Environmental Impact Assessment (EIA) Report for Establishment of Fish Culture Zone at Wong Chuk Kok Hoi

Table 3.1 Summary of Water Quality Objectives for Mirs Bay WCZ and Tolo Harbour and Channel WCZ

	Water Quality Objective	Mirs Bay WCZ	Tolo Harbour and Channel WCZ
A	AESTHETIC APPEARANCE
a)	Waste discharges shall cause no objectionable odours or discolouration of the water.	Whole zone	Not applicable
b)	Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.	Whole zone	Not applicable
c)	Mineral oil should not be visible on the surface. Surfactants should not give rise to lasting foam.	Whole zone	Not applicable
d)	There should be no recognisable sewage-derived debris.	Whole zone	Not applicable
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	Not applicable
f)	Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.	Whole zone	Not applicable
g)	Waste discharges shall cause no noxious or offensive odour or offensive taint or colour in either waters or edible aquatic organisms in the subzone to be present in concentrations detectable by bioassay or organoleptic tests.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.
h)	Waste discharges shall cause no visible foam, oil, grease, scum, litter or other objectionable matter in waters of the subzone.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.
B	BACTERIA
a)	The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in one calendar year.	Secondary Contact Recreation Subzones and Fish Culture Subzones	Secondary Contact Recreation Subzones and Fish Culture Subzones
b)	The level of Escherichia coli should be zero per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.	Water Gathering Ground Sub-zones	Not applicable
c)	The level of Escherichia coli should not exceed 1 000 per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.	Other inland waters of the Zone	Not applicable
C	COLOUR
a)	Waste discharges shall not cause the colour of water to exceed 30 Hazen units.	Water Gathering Ground Sub-zones	Not applicable
b)	Waste discharges shall not cause the colour of water to exceed 50 Hazen units	Other inland waters of the Zone	Not applicable
D	DISSOLVED OXYGEN
a)	Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as the water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth, and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.	Marine waters excepting Fish Culture Subzones	Not applicable
b)	The dissolved oxygen level should not be less than 5 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.	Fish Culture Subzones	Not applicable
c)	Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre.	Water Gathering Ground Sub-zones and Other inland waters of the Zone	Not applicable
d)	Waste discharges shall not cause the level of dissolved oxygen in waters of the subzone to be less than 2 milligrams per litre within two metres of the bottom, or to be less than 4 milligrams per litre in the remainder of the water column.	Not applicable	Harbour subzone
e)	Waste discharges shall not cause the level of dissolved oxygen in waters of the subzone to be less than 3 milligrams per litre within two metres of the bottom, or to be less than 4 milligrams per litre in the remainder of the water column.	Not applicable	Buffer subzone
f)	Waste discharges shall not cause the level of dissolved oxygen in waters of the subzone to be less than 4 milligrams per litre at any point in the water column.	Not applicable	Channel subzone
E	pH
a)	The pH of the water should be within the range of 6.5-8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 units.	Marine waters	Not applicable
b)	Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 units.	Water Gathering Ground Sub-zones	Not applicable
c)	The pH of the water should be within the range of 6.0-9.0 units.	Other inland waters of the Zone	Not applicable
d)	Waste discharges shall not cause the normal pH range of any waters of the subzone to be extended by greater than +/- 0.5 pH units at any time.	Not applicable	Harbour subzone
e)	Waste discharges shall not cause the normal pH range of any waters of the subzone to be extended by greater than +/- 0.3 pH units at any time.	Not applicable	Buffer subzone
f)	Waste discharges shall not cause the normal pH range of any waters of the subzone to be extended by greater than +/- 0.1 pH units at any time.	Not applicable	Channel subzone
F	TEMPERATURE
a)	Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 degree Celsius.	Whole Zone	Not applicable
b)	Waste discharges shall not cause the natural daily temperature range in waters of the subzone to be extended by greater than +/- 1.0℃ at any location or time. The rate of temperature change shall not exceed 0.5℃ per hour at any location, unless due to natural phenomena.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.
G	SALINITY
a)	Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.	Whole Zone	Not applicable
b)	Waste discharges shall not cause the normal salinity range of any waters of the subzone to be extended by greater than +/- 3 parts per thousand at any time.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.
H	SUSPENDED SOLIDS
a)	Waste discharges shall neither cause the natural ambient level to be raised by 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities.	Marine waters	Not applicable
b)	Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.	Water Gathering Ground Sub-zones and Other inland waters of the Zone	Not applicable
I	AMMONIA
	The un-ionized ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean).	Whole Zone	Not applicable
J	NUTRIENTS
	Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.	Marine waters	Not applicable
	Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 milligram per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed).	Marine waters	Not applicable
K	5-DAY BIOCHEMICAL OXYGEN DEMAND
a)	Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.	Water Gathering Ground Sub-zones	Not applicable
b)	Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.	Other inland waters of the Zone	Not applicable
L	CHEMICAL OXYGEN DEMAND
a)	Waste discharges shall not cause the chemical oxygen demand to exceed 15 milligrams per litre.	Water Gathering Ground Sub-zones	Not applicable
b)	Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.	Other inland waters of the Zone	Not applicable
M	TOXINS / TOXICANTS
a)	Waste discharges shall not cause the toxins in water to attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other.	Whole Zone	Not applicable
b)	Waste discharges of dangerous substances shall not put a risk to any beneficial uses of the aquatic environment.	Whole Zone	Not applicable
c)	Waste discharges shall not cause the toxicants in waters of the subzone to attain such a level as to produce significant toxic effects in humans, fish or any other aquatic organism, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.
N	CHLOROPHYLL-A
a)	Waste discharges shall not cause the level of chlorophyll-a in waters of the subzone to exceed 20 milligrams per cubic metre, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth.	Not applicable	Harbour subzone
b)	Waste discharges shall not cause the level of chlorophyll-a in waters of the subzone to exceed 10 milligrams per cubic metre, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth.	Not applicable	Buffer subzone
c)	Waste discharges shall not cause the level of chlorophyll-a in waters of the subzone to exceed 6 milligrams per cubic metre, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth.	Not applicable	Channel subzone
O	LIGHT PENETRATION
a)	No changes in turbidity, suspended material, colour or other parameters arising from waste discharges shall reduce light transmission by more than 20 per cent of the normal level in the subzone at any location or any time.	Not applicable	Harbour subzone
b)	No changes in turbidity, suspended material, colour or other parameters arising from waste discharges shall reduce light transmission by more than 15 per cent of the normal level in the subzone at any location or any time.	Not applicable	Buffer subzone
c)	No changes in turbidity, suspended material, colour or other parameters arising from waste discharges shall reduce light transmission by more than 10 per cent of the normal level in the subzone at any location or any time.	Not applicable	Channel subzone
P	SETTLEABLE MATERIAL
	Waste discharges shall give rise to no bottom deposits or submerged objects which adversely influence bottom living communities, alter the basic Harbour geometry or shipping channels, present any hazard to shipping or diving activities, or affect any other beneficial use of the waters of the subzone.	Not applicable	(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone.

(1) CAP358U Statement of Water Quality Objectives (Mirs Bay Water Control Zone)

(2) CAP358B Tolo Harbour and Channel Water Control Zone Statement of Water Quality Objectives

In accordance with the Study Brief, the Assessment Area for water quality impact assessment covers the Mirs Bay WCZ and the Tolo Harbour and Channel WCZ. Wong Chuk Kok Hoi, where the proposed Wong Chuk Kok Hoi FCZ is located, is an embayment between the Wong Chuk Kok Tsui landmass and the Double Island. The embayment is generally over 10 m deep except for the nearshore areas as well as the south-western corner. The embayment connects to the Mirs Bay in the north-eastern direction, which itself is also an embayment. Water depth for the majority of Mirs Bay is around 10 m – 20 m.

3.3.2 Marine Water Quality

Baseline marine water quality of the Assessment Area has been determined through a review of EPD routine water quality monitoring data collected between 1986 and 2020. 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. Water quality monitoring data from EPD monitoring stations that are located within or close to the Assessment Area were reviewed and summarised in Table 3.2. Locations of these stations are presented in Figure 3.1.

According to EPD’s Marine Water Quality in Hong Kong in 2020, Mirs Bay attained an overall marine WQO compliance rate of 98% in 2020. The water quality was very good with high DO, and low nutrient and E. coli levels. For the Tolo Harbour and Channel WCZ, the overall marine WQO compliance rate in 2020 was 93%. Tolo Harbour consistently complied with the bacteriological WQO for secondary contact recreational uses applicable to the entire marine waters of the WCZ. Tolo Channel, however, was subject to a natural hydrological phenomenon of water column stratification and associated lower bottom DO level due to restricted water exchange with the open waters. Compliance with the WQOs is generally observed in most parameters at the selected monitoring stations at the two WCZs. There have been exceedances of chlorophyll-a level at TM8 (Tolo Channel subzone) but the situation has significantly improved since the implementation of the Tolo Harbour Effluent Export Scheme (THEES) as well as a number of measures under the Livestock Waste Control Scheme (LWCS). According to EPD’s Marine Water Quality in Hong Kong (various years), the percentage of samples taken at TM8 with ≤6 µg/L level of chlorophyll-a gradually increases from the low point of 70.7% in 1988 up to average of around 90% in the recent 10 years from 2011-2020 (with 100% in 2020).

