4.1
Introduction
4.1.1
Water quality impact assessment
has been conducted as part of the EIA study, as required in the EIA Study Brief
(ESB-0010/1998). Marine works for the proposed
YTB reclamation such as sand filling and mud dredging may adversely affect the
water quality of the neighbouring waters.
Key water quality issues to be addressed for the construction phase
include the potential cumulative impacts on water quality due to concurrent
construction activities in Victoria Harbour and Junk Bay around YTB and the impact of the temporary diversion of the
stormwater culvert in YTB. During the
operation phase, the key water quality issues include the effect of the
proposed YTB reclamation on tidal flows through Victoria Harbour and
the potential water quality deterioration under the concrete decking section
proposed near the northern part of YTB.
4.1.2
The objective of the present
study is to evaluate the potential water quality impacts as a result of the
construction and operation of the YTB reclamation. The environmental acceptability of these
potential water quality impacts is assessed, with a view to identifying
appropriate mitigation measures to reduce any identified adverse impacts to
acceptable levels. The site layout plan
for the project is shown in Figure 4.1.
4.2
Environmental Legislation, Standards and Criteria
4.2.1
Statutory and guideline criteria
relevant to the water quality impact assessment of the proposed YTB reclamation
are described below.
Environmental Impact Assessment Ordinance
(EIAO), Cap.499, S16
4.2.2
YTB reclamation is a Designated
Project under Schedule 2 of the EIAO.
The “Technical Memorandum on
Environmental Impact Assessment Process (TM on EIA Process)” was issued by
Environmental Protection Department (EPD) under Section 16 of the EIAO. The TM on EIA Process specifies the
assessment method and criteria that will be followed in this study. Sections in the TM on EIA Process relevant to
the water quality impact assessment are:
·
Annex 6 - Criteria for
Evaluating Water Pollution; and
·
Annex 14 - Guidelines for
Assessment of Water Pollution.
Water Quality Objectives (WQOs)
4.2.3
The Water Pollution Control
Ordinance (WPCO) (Cap.358) provides the major statutory framework for the
protection and control of water quality in Hong
Kong.
According to the Ordinance and its subsidiary legislation, the whole Hong Kong waters are divided
into ten Water Control Zones (WCZs). The
WCZ boundaries in the vicinity of YTB are shown in Figure 4.2. Corresponding statements of Water Quality
Objectives (WQO) are stipulated for different water regimes (marine waters, inland
waters, bathing beaches subzones, secondary contact recreation subzones and
fish culture subzones) in the WCZ based on their beneficial uses. The proposed YTB reclamation site is located
within the Victoria Harbour (Phase One) WCZ and the corresponding WQOs, implemented since
November 1994, are listed in Table 4.1.
Table 4.1 Summary of Water Quality
Objectives for the Victoria Harbour Water Control Zone
Parameters
|
Objectives
|
Sub-Zone
|
Offensive
Odour, Tints
|
Not to be present
|
Whole zone
|
Colour
|
Not to exceed 50 Hazen
units, due to human activity
|
Inland waters
|
Visible foam,
oil scum, litter
|
Not to be present
|
Whole zone
|
E. coli
|
Not to exceed 1000 counts per
100 mL, calculated as the geometric mean of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days
|
Inland waters
|
Dissolved
Oxygen (DO) within 2 m of the seabed
|
Not less than 2.0 mgL-1
for 90% of samples
|
Marine waters
|
Depth averaged
DO
|
Not less than 4.0 mgL-1
for 90% of samples
|
Marine waters
|
Dissolved
Oxygen
|
Not less than 4.0 mgL-1
|
Inland waters
|
pH
|
To be in the range of 6.5
- 8.5, change due to human activity not to exceed 0.2
|
Marine waters
|
|
Not to exceed the range of
6.0 - 9.0 due to human activity
|
Inland waters
|
Salinity
|
Change due to human
activity not to exceed 10% of ambient
|
Whole zone
|
Temperature
|
Change due to
human activity not to exceed 2 oC
|
Whole zone
|
Suspended solids
|
Not to raise the ambient
level by 30% caused by human activity
|
Marine waters
|
|
Annual median not to
exceed 25 mgL-1 due to human activity
|
Inland waters
|
Ammonia
|
Annual mean not to exceed
0.021 mg L-1 as unionised form
|
Whole zone
|
Nutrients
|
Shall not cause
excessive algal growth
|
Marine waters
|
|
Annual mean depth averaged
inorganic nitrogen not to exceed 0.4 mgL-1
|
Marine waters
|
BOD5
|
Not to exceed 5 mgL-1
|
Inland waters
|
Chemical Oxygen
Demand
|
Not to exceed
30 mgL-1
|
Inland waters
|
Toxic substances
|
Should not
attain such levels as to produce significant toxic, carcinogenic, mutagenic
or teratogenic effects in humans, fish or any other aquatic organisms.
|
Whole zone
|
|
Human activity should
not cause a risk to any beneficial use of the aquatic environment.
|
Whole zone
|
Source: Statement
of Water Quality Objectives (Victoria Harbour (Phases One, Two and Three) Water
Control Zone).
Technical Memorandum on Standards for
Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (TM on Effluent Standards)
4.2.4
Besides setting the WQOs, the
WPCO controls effluent discharging into the WCZ through a licensing
system. The TM on Effluent Standards was
issued under the WPCO which gives guidance on the permissible effluent
discharges based on the type of receiving waters (foul sewers, stormwater
drains, inland and coastal waters). The
limits control the physical, chemical and microbial quality of effluents,
discharging into the marine waters of Victoria Harbour. Relevant effluent standards are reproduced in
Table 4.2.
Table 4.2 Standards for Effluent
Discharged into the inshore waters of the Victoria Harbour Water Control Zone
Flow
rate (m3 day-1)
Determinand
|
<=10
|
>10 and <200
|
>200 and <400
|
>400 and <600
|
>600 and <800
|
>800 and <1000
|
>1000 and <1500
|
>1500 and
<2000
|
>2000 and <3000
|
>3000 and <4000
|
>4000 and <5000
|
>5000 and <6000
|
pH (pH units)
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
6 - 9
|
Temperature (oC)
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
40
|
Colour (lovibond units) (25 mm cell
length)
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
Suspended solids
|
50
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
BOD
|
50
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
COD
|
100
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
Oil & Grease
|
30
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
Iron
|
15
|
10
|
10
|
7
|
5
|
4
|
2.7
|
2
|
1.3
|
1
|
0.8
|
0.6
|
Boron
|
5
|
4
|
3
|
2.7
|
2
|
1.6
|
1.1
|
0.8
|
0.5
|
0.4
|
0.3
|
0.2
|
Barium
|
5
|
4
|
3
|
2.7
|
2
|
1.6
|
1.1
|
0.8
|
0.5
|
0.4
|
0.3
|
0.2
|
|
0.1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
Cadmium
|
0.1
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
Other toxic metals individually
|
1
|
1
|
0.8
|
0.7
|
0.5
|
0.4
|
0.25
|
0.2
|
0.15
|
0.1
|
0.1
|
0.1
|
Total toxic metals
|
2
|
2
|
1.6
|
1.4
|
1
|
0.8
|
0.5
|
0.4
|
0.3
|
0.2
|
0.14
|
0.1
|
Cyanide
|
0.2
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
0.05
|
0.05
|
0.03
|
0.02
|
0.02
|
0.01
|
|
0.5
|
0.5
|
0.5
|
0.3
|
0.25
|
0.2
|
0.13
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
Sulphide
|
5
|
5
|
5
|
5
|
5
|
5
|
2.5
|
2.5
|
1.5
|
1
|
1
|
0.5
|
Total residual chlorine
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
Total nitrogen
|
100
|
100
|
100
|
100
|
100
|
100
|
80
|
80
|
50
|
50
|
50
|
50
|
Total phosphorus
|
10
|
10
|
10
|
10
|
10
|
10
|
8
|
8
|
5
|
5
|
5
|
5
|
Surfactants (total)
|
20
|
15
|
15
|
15
|
15
|
15
|
10
|
10
|
10
|
10
|
10
|
10
|
E.
coli (count per 100mL)
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
5000
|
Notes
1. All
units are in mgL-1 unless otherwise stated.
2. All
figures are upper limits unless otherwise indicated.
Source: EPD
Technical Memorandum on Standards for Effluents Discharged into Drainage and
Sewerage Systems, Inland and Coastal Waters, Table 9a.
ProPECC Practice Notes
4.2.5
Practice notes (PN) for
professional persons were issued by the EPD to provide guidelines for handling
and disposal of construction site discharges.
The ProPECC PN 1/94 “Construction Site Drainage” provides good practice
guidelines for dealing with ten types of discharge from a construction
site. These include surface runoff,
groundwater, boring and drilling water, bentonite slurry, water for testing and
sterilization of water retaining structures and water pipes, wastewater from
building constructions, acid cleaning, etching and pickling wastewater, and
wastewater from site facilities.
Practices given in the PN should be followed as far as practicable
during construction to minimize the water quality impact due to construction
site drainage.
Hong Kong Planning Standards and Guidelines
(HKPSG)
4.2.6
The Hong Kong Planning
Standards and Guidelines (HKPSG), Chapter 9 (Environment), provides additional
information on regulatory guidelines against water pollution for sensitive uses
such as aquaculture and fisheries zones, bathing waters and other contact
recreational waters.
Water Supplies Department (WSD) Sea Water
Quality Standards
4.2.7
The Water Supplies Department
(WSD) has also specified a set of seawater quality standards to be maintained
at their saltwater intakes for flushing purposes (Table 4.3). For suspended solids concentration (SS),
there is also a tolerable limit of 20 mgL-1. WSD have indicated in the EIA study for the
SEKD that the tolerable
limit should be met at all times while aiming to achieve the target limit of 10
mgL-1.
Table 4.3 WSD Standards at Sea Water
Intake Point
Parameter (in mg L-1 unless otherwise
stated)
|
WSD Target Limit
|
Colour (HU)
|
< 20
|
Turbidity (NTU)
|
< 10
|
Threshold Odour Number (odour unit)
|
< 100
|
Ammoniacal Nitrogen
|
< 1
|
Suspended Solids
|
< 10
|
Dissolved Oxygen
|
> 2
|
Biochemical Oxygen Demand
|
< 10
|
Synthetic Detergents
|
< 5
|
E. coli (count per 100
mL)
|
< 20,000
|
Sea Water Quality Standard for the Dairy Farm
Ice Factory Saltwater Intake (DFSI)
4.2.8
The Dairy Farm Ice Factory on
Cha Kwo Ling Road, next to the WSD Cha Kwo Ling Pumping Station, extracts sea
water for cooling purposes. The sea
water quality standard to be maintained at this intake is specified for SS
which should be kept below 20 mgL-1. This is less stringent than the target limit
for SS at the WSD saltwater intakes.
4.3
Baseline Conditions
Existing Water Quality in Victoria Harbour
4.3.1
EPD has been conducting routine
monitoring of the quality of Hong Kong waters for a long period of time. Figure 4.3
shows the location of marine water quality monitoring stations near YTB. Based on the EPD marine water quality data
for the year 1997, statistics of the selected parameters are calculated and
shown in Table 4.4 at the two monitoring stations
near YTB:
·
VM1 – to the south of YTB, near
Lei Yue Mun.
·
VM2 – to the west of YTB, near
Quarry Bay.
Table 4.4 Summary statistics of EPD marine water quality
data in Victoria Harbour WCZ for 1999
Determinand
|
|
Victoria Harbour East
|
|
|
VM1
|
VM2
|
Number of
samples
|
|
12
|
12
|
Temperature (°C)
|
|
23.1
(17.7-27.3)
|
23.3
(17.7-27.3)
|
Salinity (ppt)
|
|
32.1
(31.1-33.9)
|
31.8
(30.8-33.7)
|
Dissolved Oxygen (mg L-1)
|
Surface
|
4.7
(3.6-6.2)
|
4.4
(2.9-5.9)
|
|
Bottom
|
4.8
(3.7-6.4)
|
4.5
(3.2-5.9)
|
Dissolved Oxygen
(% Saturation)
|
Surface
|
65
(52-81)
|
62
(43-77)
|
|
Bottom
|
67
(53-82)
|
62
(48-77)
|
pH
|
|
8.0
(7.7-8.5)
|
8.0
(7.7-8.4)
|
Secchi Disc Depth (m)
|
|
2.6
(2.0-3.0)
|
2.3
(1.9-3.5)
|
Turbidity (NTU)
|
|
8.8
(3.7-21.7)
|
7.8
(3.8-19.2)
|
Suspended Solids (mg L-1)
|
|
5.8
(1.8-14.5)
|
4.7
(1.6-8.3)
|
5-day Biochemical Oxygen
Demand (mg L-1)
|
|
0.7
(0.4-1.1)
|
0.9
(0.5-1.6)
|
Ammoniacal Nitrogen (mg L-1)
|
|
0.19
(0.01-0.34)
|
0.23
(0.03-0.37)
|
Unionized Ammonia (mg L-1)
|
|
0.007
(0.001-0.013)
|
0.008
(0.003-0.015)
|
Nitrite Nitrogen (mg L-1)
|
|
0.02
(0.01-0.04)
|
0.02
(0.01-0.04)
|
Nitrate Nitrogen (mg L-1)
|
|
0.08
(0.03-0.14)
|
0.10
(0.03-0.18)
|
Total Inorganic Nitrogen
(mg L-1)
|
|
0.30
(0.15-0.45)
|
0.35
(0.20-0.46)
|
Total Kjeldahl Nitrogen
(mg L-1)
|
|
0.48
(0.22-0.71)
|
0.53
(0.33-0.74)
|
Total Nitrogen (mg L-1)
|
|
0.59
(0.35-0.83)
|
0.65
(0.51-0.83)
|
Ortho-phosphate Phosphorus
(mg L-1)
|
|
0.04
(0.02-0.06)
|
0.04
(0.03-0.07)
|
Total Phosphorus (mg L-1)
|
|
0.06
(0.03-0.09)
|
0.07
(0.04-0.09)
|
Silica (as SiO2) (mg L-1)
|
|
0.9
(0.3-1.3)
|
1.0
(0.5-1.5)
|
Chlorophyll-a (mg L-1)
|
|
2.6
(1.2-5.2)
|
2.3
(1.1-5.2)
|
Phaeo-pigment (mg L-1)
|
|
1.0
(0.2-3.8)
|
0.8
(0.2-3.2)
|
E.coli.
(cfu/100mL)
|
|
8900
(2400-26000)
|
11000
(1900-93000)
|
Faecal Coliforms
(cfu/100mL)
|
|
16000
(3700-45000)
|
22000
(4500-150000)
|
Notes:
1. Data presented are depth-averaged data, unless specified otherwise.
2. Data presented are annual arithmetic means except for E.coli. and
faecal coliform data which are geometric means.
3. Data enclosed in brackets indicate the ranges.
4.3.2
For mud dredging and sand
filling during the construction phase, the suspended solid (SS) concentration
is the most crucial parameter pertinent to the water quality assessment. The depth averaged SS reading between the
period 1/1996 to 8/1998 at VM1 and VM2 are shown in Table 4.5. The variance at station VM1 is higher than
that in VM2 which may be attributed to reclamation activities, such as Aldrich Bay, within
this period. However, the 90 percentile
depth averaged SS concentrations of the two stations are in close
agreement. Hence, the 90 percentile SS
concentration of 10.68 mgL-1 (depth-averaged) at station VM1, which
is close to YTB, is taken to represent the ambient SS level in the study
area.
Table 4.5 Depth averaged suspended
solids concentration for stations VM1 and VM2
Depth averaged SS [mgL-1]
|
1996
|
1997
|
1998(1)
|
Overall average(2)
|
Monitoring station VM1
|
Mean(2)
|
8.63 (5.7)
|
5.64 (3.26)
|
4.64 (3.89)
|
6.51 (4.33)
|
Range
|
3.9-17.1
|
2.63-10.8
|
1.77-7
|
1.77-17.1
|
90 percentile
|
15.87 (8.22)
|
7.95 (4.35)
|
6.7 (5.93)
|
10.68 (6.6)
|
Monitoring station VM2
|
Mean(2)
|
7.19 (6.68)
|
5.48 (4.26)
|
5.03 (4.83)
|
6.01 (5.31)
|
|
3.4-11.5
|
2.23-10.43
|
2.6-13
|
2.23-13
|
90 percentile
|
9.91 (9.45)
|
9.48 (4.97)
|
7.54 (7.64)
|
9.98 (9.27)
|
Notes:
1.
Average is obtained for the
first 8 months, i.e. between 1/98 – 8/98.
2.
Surface layer values are shown
in brackets.
Data source: EPD routine marine
water quality monitoring program.
Future Water Quality in Victoria Harbour
4.3.3
Under the YTB reclamation, the existing
ship building and repairing facilities at all marine lots in the site will be
decommissioned, thus removing direct sources of pollution to the bay. The demolition of industries and workshops
along the waterfront will also remove potential sources of effluent discharge
into the bay and the neighbouring water body.
4.3.4
With the increased enforcement
exerted over industrial effluents to comply with the TM on Effluent Standards
for the VHWCZ under the WPCO, the water quality in Victoria Harbour is anticipated
to improve in the future. The
implementation of the Strategic Sewage Disposal Scheme (SSDS) Stage 1 would
provide the necessary infrastructure for sewage collection and treatment to
minimize the pollution load discharging into Victoria Harbour and thus the
water quality is expected to improve further.
4.4
Assessment Methodology and Criteria
Hydrodynamic and Water Quality Modelling
4.4.1
In the present study, computer
modelling is employed to assess the potential water quality impacts on the
harbour waters and the beneficial uses as described in Section 4.5 for different tidal conditions (dry and
wet seasons, spring and neap tides). The
hydrodynamic and water quality models were developed by the Danish Hydraulic Institute
(DHI) and the program runs are performed by MEMCL. The DHI models, namely the MIKE 21 and MIKE
3, have been calibrated and accepted by EPD for many EIA studies. Particularly relevant applications included
the South East Kowloon Development (SEKD) Feasibility Study and Tseung Kwan O
(TKO) Area 131 Cargo Working Area EIA Study, which are adjacent to the present
study area.
4.4.2
The main objective of the
modelling was to determine whether the proposed YTB reclamation would result in
non-compliance with the WQOs of the Victoria Harbour WCZ as stipulated in the
WPCO, during both the construction and operation phases. In addition, the potential impact on the
neighbouring sensitive receivers due to the dredging and filling activities
will also be assessed. As highlighted in
Section 2,
the Full Reclamation option is expected to have a greater effect on the flow
and water quality in Victoria Harbour than the Minimized Reclamation option. The Full Reclamation option is therefore
taken to represent the worst case scenario of the YTB reclamation and is
quantitatively assessed in the present study.
Due to the similar construction approach of the two reclamation options
and a smaller reclamation area in the Minimized Reclamation, an environmentally
acceptable Full Reclamation would suggest that the minimized reclamation is
also environmentally acceptable.
Model Setup
4.4.3
DHI’s 2D model, namely MIKE 21,
was used to simulate the dry season hydrodynamic condition of the Hong Kong
waters. To account for the effect of
stratification in the water column, the 3D model, MIKE 3, is employed for the
wet season simulation.
4.4.4
The model setup consists of a
set of dynamically nested grids, distributed in a way to resolve the high
resolution required in the harbour and narrow channels, while providing a total
coverage of the whole of Hong Kong. Two
sets of model grids are used:
·
Large grid (3 levels) (Figure 4.4a):
Grid size ranges from 675m down to
225m and 75m, covering the whole of Hong Kong and the Pearl Estuary. The resolution in the Victoria Harbour region
is enhanced using the small grid size of 75m.
·
Local grid (2 levels) (Figure 4.4b)
Grid size ranges
from 75m down to 25m, covering the Victoria Harbour with emphasis placed in the
vicinity of YTB.
4.4.5
The different levels of the
large and local grids are dynamically nested which enable the exchange of
boundary conditions. The large grid is
mainly used for the hydrodynamic (HD) simulation and the water level or tidal
variation is extracted as boundary input to the local grid. The HD simulation is then re-run using the
local grid to resolve the finer details in the proximity of YTB. Based on the local grid HD results, particle
tracking or sediment plume (PA) modelling is performed to assess the impact of
the dredging and filling activities during construction.
The model were run for the following
simulation periods:
·
Dry season, spring and neap
tides: 1990/2/7 – 1990/2/21
(14 days)
·
Wet season, spring tide: 1990/6/19 –
1990/6/24 (4.5 days)
·
Wet season, neap tide: 1990/6/26 –
1990/7/1 (4.5 days)
4.4.6
To ensure convergence of the
model, a warm up period of 1.5 days was added to the beginning of the above
periods in the nested HD simulations using the large grid and the local
grids. Typical time series plot of the
SS elevation at the WSRs during the YTB reclamation are shown in Appendix
4D.
