Water Quality Modelling Method Statement...modelling exercise. 1.5 COASTLINE CONFIGURATIONS &...
Transcript of Water Quality Modelling Method Statement...modelling exercise. 1.5 COASTLINE CONFIGURATIONS &...
Annex 7B
Water Quality Modelling
Method Statement
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1 INTRODUCTION
1.1 BACKGROUND
Castle Peak Power Company Limited (CAPCO) proposes to install up to two
additional gas-fired generation units (combined cycle gas turbine, CCGT) at
Black Point Power Station (BPPS) (hereafter referred to as “the Project”) to
increase the use of natural gas for local power generation and reduce the
carbon intensity of local electricity generation. The Project requires an
Environmental Permit from the Hong Kong SAR Government. In relation to
this, CAPCO has prepared a Project Profile for application for an
Environmental Impact Assessment (EIA) Study Brief, which was submitted to
Environmental Protection Department (EPD) on 22 April 2015. The EIA
Study Brief (No. ESB-286/2015) was issued by EPD on 2 June 2015.
Environmental Resources Management (ERM) was commissioned by CAPCO
for the EIA Study for the proposed Project. As part of the EIA,
computational hydrodynamic and water quality modelling will be undertaken
to quantify and evaluate potential water quality impacts associated with the
construction and operation of this Project.
The proposed location for the additional CCGT units is shown in Figure 1.1.
If only one CCGT unit is installed, no marine works will be required. The
key project elements related to water quality on the construction and
operation of the Project include:
a) Marine construction of the seawater intake and discharge outfall, if a
second CCGT unit is installed;
b) Increase in cooling water and chlorine discharge from the proposed
additional CCGT units;
c) Minor capital and maintenance dredging required at the seawater intake
and discharge outfall, if a second CCGT unit is installed; and
d) Potential increase in other loadings in runoff to marine waters during
project operation.
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Figure 1.1 Location of the Proposed Additional CCGT Units at BPPS
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1.2 PURPOSE OF THE METHOD STATEMENT
This Method Statement presents information on the approach for numerical
modelling and assessment works for the EIA. It is important to note that at
the time of writing this Method Statement, the detailed engineering information
for both construction and operation activities is yet to be confirmed and
therefore a general approach as to how the modelling works would be carried
out is presented herein, with relevant assumptions provided as appropriate.
The methodology has been based on the following three focus areas:
Model Selection;
Input Data; and
Scenarios.
1.3 KEY ISSUES FOR MODELLING
The objectives of the modelling exercise are to assess:
Water quality impacts from marine construction of a seawater intake and
cooling water discharge outfall, which is only required if the proposed
second additional CCGT unit is to be installed;
Water quality impacts from the additional cooling water and chlorine
discharge from the proposed additional CCGT units via the outfall;
Water quality impacts from minor capital and maintenance dredging at
the new seawater intake and cooling water discharge outfall; and
Any cumulative impacts due to other projects or activities within the
study area.
The construction and operational impacts on water environment will be
studied by means of computer models.
1.4 MODEL SELECTION
The Delft3D suite of models will be utilized to provide a modelling platform
for hydrodynamic and water quality modelling. A Delft3D model (referred
to as the Black Point Model), based on the Western Harbour Model (WHM)
was developed for the Black Point Gas Supply Project EIA (AEIAR-150/2010)
and would be adopted in this modelling exercise. The Black Point Model is a
four-grid domain decomposition (DD) model, which allows flexible spatial-
varying grid resolution. The highest grid resolution (approximately 15 m ×
30 m) is allowed in the Black Point Domain (BPP) which covers the immediate
vicinity of the BPPS. All four DD domains include:
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WHM - an overall domain which covers most of the North Western WCZ
and the waters west to the HK marine border;
TFW - an intermediate domain provides enhanced resolution in a wider
area around the BPPS;
SHZ - Deep Bay domain; and
BPP – local BPPS domain with the highest resolution.
The Black Point Model adopted in the Black Point Gas Supply Project EIA
covers the western waters of Hong Kong. The four domains of the Black
Point Model are shown in Figure 1.2 below.
Figure 1.2 Domain Decomposition of the Black Point Model
The Black Point Model was calibrated and verified in the previous approved
EIA of Black Point Gas Supply Project. In view of the latest update on future
coastline configuration in the North Western WCZ, such as the reclamation for
the Hong Kong-Zhuhai-Macau Bridge Hong Kong Boundary Crossing
Facilities (HKBCF), Hong Kong Link Road (HKLR), Tuen Mun-Chek Lap Kok
Link (TM-CLKL) and the Expansion of the Hong Kong International Airport
into Three Runway System (3RS-HKIA) which are not taken into account in
the previously developed Black Point model, updates have been made to the
eastern boundary of the WHM domain of the Black Point Model to
accommodate these changes. Verification of the modified version of the
SHZ
WHM
TFW
BPP
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hydrodynamic model would be conducted to demonstrate the consistency in
performance of the updated Black Point Model with the original WHM.
The proposed discharge of additional cooling water from the new CCGT units
will be similar to that of the existing arrangement. Existing and proposed
thermal discharge outfalls are located at the surface (only submerged under
highest astronomical tide). Since the thermal plume is less dense than
ambient seawater and would stay on the top layer of the water column, the
thermal discharge would be simulated accordingly in the Delft3D FLOW
modelling exercise.
1.5 COASTLINE CONFIGURATIONS & BATHYMETRY
The latest coastline configuration for the assessment year of 2020 will be
adopted in model simulations of the potential impact from the Project in this
EIA study. Changes in coastline configuration due to reclamation and other
development activities will be reflected in the model setup. The changes in
coastline configuration include the effects by the following development
projects (1):
Sunny Bay Reclamation;
Reclamation for 3RS-HKIA
TM-CLKL;
HKBCF;
HKLR;
Kwai Tsing Container Terminal Basin dredging;
Cruise Terminal at Kai Tak; and
Lantau Logistic Park.
The bathymetry in the vicinity of the Project as shown in Figure 1.3 is used for
the Black Point Model. The bathymetry data are obtained from the
Hydrographic Office, Hong Kong Electronic Navigational Chart (ENC), 2011.
The reference level of the Black Point Model is Principal Datum Hong Kong
and the depth data are relative to this datum.
(1) Projects which are beyond the coverage of the Black Point Model would be taken into account in the Western Harbour
Model. The effect on the flow regime from these Projects would eventually be reflected in the Black Point Model via
model nesting.
