6 WatER qUALITY impact

6.1 Introduction

This Section describes the potential impacts on water quality from the construction and operation of the proposed offshore wind farm. Computer modelling has been used to predict potential impacts to water quality, which are then assessed with reference to the relevant environmental legislation and standards.

6.2 Legislation Requirements and Evaluation Criteria

The following relevant legislation and associated guidance are applicable to the evaluation of water quality impacts associated with the Project:

· Water Pollution Control Ordinance (WPCO);

· Environmental Impact Assessment Ordinance (Cap. 499. S.16), Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), Annexes 6 and 14; and

· Other guidelines, such as, Management of Dredged / Excavated Sediment, ETWBTC No. 34/2002.

6.2.1 Water Pollution Control Ordinance (WPCO)

Under the WPCO, Hong Kong waters are divided into 10 Water Control Zones (WCZs), each of which has a set of statutory Water Quality Objectives (WQOs) designed to protect the marine environment and its users.

The proposed wind farm site lies in the Southern Waters WCZ as defined by the EPD, which covers 400 km² of water stretching from Hong Kong Island south to Lantau Island facing the South China Sea ([1]) (see Figure 6.1).

The applicable WQOs of the Southern Waters WCZ are provided in Table 6.1.

Table 6.1 Water Quality Objectives Applicable to the Southern Waters WCZ ([2])

Water Quality Objective	Applicable Area
A. AESTHETIC APPEARANCE
a) Waste discharges shall cause no objectionable odours or discolouration of the water.	Whole zone
b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.	Whole zone
c) Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.	Whole zone
d) There should be no recognisable sewage-derived debris.	Whole 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
f) Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.	Whole zone
B. BACTERIA
The level of Escherichia coli should not exceed 610 per 100 mg per litre, calculated as the geometric mean of all samples collected in one calendar year.	Secondary Contact Recreation Subzone & Fish Culture Zones
C. DISSOLVED OXYGEN
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.	Whole zone
D. pH
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.	Whole zone
E. TEMPERATURE
Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 ^oC.	Whole zone
F. SALINITY
Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.	Whole zone
G. SUSPENDED SOLIDS
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 of the whole zone
H. 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
I. NUTRIENTS
Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.1 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).	Whole zone
J. TOXINS
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

6.2.2 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 zone are that it must not impair the integrity of the water body as a whole and must not damage the ecosystem.

6.2.3 Suspended Solid Impacts

The WQO for suspended solids in marine waters of the Southern Waters 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 data from the years of 1998 to 2007 has been undertaken to determine the allowable increase in suspended solids concentrations within the WCZ. Data from EPD monitoring stations SM18, SM5, SM6 and SM7 have been used to determine the allowable increase at the sensitive receivers in proximity to the offshore wind farm and cable route (Figure 6.2).

SS Criterion for Seawater Intakes

Power station intakes have specific requirements for intake water quality. The applicable criteria for the Lamma Power Station seawater intake is suspended sediment levels below 100 mg L^-1 ([3]).

The Water Supplies Department (WSD) also has a set of standards for the quality of abstracted seawater (Table 6.2). Water quality at the WSD seawater intakes has been assessed against these standards, in addition to the WQOs.

Table 6.2 WSD Water Quality Criteria for Abstracted Seawater

Parameter	Criterion
Colour (HU)	< 20
Turbidity (NTU)	< 10
Threshold Odour No.	< 100
Ammoniacal Nitrogen (mg L^-1)	< 1
Suspended Solids (mg L^-1)	< 10 (20 is the upper threshold)
Dissolved Oxygen (mg L^-1)	> 2
5-day Biochemical Oxygen Demand (mg L^-1)	< 10
Synthetic Detergents (mg L^-1)	< 5
E. coli (cfu 100mL^-1)	< 20,000

SS Criterion for Fish Culture Zones

There is a general water quality protection guideline for suspended solids (SS), which has been proposed by AFCD ([4]). The guideline requires the maximum SS levels remain below 50 mg L^-1. This criterion has been adopted in previous approved EIA Reports ([5]) ([6]) ([7]). Thus, for the purposes of this assessment, both the AFCD criterion and the WQO are considered to be generally applicable.

6.2.4 Sediment Quality

Dredged sediments destined for marine disposal are classified according to a set of regulatory guidelines (Management of Dredged / Excavated Sediment, ETWBTC No. 34/2002) issued by the Environment, Transport and Works Bureau (ETWB) in August 2002. These guidelines comprise a set of sediment quality criteria for organic pollutants and other substances. The requirements for the marine disposal of sediment are specified in the ETWBTC No. 34/2002. Marine disposal of dredged materials is controlled under the Dumping at Sea Ordinance 1995.

6.2.5 Other Assessment Criteria

Sediment Deposition

Impacts to artificial reefs (ARs) have been assessed with regard to sediment deposition. The assessment criterion of 100 g m^-2 day^-1, has been used in approved EIA Reports ([8]) ([9]) and has been adopted here.

Dissolved Oxygen

The release of sediment into the water column due to the Project may consume the dissolved oxygen (DO) in the receiving water. The oxygen depletion resulting from the dredging operations will be assessed against the WQO. The allowable change in DO levels in the WCZ has been calculated based on the EPD routine water quality monitoring data for the period 1998 to 2007.

The DO assessment criterion, for each sensitive receiver is discussed in Section 6.3.4.

In addition, the WQO that is specific to Fish Culture Zones is set at no less than 4 mg L^-1measured at 1 m below the water surface (Table 6.1).

6.3 Baseline Conditions and Water Quality Sensitive Receivers

6.3.1 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 NE Monsoon is generally stronger and more persistent than the SW 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. Hong Kong's waters are therefore characterised by the interaction of oceanic and estuarine water masses, which vary in relative effects throughout the year. The variable freshwater discharge from the Pearl River has a marked influence on Hong Kong waters.

During the summer, an oceanic flow from the south-west to the north-east brings the warm, high-salinity water of the Hainan Current into Hong Kong waters. This interacts with fresh water from the Pearl River and divides Hong Kong into three distinct zones. In the west, where the fresh water influence is greatest, the environment is estuarine and the water is brackish. In the east, the water is mainly oceanic with relatively minor dilution from rainfall and runoff from streams. The limits of the central transitional zone vary depending upon the relative influence of Pearl River water and marine currents.

During the winter dry season, the Kuroshio oceanic current brings warm water of high salinity from the Pacific through the Luzon Strait. The freshwater discharge of the Pearl River is much lower than in the summer and salinity is more uniform across Hong Kong. The coastal Taiwan current also brings cold water from the north-east down the South China coast, affecting inshore waters.

The maximum tidal range is 2.8 m during spring tides and 1m during neaps. The tidal pattern is complex due to the relative effects of the diurnal and semi-diurnal components. The tides in Hong Kong are ‘mixed’ so that there are semi-diurnal tides at the time of springs and diurnal tides at the time of neaps.

The basic pattern during flood tides is for oceanic water to flow north into Mirs Bay and west through Lei Yue Mun into Victoria Harbour and through Kap Shui Mun and the Ma Wan Channel. This flow is reversed during the ebb tide. The dominant flow direction at the site is North-South. Peak tidal water velocities can be expected to lie at around 0.8 ms^-1.

The dry season flow condition is characterized by a high salinity and negligible stratification in the Hong Kong area. The NE monsoon with average wind of 5 ms^-1from NE, the coastal current and a NE-SW oriented mean sea level gradient direct the Pearl River outfall plume in a south-westerly direction. The average Pearl River discharge of the dry season is about 4,100 m³s^-1. In the wet season the large Pearl River outfall plume (with an average wet season discharge of about 19,400 m³s^-1) is forced on a more easterly track by the SW monsoon with an average wind of 5 ms^-1 from SW, and a reverse mean sea level gradient. The fresh water plume enters the Hong Kong channels and the flow becomes stratified.

Hydrodynamic modelling has been carried out over a spring-neap cycle in both the wet and dry season. The modelling has been used to determine the baseline hydrodynamic conditions over a spring-neap cycle in both the dry and wet seasons for bottom and surface layers over ebb and flood tides. The outputs from this work are presented in Annex 6A.

Hydrodynamic modelling results generally show a northwest to southeast flow on the ebb tide and a southeast to northwest flow on the flood tide at the wind farm site. To the north of the site flows change to a north – south direction. There is also a change of flow at the western side of Lamma Island as currents move towards and away from the shore.

In the wet season, surface flows are generally stronger than bottom flows on both the ebb and flood tides. On the ebb tide, flows at the surface are generally less than 0.7 ms^-1 at the surface and less than 0.3 ms^-1near the seabed at the wind farm site. Flows are higher to the north, east and south of the wind farm site. All flows during the flood tide are weaker than on the ebb tide. Flows on the flood tide are generally less than 0.4 ms^-1at the surface and less than 0.2 ms^-1near to the seabed at the wind farm site.

In the dry season, surface flows are again generally higher than bottom flows. However the difference is smaller than in the wet season. On the ebb and flood tides, flows at the surface are generally less than 0.4 ms^-1and less than 0.3 ms^-1 near to the seabed.

Surface flows are stronger in the wet season than in the dry season on the ebb tide. The difference between the wet and dry seasons with respect to flood tide flows and bottom flows over different parts of the tidal cycle is less apparent.

6.3.2 Water Quality

Water quality has been determined through a review of EPD routine water quality monitoring data. 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.

One water quality sampling station is located adjacent to the wind farm site (SM18) and three stations (SM5, SM6 and SM7) are located in proximity to the wind farm site and cable route. SM5 is located nearshore to Lamma Island (see Figure 6.2).

The results of EPD monitoring at the above sites between the period 2003 and 2007 are shown in Table 6.3. Only key parameters that have the potential to be affected by the Project are listed here.

Table 6.3 Results of EPD Water Quality Monitoring at Stations in proximity to the Southwest Lamma Site (2003 – 2007) ([10])

Parameter	EPD Monitoring Station
Temperature (ºC)	24.0 (19.1 – 28.5)	23.7 (19.1 – 27.6)	23.8 (19.3 – 27.6)	23.5 (19.0 – 27.3)
pH	8.2 (7.6 – 8.6)	8.2 (7.6 – 8.6)	8.1 (7.6 – 8.5)	8.2 (7.6 – 8.6)
Dissolved Oxygen (mg L^-1) Depth-averaged	6.3 (5.3 – 7.5)	6.2 (5.2 – 7.2)	6.3 (4.6 – 7.1)	6.0 (4.4 – 6.9)
Dissolved Oxygen (mg L^-1) Bottom	5.9 (3.3 – 7.4)	5.6 (1.6 – 7.2)	5.9 (4.2 – 7.0)	5.4 (1.6 – 7.1)
Dissolved Oxygen (% sat.) Depth-averaged	90 (80 – 106)	88 (78 – 102)	89 (70 – 101)	85 (67 – 94)
Dissolved Oxygen (% sat.) Bottom	83 (48 - 103)	79 (22 - 101)	83 (60 - 98)	76 (22 - 96)
5-day Biochemical Oxygen Demand (mg L^-1)	1.2 (0.2 – 3.5)	1.1 (0.2 – 2.9)	1.2 (0.3 – 3.0)	0.8 (0.1 – 1.9)
Suspended Solids (mg L^-1)	4.1 (1.6 – 7.5)	5.0 (1.3 – 20.3)	6.0 (1.6 – 12.3)	4.4 (0.9 – 12.7)
Total Inorganic Nitrogen (mg L^-1)	0.15 (0.04 – 0.38)	0.16 (0.04 – 0.41)	0.27 (0.07 – 0.57)	0.12 (0.03 – 0.27)
Unionised Ammonia (mg L^-1)	0.004 (<0.001 – 0.013)	0.003 (<0.001 – 0.011)	0.005 (<0.001 – 0.009)	0.003 (<0.001 – 0.010
Chlorophyll-a (µL^-1)	3.4 (0.8 – 11.9)	3.6 (0.7 – 14.2)	7.1 (0.6 – 27.2)	2.2 (0.7 – 6.8)
Escherichia coli (cfu 100mL^-1)	2 (1 – 14)	2 (1 – 95)	21 (1 – 870)	1 (1 – 2)
Notes: 1. Values in non-brackets represent the mean value across the data set. Values in brackets represent the range in the data set. 2. 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. 3. Data presented are annual arithmetic means except for E. coli, which are geometric means. 4. Data enclosed in brackets indicate the ranges regardless of the depths. 5. Shaded cells indicate non-compliance with the WQOs.