4.4.7
Parameters used in the nested sediment
plume model are summarized in Table 4.6. These were adopted in the previous SEKD
Feasibility Study.
Table 4.6 Summary of parameters for the
nested sediment plume model (NPA)
Nested sediment plume (NPA) model
|
Longitudinal
dispersion factor IL
|
15 m
|
Minimum
dispersion 1 m2 s-1
|
Transversal
dispersion factor IT
|
15 m
|
Minimum
dispersion 1 m2 s-1
|
Neutral
dispersion D0
|
0.03 m2
s-1
|
|
Vertical
dispersion of suspended solids (SS) Dv
|
0.0001 m2
s-1
|
|
Particle
settling velocity
|
0.0001 m
s-1
|
Grain
size diameter of 10 mm
|
Modelling Scenarios
4.4.8
The year 2006 Scenario A2 in
the SEKD Feasibility Study will be used as the basis of the present study. The bathymetry or coastline of the model is
modified to reflect changes for each scenario as described in the following
paragraphs. The scenarios can be divided
into two main classes, namely, operation phase and construction phase impacts.
Operation phase impact in year 2007
4.4.9
The long term implication of
the YTB reclamation (Full Reclamation Option), representing the worst case
impact with respect to the extent of reclamation, is assessed in the following
scenarios:
·
Scenario 1A – Baseline scenario
excluding YTB reclamation
The latest
coastline is updated to include the recent modifications in the SEKD study as
at March 1999 and the reclamation for the Western Coast Road (WCR-Coastal
option) when the modelling study was performed, while excluding the YTB reclamation
in year 2007.
·
Scenario 1B – Development
scenario with YTB reclaimed
This is the same as Scenario 1A with the inclusion of the YTB
reclamation (Full Reclamation option).
·
Scenario 1C – Impact of the new
Kwun Tong nullah, proposed in the SEKD Feasibility Study, and the proposed
stormwater culvert in YTB on the water quality under the proposed concrete
decking (Figure 4.5a).
Construction phase impact in year 2004
4.4.10
The YTB reclamation works for
the Full Reclamation option will be conducted in stages, namely seawall
construction, Phase 1 and Phase 2 reclamations and Phase 3
construction of concrete decking at the mouth of YTB (Figure 2.1). The water quality impacts associated with
these interim construction stages and methods are assessed in the following
scenarios using the particle model (PA):
·
Scenario 2A – Construction
impact of YTB reclamation alone (worst-case scenario)
To assess the worst case scenario
of the YTB reclamation (Full Reclamation), the three interim construction
stages were considered:
1.
Scenario 2A_SW – Seawall
construction
This involves mud
dredging and sand filling for the seawall foundation.
2.
Scenario 2A_P1 – Phase 1
reclamation
The area to be reclaimed is approximately 13.8 hectares (Figure 2.1). Taking a conservative approach, the maximum
production rate of 10,000 m3day-1 is assumed for
sand filling in the Phase 1 reclamation and will be incorporated in the
sediment plume model to test its environmental acceptability.
3.
Scenario 2A_P2 – Phase 2
reclamation
The area of Phase 2 reclamation is approximately 4 times
smaller than the Phase 1 reclamation.
The maximum production rate of 10,000 m3day-1
is assumed in the sediment plume model, similar to that in Scenario 2A_P1.
·
Scenario 2B – Cumulative
impacts from neighbouring construction activities
Two cases were considered:
1.
Scenario 2B_BK – Cumulative
Impacts of Other Projects
Based on the latest information as
at March, 1999, the concurrent construction activities in Victoria Harbour and
Junk Bay between Jan 2001 and Dec 2011 are incorporated into the sediment plume
model, excluding the YTB reclamation.
2.
Scenario 2B_CI – Cumulative
Impact including YTB reclamation
In addition to the concurrent
projects included in Scenario 2B_BK, sand filling for the Phase 1 reclamation,
with the highest production rate, is taken into account in the sediment plume
model.
·
Scenario 2C – Impact of the
temporary diversion of stormwater culvert in YTB.
The stormwater culvert in YTB will
be temporarily diverted along the southern seawall of YTB to the proposed water
front before the main reclamation begins.
The proposed discharge location is assessed for possible water quality
deterioration in Victoria Harbour and at the water sensitive receivers (Figure 4.5b).
4.4.11
The proposed Phase 3
construction works for the Full Reclamation option involve the construction of
155 uniformly spaced piles of approximately 0.9m in diameter to support
the concrete decking at the mouth of YTB.
The works will not involve marine works like dredging or filling that
will generate significant elevations of suspended solids. Marine sediment that may be disrupted by the
piling activities at the seabed will essentially be re-suspended near the
seabed (about 5m from sea surface) and will subsequently re-deposit at the
seabed. It is therefore considered that
the associated water quality (SS)_ impact upon the existing WSD intakes that
are close to the sea surface will be minor.
The impact will be further minimised after the implementation of silt
screens recommended in Section 4.8. The effect of the
concrete piles on the flow under the decking has been taken into account in the
hydrodynamic simulation for the operation phase scenario. Furthermore, the concrete decking for the Minimized
Reclamation option will be reduced proportionately and thus reducing the size
of the embayment. Tidal flushing of the
smaller embayment and thus the water quality under the concrete decking is
expected to be better than those for the Full Reclamation option. Hence, the above simulations scenarios will
be sufficient for the purpose of environmental impact assessment.
General Notes and Assumptions
4.4.12
Hydrodynamic (HD) simulation
using the large grid is performed for Scenario 1A. The variation of water level is then
extracted as boundary input to the local grid HD simulations for all the
scenarios. With the local grid HD
results, sediment plume modellings are conducted for Scenarios 1C, 2A, 2B
and 2C.
4.4.13
For Scenarios 1C and 2C, a
conservative source for the sediment plume or particle model is used to
simulate the pollutant dispersion of the new Kwun Tong nullah, the new and the
temporary stormwater culvert in YTB, with an arbitrary discharge rate of
1 kg s-1 (86400 kg day-1). The discharge locations are shown in
Figure 4.5.
4.4.14
With reference to the
preliminary construction program for YTB reclamation, assuming an average
production rate of 4,000 m3day-1, the dredging and
filling activities will take place between February 2004 and March 2007 (Appendix 2A). If the maximum production rate of
10,000 m3day-1, as assumed in the sediment plume
model, is maintained through out the whole construction period, the program may
be shortened accordingly.
4.4.15
Based on the latest
construction program as at March 1999 for the South East Kowloon Development
(SEKD), the Western Coast Road (WCR-Coastal option), the Tseung Kwan O (TKO)
New Town Intensification and Extension (NTIE) and the TKO Cargo Working Area
(CWA), the potentially concurrent activities in the vicinity of YTB between Jan
2001 and Dec 2011 were identified for cumulative impact assessment
(Scenario 2B). The construction
activities which correspond to the highest production rates for each project
are listed in Table 4.7 and the corresponding
locations are shown in Figure 4.6a. These construction activities with the highest
production rate only occur for a short period of time and, in reality, these
activities are unlikely to take place simultaneously or at least not at the
highest production rate. Hence, the
present assessment which assumes concurrent construction for the different
projects in Victoria Harbour at their highest production rates, provides a
conservative estimate of the cumulative water quality impacts.
4.4.16
Since the daily production
rates for the WCR - Coastal Option reclamation during the seawall construction
for the YT and TKO sections are higher than those during the main reclamations,
the former is taken to represent the worst case of WCR construction. This is further supported by the fact that
the main reclamations for the WCR will commence after the seawall construction
and the sediment plume is effectively contained within the seawall minimizing
the impact on the sensitive receivers.
4.4.17
According to the EIA studies of
the concurrent projects, mitigation measures were proposed to be implemented
during the construction phase. Hence,
the proposed mitigation measures are also included in the sediment plume
modelling, giving a more realistic view of the pollution level at the time when
YTB reclamation takes place. The main
mitigation measure proposed in the SEKD, WCR-Coastal option and TKO CWA EIA
studies is to use close grab dredgers with silt curtains for both the dredging
and filling operations, which gives a sediment loss reduction of 5 times lower
than that using open grab alone.
4.4.18
Since the TKO New Town intensification
and extension EIA study was in progress when the modelling study was performed,
mitigation measure had not been proposed.
Hence, the corresponding spill loss rates for the dredging and filling
works shown in Table 4.7 were unmitigated. The present cumulative impact study (Scenario
2B) serves as conservative assessment of the potential impact of the concurrent
activities around YTB.
4.4.19
In the YTB reclamation, the
daily production rate for the main reclamation is much higher than that during
the seawall construction. Hence, the
Phase 1 main reclamation is used to represent the worst case scenario of
YTB reclamation in the cumulative impact study (Scenario 2B). This will be further justified by comparing
the impacts associated with the different construction phases of YTB
reclamation in Scenario 2A.
4.4.20
The dry densities of filling
sand and harbour mud are 1800 kg m-3 and
1400 kg m-3 respectively except for those in the YTB
reclamation. Based on the geotechnical
site investigation, the dry densities of filling sand and harbour mud involved
in the YTB reclamation are 1835 kg m-3 and
1750 kg m-3 respectively.
4.4.21
The dredging and filling works
are assumed to take place 10 hours per day, 7 days per week while
those of the SEKD and the TKO CWA will operate for 24 hours per day and
16 hours per day respectively.
4.4.22
The spill amount will be 1.8%
and 3.7% of the mud dredged and sand filled respectively. Spilling is assumed to take place uniformly
over the working hours.
4.4.23
With respect to rate of
sediment loss during dredging, the Contaminated Spoil Management Study (Mott
MacDonald, 1991; Table 6.12) reviewed relevant literature and concluded that
losses from open-grab dredgers were estimated at 12‑25 kg m-3
of mud removed. Taking the upper figure
of 25 kg m-3, and assuming an in-situ mud density of
1400 kg m-3, this represents a loss to the water column of
1.8%. This rate of loss represents a
conservative or worst case estimate.
4.4.24
According to the PSD test results
reported in the Technical Note 3/93 – Review of Specifications for Marine Fill
Material for Reclamation prepared by GEO, CED in October, 1993, the average
fines content of the filling sand from the marine borrow areas, e.g. South
Tatong and East Tung Lung Chau, ranges from 2% to 7% with an average value of
3.5%. As a conservative assumption, the
spill loss rate of 3.7% for sand filling is assumed for the present study. Similar assumptions have been made in the
SEKD study.
4.4.25
According to the information
provided by the Planning Department on 9 December 1999, the “Study on
Village Improvement and Upgrading of Lei Yue Mun Area” involves the assessment
of a number of improvement options for the Lei Yue Mun area. Mud dredging and cleaning at the Sam Ka Tsuen
Typhoon Shelter and the construction of a tidal barrier along the Lei Yue Mun
Villages are the proposed marine works which might have potential water quality
impact on the neighbouring water. The
study is in the preliminary engineering feasibility assessment stage and no
detailed dredge and fill volumes are available at present. Moreover, the proposed marine works are
relatively minor as compared to the neighbouring reclamation works and are not
expected to have major impact on the water sensitive receivers near YTB. Hence, these proposed works will not be
included in the present assessment.
Table 4.7 Details of Dredging and Filling Activities
between Jan 2001 and Dec 2011
Location/Source
ID
|
Activity
|
Production
Rate
(m3
day-1)
|
Sediment
Loss Rate (kg s-1)
|
South East
Kowloon Development (1, 3, 6)
|
Feb 2003–Mar
2003 (11)
|
A
|
Mud dredging for Cha Kwo
Ling PCWA reclamation
work package WP31:
KTNCRC6800
|
4187
|
0.24
|
B
|
Mud dredging for KBR1A
reclamation
work package WP04: KB1CRC1001
|
2101
|
0.12
|
C
|
Sand filling for Kai Tak
nullah (KTN) reclamation, stage 2
work package WP07:
KTNCRC6322
|
5265
|
0.81
|
D
|
Sand filling for the Kwun Tong Typhoon
Shelter (KTTS) Reclamation (north)
work package
WP29: KTNCRC6350
|
4744
|
0.73
|
E
|
Sand filling
for Cha Kwo Ling PCWA Reclamation
work package
WP31: KTNCRC6800
|
5895
|
0.91
|
F
|
Sand filling
for KBR1A and KBR1B Reclamations
work package
WP04: KB1CRC1001, KB1CRC1003
|
8507
|
1.31
|
G
|
Sand filling for KBR south
seawall foundation works
work package WP13:
KB1PTT1315
|
5000
|
0.77
|
Western Coast
Road (WCR) – Yau Tong Section (1, 3, 5)
|
Sept 2002–Oct
2002 (11)
|
H
|
Mud Dredging for seawall
foundation
|
1892
|
0.26
|
I
|
Sand filling for construction
of seawall foundation
|
900
|
0.33
|
-
|
Main Reclamation
|
2322
|
0.86
|
Western Coast
Road (WCR) – Tseung Kwan O Section (1, 3, 5)
|
Jun 2002–Sept
2002 (11)
|
J
|
Mud Dredging for seawall
foundation
|
1662
|
0.23
|
K
|
Sand filling for
construction of seawall foundation
|
2202
|
0.81
|
-
|
Main Reclamation
|
1787
|
0.66
|
Tseung Kwan O
New Town Intensification and Extension
– Area 138 (1,4,5)
|
Apr 2004–Jun
2004 (11)
|
L
|
Mud dredging for southern seawall
foundations
|
6000
|
4.2
|
M
|
Sand filling for the main
reclamation and eastern seawall
|
26000
|
48.1
|
Tseung Kwan O
Cargo Working Area (CWA) – Area 131 (1, 3, 7)
|
Apr 2003–Mar 2004 (11)
|
P
|
Mud dredging
for CWA outer arm
|
6358
|
0.56
|
Q
|
Sand filling for CWA outer
arm
|
5694
|
1.32
|
Yau Tong Bay
Reclamation (2, 4, 5, 8)
|
May 2004–July 2006 (11)
|
R1
|
Sand filling
for Phase 1 main reclamation
|
10000
|
18.86
|
|
|
|
|
|
Notes:
1. The dry densities of filling sand and harbour mud are
1800 kg m-3 and 1400 kg m-3
respectively unless specified otherwise.
2.
Based on the geotechnical site
investigation, the dry densities of filling sand and harbour mud involved in
the YTB reclamation are 1835 kg m-3 and
1750 kg m-3 respectively.
3.
Close grab with silt curtain
was adopted as a mitigation measure for sand filling and mud dredging in the
EIA studies for SEKD, WCR-Coastal option and TKO CWA. Spilling is assumed to occur uniformly over
the working hours with a sediment loss reduction factor of 5 times lower than
that using open grab alone.
4.
No mitigation measure is
applied in the model for the TKO New Town intensification and extension and YTB
reclamation
5.
The dredging and filling works
are assumed to take place 10 hrs per day, 7 days per week, except for the SEKD
and the TKO CWA.
6.
Operations for SEKD are carried
out continuously 24 hrs per day, 7 days per week.
7.
Operations for TKO CWA are
carried out continuously 16 hrs per day, 7 days per week.
8.
Source R1 is incorporated into
the model to represent the YTB reclamation.
9.
The spill amount will be 1.8%
and 3.7% for mud dredging and sand filling respectively.
10.
Spilling is assumed to take
place at the mid water depth.
11.
The period corresponds to the
time when the highest production rate for each project will occur with
reference to their latest construction programs as at March 1999.
Yau Tong Sewage Pumping Station Emergency
Outfall
4.4.26
As part of the proposed YTB
reclamation (Full Reclamation option), land provision has been considered and
identified at the new waterfront of the reclaimed land for potential relocation
or upgrading of the existing WSD Cha Kwo Ling saltwater pumping station and its
intake. The potential intake point may
be located at approximately 360m from the Yau Tong sewage PS emergency
outfall. The potential water quality
impact from the emergency discharge on the potential site for a new WSD intake
has been assessed using the Cornell Mixing Zone Expert System (CORMIX). The CORMIX3 model, in particular, was
designed to assess the near field mixing of a surface buoyant discharge which
is most relevant to the present study.
The CORMIX models were developed by the USEPA and have been used to
assess near field water quality impacts within the mixing zone for other EIA
studies in Hong Kong.
Assessment Criteria
4.4.27
A sediment plume model was used
to predict the elevations in SS concentration above the ambient levels in
Victoria Harbour and at the identified water sensitive receivers (WSRs). The predicted SS concentrations in Victoria
Harbour will be compared against the relevant assessment criteria for SS to
indicate compliance or non-compliance with the WQO.
4.4.28
The criteria for evaluating
impacts on marine water quality are given in Annex 6 of the TM on EIA Process
and have been adopted in this project.
The WQO for SS states that the marine activities during the construction
works must not cause the natural ambient level to be raised by more than 30%
nor give rise to accumulation of suspended solids. As discussed in Section 4.3.2, the 90 percentile
depth-averaged SS concentration is taken to represent the ambient SS
concentrations in the study area and, in accordance with the WQO for SS, an increase
in SS concentrations of not greater than 3.2 mg L-1 in the
marine waters will deemed to be acceptable.
4.4.29
For the assessment of SS
concentration at the WSRs, the 90 percentile surface SS concentration of
6.6 mgL-1 will be added to the predicted surface SS elevation
from the sediment plume model to give the absolute SS concentration (Table 4.5).
The absolute SS concentration will be used for comparison with the WSD’s
target and tolerable SS limits for saltwater intakes.
4.5
Sensitive Receivers
4.5.1
Yau Tong Bay is situated in the Victoria Harbour WCZ (VHWCZ) (Figure 4.2) which is bounded by the
Junk Bay WCZ to the east and the Eastern Buffer WCZ to the west. Water sensitive receivers in the study area
most likely to be affected by the YTB reclamation are identified below (Figure 4.7):
Existing water sensitive receivers
(WSRs)
·
Two WSD saltwater pumping
stations, namely the Cha Kwo Ling Saltwater Pumping Station (CKLSPS) and Yau
Tong Saltwater Pumping Station (YTSPS), which supply flushing water to the
neighbouring areas;
·
The Dairy Farm Factory
Saltwater Cooling Intake (DFSI);
Planned sensitive receivers
·
The potential sites for future
reprovisioning of the Cha Kwo Ling (NCKLSPS) and Yau Tong (NYTSPS) saltwater
pumping stations after the completion of the YTB reclamation (Full Reclamation
option) and the Western Coast Road (WCR-Coastal option), Yau Tong Section
reclamation.
4.5.2
The nearest WSD saltwater intake
on Hong Kong Island is the Sai Wan Ho saltwater intake which is located more
than 1 km from YTB. Hence, no major
water quality impact arising from the YTB reclamation is expected at the WSD
intakes on Hong Kong Island.
4.5.3
The nearest fish culture zone
(FCZ) to the study area is located at Tung Lung Chau, approximately 7 km
from YTB. The Tung Lung Chau FCZ has an
area of 80,000 m2, with 55 licensees as on 24 December 1998,
occupying a licensed raft area of 12,795 m2. Half of the total area is used for fish
culture and the species commonly reared include Groupers, Seabreams, Snapper,
Pampano, Cobia etc.
4.6
Operation Phase Impact Assessment
Potential Sources of Impact
4.6.1
The major concern is the effect
of the proposed YTB reclamation on Victoria Harbour. A reduction in tidal exchange in Victoria
Harbour may lead to the accumulation of pollutants from sewerage and storm
culvert discharges, and thus, adversely affecting the water quality. Since YTB lies close to Lei Yue Mun, it is
important to ensure that the flow through Lei Yue Mun as well as other major
channels is not significantly affected.
The cumulative effects from other reclamations and developments in Hong
Kong SAR are also considered.
4.6.2
A concrete decking over the two
submarine pipelines was proposed to the north of YTB as part of the reclamation
project (Phase 3). The water flow under
the decking may be relatively low and may lead to deterioration of water
quality. Hence, the water quality under
the proposed decking will be assessed in this section.
4.6.3
Raw sewage from the Yau Tong
area is currently conveyed to the Kwun Tong Sewage Treatment Plant via the Yau
Tong Pumping Station (PS) located at Ko Fai Road. There is an existing emergency outfall from
the Yau Tong PS which discharges into Victoria Harbour at the seawall. Under the WCR-Coastal option reclamation, the
existing WSD Yau Tong Saltwater Pumping
Station (YTSPS) as well as the emergency outfall from the Yau Tong PS will be
relocated to the new water front of the reclaimed land, while land provision
has been made on the YTB reclamation (Full Reclamation option) for potential
reprovisioning of the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS)
(Figure 4.7). The potential water quality impact in the
event of an emergency discharge from the Yau Tong PS on the potential sites for
reprovisioning of the WSD saltwater intakes will be assessed.
