Black Point Gas Supply Project

Table 6.1 Water Quality Objectives Applicable to the Study

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.	Whole zone	Whole zone (including North Western 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
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 ^oC.	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%.	Whole zone	Whole zone (including North Western 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	Marine waters (including North Western Supplementary Zone)
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)	Marine waters (including North Western Supplementary Zone) 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
a) 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	Inland waters (except the subzones stated in b))
b) 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
L. CHEMICAL OXYGEN DEMAND
a) 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	Inland waters (except the subzones stated in b))
b) 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
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	Whole zone (including North Western Supplementary Zone)
b) Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.	Whole zone	Whole zone (including North Western Supplementary 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

6.2.2 Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-ICW)

All discharges during both the construction and operation phases of the proposed development 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.

6.2.3 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 subjected 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.

6.2.4 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 provide useful guidelines on water pollution associated with construction activities.

6.3 Assessment Criteria

6.3.1 Suspended Solids

The Water Quality Objective (WQO) for suspended solids (SS) in marine waters of the Deep Bay WCZ and the North Western WCZ states that:

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

Analysis of EPD routine water quality monitoring data from the years of 1998 to 2007 ([1]) has been undertaken to determine the allowable increase in suspended solids concentrations within the WCZ. Data have been analysed from the EPD monitoring stations that are in the proximity of the proposed works (Figure 6.2).

WQO for SS in Deep Bay Water Control Zone

SS data from EPD monitoring station DM5, have been analysed to determine the allowable increase at the sensitive receivers close to the shore approach at Black Point within the outer Deep Bay WCZ. For those sensitive receivers within the inner Deep Bay WCZ, the SS criterion will make reference to station DM4.

WQO for SS North Western Water Control Zone

SS data from EPD monitoring station NM5 have been analysed to determine the allowable increase at the sensitive receivers close to the Project site.

SS Criterion for Seawater Intakes

The power station intakes have specific requirements for intake water quality. The applicable criteria for the Black Point Power Station and Castle Peak Power Station seawater intakes are temperature between 17 and 32°C and SS levels below 764 mg L^-1 respectively. It is hence reasonable to adopt an SS assessment criterion of 700 mg L^-1 for these two seawater intakes.

There are no particular criteria specified for the industrial intakes at Tuen Mun Area 38 and Shiu Wing Steel Mill, and hence the WQO was used as the criteria for these intakes.

6.3.2 Sediment Quality

Dredged sediments destined for marine disposal are classified according to a set of regulatory guidelines (Management Framework for Disposal of Dredged/Excavated Sediment, PNAP 252) issued by the Buildings Department in April 2007. These guidelines comprise a set of sediment quality criteria, which include organic pollutants and other substances. The requirements for the marine disposal of sediment are specified in the PNAP 252. Marine disposal of dredged materials is controlled under the Dumping at Sea Ordinance 1995.

6.3.3 Sediment Deposition

Impacts to artificial reefs (ARs) have been assessed with regard to sediment deposition. The assessment criterion of 200 g m^-2 day^-1, has been used in approved EIA Reports ([2]) ([3]) and has been adopted here.

6.3.4 Dissolved Oxygen

Oxygen depletion resulting from the dredging operations will be assessed against the WQO. The allowable changes in DO levels in the Deep Bay WCZ and North Western has been calculated based on the EPD routine water quality monitoring data over the period 1998 to 2007.

The assessment criterion for DO, in accordance with the WQO, at each sensitive receiver is discussed in Table 6.8.

6.3.5 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 the relevant international standards and this approach has been adopted in the previous approved EIAs, i.e., EIA for Decommissioning of Cheoy Lee Shipyard at Penny’s Bay ([4]), EIA for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit ([5]), EIA for Wanchai Development Phase II ([6]), EIA for Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities ([7]), and EIA for Hong Kong Offshore Wind Farm in Southeastern Waters ([8]).

Table 6.2 shows the assessment criteria for dissolved metals and organic pollutants for this Study.

Table 6.2 Summary of Assessment Criteria for Dissolved Metals and Organic Compounds

Parameter	Unit	Assessment Criteria for this Study
Heavy Metals
Cadmium (Cd)	ug L^-1	2.5 ^{(a) (b)}
Chromium (Cr)	ug L^-1	15 ^{(a) (b)}
Copper (Cu)	ug L^-1	5 ^{(a) (b)}
Nickel (Ni)	ug L^-1	30 ^{(a) (b)}
Lead (Pb)	ug L^-1	25 ^{(a) (b)}
Zinc (Zn)	ug L^-1	40 ^{(a) (c)}
Mercury (Hg)	ug L^-1	0.3 ^{(a) (b)}
Arsenic (As)	ug L^-1	25 ^{(a) (b)}
Silver (Ag)	ug L^-1	1.9 ^(e)
PAHs (Low Molecular Weight)
Naphthalene	ug L^-1	5 ^(a) (annual average)
Total PAHs	ug L^-1	3.0 ^(d)
PCBs
Total PCBs	ug/L	0.03 ^(e)
Chlorinated Pesticides
Heptachlor	ug/L	0.053 ^(e)
Aldrin	ug/L	0.01 ^(a) (annual average)
Heptachlor epoxide	ug/L	0.053 ^(e)
Alpha-Endosulfan	ug/L	0.034 ^(e)
Endosulfan	ug/L	0.003 ^(a) (annual average)
Total DDT (all four isomers)	ug/L	0.025 ^(a)
p, p'-DDT	ug/L	0.01 ^(a) (annual average)
Organotins
Tributyltin (TBT)	ug/L	0.002 ^(a) (maximum concentration)

Notes:

(a) UK Environment Agency, Environmental Quality Standards (EQS) for List 1 & 2 dangerous substances, EC Dangerous Substances Directive (76/464/EEC) (http://www.environment-agency.gov.uk/research/library/data/41315.aspx)

(b) Annual average dissolved concentration (ie usually involving filtration a 0.45-um membrane filter before analysis).

(d) Australian and New Zealand Environment and Conservation Council (ANZECC), Australian and New Zealand Guidelines for Fresh and Marine Water Quality (2000) – Trigger values for protection of 90% of species. (http://www.mincos.gov.au/publications/australian_and_new_zealand_guidelines_for_fresh_and_marine_water_quality)

(e) 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 (ie 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.

6.4 Baseline Conditions and Water Quality Sensitive Receivers

6.4.1 Hydrodynamics

In general, long period swell waves generated in the South China Sea propagate into Hong Kong waters, with energy dissipation due to refraction, diffraction, shoaling, wave breaking, bottom friction and shielding due to offshore islands. This results in wave energy reduction inshore of the outer islands and into shallower Hong Kong waters. It also gives Hong Kong a distinctive two peak frequency distribution, where one peak represents offshore swells and the other the shorter period inshore wind-driven waves. The north-east Monsoon is generally stronger and more persistent than the south-west Monsoon. The highest percentage of strong winds and hence waves are generated from north to southeast.

Current velocities are influenced by the semi-diurnal tidal regime of the South China Sea and the freshwater flows of the Pearl River Delta during the wet season. The further upstream of the Pearl River Estuary the greater the tidal distortion, shorter floodtide, longer ebb, and the greater the effect of fresh water flows.

Deep Bay Water Control Zone

The Black Point landing point is surrounded by a shallow and sediment-laden water body in the Outer Deep Bay region between Hong Kong and Shenzhen. Deep Bay has a surface area of approximately 112 km² (11,200 ha) with a length of about 15 km and an average depth of 3 m ([9]). The hydrodynamic regime of the Deep Bay area is unidirectional and the current direction reverses during ebb and flood tides. Tidal flow is dynamic and complex in the Deep Bay areas due to the seasonal influx of freshwater from the Pearl River to the Urmston Road. The Urmston Road is one of the main flow routes into and out of the Pearl River Estuary and carries significant volumes of water on each tide ([10]).

North Western Water Control Zone

The North Western WCZ is situated at the mouth of the Pearl River Estuary and, as such, is heavily influenced by the freshwater flows from the hinterland. The area shows distinct seasonality as a result of the seasonal influx of freshwater from the Pearl River. The estuarine influence is especially pronounced in the wet summer months when the freshwater flows are greatest and strong salinity and temperature stratification is prominent. During the winter months water conditions are more typically marine (with lower nutrient levels and higher DO levels) and salinity and other parameters vary less with depth. Ebb tide currents are towards the southeast where the flood tide currents move to the northwest. Current velocities in areas near to Sha Chau have been predicted in previous studies to reach up to 2.0 ms^-1 ([11]).

6.4.2 Water Quality

Water quality has been determined through a review of EPD routine water quality monitoring data collected between 1998 and 2007. 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.

Deep Bay Water Control Zone

On the basis of the 1998 to 2007 monitoring data, Dissolved Oxygen (DO) levels in Deep Bay the WCZ exhibited a decline from 1998 to 2003 followed by an increase thereafter. Total Inorganic Nitrogen (TIN) and Unionised Ammonia have been increasing over time. An increasing trend of SS levels between 1998 and 2001 is observed; however, between 2002 and 2007 SS levels have been declining.

Water quality in the Deep Bay Outer Subzone is generally compliant with the WQOs. The exception has been TIN, the levels of which have exceeded the WQO of < 0.5 mg L^-1 in all years (Table 6.3).

North Western Water Control Zone

The water quality in the North Western WCZ is influenced by effluent discharges from sewage treatment works, such as those at Siu Ho Wan and Pillar Point and Pearl River Delta flows in general. Data collected between 1998 and 2007 indicate that there have been elevations of SS and Unionised Ammonia. A decreasing trend for DO is observed from 1998 to 2003 and an increase is found in recent years. However, there was a drop in the compliance with the DO objective in 2007. Similar to the Deep Bay WCZ, the TIN levels in the North Western WCZ exceed the WQO of 0.5 mg L^-1 on a continual basis, especially at NM5 (Table 6.3). Of these monitoring stations, NM5 recorded the highest geometric mean of E. coli, 564 cfu 100 mL^-1.

Table 6.3 EPD Routine Water Quality Monitoring Data for the Deep Bay and North Western Water Control Zones (1998 – 2007)

Water Quality Parameter	Deep Bay WCZ		North Western WCZ
	DM4	DM5	NM5
Temperature (ºC)	24.1	23.8	23.6
	(14.4 - 32.8)	(14.4 - 31.1)	(15.5 - 30.7)
pH	7.9	7.9	8.0
	(6.3 - 9.0)	(6.2 - 9.3)	(7.3 - 8.7)
Dissolved Oxygen (mg L^-1) Depth-averaged	5.9	5.8	5.9
Dissolved Oxygen (mg L^-1) Depth-averaged	(2.9 - 10.2)	(2.6 - 10.0)	(2.1 - 9.6)
Dissolved Oxygen (mg L^-1) Bottom	5.9	5.7	5.5
Dissolved Oxygen (mg L^-1) Bottom	(2.9 - 10.2)	(2.6 - 10.0)	(2.1 - 9.2)
Dissolved Oxygen (% sat.) Depth-averaged	81.3	81.2	80.6
Dissolved Oxygen (% sat.) Depth-averaged	(40.0 - 164.0)	(38.0 - 183.0)	(30.0 - 130.0)
Dissolved Oxygen (% sat.) Bottom	80.7	79.0	76.4
Dissolved Oxygen (% sat.) Bottom	(40.0 - 145.0)	(38.0 - 122.0)	(30.0 - 116.0)
5-day Biochemical Oxygen Demand (mg L^-1)	1.1	1.0	0.8
5-day Biochemical Oxygen Demand (mg L^-1)	(<0.1 - 5.1)	(<0.1 - 11.0)	(<0.1 - 4.1)
Suspended Solids (mg L^-1)	13.5	10.5	12.5
	(2.2 - 62.0)	(1.1 - 62.0)	(1.2 - 81.0)
Total Inorganic Nitrogen (mg L^-1)	1.04	0.70	0.58
Total Inorganic Nitrogen (mg L^-1)	(0.33 - 2.77)	(0.15 - 2.46)	(0.03 - 2.30)
Unionised Ammonia (mg L^-1)	0.012	07	07
Unionised Ammonia (mg L^-1)	(<01 - 0.050)	(<01 - 0.037)	(<01 - 0.027)
Chlorophyll-a (µg L^-1)	4.1	3.1	3.2
Chlorophyll-a (µg L^-1)	(0.2 - 63.0)	(0.3 - 72.0)	(0 - 37)
Escherichia coli (cfu 100mL^-1)	256	401	564
Escherichia coli (cfu 100mL^-1)	(3 - 9,500)	(2 - 6,000)	(2 - 28,000)

Notes:

1. Data presented are depth averaged calculated by taking the means of three depths, i.e. surface (S), mid-depth (M) and bottom (B), except as specified.