Parameter

EPD Monitoring Station

SM5

SM6

SM7

SM18

Temperature (ºC)

24.0

(19.1 – 28.5)

23.7

(19.1 – 27.6)

23.8

(19.3 – 27.6)

23.5

(19.0 – 27.3)

8.2

(7.6 – 8.6)

8.2

(7.6 – 8.6)

8.1

(7.6 – 8.5)

8.2

(7.6 – 8.6)

Dissolved Oxygen (mg L^-1) Depth-averaged

6.3

(5.3 – 7.5)

6.2

(5.2 – 7.2)

6.3

(4.6 – 7.1)

6.0

(4.4 – 6.9)

Dissolved Oxygen (mg L^-1) Bottom

5.9

(3.3 – 7.4)

5.6

(1.6 – 7.2)

5.9

(4.2 – 7.0)

5.4

(1.6 – 7.1)

Dissolved Oxygen (% sat.) Depth-averaged

(80 – 106)

(78 – 102)

(70 – 101)

(67 – 94)

Dissolved Oxygen (% sat.) Bottom

(48 - 103)

(22 - 101)

(60 - 98)

(22 - 96)

5-day Biochemical Oxygen Demand (mg L^-1)

1.2

(0.2 – 3.5)

1.1

(0.2 – 2.9)

1.2

(0.3 – 3.0)

0.8

(0.1 – 1.9)

Suspended Solids (mg L^-1)

4.1

(1.6 – 7.5)

5.0

(1.3 – 20.3)

6.0

(1.6 – 12.3)

4.4

(0.9 – 12.7)

Total Inorganic Nitrogen (mg L^-1)

0.15

(0.04 – 0.38)

0.16

(0.04 – 0.41)

0.27

(0.07 – 0.57)

0.12

(0.03 – 0.27)

Unionised Ammonia (mg L^-1)

0.004

(<0.001 – 0.013)

0.003

(<0.001 – 0.011)

0.005

(<0.001 – 0.009)

0.003

(<0.001 – 0.010

Chlorophyll-a (µL^-1)

3.4

(0.8 – 11.9)

3.6

(0.7 – 14.2)

7.1

(0.6 – 27.2)

2.2

(0.7 – 6.8)

Escherichia coli (cfu 100mL^-1)

(1 – 14)

(1 – 95)

(1 – 870)

(1 – 2)

Notes:

1. Values in non-brackets represent the mean value across the data set. Values in brackets represent the range in the data set.

2. 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.

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

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

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

The above sites fully complied with Water Quality Objectives (WQOs) for most parameters measured with the exception of Total Inorganic Nitrogen.

6.3.3 Sediment Quality

EPD Sediment Quality Monitoring

EPD collects sediment quality data as part of the marine water quality monitoring programme. 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 Environment Transport & Works Bureau Technical Circular No 34/2002 Management of Dredged/Excavated Sediment (ETWBTC 34/2002).

Two sediment sampling stations (SS3 and SS4) are located in proximity to the wind farm site and cable route located in water depths of 8 - 14m. The location of these sampling stations is shown in Figure 6.2. The results of EPD monitoring at the above sites between the period 2003 and 2007 is shown in Table 6.4.

A comparison of the data with the sediment quality criteria (i.e., Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL) (see Table 6.4) shows that the sediments in the local area of the wind farm site are largely comprised of fine material and are relatively unpolluted with levels below exceedance limits. Levels of contaminants found are comparable with other areas of Hong Kong waters, with the exception of Victoria Harbour where higher levels of some pollutants have been recorded.

Table 6.4 Results of EPD Sediment Monitoring at Stations in proximity to the Southwest Lamma Site (2003-2007) ([11])

Parameter	EPD Monitoring Station		LCEL	UCEL
	SS3	SS4
PSD <63 μm (%w/w)	73 (52 - 92)	74 (46 - 96)	-	-
COD (mg kg^-1)	18000 (15000 – 25000)	16000 (14000 – 23000)	-	-
Ammonia Nitrogen (mg kg^-1)	5.4 (1.7 – 13.0)	3.4 (1.3 – 6.5)	-	-
Total Kjeldahl Nitrogen (mg kg^-1)	380 (240 - 470)	370 (240 – 500)	-	-
Total Phosphorous (mg kg^-1)	220 (180 – 270)	190 (150 – 250)	-	-
Total Sulphide (mg kg^-1)	33 (4 – 72)	41 (8 – 140)	-	-
Total Carbon (%w/w)	0.9 (0.6 - 1.0)	0.8 (0.6 - 1.0)	-	-
Arsenic (mg kg^-1)	7.0 (6.1 - 7.9)	7.3 (6.1 – 8.8)	12	42
Cadmium (mg kg^-1)	<0.1 (<0.1 - <0.1)	<0.1 (<0.1 - <0.1)	1.5	4
Chromium (mg kg^-1)	32 (25 - 38)	34 (26 - 41)	80	160
Copper (mg kg^-1)	19 (15 - 23)	28 (18 - 38)	65	110
Lead (mg kg^-1)	35 (23 - 41)	38 (25 - 49)	75	110
Mercury (mg kg^-1)	0.1 (0.08 - 0.10)	0.11 (0.08 - 0.20)	0.5	1
Nickel (mg kg^-1)	23 (19 - 25)	22 (16 - 26)	40	40
Silver (mg kg^-1)	0.2 (<0.2 – 0.2)	0.4 (0.2 – 0.6)	1	2
Zinc (mg kg^-1)	93 (75 – 110)	100 (75 – 130)	200	270
Total PCBs (µg kg^-1)	18 (18 – 18)	18 (18 – 18)	23	180
Low Molecular Weight PAHs (µg kg^-1)	91 (90 – 95)	93 (90 – 110)	550	3160
High Molecular Weight PAHs (µg kg^-1)	58 (23 – 110)	89 (40 – 160)	1700	9600
1. Values in non-brackets represent the mean value across the data set. Values in brackets represent the range in the data set. 2. Data enclosed in brackets indicate the ranges regardless of the depths. 3. Data presented are arithmetic mean and data presented in bracket indicate the minimum and maximum data range of each parameter. 4. Low Molecular Wt PAHs include acenaphthene, acenaphthylene, anthracene, fluoreneand phenanthrene. 5. High Molecular Wt PAHs include benzo[a]anthracene, benzo[a]pyrene, chrysene, dibenzo[a,h]anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, indeno[1,2,3- c,d]pyrene and benzo[g,h,I]perylene. 6. LCEL = Lower Chemical Exceedance Level 7. UCEL = Upper Chemical Exceedance Level

A sediment survey was carried out in April 2009. A total of 5 samples were collected in the nearshore area close to the landing point for contaminant analyses. The location of the sample points are shown in Figure 6.3. Results from the survey are presented in Table 6.5.

Table 6.5 Results from Sediment Survey in April 2009

Parameter	Survey Station					LCEL	UCEL
	1	2	3	4	5
Ammonia Nitrogen (mg kg^-1)	<10	<10	<10	<10	<10	-	-
Nitrite (mg kg^-1)	<0.5	<0.5	<0.5	<0.5	<0.5
Nitrate (mg kg^-1)	<0.5	<0.5	<0.5	<0.5	<0.5
Total Kjeldahl Nitrogen (mg kg^-1)	1170	1300	1150	1220	300	-	-
Total Phosphorous (mg kg^-1)	624	911	702	778	300	-	-
Total Carbon (%w/w)	0.98	1.03	1.02	1.04	1.07	-	-
Arsenic (mg kg^-1)	8	10	10	10	10	12	42
Cadmium (mg kg^-1)	<0.2	<0.2	<0.2	<0.2	<0.2	1.5	4
Chromium (mg kg^-1)	44	41	42	44	43	80	160
Copper (mg kg^-1)	74	26	25	32	25	65	110
Lead (mg kg^-1)	39	39	41	44	37	75	110
Mercury (mg kg^-1)	0.07	0.07	0.09	0.10	0.07	0.5	1
Nickel (mg kg^-1)	27	26	27	28	26	40	40
Silver (mg kg^-1)	0.2	0.2	0.2	0.2	0.2	1	2
Zinc (mg kg^-1)	121	116	115	121	115	200	270
Total PCBs (µg kg^-1)	<3.0	<3.0	<3.0	<3.0	<3.0	23	180
Low Molecular Weight PAHs (µg kg^-1)	<550	<550	<550	<550	<550	550	3160
High Molecular Weight PAHs (µg kg^-1)	<1700	<1700	<1700	<1700	<1700	1700	9600

The results of the nearshore sediment survey show that sediments in the area that will be disturbed as a result of this Project are largely uncontaminated. However, copper was elevated above LCEL at sampling station 1. This record is isolated and is considered to be representative of the heterogeneous nature of marine sediments. It is noted that station 1 is outside of the footprint of the proposed grab dredging and sediments in this area will not be disturbed (see Section 7).

No sediment sampling and elutriate tests were conducted within the development area for the turbines as no dredging will take place within this area. Elutriate tests carried out in the area of grab dredging along the cable route to assess the potential for a release of heavy metals and micro-organic pollutants from the dredged marine mud may, however, be considered indicative of the sediments across the proposed development area. The results show that dissolved metal concentrations for all samples are below the reporting limits. The results also show that all PAHs and PCBs and chlorinated pesticides are all below the reporting limits. Should any dredging be required within the later stage of the design of the development area, a focused sediment testing programme would be conducted prior to any dredging or jetting works and the results presented to the EPD and other HKSARG departments as appropriate.