Table 3.2 Summary of EPD Routine Water Quality Monitoring Data from Selected Stations of the Tolo Harbour and Channel WCZ and Mirs Bay WCZ (1986 – 2020)

Parameters	TM8	MM7	MM17
Temperature (°C)	22.7	23.5	23.8
Temperature (°C)	(11.7-30.4)	(11.5-30.4)	(14.1-29.7)
Salinity (psu)	32.1	32.1	32.2
Salinity (psu)	(26.8-35.4)	(24.0-34.2)	(30.3-34.3)
Dissolved Oxygen (mg/L)	6.1	6.4	6.2
Dissolved Oxygen (mg/L)	(1.4-14.2)	(2.4-12.1)	(4.2-9.0)
Dissolved Oxygen (mg/L) - Bottom	5.0	5.8	5.4
Dissolved Oxygen (mg/L) - Bottom	(0.0-19.5)	(0.2-12.4)	(1.1-8.6)
Dissolved Oxygen (%saturation)	84	90	87
Dissolved Oxygen (%saturation)	(33-167)	(38-144)	(63-115)
Dissolved Oxygen (%saturation) - Bottom	68	80	75
Dissolved Oxygen (%saturation) - Bottom	(0-200)	(3-160)	(16-109)
pH	8.2	8.1	8.0
pH	(7.5-8.9)	(7.5-8.6)	(7.6-8.3)
Secchi Disc Depth (M)	3.5	3.5	3.7
Secchi Disc Depth (M)	(0.5-13.0)	(1.1-9.1)	(1.5-7.0)
Turbidity (NTU)	3.9	4.1	1.4
Turbidity (NTU)	(0.2-33.1)	(0.3-17.5)	(0.1-5.5)
Suspended Solids (mg/L)	3.2	2.9	5.1
Suspended Solids (mg/L)	(0.5-71.2)	(0.5-17.7)	(0.7-16.0)
5-day Biochemical Oxygen Demand (mg/L)	1.1	1.0	0.8
5-day Biochemical Oxygen Demand (mg/L)	(0.1-5.8)	(0.2-3.2)	(0.2-2.0)
Ammonia Nitrogen (mg/L)	0.044	0.040	0.029
Ammonia Nitrogen (mg/L)	(0.01-0.68)	(0.01-0.57)	(0.01-0.08)
Unionised Ammonia (mg/L)	0.003	0.002	0.002
Unionised Ammonia (mg/L)	(0.000-0.077)	(0.001-0.044)	(0.000-0.003)
Nitrite Nitrogen (mg/L)	0.013	0.012	0.011
Nitrite Nitrogen (mg/L)	(0.002-0.103)	(0.002-0.101)	(0.002-0.067)
Nitrate Nitrogen (mg/L)	0.026	0.023	0.028
Nitrate Nitrogen (mg/L)	(0.002-0.609)	(0.002-0.160)	(0.003-0.103)
Total Inorganic Nitrogen (mg/L)	0.07	0.06	0.06
Total Inorganic Nitrogen (mg/L)	(0.01-0.70)	(0.01-0.60)	(0.01-0.15)
Total Kjeldahl Nitrogen (mg/L)	0.37	0.26	0.38
Total Kjeldahl Nitrogen (mg/L)	(0.08-4.79)	(0.08-1.13)	(0.11-0.88)
Total Nitrogen (mg/L)	0.40	0.28	0.41
Total Nitrogen (mg/L)	(0.05-4.80)	(0.08-1.13)	(0.12-0.89)
Orthophosphate Phosphorus (mg/L)	0.013	0.010	0.008
Orthophosphate Phosphorus (mg/L)	(0.002-0.068)	(0.002-0.081)	(0.002-0.028)
Total Phosphorus (mg/L)	0.05	0.04	0.04
Total Phosphorus (mg/L)	(0.02-0.58)	(0.02-0.24)	(0.02-0.11)
Silica (mg/L)	0.77	0.65	0.66
Silica (mg/L)	(0.05-2.00)	(0.06-2.16)	(0.07-1.24)
Chlorophyll-a (μg/L)	3.4	3.0	2.1
Chlorophyll-a (μg/L)	(0.3-120.8)	(0.3-14.4)	(0.3-5.1)
E. coli (cfu/100mL)	2	2	2
E. coli (cfu/100mL)	(1-510)	(1-161)	(1-32)
Faecal Coliforms (cfu/100mL)	3	3	2
Faecal Coliforms (cfu/100mL)	(1-6000)	(1-1171)	(1-59)

Notes:

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

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

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

3.3.3 Marine Sediment Quality

Baseline marine sediment quality in the Assessment Area has been determined through a review of EPD routine sediment quality monitoring data collected between 1986 and 2020. Sediment monitoring data from EPD monitoring stations that are located within or close to the Assessment Area were reviewed and summarised in Table 3.3. Locations of these stations are presented in Figure 3.1.

Sediment monitoring data from the EPD monitoring stations were compared with the relevant sediment quality criteria specified in ETWB TC(W) No. 34/2002 Management of Dredged/Excavated Sediment. The EPD routine monitoring data indicate that the contaminant levels in the sediments in the vicinity of the Project are all below the Lower Chemical Exceedance Level (LCEL).

Table 3.3 Summary of EPD Routine Sediment Monitoring Data from Selected Stations of the Tolo Harbour and Channel WCZ and Mirs Bay WCZ (1986 – 2020)

Parameters	LCEL	UCEL	TS5	MS7	MS17
Arsenic (mg kg^-1)	12	42	6.6	7.2	6.9
Arsenic (mg kg^-1)			(3.2-12.0)	(4.0-10.0)	(2.2-11.0)
Cadmium (mg kg^-1)	1.5	4	0.5	0.4	0.3
Cadmium (mg kg^-1)			(0.1-7.5)	(0.1-9.8)	(<0.1-8.3)
Chromium (mg kg^-1)	80	160	32.5	34.5	32.8
Chromium (mg kg^-1)			(11.0-85.0)	(25.0-57.0)	(6.0-44.0)
Copper (mg kg^-1)	65	110	21.8	19.9	16.3
Copper (mg kg^-1)			(5.0-70.0)	(11.0-28.0)	(<0.2-55.0)
Lead (mg kg^-1)	75	110	53.1	43.8	43.9
Lead (mg kg^-1)			(35.0-86.0)	(27.0-65.0)	(26.0-67.0)
Mercury (mg kg^-1)	0.5	1	0.10	0.08	0.06
Mercury (mg kg^-1)			(<0.05-0.59)	(0.05-0.38)	(<0.05-0.55)
Nickel (mg kg^-1)	40	40	23.3	23.4	23.9
Nickel (mg kg^-1)			(7.0-50.0)	(17.0-35.0)	(6.0-34.0)
Silver (mg kg^-1)	1	2	<0.2	<0.2	<0.2
Silver (mg kg^-1)			(<0.2-<0.2)	(<0.2-<0.2)	(<0.2-0.5)
Zinc (mg kg^-1)	200	270	121.3	99.2	96.9
Zinc (mg kg^-1)			(64.0-220.0)	(77.0-140.0)	(36.0-170.0)
Total Polychlorinated Biphenyls (PCBs) (μg kg^-1)	23	180	18	18	14
Total Polychlorinated Biphenyls (PCBs) (μg kg^-1)			(8-26)	(10-18)	(3-18)
Low Molecular Weight Polycyclic Aromatic Hydrocarbons (PAHs) (μg kg^-1)	550	3,160	<180	<180	<180
			(<180-<180)	(<180-260)	(<180-185)
High Molecular Weight Polycyclic Aromatic Hydrocarbons (PAHs) (μg kg^-1)	1,700	9,600	36	50	35
			(<32-130)	(<32-267)	(<32-139)
Chemical Oxygen Demand (mg kg^-1)	--	--	18796	17537	16266
Chemical Oxygen Demand (mg kg^-1)			(8300-40000)	(12000-28000)	(8400-38000)
Total Kjeldahl Nitrogen (mg kg^-1)	--	--	737.4	715.4	669.7
Total Kjeldahl Nitrogen (mg kg^-1)			(23.0-2000.0)	(210.0-3600.0)	(18.0-1600.0)

Note:

1. Data presented are arithmetic means; data in brackets indicate ranges.

2. All data are on a dry weight basis unless stated otherwise.

Figure 3.1 Location of Water Sensitive Receivers and Nearby EPD Marine Water / Sediment Quality Monitoring Stations

Map

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3.3.4 Water Sensitive Receivers

The WSRs have been identified in accordance with Annex 14 of the Technical Memorandum on EIA Process (EIAO, Cap.499, S.16) and Section 3.4.3.2 of the Study Brief. These WSRs are illustrated in Figure 3.1 and listed in Table 3.4. Key WSRs include:

n Recreational areas, such as secondary contact recreation subzones of WCZs ([1]);

n Yan Chau Tong Marine Park (MP1), as well as the Hoi Ha Wan Marine Park (MP2);

n Existing FCZs at Wong Wan and other nearby areas (F1 to F4);

n Proposed FCZs at Outer Tap Mun and Mirs Bay (Site B and Site C, respectively);

n Ecological habitats for marine organisms including coral and benthic communities, and Finless Porpoise ([2]) at / near the Project site (CR1 to CR3, CR8 to CR16, M1 to M5);

n Spawning ground and nursery areas of commercial fisheries resources ([3]);

n Artificial reefs in Yan Chau Tong Marine Park (MP1) and Hoi Ha Wan Marine Park (MP2);

n Intertidal area of Plover Cove Country Park (M1 to M5);

n Hoi Ha Wan SSSI (SSSI1); and

n Non-gazetted beach (B1).

There is no seawater intake identified within 5 km from the Project Site, and other WSRs outside of 5 km from the Project Site is expected to be too far away to be impacted by the proposed mariculture operation. They are therefore not considered in this assessment.

In accordance with the Study Brief, the Project site itself is also considered as a sensitive receiver for assessment.