2. Data presented are annual arithmetic means except for E. coli, which are geometric means.

3. Data enclosed in brackets indicate the ranges regardless of the depths.

4. Shaded cells indicate non-compliance with the WQOs.

5. Outliers (i.e. Interquartile Range computation) have been removed.

Water Quality of Marine Parks

The Agriculture, Fisheries and Conservation Department (AFCD) commenced a routine water quality monitoring programme in 1999 to collect baseline water quality data from existing and proposed Marine Parks/Marine Reserves in Hong Kong. The water quality monitoring results for the Sha Chau and Lung Kwu Chau Marine Park (1999 – 2009) are summarised in Table 6.4.

Table 6.4 Summary of Water Quality in the Sha Chau and Lung Kwu Chau Marine Park ([12])

Water Quality Parameter	Sha Chau and Lung Kwu Chau Marine Park
	N Lung Kwu Chau	N Sha Chau	Pak Chau	SE Sha Chau
	(1999 – 2009)	(1999 – 2000)	(1999 – 2009)	(1999 – 2000)
Temperature (°C)	24.0	24.3	24.1	24.3
Salinity (ppt)	25.2	23.9	25.9	25.1
pH	8.0	8.1	8.0	8.1
Dissolved Oxygen (mg L^-1)	5.8	5.8	5.9	5.8
Suspended Solids (mg L^-1)	16.6	9.7	23.4	10.0
BOD₅ (mg L^-1)	1.1	0.8	1.2	0.7
Ammonia Nitrogen (mg L^-1)	0.2	0.2	0.2	0.2
Unionized Ammonia (mg L^-1)	0.041	0.029	0.050	0.030
Nitrite Nitrogen (mg L^-1)	0.29	0.34	0.28	0.33
Nitrate Nitrogen (mg L^-1)	1.48	3.77	1.36	3.68
Total Inorganic Nitrogen (mg L^-1)	1.37	0.54	1.30	0.56
Total Kjeldahl Nitrogen (mg L^-1)	2.06	3.98	2.15	3.81
Total Nitrogen (mg L^-1)	4.97	14.82	4.89	16.21
Orthophosphate Phosphorus (mg L^-1)	0.15	0.06	0.11	0.05
Total Phosphorus (µg L^-1)	0.55	0.10	0.43	0.09
Silica (mg L^-1)	0.97	1.16	1.02	1.10
Chlorophyll-a (µg L^-1)	3.18	2.59	2.90	2.78
Phaeo-pigment (µg L^-1)	2.18	1.07	1.81	1.09
E. coli (CFU/100 mL)	277	54	149	58
Faecal Coliforms (CFU/100 mL)	1090	117	960	114

6.4.3 Sediment Quality

EPD Sediment Quality Monitoring

EPD collects sediment quality data as part of the marine water quality monitoring programme. There are three relevant monitoring stations in the vicinity of the Project site, i.e., Stations DS3 and DS4 in the Deep Bay WCZ and Station NS4 in the North Western WCZ. The locations of these stations are shown in Figure 6.2.

Data for these stations obtained from the EPD and are presented in Table 6.5. The data represent the range of values obtained over the period 2003 to 2007. As with the water quality data, this dataset provides Hong Kong’s most comprehensive long term sediment quality monitoring data and provides an indication of temporal and spatial change in marine sediment quality in Hong Kong.

The values for metals, Polycyclic Aromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs) may also be compared to the relevant sediment quality criteria specified in Management Framework for Disposal of Dredged/Excavated Sediment, Buildings Department Practice Note for Authorized Persons and Registered Structural Engineers 252 (PNAP 252).

A comparison of the data with the sediment quality criteria (i.e., Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL)) shows that the levels of arsenic (expressed as the arithmetic mean) for Stations DS3 and DS4 have exceeded the LCEL and hence they are classified as Category M. Although the maximum values of arsenic recorded at NS4 and copper and zinc at DS3 have exceeded the LCELs, their mean values were below the UCELs. Sediment with only one contaminant concentration (arithmetic mean) exceeding the LCEL levels and none exceeding the UCEL would not be expected to be a threat to the marine environment.

Parameter	Deep Bay WCZ	North Western WCZ	PNAP 252 Sediment Quality Criteria
COD (mg kg^-1)	16,000	15,000	16,000	-	-
(12,000 - 18,000)	(13,000 - 18,000)	(12,000 - 19,000)
Total Carbon (% w/w)	0.6	0.6	0.7	-	-
(0.5 - 0.7)	(0.4 – 0.8)	(0.6 - 0.8)
Ammonia Nitrogen (mg kg^-1)	1.6	2.7	14.0	-	-
(<0.05 - 7.9)	(<0.05 - 15.0)	(0.2 - 30.0)
TKN (mg kg^-1)	290	240	280	-	-
(160 - 430)	(100 - 410)	(160 - 350)
Total Phosphorous (mg kg^-1)	200	150	170	-	-
(120 - 270)	(70 - 240)	(92 - 230)
Total Sulphide (mg kg^-1)	59	12	30	-	-
(2 - 160)	(1 - 68)	(3 - 77)
Arsenic (mg kg^-1)	13.0	12.1	10.1	12	42
(7.7 – 15.0)	(7.6 – 18.0)	(9.1 – 11.0)
Cadmium (mg kg^-1)	0.3	0.1	0.1	1.5	4
(<0.1 - 0.4)	(<0.1 - 0.2)	(<0.1 - 0.1)
Chromium (mg kg^-1)	44	32	29	80	160
(24 - 53)	(16 - 47)	(26 - 36)
Copper (mg kg^-1)	58	21	28	65	110
(12 - 77)	(9 - 64)	(18 - 42)
Lead (mg kg^-1)	54	40	36	75	110
(32 - 69)	(31 – 58)	(29 - 46)
Mercury (mg kg^-1)	0.13	0.06	0.09	0.5	1
(<0.05 - 0.16)	(<0.05 - 0.14)	(0.06 - 0.20)
Nickel (mg kg^-1)	30	19	19	40	40
(16 - 35)	(15 - 31)	(16 - 22)
Silver (mg kg^-1)	0.6	0.2	0.3	1	2
(<0.2 - 0.8)	(<0.2 - 0.5)	(<0.2 - 0.3)
Zinc (mg kg^-1)	160	88	100	200	270
(81 - 230)	(69 - 140)	(99 - 110)
Total PCBs (µg kg^-1)	18	18	18	23	180
(18 - 18)	(18 - 18)	(18 - 18)
Low Molecular Wt PAHs (µg kg^-1)	92	91	92	550	3,160
(90 - 98)	(90 - 95)	(90 - 99)
High Molecular Wt PAHs (µg kg^-1)	100	39	64	1,700	9,600
(29 – 280)	(16 - 82)	(35 - 120)

Table 6.6 Approximate Shortest Distance to Water Quality Sensitive Receivers (SRs) around Proposed GRSs at Black Point and Submarine Pipelines (HKSAR Section)

Sensitive Receiver	Name	ID	Approximate Shortest Distance to the Reclamation (km)	Approximate Shortest Distance to the Pipelines (km)	Assessment Criteria
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	5.18	5.21	· Water Quality Objectives (WQO)
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	4.74	4.83	· Water Quality Objectives (WQO)
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	8.55	7.79	· Water Quality Objectives (WQO) · Deposition Rate below 200 g m^-2 day^-1
*Marine Ecological Sensitive Receivers*
Mangroves	Sheung Pak Nai	SR2	5.18	5.21	· Water Quality Objectives (WQO)
	Ngau Hom Shek	SR2a	6.73	6.75	· Water Quality Objectives (WQO)
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	5.14	2.97	· Water Quality Objectives (WQO)
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	4.14	3.34	· Water Quality Objectives (WQO)
Intertidal Mudflats	Ha Pak Nai	SR1	3.06	3.10	· Water Quality Objectives (WQO)
Seagrass Beds	Sheung Pak Nai	SR2	5.18	5.21	· Water Quality Objectives (WQO)
Seagrass Beds	Ha Pak Nai	SR1	3.06	3.10	· Water Quality Objectives (WQO)
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	3.06	3.10	· Water Quality Objectives (WQO)
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	6.73	6.75	· Water Quality Objectives (WQO)
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	1.92	2.00	· Water Quality Objectives (WQO)
Non-gazetted Beaches	Lung Kwu Tan	SR5b	3.67	3.74	· Water Quality Objectives (WQO)
Secondary Recreation Subzone	NW WCZ	SR5b	3.67	3.74	· Water Quality Objectives (WQO)
Seawater Intakes	Black Point Power Station	SR4	1.04	1.12	· Temperature between 17-30 °C · SS elevations less than 700 mg L^-1
	Castle Peak Power Station	SR7a	4.78	4.86	· Temperature between 17-30 °C · SS elevations less than 700 mg L^-1
	Tuen Mun Area 38	SR7b	6.27	6.34	· Water Quality Objectives (WQO)
	Shiu Wing Steel Mill	SR7i	5.62	5.70	· Water Quality Objectives (WQO)

Notes:

1. Distances are approximate and will depend on the final design of the alignment of the submarine utilities which will be determined during the detailed design stage.

2. Refer to next two tables for the details of the WQO criteria for SS and DO at each station.

Table 6.7 Ambient Level and Allowable Increase in Suspended Solids (SS) at Sensitive Receivers (SRs) around Proposed Submarine Pipelines (HKSAR Section)

Sensitive Receiver	Name	ID	Respective EPD Monitoring Station	Relevant Depth	Suspended Solids (mg L^-1)
					Annual			Dry (Nov to Mar)		Wet (Apr to Oct)
					Ambient Level ¹		WQO Allowable Increase ²	Ambient Level ¹	WQO Allowable Increase ²	Ambient Level ¹	WQO Allowable Increase ²
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	DM4	Surface ³	21.0	6.3		21.1	6.3	18.2	5.5
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
				Bottom	51.0	15.3		46.8	14.0	51.0	15.3
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
				Bottom	51.0	15.3		46.8	14.0	51.0	15.3
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	DM4	Surface ³	21.0	6.3		21.1	6.3	18.2	5.5
	Ngau Hom Shek	SR2a	DM4	Surface ³	21.0	6.3		21.1	6.3	18.2	5.5
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a,c	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
Intertidal Mudflats	Ha Pak Nai	SR1	DM5	Surface ³	15.1	4.5		19.8	5.9	13.1	3.9
Seagrass Beds	Sheung Pak Nai	SR2	DM4	Surface ³	21.0	6.3		21.1	6.3	18.2	5.5
	Ha Pak Nai	SR1	DM5	Surface ³	15.1	4.5		19.8	5.9	13.1	3.9
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	DM5	Depth-averaged	22.4	6.7		33.1	9.9	18.5	5.6
	Ngau Hom Shek	SR2a	DM4	Depth-averaged	31.2	9.3		31.2	9.3	31.7	9.5
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
	Lung Kwu Tan	SR5b	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
Secondary Contact Recreation Subzone	NW WCZ	SR5b	NM5	Depth-averaged	23.3	7.0		27.1	8.1	21.5	6.4
Seawater Intakes	Tuen Mun Area 38	SR7b	NM5	Bottom	51.0	15.3		46.8	14.0	51.0	15.3
	Shiu Wing Steel Mill	SR7i	NM5	Bottom	51.0	15.3		46.8	14.0	51.0	15.3
	Black Point Power Station	SR4	DM5	Bottom	34.1	700 ⁽⁴⁾		43.1	700 ⁽⁴⁾	26.2	700 ⁽⁴⁾
	Castle Peak Power Station	SR7a	NM5	Bottom	51.0	700 ⁽⁴⁾		46.8	700 ⁽⁴⁾	51.0	700 ⁽⁴⁾

Notes:

1. Ambient level is calculated as 90^th percentile of the EPD routine monitoring data (1998-2007) at respective EPD station close to the WSRs.

