5 WATER QUALITY Impact

5.1 Introduction

5.1.1 This section presents the assessment results of the potential water quality impact associated with the proposed dredging works. Mitigation measures are also recommended to minimise potential adverse impacts and to ensure the acceptability of any residual impact (that is, after mitigation).

5.1.2 With reference to the EIA Study Brief (No.ESB-159/2006), the study area for this water quality assessment shall cover the North Western, Western Buffer, Victoria Harbour, Eastern Buffer, Junk Bay and Port Shelter WCZs (Figure 5.1). It is however considered that the potential water quality impacts upon the distant receivers in Western Buffer and Port Shelter WCZs would be minimal. The water quality impact assessment will focus on the areas that would be likely affected by the Project including the Victoria Harbour, Junk Bay and Eastern Buffer WCZs.

5.2 Water Quality Sensitive Receivers

5.2.1 In order to evaluate the potential water quality impacts from the Project, water quality sensitive receivers (WSRs) in the Victoria Harbour and its adjacent waters were considered. Major WSRs identified include:

l WSD Flushing Water Intakes;

l Cooling Water Intakes;

l Corals; and

l Fish Culture Zones

5.2.2 Water quality and ecological sensitive receivers identified within the Victoria Harbour and its adjacent waters are shown in Figure 5.2. These WSRs are included for water quality impact assessment as they are potentially affected by the proposed dredging works. Potential adverse impacts on far field coral communities (in terms of suspended solids elevation and sedimentation rate) and fish culture zones (in terms of oxygen depletion and suspended solids elevation) have been addressed.

5.2.3 According to the recent dive surveys, the seabed of the dredging site was found to be mainly composed of muddy and sandy bottom and of low habitat quality. Limited marine life was seen except only some small and isolated patches of single species of hard coral (Oulastrea crispate) were found in the Kai Tak Development (KTD) area and this species is common in Hong Kong waters and known to tolerate more turbid and harsh environment. Most of the isolated colonies were attached on the surface of the boulders and rocks with very low coverage (<1%) and small size (~3 cm to 8 cm). Some of them were even less than 1 cm in diameter. The isolated coral colonies found in the KTD area are not considered as sensitive coral site and are therefore not covered in this water quality impact assessment. Details of the dive surveys and full description of the identified coral colonies are provided in Section 8.

5.3 Environmental Legislation, Policies, Plans, Standards and Criteria

5.3.1 The criteria for evaluating water quality impacts in this EIA Study include:

Environmental Impact Assessment Ordinance (EIAO)

5.3.2 The Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM) was issued by EPD under Section 16 of the EIAO. It specifies the assessment method and criteria that are to be followed in this Study. Reference sections in the EIAO-TM provide the details of assessment criteria and guidelines that are relevant to the water quality impact assessment, including:

l Annex 6 – Criteria for Evaluating Water Pollution

l Annex 14 – Guidelines for Assessment of Water Pollution.

Water Quality Objectives

5.3.3 The Water Pollution Control Ordinance (WPCO) provides the major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs). Corresponding statements of Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZs based on their beneficial uses. The WQOs for the Victoria Harbour, Eastern Buffer and Junk Bay WCZs are listed in Table 5.1 to Table 5.3 respectively.

^{Table 5.1 Summary of Water Quality Objectives for Victoria Harbour WCZ}

Parameters	Objectives	Sub-Zone
Offensive odour, tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved oxygen (DO) within 2m of the seabed	Not less than 2.0mg/l for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0mg/l for 90% of samples	Marine waters
pH	To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2	Marine waters
Salinity	Change due to human activity not to exceed 10% of ambient	Whole zone
Temperature	Change due to human activity not to exceed 2 ^oC	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by human activity	Marine waters
Unionised ammonia (UIA)	Annual mean not to exceed 0.021mg/l as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total inorganic nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.4mg/l	Marine waters
Toxic substances	Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.	Whole zone
	Human activity should not cause a risk to any beneficial use of the aquatic environment.	Whole zone

Source: Statement of Water Quality Objectives (Victoria Harbour (Phases One, Two and Three) Water Control Zone).

^{Table 5.2 Summary of Water Quality Objectives for Eastern Buffer WCZ}

Parameters	Objectives	Sub-Zone
Offensive odour, tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved oxygen (DO) within 2m of the seabed	Not less than 2.0mg/l for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0mg/l for 90% of samples	Marine waters excepting fish culture subzones
	Not less than 5.0mg/l for 90% of samples	Fish culture subzones
	Not less than 4.0mg/l	Water gathering ground subzone and other Inland waters
5-Bay biochemical oxygen demand (BOD5)	Change due to waste discharges not to exceed 3mg/l	Water gathering ground subzones
	Change due to waste discharges not to exceed 5mg/l	Inland waters
Chemical oxygen demand (COD)	Change due to waste discharges not to exceed 15mg/l	Water gathering ground subzones
	Change due to waste discharges not to exceed 30mg/l	Inland waters
PH	To be in the range of 6.5 – 8.5, change due to waste discharges not to exceed 0.2	Marine waters
	To be in the range of 6.5 – 8.5	Water gathering ground subzones
	To be in the range of 6.0 – 9.0	Inland waters
Salinity	Change due to waste discharges not to exceed 10% of ambient	Whole zone
Temperature	Change due to waste discharges not to exceed 2 ^oC	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities	Marine waters
	Change due to waste discharges not to exceed 20mg/l of annual median	Water gathering ground subzones
	Change due to waste discharges not to exceed 25mg/l of annual median	Inland waters
Unionized ammonia (UIA)	Annual mean not to exceed 0.021mg/l as unionized form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total inorganic nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.4mg/l	Marine waters
Dangerous substances	Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms	Whole zone
	Waste discharges should not cause a risk to any beneficial use of the aquatic environment	Whole zone
Bacteria	Not exceed 610 per 100ml, calculated as the geometric mean of all samples collected in one calendar year	Fish culture subzones
	Less than 1 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Water gathering ground subzones
	Not exceed 1000 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Inland waters
Colour	Change due to waste discharges not to exceed 30 Hazen units	Water gathering ground
	Change due to waste discharges not to exceed 50 Hazen units	Inland waters

Source: Statement of Water Quality Objectives (Eastern Buffer Water Control Zone).

^{Table 5.3 Summary of Water Quality Objectives for Junk Bay WCZ}

Parameters	Objectives	Sub-Zone
Offensive odour, tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved oxygen (DO) within 2m of the seabed	Not less than 2.0mg/l for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0mg/l for 90% of samples	Marine waters excepting fish culture subzones
	Not less than 5.0mg/l for 90% of samples	Fish culture subzones
	Not less than 4.0mg/l	Inland waters
5-Bay biochemical oxygen demand (BOD5)	Change due to waste discharges not to exceed 5mg/l	Inland waters
Chemical oxygen demand (COD)	Change due to waste discharges not to exceed 30mg/l	Inland waters
pH	To be in the range of 6.5 - 8.5, change due to waste discharges not to exceed 0.2	Marine waters
	To be in the range of 6.0 –9.0	Inland waters
Salinity	Change due to waste discharges not to exceed 10% of ambient	Whole zone
Temperature	Change due to waste discharges not to exceed 2 ^oC	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities	Marine waters
	Change due to waste discharges not to exceed 25mg/l of annual median	Inland waters
Unionized ammonia (UIA)	Annual mean not to exceed 0.021mg/l as unionized form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total inorganic nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.3mg/l	Marine waters
Dangerous substances	Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms	Whole zone
	Waste discharges should not cause a risk to any beneficial use of the aquatic environment	Whole zone
Bacteria	Not exceed 610 per 100ml, calculated as the geometric mean of all samples collected in one calendar year	Secondary contact recreation subzones and fish culture subzones
	Not exceed 1000 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Inland waters
Colour	Change due to waste discharges not to exceed 50 Hazen units	Inland waters

Source: Statement of Water Quality Objectives (Junk Bay Water Control Zone).

Water Supplies Department (WSD) Water Quality Criteria

5.3.4 Besides the WQOs stipulated under the WPCO, the WSD has specified a set of objectives for water quality at flushing water intakes. The list is shown in Table 5.4. The target limit for suspended solids (SS) at these intakes is 10mg/l or less.

^{Table 5.4 WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes}

Parameter (in mg/l unless otherwise stated)	Target Limit
Colour (HU)	< 20
Turbidity (NTU)	< 10
Threshold Odour Number (odour unit)	< 100
Ammoniacal Nitrogen	< 1
Suspended Solids	< 10
Dissolved Oxygen	> 2
Biochemical Oxygen Demand	< 10
Synthetic Detergents	< 5
E. coli (no. per 100ml)	< 20,000

Cooling Water Intake Standards

5.3.5 Based on a questionnaire survey conducted under the approved Comprehensive Feasibility Study for Wan Chai Development Phase II (CFSWDII) EIA ^([1]), a SS limit of 40mg/l was adopted as the assessment criterion for Admiralty Centre intake and MTRC South intake. No information on the SS limit is available for other cooling water intakes. These findings have been confirmed by a telephone survey conducted under the recent approved EIA for the Hong Kong Convention and Exhibition Centre (HKCEC) Atrium Link Extension (ALE). The locations of the cooling water intakes are shown in Figure 5.2.

Technical Memorandum

5.3.6 Discharges of effluents are subject to control under the WPCO. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluents. Any effluent from the Project must comply with the standards for effluents discharged into the foul sewers, inshore waters or marine waters of Victoria Harbour WCZ, as given in the TM-DSS.

Practice Note

5.3.7 A Practice Note for Professional Persons (ProPECC) was issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with ten types of discharge from a construction site. These include surface runoff, groundwater, boring and drilling water, bentonite slurry, water for testing and sterilisation of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities. Practices given in the ProPECC PN 1/94 should be followed as far as possible during construction to minimise the water quality impact due to construction activities.

Assessment Criteria for Coral

5.3.8 Potential impacts on benthic organisms, including corals, may arise through excessive sediment deposition. The magnitude of impacts on marine ecological sensitive receivers was assessed based on the predicted sedimentation rate.

5.3.9 According to Pastorok and Bilyard ⁽[2]⁾ and Hawker and Connell ⁽[3]⁾, a sedimentation rate higher than 0.1 kg/m²/day would introduce moderate to severe impact upon corals. This criterion has been adopted for protecting the corals in Hong Kong under other approved EIAs such as Tai Po Sewage Treatment Works Stage 5 EIA ^([4]), Further Development of Tseung Kwan O Feasibility Study EIA, Wan Chai Reclamation Phase II EIA, Eastern Waters MBA Study ^([5]), West Po Toi MBA Study ^([6]) and Tai Po Gas Pipeline Study ^([7]). This sedimentation rate criterion is considered to offer sufficient protection to marine ecological sensitive receivers and is anticipated to guard against unacceptable impacts. This protection has been confirmed by previous EM&A results which have indicated no adverse impacts to corals have occurred when this assessment criterion has been adopted.

5.3.10 The assessment criteria used in this Project for protection of corals identified at Green Island, Junk Bay and Cape Collinson is also based on the WQO for SS established under the WPCO, i.e. the SS elevations should be less than 30% of ambient baseline conditions. The WQO for SS has also been adopted under the approved Tai Po Sewage Treatment Works Stage 5 EIA as one of the assessment criteria for evaluating the water quality impact from the sewage effluent on corals identified at Tolo Harbour, Green Island and Junk Bay.

5.3.11 The above assessment criteria would be used to assess water quality impact to coral habitats (i.e. the far field ecological sensitive receivers) as identified and indicated in Figure 5.2. As discussed in Section 5.2, the isolated coral colonies found in the KTD area are not considered as sensitive coral site and are therefore not covered in this water quality impact assessment.

Sediment Quality Assessment Criteria

5.3.12 Environment, Transport and Works Bureau (ETWB) Technical Circular Works (TCW) No. 34/2002 “Management of dredged/excavated sediment” sets out the procedure for seeking approval to dredge / excavate sediment and the management framework for marine disposal of dredged / excavated sediment. This Technical Circular outlines the requirements to be followed in assessing and classifying the sediment. Sediments are categorized with reference to the Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL), as follows:

l Category L Sediment with all contaminant levels not exceeding the LCEL. The material must be dredged, transported and disposed of in a manner that minimises the loss of contaminants either into solution or by suspension.

l Category M Sediment with any one or more contaminant levels exceeding the LCEL and none exceeding the UCEL. The material must be dredged and transported with care, and must be effectively isolated from the environment upon final disposal unless appropriate biological tests demonstrate that the material will not adversely affect the marine environment.

l Category H Sediment with any one or more contaminant levels exceeding the UCEL. The material must be dredged and transported with great care, and must be effectively isolated from the environment upon final disposal.

5.3.13 The sediment quality criteria for the classification of sediment are presented in Table 5.5.

^{Table 5.5 Sediment Quality Criteria for the Classification of Sediment}

Contaminants	LCEL	UCEL
Heavy Metal (mg/kg dry weight)
Cadmium (Cd)	1.5	4
Chromium (Cr)	80	160
Copper (Cu)	65	110
Mercury (Hg)	0.5	1
Nickel (Ni)	40	40
Lead (Pb)	75	110
Silver (Ag)	1	2
Zinc (Zn)	200	270
Metalloid (mg/kg dry weight)
Arsenic	12	42
Organic-PAHs (µg/kg dry weight)
PAHs (Low Molecular Weight)	550	3160
PAHs (High Molecular Weight)	1700	9600
Organic-non-PAHs (µg/kg dry weight)
Total PCBs	23	180

Source: Appendix A of ETWB TCW No. 34/2002 Management of Dredged / Excavated Sediment

Note: LCEL – Lower Chemical Exceedance Level

UCEL – Upper Chemical Exceedance Level

5.4 Description of the Environment

Marine Water Quality in Victoria Harbour

5.4.1 The marine water quality monitoring data routinely collected by EPD in the Victoria Harbour were used to establish the baseline condition. A summary of water quality data for selected EPD monitoring stations extracted from EPD’s publication “20 Years of Marine Water Quality in Hong Kong (1986 – 2005)” (which is the latest version available at the time of preparing this EIA Report) is presented in Table 5.6 and Table 5.7 for the Victoria Harbour WCZ (VM1 VM2, VM4-VM8, VM12 and VM15), Eastern Buffer WCZ (EM1, EM2) and Junk Bay WCZ (JM3, JM4). Locations of the monitoring stations are shown in Figure 5.2. As the HATS Stage I was commissioned in late 2001, the data shown in Table 5.6 and Table 5.7 represent the situation after the commissioning of HATS Stage I.

Victoria Harbour

5.4.2 In 2005, the marked improvements in the eastern Victoria Harbour (VM1 and VM2) and moderate improvements in the mid harbour area (VM4 and VM5) since HATS Stage 1 was commissioned were generally sustained. Several monitoring stations in the WCZ are located close to sewage outfalls, including VM5 (Wan Chai East and Wan Chai West PTW outfall), VM6 (Central PTW outfall), VM4 (North Point PTW outfall) and VM8 (Stonecutters Island STW – HATS Stage I outfall). The water quality at these stations was inevitably subject to the direct impact of sewage discharge from these outfalls.

5.4.3 The compliance with WQO for TIN was 50% in 2005. Full compliance with WQOs for DO and UIA was achieved in 2005 at all stations (Table 5.6).

Junk Bay and Eastern Buffer

5.4.4 The water quality at Junk Bay and Eastern Buffer was stable and improvements since HATS Stage 1 were sustained. Full compliance with all the WQOs was achieved in 2005 (Table 5.7).

^{Table 5.6 Summary Statistics of 2005 Marine Water Quality in Victoria Harbour}

Parameter		Victoria Harbour East		Victoria Harbour Central			Victoria Harbour West		Stonecutters Island	WPCO WQO (in marine waters)
		VM1	VM2	VM4	VM5	VM6	VM7	VM8	VM15
Temperature (^oC)		22.6 (15.7 – 27.9)	22.9 (15.8 – 28.0)	22.9 (15.8 – 27.8)	23.0 (15.9 -27.9)	23.0 (15.9 – 27.8)	23.1 (15.8 – 27.9)	23.1 (15.6 – 27.7)	23.0 (16.0 – 27.8)	Not more than 2 ^oC in daily temperature range
Salinity		32.3 (30.4 – 33.4)	31.9 (28.5 – 33.3)	31.8 (28.9 – 33.2)	31.4 (27.3 – 32.9)	31.3 (26.8 – 32.8)	30.9 (26.3 – 32.8)	31.1 (27.4 – 32.9)	31.3 (26.6 – 32.9)	Not to cause more than 10% change
Dissolved Oxygen (DO) (% Saturation)	Depth average	79 (59 – 94)	78 (66 – 92)	75 (63 – 88)	76 (68 – 99)	77 (68 – 96)	78 (72 – 99)	80 (61 – 108)	77 (64 – 105)	Not available
	Bottom	78 (46 – 93)	77 (54 – 90)	74 (51 – 88)	74 (46 – 99)	73 (45 -94)	75 (54 – 94)	78 (35 – 108)	74 (43 – 101)	Not available
Dissolved Oxygen (DO) (mg/l)	Depth average	5.7 (4.2 – 6.9)	5.6 (4.4 – 6.8)	5.4 (4.4 – 6.6)	5.5 (4.7 – 6.6)	5.5 (4.8 – 6.5)	5.6 (4.9 – 6.6)	5.8 (4.3 – 7.1)	5.5 (4.5 – 7.0)	Not less than 4mg/l for 90% of the samples
	Bottom	5.6 (3.3 – 6.9)	5.6 (3.8 – 6.8)	5.3 (3.6 – 6.5)	5.3 (3.3 – 6.6)	5.3 (3.2 – 6.5)	5.4 (3.8 – 6.5)	5.6 (2.5 – 7.1)	5.3 (3.1 – 6.7)	Not less than 2mg/l for 90% of the samples
pH		8.1 (7.8 – 8.3)	8.1 (7.7 – 8.3)	8.0 (7.7 – 8.3)	8.0 (7.6 – 8.3)	8.0 (7.6 – 8.2)	8.0 (7.7 – 8.2)	8.1 (7.7 – 8.2)	8.0 (7.6 – 8.2)	6.5 - 8.5 (± 0.2 from natural range)
Secchi disc Depth (m)		2.3 (1.5 – 2.8)	2.2 (1.2 – 3.5)	2.1 (1.5 – 3.2)	2.1 (1.3 – 3.1)	2.1 (1.2 – 3.3)	1.8 (0.9 – 3.2)	1.9 (1.2 – 2.5)	1.9 (1.2 – 2.7)	Not available
Turbidity (NTU)		10.0 (5.1 – 16.2)	9.8 (4.8 – 15.8)	9.6 (4.5 – 15.3)	9.8 (4.9 – 14.5)	9.8 (5.0 – 14.8)	10.8 (5.9 – 16.1)	11.9 (5.4 – 22.0)	10.7 (5.8 – 16.2)	Not available
Suspended Solids (SS) (mg/l)		4.5 (0.9 – 10.8)	3.6 (1.3 – 8.5)	3.6 (1.3 – 9.8)	3.4 (1.7 – 5.3)	3.7 (1.3 – 8.2)	4.1 (2.1 – 8.7)	5.2 (1.8 – 16.3)	5.1 (2.1 – 10.3)	Not more than 30% increase
5-day Biochemical Oxygen Demand (BOD5) (mg/l)		0.8 (0.5 – 1.2)	0.9 (0.4 – 1.5)	0.9 (0.5 – 1.1)	1.1 (0.6 – 1.4)	0.9 (0.4 – 1.4)	1.0 (0.6 – 1.4)	0.8 (0.5 – 1.4)	0.8 (0.5 – 1.2)	Not available
Nitrite Nitrogen (NO2-N) (mg/l)		0.02 (0.01 – 0.05)	0.02 (0.01 – 0.05)	0.03 (0.01 – 0.05)	0.03 (0.01 – 0.05)	0.03 (0.01 – 0.05)	0.03 (0.01 – 0.06)	0.04 (0.01 – 0.07)	0.03 (0.02 – 0.06)	Not available
Nitrate Nitrogen (NO3-N) (mg/l)		0.10 (0.04 – 0.17)	0.12 (0.03 – 0.23)	0.13 (0.05 – 0.24)	0.15 (0.05 – 0.31)	0.16 (0.06 – 0.34)	0.19 (0.08 – 0.45)	0.18 (0.08 – 0.49)	0.16 (0.09 – 0.31)	Not available
Ammonia Nitrogen (NH3-N) (mg/l)		0.09 (0.05 – 0.16)	0.13 (0.04 – 0.21)	0.15 (0.06 – 0.27)	0.19 (0.06 – 0.29)	0.19 (0.07 – 0.26)	0.21 (0.12 – 0.32)	0.18 (0.09 – 0.30)	0.23 (0.08 – 0.32)	Not available
Unionised Ammonia (UIA) (mg/l)		0.004 (0.002 – 0.010)	0.006 (0.002 – 0.015)	0.006 (0.003 – 0.015)	0.007 (0.005 – 0.015)	0.008 (0.004 – 0.014)	0.009 (0.004 – 0.08)	0.009 (0.003 – 0.022)	0.009 (0.005 – 0.014)	Not more than 0.021mg/l for annual mean
Total Inorganic Nitrogen (TIN) (mg/l)		0.22 (0.11 – 0.32)	0.28 (0.08 – 0.46)	0.31 (0.12 – 0.54)	0.37 (0.12 – 0.64)	0.38 (0.14 – 0.65)	0.43 (0.28 – 0.83)	0.40 (0.22 – 0.76)	0.42 (0.19 – 0.63)	Not more than 0.4mg/l for annual mean
Total Nitrogen (TN) (mg/l)		0.34 (0.23 – 0.47)	0.43 (0.22 – 0.63)	0.47 (0.26 – 0.69)	0.55 (0.28 – 0.77)	0.55 (0.29 – 0.79)	0.58 (0.47 – 0.93)	0.59 (0.34 – 1.16)	0.58 (0.36 – 0.76)	Not available
Orthophosphate Phosphorus (PO4) (mg/l)		0.02 (0.01 – 0.03)	0.03 (<0.01 – 0.04)	0.03 (0.01 – 0.04)	0.04 (0.01 – 0.05)	0.03 (0.01 – 0.05)	0.04 (0.02 – 0.05)	0.03 (0.01 – 0.05)	0.04 (0.02 – 0.05)	Not available
Total Phosphorus (TP) (mg/l)		0.03 (0.02 – 0.05)	0.04 (0.02 – 0.06)	0.05 (0.03 – 0.06)	0.05 (0.03 – 0.07)	0.05 (0.03 – 0.07)	0.05 (0.04 – 0.06)	0.05 (0.03 – 0.17)	0.05 (0.03 – 0.07)	Not available
Chlorophyll-a (µg/l)		2.5 (0.9 – 6.0)	2.4 (0.8 – 6.0)	2.4 (0.9 – 7.2)	2.8 (0.8 – 9.1)	2.6 (0.8 – 9.0)	2.2 (0.8 – 7.6)	2.0 (0.9 – 6.4)	3.2 (0.7 – 12.3)	Not available
E coli (cfu/100ml)		640 (88 – 4500)	1600 (120 – 31000)	2400 (310 – 11000)	7700 (2500 – 23000)	5700 (1200 – 33000)	9100 (1200 – 35000)	4900 (790 – 40000)	5400 (490 – 22000)	Not available
Faecal Coliforms (cfu/100ml)		1300 (300 – 9100)	3600 (340 – 50000)	5200 (770 – 33000)	17000 (6800 – 40000)	12000 (2300 – 89000)	21000 (2700 – 130000)	12000 (100 – 140000)	13000 (1800 – 97000)	Not available