Table 3.4 Water Sensitive Receivers (WSRs) in the Vicinity of the Proposed FCZ Site at Wong Chuk Kok Hoi

WSR ID	WSR	Distance to the Proposed FCZ site at Wong Chuk Kok Hoi (km)
B1	Non-gazetted beach of Crescent Bay	2.0
CR1	Coral at Northeast Crooked Island	4.1
CR2	Coral at Crescent Island and Double Island	0.8
CR3	Coral at Port Island	3.3
CR8	Coral at Wong Wan Tsai	3.1
CR9	Coral at Fung Wong Wat	2.1
CR10	Coral at Gruff Head	2.6
CR11	Coral at South Wong Wan Tsui	0.9
CR12	Coral at Wong Chuk Kok Tsui	1.3
CR13	Coral at Hoi Ha Wan Moon Island	3.4
CR14	Coral at Hoi Ha Wan Coral Beach	4.0
CR15	Coral at Sam Mun Shan	4.9
CR16	Coral at Heung Lo Kok	3.1
F1	O Pui Tong Fish Culture Zone	4.0
F2	Sai Lau Kong Fish Culture Zone	3.7
F3	Wong Wan Fish Culture Zone	0.9
F4	Tap Mun Fish Culture Zone	4.4
M1	Mangrove Stand / Intertidal at Ngau Shi Wu Wan	4.1
M2	Mangrove Stand / Intertidal at Ngor Tau Tsui	4.5
M3	Mangrove Stand / Intertidal at Tung Wan	1.0
M4	Mangrove Stand / Intertidal at Sam A Chung	4.5
M5	Mangrove Stand / Intertidal at Fung Wong Wat	2.3
MP1	Yan Chau Tong Marine Park and Artificial Reef within the Marine Park	1.1
MP2	Hoi Ha Wan Marine Park and Artificial Reef within the Marine Park	2.7
SSSI1	Hoi Ha Wan SSSI	2.8
Site A	Proposed Wong Chuk Kok Hoi FCZ	Project Site
Site B	Proposed Outer Tap Mun FCZ	3.9
Site C	Proposed Mirs Bay FCZ	6.3

3.4 Assessment Criteria

The proposed establishment of new fish culture zone would potentially result in an increase in pollution from fish farming operation. Such pollution may increase nutrient levels as well as decrease dissolved oxygen level in the surrounding waters. The relevant assessment criteria for non-FCZ WSRs are stipulated in the WQO and are shown in Table 3.5.

Table 3.5 Summary of Assessment WQO Criteria

Parameters	Mirs Bay WCZ	Tolo Harbour and Channel WCZ
Dissolved Oxygen (Bottom) (mg/L)	Not less than 2 mg/L for 90% of samples	Not less than 2 mg/L for the Harbour subzone. Not less than 3 mg/L for the Buffer subzone. Not less than 4 mg/L for the Channel subzone.
Dissolved Oxygen (Depth-averaged) (mg/L)	Not less than 4 mg/L for 90% of samples	Not less than 4 mg/L.
Suspended Solids (mg/L)	Change not more than 30% due to waste discharge	Not applicable
Total Inorganic Nitrogen (mg/L)	≤ 0.3	Not applicable
Unionized Ammonia (mg/L)	≤ 0.021 mg/L	Not applicable
Chlorophyll-a (μg/L)	Not applicable	5-day running average not more than 20 μg/L for the Harbour subzone. 5-day running average not more than 10 μg/L for the Buffer subzone. 5-day running average not more than 6 μg/L for the Channel subzone.
E.coli (no./100mL)	≤ 610 no./100mL for the Secondary contact recreation subzone and the Fish culture subzones	≤ 610 no./100mL for the Secondary contact recreation subzone and the Fish culture subzones

In addition to the WQO criteria for various water quality parameters in the two WCZs, reference has been made to other past approved EIA reports / project profiles for applicable assessment criterion for protection of coral within the Tolo Harbour and Channel WCZ. Assessment criterion of 10 mg/L of total suspended solids levels would be adopted following the approved EIA of Development of a Bathing Beach at Lung Mei, Tai Po (AEIAR-123/2008), as well as the Project Profile for Sediment Removal at Yim Tin Tsai, Yim Tin Tsai (East) Fish Culture Zones and Shuen Wan Typhoon Shelter (DIR-191/2009). For fish culture zone in Mirs Bay, an additional criterion for chlorophyll-a of 20 µg/L would be adopted to protect the fish stock from excessive algal growth based on criterion adopted in previous Project WATERMAN Study ([4]). A summary of applicable assessment criteria for each category of WSRs are provided below in Table 3.6.

There will be no marine dredging or other major marine works that could cause significant sediment disturbance and the associated release of sediment-bounded contaminants. Therefore, assessment criteria for dissolved metals and organic compounds are not necessary for this Study.

Table 3.6 Summary of Applicable Assessment Criterion for Identified WSRs

Category of WSR	ID	WSR	Annual
			10^th-percentile		Mean						Geomean
			Depth-averaged	Bottom	Depth-averaged	Bottom	Depth-averaged
			Dissolved Oxygen				Total Inorganic Nitrogen	Unionized Ammonia	Chlorophyll-a	Suspended Solids	**E.coli^Note**
			(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(µg/L)	(mg/L)	(no./100 mL)
Non-gazetted beach – Mirs Bay	B1	Non-gazetted beach of Crescent Bay	≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
Coral – Mirs Bay	CR1	Coral at NE Crooked Island	≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
	CR2	Coral at Crescent Island and Double Island
	CR3	Coral at Port Island
	CR12	Coral at Wong Chuk Kok Tsui
Coral – Tolo Harbour and Channel	CR8	Coral at Wong Wan Tsai	N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
	CR9	Coral at Fung Wong Wat
	CR10	Coral at Gruff Head
	CR11	Coral at South Wong Wan Tsui
	CR13	Coral at Hoi Ha Wan Moon Island
	CR14	Coral at Hoi Ha Wan Coral Beach
	CR15	Coral at Sam Mun Shan
	CR16	Coral at Heung Lo Kok
Fish Culture Zone – Mirs Bay	F1	O Pui Tong Fish Culture Zone	≥5	≥2	N/A	N/A	≤0.3	≤0.021	≤20	increase ≤30% baseline	≤610
	F2	Sai Lau Kong Fish Culture Zone
	F3	Wong Wan Fish Culture Zone
	F4	Tap Mun Fish Culture Zone
	Project site	Proposed Wong Chuk Kok Hoi FCZ
	Site B	Proposed Outer Tap Mun FCZ
	Site C1	Proposed Mirs Bay FCZ (Northern Part)
Mangrove Stand / Intertidal – Mirs Bay	M1	Mangrove Stand / Intertidal at Ngau Shi Wu Wan	≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
	M2	Mangrove Stand / Intertidal at Ngor Tau Tsui
	M3	Mangrove Stand / Intertidal at Tung Wan
	M4	Mangrove Stand / Intertidal at Sam A Chung
Mangrove Stand / Intertidal – Tolo Harbour and Channel	M5	Mangrove Stand / Intertidal at Fung Wong Wat	N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
Marine Park – Mirs Bay	MP1	Yan Chau Tong Marine Park and Artificial Reef within the Marine Park	≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
Marine Park – Tolo Harbour and Channel	MP2	Hoi Ha Wan Marine Park and Artificial Reef within the Marine Park	N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
SSSI – Tolo Harbour and Channel	SSSI1	Hoi Ha Wan SSSI	N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610

Note: WQO criterion for E.coli is only applicable to fish culture zones, bathing beaches as well as secondary contact recreation subzone. Given secondary contact recreation subzone covers significant area around the Project Site and is represented by a lot of WSRs in this list, the criterion is deemed applicable to these WSRs groups as well.

3.5 Assessment Methodology

3.5.1 General Methodology

The methodology employed to quantitatively assess potential water quality impacts associated with the operation of the Project is presented in the Water Quality Modelling Plan (Appendix 3A), which provides full technical details of the modelling works as well as model validation. The WSRs assessed are presented in Figure 3.1.

For other potential sources of water quality impact in construction and operation phase, qualitative approach would be adopted in the assessment.

3.5.2 Uncertainties in Assessment Methodology

The uncertainties associated with the operation phase water quality modelling and carrying capacity estimation include:

n Potential change in pollution loading from the Guangdong side of Mirs Bay; and

n Potential change in mariculture practice which leads to different level of pollution loading from fish farms.

Future year of 2023 was chosen because the future loading from the Guangdong Province of China is expected to decrease continuously and therefore the estimated loading in 2023 would be conservative (Section 4 of Appendix 3A referred). Model prediction of water quality under 2016 presented in Appendix 3D compared observed and predicted water quality at EPD Marine Water Quality Monitoring Stations. Results indicated the model developed can generally represent key water quality features including stratification and seasonal differences, while providing predictions that are generally more conservative the observed conditions. This means the model would provide conservative estimation of water quality thus being acceptable.

In terms of change in mariculture practice, the overall trend has been heading towards a more environmentally friendly direction in the past decades. The wider adoption of pellet feed has reduced wastage. Improved fish farming practice has reduced overfeeding, disease and fish mortality. Future improvement in technology and fish farming practice is expected to further the trend on small environmental footprint for mariculture, and thus the current assumptions are considered conservative and appropriate for impact assessment. In particular, the pollution loading from mariculture operation at the Project site was based on feed conversion ratio (FCR) of 2, whereas literatures reviewed under this Study indicated typical pellet feed nowadays can achieve FCR of close to 1 ([5]) ([6]) ([7]). The adoption FCZ of 2 instead of 1 means the amount of feed assumed for mariculture operation would be doubled, and the associated wastage, leachage ([8]) of nutrient from waste would be notably higher than typical average conditions for fish farm using pellet feeds. This will ensure conservative estimation of pollution load from the mariculture operation at the Project site.

