7 WATER QUALITY 7.1 INTRODUCTION · Systems, Inland and Coastal Waters (TM-ICW) All discharges from...

ENVIRONMENTAL RESOURCES MANAGEMENT CASTLE PEAK POWER COMPANY LIMITED

0308057_S7_WATER_REV 3.DOCX APRIL 2016

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7 WATER QUALITY

7.1 INTRODUCTION

This Section presents an evaluation of the potential water quality impacts

from the construction and operation of the proposed additional CCGT units at

the BPPS. Mathematical modelling has been used to predict potential

impacts to water quality, the results of which have then been assessed with

reference to the relevant environmental legislation, standards and tolerance

criteria.

7.2 RELEVANT LEGISLATION & GUIDELINES

The following legislation and relevant guidance or non-statutory guidelines

are applicable to the evaluation of water quality impacts associated with the

construction and operation of the Project:

Water Pollution Control Ordinance (WPCO);

Technical Memorandum for Effluents Discharged into Drainage and Sewerage

Systems, Inland and Coastal Waters (TM- ICW);

Environmental Impact Assessment Ordinance (EIAO) and the Technical

Memorandum on EIA Process (EIAO-TM), Annexes 6 and 14; and

Practice Note for Professional Persons, Construction Site Drainage (ProPECC

PN1/94).; and

Town Planning Board Guidelines for Application for Developments within Deep

Bay Area under Section 16 of the Town Planning Ordinance (TPB PG-No.

12C).

7.2.1 Water Pollution Control Ordinance (WPCO)

The Water Pollution Control Ordinance (WPCO) is the primary legislation for the

control of water pollution and water quality in Hong Kong. Under the

WPCO, Hong Kong waters are divided into 10 Water Control Zones (WCZs).

Each WCZ has a designated set of statutory Water Quality Objectives (WQO).

The proposed Project is located close to the boundary between the Deep Bay

WCZ and North Western WCZ. Location of the additional CCGT units is

shown in Figure 3.1. The applicable WQOs for these two WCZs are

presented below in Table 7.1.



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Table 7.1 Water Quality Objectives Applicable to this Water Quality Impact Assessment

Water Quality Objective Deep Bay WCZ North Western WCZ

A. AESTHETIC APPEARANCE

a) Waste discharges shall cause no objectionable odours or discolouration of the water.

Whole zone

Whole zone (including North Western Supplementary Zone)

b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any

other substances should be absent.

Whole zone Whole zone (including North Western

Supplementary Zone)

c) Mineral oil should not be visible on the surface. Surfactants should not give

rise to a lasting foam.


Supplementary Zone)

d) There should be no recognisable sewage-derived debris. Whole zone Whole zone (including North Western Supplementary Zone)

e) Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be

absent.

Whole zone Whole zone

(including North Western Supplementary Zone)

f) Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.

Whole zone Whole zone

(including North Western Supplementary

Zone)

B. BACTERIA

a) The level of Escherichia coli should not exceed 610 per 100 mL, calculated as

the geometric mean of all samples collected in one calendar year.

Secondary Contact Recreation Subzone and

Mariculture Subzone

Secondary Contact Recreation Subzone and

North Western Supplementary Zone

b) The level of Escherichia coli should not exceed 180 per 100 mL, calculated as

the geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar

month at intervals of between 3 and 14 days.

Yung Long Bathing Beach Subzone

Bathing Beach Subzone

D. DISSOLVED OXYGEN

a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4

mg per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.

Inner Marine Subzone excepting Mariculture

Subzone

-

b) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the year; values should be calculated as water column average. In addition, the concentration of

dissolved oxygen should not be less than 2 mg per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.

Outer Marine Subzone excepting Mariculture Subzone (water column average specified as arithmetic mean of at least 2 measurements at

1 metre below surface and 1 metre above seabed)

Marine Waters (water column average specified as arithmetic mean of at least 3 measurements at 1 metre below surface, mid-

depth and 1 metre above seabed); and North Western Supplementary Zone

c) The dissolved oxygen level should not be less than 5 mg per litre for 90% of

the sampling occasions during the year; values should be taken at 1 metre below surface.

Mariculture Subzone

-

E. pH



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a) The pH of the water should be within the range of 6.5 - 8.5 units. In addition, waste discharges shall not cause the natural pH range to be

extended by more than 0.2 units.

Marine waters excepting Yung Long Bathing Beach Subzone

Marine waters (including North Western Supplementary Zone)

excepting Bathing Beach Subzones

b) The pH of the water should be within the range of 6.0 - 9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range

to be extended by more than 0.5 units.

Yung Long Bathing Beach Subzone

Bathing Beach Subzones

F. TEMPERATURE

Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 °C.

Whole zone Whole zone (including North Western Supplementary Zone)

G. SALINITY

Waste discharges shall not cause the natural ambient salinity level to change by

more than 10%.


Supplementary Zone)

H. SUSPENDED SOLIDS

a) Waste discharges shall neither cause the natural ambient level to be raised by

30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities.

Marine waters Marine waters (including North Western

Supplementary Zone)

I. AMMONIA

The un-ionized ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean).

Whole zone Whole zone (including North Western Supplementary Zone)

J. NUTRIENTS

a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.

Inner and Outer marine Subzones


b) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 mg per litre, expressed as annual water

column average (arithmetic mean of at least 3 measurements at 1m below surface, mid-depth and 1m above seabed).

- Castle Peak Bay Subzone

c) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.7 mg per litre, expressed as annual mean.

Inner Marine Subzone

-

d) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg per litre, expressed as annual water

column average.

Outer Marine Subzone (water column average specified as arithmetic mean of at least 2

measurements at 1 metre below surface and 1 metre above seabed)


excepting Castle Peak Bay Subzone (water column average specified as arithmetic mean

of at least 3 measurements at 1m below surface, mid-depth and 1m above seabed)

K. 5-DAY BIOCHEMICAL OXYGEN DEMAND



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a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone

and Water Gathering Ground Subzones

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground

Subzones)

b) Waste discharges shall not cause the 5-day biochemical oxygen demand to

exceed 5 milligrams per litre.

Yuen Long & Kam Tin (Lower) Subzone and

other inland waters

Other Inland waters

L. CHEMICAL OXYGEN DEMAND

a) Waste discharges shall not cause the chemical oxygen demand to exceed 15

milligrams per litre.

Yuen Long & Kam Tin (Upper) Subzone, Beas

Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

Tuen Mun (A), Tuen Mun (B) and Tuen Mun

(C) Subzones and Water Gathering Ground Subzones)

b) Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Other Inland waters

M. TOXINS

a) Waste discharges shall not cause the toxins in water to attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in

humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to interactions of toxic substances with each other.

Whole zone


b) Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.

Whole zone


N. PHENOLS

Phenols shall not be present in such quantities as to produce a specific odour, or

in concentration greater than 0.05 mg per litre as C6H5OH.

Yung Long Bathing Beach Subzone Bathing Beach Subzones

O. TURBIDITY

Waste discharges shall not reduce light transmission substantially from the

normal level.

Yung Long Bathing Beach Subzone Bathing Beach Subzones



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7.2.2 Technical Memorandum for Effluents Discharged into Drainage and Sewerage

Systems, Inland and Coastal Waters (TM-ICW)

All discharges from the construction and operation phases of the proposed

Project are required to comply with the Technical Memorandum Standards for

Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal

Waters (TM-ICW) issued under Section 21 of the WPCO.

The TM-ICW defines acceptable discharge limits to different types of receiving

waters. Under the TM-ICW, effluents discharged into the drainage and

sewerage systems, inshore and coastal waters of the WCZs are subject to

pollutant concentration standards for specified discharge volumes. These are

defined by the Environmental Protection Department (EPD) and are specified

in licence conditions for any new discharge within a WCZ.

7.2.3 Technical Memorandum on Environmental Impact Assessment Process

(EIAO-TM)

Annexes 6 and 14 of the EIAO-TM provide general guidelines and criteria to be

used in assessing water quality impacts.

The EIAO-TM recognises that, in the application of the above water quality

criteria, it may not be possible to achieve the WQO at the point of discharge as

there are areas which are subject to greater impacts (which are termed by the

EPD as the mixing zones), where the initial dilution of the discharge takes

place. The definition of this area is determined on a case-by-case basis. In

general, the criteria for acceptance of the mixing zones are that it must not

impair the integrity of the water body as a whole and must not damage the

ecosystem.

7.2.4 Practice Note for Professional Persons, Construction Site Drainage

Apart from the above statutory requirements, the Practice Note for Professional

Persons, Construction Site Drainage (ProPECC PN 1/94), issued by EPD in 1994,

also provides useful guidelines on the prevention of water pollution

associated with construction activities.

7.2.5 Town Planning Board Guidelines for Application for Developments within

Deep Bay Area under Section 16 of the Town Planning Ordinance (TPB PG-

No. 12C)

Under TPB PG-No. 12C, any development within the Wetland Conservation

Area (WCA) or Wetland Buffer Area (WBA) stipulated under this guideline

“should not add to the pollution load of the Deep Bay Area”. It is known as

the “No Net Increase in Pollution Load in Deep Bay” policy and would be

observed for the operation phase of the development. The same requirement

is stipulated under Section 4(xi) of the EIA Study Brief for this Project. As

such, the requirement would be observed and the additional CCGT units

would be designed such that there would be no net increase in pollution load

to the Deep Bay waters during the operation phase.



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7.3 BASELINE CONDITIONS

7.3.1 Assessment Area

In accordance with the EIA Study Brief, the Assessment Area for the water

quality assessment covers the Deep Bay WCZ and the North Western WCZ

and the water quality sensitive receivers (WSRs) in the vicinity of the Project.

WSRs within 9 km from the Project were identified and described in detail in

Section 7.3.4. Water quality modelling study was conducted under this Study

using Delft3D suite of model. Fine grid models, covering the whole Deep

Bay WCZ, North Western WCZ and waters west to the HK marine boundary,

are used to study the potential change in hydrodynamic and water quality.

Details about model coverage and settings are provided in Annex 7B.

7.3.2 Marine Water Quality

Baseline marine water quality in the vicinity of the Project has been

determined through a review of EPD routine water quality monitoring data

collected between 2005 and 2014. This dataset provides Hong Kong’s most

comprehensive long-term water quality monitoring data and allows an

indication of temporal and spatial change in marine water quality in Hong

Kong. Four EPD monitoring stations are identified in the vicinity of the

Project and the locations of these stations are presented in Figure 7.1.

According to EPD’s Marine Water Quality in Hong Kong in 2014, the WQO

compliance rate of the Deep Bay WCZ in 2014 was 40%, same as from 2008 to

2013 except in 2012 (53%). Similar to the previous years, the Deep Bay WCZ

had relatively high nutrient levels in 2014. The total inorganic nitrogen (TIN)

level in the Deep Bay outer subzone (0.9 – 1.2 mg L-1) was higher than the

respective TIN objective of 0.5 mg L-1.

The collaboration of EPD with its Shenzhen counterpart in reducing pollution

load, and the voluntary farm surrender schemes for poultry and pig farms

implemented in 2005-2008 result in water quality improvement since mid-

2000s. The declining water quality trend observed during the period 1986-

2007 was reversed after 2007. A comparison of the monitoring results

collected between 1997-2006 and 2007-2014 suggests that the water quality of

Deep Bay has improved in terms of reduction in organic loading (i.e., 5-day

biochemical oxygen demand, BOD5), nutrients (e.g., ammonia nitrogen, TIN

and orthophosphate) and bacterial levels.

In 2014, the North Western WCZ attained an overall WQO compliance rate of

61% because of lower compliance with the dissolved oxygen (DO) objective

(50%) due to the hot summer weather. Compliance with unionized ammonia

(UIA) and TIN objectives in this WCZ was 100% and 33% respectively. The

higher levels of TIN (annual mean 0.42 - 0.74 mg L-1) might be associated with

the higher background level of the discharges from the Pearl River, and some

local discharges and surface run-off from the Northwest New Territories as

well as north Lantau.



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Table 7.2 Summary of EPD Routine Water Quality Monitoring Data from Selected

Stations of the Deep Bay and North Western Water Control Zones (2005 -

2014)

Parameter DM4 DM5 NM3 NM5

Temperature (C) 24.4 24.2 23.5 23.6

(15.4-31.0) (15.8-30.6) (15.2-29.6) (15.4-29.7)

Salinity (psu) 23.1 25.8 28.9 27.6

(4.3-31.6) (7.6-33.0) (18.2-33.2) (15.7-33.1)

Dissolved Oxygen (mg L-1) -

Depth Averaged

6.1 6.1 6.0 5.9

(3.3-11.2) (3.6-11.1) (3.2-9.6) (3.0-9.8)

Dissolved Oxygen (mg L-1) -

Bottom

6.0 5.9 5.7 5.6

(3.1-11.1) (3.2-10.5) (2.4-9.9) (2.1-9.5)

Suspended Solids (mg L-1) 12.9 8.4 7.8 11.1

(2.2-88.5) (1.8-36.4) (1.8-30.7) (2.0-53.8)

5-day Biochemical Oxygen

Demand (mg L-1)

0.9 0.8 0.7 0.8

(0.2-3.9) (0.2-6.4) (0.2-2.5) (0.2-2.7)

Unionised Ammonia (mg L-

1)

0.009 0.006 0.005 0.006

(0.002-0.068) (0.001-0.033) (0.001-0.013) (0.001-0.017)

Total Inorganic Nitrogen

(mg L-1)

1.19 0.87 0.53 0.67

(0.47-2.85) (0.24-2.16) (0.12-1.48) (0.13-1.94)

Orthophosphate

Phosphorus (mg L-1)

0.055 0.037 0.025 0.030

(0.006-0.135) (0.004-0.092) (0.006-0.053) (0.007-0.059)

Total Phosphorus (mg L-1) 0.08 0.06 0.05 0.05

(0.05-0.29) (0.03-0.22) (0.03-0.08) (0.03-0.11)

Chlorophyll-a (g L-1) 4.2 3.5 3.5 3.5

(0.3-43.0) (0.5-42.0) (0.5-22.0) (0.4-23.0)

Escherichia coli (cfu/100ml) 181 333 339 930

(2-5190) (40-2267) (10-9147) (11-11385)

Notes:

(a) Data presented are depth-averaged values calculated by taking the means of three depths, i.e. surface (S), mid-

depth (M) and bottom (B), except as specified.

(b) Data presented are annual arithmetic means except for E. coli, which are geometric means of depth-average values..

(c) Data in brackets indicate the ranges for the corresponding depths.

(d) Bold and underlined figures indicate non-compliance with the WQOs: DO = 4 mg L-1 for depth-averaged level, UIA

= 0.021 mg L-1, TIN = 0.5 mg L-1 for Deep Bay WCZ (Outer Subzone) and North Western WCZ.

7.3.3 Marine Sediment Quality

Baseline marine sediment quality in the vicinity of the Project has been

determined through a review of EPD routine monthly sediment quality

monitoring data collected in 2005 to 2014. Four EPD monitoring stations are

identified in the vicinity of the Project and the locations of these stations are

presented in Figure 7.1.

Sediment monitoring data from the EPD monitoring stations were compared

with the relevant sediment quality criteria specified in ADV-21 Management

Framework for Disposal of Dredged/Excavated Sediment. The EPD routine

monitoring data indicated a mild level of sediment contamination in the

vicinity of the Project. Exceedance of the Lower Chemical Exceedance Level

(LCEL) of arsenic is identified at all selected monitoring stations. Exceedance

of the Upper Chemical Exceedance Level (UCEL) for copper is identified at

monitoring station DS3 (Table 7.3).



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Sediment sampling and testing was conducted under this EIA to identify the

level of sediment contamination within the marine construction works area.

Sediment sampling locations are shown in Figure 7.2. Sediment elutriate test

was conducted using sediment samples from these sampling stations to

identify the potential of release of sediment-bounded nutrients, heavy metals

and trace organic pollutants due to disturbance from marine works under this

Project. Sediment testing and the associated elutriate testing results from the

laboratory are enclosed in Annex 7A.

The sediment testing results are compared against the LCEL and UCEL, which

show minor exceedances in LCEL for arsenic in all sediment samples (Table

7.4). This is consistent with the results of the nearby EPD sediment quality

monitoring data (and the general pattern all over Hong Kong). The sediment

elutriate test results showed no significant release of heavy metals (including

arsenic), trace organics, tributyltin, nitrate, nitrite, and total phosphorus (Table

7.5).



