality
impact is anticipated from the installation works.
5.4.2.14
For the permanent pier,
the above-water construction works would involve the establishment of a proposed
pier of concrete structure of typically about 6m to 8m wide, increased to 15.5m
at the pier head, and 155m long above the sea. The
scale of the construction works is considered minor. Prefabrication approach will first be
considered when designing concrete superstructures. Selected concrete structures will be
formed by pre-cast concrete offsite in a controlled environment and installed
on site when ready. This can directly avoid on-site casting activities that would
have potential impact on water quality. Moreover, this approach can minimise
the extent and duration of on-site construction activities. As a result, the
water quality impacts associated with these construction activities including
site run-off, accidental spillage of chemicals and sewage from workforce could
thus be avoided or minimised.
5.4.2.15
However,
due to site constraints or design requirements, prefabrication approach may not
be always feasible. For small quantities of structural elements e.g. docks
above shallow waters to be casted on site and in-situ stitching, the formworks
shall be water-tight to avoid leakage. Concrete shall be poured slowly with due
care to avoid spillage of concrete into nearby water bodies.
Demolition Works
5.4.2.17
Silt
curtain will be installed around the piles prior to demolition work. Therefore,
no adverse water quality impact is anticipated.
Hydrodynamic Impact
5.4.2.18 The Project is located at the eastern coast area of Crooked Harbour near Lai Chi Wo. The cove is partly surrounded by the natural terrain with a wide coastal inlet of about 800m formed by Kau Ma Shek and Chung Wan Tsui. The deepest seabed level along the inlet is approximately -8mPD which has a water depth of about 8.5m at the mean lower low water (MLLW).
5.4.2.19 Within the cove area, the seabed level varies from -2mPD to -8mPD (i.e. approximately 2.5m to 8.5m water depth at MLLW) except at the estuary of Lai Chi Wo creek, where mudflat has been accumulated over the years and mangroves are also identified to the immediate south. There are however very limited mangroves located to the north of the estuary of the creek. The separation distance between the existing pier and the creek debouch point where the water depth is the shallowest is approximately 240m. Figure 5.2 shows the relative location of the Project in relation to the cove area.
5.4.2.20 The existing pier is a solid finger pier with concrete structures. Based on the hydrographic survey (see Figure 5.3), the seabed of the existing per head is about -1.0mPD which has a water depth of about 1.5m at MLLW. As explained in Section 2.4.5, the proposed pier is extending from the existing pier head to the deeper water region of seabed level of about -2.4mPD or lower (i.e. 2.9m depth at MLLW) which would be sufficient for vessels to manoeuvre.
5.4.2.21 It should also be noted that the design of the proposed pier has duly considered all practicable approaches to minimise hydrodynamic impacts as far as practicable. Instead of adopting a solid pier design (similar to the existing pier), the proposed pier would adopt piled foundation to support the pier structures. Along the total length of 155m for the new pier structure, there would be about 46 nos. of approximately 0.8m diameter bored piles and 6 nos. of approximately 1m diameter bored piles with typical spacing around 5m to 8m. It is noted that the actual area that would be occupied by those piles is not significant. The pile configuration is typical for other piers in Hong Kong[2] which are of similar dimensions. (see Figure 5.4)
5.4.2.22
For
the temporary pier, it will be constructed about 30m to the north of the
existing pier. This would also avoid the shallowest area within the cove area. The
length of the temporary pier will be about 70m, which is comparable to that of
the existing pier of 64m. During construction of the temporary pier, around 14
nos. of piles will be constructed. The diameter of the piles would be
approximately 800mm and the pile spacing is approximately 9.5m.
5.4.2.23
As
the temporary pier will be oriented in parallel with the existing pier and the
piles of the temporary pier will be only occupied a small footprint, the piles and
pier structures of the temporary pier are unlikely cause any changes of the
existing flow regime and tidal flux in the eastern coastal area of Crooked Harbour.
5.4.2.24
Due
to small footprint of the piled foundation, changes in the flow regime and
hydrodynamic in the eastern coastal area of Crooked Harbour are limited during
the construction phase of the Project.
Site Run-off from General Site Operation
5.4.2.25
Runoff
could likely come from the works during construction. The surface runoff might
be polluted by:
·
Wastewater
from structure construction and site facilities;
·
Acid
cleaning, etching and pickling wastewater; and
·
Accidental
spillage of chemicals.