Notes: 1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2. Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3. Data in brackets indicate the ranges.

^{Table 5.7 Summary Statistics of 2005 Marine Water Quality in Junk Bay and Eastern Buffer}

Parameter		Junk Bay WCZ			Eastern Buffer WCZ
		JM3	JM4	WPCO WQO (in marine waters)	EM1	EM2	WPCO WQO (in marine waters)
Temperature (^oC)		23.0 (15.9 – 27.9)	22.8 (15.8 – 27.9)	Not more than 2 ^oC in daily temperature range	22.7 (15.8 – 28.0)	22.8 (15.7 – 27.9)	Not more than 2 ^oC in daily temperature range
Salinity		32.1 (27.0 – 33.5)	32.3 (29.0 – 33.7)	Not to cause more than 10% change	32.4 (29.7 – 33.8)	32.4 (29.2 – 33.8)	Not to cause more than 10% change
Dissolved Oxygen (DO) (% Saturation)	Depth average	83 (53 – 101)	81 (56 – 95)	Not available	80 (64 – 97)	84 (68 -109)	Not available
	Bottom	79 (45 – 96)	78 (50 – 96)	Not available	79 (51 – 98)	82 (51 – 101)	Not available
Dissolved Oxygen (DO) (mg/l)	Depth average	5.9 (3.7 – 7.0)	5.8 (4.0 – 7.2)	Not less than 4mg/l for 90% of the samples	5.7 (4.3 – 6.8)	6.0 (4.7 – 7.2)	Not less than 4mg/l for 90% of the samples
	Bottom	5.7 (3.2 – 6.9)	5.6 (3.6 – 7.1)	Not less than 2mg/l for 90% of the samples	5.7 (3.7 – 6.8)	5.9 (3.6 – 7.1)	Not less than 2mg/l for 90% of the samples
pH		8.2 (7.9 – 8.5)	8.2 (7.8 – 8.5)	6.5 - 8.5 (± 0.2 from natural range)	8.1 (7.8 – 8.4)	8.2 (7.8 – 8.5)	6.5 - 8.5 (± 0.2 from natural range)
Secchi disc Depth (m)		2.6 (2.0 – 3.5)	2.4 (1.6 – 3.5)	Not available	2.1 (1.5 – 2.7)	2.4 (1.5 – 3.7)	Not available
Turbidity (NTU)		9.8 (4.5 – 15.6)	9.8 (5.1 – 14.4)	Not available	10.0 (5.0 – 14.9)	9.7 (5.1 – 14.1)	Not available
Suspended Solids (SS) (mg/l)		2.7 (1.3 – 4.3)	3.2 (1.1 – 8.0)	Not more than 30% increase	3.2 (1.3 – 5.0)	3.2 (0.7 – 6.5)	Not more than 30% increase
5-day Biochemical Oxygen Demand (BOD5) (mg/l)		0.7 (0.2 – 1.5)	0.6 (0.2 – 1.0)	Not available	0.6 (0.2 – 1.0)	0.5 (0.2 – 1.1)	Not available
Nitrite Nitrogen (NO2-N) (mg/l)		0.02 (<0.01 – 0.05)	0.02 (<0.01 – 0.05)	Not available	0.02 (0.01 – 0.05)	0.01 (<0.01 – 0.05)	Not available
Nitrate Nitrogen (NO3-N) (mg/l)		0.08 (0.02 – 0.16)	0.07 (0.03 – 0.15)	Not available	0.07 (0.03 – 0.17)	0.06 (0.02 – 0.18)	Not available
Ammonia Nitrogen (NH3-N) (mg/l)		0.06 (0.04 – 0.12)	0.06 (0.03 – 0.13)	Not available	0.07 (0.03 – 0.12)	0.05 (0.02 – 0.09)	Not available
Unionised Ammonia (UIA) (mg/l)		0.004 (0.001 – 0.009)	0.004 (0.001 – 0.010)	Not more than 0.021mg/l for annual mean	0.004 (0.001–0.013)	0.003 (0.001 – 0.012)	Not more than 0.021mg/l for annual mean
Total Inorganic Nitrogen (TIN) (mg/l)		0.16 (0.08 – 0.23)	0.15 (0.08 – 0.24)	Not more than 0.3mg/l for annual mean	0.16 (0.07 – 0.25)	0.12 (0.05 – 0.25)	Not more than 0.4mg/l for annual mean
Total Nitrogen (TN) (mg/l)		0.27 (0.17 – 0.39)	0.26 (0.14 – 0.33)	Not available	0.27 (0.14 – 0.40)	0.23 (0.13 – 0.40)	Not available
Orthophosphate Phosphorus (PO4) (mg/l)		0.01 (<0.01 – 0.03)	0.02 (0.01 – 0.02)	Not available	0.02 (0.01 – 0.02)	0.01 (0.01 – 0.02)	Not available
Total Phosphorus (TP) (mg/l)		0.03 (0.02 – 0.03)	0.03 (0.02 – 0.04)	Not available	0.03 (0.02 – 0.05)	0.02 (0.02 – 0.04)	Not available
Chlorophyll-a (µg/l)		2.1 (0.6 – 8.6)	1.8 (0.5 – 4.9)	Not available	1.7 (0.8 – 5.1)	1.7 (0.5 – 5.1)	Not available
E. coli (cfu/100ml)		67 (15 – 7100)	100 (23 – 550)	Not available	130 (29 – 1300)	36 (2 – 1800)	Not available
Faecal Coliforms (cfu/100ml)		180 (66 – 10000)	240 (40 – 1200)	Not available	290 (41 – 4200)	86 (3 – 4400)	Not available

Notes: 1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2. Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3. Data in brackets indicate the ranges.

Marine Water Quality within Kwun Tong and To Kwa Wan Typhoon Shelter

5.4.5 A summary of published EPD monitoring data (in 2005) collected from the monitoring stations at the Kwun Tong Typhoon Shelter (VT4) and To Kwa Wan Typhoon Shelter (VT11) is presented in Table 5.8 ⁽[8]⁾. Locations of VT4 and VT11 are shown in Figure 5.2.

^{Table 5.8 Summary Statistics of 2005 Marine Water Quality at the Kwun Tong and To Kwa Wan Typhoon Shelter}

Parameter		VT4	VT11	WPCO WQOs (in marine waters)
Temperature (^oC)		22.6 (16.2 – 26.2)	22.4 (16.0 – 26.3)	Not more than 2 ^oC in daily temperature range
Salinity (ppt)		30.0 (27.6 – 31.5)	31.2 (27.6 – 32.7)	Not to cause more than 10% change
Dissolved Oxygen (DO) (% saturation)	Depth average	60 (37 – 97)	85 (55 – 115)	Not available
	Bottom	64 (47 – 72)	84 (56 – 110)	Not available
Dissolved Oxygen (DO) (mg/l)	Depth average	4.3 (2.9 – 6.7)	6.1 (3.7 – 8.0)	Not less than 4mg/l for 90% of the samples
	Bottom	4.7 (3.2 – 5.5)	6.1 (3.8 – 7.7)	Not less than 2mg/l for 90% of the samples
pH value		8.0 (7.7 – 8.1)	8.2 (8.0 – 8.4)	6.5 - 8.5 (± 0.2 from natural range)
Secchi disc (m)		1.2 (0.7 – 1.7)	1.7 (1.0 – 2.2)	Not available
Turbidity (NTU)		8.6 (4.9 – 9.8)	8.8 (5.6 – 10.7)	Not available
Suspended Solids (SS) (mg/l)		2.6 (1.3 – 3.9)	4.4 (1.3 – 7.3)	Not more than 30% increase
Silica (as SiO2) (mg/l)		1.3 (0.5 – 2.2)	0.8 (0.3 – 1.1)	Not available
5-day Biochemical Oxygen Demand (BOD5) (mg/l)		2.1 (1.4 – 4.4)	1.5 (0.7 – 3.4)	Not available
Nitrite Nitrogen (NO2-N) (mg/l)		0.11 (0.03 – 0.22)	0.03 (0.02 – 0.05)	Not available
Nitrate Nitrogen (NO3-N) (mg/l)		0.38 (0.22 – 0.63)	0.16 (0.09 – 0.23)	Not available
Ammoniacal Nitrogen (NH3-N) (mg/l)		0.44 (0.26 – 0.7)	0.14 (0.06 – 0.19)	Not available
Unionised Ammonia (UIA) (mg/l)		0.015 (0.007 – 0.029)	0.008 (0.004 – 0.015)	Not more than 0.021mg/l for annual mean
Total Inorganic Nitrogen (TIN) (mg/l)		0.93 (0.63 – 1.16)	0.33 (0.27 – 0.41)	Not more than 0.4mg/l for annual mean
Total Nitrogen (TN) (mg/l)		1.23 (0.84 – 1.73)	0.53 (0.51 – 0.58)	Not available
Ortho-Phosphate (PO4) (mg/l)		0.18 (0.10 – 0.33)	0.03 (0.01 – 0.04)	Not available
Total Phosphorus (TP) (mg/l)		0.21 (0.13 – 0.37)	0.05 (0.04 – 0.09)	Not available
Chlorophyll-a (µg/l)		10.6 (0.6 – 44.7)	7.3 (0.5 – 32.3)	Not available
E. coli (cfu per 100ml)		8,200 (1,500 – 26,000)	690 (150 – 2,800)	Not available
Faecal Coliforms (cfu per 100ml)		16,000 (3,200 – 50,000)	1,900 (880 – 7,200)	Not available

Note: 1. Except as specified, data presented are depth-averaged data.

2. Data presented are annual arithmetic means except for E. coli and faecal coliforms that are geometric means.

3. Data enclosed in brackets indicate ranges.

5.4.6 Due to the embayment form and reduced flushing capacity of the typhoon shelter, marine water within the typhoon shelter is vulnerable to pollution. In 2005, high levels of E.coli were recorded at the Kwun Tong and To Kwa Wan Typhoon Shelters indicating faecal contamination. High level of total inorganic nitrogen (TIN) and ammonia was also recorded at Kwun Tong Typhoon Shelter which breached the WQOs.

Sediment Quality

5.4.7 A marine site investigation (SI) was conducted to determine the contamination level of the sediments within the proposed dredging area for the cruise terminal. Phase 1 of the marine SI works for the Project commenced on 15 January 2007 and was completed on 23 January 2007 and comprised 30 sampling stations (stations A01-A30) (refer to Figure 6.1). Phase 2 of the marine SI works commenced on 23 February 2007 and was completed on 10 March 2007 and comprised 41 sampling stations (stations B01-B41) (refer to Figure 6.1). The marine SI works comprised grab sampling and vibrocoring to obtain sediment samples for chemical testing and biological screening.

5.4.8 The results of marine sediment quality analysis from the marine SI works at the Project site are presented in Section 6. The sediment testing results available from the marine SI works indicates that about 69% of marine sediments to be dredged at the Project area were classified as uncontaminated (or Category L sediment). The estimated extent of contaminated mud is illustrated in Figure 6.1. Details of the sediment quality criteria and estimated volumes of contaminated sediments to be generated from the Project are given in Section 6.

5.4.9 A summary of published EPD sediment data (in 2005) collected from the monitoring stations at the Kwun Tong Typhoon Shelter (VS14), To Kwa Wan Typhoon Shelter (VS20) and Victoria Harbour (VS3) in vicinity of the Project site is presented in Table 5.9 ⁽[9]⁾.

^{Table 5.9 Summary Statistics of 2005 Bottom Sediment Quality}

Contaminants	VS14	VS20	VS3	Sediment Quality Criteria
				LCEL	UCEL
Heavy Metal (mg/kg dry weight)
Cadmium (Cd)	4.2 (3.0 – 5.3)	1 (0.4 – 1.6)	0.4 (<0.1 - 0.6)	1.5	4
Chromium (Cr)	405 (250 – 560)	100 (64 – 130)	38 (12 – 60)	80	160
Copper (Cu)	2640 (1700 – 4000)	629 (410 – 810)	112 (27 – 190)	65	110
Mercury (Hg)	1.03 (0.77 – 1.4)	1.12 (0.65 – 1.4)	0.32 (<0.05 – 0.72)	0.5	1
Nickel (Ni)	113 (68 – 170)	36 (29 – 40)	18 (6 – 27)	40	40
Lead (Pb)	154 (100 – 230)	99 (77 – 130)	42 (21 – 62)	75	110
Silver (Ag)	11.9 (8.0 – 16.0)	5.7 (3.0 – 9.0)	3.3 (1.0 – 5.6)	1	2
Zinc (Zn)	526 (420 – 670)	264 (180 – 320)	134 (17 – 230)	200	270
Metalloid (mg/kg dry weight)
Arsenic	8.1 (5.9 – 10.0)	7.7 (6.3 – 9.0)	6.1 (0.9 – 9.4)	12	42
Organic-PAHs (g/kg dry weight)
PAHs (Low Molecular Weight)	164 (145 – 191)	8544 (2974 – 17405)	104 (90 – 124)	550	3160
PAHs (High Molecular Weight)	1429 (1052 – 2058)	62412 (2137 – 132600)	321 (66 – 550)	1700	9600
Organic-non-PAHs (g/kg dry weight)
Total PCBs	186 (35 – 293)	78 (18 – 120)	19 (18 – 21)	23	180

Note: Shaded value – Exceed the LCEL – Lower Chemical Exceedance Level

Shaded and bolded value – Exceed the UCEL – Upper Chemical Exceedance Level

5.4.10 The sediments collected at both typhoon shelters are considered highly contaminated in terms of heavy metals and trace organics (PCBs and PAHs) based on the 2005 field data. For Station VS3 located in the Victoria Harbour channel, the sediment quality is relatively better but still exceeds the criteria for heavy metals. On the other hand, levels of metalloid (arsenic) were low at all the stations.

5.5 Identification of Environmental Impacts

5.5.1 Details of the proposed dredging works for cruise terminal are given in Section 2. Figure 2.4 shows the dredging stages. Estimated volume of dredged materials is provided in Section 2 and further discussed in Section 6. Key water quality concerns during the capital and maintenance dredging works are identified as follows:

Suspended Solids

5.5.2 Dredging works will disturb the marine bottom sediment. As a result, fine sediment (less than 63 µm) will be lost to suspension causing an increase in SS concentrations in the water column. The suspended solids will be transported by currents to form sediment plumes along the tidal flows, which will gradually resettle. Potential impacts on water quality from dredging will vary according to the quantities and level of contamination, as well as the nature and locations of the WSRs at or near the dredging sites. These impacts are summarised as follows:

l Increased suspension of solids in the water column during dredging activities, with possible consequence of reducing DO levels and increasing nutrient levels.

l Release of previously bound organic and inorganic constituents such as heavy metals, polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) into the water column, either via suspension or by disturbance as a result of dredging activities.

l Release of the same contaminants due to leakage and spillage as a result of poor handling and overflow from barges during dredging and transport.

5.5.3 Any sediment plume will cause the ambient suspended solids concentrations to be elevated and the extent of elevation will determine whether or not the impact is adverse or not. The determination of the acceptability of any elevation is based on the WQO. The WQO of SS is defined as being an allowable elevation of 30% above the background. For assessing the environmental impacts of released SS, the ambient value is represented by the 90th percentile (90%ile) of baseline (pre-Project) concentrations for conservative assessment.

General Construction Activities

5.5.4 The general construction works could result from the accumulation of solid waste such as construction materials, and liquid waste such as sewage effluent from the construction work force, spillage of oil, diesel or solvents by vessels and vehicles involved during dredging and transport. If uncontrolled, any of these could lead to deterioration in water quality. Increased nutrient levels result from contaminated discharges and sewage effluent could also lead to a number of secondary water quality impacts including decreases in DO concentrations and localised increase in NH₃-N concentrations which could stimulate algal growth and reduction in oxygen levels.

5.5.5 Sewage will arise from sanitary facilities provided for the on-site construction work force. It is characterised by high level of BOD, NH₃-N and E.coli counts. There will be no public sewers available for domestic sewage discharge on-site.

5.6 Assessment Methodology

5.6.1 To assess the potential water quality impacts due to the capital and maintenance dredging, the sources and natures of water pollution to be generated have been identified and their impacts have been quantified where practicable.

Kai Tak Development (KTD) Components

Proposed Dredging Works for Cruise Terminal

Capital Dredging

5.6.2 The capital dredging works will be carried out in two stages, in the areas as indicated in Figure 2.4. The scale and extent of dredging presented in this EIA are based on the outcome of the detailed engineering assessment including vessel navigation simulations. The assessment assumptions (including the dredging rates) represent the worst case.

5.6.3 The rates of dredging from existing seabed to provide the proposed manoeuvring area will not exceed 4,000m³ per day during both Stage 1 and Stage 2 dredging period. The maximum production rate of 4,000m³ per day during the Stage 1 capital dredging has taken account of the required dredging for removal of the abandoned KTR submarine outfall for worst case assessment (refer to Section 2.1).