It should be highlighted that the water quality modelling exercise covered a typical annual cycle based on typical hydrodynamic of spring neap cycle in dry and wet seasons. Extreme conditions, such as typhoon is not expected to result in water quality conditions much worse than the typical conditions and is typically not considered in other water quality simulation in past EIAs. Also, in case of deterioration of water quality, it is typical for mariculturists to move the mariculture operation within or out of the Project site temporarily, which in the sense of modelling exercise means moving sensitive receiver as well as pollution source. In this Study, such movement has not been taken into account and thus represents the worst case scenario where avoidance is not possible.

To ensure robustness of the modelling exercise, performance of the hydrodynamic and water quality prediction have been demonstrated to be on par with past approved model (Annex A-B of Appendix 3A) and able to reproduce realistic water quality conditions in the past (Appendix 3D). This shows the adopted model would be able to predict the water quality conditions under the baseline and project scenarios of the Project with reasonable accuracy and reliability, ensure reliable assessment and conclusion be drawn.

3.6 Potential Sources of Impact

3.6.1 Construction Phase

The construction for this Project will not involve civil or marine works. Most of the construction works would involve the assembly of parts to form fish rafts for mariculture, as well as the towing and anchoring of fish rafts from other location(s) to the new FCZ using tug boat. Potential water quality impact from the assembly of parts to form fish rafts would include accidental spillage, construction waste, as well as sewage from construction workforce. Anchoring and de-anchoring of fish rafts may result in transient, localised elevation of suspended solids near seabed.

3.6.2 Operation Phase

Maintenance dredging and sediment removal were typically needed at FCZs sited at shallow and sheltered as a result of building up of organic content at the seabed level of the FCZs because of prolong mariculture operation. Build-up of organic content could be contributed by fish faeces, unconsumed feed, lodged off attached growth from cleaning, etc., and could results in deterioration of local water quality, increased risk of local red tide and upwelling of anoxic and toxic gas ([9]). The Project site was chosen to be deep enough to (1) allow sufficient dispersion of any mariculture waste (fish faeces, unconsumed feed, lodged off attached growth, etc.) that sinks could be brought away by tidal current and dispersed at a larger area of the seabed so there is no significant build-up of the seabed, and (2) provide sufficient distance from the seabed to the bottom level of fish cages. Specifically, at least 2 m of clearance from the seabed would be maintained at all times. Maintenance dredging and sediment removal are therefore not required for the Project and hence no water quality impact would be expected from maintenance dredging and sediment removal.

In case of adverse weather / water quality conditions or approaching of harmful algal bloom, there may be a need for mariculturists to temporarily relocate their fish rafts (or equivalent) to safe location(s) to avoid fish kill or other damage. During the brief period of relocation, the pollution load from the relocated mariculture operation would be released into the relocated locations, thus affect the local water quality.

3.7 Impact Assessment – Construction Phase

The towing and anchoring of fish rafts is expected to have very limited impact on water quality, as the level of sediment suspended in the water column from anchoring will be very limited, primarily localised near the seabed and the impact will be transient because suspended sediment will settle shortly close to the anchor. Anchoring is routinely conducted for all kinds of vessel activities and floating structures in the surrounding waters and is considered to have limited level of impact on water body. The Project site is more than 10 m in water depth such that propeller would not have interaction with the seabed sediment and so SS elevation due to propeller wash is not anticipated.

Depending on the design and specifications, required works to assemble fish rafts onsite could vary and may include tighten up connections by nuts and bolts, ropes or equivalent, assembling parts with pre-casted grooves, etc. Modern fish rafts are available in modular form and with appropriate surface treatment ([10]), hence the onsite assembly can be done quicker and will require less onsite use of equipment and materials. In general, construction materials and tools are inert and use of these items is not expected to result in notable changes in water quality. It is noted that wood or other structural materials that require surface treatment (e.g. water-proofing, anti-fouling) are generally treated offsite (in factories / workshops) instead of onsite during assembly. The use of chemicals onsite is expected to be minimal and no unacceptable water quality impact from the onsite installation of fish raft would be expected. Details of tools and materials adopted on-site would be determined by the future licensees.

Because of the lack of major works to be conducted, it is unlikely there will be a significant workforce presence during construction phase, and any sewage / wastewater generated shall be collected at the transportation / work vessel(s) for disposal at appropriate facilities on land. Discharge of sewage from workforce or other wastewater should be strictly forbidden. No unacceptable water quality impact from sewage / wastewater from workforce is anticipated.

In view of the above, no unacceptable water quality impact is anticipated from fish raft installation.

3.8 Impact Assessment – Operation Phase

3.8.1 Changes in Water Quality from Pollution Loadings arising from Mariculture Operation

Mariculture activities at the Project site would result in an increase in pollution loads primarily from fish feed, feed wastage, fish excretion and dead fish. The increase in pollution loads would result in a change in water quality in the receiving waters, affecting the water quality at nearby sensitive receivers, such as other existing FCZs, marine ecological as well as fisheries resources. A carrying capacity ([11]) estimation was conducted (detailed in Appendix 3B) to determine the suitable production capacity allowed onsite to ensure mariculture activities there would not result in, or be affected by, water quality impact from over-stocking. The estimation of carrying capacity was conducted using the methodology and box model developed by Project WATERMAN which was used in the carrying capacity estimation for the existing FCZs in Hong Kong. The carrying capacity estimation took into account various aspects affecting the water quality for mariculture operation, including tidal flushing, loading contribution from mariculture activities, as well as various water quality parameters interaction (e.g. nitrogen, phosphorus, dissolved oxygen). Based on the WATERMAN model, the carrying capacity for mariculture operation at the Project Site is found to be limited by the criterion for total inorganic nitrogen in both wet and dry seasons. The carrying capacity estimation indicated the Project site can support mariculture operation of 755.2 ton of standing stock based on typical mariculture practice in HK without significant deterioration of water quality under the typical average condition. The corresponding pollution load from such level of mariculture operation is presented in Appendix 3B.

The estimated loading at Project site was taken into account in the Delft3D model to verify the acceptability of change in water quality at Project site itself as well as to determine the offsite water quality impact on nearby WSRs. Two modelling scenarios were conducted. The baseline scenario covers the “without project” condition of the Assessment Area in 2023. The project scenario has taken into account the additional pollution load from Project site, as well as the other nearby proposed new fish culture zones at Outer Tap Mun and Mirs Bay (each at their carrying capacity) ([12]). The change in water quality as a result of the additional mariculture activities were assessed according to the WQO. Statistics of key water quality parameters are presented in Table 3.8 ([13]). Contour plots showing spatial distribution of key water quality parameters are presented in Appendix 3C.

Following sections discuss the predicted level and change for key water quality parameters separately at the Project site as well as major nearby WSRs.

3.8.1.1 Dissolved Oxygen

Predicted levels of dissolved oxygen were generally good in most identified WSRs under both baseline and project scenarios except for certain embayed areas, mostly at the north, as a result of relatively high pollution loading from dry weather load and treated sewage effluent from the Starling Inlet (also known as Sha Tau Kok Hoi), as well as pollution load from Yantian area of Guangdong. Typical depth-averaged levels of dissolved oxygen were predicted to be around 5 mg/L to 7 mg/L, which were close to the observed range at EPD Marine Water Quality Monitoring Stations (Table 3.2). Predicted levels of dissolved oxygen are generally lower in the bottom level and the predicted depth-averaged levels are typically slightly higher than that of the bottom level. Changes in dissolved oxygen due to mariculture production at the Project site and other locations were predicted to be limited at most locations away from these proposed new FCZ sites.

Within the Wong Chuk Kok Hoi embayment, the levels of dissolved oxygen were predicted to remain rather stable with and without project operation outside of the Project Site. The mean level of depth-averaged dissolved oxygen at the existing Wong Wan FCZ, which is the closest WSR to the Project site, was predicted to be 6.6 mg/L for baseline scenario and 6.4 mg/L for project scenario, and the mean levels of bottom dissolved oxygen were predicted to be 6.4 mg/L and 6.2 mg/L for respectively. For the Project Site, the predicted mean levels of depth-averaged dissolved oxygen at the predicted to be 5.8 mg/L for both scenarios, and the mean level of bottom dissolved oxygen was predicted to be 5.2 mg/L and 5.1 mg/L baseline and project scenarios respectively. The lower dissolved oxygen level at the Project site is a result of much deeper water at the Project site. In general, deeper water is more likely have lower dissolved oxygen level because of much longer diffusion distance from surface (particularly for sheltered waters with limited vertical mixing) and reduced photosynthesis. The predicted 10^th-percentile depth-averaged dissolved oxygen levels at the existing Wong Wan FCZ were above the proposed assessment criterion of 5 mg/L under both scenarios while those at the Project Site are below 5 mg/L were below assessment criterion. The predicted 10^th-percentile depth-averaged dissolved oxygen levels at the Project site was 4.0 mg/L under both scenarios. The relatively low dissolved oxygen levels at Project Site is contributed by the higher water temperature and stratification during the summer period. Such episodes of low dissolved oxygen levels were also observed at Wong Wan in the past years (Figure 3.2), without affecting the mariculture operation which are typically driven by low bottom dissolved oxygen levels in summer months, and the situation at the Project Site is worse than that of the existing Wong Wan FCZ given the higher water depth. It should be highlighted that even though the 10^th-percentile depth-averaged dissolved oxygen levels at Site A was predicted to be lower than the corresponding assessment criterion of 5 mg/L, the dissolved oxygen levels predicted at the upper part of the water column (where the majority of fish stock is expected to stay) is generally higher. Based on AFCD’s past records, dissolved oxygen levels of 4 mg/L or higher at surface level would not cause any notable impact to mariculture operation in general.