Prediction and Evaluation of Impact
Impact in Victoria
Harbour
Hydrodynamic Impact in Victoria Harbour –
Scenarios 1A and 1B
4.6.4
The hydrodynamic impact arising
from the YTB reclamation was assessed by comparing the modelling results of
Scenarios 1A and 1B. A
detailed discussion of the findings are presented in this section.
4.6.5
Predicted wet and dry seasons,
flood and ebb tides flow patterns in Victoria Harbour without the YTB
reclamation (Scenario 1A) are shown in Figures 4.8–4.11, while those of
with YTB reclaimed (Scenario 1B) are shown in Figures 4.12–4.15. The instantaneous flow patterns correspond to
the maximum flow discharges across the Victoria Harbour between Tsim Sha Tsui
and Wan Chai, namely the peak ebb and peak flood tidal flows.
4.6.6
Based on the peak ebb and peak
flood tidal flow patterns (Figures 4.8–4.15), the following observations
are made:
·
The flow patterns in Victoria
Harbour with or without YTB reclamation (Full Reclamation option)
(Scenarios 1A and 1B) are similar with minor deviation near YTB. The maximum flow speeds for the two scenarios
are roughly the same for each of the different tidal conditions, namely the wet
and dry seasons, spring and neap tides.
·
As observed in the flow speed
contours, the wet season flow speed in Victoria Harbour is generally higher
than that in the dry season. The maximum
flood tide flow speed of 1.11 ms–1 in the wet season is higher
than that of 0.71 ms–1 in the dry season (Table 4.8). Similar observation is made for the ebb tide
flow.
·
Furthermore, the ebb tide flow
speed is higher than that of the flood tide with the corresponding maxima of
0.79 ms–1 and 0.71 ms–1 in the dry season (Table 4.8). Similar observation is made in the wet
season.
·
The flow rates in the decked
region under ebb and flood tides during the dry and wet seasons will be in the
order of 0.1ms-1.
Table 4.8 Maximum Flow Speed in
Scenarios 1A and 1B
Maximum flow speed [ms-1]
|
Scenario 1A
|
Scenario 1B
|
Dry Season
|
Flood Tide
|
0.71
|
0.69
|
|
Ebb Tide
|
|
0.79
|
Wet Season
|
Flood Tide
|
1.11
|
1.11
|
|
Ebb Tide
|
1.24
|
1.24
|
4.6.7
The above observations
suggested that the maximum flow speeds and the flow patterns in Victoria
Harbour are rather insensitive to the YTB reclamation (Full Reclamation
option). With a reduction in the
reclamation area and a more streamlined water front in the Minimized
Reclamation option, it is expected that the effect of the Minimized Reclamation
on the hydrodynamics in Victoria Harbour will be minimal and unacceptable
impact is not anticipated.
4.6.8
To assess further the changes
in flow speed due to the YTB reclamation (Full Reclamation option), the maximum
flow discharge rates across the two major channels to the east and west of YTB
are shown in Table 4.9. The cross section locations are shown in Figure 4.16. Positive discharge indicates an ebb tide flow
in a direction pointing eastwards towards Lei Yue Mun and vice versa.
Table 4.9 Change in Ebb and Flood
Discharges with and without YTB reclamation
Cross section
|
Current
|
Scenario 1A
(Without YTB Reclamation)
|
Scenario 1B
(With YTB Reclaimed)
|
% Change
|
Discharge Rate [m3s-1]
|
Peak
|
Tidal Average
|
Peak
|
Tidal Average
|
Peak
|
Tidal Average
|
Dry Season
|
Tsim Sha Tsui / Wan Chai
|
Flood
|
-6506
|
-3108
|
-6447
|
-3114
|
-0.9%
|
0.2%
|
|
Ebb
|
8113
|
3193
|
8194
|
3189
|
1.0%
|
-0.1%
|
Lei Yue Mun
|
Flood
|
-7262
|
-3372
|
-7358
|
-3358
|
1.3%
|
-0.4%
|
|
Ebb
|
9417
|
3615
|
9456
|
3623
|
0.4%
|
0.2%
|
Wet Season
|
Tsim Sha Tsui / Wan Chai
|
Flood
|
-8074
|
-2731
|
-8079
|
-2733
|
0.1%
|
0.1%
|
|
Ebb
|
9167
|
1921
|
9176
|
1924
|
0.1%
|
0.2%
|
Lei Yue Mun
|
Flood
|
-9037
|
-3021
|
-9029
|
-3019
|
-0.1%
|
-0.1%
|
|
Ebb
|
10874
|
2201
|
10859
|
2200
|
-0.1%
|
0%
|
Annual (Dry and Wet)
Average
|
Tsim Sha Tsui / Wan Chai
|
Flood
|
-7290
|
-2920
|
-7263
|
-2923
|
-0.4%
|
0.1%
|
|
Ebb
|
8640
|
2557
|
8685
|
2556
|
0.5%
|
0%
|
Lei Yue Mun
|
Flood
|
-8149
|
-3197
|
-8193
|
-3189
|
0.5%
|
-0.3%
|
|
Ebb
|
10145
|
2908
|
10158
|
2912
|
0.1%
|
0.1%
|
Note: The
simulation results are based on the Full Reclamation option. With the reduction in reclamation area for
the Minimized YTB Reclamation, the difference in flow discharges with and
without the minimized reclamation is expected to be smaller than that of the
Full Reclamation option.
4.6.9
Due to the smaller channel
cross section area at Lei Yue Mun, the corresponding discharge rate is
approximately 15 % higher than that between Tsim Sha Tsui and Wan Chai (Table 4.9).
The maximum flow discharges in ebb tide, for both the wet and dry
seasons, are generally higher than those in flood tide (Table 4.9). The percentage change before and after the
YTB reclamation (Full Reclamation option) (i.e. Scenarios 1A and 1B
respectively) is very small with a change in annual average discharge rate of
less than 0.5%. This further confirms
that the YTB reclamation is likely to have negligible effect on the tidal flow
in Victoria Harbour. As explained in the
previous paragraphs, the effect of the Minimized Reclamation option on the
tidal flow is expected to be even smaller.
Water Quality Impact in Victoria Harbour
4.6.10
Raw sewage from the Yau Tong
Area is currently diverted to the Kwun Tong Screening Plant. By the year 2002 it is expected that all
screened sewage from the Kwun Tong Screening Plant would be diverted to the
Stonecutters Island STW and discharged via the interim outfall under Stage 1 of
the SSDS. The sewage arising from the
YTB Comprehensive Development Area (CDA) will be conveyed to the Kwun Tong
Screening Plant and discharge through the SSDS Stage I outfall. In view of the negligible change in flow
regime in Victoria Harbour, it is concluded that the YTB reclamation is
unlikely to have any adverse impact on the water quality in Victoria Harbour.
Impacts of the New Kwun Tong Nullah and the
New Storm Culvert in YTB– Scenario 1C
4.6.11
As part of the YTB development,
a concrete decking is proposed to be built over the existing submarine
pipelines near the northern part of YTB.
Since polluted stormwater may be discharged through the new Kwun Tong
nullah (NKTN) and the new YTB stormwater culvert (NYTBSC) near the decking, the
low flow speed under the decking may result in a potential accumulation of
pollutants. In Scenario 1C, the
potential water quality impact is assessed using a tracer particle method (Appendix 4A). The dispersion and dilution of pollutants
under the tidal influence is modelled using the 2D model, MIKE 21. The impact on the planned WSRs, namely, the
potential sites for future reprovisioning of the Cha Kwo Ling Saltwater Pumping
Station (NCKLSPS) and the reprovisioned Yau Tong Saltwater Pumping Station
(NYTSPS), will be presented.
The New Kwun Tong Nullah (KTN)
4.6.12
With the implementation of the
Sewerage Master Plans (SMPs) and remedial measures to reduce loads from
expedient sewerage connections, only 5% of the sewage flow in the catchment
area is assumed to remain in the stormwater system in the SEKD1,
including the new Kwun Tong nullah.
Based on the East Kowloon SMP, the flow and loads into the new KTN in
year 2011 have been estimated in the SEKD Feasibility Study2 and are
shown in Table 4.10.
Table 4.10 Flow and loads
into the new Kwun Tong Nullah in year 2011
Parameter
|
5% residual flows from expedient connections
|
1% residual flows from expedient connections
|
Flow (1)
(m3 d-1)
|
10,121
|
2,024
|
BOD5
(kg d-1)
|
2,305
|
461
|
SS (kg d-1)
|
2,029
|
406
|
Ammoniacal
Nitrogen (kg d-1)
|
178.4
|
35.7
|
E. coli (count per day)
|
1.48 x
1015
|
2.97 x
1014
|
Note: 1)
A dissolved oxygen level of 2 mgL-1, as adopted in the SEKD
Feasibility Study2, is assumed
4.6.13
A simple one dimensional
segmented steady state water quality model, similar to the Kai Tak Nullah model
adopted in the SEKD Feasibility Study2, which takes into account the
tidal mixing and decay within the nullah decking of approximately 1 km in
length, was used to assess the effluent quality at the outfall of the new
KTN. In the previous study2,
a dissolved oxygen (DO) level of 2 mgL-1 was considered
adequate in maintaining the WQOs in terms of aesthetic appearance in the open
channel of the new KTN. Since the
effluent DO level of the new KTN is unavailable, the same DO level of
2 mgL-1 was assumed in the steady state water quality model for
the new KTN impact.
4.6.14
The modelled effluent quality
at the outfall of the new Kwun Tong nullah is shown in Table 4.11. The effluent dissolved oxygen (DO) content of
3.78 mgL-1 at the outfall is above the WSD target limit at saltwater
intake of 2 mgL-1 but slightly lower than the WQO of 4 mgL-1. With further mixing in Victoria Harbour, it is
anticipated that the dissolved oxygen will increase to the ambient depth
averaged level of 4.85mgL-1 (Table 4.4),
satisfying the WQO.
Table 4.11 Predicted
Effluent Quality at the outfall of the new Kwun Tong Nullah
Assumption
|
Flow
Rate (3)
[m3
d-1]
|
DO
[mgL-1]
|
BOD5
[mgL-1]
|
SS
[mgL-1]
|
Ammoniacal
Nitrogen [mgL-1]
|
E. coli [count per 100 mL]
|
With 5% residual flows from expedient connections
|
77000
|
3.78
|
0.83
|
31.2
|
0.15
|
2404
|
With 1% residual flows from expedient connections
|
68900
|
4.73
|
0.04
|
11.3
|
0.01
|
106
|
Notes:
1.
Calculations were based on EPD routine
monitoring data at station VM1 in year 1997.
2.
Depth averaged values were
assumed.
3.
Flow rate include the tidal
flow within the new Kwun Tong nullah.
4.6.15
The effective pollution load at
the outfall of the new Kwun Tong nullah is estimated in Table 4.12
by multiplying the effluent pollutant concentration and the discharge flow
rate, which included the tidal flow within the nullah (Table 4.11). Significant reductions in loadings of BOD5
and ammoniacal nitrogen at the outfall are predicted, which are the results of
continuous mixing by large volume of tidal flow and the rapid decay rates of
parameters within the well-mixed effluent.
Table 4.12 Effective load at the
outfall of the new Kwun Tong Nullah in year 2011
Parameter
|
5%
residual flows from expedient connections
|
1%
residual flows from expedient connections
|
BOD5
(kg d-1)
|
64
|
3
|
SS (kg d-1)
|
2404
|
780
|
Ammoniacal
Nitrogen (kg d-1)
|
11.6
|
0.6
|
E. coli (count per day)
|
1.85 x
1012
|
7.32 x
1010
|
Water Quality in Victoria Harbour Water
Control Zone (VHWCZ)
4.6.16
Dilution and dispersion in the
vicinity of the outfall for the Full Reclamation option is simulated using the
2D particle model and the details are given in Appendix 4A. In general, the particle model result
suggests that the pollutant concentration will be diluted by more than 10 times
within 500 m from the outfall of the new KTN.
4.6.17
Based on the effective loading
at the new KTN outfall (Table 4.12) and the
particle model results (Appendix 4A), the predicted
increase in biochemical oxygen demand (BOD5), SS, Ammoniacal
Nitrogen and E. coli in Victoria
Habour and at the WSRs are shown in Table 4.13. No
decay factor was incorporated in the particle model giving a conservative
prediction. Comparing the predicted and
ambient values, obtained from EPD routine monitoring data at station VM1 in
year 1997 (Table 4.4), only slight increase in the
above parameters is observed in the Victoria Harbour WCZ, satisfying the WQOs (Table 4.13).
Typically, SS in the VHWCZ increases by 0.14 mgL-1 (3%)
above the ambient of 5.6 mgL-1,
which is lower than the WQO requirement.
Neither secondary contact recreation zone nor bathing beach zone has
been identified in the study area, therefore the predicted increase in E. coli of 11 counts per 100mL, over the
ambient of 5780 counts per 100mL (Table 4.13), is
considered acceptable. From the particle
model results (Appendix 4A), the pollutant
concentration will be diluted by more than 10 times within 500 m from the
outfall of the new Kwun Tong nullah. Assuming the ambient DO level of
4.85 mgL-1 from EPD’s routine monitoring data at station VM1 (Table 4.4), the 10 times dilution corresponds to
an increase in the DO level from 3.78 mgL-1 to 4.74 mgL-1. Taking into account the BOD5 of
less than 0.71 mgL-1, the DO level in the VHWCZ is expected to meet
the WQO.
Table 4.13 Impact of the New Kwun Tong Nullah - Comparison of Predicted Water
Quality with WQO and WSD Standards at Saltwater Intakes
Description
|
BOD5
[mgL-1]
|
SS
[mgL-1]
|
Ammoniacal
Nitrogen [mgL-1]
|
E. coli [count per 100mL]
|
Victoria Harbour Water Control Zone (VHWCZ)
|
Ambient level (1)
|
0.7
|
5.6
|
0.22
|
5780
|
Predicted
increase in VHWCZ
|
< 0.01
|
< 0.14
|
< 6.71 x 10-4
|
< 11
|
Predicted
increase under the proposed concrete decking
|
< 0.01
|
< 0.56
|
< 2.68 x 10-3
|
< 43
|
WQO
|
N/A (6)
|
< 30% over ambient and
median < 25 mgL-1
|
< 0.44 (5)
|
N/A (4)
|
Existing Water Sensitive Receivers (WSRs)
|
Maximum
increase at CKLSPS (2)
|
0.01
|
0.54
|
2.6 x 10-3
|
41
|
Maximum
increase at YTSPS (2)
|
0.01 (7)
|
0.31 (7)
|
1.48 x 10-3 (7)
|
24 (7)
|
Planned Water Sensitive Receivers (WSRs)
|
Maximum
increase at NCKLSPS (2)
|
0.02
|
0.68
|
3.3 x 10-3
|
53
|
Maximum
increase at NYTSPS (2)
|
0.01
|
0.31
|
1.48 x 10-3
|
24
|
WSD target
limit at saltwater intake
|
< 10
|
< 10
|
<1
|
< 20000
|
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year
1997.
2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater
pumping stations respectively, while NCKLSPS and NYTSPS represent the potential
sites for reprovisioning of the CKLSPS and the reprovisioned YTSPS on the
WCR-Coastal option reclamation respectively.
3. Data presented are depth averaged, except at the WSRs where top 5m
layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is
identified in VHWCZ.
5. With reference to the WQO of 0.021 mgL-1 for unionized
ammonia, the total ammonia present at 23oC and pH 8 is estimated to be
0.44. Calculations are based on EPD’s
monitoring data at VM1 in year 1997.
6. No WQO standards for BOD5 in marine waters.
7. The existing YTSPS intake location will be reclaimed by the
WCR-Coastal option development and thus the YTSPS have to be reprovisioned.
Since NYTSPS is located at approximately the same distance away from the Kwun
Tong Nullah as the YTSPS, similar impact is expected.
8. The results presented are based on the Full Reclamation option.
Water Quality under the Proposed Concrete
Decking
4.6.18
For the Full Reclamation
option, the water quality under the proposed concrete decking also satisfies
the WQOs with small increase in BOD5, SS, Ammoniacal Nitrogen and E. coli (Table 4.13). Based on the predicted pollutant dilution of
2.85 times from the outfall to under the decking, the DO level is estimated to
be approximately 4.5 mgL-1.
Considering the low level of predicted BOD5 and ammoniacal
nitrogen from the new Kwun Tong nullah, no odour problem is expected.
4.6.19
The particle model result also
revealed that the pollutants discharged from the new Kwun Tong nullah will take
an average time of less than 4 hours to be flushed out of the decking section
and into Victoria Harbour (Appendix 4A). This suggests that tidal flushing will
prevent the accumulation of pollutants under the decking and thus, unacceptable
water quality is not expected.
4.6.20
With a smaller reclamation area
and concrete decking at the mouth of YTB, and a more streamline water front in
the Minimized Reclamation option, the tidal flushing under the proposed
concrete decking is expected to improve as the inner part of the embayment is
more exposed to the flow current in Victoria Harbour than that in the Full
Reclamation option. Hence, water quality
under the proposed concrete decking is likely to be better in the Minimized
Reclamation option than that predicted in Table 4.13.
Water Quality
at the WSD Saltwater Pumping Stations
4.6.21
In the Full Reclamation option,
the BOD5, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station
(CKLSPS), taking into account the predicted maximum increases associated with
the NKTN and the ambient levels, are well within the WSD target limit (Table 4.13), and thus, unacceptable impact is not
expected. For the two planned water
sensitive receivers, namely the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS) under the
WCR-Coastal option reclamation and the potential site reserved for the
reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) under
the YTB reclamation (Full Reclamation option), the relevant water quality
parameters is also expected to satisfy the WSD target limit (Table 4.13).
4.6.22
Despite of the compliance of
the WSD target limit at the existing and the potential site for future
reprovisioning of the CKLSPS, the predicted results suggested that the water
quality at the existing CKLSPS intake will be slightly better than that at the
potential site for its reprovisioning.
Hence, reprovisioning of the existing CKLSPS intake will not be required
in the YTB reclamation (Full Reclamation option).
4.6.23
The existing Yau Tong saltwater
intake location will be reclaimed by the WCR-Coastal option development and the
Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of
the uncertainties in the programme of various projects, the YTSPS may continue
to operate at the existing location during the YTB reclamation. Considering
that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS)
are located at approximately the same distance from the new Kwun Tong Nullah
outfalls, it is expected that the water quality at the existing YTSPS will be
similar to those predicted at the reprovisioned YTSPS. In light of the large
margin between the predicted water quality and the WSD target limit at
saltwater intake, unacceptable impact is not expected at the existing YTSPS.
4.6.24
For the Minimized Reclamation
option, the more streamline flow in the vicinity of YTB favours the dispersion
and dilution of pollutants from the NKTN and thus the water quality at the
existing YTSPS intake is expected to be similar to, if not better than, that at
the reprovisioned location in the Full Reclamation option, satisfying the WSD’s
target limit at saltwater intakes. As
discussed in the previous paragraphs, the water quality at the existing CKLSPS
under the proposed concrete decking is expected to improve in the Minimized
Reclamation option for YTB, as compared to that in the Full reclamation option,
satifying the WSD’s target limit at saltwater intakes. Hence, no reprovisioning
of the existing CKLSPS and the YTSPS intakes will be required in the Minimized
Reclamation for YTB.
The new YTB Stormwater Culvert
4.6.25
The existing stormwater culvert
in YTB will be extended to the new waterfront of the YTB reclamation (Full
Reclamation option). Based on the
population estimates in year 2011 and the load factors (Appendices 4B-1
and 4B-2), obtained from the
Kowloon District Office of Planning Department and DSD Sewerage Manual, the total
pollution load in the Yau Tong sewage catchment is estimated (Table 4.14).
Despite the fact that new sewerage network will be built for the new
developments in the YT area, it is conservatively assumed that 5% of the total
load in the YT sewage catchment will enter the new YTB stormwater culvert
through expedient connections. This is a
conservative assumption as all the future developments in the Yau Tong area
will be connected to public sewers which minimizes the pollution load to the
stormwater culvert through expedient connections, and the % load interception
by the storm system is expected to lower.
With the increase in impermeable area due to the YTB reclamation,
surface runoff and the associated pollution load will also increase. Hence, the pollution load from surface runoff
is also taken into account in the total load of the new YTB stormwater culvert
(Table 4.14).
It is observed that the pollution load in the new stormwater culvert in
YTB is much lower than that in the new KTN (Tables 4.10
and 4.14).
Similar to the SEKD Feasibility Study, the effluent DO level is assumed
to be 2 mgL-1. Tidal
mixing and decay within the new stormwater culvert has not been taken into
account at present to provide a conservative worst case assessment.