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Figure 1.3 Bathymetry to be used in the Black Point Model
Source: (1) Hydrographic Office, Hong Kong Electronic Navigational Chart (ENC), 2011
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1.6 BOUNDARY CONDITIONS AND INITIAL CONDITIONS
The same boundary conditions from the previous modelling exercise of the
approved EIA of the Black Point Gas Supply Project were adopted in this
modelling exercise. Improvement at the eastern boundary of the WHM
domain has been conducted by redoing the nesting with the Western Harbour
Model with the latest coastline configurations. The hydrodynamic modelling
of the Western Harbour Model, into which the Black Point Model eventually
nests, covers the outer regions of Pearl River Estuary, Macau, Lamma Channel
and Deep Bay. All major influences on hydrodynamics in the outer regions
are therefore incorporated.
1.7 AMBIENT ENVIRONMENTAL CONDITIONS – BACKGROUND TEMPERATURE, SOLAR
RADIATION AND WIND
The ambient environmental conditions are closely linked to the processes of
hydrodynamic changes. The wind conditions applied in the hydrodynamic
simulation are 5 m/s NE for dry season and 5 m/s SW for the wet season.
The same average wind speed and direction were adopted in the Update
model and WHM.
The hydrodynamic model has included the fresh water inflows from four
Pearl River outlets as well as from Shenzhen River in Deep Water. The
salinity of the river outflows was assumed to be 0.1 ‰ and the temperatures
in the dry and wet seasons were attributed to be 23 ºC and 30 ºC, respectively.
1.8 SIMULATION PERIODS
The simulation periods covered by the Black Point Model are the same as the
previous modelling exercise under the approved EIA of the Black Point Gas
Supply Project EIA. A 22-day single domain run using Western Harbour
Model would be conducted with this model to ensure that salinity and
temperature fields would be sufficiently spun up. Suitable salinity and
temperature fields would be selected from the single domain runs and
interpolated on the four domain model. These fields would be used as initial
conditions for the production runs covering a period of 22 days of which the
first seven days were used to spin up water levels and currents whilst the last
15 days as production.
Table 1.1 Model Simulation Periods
Season Spin Up Model Start Time Model End Time
Wet 19 July 00:00:00 – 26
July 00:00:00
26 July 00:00:00 10 Aug 00:00:00
Dry 02 Feb 00:00:00 –
09 Feb 00:00:00
09 Feb 00:00:00 24 Mar 00:00:00
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1.9 UNCERTAINTIES IN ASSESSMENT METHODOLOGIES
1.9.1 Uncertainties in Sediment Transport Assessment
Uncertainties in the assessment of the impacts from suspended sediment
plumes will be considered when drawing conclusions from the assessment.
In carrying out the assessment, the worst case assumptions have been made in
order to provide a conservative assessment of environmental impacts. These
assumptions are as follows:
The assessment is based on the peak sediment release rate for grab
dredging. In reality, these will only occur for short period of time;
The calculations of loss rates of sediment to suspension are based on
conservative estimates for the types of plant and methods of working;
While the marine dredging required would be completed within 10 (1) days
at the assessed peak dredging rate of 4,000 m3/day, the modelled sediment
release is assumed to last for 15 days (i.e. one typical spring-neap cycle in
Hong Kong). This ensures the worst tidal conditions are modelled and
conservative predictions could be made for capital and maintenance
dredging simulations.
The following uncertainties have not been included in the construction /
operation phase marine construction modelling assessment:
Ad hoc navigation of marine traffic;
Propeller scour of seabed sediments from vessels;
Near shore scouring of bottom sediment; and
Access of marine barges back and forth the site.
1.9.2 Uncertainties in Operation Phase Thermal Discharge Modelling
The following uncertainties in the operations have not been included in the
operation phase thermal discharge modelling assessment:
Short term change in ambient conditions due to adverse weather
conditions;
Change in seabed level due to siltation; and
Change in flow regime due to reclamations which are not included in the
modelling exercise (as discussed under sections 1.5 and 5).
(1) At seawater intake: 20,000 m3 (in-situ volume) ÷ 4,000 m3/day = 5 days. At seawater outfall: 20,000 m3 (in-situ
volume) ÷ 4,000 m3/day = 5 days.
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2 WATER SENSITIVE RECEIVERS
The water quality sensitive receivers (WSRs) have been identified in
accordance with Annex 14 of the Technical Memorandum on EIA Process (EIAO,
Cap.499, S.16) and Environmental Impact Assessment Study Brief for Additional
Gas-fired Generation Units Project (No. ESB-286/2015). These WSRs are
illustrated in and listed in Table 2.1 and Figure 2.1.
Table 2.1 Water Quality Sensitive Receivers (WSRs) in the Vicinity of the Project Site
Description Location Model
Output
Location
Approximate Shortest
Distance by Sea from
Project Site (km)
Fisheries Sensitive Receivers
Oyster Production Area Sheung Pak Nai SR14 3.5
Recognised Spawning/
Nursery Grounds
Fisheries Spawning Ground in
North Lantau
SR15 4.1
Artificial Reef Deployment
Area
Sha Chau and Lung Kwu Chau SR12 7.9
Marine Ecological Sensitive Receivers
Mangroves Ngau Hom Shek SR1 6.5
Sheung Pak Nai SR2 4.9
Marine Park Designated Sha Chau and Lung
Kwu Chau
SR6 4.4
SR7 3.3
SR13 8.5
Intertidal Mudflats Ha Pak Nai SR3 3.5
Seagrass Beds Sheung Pak Nai SR2 4.9
Ha Pak Nai SR3 3.5
Horseshoe Crab Nursery
Grounds
Ha Pak Nai SR3 3.5
Ngau Hom Shek SR1 6.5
Lung Kwu Sheung Tan SR5 2.4
Coral Colonies Identified
Along Survey Transect under
this Project
Transect D SR17 At the proximity of the
Project Site
Transect C SR18 At the proximity of the
Project Site
Water Quality Sensitive Receivers
Non-gazetted Beaches Lung Kwu Sheung Tan SR5 2.4
Lung Kwu Tan SR8 3.8
Secondary Recreation Subzone North Western Water Control Zone SR8 3.8
Seawater Intakes Black Point Power Station SR4 At the proximity of the
Project Site
Castle Peak Power Station SR9 4.8
Tuen Mun Area 38 SR11 6.5
Shiu Wing Steel Mill SR10 5.6
Sludge Treatment Facilities SR16 1.5
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Figure 2.1 Water Sensitive Receivers in the Vicinity of the Proposed Project Site
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3 CONSTRUCTION PHASE
Marine activities which include sediment dredging and minor construction
would be required under this Project for the construction of proposed
seawater intake and outfall for the second CCGT unit. For the construction
phase the Delft-WAQ model will be used to directly simulate the following
parameters from marine construction of this Project and the concurrent
projects:
Suspended sediments (SS);
Sediment deposition; and
Release of sediment-bounded pollutants.