5.6.4 The dredging at or near the seawall for berth construction will also be conducted at a maximum rate of 4,000m³ per day. It is assumed in the modelling assessment that dredging for berth construction will be undertaken concurrently with the Stage 1 dredging in the manoeuvring area for worst case assessment. Therefore, the maximum dredging rate assumed for modelling would be 8,000 m³ per day during the Stage 1 dredging period (including the dredging of 4,000 m³ per day at or near the seawall for berth construction using 2 closed grab dredgers plus the dredging of 4,000 m³ per day in the manoeuvring area for the Phase I Berth using another 2 closed grab dredgers). It is assumed that no more than 2 grab dredgers will be in operation simultaneously during the Stage 2 dredging period.

5.6.5 Dredging required for operation of the Phase I Berth is currently scheduled to be carried out during the period from later half of 2008 to 2011 as the first stage. The water quality impact assessment for Stage 1 dredging has considered the cumulative impacts from all concurrent activities anticipated in the period from 2008 to 2011 to allow the possible change of the Stage 1 dredging programme to commence in 2008. As the programme for Stage 2 dredging is unconfirmed, for the purpose of this EIA, it is assumed that the Stage 2 dredging would be carried out from 2013 to 2014, following the Stage 1 dredging and decommissioning and removal of the existing gas mains in 2013. The period of 2013 - 2014 is selected as the time horizon for Stage 2 dredging for impact assessment only. The selected time horizon is the earliest possible timing for Stage 2 dredging. Our modelling assessment for Stage 2 dredging has included the impacts of all possible concurrent marine works anticipated in or beyond 2012 and therefore is a worst-case scenario.

5.6.6 Phasing of the proposed dredging works with reference to other concurrent marine works as discussed below is provided in Appendix 2.1.

Maintenance Dredging

5.6.7 It is assumed that the siltation rate at the Project site would be in the order of 50mm to 100mm per year (refer to Section 2.7 of this EIA report). As such up to 500mm of sediment will need to be dredged every 5 to 10 years. Given that the area needed for manoeuvring of vessels is approximately 700,000 m², then this represents a dredged volume of approximately 350,000 m³ every 5 to 10 years. This would take one grab dredger approximately 8 months to dredge the whole site for both berths assuming a maximum rate of 2,000m³ per day and limited access. Dredging duration for each berth would be less than 6 months. Maintenance dredging will not be conducted concurrently with the Stage 2 capital dredging (See Section 5.9.19).

Runway Opening

5.6.8 Opening a 600m wide gap at the northern section of the former Kai Tak Airport runway was considered under the KTPR ⁽[10]⁾ as a potential mitigation measure to improve the water circulation and water quality in Kai Tak Approach Channel (Figure 2.12). The opening would be covered by a piled deck. Technical assessment will be carried out to confirm the environmental acceptability of this mitigation option as part of the forthcoming Schedule 3 EIA for the feasibility study of Kai Tak Development.

5.6.9 For the purpose of this water quality assessment, it is assumed that removal of existing seawalls at the 600m opening of the runway will commence in early 2014 after completion of all the dredging works for construction of the cruise terminal at Kai Tak. It is possible that this programme could be accelerated slightly and it is noted that this will be a large complex structure which will take a long time to construct. It is considered that the runway opening works will not coincide with the Stage 1 dredging works for cruise terminal construction. However, for worst-case assessment, modelling of impacts arising from the Stage 2 dredging works covers both the scenario “with 600m opening at the runway” and the scenario “without any opening at the runway”. The acceptability of the potential impacts under the Stage 2 dredging works was examined based on the model results for the two base case scenarios, which already cover the maximum extent (600m) of opening at the runway as compared to the minimum extent (with no runway opening at all). The scenario with a lesser extent of opening (i.e. less than 600m) at the runway is considered not necessary as this would not change the overall conclusion and validity of the base case model results. The effect of the piled deck has been included under the runway opening scenario as discussed in Sections 5.6.80 and 5.6.81 below. Sensitivity tests / analysis for the possible refinement of the size of the runway opening will be carried out under the Schedule 3 EIA for the feasibility study of Kai Tak Development.

5.6.10 Demolition of existing runway will involve excavation of bulk fill and dredging to -5mPD. The proposed construction method adopts an approach where the existing seawall at the runway will not be removed until completion of all excavation and dredging works for demolition of the runway. Thus, excavation of bulk fill and majority of the dredging works will be carried out behind the existing seawall, and the sediment plume can be effectively contained within the works area. Demolition of existing seawall will involve removal of gravel only, which would not create significant SS impact. Fines content in the filling materials in the seawall would be negligible and loss of fill material during seawall demolition is not expected.

5.6.11 As there is likely some accumulation of sediments alongside the runway, there will be a need to dredge the existing seabed after completion of all the demolition works. Thus, potential water quality impact of SS will arise from the dredging on either side of the 600m opening. Therefore, dredging alongside the 600m opening has been included in the water quality modelling for cumulative assessment under the “with runway opening” during the Stage 2 dredging works. To match the construction programme, dredging alongside the 600m opening will be carried out at a maximum production rate of 2,000m³ per day using one grab dredger.

Public Landing Steps cum Fireboat Berth

5.6.12 A section of the existing seawall at the former Kai Tak Airport runway will need to be re-constructed for the proposed public landing steps cum fireboat berth (Figure 2.12) under the Kai Tak Development. Seawall reconstruction would involve excavation and dredging at and near the existing seawall of the runway. Based on the current construction programme, these dredging works will be carried out in 2010 concurrently with the Stage 1 dredging works for cruise terminal (Appendix 2.1). Dredging at and near the seawall area will be carried out at a maximum production rate of 1,000m³ per day using one grab dredger.

Disused Fuel Dolphin

5.6.13 There is a disused fuel dolphin at inner Kowloon Bay that would be decommissioned in the future. The fuel dolphin structure and its connecting fuel pipelines are considered as part of the fuelling facilities of the former Kai Tak Airport and hence the possible water quality impacts arising from the decommissioning of these facilities have been reviewed under the EIA Study for Decommissioning of the Former Kai Tak Airport other than the North Apron.

5.6.14 Since the review of historical sediment quality data indicated the presence of highly contaminated sediment in To Kwa Wan Typhoon Shelter, it is recommended from the environmental perspective not to adopt dredging works for the removal of the disused fuel dolphin structure and to leave the associated abandoned fuel pipeline in-situ.

5.6.15 The existing fuel dolphin is supported by 26 number of 450mm x 450mm precast concrete piles. It is proposed that the disused fuel dolphin structure would be demolished by cutting off the piles to 1m below existing seabed. The sediment around the piles would be pushed aside to facilitate the pile cutting and no dredging would be required for the demolition works. It is estimated that the total volume of sediments that would potentially be disturbed by the pile cutting would be 130m³ only. The disused fuel pipelines will be left in place and, if necessary, grouted with concrete.

5.6.16 As no dredging would be required for the proposed decommissioning works, any loss of fine sediment to suspension from disturbance of the seabed around the dolphin is expected to be minor. The dolphin removal works would be undertaken at inner Kowloon Bay within the semi-enclosure of the breakwaters of To Kwa Wan Typhoon Shelter where the water currents are slow. Therefore, it is expected that suspended solids, if any, released from the decommissioning works would not be transported off site and would be gradually resettled in the vicinity of the work site. In view that the area of the work site would be small, any release of inorganic and organic contaminants and increase in turbidity from the decommissioning works would be localized and transient. No cumulative marine water quality impact with the cruise terminal dredging would be expected from the dolphin removal work.

Sediments Transportation and Disposal

5.6.17 The dredged marine sediments would be loaded onto barges and transported to the designated disposal sites allocated by the MFC depending on their level of contamination. Good site practices and mitigation measures have been recommended in Section 5.9 and Section 6.7 to avoid sediment loss during transportation and loading of the dredged marine sediments. With the implementation of all the recommended mitigation measures, sediment loss during loading and transportation is not expected. In addition, the designated disposal sites will be located outside the Study Area of this EIA and no cumulative water quality impacts would be expected from the sediment transportation and disposal activities.

Other Concurrent Projects

Submarine Gas Main Relocation

5.6.18 Twin 400mm diameter steel submarine gas pipelines are currently aligned 235m west of and parallel to the former Kai Tak Airport runway as shown in Figure 2.4. The pipelines serve as a strategic gas supply to Hong Kong Island and is covered under an existing wayleave agreement. They run between a gas offtake and pigging station at Ma Tau Kok (MTK) and a gas pigging station at Quarry Bay.

5.6.19 In a letter dated 15^th March 2007 from the Hong Kong and China Gas Company Limited (HKCGCL), they indicated that their current programme is to undertake the gas main diversion “from 2009/2010 to 2011”. The currently assumed programme is consistent with this advice from HKCGCL although it is noted that this programme is subject to confirmation by HKCGCL’s detailed designers who have recently been appointed. The gas main would not affect operation of the Phase I Berth with the turning basin squeezed between the runway tip and the gas pipeline. However, the existing pipeline is located within the manoeuvring space and the dredging zone of the Phase II Berth. Hence, the pipeline would need to be reprovisioned before dredging can commence for the Phase II Berth.

5.6.20 HKCGCL have indicated two possible alignments for the new gas main crossing namely an east option (1.4km from the tip of the existing runway) and a west option (2.8km from Ma Tau Kok to North Point) as shown in Figure 2.4. The west option will require more dredging and is closer to the WSRs, and therefore has been assumed for input to the water quality modelling (Figure 2.12). The possible alignment for the new gas main crossing as indicated in Figure 2.12 is indicative only and will be subject to detailed design being conducted by the HKCGCL.

5.6.21 The dredging associated with removal of the existing submarine gas mains will be incorporated into the Stage 2 dredging works for cruise terminal construction (the actual removal work will be undertaken by HKCGCL). Construction of the new gas main may involve dredging and backfilling activities. Backfilling of rock and armour would not be a water quality issue of concern. Only the dredging and sand filling, if any, would cause potential water quality impact. It is expected that backfilling would be carried out after the dredging and laying of the new gas mains is completed. As the possible dredging and backfilling activities would be conducted in sequence rather than concurrently, the worst-case impacts would be during the dredging of seabed as the dredged sediment might be contaminated. Furthermore, the rate of dredging would be larger than the rate of sand filling.

5.6.22 It is assumed under the base case scenario that dredging of seabed would be conducted at a maximum rate of 1,000m³ per day, using small trailer hopper dredger in the fairway and grab dredger at the remaining areas. The trailer hopper dredger is required in the fairway as it is more manoeuvrable and self-powered. Grab dredgers are assumed elsewhere as a worst case for water quality impact. It should be noted that construction of the new gas main is a designated project and will be subject to detailed assessment under separate EIA study.

5.6.23 The dredging rate of 1,000m³ per day was calculated based on the best available information obtained at the time when the sediment plume model for this EIA was being set up. According to the advice in HKCGCL’s letter of 15^th March 2007 that their dredge volume will be approximately 54 m³/m run. Assuming 2.8 km of pipes for the West Option (worst case) will give a total dredge volume of approximately 150,000 m³ of mud to be dredged.  It is further assumed that the dredging rate will be relatively slow due to: the need for tight control on the grab to create the relatively narrow trench; the need for accurate alignment; and limited access/working hours when crossing the fairway in the Victoria Harbour. Allowing approximately 6 months to complete this dredging and working 6 days per week gives the assumed dredging rate of approximately 1,000m³ per day.

5.6.24 However, after the sediment plume modelling exercise for the base case scenarios was completed for this EIA, latest construction information for the new gas main was available from the Project Profile submitted by the HKCGCL in September 2007 under the EIAO for application of EIA study brief. Based on the Project Profile for the new gas main, the west alignment option (from Ma Tau Kok to North Point) would be adopted but the latest alignment will be laid within a 500m corridor in Victoria Harbour and the exact alignment of the new gas main will be determined during the feasibility study and detail design stage. Under this EIA, the sediment spill location for the gas main construction is assumed at a point close to the WSD flushing intake at Tai Wan as shown in Figure 5.3 (Source ID: A6) which represents a worst case for cumulative impact assessment. Based on the latest alignment corridor provided in the Project Profile for the new gas main, the shortest distance between the new gas pipeline and the Tai Wan WSD intake is similar to that assumed under this EIA. Therefore, the dredging location (Source ID: A6) assumed in this EIA is still considered representative, considering that the Tai Wan intake was also identified in the Project Profile for the new gas main as one of the nearest water sensitive receivers. Besides, a sensitivity test was also conducted under this EIA using a higher dredging rate of 5,000 m³ per day to address the possible change of dredging rate for the gas main construction.

Road T2 and Central Kowloon Route (CKR)

5.6.25 It should be noted that the Central Kowloon Route and Road T2 will join up to provide an east-west road link across Kowloon, from Tseung Kwan O in the east to West Kowloon in the west. Road T2 includes an immersed tube section from Cha Kwo Ling to the South Apron area of the former airport. The road is then at-grade connecting to the Central Kowloon Route near the north end of the former runway. The Central Kowloon Route then enters a short section of immersed tube in inner Kowloon Bay before entering a tunnel beneath To Kwa Wan. Both the immersed tube sections of Road T2 and CKR will require dredging.

5.6.26 The construction program for CKR and Road T2 is not confirmed at this stage. It is likely that these two concurrent works cannot commence before 2012. For the purpose of this EIA, it is assumed that construction of CKR and Road T2 would coincide with the Stage 2 cruise terminal dredging for worst case assessment.

5.6.27 In view that the section of CKR alignment is small (Figure 2.12), it is assumed that dredging and backfilling would be conducted in sequence rather than occurring at the same time. Dredging is considered more critical activity and was assumed for water quality modelling purposes. The area of dredging for CKR is small and relatively confined - it is likely that there would only be one dredger and the small volume of dredging means that the dredging programme would highly unlikely be a critical path activity.  Hence, it is assumed a low dredging rate of 1,000m³ per day under the base case modelling scenario, and in view of the sensitivity of the water quality issue. Nevertheless, a sensitivity test with a higher dredging rate of 2,000m³ per day was conducted to address the possible change of dredging rate for the CKR.  In view of the potential contamination of sediment in the Kowloon Bay area, it is considered that the CKR dredging should be carried out in a careful and controlled manner.  The rate of 2,000m³ per day is a reasonable dredging rate that can practically be achieved by a single dredger working within such a limited working area. This working rate is also consistent with other dredging rates assumed for the cruise terminal dredging.  It should be noted that the CKR project is a designated project and will be subject to a separate EIA study, and the cumulative environmental impacts associated with the CKR will be examined in detail under the EIA for CKR.

5.6.28 The dredging and filling activities for construction of Road T2 would be at a larger scale. It is assumed that dredging and filling operations could be conducted at the same time. Based on the construction programme, dredging for Road T2 would be conducted at a maximum rate of 8,000m³ per day (using four grab dredgers) at the same time when sand filling is conducted at a maximum rate of 2,000m³ per day (using another two grab dredgers).Removal of the existing breakwater and subsequent reinstatement need to be allowed for construction of Road T2. The plant used for removing and reinstating the breakwater would be similar to the plant used for dredging marine sediments. The material being dredged from the breakwaters will be largely rockfill which will have lower fines content and therefore less water quality impact than dredging of the adjacent muds. The Road T2 project is also a designated project and the cumulative environmental impacts associated with the Road T2 will be examined in detail under separate EIA study.

Wan Chai Reclamation Phase II (WDII)

5.6.29 The WDII reclamation is currently scheduled to commence in 2009 for completion by 2016. Based on the information available from the WDII Planning and Engineering Review, dredging for three WDII activities would be conducted in the open harbour including:

· construction of the water main between Wan Chai and Tsim Sha Tsui

· construction of the Wan Chai sewage submarine outfall

· construction of the temporary Causeway Bay typhoon shelter

5.6.30 Dredging for the above three WDII activities is considered critical as they will be conducted at or near the main harbour channel with high current speeds where deployment of silt curtain is not practical and may contribute cumulative impacts with the cruise terminal dredging which is also being conducted in the open harbour.

5.6.31 The remaining WDII dredging activities would be confined within the embayed areas or near shore regions for seawall construction along the coastlines where the water currents would be relatively small and, with the implementation of mitigation measures such as deployment of silt curtains around the dredging operations, the impacts from these remaining WDII dredging activities are expected to be localized.

5.6.32 Based on the latest construction programme for WDII, the three critical WDII dredging activities would be conducted in sequence rather than concurrently and all of them would be completed in mid 2010. The majority of the dredging activities for seawall construction along the coastlines would also be finished before 2012.

5.6.33 According to the construction programme for cruise terminal construction, dredging at or near the seawall for berth construction will take place in later half of 2008 for completion in late 2010. Stage 1 dredging in the manoeuvring basin for the Phase I Berth will then proceed in early 2011. Dredging for berth construction would mainly involve removal of rubble/rockfill from the existing seawall which would not contribute significant SS impact with the WDII dredging activities. Also, the most critical dredging activities for WDII (in the open harbour) would all be completed in mid 2010 before commencement of the Stage 1 dredging in the manoeuvring basin. No adverse cumulative impact is therefore expected from the WDII construction

5.6.34 However, to address the possible change of the construction programme for cruise terminal dredging, it is assumed that the critical or worst-case scenario for WDII (with dredging in the open harbour) will be undertaken concurrently with the Stage 1 dredging for construction of the manoeuvring basin (also in the open harbour) to investigate the cumulative impact. Based on the information available from the WDII Planning and Engineering Review, the worst case scenario for WDII dredging would occur in early 2009 where there would be dredging at or near the main harbour channel of 3,000m³ per day for construction of the water main between Wan Chai and Tsim Sha Tsui and the temporary breakwater outside the existing Causeway Bay typhoon shelter as well as dredging of about 20,000m³ per day along the coastlines of Wan Chai, North Point and within the Causeway Bay typhoon shelter for construction of seawall foundation. As the majority of the dredging activities for WDII would be completed before 2012, the cumulative impact from WDII was only assessed for the Stage 1 cruise terminal dredging.

Western Cross Harbour Main

5.6.35 A new cross-harbour water main would be constructed to provide security of water supply from West Kowloon to Sai Ying Pun. According to the EIA report “Laying of Western Cross Harbour Main and Associated Land Mains (Western Harbour Main)” (EIAO Register No.: AEIAR-109/2007), construction of the water main is currently scheduled for completion in 2009 and the dredging works would be conducted at a maximum production rate of 4,000m³ per day, using one grab dredger.

Further Development of Tseung Kwan O

5.6.36 Based on the approved EIA for Further Development of Tseung Kwan O Feasibility Study (TKOFS), the worst-case construction impacts would occur during the seawall construction for Phase I reclamation when dredging and filling operations are carried out concurrently at the southern area of the TKO reclamation site. According to the reclamation programme given in the approved EIA, these dredging and filling operations would commence in 2010. Based on the latest information obtained from CEDD under this EIA, the Phase 1 seawall construction would likely to commence in early 2012, and in-situ soil improvement measures would be explored under the detailed design to avoid dredging. Therefore, it is possible that no dredging would be carried out for the TKO reclamation works.

5.6.37 Nevertheless, the cumulative effects of the possible dredging and filling works for TKO reclamation have been considered under this modelling exercise.  The modelling works aimed to investigate whether the KTD works would contribute any cumulative water quality impacts with the TKO reclamation works. As the dredging rates for KTD works would be larger during the cruise terminal Stage 1 dredging period as compared to the Stage 2 dredging period, the TKO works have been included in the modelling exercise for the cruise terminal Stage 1 dredging period for worst case assessment. It is assumed that one close grab dredger would be used for dredging and one pelican barge would be used for sand filling under the TKO works. The production rates for dredging and filling would be 1400m³ per day and 3000m³ per day respectively according to the approved EIA for TKOFS.

Lei Yue Mun Waterfront Enhancement

5.6.38 A new landing facility will be built at Lei Yue Mun under this water enhancement project. Construction of the landing facility would require dredging off the landing area and construction of a new breakwater. Based on the modelling results provided in the Preliminary Environmental Review Report for this waterfront enhancement project, the operation of the proposed landing facility and breakwater would not change the overall flow regime in the Victoria Harbour. With regard to the dredging impact during the construction phase, the mixing zone for SS elevation was predicted to be highly localized around the work site (within about 100 m) at both dry and wet seasons. The proposed waterfront enhancement works would not cause any cumulative water quality impact with the cruise terminal dredging, considering that the waterfront enhancement works are located at least 3km away from the cruise terminal site.