6.3.4 Water Quality Sensitive Receivers

The construction phase of the proposed wind farm development has the potential to affect local water quality. The Water Sensitive Receivers (WSRs) that may be affected by changes in water quality are identified in accordance with the EIAO-TM. For each of the sensitive receivers, established threshold criteria or guidelines have been utilised for establishing the significance of impacts due to potential changes in water quality. WSRs are illustrated in Figure 6.4. In addition to WSRs, modelling points have been added adjacent to the cable route to understand the extent of impacts associated with jetting activities. A series of modelling output points and WSRs are plotted as discrete points for evaluation in the assessment against the above criteria and guidelines (see Figure 6.5). A summary of each of the sensitive receivers is presented and the evaluation criteria are also described in Table 6.6. Shortest distance to the wind farm site and cable route are also shown for each sensitive receiver. It should be noted that these distances are measured “as the crow flies”, or directly without taking into account land mass or other structures. The presence of such masses would naturally affect any direct / indirect impact to these receivers; however, for conservatism they have been removed. The SS and DO assessment criteria for the sensitive receivers are presented in Tables 6.7 and 6.8, respectively.

Table 6.6 Water Quality Sensitive Receivers (WSRs) in the vicinity of Wind Farm Site and Cable Route

Sensitive Receiver	Name	ID	Shortest distance to the wind farm site (km)	Shortest distance to the cable route (km)	Assessment Criteria
*Fisheries and Marine Ecological Sensitive Receivers*
*Fisheries Resources*
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	5.1	6.1	Water Quality Objectives (WQO)
	Spawning / Nursery Grounds to the East	SR21 SR14	4.3 1.7	5.0 2.8	Water Quality Objectives (WQO)
	Spawning / Nursery Grounds to the North	SM6	1.5	1.0	Water Quality Objectives (WQO)
Fish Culture Zone	Lo Tik Wan	SR2	6.1	3.2	SS elevations below 50 mgL^-1 Water Quality Objectives (WQO)
	Sok Kwu Wan	SR3	5.0	3.0	SS elevations below 50 mgL^-1 Water Quality Objectives (WQO)
*Marine Ecological Resources*
Potential Coral Communities	Nam Tsui to Tai Kok hard coral communities	SR4 SR23 SR9	7.6 6.0 5.2	3.9 2.2 2.0	Water Quality Objectives (WQO) SS elevations below 10 mgL^-1 Deposition rate below 100 g m^-2 day^-1
		SR10 SR19 SR24 SR20 SR21	4.1 3.0 2.1 2.8 4.3	2.3 2.9 2.7 3.5 5.0
Coral Communities	Lamma Power Station Extension Seawall	SR15	3.8	0.2	Water Quality Objectives (WQO) SS elevations below 10 mgL^-1 Deposition rate below 100 g m^-2 day^-1
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	5.0	3.0	Water Quality Objectives (WQO)
Marine Mammal Habitat	Southwest Lamma Waters	SR1 SM5	1.5 3.2	2.0	Water Quality Objectives (WQO)
Green Turtle Habitat	Sham Wan	SR6	4.5	4.3	Water Quality Objectives (WQO)
Potential Marine Park	South Lamma	SR1 SR6 SR13 SR14	1.5 4.5 5.7 1.7	2.0 4.3 6.0 2.8	Water Quality Objectives (WQO)
*Water Quality Sensitive Receivers*
Gazetted Beaches	Cheung Chau Tung Wan	SR7	6.0	6.3	Water Quality Objectives (WQO)
	Kwun Yam	SR8	5.3	5.6	Water Quality Objectives (WQO)
	Hung Shing Yeh	SR9	5.2	2.0	Water Quality Objectives (WQO)
	Lo So Shing	SR10	4.1	2.3	Water Quality Objectives (WQO)
Seawater Intakes	Cheung Chau	SR11	6.8	6.9	Water Quality Objectives (WQO)
	Lamma Power Station	SR12	4.4	0.9	Water Quality Objectives (WQO) SS elevations less than 100 mg L-¹
	Yuen Kok	SR13	5.7	6.0	Water Quality Objectives (WQO)
*Jetting Mixing Zone*
Mixing zone	Cable Route	SR18 SR17 SR16	2.3 2.7 3.2	0.005 0.012 0.009	Water Quality Objectives (WQO)

Table 6.7 Ambient Level and Allowable Increase in SS at WSRs around the proposed offshore wind farm and cable route

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	WQO Allowable Increase			Ambient Level			WQO Allowable Increase		Ambient Level		WQO Allowable Increase
*Fisheries and Marine Ecological Sensitive Receivers*
*Fisheries Resources*
Spawning / Nursery Grounds		Spawning / Nursery Grounds to the West		SR22	SM6		Depth-averaged		11.5		3.4		14.8			4.4		10.4		3.1
		Spawning / Nursery Grounds to the East		SR21 SR14	SM5		Depth-averaged		10.0		3.0		10.0			3.0		9.9		3.0
		Spawning / Nursery Grounds to the north		SM6	SM6		Depth-averaged		11.5		3.4		14.8			4.4		10.4		3.1
Fish Culture Zone		Lo Tik Wan		SR2	SM5		Depth-averaged		10.0		40.0 (AFCD) 3.0 (WQO)		10.0			40.0 (AFCD) 3.0 (WQO)		9.9		40.0 (AFCD) 3.0 (WQO)
		Sok Kwu Wan		SR3	SM5		Depth-averaged		10.0		40.0 (AFCD) 3.0 (WQO)		10.0			40.0 (AFCD) 3.0 (WQO)		9.9		40.0 (AFCD) 3.0 (WQO)
*Marine Ecological Resources*
Potential Coral Communities		Nam Tsui to Tai Kok hard coral communities		SR4 SR23 SR9 SR10 SR19 SR24 SR20 SR21	SM5		Depth-averaged		10.0		N/A		10.0			N/A		9.9		N/A
Coral Communities		Lamma Power Station Extension Seawall		SR15	SM5		Depth-averaged		10.0		N/A		10.0			N/A		9.9		N/A
Horseshoe Crab Nursery Grounds		Sok Kwu Wan		SR3	SM5		Depth-averaged		10.0		3.0		10.0			3.0		9.9		3.0
Marine Mammal Habitat		Southwest Lamma Waters		SR1 SM5	SM5		Depth-averaged		10.0		3.0		10.0			3.0		9.9		3.0
Green Turtle Habitat		Sham Wan		SR6	SM5		Depth-averaged		10.0		3.0		10.0			3.0		9.9		3.0
Potential Marine Park		South Lamma		SR1 SR6 SR13 SR14	SM5		Depth-averaged		10.0		3.0		10.0			3.0		9.9		3.0
*Water Quality Sensitive Receivers*
Gazetted Beaches		Cheung Chau Tung Wan		SR7		SM6	Depth-averaged		11.5		3.4		14.8		4.4			10.4		3.1
		Kwun Yam		SR8		SM6	Depth-averaged		11.5		3.4		14.8		4.4			10.4		3.1
		Hung Shing Yeh		SR9		SM5	Depth-averaged		10.0		3.0		10.0		3.0			9.9		3.0
		Lo So Shing		SR10		SM5	Depth-averaged		10.0		3.0		10.0		3.0			9.9		3.0
Seawater Intakes		Cheung Chau		SR11		SM6	Bottom		19.9		6.0		21.4		6.4			19.4		5.8
		Lamma Power Station		SR12		SM5	Bottom		14.9		4.5		15.6		4.7			14.0		4.2
		Yuen Kok		SR13		SM5	Bottom		14.9		4.5		15.6		4.7			14.0		4.2
*Jetting Mixing Zone*
Mixing zone		Cable Route		SR18 SR17 SR16		SM6	Depth-averaged		11.5		3.4	14.8			4.4			10.4		3.1
Notes:
1. The tolerance criterion of 100 mg L^-1 was adopted for the seawater intake at Lamma Power Station 2. Ambient level is calculated as 90^th percentile of the EPD routine monitoring data (1998-2007) at respective EPD station close to the WSRs. 3. Allowable increase is calculated as 30% of the ambient SS levels in accordance with the WQO. 4. This table is applicable for those sensitive receivers which were assessed against the WQO. “N/A” denotes that the WQO is not applicable for the assessment and it should refer to the specific assessment criterion of SS for this type of sensitive receiver. The value for Fish Culture Zones is 50 mg L^-1 and the value for coral communities is 10 mg L^-1

Table 6.8 Ambient Level and Allowable Change in DO at WSRs around the proposed offshore wind farm and cable route

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	Allowable Change		Ambient Level		Allowable Change		Ambient Level		Allowable Change
*Fisheries and Marine Ecological Sensitive Receivers*
*Fisheries Resources*
Spawning / Nursery Grounds		Spawning / Nursery Grounds to the West		SR22	SM6		Depth-averaged		7.7		-3.7	8.0		-4.04		7.4		-3.4
		Spawning / Nursery Grounds to the East		SR21 SR14	SM5		Depth-averaged		8.0		-3.0	7.9		-2.9		8.0		-3.0
		Spawning / Nursery Grounds to the north		SM6	SM6		Depth-averaged		7.7		-3.7	8.0		-4.04		7.4		-3.4
Fish Culture Zone		Lo Tik Wan		SR2	SM5		Depth-averaged		8.0		-3.0	7.9		-2.9		8.0		-3.0
		Sok Kwu Wan		SR3	SM5		Depth-averaged		8.0		-3.0	7.9		-2.9		8.0		-3.0
*Marine Ecological Resources*
Coral Communities		Nam Tsui to Tai Kok hard coral communities		SR23 SR9 SR10 SR19 SR24 SR20 SR21	SM5		Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
Coral Communities		Lamma Power Station Extension Seawall		SR15	SM5		Depth-averaged		10.0		N/A	10.0		N/A		9.9		N/A
Horseshoe Crab Nursery Grounds		Sok Kwu Wan		SR3	SM5		Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
Marine Mammal Habitat		Southwest Lamma Waters		SR1 SM5	SM5		Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
Green Turtle Habitat		Sham Wan		SR6	SM5		Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
Potential Marine Park		South Lamma		SR1 SR6 SR13 SR14	SM5		Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
*Water Quality Sensitive Receivers*
Gazetted Beaches		Cheung Chau Tung Wan		SR7		SM6	Depth-averaged		7.7		-3.7	8.0		-4.0		7.4		-3.4
		Kwun Yam		SR8		SM6	Depth-averaged		7.7		-3.7	8.0		-4.0		7.4		-3.4
		Hung Shing Yeh		SR9		SM5	Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
		Lo So Shing		SR10		SM5	Depth-averaged		8.0		-4.0	7.9		-3.9		8.0		-4.0
Seawater Intakes		Cheung Chau		SR11		SM6	Bottom		7.7		-5.7	8.1		-6.1		6.8		4.8
		Lamma Power Station		SR12		SM5	Bottom		7.8		-5.8	8.0		-6.0		7.4		-5.4
		Yuen Kok		SR13		SM5	Bottom		7.8		-5.8	8.0		-6.0		7.4		-5.4
*Jetting Mixing Zone*
Mixing zone		Cable Route		SR18 SR17 SR16		SM6	Depth-averaged		7.7		-5.7	8.1		-6.1		6.8		4.8
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 the ambient level minus the WQO criterion of 4 mg L^-1. 3. For bottom layer, allowable change is calculated as the ambient level minus the WQO criterion of 2 mg L^-1. 4. For Fish Culture Zones, allowable change is calculated as the ambient level minus the FCZ specific criterion of 5 mg L^-1. “N/A” denotes that the WQO is not applicable for the assessment and it should refer to the specific assessment criterion of DO for this type of sensitive receiver.