Based on the latest design information, the seawater intake and cooling water
outfall for the proposed second CCGT unit will be constructed according to
the below sequence:
1. Removal of sediment (up to 5 m below the existing seabed level) at the
seabed near the proposed intake and outfall by grab dredger (not
concurrent);
2. Filling of rock fill at the dredged area and affected seawall near the
proposed intake and outfall by grab dredger (not concurrent);
3. Cofferdam construction near the proposed intake and outfall;
4. Installation of water cut-off measures and removal of water from within
the cofferdams;
5. Land-based construction of intake and outfall structures within
cofferdams;
6. Removal of cofferdams
Disturbance to seabed and release of fine sediments into the water column are
anticipated in steps 1, 2, 3 and 6 stipulated above. Among all, sediment
dredging stipulated in step 1 is expected to result in the most significant
release of sediment to the water column when comparing to other
construction steps. Rock fill used generally consists of only large granular
material with negligible amount of fines, thus would not contribute to
significant loss of fines to the water column. Cofferdam construction and its
subsequent removal may result in minor and localized disturbance of bottom
sediment. For construction of intake and outfall structures within
cofferdams, no release of sediment would be expected as the cofferdam would
fully enclose the works area close to the seawater intake and discharge outfall
and the works area would be kept drained throughout the construction
period. In view of this, the sediment removal at the proposed seawater
intake and outfall locations would be the major marine construction activities
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under this Project that would disturb the seabed sediment and be assessed
using Delft-WAQ accordingly.
Dissolved oxygen (DO) depletion will be calculated using the modelled
maximum SS concentrations. This method has been adopted in recently
approved EIAs (1) (2). Total inorganic nitrogen (TIN), unionized ammonia
(UIA), heavy metals and organic compounds will be modelled as inert tracers
which release at the same time as the disturbed sediment for conservative
reason.
3.1 ASSESSMENT CRITERIA FOR CONSTRUCTION PHASE
The study area will cover Deep Bay and North Western Water Control Zones
(WCZs) as shown in Figure 1.3. Hence, Water Quality Objectives (WQOs) in
these WCZs will be used to assess water quality impacts in SS, DO, TIN and
NH3-N released in the process of dredging (Table 3.1).
Table 3.1 Summary of Assessment WQO Criteria for Construction Phase
Parameters (1) Inner Deep Bay Outer Deep Bay North Western
Dissolved Oxygen
(Bottom) (mg/L) Not less than 2 mg/L for 90% of samples for all WCZs
Dissolved Oxygen
(Depth-averaged)
(mg/L)
Not less than 4 mg/L for 90% of samples for all WCZs
Temperature (°C) Increase < 2
Total Inorganic
Nitrogen (mg/L) < 0.7 < 0.5 < 0.5
Unionized Ammonia
(mg/L) < 0.021 mg/L for all WCZs
Suspended Solids
(mg/L) Not to raise the natural ambient level by 30%
It should be highlighted that continual exceedance in TIN was observed in
Deep Bay and North Western WCZs from 2005 to 2014. Assessing the
potential elevation in TIN against the WQO criterion with such high
background level would be overly conservative and an alternative assessment
criterion would be adopted for this Study. For this Study, the proposed
allowed TIN increase from marine construction would be limited to 1% of the
WQO TIN criterion for the corresponding WCZs. The proposed TIN
elevation criterion would be 0.005 mg/L for all WSRs (since there is no WSRs
identified in Inner Deep Bay) except SR4 and SR9 (seawater intake for BPPS
and CPPS) which are not considered sensitive to elevation in TIN. In view of
the relatively high background TIN level (mean TIN level from 2005 to 2014
(1) ERM - Hong Kong, Ltd (2006) EIA Study for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities.
For CAPCO. Register No.: AEIAR-106/2007,
http://www.epd.gov.hk/eia/register/report/eiareport/eia_1252006/html/index.htm
(2) ERM - Hong Kong, Ltd (2010) EIA Study for Black Point Gas Supply Project. For CAPCO. Register No. AEIAR-
150/2010, http://www.epd.gov.hk/eia/register/report/eiareport/eia_1782009/index.html
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among four nearby EPD marine water quality monitoring stations all
exceeded 0.5 mg/L), the proposed TIN elevation criteria would also be below
1% of the mean ambient level. Therefore, such an increase in TIN level
would be insignificant in term of water quality and would be considered
acceptable.
There are no known water quality criteria for seawater intakes at Tuen Mun
Area 38 and Shiu Wing Steel Mill. The above WQO criteria for SS would be
adopted for water quality assessment for these two seawater intakes. For the
existing seawater intakes for BPPS and Castle Peak Power Station (CPPS), the
criteria for maximum water temperature is 30 °C and the maximum allowable
elevation of suspended solids is 700 mg/L. These levels have been adopted
in the approved EIA of the Black Point Gas Supply Project.
Criterion for maximum sedimentation of 200 g/m2/day is adopted at the
artificial reef deployment area in Sha Chau and Lung Kwu Chau Marine Park.
There are no existing regulatory standards or guidelines for dissolved metals
and organic contaminants in the marine waters of Hong Kong. It is thus
proposed to make reference to relevant international standards and this
approach has been adopted in previous approved EIAs, i.e., EIA for
Decommissioning of Cheoy Lee Shipyard at Penny’s Bay (1), EIA for Disposal of
Contaminated Mud in the East Sha Chau Marine Borrow Pit (2), EIA for Wanchai
Development Phase II (3), EIA for Liquefied Natural Gas (LNG) Receiving Terminal
and Associated Facilities (4),EIA for Hong Kong Offshore Wind Farm in Southeastern
Waters (5) and EIA for Shatin to Central Link Cross Harbour Section (Phase II -
Hung Hom to Admiralty) (6). Table 3.2 shows the assessment criteria for
dissolved metals and organic pollutants for this Study.
Table 3.2 Summary of Assessment Criteria for Dissolved Metals and Organic
Compounds for Construction Phase
Parameter Unit Assessment Criteria for this Study
Metals
Cadmium (Cd) g/L 2.5 (a) (b)
Chromium (Cr) g/L 15 (a) (b)
Copper (Cu) g/L 5 (a) (b)
Nickel (Ni) g/L 30 (a) (b)
Lead (Pb) g/L 25 (a) (b)
(1) Maunsell (2002). EIA for Decommissioning of Cheoy Lee Shipyard at Penny's Bay. For Civil Engineering
Department, Hong Kong SAR Government.. Register No.: AEIAR-055/2002
(2) ERM – Hong Kong (1997). EIA for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit. For
Civil Engineering Department, Hong Kong SAR Government. . Register No.: EIA-106/BC
(3) Maunsell (2001). EIA for Wanchai Development Phase II - Comprehensive Feasibility Study. For Territory
Development Department, Hong Kong SAR Government. . Register No.: AEIAR-042/2001
(4) ERM - Hong Kong, Ltd (2006). EIA for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities.