5.4.2.26
Construction
runoff may cause physical, biological and chemical effects. The physical
effects include potential increase in suspended solids levels. Runoff
containing significant amounts of concrete and cement-derived material may
cause primary chemical effects such as increasing turbidity and discoloration,
elevation in pH, and accretion of solids. A number of secondary effects may
also result in toxic effects to water biota due to elevated pH values, and
reduced decay rates of faecal micro-organisms and photosynthetic rate due to
the decreased light penetration. Appropriate precautionary measures shall be
adopted to prevent site runoff to the Marine Park.
Accidental Spillage of Chemicals
5.4.2.27
The
chemicals used during construction, such as fuel, oil, solvents and lubricants
from maintenance of construction machinery and equipment, may cause pollution
and trigger physicochemical effects in the nearby water bodies if accidental
spillage occurs. To avoid adverse impacts of chemical spillage, best practices
of chemical storage practices such as storage under a covered area, provision
of secondary containment and material safety data sheets are advised. Spill
kits are also advised to handle spillage and the staff should be trained for
handling spillage. Emergency Spillage Plan should also be prepared by the
future Contractor as a precautionary measure for accidental spillage of
chemicals. With the implementation of mitigation measures stated in Section 5.4.3, neither adverse nor cumulative water quality impact is anticipated.
Sewage from Workforce
5.4.2.28
According to Table T-2 of Guidelines for Estimating
Sewage Flows for Sewage Infrastructure Planning, the unit flow is 0.23 m3/day/employee.
The number of workforce (clerical staff
and workers) to be employed for the Project is around 10 during the construction
period. It is estimated that the volume of sewage from workforce would be around 2.3 m3/day.
Because temporary sanitary facilities, e.g. portable chemical toilets, and sewage holding tanks will be provided on vessels,
no adverse water quality impact is anticipated.
5.4.3
Summary
of Environmental Impact on WSRs
5.4.3.1
The
Project involves various marine-based construction works, including site
investigation, foundation works for temporary pier and proposed pier, and
demolition of the temporary pier. Potential water quality impacts are
anticipated on the nearby Yan Chau Tong Marine Park (LCW-W1), Lai Chi Wo Beach
SSSI (LCW-W3) and coral colonies at Kau Ma Shek (LCW-W4). Nevertheless, the site
investigation will be carried out with deployment of outer casing while foundation
works will be carried out with deployment of silt curtain. Drilling fluid will
not be in contact with the open sea water bodies. Drilling fluid will also be
recycled for subsequent works after sedimentation.
5.4.3.2
All
drilling fluid would be discharged offsite with a valid discharge license under
the WPCO with the provision of silt removal facilities. No discharge shall be
permitted within the Marine Park area so that there will not be any negative
impact on the beneficial uses of the Marine Park. The discharge requirements
shall comply with TM-WPCO. In addition, other potential water quality impact
could arise from the site surface runoff, accidental spillage of chemicals and
sewage from workforce. Mitigation measures are recommended in Section 5.4.4 to minimise the potential
water quality impact.
5.4.3.3
As
the Project only involves minor works such as installation of precast structures
at the edge of the Plover Cove Country Park (LCW-W2) near the existing hiking
trail, water quality impact from the Project is not anticipated on this WSR. As
regards the two watercourses (LCW-W5 and LCW-W6) and the two conservation areas
(LCW-W7 and LCW-W8), they are located at inland area of LCW area. The
watercourses are located at upstream of the Project and hydrologically
separated from the Project. Adverse water quality impact is therefore not
anticipated. Likewise, Lai Chi Wo Special Area (LCW-W9) is located at the
inland area of Lai Chi Wo. It is not hydrologically linked with the Project and
adverse water quality impact is therefore not anticipated.
5.4.3.4
The
Fish Culture Zone at Sai Lau Kong (LCW-W10) is located more than 2km from the
Project. Given the small scale of the Project, the water quality impact on this
fish culture zone is not anticipated. As regards the spawning grounds of
commercial fisheries resources (LCW-W11) and nursery grounds of commercial
fisheries (LCW-W12), since only piles will be constructed into the seabed,
large scale release of contaminants from the sediment would not occur, and the
suspended solids would be further localised with the use of silt curtain during
the piling works. Potential fisheries impact during the construction phase are
discussed in Section 10.5.3.