Fisheries Resources

Commercial Fisheries Spawning Grounds/Nursery Areas

The waters in which the wind farm site and cable route will be located have been identified as important fisheries spawning/nursery grounds for commercial fisheries in Hong Kong ([12]).

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 ([13]), 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). Although a maximum concentration is recommended, the study acknowledges that site-specific data should be considered on a case-by-case basis. Consequently, a conservative approach has been used and the Water Quality Objective (WQO) has been adopted.

With regard to the water quality modelling, impacts to these and other transitory or mobile sensitive receivers were not plotted as discrete points, rather, an assessment of potential impacts was undertaken through a review of the modelling results and is discussed separately in the Fisheries Impact Assessment (see Section 10).

Fish Culture Zones

Although no Fish Culture Zones (FCZs) are located close to the wind farm site or along the proposed cable route consideration is given to potential water quality impacts on this site. The closest FCZs are located at Lo Tik Wan and Sok Kwu Wan (see Figure 6.4). The Water Quality Objective (WQO) specific to FCZs for dissolved oxygen is set at no less than 5 mg L^-1 whereas that for SS is no greater than 30% above ambient. There is also a general water quality protection guideline for SS, which has been proposed by AFCD ([14]). The guideline requires the SS levels remain below 50 mg L^-1. This maximum concentration value has been used in approved EIA Reports ([15]) ([16]) ([17]) under the EIAO and has also been taken as an assessment criterion.

In the water quality modelling works, the FCZs were included as discrete points for evaluation in the assessment against the above criteria and guideline (see Figures 6.4 and 6.5).

Marine Ecological Resources

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

· Coral Communities;

· Horseshoe Crab Nursery Grounds;

· Marine Mammal Habitat;

· Green Turtle Habitat; and

· Potential Marine Parks.

Coral Communities

Coral communities of conservation value have been identified along the coastline to the west of Lamma Island. In addition, nearshore dive surveys carried out for this project have identified hard corals on the Lamma Power Station Extension seawall. There are no established legislative criteria for water quality at coral communities; however, information on hard coral tolerances to SS indicates that a 20% reduction in annual growth rate corresponds to a 30% increase in average long-term background SS levels. In several studies, including those in the eastern waters of Hong Kong, an elevation criterion of 10 mg L^-1 has been adopted as the critical value above which impacts to corals may occur ([18]) ([19]) ([20]) ([21]) ([22]) . This criterion is utilised in this EIA assessment for determining the acceptability of impacts hard corals, soft corals and black corals. The criterion is considered to be protective of impacts to soft and black corals as these species are usually found in deeper water, that is often more turbid with lower light intensity, than hard corals. This is because hard corals require light for the zooxanthellae within their tissues to photosynthesise. Soft and black corals do not usually contain zooxanthellae and are therefore often found in much deeper and darker waters. This information is supported by the documented presence of soft and black corals in parts of Hong Kong waters than experience higher average turbidity and SS levels than areas where hard corals are recorded, eg the area in proximity to the Lamma Power Station ([23]), Green Island ([24]) and the Lamma Island ([25]).

Impacts to hard coral communities have also been assessed with regard to sediment deposition. Hard or hermatypic corals are susceptible to increased rates of deposition, with the species sensitivities to sedimentation being determined largely by the particle-trapping properties of the colony and ability of individual polyps to reject settled materials. Horizontal platelike colonies and massive growth forms present large stable surfaces for the interception and retention of settling solids while vertical plates and upright branching forms are less likely to retain sediments. Tall polyps and convex colonies are also less susceptible to sediment accumulation than other growth forms. It is also acknowledged that sensitivities to sediment loads can also vary markedly between species within the same genus ([26]).

Information presented by Pastorok and Bilyard (1985) ([27]) has been regarded as the primary text when discussing the effects of sedimentation on corals. Pastorok and Bilyard have suggested the following criteria:

* 10 - 100 g m^-2 day^-1 slight to moderate impacts

* 100 - 500 g m^-2 day^-1 moderate to severe impacts

* > 500 g m^-2 day^-1 severe to catastrophic impacts

Fringing and inshore reefal environments, however, are known to experience sedimentation events in exceedance of the 500 g m^-2 day^-1 criterion and support flourishing coral communities ([28]). It is clear from the above that the adoption of strict criteria for impact assessment based on Pastorok & Bilyard's system of assessment for open water communities may well be overly protective in an environment such as Hong Kong. However, using a precautionary approach, it is proposed to adopt a value of 100 g m^-2 day^-1 as the assessment criterion for deposition, which is at the lower end of the range for moderate to severe impacts specified above, for the purposes of this Study. This criterion has been utilised in Hong Kong (Western Waters) before and deemed to be sufficiently protective during EM&A ([29]) ([30]). It should be noted that exceedance of this value should trigger further assessment and should not be deemed to imply that damage would necessarily occur. The results from EM&A programmes in Hong Kong that have adopted 10 mg L^-1 and 100 g m^-2 day^-1 have indicated that no adverse impacts to corals have occurred.

These habitats have been plotted as discrete points for evaluation (see Figures 6.4 and 6.5).

Horseshoe Crabs Nursery Grounds

Areas where horseshoe crabs are known to breed are identified in Figure 6.4 (see also Sections 3 and 9). There are no specific legislative water quality criteria for this habitat and hence water quality impacts are assessed against compliance with the WQO. These habitats have been plotted as discrete points for evaluation (see Figure 6.5).

Marine Mammal Habitat

There are very low sightings of Indo-Pacific humpback dolphins (Sousa chinensis) in the potential development area (see Section 9 for further details). The southwestern tip of Lamma Island has been identified as a calving area for the finless porpoise (Neophocaena phocaenoides). The porpoises are typically most abundant during winter and spring in this part of Hong Kong waters (see Section 9). There are no specific legislative water quality criteria for this habitat and hence water quality impacts are assessed against compliance with the WQOs. Given that these habitats cover large areas for the modelling works we have included discrete points within the areas to provide information on water quality changes (see Figures 6.4 and 6.5).

Green Turtle Habitat

A green turtle (Chelonia mydas) nesting ground is located at Sham Wan SSSI, Southwest Lamma Island, which is ~2.5km from the development site boundary. Turtles have also been reported by AFCD to move around Lamma Island during the nesting season, which is between June and October (see Sections 3 and 9). There are no specific legislative water quality criteria for this habitat and hence water quality impacts are assessed against compliance with the WQOs. These habitats have been plotted as discrete points for evaluation (see Figures 6.4 and 6.5).

Potential Marine Park

The potential South Lamma Marine Park is located to the east of the proposed development area. There are no specific legislative water quality criteria for Marine Parks and the water quality at this sensitive receiver is typically compared with the WQOs. For the water quality assessment, discrete points have been plotted at a number of locations within the boundary of the Potential Marine Park (see Figures 6.4 and 6.5). Note that as the proposed Soko Marine Park and Fan Lau Marine Park are located in excess of 15km from the proposed development site, these areas are considered to be outside of the project area of influence and are hence not discussed further.

Marine Reserve

The Cape d’Aguilar Marine Reserve is located over 15 km from the proposed development site. Due to its distance from the works, this site is considered to be outside of the project area of influence and hence is not discussed further.

Other Water Quality Sensitive Receivers

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

· Bathing Beaches; and

· Seawater Intakes.

Bathing Beaches

There are four gazetted bathing beaches located on the west coast of Lamma Island (~2.5 km away from the development area boundary) and east coast of Cheung Chau (~4 km away from the development boundary). Gazetted beaches include the beaches at Cheung Chau Tung Wan, Kwun Yam, Hung Shing Yeh and Lo So Shing as shown in Figure 6.4. Bathing beaches have been plotted as discrete points for evaluation in the water quality assessment. Water quality impacts at gazetted and non-gazetted bathing beaches have been determined based on the compliance with the WQOs (Table 6.1).

Seawater Intakes

There are two seawater intakes identified as potential sensitive receivers, namely those at Lamma Power Station and the Water Supplies Department’s (WSD) Flushing Water Intakes at Cheung Chau and Yuen Kok as shown in Figure 6.4. WQOs have been adopted for WSD other sea water intakes.

The applicable criteria for suspended sediments for the Lamma Power Station intake is 100 mg L^-1. This value has, therefore, been taken as the assessment criteria. The intakes have been plotted as discrete points for evaluation in the water quality assessment (see Figure 6.5).

6.4 Potential Sources of Impact

Potential sources of impacts to water quality as a result of the Project may occur during both the construction and operation phases. Each is discussed in turn below.

6.4.1 Construction Phase

The major construction activities associated with the proposed Project that may cause impacts to water quality involve the following:

· Generation of suspended sediments;

· Potential for dispersal of contaminants;

· Discharge of contaminants from plant and/or vessels; and

· Discharge of contaminants from onshore activities.

6.4.2 Operational Phase

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

· Generation of suspended sediments which may release contaminated sediments into the water column;

· Vessel discharges;

· Other discharges to the marine environment; and

· Changes to the hydrodynamic regime.

6.5 Water Quality Impact Assessment Methodology

6.5.1 General Methodology

The methodology employed to assess the above impacts is presented in the Water Quality Method Statement (Annex 6B) and has been based on the information presented in the Project Description (Section 5).

Impacts due to the dispersion of fine sediment in suspension during the construction of the proposed offshore wind farm have been assessed using computational modelling. Mitigation measures, as proposed in Section 6.8 such as the use of silt curtain, were assumed to be absent for modelling the worst case scenario.

The simulation of operational impacts on water quality has also been studied by means of computational modelling. The models have been used to simulate the effects of the offshore wind farm structures on hydrodynamics.

Full details of the scenarios examined in the modelling works are provided in Annex 6B. As discussed previously, the WSRs as well as the water quality modelling output points in the vicinity of the proposed offshore wind farm and cable route are presented in Figures 6.4 and 6.5.

6.5.2 General Assumptions in the Assessment Methodology

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 peak dredging and jetting rates. In reality these will only occur for a short period of time;

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

· For foundation construction, the largest potential for sediment disturbance is associated with the construction of monopile foundations with scour protection. As discussed in Section 4, foundation pile diameter for the wind monitoring mast is much smaller than that of the monopiles for the wind turbines, water quality impact associated with wind monitoring mast foundation construction is much less compared with the impact associated with monopile construction. Nevertheless, it is prudent to carry out water quality modelling for wind monitoring mast foundation using the impact as if it is a monopile foundation to cater for the conservative assumption; and

· Construction of a pile and scour protection can occur simultaneously in a short period of time (prior experience overseas has indicated that such work can be completed in one working day) meaning that there will be one disturbance event for the construction of each foundation.

The modelling will not consider the following aspects. These omissions have previously been adopted in modelling works for other projects approved under the EIAO in Hong Kong ([31]).

· The movement of marine vessels, including barges, to and from site, which could have a very localised affect on sediment processes.