2. Allowable increase is calculated as 30% of the ambient SS levels in accordance with the WQO

3. These intertidal sensitive receivers occur at the water surface and are in fact completely unsubmerged for a substantial proportion of the time. Tidal range in Hong Kong is 2.5 m and this is the maximum depth these sensitive receivers would be submerged during the tidal cycle. It is considered that water quality reflecting surface conditions is appropriate for these periodically submerged sensitive receivers.

4. Power station intake has specific requirements for intake water quality. The applicable criterion for SS is between 30 and 764 mg L^-1. The tolerance criterion of 700 mg L^-1 was adopted

Table 6.8 Ambient Level and Allowable Decrease in Dissolved Oxygen (DO) at Sensitive Receivers (SRs) around Proposed Submarine Pipelines (HKSAR Section)

Sensitive Receiver	Name	ID	Respective EPD Monitoring Station	Relevant Depth	Dissolved Oxygen (mg L^-1)
					Annual			Dry (Nov to Mar)			Wet (Apr to Oct)
					Ambient Level ¹		WQO Allowable Depletion ²	Ambient Level ¹	WQO Allowable Depletion ²		Ambient Level ¹	WQO Allowable Depletion ²
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	DM4	Surface ³	7.6	3.6		7.6		3.6	7.4		3.4
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
				Bottom	7.5	5.5		8.0		6.0	6.3		4.3
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
				Bottom	7.5	5.5		8.0		6.0	6.3		4.3
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	DM4	Surface ³	7.6	3.6		7.6		3.6	7.4		3.4
	Ngau Hom Shek	SR2a	DM4	Surface ³	7.6	3.6		7.6		3.6	7.4		3.4
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a,c	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
Intertidal Mudflats	Ha Pak Nai	SR1	DM5	Surface ³	7.3	3.3		8.1		4.1	6.9		2.9
Seagrass Beds	Sheung Pak Nai	SR2	DM4	Surface ³	7.6	3.6		7.6		3.6	7.4		3.4
	Ha Pak Nai	SR1	DM5	Surface ³	7.3	3.3		8.1		4.1	6.9		2.9
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	DM5	Depth-averaged	7.3	3.3		7.8		3.8	6.6		2.6
	Ngau Hom Shek	SR2a	DM4	Depth-averaged	7.6	3.6		7.6		3.6	7.4		3.4
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
	Lung Kwu Tan	SR5b	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
Secondary Contact Recreation Subzone	NW WCZ	SR5b	NM5	Depth-averaged	7.7	3.7		8.2		4.2	6.9		2.9
Seawater Intakes	Tuen Mun Area 38	SR7b	NM5	Bottom	7.5	5.5		8.0		6.0	6.3		4.3
	Shiu Wing Steel Mill	SR7i	NM5	Bottom	7.5	5.5		8.0		6.0	6.3		4.3
	Black Point Power Station	SR4	DM5	Bottom	7.4	-- ⁽⁴⁾		7.8		-- ⁽⁴⁾	6.4		-- ⁽⁴⁾
	Castle Peak Power Station	SR7a	NM5	Bottom	7.5	-- ⁽⁴⁾		8.0		-- ⁽⁴⁾	6.3		-- ⁽⁴⁾

Notes:

1. Ambient level is calculated as 90^th percentile of the EPD routine monitoring data (1998-2007) at respective EPD station close to the WSRs.

2. For depth-averaged, surface layer and middle layer, allowable change is calculated as WQO criterion of 4 mg L^-1minus the ambient level, with the exception for the Fish Culture Zone.

4. There is no DO criterion for Black Point Power Station and Castle Peak Power Station intakes.

6.4.5 Fisheries Resources

The following fisheries resources have been identified as water quality sensitive receivers:

· Oyster Production Area;

· Recognised Commercial Fisheries Spawning Grounds; and

· Artificial Reef Deployment Sites.

Brief descriptions of these sensitive receivers are presented below.

Oyster Production Area

There is an area of oyster production along the coast of Deep Bay in Hong Kong waters (Figure 6.3). The shallowness of Deep Bay as a result of silt carried down from the Pearl River and typical estuarine conditions within Deep Bay enhances oyster cultivation.

There is no specific water quality criterion for the oyster production area, thus the WQOs have been adopted.

The area nearest to the works site was included as a discrete assessment point in the model.

Recognised Commercial Fisheries Spawning Grounds

The waters of Northwest Lantau have been identified as important fisheries spawning for commercial fisheries in Hong Kong ([13]).

To date there are no legislated water quality standards for spawning and nursery grounds in Hong Kong. Guideline values have been identified for fisheries and selected marine ecological sensitive receivers as part of the AFCD study ([14]), Consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment. The AFCD study recommends a maximum SS concentration of 50 mg L^-1 (based on half of the No Observable Effect Concentration). However, the study cautioned that site-specific data should be considered in environmental assessments on a case-by-case basis. In order to provide a more conservative assessment (i.e. with a lower tolerance criterion), the WQOs are adopted instead in this study as the assessment criteria.

With regard to the water quality modelling, impacts to other transitory or mobile sensitive receivers were not plotted as discrete points.

Artificial Reef Deployment Sites

There is one gazetted Artificial Reef Deployment Site (AR) situated within the Sha Chau and Lung Kwu Chau Marine Park (Figure 6.3). The Sha Chau and Lung Kwu Chau AR site is approximately 6 km from the Project site. The AR has been deployed to act as a fisheries resource enhancement tool, to encourage growth and development of a variety of marine organisms, and to provide feeding opportunities for the Indo-Pacific Humpback Dolphin (see Section 8, Marine Ecology Assessment).

There is no specific water quality criterion for the AR site, thus the WQOs criteria have been adopted. The AR site will be treated as a discrete assessment point in the model.

6.4.6 Marine Ecological Resources

The following Marine Ecological Resources have been identified as water quality sensitive receivers.

· Sha Chau and Lung Kwu Chau Marine Park; and

· Seagrass Beds, Mangroves, Intertidal Mudflats and Horseshoe Crab Nursery Grounds.

Marine Park

The Sha Chau and Lung Kwu Chau Marine Park, designated specifically for the protection of the Indo-Pacific Humpback Dolphin (Sousa chinensis), lies within the study area (Figure 6.3). There are no specific legislative water quality criteria for Marine Parks and the water quality at this sensitive receiver is typically compared with the WQO. For the water quality assessment, discrete points have been plotted at a number of locations along the boundaries of the Marine Park.

Seagrass Beds, Mangroves, Intertidal Mudflats & Horseshoe Crab Nursery Grounds

Seagrass beds, mangroves and intertidal mud flats are areas where horseshoe crabs are known to breed and have been identified for the study (Figure 6.3). There are no specific legislative water quality criteria for these habitats and hence potential water quality impacts on these habitats are assessed against compliance with the WQO. These habitats have been plotted as discrete points for evaluation.

6.4.7 Other Water Quality Sensitive Receivers

The following additional water quality sensitive receivers have been identified and included in the assessment.

· Bathing Beaches;

· Seawater Intakes.

Bathing Beaches

The two non-gazetted bathing beaches are located at Lung Kwu Sheung Tan and Lung Kwu Tan (Figure 6.3). The closest non-gazetted beach to the proposed pipeline is Lung Kwu Sheung Tan, at a distance of approximately 2 km. Bathing beaches have been plotted as discrete points for evaluation in the water quality assessment.

Water quality impacts at non-gazetted bathing beaches have been determined based on the compliance with the WQOs (Table 6.7).

Seawater Intakes

There are four seawater intakes identified as potential sensitive receivers, namely those at Black Point Power Station, Castle Peak Power Station, Tuen Mun Area 38 and Shiu Wing Steel Mill.

Both power station intakes have specific requirements for intake water quality. The applicable criteria for temperature and SS for the Black Point Power Station and Castle Peak Power Station seawater intakes are between 17 and 30°C and between 30 and 764 mg L^-1, respectively. These values have, therefore, been taken as the assessment criteria. There are no particular criteria specified for the Tuen Mun Area 38 and Shiu Wing Steel Mill intakes and hence WQOs have been adopted (Table 6.7). These intakes have been plotted as discrete points for evaluation in the water quality assessment.

The existing seawater intake of the Water Supplies Department (WSD) at Tuen Mun is at least 10 km from the Project and is unlikely to be affected. It is thus not included in this assessment.

6.5 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.

6.5.1 Construction Phase

The main construction activities associated with the Project that have the potential to cause water quality impacts involve the following:

· Installation of the submarine pipelines using methods traditionally used in Hong Kong, i.e. grab dredging and/ or jetting;

· Backfilling pipeline trenches (potentially with gravel and rock) to provide armouring protection;

· Dredging for the GRS reclamation works;

· Filling the reclamation area with sand and suitable fill material and seawall formation; and

· Site runoff and pollutants entering the receiving waters.

6.5.2 Operation Phase

The potential impacts to water quality arising from the operation of the Project have been identified as follows:

· Changes to the hydrodynamic regime through the reclamation of the GRS and thereby affecting the water quality, local erosion and sedimentation patterns etc; and

· Storm water run-off from the GRSs.

6.6 Assessment Methodology

6.6.1 General Methodology

The methodology employed to assess the above impacts is presented in the Water Quality Method Statement (Annex 6A) and has been based on the information presented in the Project Description (Section 3).

Impacts due to the dispersion of fine sediment in suspension during the construction of the proposed submarine pipelines and associated reclamation have been assessed using computational modelling. Mitigation measures, as proposed in Section 6.9, were assumed to be absent in the modelling so that worse case scenarios could be examined.

Operational impacts on water quality have also been studied by means of computational modelling. The models have been used to simulate the effects of operation due to reclamation, including potential effects on flows and subsequent water quality effects due to changing flows, and any changes in local erosion and sedimentation patterns the new reclamation.

Full details of the scenarios examined in the modelling works are provided in Annex 6A. Annex 6B provides snap shots of the simulated currents (vectors) at ebb and flood tides in both dry and wet seasons under the baseline conditions. The water quality sensitive receivers shown in Figure 6.4 are also the water quality modelling output points.

6.6.2 Uncertainties in Assessment Methodology

Uncertainties in the assessment of the impacts from SS plumes should be considered when drawing conclusions from the assessment. In carrying out the assessment, the worst case assumptions have been made in order to provide a conservative assessment of environmental impacts. These assumptions are as follows:

· The assessment is based on the peak dredging/ jetting and filling rates. In reality, these will only occur for short period of time; and,

· The calculations of loss rates of sediment to suspension are based on conservative estimates for the types of plant and methods of working.

The worst case assumptions presented above allow a prudent approach to be applied to the water quality assessment.

The following uncertainties have not been included in the modelling assessment.