Table
4.14 Estimated Pollution Loads in the New
Stormwater Culvert in YTB in Year 2011
Parameter
|
Total Load in Yau Tong Sewage Catchment(1)
|
Load from Surface Runoff
|
Total Load in the New YTB Stormwater Culvert (2)
|
Flow (m3
d-1)
|
50717
|
6677
|
9213
|
BOD5
(kg d-1)
|
11761
|
150
|
738
|
SS (kg d-1)
|
10056
|
289
|
792
|
Ammoniacal
Nitrogen (kg d-1)
|
961
|
1
|
49
|
E. coli (count per day)
|
8.19 x 1015
|
0
|
4.09 x 1014
|
Notes:
1.
Calculations are based on the
population estimate in year 2011 obtained from the Kowloon District Office of
Planning Department and the per capita load factor from DSD Sewerage Manual,
Part I, 1995 (Appendices 4B-1
and 4B-2).
2.
It is assumed that 5% of the
total load in Yau Tong sewage catchment, together with the load from surface
runoff, will enter the stormwater system and discharged through the new YTB
stormwater culvert into Victoria Harbour.
This is a conservative assumption as all the future developments in the
Yau Tong area will be connected to public sewers which minimizes the pollution
load to the stormwater culvert through expedient connections, and the % load
interception by the storm system is expected to lower.
Water Quality in Victoria Harbour Water Control
Zone (VHWCZ)
4.6.26
Using the 2D particle model,
similar to that used in the study of the new KTN (Appendix 4A),
the pollutant dilution and dispersion near the outfall of the new YTB storm
culvert in the Full Reclamation option is simulated (Appendix 4C). In general, the particle model result
indicated that the pollutant concentration will be diluted by more than
6 times within 100 m from the new water front near the new YTB
stormwater culvert outfall (Appendix 4C).
4.6.27
The predicted increase in
biochemical oxygen demand (BOD5), SS, Ammoniacal Nitrogen and E.
coli in Victoria Habour and at the WSRs are shown in Table 4.15. The predicted increases generally satisfy the
WQOs in the VHWCZ (Table 4.15). Based on the ambient DO level of
4.85 mgL-1, from EPD’s routine monitoring data at station VM1
in year 1997 (Table 4.4), and the predicted
pollutant dilution of more than 6 times within 100 m from the storm culvert
outfall to the new water front, it is predicted that the DO level would
increase from 2 mgL-1 at the storm culvert outfall to 4.38 mgL-1
in the VHWCZ. Taking into account the
BOD5 of less than 0.74 mgL-1, the DO level is
expected to meet the WQO in the VHWCZ.
Since mixing and decay within the new YTB stormwater culvert have not
been taken into account, it is anticipated that the actual pollutant
concentration will be lower than those predicted in Table 4.15. The cumulative water quality impact of the
New Kwun Tong Nullah and New YTB Stormwater Culvert is shown in Table 4.15a.
Non-compliance of WSD water quality criteria or WQOs within the Victoria
Harbour is not expected.
Table 4.15 Impact
of the New YTB Stormwater Culvert – Comparison of Predicted Water Quality with
WQO and WSD Standards at Saltwater Intakes
Description
|
BOD5
[mgL-1]
|
SS
[mgL-1]
|
Ammoniacal Nitrogen [mgL-1]
|
E. coli [count per 100mL]
|
|
Ambient level (1)
|
0.7
|
5.6
|
0.22
|
5780
|
|
< 0.04
|
< 0.05
|
< 2.86 x 10-3
|
< 2370
|
Predicted increase under the
proposed concrete decking
|
< 0.09
|
< 0.09
|
< 5.72 x 10-3
|
< 4740
|
WQO
|
N/A (6)
|
< 30% over ambient and
median < 25mgL-1
|
< 0.44 (5)
|
N/A (4)
|
Existing Water Sensitive Receivers (WSRs)
|
Maximum
increase at CKLSPS (2)
|
0.08
|
0.09
|
5.4 x 10-3
|
4455
|
Maximum
increase at YTSPS (2)
|
0.12 (7)
|
0.13 (7)
|
8.12 x 10-3 (7)
|
6730 (7)
|
|
Maximum increase at NCKLSPS (2)
|
0.22
|
0.24
|
1.48 x 10-2
|
12228
|
Maximum increase at NYTSPS (2)
|
0.12
|
0.13
|
8.12 x 10-3
|
6730
|
|
< 10
|
< 10
|
< 1
|
< 20000
|
|
|
|
|
|
|
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year
1997.
2.
CKLSPS and YTSPS represent the
existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively,
while NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the
CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation
respectively.
3. Data presented are depth averaged, except at the WSRs where top 5m
layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is identified
in VHWCZ.
1. With reference to the WQO of 0.021 mgL-1 for unionized
ammonia, the total ammonia present at 23oC and pH 8 is estimated to
be 0.44. Calculations are based on EPD’s
monitoring data at VM1 in year 1997.
2.
No WQO standards for BOD5
in marine waters.
3.
The existing YTSPS intake
location will be reclaimed by the WCR-Coastal option development and thus the
YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the
same distance away from the new YTB stormwater outfall as the YTSPS, similar
impact is expected.
4.
The results presented are based
on the Full Reclamation option.
Water Quality under the Proposed Concrete
Decking
4.6.28
In the Full Reclamation option
for YTB, the water quality under the proposed concrete decking due to the new
YTB stormwater culvert discharge also satisfies the WQOs with small increase in
BOD5, SS, Ammoniacal Nitrogen and E. coli (Table 4.15). It is predicted that the pollutant
concentration will be diluted by more than 3 times from the outfall of the new
stormwater culvert to under the proposed concrete decking. Correspondingly, the DO level is estimated to
be approximately 3.9 mgL-1.
Taking into account tidal mixing within the new stormwater culvert, the
WQO for DO is expected to be satisfied.
At low level of BOD5 and ammoniacal nitrogen, no odour
problem is expected under the decking.
4.6.29
For the Minimized Reclamation
option, with a reduction in the size of the proposed concrete decking, the
tidal flushing under the proposed concrete decking is expected to improve as
the inner part of the embayment is more exposed to the flow current in Victoria
Harbour than that in the Full Reclamation option. Hence, water quality under the proposed concrete
decking is likely to be better in the Minimized Reclamation option than that
predicted in Table 4.15.
Water Quality at the WSD Saltwater Pumping
Stations
4.6.30
In the Full Reclamation option,
the BOD5, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station
(CKLSPS), taking into account the predicted maximum increases associated with
the New Yau Tong Bay Stormwater Culvert and the ambient levels, are well within
the WSD target limit (Table 4.15), and thus,
unacceptable impact is not expected. For
the two planned WSRs, namely the reprovisioned Yau Tong Saltwater Pumping
Station (NYTSPS) under the WCR-Coastal option reclamation and the potential
site reserved for the reprovisioning of the Cha Kwo Ling Saltwater Pumping
Station (NCKLSPS) under the YTB reclamation (Full Reclamation option), the
relevant water quality parameters is also expected to satisfy the WSD target
limit (Table 4.15). As noted under the discussion of the NKTN
impact, the water quality at the existing CKLSPS intake will be slightly better
than that at the potential site for its reprovisioning. Hence, reprovisioning of the existing CKLSPS
intake will not be required in the YTB reclamation (Full Reclamation option).
4.6.31
The existing Yau Tong saltwater
intake location will be reclaimed by the WCR-Coastal option development and the
Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of
the uncertainties in the programme of various projects, the YTSPS may continue
to operate at the existing location during the YTB reclamation. Considering
that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS)
are located at approximately the same distance from the new YTB stormwater
culvert, it is expected that the water quality at the existing YTSPS will be
similar to those predicted at the reprovisioned YTSPS. In light of the large margin between the
predicted water quality and the WSD target limit at saltwater intake, unacceptable
impact is not expected at the existing YTSPS.
4.6.32
For the Minimized Reclamation
option, the more streamline flow in the vicinity of YTB, favours the dispersion
and dilution of pollutants from the new YTB stormwater culvert and thus the
water quality at the existing YTSPS intake is expected to be similar to, if not
better than, that at the reprovisioned location in the Full Reclamation option,
satisfying the WSD’s target limit at saltwater intakes. As discussed in the previous paragraphs, the
water quality at the existing CKLSPS under the proposed concrete decking is
expected to improve in the Minimized Reclamation option for YTB, as compared to
that in the Full reclamation option, satifying the WSD’s target limit at
saltwater intakes. Hence, no reprovisioning of the existing CKLSPS and the
YTSPS intakes will be required in the Minimized Reclamation for YTB.
4.6.33
Considering the minor impact of
the new Kwun Tong nullah and the new YTB stormwater culvert (Tables 4.13 and 4.15),
their cumulative effects are still within the WQO and WSD target limit at the
saltwater intakes (Table 4.15a). Hence, no insurmountable impact is expected
in the VHWCZ, at the WSRs and under the proposed concrete decking. Also, as a result of the minor impact, the
effect of stratification is considered insignificant and only the 2D particle
model is necessary in this scenario.
Table 4.15a Cumulative
Impact of the New Kwun Tong Nullah and New YTB Stormwater Culvert – Comparison
of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes
Description
|
BOD
[mg L-1]
|
SS
[mg L-1]
|
Ammoniacal
Nitrogen [mg L-1]
|
E. coli [count per 100 mL]
|
Victoria
Harbour Water Control Zone (VHWCZ)
|
Ambient level (1)
|
0.7
|
5.6
|
0.22
|
5780
|
Predicted increase in VHWCZ
|
< 0.05
|
< 0.19
|
< 3.531 x 10-3
|
< 2381
|
Predicted increase under the proposed
concrete decking
|
< 0.1
|
< 0.65
|
8.40 x 10-3
|
< 4783
|
WQO
|
N/A (6)
|
< 30% over ambient and median < 25
mg L-1
|
< 0.44 (5)
|
N/A (4)
|
Existing
Water Sensitive Receivers (WSRs)
|
Maximum increase at CKLSPS (2)
|
0.09
|
0.63
|
8.0 x 10-3
|
4496
|
Maximum increase at YTSPS (2)
|
0.13 (7)
|
0.44 (7)
|
9.60 x 10-3 (7)
|
6754 (7)
|
Planned
Water Sensitive Receivers (WSRs)
|
Maximum increase at NCKLSPS (2)
|
0.24
|
0.92
|
1.81 x 10-2
|
12281
|
Maximum increase at NYTSPS (2)
|
0.13
|
0.44
|
9.60 x 10-3
|
6754
|
WSD target limit at saltwater intake
|
< 10
|
< 10
|
< 1
|
< 20000
|
Notes:
1.
Data source: EPD routine
monitoring data at station VM1 in year 1997.
2.
CKLSPS and YTSPS represent the existing
Cha Kwo Ling and Yau Tong saltwater pumping stations respectively, while
NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the
CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation
respectively.
3.
Data presented are depth
averaged, except at the WSRs where top 5m layer data are considered.
4.
No secondary contact recreation
and bathing beach sub-zone is identified in VHWCZ.
5.
With reference to the WQO of
0.021 mgL-1 for unionized ammonia, the total ammonia present at 23oC
and pH 8 is estimated to be 0.44.
Calculations are based on EPD’s monitoring data at VM1 in year 1997.
6.
No WQO standards for BOD5
in marine waters.
7.
The existing YTSPS intake
location will be reclaimed by the WCR-Coastal option development and thus the
YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the
same distance away from the new YTB stormwater outfall as the YTSPS, similar
impact is expected.
8.
The
results presented are based on the Full Reclamation option.
Impact from the emergency discharge of the DSD
Yau Tong Sewage Pumping Station
4.6.34
There is an existing emergency
outfall for the Yau Tong Sewage PS located along Ko Fai Road which discharges
into Victoria Harbour at the seawall.
This outfall is 1.425m in diameter and the invert level is at 0.02
mPD. According to DSD records, only one
emergency discharge on 30 April 1998 was recorded for repairing the rising main
and no records of other bypass discharges was found before this date. Approximately 3,500 m3 of raw
sewage was discharged over 12 hours (7000 m3 day-1). According to the East Kowloon Sewerage Master
Plan and the preliminary pollution loading inventory being compared under a
separate study, the sewage flow in year 2002 served by the Yau Tong sewage PS
is estimated as 6,683 m3 day-1. This estimate agrees well with the discharge
record by DSD given above. As population
grows in the Yau Tong area, it is estimated that the sewage flow served by the
Yau Tong Sewage Pumping Station (YTPS) will be increased to 50717 m3 day-1
in year 2011.
4.6.35
As assessed in the previous
sub-sections on the impact from the NKTN and the new YTB stormwater culvert at
the existing WSD CKLSPS intake, reprovisioning of the CKLSPS will not be required
under the YTB reclamation (Full Reclamation option). However, a potential site for future
reprovisioning of the CKLSPS saltwater intake have been proposed on the new
waterfront of the YTB reclamation (Full Reclamation option),which is closer to
the Yau Tong Sewage PS emergency outfall than the existing case. The potential water quality impact from the
emergency discharge at the potential site for reprovisioning of the CKLSPS
saltwater intake in the Full Reclamation option has been assessed using the Cornell
Mixing Zone Expert System (CORMIX). The
CORMIX3 model has been run for the existing and future scenarios of the Yau
Tong Sewage PS emergency outfall with the model parameters given in Table 4.16 below.
Table 4.16 CORMIX Modelling Parameters
Parameter
|
Existing (1)
|
Future (1)
|
Outfall Parameters
|
Outfall Invert Level
|
+0.02 mPD
|
Outfall Cross Sectional Area
|
1.594 m2
|
Effluent Density
|
1000 kg m-3
|
Effluent Flow
|
6,683 m3 day-1
|
50717 m3 day-1
|
|
Environmental parameters
|
High Water Level
|
+2.35mPD
|
Low Water Level
|
+0.35mPD
|
Ambient Water Depth
|
10m
|
Ambient Current Speed
|
0.1m s-1
|
Ambient Water Density
|
1018 kg m-3 (wet season)
and
1023 kg m-3 (dry season)
|
Darcy-Weisbach Friction Factor
|
0.023
|
Note:
1. The existing and future scenarios are based on the sewage flow
served by the YTPS in year 2002 and year 2011 respectively.
4.6.36
As the density difference between
the effluent and the ambient receiving waters will affect the buoyancy of the
sewage plume, the model was run for a range of ambient water densities
representing the wet and dry season conditions.
The model results are presented graphically in Figures 4.17 and 4.18 for the existing and future
scenarios respectively.
4.6.37
For both the existing and
future scenarios, the sewage plume will attach to the shoreline due to the
relatively low effluent velocity. It
will also be buoyant due to the density difference between the sewage effluent
and the ambient marine water in both the wet and dry seasons. The initial dilution values shown in Figures 4.17 and 4.18 represent the average dilution
within the plume at various distances.
The potential site for future reprovisioning of the Cha Kwo Ling
saltwater pumping station intake (NCKLSPS) will be approximately 360m from the
Yau Tong Sewage PS emergency outfall. At
this distance from the outfall, the sewage plume thickness range between
0.19–0.37m from the surface in the existing and future scenarios, wet and dry
seasons. The existing Cha Kwo Ling
saltwater intake (CKLSPS) will be approximately 250 m further away from
the emergency outfall than that of the NCKLSPS and less impact is
expected. Hence, the present assessment
at the NCKLSPS intake represents the worst case scenario.
4.6.38
Assuming the following typical
raw sewage strength of:
·
BOD 250 mg L-1
·
Suspended Solids (SS) 250 mg L-1
·
E. coli 2.00E+07
counts per 100mL
·
Ammoniacal Nitrogen (NH3-N) 25 mg L-1
4.6.39
With the background mean
ambient water quality concentration as given in Table 4.4,
the predicted water quality levels within the sewage plume and the depth
averaged values at a distance of approximately 360m from the outfall are given
in Table 4.17.
Table 4.17 Predicted water quality within sewage plume
|
Pollutant Concentration
at 360m from Outfall
|
WSD Standards at Saltwater Intake
|
Within the Plume
|
Depth Averaged (1,2)
|
Existing
|
Future
|
Existing
|
Future
|
Wet Season Scenario
|
Dilution
Factor
|
57.0
|
8.4
|
1532.3
|
386.3
|
N/A
|
BOD (mg L-1)
|
5.1
|
30.3
|
0.9
|
1.3
|
<10
|
SS (mg L-1)
|
10.0
|
35.2
|
5.8
|
6.2
|
<10 (target),
<20 (tolerable)
|
NH3-N
(mg L-1)
|
0.66
|
3.18
|
0.24
|
0.28
|
<1
|
E. coli (count per
100 mL)
|
3.57 x 105
|
2.37 x 106
|
1.88 x 104
|
5.76 x 104
|
<20,000
|
Dry Season Scenario
|
Dilution
Factor
|
51.8
|
8.2
|
1626.0
|
431.4
|
N/A
|
BOD (mg L-1)
|
5.5
|
31.1
|
0.9
|
1.3
|
<10
|
SS (mg L-1)
|
10.4
|
36
|
5.8
|
6.2
|
<10 (target),
<20 (tolerable)
|
NH3-N
(mg L-1)
|
0.7
|
3.3
|
0.24
|
0.28
|
<1
|
E. coli (count per
100 mL)
|
3.92 x 105
|
2.44 x 106
|
1.81 x 104
|
5.21 x 104
|
<20,000
|
Notes:
1. The wet season plume thickness for the existing and future scenarios
are 0.37 m and 0.22 m respectively, while those of the dry season are
0.32 m and 0.19 m respectively.
2. The depth averaged values are calculated based on a water depth of
10 m and the corresponding plume thickness.
3. The results presented are based on the Full Reclamation option.
Table 4.17a Cumulative
Impact of the New Kwun Tong Nullah, New YTB Stormwater Culvert and Emergency
Discharge from the Yau Tong Sewage Pumping Station – Comparison of Predicted
Water Quality with WQO within sewage plume at the NCKLSPS Saltwater Intake
|
Pollutant Concentration
at 360 m from Outfall
|
WSD Standards at
Saltwater Intake
|
Depth Averaged
|
|
Within the Plume (1)
|
Depth Averaged (2)
|
|
Wet Season Scenario
|
|
|
|
BOD (mg L-1)
|
30.54
|
1.54
|
<
10
|
SS (mg L-1)
|
36.12
|
7.12
|
<
10 (target), < 20 (tolerable)
|
NH3-N (mg L-1)
|
3.20
|
0.30
|
<
1
|
E. coli (count per 100 mL)
|
2.38
x 106
|
69881
|
< 20000
|
Dry Season Scenario
|
|
|
|
BOD (mg L-1)
|
31.34
|
1.54
|
<
10
|
SS (mg L-1)
|
36.92
|
7.12
|
<
10 (target), < 20 (tolerable)
|
NH3-N (mg L-1)
|
3.32
|
0.30
|
<
1
|
E. coli (count per 100 mL)
|
2.45
x 106
|
64381
|
< 20000
|
Notes:
1.
The wet season plume thickness for
the existing and future scenarios are 0.37 m and 0.22 m respectively,
while those of the dry season are 0.32 m and 0.19 m respectively.
2.
The depth averaged values are
calculated based on a water depth of 5 m and the corresponding plume
thickness.
3.
The results
presented are based on the Full Reclamation option.
4.6.40
The depth averaged results
indicated that the WSD water quality standards, in terms of BOD5, SS
and ammoniacal nitrogen, at the
saltwater intake will be satisfied, while the E. coli standards will be exceeded in the future scenario (Tables 4.17 and 4.17a). However, the sewage plume is buoyant at the
surface, where pollutants are concentrated with a thickness of less than
0.37m. To avoid abstracting the sewage
plume water, it is therefore recommended that the saltwater intake should be
located below a depth of approximately -2.0 mPD. The intake water will then be expected to
meet all the WSD standards.
4.6.41
Discharge through the emergency
outfall is a rare event. Should a
discharge be made through the emergency outfall, it is recommended that DSD
should inform WSD of the details of such discharge, e.g. volume, timing and
duration, in advance if possible. It is
also recommended that DSD should minimize the discharge and liaise with WSD to
avoid discharge during the peak operation hours of the WSD’s saltwater pumping
station.
4.6.42
In the Minimized Reclamation
option, the CKLSPS saltwater intake and the Yau Tong Sewage Pumping Station
emergency outfall will remain at their existing location, which are separated
further apart than that in the proposed reprovisioned locations. Hence, unacceptable water quality impact at
the existing CKLSPS intake is not anticipated.
4.7
Construction Phase Impact Assessment
Potential Sources of Impact
4.7.1
Potential water quality impacts
during the construction phase of YTB reclamation (Full Reclamation option) are
summarized below:
·
Increase of SS concentration
due to dredging and filling activities within the site, and the cumulative
impacts from concurrent construction activities in the vicinity of YTB, such as
South East Kowloon Development (SEKD), Reclamations for the Western Coast Road
(WCR-Coastal option), Tseung Kwan O (TKO) Cargo Working Area (CWA) and TKO New
Town intensification and extension;
·
Release of contaminants during
dredging of marine mud;
·
Release of contaminants through
vertical band drains during consolidation of reclamation; and
·
Local deterioration of water
quality due to temporary diversion of stormwater culvert during interim stage
of the reclamation.
