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. The Project site is located within Tung Ping Chau Marine Park, but outside the core areas of the marine park at Tai Tong Wan (i.e. about 240m to the north of the Project) and A Ma Tsui (i.e. about 510m to the south of the Project). Coral colonies and algae are commonly found within Tung Ping Chau Marine Park. Coral colonies are readily discovered around the Project site while algae mostly grow in the west coast of Tung Ping Chau where the water quality is not anticipated to be affected by the Project.
5.2.1.2 Furthermore, several land-based WSRs have been identified including Plover Cove (Extension) Country Park, which is 100m away from the Project, and the two watercourses at Tung Ping Chau, which are 200m and 350m away from the Project respectively.
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.
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 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] |
||
|
MM4 |
MM5 |
||
|
Temperature (°C) |
23.3 |
23.2 |
|
|
Salinity (‰) |
32.4 |
32.4 |
|
|
Dissolved Oxygen (mg/L) |
Depth Average |
6.5 |
6.4 |
|
Bottom |
6.0 |
5.7 |
|
|
Dissolved Oxygen (% saturation) |
Depth Average |
91 |
89 |
|
Bottom |
83 |
79 |
|
|
pH |
7.8 |
7.8 |
|
|
Secchi Disc Depth (m) |
3.8 |
4.3 |
|
|
Turbidity
(NTU) |
2.0 |
2.7 |
|
|
Suspended Solids (mg/L) |
6.2 |
6.1 |
|
|
5-day Biochemical Oxygen Demand (mg/L) |
0.6 |
0.6 |
|
|
Ammonia Nitrogen (mg/L) |
0.020 |
0.019 |
|
|
Unionised Ammonia (mg/L) |
<0.001 |
<0.001 |
|
|
Nitrite Nitrogen (mg/L) |
0.006 |
0.007 |
|
|
Nitrate Nitrogen (mg/L) |
0.013 |
0.014 |
|
|
Total Inorganic Nitrogen (mg/L) |
0.04 |
0.04 |
|
|
Total Kjeldahl Nitrogen
(mg/L) |
0.36 |
0.34 |
|
|
Total Nitrogen (mg/L) |
0.38 |
0.36 |
|
|
Orthophosphate Phosphorus (mg/L) |
0.006 |
0.006 |
|
|
Total Phosphorus (mg/L) |
0.02 |
0.02 |
|
|
Silica (as SiO2) (mg/L) |
0.47 |
0.50 |
|
|
Chlorophy ll-a (µg/L) |
1.8 |
1.8 |
|
|
E.coli (cfu/100mL) |
1 |
<1 |
|
|
Faecal Coliforms (cfu/100mL) |
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] |
|
|
MS4 |
MS5 |
|
|
Particle Size Fractionation <63μm (%w/w) |
85 |
92 |
|
Electrochemical Potential (mV) |
-286 |
-268 |
|
Total Solids (%w/w) |
41 |
39 |
|
Total Volatile Soilds
(%TS) |
8.3 |
8.9 |
|
Chemical Oxygen Demand (mg/kg) |
13300 |
13350 |
|
Total Carbon (%w /w ) |
0.8 |
0.7 |
|
Ammonical Nitrogen (mg/kg) |
8 |
5.28 |
|
Total Kjeldahl Nitrogen
(mg/kg) |
650 |
630 |
|
Total Phosphorus (mg/kg) |
220 |
210 |
|
Total Sulphide (mg/kg) |
33.3 |
21 |
|
Total Cyanide (mg/kg) |
0.1 |
0.1 |
|
Arsenic (mg/kg) |
7.1 |
7.4 |
|
Cadmium (mg/kg) |
0.1 |
<0.1 |
|
Chromium (mg/kg) |
32 |
31 |
|
Copper (mg/kg) |
15 |
15 |
|
Lead (mg/kg) |
36 |
39 |
|
Mercury (mg/kg) |
0.05 |
0.05 |
|
Nickel (mg/kg) |
22 |
22 |
|
Silver (mg/kg) |
<0.2 |
<0.2 |
|
Zinc (mg/kg) |
87 |
94 |
|
Total Polychlorinated Biphenyls (PCBs) (µg/kg) |
18 |
18 |
|
Low Molecular Weight Polycylic
Aromatic Hydrocarbons (PAHs) (µg/kg) [5] [7] |
140 |
130 |
|
High Molecular Weight Polycylic
Aromatic Hydrocarbons (PAHs) (µg/kg) [6] [7] |
63 |
51 |
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 Tung Ping Chau Marine Park is carried out
quarterly by AFCD. The water quality monitoring at Tung Ping Chau Marine Park
is taken at two sites at Ma Kok Tsui and Cheung Sha Wan 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 5.4.