Hong Kong Offshore Wind Farm

5.6.39 The wind farm project involves burying a submarine transmission cable connecting the land facility to the offshore wind farm. Two alternative site locations, namely the Southwest Lamma site and the Southeast Ninepins site respectively, were considered in the Project Profile for this offshore wind farm project. The Southwest site is located in the Southern WCZ which is outside the Study Area for this EIA. The Southeast site involves the burying of a cable between the land point at the southeast of Junk Bay to the offshore wind farm in the Mirs Bay WCZ. The EIA for the offshore wind farm project was still at an initial stage when this EIA report was being prepared. No modelling assessment and no construction method for the cable burying was available for this offshore wind farm project. It is however considered that the water in the southeast of Junk Bay would be outside the influence zone of the cruise terminal dredging only (refer to Appendix 5.10 to Appendix 5.15) and significant cumulative impact would not be expected. This has been confirmed by the modelling assessment undertaken for this EIA.

Dredging Scenarios for Capital Dredging

5.6.40 With reference to the construction programme (Appendix 2.1) and likely concurrent projects, representative worst case scenarios have been selected for modelling, including all the potentially concurrent dredging activities envisaged during the proposed capital dredging works for cruise terminal.

Scenario 1A – Stage 1 Dredging without Runway Opening

5.6.41 Scenario 1A assumes that the following marine works will take place concurrently in 2010.

(i) Stage 1 dredging at and near the existing seawall of the former Kai Tak Airport runway for construction of the Phase I Berth (Source ID: A1 and A2);

(ii) Stage 1 dredging in the Harbour area for cruise vessel approach to the Phase I Berth (Source ID: A3 and A4 / A3a and A4a);

(iii) Dredging for seawall foundation at the former Kai Tak Airport runway for the new public landing steps cum fireboat berth (Source ID: A5);

(iv) Dredging for submarine gas main relocation (Source ID: A6);

(v) Dredging for construction of the western harbour water main from West Kowloon to Sai Ying Pun (Source ID: A7);

(vi) Dredging for construction of the water main between Wan Chai and Tsim Sha Tsui and the temporary typhoon shelter outside the existing Causeway Bay typhoon shelter as well as dredging for seawall foundation at Wan Chai, Causeway Bay and North Point water front under the WDII reclamation (Source ID: A8, A9, A10, A11 A12 and A13 / A13a); and

(vii) Dredging at Junk Bay for the reclamation works proposed under the TKOFS (Source ID: F1 and D1).

5.6.42 Figure 5.3 shows the coastline configuration (with no runway opening) and sediment source locations.

5.6.43 For construction of the manoeuvring basin for the Phase I Berth, Item (ii) above, only two closed grab dredgers will be working simultaneously. For the purpose of modelling, alternative dredging locations have been considered to cover the Stage 1 dredging area. They are:

¨ Case 1: Two closed grab dredgers (Source ID: A3 and A4) working near the fairway; and

¨ Case 2: Two closed grab dredgers (Source ID: A3a and A4a) working near the southern tip of the runway.

5.6.44 Based on the review of the assumed source points (Case 1 and Case 2) for Stage 1 dredging, more alternative spill locations may be considered to investigate the worst-case impacts on the seawater intakes (i.e. adjusting the dredging location to a point that is closer to a particular seawater intake may potentially increase the SS elevation at that particular intake point). For example, moving Source Point A4a to further east may potentially increase the SS level at the WSD’s Cha Kwo Ling intake. However, based on the model simulation results for Case 1 and Case 2, no significant difference in the predicted SS levels was found between these two alternative cases at the identified seawater intakes. It is considered that the SS levels predicted at the seawater intakes are not sensitive to the change of spill locations within the Stage 1 dredging area. Further adjustment of the source points (e.g. moving Source Point A4a to further east) would not change the overall assessment results. The selected spill locations (Case 1 and Case 2) are considered appropriate to represent a reasonable worst-case for the overall water quality impact.

5.6.45 For the submarine gas main, Item (iv) above, the sediment release point (Source ID: A6) was chosen at a location closest to the WSD Tai Wan flushing water intake for worst case assessment.

5.6.46 Based on the EIA report for Western Harbour Main, one closed grab dredger (Source ID: A7) is assumed to be working in the main Harbour channel between West Kowloon and Sai Ying Pun for the purposes of cumulative assessment. It should be noted that the western harbour water main is currently scheduled for completion by 2009, however, the dredging work is included in this 2010 scenario for worst case assessment.

5.6.47 The sediment source locations (Source ID: A8, A9, A10, A11, A12 and A13 / A13a) for WDII, Item (vi) above, are based on the updated information available from the WDII Planning and Engineering Review.

5.6.48 The assumed source locations for dredging and filling (Source ID: D1 and F1 respectively) for TKO reclamation, Item (vii), are based on the information from the approved TKOFS EIA Report.

Scenario 1B – Stage 2 Dredging without Runway Opening

5.6.49 Scenario 1B assumes that the following marine works will take place concurrently in 2013.

(viii) Stage 2 dredging in the Harbour area for cruise vessel approach to the Phase II Berth (Source ID: B1 and B2);

(ix) Dredging for construction of CKR (Source ID: B3); and

(x) Dredging and sand filling for construction of Road T2 (Source ID: B4, B5, B6 and B7).

5.6.50 Figure 5.4 shows the assumed coastline configuration (with no runway opening) and sediment source locations for Scenario 1B.

5.6.51 It is assumed under Item (viii) that there would be two closed grab dredgers (Source ID: B1 and B2) working near the fairway to the south of the runway.

5.6.52 Construction of Road T2, Item (x), would include four grab dredgers for dredging and another two for sand filling. Dredging would be the most critical activities and the associated sediment release points have been included in the area outside the breakwaters of Kwun Tong Typhoon Shelter (KTTS) for worst case assessment. For the purpose of water quality modelling, only two source points (Source ID: B6 and B7), have been assumed to represent the dredging work and each source point would cover the sediment loss from two grab dredgers. Two sand filling points (Source ID: B4 and B5) are included inside the KTTS breakwater.

Scenario 1C – Stage 2 Dredging with Runway Opening

5.6.53 Scenario 1C assumes that the following marine works will take place concurrently in 2013.

(xi) Stage 2 dredging in the Harbour area for cruise vessel approach to the Phase II Berth (Source ID: C1 and C2);

(xii) Dredging of sediments alongside the runway opening (Source ID: C3).

(xiii) Dredging for construction of CKR (Source ID: C4); and

(xiv) Dredging and sand filling for construction of Road T2 (Source ID: C5, C6, C7 and C8).

5.6.54 Figure 5.5 shows the assumed coastline configuration (with a 600m opening at the runway) and sediment source locations for Scenario 1C. This scenario is the same as Scenario 1B except that the dredging work for runway opening is included with 600m opening at the runway.

Sediment Loss Rates

5.6.55 Assumptions made in the sediment plume modelling simulations are as follows:

l Sediment loss rates during dredging and sand filling activities for construction of the TKO reclamation are based on the values adopted under the approved TKOFS EIA. Mitigation measures have been proposed under the TKOFS EIA to minimize the water quality impacts. The loss rates for TKO reclamation adopted in this EIA represent the mitigated scenarios.

l Sediment loss rates during dredging activities for construction of the WDII reclamation are based on the values adopted under the WDII Planning and Engineering Review. Mitigation measures have been proposed under the EIA study for WDII to reduce the water quality impact to an acceptable level. The loss rates for WDII adopted in this EIA represent the mitigated scenarios.

l Sediment loss rates during dredging for construction of the Western Harbour Main are based on the values provided in the EIA report for Western Harbour Main.

l Closed grab dredger and pelican barge is assumed for dredging and filling respectively at the TKO reclamation site based on the approved TKOFS EIA. For WDII reclamation, closed grab dredger is assumed for dredging based on the WDII Planning and Engineering Review. Closed grab dredger is also assumed for construction of the water main based on the EIA report for Western Harbour Main.

l Closed grab dredger is assumed to be used for all other dredging and filling activities considered in this EIA except the dredging work in fairway for gas main relocation which is assumed to be carried out by small trailer hopper dredger. Use of closed grab dredger is a practical method most commonly adopted in Hong Kong to reduce sediment loss from dredging and filling. The assumed water quality mitigation measures for other designated projects including CKR, Road T2 and Gas Main Diversion will be subject to detailed assessment under separate EIA studies. In addition, the runway opening and the public landing steps cum fireboat berth are proposed under the Kai Tak Development (KTD) and the assumed water quality mitigation measure for these two KTD components will be subject to the Schedule 3 EIA for the feasibility study of KTD.

l With respect to rate of sediment loss, the Contaminated Spoil Management Study ^([11]) (Mott MacDonald, 1991, Table 6.12) reviewed relevant literature and concluded that losses from closed grab dredgers were estimated at 11 – 20 kg/m³ of mud removed. The sediment loss rate (in g/s) for the dredging for cruise terminal and other concurrent works was calculated by applying the daily production (in m³/day) to the maximum sediment loss density of 20 kg/m³ except for WDII reclamation, TKO reclamation and laying of western harbour main where the loss rates are directly extracted from their respective EIA reports.

l The sand fill density is 1,600 kg/m³ with 20 % fine portion based on the SEKDCFS EIA. This density was applied to the sand filling at Road T2. Close grab dredger would be used for Road T2 and a higher spill rate of 5% has been conservatively taken to calculate the loss rate in kg/s based on the daily production rate for sand filling. The value of sand fill loss rate of 5% was previously used under various approved EIAs including the SEKDCFS EIA and TKOFS EIA.

l With reference to the latest information on construction programme, the working hours of the dredging works for cruise terminal construction would be from 0700 to 1900 hours and 6 days a week (not including Sunday and Public Holiday). Spill loss during mud dredging by closed grab dredger will thus be continuous, 12 hours a day, 6 days per week except for WDII reclamation where the closed grab dredger will work 16 hours a day and laying of Western Harbour Main where the closed grab dredger will work 24 hours a day.

5.6.56 The calculated sediment loss rates for Scenario 1A, Scenario 1B and Scenario 1C are shown in Table 5.10, Table 5.11 and Table 5.12 respectively. The production rates for different construction activities are identified. The corresponding source locations are given in Figure 5.3 to Figure 5.5. As deployment of silt curtains around the dredging operations are recommended as mitigation measures under the WDII Planning Review and the approved TKOFS EIA, the loss rates shown in Table 5.10 for WDII and TKO reclamations are the reduced loss rates under the mitigated scenarios which have considered the effect of silt curtains. On the other hand, deployment of silt curtains have not been considered in calculating the sediment loss rates from cruise terminal dredging and other concurrent activities within the KTD area as shown in Table 5.10 to Table 5.12. These sediment loss rates represent the worst case under the unmitigated scenario. It is assumed that silt curtains will only be deployed if the water quality impacts are found to be unacceptable. Deployment of silt curtains have been considered under the mitigated scenario discussed in Section 5.9.

^{Table 5.10 Maximum Production Rates – Scenario 1A (2010)}

Source ID (Figure 5.3)		Activity	Approx.Duration (months)	Work Hours per Day	Production Rate			Loss Rate (kg/s)
					(m^3 per day)		(m^3 per hour)
Kai Tak Development - Cruise Terminal –Dredging at and near the Seawall
A1		Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000		167	0.93
A2		Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000		167	0.93
Kai Tak Development - Cruise Terminal –Dredging in the Manoeuvring Area for the Phase I Berth (including the dredging for removal of the abandoned KTR submarine outfall)
Alternative dredging locations: either A3 and A4 / A3a and A4a		Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000		167	0.93 (for A3 or A3a)
		Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000		167	0.93 (for A4 or A4a)
Kai Tak Development – Public Landing Steps cum Fireboat Berth
A5		Dredging (1 closed grab dredger of 8m^3 capacity)	6	12	1000		83	0.46
Submarine Gas Main Relocation
A6		Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	1000 (or 5000**)	83 (or 167**)		0.46 (or 2.31**)
Western Harbour Main between West Kowloon to Sai Ying Pun
A7		Based on the EIA report for Western Harbour Main						0.93
Wan Chai Reclamation Phase II
A8	Based on the latest information from WDII Planning and Engineering Review (under mitigated scenario)							0.13
A9								0.52
A10								1.73
A11								0.52
A12								0.52
Two alternative dredging locations: either A13 or A13a								0.52
Further Development of Tseung Kwan O
D1	Based on the approved EIA for TKOFS EIA (under mitigated scenario)							0.44
F1								0.15

Note: ** Values in bracket are used for sensitivity test (refer to Section 5.6.24).

^{Table 5.11 Maximum Dredging Rates - Scenario 1B (2013)}

Source ID (Figure 5.4)	Activity	Approx. Duration (months)	Work Hours per Day	Production Rate		Sediment Loss Rate (kg/s)
				(m^3 per day)	(m^3 per hour)
Kai Tak Development - Cruise Terminal – Dredging in the Manoeuvring Area for the Phase II Berth
B1	Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000	167	0.93
B2	Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000	167	0.93
Central Kowloon Route
B3	Dredging (1 closed grab dredger of 8m^3 capacity)	6	12	1000 (or 2000 **)	83 (or 167**)	0.46 (or 0.93**)
Road T2
B4	Sand filling (1 closed grab dredger of 8m^3 capacity)	12	12	1000	83	0.37
B5	Sand filling (1 closed grab dredger of 8m^3 capacity)	12	12	1000	83	0.37
B6	Dredging (2 closed grab dredger of 8m^3 capacity)	12	12	4000	333	1.85
B7	Dredging (2 closed grab dredger of 8m^3 capacity)	12	12	4000	333	1.85

Note: ** Values in bracket are used for sensitivity test (refer to Section 5.6.27).

^{Table 5.12 Maximum Dredging Rates - Scenario 1C (2013)}

Source ID (Figure 5.5)	Activity	Approx. Duration (months)	Work Hours per Day	Production Rate		Sediment Loss Rate (kg/s)
				(m^3 per day)	(m^3 per hour)
Kai Tak Development - Cruise Terminal – Dredging in the Manoeuvring Area for the Phase II Berth
C1	Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000	167	0.93
C2	Dredging (1 closed grab dredger of 8m^3 capacity)	12	12	2000	167	0.93
Kai Tak Development – Runway Opening
C3	Dredging (1 closed grab dredger of 8m^3 capacity)	6	12	2000	83	0.93
Central Kowloon Route
C4	Dredging (1 closed grab dredger of 8m^3 capacity)	6	12	1000 (or 2000 **)	83 (or 167**)	0.46 (or 0.93**)
Road T2
C5	Sand filling (1 closed grab dredger of 8m^3 capacity)	12	12	1000	83	0.37
C6	Sand filling (1 closed grab dredger of 8m^3 capacity)	12	12	1000	83	0.37
C7	Dredging (2 closed grab dredger of 8m^3 capacity)	12	12	4000	333	1.85
C8	Dredging (2 closed grab dredger of 8m^3 capacity)	12	12	4000	333	1.85

Note: ** Values in bracket are used for sensitivity test (refer to Section 5.6.27).

Dredging Scenario for Maintenance Dredging

5.6.57 The maximum dredging rate during maintenance dredging (2,000 m³ per day) would be lower than that during the capital dredging (total of 8,000 m³ per day during Stage 1 dredging and 4,000 m³ per day during Stage 2 dredging). The number of dredger to be employed during maintenance dredging (one number) is also less than that to be employed during capital dredging (4 numbers during Stage 1 dredging and 2 numbers during Stage 2 dredging).

5.6.58 Modelling for capital dredging has covered different dredging locations within the Project site. Based on the review of the modelling results available for the capital dredging scenarios, dredging close to the fairway within the manoeuvring basin for the Phase II Berth would cause the largest potential water quality impact. For the purpose of modelling the maintenance dredging impact, one grab dredger is therefore assumed to be working in the manoeuvring basin for the Phase II Berth near the fairway to investigate the potential worst case impacts. It is considered that the scenario with a 600 m opening at the runway would also be the worst case for modelling the maintenance dredging as the 600 m opening would allow the discharge of polluted water from the KTAC to the open harbour and increase the background SS level. Modelling scenarios for maintenance dredging are summarized in Table 5.12a and Figure 5.8a. No other concurrent dredging is assumed for the purpose of modelling the maintenance dredging impact.

^{Table 5.12a Modelling Scenario for Maintenance Dredging}

Scenario ID	Description	Assumptions
Scenario 1D (Figure 5.8a)	Coastline Configuration:	With a 600 m opening at the runway
	Activity:	Dredging (using 1 closed grab dredger of 8m^3 capacity)
	Approximate Duration:	Less than 6 month for each berth
	Production Rate:	2000 m^3 per day
	Sediment Loss Rate:	0.93 kg/s
	Number of Source Point:	One
	Assumed Source Location:	Source ID “D1” as shown in Figure 5.8a

Modelling Tools

5.6.59 Computer modelling was used to assess the potential impacts on water quality in the Victoria Harbour associated with the Project. The hydrodynamic and water quality modelling platforms were developed by Delft Hydraulics, namely the Delft3D-FLOW and Delft3D-WAQ respectively.

5.6.60 Delft3D-FLOW is a 3-dimensional hydrodynamic simulation programme with applications for coastal, river and estuarine areas. This model calculates non-steady flow and transport phenomena that result from tidal and meteorological forcing on a curvilinear, boundary fitted grid.

5.6.61 Delft3D-WAQ is a water quality model framework for numerical simulation of various physical, biological and chemical processes in 3 dimensions. It solves the advection-diffusion-reaction equation for a predefined computational grid and for a wide range of model substances.

5.6.62 The detailed SEK model developed using Delft3D-FLOW and Delft3D-WAQ has been employed for this EIA. The SEK model was developed under the KTPR and is a cut out from the Update model. The Update model is a regional model covering the whole HKSAR waters and the adjacent Mainland waters, which was constructed, calibrated and verified under the EPD Cumulative Effect Study ⁽[12]⁾. The SEK Model was refined in KTD area to give a better representation of the hydrodynamic and water quality conditions. The grid layout of the SEK model has a high resolution of less than 75m by 75m at the KTAC and Kowloon Bay area. There are a total 4 grid cells across the KTAC to resolve transverse variations of the KTAC.

5.6.63 The performance of SEK model has been checked against that of the Update model. The model was also extensively calibrated by comparing computational results with the field measurements collected in the KTAC, Kowloon Bay and Victoria Harbour Channel as part of the KTPR. Details of the model setup and verification are described in the “Water Quality Model Calibration and Assessment Final Model Calibration Report” prepared under the KTPR.

5.6.64 The detailed SEK Model is linked to the regional Update Model. Computations were first carried out using the Update Model to provide open boundary conditions to the SEK Model. The Update model covers the whole Hong Kong and the adjacent Mainland waters including the discharges from Pearl River. The influence on hydrodynamics and water quality in these outer regions would be fully incorporated into the SEK Model. The model coverage and the grid schematization are given in Appendix 5.1.

Suspended Solids

Sediment Plume Model

5.6.65 Sediment plumes arising from the mud dredging and sand filling activities during the dredging works have been simulated using Delft3D-PART. This model has been used for sediment plume modelling in a number of previous reclamation studies in Hong Kong including the approved Comprehensive Feasibility Study for WDII EIA and Northshore Lantau Development Feasibility Study ⁽[13]⁾.

5.6.66 The loss of fines to the water column during dredging operations is represented by discrete particles in the model. These discrete particles are transported by advection, due to the tidal flows determined from hydrodynamic simulation, and turbulent diffusion and dispersion, based on a random walk technique. The Delft3D-FLOW was used to provide the hydrodynamic information for particle tracking. The detailed SEK model was used as a basis for hydrodynamic simulations.

5.6.67 The Delft3D-PART model takes into account the sedimentation process by means of a settling velocity, while erosion of bed sediment, causing re-suspension of sediment, is governed by a function of the bed shear stress. The parameters adopted in the present study are summarised in Table 5.13.