Prediction and Evaluation of Impact
Sediment Plume Modelling for Dredging and
Filling Activities
4.7.2
One of the major concerns of
the present study is to minimize the water quality impact, particularly the SS
concentration, associated with the sand filling and mud dredging of the YTB
reclamation. The potential release of
contaminants during dredging of contaminated mud will also be addressed.
4.7.3
Numerical models, namely MIKE
21 and MIKE 3, from the Danish Hydraulic Institute (DHI) were used to simulate
the dispersion and transport of sediment released during the dredging and
filling activities. The modelling
details are included in Section 4.4 and the
results are presented in the following sections.
Worst-Case Impact of YTB reclamation (Full
Reclamation option) – Scenario 2A
4.7.4
Assumptions made in the
simulations for the YTB reclamation are as follows:
·
The dry densities of filling
sand and harbour mud are 1835 kg m-3 and
1750 kg m-3 respectively, based on the geotechnical site
investigation for the YTB reclamation.
·
Sand filling will be carried
out by barges using bottom dumping.
Spilling occurs during the first 10 minutes for each 1 hour dumping
cycle, 10 hours per day, 7 days per week.
·
Spill loss during mud dredging
by 2 x 10 m3 open bucket grab dredger will be continuous, 10
hours a day, 7 days per week.
·
The spill amount will be 1.8%
and 3.7% of the mud dredged and sand filled respectively.
·
Spilling is assumed to take
place at the water surface.
4.7.5
According to the preliminary
construction program (Appendix 2A),
the YTB reclamation (Full Reclamation option) can be divided into 3 different
phases, namely, the seawall construction, Phase 1 and Phase 2 reclamations. The
highest dredging or filling rate for the different construction phases were
identified (Table 4.18). The corresponding source locations are given
in Figure 4.6b.
4.7.6
The reclamation phasing
mentioned above is also valid for the Minimized Reclamation with the
reclamation extent reduced to the mouth of YTB.
Furthermore, it is envisaged that the production rate for the Minimized
Reclamation option will be the same as, if not less than, that of the Full
Reclamation option. Hence, the present
simulation, assuming the Full Reclamation option for YTB, represents the
conservative worst case construction impact.
The recommended mitigation measures proposed under this section is fully
applicable to both the Full and the Minimized Reclamation options. For simplicity, it will be assumed in the
following discussions of construction phase impacts that “YTB reclamation”
refers to the “Full Reclamation option”, unless specified otherwise.
Table 4.18 Highest
Dredging and Filling Rates of YTB Reclamation (Full Reclamation Option)
(Scenario 2A)
Source ID
|
Activity
|
Approx. Duration (5)
[days]
|
Maximum Production Rate
[m3 day-1]
|
Sediment Loss Rate [kg s-1]
|
Seawall Construction
|
S
|
Mud
dredging for seawall foundation
|
48
|
1554
|
1.36
|
T
|
Sand
filling for seawall foundation and conventional seawall construction
|
48
|
2260
|
4.26
|
Phase 1 Main Reclamation
|
R1
|
Place
sand blanket (1m) and bulk filling below sea level for Phase 1 main
reclamation of YTB
|
320
|
10000 (6)
|
113.2
|
Phase 2 Main Reclamation
|
R2
|
Place
sand blanket (1m) and bulk filling below sea level for Phase 2 main
reclamation of YTB
|
80
|
10000 (6)
|
113.2
|
Notes:
1. The dry densities of filling sand and harbour mud are 1835 kg m-3
and 1750 kg m-3 respectively.
2. For sand filling by bottom dumping, spilling will only occur during
the first 10 minutes for each 1 hr dumping cycle, 10 hours per day, 7
days per week.
3.
Spill loss during mud dredging
by 2 x 10 m3 open bucket grab dredger will be continuous, 10
hours a day, 7 days per week.
4.
The spill amount will be 1.8% and
3.7% for mud dredging and sand filling respectively.
5.
The duration of each operation
is based on the preliminary construction program for the Full Reclamation
option (Appendix 2A). The period will be shortened accordingly if
the Minimized Reclamation option is chosen instead.
6.
In the preliminary construction
program (Appendix 2A),
an average production rate of 4000 m3 day-1 is
assumed, while the sand filling rate of 10,000 m3 day-1
is the highest practicable rate envisaged in the YTB reclamation.
4.7.7
To determine the worst case of
the YTB reclamation (Full Reclamation option), model runs were performed for
the three different phases. The results
are presented below.
Seawall Construction Impact – Scenario 2A_SW
4.7.8
The major source of sediment
spill during the seawall construction can be associated with the mud dredging
(Source S) and back filling with sand (Source T) for the seawall foundation. Open bucket grab dredgers are assumed for
both dredging and filling activities.
Water Quality in Victoria Harbour Water
Control Zone (VHWCZ)
4.7.9
The predicted suspended solid
(SS) elevations in Victoria Harbour are shown in
Figures 4.19 – 4.22 for the dry season and
Figures 4.23 – 4.30 for the wet season, spring and neap tides.
4.7.10
The dry season depth averaged
SS concentration indicated that the sediment plume due to the seawall
construction is localized in the vicinity of YTB
(Figures 4.19 – 4.20).
The allowable increase in depth averaged SS concentration of 3.2mgL-1,
i.e. 30% above the ambient level as required by the WQO (Section 4.3.2),
is satisfied in the VHWCZ. SS elevation
of up to 9 mgL-1, exceeding the WQO, is limited to within 100m
from the waterfront extending from the Eastern Breakwater in SEKD to the mouth
of Sam Ka Tsuen Typhoon Shelter. The top
5m average SS concentration indicates that the surface plume is slightly
smaller than the depth average plume (Figures 4.21 – 4.22).
4.7.11
The WQO for SS in the VHWCZ is
also satisfied in the wet season. The
sediment plume in the wet season neap tide is similar to that in the dry
season, with a slightly lower exceedance between YTB and Sam Ka Tsuen Typhoon
Shelter (Figures 4.27 – 4.28).
During wet season spring tide, the sediment plume is drifted towards the
western side of YTB with depth averaged SS concentration of up to 15 mgL-1
between the Eastern Breakwater and YTB, which is higher than that in the dry
season.
Water Quality at the Water Sensitive
Receivers (WSRs)
4.7.12
As discussed earlier in Section 4.5,
three main WSRs, namely, Dairy Farm saltwater intake (DFSI), WSD’s Cha Kwo Ling
(CKLSPS) and Yau Tong (YTSPS) Saltwater Pumping Stations, were identified in
the present study. In general, these
intakes are located within a few metres from the water surface, where the water
quality is of main concern. In the
sediment plume model, results are extracted for the top 5m layer for
comparison. To assess the impact at the
WSRs, time series of the SS elevation are extracted (Appendix 4D) and
added to the ambient 90 percentile surface SS concentration of 6.6 mgL-1,
based on EPD’s routine monitoring data (Table 4.5),
giving the absolute SS concentration at the WSR. The statistics of SS concentration at the
WSRs are summarised in Table 4.19. The warm up period of the first
1.5 days, as shown in the time series plot in Appendix 4D, are
excluded from the statistical calculations.
4.7.13
During the seawall construction
(Scenario 2A_SW) in the wet and dry seasons, the mean SS concentration ranges
from 8.7 mgL-1 at the YTSPS to 21 mgL-1 at the
DFSI, while the maximum SS concentration ranges from 26.1 mgL-1
at the YTSPS to 91 mgL-1 at the DFSI (Table 4.19). It should be noted that the variation of SS
concentration at the WSRs in the wet season is generally greater than that in
the dry season (Table 4.19).
4.7.14
In general, the SS
concentration at the existing WSRs is in exceedance of the WSD target
(tolerable) limit of 10 mgL-1 (20 mgL-1) (Table 4.19).
The percentage time in compliance with the WSD target (tolerable) limit
at the CKLSPS and YTSPS are 42.9% (68.5%) and 51.3% (80%) respectively,
while the SS standard of 20 mgL-1 at the DFSI is satisfied for
69.6% of the time. The above suggests
that the CKLSPS is the most susceptible to the impact of the dredging and
filling works for the seawall foundation.
Table 4.19 A Summary of Time Series Statistics of SS
concentration at the WSRs for Scenario 2A
Absolute SS concentration (2) [mgL-1]
|
Unmitigated
|
Mitigated
|
Diary Farm Saltwater Intake
(DFSI)
|
Cha Kwo Ling Saltwater
Intake (CKLSPS)
|
Yau Tong Saltwater Intake (YTSPS)
|
Diary Farm Saltwater Intake
(DFSI)
|
Cha Kwo Ling Saltwater
Intake (CKLSPS)
|
Yau Tong Saltwater Intake (YTSPS)
|
Scenario 2A_SW - YTB Seawall Construction
5(a,b,d)
|
Dry Season,
Spring-Neap Cycle
|
Mean SS
conc
|
19.3
|
17.9
|
14.6
|
3.7
|
3.5
|
3.3
|
Maximum SS
conc
|
79.0
|
74.6
|
63.9
|
8.4
|
8.1
|
7.2
|
Percentage
time with SS < 10 mgL-1
|
46.1%
|
42.9%
|
51.3%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
69.6%
|
68.5%
|
80.0%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season,
Spring Tide
|
Mean SS
conc
|
21.0
|
18.6
|
8.7
|
3.8
|
3.6
|
2.8
|
Maximum SS
conc
|
78.5
|
74.8
|
26.1
|
8.4
|
8.1
|
4.2
|
Percentage
time with SS < 10 mgL-1
|
48.4%
|
50.8%
|
77.2%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
69.5%
|
69.7%
|
98.8%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season,
Neap Tide
|
Mean SS
conc
|
18.9
|
17.1
|
11.5
|
3.6
|
3.5
|
3.0
|
Maximum SS
conc
|
91.0
|
70.9
|
43.1
|
9.4
|
7.8
|
5.6
|
Percentage
time with SS < 10 mgL-1
|
52.7%
|
53.2%
|
76.6%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
76.7%
|
77.7%
|
85.3%
|
100.0%
|
100.0%
|
100.0%
|
Scenario 2A_P1 - YTB Phase 1 Reclamation 5(c,d)
|
Dry
Season, Spring-Neap Cycle
|
Mean SS conc
|
19.6
|
20.0
|
15.9
|
1.9
|
1.9
|
1.7
|
Maximum SS conc
|
90.2
|
145.0
|
90.5
|
6.4
|
9.9
|
6.4
|
Percentage time with SS
< 10 mgL-1
|
26.8%
|
40.8%
|
50.6%
|
100.0%
|
100.0%
|
100.0%
|
Percentage time with SS
< 20 mgL-1
|
62.4%
|
64.5%
|
75.0%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Spring Tide
|
Mean SS
conc
|
9.7
|
10.1
|
25.4
|
1.3
|
1.3
|
2.3
|
Maximum SS
conc
|
56.2
|
52.7
|
183.7
|
4.2
|
4.0
|
12.4
|
Percentage
time with SS < 10 mgL-1
|
74.2%
|
75.7%
|
49.6%
|
100.0%
|
100.0%
|
99.3%
|
Percentage time
with SS < 20 mgL-1
|
95.0%
|
93.7%
|
70.1%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Neap Tide
|
Mean SS
conc
|
21.0
|
19.1
|
31.6
|
2.0
|
1.9
|
2.7
|
Maximum SS
conc
|
99.0
|
145.3
|
177.0
|
7.0
|
9.9
|
12.0
|
Percentage
time with SS < 10 mgL-1
|
41.1%
|
52.3%
|
43.8%
|
100.0%
|
100.0%
|
96.7%
|
Percentage
time with SS < 20 mgL-1
|
63.4%
|
70.4%
|
62.0%
|
100.0%
|
100.0%
|
100.0%
|
Scenario 2A_P2 - YTB Phase 2 Reclamation
5(c,d,e)
|
Dry Season, Spring-Neap Cycle
|
Mean SS conc
|
69.3
|
67.4
|
25.0
|
3.5
|
3.4
|
1.8
|
Maximum SS
conc
|
209.8
|
210.2
|
147.2
|
8.9
|
8.9
|
6.5
|
Percentage
time with SS < 10 mgL-1
|
1.2%
|
3.0%
|
37.5%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
8.2%
|
12.7%
|
58.5%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Spring Tide
|
Mean SS
conc
|
14.6
|
14.9
|
19.4
|
1.4
|
1.4
|
1.5
|
Maximum SS
conc
|
43.1
|
83.7
|
153.4
|
2.5
|
4.0
|
6.7
|
Percentage
time with SS < 10 mgL-1
|
46.3%
|
61.9%
|
50.0%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
80.4%
|
78.9%
|
71.0%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Neap Tide
|
Mean SS
conc
|
42.3
|
43.5
|
23.5
|
2.4
|
2.5
|
1.7
|
Maximum SS
conc
|
145.6
|
164.5
|
142.3
|
6.4
|
7.1
|
6.3
|
Percentage
time with SS < 10 mgL-1
|
13.3%
|
25.5%
|
54.6%
|
100.0%
|
100.0%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
27.5%
|
39.7%
|
68.5%
|
100.0%
|
100.0%
|
100.0%
|
Notes:
1.
Calculations are based on the top 5m layer SS
elevation modelling results at the WSRs.
2.
Absolute SS concentration takes into account surface
mean SS concentration of 6.6 mgL-1. (Data source: EPD
Monitoring Station VM1 for period 1/96 to 8/98)
3.
The WSD target and tolerable limits for SS
concentration are 10 mgL-1 and 20 mgL-1 respectively.
4.
Sand filling by bottom dumping is assumed for the
main reclamation in Phases 1 and 2. The duration of spill is assumed to take
place in 10 minutes per 1 hr operation cycle, 10 cycles per day.
5.
Mitigation measures:
a.
Closed grab with silt curtain
will be used for both filling and dredging activities during the construction
of seawall, which gives a sediment loss reduction factor of 5 times as compared
to that using the open grab alone.
b.
A single layer of silt screen
will be placed around the WSRs.
c.
2 layers of silt screen will be
placed around the WSRs and a single layer of silt screen will be placed across
the YTB marine access to Phase 1 and Phase 2 reclamation.
d.
SS reduction factor of 2.5
times can be achieved using a silt screen. (WCR Final EIA Report and Pak Shek
Kok Reclamation - Public Dump EIA Study, Final Report)
e.
The production rate is reduced
to 6,000 m3 day-1.
6.
The results presented are based on the Full
Reclamation option.
4.7.15
Non-compliances with the WQO
near YTB and the WSD target (tolerable) limits at the identified WSRs, during
the seawall construction (Scenario 2A_SW), necessitate the implementation
of mitigation measures to minimize the impact on water quality. Hence, mitigation measures for the dredging
and filling works have been devised and are described in detail in Section 4.8.3. The mitigated SS concentration is estimated
and shown in Table 4.19.
4.7.16
The existing and reprovisioned
Yau Tong Saltwater Pumping Stations (YTSPS) under the WCR-Coastal option
reclamation are located at approximately the same distance from the YTB
reclamation works. Hence, the water
quality impact at the reprovisioned YTSPS is expected to be similar to those
predicted at the existing YTSPS. In the
unlikely event that the reprovisioned YTSPS commences operation during the YTB
reclamation (Full Reclamation option), the recommended mitigation measure for
the existing YTSPS should be implemented at the reprovisioned YTSPS to ensure
that water quality complies with the WSD target limit at the saltwater intake.
Mitigation Measures for Stormwater Box
Culvert and Seawall Construction
4.7.17
The mitigation measure proposed
for the stormwater box culvert and the seawall construction in YTB include:
·
Close grab with silt curtain
will be used for the dredging and filling operations, which gives a SS loss
reduction factor of 5 times lower that using an open grab alone (Figure 4.79);
·
A single layer of silt screen
will also be placed at the saltwater intakes of the WSRs giving a SS reduction
of 2.5 times at the WSRs (Figures 4.79).
Mitigated Water Quality in VHWCZ
4.7.18
From the unmitigated result for
the seawall construction (Scenario 2A_SW) (Section 4.7.11), the highest depth
averaged SS elevation of 15 mgL-1 in the vicinity of YTB is
found in the wet season spring tide (Figures 4.27–4.28). With the implementation of the close grab
with silt curtain, the maximum elevation will be reduced to 3 mgL-1,
satisfying the WQO of 3.2 mgL-1 in the VHWCZ.
Mitigated Water Quality at the WSRs
4.7.19
With the implementation of the
proposed mitigation measures during the seawall construction (Sections 4.7.17
and 4.8.3),
the mean SS concentration at the WSRs is reduced and varies from 2.8 mgL-1
at the YTSPS to 3.8 mgL-1 at the DFSI (Table 4.19). The maximum SS concentration is also reduced
correspondingly and ranges from
4.2 mgL-1 at the YTSPS to 9.4 mgL-1 at
the DFSI. These are lower than the WSD
target limit for SS at the saltwater intakes and thus, 100% compliance can be
achieved at the WSRs.
Impact of Phase 1 Reclamation – Scenario
2A_P1
4.7.20
When the seawall is formed
across the mouth of YTB, the main reclamation in Phase 1 will begin (Figure 2.4b). The main works involves bulk filling by
bottom dumping within the partially enclosed YTB with a 50 m opening at
the seawall for marine access (Figure
4.82).
4.7.21
It is estimated that the
maximum possible filling rate by bottom dumping is 10000 m3 day-1. Based on the assumptions made in Section 4.7.3,
the sediment loss rate is estimated to be 113.2 kg s-1 (Table 4.18).
In Scenario 2A_P1, a single source (Source R1) is used to
model the sediment plume due to bulk filling in Phase 1 reclamation (Figure 4.6b).
Water Quality in Victoria Harbour Water Control
Zone (VHWCZ)
4.7.22
The predicted SS elevations in
Victoria Harbour are shown in Figures 4.31–4.34 for the dry season and
Figures 4.35–4.42 for the wet season, spring and neap tides.
4.7.23
In the dry season, the depth
averaged sediment plume of Phase 1 reclamation (Scenario 2A_P1) is
effectively contained within YTB bounded by the seawall
(Figures 4.35–4.36). The depth
averaged SS elevation in Victoria Harbour is generally below 3 mgL-1,
lower than allowable increase of 3.2 mgL-1 as stipulated in the
WQO of VHWCZ. Nevertheless, exceedance
with depth averaged SS elevation of up to 23 mgL-1 is observed
near YTB, extending along the coastline between the reprovisioned Kwun Tong
Typhoon Shelter (NKTTS) and Lei Yue Mun.
The area of exceedance lies within 500 m from the existing
coastline near the Eastern Breakwater in the SEKD and 100 m from the mouth
of Sam Ka Tsuen Typhoon Shelter.
Furthermore, the top 5m surface plume is generally smaller than the
depth averaged plume (Figures 4.37-4.38).
4.7.24
The sediment plumes in the wet
season, spring and neap tides are similar to the dry season plume. However, the plume in the wet season, spring
tide does not extend into the reprovisioned Kwun Tong Typhoon Shelter which is
different from the dry season plume. In
general, the wet season plumes extend by approximately 250 m further away
from the coastline at the mouth of Sam Ka Tsuen Typhoon Shelter than that of
the dry season plume. Furthermore, the
surface plumes in the wet season, spring and neap tides are generally smaller
than the depth averaged plumes similar to that in the dry season.
Water Quality at the Water Sensitive
Receivers (WSRs)
4.7.25
The time series statistics of
the SS concentration at the WSRs in Scenario 2A_P1 are shown in Table 4.19.
In the wet and dry seasons, the mean SS concentration during the
Phase 1 reclamation, which varies between 9.7 mgL-1 at the
DFSI and 31.6 mgL-1 at the YTSPS, is higher than that during
the seawall construction. The maximum SS
concentrations, ranging from 52.7 mgL-1 at the CKLSPS to
183.7 mgL-1 at the YTSPS, are in exceedance of the WSD target
(tolerable) limit of 10 mgL-1 (20 mgL-1). The percentage time in compliance with the
WSD target (tolerable) limit at the CKLSPS and YTSPS are 40.8% (64.5%) and
43.8% (62%) respectively, while the SS standard of 20 mgL-1 at
the DFSI is satisfied for 62.4% of the time.
The above observations suggest that the YTSPS is the most susceptible to
the impact of the filling works during the Phase 1 reclamation
(Scenario 2A_P1).