Register No.: AEIAR-106/2007
(5) BMT Asia Pacific Ltd (2009). EIA for Hong Kong Offshore Wind Farm in Southeastern Waters. For HK Offshore
Wind Limited. Register No.: AEIAR-140/2009
(6) AECOM (2011). EIA for Shatin to Central Link Cross Harbour Section (Phase II - Hung Hom to Admiralty) for
MTR. Register No.: AEIAR-166/2012
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Parameter Unit Assessment Criteria for this Study
Zinc (Zn) g/L 40 (a) (c)
Mercury (Hg) g/L 0.3 (b)
Arsenic (As) g/L 25 (a) (b)
Silver (Ag) g/L 1.9 (d)
Total PAHs g/L 3.0 (f)
PCBs
Total PCBs g/L 0.03 (d)
Organotins
Tributyltin (TBT) g/L 0.1 (e)
(maximum concentration)
Notes:
(a) UK Environment Agency, Environmental Quality Standards (EQS) for List 1 & 2
dangerous substances, EC Dangerous Substances Directive (76/464/EEC)
(http://www.ukmarinesac.org.uk/activities/water-quality/wq4_1.htm).
(b) Annual average dissolved concentration (i.e. usually involving filtration a 0.45-um
membrane filter before analysis).
(c) Annual average total concentration (i.e. without filtration).
(d) U.S. Environmental Protection Agency, National Recommended Water Quality Criteria,
2009. (http://www.epa.gov/waterscience/criteria/wqctable). The Criteria Maximum
Concentration (CMC) is an estimate of the highest concentration of a material in surface
water (i.e. saltwater) to which an aquatic community can be exposed briefly without
resulting in an unacceptable effect. CMC is used as the criterion of the respective
compounds in this study.
(e) Salazar MH, Salazar SM (1996) Mussels as Bioindicators: Effects of TBT on Survival,
Bioaccumulation, and Growth under Natural Conditions. In Organotin, edited by M.A.
Champ and P.F. Seligman. Chapman & Hall, London.
(f) Australian and New Zealand Environment and Conservation Council (ANZECC),
Australian and New Zealand Guidelines for Fresh and Marine Water Quality (1992)
There are no existing regulatory standards or guidelines for total PCBs, total
PAHs and TBT in water and hence reference has been made to the USEPA
water quality criteria, Australian water quality guidelines, and international
literature, respectively. The assessment criteria for total PCBs, total PAHs
and TBT are 0.03 μg/L, 3.0 μg/L and 0.1 μg/L respectively. The same
assessment criteria for these 3 chemicals are adopted in past approved EIA
such as the approved EIA of Shatin to Central Link (AEIAR-166/2012).
3.2 OUTLINE MARINE ACTIVITIES
At this early stage it is understood that the seawater intake and discharge
outfall of the proposed 2nd CCGT unit is located next to the existing seawall.
Dredging is anticipated to be required for the seabed area around the
proposed intake and discharge to allow for siltation. Other marine works for
the construction of seawater intake and discharge outfall may include:
Installation (and removal) of cofferdam comprise of pipe-pile or sheet-pile
walls;
Removal (and reinstatement) of rock armours;
Removal of the existing crest wall;
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Installation of water cut-off measures, e.g. precast concrete blocks and sand
bags by mobile crane from landside;
In-situ construction of Cooling Water Intake Pump House (and part of the
culvert) as well as reinforced concrete outfall apron;
Backfilling of the excavated part of the sloping seawall by rock fill and rock
armour to the original configuration;
Laying of rock fill / sand fill and then granular bedding material by derrick
lighter onto the dredged seabed for foundation of the culvert. The laid
foundation will be tamped by precast concrete blocks maneuvered; and
Installation of precast segment by derrick lighter or crane barge.
The potential disturbance to seabed from these marine construction activities
is expected to be insignificant when compared with that of the marine
dredging required. Therefore, the potential impact on water quality from the
proposed marine dredging for seawater intake and discharge outfall would be
assessed quantitatively for the purpose of this EIA.
3.3 WORKING TIME
The works programme for construction activities is based on the assumption
of a 16 working hour day with 7 working days per week. The proposed rate
of sediment removal within cofferdam is 4,000 m3/day.
3.4 OVERVIEW OF DREDGING PLANT - GRAB DREDGERS
Grab dredgers may release sediment into suspension by the following
mechanisms:
Impact of the grab on the seabed as it is lowered;
Washing of sediment off the outside of the grab as it is raised through the
water column and when it is lowered again after being emptied;
Leakage of water from the grab as it is hauled above the water surface;
Spillage of sediment from over-full grabs;
Loss from grabs which cannot be fully closed due to the presence of
debris;
Release by splashing when loading barges by careless, inaccurate
methods; and
Disturbance of the seabed as the closed grab is removed.
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In the transport of dredged materials, sediment may be lost through leakage
from barges. However, dumping permits in Hong Kong include
requirements that barges used for the transport of dredging materials have
bottom-doors that are properly maintained and have tight-fitting seals in
order to prevent leakage. Given this requirement, sediment release during
transport is not proposed for modelling and its impact on water quality will
not be addressed under this Study.
Sediment is also lost to the water column when discharging material at
disposal sites. The amount that is lost depends on a number of factors
including material characteristics, the speed and manner in which it is
discharged from the vessel, and the characteristics of the disposal sites. It is
considered that potential water quality issues associated with disposal at the
intended government disposal site(s) have already been assessed by Civil
Engineering and Development Department (CEDD) and permitted by EPD,
hence and the environmental acceptability of such disposal operations is
demonstrated. Therefore modelling of impacts at disposal sites does not
need to be addressed and reference to relevant studies will be provided in the
EIA for this Project where appropriate.
Loss rates have been taken from previously accepted EIAs in Hong Kong (1)(2)(3)(4) and have been based on a review of worldwide data on loss rates from
dredging operations undertaken as part of assessing the impacts of dredging
areas of Kellett Bank for mooring buoys (5). The assessment concluded that
for 8 m3 (minimum) grab dredgers working in areas with significant amounts
of debris on the seabed (such as in the vicinity of existing mooring buoys) that
the loss rates would be 25 kg m-3 dredged, while the grab dredger bucket size
in areas where debris is less likely to hinder operations could be 12 or 16 m3,
with a loss rate of 17 kg m-3. It is assumed there is little debris based on the
fact the area is away from marine works and heavy marine traffic / industry.
The value of 17 kg m-3, for dredgers with grab size of 12 or 16 m3, will
therefore be used for this Study.