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Table 7.3 Summary of EPD Routine Marine Sediment Quality Monitoring Data from Selected Station of the Deep Bay and North Western

Water Control Zones (2005 - 2014)

Parameter ETWB TC(W) No. 34/2002 Guideline Deep Bay WCZ North Western WCZ

LCEL UCEL DS3 DS4 NS3 NS4

Arsenic (mg kg-1) 12 42 11.8 11.4 11.2 10.5

(5.5 - 15.0) (8.5 - 15.0) (8.3 - 14.0) (8.1 - 15.0)

Cadmium (mg kg-1) 1.5 4 0.2 0.1 0.1 0.1

(<0.1 - 0.3) (<0.1 - 0.2) (<0.1 - 0.1) (<0.1 - 0.1)

Chromium (mg kg-1) 80 160 39 33 33 30

(22 - 53) (16 - 49) (19 - 44) (22 - 47)

Copper (mg kg-1) 65 110 56 30 31 28

(12 - 230) (9 - 65) (13 - 48) (12 - 51)

Lead (mg kg-1) 75 110 45 39 39 36

(29 - 61) (24 - 58) (26 - 51) (29 - 53)

Mercury (mg kg-1) 0.5 1 0.11 0.10 0.11 0.09

(<0.05 - 0.16) (<0.05 - 0.14) (0.06 - 0.16) (<0.05 - 0.23)

Nickel (mg kg-1) 40 40 24 20 20 18

(12 - 35) (14 - 31) (11 - 26) (13 - 27)

Silver (mg kg-1) 1 2 0.3 0.1 0.1 <0.2

(<0.2 - 1.0) (<0.2 - 1.0) (<0.2 - 1.0) (<0.2 - <0.2)

Zinc (mg kg-1) 200 270 125 98 99 100

(65 - 200) (63 - 140) (62 - 130) (78 - 130)

Total Polychlorinated Biphenyls (PCBs)

(g kg-1)

23 180 18 18 18 18

(18 - 18) (18 - 18) (18 - 18) (18 - 18)

Low Molecular Weight Polycyclic Aromatic

Hydrocarbons (LMW PAHs) (μg kg-1)

550 3,160 95.7 57.5 116.5 107.1

(90.0 - 116.5) (45.0 - 169.5) (90.0 - 502.5) (90.0 - 243.5)

High Molecular Weight Polycyclic Aromatic

Hydrocarbons (HMW PAHs) (μg kg-1)

1,700 9,600 86.7 50.5 111.4 72.6

(28.5 - 276.5) (16.0 - 92.5) (24.0 - 694.0) (24.0 - 126.5)

Chemical Oxygen Demand (mg kg-1) -- -- 13155 13270 13755 13855

(9300 - 18000) (7400 - 18000) (9400 - 23000) (9100 - 19000)

Total Kjeldahl Nitrogen (mg kg-1) -- -- 351 305 366 336

(160 - 590) (100 - 560) (170 - 570) (110 - 600)

Ammonia Nitrogen (mg kg-1) -- -- 3.51 5.07 5.82 8.10

(<0.01 - 23.00) (<0.05 - 15.00) (<0.05 - 21.00) (0.11 - 28.00)



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Parameter ETWB TC(W) No. 34/2002 Guideline Deep Bay WCZ North Western WCZ

LCEL UCEL DS3 DS4 NS3 NS4

Total Phosphorus (mg kg-1) -- -- 209 175 196 184

(100 - 310) (60 - 270) (130 - 250) (77 - 260)

Notes:

Bold figures indicate non-compliance with the LCEL.

Bold and underlined figures indicate non-compliance with the UCEL

LCEL: Lower Chemical Exceedance Level; UCEL: Upper Chemical Exceedance Level

Table 7.4 Summary of Marine Sediment Quality at Sampling Stations of this EIA

Parameter (Unit) LOR LCEL UCEL IT1 IT2 OF1 Reference Sample

Silver (mg kg-1) 0.1 1 2 0.5 0.4 0.4 <0.1

Arsenic (mg kg-1) 1 12 42 14 16 15 3

Cadmium (mg kg-1) 0.2 1.5 4 0.2 0.3 <0.2 0.6

Chromium (mg kg-1) 1 80 160 50 49 48 26

Copper (mg kg-1) 1 65 110 63 53 53 13

Nickel (mg kg-1) 1 40 40 35 32 34 19

Lead (mg kg-1) 1 75 110 53 51 52 29

Zinc (mg kg-1) 1 200 270 151 137 143 69

Mercury (mg kg-1) 0.05 0.5 1 0.13 0.1 0.11 <0.05

Total PCBs (µg kg-1) 18 23 180 <18 <18 <18 <18

LMW PAHs (µg kg-1) 550 550 3160 <550 <550 <550 <550

HMW PAHs (µg kg-1) 1700 1700 9600 <1700 <1700 <1700 <1700

TBT (µg kg-1) 0.015 0.15 0.15 <0.015 <0.015 <0.015 <0.015

Notes:

Bold figures indicate non-compliance with the LCEL.

Reference sample was taken from EPD marine sediment monitoring station PS6 (HK8 coordinate: E850234 N820057).

LOR: Limit of Reporting; LCEL: Lower Chemical Exceedance Level; UCEL: Upper Chemical Exceedance Level



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Table 7.5 Summary of Sediment Elutriate Test Results at Sampling Stations of this EIA

Parameter (Unit) WQC LOR IT1 IT2 OF1

Elutriate

Blank

IT1

Elutriate

Blank

IT2

Elutriate

Blank

OF1

Mercury (µg L-1) 0.3 1 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

Arsenic (µg L-1) 25 10 <10 <10 <10 <10 <10 <10

Cadmium (µg L-1) 2.5 0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1

Chromium (µg L-1) 15 1 <1 <1 <1 <1 <1 <1

Copper (µg L-1) 5 1 <1 <1 <1 4 2 5

Lead (µg L-1) 25 1 <1 <1 <1 <1 <1 <1

Nickel (µg L-1) 30 5 2 2 2 2 1 2

Silver (µg L-1) 1.9 1 <1 <1 <1 <1 <1 <1

Zinc (µg L-1) 40 10 <10 <10 <10 <10 <10 14

Total PAHs (µg L-1) 3 3 <3 <3 <3 <3 <3 <3

Total PCBs (µg L-1) 0.03 0.03 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03

TBT (µg L-1) 0.1 0.015 <0.015 <0.015 <0.015 <0.015 <0.015 <0.015

Notes:

WQC: Water quality assessment criteria (stipulated under Table 7.10); LOR: Limit of Reporting

Elutriate blanks are conducted using only seawater taken from the sampling stations stipulated.



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7.3.4 Water Quality Sensitive Receivers

The sensitive receivers that may be affected by changes in water quality

arising from the Project are identified in accordance with the EIAO-TM. For

each of the sensitive receivers, established threshold criteria or guidelines

have been utilised for establishing the significance of impacts to water quality.

The locations of the identified WSRs are provided in Figure 7.1. The

approximate shortest distances by sea from the Project are detailed in Table

7.6.

Table 7.6 Water Quality Sensitive Receivers in the Vicinity of the Project

Description Location Model

Output

Location

Approximate Shortest

Distance by Sea from

Project (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

Transect C SR18 At the proximity of

the Project

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

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

The WSRs of this Project cover marine waters of about 9 km from the Project

by sea. Other sensitive receivers within the Deep Bay and North Western

WCZs beyond this distance are considered too far away to be affected by the



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construction and operation of the Project. They are therefore not considered

in this assessment.

It should be noted that coral identified at coral survey transect D (SR17) under

this EIA is located within the direct footprint of sediment dredging for

construction phase. The coral colony is hence expected to be removed during

project construction and therefore would not be considered in this water

quality assessment.

7.4 ASSESSMENT CRITERIA

7.4.1 Suspended Solids (SS)

Specific water quality criteria for SS level allowed at seawater intakes for the

BPPS and the Castle Peak Power Station (CPPS) are stipulated below. For all

other WSRs with no specific water quality criteria, elevation in SS

concentrations resulting from the Project’s construction and operational

activities were assessed against the WQO. The WQO for SS is defined as not

to raise the natural ambient level by 30%, nor cause the accumulation of SS

which may adversely affect aquatic communities. The assessment criterion is

hence defined as the WQO allowable increase in SS concentrations within the

corresponding WCZs.

SS data from EPD’s routine water quality monitoring programme in 2005-2014

have been analysed to determine the WQO allowable increase at the WSRs.

This is calculated as 30% of the ambient level (90th-percentile value (1)) from the

2005-2014 baseline marine water quality data. For each WSR, ambient level

was derived from the closest EPD water quality monitoring station. The

assessment criterion for SS at each WSR is summarised in Table 7.7.

Both power station intakes (SR4 and SR9) have specific requirements for

intake water quality. The applicable criteria for temperature and SS for the

BPPS and CPPS seawater intakes are below 30°C and 764 mg L-1, respectively.

In view of the relatively high level of ambient SS, the tolerance level of 700 mg

L-1 for maximum SS elevation at these two WSRs would be taken as

assessment criteria. There are no particular criteria specified for the seawater

intakes of Tuen Mun Area 38 (SR11), Shiu Wing Steel Mill (SR10) and Sludge

Treatment Facilities (SR16) and hence WQOs have been adopted (Table 7.7).

(1) The use of 90th-percentile value of baseline SS level from nearby EPD marine water quality monitoring stations are

common practices in past approved EIA, including the Black Point Gas Supply Project EIA (AEIAR-150/2010),

Development of the Integrated Waste Management Facilities Phase 1 EIA (AEIAR-163/2012) as well as the recently

approved Expansion of Hong Kong International Airport into a Three-Runway System EIA (AEIAR-185/2014).



7-14

Table 7.7 Water Quality Assessment Criteria for Suspended Solids (mg L-1) at WSRs

Sensitive Receivers Name Model

Output

Location

EPD

Station

Relevant Depth for

Assessment

Dry Season Wet Season

Ambient Level (a)

WQO

Allowable

Change

Ambient Level (a)

WQO

Allowable

Change


Oyster Production

Area

Sheung Pak Nai SR14 DM4 Depth-averaged 26.05 7.82 20.60 6.18

Recognised

Spawning/ Nursery

Grounds

Fisheries Spawning

Ground in North

Lantau

SR15 NM5 Depth-averaged 20.70 6.21 20.21 6.06

Artificial Reef

Deployment Area

Sha Chau and Lung

Kwu Chau

SR12 NM5 Bottom 32.20 9.66 36.20 10.86

Ecological Sensitive Receivers

Mangroves Ngau Hom Shek SR1 DM4 Bottom 32.30 9.69 24.00 7.20

Sheung Pak Nai SR2 DM4 Bottom 32.30 9.69 24.00 7.20

Marine Park Designated Sha

Chau and Lung

Kwu Chau




Intertidal Mudflats Ha Pak Nai SR3 DM4 Bottom 32.30 9.69 24.00 7.20

Seagrass Beds Sheung Pak Nai SR2 DM4 Bottom 32.30 9.69 24.00 7.20

Ha Pak Nai SR3 DM4 Bottom 32.30 9.69 24.00 7.20

Horseshoe Crab

Nursery Grounds

Ha Pak Nai SR3 DM4 Bottom 32.30 9.69 24.00 7.20

Ngau Hom Shek SR1 DM4 Bottom 32.30 9.69 24.00 7.20

Lung Kwu Sheung

Tan

SR5 NM5 Bottom 32.20 9.66 36.20 10.86

Coral Colonies

Identified Along

Survey Transect

under this Project

Transect C SR18 DM5 Bottom 28.30 8.49 15.00 4.50




7-15


Output

Location

EPD

Station

Relevant Depth for

Assessment


Ambient Level (a)

WQO

Allowable

Change

Ambient Level (a)

WQO

Allowable

Change

Non-gazetted

Beaches

Lung Kwu Sheung

Tan


Lung Kwu Tan SR8 NM5 Depth-averaged 20.70 6.21 20.21 6.06

Secondary

Recreation Subzone

North Western

Water Control

Zone


Seawater Intakes Black Point Power

Station

SR4 DM5 Bottom 28.30 700.00 (c) 15.00 700.00 (c)

Castle Peak Power

Station

SR9 NM5 Bottom 32.20 700.00 (c) 36.20 700.00 (c)

Tuen Mun Area 38 SR11 NM3 Bottom 18.30 5.49 20.00 6.00

Shiu Wing Steel

Mill

SR10 NM3 Bottom 18.30 5.49 20.00 6.00

Sludge Treatment

Facilities

SR16 DM5 Bottom 28.30 8.49 15.00 4.50

Notes:

(a) Ambient level is calculated as 90th percentile of the EPD routine monitoring data of 2005-2014 at respective EPD station close to the WSRs.

(b) This table is applicable for those WSRs which were assessed against the WQO.

(c) Assessment of cooling water intakes of power stations (SR4 and SR9) should refer to the specific assessment criterion of SS for this type of WSR. The

applicable criterion for SS is below 764 mg L-1. The tolerance criterion of 700 mg L-1 was adopted.



7-16

7.4.2 Sediment Deposition

Impacts to artificial reefs (SR12) as well as coral colonies identified on

shoreline of BPPS in dive survey conducted under this Study (SR18) have been

assessed with regard to sediment deposition. The assessment criterion of 200

gram per square metre per day (200 g m-2 d-1), has been used in approved EIA

Reports (1) (2) (3) and has been adopted here.

7.4.3 Dissolved Oxygen

Oxygen depletion resulting from the Project’s construction activities will be

assessed against the WQO. The assessment criterion is defined as the WQO

allowable depletion in DO levels at the WSRs. The depletion of dissolved

oxygen in the water column is not expected to affect the operation of cooling

water intakes for BPPS and CPPS (SR4 and SR9). Therefore no assessment

criteria for these two WSRs are proposed.

DO data from EPD’s routine water quality monitoring programme from 2005-

2014 have been analysed to determine WQO allowable depletion at the WSRs.

Allowable DO depletion is calculated as the ambient DO level minus the

WQO, i.e. 4 mg L-1 for depth-averaged, surface and middle layers, and 2 mg L-

1 for bottom layer. Ambient level is calculated as the 10th-percentile value

from the 2005-2014 marine water quality data for assessment against the WQO

criterion for DO (Table 7.1 refers). For each WSR, ambient level was derived

from the closest EPD water quality monitoring station. The assessment

criteria for DO at each WSR are summarised in Table 7.8.

(1) ERM – Hong Kong, Ltd (2000) EIA for Construction of an International Theme Park in Penny's Bay of North

Lantau together with its Essential Associated Infrastructures - Environmental Impact Assessment. Final EIA

Report. For Civil Engineering Department, Hong Kong SAR Government.

(2) ERM - Hong Kong, Ltd (2006) Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. For

CAPCO. Final EIA Report. December 2006.

(3) ERM - Hong Kong, Ltd (2010) Black Point Gas Supply Project. For CAPCO. Final EIA Report. Febuary 2010.



7-17

Table 7.8 Water Quality Assessment Criteria for Dissolved Oxygen (mg L-1) at WSRs


Output

Location

EPD

Station

Relevant Depth

for Assessment

Annual Dry Season Wet Season

Ambient

Level (a)

WQO

Allowable

Change

Ambient

Level (a)

WQO

Allowable

Change

Ambient

Level (a)

WQO

Allowable

Change


Oyster Production

Area

Sheung Pak Nai SR14 DM4 Depth-averaged 4.69 0.69 5.75 1.75 4.32 0.32

Recognised

Spawning/

Nursery Grounds

Fisheries

Spawning Ground

in North Lantau

SR15 NM5 Depth-averaged 4.19 0.19 5.98 1.98 3.90 - (c)

Artificial Reef

Deployment Area

Sha Chau and

Lung Kwu Chau

SR12 NM5 Bottom 3.09 1.09 5.98 3.98 2.89 0.89


Mangroves Ngau Hom Shek SR1 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Sheung Pak Nai SR2 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Marine Park Designated Sha

Chau and Lung

Kwu Chau




Intertidal Mudflats Ha Pak Nai SR3 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Seagrass Beds Sheung Pak Nai SR2 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Ha Pak Nai SR3 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Horseshoe Crab

Nursery Grounds

Ha Pak Nai SR3 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Ngau Hom Shek SR1 DM4 Bottom 4.40 2.40 5.69 3.69 4.08 2.08

Lung Kwu Sheung

Tan

SR5 NM5 Bottom 3.09 1.09 5.98 3.98 2.89 0.89

Coral Colonies

Identified Along

Survey Transect

under this Project

Transect C SR18 DM5 Bottom 4.09 2.09 6.09 4.09 3.90 1.90




7-18


Output

Location

EPD

Station

Relevant Depth

for Assessment


Ambient

Level (a)

WQO

Allowable

Change

Ambient

Level (a)

WQO

Allowable

Change

Ambient

Level (a)

WQO

Allowable

Change

Non-gazetted

Beaches

Lung Kwu Sheung

Tan


Lung Kwu Tan SR8 NM5 Depth-averaged 4.19 0.19 5.98 1.98 3.90 - (c)

Secondary

Recreation Subzone

North Western

Water Control

Zone



Station

SR4 DM5 Bottom 4.09 N/A (b) 6.09 N/A (b) 3.90 N/A (b)

Castle Peak Power

Station

SR9 NM5 Bottom 3.09 N/A (b) 5.98 N/A (b) 2.89 N/A (b)

Tuen Mun Area 38 SR11 NM3 Bottom 3.40 1.40 5.90 3.90 3.10 1.10

Shiu Wing Steel

Mill

SR10 NM3 Bottom 3.40 1.40 5.90 3.90 3.10 1.10

Sludge Treatment

Facilities

SR16 DM5 Bottom 4.09 2.09 6.09 4.09 3.90 1.90

Notes:

(a) Ambient level is calculated as 10th percentile of the EPD routine monitoring data of 2005-2014 at respective EPD station close to WSRs.