Table 5.5 Water Quality of Tung Ping Chau Marine Park in Year 2019
|
Parameters |
Ma
Kok Tsui |
Cheung
Sha Wan |
||
|
Water
Depth Surface |
Surface |
Bottom |
Surface |
Bottom |
|
Air
Temperature (°C) |
25.68 |
25.83 |
||
|
Temperature
(°C) |
25.48 |
24.96 |
25.56 |
24.78 |
|
Salinity
(‰) |
32.34 |
32.50 |
32.34 |
32.82 |
|
Dissolved
Oxygen (mg/L) |
7.19 |
7.04 |
7.18 |
6.27 |
|
pH |
8.11 |
8.14 |
8.06 |
8.14 |
|
Secchi
Disc Depth (m) |
1.9 |
3.1 |
||
|
Turbidity
(NTU) |
<1 |
<1 |
1.13 |
<1 |
|
Suspended
Solids (mg/L) |
2.75 |
3.13 |
3.13 |
3.38 |
|
5-Day
Biochemical Oxygen Demand (mg/L) |
2.38 |
2.50 |
2.13 |
3.38 |
|
Ammoniacal
Nitrogen (mg/L) |
0.02 |
0.02 |
0.02 |
0.02 |
|
Unionized
Ammonia (mg/L) |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
|
Nitrite
Nitrogen (mg/L) |
<0.01 |
<0.01 |
<0.01 |
<0.01 |
|
Nitrate
Nitrogen (mg/L) |
0.06 |
0.06 |
0.06 |
0.06 |
|
Total
Inorganic Nitrogen (mg/L) |
0.08 |
0.07 |
0.07 |
0.07 |
|
Total
Kjeldahl Nitrogen (mg/L) |
0.48 |
0.45 |
0.44 |
0.59 |
|
Total
Nitrogen (mg/L) |
0.54 |
0.50 |
0.49 |
0.65 |
|
Orthophosphate
Phosphorus (mg/L) |
0.01 |
0.01 |
0.01 |
0.01 |
|
Total
Phosphorus (mg/L) |
<0.1 |
<0.1 |
<0.1 |
<0.1 |
|
Chlorophyll-a
(μg/L) |
0.66 |
0.59 |
0.84 |
0.86 |
|
E. coli
(cfu/100 mL) |
1 |
0 |
0 |
0 |
|
Faecal
Coliforms (cfu/100 mL) |
21 |
34 |
7 |
3 |
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-306/2017). 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 Tung Ping Chau Marine Park. 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 are indicated in Figure 5.1. They include Marine Park, SSSI, Country Park, coral colonies and watercourses as summarised in Table 5.4.
Table 5.6 WSRs within the assessment area
|
WSR |
Description |
Type |
Nearest distance from the Project (m) |
|
TPC-W1 |
Tung Ping Chau Marine Park |
Marine Park and Coral
Colonies |
Project within the marine park |
|
TPC-W2 |
Plover Cove (Extension) Country Park |
Country Park |
100 |
|
TPC-W3 |
Ping Chau SSSI |
SSSI |
Project adjacent to SSSI |
|
TPC-W4 |
Watercourse near Chan Uk |
Inland Natural
Watercourse |
200 |
|
TPC-W5 |
Watercourse near Sha Tau |
Inland Natural
Watercourse |
350 |
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 minor 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 working barge and/or steel structures supported by piles to maintain access to Tung Ping Chau until a new berth of the pier is available for use;
· Removal of temporary pier, modification of the existing pier and installation of piles for the new pier;
· Construction of new pier structures (e.g. installation of precast elements on the pier structure etc.); and
· Construction of associated facilities on the new pier.
5.4.1.2
Potential
water quality pollution sources from the Project during the construction phase
are summarized as follows.
·
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
5.4.2.1
Before
sampling, the jack-up barge will be fixed in a position by extending its 4 legs
into the seabed, the legs and borehole locations will be inspected by diver
survey to ascertain no coral colonies will be affected as far as practicable. After
positioning, the barge will be jacked up until the barge bottom is elevated
above the high tide level. Minimal disturbance of existing seabed level during
positioning would be resulted but
significant dispersion of suspended solids is not expected.