· Ad hoc navigation of marine traffic;

· Near shore scouring of bottom sediment; and

· Access of marine barges back and forth across the site.

It is noted that, although minor localised and short term elevations in SS levels may occur during construction due to the above mechanisms, unacceptable water quality impacts at sensitive receivers are not anticipated.

6.7 Impact Assessment – Construction Phase

6.7.1 Suspended Sediment Dispersion

The main 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 physico-chemical changes in the water column.

It is noted that the construction of the first pipeline, and the construction of the second pipeline and the reclamation, will involve two phases. To assess potential project-specific impacts of this phased construction, computational modelling was conducted separately for the First Phase (construction of Pipeline 1) and Second Phase construction (construction of Pipeline 2 and the reclamation) ([15]). For each construction phase, two modelling scenarios have been developed (Table 6.9). Scenarios are based on the tentative construction programme and indicative construction sequence (Annex 6A) and represent periods when the maximum number of activities may take place at any given time.

The locations of the marine works, including the reclamation for the construction of the GRS and the installation of different sections of the submarine pipeline, are shown in Figures 6.5 and 6.6.

Assessment of each scenario enables the examination of impacts due to the concurrent activities. Whenever the scenarios are compliant with assessment criteria, the individual activities are considered to be environmentally acceptable. When any non-compliances with the WQO or specific assessment criteria are identified in the assessment, further discussions on the activity(ies) that contribute to the exceedance will be given. Mitigation measures to reduce impacts to acceptable levels, if deemed necessary, are then recommended.

The results from each scenario have been presented as contours of maximum and mean SS concentrations above ambient at the surface, middle layer, bottom and depth-averaged (Annex 6C). Data were extracted from the modelling results to determine the predicted levels of SS at each of the sensitive receivers. The maximum and mean elevations of SS at the relevant depth for the respective sensitive receivers are presented under each scenario.

The determination of the acceptability of any elevation in SS levels has been based on the WQO or specific tolerance criteria. It should be noted that elevations in the SS level due to concurrent activities have been assessed as the maximum concentrations at relevant water depths over a full 15 day spring-neap tidal cycle in both the dry and wet season, as required by the EIA Study Brief (ESB-208/2009).

In the following text, each scenario shown in Table 6.9 will be discussed in the subsequent paragraphs.

It should be noted that these scenarios are highly conservative for the following reasons:

· Although potential concurrent activities have been simulated to assess for impacts, it would be unlikely to have dredgers/pelican barge operating simultaneously on the site (see Annex 6A).

· The sandfilling works for the seawall trench are assumed to be continuous within a whole spring-neap cycle. In fact, the sandfilling works will be completed within a shorter period (see Annex 6A).

· The assumptions of the dredger forward speed are made only for the modelling purpose but the actual dredging rates will be subject to the weather constraints, site conditions and continued operational progress. In reality, the dredger moving speed should be calculated from the result of dividing the total volume of dredged materials (m³) by the duration of the dredging works (day).

Scenario ID	Tasks	Details of Construction Activities	Plant Type
Scenario 1	Submarine Pipeline 1 (HKSAR & PRC Sections)	Concurrent Grab Dredging at Black Point Shore Approach (KP4.89 – KP4.78), across Urmston Road (KP2.52 – KP0.73) and from HKSAR boundary to western boundary of the Tonggu Fairway (KP0 – SZ-KP2.5)	Grab Dredger
Scenario 2a	Submarine Pipeline 1 (HKSAR Section)	Jetting from Black Point to Urmston Road (KP 4.78 – KP 2.52)	Jetting Machine
Scenario 2b	Submarine Pipeline 1 (HKSAR Section)	Jetting from HKSAR boundary to Urmston Road (KP 0.73 – KP 0)	Jetting Machine
Scenario 2c	Submarine Pipeline 1 (PRC Section)	Jetting from HKSAR boundary to western boundary of the Tonggu Fairway (KP0 – SZ-KP2.5)	Jetting Machine
Scenario 3	Gas Receiving Station	Grab dredging at reclamation seawall trench	Grab Dredger
	Gas Receiving Station	Backfilling	Pelican Barge
	Submarine Pipeline 2 (HKSAR & PRC Sections)	Concurrent Grab Dredging at Black Point Shore Approach (KP4.89 – KP4.78), across Urmston Road (KP2.52 – KP0.73) and from HKSAR boundary to western boundary of the Tonggu Fairway (KP0 – SZ-KP2.5)	Grab Dredger
Scenario 4a	Submarine Pipeline 2 (HKSAR Section)	Jetting from Black Point to Urmston Road (KP 4.78 – KP 2.52)	Jetting Machine
Scenario 4b	Submarine Pipeline 2 (HKSAR Section)	Jetting from HKSAR boundary to Urmston Road (KP 0.73 – KP 0)	Jetting Machine
Scenario 4c	Submarine Pipeline 2 (PRC Section)	Jetting from HKSAR boundary to western boundary of the Tonggu Fairway (KP0 – SZ-KP2.5)	Jetting Machine

Table 6.10 Predicted SS Elevation (mg L^-1) in Scenario 1 (First Phase Construction)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.3	0.4	0.1	0.1	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.5	0.6	0.1	0.1	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.5	0.4	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.6	0.4	0.0	0.1	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	1.4	1.4	0.2	0.2	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.5	0.5	0.1	0.1	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.1	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.1	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.1	0.1	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	0.4	0.1	0.0	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	0.5	0.2	0.0	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	0.5	0.2	0.0	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	0.5	0.2	0.0	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	0.5	0.3	0.0	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	2.3	2.7	0.2	0.2	1.8	1.8
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	0.6	0.4	0.1	0.0	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

First Phase Construction: Scenario 2

Scenario 2 assesses the impacts of sequential jetting works for installing specific sections of Pipeline 1 in HKSAR and PRC waters. This includes sections 2 (from Black Point to Urmston Road) and 4 (from Urmston Road to HKSAR Boundary) in HKSAR waters and about 2.5 km of pipeline (from the HKSAR boundary) in PRC waters. It is expected that the jetting works in both HKSAR and PRC waters will take place after the completion of Pipeline 1 grab dredging activities, i.e. completion of works simulated under Scenario 1.

It is expected that only one jetting machine would be used for post-trenching of both the HKSAR and PRC pipeline sections. Therefore, under this assumption the jetting operations in different pipeline sections in HKSAR and PRC waters will not be concurrent, hence three separate scenarios (Scenarios 2a, 2b and 2c) were simulated.

The modelling results of Scenario 2a, 2b and 2c (Tables 6.11, 6.12 and 6.13) show that compliances with the WQO for allowable SS elevations would be anticipated in either season at any sensitive receivers.

Contours of SS concentrations (Annex 6C) demonstrate the plumes are generally confined to the bed layer, thereby not affecting the main body of the water column. It is concluded that the jetting works have short-term, transient and acceptable impacts on the water quality of the study area and sensitive receivers in HKSAR waters.

Table 6.11 Predicted SS Elevation (mg L^-1) in Scenario 2a (First Phase Construction – HKSAR Section 2)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.5	0.4	0.1	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.7	0.5	0.1	0.1	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.1	0.2	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.2	0.2	0.0	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.3	0.2	0.0	0.0	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.1	0.3	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.1	0.3	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.2	0.4	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	1.2	0.5	0.1	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	2.5	1.1	0.1	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	2.5	1.1	0.1	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	1.2	0.4	0.1	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	1.3	0.7	0.1	0.1	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	29.6	26.5	1.3	1.5	3.7	5.6
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	1.8	1.0	0.2	0.1	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Table 6.12 Predicted SS Elevation (mg L^-1) in Scenario 2b (First Phase Construction – HKSAR Section 4)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.5	0.2	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.9	0.4	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.4	0.2	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.5	0.2	0.0	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	1.5	0.5	0.1	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	1.4	1.0	0.1	0.0	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	0.2	0.2	0.0	0.0	1.8	1.8
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	0.1	0.0	0.0	0.0	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Table 6.13 Predicted SS Elevation (mg L^-1) in Scenario 2c (First Phase Construction – PRC Section)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.3	0.2	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.5	0.3	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	1.0	0.5	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	1.4	0.6	0.1	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	5.7	3.7	0.5	0.3	1.9	1.9
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.6	0.7	0.1	0.1	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	0.1	0.0	0.0	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	0.3	0.4	0.0	0.0	1.8	1.8
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	0.1	0.0	0.0	0.0	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Second Phase Construction: Scenario 3

Scenario 3 allows the assessment of impacts through concurrent activities in HKSAR and PRC waters, including:

· Reclamation works, i.e. dredging underneath the seawall and backfilling works for the construction of the reclamation; and

· Pre-trenching for the installation of specific sections of Pipeline 2, including dredging works for pipeline sections 1 (Black Point Shore Approach) and 3 (across Urmston Road) in HKSAR waters and about 2.5 km of pipeline (from the HKSAR boundary) in PRC waters.

In this scenario dredging works have been modelled assuming the use of closed grab dredgers.

The modelling results indicate that SS elevations will be compliant with the WQO at all sensitive receivers in both seasons (Table 6.14). No unacceptable water quality impacts associated with the marine works would be expected to occur.

As discussed in Section 6.7.1, it would be unlikely to have dredgers/pelican barge operating simultaneously on the site. Also modelling of sand filling works can be assumed to be highly conservative as they have been modelled over a whole spring-neap cycle, whereas, in reality, will be completed within a shorter period.

It should be noted that in the model construction activities are assumed to be undertaken without applying any mitigation measures, i.e. the most conservative case. In reality, a completed seawall (with a 50 - 100 m opening for barge access) will be in place while sand filling works are taking place, hence reducing the potential sediment loss by about 80% ([16]). The tentative layout of the seawall is illustrated in Figure 6.7. Seawalls which are constructed above the high tide level are an effective barrier against the washing out of filling materials by water currents. Therefore, the impact of sand filling on the surrounding water and SS elevations will be substantially reduced from those predicted in this assessment.

Table 6.14 Predicted SS Elevation (mg L^-1) in Scenario 3 (Second Phase Construction)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.8	0.8	0.2	0.2	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	1.7	1.2	0.2	0.2	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.5	0.5	0.0	0.1	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.7	0.6	0.1	0.1	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	1.4	1.5	0.3	0.2	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.8	0.7	0.2	0.2	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	1.4	3.5	0.0	0.1	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	1.4	3.5	0.0	0.1	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	2.2	4.5	0.1	0.1	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	4.7	1.7	0.4	0.1	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	7.0	3.1	0.5	0.1	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	7.0	3.1	0.5	0.1	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	3.0	1.3	0.3	0.1	1.9	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	3.4	2.2	0.4	0.2	2.0	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	161.3	137.8	4.3	7.7	9.1	21.6
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	4.8	3.0	0.7	0.4	2.8	1.9

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Second Phase Construction: Scenario 4

Scenario 4 is the same as Scenario 2 except that the sequential pipeline jetting works are for the installation of Pipeline 2. Impacts of post-trenching along sections 2 (from Black Point to Urmston Road) and 4 (from Urmston Road to HKSAR Boundary) in HKSAR waters and about 2.5 km of pipeline (from the HKSAR boundary) in PRC waters were assessed. The works assumptions adopted in Scenario 2 are also adopted in this Scenario.

The results presented in Table 6.15 show that, as with the results of Scenario 2, compliances of the WQO is anticipated in either season at the identified sensitive receivers.

Contours of SS concentrations (Annex 6C) demonstrate the plumes are generally confined to the bed layer, thereby not affecting the main body of the water column. It is concluded that the jetting works have a short-term, transient and acceptable impact on the water quality of the study area and sensitive receivers in HKSAR waters.