^{Table 5.13 Summary of Parameters for Sediment Plume Model (Delft3D-PART)}

Sediment Plume Model Parameters
Horizontal Dispersion Coefficient DH (m^2/s)	a = 0.003 b = 0.4	DH = a t ^b, Where t is the age of particle from the instant of discharge in seconds
Vertical Dispersion Coefficient DV (m^2/s )	5x10^-3 1x10^-5	Dry Season Wet Season
Particle Settling Velocity	0.0001m/s (Constant)	Grain size diameter of 10 μm
Critical Shear Stress	0.05 Pa 0.15 Pa	Sedimentation Erosion

Simulation Periods

5.6.68 For each modelling scenario, the simulation period of the hydrodynamic model (Delft3D-FLOW) has covered two 15-day full spring-neap cycles (excluding the spin-up period) for dry and wet seasons respectively. The hydrodynamic results (for the actual simulation period) have been used repeatedly to drive the particle tracking simulations (Delft3D-PART). The simulation period of the Delft3D-PART model has also covered two 15-day full spring-neap cycles (excluding the spin-up period) for dry and wet seasons respectively. Sufficient spin-up period has been provided to ensure that initial condition effects can be neglected.

Output Parameters

5.6.69 The Delft3D-PART was used for predication of SS elevations at the receiving water and sedimentation rates for assessment of the potential impacts on corals.

Contaminant Release during Dredging

5.6.70 The loss of sediment to suspension during dredging may have chemical effects on the receiving waters. This is because the sediment may contain organic and chemical pollutants.

5.6.71 The 5-day sediment oxygen demand (SOD₅)[14]^([15]) of the sediment samples collected from marine site investigation (SI) has been used to determine the reductions in dissolved oxygen (DO) concentration, based on the predicted increases in suspended sediment concentrations. The reductions are compared with the baseline levels to determine the relative effects of the increases in SS concentrations on DO.

5.6.72 An indication of the likelihood of release of contaminants (including nutrients, heavy metals, PCBs, PAHs and TBT) from the sediment during dredging is given by the results of the elutriation tests from the marine SI works. Sediment samples mixed with a solution, i.e. the ambient seawater collected from the same site, were vigorously agitated during the tests to simulate the strong disturbance to the seabed sediment during dredging. Pollutants absorbed onto the sediment particles would be released and increasing the pollutant concentrations in the solution. The laboratory testing was to analyse the pollutant concentrations in the solution (elutriate). If the contaminant levels are higher in the elutriates in comparison with the blanks (i.e. marine water from the same site), it can be concluded that the contaminants are likely to be released into the marine waters during dredging activities. As there is no existing legislative standard or guideline for individual heavy metal contents in marine waters, the UK Water Quality Standards for Coastal Surface Water ^([16]) are adopted as the assessment criteria.

5.6.73 The elutriate tests conducted in the marine SI provided information on the release of contaminants from the marine mud during dredging operation. An inactive tracer was defined in the model at the dredging locations to determine the dilution in the vicinity of the dredging site. The dilution information was then used to determine the decreases in concentrations of the concerned parameters and to evaluate the potential impacts to the marine environment.

Coastline Configurations

5.6.74 For the modelling of this EIA, a regional Update Model was setup to cover the whole of Hong Kong and the Pearl Estuary. The Regional Model was used to provide the boundary inputs to the local SEK Model. The SEK Model covers the neighbouring waters of Hong Kong Island, including Victoria Harbour. The dredging scenarios were simulated using the SEK Model.

5.6.75 Boundary conditions for the detailed SEK Model were generated using the Update Model. For the purpose of setting up the Update Model properly, the coastline configurations were updated to mimic the envisaged conditions for the modelling scenarios. The details of the coastal developments incorporated in the Stage 1 (2010) and Stage 2 (2013) coastline configurations, the source of information, and the current status of the planned developments are summarised in Table 5.14. Layout of individual reclamation project can be referred to Figure 5.9.

^{Table 5.14 Coastal Developments Incorporated in the 2010 and 2013 Coastline Configurations}

Coastal Development	Information Source	Included in 2010 Stage 1 Scenario (Figure 5.9)	Included in 2013 Stage 2 Scenario (Figure 5.9)
Sunny Bay Reclamation,	EIA Report for “Northshore Lantau Development Feasibility Study” (EIAO Register No.: AEIAR-031/2000).	Yes	Yes
Logistic Park Reclamation,	EIA Report for “Northshore Lantau Development Feasibility Study” (EIAO Register No.: AEIAR-031/2000).	Yes	Yes
Penny’s Bay Reclamation	EIA Report for “Construction of an International Theme Park in Penny's Bay of North Lantau together with its Essential Associated Infrastructures” (EIAO Register No.: AEIAR-032/2000).	Yes	Yes
Sham Tseng Further Reclamation	EIA Report for “Planning and Engineering Feasibility Study for Sham Tseng Development” (EIAO Register No.: AEIAR-057/2002).	Yes	Yes
Lamma Power Station Extension	EIA Report for “1,800 MW Gas-fired Power Station at Lamma Extension” (EIAO Register No.: AEIAR-010/1999).	Yes	Yes
Wan Chai Reclamation Phase II	Draft EIA Report for “Wan Chai Development Phase II and Central-Wan Chai Bypass”	Yes	Yes

5.6.76 The baseline coastline configurations assumed for 2010 and 2013, highlighting the incorporated coastal developments, are shown in Figure 5.9. The change in coastline within the Kai Tak Development (due to the 600m opening) will be included in the 2013 scenario as shown in Figure 2.12.

5.6.77 The reclamations for Yau Tong Bay Reclamation (YTBR) were excluded as they were still subject to planning review when this EIA report was prepared. It should be noted that the reclamation for Central Reclamation Phase III (CRIII) has been incorporated into the existing coastline as shown in Figure 5.9.

5.6.78 As there is no significant change in coastline configuration between the two assessment years, the simulation results generated from the Update Model under the 2010 Stage 1 scenario were used to provide boundary conditions to the SEK Model for both Stage 1 and Stage 2 scenarios (namely Scenario 1A, Scenario 1B, and Scenario 1C). Although these dredging scenarios would involve some changes in the coastline at the Kai Tak (i.e. the 600m runway gap) and at the WDII as the WDII reclamation proceeds, the change is relatively small and is unlikely to have a major effect on the boundary conditions of the detailed SEK model. The boundaries of the SEK model are outside the Victoria Harbour, Junk Bay and Eastern Buffer WCZs in the far field.

Bathymetry

5.6.79 The existing seabed levels as shown in Figure 2.5 were used for the Stage 1 dredging scenario in 2010. For 2013 Stage 2 scenarios (Scenarios 1B and 1C), it is assumed that the seabed within the Stage 1 dredging area would be dredged to -12mCD (refer to Section 2.2).

Pile Friction

5.6.80 Pile deck will be constructed at the runway opening under the 2013 scenario (Scenario 1C). The presence of these piles may affect the flushing and dispersion of sediment and pollutants and were therefore incorporated into Stage 2 dredging scenario for 2013 (Scenario 1C). The marine piles have variable separation distance. As the dimensions of the marine piles are much smaller than the grid size, the exact pier configurations cannot be adopted in the model simulation. Instead, only the overall influence of the piles on the flow is taken account. This overall influence was modelled by a special feature of the Delft3D-FLOW model, namely “Porous Plate”. “Porous Plate” represents transparent structures in the model and is placed along the model gridline where momentum can still be exchanged across the plates. The porosity of the plates is controlled by a quadratic friction term in the momentum to simulate the energy losses due to the presence of the piles. The forces on the flow due to a vertical pile or series of piles are used to determine the magnitude of the energy loss terms. The mathematical expressions for representation of piles friction were based on the Cross Border Link Study ⁽[17]⁾ and the Delft3D-FLOW module developed by Delft Hydraulics.

5.6.81 For each grid cell where the piles will be located, two loss coefficients have been specified in the model for two different flow directions respectively (i.e. the two directions perpendicular to the model gridline, namely u-direction and v-direction respectively). Details of the equations used in the modelling are contained in Appendix 5.2.

Background Water Quality

5.6.82 The sediment plume modelling has considered the effect of the possible scenario with a large gap at the former Kai Tak Airport runway (which is one of the mitigation measures being considered to improve the water quality of KTAC). The proposed runway opening would allow the discharge of polluted water from KTAC to the open harbour and would potentially cause an increase in the background SS level in the nearby seawater intakes (as compared to the existing condition). It is considered that use of EPD routine monitoring results for establishing the background water quality cannot address the above potential water quality concern. In addition, most of the sensitive receivers (i.e. the seawater intakes) are located at the waterfront and are potentially affected by the pollutants discharged from the nearby storm outfalls. On the other hand, all the EPD routine monitoring stations are located further away from the waterfront in the main harbour channel which may not be representative of the local water quality characteristics at the seawater intake points. As such, water quality simulations (Delft3D-WAQ) were performed using the SEK model to provide information on the baseline (pre-Project) water quality to take account the possible scenarios with and without the runway opening. The performance of the SEK model has been checked against the field data and has been fully calibrated and verified under the KTPR to be acceptable for prediction of water quality in the Victoria Harbour including the KTD area. Relevant information on the SEK model calibration is provided in Appendix 5.2a for reference. Simulation period for Delft3D-WAQ was performed for one complete tidal cycle (excluding the spin up) under each of the dry and wet season conditions. The 10 percentile DO and 90 percentile SS, TIN and UIA predicted under the pre-Project scenario at the receivers were used as the background levels.

5.6.83 As there is no obvious change in the coastline configuration between the assessment years (2010 and 2013), major factors that would affect the background (baseline) water quality would be the change in background pollution loading discharged from storm and sewage outfalls.

5.6.84 Sewage effluent discharged from the Harbour Area Treatment Scheme (HATS) would be the key background pollution source affecting the water quality in Victoria Harbour. Stage 1 of HATS, comprising the Stonecutters Island Sewage Treatment Works (SCISTW) and the deep tunnels, was commissioned in late 2001, which collects sewage from Kwai Chung, Tsing Yi, Tseung Kwan O, parts of eastern Hong Kong Island and all of Kowloon and deliver it to SCISTW for chemically enhanced primary treatment (CEPT). Stage 2 of HATS would be implemented in two phases, namely Stage 2A and Stage 2B. Under Stage 2A, deep tunnels would be built to bring sewage from the northern and western areas of Hong Kong Island to SCISTW and the design capacity of the SCISTW would be expanded to meet the future demands. Stage 2A is currently scheduled for implementation by 2014. Stage 2B of HATS involves the provision of biological treatment at the SCISTW to improve the effluent quality. Stage 2B is tentatively scheduled for implementation by 2021. It should however be highlighted that the way forward of the HATS is still being studied and the timing for implementation of Stage 2B is still subject to review.

5.6.85 The 2010 and 2013 scenarios represent the HATS Stage 1 condition before commissioning of HATS Stage 2A. This is a worst-case in terms of the Harbour water quality because the Harbour water is currently impacted by sewage discharged from Wan Chai East and Wan Chai West PTW outfall, Central PTW outfall and North Point PTW outfall. Stage 2A would involve decommissioning of these sewage outfalls and diversion of the sewage effluents to the Stonecutters Island STW for CEPT treatment.

5.6.86 The pollution loading inventory was compiled for Year 2013 for model input under both 2010 scenario (for Stage 1 modelling) and 2013 scenario (for Stage 2 modelling). The background loading for 2013 would be slightly larger than that for 2010 due to population growth which is a worse case. The background pollution loading was estimated for the whole HKSAR waters by desk-top method and was input to the water quality model for cumulative impact assessment.

5.6.87 The inventory incorporates all possible pollution sources within the HKSAR waters including those from landfill sites, marine culture zones, beach facilities and typhoon shelters, non-point source surface run-off and sewage from cross connections etc. The inventory has taken into account the removal of pollutants due to wastewater treatment facilities and the possible redistribution of pollution loads due to different sewage disposal plans and sewage export schemes. The methodologies for compiling the pollution loading are given in Appendix 5.3.

5.6.88 To take account of the key background pollution loading for cumulative assessment, pollution loading from the HATS was considered separately. Chemically enhanced primary treatment (CEPT) with disinfection is assumed as the treatment process of HATS in this EIA study for water quality modelling which involves a discharge of effluent at the existing Stonecutters Island Sewage Treatment Works (SCISTW). The HATS loading assumed in this EIA is given in Table 5.15.

^{Table 5.15 Pollution Loading from Stonecutters Sewage Treatment Works under HATS}

Parameters	2013 Scenario (HATS Stage 1)
	Assumed Concentration	Assumed Flow and Loads
Flow rate	-	1,540,000m^3/day ^(1)
BOD5	68mg/l ^(2)	190400000 g/day
SS	42mg/l ^(2)	117600000 g/day
Organic Nitrogen	9.93mg/l ^(2)	2780400 g/day
NH3-N	17.43mg/l ^(2)	48804000 g/day
E. coli	200,000no./100ml ^(2)	5.6E+14no./day
Total Phosphorus	3mg/l ^(2)	8400000 g/day
Ortho-Phosphate	1.8mg/l ^(2)	5040000 g/day
Silicate	8.6mg/l ^(2)	24080000 g/day
Total nitrite and nitrate	0mg/l ^(2)	0 g/day
Total Residual Chlorine	0.2mg/l ^(2)	560000 g/day

Notes: 1 The projected flow rate for 2013 was estimated using the latest planning and employment statistics as detailed in Appendix 5.3.

2 Based on the “Environmental and Engineering Feasibility Assessment Studies in Relation to the Way Forward of the Harbour Area Treatment Scheme (HATS EEFS) Final Study Report”.

5.6.89 The methodologies described in Appendix 5.3 were used to compile the background pollution loading from catchments outside the KTD area for cumulative assessment. The water pollution sources within the KTD areas such as urban runoff, expedient connections / cross connections were quantified based on the actual field measurements collected under the KTPR. It is expected that adequate sewerage will be provided for the planned developments at Kai Tak and the wastewater generated from the new KTD will be diverted to the Harbour Area Treatment Scheme (HATS) for treatment and disposal in the western Victoria Harbour via a submarine outfall to the south of Tsing Yi Island.

5.7 Uncertainties in Assessment Methodology

5.7.1 Quantitative uncertainties in the modelling need to be considered when making an evaluation of the modelling predictions.  The following approach was adopted to enhance the model performance:

l The computational grid of the detailed SEK Model was fine grid model which is capable to represent the coastal features at the Study Area;

l Use of a fully calibrated and validated regional Update Model to provide boundary and initial conditions to the detailed SEK Model;

l The performance of the detailed SEK Model was extensively calibrated and validated with reference to the field data to ensure that reliable predictions of hydrodynamics and water quality are provided for the Study area.

l The simulation comprises a sufficient spin up period so that the initial conditions do not affect the results.

5.7.2 It should be noted that all the predictions made in this section were based on the latest available information and assumptions discussed in Section 5.6 above. If there are any major changes to the key assumptions during the actual implementation of the Project in the future, including those for the concurrent projects, the prediction and assessment findings presented in this EIA report should be reviewed accordingly.

5.8 Prediction and Evaluation of Potential Environmental Impacts

Impact from Capital Dredging

Suspended Solids

5.8.1 Under the sediment plume modelling scenarios, deployment of silt curtain around the dredging operations is assumed for the WDII and TKO reclamation as recommended in their respective EIA studies.

5.8.2 Each modelling scenario was modelled with an actual simulation period (excluding spin-up) of one typical spring-neap tidal cycle in both dry and wet seasons. Absolute maximum and tidal-averaged SS concentrations predicted over a spring-neap cycle at the seawater intake, taking into account the background SS concentration, are presented in Table 5.16 to Table 5.18 for the base case scenarios. The 90 percentile SS level predicted at the corresponding indicator points under the pre-construction scenario is used as the background SS concentrations for conservative predictions. The SS elevations and sedimentation rates predicted at the coral communities are provided in Table 5.19 to Table 5.21 for the base case scenarios. Sensitivity tests were conducted using higher dredging rates for the new gas main and CKR (refer to Sections 5.6.24 and 5.6.27), and their results are given in Table 5.16a to Table 5.21a. The results shown in these tables indicate exceedances (highlighted in bold) of assessment criteria for WSD flushing water intakes under all the assessment scenarios. All the coral sites would however comply with the relevant criteria, except the coral site at Cape Collinson under the sensitivity test (Table 5.19a), where the maximum SS elevation would only marginally exceed the WQO with compliance rate of over 99%. Mitigation measures are considered in Section 5.9 to mitigate the water quality impacts.

5.8.3 The contour maps of cumulative SS elevations and sedimentation rates caused by all concurrent activities predicted under the unmitigated scenarios are given in Appendix 5.4 to Appendix 5.9. Based on the review of the model results, there is no significant difference in the sediment plume size predicted under the base case scenarios and the sensitivity tests. Therefore, the contour maps are presented for the base case scenarios only. Each figure attached to these appendices contains two contour plots where the upper plot shows the unmitigated scenarios and the lower plot shows the mitigated scenarios. Discussion on the mitigated scenarios is given in Section 5.9.

^{Table 5.16 Predicted SS Concentrations at Seawater Intakes for Scenario 1A – Unmitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.3	9.7	100.0%	5.3	6.6	100.0%
China H.K. City (C15)	-	8.3	9.4	-	5.4	5.9	-
Harbour City (C16)	-	8.3	9.5	-	5.3	5.4	-
Ocean Centre (C17)	-	8.3	9.5	-	5.3	5.4	-
Ocean Terminal (C18)	-	8.7	13.0	-	5.7	6.8	-
Government Premises (C19)	-	9.5	16.0	-	5.7	7.3	-
New World Centre (C20)	-	9.7	13.8	-	5.7	6.6	-
East Rail Extension (C21)	-	9.5	12.4	-	5.3	6.5	-
Dairy Farm Ice Plant (C22)	-	11.5	21.2	-	5.9	35.4	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	7.0	8.2	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	11.5	29.3	-	6.8	10.2	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	11.4	19.0	0.0%	5.8	29.4	96.1%
Tseung Kwan O (WSD12)	< 10	7.5	8.1	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.4	8.0	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	9.3	21.4	76.2%	4.8	8.2	100.0%
Quarry Bay (WSD17)	< 10	9.7	23.0	68.7%	5.0	11.2	99.4%
Sheung Wan (WSD19)	< 10	9.2	12.7	88.1%	6.1	8.2	100.0%
Wan Chai (WSD21) ^See Note 1	< 10	7.9	24.1	82.8%	5.3	15.7	98.1%
Tai Wan (WSD9)	< 10	9.7	17.1	67.9%	6.2	14.5	95.6%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

Note 1: The dredging activities for WDII are included in Scenario 1A only. As the WSD Wan Chai flushing water intake is located within the WDII reclamation site boundary, the SS elevation at this flushing water intake should mainly be caused by the WDII dredging activities. Under the WDII Planning and Engineering Review, a different model (namely the refined detailed VH model) was used to predict the SS elevations in the Victoria Harbour from the exact same concurrent dredging activities considered under Scenario 1A. The grid mesh of the refined detailed VH model has a higher resolution within the WDII reclamation site aiming to provide a detailed prediction on the water quality impact generated from the WDII activities. The refined detailed VH model can therefore give a more accurate SS elevation profile within the WDII reclamation site where the WSD Wan Chai flushing water intake is located. Therefore, the predicted SS concentrations for Wan Chai flushing water intake as shown in the above table are directly extracted from the model results available under the WDII Planning and Engineering Review for the exact same concurrent dredging scenario. No other WSD flushing water intake is located within the dredging site.