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 suspended solids 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 marine
sediment is anticipated to be collected from the site investigation works.
Hence, impact of marine sediment on water quality is not anticipated.
Marine-based Foundation Works (for Temporary Pier
and Proposed Pier)
5.4.2.3
The
pre-drilling works of foundation for proposed TPC Public Pier would be in the
similar fashion as the site investigation work as described in Section 5.4.2.1 and Section 5.4.2.2.
Pile Installation Works
5.4.2.4
The
foundations of the proposed TPC Public 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 barges will be fixed in a
position by anchoring concrete mooring sinkers onto the seabed while the mini-piles used to support the temporary steel structure
would follow the confined pile casing 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. Prior to the construction work, the sinkers and/or mini-piles
locations will be inspected by diver survey to ascertain no coral colonies will
be affected as far as practicable before installation. Minimal disturbance of existing seabed level during positioning would be
resulted but significant dispersion of suspended solids is not expected.
5.4.2.5
For
each pile construction, confined pile casing method as
discussed in Section 2.6.3.2
and Section 2.6.3.3 would
also be followed. Inner casing of approximately 0.8-1.0m in diameter will be
installed into the seabed by using hydraulic oscillator from a working
platform. Pile shaft excavation by using hammer grab will be carried out within
the casing. Closed grab excavator will be deployed to minimise the leakage of
material collected during the process. The grabbed material will be bought to
and be settled in the sedimentation tank. The steel casing will then be jacked
down into the ground by oscillator prior to carry out next grabbing process
until reaching rockhead. Reverse Circulation Drill (RCD) will be deployed to
drill through the bedrock and any hard material encountered until reaching the required
level. No grabbed material will be made in direct contact with the open sea
water.
5.4.2.6
Such
confined pile casing method has been adopted for the Hong Kong-Zhuhai-Macau
Bridge Hong Kong Link Road construction of marine bored piles for the piers of viaducts.
The set-up avoids the use of silt curtains for the protection of Chinese White
Dolphin. Based on the environmental monitoring data of the project, there were
no project-induced exceedances of water quality monitoring parameters. Likewise,
for this Project, the movement of the silt curtain due to the water current may
cause damage and injury to the coral colonies nearby. Deployment of silt
curtain is therefore considered not suitable for this Project. Based on the
previous experience, confined pile casing method is therefore proposed for
effective confinement of the suspended solids inside the pile casing for this
Project. 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
Seabed
disturbance is anticipated during the insertion and removal of pile casings. As
discussed in Section 11.5.2.1, the seabed features in the vicinity of
the Project are mostly sand/silt, boulders and rocks. No sediment and clay are
found within the Project site. As sand and silt have higher density and larger
particle sizes than clay or marine sediment, the sand and silt particles have
much higher settling velocity, and re-suspended solids in the water column
could be quickly settled. Moreover, the pile casings would be inserted and
removed in a gradual manner to reduce the disturbance of the seabed. Adverse
water quality impacts due to the installation and removal of the casings are
therefore not anticipated.
5.4.2.8
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.
5.4.2.9
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).
5.4.2.10
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 suspended solids will be settled and collected in
the tank. The recycled fluid will be used for the subsequent piling works. No
drilling fluid and suspended solids will be discharged on site or within the
boundary of Tung Ping Chau Marine Park, Plover Cove (Extension) Country Park,
Ping Chau SSSI and the other identified WSRs.
5.4.2.11
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
5.4.2.12
The proposed deck of the temporary pier would
be a steel structure of about 20m long and 5.5m wide above the sea. Prefabricated elements of
steel structure will be shipped and installed on site. No adverse water quality
impact is anticipated from the installation work.
5.4.2.13 For the permanent pier, the above-water construction works would involve the establishment of a proposed pier of concrete structure of typically about 5.5m to 6m wide, increased to 15m at the head, and 123m long above the sea. The scale of the construction works is considered to be 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.