Additional time series plots of predicted dissolved oxygen levels at the surface, mid-depth and bottom levels at 4 locations within the Project site under both baseline and project scenarios are provided in Appendix 3C. As shown, the predicted dissolved oxygen levels at various locations of the proposed site showed similar pattern of seasonal variation, with higher level in dry season and lower level in wet season. Also, some level of stratification is also predicted in wet season, with difference in dissolved oxygen levels up to 2 mg/L between the surface and bottom levels up in the deeper corner of the proposed site (northwestern corner), while that for the shallower side (southern) is predicted to around 1 mg/L. In terms of changes due to project operation, the predicted levels of dissolved oxygen for both baseline and project scenarios match each other very closely and have similar range of fluctuation.

Outside of the Wong Chuk Kok Hoi embayment, one FCZ WSR at O Pui Tong FCZ (F1) was predicted to have 10^th-percentile depth-averaged dissolved oxygen levels below the corresponding assessment criterion in both scenarios and there is no predicted deterioration of DO level under the project scenario. Therefore, no unacceptable change in dissolved oxygen level at O Pui Tong FCZ would be expected.

Overall, according to the results listed in Table 3.8, there is limited change in the predicted dissolved oxygen levels between baseline and project scenarios, the proposed mariculture operation at the Project site is not expected to result in significant deterioration of dissolved oxygen levels at the surrounding waters and identified WSRs.

Figure 3.2 Observed Dissolved Oxygen Level at Wong Wan FCZ from 2015-2021 (Source: AFCD Monitoring Data)

Chart, line chart

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3.8.1.2 Total Inorganic Nitrogen

Predicted levels of total inorganic nitrogen were generally low in the assessment area. Predicted levels at WSRs were generally around 0.1 mg/L, which are lower than the assessment criterion of 0.3 mg/L for Mirs Bay. Similar levels were recorded at nearby EPD Marine Water Quality Monitoring Stations shown in Table 3.2. The differences between baseline and project scenarios were predicted to be limited at WSRs away from proposed new FCZ sites at the Project site and other locations.

At the Wong Wan FCZ, the predicted level of total inorganic nitrogen remains stable with the mariculture operation at Project site. Predicted levels of total inorganic nitrogen at the Wong Wan FCZ were 0.05 mg/L under baseline scenario and 0.07 mg/L under project scenario. For the Project site, the mariculture operation result in slight increase of predicted levels of total inorganic nitrogen from 0.10 mg/L to 0.13 mg/L, which are both below the corresponding assessment criterion of 0.3 mg/L. No unacceptable elevation in total inorganic nitrogen is expected from the proposed mariculture operation at the Project site.

As shown in Table 3.8, total inorganic nitrogen levels at all other identified WSRs were predicted to be below the corresponding assessment criterion of 0.3 mg/L under both baseline and project scenario. No unacceptable change in TIN level would be expected from the proposed mariculture operation at the Project site.

3.8.1.3 Unionized Ammonia

Given the small increase in total inorganic nitrogen level due to the operation of the Project, the corresponding predicted increase in unionized ammonia is also small. The increases at all WSRs between the baseline and project scenarios in unionized ammonia levels were either undetectable or at most 0.002 mg/L. The predicted levels of unionized ammonia were at or below 0.010 mg/L at all identified WSRs, which is below the assessment criterion of 0.021 mg/L. Predicted levels of unionized ammonia at Wong Wan FCZ were 0.003 mg/L in baseline scenario and 0.004 mg/L in project. For the Project site, predicted levels of unionized ammonia were 0.006 mg/L and 0.008 mg/L respectively in baseline and project scenarios. No unacceptable elevation in unionized ammonia is expected from the proposed mariculture operation at the Project site.

3.8.1.4 Suspended Solids

Predicted levels of suspended solids varies spatially across the assessment area, ranging from 1 to 6 5 mg/L. There are limited or no change for the predicted levels between baseline and project scenarios at all identified WSRs. Predicted SS level at Wong Wan FCZ was 2.6 mg/L under baseline scenario and 2.7 mg/L under project scenario, while that for the Project site was 2.0 mg/L and 2.1 mg/L respectively for baseline and project scenarios. None of the identified WSR show change in SS levels that exceed assessment criterion of 30% change level in baseline level. No unacceptable change in suspended solids level is expected.

3.8.1.5 Chlorophyll-a

Predicted levels of chlorophyll-a also vary spatially across the assessment area, ranging up to above 20 µg/L. Similar to the case of dissolved oxygen, chlorophyll-a levels are generally higher at surface level and thus area with shallower depth tends to have higher chlorophyll-a levels. The differences between baseline and project scenarios were predicted to be limited at WSRs away from proposed new FCZ sites at the Project site and other locations. No exceedance of chlorophyll-a criterion was predicted at all identified WSRs. No unacceptable water quality impact on chlorophyll-a is expected from the mariculture operation of the Project.

3.8.1.6 E.coli

In both baseline and project scenarios, the predicted levels of E.coli around the Project site were predicted to be very low because of the lack of major sources of E.coli (e.g. sewage). Since faecal pollution of dogs/cats is not expected within the Project site ([14]), the operation of fish farm at Project site will not introduce additional E.coli loading and thus the prediction under baseline and project scenarios are the same. No unacceptable water quality impact on identified beach, secondary contact recreation subzone and fish culture zone is expected. Further discussion on sewage and wastewater generation from staff and visitors onsite is provided under Sections 3.8.4 and 3.8.5 below.

3.8.1.7 Impact on the Use of IMTA

As discussed under Section 2.6.2.3, the use of IMTA would be considered at the Project Site to (1) enhance productivity and (2) reduce environmental impact by utilizing waste feed and other waste from the fish stock onsite. Given the uncertain nature of its implementation (e.g. trophic levels / species involved / other designs), the effect on the pollution loading from these non-fish secondary trophic level(s) has not been taken into account in the pollution loading estimation for the proposed mariculture operation at the Project Site. The following section provides a simple analysis on the potential impact on pollution loading estimation from these non-fish trophic level.

Deposit feeders in IMTA typically feed on wasted feed, fecal matters and other waste sink from the fish stock on top. This means their presence would reduce the pollution loading from waste feed and fish faeces from the mariculture operation. According to the pollution loading estimation provided under Table 4.16 of Appendix 3A, the combined contribution of these two sources of pollution from mariculture would be over 90% of all pollution from mariculture for all parameters except for ammonia-N (which is mainly contributed from fish excretion). Since these deposit feeders will only consume and assimilate the organic part of these waste, therefore the introduction of deposit feeders could potential affect about 13.9% of the total nitrogen budget, 67.4% of the total phosphorus budget and 100% of the 5-day biochemical oxygen demand budget.

Table 3.7 Pollution Loading Contribution from Wasted Feed and Fish Faeces for Production Level of 1 ton at Proposed FCZs

Sources	Wasted Feed	% Contribution	Fish Faeces	% Contribution	Total % Contribution	Total
Oxidized-N (g/day)	0.0968	7.1%	1.205	88.6%	95.7%	1.3597
Ammonia-N (g/day)	0.0415	0.0%	0.371	0.2%	0.2%	236.0373
Org-N (g/day)	21.9176	57.4%	16.265	42.6%	100.0%	38.1865
TIP (g/day)	0.0394	2.3%	1.624	95.7%	98.0%	1.6969
TOP (g/day)	2.6986	76.8%	0.813	23.1%	100.0%	3.5119
BOD (g/day)	45.2051	8.4%	495.095	91.6%	100.0%	540.3082
TSS (g/day)	24.6477	92.2%	-		92.2%	26.7298

Filter feeders, including oysters, clams and mussels, which are commercially cultivated feed on planktons or suspended organic matters. According to Jansen et. al. (2019) ([15]), biodeposit represents a significant pathway in bivalve nutrient recycling. Jansen et. al. reviewed a number of literature for mussel farming and indicated biodeposition rate could be up to around 10% of soft body weight of the mussel population in a culture area. The biodeposit could constitute of 0.3% to 2.3% of nitrogen and 0.08% to 0.3% phosphorus. Since biodeposit is solids and could sink to the bottom, a significant portion of the nutrient would be lock up and will not return to the water column quickly. Furthermore, the growth of fleshy tissues of these bivalves also lock up a notable amount of organic nutrients from the water column. For instance, Jansen et. al. reviewed a number of literature for nutrients composition in mussel tissue, which constitutes of 33.3% to 62.3% of organic carbon, 5.5% to 12.6% of organic nitrogen and 0.4% to 1.2% of organic phosphorus. While these figures are indicative of only several species covered in the review and may vary from species, locations and cultivation method, this still support the notion of additional cultivation of filter feeders would result in a net reduction of pollution load from the water column, thus be beneficial to the water quality.

Overall, the inclusion of IMTA would result in different levels of pollution reduction from the proposed mariculture operation at the Project Site by means of (1) reduction of wasted feed, fecal matters and other waste, and (2) filter feeding of plankton and biodeposition. While the effect of IMTA on water quality cannot be quantified given the lack of detail design information, its effect would positively affect the water quality at the Project Site if implemented in sufficient scale.