Mitigation Measures for Phase 1
Reclamation
4.7.26
In order to minimize the water
quality impact in the VHWCZ and at the WSRs, mitigation measures are proposed
for the Phase 1 reclamation (Scenario 2A_P1). The mitigation measures proposed for
Scenario 2A_P1 are as follows:
·
A single layer of silt curtain
will be placed across the 50 m opening of the seawall (Figure 4.80), giving a SS reduction
factor of 2.5 times, before bottom dumping is performed;
·
Double layers of silt screen
will be placed at the saltwater intakes of the WSRs giving an overall SS
reduction factor of 6.25 times at the WSRs (Figures 4.80).
Mitigated Water Quality in VHWCZ-
4.7.27
As discussed in Sections 4.7.22 –
4.7.24, the SS elevation in Victoria Harbour before
mitigation generally satisfies the WQO for SS in the VHWCZ. With a silt curtain at the seawall opening in
place, the sediment plume size is expected to be reduced and the sediment spill
will be effectively contained within Phase 1 behind the seawall. It is anticipated that the SS elevation in
the vicinity of YTB will also be reduced by 2.5 times. Hence, no major adverse impact in the VHWCZ
is expected.
Mitigated Water Quality at the WSRs
4.7.28
With the implementation of
double layers of silt screen at the WSRs and a silt curtain at the seawall
opening (Sections 4.7.26
and 4.8.3),
the mean SS concentration at the WSRs, which varies from 1.3 mgL-1
at the CKLSPS to 2.7 mgL-1 at the YTSPS, is significantly
reduced as compared to the unmitigated case (Table 4.19). The maximum SS concentration is also reduced
and ranges from 4 mgL-1 at the CKLSPS to 12.4 mgL-1
at the YTSPS. Slight exceedance of
2–2.4 mgL-1 above the WSD target limit for SS is observed only
in the wet season at the YTSPS.
Nevertheless, the target limit of 10 mgL-1 is satisfied
at the YTSPS for at least 96.7% of the time in the wet season, while the
tolerable limit of 20 mgL-1 will be satisfied at all times.
Impact of Phase 2 Reclamation – Scenario
2A_P2
4.7.29
The Phase 2 reclamation is
very similar to that in Phase 1 and will commence after the bored pile seawall,
near the submarine pipelines, is constructed.
The area of the Phase 2 reclamation is approximately one forth of
the Phase 1 reclamation. Assuming
the same production rate as for Phase 1 reclamation, the duration of bulk
filling is also shortened proportionately (Table 4.18).
4.7.30
The maximum filling rate by
bottom dumping for the Phase 2 reclamation (Scenario 2A_P2) is
assumed to be 10,000 m-3 day-1, which is the
same as that in Phase 1. Hence, the
sediment loss rate of 113.2 kg s-1 is also the same as
that in Phase 1. In
Scenario 2A_P2, a single source (Source R2) is used to model the
sediment plume due to bulk filling in Phase 2 reclamation (Figure 4.6b).
Water Quality in Victoria Harbour Water
Control Zone (VHWCZ)
4.7.31
The predicted SS elevations in
Victoria Harbour are shown in Figures 4.43–4.46 for the dry season and
Figures 4.47–4.54 for the wet season, spring and neap tides.
4.7.32
Due to the similarity of the
bulk filling operations in the Phase 1 and Phase 2 reclamations, the
size and extent of the sediment plumes are similar in the two cases (Figures 4.31 and 4.43).
However, the sediment plumes for the Phase 2 reclamation
(Scenario 2A_P2), in general, extend further into the reprovisioned Kwun
Tong Typhoon Shelter than those in the Phase 1 reclamation
(Scenario 2A_P1).
4.7.33
During the Phase 2
reclamation (Scenario 2A_P2), the SS elevation in Victoria Harbour are
generally below 3 mgL-1, satisfying the WQO for SS of
3.2 mgL-1 in the VHWCZ (Figures 4.43–4.44). In the dry season, SS elevation of up to
123 mgL-1, which is higher than that in the Phase 1
reclamation, is observed in the vicinity of YTB (Figure 4.44). The top 5m surface plume is smaller than the
depth averaged plume (Figures 4.45–4.46).
4.7.34
In the wet season, spring tide,
the sediment plume during the Phase 2 reclamation (Scenario 2A_P2) is
similar to that in the dry season, while the plume in the wet season, neap tide
extends even further into the reprovisioned Kwun Tong Typhoon Shelter. However, SS elevation of up to 83 mgL-1
in the vicinity of YTB is lower than that in the dry season.
Water Quality at the Water Sensitive Receivers
(WSRs)
4.7.35
Since the Phase 2
reclamation (Scenario 2A_P2) is closer to the DFSI and the CKLSPS than the
Phase 1 reclamation, it is anticipated that the SS concentration will be
higher during the Phase 2 reclamation.
The mean SS concentration is between 14.6 mgL-1 and
69.3 mgL-1 at the DFSI, while the maximum ranges from
43.1 mgL-1 at the DFSI to 210.2 mgL-1 at the
CKLSPS (Table 4.19). These are in exceedance of the WSD target and
tolerable limits which require mitigation.
Mitigation Measures for Phase 2
Reclamation
4.7.36
In order to minimize the water
quality impact in the VHWCZ and at the WSRs, mitigation measures are proposed
for the Phase 2 reclamation (Scenario 2A_P2), similar to those for
the Phase 1 reclamation. The mitigation
measures proposed for Scenario 2A_P2 are as follows:
·
A single layer of silt curtain
will be placed across the 50 m opening of the seawall (Figure 4.81), giving a SS reduction
factor of 2.5 times, before bottom dumping is performed;
·
Double layers of silt screen
will be placed at the saltwater intakes of the WSRs giving an overall SS
reduction factor of 6.25 times at the WSRs (Figures 4.81);
·
Since the area of the
Phase 2 reclamation is smaller than that of the Phase 1 reclamation,
it is envisaged that a maximum filling rate of 6,000 m3 day-1
is more likely to be the actual case.
Mitigated Water Quality in VHWCZ
4.7.37
As discussed in Sections 4.7.31 –
4.7.34, the SS elevation in Victoria Harbour before
mitigation generally satisfies the WQO in the VHWCZ. With the reduction in the production rate and
the implementation of a silt curtain at the seawall opening, the size of the
plume is expected to reduce significantly and thus, no major impact is expected
in the VHWCZ.
Mitigated Water Quality at the WSRs
4.7.38
With the implementation of the
proposed mitigation measures in the Phase 2 reclamation (Sections 4.7.36
and 4.8.3), the mean SS concentration at the WSRs
is significantly reduced as compared to the unmitigated case to below
3.5 mgL-1 (Table 4.19). Meanwhile, the maximum SS concentration at
the WSRs is also reduced to below 8.9 mgL-1. Hence, the WSD target limit for SS of
10 mgL-1 at the WSRs is expected to be satisfied at all times.
Summary of YTB Reclamation (Full Reclamation
option) Impact for Different Construction Phases – Scenario 2A
4.7.39
From the sediment plume model
results for the different construction phases (Scenarios 2A_SW, 2A_P1 and
2A_P2), it is predicted that the impact of the YTB reclamation (Full
Reclamation option) on Victoria Harbour is minimal and the WQO is satisfied in
the VHWCZ, except in the vicinity of YTB.
However, the SS concentration at the WSRs exceeds the corresponding SS
requirements. Hence, mitigation
measures, such as the use of silt curtain at the seawall openings, were
proposed accordingly for the various construction phases. With the proposed mitigations, it is
anticipated that the impact on Victoria Harbour and at the WSRs will be
significantly reduced. The predicted SS
concentration at the WSRs with mitigation is expected to satisfy the WSD target
limit for SS of 10 mgL-1 and the in house SS standard of
20 mgL-1 at the DFSI.
However, marginal exceedance for less than 3.3% of the time in the wet
season is observed at the YTSPS during the Phase 1 reclamation which forms the
worst case scenario (Scenario 2A_P1) for the YTB reclamation (Full
Reclamation option).
4.7.40
With a reduction in the
reclamation extent and duration of construction, together with a more
streamlined new water front in the YTB reclamation (Minimized Reclamation
option), it is expected that the water quality impacts, arising from the
corresponding reclamation works, will be similar, and in reality less
significant, than those predicted for the worst case scenario of the YTB
reclamation (Full Reclamation option).
Hence, with the implementation of the recommended mitigation measures as
proposed in the different construction phases for the YTB reclamation (Full
Reclamation option), unacceptable water quality impact is not anticipated
during the construction phase of the Minimized Reclamation option.
Cumulative Impacts during Construction Phase –
Scenario 2B
4.7.41
Cumulative impacts on water
quality may arise during the dredging and filling works for the YTB Reclamation
should other dredging and filling activities be underway near the study
area. As described in Section 2,
the dredging and filling works for the Yau Tong Bay Reclamation (Full
Reclamation option) are estimated to commence in February, 2004 and will be
completed by March, 2007. Possible concurrent
construction works near the study area are indicated in Table 4.7,
based on the construction programs for the South East Kowloon Development
(SEKD), Western Coast Road (WCR-Coastal option), Tseung Kwan O (TKO) Cargo Working Area (CWA)
and TKO New Town Intensification and Extension (NTIE). These are identified as the concurrent
projects and are represented by 15 sediment sources (Sources A–M, P,
Q) in the sediment plume model (Table 4.7).
4.7.42
The cumulative impacts of the
concurrent construction works other than the YTB reclamation, are first
simulated (Scenario 2B_BK). The
impact of the YTB reclamation (Full Reclamation option) in Phase 1 (Source R1)
is then added to the former giving the cumulative impact
(Scenario 2B_CI). Details of the
modelling assumptions in Scenario 2B are presented in Section 4.4.4 and the results are
presented in the following sections.
Cumulative Impacts from Other Projects – Scenario 2B_BK
Water Quality in the VHWCZ
4.7.43
The predicted SS elevation in
Victoria Harbour due to the construction activities of the concurrent projects,
but without the YTB reclamation, is shown in Figures 4.55–4.58 for the dry
season and Figures 4.59–4.66 for the wet season, spring and neap tides.
4.7.44
Since mitigation measures are
assumed for all the concurrent projects listed in Table 4.7,
except for the TKO New Town Intensification and Extension, the sediment plumes
associated with the different dredging and filling activities are mainly
localized in the corresponding works area, such as the Kowloon Bay
(Sources B, F) and Kwun Tong Typhoon Shelters (Sources C, D)
(Figures 4.55–4.56). The allowable
increase in SS concentration under the WQO in the VHWCZ (i.e. 3.2mgL-1)
is generally satisfied for the wet and dry seasons. Nevertheless, the depth averaged sediment
plume in the wet season, spring and neap tides are larger than that in the dry
season, with slight exceedance across Victoria Harbour,
towards Shau Kei Wan Typhoon Shelter (Figures 4.60
and 4.64). The wet season is, thus, the worst case
scenario.
4.7.45
Without mitigation, the TKO New
Town Intensification and Extension generates a large plume due to the high
production rates and extends from Junk Bay into the Lei Yue Mun Channel, with
SS elevation of up to 63 mgL-1 in Junk Bay area. This explains the exceedance of the WQO for
SS near the Shau Kei Wan Typhoon Shelter in the wet season.
4.7.46
Although YTB reclamation is not
taken into account in the present Scenario 2B_BK, the sediment plume due
to the construction works in the SEKD and the WCR-Coastal option extends across
YTB with SS elevation of up to 23 mgL-1. This suggests that the SS concentration in
the vicinity of YTB due to the concurrent projects is in exceedance of the
WQO. Hence, exceedance of the WQO
locally around YTB is anticipated as the YTB reclamation commences.
Water Quality at the WSRs
4.7.47
A single layer of silt screen
was proposed in the SEKD and WCR-Coastal option EIA studies to protect the WSRs
from the construction impact. Together
with the use of close grab with silt curtain for the dredging and filling
activities, the SS concentration at the CKLSPS and DFSI is expected to meet the
WSD target limit of 10 mgL-1 and the in house SS standard of
20 mgL-1 respectively at all times (Table 4.20). However, the variation of SS concentration at
the YTSPS reveals that the cumulative impacts from other projects, without YTB
reclamation, exceeds the WSD target (tolerable) limit of 10 mgL-1 (20 mgL-1) for up to 3.8%
(1%) of the time. This can be attributed
mainly to the unmitigated works of the TKO New Town Intensification and
Extension (NTIE). With appropriate
mitigation measures for the TKO NTIE, the SS concentration at the YTSPS is
expected to satisfy the WSD target (tolerable) limit.
Table 4.20 A Summary of Time Series Statistics of SS
concentration at the WSRs for Scenario 2B
Absolute
SS concentration (2) [mgL-1]
|
Unmitigated
|
Mitigated
|
Diary
Farm Saltwater Intake (DFSI)
|
Cha
Kwo Ling Saltwater Intake (CKLSPS)
|
Yau
Tong Saltwater Intake (YTSPS)
|
Diary
Farm Saltwater Intake (DFSI)
|
Cha
Kwo Ling Saltwater Intake (CKLSPS)
|
Yau
Tong Saltwater Intake (YTSPS)
|
Scenario 2B_BK - Cumulative Impacts from
Other Projects (excluding YTB reclamation) 7(a,b,d)
|
Dry Season, Spring-Neap Cycle
|
Mean SS
conc
|
N/A
|
N/A
|
N/A
|
3.8
|
3.5
|
4.3
|
Maximum SS
conc
|
N/A
|
N/A
|
N/A
|
14.7
|
7.2
|
17.1
|
Percentage
time with SS < 10 mgL-1
|
N/A
|
N/A
|
N/A
|
99.1%
|
100.0%
|
96.6%
|
Percentage
time with SS < 20 mgL-1
|
N/A
|
N/A
|
N/A
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Spring Tide
|
Mean SS
conc
|
N/A
|
N/A
|
N/A
|
3.3
|
2.9
|
4.4
|
Maximum SS
conc
|
N/A
|
N/A
|
N/A
|
13.0
|
4.5
|
32.0
|
Percentage
time with SS < 10 mgL-1
|
N/A
|
N/A
|
N/A
|
98.2%
|
100.0%
|
96.5%
|
Percentage
time with SS < 20 mgL-1
|
N/A
|
N/A
|
N/A
|
100.0%
|
100.0%
|
99.0%
|
Wet Season, Neap Tide
|
Mean SS
conc
|
N/A
|
N/A
|
N/A
|
3.2
|
3.1
|
4.2
|
Maximum SS
conc
|
N/A
|
N/A
|
N/A
|
7.0
|
4.2
|
21.0
|
Percentage
time with SS < 10 mgL-1
|
N/A
|
N/A
|
N/A
|
100.0%
|
100.0%
|
96.2%
|
Percentage
time with SS < 20 mgL-1
|
N/A
|
N/A
|
N/A
|
100.0%
|
100.0%
|
99.6%
|
Scenario 2B_CI – Cumulative impact
(including YTB reclamation) 7(a,c,d)
|
Dry Season, Spring-Neap Cycle
|
Mean SS
conc
|
22.5
|
22.1
|
20.2
|
2.4
|
2.2
|
2.3
|
Maximum SS
conc
|
91.7
|
148.5
|
94.7
|
6.7
|
10.5
|
7.1
|
Percentage
time with SS < 10 mgL-1
|
14.3%
|
26.4%
|
29.3%
|
100.0%
|
99.9%
|
100.0%
|
Percentage
time with SS < 20 mgL-1
|
53.0%
|
60.2%
|
65.1%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Spring Tide
|
Mean SS
conc
|
11.3
|
10.8
|
29.7
|
1.5
|
1.4
|
2.9
|
Maximum SS
conc
|
57.5
|
53.4
|
185.8
|
5.2
|
4.1
|
12.9
|
Percentage
time with SS < 10 mgL-1
|
69.3%
|
72.2%
|
36.4%
|
100.0%
|
100.0%
|
97.7%
|
Percentage time
with SS < 20 mgL-1
|
91.7%
|
93.6%
|
63.6%
|
100.0%
|
100.0%
|
100.0%
|
Wet Season, Neap Tide
|
Mean SS
conc
|
22.5
|
20.2
|
35.5
|
2.2
|
2.0
|
3.3
|
Maximum SS
conc
|
99.7
|
146.5
|
194.1
|
7.1
|
10.1
|
16.7
|
Percentage
time with SS < 10 mgL-1
|
34.2%
|
46.6%
|
39.9%
|
100.0%
|
100.0%
|
94.8%
|
Percentage
time with SS < 20 mgL-1
|
60.0%
|
70.0%
|
59.5%
|
100.0%
|
100.0%
|
100.0%
|
Notes:
1. Calculations are based on the top 5m layer SS
elevation modelling results at the WSRs.
2. Absolute SS concentration takes into
account the 90 percentile surface SS concentration of 6.6 mgL-1.
(Data source: EPD Monitoring Station VM1 for period 1/96 to 8/98).
3. The WSD target and tolerable limits for SS concentration
are 10 mgL-1 and 20 mgL-1 respectively.
4. The works for all the projects, including
the WCR-Coastal option construction, TKO New Town Intensification and Extension
and YTB reclamation, are assumed to take place 10 hrs daily, except for
the works of the TKO CWA and the SEKD which operate 24 hrs and 16 hrs
per day respectively.
5. All concurrent projects identified are
assumed to be mitigated as recommended in their corresponding EIA studies,
except for the TKO New Town Intensification which EIA study is in progress.
6. Sand filling by bottom dumping is assumed
for the Phases 1 reclamation of YTB. The
duration of spill is assumed to take place in 10 minutes per 1 hr operation
cycle, 10 cycles per day.
7. Mitigation measures:
a)
For
all concurrent projects identified, except the YTB reclamation and TKO New Town
Intensification and Extension, closed grab with silt curtain will be used for
both filling and dredging activities giving a sediment loss reduction factor of
5 times as compared to that using the open grab alone.
b)
A
single layer of silt screen will be placed around the WSRs as recommended in
other EIA studies.
c)
A
total of 2 layers of silt screen will be placed around the WSRs and a single
layer of silt screen will be placed across the YTB marine access of Phase 1 and
Phase 2 reclamation.
d)
SS
reduction factor of 2.5 times can be achieved using a silt screen. (WCR Final
EIA Report and Pak Shek Kok Reclamation - Public Dump EIA Study, Final Report)
8. The results presented are based on the Full
Reclamation option.
Cumulative Impact including YTB Reclamation
(Full Reclamation option) – Scenario 2B_CI
Water Quality in the VHWCZ
4.7.48
Taking into account the
Phase 1 reclamation of YTB (Source R1), without mitigation, the mean SS
concentration in Victoria Harbour is shown in Figures 4.67–4.70 for the
dry season and Figures 4.71–4.78 for the wet season, spring and neap
tides.
4.7.49
With the contribution of the
YTB reclamation (Scenario 2B_CI), the sizes of the sediment plume in the
wet and dry seasons are marginally increased near YTB. Exceedance of the WQO for SS of up to
23 mgL-1 is only observed locally. Hence, the WQO in the VHWCZ is expected to be
satisfied with no major impact on Victoria Harbour.
Mitigated Water Quality in VHWCZ
4.7.50
Assuming the same mitigation
measures proposed earlier for the Phase 1 reclamation of YTB
(Scenario 2A_P1, Section 4.7.26), the contribution of the YTB
reclamation to the sediment plume in the neighbouring waters will be reduced. It is anticipated that a SS reduction of 2.5
times across the silt curtain at the seawall opening in Phase 1 can be
achieved, minimizing the impact of the YTB reclamation on Victoria Harbour.
Water Quality at the WSRs
4.7.51
Without mitigation for the YTB
reclamation, the mean SS concentration at the WSRs due to the impacts of the
concurrent activities varies between 10.8 mgL-1 at the CKLSPS
and 35.5 mgL-1 at the YTSPS (Table 4.20). Meanwhile, the maximum SS concentration
ranges from 53.4 mgL-1 at the CKLSPS to 194.1 mgL-1
at the YTSPS which are in exceedance of the WSD target and tolerable limits.
Mitigated Water Quality at the WSRs
4.7.52
Mitigation measures proposed
for the Phase 1 reclamation of YTB (Scenario 2A_P1, Section 4.7.26)
are also used to minimize the impact at the WSRs. SS reduction of 6.25 times can be
achieved across the double layers of silt screen at the WSRs, while the silt
curtain at the seawall opening of Phase 1 reclamation of YTB gives a SS
reduction of 2.5 times. With the
implementation of the above mitigation measures, it is anticipated that the
mean and maximum SS concentration at the WSRs will be below 3.3 mgL-1
and 16.7 mgL-1. The WSD
target limit for SS of 10 mgL-1 is generally satisfied at the
CKLSPS and YTSPS with slight exceedance at the latter for upto 5.2% of the time
in the wet season, while the WSD’s in house tolerable limit for SS of
20 mgL-1 will be satisfied at all times. The above represents
the worst case cumulative impact at the YTSPS, taking into account the
unmitigated works of the Tseung Kwan O New Town Intensification and Extension
in Area 138 (TKO NTIE), is considered acceptable. With appropriate mitigation measures for the
TKO NTIE, sediment plume dispersion of the marine works of TKO NTIE will be
essentially confined within Junk Bay and the residual SS concentration at the
YTSPS is expected to very similar to the mitigated water quality under the
Scenario 2A_P1 (as presented in paragraph 4.7.28).