^{Table 5.16a Predicted SS Concentrations at Seawater Intakes for Scenario 1A – Unmitigated (Sensitivity Test using Higher Dredging Rate for Gas Main Construction)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.3	10.4	100.0%	5.6	10.2	100.0%
China H.K. City (C15)	-	8.4	9.7	-	5.5	7.1	-
Harbour City (C16)	-	8.3	9.9	-	5.4	5.4	-
Ocean Centre (C17)	-	8.3	9.9	-	5.4	5.4	-
Ocean Terminal (C18)	-	8.9	15.0	-	6.1	9.8	-
Government Premises (C19)	-	10.0	18.6	-	6.1	9.1	-
New World Centre (C20)	-	10.2	15.4	-	5.9	7.4	-
East Rail Extension (C21)	-	10.0	14.6	-	5.5	7.2	-
Dairy Farm Ice Plant (C22)	-	11.7	21.2	-	6.0	35.5	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	7.1	8.4	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	11.7	29.4	-	6.8	10.4	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	11.5	19.0	0.0%	5.8	29.6	95.8%
Tseung Kwan O (WSD12)	< 10	7.5	8.2	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.5	8.3	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	9.4	21.4	74.8%	4.8	8.3	100.0%
Quarry Bay (WSD17)	< 10	9.9	23.0	64.5%	5.0	11.4	99.4%
Sheung Wan (WSD19)	< 10	9.2	12.7	87.8%	6.2	8.4	100.0%
Wan Chai (WSD21) ^See Note 1	< 10	8.0	24.1	82.8%	5.3	15.7	98.1%
Tai Wan (WSD9)	< 10	10.3	20.8	57.9%	6.8	14.7	91.4%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

Note 1: The dredging activities for WDII are included in Scenario 1A only. As the WSD Wan Chai flushing water intake is located within the WDII reclamation site boundary, the SS elevation at this flushing water intake should mainly be caused by the WDII dredging activities. Under the WDII Planning and Engineering Review, a different model (namely the refined detailed VH model) was used to predict the SS elevations in the Victoria Harbour from the exact same concurrent dredging activities considered under Scenario 1A. The grid mesh of the refined detailed VH model has a higher resolution within the WDII reclamation site aiming to provide a detailed prediction on the water quality impact generated from the WDII activities. The refined detailed VH model can therefore give a more accurate SS elevation profile within the WDII reclamation site where the WSD Wan Chai flushing water intake is located. Therefore, the predicted SS concentrations for Wan Chai flushing water intake as shown in the above table are directly extracted from the model results available under the WDII Planning and Engineering Review for the exact same concurrent dredging scenario. No other WSD flushing water intake is located within the dredging site.

^{Table 5.17 Predicted SS Concentrations at Seawater Intakes for Scenario 1B – Unmitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.1	9.7	100.0%	5.2	6.0	100.0%
China H.K. City (C15)	-	8.2	9.1	-	5.4	5.7	-
Harbour City (C16)	-	8.1	9.0	-	5.3	5.3	-
Ocean Centre (C17)	-	8.1	9.0	-	5.3	5.3	-
Ocean Terminal (C18)	-	8.4	10.8	-	5.6	6.7	-
Government Premises (C19)	-	9.0	12.6	-	5.5	6.5	-
New World Centre (C20)	-	9.1	11.9	-	5.5	6.5	-
East Rail Extension (C21)	-	9.0	10.9	-	5.1	5.9	-
Dairy Farm Ice Plant (C22)	-	11.0	26.0	-	5.8	12.6	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	6.5	6.9	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	8.9	12.3	-	5.4	6.1	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	11.0	22.5	0.0%	5.8	13.5	96.1%
Tseung Kwan O (WSD12)	< 10	7.5	8.0	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.3	7.2	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	7.9	10.4	99.7%	4.4	5.5	100.0%
Quarry Bay (WSD17)	< 10	8.4	24.1	95.3%	4.5	6.5	100.0%
Sheung Wan (WSD19)	< 10	8.9	9.6	100.0%	5.6	6.2	100.0%
Wan Chai (WSD21)	< 10	8.2	10.6	99.7%	4.9	5.1	100.0%
Tai Wan (WSD9)	< 10	9.3	16.4	78.9%	5.2	7.9	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.17a Predicted SS Concentrations at Seawater Intakes for Scenario 1B – Unmitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.2	9.9	100.0%	5.2	6.0	100.0%
China H.K. City (C15)	-	8.2	9.4	-	5.4	5.7	-
Harbour City (C16)	-	8.1	9.1	-	5.3	5.3	-
Ocean Centre (C17)	-	8.1	9.1	-	5.3	5.3	-
Ocean Terminal (C18)	-	8.4	11.1	-	5.6	6.7	-
Government Premises (C19)	-	9.1	12.8	-	5.5	6.5	-
New World Centre (C20)	-	9.3	12.0	-	5.5	6.5	-
East Rail Extension (C21)	-	9.1	11.5	-	5.1	5.9	-
Dairy Farm Ice Plant (C22)	-	11.0	26.0	-	5.8	12.6	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	6.5	7.0	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	8.9	12.3	-	5.4	6.1	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	11.0	22.5	0.0%	5.8	13.5	96.1%
Tseung Kwan O (WSD12)	< 10	7.5	8.0	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.3	7.2	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	7.9	10.4	99.7%	4.4	5.5	100.0%
Quarry Bay (WSD17)	< 10	8.4	24.1	94.7%	4.5	6.5	100.0%
Sheung Wan (WSD19)	< 10	8.9	9.6	100.0%	5.6	6.2	100.0%
Wan Chai (WSD21)	< 10	8.2	10.6	99.7%	4.9	5.1	100.0%
Tai Wan (WSD9)	< 10	9.5	19.8	75.9%	5.2	7.9	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.18 Predicted SS Concentrations at Seawater Intakes for Scenario 1C – Unmitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	9.8	12.1	100.0%	5.5	6.1	100.0%
China H.K. City (C15)	-	9.7	11.8	-	5.4	5.7	-
Harbour City (C16)	-	9.6	10.7	-	5.4	5.5	-
Ocean Centre (C17)	-	9.6	10.7	-	5.4	5.5	-
Ocean Terminal (C18)	-	9.9	12.2	-	5.6	6.1	-
Government Premises (C19)	-	10.3	14.2	-	5.5	6.0	-
New World Centre (C20)	-	10.6	13.0	-	5.5	5.8	-
East Rail Extension (C21)	-	10.3	12.5	-	5.1	5.4	-
Dairy Farm Ice Plant (C22)	-	12.3	30.4	-	6.4	20.2	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	8.2	9.0	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	10.4	12.7	-	5.5	6.2	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	12.3	31.4	0.0%	6.3	16.6	91.4%
Tseung Kwan O (WSD12)	< 10	8.5	9.4	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	7.9	9.4	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	9.8	11.3	66.8%	4.4	5.2	100.0%
Quarry Bay (WSD17)	< 10	10.4	16.3	50.1%	4.5	6.3	100.0%
Sheung Wan (WSD19)	< 10	9.7	12.5	82.5%	5.6	6.2	100.0%
Wan Chai (WSD21)	< 10	10.1	15.5	56.8%	4.9	5.1	100.0%
Tai Wan (WSD9)	< 10	11.5	18.0	0.0%	5.1	6.3	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.18a Predicted SS Concentrations at Seawater Intakes for Scenario 1C – Unmitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	9.8	12.2	100.0%	5.5	6.1	100.0%
China H.K. City (C15)	-	9.7	11.9	-	5.4	5.7	-
Harbour City (C16)	-	9.6	10.8	-	5.4	5.5	-
Ocean Centre (C17)	-	9.6	10.8	-	5.4	5.5	-
Ocean Terminal (C18)	-	10.0	12.2	-	5.6	6.1	-
Government Premises (C19)	-	10.3	14.3	-	5.5	6.0	-
New World Centre (C20)	-	10.6	13.1	-	5.5	5.8	-
East Rail Extension (C21)	-	10.3	12.6	-	5.1	5.4	-
Dairy Farm Ice Plant (C22)	-	12.3	30.4	-	6.4	20.2	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	8.2	9.1	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	10.4	12.7	-	5.5	6.2	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	12.3	31.5	0.0%	6.3	16.6	91.4%
Tseung Kwan O (WSD12)	< 10	8.5	9.4	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	8.0	9.4	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	9.9	11.3	65.7%	4.4	5.2	100.0%
Quarry Bay (WSD17)	< 10	10.4	16.3	50.1%	4.5	6.3	100.0%
Sheung Wan (WSD19)	< 10	9.7	12.6	82.5%	5.6	6.2	100.0%
Wan Chai (WSD21)	< 10	10.1	15.5	56.2%	4.9	5.1	100.0%
Tai Wan (WSD9)	< 10	11.5	18.0	0.0%	5.1	6.3	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.19 Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1A - Unmitigated (Base Case Scenario)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.19	< 2.09	0.28	0.97	100.0%	< 100	6.73	13.35	100.0%
Junk Bay - Junk Island (CR28)	5.95	< 1.76	0.37	1.01	100.0%	< 100	6.62	19.89	100.0%
Cape Collinson (CR44)	5.46	< 1.54	0.44	1.44	100.0%	< 100	3.91	17.44	100.0%
Dry Season
Junk Bay ( CR27 )	3.93	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.54	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.04	100.0%	< 100	3.22	5.18	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.06	100.0%	< 100	3.18	6.16	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

^{Table 5.19a Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1A - Unmitigated (Sensitivity Test using Higher Dredging Rate for Gas Main Construction)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.19	< 2.09	0.30	1.02	100.0%	< 100	6.84	13.77	100.0%
Junk Bay - Junk Island (CR28)	5.95	< 1.76	0.42	1.13	100.0%	< 100	6.93	22.15	100.0%
Cape Collinson (CR44)	5.46	< 1.54	0.50	1.65	99.7%	< 100	3.91	19.24	100.0%
Dry Season
Junk Bay ( CR27 )	3.93	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.54	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.05	100.0%	< 100	3.23	5.68	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.06	100.0%	< 100	3.18	6.57	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

^{Table 5.20 Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1B – Unmitigated (Base Case Scenario)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.17	< 2.09	0.09	0.38	100.0%	< 100	5.12	9.17	100.0%
Junk Bay - Junk Island (CR28)	5.95	< 1.76	0.29	1.03	100.0%	< 100	5.71	12.94	100.0%
Cape Collinson (CR44)	5.46	< 1.54	0.25	0.61	100.0%	< 100	3.90	13.16	100.0%
Dry Season
Junk Bay ( CR27 )	3.93	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.50	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.02	100.0%	< 100	3.20	4.19	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.03	100.0%	< 100	3.19	4.69	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

^{Table 5.20a Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1B - Unmitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.17	< 2.09	0.10	0.38	100.0%	< 100	5.13	9.18	100.0%
Junk Bay - Junk Island (CR28)	5.95	< 1.76	0.29	1.04	100.0%	< 100	5.74	13.08	100.0%
Cape Collinson (CR44)	5.46	< 1.54	0.26	0.62	100.0%	< 100	3.90	13.25	100.0%
Dry Season
Junk Bay ( CR27 )	3.93	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.50	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.02	100.0%	< 100	3.20	4.19	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.03	100.0%	< 100	3.19	4.69	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

^{Table 5.21 Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1C – Unmitigated (Base Case Scenario)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.94	< 2.35	0.26	0.90	100.0%	< 100	7.24	14.61	100.0%
Junk Bay - Junk Island (CR28)	6.99	< 2.07	0.53	1.88	100.0%	< 100	8.09	24.29	100.0%
Cape Collinson (CR44)	6.70	< 1.87	0.25	0.76	100.0%	< 100	4.65	14.33	100.0%
Dry Season
Junk Bay ( CR27 )	3.92	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.49	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.02	100.0%	< 100	3.20	4.03	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.02	100.0%	< 100	3.19	4.32	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

^{Table 5.21a Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1C - Unmitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.94	< 2.35	0.26	0.90	100.0%	< 100	7.26	14.63	100.0%
Junk Bay - Junk Island (CR28)	6.99	< 2.07	0.53	1.89	100.0%	< 100	8.11	24.30	100.0%
Cape Collinson (CR44)	6.70	< 1.87	0.26	0.77	100.0%	< 100	4.65	14.42	100.0%
Dry Season
Junk Bay ( CR27 )	3.92	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.49	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.02	100.0%	< 100	3.20	4.03	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.02	100.0%	< 100	3.19	4.32	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

Cumulative Impact from Marine Works in Junk Bay

5.8.4 The possible dredging and filling works for TKO reclamation have been included in the model for the cruise terminal Stage 1 dredging under Scenario 1A to assess the potential cumulative impact. The model results indicate that the influence of the TKO works would be insignificant at the seawater intake points along the waterfront of the Victoria Harbour. The contour maps of SS elevations and sedimentation rates caused by the KTD works alone are given in Appendix 5.10 to Appendix 5.15. The model results suggested that Junk Bay is outside the influence zone of the sediment plume contributed from the KTD works alone. Therefore, the TKO reclamation works as well as the cable burying works for the offshore wind farm would not contribute cumulative impact with the KTD works.

Compliance with WQO for SS Elevation

5.8.5 Non-compliance with the WQO for SS (i.e. elevation of less than 30% of ambient baseline level) is predicted in the Victoria Harbour near the cruise terminal dredging site during both Stage 1 and Stage 2 dredging. The worst case impact in terms of the relative SS elevation would occur during the Stage 1 dredging (Scenario 1A) in the dry season. The maximum dimension of the mixing zone for SS elevation is shown in Appendix 5.15a. Based on the review of the model results, there is no significant difference in the sediment plume size predicted under the base case scenarios and the sensitivity tests (refer to Sections 5.6.24 and 5.6.27). Therefore, the contour maps are presented for the base case scenarios only. This appendix contains two contour plots where the upper plot shows the unmitigated scenarios and the lower plot shows the mitigated scenarios. As shown in the contour plots, the mixing zone predicted under the worst-case scenario would be localized. Full compliance with the WQO is predicted at all the identified water sensitive receivers. The mixing zones for DO, nutrients are discussed in Sections 5.8.17 and 5.8.21.

Impact on Coral Communities and Fish Culture Zones

5.8.6 The model results as shown in Table 5.19 to Table 5.21 and Table 5.19a to Table 5.21a suggested that full compliance with the WQO for SS elevation and the criteria value for sedimentation rate would be achieved at all the coral sites identified in Green Island, Junk Bay. The maximum SS elevation predicted at the coral site identified in Cape Collinson would only marginally exceed the WQO with a compliance rate of over 99% under the sensitivity test for Stage 1 dredging only (Table 5.19a). Mitigation measures are recommended in Section 5.9 to mitigate the water quality impacts. With the recommended mitigation measures, full compliance with the WQO for SS elevation would be achieved at the coral site in Cape Collinson. Hence, no adverse effect upon these far field coral sites would be expected from the proposed dredging works. Impact from maintenance dredging is assessed in Section 5.8.23. The model results have considered the possible scenario of opening a large gap at the runway (under Scenario 1C).

5.8.7 As shown in Appendix 5.4 to Appendix 5.9, the Tung Lung Chau and Ma Wan fish culture zones are located outside the influence zone of the sediment plumes. Thus, no adverse water quality impact on these fish culture zones would be expected from the proposed dredging works.

Potential Contaminant Release During Dredging

5.8.8 An indication of the likelihood of release of contaminants from the marine mud during dredging is given by the results of the elutriation tests from the laboratory testing conducted under the marine SI for selected sediment sampling stations as shown in Table 5.22 and Table 5.23. Description of the marine SI is given in Section 5.4.7. Sediment samples mixed with a solution, i.e. the ambient seawater collected from the same site, were vigorously agitated during the tests to simulate the strong disturbance to the seabed sediment during dredging. Pollutants absorbed onto the sediment particles would be released and increasing the pollutant concentrations in the solution. The laboratory testing was to analyse the pollutant concentrations in the solution (elutriate). If the contaminant levels are higher in the elutriates in comparison with the blanks (i.e. marine water from the same site), it can be concluded that the contaminants are likely to be released into the marine waters during dredging activities. As there is no existing legislative standard or guideline for individual heavy metal contents in marine waters, the UK Water Quality Standards for Coastal Surface Water ⁽[18]⁾ have been adopted as the assessment criteria.

5.8.9 The elutriate samples were analyzed for heavy metals, TBT, total PCBs, total PAHs, NH₃-N , TIN and chlorinated pesticides (including alpha-BHC, beta-BHC, gamma-BHC, delta-BHC, heptachlor, Aldrin, heptachlor epoxide, endososulfan, p,p’-DDT, p,p’-DDD, p,p’-DDE, endosulfan sulphate). The measured NH₃-N released from the sediment will result in a concentration of total NH₃-N in the receiving waters. The levels of NH₃-N were converted to unionized NH₃-N which is a more critical parameter of concern. Review of data collected at the EPD monitoring stations VM2, VT10 and VT11 (closest to the dredging site) in the period from 2002 to 2005 indicates that the maximum contribution of unionised NH₃-N in the total NH3-N concentration was 5.7%. This maximum contribution was used to calculate the levels of unionized NH₃-N in the elutriate samples.

5.8.10 Table 5.22 and Table 5.23 show the elutriate testing results for heavy metals, TBT, total PCBs, total PAHs, NH₃-N and TIN. The measured levels of all the chlorinated pesticides chemicals were below the detection limit and their associated impact is discussed in Section 5.8.11.

^{Table 5.22 Comparison of Phase 1 Marine Site Investigation Sediment Elutriate Test Results with the Water Quality Standards}

Vibrocore (Figure 6.1)	Sampling Depth (m)	Metal content (mg/l)									Organic Compounds Content (mg/l)			Nutrients (mg/l)
		Ag	Cd	Cu	Ni	Pb	Zn	Cr	As	Hg	Total PCBs	Total PAHs	TBT	UIA	TIN
Water Quality Standards		2.3^(2)	2.5 ^(2)	5 ^(2)	30 ^(2)	25 ^(2)	40 ^(2)	15 ^(2)	25 ^(2)	0.3 ^(2)	0.03 ^(3)	3.0 ^(4)	0.1 ^(5)	0.021 ^(6)	0.4 ^(6)
A08	0.0-0.9	<1	<0.2	17	13.0	<1	<4	<1	7	0.20	<0.01	<0.4	<0.015	0.006	0.244
	0.9-1.9	<1	<0.2	15	16	<1	<4	<1	21	0.20	<0.01	<0.4	<0.015	0.025	0.627
	1.9-2.9	<1	<0.2	29	55	<1	<4	<1	7.7	<0.1	<0.01	<0.4	<0.015	0.017	0.354
	Blank	<1	<0.2	17	1.6	10	20	4.9	2.3	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A02	0.0-0.9	<1	0.20	14	16	1.8	4.9	<1	13	<0.1	<0.01	<0.4	<0.015	0.023	0.553
	0.9-1.9	<1	0.20	13	17.0	<1	<4	<1	15	0.50	<0.01	<0.4	<0.015	0.024	0.539
	1.9-2.9	<1	0.30	6.6	11	<1	<4	<1	35	<0.1	<0.01	<0.4	<0.015	0.020	0.507
	2.9-3.9	<1	0.40	8.3	18	<1	<4	<1	27	<0.1	<0.01	<0.4	<0.015	0.015	0.415
	3.9-4.9	<1	0.60	18	46	<1	<4	<1	45	<0.1	<0.01	<0.4	<0.015	0.015	0.415
	Blank	<1	<0.2	<1	<1	<1	5.4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.008	0.235
A26	0.0-0.9	<1	0.30	29	75	<1	<4	<1	20	<0.1	<0.01	<0.4	<0.015	0.011	0.337
	0.9-1.9	<1	0.30	25	54	<1	<4	<1	20	<0.1	<0.01	<0.4	<0.015	0.009	0.299
	1.9-2.9	<1	<0.2	14	30	<1	<4	<1	17	<0.1	<0.01	<0.4	<0.015	0.013	0.335
	Blank	<1	<0.2	3	<1	<1	6.1	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.008	0.246
A06	0.0-0.9	<1	3.60	9.8	5.9	4.1	5.4	<1	16	0.10	<0.01	<0.4	<0.015	0.021	0.521
	0.9-1.9	<1	<0.2	6.0	2.5	<1	<4	<1	16	<0.1	<0.01	<0.4	<0.015	0.023	0.545
	1.9-2.9	<1	0.60	18	5.4	<1	4.3	21	27	<0.1	<0.01	<0.4	<0.015	0.026	0.594
	Blank	<1	<0.2	<1	<1	<1	<4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A13	0.0-0.9	<1	0.30	4.9	3.7	<1	7.9	<1	5.5	<0.1	<0.01	<0.4	<0.015	0.011	0.325
	0.9-1.9	<1	1.30	18	5.8	<1	<4	<1	18	<0.1	<0.01	<0.4	<0.015	0.006	0.244
	1.9-2.9	<1	<0.2	2.1	2.9	<1	<4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.007	0.267
	Blank	<1	<0.2	8.9	<1	4.2	7.6	2.6	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A15	0.0-0.9	<1	<0.2	<1	7.8	<1	<4	<1	12	<0.1	<0.01	<0.4	<0.015	0.013	0.331
	0.9-1.9	<1	0.30	<1	2.4	1.6	<4	<1	14	<0.1	<0.01	<0.4	<0.015	0.028	0.627
	Blank	<1	<0.2	1.4	<1	<1	<4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A16	0.0-0.9	<1	0.20	2.1	2.6	<1	<4	<1	24	<0.1	<0.01	<0.4	<0.015	0.025	0.611
	0.9-1.9	<1	0.40	1.9	2.9	<1	5.1	1.2	12	<0.1	<0.01	<0.4	<0.015	0.011	0.314
	Blank	<1	<0.2	1.5	<1	<1	<4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A25	0.0-0.9	<1	0.30	18	6.0	<1	10	<1	2.0	<0.1	<0.01	<0.4	<0.015	0.007	0.233
	0.9-1.9	<1	0.20	<1	1.1	<1	<4	<1	16	<0.1	<0.01	<0.4	<0.015	0.019	0.448
	1.9-2.9	<1	0.40	2.5	1.9	<1	<4	<1	15	<0.1	<0.01	<0.4	<0.015	0.006	0.244
	2.9-3.9	<1	0.30	<1	2.3	<1	32	<1	9.1	<0.1	<0.01	<0.4	<0.015	0.010	0.307
	Blank	<1	<0.2	1.2	<1	<1	26	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200
A23	0.0-0.9	<1	0.30	2.5	3.4	<1	5.2	<1	5.5	<0.1	<0.01	<0.4	<0.015	0.020	0.490
	0.9-1.9	<1	0.50	<1	4.0	<1	<4	<1	52	<0.1	<0.01	<0.4	<0.015	0.006	0.244
	1.9-2.9	<1	0.30	1.2	2.0	<1	<4	<1	13	<0.1	<0.01	<0.4	<0.015	0.012	0.354
	Blank	<1	<0.2	1.2	<1	<1	<4	<1	<2.0	<0.1	<0.01	<0.4	<0.015	0.006	0.200

Notes: (1) Value in bold indicates exceedance of the Water Quality Standard.