Table 3.8 Predicted Water Quality under Baseline and Project Scenarios

ID	WSR	Scn.	Annual
			10^th-percentile		Mean						Geomean
			Depth-averaged	Bottom	Depth-averaged	Bottom	Depth-averaged
			Dissolved Oxygen				Total Inorganic Nitrogen	Unionized Ammonia	Chlorophyll-a	Suspended Solids ^Note2	*E.coli*
			(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(mg/L)	(µg/L)	(mg/L)	(no./100 mL)
Non-gazetted beach – Mirs Bay Assessment Criteria			≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
B1	Non-gazetted beach of Crescent Bay	Baseline	5.2	5.0	6.3	6.2	0.06	0.003	6	1.9	0
B1	Non-gazetted beach of Crescent Bay	Project	5.2	4.7	6.3	6.1	0.07	0.003	7	2.0	0
Coral – Mirs Bay Assessment Criteria			≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
CR1	Coral at NE Crooked Island	Baseline	5.2	4.5	6.4	6.0	0.07	0.003	7	2.0	0
CR1	Coral at NE Crooked Island	Project	5.2	4.4	6.3	6.0	0.07	0.004	7	2.1	0
CR2	Coral at Crescent Island and Double Island	Baseline	4.2	3.4	5.9	5.6	0.09	0.005	6	1.9	0
CR2	Coral at Crescent Island and Double Island	Project	4.2	3.3	5.8	5.5	0.10	0.005	6	2.0	0
CR3	Coral at Port Island	Baseline	5.2	5.1	6.4	6.2	0.07	0.003	4	1.5	0
CR3	Coral at Port Island	Project	5.2	5.1	6.4	6.2	0.08	0.003	5	1.6	0
CR12	Coral at Wong Chuk Kok Tsui	Baseline	5.2	5.0	6.3	6.2	0.07	0.003	5	1.7	0
CR12	Coral at Wong Chuk Kok Tsui	Project	5.2	5.0	6.3	6.2	0.09	0.004	6	1.8	0
Coral – Tolo Harbour and Channel Assessment Criteria			N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
CR8	Coral at Wong Wan Tsai	Baseline	5.1	4.4	6.2	6.0	0.07	0.003	3	1.4	0
CR8	Coral at Wong Wan Tsai	Project	5.0	4.3	6.1	5.9	0.09	0.004	3	1.5	0
CR9	Coral at Fung Wong Wat	Baseline	5.1	4.7	6.2	6.1	0.07	0.003	3	1.4	0
CR9	Coral at Fung Wong Wat	Project	5.0	4.5	6.1	6.0	0.09	0.004	3	1.5	0
CR10	Coral at Gruff Head	Baseline	5.2	4.6	6.3	6.0	0.07	0.003	3	1.5	0
CR10	Coral at Gruff Head	Project	5.1	4.4	6.2	5.9	0.09	0.004	4	1.6	0
CR11	Coral at South Wong Wan Tsui	Baseline	5.1	4.8	6.2	6.2	0.07	0.003	3	1.4	0
CR11	Coral at South Wong Wan Tsui	Project	4.9	4.6	6.2	6.1	0.09	0.004	4	1.5	0
CR13	Coral at Hoi Ha Wan Moon Island	Baseline	5.1	4.5	6.2	6.0	0.09	0.004	3	1.4	0
CR13	Coral at Hoi Ha Wan Moon Island	Project	5.0	4.3	6.1	5.9	0.11	0.004	4	1.5	0
CR14	Coral at Hoi Ha Wan Coral Beach	Baseline	5.2	4.3	6.3	6.0	0.08	0.004	4	1.6	0
CR14	Coral at Hoi Ha Wan Coral Beach	Project	5.1	4.3	6.2	5.9	0.10	0.005	5	1.7	0
CR15	Coral at Sam Mun Shan	Baseline	5.1	4.4	6.2	6.0	0.07	0.003	3	1.5	0
CR15	Coral at Sam Mun Shan	Project	4.8	4.3	6.1	5.9	0.08	0.004	4	1.6	0
CR16	Coral at Heung Lo Kok	Baseline	5.1	4.4	6.2	6.0	0.09	0.004	3	1.4	0
CR16	Coral at Heung Lo Kok	Project	5.0	4.3	6.1	5.9	0.10	0.004	4	1.5	0
Fish Culture Zone – Mirs Bay Assessment Criteria			≥5	≥2	N/A	N/A	≤0.3	≤0.021	≤20	increase ≤30% baseline	≤610
F1	O Pui Tong Fish Culture Zone	Baseline	4.2	2.3	5.9	4.9	0.09	0.006	8	2.2	0
F1	O Pui Tong Fish Culture Zone	Project	4.2	2.2	5.9	4.8	0.10	0.006	8	2.3	0
F2	Sai Lau Kong Fish Culture Zone	Baseline	5.2	4.3	6.5	6.1	0.06	0.003	11	2.4	0
F2	Sai Lau Kong Fish Culture Zone	Project	5.2	4.2	6.5	6.1	0.07	0.004	11	2.5	0
F3	Wong Wan Fish Culture Zone	Baseline	5.2	5.2	6.6	6.4	0.05	0.003	12	2.6	0
F3	Wong Wan Fish Culture Zone	Project	5.1	4.9	6.4	6.2	0.07	0.004	12	2.7	0
F4	Tap Mun Fish Culture Zone	Baseline	5.4	5.2	6.5	6.4	0.08	0.003	4	1.5	0
F4	Tap Mun Fish Culture Zone	Project	5.4	5.2	6.5	6.4	0.10	0.004	5	1.6	0
Project site	Proposed Wong Chuk Kok Hoi FCZ	Baseline	4.0	2.9	5.8	5.2	0.10	0.006	6	2.0	0
Project site	Proposed Wong Chuk Kok Hoi FCZ	Project	4.0	2.8	5.8	5.1	0.13	0.008	7	2.1	0
Site B	Proposed Outer Tap Mun FCZ	Baseline	5.2	4.2	6.3	5.8	0.10	0.004	3	1.4	0
Site B	Proposed Outer Tap Mun FCZ	Project	5.2	4.2	6.2	5.7	0.12	0.005	4	1.5	0
Site C1	Proposed Mirs Bay FCZ (Northern Part)	Baseline	5.2	4.2	6.1	5.7	0.12	0.005	3	1.4	0
Site C1	Proposed Mirs Bay FCZ (Northern Part)	Project	5.1	4.2	6.1	5.6	0.15	0.006	3	1.4	0
Mangrove Stand / Intertidal – Mirs Bay Assessment Criteria			≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
M1	Mangrove Stand / Intertidal at Ngau Shi Wu Wan	Baseline	4.2	2.2	6.1	5.1	0.08	0.005	11	2.5	0
M1	Mangrove Stand / Intertidal at Ngau Shi Wu Wan	Project	4.1	2.0	6.1	5.0	0.08	0.006	11	2.6	0
M2	Mangrove Stand / Intertidal at Ngor Tau Tsui	Baseline	5.2	3.6	6.5	5.7	0.05	0.004	22	4.2	0
M2	Mangrove Stand / Intertidal at Ngor Tau Tsui	Project	5.1	3.4	6.4	5.6	0.06	0.004	23	4.4	0
M3	Mangrove Stand / Intertidal at Tung Wan	Baseline	4.5	4.2	6.2	6.0	0.07	0.004	8	2.1	0
M3	Mangrove Stand / Intertidal at Tung Wan	Project	4.4	4.2	6.2	5.9	0.08	0.004	8	2.1	0
M4	Mangrove Stand / Intertidal at Sam A Chung	Baseline	5.1	4.2	6.6	6.2	0.03	0.002	27	5.6	0
M4	Mangrove Stand / Intertidal at Sam A Chung	Project	5.1	4.0	6.6	6.2	0.03	0.003	29	5.9	0
Mangrove Stand / Intertidal – Tolo Harbour and Channel Assessment Criteria			N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
M5	Mangrove Stand / Intertidal at Fung Wong Wat	Baseline	5.2	5.1	6.3	6.2	0.06	0.003	4	1.5	0
M5	Mangrove Stand / Intertidal at Fung Wong Wat	Project	5.2	5.0	6.3	6.1	0.08	0.003	4	1.6	0
Marine Park – Mirs Bay Assessment Criteria			≥4	≥2	N/A	N/A	≤0.3	≤0.021	N/A	increase ≤30% baseline	≤610
MP1	Yan Chau Tong Marine Park and Artificial Reef within the Marine Park	Baseline	4.2	3.2	5.9	5.2	0.09	0.005	7	2.2	0
MP1		Project	4.2	3.1	5.9	5.2	0.09	0.006	7	2.3	0
Marine Park – Tolo Harbour and Channel Assessment Criteria			N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
MP2	Hoi Ha Wan Marine Park and Artificial Reef within the Marine Park	Baseline	5.2	4.6	6.2	6.0	0.09	0.004	4	1.5	0
MP2		Project	5.1	4.4	6.2	5.9	0.11	0.004	4	1.6	0
SSSI – Tolo Harbour and Channel Assessment Criteria			N/A	N/A	≥4	≥4	N/A	N/A	≤6	≤10	≤610
SSSI1	Hoi Ha Wan SSSI	Baseline	5.1	4.3	6.2	5.9	0.09	0.004	3	1.4	0
SSSI1	Hoi Ha Wan SSSI	Project	5.1	4.3	6.1	5.8	0.11	0.005	4	1.5	0
EPD Marine WQ Monitoring Stations Assessment Criteria			N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
TM8	EPD Marine WQ Monitoring Station	Baseline	5.2	4.2	6.2	5.8	0.07	0.003	3	1.5	0
TM8	EPD Marine WQ Monitoring Station	Project	5.1	4.2	6.2	5.6	0.08	0.004	4	1.6	0
MM7	EPD Marine WQ Monitoring Station	Baseline	4.2	3.2	5.9	5.3	0.09	0.005	7	2.2	0
MM7	EPD Marine WQ Monitoring Station	Project	4.2	3.1	5.9	5.2	0.09	0.006	8	2.3	0
MM17	EPD Marine WQ Monitoring Station	Baseline	4.3	3.3	5.9	5.2	0.10	0.004	3	1.5	0
MM17	EPD Marine WQ Monitoring Station	Project	4.3	3.2	5.9	5.1	0.11	0.005	3	1.5	0

Note1: Values in exceedance of the corresponding assessment criteria are bold and shaded.

Note2: Assessment criterion for suspended solids is based on 30% of the predicted values for each WSRs under the baseline scenario and thus cannot be listed in the assessment criterion row for each group of WSRs.

Note3: As a result of the relatively low baseline dissolved oxygen level at Project Site in wet season, the project scenario considered the effect of aeration at individual fish farm operation of the Project Site. Please refer to Appendix 3E for details.