· Scouring of bottom sediment around the turbine foundation during operation. This is excluded as it is expected that the disturbance to sediments will be minimal (see Section 5).

· The impacts in terms of contaminants released (i.e. TIN and NH₃-N) and DO depletion will not be modelled explicitly. Instead, they will be quantified on the basis of the modelled maximum suspended sediment concentrations. This method has been used in a recently approved EIA ([1]).

· The jacking-up operation for turbine foundation emplacement is likely to cause negligible disturbance to the seabed due to the method of operation. The jackup vessel will be towed onto location with its legs up and the barge section floating on the water. Upon arrival at the location, the legs are jacked down onto the seafloor, preloaded to securely drive them into the seabed, and then all three legs are jacked further down. Figure 6.6 shows an indicative procedure of how a jack-up rig is secured on the seabed. Since the legs have been preloaded and will not penetrate the seafloor further, this jacking down of the legs has the effect of raising the jacking mechanism, which is attached to the barge. As the procedure will be conducted in a relatively slow and controlled manner with only limited contact to the seabed, suspended sediments released would be minimal and settle within close proximity to the jackup legs. As environmental studies have shown that jack-up rigs can be used in sensitive environments (e.g. in close proximity to corals) and no adverse impacts are recorded through deployment and disturbance, adverse water quality impacts arising from these activities are not expected ([32]) .

· Impacts on hydrodynamics in the construction phase are typically only likely to be associated with the presence of engineering equipment, e.g. jack-up barges, placed temporarily on site. As such equipment is only likely to be positioned at one site at a time for a relatively short period of time, the effects on the hydrodynamic regime is deemed to be very small in magnitude and localised over both temporal and spatial scales.

It is noted that the above presents mechanisms through which minor localised and short term changes in water quality may occur during construction / operation. Elevations will be picked up and monitored during the water quality monitoring programme which is presented in Section 6.9 and checked for compliance against Action and Limit levels.

Figure 6.6 Typical Method of Jack-Up Rig

6.6 Construction Phase Water Quality Impact Assessment

As detailed in Annex 6B, three construction scenarios have been modelled in line with the proposed activities set out in Section 5. Construction scenarios have been based on the base case option of the installation of an offshore substation. Should an onshore substation be selected during the detail design stage, the assessment is considered to remain valid as works activities and locations would remain largely the same, ie grab dredging at existing seawall jetting for cable installation etc. Impact statements and the need for mitigation measures would thus also not be expected to change for this alternative design option.

6.6.1 Suspended Solids

The main potential impacts to water quality arising from this project during the construction phase relate to disturbances to the seabed and re-suspension of some marine sediment leading to the potential for physio-chemical changes in the water column. Modelling results predicting potential sediment plumes associated with works are presented in Annexes 6C and 6D. Annex 6C only provides time series data for those WSRs that are seen to have elevations of suspended sediments above water quality criteria (see below).

Grab Dredging

As discussed in Section 5, grab dredgers will be utilised in the nearshore cable landing area to construct a short underwater trench. Grab dredgers may release sediment into suspension by the following mechanisms:

· Impact of the grab on the seabed as it is lowered;

· Washing of sediment off the outside of the grab as it is raised through the water column and when it is lowered again after being emptied;

· Leakage of water from the grab as it is hauled above the water surface;

· Spillage of sediment from over-full grabs;

· Loss from grabs which cannot be fully closed due to the presence of debris ([33]);

· Release by splashing when loading barges by careless, inaccurate methods; and

· Disturbance of the seabed as the closed grab is removed.

Data were extracted from the modelling results to determine the predicted levels of suspended sediment at each of the sensitive receivers. The maximum elevations of SS at relevant depths 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, where applicable, specific tolerance criteria. It should be noted that elevations in SS levels due to concurrent operations have been assessed as the maximum concentrations at 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-151/2006).

Modelling results show that elevated SS levels are very localised to the area around the Lamma Power Extension seawall (Table 6.9). A recent dive survey carried out at the Lamma Power Station Extension seawall has identified the presence of some isolated colonies of encrusting corals of low conservation value. The impacts to these isolated corals have been discussed and assessed in Section 9. At other WSRs, results indicate that SS elevations are very small or nil during both the wet and dry seasons.

Modelling results show that the elevation at the Lamma Power Station Extension area will be transient with a plume of relatively low SS is predicted to arise from approximately 2 days of grab dredging – the period in which works should be completed. This is evidenced in the time-series plots shown in Annex 6C and dispersal contour plots shown in Annex 6D. This assessment also does not consider the use of closed grab dredgers and application of silt curtains.

The use of cage type silt curtains (which can reduce levels of suspended sediments by up to 75% ([34])) would reduce the release of SS. However, the seawall in this area will be removed as part of the cable landing works and therefore any corals in this area that would be sensitive to changes in SS levels would be removed as part of the construction works. No unacceptable water quality impacts would be expected to occur with the adoption of appropriate mitigation. Impacts on hard coral communities associated with elevated suspended sediment levels are discussed separately in Section 9

Jetting

As discussed in Section 5, it is assumed that, with the exception of the landing point, cable installation will be undertaken using jetting methods. During jetting a small trench will be ploughed by fluidizing the seabed using water jets and the cable(s) will be laid into the trench simultaneously. Only a small amount of sediment will be disturbed at the seabed and the majority will subsequently settle over the cables.

Modelling results show that increased SS levels are very localised to the area beneath and immediately adjacent to the cable route (Table 6.10). Modelling results indicate that for the model output locations within immediately the cable circuit footprint, elevations can be expected to be up to 98 mg L^-1 (SR 17) but that the values decrease rapidly with distance from the works area, ie outpoint point SM6 = 2.3 mg L^-1 which is less than 1 km from the cable circuits (Table 6.10). In areas remote from the works area results indicate that SS elevations are very small or nil during both the wet and dry seasons. It is noted from Section 9 that isolated soft coral and black coral colonies were recorded on dumped material along the cable route. These colonies would experience high levels of SS during jetting. Consequently, if they are observed still to be present prior to jetting, following a dive survey, then they will be relocated to a suitable area away from the works (see Section 9.12 for further information).

Modelling results show that short term elevations in SS will occur along the Lamma Extension seawall as well as at one of the modelling points located at the boundary of the proposed marine park. Some isolated colonies of encrusting corals have been reported from a recent survey along the seawall. As the SS elevations are predicted to be transient, as evidenced in the time-series plots shown in Annex 6C and dispersal contour plots shown in (Annex 6D), the impact is not considered adverse. The SS plume will not reach the nearshore sensitive receivers around the coast of Lamma Island and Cheung Chau.

Foundation Construction

The impact associated with the construction of monopile has been assessed (see Annex 6B). As the monopiles will be installed through percussive piling techniques, which lead to only negligible sediment disturbance at the point of entry, these activities under assessment relate to the installation of scour protection which may disturb seabed surface sediments with subsequent release into the water column.

Again, modelling results show that increased SS levels are localised to the within and immediately adjacent to the wind farm site (Table 6.11). In wider areas results indicate that SS elevations are very small or nil during both the wet and dry seasons. Modelling results show that all increases in SS are short term. This is evidenced in the time-series plots shown in Annex 6C and dispersal contour plots shown in (Annex 6D). The SS plume will not reach the WSRs identified and all elevations are compliant with WQOs. The adoption of appropriate mitigation, i.e. the careful placement of rock scour material will mean that the potential for sediment disturbance will be further minimised and is therefore unlikely to lead to significant impacts.

Table 6.9 Predicted SS Elevation (mg L^-1) for Grab Dredging at the Landing Point for the Proposed Submarine Cable

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	Allowable Elevation/Criteria		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	A	4.4	3.1	0.0	0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	3.0	3.0	0.0	0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM6	a	4.4	3.1	0.0	0.0
Fish Culture Zone^(e)	Lo Tik Wan	SR2	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Fish Culture Zone	Sok Kwu Wan	SR3	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a	10	10	0.1	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	10	10	0.2	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	10	10	0.0	0.0
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	10	10	25	31
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	3.0	3.0	0.0	0.0
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	4.4	3.1	0.0	0.1
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	4.4	3.1	0.1	0.1
Green Turtle Habitat	Sham Wan	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR1	a	3.0	3.0	0.0	0.1
Potential Marine Park	South Lamma	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR13	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR14	a	3.0	3.0	0.0	0.0
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Kwun Yam	SR8	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Hung Shing Yeh	SR9	a	3.0	3.0	0.0	0.0
Gazetted Beaches	Lo So Shing	SR10	a	3.0	3.0	0.0	0.0
Seawater Intakes	Cheung Chau	SR11	b	6.4	5.8	0.0	0.0
Seawater Intakes	Lamma Power Station	SR12	b	4.7	4.2	0.0	0.0
Seawater Intakes	Yuen Kok	SR13	b	4.7	4.2	0.0	0.0
Mixing zone	Cable Route	SR18	a	4.4	3.1	0.0	0.0
Mixing zone	Cable Route	SR17	a	4.4	3.1	0.0	0.0
Mixing zone	Cable Route	SR16	a	4.4	3.1	0.0	0.0
Notes: a. b = bottom, a = depth-averaged b. The tolerance assessment criterion of 100 mg L^-1 was adopted for these seawater intakes. c. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation. d. Shaded cells mean non-compliance with the WQO. e. Note full compliance with WQO as well

Table 6.10 Predicted SS Elevation (mg L^-1) for the Jetting Scenario

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	Allowable Elevation/Criteria		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	a	4.4	3.1	0.0	0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	3.0	3.0	0.0 0.0	0.0 3.1
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM6	a	4.4	3.1	2.9	1.8
Fish Culture Zone^(e)	Lo Tik Wan	SR2	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Fish Culture Zone	Sok Kwu Wan	SR3	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a	10	10	0.1	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	10	10	0.3	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	10	10	0.0	0.0
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	10	10	0.1	1.4
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	3.0	3.0	0.0	0.0
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	4.4	3.1	0.1	0.2
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	4.4	3.1	0.1	0.1
Green Turtle Habitat	Sham Wan	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR1	a	3.0	3.0	0.1	0.2
Potential Marine Park	South Lamma	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR13	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR14	a	3.0	3.0	0.0	3.1
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Kwun Yam	SR8	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Hung Shing Yeh	SR9	a	3.0	3.0	0.0	0.0
Gazetted Beaches	Lo So Shing	SR10	a	3.0	3.0	0.0	0.0
Seawater Intakes	Cheung Chau	SR11	b	6.4	5.8	0.0	0.0
Seawater Intakes	Lamma Power Station	SR12	b	4.7	4.2	0.0	0.0
Seawater Intakes	Yuen Kok	SR13	b	4.7	4.2	0.0	0.0
Mixing zone	Cable Route	SR18	a	4.4	3.1	64	2
Mixing zone	Cable Route	SR17	a	4.4	3.1	24	98
Mixing zone	Cable Route	SR16	a	4.4	3.1	70	76
Notes: a. b = bottom, a = depth-averaged b. The tolerance assessment criterion of 100 mg L^-1 was adopted for these seawater intakes. c. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation. d. Shaded cells mean non-compliance with the WQO. e. Note full compliance with WQO as well

