Water Quality Modelling Method Statement...modelling exercise. 1.5 COASTLINE CONFIGURATIONS &...

Annex 7B

Water Quality Modelling

Method Statement

ENVIRONMENTAL RESOURCES MANAGEMENT CASTLE PEAK POWER COMPANY LIMITED

0308057_WQ MODELLING_REV 1.DOCX 8 OCTOBER 2015

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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;

http://www.epa.gov/waterscience/criteria/wqctable



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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



18

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



19

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.



20

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



21

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.



22

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



23

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.



24

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.



25

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

https://www.fccihk.com/files/dpt_image/5_committees/Infrastructure/ELSS%20-%20Briefing%20French%20Chamber%20(140120).pdf

https://www.fccihk.com/files/dpt_image/5_committees/Infrastructure/ELSS%20-%20Briefing%20French%20Chamber%20(140120).pdf



26

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



27

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

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