5.4.4
Mitigation
Measures
5.4.4.1
For
any works in the Marine Park, the following good site practices and mitigation
measures shall be followed:
·
Observe
and obey the guidelines stipulated under the Marine Parks Ordinance (Cap. 476)
and the Marine Parks and Marine Reserves Regulation (Cap. 476A);
·
The
power-driven vessel shall not exceed a speed of 10 knots at any time inside the
marine park;
·
Restrict
anchor or moor except under and in accordance with a permit or at mooring sites
provided by the Authority;
·
Obstruct
the pollution of the water body or discharge of waste; and
·
Restrict
the collection of any marine life and resources in or from the Marine Park.
Marine-based Site Investigation Works
·
Before
commencement of drilling works, all drill rig, circulation tank and equipment
shall be thoroughly cleaned off-site;
·
Throughout
the drilling process, seawater shall be used for flushing medium and no
lubricant, hydraulic fluid or other additives shall be introduced;
·
The
drilling fluid shall be circulated within the system through the circulation
tank, where the recycled fluid with small amount of sediment shall be settled
and collected in the tank;
·
Prior
to actual sampling, an outer casing shall be placed on the seabed level to
avoid the spillage of sediment and water containing SS;
·
After
the completion of sampling work, casing shall be cleaned by the recycled water
and collected back to the circulation tank. The inner and outer casing shall
then be extracted slowly to the barge deck and the sediment collected in the
tank during the drilling process shall be delivered to the depot of the
Contractor;
·
Final
disposal of the drilling fluid should be discharged offsite and outside the
Country Park, Marine Park, SSSI and other WSRs with a valid discharge license
under the WPCO with the provision of silt removal facilities, or to the depot
of the Contractor; and
·
To
ensure all geotechnical and environmental samples will be collected within the
casing without any contact with the surrounding waterbodies.
Marine-based Foundation Works
Pre-drilling Works
Pile Construction Works
5.4.4.4
The
construction methodology will incorporate all the best practices for the marine
works to avoid and minimise water quality impacts. These good practices are
summarised below.
·
Silt
curtains should be deployed around active marine works areas prior to
starting marine-based foundation works to avoid water quality impact. The
Contractor shall prepare a Silt Curtain Deployment Plan to the approval of EPD prior
to the commencement of works to ensure the implementation of the silt curtains
would be effective and compatible with the aquatic environment (e.g. considering
the tidal effect, wind and current speed, etc.). They should only be removed
when all marine-based works are completed;
·
Pile
casing should be used for the construction of foundations;
·
Excavation
should only be conducted inside pile casing. Only one grab should be used for
excavation at the same time;
·
All
vessels deployed should have adequate clearance from the seabed at all tide
levels to ensure no undue turbidity is generated from propeller wash;
·
There
should only be 1-2 piles to be constructed at the same time;
·
Drilling
fluid in the pile casing should be continuously pumped out to the circulation
tanks on the barge to avoid muddy water overflown from the casing to the sea
directly. The circulation tanks shall be provided with
adequate capacity to avoid if any overflow of drilling fluid;
·
The
drilling fluid shall be circulated within the system through the circulation
tank, where the recycled fluid with small amount of sediment shall be settled
and collected in the tank; and
·
Final
disposal of the drilling fluid should be discharged offsite and outside the
Country Park, Marine Park, SSSI and other WSRs with a valid discharge license
under the WPCO with the provision of silt removal facilities, or to the depot
of the Contractor.
Above-water
construction works
5.4.4.5
To avoid and minimise any potential water quality
impacts arising from the above-water construction works, the following mitigation
measures are proposed.
·
Prefabrication
methods should be adopted during construction as far as practicable;
·
If
in-situ concrete casting is required,
formworks should be designed to be water-tight and concrete should be poured
into the formwork slowly and evenly to avoid accidental spillage to water
bodies; and
·
Silt curtain will also be deployed throughout the
concrete casting process to the surrounding waters during construction to
control any residual release.
Site Run-off from General Site
Operation
5.4.4.6
To
reduce the potential water quality impact due to construction site runoff, the
following good site practices in accordance to Practice Note for Professional
Persons on Construction Site Drainage, Environmental Protection Department,
1994 (ProPECC PN 1/94) should be implemented to avoid potential adverse water
quality impacts.