Generally, a split-bottom barge could have a capacity of 900 m³. A bulk
factor of 1.3 would normally be applied, giving a dredging rate of about 700
m³ per barge. The hopper dry density for an 800 to 1,000 m3 capacity barge is
around 0.75 to 1.24 ton m-3. Assuming 16 working hours per day for the
proposed construction activities, with allowance on the demobilisation of
(1) ERM - Hong Kong, Ltd (2006) EIA Study for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities.
For CAPCO. Register No.: AEIAR-106/2007,
http://www.epd.gov.hk/eia/register/report/eiareport/eia_1252006/html/index.htm
(2) ERM (2005). Detailed Site Selection Study for a Contaminated Mud Disposal Facility within the Airport East/East of Sha
Chau Area. EIA and Final Site Selection Report. For CEDD. Approved on 1 September 2005. Register No.: AEIAR-
089/2005, http://www.epd.gov.hk/eia/register/report/eiareport/eia_1062005/index.htm
(3) ERM (2000). Construction of an International Theme Park in Penny’s Bay of North Lantau together with its Essential
Associated Infrastructures – Final EIA Report. For CEDD. Approved on 28 April 2000. Register No.: AEIAR-032/2000
http://www.epd.gov.hk/eia/register/report/eiareport/eia_0412000/index.html
(4) ERM - Hong Kong, Ltd (2010) EIA Study for Black Point Gas Supply Project. For CAPCO. Register No. AEIAR-
150/2010, http://www.epd.gov.hk/eia/register/report/eiareport/eia_1782009/index.html
(5) ERM (1997). EIA: Dredging an Area of Kellett Bank for Reprovisioning of Six Government Mooring Bays. Working Paper on
Design Scenarios. For CEDD.
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filled barge and remobilisation of empty barges, approximately 5-6 barges
could be filled per day, giving a daily dredging rate of approximately 4,000
m3.
3.5 CONSTRUCTION SCENARIO –GRAB DREDGING FOR SEAWATER INTAKE AND
DISCHARGE OUTFALL
The dredging operations for the seawater intake and discharge outfall will be
carried out by one closed grab dredger. The estimated maximum dredged
volumes are approximately 20,000 m3 for each of the seawater intake and
discharge outfall. Working hours are assumed to be 16 hours per day with a
maximum dredging rate of 4,000 m3/day (i.e. 0.069 m3/s) per dredger, giving
a rate of release (in kg/s) of sediment for one dredger as follows:
Loss Rate (kg/s)
= Dredging Rate (m3/s) * Loss Rate (kg/m)
= 0.069 m3/s * 17 kg/m3
= 1.1806 kg/s
Therefore a continuous release rate of 1.1806 kg/s for one dredger will be
adopted in the model for release throughout the whole water column. Given
the small extent of marine dredging area, one stationary source at the
seawater intake and another stationary source at the discharge outfall are
assumed in the model to represent the grab dredger. It should be noted that
while the whole dredging would last for only 5 days at the assessed peak
dredging rate (20,000 m3 ÷ 4,000 m3/day = 5 day) for dredging at both
locations, the modelled sediment release would last for a whole 15-day spring-
neap cycle to ensure all possible worst-case tidal conditions are included in
the simulation. The sediment plume modelling period would last for one
more spring-neap cycle (total simulation period: 30 days) to allow sufficient
time for any suspended solid release to reach the potential WSRs.
For a conservative worst-case assessment it is assumed no silt curtain would
be installed to contain the sediment loss from the marine dredging under
unmitigated scenario. There will be no concurrent marine dredging at the
proposed discharge outfall and seawater intake and the marine construction at
these two locations would be modelled in two separate scenarios. Table 3.3
summarises the inputs defined in the sediment dispersion simulation for
construction phase modelling scenario.
Table 3.3 Summary of Model Inputs for Construction Phase Sediment Dredging at
Seawater Intake and Discharge Outfall
Emission Point Dredging for Seawater Intake and
Submarine Outfall
No. of Working Plant 1 Grab Dredger with a grab size of 12 or
16m3
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Dredging Rate m3/day/plant 4,000
Operation Duration hours 16
Loss Type Continuous
Loss Rate Kg/m3 17
Loss Rate Kg/s 1.1806
Input Layer Whole Column
3.6 SEDIMENT INPUT PARAMETERS
For simulating sediment impacts the following general parameters will be
assumed:
Settling velocity – 0.5 mm/s
Critical shear stress for deposition – 0.2 N/m2
Critical shear stress for erosion – 0.3 N/m2
Minimum depth where deposition allowed – 0.1 m
Resuspension rate – 30 g/m2/d
The above parameters have been used to simulate the impacts from sediment
plumes in Hong Kong associated with uncontaminated mud disposal into the
Brothers MBA (1) and dredging for the Permanent Aviation Fuel Facility at Sha
Chau (2). The critical shear stress values for erosion and deposition were
determined by laboratory testing of a large sample of marine mud from Hong
Kong as part of the original Water Quality and Hydraulic Mathematical
Model (WAHMO) studies associated with the new airport at Chek Lap Kok.
(1) Mouchel (2002a). Environmental Assessment Study for Backfilling of Marine Borrow Pits at North of the Brothers.
Environmental Assessment Report.
(2) Mouchel (2002b). Permanent Aviation Fuel Facility. EIA Report. Environmental Permit EP-139/20
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4 OPERATION PHASE
4.1 IDENTIFICATION OF POTENTIAL SOURCES OF IMPACT
Increase in thermal discharge from the additional CCGT units would be the
potential source of water quality impact during in the operation phase.
Computational modelling using Delft3D FLOW would be conducted to
simulate the potential change in thermal plume due to the operation of the
additional CCGT units.
As per the current practice at BPPS, electrochlorination of seawater would be
conducted to control biofouling of the cooling water system. Maximum
residual chlorine level is 0.5 mg/L for cooling water discharge from the
existing plant. The level of residual chlorine in the thermal discharge of the
proposed CCGT units is expected to be of similar level. The dispersion and
decay of residual chlorine would be simulated using Delft3D-WAQ as a
decayable tracer. A past HK study by the City University of Hong Kong (1)
suggested that ecotoxicity may arise at marine ecological WSRs for residual
chlorine level above 0.02 mg/L. This would be adopted as the assessment
criterion for marine ecological WSRs under this EIA.
There are other potential waste streams from the operation of the additional
CCGT units, which include (1) plant effluent, (2) site runoff, and (3) sewage
effluent from workforce. These waste streams are considered incremental to
the existing streams from the operation. Existing measures are available for
handling these waste streams and no major water quality impacts from these
waste streams are expected. The potential issues with these waste streams
would be qualitatively assessed in the EIA and would not be further discussed
in this document.