That is, the residual SS level at the intake of YTSPS will comply the
WSD SS tolerable limit (20 mgL-1) all the time, but marginal
exceedance of SS target limit (10 mgL-1) (by maximum 2.4 mgL-1)
will occur for less than 3.3% of the time in the wet season.
Summary of Cumulative Impacts during
Construction Phase – Scenario 2B
4.7.53
From the above discussions of
the cumulative impacts due to the other concurrent activities in Victoria
Harbour (Scenario 2B_BK) and the contribution from the YTB reclamation
(Full Reclamation option) (Scenario 2B_CI), it is found that the YTB
reclamation contributes significantly to safeguard the water quality of the
harbour and only poses a minor impact to the neighbouring waters. Furthermore, by adopting the mitigation
measures proposed for the Phase 1 reclamation of YTB
(Scenario 2A_P1), the impact at the WSRs will be minimize with the SS
concentration satisfying both the WSD target limit at the saltwater intakes and
the in house standard for the DFSI.
Although SS exceedance is predicted at the YTSPS as a result of the
cumulative impacts from other projects (Scenario 2B_BK), the proposed
mitigation measure is sufficient to reduce the overall impact, including the
YTB reclamation (Full Reclamation option), to the relevant standards. In addition, it is most likely that
mitigation measure will be imposed on the TKO New Town Intensification and
Extension works, and thus, the present result serves as a conservative
prediction.
4.7.54
With a reduction in the
reclamation extent and duration of construction, together with a more
streamlined new water front in the YTB Reclamation (Minimized Reclamation
option), it is expected that the water quality impacts, arising from the
corresponding reclamation works, will be similar, and in reality less
significant, than those predicted for the worst case scenario of the YTB
reclamation (Full Reclamation option).
Hence, with the implementation of the recommended mitigation measures as
proposed in the different construction phases for the YTB reclamation (Full
Reclamation option), unacceptable water quality impact is not anticipated
during the construction phase of the Minimized Reclamation option.
Impact of the temporary YTB Stormwater Culvert
- Scenario 2C
4.7.55
Before the Phase 1
reclamation of YTB, the existing YTB stormwater culverts have to be diverted to
avoid discharging into an embayment formed by the seawall (Figures 2.4a-d). A temporary stormwater culvert, in the form
of an open channel, will be formed along the southern seawall extending to the
mouth of YTB. Potential water quality
deterioration and pollutant accumulation in Victoria Harbour are
evaluated using the particle model (Appendix 4E), similar to
that used for the impact assessment of the new Kwun Tong nullah and the new YTB
storm culvert (Appendices 4A and 4C). The impact on the two existing WSRs, namely,
the Cha Kwo Ling (CKLSPS) and Yau Tong (YTSPS) saltwater pumping stations, will
be addressed.
4.7.56
Based on the population
estimates in year 2011 from the Kowloon District Office of the Planning
Department and the per capita load factor in the DSD Sewerage Manual, the total
load generated in the Yau Tong catchment are estimated and shown in Table 4.14.
The details of population estimates are given in Appendices 4B-1
and 4B-2. With the implementation of the SMPs, it is conservatively assumed that 5% of the total load in the Yau
Tong sewage catchment, as adopted in the SEKD Feasibility Study, will be
discharged through the existing YTB stormwater culvert during the YTB
reclamation. Dilution and dispersion are
simulated using the particle model (Appendix 4E). To assess the worst case impacts, tidal
mixing and decay within the channel are not taken into account at present. This
is a conservative assumption as all the new developments in the Yau Tong area
will be connected to public sewers which minimizes the pollution load to the
stormwater culvert through expedient connections, and the % load interception
by the storm system is expected to lower.
4.7.57
The increase in BOD5,
SS, Ammoniacal Nitrogen and E. coli
are predicted according to the estimated pollution load for the temporary YTB
stormwater culvert and the particle model results. Comparison between the predicted values and
the ambient in year 1997 are shown in Table 4.21. The predicted increase in BOD5, SS
and Ammoniacal Nitrogen are very low in comparison with the WQOs for the
VHWCZ. Since no secondary contact
recreation zone has been identified within Victoria Harbour, the increase in E. coli of 2370 counts per 100mL as
compared to the ambient level of 5780 counts per 100mL is considered
acceptable. The above confirms that
minor impact is expected in the VHWCZ.
At the existing WSRs, the BOD5, SS and E. coli levels, taking into account the predicted maximum increases
and the ambient levels, are lower than the WSD target limits, indicating that
the WSD saltwater intakes are only marginally affected by the temporary
diversion of the stormwater culvert. As
mentioned in the previous paragraph, decay and mixing processes in the
stormwater culvert are omitted in the present calculation, which tend to reduce
the pollutant concentration in the storm effluent and thus the effective
pollution load discharging into Victoria Harbour. Hence, the actual water quality is expected
to be better than that predicted.
Table 4.21 Impact of Temporary Stormwater Culvert in YTB (Scenario 2C) –
Comparison of Predicted Water Quality with WQO in VHWCZ and WSD Standards at
Saltwater Intakes
Description
|
BOD5
[mgL-1]
|
SS
[mgL-1]
|
Ammoniacal Nitrogen
[mgL-1]
|
E. coli [count per 100mL]
|
|
Ambient level (1)
|
0.7
|
5.6
|
0.22
|
5780
|
|
< 0.04
|
< 0.05
|
< 2.86 x 10-3
|
< 2370
|
WQO
|
N/A (6)
|
< 30% over ambient and
median < 25mgL-1
|
< 0.44 (5)
|
N/A (4)
|
|
Maximum increase at CKLSPS (2)
|
0.03
|
0.03
|
2.12 x 10-3
|
1750
|
Maximum increase at YTSPS (2)
|
0.2
|
0.21
|
1.32 x 10-2
|
10900
|
|
< 10
|
< 10
|
< 1
|
< 20000
|
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year
1997.
2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong
saltwater pumping stations respectively.
Water quality impacts on the potential reprovisioned CKLSPS and the
reprovisioned YTSPS are not anticipated during the construction phase of the
YTB reclamation (see para. 4.7.12.4 and 4.7.12.5).
3. Data presented are depth averaged, except at the WSRs where top 5m
layer data are considered.
4. No secondary contact recreation and bathing beach sub-zone is
identified in VHWCZ.
1. With reference to the WQO of 0.021 mgL-1 for unionized
ammonia, the total ammonia present at 23oC and pH 8 is estimated to
be 0.44. Calculations are based on EPD’s
monitoring data at VM1 in year 1997.
2. No WQO standards for BOD5 in marine waters.
3. The results presented are based on the Full Reclamation option.
4.7.58
In the unlikely event that the
reprovisioned YTSPS commences operation before the YTB reclamation begins, the
temporary stormwater culvert in YTB will have to be extended to the new
waterfront of the Western Coast Road (WCR-Coastal option) Reclamation. The relative position of the extended temporary
stormwater culvert outfall and the reprovisioned YTSPS will be approximately
the same as that between the proposed temporary outfall and the existing
YTSPS. Considering the large margin
between the predicted water quality and the WSD target limit at existing YTSPS,
unacceptable impact is not expected at the reprovisioned YTSPS.
4.7.59
As discussed in the operation
phase water quality impact assessment sections, reprovisioning of the CKLSPS
will not be required under the proposed YTB development. An advantage of the
Full Reclamation option over the Minimized Reclamation option is that land
provisions can be made available at the new water front of the YTB reclamation
for future reprovisioning or upgrading of the CKLSPS. However, this potential reprovisioning of the
CKLSPS will not be possible before or during the YTB reclamation. Hence, no
water quality impact on the reprovisioned CKLSPS is envisaged from the YTB
reclamation and the temporary stormwater culvert.
Potential Release of Contaminants during
Dredging and Surcharging
4.7.60
The assessment of sediment
contamination were performed which included sampling and testing of mud from
the seabed at 9 locations so as to quantify the extent of contamination within
the proposed reclamation area (Full Reclamation option). The locations of vibrocores are shown in Figure 5.1. Sediment samples recovered from vibrocoring
were laboratory tested for heavy metals.
The results of the sediment testing indicate that seriously
contaminated, Class C material, was found at all four vibrocore locations along
the proposed seawall and at the five vibrocores within the reclamation site for
the Full Reclamation option. Full
details of the sediment quality analysis, the parameters tested, and the
contaminated sediments classification are presented in Section 5.4.
4.7.61
During the dredging of
contaminated sediments, there is a potential impact on water quality through
the release of heavy metals into the surrounding water column. As stipulated in the EPD Technical Circular No. 1-1-92, Classification of Dredged Sediments for
Marine Disposal, the seriously contaminated material must be dredged and
transported with great care. The dredged
sediment cannot be dumped in the gazetted marine disposal grounds and must be
effectively isolated from the environment upon final disposal. Therefore appropriate dredging methods have
been incorporated into the recommended mitigation measures and include the use
of closed-grab dredgers.
4.7.62
An indication of the likelihood
of release of heavy metals from the excavated marine mud is given by the
results of the elutriation tests as described in Section 5.4. If the contaminant levels are higher in the
elutriates in comparison with the blanks (marine water from the same site), it
can be concluded that the contaminants are likely to be released into the
marine waters during dredging activities.
The concentrations of the metals copper, nickel, zinc and lead in the
elutriate samples were higher than the background values recorded in the marine
water sample. The results indicate that
these four heavy metal species are likely to be released from the sediment into
the marine waters when the seabed is disturbed during dredging activities. As there is no existing legislative standard
or guideline for individual heavy metal contents in marine waters, the UK Water
Quality Standards for Coastal Surface Water is adopted as the assessment
criteria. As shown in Table 4.22 below, the heavy metal concentrations
(other than mercury) in the elutriate samples fall within the UK Water Quality
Standards. The detection limit for
mercury is higher than the UK Water Quality Standard and therefore it is not
possible to draw a similar conclusion based on the elutriate test results. Hence, an alternative method is considered
below.
4.7.63
A quantification of the
predicted release of the metal mercury from pore water during dredging has been
made based on the equation adopted from the “Water Quality Prevention,
Identification and Management of Diffuse Pollution” by Vladimir Novotny &
Harvey Olem, Van Nostrand Reinhold, New York, 1994. (This equation was used in
the water quality assessment undertaken in the EIA Study for the South East
Kowloon Development Feasibility Study).
Based on the measured concentration of mercury in the marine sediment
(the highest concentration of 4.5 mg/kg recorded at vibrocore V4 was used as a
worst-case scenario), the predicted maximum desorbed concentration of mercury
in the pore water is estimated to be 0.026mg
l-1, which is below the UK Water Quality Standard. Details of the calculation are provided in Appendix
4F. Therefore it is concluded that adverse water quality impacts
arising from the release of heavy metals from the contaminated sediment are not
anticipated during the dredging works.
Table 4.22 Comparison
of Sediment Elutriate Test Results with UK Water Quality Standards
Metal Content
(mg l-1)
|
Vibrocore
Location
|
Water Quality Standard of Receiving Water
(mg l-1)
|
Exceedance of
Water Quality Standard
|
|
V1
|
V2
|
V3
|
V4
|
V5
|
V6
|
V7
|
V8A
|
V9B
|
|
|
Cu
|
0.8
|
0.9
|
1.8
|
<0.5
|
<0.5
|
0.7
|
1
|
3.2
|
<0.5
|
5
|
No
|
Ni
|
<3
|
<3
|
<3
|
<3
|
7
|
5
|
3
|
8
|
12
|
30
|
No
|
Zn
|
5
|
8
|
5
|
7
|
8
|
5
|
5
|
5
|
6
|
40
|
No
|
Pb
|
<0.5
|
0.7
|
0.6
|
<0.5
|
0.6
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
25
|
No
|
Cd
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
2.5
|
No
|
Cr
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
<0.5
|
15
|
No
|
Hg
|
<2
|
<2
|
<2
|
<2
|
<2
|
<2
|
<2
|
<2
|
<2
|
0.3
|
*
|
* Detection
limit for Hg is higher than the UK Water Quality Standard of 0.3 mg l-1
4.7.64
Elutriation tests were also
conducted to assess the likelihood of release of organic compounds, such as
total polychlorinated biphenyls (PCBs) and total polyaromatic hydrocarbons
(PAHs), and tributyltin (TBT) from the marine mud during dredging
activities. As there are no existing legislative
standards or guidelines for the contaminants PCB, PAH and TBT in marine waters,
reference is made to the recommendations and conclusions of the consultancy
study Review of Marine Water Quality
Objectives of Hong Kong (Final Report, January 1997, Mouchel Asia Ltd. for
EPD). This study concluded that PCBs and
PAHs are primarily associated with sediments and therefore WQO for these
parameters are not required. For TBT, a
WQO was not recommended for Beneficial Uses 6, 7 and 8. The identified water sensitive receivers in
the study area comprise saltwater intakes, which represent Beneficial Use 6
i.e. domestic and industrial purposes.
As described in Section 5.4.8, the
measured PCB and PAH concentrations in the elutriate samples tested from each
vibrocore location were not higher than the background values recorded in the
seawater sample from the site.
Similarly, the measured TBT concentrations in the elutriate samples were
not higher than the background values recorded in the seawater sample. Therefore, it can be concluded that adverse
water quality impacts due to the potential release of the contaminants PCB, PAH
and TBT from the sediment are not anticipated during the dredging activities.
4.7.65
Since the nutrient levels in
the sediment is not expected to be a major concern in Yau Tong Bay, testing of
nutrient levels is not included in the sediment testing plan. For the assessment of nutrient release during
dredging, the typhoon shelter sediment quality data extracted from “Marine
Water Quality in Hong Kong in 1997” prepared by EPD is used, which is similar
to that in YTB (Appendix 4G). The sediment quality in the six typhoon
shelters in the vicinity of YTB, namely, To Kwa Wan (VS20), Kwun Tong (VS14),
Sam Ka Tsuen (VS13), Causeway Bay (VS12), Aldrich Bay (VS18) and Chai Wan (ES3)
Typhoon Shelter, between 1993 and 1997, were analysed (Appendix 4G). The maximum levels of Ammoniacal Nitrogen (NH4N),
Total Kjeldahl Nitrogen (TKN) and Total Phosphorus (TP) were
140 mg kg-1, 1400 mg kg-1 and
540 mg kg-1 respectively.
Assuming all the nutrients in the sediment will be released into the
water column and based on the SS concentration of 3 mgL-1 at
the outer edge of the sediment plume from the modelling predictions (Figure 4.20), the corresponding
increase in concentration of NH4N, TKN and TP at the plume boundary will be
4.2x10-4 mgL-1, 4.2x10-3 mgL-1,
1.62 x10-3 mgL-1 respectively. The predicted increases of NH4N, TKN and TP
are less than 2% of the ambient levels, based on EPD’s routine monitoring data
(Table 4.23), and the water quality is expected
to satisfy the WQOs in the VHWCZ.
Table 4.23 Predicted
Maximum Elevation of Nutrients Concentration during Mud Dredging for the
Seawall Foundation.
Determinand
|
Elevation at Plume
Boundary [mgL-1]
|
Ambient Concentration in
VHWCZ(1) [mgL-1]
|
WQO
[mgL-1]
|
Ammoniacal Nitrogen (NH4N)
|
4.2x10-4
(0.2%)(3)
|
0.22
|
<
0.44(2)
|
Total Kjeldahl Nitrogen (TKN)
|
4.2x10-3
(0.4%)(3)
|
1.05
|
NA
|
Total Phosphorus (TP)
|
1.62x10-3
(2%)(3)
|
0.1
|
NA
|
Chemical Oxygen Demand (COD)
|
0.15
|
NA
|
NA
|
Notes:
1. Data source: EPD routine monitoring data at station VM1 in year
1997.
2. With reference to the WQO of 0.021 mgL-1 for unionized
ammonia, the total ammonia present at 23oC and pH 8 is estimated to
be 0.44. Calculations are based on EPD’s
monitoring data at VM1 in year 1997.
3. Numbers in bracket represent the percentage increase over the
ambient levels.
4.7.66
Similarly, the maximum Chemical
Oxygen Demand (COD) of 50000 mg kg-1 is expected to be
reduced to 0.15 mgL-1 at the sediment plume boundary. Considering the dissolved oxygen (DO) level
of 5 mgL-1 in Victoria Harbour, based on EPD’s routine
monitoring at station VM1 in 1997, and the low COD of 0.15 mgL-1,
the WQO for DO of 4 mgL-1 in the VHWCZ is expected to be
satisfied. The above serves as a
conservative or worst case assessment of the impact of nutrients release during
dredging of marine mud and the actual situation is expected to be better than
those predicted.
4.7.67
The proposed seawall for the Minimized
Reclamation will be shortened accordingly and thus potential water quality
impacts associated with dredging works will be minimized in terms of the
duration of impact and the water quality is expected to be similar to those
predicted above for the Full Reclamation option.
4.7.68
During the consolidation of the
reclamation, the potential release of heavy metals and other sediment
constituents in the contaminated pore water, which may escape through the
installed vertical band drains, may affect water quality in Victoria Harbour.
4.7.69
As shown in Table 4.22,
the measured heavy metal concentrations in the elutriate samples do not exceed
the UK Water Quality Standards. Furthermore, as described in the previous
paragraphs, the predicted maximum desorbed concentration of mercury in the
sediment pore water of 0.026mg
l-1 is below the UK Water Quality Standard. The measured concentrations of PCB, PAH and TBT
in the elutriate samples did not exceed the background concentrations recorded
in the seawater sample taken from the site.
Therefore it is concluded that adverse water quality impacts arising
from the release of contaminated pore water from the sediment are not
anticipated during the surcharge period.
4.7.70
With a reduction in the
reclamation extent and the surcharging area in the YTB Reclamation (Minimized
Reclamation option), it is expected that the potential impacts arising from the
release of contaminated pore water from the sediment, will be reduced
proportionately from those predicted above for the Full Reclamation
option. Hence, unacceptable water
quality is not anticipated.
4.8
Mitigation of Adverse Impacts
Construction Phase
4.8.1
It is important that appropriate
measures be undertaken to ensure that potential impacts on water quality during
construction phase of the YTB Reclamation (Full Reclamation option) can be kept
to within acceptable levels as defined by the WQO. Temporary mitigation measure is necessary to
protect the water sensitive receivers (WSRs), so that the WSD target limit and
other in house water quality standards at saltwater intakes can be
satisfied. The use of appropriate
dredging and filling methods will reduce the amount of sediment suspension,
and, in turn, minimize adverse impacts on the WSRs. As the Full Reclamation option represents the
worst case scenario for the YTB Reclamation, the recommended mitigation
measures for the Full Reclamation option will also be applicable to the Minimized
Reclamation option.
Temporary Diversion of YTB Stormwater Box
Culvert
4.8.2
To avoid the accumulation of
the pollutants within the embayed water during construction, a temporary
channel / culvert will be constructed to divert the existing culvert outfalls
out of the YTB before the commencement of marine works.
Dredging / Filling Works for the Stormwater
Box Culvert and the Seawall Construction
4.8.3
Based on the predicted impacts,
low impact dredging techniques such as closed grab dredgers are
recommended. In addition, the use of
silt curtains around the barge is recommended for the dredging and filling
activities to minimize the dispersion of sediment plumes (Figure 4.79). To provide further protection at the WSD
saltwater pumping stations in the study area during dredging and filling works,
it is recommended that silt screens (typically made from synthetic geotextile
fabrics) be placed across the Dairy Farm saltwater intake and the intakes of
the Yau Tong and Cha Kwo Ling saltwater pumping stations (Figures 4.79). On-site environmental team should regularly
check the proper implementation and functioning of the silt screens through
visual inspections and review of marine water quality at the intakes.
4.8.4
Although dredging and filling
may take place simultaneously as modelled in Scenario 2A_SW, it is
recommended that the maximum daily production rate, during the seawall
construction, shall not exceed 1550 m3 day-1
for dredging and 2200 m3 day-1 for sand filling, as
derived from the preliminary construction program as at January, 2001 (Appendix 2A).
Bulk Filling Works for the Phase 1 and
Phase 2 Reclamations
4.8.5
Since seawall will be formed
before the commencement of Phase 1 and Phase 2 reclamations, the
major impact of bulk filling by bottom dumping is effectively contained behind
the seawall in YTB. Nevertheless, the
50 m opening of the seawall for marine access allows tidal flushing of
sediment into Victoria Harbour. In order
to minimize the water quality impact in the VHWCZ, a single layer of silt
curtain (made from impervious material such as coated nylon) is recommended to
be placed across the seawall opening (Figures
4.80 and 4.81) before bottom
dumping is performed. The WSRs, namely
the Yau Tong and Cha Kwo Ling Saltwater Pumping Station and the Dairy Farm Ice
Factory, should be further protected by double layers of silt screen at the
saltwater intakes locations (Figures 4.80
- 4.81). On-site environmental team should regularly
check the proper implementation and functioning of the silt screens and silt
curtains through visual inspections and review of marine water quality at the
intakes.