(b) This table is applicable for those WSRs which were assessed against the WQO. WQO is not applicable for the assessment of cooling water intakes for

power stations (SR4 and SR9).

(c) As stated in item D(b) under Table 7.1, the DO criteria for WQO requires depth-averaged DO criteria for 90% of incident throughout the year.

Background ambient depth-averaged DO level is below 4 mg L-1 at NM5 in wet season. Assessing potential DO depletion based on background DO

levels of two seasons at WSRs near NM5 would be too conservative in view of the low DO level in wet season. For WSRs near NM5, the assessment for

DO depletion would be made with reference to the annual baseline data.



7-19

7.4.4 Nutrients

Elevation in the levels of nutrients as a result of the Project’s construction

activities, if any, will be compared against the respective WQO. It should be

highlighted that continual exceedance in TIN was observed in Deep Bay and

North Western WCZs from 2005 to 2014 (refer to Table 7.2). Assessing the

potential elevation in TIN against the WQO criterion with such high

background level (mean TIN level from 2005 to 2014 at the four nearby EPD

marine water quality monitoring stations all exceeded 0.5 mg L-1) would be

too conservative and an alternative assessment criterion was adopted for this

EIA. The proposed allowed TIN increase from marine construction would be

limited to 1% of the WQO TIN criterion for the corresponding WCZs, which is

0.005 mg L-1 for all WSRs (1) except SR4 and SR9 (seawater intake for BPPS and

CPPS) which are not considered sensitive to elevation in TIN. The proposed

TIN elevation criteria would also be below 1% of the mean ambient level,

which is expected to be well within seasonal variation (which is significantly

affected by the Pearl River Delta discharge as stated in EPD’s Marine Water

Quality in Hong Kong in 2014). Therefore, such a short term increase in TIN

level would be insignificant in term of water quality and would be considered

acceptable.

The increase in UIA from the proposed dredging works at seawater intake

and discharge outfall was assessed against the corresponding WQO criterion

for UIA. Again, this assessment criterion does not apply to SR4 and SR9.

The proposed assessment criteria for TIN and UIA are summarised below in

Table 7.9.

Table 7.9 Proposed Assessment Criteria for Nutrients from Marine Dredging

Assessment Criteria

Deep Bay WCZ (Outer Subzone) North Western WCZ

TIN (mg L-1) 0.005 (elevation) 0.005 (elevation)

UIA (mg L-1) 0.021 (total)

0.012 (allowed elevation near DM4)

0.015 (allowed elevation near DM5)

0.021 (total)

0.016 (allowed elevation near NM3)

0.015 (allowed elevation near NM5)

Note: While the Assessment Area also covers the Deep Bay WCZ (Inner Subzone), no WSR is

identified within the Inner Subzone. Therefore no assessment criterion is proposed.

7.4.5 Water Temperature

Cooling water discharge from the proposed additional CCGT units would

result in elevation of ambient seawater temperature. The predicted elevation

in ambient seawater temperature will be assessed against the WQO for all

WSRs except for those discussed below. The WQO allowable increase in

water temperature above ambient is 2°C at WSRs.

(1) The WQO TIN criteria is 0.7 mg L-1 for Deep Bay WCZ (Inner Subzone), yet there is no WSRs identified within the part

of the Assessment Area which is located within the Subzone.



7-20

As discussed in the previous section, the optimal operation temperature for

cooling water systems for BPPS and CPPS is below 30°C. This has been

adopted for assessment under this EIA.

Coral colonies identified along survey transect under this Project (SR18) are

located very close to existing cooling water discharge outfall of BPPS. These

coral colonies are considered adapted to thermal discharge with relatively

high ambient water temperature. The proposed assessment criterion is

considered only for reference at this WSR.

7.4.6 Criteria for Dissolved Metals and Organic Compounds

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), and EIA for Hong Kong

Offshore Wind Farm in Southeastern Waters ( 5 ). Table 7.10 shows the

assessment criteria for dissolved metals and organic compounds for this

Study.

Table 7.10 Summary of Assessment Criteria for Dissolved Metals and Organic

Compounds

Parameter Unit Assessment Criteria for this EIA

Metals

Cadmium (Cd) g L-1 2.5 (a) (b)

Chromium (Cr) g L-1 15 (a) (b)

Copper (Cu) g L-1 5 (a) (b)

Nickel (Ni) g L-1 30 (a) (b)

Lead (Pb) g L-1 25 (a) (b)

Zinc (Zn) g L-1 40 (a) (c)

Mercury (Hg) g L-1 0.3 (b)

Arsenic (As) g L-1 25 (a) (b)

Silver (Ag) g L-1 1.9 (d)

Total PAHs g L-1 3.0 (f)

Total PCBs g L-1 0.03 (d)

Tributyltin (TBT) g L-1 0.1 (e)

Notes:

(1) Maunsell (2002). EIA for Decommissioning of Cheoy Lee Shipyard at Penny's Bay. For Civil Engineering

Department, Hong Kong SAR Government.

(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.

(3) Maunsell (2001). EIA for Wanchai Development Phase II - Comprehensive Feasibility Study. For Territory

Development Department, Hong Kong SAR Government.

(4) ERM - Hong Kong, Ltd (2006) EIA Study for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities.

For CAPCO. 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



7-21

(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 tributyltin (TBT) in water and hence reference has been made to the

United States Environmental Protection Agency (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-1, 3.0 μg L-1 and 0.1 μg L-1 respectively.

7.4.7 Criteria for Total Residual Chlorine

As per the current practice at BPPS, electrochlorination of seawater would be

conducted to control biofouling of the cooling water system. The same

arrangement would be adopted in the proposed additional CCGT units. The

stream of cooling water discharge would carry low level of residual chlorine

of less than or equal to 0.5 mg L-1 (which is the same as the existing thermal

discharge at BPPS) and be discharged into marine waters. Previous studies (1) (2 ) indicated adverse impacts on marine organisms may arise for total

residual chlorine (TRC) at or above 0.02 mg L-1. This criterion was adopted

in approved EIAs of Kai Tak Development (AEIAR-130/2009) and Desalination

Plant in Tseung Kwan O (AEIAR-192/2015), and was adopted as assessment

criterion in this EIA.

Seawater intakes (SR4, SR9, SR10, SR11 and SR16), non-gazetted beaches (SR5

and SR8) and secondary recreation subzone (SR8) are not considered sensitive

to TRC. No assessment criterion is proposed for these WSRs.

Coral colonies identified along survey transect under this Project (SR18) are

located very close to existing cooling water discharge outfall. These coral

colonies are considered adapted to exposure to thermal discharge and

associated level of TRC. Similarly, the horseshoe crab nursery grounds at

Lung Kwu Sheung Tan (SR5) are influenced by the cooling water discharge

(1) Langford, T. E. (1983). Electricity Generation and the Ecology of Natural Waters.

(2) 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.

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



7-22

from the nearby CPPS which contains TRC. These marine ecological

sensitive receivers are considered adapted to exposure to a background TRC

level and the proposed assessment criterion is considered only for reference at

these WSRs.

7.5 ASSESSMENT METHODOLOGY

7.5.1 General Methodology

The methodology employed to assess potential water quality impacts

associated with the construction and operation of the Project is presented in

the Water Quality Modelling Method Statement (Annex 7B) and has been

based on the information presented in the Project Description (Section 3).

Full details of the scenarios examined in the modelling works are provided in

Annex 7B. Results of model verification are provided in Annex 7C. The

WSRs assessed are presented in Figure 7.1.

7.5.2 Uncertainties in Assessment Methodology

Uncertainties in Sediment Transport Assessment

Uncertainties in the assessment of the impacts from sediment plumes have

been 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 considered in detail in Annex 7B Water Quality Modelling

Method Statement and are not further discussed here.

Uncertainties arising from Operations

Uncertainties in operation phase thermal discharge modelling have been

identified in Annex 7B Water Quality Modelling Method Statement. To ensure

robustness of modelling assessment, conservative assumptions have been

made to address the uncertainties from future operation. These assumptions

include:

Temperature and level of TRC of effluent from the additional CCGT units

were assumed to be released at their maximum level (40°C and 0.5 mg L-1)

from the plant. This ensures any fluctuation in effluent quality of

effluent from the additional CCGT units within specified limit will not

result in water quality impact beyond the modelled worst case; and

Model spin up was conducted for multiple tidal spring-neap cycles to

ensure sufficient background build-up of heat and TRC, if any, could be

captured in the modelling.



7-23

7.6 POTENTIAL SOURCES OF IMPACT

Potential sources of impacts to water quality arising from the Project may

occur during both the construction and operation phases. Each is discussed

in turn below.

7.6.1 Construction Phase

As described in Section 3, the Project would be implemented in phases for the

two additional CCGT units. No marine works would be required for the

construction of CCGT Unit No.1. Land-based construction activities of

CCGT Unit No.1 have the potential to affect water quality through land-based

site runoff, sewage effluent from construction workforce, and chemical

cleaning during pre-commissioning activities.

Should the additional CCGT Unit No.2 be installed, marine-based and land-

based construction activities have the potential to affect water quality through:

Changes in water quality, including suspended sediment dispersion,

sediment deposition, DO depletion, and elevated concentrations of

nutrients, heavy metals and micro-organic pollutants, due to marine

dredging at proposed outfall and seawater intake. Other marine

construction detailed in Section 3 and Annex 7B would not involve

significant sediment disturbance;

Vessel discharges;

Land-based site runoff;

Sewage effluent from construction workforce; and

Chemical cleaning during pre-commissioning activities.

7.6.2 Operation Phase

The potential impacts to water quality arising from the operation of the Project

have been identified as follows:

Increase in the seawater temperature and TRC level due to the increase in

cooling water discharge from the additional CCGT units;

Potential risk of fuel spill due to the operation of the additional CCGT

units;

Potential increase in pollution loads from the increased effluent from

plant and oil interceptors;

Chemical cleaning during plant operation; and



7-24

Potential water quality impact from maintenance dredging at the

proposed seawater intake and discharge outfall for the additional CCGT

Unit No.2.

7.7 IMPACT ASSESSMENT – CONSTRUCTION PHASE

Additional cooling water intake and discharge outfall may be required for the

additional CCGT Unit No.2. Marine dredging would be required for the

construction of the cooling water intake and discharge outfall. The major

potential impacts to water quality arising from this Project during the

construction phase relate to disturbances to the seabed, re-suspension of

marine sediment, and potential physio-chemical changes in the water column

from such marine dredging. Other marine construction activities related to

the construction of intake and outfall structures for the additional CCGT Unit

No.2 include installation (and removal) of cofferdam, removal (and

reinstatement) of rock armours, filling activities etc. which may also result in

disturbance to seabed. The potential impacts on water quality are, however,

expected to be far less significant than those from the dredging operation.

Therefore the potential impact on marine water quality from dredging

operation at the proposed cooling water intake and discharge outfall would be

assessed by mathematical modelling as worst case scenario for construction

phase.

7.7.1 Suspended Solids Dispersion and Sedimentation

Marine dredging near the proposed intake and outfall will not be concurrent.

Simulation results of SS elevation arising from the marine dredging at the

proposed seawater intake in both the dry and wet seasons are presented in

Table 7.11. Results for SS elevation from the marine dredging at the proposed

discharge outfall are presented in Table 7.12. It should be highlighted that the

values presented in Table 7.11 and Table 7.12 are the maximum SS elevation

throughout the simulated tidal cycle at the specified water depth for

assessment at the WSRs. The predicted SS elevation is compared with the

proposed assessment criteria described in Section 7.4.1 and Table 7.7. Contour

plots of maximum depth-averaged and bottom SS elevation over the

simulation period for dredging at seawater intake and discharge outfall in

unmitigated scenario are also provided in Annex 7D for both seasons.



7-25

Table 7.11 Predicted Maximum Elevation in Suspended Solids and Sediment Deposition

at WSRs from Marine Dredging at Seawater Intake – Unmitigated Scenario

WSR (ID) SS Elevation (mg L-1)

Sediment Deposition

(g m-2 d-1)

Dry Season Wet Season Criteria

Dry

Season

Wet

Season

Criteria Max Criteria Max Max Max


Oyster Production Area - Sheung Pak Nai (SR14) 7.82 2.1043 6.18 1.1264 - - -

Recognised Spawning/ Nursery Grounds - Fisheries

Spawning Ground in North Lantau (SR15)

6.21 0.4594 6.06 0.3992 - - -

Artificial Reef Deployment Area - Sha Chau and Lung

Kwu Chau (SR12)

9.66 0.0952 10.86 0.0691 200 2.8120 2.3965


Mangroves - Ngau Hom Shek (SR1) 9.69 0.5920 7.20 0.4838 - - -

Mangroves - Sheung Pak Nai (SR2) 9.69 3.7076 7.20 0.9238 - - -

Marine Park - Designated Sha Chau and Lung Kwu Chau

(SR6)

6.21 0.0896 6.06 0.0378 - - -


(SR7)

6.21 0.2972 6.06 0.2453 - - -


(SR13)

6.21 0.0976 6.06 0.0619 - - -

Intertidal Mudflats - Ha Pak Nai (SR3) 9.69 1.6588 7.20 1.9657 - - -

Seagrass Beds - Sheung Pak Nai (SR2) 9.69 3.7076 7.20 0.9238 - - -

Seagrass Beds - Ha Pak Nai (SR3) 9.69 1.6588 7.20 1.9657 - - -

Horseshoe Crab Nursery Grounds - Ha Pak Nai (SR3) 9.69 1.6588 7.20 1.9657 - - -

Horseshoe Crab Nursery Grounds - Ngau Hom Shek

(SR1)

9.69 0.5920 7.20 0.4838 - - -

Horseshoe Crab Nursery Grounds - Lung Kwu Sheung

Tan (SR5)

9.66 9.6917 10.86 6.7096 - - -

Coral Colonies Identified Along Survey Transect under

this Project - Transect C (SR18)

8.49 266.7900 4.50 241.8500 200 3604.8 3605.8


Non-gazetted Beaches - Lung Kwu Sheung Tan (SR5) 6.21 4.9835 6.06 3.3953 - - -

Non-gazetted Beaches - Lung Kwu Tan (SR8) 6.21 6.3219 6.06 3.4352 - - -

Secondary Recreation Subzone - North Western Water

Control Zone (SR8)

6.21 6.3219 6.06 3.4352 - - -

Seawater Intakes - Black Point Power Station (SR4) 700.00 7.0058 700.00 29.0970 - - -

Seawater Intakes - Castle Peak Power Station (SR9) 700.00 2.1536 700.00 1.5957 - - -

Seawater Intakes - Tuen Mun Area 38 (SR11) 5.49 1.3638 6.00 0.8333 - - -

Seawater Intakes - Shiu Wing Steel Mill (SR10) 5.49 1.6632 6.00 0.9952 - - -

Seawater Intakes - Sludge Treatment Facilities (SR16) 8.49 8.5693 4.50 11.1400 - - -

Note:

Bold and underlined figures indicate exceedance of WQO.



7-26


at WSRs from Marine Dredging at Discharge Outfall – Unmitigated Scenario


Sediment Deposition

(g m-2 d-1)


Dry

Season

Wet

Season






6.21 0.3933 6.06 0.2979 - - -


Kwu Chau (SR12)

9.66 0.0919 10.86 0.0625 200 2.6432 1.6105





(SR6)

6.21 0.0829 6.06 0.0328 - - -


(SR7)

6.21 0.2534 6.06 0.1743 - - -


(SR13)

6.21 0.0941 6.06 0.0456 - - -






(SR1)

9.69 1.4292 7.20 1.0506 - - -


Tan (SR5)

9.66 8.5051 10.86 5.3648 - - -



8.49 191.0800 4.50 72.4190 200 3,444.8 1,225.9





Control Zone (SR8)

6.21 3.5000 6.06 2.6116 - - -






Note:


Compliance with the corresponding assessment criteria for SS elevation and

sedimentation flux is predicted at a majority of the WSRs in both seasons. A

number of exceedances of the WQO SS elevation criterion are predicted for

dredging at the seawater intake and discharge outfall in both seasons. For

dredging at seawater intake in the dry season, the sediment plume mainly

affects WSRs along the shoreline of Deep Bay as well as the Lung Kwu Tan

embayment (Annex 7D). Elevation of SS is predicted to be above the

corresponding assessment criteria at coral colonies identified along survey

transect under this Project at Transect C (SR18), horseshoe crab nursery

ground at Lung Kwu Sheung Tan (SR5) and seawater intake for Sludge



7-27

Treatment Facilities (SR16) for dredging at seawater intake in the dry season.