Table 6.15 Predicted SS Elevation (mg L^-1) in Scenario 4a (Second Phase Construction – HKSAR Section 2)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.5	0.4	0.1	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.7	0.4	0.1	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.1	0.1	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.2	0.2	0.0	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.3	0.2	0.0	0.0	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.1	0.4	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.1	0.4	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.2	0.5	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	1.1	0.5	0.1	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	2.4	1.1	0.1	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	2.4	1.1	0.1	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	1.1	0.4	0.1	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	1.2	0.7	0.1	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	26.4	24.5	1.3	1.4	3.8	5.1
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	1.7	0.9	0.2	0.1	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Table 6.16 Predicted SS Elevation (mg L^-1) in Scenario 4b (Second Phase Construction – HKSAR Section 4)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.4	0.2	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.7	0.3	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	0.4	0.2	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	0.5	0.2	0.0	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	1.2	0.5	0.1	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	1.2	0.9	0.1	0.0	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	0.2	0.1	0.0	0.0	1.8	1.8
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	0.1	0.0	0.0	0.0	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

Table 6.17 Predicted SS Elevation (mg L^-1) in Scenario 4c (Second Phase Construction – PRC Section)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable SS Increase (mg L^-1)		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)	Mean ^(c)	Mean ^(c)	90%-tile ^(e)	90%-tile ^(e)
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	8.1	6.4	0.3	0.2	0.0	0.0	1.8	1.8
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	14.0	15.3	0.4	0.3	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	8.1	6.4	1.0	0.5	0.0	0.0	1.8	1.8
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	14.0	15.3	1.4	0.5	0.1	0.0	1.8	1.8
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Mangroves	Ngau Hom Shek	SR2a	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	8.1	6.4	5.0	3.7	0.4	0.3	1.9	1.9
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	8.1	6.4	0.5	0.8	0.1	0.1	1.8	1.8
Intertidal Mudflats	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Sheung Pak Nai	SR2	s	6.3	5.5	0.0	0.0	0.0	0.0	1.8	1.8
Seagrass Beds	Ha Pak Nai	SR1	s	5.9	3.9	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	9.9	5.6	0.0	0.0	0.0	0.0	1.8	1.8
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	9.3	9.5	0.0	0.0	0.0	0.0	1.8	1.8
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	8.1	6.4	0.0	0.0	0.0	0.0	1.8	1.8
Seawater Intakes	Tuen Mun Area 38	SR7b	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Shiu Wing Steel Mill	SR7i	b	14.0	15.3	0.0	0.0	0.0	0.0	1.8	1.8
	Black Point Power Station	SR4	b	700 ^(d)	700 ^(d)	0.2	0.3	0.0	0.0	1.8	1.8
	Castle Peak Power Station	SR7a	b	700 ^(d)	700 ^(d)	0.1	0.0	0.0	0.0	1.8	1.8

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

c. “Mean” denotes arithmetic mean values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

d. The tolerance assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

e. The 90%-tile values are only reliable if average concentrations exceed approximately 5 – 10 mg L^-1 due to numerical limitation.

f. Shaded cells indicate non-compliance with the WQOs.

6.7.2 Sediment Deposition

The majority of SS elevations in water have been predicted to be temporary and to remain within relatively close proximity to the dredging works and, as such, the majority of sediment has been predicted to settle within relatively close proximity to the works areas.

The simulated deposition rates ([17]) at the artificial reefs (ARs), i.e., SR6e during the dry and wet seasons have been assessed for the respective construction works (Annex 6C). The predicted deposition rates at SR6e are negligible at < 10 g m^-2 day^-1 which is well below the assessment criterion of 200 g m^-2 day^-1 and will not cause any adverse impacts (Table 6.18).

Table 6.18 Predicted Deposition Rate (g m^-2 day^-1) for the Marine Works at the Artificial Reefs (SR6e)

Scenario	Dry Season (g m^-2 day^-1)	Wet Season (g m^-2 day^-1)
*First Phase Construction*
Scenario 1	2	2
Scenario 2a	1	1
Scenario 2b	2	1
Scenario 2c	3	2
*Second Phase Construction*
Scenario 3	2	3
Scenario 4a	1	1
Scenario 4b	2	1
Scenario 4c	3	2

Assessment Criterion = 200 g m^-2 day ^-1

6.7.3 Dissolved Oxygen Depletion

The dispersion of sediment due to marine construction activities is not expected to affect the general water quality of the receiving waters. Due to the low nutrient content of the sediments ([18]), the elevation in SS levels is not expected to cause a pronounced increase in oxygen demand and, therefore, the effect on dissolved oxygen (DO) is anticipated to be minor. The effects of increased SS concentrations as a result of the proposed works on levels of dissolved oxygen, biochemical oxygen demand and nutrients (as unionised ammonia) are predicted to be minimal.

To further assess the impact of the release of SS during marine construction activities, the depletion of dissolved oxygen has been calculated. The degree of oxygen depletion exerted by a sediment plume is a function of the sediment oxygen demand (SOD) of the sediment, its concentration in the water column and the rate of oxygen replenishment.

The impact of the sediment oxygen demand on dissolved oxygen concentrations has been calculated based on the following equation ([19]):

The assumption behind this equation is that all the released organic matter is eventually re-mineralised within the water column, neglecting any transport of oxygen to compensate the associated oxygen consumption. This leads to an estimated depletion with respected 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 carbon content of the particles can be calculated as total carbon (%WW) divided by total solids (%WW). By reviewing the EPD sediment quality monitoring data, the average carbon content of the particles equals 1.0 (%DW) (i.e. organic carbon content = 0.01 g C/g DW) at both EPD Sediment Monitoring Stations NS4 and DS4.

Assuming that every gram of carbon potentially consumes 2.67 grams of O₂during its oxidation and organic carbon is 100% mineralised, the maximum oxygen depletion can be expressed as 0.0267 g O₂/g DW.

The most sensitive receivers to DO depletion are likely to be the ecological and fisheries resources. Maximum decreases in dissolved oxygen were found to be minimal at all sensitive receivers so breaches of the WQO would not occur for oxygen depletion (Tables 6.19 and 6.20). Contour plots of maximum and mean DO depletion (Annex 6D) show that the largest reduction in dissolved oxygen concentrations is in the immediate vicinity of the dredging/ jetting works. The contour plots also illustrate that the plumes will not extend to the fisheries spawning ground in northwest Lantau or to high-value ecological resources in inner Deep Bay and hence no adverse water quality impacts on these sensitive receivers are expected.

It is concluded that the marine construction works are unlikely to deteriorate the dissolved oxygen conditions in the receiving waters and will not affect the WSRs.

Table 6.19 Predicted Dissolved Oxygen Depletion (mg L^-1) due to SS Elevations (Scenarios 1 & 2 for First Phase Construction)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable DO Depletion (mg L^-1)		Predicted DO Depletion (mg L^-1) (Maximum)
				Dry	Wet	Scenario 1		Scenario 2a		Scenario 2b		Scenario 2c
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	4.2	2.9	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	6.0	4.3	0.01	0.01	0.02	0.01	0.02	0.01	0.01	0.01
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	4.2	2.9	0.01	0.01	0.00	0.00	0.01	0.01	0.03	0.01
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	6.0	4.3	0.02	0.01	0.00	0.01	0.01	0.01	0.04	0.01
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Mangroves	Ngau Hom Shek	SR2a	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	4.2	2.9	0.04	0.04	0.00	0.00	0.04	0.01	0.15	0.10
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	4.2	2.9	0.01	0.01	0.01	0.01	0.04	0.03	0.01	0.02
Intertidal Mudflats	Ha Pak Nai	SR1	s	4.1	2.9	0.00	0.00	0.00	0.01	0.00	0.00	0.00	0.00
Seagrass Beds	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Seagrass Beds	Ha Pak Nai	SR1	s	4.1	2.9	0.00	0.00	0.00	0.01	0.00	0.00	0.00	0.00
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	3.8	2.6	0.00	0.00	0.00	0.01	0.00	0.00	0.00	0.00
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	4.2	2.9	0.01	0.00	0.03	0.01	0.00	0.00	0.00	0.00
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	4.2	2.9	0.01	0.01	0.07	0.03	0.00	0.00	0.00	0.00
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	4.2	2.9	0.01	0.01	0.07	0.03	0.00	0.00	0.00	0.00
Seawater Intakes	Tuen Mun Area 38	SR7b	b	6.0	4.3	0.01	0.00	0.03	0.01	0.00	0.00	0.00	0.00
	Shiu Wing Steel Mill	SR7i	b	6.0	4.3	0.01	0.01	0.03	0.02	0.00	0.00	0.00	0.00
	Black Point Power Station	SR4	b	-- ^(b)	-- ^(b)	0.06	0.07	0.79	0.71	0.01	0.01	0.01	0.01
	Castle Peak Power Station	SR7a	b	-- ^(b)	-- ^(b)	0.02	0.01	0.05	0.03	0.00	0.00	0.00	0.00

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. There is no DO criterion for Black Point Power Station and Castle Peak Power Station intakes.

c. Shaded cells indicate non-compliance with the WQOs.

Table 6.20 Predicted Dissolved Oxygen Depletion (mg L^-1) due to SS Elevations (Scenarios 3 & 4 for Second Phase Construction)

Sensitive Receiver	Name	ID	Relevant Depth ^(a)	WQO Allowable DO Depletion (mg L^-1)		Predicted DO Depletion (mg L^-1) (Maximum)
				Dry	Wet	Scenario 3		Scenario 4a		Scenario 4b		Scenario 4c
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
*Fisheries Sensitive Receivers*
Oyster Production Area	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	a	4.2	2.9	0.02	0.02	0.01	0.01	0.01	0.01	0.01	0.01
Recognised Spawning/ Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR8	b	6.0	4.3	0.05	0.03	0.02	0.01	0.02	0.01	0.01	0.01
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	a	4.2	2.9	0.01	0.01	0.00	0.00	0.01	0.01	0.03	0.01
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR6e	b	6.0	4.3	0.02	0.02	0.00	0.00	0.01	0.01	0.04	0.01
*Marine Ecological Resources*
Mangroves	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Mangroves	Ngau Hom Shek	SR2a	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6a	a	4.2	2.9	0.04	0.04	0.00	0.00	0.03	0.01	0.13	0.10
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR6c	a	4.2	2.9	0.02	0.02	0.01	0.01	0.03	0.02	0.01	0.02
Intertidal Mudflats	Ha Pak Nai	SR1	s	4.1	2.9	0.04	0.09	0.00	0.01	0.00	0.00	0.00	0.00
Seagrass Beds	Sheung Pak Nai	SR2	s	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Seagrass Beds	Ha Pak Nai	SR1	s	4.1	2.9	0.04	0.09	0.00	0.01	0.00	0.00	0.00	0.00
Horseshoe Crab Nursery Grounds	Ha Pak Nai	SR1	a	3.8	2.6	0.06	0.12	0.01	0.01	0.00	0.00	0.00	0.00
Horseshoe Crab Nursery Grounds	Ngau Hom Shek	SR2a	a	3.6	3.4	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
*Water Quality Sensitive Receivers*
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR5a	a	4.2	2.9	0.12	0.04	0.03	0.01	0.00	0.00	0.00	0.00
Non-gazetted Beaches	Lung Kwu Tan	SR5b	a	4.2	2.9	0.19	0.08	0.06	0.03	0.00	0.00	0.00	0.00
Secondary Contact Recreation Subzone	NW WCZ	SR5b	a	4.2	2.9	0.19	0.08	0.06	0.03	0.00	0.00	0.00	0.00
Seawater Intakes	Tuen Mun Area 38	SR7b	b	6.0	4.3	0.08	0.03	0.03	0.01	0.00	0.00	0.00	0.00
	Shiu Wing Steel Mill	SR7i	b	6.0	4.3	0.09	0.06	0.03	0.02	0.00	0.00	0.00	0.00
	Black Point Power Station	SR4	b	-- ^(b)	-- ^(b)	4.31	3.68	0.71	0.65	0.01	0.00	0.01	0.01
	Castle Peak Power Station	SR7a	b	-- ^(b)	-- ^(b)	0.13	0.08	0.05	0.03	0.00	0.00	0.00	0.00

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. There is no DO criterion for Black Point Power Station and Castle Peak Power Station intakes.

c. Shaded cells indicate non-compliance with the WQOs.