5.4.2.14 However, due to site constraints or design requirements, prefabrication approach may not be always feasible. For small quantities of structural elements e.g. decks 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
5.4.2.15
The
temporary pier and part of existing pier will be demolished after the
completion of a new berth of the pier. The temporary pier and part of the
existing pier will be cut into parts and shipped away by vessels. Piles of temporary pier will be cut by wire saw, blade saw or
similar method as close to the seabed as possible, and the demolished portions
of the piles will be removed off site. The portions of the piles embedded in
the ground will be left untouched below the seabed.
5.4.2.16
Part of the existing pier will also
be cut by wire saw, blade saw or similar method above and some of the concrete
blocks of the existing pier will be removed one-by-one by the crane directly.
All demolished portions will be removed off site. Neither open sea dredging works nor disturbance
to seabed is anticipated. Therefore,
no adverse water quality impact is anticipated.
Hydrodynamic Impact
5.4.2.17 The Project is located at the eastern coast area of Tung Ping Chau facing towards Ping Chau Hoi. The island is in a slight crescent shape where the Project is located around the mid-point of its eastern side. In a wider geographical context, Tung Ping Chau is located in the Mirs Bay, which is embraced by Yantain and Dapeng Ren to the north and the east respectively. In the Ping Chau Hoi area, the deepest seabed level is approximately -9mPD which has a water depth of about 9.5m at the mean lower low water (MLLW). Figure 5.2 shows the relative location of the Project in relation to the cove area.
5.4.2.18
Based on the hydrographic
survey (see Figure 5.3), the seabed of the existing pier head is about ‑3.0mPD
which has a water depth of about 3.5m at MLLW. Since the water depth of the existing pier is adequate for berthing,
only a relatively short extension length of 26m is required for the Project.
Along the new pier structure that is 26m long and 15m wide, there would be
about 27 nos. of approximately 0.8m dia. bored piles and 6 nos. of approximately
1m dia. bored piles with typical spacing around 5m to 8m. It is noted the
actual area that would be occupied by those marine piles is not significant. The
pile configuration is typical for other piers in Hong Kong[1] which are of similar dimensions. (see Figure 5.4)
5.4.2.19
For the
temporary pier, it will be constructed near the pier head of the existing pier.
The proposed temporary pier is in the southeast of the existing pier and is
about 20m long and 5.5m wide. During the construction of the temporary pier, 8
nos. of approximately 0.8m dia. bored piles with approximately 7.0m spacing
will be constructed. Regard to the small footprint of the temporary pier and
piles, the piles and pier structures of the temporary pier are likely cause
insignificant changes of the existing flow regime and tidal flux in the eastern
coastal area of Tung Ping Chau in Ping Chau Hoi.
5.4.2.20
Due to the
small footprint of the piled foundation, changes in the flow regime and
hydrodynamic in the eastern coastal area of Tung Ping Chau in Ping Chau Hoi are
limited during the construction phase of the Project.
Site Run-off from General Site Operation
5.4.2.21
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.
5.4.2.22
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 increase in 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
5.4.2.23
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
5.4.4,
neither adverse nor cumulative water quality impact is anticipated.
Sewage from Workforce
5.4.2.24
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. Since 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 Tung Ping Chau Marine Park (TPC-W1) and Ping Chau
SSSI (TPC-W3). The Project will not encroach on the core areas of the marine
park at Tai Tong Wan (i.e. about 240m to the north of the Project) and A Ma
Tsui (i.e. about 510m to the south of the Project) which are not anticipated to
be affected by the Project. Nevertheless, the marine-based site investigating,
and drilling will be contained in outer casing. 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.
5.4.3.2
As
the works area of the Project would not encroach on Plover Cove (Extension)
Country Park (TPC-W2), water quality impact form the Project is not anticipated
on this WSR. Regarding the two watercourses (TPC-W4 and TPC-W5), they are
located at inland area of Tung Ping Chau. The watercourses are located at the
upstream of the Project and hydrologically isolated from the Project. Adverse
water quality impact is therefore not anticipated.
5.4.4 Mitigation Measures
Working in Marine Park
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
5.4.4.2 A number of good site practices and mitigation measures recommended for site investigation works are summarised below.
·
Before
commencement of drilling works, all drill rig, circulation tank and equipment
shall be thoroughly cleaned off-site;
·
Diver
inspection shall be carried out to ascertain no coral colonies will be affected
during the legs positioning and drilling works as far as practicable;
·
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 suspended
solids 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 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 drilling fluid collected in the tank during the drilling
process shall be delivered 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
5.4.4.3
Good
site practices and mitigation measures shall be referred to that of
marine-based Site Investigation Works (Section 5.4.4.2).