Table 6.11 Predicted SS Elevation (mg L^-1) for the Foundation Construction Scenario

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	Allowable Elevation/Criteria		Predicted SS Elevation (mg L^-1)
				Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	a	4.4	3.1	0.0	0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	3.0	3.0	0.0 0.0	0.0 0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SS3	a	4.4	3.1	0.3	0.5
Fish Culture Zone^(e)	Lo Tik Wan	SR2	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Fish Culture Zone	Sok Kwu Wan	SR3	a	40.0 (AFCD) 3.0 (WQO)	40.0 (AFCD) 3.0 (WQO)	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	10	10	0.0	0.0
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	10	10	0.0	0.0
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	10	10	0.0	0.0
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	3.0	3.0	0.0	0.0
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	4.4	3.1	0.0	0.0
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	4.4	3.1	0.0	0.0
Green Turtle Habitat	Sham Wan	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR1	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR6	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR13	a	3.0	3.0	0.0	0.0
Potential Marine Park	South Lamma	SR14	a	3.0	3.0	0.0	0.2
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Kwun Yam	SR8	a	4.4	3.1	0.0	0.0
Gazetted Beaches	Hung Shing Yeh	SR9	a	3.0	3.0	0.0	0.0
Gazetted Beaches	Lo So Shing	SR10	a	3.0	3.0	0.0	0.0
Seawater Intakes	Cheung Chau	SR11	b	6.4	5.8	0.0	0.0
Seawater Intakes	Lamma Power Station	SR12	b	4.7	4.2	0.0	0.0
Seawater Intakes	Yuen Kok	SR13	b	4.7	4.2	0.0	0.0
Mixing zone	Cable Route	SR18	a	4.4	3.1	0.0	0.0
Mixing zone	Cable Route	SR17	a	4.4	3.1	0.0	0.0
Mixing zone	Cable Route	SR16	a	4.4	3.1	0.0	0.0
Notes: a. b = bottom, a = depth-averaged b. The tolerance assessment criterion of 100 mg L^-1 was adopted for these seawater intakes. c. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation. d. Shaded cells mean non-compliance with the WQO. e. Note full compliance with WQO as well

Table 6.12 Predicted Worst Case DO Depletion (mg L-1) for all Construction Scenarios due to Increase in SS Concentrations (only results where depletions are predicted have been presented)

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	WQ Allowable Depletion		Predicted WQ Depletion (mg L^-1)
				Dry	Wet	Dry	Wet
				Dry	Wet	Max ^(b)	Max ^(b)
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	a	-4.04	-3.4	7.28x10^-4	2.16x10^-5
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	-2.9	-3.0	1.91x10^-4 6.69x10^-4	3.51x10^-4 7.12x10^-2
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM6	a
Fish Culture Zone	Lo Tik Wan	SR2	a	-2.9	-3.0	1.29x10^-4	4.16x10^-6
Fish Culture Zone	Sok Kwu Wan	SR3	a	-2.9	-3.0	4.00x10^-7	2.53x10^-7
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a			3.95x10^-3	6.09x10^-5
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	-3.9	-4.0	6.11x10^-3	1.60x10^-4
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	-3.9	-4.0	1.10x10^-6	2.35x10^-5
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	-3.9	-4.0	2.88x10^-5	5.23x10^-6
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	-3.9	-4.0	8.57x10^-5	6.51x10^-5
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	-3.9	-4.0	1.30x10^-4	9.22x10^-4
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	-3.9	-4.0	1.42x10^-4	5.90x10^-4
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	-3.9	-4.0	1.91x10^-4	3.51x10^-4
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	N/A	N/A	0.27	0.21
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	-3.9	-4.0	4.00x10^-7	2.53x10^-7
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	-3.9	-4.0	1.44x10^-3	6.16x10^-3
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	-3.9	-4.0	1.70x10^-3	1.46x10^-3
Green Turtle Habitat	Sham Wan	SR6	a	-3.9	-4.0	2.05x10^-5	7.96x10^-8
Potential Marine Park	South Lamma	SR1	a	-3.9	-4.0	1.44x10^-3	6.16x10^-3
Potential Marine Park	South Lamma	SR6	a	-3.9	-4.0	2.05x10^-5	7.96x10^-8
Potential Marine Park	South Lamma	SR13	a	-3.9	-4.0	1.78x10^-4	5.90x10^-5
Potential Marine Park	South Lamma	SR14	a	-3.9	-4.0	6.69x10^-4	7.12x10^-2
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	-4.0	-3.4	1.28x10^-5	1.36x10^-6
Gazetted Beaches	Kwun Yam	SR8	a	-4.0	-3.4	1.82x10^-5	2.96x10^-6
Gazetted Beaches	Hung Shing Yeh	SR9	a	-3.9	-4.0	1.10x10^-6	2.35x10^-5
Gazetted Beaches	Lo So Shing	SR10	a	-3.9	-4.0	2.88x10^-5	5.23x10^-6
Seawater Intakes	Cheung Chau	SR11	b	-6.1	4.8	1.42x10^-5	4.66x10^-8
Seawater Intakes	Lamma Power Station	SR12	b	-6.0	-5.4	8.77x10^-5	4.90x10^-4
Seawater Intakes	Yuen Kok	SR13	b	-6.0	-5.4	1.78x10^-4	5.90x10^-5
Mixing zone	Cable Route	SR18	a	-6.1	4.8	1.56	0.06
Mixing zone	Cable Route	SR17	a	-6.1	4.8	0.53	2.23
Mixing zone	Cable Route	SR16	a	-6.1	4.8	1.59	1.73
Notes: a. b = bottom, a = depth-averaged b. The tolerance assessment criterion of 100 mg L^-1 was adopted for these seawater intakes. c. “Max” denotes maximum values recorded at a relevant water depth at the sensitive receiver over a complete spring-neap cycle simulation. d. Shaded cells mean non-compliance with the WQO.

Table 6.13 Predicted TIN Elevations (mg L^-1) for all Construction Scenarios

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	WQO	Grab Dredging		Jetting		Foundation Construction
					Dry	Wet	Dry	Wet	Dry	Wet
					Max	Max	Max	Max	Max	Max
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	a	0.1	0.0	0.0	0.0	0.0	0.0	0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	0.1	0.0	0.0	0.0 0.0	0.0 0.0000341	0.0 0.0	0.0 0.0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM6	a	0.1	0	0	0.0000319	0.0000198	0.0000033	0.0000055
Fish Culture Zone	Lo Tik Wan	SR2	a	0.1	0	0	0	0	0	0
Fish Culture Zone	Sok Kwu Wan	SR3	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a	0.1	0.0000011	0	0.0000011	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	0.1	0.0000022	0	0.0000033	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	0.1	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	0.1	0	0	0	0	0	0
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	0.1	0.000275	0.000341	0.0000011	0.0000154	0	0
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	0.1	0	0	0	0	0	0
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	0.1	0	0.0000011	0.0000011	0.0000022	0	0
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	0.1	0.0000011	0.0000011	0.0000011	0.0000011	0	0
Green Turtle Habitat	Sham Wan	SR6	a	0.1	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR1	a	0.1	0	0.0000011	0.0000011	0.0000022	0	0
Potential Marine Park	South Lamma	SR6	a	0.1	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR13	a	0.1	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR14	a	0.1	0	0	0	0.0000341	0	0.0000022
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	0.1	0	0	0	0	0	0
Gazetted Beaches	Kwun Yam	SR8	a	0.1	0	0	0	0	0	0
Gazetted Beaches	Hung Shing Yeh	SR9	a	0.1	0	0	0	0	0	0
Gazetted Beaches	Lo So Shing	SR10	a	0.1	0	0	0	0	0	0
Seawater Intakes	Cheung Chau	SR11	b	0.1	0	0	0	0	0	0
Seawater Intakes	Lamma Power Station	SR12	b	0.1	0	0	0	0	0	0
Seawater Intakes	Yuen Kok	SR13	b	0.1	0	0	0	0	0	0
Mixing zone	Cable Route	SR18	a	0.1	0	0	0.000704	0.000022	0	0
Mixing zone	Cable Route	SR17	a	0.1	0	0	0.000264	0.001078	0	0
Mixing zone	Cable Route	SR16	a	0.1	0	0	0.00077	0.000836	0	0

Table 6.13 Predicted Unionised Ammonia Elevations (mg L^-1) for all Construction Scenarios

Sensitive Receiver	Name	ID	Relevant Water Depth ^(a)	WQO	Grab Dredging		Jetting		Foundation Construction
					Dry	Wet	Dry	Wet	Dry	Wet
					Max	Max	Max	Max	Max	Max
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the West	SR22	a	0.021	0	0	0	0	0	0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the East	SR21 SR14	a	0.021	0 0	0 0	0 0	0 0.0002015	0 0	0 0
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM6	a	0.021	0	0	0.0001885	0.000117	0.0000195	0.0000325
Spawning / Nursery Grounds	Spawning / Nursery Grounds to the north	SM18	a	0.021	0	0	0.00013	0.00039	0.000715	0.0009425
Fish Culture Zone	Lo Tik Wan	SR2	a	0.021	0	0	0	0	0	0
Fish Culture Zone	Sok Kwu Wan	SR3	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR4	a	0.021	0.0000065	0	0.0000065	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR23	a	0.021	0.000013	0	0.0000195	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR9	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR10	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR19	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR24	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR20	a	0.021	0	0	0	0	0	0
Potential Coral Communities	Nam Tsui to Tai Kok	SR21	a	0.021	0	0	0	0	0	0
Coral Communities	Lamma Power Station Extension Seawall	SR15	a	0.021	0.001625	0.002015	0.0000065	0.000091	0	0
Horseshoe Crab Nursery Grounds	Sok Kwu Wan	SR3	a	0.021	0	0	0	0	0	0
Marine Mammal Habitat	Southwest Lamma Waters	SR1	a	0.021	0	0.0000065	0.0000065	0.000013	0	0
Marine Mammal Habitat	Southwest Lamma Waters	SM5	a	0.021	0.0000065	0.0000065	0.0000065	0.0000065	0	0
Green Turtle Habitat	Sham Wan	SR6	a	0.021	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR1	a	0.021	0	0.0000065	0.0000065	0.000013	0	0
Potential Marine Park	South Lamma	SR6	a	0.021	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR13	a	0.021	0	0	0	0	0	0
Potential Marine Park	South Lamma	SR14	a	0.021	0	0	0	0.0002015	0	0.000013
Gazetted Beaches	Cheung Chau Tung Wan	SR7	a	0.021	0	0	0	0	0	0
Gazetted Beaches	Kwun Yam	SR8	a	0.021	0	0	0	0	0	0
Gazetted Beaches	Hung Shing Yeh	SR9	a	0.021	0	0	0	0	0	0
Gazetted Beaches	Lo So Shing	SR10	a	0.021	0	0	0	0	0	0
Seawater Intakes	Cheung Chau	SR11	b	0.021	0	0	0	0	0	0
Seawater Intakes	Lamma Power Station	SR12	b	0.021	0	0	0	0	0	0
Seawater Intakes	Yuen Kok	SR13	b	0.021	0	0	0	0	0	0
Mixing zone	Cable Route	SR18	a	0.021	0	0	0.00416	0.00013	0	0
Mixing zone	Cable Route	SR17	a	0.021	0	0	0.00156	0.00637	0	0
Mixing zone	Cable Route	SR16	a	0.021	0	0	0.00455	0.00494	0	0

6.6.6 Concurrent Construction Activities

As highlighted in Section 5, it is possible for grab dredging, jetting and foundation construction works to occur concurrently. However, impacts associated with individual activities are shown to be very localised and transient. It is not likely that foundation construction would lead to any combined effects on WSRs if undertaken at the same time as grab dredging. Jetting within the wind farm array could lead to combined effects with foundation construction. However, it is unlikely that jetting would take place immediately adjacent to foundation construction works and therefore would be at least 500 m away (for navigation safety). Given the localised and minor nature of impacts (outside of the mixing zone) cumulative effects are likely to be negligible. Regarding any cumulative effects with dredging works, of greatest concern would be potential effects on coral communities adjacent to the Lamma Power Station Extension – although these communities are only of low ecological value. However, jetting works will be approximately 100 m away from these areas. In addition, grab dredging works will be undertaken in two days and jetting works nearby would also be very short term. Therefore any combined effects between grab dredging and jetting would be very short term.