For SR18, the predicted SS elevations are high because of the short distance

from the dredging area, and the corresponding maximum sedimentation flux

is predicted to exceed the assessment criterion for sedimentation. A similar

pattern of SS elevation and exceedance of the corresponding assessment

criteria is also predicted for dredging at seawater intake in the wet season.

For dredging at discharge outfall, the overall zone of influence of SS elevation

is predicted to shift to the northeast of the dredging area. The predicted SS

elevation at the Lung Kwu Tan embayment is significantly smaller due to the

longer distance from the dredging area. Also, as the dredging area for the

proposed new outfall is located northeast to the existing outfall, the discharge

from the existing outfall carries the sediment plume from the dredging area

away from the shore and dilute the sediment plume. As a result, the

predicted SS elevation is much lower for most of the WSRs. Elevation of SS

above the corresponding assessment criterion is predicted at SR16 and SR18 in

both seasons. SR18 remains the most impacted receivers in both seasons

because of the very short distance from the dredging area.

To mitigate potential impacts on SR 16 and SR18, mitigation measures in form

of silt curtain around grab dredger are proposed to be adopted for the

dredging at both the proposed seawater intake and discharge outfall. Silt

curtains are highly effective in areas where current speeds are low, but the

effectiveness of the silt curtains will be reduced in areas of high current

speeds. Hydrodynamic simulation by Delft3D indicated that tidal current

near the proposed outfall and seawater intake would be in general below 0.2

m/s, which is deemed appropriate for the use of silt curtain. According to

the Contaminated Spoil Management Study (1), the implementation of silt

curtain around the closed grab dredgers will reduce the dispersion of SS by a

factor of 4 (or about 75%). This SS reduction factors have been adopted in a

number of past studies involving release of marine sediment, including the

approved SCL Hung Hom to Admiralty Section, IWMF, WDII & CWB EIA,

CT Dredging EIA as well as the Western Coast Road EIA study.

Furthermore, the rate of dredging at the both the seawater intake and

discharge outfall is also proposed to be reduced from 4,000 m3 per day (in the

unmitigated scenario) to 740 m3 per day. Under the mitigated scenario of

this Project, the combined use of silt curtain and reduction of dredging rate

would significantly reduce the level of SS elevation at SR16 and SR18. To

provide further protection to coral colonies at SR18, an additional single layer

of floating type silt curtain is proposed to surround the coral colonies at SR18.

Similar arrangement was proposed in the approved EIA for Liquefied Natural

Gas (LNG) Receiving Terminal and Associated Facilities (2) for the protection

of nearby marine ecological and fisheries WSRs. A sediment reduction factor

of 2.5 (equivalent to 60% reduction) was assumed in the approved LNG EIA

and is also adopted in this assessment. The predicted SS elevations and

(1) Mott MacDonald (1991). Contaminated Spoil Management Study, Final Report, Volume 1, for EPD, October 1991.

(2) ERM - Hong Kong, Ltd (2006) EIA Study for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities.

For CAPCO. Register No.: AEIAR-106/2007.



7-28

sediment deposition with the implementation of silt curtains and reduced

dredging rate are presented in Table 7.13 and Table 7.14 for dredging at

seawater intake and discharge outfall respectively. Full compliance with the

corresponding assessment criteria for SS elevation and sedimentation flux is

predicted in both seasons. The corresponding instantaneous SS elevation at

depth-averaged and bottom layer of the water column on typical working day

for dredging at seawater intake and discharge outfall for mitigated scenario

are also provided in Annex 7D for both seasons.


at WSRs from Marine Dredging at Seawater Intake – Mitigated Scenario


Sediment Deposition

(g m-2 d-1)


Dry

Season

Wet

Season






6.21 0.0212 6.06 0.0185 - - -

Artificial Reef Deployment Area - Sha Chau and Lung Kwu

Chau (SR12)

9.66 0.0044 10.86 0.0032 200 0.1301 0.1108





(SR6)

6.21 0.0041 6.06 0.0017 - - -


(SR7)

6.21 0.0137 6.06 0.0113 - - -


(SR13)

6.21 0.0045 6.06 0.0029 - - -





Horseshoe Crab Nursery Grounds - Ngau Hom Shek (SR1) 9.69 0.0274 7.20 0.0224 - - -

Horseshoe Crab Nursery Grounds - Lung Kwu Sheung Tan

(SR5)

9.66 0.4482 10.86 0.3103 - - -

Coral Colonies Identified Along Survey Transect under this

Project - Transect C (SR18)

8.49 4.9356 4.50 4.4742 200 66.6888 66.7073





Control Zone (SR8)

6.21 0.2924 6.06 0.1589 - - -






Note:




7-29


at WSRs from Marine Dredging at Discharge Outfall – Mitigated Scenario


Sediment Deposition

(g m-2 d-1)


Dry

Season

Wet

Season






6.21 0.0182 6.06 0.0138 - - -

Artificial Reef Deployment Area - Sha Chau and Lung Kwu

Chau (SR12)

9.66 0.0043 10.86 0.0029 200 0.1222 0.0745





(SR6)

6.21 0.0038 6.06 0.0015 - - -


(SR7)

6.21 0.0117 6.06 0.0081 - - -


(SR13)

6.21 0.0044 6.06 0.0021 - - -





Horseshoe Crab Nursery Grounds - Ngau Hom Shek (SR1) 9.69 0.0661 7.20 0.0486 - - -

Horseshoe Crab Nursery Grounds - Lung Kwu Sheung Tan

(SR5)

9.66 0.3934 10.86 0.2481 - - -

Coral Colonies Identified Along Survey Transect under this

Project - Transect C (SR18)

8.49 3.5350 4.50 1.3398 200 63.7288 22.6792





Control Zone (SR8)

6.21 0.1619 6.06 0.1208 - - -






Note:


In conclusion, with the implementation of mitigation measures to control the

dispersion of SS, including (1) reduction from dredging rate from 4,000 m3 per

day to 740 m3 per day, (2) implementation of silt curtain at grab dredger

(which reduce sediment loss rate by 75% and (3) implementation of silt curtain

near coral colonies SR18 (which reduce sediment level at SR18 by 60%), no

unacceptable water quality impact on nearby WSRs would be expected.



7-30

7.7.2 Dissolved Oxygen Depletion

The degree of DO depletion exerted by a sediment plume is a function of the

sediment oxygen demand of the sediment, its concentration in the water

column and the rate of oxygen replenishment. The impact of the sediment

oxygen demand on DO concentrations has been calculated based on the

following equation (1):

DO (mg O2 L-1) = DO ( g O2/m3) = SS (g DW/m3) × fraction of organic matter

in sediment (g C/g DW) × 2.67 (g O2/gC)

The assumption behind this equation is that all the released organic matter is

eventually re-mineralized within the water column. This leads to an

estimated depletion with respect to the background DO concentrations. This

DO depletion depends on the quality of the released sediments, i.e. on the

percentage of organic matter in the sediment. The fraction of organic matter

in sediment (Chemical oxygen demand in Table 7.3) was taken as 18,000 mg

kg-1 based on maximum data from EPD sediment monitoring station DS4

located near the Project from 2005-2014. It should be noted that other EPD

sediment monitoring stations are much further away from the Project site (>3

km) and therefore the adoption of DS4 is deemed the most appropriate.

This is a conservative prediction of DO depletion since oxygen depletion is not

instantaneous and will depend on tidally averaged suspended sediment

concentrations. It is worth noting that the above equation does not account

for re-aeration which would tend to reduce impacts of the SS on DO

concentrations in the water column. The proposed analysis, which is on the

conservative side, will not, therefore, underestimate the DO depletion.

Further, it should be noted that, for sediment in suspension to exert any

oxygen demand in the water column it will take time and, at the same time,

the sediment will be transported and mixed or dispersed with oxygenated

water. As a result, the oxygen demand and the impact on DO concentrations

will diminish as the suspended sediment concentrations decrease.

The predicted maximum DO depletion at all WSRs are presented in Table 7.15

and Table 7.16 for dredging at seawater intake and discharge outfall

respectively. Overall, the predicted maximum DO depletion is quite low at

all WSRs, with maximum DO depletion predicted to be below 0.1 mg L-1.

Contour plots showing the predicted maximum DO depletion are also

provided in Annex 7D.

(1) ERM - HK Ltd (2010). Development of an Offshore Wind Farm in Hong Kong. Final Environmental Impact

Assessment. For the Hong Kong Electric Company



7-31

Table 7.15 Predicted Maximum Dissolved Oxygen Depletion from Marine Dredging at

Seawater Intake – Mitigated Scenario

WSR (ID) Unit for SS Elevation and DO Depletion: mg L-1


Max SS

Elevation(a)

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion


Oyster Production Area -

Sheung Pak Nai (SR14)

0.0973 0.69 0.0018 0.0973 1.75 0.0018 0.0521 0.32 0.0009

Recognised Spawning/

Nursery Grounds -

Fisheries Spawning

Ground in North Lantau

(SR15)

0.0212 0.19 0.0004 0.0212 1.98 0.0004 0.0185 - (b) 0.0003

Artificial Reef

Deployment Area - Sha

Chau and Lung Kwu

Chau (SR12)

0.0044 1.09 0.0001 0.0044 3.98 0.0001 0.0032 0.89 0.0001


Mangroves - Ngau Hom

Shek (SR1) 0.0274 2.40 0.0005 0.0274 3.69 0.0005 0.0224 2.08 0.0004

Mangroves - Sheung Pak

Nai (SR2) 0.1715 2.40 0.0031 0.1715 3.69 0.0031 0.0427 2.08 0.0008

Marine Park - Designated

Sha Chau and Lung Kwu

Chau (SR6)

0.0041 0.19 0.0001 0.0041 1.98 0.0001 0.0017 - (b) 0.0000



Chau (SR7)

0.0137 0.19 0.0002 0.0137 1.98 0.0002 0.0113 - (b) 0.0002



Chau (SR13)

0.0045 0.19 0.0001 0.0045 1.98 0.0001 0.0029 - (b) 0.0001

Intertidal Mudflats - Ha

Pak Nai (SR3) 0.0909 2.40 0.0016 0.0767 3.69 0.0014 0.0909 2.08 0.0016

Seagrass Beds - Sheung

Pak Nai (SR2)

0.1715 2.40 0.0031 0.1715 3.69 0.0031 0.0427 2.08 0.0008

Seagrass Beds - Ha Pak

Nai (SR3)

0.0909 2.40 0.0016 0.0767 3.69 0.0014 0.0909 2.08 0.0016

Horseshoe Crab Nursery

Grounds - Ha Pak Nai

(SR3)

0.0909 2.40 0.0016 0.0767 3.69 0.0014 0.0909 2.08 0.0016


Grounds - Ngau Hom

Shek (SR1)

0.0274 2.40 0.0005 0.0274 3.69 0.0005 0.0224 2.08 0.0004


Grounds - Lung Kwu

Sheung Tan (SR5)

0.4482 1.09 0.0081 0.4482 3.98 0.0081 0.3103 0.89 0.0056

Coral Colonies Identified

Along Survey Transect

under this Project -

Transect C (SR18)

4.9356 2.09 0.0888 4.9356 4.09 0.0888 4.4742 1.90 0.0805


Non-gazetted Beaches -

Lung Kwu Sheung Tan

(SR5)

0.2305 0.19 0.0041 0.2305 1.98 0.0041 0.157 - (b) 0.0028


Lung Kwu Tan (SR8) 0.2924 0.19 0.0053 0.2924 1.98 0.0053 0.1589 - (b) 0.0029

Secondary Recreation

Subzone - North Western

Water Control Zone (SR8)

0.2924 0.19 0.0053 0.2924 1.98 0.0053 0.1589 - (b) 0.0029

Seawater Intakes - Black

Point Power Station (SR4)

1.3457 N/A (c) 0.0242 0.324 N/A (c) 0.0058 1.3457 N/A (c) 0.0242



7-32



Max SS

Elevation(a)

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Seawater Intakes - Castle

Peak Power Station (SR9)

0.0996 N/A (c) 0.0018 0.0996 N/A (c) 0.0018 0.0738 N/A (c) 0.0013

Seawater Intakes - Tuen

Mun Area 38 (SR11)

0.0631 1.40 0.0011 0.0631 3.90 0.0011 0.0385 1.10 0.0007

Seawater Intakes - Shiu

Wing Steel Mill (SR10)

0.0769 1.40 0.0014 0.0769 3.90 0.0014 0.046 1.10 0.0008

Seawater Intakes - Sludge

Treatment Facilities

(SR16)

0.5152 2.09 0.0093 0.3963 4.09 0.0071 0.5152 1.90 0.0093

Note:

(a) Max SS elevation for “Annual” column is the higher prediction among two seasons.

(b) For WSRs where DO level is below the corresponding WQO criterion, the “Allowed DO Depletion” is shown as “ -“. Any

observable level of DO depletion (i.e. ≥0.0001) is considered exceedance and is shown in bold and underline under such circumstance.

(c) Cooling water intakes for power stations are not considered sensitive to DO depletion. Therefore no assessment criterion and

allowed DO depletion are provided. The predicted values for DO depletion are for reference only.

Table 7.16 Predicted Maximum Dissolved Oxygen Depletion from Marine Dredging at

Discharge Outfall – Mitigated Scenario



Max SS

Elevation(a)

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion




0.1637 0.69 0.0029 0.1637 1.75 0.0029 0.1072 0.32 0.0019


Nursery Grounds -

Fisheries Spawning

Ground in North Lantau

(SR15)

0.0182 0.19 0.0003 0.0182 1.98 0.0003 0.0138 - (b) 0.0002

Artificial Reef

Deployment Area - Sha

Chau and Lung Kwu

Chau (SR12)

0.0043 1.09 0.0001 0.0043 3.98 0.0001 0.0029 0.89 0.0001


Mangroves - Ngau Hom

Shek (SR1) 0.0661 2.40 0.0012 0.0661 3.69 0.0012 0.0486 2.08 0.0009

Mangroves - Sheung Pak

Nai (SR2) 0.2728 2.40 0.0049 0.2728 3.69 0.0049 0.0902 2.08 0.0016



Chau (SR6)

0.0038 0.19 0.0001 0.0038 1.98 0.0001 0.0015 - (b) 0.0000



Chau (SR7)

0.0117 0.19 0.0002 0.0117 1.98 0.0002 0.0081 - (b) 0.0001



Chau (SR13)

0.0044 0.19 0.0001 0.0044 1.98 0.0001 0.0021 - (b) 0.0000

Intertidal Mudflats - Ha

Pak Nai (SR3)

0.3538 2.40 0.0064 0.3538 3.69 0.0064 0.1904 2.08 0.0034

Seagrass Beds - Sheung

Pak Nai (SR2)

0.2728 2.40 0.0049 0.2728 3.69 0.0049 0.0902 2.08 0.0016



7-33



Max SS

Elevation(a)

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Max SS

Elevation

Allowed

DO

Depletion

Max DO

Depletion

Seagrass Beds - Ha Pak

Nai (SR3)

0.3538 2.40 0.0064 0.3538 3.69 0.0064 0.1904 2.08 0.0034


Grounds - Ha Pak Nai

(SR3)

0.3538 2.40 0.0064 0.3538 3.69 0.0064 0.1904 2.08 0.0034


Grounds - Ngau Hom

Shek (SR1)

0.0661 2.40 0.0012 0.0661 3.69 0.0012 0.0486 2.08 0.0009


Grounds - Lung Kwu

Sheung Tan (SR5)

0.3934 1.09 0.0071 0.3934 3.98 0.0071 0.2481 0.89 0.0045


Along Survey Transect

under this Project -

Transect C (SR18)

3.535 2.09 0.0636 3.535 4.09 0.0636 1.3398 1.90 0.0241



Lung Kwu Sheung Tan

(SR5)

0.1575 0.19 0.0028 0.1575 1.98 0.0028 0.1236 - (b) 0.0022


Lung Kwu Tan (SR8) 0.1619 0.19 0.0029 0.1619 1.98 0.0029 0.1208 - (b) 0.0022




0.1619 0.19 0.0029 0.1619 1.98 0.0029 0.1208 - (b) 0.0022

Seawater Intakes - Black

Point Power Station (SR4)

1.0454 N/A (c) 0.0188 0.1878 N/A (c) 0.0034 1.0454 N/A (c) 0.0188

Seawater Intakes - Castle

Peak Power Station (SR9)

0.0765 N/A (c) 0.0014 0.0765 N/A (c) 0.0014 0.0627 N/A (c) 0.0011

Seawater Intakes - Tuen

Mun Area 38 (SR11) 0.0535 1.40 0.0010 0.0535 3.90 0.0010 0.035 1.10 0.0006

Seawater Intakes - Shiu

Wing Steel Mill (SR10) 0.0615 1.40 0.0011 0.0615 3.90 0.0011 0.0404 1.10 0.0007


Treatment Facilities

(SR16)

1.3049 2.09 0.0235 1.3049 4.09 0.0235 0.9101 1.90 0.0164

Note:

(a) Max SS elevation for “Annual” column is the higher prediction among two seasons.