4.8.6
It is recommended that the
maximum sand filling rate for the Phase 1 and Phase 2 reclamations
shall not exceeded 10,000 m3 day-1 and
6,000 m3 day-1 respectively as derived from the
modelling results of Phase 1 and Phase 2 reclamations
(Scenarios 2A_P1 and 2A_P2).
4.8.7
The double silt screens at the
WSRs should be maintained throughout the construction of the proposed concrete
decking near the mouth of YTB (Phase 3).
It is recommended that the developer or its representative be
responsible for the inspection and maintenance of the silt screens and curtains
during the construction phases of the YTB reclamation.
Design Consideration
for the future reprovisioning or upgrading of Cha Kwo Ling Saltwater Intake
4.8.8
The modelling results suggested
that the potential sewage plume arising from the Yau Tong Sewage Pumping
Station emergency outfall at Ko Fai Road will be confined to the water surface
along the new water front of the YTB reclamation. If the CKLSPS is to be reprovisioned or
upgraded in the future at the potential site suggested under the Full
Reclamation option, the intake level is recommended to be located below
-2.0 mPD to avoid possible abstraction of the surface sewage plume
discharged from Yau Tong Sewage Pumping Station. Optimal intake configuration should be
reviewed and decided in the detailed design stage for the reprovisioning or
upgrading of the Cha Kwo Ling Saltwater Pumping Station.
4.8.9
To avoid accumulation of
floating debris at water below the decked promenade near the intake of existing
CKLSPS, floating booms shall be deployed near the intake (Figure 4.82) and any floating debris
detained by the floating booms should be collected and removed regularly. Air slots should be included in the detailed
design of the decked promenade to enhance the air flow below.
Good Operational Practices
4.8.10
The contractor will be required
to minimize potential adverse impacts on water quality resulting from dredging
and dumping operations to within acceptable levels as defined by the WQO. To achieve these requirements the contractor
should design and implement methods of working, to the maximum practicable
extent, that:
·
minimize disturbance to the
seabed while dredging;
·
minimize leakage of dredged
material during lifting;
·
prevent loss of material during
transport of dredged material;
·
prevent discharge of dredged
material except at approved locations;
·
dredging operations should
involve leaving sediment in place whenever practicable; and
·
ensure that the construction
works will cause no visible foam, oil, grease, scum, litter or other objectionable
matter to be present in the water within and adjacent to the site or dumping
grounds.
4.8.11
The licensee should formulate
his design and construction methods with these factors in mind, and provide
specification in the tender submission.
4.8.12
The contractor should provide
the work schedule of the dredging and filling activities to WSD before the
construction works starts.
Disposal of Sewage from Construction Workers
and Soil Remediation Works
4.8.13
There will be generation of
wastewater from the construction workers for the reclamation works. The wastewater volume is expected to be less
than 700 m3/d (based on about
2000 workers). Chemical toilets or other
suitable facilities should be provided by the reclamation contractors to ensure
work-site hygiene and proper sewage disposal.
There should be minimal impact on the downstream sewers, because of the
expected small volumes. Another source
of possible wastewater generated from the soil remediation works will be
disposed vide recharge to the ground water.
Any Leachate collected from the contaminated soil remediation works
shall be treated to remove all floating TPH product before recharging back to
the groundwater table.
Pollution Avoidance Measures During Dredging and Dumping
4.8.14
Pollution avoidance measures shall
include, but not be limited to, the following:
·
mechanical grabs shall be
designed and maintained to avoid spillage and shall seal tightly while being
lifted (closed-grab clamshell dredgers);
·
all vessels shall be sized such
that adequate clearance is maintained between vessels and the sea bed at all
states of the tide to ensure that undue turbidity is not generated by
turbulence from vessel movement or propeller wash;
·
all pipe leakages shall be
repaired promptly and plant shall not be operated with leaking pipes;
·
excess material shall be
cleaned from the decks and exposed fittings of barges before the vessel is
moved;
·
adequate freeboard shall be
maintained on barges to ensure that decks are not washed by wave action;
·
all barges shall be fitted with
tight fitting seals to their bottom openings to prevent leakage of material;
and
·
loading of barges shall be
controlled to prevent splashing of dredged material to the surrounding water,
and barges shall not be filled to a level which will cause the overflow of materials
or polluted water during loading or transportation.
Contaminated Marine Sediments
4.8.15
Additional provisions will be
required where marine sediments are contaminated. The results of the sediment quality analyses
indicate that the marine sediments along the proposed seawall foundation are
seriously contaminated (Class C). The
locations and depths of areas of contaminated marine sediments shall be
indicated in the construction contract.
The contractor shall ensure that contaminated marine sediments are
dredged, transported and placed in approved special dumping grounds in
accordance with the EPD Technical
Circular No. 1-1-92 Classification of Dredged Sediments for Marine Disposal,
Works Branch Technical Circular (WBTC) No. 22/92 Marine Disposal of Dredged Mud and WBTC No. 6/92 Fill Management.
Special EPD procedures for the avoidance of pollution during the
dredging, transportation and disposal of designated contaminated marine
sediment are listed below:
(a)
Uncontaminated mud shall not be
dumped other than in dumping grounds as may be approved for the purpose by the
Director of Environmental Protection (DEP) and in accordance with the Dumping
at Sea Ordinance. If the contaminated
mud cannot be left in situ, it shall be dumped at East Sha Chau Contaminated
Mud Disposal Pits (CMPs) or other disposal pits as may be approved for the
purpose by the DEP. The Contractor shall
be responsible for obtaining all necessary licences for these operations.
Notes: The Engineer shall ensure that the Contractor
has access to WBTC No. 22/92; EPD TC No. 1.1.92; and Fill Management Committee
General Allocation Conditions for Marine Borrow Areas and Mud Disposal Sites.
(b)
When the Contractor dumps the contaminated
mud at East Sha Chau CMPs, he shall place the contaminated mud at a location
and in such a manner as directed by the Management Team of the Civil
Engineering Department. The Contractor
shall proceed with the disposal operation as instructed by the Management Team
and in accordance with guidance notes which are issued by the Management
Team. The Contractor shall not carry out
any dumping without permission of the Management Team or when the Management Team
is not in operation.
(c)
The Contractor shall carry out
the dumping operation in strict accordance with the method statement agreed by
the DEP, any non-compliance with the agreed method shall be a breach of
conditions of the relevant licence issued by the DEP and is an offence under
the Dumping at Sea Ordinance.
(d)
When dredging, transporting and
disposing of designated contaminated marine mud, the Contractor shall implement
additional special procedures for the avoidance of pollution which shall
include, but not be limited to, the following:
(i) employ a grab
dredger with a closed watertight grab for dredging of designated contaminated
marine mud;
(ii)
transport designated
contaminated marine mud by split barge of not less than 750m3
capacity, well maintained and capable of rapid opening and discharge at the
disposal site;
(iii)
design properly and maintain
carefully all operational plant so as to minimize the risk of sediments or
other pollutants being released into the water column and deposited in the
seabed other than designated locations.
The Contractor’s work shall cause no visible foam, oil, grease, scum,
litter or other objectionable matter to be present in the water within the
site;
(iv) fit all barges with
tight fitting seals to their bottom openings to prevent leakage of material;
(v) release the mud
rapidly and close the hoppers immediately; any material adhering to the sides
of the hopper shall not be washed out of the hopper and the hopper shall
reclosed until the barge next returns to the disposal site. The Contractor shall ensure that the dumping
vessel shall be stationary throughout the dumping operation;
(vi) size all vessels such
that adequate clearance is maintained between the seabed and vessels at all
states of the tide, to ensure that undue turbidity is not generated by turbulence
from vessel movement or propeller wash.
Adequate freeboard shall be maintained on barges to ensure that decks
are not washed by wave action;
(vii) employ only barges
equipped with automatic self-monitoring devices for the dumping operation, and
shall co-operate with and facilitate the DEP to inspect the device and retrieve
the record stored in the device on a regular basis;
(viii) provide experienced
full time personnel on board all dumping vessels and provide suitable training
to ensure that appropriate methods to minimize pollution are implemented. Records shall be maintained to satisfy the
DEP that there is no short dumping or dumping outside the Designated Dumping
Area. The Contractor shall also make
available to the DEP and the secretary of Fill Management Committee (S/FMC),
Civil Engineering Department, at any time upon the written request of the DEP,
all information and records relevant to the dredging and mud disposal
operation. This information shall
include, but not be limited to, all data on the plant used by the Contractor,
up-to-date periodic data on production rates and record copies of Notification
of Dumping which have been sent to the Management Team, etc.
Operation Phase
4.8.16
In the present study, it was
found that the proposed YTB reclamation (Full or Minimized Reclamation option)
will have negligible effect on the flow condition within Victoria Harbour and
thus, unacceptable water quality is not expected in the long run. In view of the concern expressed by WSD
regarding the potential impact of the emergency sewage discharge at the Yau
Tong sewage pumping station on the neighbouring WSD’s saltwater pumping
station, it is proposed that a communication channel be established between WSD
and DSD for dealing with this event. It is recommended that this
communication procedure between the two government departments be established
at the detailed design stage. Should
discharge of sewage be made through the emergency outfall, DSD should inform WSD of the
details of such discharge, e.g. volume, timing and duration, in advance where
possible. It is also recommended that
DSD should minimize the discharge and liaise with WSD to avoid discharge during
the peak operation hours of WSD’s saltwater pumping station. Details of the
liaison mechanisms between DSD and WSD should be established for the operation
stage, notably with regard to discharges through the emergency outfall and
potential impacts on WSD saltwater pumping station performance, during the
detail design stage of the project.
4.8.17
No other mitigation measure is
recommended for the operation phase in the present study. Furthermore, the scope of the present EIA
study covers mainly the environmental impact of the Yau Tong Bay reclamation
during the construction phase. The
impact of the subsequent development on the reclaimed land will be addressed
under a separate EIA study. Hence,
mitigation measures, if any, for the subsequent development will be addressed
in the corresponding EIA study.
4.9
Environmental Monitoring and Audit Requirements
4.9.1
A design audit in terms of
water quality impact is recommended to be carried out at the detailed design
stage to review the updated information.
Should any adverse water quality impacts other than those assessed in this
report be identified during the detailed design stage, appropriate measures
will be proposed to mitigate the adverse impacts. The EM&A manual should then be revised,
where necessary, to included the recommended mitigation measures.
4.9.2
Based on the water quality
impact assessment results in this report, it is recommended that environmental
monitoring and auditing (EM&A) of marine water quality be carried out at
the Yau Tong and Cha Kwo Ling WSD saltwater intakes and the Dairy Farm seawater
intake during the construction phase. In
particular, monitoring of water quality during dredging and sand filling
activities for the seawall foundation, Phase I and Phase II reclamations
will be required. An EM&A program
will be required to ensure the implementation of the recommended water quality
mitigation measures and to assess the effectiveness of these measures during
the construction works. Details of the
EM&A procedures are presented in Section 9.2. If monitoring results indicate that the
dredging and/or sand filling works have caused an adverse impact on water
quality at the above sensitive receivers, the construction program should be
carefully reviewed so as to slow down the rate of dredging or sand filling
accordingly, such that the water quality at these sensitive receivers is in
compliance with the water quality criteria.
4.10
Definition and Evaluation of Residual Impacts
4.10.1
With the full and strict
implementation of the recommended mitigation measures for the construction of
the YTB reclamation, no unacceptable residual impacts on marine water quality
are anticipated to arise. In addition,
it is considered that no adverse environmental effects will result from the
employment of the recommended water quality mitigation measures for the
reclamation works, as described in Section 4.8.
4.11
Conclusions
Operation Phase
4.11.1
Detailed hydrodynamic modelling
was conducted using the DHI models, MIKE 21 and MIKE 3, to determine the impact
of the completed YTB reclamation (Full Reclamation option) on tidal flow
patterns in Victoria Harbour. The
percentage change in flow discharge rates through Victoria Harbour from the
baseline scenario without the YTB reclamation to the development scenario with
YTB reclaimed is very small, with a
change in annual average discharge rate of less than 0.5%. The tidal flow patterns were observed to be
similar for the baseline and development scenarios with minor deviation near
YTB, and the maximum flow speeds for the two scenarios were also similar for
the wet and dry seasons, spring and neap tides.
The results of the hydrodynamic modelling indicate that the YTB
reclamation (Full Reclamation option) is likely to have negligible effect on the
tidal flow regime in Victoria Harbour. As the reclamation extent of the
Minimized Reclamation option is smaller than that for the Full Reclamation
option, the corresponding impact is expected to be less significant than that
for the Full Reclamation option.
4.11.2
The potential water quality
impact of an emergency discharge from the Yau Tong Sewage Pumping Station on
the potential site proposed under the YTB Reclamation (Full Reclamation option)
for future reprovisioning of the CKLSPS has been assessed for both wet and dry
seasons. The model results indicate that
the depth averaged water quality in terms of BOD5, SS and ammoniacal
nitrogen is expected to meet the WSD standards at the reprovisioned CKLSPS;
however, the E. coli standards will
be exceeded. The sewage plume is shown
to attach to the shoreline and is buoyant at the surface with a thickness of
less than 0.4m. To avoid abstracting the
sewage plume water, it is recommended that the future reprovisioned CKLSPS saltwater
intake should be located below -2.0 mPD. The intake water would then be
expected to comply with the WSD water quality standards. The optimal intake configuration should be
reviewed and decided at the detailed design stage for the reprovsioning of the
CKLSPS. Under the Minimized Reclamation
option, no provisions have been made for the relocation or upgrading of the
CKLSPS which will remain in operation at the existing location where the water
quality is expected to meet the WSD target limits at the saltwater intakes.
4.11.3
No adverse water quality impact
in Victoria Harbour and, in particular, at the existing and potentially
reprovisioned CKLSPS, under the YTB reclamation (Full Reclamation option), and
the reprovisioned YTSPS, under the WCR-Coastal option reclamation, is expected
from the polluted stormwater in the new Kwun Tong nullah and the new YTB
stormwater culvert (with the conservative assumption of 5% residual flows from
expedient connections). The model result
suggested that tidal flushing will prevent the accumulation of pollutants under
the proposed concrete decking at the mouth of YTB and the water quality is
expected to comply with the WSD’s target limits at the saltwater intakes. Since the proposed concrete decking under the
Minimized Reclamation will be reduced in size and is more exposed to the tidal
flow in Victoria Harbour, the water quality under the concrete decking is
expected to be better than that for the Full Reclamation option. Hence, it is concluded that reprovisioning of
the CKLSPS will not be required under the YTB reclamation (Full or Minimized
Reclamation option).
Construction Phase
4.11.4
Sediment plume modelling of the
different construction phases was conducted to assess the water quality impact
of the dredging and filling activities for the proposed YTB reclamation (Full
Reclamation option), which represents the worst case scenario. The three main
construction phases identified were the seawall construction, Phase 1 and
Phase 2 reclamations. Sediment loss
rates for dredging and filling were estimated based on the employment of open
grab dredgers without silt curtains and bottom dumping barges. With the same construction sequence and
methodology as adopted in the Full Reclamation option, the water quality impact
arising from the Minimized Reclamation option is expected to similar, if not
less significant, than the former.
Hence, the recommended mitigation measures for the Full Reclamation
option will be fully applicable to the Minimized Reclamation.
4.11.5
The predicted elevation in SS
concentration in Victoria Harbour generally satisfies the stipulated WQO for SS
in both the wet and dry seasons, spring and neap tides. Exceedance of the WQO for SS is only found
locally within the sediment plume near YTB.
High SS concentration are predicted at the WSD's Yau Tong and Cha Kwo Ling
Saltwater Pumping Stations and the Dairy Farm saltwater intake for the various
construction phases, which are in exceedance of the WSD target (tolerable)
limit for SS at saltwater intakes. The
non-compliance of the WQO and WSD standard at saltwater intakes necessitate the
implementation of the proposed mitigation measures during the construction
period.
4.11.6
The proposed mitigation
measures include: the use of closed grab dredgers with silt curtain for the
dredging and filling of seawall construction and dredging of stormwater box
culvert; a silt curtain to be placed across the seawall opening for the
Phase 1 and Phase 2 reclamations using bottom dumping; double layers
of silt screen to be installed at the Yau Tong (YTSPS) and Cha Kwo Ling (CKLSPS)
Saltwater Pumping Stations and the Dairy Farm Saltwater Intake (DFSI); and the
reduction of Phase 2 reclamation filling rate to 6,000 m3day-1. Details of the mitigation measures to be
implemented are discussed in Section 4.8 and summarized
in the Implementation Schedule for Water Quality Control (Table 11.2).
4.11.7
With the proposed mitigation
measures fully implemented, it is anticipated that the size of the sediment
plume of the YTB reclamation (Full Reclamation option) will be reduced,
minimizing the impact on Victoria Harbour.
It is also expected that the SS concentration at the WSRs will satisfy
the WSD tolerable limit for SS (20 mgL-1) at the CKLSPS and
YTSPS, and the in-house standard of 20 mgL-1 for SS at the DFSI
at all times.
4.11.8
Based on the available
information, the dredging and filling works for the South East Kowloon
Development (SEKD), Western Coast Road (WCR-Coastal option), Tseung Kwan O
(TKO) Cargo Working Area (CWA) and TKO New Town Intensification and Extension
(NTIE), potentially concurrent to the YTB reclamation were identified.
4.11.9
An assessment of the water
quality impacts due to the concurrent works in Victoria Harbour, except the YTB
reclamation, was performed to establish a reference level (Scenario 2B_BK). The WQO for SS in the VHWCZ was generally
satisfied with the sediment plumes associated with the different projects being
localized. With the available information,
mitigation measure was implemented for all the concurrent projects except for the
TKO NTIE works. Hence, the plume
associated with the TKO NTIE works is relatively large, extending into the Lei
Yue Mun Channel and across Victoria Harbour to the Shau Kei Wan Typhoon
Shelter, particularly, in the wet season.
The surface SS concentration due to the cumulative impacts from other
projects generally complies with the WSD target limit for SS at the CKLSPS and
the in-house SS standard at the DFSI.
However, exceedance of the WSD target (tolerable) limit is observed at
the YTSPS, which can be attributed to the unmitigated works of the TKO NTIE.
4.11.10
The cumulative impact of the
YTB reclamation is taken into account by comparing the contribution of the YTB
reclamation and the concurrent works (Scenario 2B_CI). The result suggests that the YTB reclamation
only contributes to a marginal increase in the size of the sediment plume
around YTB. Hence, no unacceptable
impact on Victoria Harbour is anticipated.
With the implementation of the proposed mitigation measures for the YTB
reclamation, the water quality at the WSRs is expected to improve over the
reference level due to the concurrent project without the YTB reclamation
(Scenario 2B_BK). Exceedance of
the WSD target limit for SS concentration of 10 mgL-1 at the YTSPS
is essentially associated with the unmitigated works of the TKO NTIE mentioned
earlier. With appropriate mitigation
measures to be proposed by the TKO NTIE EIA study, sediment plume dispersion of
the marine works of TKO NTIE will be essentially confined within Junk Bay and
the residual SS concentration at the YTSPS is expected to very similar to the
mitigated water quality under the Scenario 2A_P1 (as presented in paragraph
4.11.2.4). That is, the residual SS
level at the intake of YTSPS will comply with the WSD SS tolerable limit (20
mgL-1) all the time.
4.11.11
No adverse impact in Victoria
Harbour and on the existing sensitive receivers are expected from polluted
stormwater due to the temporary diversion of the stormwater culvert to the
mouth of YTB before the reclamation starts.
The diverted stormwater will be directly discharged into Victoria
Harbour and thus, prevents the accumulation of pollutants in the temporary
embayment. The results also suggested
that pollutants from stormwater discharge is unlikely to cause unacceptable
water quality impacts in the VHWCZ during the construction period.
4.11.12
Adverse impacts on water
quality arising from the release of heavy metals from contaminated sediment are
not anticipated during the dredging works.
A quantification of the release of heavy metals from the sediment pore
water indicates that the predicted heavy metal concentrations in the marine
waters surrounding the dredging site will not exceed the UK Water Quality
Standards for Coastal Surface Water.
4.11.13
Environmental monitoring and
auditing (EM&A) program will be required to monitor and audit the
implementation and efficacy of measures to mitigate any adverse impacts,
arising from the YTB reclamation works, on the water quality sensitive
receivers, as detailed in Section 9.2.