The “No Net Increase in Pollution Load in Deep Bay” policy will be observed
when controlling any additional runoff or effluent discharging into the Deep
Bay Water Control Zone. Measures will be taken to control the overall loads
discharging into the Deep Bay Water Control Zone to ensure compliance with
the policy. These measures will be discussed in detail in the water quality
section of the EIA report.
Based on the latest design information, there will be a new chemical storage
for the operation of the additional CCGT units. Well-established existing
safety and control measures would be implemented to minimize the risk of
leaks and spillages associated with storage and handling of chemicals at the
new chemical store. As sufficient existing protection measures would be
provided at the new chemical storage, no significant increase in the risk of
chemical spillage would be expected. On the other hand, fuel spillage from
CCGT units is not considered a major water quality issue because natural gas
1 Tender Ref. WP 98-567 Provision of Service for Ecotoxicity Testing of Marine Antifoulant – Chlorine in Hong Kong Final
Report January 2000. Submitted to Environmental Protection Department by the Centre for Coastal Pollution and
Conservation, City University of Hong Kong.
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used in CCGT vaporizes at ambient temperature. Boiling point of the main
component in natural gas, methane, boils at −161.6°C at 1 atmospheric
pressure. In view of the above, the potential issues associated with any
chemical spillage from the operation of the additional CCGT units would be
qualitatively assessed in the EIA and would not be further discussed in this
document.
Maintenance dredging at the intake and outfall is expected to be conducted
every 4 to 5 years to avoid siltation from affecting the normal operation of the
intake and outfall. The footprint for maintenance dredging would be similar
to that of the sediment removal duration of construction phase. It is
anticipated that the scale of dredging required for maintenance dredging
would be much smaller than that of the dredging in the construction phase.
The production rate for maintenance dredging would also be lower as a result
of thinner layer of deposited sediment that needs to be dredged. Therefore
the potential extent of water quality impact from maintenance dredging is
anticipated to be less than that of the construction phase dredging. The
prediction for water quality impact from construction phase dredging would
be referred for the maintenance dredging and additional modelling is
considered not required.
4.2 ASSESSMENT CRITERIA FOR OPERATION PHASE
Table 4.1 Summary of Assessment WQO Criteria for Operation Phase
Parameters (1) Inner Deep Bay Outer Deep Bay North Western
Temperature Not to change the natural ambient level by 2°C
As discussed in the previous section, assessment criterion of 0.02 mg/L would
be adopted for total residual chlorine (TRC) for marine ecological WSRs under
this Study. Other WSRs, such as cooling water intakes and bathing beaches
are not sensitive to TRC and this criterion would not be applicable to these
non-ecological WSRs.
4.3 OPERATION PHASE THERMAL DISCHARGE
The characteristics of thermal discharge from the existing and additional
CCGT units are summarized in Table 4.2.
Table 4.2 Characteristics of Thermal Discharge from BPPS
Effluent Characteristic From Existing 8 CCGT
Units
(from existing WPCO
discharge permit)
From Proposed CCGT Unit
(per unit)
Flow (m3/day) 4,600,000 950,400
Maximum Discharge Temperature
(°C)
40 40
Maximum total residual chlorine 0.5 mg/L 0.5 mg/L
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Based on the latest design information, the proposed discharge outfall for the
2nd CCGT unit would be located at the seawall next to the existing outfall.
The existing and proposed outfalls are both box culvert located at the top of
the water column (at about 2 mPD, just below the highest astronomical tide
level). Since the thermal discharge is expected to be slightly less dense than
the ambient seawater, the thermal plume will tend to remain on the surface
layer of the water column. This will be simulated accordingly in the Delft3D-
FLOW and WAQ modelling exercise.
4.4 OPERATION PHASE MAINTENANCE DREDGING
As discussed in the previous section, maintenance dredging is anticipated to
be required at the seawater intake and outfall during the operation phase of
the second additional CCGT unit. The scale of maintenance dredging and
potential water quality impact associated would be sufficiently covered by the
prediction for the construction phase dredging. No additional water quality
modelling exercise would be required.
4.5 MODELLING SCENARIOS FOR OPERATION PHASE
For the study of operational effects, the approach requires several steps:
1) Running Delft3D-FLOW model without any thermal discharge to provide
ambient condition water temperature.
2) Running Delft3D-FLOW model with adapting the operation of the
existing BPPS (i.e. no additional CCGT units) discharge condition
covering a spring-neap cycle.
3) Running Delft3D-FLOW model with adapting the operation of the future
operation of BPPS (i.e. existing units and proposed CCGT units) discharge
condition covering a spring-neap cycle. The change in water
temperature at the nearby WSRs predicted (from modelling prediction
under step 1 to step 3) would be assessed against the WQO criteria
accordingly.
4) Running Delft-WAQ model to simulate the dispersion and decay of TRC
explicitly. In the modelling process, it is assumed that TRC will be
modelled as decayable tracer with decay value T90 = 8289s, which were
adopted in both EIAs of HATS 2A (1) and Express Rail Link (2). This T90
factor is the most conservative value and upon our review of relevant past
EIA studies.
(1) ENSR Asia (HK) Ltd (2008). Harbour Area Treatment Scheme Stage 2A EIA Study – Investigation. Environmental Impact
Assessment Report.
(2) AECOM Asia Co. Ltd (2009). Environmental Impact Assessment of Hong Kong Section of Guangzhou-Shenzhen-Hong Kong
Express Rail Link. Environmental Impact Assessment Report.
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5 CUMULATIVE IMPACTS
According to publicly available sources, a list of identified projects in the
vicinity of BPPS is summarized below in Table 5.1.