Pile Construction Works
5.4.4.5 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.
· Diver inspection shall be carried out to ascertain no coral colonies will be affected during the legs positioning and drilling works as far as practicable;
· Pile casing should be used for the construction of foundations;
· A temporary funnel to avoid spillage of concrete/ excavated materials should be installed at the top of the pile casing prior to excavation;
· Excavation should only be conducted inside pile casing. Only one closed grab should be used for excavation at the same time;
·
The barge receiving the grabbed
materials will be located as close to the pile casing as possible and
underneath the Y-shaped funnel to avoid the grabbed materials from accidentally
dropped into the surrounding water body;
· 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 1-2 piles be constructed at the same time;
· Drilling fluid in the pile casing shall be pumped out to the circulation tanks on the barge to avoid drilling fluid 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;
· Drilling fluid shall not be discharged on site or within the boundary of Tung Ping Chau Marine Park, Plover Cove (Extension) Country Park or any other identified WSRs; and
· Final discharge of waste water/ effluent shall 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.
Above-water Construction Works
5.4.4.6
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 whenever possible; and
·
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.
Site Run-off from General Site Operation
5.4.4.7 To reduce the potential water quality impact due to construction site runoff, other than the timely implementation of the water storage tanks, 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;
·
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.
5.4.4.8 With the adoption of best management practices, it is anticipated that the impacts arising from general site operation will be reduced to satisfactory levels before discharge. The details of best management practices will be highly dependent on the actual site conditions and contractor shall apply for a discharge license under WPCO if discharge is required.
Accidental Spillage of Chemicals
5.4.4.9
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.
·
Properly store
and contain the chemicals used during construction, such as fuel, oil, solvents
and lubricants in a designated area with secondary containment to prevent
spillage and contamination of the nearby water environment.
·
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 register as a chemical waste producer and employ licensed
collector for collection of chemical waste from the construction site. Any
chemical waste generated shall be managed in accordance with the Waste Disposal
(Chemical Waste) (General) Regulation.
·
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
5.4.4.10
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 improve the existing pier facilities such as providing standard landing steps, adequate berthing space and enhancing accessibility to those in need. There is neither 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 operational phase.
5.5.1.2
As
discussed in Section 5.4.2.17, the Project is located at the
eastern coast area of Tung Ping Chau facing towards Ping Chau Hoi. Based on the
hydrographic survey, the seabed of the existing pier head is about -3.0mPD which has a water depth of about 3.5m at MLLW. The proposed pier is extending from the existing pier towards a
slightly deeper water region of -3.5mPD (i.e. about 4m water depth at MLLW).
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 design as the existing pier, the proposed pier would adopt marine piles with a deck above. Along the new pier structure that is 26m long and 4-5m wide, there would be about 27 nos. of approximately 0.8m dia. bored piles and 6 nos. of approximately 1m dia. bored piles with typical spacing of approximate 6m. It is noticed that the actual area that would be occupied by those piles is not significant. Such a configuration is typical for other similar piers in Hong Kong. (See Figure 5.4)
5.5.1.4
Due to the
small footprint of the piled foundation, changes in the flow regime and
hydrodynamic in the eastern coastal area of Tung Ping Chau in Ping Chau Hoi are
limited during the operational 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 33 nos. of bored piles of about 0.8-1m in
diameters with sufficient spacing, the change of flow
regime in the Ping Chau Hoi by the Project is limited. Adverse hydrodynamic
impact on the Tung Ping Chau Marine Park (TPC-W1) and Ping Chau SSSI (TPC - W3)
is not anticipated. For the other WSRs including Plover Cove (Extension)
Country Park (TPC-W2), and the two watercourses (TPC-W4 and TPC-W5), they are
hydrologically isolated from the Project. No impact is expected for these WSRs.
5.5.2.2
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, migration 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 (EM&A)
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
structures of 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, the seabed features in the vicinity of the Project are mostly sand/silt, boulders and rocks, which have much higher settling velocity and could be quickly settled. With the implementation of recommended mitigation measures such as the use of double casing system, Y-shape funnel and closed grab to be implemented during marine-based site investigation and construction works, adverse water quality impact is not anticipated. There will neither be directly discharge on-site, within the Tung Ping Chau 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 structures of the improved pier is not anticipated.