(b) For WSRs where DO level is below the corresponding WQO criterion, the “Allowed DO Depletion” is shown as “ -“. Any

observable level of DO depletion (i.e. ≥0.0001) is considered exceedance and is shown in bold and underline under such circumstance.

(c) Cooling water intakes for power stations are not considered sensitive to DO depletion. Therefore no assessment criterion and

allowed DO depletion are provided. The predicted values for DO depletion are for reference only.

While the highest maximum DO depletion is predicted at the coral colonies

(SR18) located next to the existing outfall which is the most impacted by SS in

both seasons, full compliance to the corresponding annual WQO assessment

criteria is predicted as well as in both seasons for this WSR. The predicted

maximum DO depletion is much lower for other WSRs. Except for those

WSRs located close to EPD monitoring station NM5, full compliance in annual

WQO DO criteria is predicted at all WSRs as well as in the dry season and wet

season separately, for both intake and outfall dredging works.

As shown in Table 7.8, the baseline 10%-percentile depth-averaged DO level is

already below the WQO criteria (4 mg L-1) at NM5 in the wet season. As

stated in item D(b) under Table 7.1, the DO criteria for WQO requires depth-

averaged DO criteria for 90% of incident throughout the year. It is



7-34

considered too conservative to assess the potential DO depletion with baseline

DO exceedance at NM5 in wet season. The annual baseline 10%-percentile

depth-averaged DO level, together with the worst case DO depletion

predicted, would be used for assessment for WSRs located near NM5 (SR6,

SR7, SR8, SR13 and SR15). For both the intake and outfall dredging works,

the predicted DO depletion at these WSRs is below 0.01 mg L-1 in both

seasons, which is considered minimal, and compliance to the annual WQO

DO criteria is also predicted at these WSRs. In view of the above, no

unacceptable DO depletion impact from both intake and outfall dredging

works is expected.

7.7.3 Nutrients

Other than readily-biodegradable organic compounds (which are assessed in

the previous section), sediment-bounded nitrogenous compounds could also

be released into the water column and result in an increase of TIN and UIA.

To quantify the elevation in TIN and UIA from the proposed dredging

operation, mathematical modelling has been conducted using an inert tracer.

Review of sediment quality data (Table 7.3) indicated that the level of TKN is

similar among the four EPD sediment monitoring stations near the Project site.

For assessing the potential release of nitrogenous species from sediment, the

maximum TKN level at DS4 (560 mg kg-1) was taken for calculation of

potential TIN and UIA elevation. While nitrate and nitrite may also be

constituent of TIN in marine water, they are generally in negligible

concentration because of low electrochemical potential of marine sediment.

Under low electrochemical potential (i.e. reducing environment), oxidized

forms of nitrogen (e.g. nitrate and nitrite) tend to be reduced to their reduced

form (e.g. ammonia), and thus is considered as part of TKN. Therefore the

contribution of TIN from nitrate and nitrite is negligible and was not

considered. Since TKN takes into account both organic nitrogen and

ammonia nitrogen, TKN level in sediment already represents the vast majority

of nitrogen content in sediment, and is thus considered sufficiently

conservative for the assessment.

EPD marine water quality monitoring data at DM5 from 2005 to 2014 also

indicated that on average 3.78% of ammonia nitrogen exists as UIA. This

ratio would be adopted to determine the elevation of UIA at WSRs from the

corresponding elevation of TIN (i.e. assuming 100% of TIN exists in form of

ammonia nitrogen).

The predicted maximum elevations of TIN and UIA at WSRs for dredging at

seawater intake and discharge outfall in the dry and wet season, taking into

account the mitigation measures recommended under Section 7.7.1, are

provided in Table 7.17. Contour plots for maximum TIN and UIA elevation

throughout the modelling period are provided in Annex 7E.



7-35

Table 7.17 Predicted Maximum TIN and UIA Elevation at WSRs for Dredging at

Seawater Intake and Discharge Outfall in Dry and Wet Season

WSR (ID) TIN (mg L-1) UIA (mg L-1)

Criteria Intake Outfall Criteria Intake Outfall

Dry Wet Dry Wet Dry Wet Dry Wet




0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001


Nursery Grounds - Fisheries

Spawning Ground in North

Lantau (SR15)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001

Artificial Reef Deployment

Area - Sha Chau and Lung

Kwu Chau (SR12)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001


Mangroves - Ngau Hom Shek

(SR1)

0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001

Mangroves - Sheung Pak Nai

(SR2)

0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001

Marine Park - Designated Sha

Chau and Lung Kwu Chau

(SR6)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001



(SR7)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001



(SR13)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001

Intertidal Mudflats - Ha Pak

Nai (SR3) 0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001

Seagrass Beds - Sheung Pak

Nai (SR2) 0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001

Seagrass Beds - Ha Pak Nai

(SR3) 0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001


Grounds - Ha Pak Nai (SR3)

0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001


Grounds - Ngau Hom Shek

(SR1)

0.005 <0.001 <0.001 <0.001 <0.001 0.012 <0.0001 <0.0001 <0.0001 <0.0001


Grounds - Lung Kwu Sheung

Tan (SR5)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001


Along Survey Transect under

this Project - Transect C

(SR18)

0.005 0.001 0.001 0.001 0.001 0.015 <0.0001 0.0001 <0.0001 <0.0001


Non-gazetted Beaches - Lung

Kwu Sheung Tan (SR5)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001

Non-gazetted Beaches - Lung

Kwu Tan (SR8)

0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001




0.005 <0.001 <0.001 <0.001 <0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001

Seawater Intakes - Black Point

Power Station (SR4)

N/A <0.001 0.001 <0.001 0.001 N/A <0.0001 <0.0001 <0.0001 <0.0001

Seawater Intakes - Castle Peak

Power Station (SR9)

N/A <0.001 <0.001 <0.001 <0.001 N/A <0.0001 <0.0001 <0.0001 <0.0001

Seawater Intakes - Tuen Mun

Area 38 (SR11)

0.005 <0.001 <0.001 <0.001 <0.001 0.016 <0.0001 <0.0001 <0.0001 <0.0001



7-36

WSR (ID) TIN (mg L-1) UIA (mg L-1)

Criteria Intake Outfall Criteria Intake Outfall

Dry Wet Dry Wet Dry Wet Dry Wet

Seawater Intakes - Shiu Wing

Steel Mill (SR10)

0.005 <0.001 <0.001 <0.001 <0.001 0.016 <0.0001 <0.0001 <0.0001 <0.0001


Treatment Facilities (SR16)

0.005 <0.001 <0.001 0.001 0.001 0.015 <0.0001 <0.0001 <0.0001 <0.0001

Note: Predicted level exceeding the proposed assessment criteria is bold and underlined.

Table 7.17 shows that the elevation in TIN level is very minimal in both

seasons at all WSRs and is far below the proposed assessment criteria of 0.005

mg L-1 elevation. No unacceptable TIN elevation from the proposed marine

dredging is expected.

Similar to the case of TIN, the predicted UIA elevation is very limited in both

seasons for dredging at the proposed seawater intake and discharge outfall,

and the predicted UIA elevations are below the corresponding WQO

assessment criteria at all WSRs. No unacceptable UIA elevation from the

proposed marine dredging is expected.

7.7.4 Heavy Metals and Micro-Organic Pollutants

The proposed dredging operation may disturb bottom sediment and result in

release of sediment-bounded pollutants, namely heavy metals, metalloid

(arsenic) and trace organic compounds (PAHs, PCBs and TBT). As shown in

Table 7.5, the sediment elutriate test results indicated that there is no

significant release of heavy metals, metalloid and trace organic compounds

from the sediment samples analysed under this EIA and the levels of these

contaminants are below the corresponding proposed assessment criteria.

Therefore the proposed marine dredging works would be unlikely to result in

a significant release of sediment-bounded pollutants into the water column.

No adverse water quality impact associated with the release of sediment-

bounded pollutants would be expected.

7.7.5 Other Marine Construction Activities

Marine construction works other than sediment dredging would be required

for the installation of intake and outfall structure. Potential disturbance to

marine sediment by these marine works are expected to be less significant

than that of sediment dredging. Therefore no adverse water quality impact

from the potential disturbance of bottom sediment is expected from these

marine construction activities.

Construction vessels have the potential for the following liquid discharges:

Uncontaminated deck drainage;

Potentially contaminated drainage from machinery spaces; and

Sewage/grey water.



7-37

Deck drainage is likely to be uncontaminated and is not likely to impact water

quality. Other sources of possible impacts to water quality may arise from

discharges of hydrocarbons (oil and grease) from machinery space drainage

and biochemical oxygen demand (BOD) and microbiological constituents

associated with sewage/grey water. These waste streams are all readily

amenable to control as part of appropriate practice on vessels. Possible

impacts associated with construction vessel discharges are therefore

considered to be negligible.

No solid wastes will be permitted to be disposed of overboard by vessels

during construction works, thus impacts from such sources will be eliminated.

7.7.6 Sewage Discharges

Sewage will arise from the construction workforce and site office’s sanitary

facilities. It is estimated that the average number of workers working onsite

is about 500. Based on the general effluent generation rate (150 L per worker

per day (1), approximately 75,000 L of effluent will be generated at the site

during the construction phase. The same per head sewage discharge rate

was adopted in the approved EIA of Black Point Gas Supply Project (AEIAR-

150/2010) and is considered appropriate. To accommodate the increase in

sewage effluent from construction workforce, chemical toilets would be

provided onsite. These chemical toilets would be regularly maintained and

cleaned by licensed contractor to avoid any environmental nuisance. As

sewage discharges into the sea are not expected to occur, no unacceptable

water quality impacts to sensitive receivers are anticipated.

7.7.7 Land Based Construction Activities

Discharges and runoff from the site during land-based construction and

installation activities may contain suspended solids which could be a source of

water pollution. However, it is anticipated that no adverse water quality

impacts would arise from the land-based works if proper mitigation

measures, described in Section 7.9.1, are in place.

7.7.8 Chemical Cleaning during Plant Pre-commissioning

Before the commissioning of the additional CCGT Unit No.1 and No.2,

passivation (i.e. make inert) of the inner surfaces of the heat recovery steam

generator of the additional CCGT units would be conducted by chemical

cleaning. Such cleaning operation is also currently undertaken for all

existing CCGT units in BPPS once every 10 to 20 years. Chemical cleaning

solution adopted in current operation consists of water, pH control (generally

hydrochloric acid, ammonia or lime), surfactant and corrosion inhibitor (i.e.

oxidizing agent(s) or other agent such as sulphuric acid, hydrogen peroxide,

etc. which form protective coating on metal surface). Chemical cleaning

solution of similar nature (with tailored formulation) would be adopted for

(1) Based on Table 2 of the Drainage Services Department's Sewerage Manual.



7-38

the additional CCGT Units No.1 and 2. These constituents are generally non-

toxic and some are commonly used in household products. Based on the

record of a recent similar cleaning event for an existing plant in the BPPS, the

volume of wastewater generated from a cleaning event of one of the

additional CCGT unit is conservatively estimated to be about 5,000 m3 per

event. Wastewater generated will be neutralised to a pH range of 6 to 10 and

discharged into the existing Effluent Treatment Facility onsite for treatment.

Since the constituent ions of the chemical cleaning solution are generally quite

abundant in marine water, no significant change in marine water quality

would be expected upon discharge after neutralization. Residual oxidizing

agent, such as hydrogen peroxide, is expected to decompose quickly into

harmless water and oxygen in the Effluent Treatment Facility. The

wastewater will be treated to appropriate discharge standards (as specified

under the existing / future WPCO discharge licence). With compliance of

the relevant discharge standards same as the existing practice, no

unacceptable water quality impact would be expected from the cleaning

events during the pre-commissioning of the additional CCGT Unit No.1 and

No.2.

7.8 IMPACT ASSESSMENT – OPERATION PHASE

The current BPPS with eight CCGT units has a maximum cooling water

discharge of 4,600,000 m3 per day with allowed maximum discharge

temperature of 40°C and maximum TRC level of 0.5 mg L-1. The proposed

two additional CCGT units would follow similar design specifications, with

cooling water discharge of 950,400 m3 per day for each of the additional CCGT

units with allowed maximum discharge temperature of 40°C and TRC level of

0.5 mg L-1. The potential change in water quality from the increase in

thermal discharge and TRC discharge were assessed separately below.

It is important to note that the two additional CCGT units are expected to be

commissioned in two phases. It is considered conservative to assess the

worst case scenario for the ultimate case of future operation with the existing

BPPS plus both of the additional CCGT units. Assessment for the

intermediate case with only the BPPS plus one CCGT unit is considered less

conservative and is not included.

7.8.1 Increase in Thermal Discharge

The potential change in water quality due to the increase in thermal discharge

was assessed by comparing the change in ambient water temperature under

two modelling scenarios, namely,

Baseline scenario: Existing BPPS discharge at 4,600,000 m3 per day at

40°C;

Future scenario (Additional CCGT Unit No.1 only): Future BPPS

discharge at 5,550,400 m3 per day (4,600,000 + 950,400) at 40°C.and



7-39

Future scenario (Additional CCGT Unit No.1 and No.2): Future BPPS

discharge at 6,500,800 m3 per day (4,600,000 + 2 × 950,400) at 40°C.

As discussed in Section 7.4.4, for WSRs except for the two cooling water

intakes for BPPS and CPPS, the maximum WQO allowable increase in water

temperature is 2°C.

The modelled mean and maximum water temperature at WSRs for the three

scenarios in both seasons are shown in Table 7.18. The change in mean and

maximum water temperature at WSRs are also provides in Table 7.18 for

comparison with the 2°C WQO criterion. Contour plots for envelope where

predicted water temperature elevation exceeded 2°C for selected tidal

conditions in dry and wet seasons are provided in Annex 7F. Predicted

average and maximum water temperature at WSRs for the two modelled

scenarios are also provided in Table 7.18 below.

The predicted elevation in mean and maximum water temperature is equal to

or below 0.6°C in both the dry and wet season of the future scenario with

additional CCGT Units No.1 & No.2 (Table 7.18), which is well within the 2°C

WQO assessment criterion. The future scenario with additional CCGT Unit

No.1 only shows lower predicted mean and maximum temperature elevation

at all WSRs. The most impacted WSRs in both seasons include SR16, which

represents seawater intake for the Sludge Treatment Facilities, SR3 (ecological

receivers along the coastline of Ha Pak Lai) and SR4 (BPPS) due to the short

distance from the outfall location. It is also observed that the WSRs in Deep

Bay are generally less affected by the thermal discharge in wet season. It is

because the difference between ambient temperature (lower in dry season and

higher in wet season) and modelled thermal discharge (constant at 40°C in

both seasons for worst case assessment) is smaller in wet season.