Given that modelling has determined that impacts would be localised and transient and that combined effects would be only very small, it was considered unnecessary to undertake additional modelling for concurrent events.

Impacts on water quality associated with concurrent construction activities are considered to be of minor significance.

6.6.7 Vessel Discharges

Construction vessels have the potential to generate the following liquid discharges:

· Uncontaminated deck drainage;

· Ballast water (in emergency situations only);

· 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.

Ballast water will be taken on and will therefore not be discharged during normal operations. In the event that ballast water does need to be discharged, it will not be contaminated and thus has no implications for 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 vessels discharges are therefore considered to be minor.

No solid wastes will be permitted to be disposed of overboard by vessels during construction works, thus impacts from such sources will be eliminated.

6.6.8 Other discharges

Offshore structures will have a protective paint coating to help prevent corrosion. Corrosion measures will be applied on land in a controlled way and that there would be no discharges to the water environment.

As discussed in Section 5, there will be a requirement to use grout during the construction of the wind turbines. Grout is a cement based product and such material entering the marine environment may have the possible effect of increasing pH levels in the immediate receiving waters. In addition, it may be necessary to use in-situ filling of grout bags for cable crossings. Under this situation the Grout Bags would be filled with cement grout offshore via a hose. These activities potentially could lead to impact on water quality if leakage occurs.

Any grout used would conform to the relevant environmental standards. For example, the use of a suitable Anti-Washout Admixture, added to the grout mix can minimise the effect of the grouting process on the immediate seafloor environment during the addition of the grout to the pre-placed bags. In addition, the adoption of appropriate operational management by the contractor should lead to low potential for leakage during the pumping phase.

Grout bags have been used for many years in continental USA to minimise scour effects of bridges and on pipelines. The Department of Transportation, Virginia in the US, has investigated the impact on the environment of grout bags ([36]) which has been a key concern of the some of these agencies, namely the Virginia Department of Environmental Quality and the U.S. Army Corps of Engineers (USACE). Their conclusions are that there is a very short term effect lasting a few hours where the grout locally affects the pH of the water immediately surrounding the grout bags, thereafter there the environmental impact is not discernable on a local scale.

As per vessel discharges, any material released to the marine environment would be expected to be rapidly dispersed due to the mixing and diluting properties of the receiving waters and the relatively small quantities of materials means that impacts would be minor. Impacts are therefore expected to be of very minor significance.

6.6.9 Land Based Construction Activities

During land based construction activities, the primary sources of potential impacts to water quality will be from pollutants in site run-off from the Laydown area, which may enter marine waters. All excavated material will be stored temporarily on-site (see details in Section 7). With the proper implementation of mitigation and waste management measures, it is anticipated that no adverse water quality impacts would arise from the land based works.

6.7 Operation Phase Water Quality Impact Assessment

The following provides a summary of the impacts that would be expected during the operation of the offshore wind farm.

6.7.1 Suspended Sediments

As discussed in Section 5, the offshore structures could lead to scour of seabed sediments around the base of foundations. This will cause a short term increase in suspended sediments. However, it is expected that a state of equilibrium would be reached very quickly, which would mean that sediments are no longer eroded (see Section 5). In addition, the construction of scour protection at the base of foundations would mean that erosion of seabed sediments would be avoided. Therefore impacts associated with increased suspended sediment levels during the operational phase are expected to be negligible. It is noted, however, that the need for scour protection will be subject to the Detailed Design. Such protection would most likely be required for monopiles. If the piles are driven to a sufficiently deep seabed level, or a sufficient thickness of steel pile is selected, the need for scour protection may be avoided.

6.7.2 Vessel Discharges

Vessels will also be required for the operational phase (including turbine maintenance). Potential impacts associated with vessel discharges are similar to those discussed for the construction phase, however, due to a limited number of vessels in comparison would likely result in negligible impacts.

6.7.3 Other Discharges

As discussed in Section 5, each of the turbines will contain lubricants and hydraulic oils (nominally 100 l of gearbox oil, 250 l of hydraulic oil, 20 l of motor oil, 2,500 l of transformer oil and potentially limited quantities of coolant depending on design). A consideration for water quality is the potential release of fluids and oils contained within turbines following accidental collision with ships. As discussed in Sections 5 and 10, an operational safety zone of 50 m radius will be in force from the offshore substation, turbine and offshore monitoring mast will apply to non-Project vessels throughout the operational period regardless of other exclusion arrangements. In addition, marine navigation measures described in Section 10 will be adopted to minimise the potential for collision. Therefore although there is potential for the release of material, the risk of collision is very low and it is likely that fluids will be contained within the turbines. Discharges of contaminants from wind turbines or other installations (e.g. offshore sub-stations) are anticipated to be extremely unlikely due to oils and fluids from gearboxes, hydraulics and pitch drive and yaw drive systems being mechanically contained ([37]) ([38]).

The Marine Department of the HKSAR Government has a Maritime Oil Spill Response Plan (MOSRP) to deal with accidental oil spill events. The plan is in compliance with the standards applicable to the international ports in the world. The Pollution Control Unit team of the Marine Department is committed to reach the scene of oil spill incident inside harbour limits within two hours of notification. An emergency plan would be developed to deal with accidental events. In case of an incident, the spills should be properly dealt with through the activation of the emergency plan and the clean-up action by the Marine Department.

Zinc anodes may be used for the protection of marine structures from corrosion. These anodes are designed to corrode, so preventing corrosion of the main structure. There will therefore be a very small release of zinc into the marine environment. Zinc inputs would be of negligible magnitude, and along with dispersal factors, impacts would be expected to be very minor (1) (2). In addition, the generators within the turbine nacelle will likely be fitted with copper slip rings. Each generator will be fitted with typically 3 to 4 slip rings with a combine weight of 2 kg. These slip rings abrade during operation and would normally be replaced after 5 years. Copper slip rings will not be completely eroded at the time of replacement. Therefore very fine copper material could be released as a fugitive dust emission into the atmosphere. It is highly likely that this would be dispersed widely with dilute inputs into the environment with negligible impacts expected (1) (2).

Routine maintenance of the offshore structure will generate waste products, such as gear oil and hydraulic fluids, and these will be disposed of by means of controlled disposal methods on land. However, there is a small risk that spillage could occur during such maintenance which may impact water quality. Any material released to the marine environment would be expected to be rapidly dispersed due to the mixing and diluting properties of the receiving waters and the relatively small quantities of materials. In addition, the adoption of appropriate operational management by the contractor should lead to low potential for leakage.

6.7.4 Hydrodynamics

Key concerns related to operational hydrodynamic impacts are possible changes in flushing capacity and current speeds at sensitive areas due to the presence of the wind farm piled structures. In order to investigate the potential magnitude of these impacts, if at all, mathematical modelling has been undertaken and key sensitive receivers selected for observation. In addition to these points, cross sections have been taken and current speeds and flushing capacity compared in hydrodynamics with and without the proposed wind farm.

The location of the modelling observation points and cross sections are shown in Figure 6.7. These have been selected based on the previously identified water quality sensitive receivers (WSRs), e.g. Sham Wan, Lo So Shing Beaches, sweater intakes at Lamma Power Station and on Cheung Chau etc, as well as key flushing channels in Hong Kong, e.g. Ma Wan and Victoria Harbour.

The predicted possible changes in current velocities and directions during both the dry and wet seasons at the selected WSRs due to the presence of the piled structures are presented in Tables 6.14 and 6.15, respectively. Based on these results it is clear that differences in both velocities and current directions would be negligible at all locations during the operation of the wind farm. All locations show either equal to or less than 0.001 m/s change in depth averaged current velocity as well as less than a 2° difference in change in current direction during both the dry and wet season. Such changes are not considered to be significant and would be unlikely to result in adverse changes to water quality or cause changes in erosion and sedimentation. On this basis, hydrodynamic impacts due to the wind farm during operation are considered to be negligible.

Table 6.14 Predicted Current Velocities and Directions at Monitoring Points (Dry Season) (Depth averaged flow / time averaged velocities / time averaged directions)

Table 6.15 Predicted Current Velocities and Directions at Monitoring Points (Wet Season) (Depth averaged flow / time averaged velocities / time averaged directions)

In order to assess changes to capacity, four areas were selected for to examine changes in discharge through cross sections. As mentioned above these are at key locations in Hong Kong and were selected at the following locations (Figure 6.7):

· Cross Section A – Ma Wan;

· Cross Section B – Victoria Harbour;

· Cross Section C – West Lamma (Lamma Power Station to Cheung Chau); and,

· Cross Section D – East Lamma (Ap Lei Chau to Lamma Island).

The computed instantaneous discharge magnitudes (m³) were accumulated through the modelling period to obtain the cumulative discharge. These are presented in Figures 6.8 to 6.15 to show the differences in discharges through each cross section in both the dry and wet seasons. Discharges in the baseline, i.e. with no wind farm present, and those during operation of the wind farm are plotted together to easily differentiate any impacts on flushing capacity at each location. It is clear from the figures that the two periods (i.e. baseline and operation) are very similar in the magnitude of discharges with the lines virtually over-lapping. Based on these results, any changes in flushing capacity at each of the four locations during operation of the wind farm would be considered to be negligible and as such no adverse impacts to either hydrodynamics or water quality would be expected to occur. Similarly, any changes to local erosion or sedimentation patterns within these channels would be unlikely to be affected during operation of the proposed wind farm.