(2) UK Water Quality Standard.

(3) USEPA salt water criterion.

(4) Australian water quality guidelines for fresh and marine waters.

(5) Michael H. Salazar and Sandra M. Salazar (1996). “Mussels as Bioindicators: Effects of TBT on Survival, Bioaccumulation, and Growth under Natural Conditions” in Organotin, edited by M. A. Champ and P. F. Seligman. Chapman & Hall, London.

(6) WQO for Victoria Harbour WCZ under the WPCO.

^{Table 5.23 Comparison of Phase 2 Marine Site Investigation Sediment Elutriate Test Results with the Water Quality Standards}

Vibrocore (Figure 6.1)	Sampling Depth (m)	Metal content (mg/l)									Organic Compounds Content (mg/l)			Nutrients (mg/l)
		Ag	Cd	Cu	Ni	Pb	Zn	Cr	As	Hg	Total PCBs	Total PAHs	TBT	UIA	TIN
Water Quality Standards		2.3^(2)	2.5 ^(2)	5 ^(2)	30 ^(2)	25 ^(2)	40 ^(2)	15 ^(2)	25 ^(2)	0.3 ^(2)	0.03 ^(3)	3.0 ^(4)	0.1 ^(5)	0.021 ^(6)	0.4 ^(6)
B05	0.0-0.9	<1	0.55	3.7	<1	<1	<4	<1	34	<0.1	<0.01	<0.4	<0.015	0.009	0.253
	0.9-1.9	<1	0.67	1	<1	<1	<4	<1	38	<0.1	<0.01	<0.4	<0.015	0.006	0.204
	Blank	<1	<0.2	<1	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B10	0.0-0.9	<1	0.96	<1	1.5	<1	<4	<1	22	<0.1	<0.01	<0.4	<0.015	0.007	0.259
	0.9-1.9	<1	0.36	<1	1.3	<1	<4	<1	4.6	<0.1	<0.01	<0.4	<0.015	0.008	0.271
	1.9-2.9	<1	<0.2	<1	<1	<1	<4	<1	<2	<0.1	<0.01	<0.4	<0.015	0.006	0.200
	Blank	<1	<0.2	3.4	<1	<1	4.1	<1	<2	<0.1	<0.01	<0.04	<0.015	0.010	0.274
B12	0.0-0.9	<1	<0.2	<1	<1	<1	<4	<1	<2	<0.1	<0.01	<0.4	<0.015	0.011	0.289
	0.9-1.9	<1	<0.2	<1	<1	<1	<4	<1	12	<0.1	<0.01	<0.4	<0.015	0.012	0.359
	Blank	<1	<0.2	<1	<1	2	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B14	0.0-0.9	<1	0.66	5.2	6.6	<1	8.9	<1	2.1	<0.1	<0.01	<0.4	<0.015	0.006	0.200
	0.9-1.9	<1	0.95	5.2	<1	<1	<4	<1	20	<0.1	<0.01	<0.4	<0.015	0.006	0.209
	1.9-2.9	<1	0.46	<1	2.0	<1	6.1	<1	12	<0.1	<0.01	<0.4	<0.015	0.006	0.205
	Blank	<1	<0.2	<1	<1	1.7	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B16	0.0-0.9	<1	0.68	<1	<1	<1	<4	<1	16	<0.1	<0.01	<0.4	<0.015	0.006	0.200
	0.9-1.9	<1	0.61	<1	<1	<1	<4	<1	14	<0.1	<0.01	<0.4	<0.015	0.010	0.270
	Blank	<1	<0.2	2.6	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B20	0.0-0.9	<1	<0.2	<1	<1	1.9	<4	<1	9.5	<0.1	<0.01	<0.4	<0.015	0.025	0.535
	0.9-1.9	<1	0.73	<1	1.0	<1	<4	<1	15	<0.1	<0.01	<0.4	<0.015	0.006	0.205
	Blank	<1	<0.2	3.7	<1	<1	5.0	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B21	0.0-0.9	<1	0.67	<1	4.1	12	6.8	<1	3.8	<0.1	<0.01	<0.4	<0.015	0.006	0.213
	0.9-1.9	<1	1.70	<1	1.5	<1	<4	<1	16	<0.1	<0.01	<0.4	<0.015	0.013	0.330
	Blank	<1	<0.2	<1	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B22	0.0-0.9	<1	0.73	<1	2.1	<1	<4	<1	4.2	<0.1	<0.01	<0.4	<0.015	0.006	0.200
	0.9-1.9	<1	0.36	<1	2.3	<1	<4	<1	4.4	<0.1	<0.01	<0.4	<0.015	0.006	0.200
	Blank	<1	<0.2	2.5	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B31	0.0-0.9	<1	0.91	1.1	2.0	<1	<4	<1	14	<0.1	<0.01	<0.4	<0.015	0.007	0.219
	0.9-1.9	<1	0.38	1.2	5.9	2.6	<4	<1	6.3	<0.1	<0.01	<0.4	<0.015	0.008	0.246
	Blank	<1	<0.2	<1	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B32	0.0-0.9	<1	0.88	<1	1.9	<1	<4	<1	10	<0.1	<0.01	<0.4	<0.015	0.010	0.267
	0.9-1.9	<1	1.10	<1	<1	<1	<4	<1	13	<0.1	<0.01	<0.4	<0.015	0.013	0.331
	Blank	<1	<0.2	2.2	<1	<1	<4	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200
B33	0.0-0.9	<1	0.69	<1	<1	<1	22	<1	18	<0.1	<0.01	<0.4	<0.015	0.008	0.240
	0.9-1.9	<1	0.73	<1	1.2	<1	<4	<1	12	<0.1	<0.01	<0.4	<0.015	0.021	0.467
	Blank	<1	<0.2	2.5	<1	1.5	4.1	<1	<2	<0.1	<0.01	<0.04	<0.015	0.006	0.200

Notes: (1) Value in bold indicates exceedance of the Water Quality Standard.

(1) UK Water Quality Standard.

(2) USEPA salt water criterion.

(3) Australian water quality guidelines for fresh and marine waters.

(4) Michael H. Salazar and Sandra M. Salazar (1996). “Mussels as Bioindicators: Effects of TBT on Survival, Bioaccumulation, and Growth under Natural Conditions” in Organotin, edited by M. A. Champ and P. F. Seligman. Chapman & Hall, London.

(5) WQO for Victoria Harbour WCZ under the WPCO.

5.8.11 Table 5.22 and Table 5.23 showed that the concentrations of cadmium, copper, nickel, mercury, UIA and TIN in the elutriate samples exceeded the assessment criteria. The highest concentrations of copper (29mg/l) and nickel (75mg/l) were recorded at Station A26. The highest concentrations of UIA (0.028mg/l) and TIN (0.6mg/l) were recorded at Station A15. The highest concentrations of cadmium (3.6mg/l) and mercury (0.5mg/l) were recorded at Stations A06 and A02 respectively. The levels of silver, lead, zinc, chromium and arsenic in the elutriate samples complied well with the relevant water quality criteria.

5.8.12 The elutriate test results of TBT, total PCBs and total PAHs do not indicate any levels higher than the blank results nor the water quality criteria. It is therefore concluded that adverse water quality impacts due to the potential release of TBT, total PCBs and total PAHs from the sediment are not expected during the dredging activities.

5.8.13 Chlorinated pesticides including alpha-BHC, beta-BHC, gamma-BHC, delta-BHC, heptachlor, Aldrin, heptachlor epoxide, endososulfan, p,p’-DDT, p,p’-DDD, p,p’-DDE, endosulfan sulphate, were also measured in both the sediment and elutriate samples. The laboratory results show that these pesticides were not detected in any of the sediment and elutriate samples. All the measured values are below the detection limit of 0.5 mg/kg for sediment and 0.1 mg/l for elutriate. Also, the elutriate test results do not indicate any levels higher than the blank results which indicated that the impact from the potential release of pesticides during dredging would not be an issue of concern.

5.8.14 Based on the elutriate test results from the Phase 2 marine SI, potential of contaminant release was found to be low at the outer stations (closer to the main Harbour channel and the fairway). As shown in Table 5.23, all the measured pollutant concentrations (other than copper at B14) in the elutriate samples from the Phase 2 marine SI complied well with the water quality criteria. The copper level measured at B14 only marginally exceeded the assessment criterion of 5mg/l. All the rest of the measured copper levels were much lower than the assessment criterion. The potential impact is therefore considered isolated and limited. No adverse water quality impacts due to the release of contaminants from the dredging are therefore expected within the outer dredging areas near the fairway.

5.8.15 The highest concentrations of cadmium, copper, nickel, mercury, UIA and TIN were all measured under the Phase 1 marine SI conducted at the inner stations (closer to the shore). Based on the detected highest concentrations, the required dilutions to meet the assessment criteria were calculated to be 1.4 (for cadmium), 6 (for copper), 2.5 (for nickel), 1.7 (for mercury), 1.3 (for UIA) and 1.5 (for TIN).

5.8.16 An assessment of contaminant release for cadmium, copper, nickel, mercury, UIA and TIN has been made in relation to the sediment quality results as presented in Table 6.4 and Table 6.5 in Section 6. Inert tracers (with zero decay) were introduced into the Delft3D-WAQ model for Scenario 1A, Scenario 1B and Scenario 1C model runs to represent the release of these contaminants during dredging. Discharge of inert tracers was assumed at a source point (discharge location). In the calculation of the contaminant loss rate for model input, it was assumed that all of the heavy metals and nutrient concentrations in the sediment would be released to the water. These are conservative assumptions and will likely result in an over-prediction of the potential impacts. The calculation was performed using the highest levels of nutrient and heavy metals measured in the sediment samples collected during the marine SI for conservative predictions. The highest levels of cadmium and copper were measured in the sediment sample collected at Station A10. The highest levels of nickel, mercury and nutrients were recorded at Stations A01, A05 and A08 respectively.

5.8.17 Eight separate tracer simulations were performed for the 8 source points respectively, namely A1, A2, A3, A4 (under Scenario 1A), B1, B2 (under Scenario 1B) and C1, C2 (under Scenario 1C) to determine the maximum dimensions of mixing zones for the contaminants including cadmium, copper, nickel, mercury, UIA and TIN. Each simulation covered two model runs for dry and wet seasons respectively. Appendix 5.16 to Appendix 5.18 show the contour plots of maximum contaminant concentrations predicted over the entire simulation period for Scenario 1A, Scenario 1B and Scenario 1C respectively. As shown in the contour plots, the maximum concentrations for all selected parameters (except copper under Scenario 1A) fully complied with their respective water quality standards. For copper (under Scenario 1A) in which the water quality standard is exceeded, the area of modelled exceedance would be highly localized and confined within 200 m from the dredging location.

5.8.18 It is considered that the mixing zone of any contaminant release from the dredging operation would be moving around the dredging site as driven by the changing water current. As the model results are presented as the maximum values predicted over the entire simulation period, the areas of modelled exceedances shown in the contour plots do not represent the actual maximum plume size. They are considered as the areas which envelop the moving plumes over the entire simulation period. The maximum instantaneous coverage of the mixing zone for copper should be much smaller. Therefore, impact on the marine ecological and fisheries resources from the potential contaminant release would be limited. It is expected that any release of contaminants during dredging would be quickly diluted by the large volume of marine water within the dredging site. The release of contaminants will also be minimized by the use of closed grab dredger (Section 5.9). Thus, it is considered that long-term off-site marine water quality impact is unlikely and any local water quality impact will be transient.

Potential Oxygen Depletion

5.8.19 An assessment of dissolved oxygen (DO) depletion during dredging has been made in relation to the results of the sediment plume modelling of dredging activities (unmitigated scenario) and the sediment quality data for the study area. The predicted maximum elevations at various indicator points were used to estimate the effects of increased SS concentrations on DO. As there is no significant difference in the overall SS impacts between the base case scenarios and the sensitivity tests, the oxygen depletion was only assessed for the base case scenarios. Seawater intakes along the waterfront were selected as reference points for presentation of the assessment results. In the calculation, it was assumed that all of the chemical oxygen demand is exerted. These are conservative assumptions and will likely result in an over-prediction of the potential impacts. The calculation was performed using the highest levels of sediment oxygen demand (SOD) measured in the sediment samples collected during the marine SI for conservative predictions. The highest SOD level was recorded at station A25.

5.8.20 The predicted maximum DO depletion during dredging was used to evaluate the water quality impacts. The 10 percentile DO levels predicted under the pre-construction scenario at the corresponding indicator points were used as the background levels for reference. The predicted maximum DO depletions are given in Table 5.24 to Table 5.26 for Scenario 1A, Scenario 1B, and Scenario 1C respectively.

5.8.21 No significant DO depletion was predicted under all the assessment scenarios. The concurrent dredging activities would cause a maximum DO depletion of less than 0.02mg/l at the nearby sensitive receivers. Full compliance with the WQO for depth-averaged and bottom DO of 4 mg/l and 2 mg/l respectively is predicted in the Victoria Harbour under both Stage 1 and Stage 2 dredging scenarios. No mixing zone for DO can therefore be identified. No adverse impacts on the DO levels at all the identified far field coral sites and fish culture zones would be expected from the dredging works.

^{Table 5.24 Calculation of the Effects of Increased Suspended Solids Concentrations on Dissolved Oxygen Concentrations under Scenario 1A}

Indicator Point (Figure 5.2a)	Maximum Predicted Depth-averaged SS Elevation (mg/l)	SOD in Sediment (mg/kg)	Maximum DO depletion (mg/l)	Background Depth-averaged DO (mg/l)	Resultant DO (mg/l)
Wet Season
MTRC Kowloon Station (C14)	2.530	640	0.0016	4.84	4.84
China H.K. City (C15)	2.029	640	0.0013	4.81	4.81
Harbour City (C16)	2.141	640	0.0014	4.81	4.81
Ocean Centre (C17)	2.141	640	0.0014	4.81	4.81
Ocean Terminal (C18)	4.914	640	0.0031	4.84	4.84
Government Premises (C19)	6.863	640	0.0044	4.82	4.81
New World Centre (C20)	3.762	640	0.0024	4.84	4.84
East Rail Extension (C21)	3.720	640	0.0024	4.82	4.81
Dairy Farm Ice Plant (C22)	5.419	640	0.0035	4.61	4.61
Pamela Youde Nethersole Eastern Hospital (C23)	1.402	640	0.0009	5.06	5.06
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	8.453	640	0.0054	4.80	4.79
Cha Kwo Ling (WSD10)	3.980	640	0.0025	4.61	4.61
Tseung Kwan O (WSD12)	0.571	640	0.0004	5.69	5.69
Siu Sai Wan (WSD13)	2.370	640	0.0015	5.41	5.41
Sai Wan Ho (WSD15)	7.562	640	0.0048	4.92	4.92
Quarry Bay (WSD17)	8.417	640	0.0054	4.85	4.84
Sheung Wan (WSD19)	4.123	640	0.0026	4.82	4.82
Wan Chai (WSD21)	12.826	640	0.0082	4.85	4.84
Tai Wan (WSD9)	7.055	640	0.0045	4.81	4.80
Dry Season
MTRC Kowloon Station (C14)	1.327	640	0.0008	6.62	6.62
China H.K. City (C15)	0.479	640	0.0003	6.62	6.62
Harbour City (C16)	0.076	640	0.0000	6.62	6.62
Ocean Centre (C17)	0.076	640	0.0000	6.62	6.62
Ocean Terminal (C18)	1.582	640	0.0010	6.62	6.62
Government Premises (C19)	2.117	640	0.0014	6.63	6.63
New World Centre (C20)	0.963	640	0.0006	6.62	6.62
East Rail Extension (C21)	1.285	640	0.0008	6.65	6.65
Dairy Farm Ice Plant (C22)	28.776	640	0.0184	6.81	6.79
Pamela Youde Nethersole Eastern Hospital (C23)	0.004	640	0.0000	6.83	6.83
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	4.831	640	0.0031	6.63	6.63
Cha Kwo Ling (WSD10)	22.030	640	0.0141	6.81	6.79
Tseung Kwan O (WSD12)	0.002	640	0.0000	6.92	6.92
Siu Sai Wan (WSD13)	0.011	640	0.0000	6.83	6.83
Sai Wan Ho (WSD15)	3.355	640	0.0021	6.82	6.82
Quarry Bay (WSD17)	5.142	640	0.0033	6.81	6.81
Sheung Wan (WSD19)	2.554	640	0.0016	6.47	6.46
Wan Chai (WSD21)	7.842	640	0.0050	6.65	6.65
Tai Wan (WSD9)	5.226	640	0.0033	6.71	6.70

^{Table 5.25 Calculation of the Effects of Increased Suspended Solids Concentrations on Dissolved Oxygen Concentrations under Scenario 1B}

Indicator Point (Figure 5.2a)	Maximum Predicted Depth-averaged SS Elevation (mg/l)	SOD in Sediment (mg/kg)	Maximum DO depletion (mg/l)	Background Depth-averaged DO (mg/l)	Resultant DO (mg/l)
Wet Season
MTRC Kowloon Station (C14)	2.271	640	0.0015	4.84	4.84
China H.K. City (C15)	1.711	640	0.0011	4.82	4.81
Harbour City (C16)	1.458	640	0.0009	4.82	4.81
Ocean Centre (C17)	1.458	640	0.0009	4.82	4.81
Ocean Terminal (C18)	3.873	640	0.0025	4.84	4.84
Government Premises (C19)	5.485	640	0.0035	4.82	4.82
New World Centre (C20)	4.238	640	0.0027	4.84	4.84
East Rail Extension (C21)	3.096	640	0.0020	4.82	4.82
Dairy Farm Ice Plant (C22)	7.979	640	0.0051	4.62	4.61
Pamela Youde Nethersole Eastern Hospital (C23)	0.629	640	0.0004	5.07	5.07
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	2.380	640	0.0015	4.80	4.80
Cha Kwo Ling (WSD10)	16.937	640	0.0108	4.62	4.61
Tseung Kwan O (WSD12)	0.324	640	0.0002	5.70	5.70
Siu Sai Wan (WSD13)	0.281	640	0.0002	5.41	5.41
Sai Wan Ho (WSD15)	1.752	640	0.0011	4.93	4.93
Quarry Bay (WSD17)	1.907	640	0.0012	4.85	4.85
Sheung Wan (WSD19)	2.289	640	0.0015	4.82	4.82
Wan Chai (WSD21)	4.177	640	0.0027	4.85	4.84
Tai Wan (WSD9)	5.996	640	0.0038	4.81	4.81
Dry Season
MTRC Kowloon Station (C14)	0.960	640	0.0006	6.62	6.62
China H.K. City (C15)	0.390	640	0.0002	6.62	6.62
Harbour City (C16)	0.056	640	0.00004	6.62	6.62
Ocean Centre (C17)	0.056	640	0.00004	6.62	6.62
Ocean Terminal (C18)	1.271	640	0.0008	6.62	6.62
Government Premises (C19)	1.471	640	0.0009	6.63	6.63
New World Centre (C20)	1.770	640	0.0011	6.62	6.62
East Rail Extension (C21)	0.849	640	0.0005	6.65	6.65
Dairy Farm Ice Plant (C22)	9.182	640	0.0059	6.81	6.80
Pamela Youde Nethersole Eastern Hospital (C23)	0.004	640	0.000003	6.83	6.83
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	1.058	640	0.0007	6.63	6.63
Cha Kwo Ling (WSD10)	12.305	640	0.0079	6.81	6.80
Tseung Kwan O (WSD12)	0.001	640	0.0000006	6.91	6.91
Siu Sai Wan (WSD13)	0.002	640	0.000001	6.83	6.83
Sai Wan Ho (WSD15)	0.912	640	0.0006	6.82	6.82
Quarry Bay (WSD17)	0.997	640	0.0006	6.82	6.81
Sheung Wan (WSD19)	0.411	640	0.0003	6.47	6.47
Wan Chai (WSD21)	0.539	640	0.0003	6.66	6.66
Tai Wan (WSD9)	1.463	640	0.0009	6.71	6.71