3.8.1.1 Temporary Relocation of Fish Rafts under Circumstances

In general, relocation of fish rafts adopting advanced mariculture technologies are not necessary under adverse weather (e.g. typhoon) given the framework of fish cages would use weather-resistant and durable materials (e.g. HDPE cages, steel truss cages). For other potential circumstances (e.g. red tide event, outbreak of fish disease), the licensees will review the need of fish raft relocation and propose the fish raft relocation plan as necessary for agreement with AFCD on a case-by-case basis, depending on the type of algal bloom (any toxicity to fish), expected duration of such circumstances, feasibility for early harvesting of fish stock, feasibility of implementing onsite control measures etc. In case fish raft relocation is considered necessary, the fish rafts will be relocated away from the areas of circumstances, avoid marine fairways and utilities and at some distance away from ecological and fisheries sensitive receivers (e.g. about 200 m away from established coral communities) to minimise potential impacts to these sensitive receivers. Such relocation will be temporary (e.g. a few weeks) and the fish rafts will return to the Project site upon the cease of the circumstances. Given the temporary nature of the fish raft relocation and the sufficient buffer distance to the ecological and fisheries sensitive receivers, unacceptable water quality impacts to these sensitive receivers near the relocated sites are not anticipated. In addition, the relocated pollution load from these mariculture operation would likely be distributed at a wider area around the proposed site. As shown in the water quality modelling exercise, the presence of additional pollution load from the mariculture operation at 755.2 ton of standing stock at the proposed site would not result in notable change in water quality. If some of the mariculture operation is temporarily relocated, the associated pollution load would likely to be more spread out and the potential change in water quality would be less significant. The relocation would involve anchoring and de-anchoring, which would result in minor disturbance to the bottom sediment as assessed under Section 3.7. In general, the water depth around Wong Chuk Kok Hoi is more than 10 m. Given the sufficient water depth at the surrounding water, sufficient clearance from the seabed is expected from the structure of fish fam during the relocation, and thus sediment disturbance is not expected during the relocation. Based on the above assessment, given the temporary nature of the fish raft relocation, relocation to be sited minimising the impacts to sensitive receivers, pollution load would spread out and potential change in water quality would be less significant than normal operation, the potential impacts due to temporary relocation of fish rafts under circumstances are expected to be minor.

3.8.1.2 Summary of Findings and Recommendations

The results of the water quality simulations indicated that the proposed mariculture operation would only result in very limited and very localized changes of water quality parameters at identified WSRs, including recreational areas, marine parks, existing and proposed FCZs, ecological habitats, spawning ground and nursery area of commercial fisheries resources and other fisheries sensitive receivers, artificial reefs, intertidal areas of various country parks, and beaches. For all WSRs identified other than the Project Site itself, the water quality parameters were predicted to be in compliance with the corresponding WQO criteria, and project operation would not result in notable deterioration. Relatively low dissolved oxygen at the Project Site was contributed by existing sources / general hydrology resulted in WQO non-compliance under the baseline conditions. The predicted reduction in dissolved oxygen at Project Site during operation could be controlled by adopting aeration as necessary and unacceptable water quality impact is not anticipated for mariculture operation at Project Site. Therefore, it is concluded that the proposed mariculture operation at the carrying capacity of 755.2 ton of standing stock or below would not result in unacceptable change in water quality at the identified WSRs. The licensees will adopt the operational measures and best practice for mariculture activities as stated in Appendix 2A to further minimise water quality impacts from the mariculture activities of the Project.

3.8.2 Changes in Hydrology and Flow Regime due to Presence of Mariculture Facilities

Structures of fish raft are highly porous to allow water flow and removal of excreta. Fouling by attached growth would increase drag and would typically be cleared regularly by mariculturists therefore such increase in drag would be limited. Separation distance of around 100 m will be provided between each fish rafts / cages with typical size around one hectare of sea area. The detailed number, size and separation distance of the fish rafts / cages would be determined during the later detailed design stage. The maintenance of separation distance will form a licensing condition for prospective licensees. Therefore, the presence of floating structures of fish rafts will not exert significant drag on the tidal stream and no notable change in flow regime due to the presence of floating structures would be expected.

3.8.3 Spillage of Fish Drugs, Pharmaceutical Chemicals, Feed Additives

The use and storage of chemicals would be limited to pharmaceuticals for fish, as well as those required to maintain equipment for the fish farm operation. Mariculturists at the Project site would be required to strictly observe the requirement under Cap. 529 Veterinary Surgeons Registration Ordinance and have strict control on prescription drugs. In addition, the mariculturists will follow the rules for using fish drugs as described in Good Aquaculture Practices published by AFCD ([16]) which detail the appropriate dosage of drugs and prohibit the use any fish drugs not prescribed by AFCD or registered veterinarian. AFCD will also provide technical support on the use of pharmaceuticals for fish. In AFCD’s regular inspection of existing FCZs in recent years, there was no identified case of excessive storage of drugs or pharmaceuticals. Therefore, it is expected that there would be very limited pharmaceuticals for fish kept onsite and those would be stored at secured locations, and discharge of water containing pharmaceuticals is not expected from daily operation. In view of the above, the risk of spillage of fish drugs or pharmaceuticals is low.

Unlike spillage of chemical, spilled/ excess fish feed with feed additives generally does not persist for considerable amount of time as the presence of fish feed with feed additives would attract existing fish population to feed on the spill feed. For floating type fish feed, the majority of feed spilled can simply be recovered by the mariculturists. Commercially available fish feed with feed additives comes in tough fabric bags of 20-25 kg each. In case such bags of feed dropping into the sea during storage or transportation, they will be recovered by the crew. Even if not recovered, the bag would limit the exchange materials such that the nutrient content would unlikely be released all at once and result in significant water quality impact. In view of this, together with the adoption of the operational measures and best practice for mariculture activities as stated in Appendix 2A, the risk and consequence of such scenario are deemed minimal and no unacceptable impact on water quality is expected.

3.8.4 Wastewater from Daily Operation of Fish Farms, Disinfection of Gears, and Sewage from Workforce

Operational activities would involve the removal of fouling organisms of the rafts. Fouling organisms are usually removed mechanically (e.g. using pressurised jet of seawater) so chemical is generally not required. Dislodged fouling biomass falling into the sea would not constitute additional pollution load because such biomass has fed on the original pollution source from the fish farm operation.

Disinfection of culture gears (primarily nets and cages) is required for disease control on regular basis (e.g. once a year prior to the start of fish farming cycle). According to AFCD’s recommendation for good practice ([17]), disinfection could be done via steaming, or submerge under water dosed with formaldehyde or bleach within enclosed containers. For any fishing gears that need to be disinfected onsite, solution of any chemical used will be required to be stored properly onsite and disposed of by licensed contractor and no onsite disposal would be allowed. It should be noted that disinfection under sunlight is considered more effective and practical option for cultural gears of large size and chemicals are not necessary to be dosed. In addition, based on the past experience of existing FCZs, it is not necessary to store and use a large amount of chemicals during FCZ operation. Therefore, it is not anticipated a large amount of chemicals would be stored and disposed during the operation of the Project.

Deep water mariculture operation at the Project site is typically manned minimally onsite and relies mostly on automated / remote control. Therefore, generation of sewage by staff and visitors onsite would be limited. Sewage shall be stored on vessels or at the mariculture facilities and be regularly disposed by licensed contractor, and no sewage from staff and visitors will be discharged into the sea.

Storage of chemicals / lubricant oil onsite would be maintained at minimal level. If major maintenance of gears or machineries onsite is needed, technicians / relevant staff should be brought to the site together with the necessary tools and chemicals. Remaining chemicals, together with any chemical waste generated from the maintenance process should be taken away by the same crew for disposal to appropriate facilities or licensed contractor when the crew leaves the site. Given the limited exposure period as well as proper storage and control, together with the adoption of the operational measures and best practice for mariculture activities as stated in Appendix 2A, no unacceptable change in water quality associated with the storage of chemicals onsite is expected.

Latest mariculture operation often rely on renewable sources of energy (solar and wind), supplemented by minor backup generator for prolonged cloudy / windless period. Limited amount of fuel may be stored onsite. To minimize potential risk of fuel spillage, fuel should be stored at sheltered and secure location for each mariculture operation. Excessive storage of fuel should be prohibited onsite as a risk control measure. Given the limited storage as well as other safety measures regarding proper storage, together with the adoption of the operational measures and best practice for mariculture activities as stated in Appendix 2A, no unacceptable change in water quality associated with the storage of fuel onsite is expected.

3.8.5 Increased Marine Traffic, Boating and Visitor Activities

Increased marine traffic would be anticipated at the Project site for moving of staff and visitors and goods (fish feed and gears, waste and produced fish etc.). Such marine traffic activities would not result in notable change in water quality. To ensure no sewage from staff and visitors be discharged into the sea, sewage should be stored on vessels or at the mariculture facilities and be regularly disposed by licensed contractor. Littering in the sea is an offence under Cap. 228 Summary Offences Ordinance and all staff and visitors should be warned against littering in the sea. Unacceptable water quality impacts due to the increased marine traffic, boating and visitor activities are not anticipated.