Table 5.1 Nearby Projects Identified
Project Duration Location Major Marine
Activity
Engineering Feasibility Study
for Industrial Estate at Tuen
Mun Area 38 (EPD Study Brief
ESB-277/2014)
Construction:
2019 to 2023
Tuen Mun Area 38
(3 km away)
(1) Construction of
submarine outfall
(2) Treated sewage
effluent discharge
from new sewage
treatment works
West New Territories (WENT)
Landfill Extensions (Register
No.: AEIAR-147/2009)
Uncertain West New
Territories (WENT)
Landfill (2 km
away)
nil
Expansion of Hong Kong
International Airport into a
Three-Runway System
(Register No.: AEIAR-
185/2014)
Construction:
2015 to 2023
HKIA and the
marine waters north
to the HKIA (> 8 km
away)
(1) Marine ground
treatment, seawall
construction,
reclamation for the
proposed third
runway
(2) Dredging for
approach beacons and
submarine cable field
joint excavation
(3) Cooling water
intake and thermal
discharge
Pyrolysis Plant at EcoPark
(EPD Study Brief ESB-
259/2013)
Construction:20
15
EcoPark of Tuen
Mun (4.5 km away)
Nil
Potential Reclamation Site at
Lung Kwu Tan
Uncertain Lung Kwu Tan (1.5
km away)
Reclamation
Enhanced Ash Utilisation and
Water Management Facilities
at Castle Peak Power Station
(CPPS) (EP-441/2012)
Construction:
2016 to 2019
Castle Peak Power
Station (3 km away)
Nil
Decommissioning of West
Portion of the Middle Ash
Lagoon at Tsang Tsui, Tuen
Mun (Register No.: AEIAR-
186/2015)
Decommission:
September 2015
to March 2016
Tsang Tsui Ash
Lagoon (1 km away)
Nil
Sludge Treatment Facilities (STF)
(Register No. AEIAR-
129/2009)
Existing
operation
Tsang Tsui (1.5 km
away)
Nil
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Project Duration Location Major Marine
Activity
Permanent Aviation Fuel
Facility (PAFF) for Hong Kong
International Airport (Register
No.: AEIAR-107/2007)
Existing
operation
Castle Peak, Tuen
Mun (4.5 km away
from)
Nil
Black Point Power Station
(BPPS)
Existing
operation
At the immediate
vicinity
Cooling water
discharge
Castle Peak Power Station
(CPPS)
Existing
operation
Castle Peak, Tuen
Mun (4 km away
from)
Cooling water
discharge
Green Island Cement Plant
Existing
operation
Castle Peak, Tuen
Mun (4 km away
from)
Nil
Shiu Wing Steel Mill Existing
operation
Castle Peak, Tuen
Mun (4 km away
from)
Nil
5.1 ENGINEERING FEASIBILITY STUDY FOR INDUSTRIAL ESTATE AT TUEN MUN AREA
38 (EPD STUDY BRIEF ESB-277/2014)
The proposed development of the industrial estate at Tuen Mun Area 38
includes the development of an industrial estate with temporary loading and
storage of petrochemical feedstock site and other road modification works in
Tuen Mun Area 38 and is currently under EIA stage. This potential
concurrent project is more than 3 km away from the BPPS, and its construction
period is tentatively scheduled from 2019 to 2023.
Based on the project information provided in its project profile, sewage
generated by development onsite would potentially be treated onsite by a new
sewage treatment plant. Accordingly, a new submarine sewage outfall
would be constructed together with the new sewage treatment plant. Since
there is no direct discharge of (treated or untreated) sewage into marine water
under this Project, the only potential cumulative impact from the proposed
development of the industrial estate at Tuen Mun Area 38 would be the water
quality impact from the potential marine construction of submarine sewage
outfall. Letter has been issued to the corresponding project proponent (the
Hong Kong Science and Technology Parks Corporation) to confirm the need
of construction of marine sewage outfall, the construction period and other
details. The potential cumulative impact from the marine construction of the
proposed development of the industrial estate at Tuen Mun Area 38 would be
taken into account in the construction phase water quality impact assessment
if there will be concurrent marine construction.
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5.2 WEST NEW TERRITORIES (WENT) LANDFILL EXTENSIONS (REGISTER NO.:
AEIAR-147/2009)
This WENT landfill extension is approximately 2 km away from the BPPS, and
is likely to commence in the near future, but the programme remains
uncertain. Based on the approved EIA, there will not be any direct discharge
of sewage or landfill leachate from the expanded operation. All additional
landfill leachate would be collected and treated in local sewage treatment
plants. Treated effluent would be diverted to the North Western New
Territory Sewage Outfall at the Urmston Road (3.5 km away from Project site).
No thermal discharge or discharge of chlorine or biocide would be involved.
No cumulative water quality impact is expected.
5.3 EXPANSION OF HONG KONG INTERNATIONAL AIRPORT INTO A THREE-RUNWAY
SYSTEM (REGISTER NO.: AEIAR- 185/2014)
The proposed 3RS-HKIA is over 8 km away from the BPPS, and its
construction would be commenced tentatively in 2015 to 2023. Major marine
construction works include (1) marine ground treatment such as deep cement
mixing and sand compaction pile at contaminated mud pits, (2) construction
of seawall at the perimeter of the proposed land formation, (3) filling for
reclamation; (4) dredging for installation of approach beacons and (5)
dredging for submarine cable field joint installation. Based on the approved
EIA, the marine construction works would be conducted from late 2015 to
2021. Based on the information available at the time of report, it is not
expected that the marine construction under this Project would be conducted
concurrently with those under the 3RS-HKIA. Therefore, cumulative impact
from the construction of 3RS-HKIA is not expected. To ensure the potential
change in flow regime due to the presence of reclamation for 3RS-HKIA
would be taken into account in the operation phase modelling of thermal
discharge and residual chlorine, the updated coastline taking into account of
the 3RS-HKIA would be adopted in the model.
5.4 PYROLYSIS PLANT AT ECOPARK (EPD STUDY BRIEF ESB-259/2013)
The proposed pyrolysis plant at EcoPark is project consists of four 5-tonne
pyrolysis furnace systems, with each system having a handling capacity of 5
tonnes of waste plastics per day. It is currently under the EIA stage and
construction is expected to commence in 2015. It is located approximately 4.5
km away from BPPS. No marine works would be required for the pyrolysis
plant development. Based on its EIA Project Profile, the cooling water for the
pyrolysis plant would be reused in closed circuit system. Therefore, no
thermal discharge and discharge of associated chlorine or biocides would be
expected. No cumulative impact with the construction and operation of the
proposed additional CCGT units is expected.
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5.5 POTENTIAL RECLAMATION SITE AT LUNG KWU TAN
This site is located along the coastal waters of Lung Kwu Tan and Lung Kwu
Sheung Tan. With an area of about 200 – 300 ha, this proposed site would
potentially be used for residential development (1). Information on project
implementation is very limited. A cumulative environmental study
(Cumulative Environmental Impact Assessment for the Three Potential Reclamation
Sites in Western Waters) was conducted to assess the potential impact from the
reclamations at three potential sites in the western water and Lung Kwu Tan
was one of the potential sites assessed under the cumulative study. There is
no known potential period of construction. In view of the lack of
information, the potential cumulative impact from the construction of the
reclamation at Lung Kwu Tan would not be taken into account for
construction. However, the potential change in flow regime would be taken
into account in the operation phase modelling assessment in view of the long
term operation of the new CCGT units.