7-40

Table 7.18 Predicted Average and Maximum Water Temperature (°C) at WSRs under Baseline and Two Future Scenarios in Dry and Wet

Seasons

Sensitive

Receivers

Name Model Output

Location

Relevant Depth for

Assessment

Baseline

Scenario

Future Scenario Future Scenario

Additional CCGT

Unit No.1 only

Predicted

Change

Additional CCGT

Unit No.1 & No.2

Predicted

Change

Mean Max Mean Max Mean Max Mean Max Mean Max

Dry Season


Oyster

Production Area

Sheung Pak Nai SR14 Depth-averaged 23.03 23.51 23.07 23.72 0.04 0.21 23.10 23.84 0.07 0.33

Recognised

Spawning/

Nursery Grounds

Fisheries Spawning

Ground in North

Lantau

SR15 Depth-averaged 21.79 22.49 21.82 22.55 0.03 0.06 21.84 22.64 0.05 0.15

Artificial Reef

Deployment Area

Sha Chau and Lung

Kwu Chau

SR12 Bottom 22.10 22.71 22.13 22.81 0.03 0.10 22.16 22.92 0.06 0.21


Mangroves Ngau Hom Shek SR1 Bottom 23.00 23.07 23.01 23.14 0.01 0.07 23.01 23.20 0.01 0.13

Sheung Pak Nai SR2 Bottom 23.02 23.23 23.04 23.36 0.02 0.13 23.06 23.46 0.04 0.23

Marine Park Designated Sha Chau

and Lung Kwu Chau




Intertidal

Mudflats

Ha Pak Nai SR3 Bottom 23.05 23.43 23.12 23.62 0.07 0.19 23.18 23.75 0.13 0.32

Seagrass Beds Sheung Pak Nai SR2 Bottom 23.02 23.23 23.04 23.36 0.02 0.13 23.06 23.46 0.04 0.23


Horseshoe Crab

Nursery Grounds


Ngau Hom Shek SR1 Bottom 23.00 23.07 23.01 23.14 0.01 0.07 23.01 23.20 0.01 0.13

Lung Kwu Sheung Tan SR5 Bottom 22.45 26.98 22.48 26.98 0.03 0.00 22.50 26.98 0.05 0.00

Coral Colonies Transect C SR18 Bottom 23.64 34.07 23.66 34.40 0.02 0.33 23.67 34.70 0.03 0.63


Non-gazetted

Beaches

Lung Kwu Sheung Tan SR5 Depth-averaged 22.97 27.16 23.02 27.16 0.05 0.00 23.05 27.16 0.08 0.00



7-41

Sensitive

Receivers

Name Model Output

Location

Relevant Depth for

Assessment

Baseline

Scenario


Additional CCGT

Unit No.1 only

Predicted

Change

Additional CCGT

Unit No.1 & No.2

Predicted

Change


Lung Kwu Tan SR8 Depth-averaged 24.38 32.90 24.42 32.93 0.04 0.03 24.44 32.96 0.06 0.06

Secondary

Recreation

Subzone

North Western Water

Control Zone



Station

SR4 Bottom 22.47 24.29 22.50 24.29 0.03 0.00 22.53 24.30 0.06 0.01

Castle Peak Power

Station

SR9 Bottom 21.64 23.20 21.65 23.23 0.01 0.03 21.66 23.24 0.02 0.04

Tuen Mun Area 38 SR11 Bottom 21.43 22.95 21.45 22.95 0.02 0.00 21.45 22.96 0.02 0.01

Shiu Wing Steel Mill SR10 Bottom 21.50 23.35 21.51 23.35 0.01 0.00 21.52 23.39 0.02 0.04

Sludge Treatment

Facilities

SR16 Bottom 23.04 24.45 23.15 24.69 0.11 0.24 23.23 24.89 0.19 0.44

Wet Season


Oyster

Production Area

Sheung Pak Nai SR14 Depth-averaged 28.33 29.14 28.37 29.18 0.04 0.04 28.40 29.20 0.07 0.06

Recognised

Spawning/

Nursery Grounds

Fisheries Spawning

Ground in North

Lantau


Artificial Reef

Deployment Area

Sha Chau and Lung

Kwu Chau

SR12 Bottom 27.51 28.32 27.53 28.47 0.02 0.15 27.53 28.47 0.02 0.15


Mangroves Ngau Hom Shek SR1 Bottom 28.19 29.10 28.21 29.10 0.02 0.00 28.21 29.10 0.02 0.00

Sheung Pak Nai SR2 Bottom 28.28 29.09 28.31 29.10 0.03 0.01 28.33 29.11 0.05 0.02

Marine Park Designated Sha Chau

and Lung Kwu Chau




Intertidal

Mudflats


Seagrass Beds Sheung Pak Nai SR2 Bottom 28.28 29.09 28.31 29.10 0.03 0.01 28.33 29.11 0.05 0.02




7-42

Sensitive

Receivers

Name Model Output

Location

Relevant Depth for

Assessment

Baseline

Scenario


Additional CCGT

Unit No.1 only

Predicted

Change

Additional CCGT

Unit No.1 & No.2

Predicted

Change


Horseshoe Crab

Nursery Grounds


Ngau Hom Shek SR1 Bottom 28.19 29.10 28.21 29.10 0.02 0.00 28.21 29.10 0.02 0.00

Lung Kwu Sheung Tan SR5 Bottom 27.93 30.73 28.02 30.82 0.09 0.09 28.05 30.92 0.12 0.19

Coral Colonies Transect C SR18 Bottom 31.64 37.11 31.70 37.26 0.06 0.15 31.76 37.44 0.13 0.34


Non-gazetted

Beaches

Lung Kwu Sheung Tan SR5 Depth-averaged 28.41 29.98 28.48 30.37 0.07 0.39 28.52 30.40 0.11 0.42

Lung Kwu Tan SR8 Depth-averaged 26.97 29.36 27.00 29.39 0.03 0.03 27.02 29.41 0.05 0.05

Secondary

Recreation

Subzone

North Western Water

Control Zone



Station

SR4 Bottom 28.10 32.19 28.24 32.57 0.14 0.38 28.31 32.74 0.21 0.55

Castle Peak Power

Station

SR9 Bottom 26.97 29.36 27.01 29.39 0.04 0.03 27.02 29.41 0.05 0.05

Tuen Mun Area 38 SR11 Bottom 26.68 28.28 26.68 28.30 0.00 0.02 26.70 28.33 0.02 0.05

Shiu Wing Steel Mill SR10 Bottom 26.86 29.32 26.90 29.32 0.04 0.00 26.91 29.34 0.05 0.02

Sludge Treatment

Facilities

SR16 Bottom 28.60 30.46 28.79 30.75 0.19 0.29 28.95 31.00 0.35 0.54

Note: 1. All numbers are rounded to 1 decimal place. “0.00” indicates all values below 0.005.

2. SR5 and SR8, which are both located within the footprint of Reclamation at Lung Kwu Tan Project and would potentially be removed by that project. The

predicted values for SR5 and SR8 presented are derived assuming these WSRs would be relocated at the new coastline of the reclaimed Lung Kwu Tan.

Since there is no available information on whether these WSRs would indeed be relocated, the predictions at these WSRs are provided for reference only.



7-43

The size of the thermal plume is generally observed to be larger in dry season

than the wet season (Annex 7F). It is because the modelling exercise assumes

constant discharge at the maximum allowed temperature limit of 40°C thus

resulting in higher temperature difference between the ambient seawater and

the thermal discharge from BPPS. This is a conservative assumption because

while the maximum allowed discharge temperature from BPPS is 40°C, the

actual discharge temperature would generally be lower than the limit. In dry

season when the ambient water temperature is lower, the discharge

temperature would generally be lower as well. It should also be highlighted

that the discharge from the Pearl River plays an important role in shaping the

thermal plume in wet season. While the discharge of thermal plume occurs

close to the surface of the water column, the continuous high discharge from

the Pearl River forces the thermal plume from BPPS (existing and additional

CCGT units altogether) to stay closer to the coastline (when compared with

the same tidal condition in dry season) and moves lower in the water column.

As shown in Annex7F, the thermal plume occurs in the lower level of the

water column for some of the tidal conditions, even though the discharge

occurs on the surface layer. Such a phenomenon also affects the dispersion

of total residual chlorine in the thermal discharge, which is addressed

separately in Section 7.8.2 below.

As discussed in Section 7.4.4, the optimal operation temperature for the two

cooling water intakes for BPPS (SR4) and CPPS (SR9) is below 30°C. As

shown in Table 7.18, the predicted maximum water temperature at SR4 in the

wet season is 32.2°C in the baseline scenario and 32.7°C in the future scenario,

which both exceeded the optimal operation temperature of 30°C. Modelling

prediction indicates that for about 2.1% of time in the wet season the water

temperature at SR4 exceeds 30°C. With the thermal discharge from the

additional CCGT units, the percentage of time with water temperature at SR4

exceeding 30°C increases to 2.3%, which is considered minimal and within the

tolerance of the existing BPPS. As discussed in the previous section, both

modelled baseline and future scenarios assume continuous discharge of

cooling water of maximum allowed temperature (40°C) at the maximum

allowed rate. The assumed discharge temperature and discharge rate are

both conservative. In reality, the discharge temperature and discharge rate

may vary but staying below the allowed rate and temperature, and thus the

temperature elevation should be lower than the model prediction.

As shown in the modelling results, the predicted level of ambient water

temperature is well below the proposed assessment criteria based on WQO,

and is considered to be within or similar to the range of daily fluctuation.

The increase in thermal discharge would lead to small increase in duration

when water temperature at the BPPS seawater intake exceeds the optimal

30°C operation criterion under the conservative assumption. The increase in

water temperature as well as the duration for exceeding 30°C is deemed

minimal for the operation of the BPPS. No unacceptable water quality

impact from the increase in thermal discharge from the proposed CCGT units

is expected.



7-44

7.8.2 Increase in Total Residual Chlorine Discharge

Electrochlorination of seawater would be conducted to control biofouling of

the cooling water system. The same arrangement would be adopted for the

proposed additional CCGT units. The maximum level of TRC in the cooling

water discharge would be 0.5 mg L-1, which is the same as that of the cooling

water discharge of the existing eight CCGT units in the BPPS. The discharge

of TRC from the additional CCGT units, together with that of the existing

eight CCGT units, are simulated using mathematical model to determine the

level of TRC at nearby identified WSRs.

As discussed in Section 7.4.7, the proposed assessment criterion for TRC at the

applicable marine ecological and fisheries sensitive receivers is 0.02 mg L-1.

Since the maximum discharge concentration of TRC from the existing and

additional CCGT plants is 0.5 mg L-1, this means a 25-times reduction, either

by mixing with ambient seawater, by decay of TRC itself or a combination of

both, would result in compliance to the proposed criterion.

The predicted average and maximum TRC levels under baseline (existing

BPPS and CPPS) and Project (future BPPS with additional CCGT Units No.1,

No.2 and CPPS) at relevant WSRs in both seasons are provided in Table 7.19.

Contour plots for maximum and average TRC level throughout the simulated

period are provided in Annex 7G.



7-45

Table 7.19 Predicted Maximum and Mean Elevation in Total Residual Chlorine

WSR (ID)

Criteria

TRC - Baseline (mg L-1) Additional CCGT Unit No.1 only

(mg L-1)

Additional CCGT Unit No.1 & No.2

(mg L-1)

Dry Season Wet Season Dry Season Wet Season Dry Season Wet Season

Mean Max Mean Max Mean Max Mean Max Mean Max Mean Max


Oyster Production Area - Sheung Pak Nai (SR14) 0.02 0.0000 0.0023 0.0000 0.0058 0.0000 0.0028 0.0000 0.0069 0.0000 0.0033 0.0000 0.0081



0.02 0.0001 0.0035 0.0000 0.0010 0.0001 0.0035 0.0000 0.0010 0.0001 0.0036 0.0000 0.0011


Kwu Chau (SR12)

0.02 0.0000 0.0010 0.0000 0.0001 0.0000 0.0010 0.0000 0.0001 0.0000 0.0012 0.0000 0.0001


Mangroves - Ngau Hom Shek (SR1) 0.02 0.0000 0.0007 0.0000 0.0025 0.0000 0.0009 0.0000 0.0031 0.0000 0.0010 0.0000 0.0036

Mangroves - Sheung Pak Nai (SR2) 0.02 0.0000 0.0018 0.0000 0.0047 0.0000 0.0022 0.0000 0.0057 0.0000 0.0026 0.0000 0.0067

Marine Park - Designated Sha Chau and Lung Kwu

Chau (SR6)

0.02 0.0000 0.0008 0.0000 0.0001 0.0000 0.0009 0.0000 0.0001 0.0000 0.0009 0.0000 0.0001


Chau (SR7)

0.02 0.0000 0.0017 0.0000 0.0003 0.0000 0.0018 0.0000 0.0004 0.0000 0.0019 0.0000 0.0005


Chau (SR13)

0.02 0.0000 0.0019 0.0000 0.0004 0.0000 0.0020 0.0000 0.0004 0.0000 0.0020 0.0000 0.0004

Intertidal Mudflats - Ha Pak Nai (SR3) 0.02 0.0001 0.0050 0.0001 0.0084 0.0001 0.0062 0.0001 0.0101 0.0001 0.0073 0.0001 0.0118

Seagrass Beds - Sheung Pak Nai (SR2) 0.02 0.0000 0.0018 0.0000 0.0047 0.0000 0.0022 0.0000 0.0057 0.0000 0.0026 0.0000 0.0067

Seagrass Beds - Ha Pak Nai (SR3) 0.02 0.0001 0.0050 0.0001 0.0084 0.0001 0.0062 0.0001 0.0101 0.0001 0.0073 0.0001 0.0118

Horseshoe Crab Nursery Grounds - Ha Pak Nai (SR3) 0.02 0.0001 0.0050 0.0001 0.0084 0.0001 0.0062 0.0001 0.0101 0.0001 0.0073 0.0001 0.0118


(SR1)

0.02 0.0000 0.0007 0.0000 0.0025 0.0000 0.0009 0.0000 0.0031 0.0000 0.0010 0.0000 0.0036


Tan (SR5)

0.02 0.0013 0.0203 0.0018 0.0243 0.0013 0.0203 0.0018 0.0243 0.0013 0.0203 0.0019 0.0243



0.02 0.0347 0.0834 0.2756 0.3472 0.0398 0.0862 0.2768 0.3639 0.0411 0.0889 0.2819 0.3823

Note:

1. All numbers are rounded to 4 decimal places. “0.0000” indicates all values below 0.00005.

2. SR5, which is both located within the footprint of Reclamation at Lung Kwu Tan Project and would potentially be removed by that project. The predicted values for SR5

presented are derived assuming this WSR would be relocated at the new coastline of the reclaimed Lung Kwu Tan. Since there is no available information on whether this

WSR would indeed be relocated, the predictions at these WSR are provided for reference only.

3. Exceedances in proposed assessment criteria are shown in bold.



7-46

As shown in Table 7.19, compliance with the proposed assessment criterion for

TRC is predicted at most marine ecological and fisheries WSRs except for SR5

and SR18. SR5 and SR18 are located in close proximity to the existing

discharge outfalls of the CPPS and BPPS respectively, and are predicted to

show non-compliance with the TRC assessment criterion without the Project,

thus no new exceedance of the proposed TRC criterion is expected with the

Project in place in both seasons. It is also important to note that the

magnitude of change in TRC level at these two WSRs with and without Project

is rather small and is deemed acceptable. Maximum TRC level is predicted

at coral colonies at SR18 in both seasons, regardless of baseline or project

scenarios. The predicted levels of TRC for other marine ecological and

fisheries WSRs are lower than that of SR5 and SR18, with mean TRC level two

orders of magnitude (i.e. one-hundredth) smaller than the proposed criteria of

0.02 mg L-1. Increase in TRC level due to the additional CCGT Units No.1

and No.2 is more observable in the Deep Bay WCZ; in the North Western

WCZ, the predicted elevation is very limited, as a result of fast current flow of

the Urmston Road and the existing discharge of the CPPS.

As shown in Annex 7G, the mixing zone of TRC (i.e. concentration above 0.02

mg L-1) discharged from the BPPS covers the shoreline along the BPPS and

part of the open waters off the shoreline. The dispersion of TRC is better in

dry season as shown by the lower build up level. On the other hand, the

dispersion of TRC is weaker and results in higher TRC buildup along the

BPPS shoreline (Annex 7G and Table 7.19). The mixing zone of TRC is also

predicted to be larger in the bottom than the rest of the water column, as a

result of higher Pearl River discharge pushing the plume close to the shoreline

and even drive the plume down the water column. These are consistent with

the observations in the operation phase thermal discharge modelling

discussed in the previous Section 7.8.1.

In short, results of modelling simulation indicate the discharge of TRC from

the existing and additional CCGT units would result in limited increase in

TRC level in ambient marine water. Compliance with the proposed

assessment criteria for TRC is predicted at all applicable WSRs. In view of

the above, no unacceptable water quality impact from the discharge of TRC

from the Project is expected.

7.8.3 Potential Risk of Fuel Spill

The primary fuel for the proposed additional CCGT Units No.1 and 2 is

natural gas and there is no risk of spillage of this fuel into marine waters, and

so no unacceptable water quality impact is anticipated and quantitative

assessment is not necessary.

The operation of the additional CCGT units will make use of fuel supply from

the three existing oil tanks at the BPPS as back up fuel, and no additional oil

tank would be built for the proposed Project. Since fuel oil would only be

utilised as back up fuel for the proposed additional CCGT units, the use of



7-47

fuel oil by the Project would be limited, and no additional associated

transhipment and transfer of fuel oil is anticipated. Therefore no significant

increase in potential risk of fuel spillage is expected. Operation staff of the

BPPS follows stringent established rules on control, operation, inspection and

maintenance of the BPPS facilities to minimise any risk of fuel and other

chemicals stored onsite. The three existing oil tanks are installed with leak

detection and other safety protections. Secondary containment is provided

for the three existing oil tanks and major oil spillage from the existing oil

tanks, if any, would be fully contained. Also, design features such as

shutdown valves and leak detectors have been included to avoid and

minimise potential fuel leak. Accidental release is unlikely as the pipes are

fully welded. Oil leakage, if any, would be promptly notified, rectified and

directed to oil contaminated drains for proper handling. Given the small

scale and prompt reaction to any leakage of fuel, major accidental release of

fuel oil from these pipelines (which are located beyond the secondary

containment) is not expected. The contingency plan for the existing

operation of the BPPS is considered sufficient for directing immediate

response to any accidental spillage event. Currently, CLP maintains an

appropriate level of spill response capability within the BPPS through onsite

staff. Sufficient spill response equipment is stored onsite to effectively

respond to the potential spill scenarios. No unacceptable water quality

impact is anticipated and quantitative assessment is not necessary.