6.7.4 Nutrients

An assessment of nutrient release during dredging has been carried out based on the SS modelling results for the unmitigated worst case scenario and the sediment testing results for the dredging area. In the calculation it has assumed that all Total Inorganic Nitrogen (TIN) and unionised ammonia (NH₃-N) concentrations in the sediments are released to the water. This is a highly conservative assumption and will result in the overestimation of the potential impacts.

The maximum predicted SS concentration at each SR is multiplied by the maximum concentration of TIN in sediment (mg kg^-1) in the corresponding WCZ to give the maximum increase in TIN (mg L^-1). The calculations of TIN (i.e. TIN = ammonia nitrogen + nitrate nitrogen + nitrite nitrogen) are shown below ([20]).

Deep Bay WCZ	NW WCZ
Maximum SS × 142 × 10^-6	Maximum SS × 100 × 10^-6

The maximum increase in TIN concentrations at all sensitive receivers is shown in Table 6E.2 (Annex 6E). The increase in TIN concentrations at all sensitive receivers would be less than 0.0229 mg L^-1, which is considered to be a minimal effect on the water quality. The dredging works will not result in a non-compliance with the WQO.

Total ammonia nitrogen is the sum of ionised ammonia nitrogen and unionised ammonia nitrogen (NH₃-N). Under normal conditions of Hong Kong waters, more than 90% of the total ammonia nitrogen would be in the ionised form. For the purpose of assessment, a correction (as a function of temperature, pH, and salinity) has been applied based on the EPD monitoring data, i.e. temperature of 24 degrees Celsius, salinity of 28 ppt and pH of 8 which represent the typical conditions of Hong Kong waters ([21]). From this it derived that total ammonia nitrogen constitutes 5% of unionised ammonia nitrogen. In view that the mineralisation of the organic nitrogen will also contribute to ammonia, the calculations of NH₃-N are based on maximum TKN concentrations (mg kg^-1) in the sediment in each WCZ. Note that it is a highly conservative approach since it is assumed that 100% of organic nitrogen will be mineralised to ammonium but this is unlikely to occur in reality.

The maximum SS concentration at each SR is multiplied by the following factors to predict the maximum NH₃-N elevations ([22]).

Deep Bay WCZ	NW WCZ
Max SS * 2,600 * 10^-6 * 5%	Max SS * 2,100 * 10^-6 * 5%

The results (see Table 6E.3, Annex 6E) indicate that the increase in NH₃-N levels due to the dredging works would be negligible comparing with the ambient concentrations. The total concentrations of NH₃-N at the water quality sensitive receivers are predicted to be well below the WQO criterion of 0.021 mg L^-1. Since it is neither an ecological sensitive receiver nor a bathing beach, the marginal exceedance will not cause significant adverse impact on the intake. In overall it is anticipated that the impacts of the SS elevations due to the dredging works on the nutrient levels are minimal and acceptable.

6.7.5 Heavy Metals and Micro-Organic Pollutants

Elutriate tests were carried out to assess the potential for a release of heavy metals and micro-organic pollutants from the marine muds as they are disturbed/agitated through dredging or jetting. The test results have been assessed and compared to the relevant water quality standards shown in Table 6E.1 (Annex 6E). The results show that most dissolved metal concentrations for all samples are below the reporting limits and are found to be in compliance with the proposed assessment criteria, with the exception of arsenic. The arsenic concentration in the sediment elutriate sample GSVB6 exceeded 1 µg L^-1 with respect to the assessment criterion of 25 µg L^-1. The maximum increase in arsenic concentrations at all sensitive receivers is calculated by multiplying the maximum predicted SS concentration at each SR by the highest arsenic concentration of all the sediment samples (i.e. 38 mg kg^-1) (see Section 7 Waste Management). It is important to note that this approach is on the conservative side based on the assumption that arsenic is released to the water column from the dredged mud. This will not, therefore, underestimate the increase in arsenic concentration as a result of dredging. As seen in Table 6E.4 (Annex 6E), the predicted arsenic elevations at all the sensitive receivers are well below the proposed assessment criterion.

The elutriate results also show that all PAHs, PCBs, TBT and chlorinated pesticides are all below the reporting limits ([23]). This indicates that the release of these pollutants into the water column at detectable levels is unlikely to occur. Unacceptable water quality impacts due to the potential release of heavy metals and micro-organic pollutants from sediments disturbed during jetting / dredging are not expected to occur.

6.7.6 Sewage Discharges

Sewage will arise from the construction workforce and site office’s sanitary facilities. It is estimated that about 30 construction workers will be on site for the post-reclamation GRS works. Based on the general effluent generation rate (150 L per worker per day ([24])), approximately 4,500 L of effluent will be generated at the site during the construction phase. For a workforce of 30 people this will equate to a flow of 4.5 m³ day^-1. In view of the small workforce and short duration of the construction works, it is expected that the existing sanitary facilities at the BPPS will be used by any of the site workers and the sewage treatment works of the BPPS should have the capacity to accommodate the additional sewage flow. As sewage discharges are not expected to occur, no unacceptable water quality impacts to sensitive receivers are foreseen.

6.7.7 Land Based Construction Activities

Discharges and runoff from the site during the construction phase, particularly during the filling and site formation works, will 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 6.9), are in place.

6.7.8 Vessel Discharges

Construction vessels have the potential for the following liquid discharges:

· Uncontaminated deck drainage;

· Potentially contaminated drainage from machinery spaces; and

· Sewage/grey water.

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.

6.7.9 Hydrotest Water

Treated freshwater will be required to hydrotest the submarine pipelines prior to commissioning and the hydrotest water is expected to be released to PRC waters in compliance with the applicable standards. It is considered that the impacts to water quality of Hong Kong waters are minimal and therefore will not be evaluated further in this EIA Report.

6.8 Impact Assessment – Operation Phase

6.8.1 Hydrodynamic Assessment

Impacts to the hydrodynamic regime have been assessed for the construction of GRS on a reclaimed land which may alter the tidal currents in the vicinity of the reclamation. Changes to water quality, sedimentation and erosion processes would arise if there was a significant change to the hydrodynamic regime of the Black Point coastline due to the reclamation works.

Annex 6B provide snap shots of the simulated currents (vectors) and temperature (colour contours) at ebb and flood tides in both dry and wet seasons under the baseline and post-project conditions. In the wet seasons the results show differences between the surface and bottom layers which is a results of the salinity stratification and would be expected because of the influence of the freshwater discharge from the Pearl River Estuary.

Modelling results show that the presence of the reclamation is unlikely to alter the overall flow regime in the Deep Bay Outer Subzone but it could reduce the flow velocity in the vicinity of the GRS, however, the changes are localised and minimal.

Impacts may also occur to the freshwater discharge rates through the region around the reclamation. Such changes would be important in that they could alter the flushing capacity of the region which in turn may affect water quality. Mathematical modelling has been carried out to examine the flushing capacity of Deep Bay. The methodology and model results are presented in Annex 6F. The model results show that the relative change of flushing capacity in inner Deep Bay due to the inclusion of reclamation with respect to the baseline ranges from -0.2% (decrease) to +0.5% (increase). The results also indicate that for Deep Bay as a whole there is a marginal decrease in flushing in the wet season. In conclusion, the change in flushing capacity, and hence in water quality, due to the reclamation at Deep Bay is minimal. No adverse impacts to water quality as a result of these minor changes in hydrodynamics are expected to occur.

The potential impacts of the reclamation on the water quality, natural sedimentation changes and nearby BPPS thermal discharge will be discussed in the following sections.

6.8.2 Water Quality

Two scenarios were modelled for a situation without the reclamation (i.e. baseline) and for a situation with the GRS on the reclaimed land (i.e. operational). The water quality impacts were assessed by calculating the differences between the water quality model simulations. The contour plots showing the differences between the baseline scenario without the reclamation and the operation scenario with the reclamation are included in Annex 6G.

Changes are presented in terms of mean concentrations of the water quality parameters including dissolved oxygen, BOD_5, suspended solids, unionised ammonia, total nitrogen, total phosphorus, ammonium, phosphates, nitrates, geometric mean E. coli and chlorophyll-a.

The contours of the above parameters show little differences between the baseline and operation scenarios in both the wet and dry seasons. The most apparent changes are shown in the vicinity of the GRS for dissolved oxygen and BOD₅. There is predicted to be a small decrease in DO and BOD₅ concentrations to the northeast of the reclamation site but an increase to the southwest of the site. For suspended solids, unionised ammonia, total nitrogen, total phosphorus and nitrates, the contour plots only show minimal changes in respective concentrations around the GRS. However, none of these changes are predicted to cause a breach of the WQO at all the sensitive receivers and as such are considered to be acceptable.

It is found that the differences between the two scenarios turn out to be discernible such that the results for some parameters are on the edge of what the Delft3D-WAQ can sensibly simulate (i.e. 4 significant digits for all numbers). Note that some minute differences are considered to be artefacts rather than real impacts. The scales of the contour plots were hence adjusted to eliminate the potential artefacts.

The conclusion for the water quality modelling results is that the reclamation has negligible impact on the water quality of the study area. This is also supported by the results of the Deep Bay flushing capacity assessment (Annex 6F) that the changes in flushing characteristics of the areas are minimal.

6.8.3 Sedimentation Changes

Any changes in the tidal currents around the reclamations could cause sedimentation changes in the in form of increase erosion and deposition. The potential for the reclamation area to affect sea bed erosion and deposition has been assessed by mean of desktop study based on the hydrodynamic modelling results as well as a review of relevant literature. A similar approach was adopted in the approved EIA for HKLNG Terminal ([25]).

Fine sediment transport in Deep Bay is found mainly driven by the tides. The average SS concentration in Deep Bay is moderate, increasing from about 10 mg L^-1 in the west to nearly 60 mg L^-1 in the east. As the typical settling velocity for fines in Deep Bay is estimated to be 0.1 mm s^-1 or below, this may limit the maximal potential deposition rate near Black Point to about 32 kg m^-2 year^-1.

In the most sheltered areas, the increase in sedimentation due to the inclusion of the reclamation is predicted to be 0.5 kg m^-2 year^-1 or less, which is equivalent to approximately 0.025 cm year^-1. However, the maximal deposition may be lower in reality as wave and re-erosion effects have not been considered in the assessment. Given a minimal change to the sedimentation regime as a result of the reclamation, no unacceptable changes are expected. Similarly, due to the small volumes maintenance dredging is not expected to be required.

6.8.4 BPPS Thermal Discharge

The proposed GRS will be built on newly reclaimed land to the north of BPPS, with a land footprint of around 0.5 ha. The site for the proposed GRS is adjacent to the existing BPPS outfall, about 60 m to the right of the outfall location. Considering the close proximity between the two facilities, the reclamation may alter the local tidal current patterns, thereby affecting the dispersion and dilution of the thermal plume.

The hydrodynamic model has been set up to cover salinity and water temperature to address the potential impacts of the reclamation on the water temperature. The effects of the intake and release of cooling water associated with BPPS on hydrodynamics have been taken into account by including an intake-outfall combination in the hydrodynamic simulations. The BBPS has been modelled at a maximum discharge flowrate of 53 m³ s^-1 with a temperature increase between the inlet and outlet of 10 ºC. The boundary conditions and assumptions have been made identical to those applied to EIA for HKLNG Terminal ([26]) where the intake was done from the bottom half of the water column and the outfall was in the top half of the water column on the basis of simulations with the near-field model CORMIX.