5.6 ENHANCED ASH UTILISATION AND WATER MANAGEMENT FACILITIES AT CASTLE
PEAK POWER STATION (CPPS) (EP-441/2012)
The Enhanced Ash Utilisation and Water Management Facilities at Castle
Peak Power Station involves the re-construction of the two existing water
lagoons at CPPS by lowering their base slabs and the construction of a new
one to increase the storage capacities of the water lagoons at CPPS. The
water lagoons are used for temporary storage of storm water runoff collected
from the coal stockyard and process water from the operation of the CPPS
which in turn can be reused for the operation of the CPPS. The project is
expected to be constructed between 2016 and 2019. It is more than 3 km
away from the BPPS site. No marine construction would be required. No
discharge of effluent, cooling water, chlorine or biocide would be required for
project operation. No accumulative water quality impact would be expected.
5.7 DECOMMISSIONING OF WEST PORTION OF THE MIDDLE ASH LAGOON AT TSANG
TSUI, TUEN MUN (REGISTER NO.: AEIAR-186/2015)
The Decommissioning of West Portion of the Middle Ash Lagoon at Tsang
Tsui, Tuen Mun involves the decommissioning of the pulverized fuel ash
(PFA) lagoon at the west portion of the Middle Ash Lagoon at Tsang Tsui,
Tuen Mun, which was operated by CAPCO for the placement of water and
PFA. The decommissioning will provide buildable land for future
developments by the HKSAR Government. The tentative decommissioning
period would be from September 2015 to March 2016. The project site is
about 1 km away from the BPPS site. No marine construction works would
be involved. Since this is a decommissioning project, there will not be an
operation phase and no discharge of cooling water, chlorine or biocide would
(1) https://www.fccihk.com/files/dpt_image/5_committees/Infrastructure/ELSS%20-
%20Briefing%20French%20Chamber%20(140120).pdf
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be expected after the completion of construction phase. No cumulative water
quality impact would be expected.
5.8 SLUDGE TREATMENT FACILITIES (STF) (REGISTER NO. AEIAR-129/2009)
The STF is located 1.5 km away from BPPS. It serves to treat dewatered
sewage sludge from the public sewage treatment works by high temperature
incineration and reduce the volume of sludge requiring final disposal at
landfill by up to 90% through the thermal process (1). The sewage effluent
from the STF operation would be treated and reused onsite. No sewage
discharge would be required. A small scale desalination plant is installed
onsite with saline discharge of about 1,000 m3/day at about 1.7 times salinity
of ambient seawater salinity. The discharge rate is quite low (about 11.6 L/s)
and is considered negligible from 1.5 km away. The seawater intake for the
desalination plant would be taken into account in the modelling exercise as a
WSR (SR16). No cumulative water quality impact from the operation of STF
would be expected.
5.9 PERMANENT AVIATION FUEL FACILITY (PAFF) FOR HONG KONG INTERNATIONAL
AIRPORT (REGISTER NO.: AEIAR-107/2007)
The PAFF is located about 4.5 km away from BPPS. It consists of a tank farm
providing jet fuel to the Hong Kong International Airport via submarine fuel
pipelines. There is no routine discharge of wastewater or contaminated
surface drainage to sea or surface watercourse in the operational phase.
Sewage from site offices is stored in a sump pit and be removed by specialist
contractor with tanker. There is no discharge of cooling water, chlorine or
biocide. No cumulative water quality impact from the operation of PAFF is
expected.
5.10 BLACK POINT POWER STATION (BPPS)
The proposed additional CCGT units are located within the BPPS. The
thermal discharge from the existing operation of the BPPS would be taken into
account in the construction and operation phase modelling exercise. The
existing discharge from the BPPS is taken into account in both the construction
and operation phase sediment plume modelling and thermal discharge
modelling. The existing seawater intake of the BPPS would be taken into
account as WSR (SR4) in the water quality modelling exercise. Also, the
thermal discharge from existing CCGT units at the BPPS would also be
modelled in the baseline and operation scenarios.
(1) http://www.epd.gov.hk/epd/english/environmentinhk/waste/prob_solutions/WFdev_TMSTF.html
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5.11 CASTLE PEAK POWER STATION (CPPS)
CPPS is a coal-fired power plant located in Tap Shek Kok in Tuen Mun,
approximately 4 km away from BPPS. The operation of CPPS is regulated
under a Specified Process licence. The existing discharge from the CPPS is
taken into account in both the construction and operation phase sediment
plume modelling and thermal discharge modelling. The existing seawater
intake of the CPPS would be taken into account as WSR (SR9) in the water
quality modelling exercise. Also, the thermal discharge from the existing
CCGT units at the BPPS would also be modelled in the baseline and operation
scenarios.
5.12 GREEN ISLAND CEMENT PLANT
This site produces cement and is operating under a Specified Process licence.
It is more than 4 km away from the BPPS site. There is no known discharge
of cooling water, chlorine or biocide to marine water from this current
operation (1). No cumulative water quality impact from the operation of the
Green Island Cement Plant is expected.
5.13 SHIU WING STEEL MILL
This site manufactures steel bars is operating under a Specified Process
licence. It is more than 4 km away from the BPPS site. There is no known
discharge of cooling water, chlorine or biocide to marine water from this
current operation. No cumulative water quality impact from the operation of
the Shiu Wing Steel Mill is expected. The seawater intake for Shiu Wing Steel
Mill is taken into account as a WSR (SR10) in the water quality modelling
exercise.
1 http://www.gich.com.hk/Facilities/f_manflow.htm
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6 MODEL SCENARIOS
The water quality modelling exercise will commence with the set-up of
hydrodynamic baseline models (covering a complete spring/neap cycle for
both the dry and wet seasons). It will be conducted with regard to two main
components, construction phase and operation phase as detailed below.
Construction Phase: the assessment will examine potential water quality
impacts arising from sediment dredging at the works area of seawater
intake and discharge outfall, with total volume of sediment removal of
about 20,000 m3 at each of the dredging location ;
Operation Phase: the assessment will examine potential water quality
impacts arising primarily from the increase in discharge of cooling water
from the operation of the proposed CCGT units via the outfall.
Table 6.1 summarizes the proposed water quality modelling scenarios below:
Table 6.1 Proposed Delft3D Modelling Scenarios
Scenario
ID
Project Phase Project Activity Seasons
Delft3D FLOW Model
W01 FLOW model for baseline Baseline Model (no thermal discharge) Wet Season
D01 Dry Season
W02 FLOW model for existing
operation
Existing thermal discharge Wet Season
D02 Dry Season
W03 FLOW model for expanded
operation
Expanded thermal discharge Wet Season
D03 Dry Season
Delft3D WAQ Model
W04 Construction phase (existing
thermal discharge)
Marine dredging at seawater intake
(4,000 m3/day)
Wet Season
D04 Dry Season
W05 Construction phase (existing
thermal discharge)
Marine dredging at discharge outfall
(4,000 m3/day)
Wet Season
D05 Dry Season
W06 Operation phase (expanded
thermal discharge)
TRC discharge under expanded
thermal discharge
Wet Season
D06 Dry Season