7.8.4 Increase in Pollution Load from Other Operational Discharge

As discussed in Section 7.2.5, the operation of the future BPPS with the two

additional CCGT units would be designed such that there would be no net

increase in pollution load to the Deep Bay waters during the operation phase.

The following sections detail the loading discharge conditions for the existing

BPPS, proposed future loads from additional CCGT units and the proposed

measures to ensure no net increase in total load from future operation.

Based on the latest WPCO discharge licence granted to CAPCO for the

operation of BPPS under Section 23 of WPCO, there are a number of discharge

streams which are discharged into the marine waters of Deep Bay. These

discharge streams and the principal pollution loads of concerns are listed in

Table 7.20.

Table 7.20 Stream of Pollution Loads for Existing BPPS

Effluent Stream WPCO Discharge

Licence ID

Flow BOD TP TN

m3 per day mg L-1 mg L-1 mg L-1

Cooling Water Effluent (1) (2) 4,600,000 N.S. N.S. N.S.

Station Effluent Treatment Plant Effluent (3) 1,000 20 10 100

Station Effluent Treatment Plant Effluent (4) 1,000 20 10 100

Oil Separator No. 1 Effluent (5) 800 20 10 100








7-48

Effluent Stream WPCO Discharge

Licence ID

Flow BOD TP TN

m3 per day mg L-1 mg L-1 mg L-1

Permanent Sewage Treatment Plant Effluent (11) 420 20 10 100

Effluent Treatment Facility Effluent (12) 1,000 20 10 100

Note: ID (1) and (2) represent cooling water effluent from the existing outfall. This effluent is expected to be

chemically similar to the ambient marine waters at the intake, with the exception of elevated TRC and defoaming

agent. Water quality parameters, including SS, BOD, chemical oxygen demand (COD), oil and grease (O&G),

total phosphorus (TP) and total nitrogen (TN), are not specified in the existing WPCO Discharge License for this

effluent. These parameters are marked as “N.S.” above.

Among the list of water quality parameters, BOD, TP and TN are of water

quality concern under TPB PG-No. 12C. They are considered as constituents

of pollution loads which should be controlled for compliance with the “no net

increase in pollution load” consideration. The maximum allowed loadings

for the existing operation of the BPPS are presented in Table 7.21.

Table 7.21 Maximum Allowed Loading for Existing BPPS

Effluent Stream WPCO

Discharge

Licence ID

Flow BOD TP TN

m3 per day kg per day kg per day kg per day

Station Effluent Treatment Plant Effluent (3) 1,000 20.0 10.0 100.0

Station Effluent Treatment Plant Effluent (4) 1,000 20.0 10.0 100.0

Oil Separator No. 1 Effluent (5) 800 16.0 8.0 80.0






Permanent Sewage Treatment Plant Effluent (11) 420 8.4 4.2 42.0

Effluent Treatment Facility Effluent (12) 1,000 20.0 10.0 100.0

Total 6,320 126.4 63.2 632.0

Note: Cooling water effluent (ID (1) & (2)) is not included because there is no specification on pollution load

associated with those effluents.

Based on the latest design information, an increase in effluent from the

additional CCGT units would be expected during project operation. Flow of

additional effluent streams which are expected from the additional CCGT

units are provided in Table 7.22. Among these streams, (13) is the cooling

water effluent (assessed in Sections 7.8.1 and 7.8.2) which carries waste heat

and TRC but no additional pollution load. For effluent streams (14) to (17)

and (19) to (22), their properties and pollution load carried should resemble

their counterpart of the existing CCGT units in BPPS. The total flow of these

additional effluent streams is 1,950 and 3,900 m3 per day for one additional

CCGT unit and two additional CCGT units respectively.

Table 7.22 Stream of Pollution Loads for the Additional CCGT Units at BPPS

Effluent Stream ID Discharge Point denoted

under WPCO Discharge

Licence

Flow

m3 per day

Additional CCGT Unit No.1

Cooling Water Effluent (13) DP1 950,400



7-49

Effluent Stream ID Discharge Point denoted

under WPCO Discharge

Licence

Flow

m3 per day

Station Effluent Treatment Plant Effluent (14) New discharge point 500

Oil Interceptor A Effluent (15) New discharge point 800

Oil Interceptor B Effluent (16) New discharge point 500

Oil Interceptor C Effluent (17) New discharge point 150

Sum of (14) to (17) 1,950


Cooling Water Effluent (18) New discharge point 950,400

Station Effluent Treatment Plant Effluent (19) New discharge point 500

Oil Interceptor A Effluent (20) New discharge point 800

Oil Interceptor B Effluent (21) New discharge point 500

Oil Interceptor C Effluent (22) New discharge point 150

Sum of (19) to (22) 1,950

Note: Cooling water effluent ID (13) will be discharged via the existing BPPS cooling water

outfall together with the cooling water effluent stream ID (1) and (2) while cooling water

effluent ID (18) is anticipated to be discharged via the proposed new discharge outfall.

It should be noted that whilst there is an increase in total flow with the

implementation of this Project, the total pollution load will remain to be

capped at the same level as the existing allowable pollution load of the BPPS

to comply with the “no net increase in pollution load” requirement.

Currently, the following measures are being implemented to control the total

daily pollution load discharge into the Deep Bay waters:

The effluents from the station effluent treatment plant and oil separator

will be discharged batch wise, i.e. the effluents in the facilities are allowed

for settlement and removal of pollutants before discharge if necessary.

Samples will be taken from the effluents for laboratory measurements to

ensure compliance with the discharge limits before batch wise discharge.

Effluents from the station effluent treatment plant, oil separator and

sewage treatment facility would be collected by licenced collectors for

treatment and disposal if needed.

The maximum pollution load for water quality parameters listed in Table 7.21

would be considered as the “cap”. Upon the commissioning of the

additional CCGT Unit(s) No.1 and / or No.2, the retention time of effluents

from the station effluent treatment plant and oil separator may need to

increase to allow further settlement and removal of pollutants (so total

pollution load does not increase despite the increase in flow. Offsite

treatment and disposal by licensed collectors would also be adopted when

needed to ensure the “cap” of pollution load into the Deep Bay waters is

properly implemented. Operation staff of the BPPS reviewed the above

control measures and confirmed it is possible to control the total pollution

loads in the effluent streams of the existing and future BPPS to remain under

the maximum total daily discharge requirements specified in Table 7.21. Such

discharge requirement would be taken into account by the BPPS operator as

well as in the WPCO Discharge License of the BPPS upon the commissioning



7-50

of the proposed first additional CCGT unit. Operation phase effluent

monitoring would be conducted in the first year of operation of each of the

Additional CCGT Unit No.1 and No. 2 to ensure compliance to the proposed

discharge standard.

With the pollution reduction in existing waste stream and control of pollution

loading in the future waste stream, no net increase in pollution load in Deep

Bay would be expected from the expanded operation of the BPPS.

Compliance with the Town Planning Board Guidelines TPB PG-No. 12C

requirement is expected.

Under existing practice, the use of defoaming agent is required to avoid the

formation of foam due to the heating of organic-rich salt water in the cooling

water system. Defoamer PS, a defoaming agent, is used in current operation

and would also be used for the proposed Additional CCGT Unit No.1 and 2.

Defoamer PS contains about 1% of 2-[hydroxymethyl)amino]ethanol by

weight as its active ingredient while the remainder is water and additives (1).

Based on the 2013 to 2014 records of the BPPS, the average concentration of 2-

[hydroxymethyl)amino]ethanol in cooling discharge is about 0.211 µg L-1 (with

minimum of 0.067µg L-1 and maximum of 0.507µg L-1) to control the

formation of foam upon discharge and similar level of dosage is be expected

for the future operation of the proposed Additional CCGT Unit No.1 and No.

2. According to the USEPA (2 ), 2-[hydroxymethyl)amino]ethanol rapidly

degrades in the environment and therefore the exposure and risk to this

compound, while slightly toxic to aquatic organisms, is expected to be

minimal. Due to its rapid degradation, bioaccumulation is not known to be a

concern. Chemical toxicity studies on aquatic organism (3) (4) (5) indicates

LC/EC50 of fish and crustacean species are at least 19.6 mg L-1. For

conservative assessment and to take into account inter- and intra-species

variation, an assessment factor of 1,000 is considered to derive Predicted No-

Effect-Concentrations ( 6 ) for the compound, which is 19.6 µg L-1. The

Predicted No-Effect-Concentrations of the compound is over 90 times of the

existing and future discharge concentration of the compound. Hence, the use

of defoaming agent is not expected to result in adverse impact on nearby

marine ecology as well as other sensitive uses, while preventing the formation

of persistent foam which is prohibited under WQO as shown in Table 7.1. No

(1) Additives consist of fatty alcohol (long-chain alcohol, which is known to be non-toxic and biodegradable. Fatty

alcohol is also used commonly as non-ionic detergent, emulsifier and even dietary supplements for human.

(2) A USEPA R.E.D. Fact (EPA-738-F-93-024) available at

http://archive.epa.gov/pesticides/reregistration/web/pdf/3070fact.pdf. Last retrieved on 7 January 2016.

(3) PAN Pesticides database. Available at http://www.pesticideinfo.org/List_AquireAll.jsp?Rec_Id=PC33060.

Last retrieved on 7 January 2016.

(4) Material safety data sheet. Available at

http://www.kellysolutions.com/erenewals/documentsubmit/KellyData%5CND%5Cpesticide%5CMSDS%5C53

83%5C5383-11%5C5383-11_MERGAL_174_9_8_2004_4_40_21_PM.pdf. Last retrieved on 7 January 2016.

(5) Material safety data sheet. Available at http://www.walter-

tools.com/SiteCollectionDocuments/downloads/ca/valcool/en-us/msds-sheet-valcool-mergal-2010-us-en.pdf.

Last retrieved on 7 January 2016.

(6) Technical Guidance Document on Risk Assessment. European Chemical Bureau, Institute for Health and

Consumer Protection, European Commission. Available at

(https://echa.europa.eu/documents/10162/16960216/tgdpart2_2ed_en.pdf. Last retrieved on 7 January 2016.

http://archive.epa.gov/pesticides/reregistration/web/pdf/3070fact.pdf

http://www.kellysolutions.com/erenewals/documentsubmit/KellyData%5CND%5Cpesticide%5CMSDS%5C5383%5C5383-11%5C5383-11_MERGAL_174_9_8_2004_4_40_21_PM.pdf

http://www.kellysolutions.com/erenewals/documentsubmit/KellyData%5CND%5Cpesticide%5CMSDS%5C5383%5C5383-11%5C5383-11_MERGAL_174_9_8_2004_4_40_21_PM.pdf

http://www.walter-/

http://www.walter-/

https://echa.europa.eu/documents/10162/16960216/tgdpart2_2ed_en.pdf



7-51

unacceptable water quality impact associated with the use of defoaming agent

is expected.

Upon the operation of the additional CCGT units, an additional 20 operation

and maintenance staff would be required for each additional CCGT unit.

The associated increase in sewage generation (20 workers per unit × 150 L per

worker per day = 3,000 L per day per unit, i.e. 3,000 L per day for one

additional CCGT unit and 6,000 L per day for two additional CCGT units) is

considered minimal when compared with the average daily workforce size of

556 for the existing BPPS operation. There is sufficient capacity in the

existing permanent sewage treatment plant (item 11 in Table 7.20 to Table 7.21)

onsite to handle the additional sewage flow from the new staff. No direct

discharge of sewage would be expected and therefore no unacceptable water

quality impact is expected.

It should also be noted that there is an established drainage system within the

Project Site and the rest of the BPPS. Stormwater is collected onsite with

appropriate pollution control facilities. Similar drainage provisions would be

included at the Project Site upon the operation of the proposed additional

CCGT units. Therefore, no significant change in stormwater or other non-

point source pollution is expected during operation phase.

7.8.5 Chemical Cleaning during Plant Operation

As stated under Section 7.7.8 chemical cleaning would be required for CCGT

unit which has been in operation once every 10 to 20 years of operation for

maintenance. It is expected the same volume (about 5,000 m3 per event per

unit) and constituents (water, corrosion inhibitor, surfactant and pH control)

of wastewater would be generated from the event. Wastewater generated

will be neutralised to a pH range of 6 to 10 and discharged into the existing

Effluent Treatment Facility onsite for treatment. The wastewater will be

treated to appropriate discharge standards (as specified under the existing /

future WPCO discharge license). With compliance of the relevant discharge

standards same as the existing practice, no unacceptable water quality impact

would be expected from the cleaning events during the operation of the

additional CCGT Unit No.1 and No.2.

It should be highlighted that the need for chemical cleaning may vary among

CCGT units due to subtle differences on operation conditions and the cleaning

frequency is anticipated to be infrequent, i.e. once every 10 to 20 years of

operation. Chemical cleaning would be properly scheduled so the events are

spread out temporally to avoid concurrent washing as far as practicable. The

effluent from every cleaning event would be properly treated before

discharge. Also, as the wastewater from chemical cleaning would be

discharged into the existing Effluent Treatment Facility onsite, its contribution

to the total loading from the BPPS would also be controlled by the specified

measures stipulated under Section 7.8.4, therefore no net increase in pollution

load in Deep Bay would be expected from the expanded operation of the

BPPS.



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7.8.6 Maintenance Dredging at Proposed Seawater Intake and Outfall for


Subject to the actual rate of sedimentation upon the operation of the additional

CCGT units, maintenance dredging at the proposed seawater intake and

discharge outfall may be required at regular intervals. The extent of

maintenance dredging would be the same as that of the proposed dredging

under construction phase, and the thickness and total volume of sediment to

be removed would be much smaller. The potential water quality impacts

from construction phase dredging operation is assessed under Section 7.7, and

the potential water quality impacts on nearby WSRs from operation phase

maintenance dredging at the same or lower rate with the same mitigation

measures is considered similar or less significant. Since no unacceptable

water quality impact is predicted at the WSRs for construction phase

dredging, the same would be expected for operation phase maintenance

dredging.

It should be highlighted that during the operation phase of the additional

CCGT units, the intake of the second additional CCGT unit would be itself a

WSR to SS elevation from the maintenance dredging. Since the intake itself

would be the most affected by the maintenance dredging near the intake,

additional modelling assessment has been conducted to determine the

potential maximum SS elevation from the maintenance dredging based on the

mitigated 740 m3 per day dredging rate with silt curtain around the grab

dredger. The predicted maximum SS elevations at the new seawater intake

for maintenance dredging near the seawater intake are presented in Table 7.23.

Table 7.23 Predicted Maximum Elevation in Suspended Solids at Seawater Intake of the

Second Additional CCGT Unit WSRs from Maintenance Dredging at

Seawater Intake



Criteria Max Criteria Max

Seawater Intake of the Second Additional CCGT Unit 700 23.66 700 14.13

The predicted SS elevations at new seawater intake are below the

corresponding assessment criteria in both seasons. In view of the far longer

separation from the new seawater intake to the dredging area at the discharge

outfall, the potential SS elevation at the new seawater intake would be much

lower for dredging at the discharge outfall and thus is not further discussed.

Other water quality parameters, such as DO depletion, nutrient, heavy metals

and tracer organic contaminants would also be affected by the maintenance

dredging. The potential water quality impacts on all WSRs identified are

expected to be the same or below that of the construction phase dredging

operation, which are all found to have no unacceptable impact. The new

seawater intake for the second additional CCGT unit is not considered to be

sensitive to these water quality parameters, and assessment for these water

quality parameters are considered not necessary. No unacceptable water



7-53

quality impact from the maintenance dredging at the proposed seawater

intake and discharge outfall is expected.

7.9 MITIGATION MEASURES


Marine Construction

To minimise potential water quality impacts from elevated SS due to the

proposed dredging works for the additional CCGT Unit No.2 at the seawater

intake and discharge outfall, the following mitigation measures are

recommended:

Reduction of dredging rate from 4,000 m3 per day to 740 m3 per day for

dredging at the seawater intake and discharge outfall;

Floating type silt curtain around grab dredger; and

Another single layer of floating type silt curtain surrounding coral colonies

identify at dive survey Transect C (SR18).

Silt curtains shall be formed from tough, abrasion resistant, permeable

membranes, suitable for the purpose, supported on floating booms in such a

way as to ensure that the sediment plume shall be restricted to within the limit

of the works area. The silt curtain shall be formed and installed in such a

way that tidal rise and fall are accommodated, with the silt curtains always

extending from the surface to the bottom of the water column and held with

anchor blocks. The silt curtain surrounding SR18 should provide sufficient

clearance to the coral colonies such that no direct impact from the installation

and anchoring of silt curtain would be inflicted on the coral colonies. The

contractor shall regularly inspect the silt curtains and check that they are

moored and marked to avoid danger to marine traffic. Regular inspection on

the integrity of the silt curtain should be carried out by the contractor and any

damage to the silt curtain shall be repaired by the contractor promptly.