·
The
design of efficient silt removal facilities should be based on the guidelines
in Appendix A1 of ProPECC PN 1/94. The detailed design of the sand/silt traps
should be undertaken by the contractor prior to the commencement of
construction;
·
Schedule
construction works to minimise surface construction works during the rainy
seasons (April to September);
·
Inspect
and maintain all drainage facilities and erosion and sediment control
structures regularly to ensure proper and efficient operation at all times and particularly
following rainstorms;
·
Cover
all construction materials at temporary storage area with tarpaulin or similar
fabric during rainstorms and implementation of measures to prevent the washing
away of construction materials, soil, silt or debris into any drainage system;
·
Cover
manholes (including newly constructed ones), if any, adequately and seal
temporarily to prevent silt, construction materials or debris being washed into
the drainage system and storm runoff being directed into foul sewers;
·
Take
precautions at any time of year when rainstorms are likely. The actions to be
taken based on the guidelines in Appendix A2 of ProPECC PN 1/94;
·
Collect,
handle and dispose construction solid waste, debris and rubbish on site to
avoid water quality impacts;
·
Provide
locks for all fuel tanks and storage areas and locate on sealed areas, within
bunds of a capacity equal to 110% of the storage capacity of the largest tank
to prevent spilled fuel oils from reaching water sensitive receivers nearby;
and
·
Regular
environmental audit on the construction site should be carried out in order to
prevent any malpractices. Notices should be posted at conspicuous locations to
remind the workers not to discharge any sewage or wastewater into the water
bodies, marsh and ponds.
Accidental Spillage of Chemicals
5.4.4.7
To reduce the potential water quality impact due to
accidental spillage of chemicals, the following mitigation measures should be
implemented to avoid potential adverse water quality impacts.
·
Preferably
carry out any maintenance activities and works with chemicals use outside the
Project site given the advantage that machineries located on barges can be
easily re-located.
·
The
Contractor shall also prepare an Emergency Spillage Plan to detail the responses
in case of spillage. The outline of the Emergency Spillage Plan is provided in Appendix 5.1.
Sewage from workforce
5.4.4.8
To mitigate the water quality impacts of sewage
arising from the on-site construction workers, the following measures should be
implemented:
·
Provide
temporary sanitary facilities, e.g. portable chemical toilets and sewage
holding tanks with adequate capacity to collect the sewage from workforce. They
should be cleaned by a licensed collector for proper disposal on a regularly basis.
·
Post
notices at conspicuous locations to remind the workers not to discharge any
sewage or wastewater into the surrounding environment during the construction
phase of the Project.
5.4.5
Cumulative
Impacts with Concurrent Projects
5.4.5.1
There is no concurrent project with potential
cumulative water quality impact in the vicinity of the Project site. Therefore,
no cumulative water quality impact is anticipated.
5.4.6
Residual
Impacts
5.4.6.1
With the implementation
of the aforementioned mitigation measures, no adverse residual environmental
impacts are anticipated.
5.5
Operational
Phase Assessment
5.5.1
Identification
and Evaluation of Environmental Impacts
5.5.1.1
As mentioned in Section 2, the main objectives of the Project are to provide
improved pier facilities and adequate structural integrity for safe pier usage.
The existing pier of 64m long and 2.5m wide will be widened and extended. The improved pier would have a width of 6m to 8m increased
to 15m at the pier head and a length of 155m. With the improved pier head
located farther away from the shoreline and at a deeper seabed level, a deeper
draft can be provided for vessel berthing. Besides, there is neither planned
increase in the existing Kaito services nor alteration of their routing. Therefore,
no adverse water quality is anticipated from the Project during the operational
phase.
Hydrodynamic Impact
5.5.1.2
As
discussed in Section 5.4.2.14, the Project is locating at
the eastern coast area of the Crooked Harbour near Lai Chi Wo. By the
hydrographic survey, the seabed of the existing pier head is about -1.0mPD which has a water depth of about 1.5m at MLLW. As
explained in Section 2.4.5, the
proposed pier is extending from the existing pier head to the deeper water
region of seabed level of about -2.4mPD or lower (i.e. 2.9m depth at MLLW)
which would be sufficient for vessels to manoeuvre.