Background surface temperatures in the dry and wet seasons were assumed to be around 23 ºC and 28 ºC, respectively. The WQO stated that the variation in temperature from human activity should not exceed 2 ºC, thus the resulting temperatures of concern were 25 ºC in dry season and 30 ºC in wet season at the sensitive receivers.

The cumulative impacts of the BPPS thermal discharge and the presence of the proposed reclamation were examined by comparing the temperature between the ‘pristine’ baseline (i.e. without BPPS thermal discharge and proposed reclamation) and the operation (i.e. with BPPS thermal discharge and proposed reclamation) scenarios. The figures presenting the statistical properties of the difference between the simulated water temperatures, with and without the reclamation and the BPPS thermal discharge, are depicted in Annex 6H. Table 6.21 summarises the tabulated maximum and mean temperature differences (i.e. operational minus ‘pristine’ baseline) at the sensitive receivers due to the inclusion of the BPPS thermal discharge and the proposed reclamation site. Note that positive values indicate a temperature increase while negative values indicate a temperature decrease. The largest change is visible in the top layer during the dry season where the temperature is predicted to increase by 2.94 ºC southwest of the GRS and BPPS outfall in open waters.

Contour plots (Annex 6H) also show the temperature differences are confined to the BPPS discharge location along the low ecological value shoreline of the BPPS and Black Point area. No sensitive receivers are expected to be affected by the temperature changes. In addition, the simulation results show the increase of the average intake temperature (0.26 ºC) at the BPPS intake (i.e. SR4 at bottom layer) which would not cause a breach of the BPPS intake temperature criterion of 30 °C.

Table 6.21 Maximum and Mean Temperature Differences at Water Quality Sensitive Receivers

Sensitive Receiver ID	Water Depth	Dry Season			Wet Season
Sensitive Receiver ID	Water Depth	Lowest ^(a)	Highest ^(b)	Mean ^(c)	Lowest ^(a)	Highest ^(b)	Mean ^(c)
SR1	Bottom	0.00	0.71	0.14	0.03	0.87	0.24
	Middle	0.00	0.59	0.10	0.03	0.87	0.23
	Surface	0.00	0.50	0.08	0.03	0.87	0.22
SR2	Bottom	0.00	0.23	0.01	0.00	0.42	0.09
	Middle	0.00	0.16	0.01	0.00	0.41	0.09
	Surface	0.00	0.08	0.01	0.00	0.41	0.09
SR2a	Bottom	0.00	0.07	0.01	0.00	0.24	0.04
	Middle	0.00	0.07	0.01	0.00	0.24	0.03
	Surface	0.00	0.07	0.01	0.00	0.24	0.03
SR4	Bottom	-0.04	1.46	0.15	-0.03	1.59	0.26
	Middle	-0.02	2.14	0.25	0.01	2.51	0.48
	Surface	0.00	2.94	0.60	-0.28	1.67	0.19
SR5a	Bottom	0.00	0.59	0.17	-0.05	0.83	0.18
	Middle	0.00	0.61	0.19	-0.03	0.49	0.19
	Surface	0.01	0.62	0.21	0.02	0.50	0.19
SR5b	Bottom	-0.03	0.52	0.14	-0.04	0.59	0.17
	Middle	-0.01	0.52	0.14	0.01	0.62	0.18
	Surface	0.00	0.54	0.15	-0.03	0.69	0.17
SR6a	Bottom	-0.05	0.27	0.04	-0.14	0.16	0.01
	Middle	-0.02	0.33	0.05	-0.09	0.16	0.01
	Surface	-0.02	0.49	0.05	-0.08	0.13	0.01
SR6c	Bottom	-0.06	0.05	-0.01	-0.25	0.21	0.00
	Middle	-0.06	0.06	0.00	-0.16	0.22	0.01
	Surface	-0.01	0.54	0.06	-0.13	0.44	0.02
SR6e	Bottom	-0.04	0.13	0.05	-0.11	0.22	0.02
	Middle	-0.04	0.15	0.06	-0.13	0.14	0.02
	Surface	0.00	0.20	0.06	-0.07	0.18	0.02
SR7b	Bottom	-0.06	0.07	-0.01	-0.09	0.12	0.01
	Middle	-0.06	0.10	0.00	-0.11	0.26	0.02
	Surface	-0.06	0.38	0.06	-0.13	0.41	0.09
SR7i	Bottom	-0.06	0.17	0.00	-0.09	0.25	0.01
	Middle	-0.06	0.21	0.01	-0.12	0.27	0.02
	Surface	-0.06	0.55	0.08	-0.19	0.61	0.12
SR8	Bottom	-0.06	0.06	-0.01	-0.19	0.15	0.00
	Middle	-0.06	0.07	-0.01	-0.15	0.41	0.01
	Surface	-0.02	0.42	0.07	-0.16	0.57	0.05

Notes:

a. “Lowest” denotes maximum temperature drop at a relevant water depth at any time during the simulation.

b. “Highest” denotes maximum temperature rise at a relevant water depth at any time during the simulation.

c. “Mean” denotes mean of difference recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

In order to differentiate the potential impacts of the proposed reclamation from the above cumulative assessment (i.e. with project-specific impact only), the temperature between the baseline (i.e. with the existing BPPS thermal discharge) and the operation (i.e. with the proposed reclamation) scenarios were compared. The figures presenting the statistical properties of the difference between the simulated water temperatures, with and without the reclamation are depicted in Annex 6H. Table 6.22 summarises the tabulated maximum and mean temperature differences (i.e. operational minus baseline) at the sensitive receivers due to the inclusion of the reclamation site. Note that positive values indicate a temperature increase due to the presence of the GRS while negative values indicate a temperature decrease. The largest impact is visible in the top layer during the dry season where the temperature is predicted to increase by 0.86 ºC southwest of the GRS.

Contour plots (Annex 6H) also show the temperature differences are confined to the discharge location with little extent to the artificial shore near BPPS of low ecological value. No sensitive receivers are expected to be affected by the temperature changes. The simulation results show a small (< 0.1 ºC) increase of the average intake temperature at the BPPS intake (i.e. SR4 at bottom layer) which would not cause a breach of the BPPS intake temperature criterion of 30 °C.

Based on the above assessment, it is concluded that no non-compliance with the WQO (D ± 2 ºC from ambient) would occur at the sensitive receivers in either the dry or wet season. No unacceptable impacts are thus anticipated.

Table 6.22 Maximum and Mean Temperature Differences at Water Quality Sensitive Receivers

Sensitive Receiver ID	Water Depth	Dry Season			Wet Season
Sensitive Receiver ID	Water Depth	Lowest ^(a)	Highest ^(b)	Mean ^(c)	Lowest ^(a)	Highest ^(b)	Mean ^(c)
SR1	Bottom	-0.17	0.03	-0.01	-0.28	0.07	-0.02
	Middle	-0.17	0.03	-0.01	-0.28	0.06	-0.02
	Surface	-0.10	0.03	0.00	-0.28	0.06	-0.02
SR2	Bottom	-0.01	0.02	0.00	-0.09	0.00	-0.01
	Middle	0.00	0.01	0.00	-0.09	0.00	-0.01
	Surface	0.00	0.01	0.00	-0.09	0.00	-0.01
SR2a	Bottom	0.00	0.00	0.00	-0.07	0.00	0.00
	Middle	0.00	0.00	0.00	-0.07	0.00	0.00
	Surface	0.00	0.00	0.00	-0.07	0.01	0.00
SR4	Bottom	-0.08	0.07	0.00	-0.25	0.49	0.02
	Middle	-0.20	0.23	0.00	-0.29	0.44	0.01
	Surface	-0.69	0.86	0.03	-0.28	0.41	-0.01
SR5a	Bottom	-0.04	0.04	0.00	-0.20	0.11	0.00
	Middle	-0.03	0.05	0.00	-0.17	0.15	0.00
	Surface	-0.02	0.05	0.00	-0.23	0.09	0.00
SR5b	Bottom	-0.03	0.07	0.00	-0.14	0.10	0.00
	Middle	-0.03	0.07	0.00	-0.14	0.10	0.00
	Surface	-0.04	0.07	0.00	-0.15	0.10	0.00
SR6a	Bottom	-0.01	0.04	0.00	-0.12	0.16	0.00
	Middle	-0.01	0.04	0.00	-0.11	0.11	0.00
	Surface	-0.03	0.04	0.00	-0.13	0.15	0.00
SR6c	Bottom	0.00	0.00	0.00	-0.19	0.18	0.00
	Middle	-0.01	0.01	0.00	-0.10	0.13	0.00
	Surface	-0.06	0.03	0.00	-0.15	0.36	0.00
SR6e	Bottom	-0.01	0.01	0.00	-0.31	0.26	0.00
	Middle	-0.01	0.01	0.00	-0.13	0.16	0.00
	Surface	-0.01	0.01	0.00	-0.08	0.13	0.00
SR7b	Bottom	0.00	0.01	0.00	-0.10	0.10	0.00
	Middle	-0.01	0.01	0.00	-0.12	0.12	0.00
	Surface	-0.02	0.04	0.00	-0.13	0.12	0.00
SR7i	Bottom	-0.01	0.01	0.00	-0.41	0.17	0.00
	Middle	-0.01	0.02	0.00	-0.15	0.13	0.00
	Surface	-0.03	0.04	0.00	-0.24	0.30	0.00
SR8	Bottom	0.00	0.00	0.00	-0.16	0.13	0.00
	Middle	-0.01	0.01	0.00	-0.18	0.29	0.00
	Surface	-0.02	0.10	0.00	-0.23	0.20	0.00

Notes:

a. “Lowest” denotes maximum temperature drop at a relevant water depth at any time during the simulation.

b. “Highest” denotes maximum temperature rise at a relevant water depth at any time during the simulation.

c. “Mean” denotes mean of difference recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation.

6.8.5 Site Runoff

There will be no discharge from the GRSs aside from storm water runoff. Given that the new GRSs will be located within the site boundary of the Black Point Power Station, storm water discharges will be controlled through engineering design and the implementation of proper management plan, and mitigation measures which are already in place for the existing BPPS premises. Hence, the impacts of storm water run-off to water quality are considered to be negligible and will not be discussed further.

6.9 Mitigation Measures

6.9.1 Construction Phase

The water quality modelling works have indicated that for both the dry and wet seasons, the works can proceed at the recommended working rates without causing unacceptable impacts to water quality sensitive receivers. In instances where there are exceedances of the applicable standards, they have been predicted to be transient.

Unacceptable impacts to water quality sensitive receivers have been avoided through the adoption of the following measures.

· Reduction in Indirect Impacts: The reclamation and pipeline alignments are located at a sufficient distance from water quality sensitive receivers so that the dispersion of sediments from the construction works does not affect the receivers at levels of concern (as defined by the WQO and tolerance criterion).

· Adoption of Acceptable Working Rates: The modelling work has demonstrated that the selected working rates for the dredging operations will not cause unacceptable impacts to the receiving water quality. Details regarding the working rates for different scenarios are presented in Annex 6A.

In addition to these pro-active measures that have been adopted for the proposed Project, the following operational constraints and standard site practice measures for dredging and construction run-off are also recommended.

Dredging and Filling

The impacts to water quality from the loss of sediment to suspension were assessed in terms of the maximum rates of dredging and /or filling during the construction of the submarine pipelines and the associated GRS. The assessment was based on the predicted loss rates of fine sediment to suspension from the different types of plant working on the site during the times of maximum dredging and/or filling. The highest loss rate was predicted to occur during the time at which the maximum rate of dredging was occurring. The maximum loss rate should then be limited to the values adopted in the Study and it was predicted that this rate of loss would not give rise to adverse impacts. It is therefore recommended that the maximum loss rate during the dredging works be kept at these limits.