Relevant marine works shall only be undertake when the repair is fixed to the

satisfaction of the engineer.

Construction of intake and outfall structure shall be conducted behind

drained cofferdam as stated in Section 3. This minimises the potential

disturbance to the seabed and the associated impact on water quality.

Furthermore, a number of standard measures and good site practices are

recommended to be implemented to avoid/minimise the potential impacts

from marine construction. These measures include:

All vessels should be well maintained and inspected before use to limit

any potential discharges to the marine environment;

All vessels must have a clean ballast system;



7-54

No discharge of sewage/grey wastewater should be allowed.

Wastewater from potentially contaminated area on working vessels

should be minimized and collected. These kinds of wastewater should

be brought back to port and discharged at appropriate collection and

treatment system; and

No soil waste is allowed to be disposed overboard.

Land-based Construction

Standard site practices outlined in ProPECC PN 1/94 “Construction Site

Drainage” will be followed as far as practicable in order to reduce surface

runoff, minimise erosion, and also to retain and reduce any SS prior to

discharge. These practices include the following:

Silt removal facilities such as silt traps or sedimentation facilities will be

provided to remove silt particles from runoff to meet the requirements of

the TM standard under the WPCO. The design of silt removal facilities

will be based on the guidelines provided in ProPECC PN 1/94. All

drainage facilities and erosion and sediment control structures will be

inspected on a regular basis and maintained to confirm proper and

efficient operation at all times and particularly during rainstorms.

Deposited silt and grit will be removed regularly.

Earthworks to form the final surfaces will be followed up with surface

protection and drainage works to prevent erosion caused by rainstorms.

Appropriate surface drainage will be designed and provided where

necessary.

The precautions to be taken at any time of year when rainstorms are likely

together with the actions to be taken when a rainstorm is imminent or

forecasted and actions to be taken during or after rainstorms are

summarised in Appendix A2 of ProPECC PN 1/94.

Oil interceptors will be provided in the drainage system where necessary

and regularly emptied to prevent the release of oil and grease into the

storm water drainage system after accidental spillages.

Temporary and permanent drainage pipes and culverts provided to

facilitate runoff discharge, if any, will be adequately designed for the

controlled release of storm flows.

The temporary diverted drainage, if any, will be reinstated to the original

condition when the construction work has finished or when the

temporary diversion is no longer required.

As the Project site is next to the shoreline, infiltration of seawater during

excavation is anticipated. Appropriate infiltration control, such as cofferdam

wall, is recommended to be adopted to limit groundwater inflow to the



7-55

excavation works areas in the Project site. Groundwater pumped out from

excavation area should be discharged into the storm system via silt removal

facilities.

Appropriate numbers of chemical toilets shall be provided by a licensed

contractor to serve the construction workers over the construction site to

prevent direct disposal of sewage into the water environment.


Modelling assessment for operation phase thermal and TRC discharge

indicated that no unacceptable water quality impact would be expected from

the discharge of additional CCGT units cooling water. To ensure compliance

with the effluent discharge standards stipulated in Sections 7.8.1 and 7.8.2,

monitoring of effluent temperature as well as TRC level is recommended for

the first year of operation of the first and second additional CCGT units.

Furthermore, water quality monitoring at nearby WSRs is recommended for

first year of operation of the first and second additional CCGT units. Details

are provided in the standalone EM&A Manual.

The additional risk associated with accidental fuel spill from the operation of

the additional CCGT units is expected to be minimal. Design features such

as shutdown valves and leak detectors are also included to avoid and

minimise potential fuel leak. The contingency plan for the existing operation

of the BPPS is considered sufficient for directing immediate response to any

accidental spillage event. No additional water quality mitigation measure is

required.

Control measures would be implemented to ensure total average daily

loading of batch wise discharge of effluents from the future operation of BPPS

remain below the maximum allowed level of the existing operation. These

measures include (1) batch wise discharge to allow settlement and removal of

part of the pollution load, (2) laboratory measurements to ensure compliance

with the discharge limits before batch wise discharge and (3) disposal of

effluent from the station effluent treatment plant, oil separator and sewage

treatment facility offsite by licensed collector for treatment if needed. This

makes the overall pollution load from the operation of the expanded BPPS (i.e.

two additional CCGT units included) remain the same at the level of the

existing operation.

There is existing drainage and sewerage infrastructure onsite which would

also cover the proposed Project upon its operation. Therefore no additional

mitigation measures would be required on these aspects.

With the implementation of the above measures, no unacceptable water

quality impact from the operation of the proposed additional CCGT units is

expected.

Mitigation measures required for maintenance dredging at seawater intake

and discharge outfall for additional CCGT Unit No.2 would be the same as



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that recommended for construction phase dredging operation under Section

7.9.1. With the implementation of the proposed measures, no unacceptable

water quality impact from the operation phase maintenance dredging is

expected.

7.10 RESIDUAL IMPACT


It is predicted that the maximum SS elevation at all WSRs would be in

compliance with the corresponding WQO SS criteria with the implementation

of proposed mitigation measures. No unacceptable residual water quality

impact from SS elevation due to marine dredging at seawater intake and

discharge outfall is expected.

No exceedance of the proposed sedimentation criterion is predicted at coral

colonies at SR18 and artificial reef at SR12 with the implementation of

proposed mitigation measures. No unacceptable sedimentation impact from

SS elevation due to marine dredging at seawater intake and discharge outfall

is expected.

With the implementation of proposed mitigation measures, no exceedance of

the WQO DO criteria is predicted at all WSRs in the mitigated scenario. No

unacceptable dissolved oxygen depletion due to marine dredging at seawater

intake and discharge outfall is expected.

With the implementation of proposed mitigation measures, no exceedance of

the proposed assessment criteria for TIN and UIA is predicted at all WSRs in

the mitigated scenario. Sediment elutriate test results indicated there is no

tendency of release of heavy metals, metalloid and trace organic contaminants

from the sediment to the water column. No unacceptable water quality

impact from release of nutrient and contaminants due to marine dredging at

seawater intake and discharge outfall is expected.

Potential water quality impacts from land-based construction activities are

expected to be controlled with the implementation of proposed mitigation

measures stipulated in Section 7.9.1. No unacceptable water quality impact

from land-based construction activities is expected.


Modelling assessment for operation phase thermal and TRC discharge

indicated that no unacceptable water quality impact would be expected from

the discharge of additional CCGT units cooling water. Some level of increase

in duration when water temperature at seawater intake exceeds the optimum

30 °C may occur. Yet the increase is minimal for normal operation of the

existing BPPS.

The additional risk associated with accidental fuel spill from the operation of

the additional CCGT units is expected to be minimal. With the



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implementation of leak control design features as well as the adoption of

contingency plan for the existing operation of the BPPS, no unacceptable

water quality impact would be expected.

With the implementation of the proposed measures in controlling overall

pollution load discharge from the BPPS into the Deep Bay WCZ, there would

be no net increase in pollution load into the Deep Bay WCZ from the BPPS

upon the future expanded operation. The discharge level of defoaming agent

would be much lower than that of the Predicted No-Effect-Concentrations for

the compound and no adverse impact to marine ecology as well as other

sensitive uses is expected. No unacceptable water quality impact from the

operation of the proposed additional CCGT units is expected.

With the implementation of the proposed measures in controlling SS

dispersion from maintenance dredging at seawater intake and discharge

outfall, no unacceptable water quality impact from the operation phase

maintenance dredging is expected.

7.11 CUMULATIVE IMPACT

According to publicly available sources, a list of identified projects in the

vicinity of BPPS is summarised in Table 5.1 of Annex 7B. Considerations with

regards to cumulative water quality impact assessment are further elaborated

below.



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Table 7.24 Nearby Projects Identified and Consideration in Water Quality Assessment in this EIA

Project Duration Location Major Marine Activity Considerations in Water Quality Assessment

Engineering Feasibility Study

for Industrial Estate at Tuen

Mun Area 38 (EIA 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

(1) Letter was issued to the Hong Kong Science and Technology Parks

Corporation (the project proponent) to obtain the letter project update.

Hong Kong Science and Technology Parks Corporation replied there is

no further update in design and project programme available. Thus

assessment was done based solely on information provided by the

submitted project profile.

(2) Based on the project profile, project construction at Tuen Mun Area

38 would tentatively be commenced in 2019 and be completed by 2023.

It is not expected that the marine construction required for the second

additional CCGT unit under this Project would be conducted

concurrently with those of the Tuen Mun Area 38 project. No

cumulative construction phase impact is expected.

(3) There is no sewage discharge under this Project. No thermal

discharge from the Tuen Mun Area 38 project is expected as well.

Therefore no cumulative water quality impact would be expected from

the discharge of treated sewage effluent under the Tuen Mun Area 38

project.

West New Territories (WENT)

Landfill Extensions (Register

No.: AEIAR-147/2009)

Uncertain West New

Territories

(WENT) Landfill

(2 km away)

nil No marine construction as well as direct discharge of sewage or landfill

leachate would be expected from the expanded operation. Therefore no

cumulative water quality impact would be expected.



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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

(1) 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 for the

second additional CCGT unit under this Project would be conducted

concurrently with those under the 3RS-HKIA. Therefore no cumulative

construction phase assessment is required.

(2) The proposed reclamation of the three runway system is expected to

be completed before the commencement of the marine construction

under this Project. Therefore the presence of reclamation of the three

runway system has been included in the modelling assessment for

construction and operation phase under this EIA.

(3) Cooling water intakes and thermal discharge from the expanded

airport operation is considered minimal and is far away from the Project

(> 9km). Therefore they are not taken into account in the modelling

assessment.

Pyrolysis Plant at EcoPark (EIA

Study Brief ESB-259/2013)

Construction: 2015 EcoPark of Tuen

Mun (4.5 km

away)

nil (1) No marine works would be required for the pyrolysis plant

development. No cumulative construction phase assessment would be

required.

(2) 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.



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Potential Reclamation Site at

Lung Kwu Tan

Uncertain Lung Kwu Tan

(1.5 km away)

Reclamation (1) Letter was issued to the Civil Engineering and Development

Department (CEDD, the project proponent) to obtain the letter project

update. CEDD replied the reclamation at Lung Kwu Chau would be

commenced in 2021 the earliest, and could be subjected to changes.

CEDD also advised the consultant to refer to Cumulative Environmental

Impact Assessment for the Three Potential Reclamation Sites in Western Waters (1) for information regarding other project information.

(2) The potential reclamation has been taken into account in the

operation phase water quality assessment to capture potential worst case

for operation. On the other hand, due to the lack of detailed

construction programme, phasing and construction method for the

reclamation at Lung Kwu Tan project, no cumulative construction phase

assessment can be conducted.

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 No marine works and major discharge to marine water would be

required for this project. No cumulative water quality assessment

would be required.

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 No marine works would be required for this project. Since this is a

decommissioning project, there will not be an operation phase and no

discharge of cooling water or chlorine would be expected after the

completion of construction phase. No cumulative water quality

assessment would be required.

(1) Agreement No. CE 14/2013 (CE) Cumulative Environmental Impact Assessment Study for the Three Potential Nearshore Reclamation Sites in the Western Waters of Hong Kong - Investigation -

Executive Summary (Final) (2013). Retrieved October 6, 2015 from Civil Engineering and Development Department, Web site:

http://www.cedd.gov.hk/eng/landsupply/doc/Executive%20Summary%20on%20Final%20Report(S2)b.pdf



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Sludge Treatment Facilities (STF)

(Register No. AEIAR-129/2009)

Existing operation Tsang Tsui (1.5

km away)

nil (1) The sewage effluent from the Sludge Treatment Facilities operation

would be treated and reused onsite. No sewage discharge would be

required.

(2) A small scale desalination plant is installed onsite with saline

discharge of about 1,000 m3 per 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 has been taken into account in the modelling exercise

as a WSR (SR16).

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)

nil No marine works and major discharge to marine water would be

required for this project. No cumulative water quality assessment

would be required.

Black Point Power Station

(BPPS)

Existing operation At the immediate

vicinity

Cooling water discharge (1) The existing thermal discharge from the existing operation of the

BPPS has been taken into account in the construction and operation

phase modelling exercise. Also, the thermal and TRC discharge from

existing CCGT units at the BPPS have also been modelled in the baseline

and operation scenarios.

(2) The existing seawater intake of the BPPS has been taken into account

as a WSR (SR4) in the water quality modelling exercise.

Castle Peak Power Station

(CPPS)


Mun (4 km away)

Cooling water discharge (1) The existing discharge from the CPPS has been taken into account in

both the construction and operation phase sediment plume modelling

and thermal discharge modelling. Also, the thermal and TRC discharge

from the existing CCGT units at the BPPS has also been modelled in the

baseline and operation scenarios.

(2) The existing seawater intake of the CPPS has been taken into account

as WSR (SR9) in the water quality modelling exercise.

Green Island Cement Plant


Mun (4 km away)

nil There is no known discharge of cooling water or chlorine to marine

water from this current operation (1). No cumulative water quality

impact from the operation of the Green Island Cement Plant is expected.

(1) Green Island Cement (holding) Limited (2013). Cement Manufacturing Process. Retrieved October 2, 2015 from, Web site: http://www.gich.com.hk/Facilities/f_manflow.htm.



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Shiu Wing Steel Mill Existing operation Castle Peak, Tuen

Mun (4 km away)

nil (1) There is no known discharge of cooling water or chlorine to marine

water from this current operation. No cumulative water quality impact

from the operation of the Green Island Cement Plant is expected.

(2) The seawater intake for Shiu Wing Steel Mill has been taken into

account as a WSR (SR10) in the water quality modelling exercise.



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7.12 ENVIRONMENTAL MONITORING AND AUDIT


Marine water quality monitoring at selected WSRs is recommended for

marine dredging at seawater intake and discharge outfall under this Project.

Site audit would also be conducted throughout the marine and land-based

construction under this Project. Details of the environmental monitoring

procedures and audit requirements are provided in the standalone EM&A

Manual.


It is expected that regular monitoring of effluent quality during normal

operation is required under the WPCO Discharge Licence of the future

expanded BPPS. To ensure compliance with the effluent standard specified

in Sections 7.8.1 and 7.8.2 (or other standard stipulated in the WPCO Discharge

Permit), marine water monitoring at selected nearby WSRs during the first

year of project commission of the first and second additional CCGT units are

recommended to ensure compliance with WQO or other water quality criteria.

Details of the environmental monitoring procedures and audit requirements


Marine water quality monitoring at selected nearby WSRs would also be

required for maintenance dredging at seawater intake and discharge outfall.

Details of the environmental monitoring procedures and audit requirements


7.13 CONCLUSION


Computational modelling has been conducted to predict various potential

water quality impacts from the proposed marine dredging operation under

this Project, including SS elevation, sedimentation, DO depletion, release of

nutrient, heavy metal and trace organic pollutants. Full compliance is

predicted at all identified WSRs for all parameters in both seasons with the

implementation of (1) reduction in dredging rate from 4,000 m3 per day to 740

m3 per day, (2) silt curtain around grab dredger and (3) another layer of silt

curtain surrounding coral colonies at SR18. To ensure environmental

compliance, marine water monitoring for the marine dredging works is

recommended.

Other potential water quality impacts from marine and land-based

construction were also addressed. Appropriate preventive and mitigation

measures are recommended to minimise the potential water quality impact

from these works. Environmental monitoring and audit is recommended to

ensure the proper implementation of these measures.



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The potential change in hydrodynamic and water quality from Project

operation was assessed in detail using Delft3D modelling tools. The changes

in water temperature as well as TRC at WSRs during normal operation were

assessed quantitatively. The increase in water temperature and TRC level is

predicted to be highly localised in both seasons. The elevation in

temperature and TRC are predicted to be diluted and dissipated soon after

leaving the discharge outfall. The predicted effluent plume would not

encroach to additional nearby marine ecology and fisheries resources. To

ensure environmental compliance, monitoring of discharge effluent quality

and marine water quality at nearby selected WSRs are recommended.

No significant increase in potential risk of fuel spillage is expected from the

operation of the additional CCGT units. Design features such as shutdown

valves and leak detectors have been included to avoid and minimise potential

fuel leak. Contingency plan for the existing operation of the BPPS would be

in place and would be sufficient for directing immediate response to any

accidental spillage event. Therefore no significant increase in potential risk

of fuel spillage is expected.

With the implementation of the proposed measures in controlling overall

pollution load discharge from the BPPS into the Deep Bay WCZ, there would

be no net increase in pollution load into the Deep Bay WCZ from the BPPS

upon the future expanded operation. No unacceptable water quality impact

from the operation of the proposed additional CCGT units is expected.

Maintenance dredging at seawater intake and discharge outfall is also

expected during operation phase of the additional CCGT Unit No.2. No

unacceptable water quality impact from the maintenance dredging is expected

to the nearby WSRs.

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