5.5.1.3 The design of the proposed pier has duly considered all practicable approaches to minimise hydrodynamic impacts as far as practicable. Instead of adopting a solid pier design (similar to the existing pier), the proposed pier would adopt piled foundation to support the pile structures. Along the total length of 155m for the new pier structure, there would be about 46 nos. of approximately 800mm diameter bored piles and 6 nos. of approximately 1m diameter bored piles which typical spacing around 6-8m. It is noted that the actual area that would be occupied by those piles is not significant. The pile configuration is typical for other similar piers in Hong Kong. (see Figure 5.4)
5.5.1.4 Due to small footprint of the piled foundation, changes in the flow regime and hydrodynamic in the eastern coastal area of Crooked Harbour are limited during the construction phase of the Project.
Water Quality
Impact
5.5.1.5
During
the operational phase, existing cleaning practices will be maintained. The pier
will be cleaned by natural cleaning mechanism such as rain without the use of
detergents or chemicals. Surface runoff from the pier will not be polluted. Thus,
water quality impact from the spillage of detergents or chemicals are not
anticipated.
5.5.2
Summary
of Environmental Impacts on WSRs
5.5.2.1
As
the pier will be constructed with around 52 nos. of bored piles of about 0.8-1m
diameters with sufficient spacing, the change of flow regime in the Crooked Harbour
by the Project is limited.
5.5.2.2
Adverse
hydrodynamic impact on the Yan Chau Tong Marine Park (LCW-W1) and Lai Chi Wo
Beach SSSI (LCW-W3) is not anticipated. For the other WSRs, they are either
hydrological isolated from the Project or located further away from the
proposed piers. No impact is expected for these WSRs.
5.5.2.3
Furthermore,
the pier will be cleaned by natural cleaning mechanism such as rain without the
use of detergents or chemicals. Thus, water quality impact is not anticipated
for all WSRs.
5.5.3
Mitigation
Measures
5.5.3.1
As the Project would not generate or induce any additional water quality
impact, mitigation measures are considered not necessary.
5.5.4
Cumulative
Impacts with Concurrent Projects
5.5.4.1
As
the Project would not generate or induce any additional water quality impact,
no cumulative water quality impact with concurrent projects during the
operational phase is anticipated.
5.5.5
Residual
Impacts
5.5.5.1
As the Project would not generate or induce any additional water quality
impact, it is anticipated that there would be no residual water quality impact
during the operational phase.
5.6 Environmental Monitoring and Audit
5.6.1.1
With the implementation of
recommended mitigation measures such as installation of silt curtain prior to
the commencement of construction works, adverse water quality impact is not
anticipated. Nevertheless, to ensure the Project will not deteriorate the water
quality in Yan Chau Tong Marine Park during the construction phase of the
Project, water quality monitoring, including SS, has been proposed at two
monitoring stations. Further details of the monitoring programme and
accompanying Event and Action Plan are provided in the EM&A Manual.
5.7.1
Construction
Phase
5.7.1.1
Potential hydrodynamic and water quality impact from
the construction activities have been assessed. Given the small scale of the pier
and the adoption of piled foundation with sufficient spacing, hydrodynamic
impact from the new pier and the temporary pier is not anticipated.
5.7.1.2
Potential water quality impact would arise from the
construction activities, in particular the marine-based site investigation and
foundation works. Nevertheless, with the implementation of recommended
mitigation measures such as the use of silt curtain to confine the SS, adverse
water quality impact is not anticipated. There will neither be directly discharge on-site, within the Yan Chau
Tong Marine Park nor other WSRs. In addition, with good site control practices,
emergency spillage plan and provision of portable toilets, adverse impacts from
surface runoff from construction site operation, accidental spillage of
chemicals and sewage from workforce are not anticipated.
5.7.2
Operational
Phase
5.7.2.1
The
main objectives of the Project are to improve the existing pier facilities such
as providing standard landing steps, adequate berthing space and enhancing
accessibility to those in need. There is no planned increase in the existing
Kaito services nor alteration of their routing. Therefore, no adverse water
quality impact is anticipated from the Project during the operation phase. Given the small scale
of the pier and the adoption of piled foundation with sufficient spacing, hydrodynamic
impact from the new pier is not anticipated.