3.9 Mitigation Measures

3.9.1 Construction Phase

No marine work or other major source of pollution is expected from the construction phase of the Project. It is unlikely there will be a significant workforce presence during construction phase (because of the lack of major works to be conducted), and any sewage / wastewater generated should be collected at the transportation / work vessel(s) for disposal at appropriate facilities on land

3.9.2 Operation Phase

During operation, the licensees will adopt the operational measures and best practice for mariculture activities as stated in Appendix 2A. Apart from these measures, the following precautionary/ mitigation measures should be implemented to minimize water quality impact from the proposed mariculture operation at the Project site:

n Standing stock should not exceed 755.2 ton at any given time. AFCD will ensure the production scale of the Project site will not exceed the maximum standing stock level by controlling the mariculture production scale permitted under individual license.

n AFCD and mariculturists should be aware of potential occurrence of low dissolved oxygen at the Project Site by self-monitoring and the mariculturists will apply suitable control measures (e.g. aeration) as necessary.

n In case of potential circumstances (e.g. red tide event, outbreak of fish disease), the licensees will review the need of fish raft relocation and propose the fish raft relocation plan as necessary for agreement with AFCD.

n Only pellet feed or alternative feed with better feed conversion ratio will be permitted within the proposed FCZ.

n No chemically-laden solution from culture gears disinfection should be discharged into the sea.

n Onsite storage of chemicals should be controlled and minimized as far as practicable. Excess chemicals as well as chemical waste generated should be removed from the site at appropriate facilities by licensed contractor as soon as possible.

n Fuel storage onsite should be minimized, and if needed, be located at sheltered and secured location.

n Littering of the sea should be prohibited.

3.10 Residual Impact

3.10.1 Construction Phase

No marine work or other major source of pollution is expected from the construction phase of the Project. No unacceptable construction phase water quality impact is expected.

3.10.2 Operation Phase

Modelling results indicated that compliance with WQO criterion is achieved at most of the water sensitive receivers, and no project contribution to exceedance in baseline scenario would be expected from the operation phase of the Project with suitable control measure (e.g. aeration) in place as necessary. No unacceptable operation phase water quality impact is expected.

3.11 Cumulative Impact

No marine work or other major source of pollution is expected from the construction phase of the Project. No unacceptable cumulative construction phase water quality impact is expected.

For operation phase, the water quality modelling assessment has already taken into account the following sources of pollution:

n mariculture operation at the Project site;

n mariculture operation at existing FCZs within Mirs Bay and Tolo Harbour and Channel ([18]);

n proposed mariculture operation at Site B (Outer Tap Mun) and Site C (Mirs Bay);

n dry weather flow (i.e. pollution load from land drainage) within Mirs Bay and Tolo Harbour and Channel;

n rainfall-related load within Mirs Bay and Tolo Harbour and Channel;

n treated sewage effluent from the Sha Tau Kok Sewage Treatment Works; and

n other sources including pollution load from the Guangdong side of Mirs Bay.

The assessment confirmed that no unacceptable cumulative water quality impact is expected.

3.12 Environmental Monitoring and Audit

With the implementation of proposed mitigation / precautionary measures, the construction and operation of the Project would not result in unacceptable change water quality at and around the Project site. Environmental monitoring is considered not necessary for construction of the Project. For project operation, water quality monitoring is recommended when the standing stock is expected to achieve 75% of the carrying capacity ([19]) (i.e. 755.2 ton x 75% = 566.4 ton) or when the standing stock is expected to achieve 95% of the carrying capacity (i.e. 755.2 ton x 95% = 717.4 ton) for at least a month in a fish farming cycle to ensure no unacceptable change in water quality at the nearby water sensitive receivers. Detailed recommendations would be provided in the stand-alone Environmental Monitoring and Audit Manual of this EIA.

In additional to the standard EM&A exercise under EIAO, AFCD will conduct regular water quality monitoring within and outside the Project site during Project operation to check the water quality (e.g. suspended solids and nutrients) for detection of abnormality and issuance of alerts to mariculturists as part of the management measures for the Project. Real time water quality monitoring stations will also be installed by AFCD at the Project site, and notification to mariculturists for the Project site will be implemented to ensure timely actions be taken. With reference to AFCD’s previous installation of real time water quality monitoring stations at the other existing FCZs including Tung Lung Chau FCZ, Sok Kwu Wan FCZ and Lo Tik Wan FCZ, mariculturists there will be alerted in case of substantial deterioration of water quality (e.g. red tide, low dissolved oxygen level). Monitoring parameters should at least include temperature, salinity, and dissolved oxygen (level and saturation).

3.13 Conclusion

3.13.1 Construction Phase

No marine work or other major source of pollution is expected from the construction phase of the Project. No unacceptable construction phase water quality impact is expected.

3.13.2 Operation Phase

Carrying capacity estimation at the Project site has been conducted to determine the standing stock that would not result in an unacceptable change in water quality. The carrying capacity estimation indicated the Project site can support mariculture operation of 755.2 ton standing stock based on typical mariculture practice in HK without significant deterioration of water quality under the typical average condition. Accordingly, the corresponding pollution load generated is calculated for subsequent Delft3D modelling.

Delft3D water quality modelling has been conducted to predict the potential change in water quality at the WSRs of the Assessment Area. Compliance with WQO criterion is achieved at most of the identified water sensitive receivers, and no project contribution to exceedance in baseline scenario is expected from the proposed mariculture operation at the Project site. The results indicated the project operation would not result in a significant change in water quality with 755.2 ton of standing stock. Unacceptable water quality impact from Project operation is not anticipated.

Other potential sources of water quality impacts from operation have been identified and assessed. Appropriate precautionary and mitigation measures have been recommended to minimise the potential water quality impact from these sources. The licensees will also adopt the operational measures and best practice for mariculture activities as stated in Appendix 2A. No unacceptable adverse impact on water quality is expected from Project operation.

([1]) The entirety of the Tolo Harbour and Channel WCZ as well as the nearshore waters of the Mirs Bay are categorized as Secondary Contact Recreation Subzone. The predicted water quality at these areas are represented by other WSRs and thus do not have the respective WSRs for Secondary Contact Recreation Subzone only. Specifically, all WSRs identified under this Study except Site C and CR3 are located within Secondary Contact Recreation Subzone.

([2]) Similar to the case of Secondary Contact Recreation Subzone, ecological habitat for finless porpoise is an areal WSR with wide coverage. The predicted water quality at these areas are represented by other WSRs and thus do not have the respective WSRs for ecological habitat for finless porpoise only. Note that according to the latest AFCD Marine Mammal Monitoring Report 2021/22, no records of finless porpoise were recorded in the assessment area.

([3]) Similar to the case of Secondary Contact Recreation Subzone and ecological habitat for finless porpoise, spawning ground and nursery area of commercial fisheries resources is an areal WSR with wide coverage. The predicted water quality at these areas are represented by other WSRs and thus do not have the respective WSRs for spawning ground and nursery area of commercial fisheries only. Specifically, all WSRs identified under this Study except Site C are located within nursery area of commercial fisheries resources. WSRs located within spawning ground of commercial fisheries resources include M1-M4, F1-F3, CR1-2, MP1 and the Project Site itself.

([4]) Wong et.al. (2012). Project WATERMAN Carrying Capacity of Fish Culture Zones in Hong Kong – Technical Note TN-2012-02

([5]) Sim SY, Rimmer MA, Toledo JD, Sugama K, Rumengan I, Williams KC, Phillips MJ (2005). A Practical Guide to Feeds and Feed Management for Cultured Groupers. NACA, Bangkok, Thailand. 18pp.

([6]) FAO (2012). Transition from low-value fish to compound feeds in marine cage farming in Asia. Fisheries and Aquaculture Technical Paper No. 573

([7]) AFCD (2009). Fish Feed Management. In Good Aquaculture Practices Series 1.

([8]) “Leachage” refers to the release of dissolvable content from materials passing through the water column.

([9]) DIR-191/2009 Sediment Removal at Yim Tin Tsai, Yim Tin Tsai (East) Fish Culture Zones and Shuen Wan Typhoon Shelter.

([10]) Surface treatment like waterproofing and rush control is typically necessary for floating facilities such as fish rafts. By using material with surface treatment completed offsite (e.g. in a factory or workshop), the time required for onsite works can be reduced.

([11]) Carrying capacity is defined as the maximum standing stock of a FCZ without significant deterioration of water quality under the typical average condition. It is a measurement of standing stock, i.e. amount of biomass of fish being kept on site.

([12]) As a result of the relatively low baseline dissolved oxygen level at Project Site in wet season, the project scenario considered the effect of aeration at individual fish farm operation of the Project Site. Please refer to Appendix 3E for details.

([13]) Table 3.8 also include prediction at nearby EPD Marine Water Quality Monitoring Stations for reference. These EPD Marine Water Quality Monitoring Stations are not WSRs.

([14]) The service provided by dogs and cats in traditional fish rafts is expected to be no longer needed in the more modern mariculture operations. Also, these new mariculture operation is not expected to be manned continuously, thus no longer suitable for keep dogs and cats onsite.

([15]) Feedbacks from Filter Feeders: Review on the Role of Mussels in Cycling and Storage of Nutrients in Oligo- Meso- and Eutrophic Cultivation Areas. Henrice Maria Jansen, Øivind Strand, Wouter van Broekhoven, Tore Strohmeier, Marc C. Verdegem, and Aad C. Smaal (2019)

([16]) Good Aquaculture Practices Series 4 - Prevention and Treatment of Fish Diseases. AFCD, 2009

([17]) Good Aquaculture Practices Series 4 - Prevention and Treatment of Fish Diseases. AFCD, 2009

([18]) Note that other mariculture operation outside of Mirs Bay and Tolo Harbour and Channel are also taken into account indirectly through model nestling for generation of boundary condition of water quality boundary.

([19]) From the modelling results, the 95^th-percentile safety margin of the carrying capacity, which is a conservative estimate taking into account possible fluctuations in the weather, hydrodynamic and environmental conditions as well as the farming practices, is about 75% of the estimated carrying capacity under typical average condition. Therefore, it is considered representative to conduct operational water quality monitoring at 75% of the maximum allowable standing stock level to monitor potential water quality at the surrounding sensitive receivers during project operation.

3. Water Quality

3.2 Relevant Legislation and Guidelines