Figure 6.8 Cumulative Flow Discharges through Cross Section at Ma Wan (A) (Dry Season)

Figure 6.9 Cumulative Flow Discharges through Cross Section at Ma Wan (A) (Wet Season)

Figure 6.10 Cumulative Flow Discharges through Cross Section in Victoria Harbour (B) (Dry Season)

Figure 6.11 Cumulative Flow Discharges through Cross Section in Victoria Harbour (B) (Wet Season)

Figure 6.12 Cumulative Flow Discharges through Cross Section at West Lamma (C) (Dry Season)

Figure 6.13 Cumulative Flow Discharges through Cross Section at West Lamma (C) (Wet Season)

Figure 6.14 Cumulative Flow Discharges through Cross Section at East Lamma (D) (Dry Season)

Figure 6.15 Cumulative Flow Discharges through Cross Section at East Lamma (D) (Wet Season)

In summary, the hydrodynamic modelling has shown that the wind farm development will have negligible near-field and far-field impacts on current flow and direction as well as flushing capacity at key channels in Hong Kong. It is therefore considered that there will be little change to existing hydrodynamics, water quality and local erosion and sedimentation patterns.

6.8 Water Quality Mitigation Measures

The water quality modelling works have indicated that, in general, the works can proceed at the recommended working rates without causing unacceptable impacts to water quality sensitive receivers.

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

· Siting: A number of locations were studied for the offshore wind farm, with the principal aim of avoiding direct impacts to sensitive receivers in nearshore areas to Lamma and Cheung Chau.

· Reduction in Indirect Impacts: The offshore wind farm and cable route is located at a sufficient distance from a large number of 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 used a worse case scenario assessment to determine the maximum potential effects of the proposed works on water quality. A summary of these rates are as follows:

o Dredging – maximum production rate of 2,500m^-3 day^-1

o Jetting – maximum jetting speed of 360 m hr^-1

In addition to these pro-active measures that have been adopted for the proposed Project, the following mitigation measures are recommended for the construction and operation phases.

Dredging

· Silt curtains will be deployed during dredging at the seawall area to reduce the elevation of suspended solids to nearby sensitive receivers. Details of silt curtain installation should be proposed by the contractor prior to the commencement of construction works and submitted to the IEC for approval.

· Closed grab dredgers should be used to reduce the potential for leakage of sediments;

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

· Disposal barges 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;

· When the dredged material has been unloaded at the disposal areas, remove any material that has accumulated on the deck or other exposed parts of the vessel and place in the hold or a hopper. Do not wash decks clean in a way that permits material to be released overboard;

· The contractor(s) will ensure 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 area of marine works; and

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

Jetting

No specific mitigation measures are recommended for jetting operations other than good practice measures.

Vessel Discharges

· All plant will be fully serviced and inspected before use to limit any potential discharges to the marine environment.

Other Discharges

· Measures to mitigate risks for navigation as outlined in Section 10, will help to minimise the potential for discharge from structures resulting from collision;

· Avoid spillage of oil, fuel and chemicals from structures by adopting appropriate good site practices;

· Any grout used would conform to the relevant environmental standards. In addition, the adoption of appropriate operational management by the contractor should lead to low potential for leakage during the pumping phase; and

· No debris shall be willingly discharged to sea. However, should debris be placed on the seabed, this will be removed (wherever practicable).

Land-Based Construction Activities

· All fuel tanks and permanent storage areas should be provided with locks and be located on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank, to prevent spilled fuel oils from reaching the coastal waters;

· Construction site runoff at the Laydown should be prevented or minimised in accordance with the guidelines stipulated in the EPD's Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94);

· The storage areas of oil, fuel and chemicals will be surrounded by bunds or other containment device to prevent spilled oil, fuel and chemicals from reaching the receiving waters;

· The Contractors will prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals; and

· Surface run-off from bunded areas will pass through oil/water separators prior to discharge to the stormwater system.

6.9 Environmental Monitoring and Audit (EM&A)

6.9.1 Construction Phase

Water quality monitoring and auditing 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.

6.9.2 Operation Phase

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

6.10 Residual Environmental Impacts

With the adoption of the recommended mitigation measures detailed in Section 6.8 are adopted then it is expected that no residual adverse environmental impacts will result from the Construction or Operation phases of the Project.

6.11 Cumulative Impacts

The identified potential concurrent projects that could lead to cumulative water quality impacts are the marine dumping activities at the South Cheung Chau uncontaminated mud disposal site (Figure 6.16). Modelling carried out for this Project show that impacts of wind farm and cable installation activities are very localised area and transient (lasting no more than 2 days in the area of activity). Sediment does not disperse at appreciable concentrations beyond the works areas. Similarly, modelling carried out as part of the Lamma Power Station Navigation Channel Improvement EIA modelled the potential dispersion of sediments disposed into the South Cheung Chau disposal ground ([39]). Results show that sediment plumes originating from disposal activities do not reach the proposed wind farm in either season (Figure 6.17 and 6.18). Concentrations would be less than 1 mg L^-1 at their closest point, which is more than 1km away from the wind farm site.

It is therefore anticipated that the works proposed for this Project would not lead to potential for increasing the loading of sediments within the wider marine environment that is associated with the uncontaminated mud disposal ground. The potential release of sediment from disposal activities at the disposal ground is far greater than what is being proposed under this Project and it is expected that the local ecology has adapted to these events and that appropriate EM&A measures are in place at South Cheung Chau to ensure that WQOs are not exceeded.

No significant cumulative impacts associated with water quality are therefore expected.

Figure 6.17 Maximum Surface and Bottom SS Concentrations through disposal of mud at South Cheung Chau Disposal Pit and dredging at Yung Shue Wan (Wet Season)

Figure 6.18 Maximum Surface and Bottom SS Concentrations through disposal of mud at South Cheung Chau Disposal Pit and dredging at Yung Shue Wan (Dry Season)

6.12 Conclusions

This Section of the EIA has described the impacts on water quality arising from the construction and operation of the proposed offshore wind farm. The purpose of the assessment was to evaluate the acceptability of predicted impacts to water quality and hydrodynamics.

Computer modelling has been used to simulate the loss of sediment to suspension during the construction phase of all works for the project ( i.e. installation of wind turbines, wind monitoring mast, offshore substation, cable connection, landing point etc). The results and findings of the computer modelling have been provided and summarized.

Potential impacts arising from all proposed construction works are predicted to be very localised and transient in nature. No unacceptable adverse impacts to water quality are predicted to occur at the sensitive receivers with the adoption of appropriate mitigation, e.g. silt curtains during dredging works.

During the operation phase, adverse impacts to water quality are not expected to occur. In addition, the proposed wind farm will have a negligible effect on hydrodynamics, local erosion and sedimentation patterns.

([1]) Environmental Protection Department (2007). Marine Water Quality in Hong Kong – 2007.

([2]) Environmental Protection Department (2007). Marine Water Quality in Hong Kong – 2007.

([3]) The Hongkong Electric Company Ltd (1999). 1,800 MW Gas Fired Power Station Extension. EIA-009/1998.

([4]) 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.

([5]) ERM – Hong Kong, Ltd (2002) EIA for the Proposed Submarine Gas Pipeline from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plank, Hong Kong. Final EIA Report. For the Hong Kong and China Gas Co., Ltd.

([6]) Maunsell (2001) EIA for Tai Po Sewage Treatment Works - Stage V. Final EIA Report. For Drainage Services Department, Hong Kong SAR Government.

([7]) ERM - Hong Kong, Ltd (2007) Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. For CAPCO. Final EIA Report. December 2006

([8]) 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.

([9]) ERM - Hong Kong, Ltd (2007) Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. For CAPCO. Final EIA Report. December 2006

([10]) Environmental Protection Department (2007). Marine Water Quality in Hong Kong – 2007.

([11]) Environmental Protection Department (2007). Marine Water Quality in Hong Kong – 2007.

([12]) 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.

([13]) 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.

([14]) City University of Hong Kong (2001) Op Cit.

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

([16]) ERM – Hong Kong, Ltd (2002) EIA for the Proposed Submarine Gas Pipeline from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plank, Hong Kong. Final EIA Report. For the Hong Kong and China Gas Co., Ltd.

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

([18]) Hyder (1997). Sand Dredging and Backfilling of Borrow Pits at the Potential Eastern Waters Marine Borrow Area, EIA Report, CED, 1997.

([19]) ERM (2001). Environmental Consultancy Services For The Proposed 11kv Cable Circuits From Tai Mong Tsai To Kiu Tsui, CLP Power, 2001.

([20]) ERM (1998). Environmental Impact Assessment of Backfilling Marine Borrow Areas at East Tung Lung Chau, CED, 1998.

([21]) ERM (2002). Environmental Consultancy Services for proposed 132kV Cable Circuits from a Kung Wan to Sai Kung Pier, CLP Power, 2002.

([22]) ERM (2002). 132kV Submarine Cable Installation for Wong Chuk Hang - Chung Hom Kok 132 kV Circuits, The Hongkong Electric Co, January 2002.

([23]) ERM-Hong Kong, Limited (1999). EIA for 1,800 MW Gas Fired Power Stations at Lamma Extension. EIA Report for Hongkong Electric Co Ltd

([24]) BBHS, Limited (1996). Green Island Development. Studies on Ecological and Water Quality Impact Assessment. Initial Assessment Report

([25]) ERM-Hong Kong, Limited (1999). Op cit

([26]) Hawker DW & Connell DW (1992). Op cit.

([27]) Pastorok RA and Bilyard GR (1985). Effects of sewage pollution on coral-reef communities. Marine Ecology Progress Series 21: 175-189.

([28]) Ayling AA and Ayling AK (1987). Is silt run-off affecting corals communities on the Cape Tribulation Fringing Reefs? In; Fringing Reef Workshop, GMRMPA Workshop series 9: 83-86. Ed CL Baldwyn

([29]) Hyder (1997). Sand Dredging and Backfilling of Borrow Pits at the Potential Eastern Waters Marine Borrow Area, EIA Report, CED, 1997

([30]) ERM-Hong Kong, Limited (2001). Focused Cumulative Water Quality Impact Assessment of Sand Dredging at the West Po Toi Marine Borrow Area Final Report

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

([32]) Browse Basin Appraisal Drilling — Managing Impacts in a Sensitive Environment. Woodside Energy Limited. Australian Petroleum Production & Exploration Association Environment Conference 2008.

([33]) According to the geophysical survey that has been conducted for the study as part of the marine archaeological investigation (see Section 12) little or no debris has been recorded within the cable route. As such, losses through grabs that are not fully closed are expected to be minimal.

([34]) ERM - Hong Kong, Ltd (2007) Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. For CAPCO. Final EIA Report. December 2006.

([35]) Deltares (2009). Modelling Memo for the Development of a 100MW Offshore Wind Farm in Hong Kong.

([36]) G. Michael Fitch (2003). Minimizing the Impact on Water Quality of Placing Grout Underwater to Repair Bridge Scour Damage. Virginia Transportation Research Council in cooperation with Federal Highway Administration, the US Department of Transportation, Charlottesville, Virginia. Final Report.

([37]) Airtricity (2005). Greater Gabbard Offshore Wind Farm – Environmental Statement. Image provided by Global Scour Control Systems Ltd

([38]) National Wind Power (2002). North Hoyle Offshore Wind Farm Environmental Statement, UK. National Wind Power Ltd.

([39]) The Hongkong Electric Co., Ltd (2003) Lamma Power Station Navigation Channel Improvement EIA. Prepared by Hyder Consulting.