The following measures shall apply at all times:

· Dredged marine mud will be disposed of in a gazetted marine disposal area in accordance with the Dumping at Sea Ordinance (DASO) permit conditions (see Section 7).

· Disposal vessels will be fitted with tight bottom seals in order to prevent leakage of material during transport.

· Barges will be filled to a level, which ensures that material does not spill over during transport to the disposal site and that adequate freeboard is maintained to ensure that the decks are not washed by wave action.

· After dredging, any excess materials will be cleaned from decks and exposed fittings before the vessel is moved from the dredging area.

· The contractor(s) will confirm that the works cause no visible foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the dredging site.

· If installed, degassing systems will be used to avoid irregular cavitation within the pump.

· Monitoring and automation systems will be used to improve the crew’s information regarding the various dredging parameters to improve dredging accuracy and efficiency.

· Control and monitoring systems will be used to alert the crew to leaks or any other potential risks.

· When the dredged material has been unloaded at the disposal areas, any material that has accumulated on the deck or other exposed parts of the vessel will be removed and placed in the hold or a hopper. Under no circumstances will decks be washed clean in a way that permits material to be released overboard.

· Dredgers will maintain adequate clearance between vessels and the seabed at all states of the tide and reduce operations speed to ensure that excessive turbidity is not generated by turbulence from vessel movement or propeller wash.

· A constructed seawall will be in place before the commencement of the sand filling works for reclamation. The seawall will be above the high water level and will have an opening of 50 - 100 m for barge access.

· As a precautionary measure silt curtain(s) will be installed during grab dredging operations along Section 1 of the proposed pipelines.

The assessment presented in Section 6.7 is based on the unmitigated situation and assumed that no mitigation measures are adopted during the marine works. No breach of WQO is predicted for both First Phase and Second Phase construction. It is expected that, with the deployment of the proposed mitigation measures during dredging and filling works, no unacceptable water quality impacts will occur.

Jetting

· Unacceptable impacts to water quality sensitive receivers are not expected during the installation of the submarine pipelines in HKSAR and PRC waters through the control of the jetting speed (i.e. no more than 360 m day^-1).

· As a precautionary measure silt curtain(s) will be installed along the marine works areas during jetting operations for the installation of Section 2 of the proposed pipelines. The extent of silt curtain(s) installation will be determined based on site condition (e.g. bathymetry of the works area) and navigation safety considerations. Details of the design and implementation of the silt curtain(s) will be developed before construction and verified by the Independent Environmental Checker (IEC) and agreed with EPD.

Construction Site Runoff and Drainage

Standard site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” will be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids 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 will be adequately designed for the controlled release of storm flows.

The temporary diverted drainage will be reinstated to the original condition when the construction work has finished or when the temporary diversion is no longer required.

General Construction Activities

· Debris and refuse generated on-site will be collected, handled and disposed of properly to avoid entering the nearby WSRs. Stockpiles of cement and other construction materials will be kept covered when not being used.

· Oil leakage or spillage will be contained and clean up immediately. Waste oil will be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.

6.9.2 Operation Phase

Hydrodynamics

The hydrodynamic modelling has predicted that the reclamations and the marine works and structures will have minimal effects on hydrodynamics and water quality. Mitigation measures are not considered to be necessary.

Surface Runoff and Drainage

· The surface runoff from the GRSs should be connected to a storm water channel via a grit and oil interceptor. These grit and oil interceptors will be regularly cleaned and maintained in good working condition. Trapped oil and grease should be disposed of periodically by waste collection contractor using a suitable liquid waste collection vehicle.

· Any oil leakage or spillage will be contained and cleaned up immediately.

· Waste oil will be collected and stored for recycling or disposal in accordance with the Waste Disposal Ordinance.

6.10 Environmental Monitoring & Audit (EM&A)

6.10.1 Construction Phase

Water quality monitoring is recommended for the construction phase. The specific monitoring requirements are detailed in the Environmental Monitoring and Audit Manual (EM&A) associated with this EIA Report.

6.10.2 Operation Phase

As no unacceptable impacts have been predicted to occur during the operation of the Project, monitoring of impacts to marine water quality during the operation phase is not considered necessary.

6.11 Residual Impacts

With the full implementation of the recommended mitigation measures for the construction phase of the Project, no residual environmental impacts from the construction works of both First Phase and Second Phase construction are envisaged.

Given that all the potential impacts arising from the presence of the new reclamation are predicted to be of minor or negligible significance, residual environmental impacts during the operation phase are not expected to occur.

6.12 Cumulative Impacts

It is expected that the construction works of this Project will commence in 2011 to allow for First Gas to arrive by 2012. According to publicly available sources, the following major developments in northwestern or western Hong Kong waters may be constructed and/or operated concurrently with the construction works for the proposed facilities at Black Point ([27]).

· Hong Kong Link Road (HKLR) of the Hong Kong – Zhuhai – Macao Bridge (HZMB), which is about 15 km south of the pipeline corridor;

· Hong Kong Boundary Crossing Facilities (HKBCF) of the HZMB, which is about 12 km south of the pipeline corridor;

· Tuen Mun – Chek Lap Kok Link (TMCLKL), which is about 10 km from the pipeline corridor; and

· Contaminated Mud Pits (CMPs) at East Sha Chau and South Brothers, which are at least 10 km from the pipeline corridor.

Results of water quality modelling (Section 6.7) showed that the extension of the sediment plumes from the construction of this Project would not be more than 3 km to the marine works areas in both wet and dry seasons. Sediment plumes of similar sizes were also reported in the EIA of the CMPs ([28]). Water quality modelling and assessment conducted as part of ARUP (2009a,b) ([29]) ([30]) suggested that the sediment plumes from the construction of the HKLR, HKBCF and TMCLKL were generally confined to within the sheltered East Tung Chung Bay and do not coincide with sediment plumes from the other concurrent projects, although the plumes could, under certain tidal conditions, slightly mix with the plumes from the (unmitigated) Lantau Logistic Park. Since the water quality mixing zone of this Project is unlikely to overlap with those of other concurrent projects in this part of Hong Kong, it can, therefore, be concluded that cumulative impacts on water quality impacts are not predicted to occur.

6.13 Conclusions

This Section of the EIA has described the water quality impacts associated with the construction of the proposed submarine pipelines and the associated gas receiving facilities at Black Point. The purpose of the assessment was to evaluate the acceptability of predicted impacts to water quality.

Mathematical modelling has been used to simulate the loss of sediments to suspension during the construction phase and the impacts of the reclamation during the operation phase. The results and findings of the computer modelling have been provided and summarised.

Potential impacts arising from the proposed marine construction works are predicted to be largely confined to the specific works areas. The sediment dispersion is expected to be transient in nature and no adverse impacts to water quality at the sensitive receivers would arise.

During the operation phase, changes to hydrodynamic regime, water quality and sedimentation pattern as a result of the construction of the GRS on a reclaimed land are predicted to be minimal and no specific mitigation measures are required.

([1]) At the time of reporting 2008 data were not available.

([2]) 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.

([3]) ERM - Hong Kong, Ltd (2006) Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. For CAPCO. Final EIA Report. December 2006.

([4]) Maunsell (2002). EIA for Decommissioning of Cheoy Lee Shipyard at Penny's Bay. For Civil Engineering Department, Hong Kong SAR Government.

([5]) 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.

([6]) Maunsell (2001). EIA for Wanchai Development Phase II - Comprehensive Feasibility Study. For Territory Development Department, Hong Kong SAR Government.

([7]) ERM - Hong Kong, Ltd (2006) Op Cit

([8]) BMT Asia Pacific Ltd (2009). EIA for Hong Kong Offshore Wind Farm in Southeastern Waters. For HK Offshore Wind Limited

([9]) Scott Wilson (2003). Extension of Existing Landfills and Identification of Potential New Waste Disposal Sites. For the Environmental Protection Department, Hong Kong SAR Government

([10]) ERM-Hong Kong, Ltd (1993). EIA of the Proposed 6000MW Thermal Power Station at Black Point: Key Issue Assessment-Marine Water Quality, Final Report, prepared for Castle Peak Power Company Limited.

([11]) ERM-Hong Kong, Ltd (2004) Detailed Site Selection Study for a Proposed Contaminated Mud Disposal Facility within the Airport East/East of Sha Chau Area. Agreement No. CE 12/2002 (EP). Environmental Impact Assessment and Final Site Section Report, for Civil Engineering and Development Department, Hong Kong SAR Government

([12]) AFCD (2005). Marine Park Water Quality Report. Web site: www.afcd.gov.hk.

([13]) ERM-Hong Kong, Ltd (1998). Fisheries Resources and Fishing Operations in Hong Kong Waters. Final Report. For the Agriculture, Fisheries and Conservation Department, Hong Kong SAR Government.

([14]) City University of Hong Kong (2001) Agreement No. CE 62/98, Consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment, Final Report, for the Agriculture, Fisheries and Conservation Department, Hong Kong SAR Government.

([15]) Annex 6I presents the results of modelling scenarios which examined pipeline installation by trailing suction hopper dredging in HKSAR waters.

([16]) ARUP (2009b) Environmental Impact Assessment of the Hong Kong - Zhuhai - Macao Bridge Hong Kong Boundary Crossing Facilities. Approved EIA Report prepared for Highways Department

([17]) The deposition rate is simulated as the maximum daily deposition at any time during the simulation. The total deposition for subsequent 24 hour periods has been calculated during the simulations (about 14 periods during a spring-neap cycle). Out of these values, the maximum value has been determined for every individual model grid cell, and these values are those have been plotted and presented in Annex 6C.

([18]) ERM - Hong Kong, Ltd (2006) Op Cit

([19]) Deltares (2009). Modelling Memo for the Black Point Gas Supply Project.

([20]) ERM - Hong Kong, Ltd (2006) Op Cit

([21]) ERM - Hong Kong, Ltd (2006) Op Cit

([22]) ERM - Hong Kong, Ltd (2006) Op Cit

([23]) The reporting limits for PCBs and silver used for the elutriate test were higher than the relevant assessment criteria. A review of the elutriate test results of the HKLNG EIA was conducted to supplement the present assessment. Elutriate tests on sediment collected from nearby locations off Black Point (about 200 m south of the proposed Pipeline 1) showed that PCBs and silver concentrations were below the detection limits (0.01 mg L-1 and 1 mg L-1 respectively) and did not exceed the relevant assessment criteria (0.03 mg L-1 and 1.9 mg L-1 respectively). Therefore it is predicted that potential release of PCBs/ silver from disturbed sediments is not expected to result in unacceptable water quality impacts.

([24]) Based on Table 2 of the Drainage Services Department's Sewerage Manual

([25]) ERM - Hong Kong, Ltd (2006) Op Cit

([26]) ERM - Hong Kong, Ltd (2006) Op Cit

([27]) Information from the Shenzhen Port Tonggu Channel Developing Office indicates that maintenance dredging of the Tonggu Waterway may take place annually. Updated information to determine if there is any overlap with the construction for this Project is not available and this will be reviewed at a later stage

([28]) ERM (2005) New Contaminated Mud Marine Disposal Facility at Airport East / East Sha Chau Area: EIA Report. Prepared for CEDD

([29]) ARUP (2009a) Environmental Impact Assessment of the Hong Kong - Zhuhai - Macao Bridge Hong Kong Link Road. Prepared for Highways Department

([30]) ARUP (2009b) Environmental Impact Assessment of the Hong Kong - Zhuhai - Macao Bridge Hong Kong Boundary Crossing Facilities. Prepared for Highways Department

6 Water Quality Assessment