^{Table 5.26 Calculation of the Effects of Increased Suspended Sediment Concentrations on Dissolved Oxygen Concentrations under Scenario 1C}

Indicator Point (Figure 5.2a)	Maximum Predicted Depth-averaged SS Elevation (mg/l)	SOD in Sediment (mg/kg)	Maximum DO depletion (mg/l)	Background Depth-averaged DO (mg/l)	Resultant DO (mg/l)
Wet Season
MTRC Kowloon Station (C14)	2.486	640	0.0016	4.44	4.44
China H.K. City (C15)	2.153	640	0.0014	4.41	4.41
Harbour City (C16)	1.478	640	0.0009	4.41	4.41
Ocean Centre (C17)	1.478	640	0.0009	4.41	4.41
Ocean Terminal (C18)	3.194	640	0.0020	4.43	4.43
Government Premises (C19)	4.195	640	0.0027	4.43	4.42
New World Centre (C20)	4.428	640	0.0028	4.43	4.43
East Rail Extension (C21)	2.971	640	0.0019	4.42	4.41
Dairy Farm Ice Plant (C22)	20.375	640	0.0130	4.28	4.27
Pamela Youde Nethersole Eastern Hospital (C23)	1.095	640	0.0007	4.82	4.82
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	3.831	640	0.0025	4.42	4.42
Cha Kwo Ling (WSD10)	21.027	640	0.0135	4.28	4.26
Tseung Kwan O (WSD12)	0.834	640	0.0005	5.17	5.17
Siu Sai Wan (WSD13)	0.949	640	0.0006	5.02	5.02
Sai Wan Ho (WSD15)	2.864	640	0.0018	4.62	4.62
Quarry Bay (WSD17)	3.198	640	0.0020	4.50	4.50
Sheung Wan (WSD19)	4.088	640	0.0026	4.45	4.45
Wan Chai (WSD21)	5.619	640	0.0036	4.48	4.48
Tai Wan (WSD9)	5.668	640	0.0036	4.29	4.29
Dry Season
MTRC Kowloon Station (C14)	0.718	640	0.0005	6.62	6.62
China H.K. City (C15)	0.259	640	0.0002	6.62	6.62
Harbour City (C16)	0.046	640	0.00003	6.62	6.62
Ocean Centre (C17)	0.046	640	0.00003	6.62	6.62
Ocean Terminal (C18)	0.763	640	0.0005	6.62	6.62
Government Premises (C19)	0.605	640	0.0004	6.63	6.63
New World Centre (C20)	1.352	640	0.0009	6.62	6.62
East Rail Extension (C21)	0.309	640	0.0002	6.64	6.64
Dairy Farm Ice Plant (C22)	10.728	640	0.0069	6.81	6.80
Pamela Youde Nethersole Eastern Hospital (C23)	0.003	640	0.0000	6.83	6.83
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	0.964	640	0.0006	6.63	6.63
Cha Kwo Ling (WSD10)	20.360	640	0.0130	6.81	6.79
Tseung Kwan O (WSD12)	0.001	640	0.0000006	6.89	6.89
Siu Sai Wan (WSD13)	0.001	640	0.0000	6.83	6.83
Sai Wan Ho (WSD15)	0.666	640	0.0004	6.82	6.82
Quarry Bay (WSD17)	0.748	640	0.0005	6.82	6.81
Sheung Wan (WSD19)	0.399	640	0.0003	6.46	6.46
Wan Chai (WSD21)	0.445	640	0.0003	6.65	6.65
Tai Wan (WSD9)	0.997	640	0.0006	6.68	6.68

Impact from Maintenance Dredging

5.8.22 The impact from maintenance dredging was assessed under Scenario 1D. Description of Scenario 1D is provided in Table 5.12a. Based on the model results for Scenario 1D, full compliance with the assessment criteria for SS elevation and sedimentation rate would be achieved for the coral sites during the maintenance dredging. However, the SS levels predicted for the WSD flushing water intakes at Cha Kwo Ling, Quarry Bay, Sheung Wan, Wan Chai and Tai Wan would exceed the WSD standard during the wet season. The maximum SS levels predicted at these 5 WSD flushing water intakes ranged from 10.5 mg/l to 13.6 mg/l as compared to the WSD standard of 10 mg/l. Full compliance with the WSD standard was however predicted at all the flushing intakes under the dry season scenario. It is recommended that the maintenance dredging should not be programmed in wet seasons (April to September) to avoid the potential water quality impacts.

5.8.23 As discussed before, no unacceptable impact with regard to the SS elevation, sediment deposition, contaminant release and DO depletion is predicted at all the identified ecological sensitive receivers (i.e. far field coral sites and fish culture zones) under the capital dredging. The mixing zones for all these relevant parameters have been identified to be acceptable for the capital dredging. Adverse impact is also not expected for these parameters during the maintenance dredging in view that the scale of maintenance dredging would be much smaller than that for capital dredging. The mixing zones for relevant parameters under maintenance dredging should be smaller that that identified for the capital dredging and are therefore not presented.

5.9 Mitigation of Environmental Impacts

Capital and Maintenance Dredging

5.9.1 The following measures have been implemented in the design of dredging works for the proposed cruise terminal to minimize the impacts on water quality:

· Dredging will be carried out by closed grab dredger to minimize release of sediment and other contaminants during both capital and maintenance dredging.

· The maximum production rate for dredging from the seabed to provide necessary manoeuvring area would not be more than 4,000m³ per day (and no more than 2 closed grab dredgers) during capital dredging and 2,000m³ per day (and no more than 1 closed grab dredger) during maintenance dredging.

· The maximum production rate for dredging at or near the seawall area would not be more than 4,000m³ per day for berth construction. No more than two closed grab dredger would be operated at the same time at or near the seawall for berth construction.

5.9.2 For the dredging works to be carried out in the middle of the Victoria Harbour channel or near the fairway, the associated sediment plume could easily be transported to farther field by the fast moving tidal currents and thus would potentially affect the sensitive use on both sides of the Victoria Harbour. As indicated in Section 5.8, exceedances of target water quality objectives at the WSD flushing water intakes are predicted during the capital and maintenance dredging.

5.9.3 As exceedances of the WSD standard for flushing water intakes are only predicted in wet seasons under the maintenance dredging scenarios, it is recommended that the maintenance dredging should not be programmed in wet seasons (April to September) to avoid the potential water quality impacts.

5.9.4 To minimize the potential SS impact from capital dredging, deployment of silt curtains around the closed grab dredgers is recommended as an appropriate mitigation measure. However, silt curtains should not be used in areas where current speeds are higher than 1.0m/s, and the effectiveness of the silt curtains will be reduced in areas of current speeds greater than around 0.5m/s. Thus, silt curtains are considered ineffective to mitigate the SS impacts in the middle of the Victoria Harbour channel or in areas close to the fairway. Therefore, silt curtains are only recommended in the embayed / sheltered areas or in the near shore regions where the predicted current speeds are less than 0.5m/s.

5.9.5 In view of the difficulties and ineffectiveness of installing silt curtains near the fairway with high current speeds, deployment of silt curtains is not recommended in the dredging basin for cruise vessel approach to both the Phase I and Phase II Berth. Table 5.27 summarizes the applications of silt curtains recommended for the capital dredging (i.e. Scenario 1A, Scenario 1B and Scenario 1C). It should be noted that the assumed water quality mitigation measures for other designated projects including CKR, Road T2 and Gas Main Diversion will be subject to detailed assessment under separate EIA studies. In addition, the runway opening and the public landing steps cum fireboat berth are proposed under the Kai Tak Development (KTD) and the assumed water quality mitigation measure for these two KTD components will be subject to the Schedule 3 EIA for the feasibility study of KTD.

^{Table 5.27 Deployment of Silt Curtains - Locations of Applications under Capital Dredging}

Scenario	Deployment of Silt Curtains ^(1)
For Capital Dredging Only
1A (Figure 5.6)		Around both the two closed grab dredgers used for dredging at or near the existing seawall of the former Kai Tak Airport runway for construction of the cruise berth
		Around the closed grab dredger used for dredging at the former Kai Tak Airport runway for construction of the new public landing steps ^(2)
1B (Figure 5.7)		Around all the dredging and filling operations for construction of Road T2 and Central Kowloon Route ^(3)
1C (Figure 5.8)		Around the dredging operation for runway opening ^(2)
		Around all the dredging and filling operations for construction of Road T2 and Central Kowloon Route ^(3)

Notes:

(1) Deployment of silt curtain should involve the use of impervious sheets or filter fabrics combined with flotation and anchoring devices to minimize the sediment transport away from the dredging operation. In moving water conditions, provisions should be made in the design of the silt curtain to prevent blocking the entire water column to allow the volume of water contained within the silt curtain to change. Dual silt curtains can be used to allowing movement of dredgers and barges by alternating the position of the opening in the curtains while maintaining continuous (overlapping) containment.

(2) The assumed mitigation measures for other concurrent KTD works, including the use of closed grab dredger and deployment of silt curtains around the dredger, will be subject to the separate Schedule 3 EIA for the feasibility study of KTD.

(3) The assumed mitigation measures for these concurrent designated projects, including the use of closed grab dredger and deployment of silt curtains around the dredger, will be subject to detailed assessment under separate EIA process.

5.9.13 Based on the modelling results, unacceptable residual SS impacts were still predicted under the wet season scenarios at some of the WSD flushing water intakes after the deployment of the silt curtains as recommended above. The unacceptable residual impact (after deployment of silt curtains) was partly caused by the sediment sources from this Project, and partly caused by the sediment releases from other concurrent marine works. Table 5.28 to Table 5.30 and Table 5.28a to Table 5.30a give the % of the residual SS levels contributed from this Project after deployment of silt curtains as recommended for the capital dredging. Only the intake points with unacceptable residual SS impacts are included in these tables.

^{Table 5.28 Contribution of SS Elevations from this Project under Capital Dredging – Scenario 1A (Base Case Scenario)}

WSD Saltwater Intakes	Contribution from this Project under Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	61.3%	92.2%
Sai Wan Ho	16.5%	38.0%
Quarry Bay	19.1%	19.3%
Tai Wan	50.9%	96.9%
Sheung Wan	7.6%	8.2%
Wan Chai	6.9%	5.6%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

^{Table 5.28a Contribution of SS Elevations from this Project under Capital Dredging – Scenario 1A (Sensitivity Test using Higher Dredging Rate for Gas Main Construction)}

WSD Saltwater Intakes	Contribution from this Project under Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	53.5%	92.2%
Sai Wan Ho	15.4%	37.8%
Quarry Bay	17.4%	19.3%
Tai Wan	35.4%	43.5%
Sheung Wan	7.2%	8.2%
Wan Chai	6.6%	5.6%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

^{Table 5.29 Contribution of SS Elevations from this Project under Capital Dredging – Scenario 1B (Base Case Scenario)}

WSD Saltwater Intakes	Contribution from this Project under Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	46.1%	61.9%
Quarry Bay	75.8%	100.0%
Tai Wan	51.5%	100.0%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

^{Table 5.29a Contribution of SS Elevations from this Project under Capital Dredging – Scenario 1B (Sensitivity Test using Higher Dredging Rate for CKR)}

WSD Saltwater Intakes	Contribution from this Project under Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	45.3%	61.9%
Quarry Bay	75.3%	100.0%
Tai Wan	48.0%	100.0%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

^{Table 5.30 Contribution of SS Elevation from this Project under Capital Dredging – Scenario 1C (Base Case Scenario)}

WSD Saltwater Intakes	Contribution from KTD works during Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	35.8%	33.2%
Sai Wan Ho	67.8%	87.2%
Quarry Bay	71.1%	93.5%
Sheung Wan	72.3%	74.6%
Wan Chai	71.4%	70.5%
Tai Wan	64.4%	95.7%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

^{Table 5.30a Contribution of SS Elevation from this Project under Capital Dredging – Scenario 1C (Sensitivity Test using Higher Dredging Rate for CKR)}

WSD Saltwater Intakes	Contribution from KTD works during Capital Dredging
	For Mean SS Elevations	For Maximum SS Elevations
Cha Kwo Ling	35.6%	33.2%
Sai Wan Ho	67.5%	86.9%
Quarry Bay	70.8%	93.5%
Sheung Wan	71.7%	74.2%
Wan Chai	71.0%	70.2%
Tai Wan	63.7%	95.7%

Remarks:

The contributions listed in the table represent a scenario after deployment of silt curtains as indicated in Table 5.27.

5.9.14 Consequently, deployment of silt screens is proposed at selected WSD salt water intakes to further minimize the residual impact under capital dredging. Table 5.31 summarizes the applications of silt screens under the modelling scenarios for capital dredging (i.e. Scenario 1A, Scenario 1B, and Scenario 1C).

^{Table 5.31 Deployment of Silt Screens - Locations of Applications under Capital Dredging}

Scenario	Deployment of Silt Screens ^(1)
1A (Figure 5.6)	WSD flushing water intakes at Cha Kwo Ling, Sai Wan Ho, Quarry Bay, Sheung Wan, Wan Chai, Tai Wan
1B (Figure 5.7)	WSD flushing water intakes at Cha Kwo Ling, Quarry Bay, Tai Wan
1C (Figure 5.8)	WSD flushing water intakes at Cha Kwo Ling, Sai Wan Ho, Quarry Bay, Sheung Wan, Wan Chai, Tai Wan ^(2)

Notes:

(1) Silt screens should be made from synthetic geotextile fabrics, which allow water to flow through but retain a fraction of the suspended solid.

(2) Exceedance of the SS standard at Sai Wan Ho, Sheung Wan and Wan Chai was only predicted when the 600 m runway opening is in place. Opening a 600m wide gap at the runway was proposed under the KTD as a potential mitigation measure to improve the water circulation and water quality in Kai Tak Approach Channel. CEDD is the project proponent of the KTD and should be responsible for the deployment of silt screens at these three intakes if the 600 m opening is in place during the Stage 2 capital dredging.

5.9.15 Based on the model results, the influence of SS upon two WSD intakes (at Sheung Wan and Wan Chai) contributed from the WDII works would be larger than that from the KTD works during the capital dredging in the Stage 1 area (Scenario 1A). Under the WDII Planning and Engineering Review, silt screens have been recommended to be installed at these two WSD intake points for the following WDII activities:

· seawall dredging and seawall trench filling for WDII reclamation;

· dredging for construction of the temporary typhoon shelter in the Harbour area

· dredging for construction of the cross harbour water mains between Wan Chai and Tsim Sha Tsui; and

· dredging for construction of the submarine sewage pipeline of the Wan Chai East Sewage Treatment Works.

5.9.16 The model results also indicate that, without these WDII activities, unacceptable residual SS impacts would still occur at the WSD Wan Chai intake during the capital Stage 1 dredging period but the degree of the unacceptable residual impacts at the intake points would be lower. As such, deployment of silt screens at this intake point is still recommended under the capital dredging in the Stage 1 area even without these WDII activities.

5.9.17 According to the Contaminated Spoil Management Study ⁽[19]⁾, the implementation of silt curtain around the closed grab dredgers will reduce the dispersion of SS by a factor of 4 (or about 75%). Similarly, the implementation of silt screen at the intake could reduce the SS level by a factor of 2.5 (or about 60%). This SS reduction factor has been established under the Pak Shek Kok Reclamation, Public Dump EIA (1997) and has been adopted in a number of recent studies, including the Western Coast Road EIA study. Figure 5.10a and Figure 5.10b shows indicative arrangement of the silt curtains and silt screens.

Residual Impact of Capital Dredging

5.9.18 Exceedance of the WSD standard for SS of 10 mg/l is predicted at the some of the flushing water intakes under the unmitigated scenarios (Table 5.16 to Table 5.18 and Table 5.16a to Table 5.18a). Exceedance of the WQO for SS elevation is also predicted at the coral site in Cape Collinson under the sensitivity test for Stage 1 dredging (Table 5.19a). No adverse impact is identified for contaminant release and oxygen depletion for the unmitigated scenarios. Table 5.32 to Table 5.34 and Table 5.32a to Table 5.34a summarize the predicted water quality at the flushing water intakes after the implementation of all the recommended mitigation measures for the base case scenarios and the sensitivity tests. Table 5.35 presents the predicted SS elevations and sedimentation rates at the far field coral sites after implementation of all the recommended mitigation measures under the sensitivity test for Stage 1 dredging. The contour maps of cumulative SS elevations and sedimentation rates caused by all concurrent activities predicted under the mitigated scenarios are given in Appendix 5.4 to Appendix 5.9. As there is no significant difference in the sediment plume size between the base case scenarios and the sensitivity tests, the contour maps are only presented for the base case scenarios. Each figure attached to these appendices contains two contour plots where the upper plot shows the unmitigated scenarios and the lower plot shows the mitigated scenarios.

5.9.19 With the recommended measures, all the WSD flushing water intakes and all the far field coral sites would achieve full compliance with the relevant assessment criteria. As the model results for Stage 2 dredging under the mitigated scenarios indicated that the maximum SS levels predicted at Sai Wan Ho and Quarry Bay only marginally complied with the WSD standard and the SS levels were mainly contributed from the dredging works at the manoeuvring basin of the cruise terminal, it is therefore recommended that maintenance dredging for Phase I Berth should not be carried out concurrently with Stage 2 dredging to minimize the potential water quality impacts at the WSD intakes.

^{Table 5.32 Predicted SS Concentrations at Seawater Intakes for Scenario 1A – Mitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.2	9.4	100.0%	5.3	6.5	100.0%
China H.K. City (C15)	-	8.3	9.1	-	5.4	5.8	-
Harbour City (C16)	-	8.3	9.2	-	5.3	5.4	-
Ocean Centre (C17)	-	8.3	9.2	-	5.3	5.4	-
Ocean Terminal (C18)	-	8.5	12.5	-	5.6	6.6	-
Government Premises (C19)	-	9.1	14.4	-	5.6	6.8	-
New World Centre (C20)	-	9.3	12.6	-	5.6	6.2	-
East Rail Extension (C21)	-	9.1	11.8	-	5.2	6.1	-
Dairy Farm Ice Plant (C22)	-	11.2	21.2	-	5.3	12.9	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	7.0	8.1	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	11.3	29.2	-	6.7	10.1	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.4	7.6	100.0%	2.1	4.6	100.0%
Tseung Kwan O (WSD12)	< 10	7.5	7.9	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.4	7.8	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	3.6	8.5	100.0%	1.9	3.2	100.0%
Quarry Bay (WSD17)	< 10	3.8	9.0	100.0%	2.0	4.5	100.0%
Sheung Wan (WSD19)	< 10	3.7	5.1	100.0%	2.4	3.2	100.0%
Wan Chai (WSD21) ^See Note 1	< 10	3.2	9.7	100.0%	2.1	6.2	100.0%
Tai Wan (WSD9)	< 10	3.7	5.5	100.0%	2.4	5.3	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

Note 1: The dredging activities for WDII are included in Scenario 1A only. As the WSD Wan Chai flushing water intake is located within the WDII reclamation site boundary, the SS elevation at this flushing water intake should mainly be caused by the WDII dredging activities. Under the WDII Planning and Engineering Review, a different model (namely the refined detailed VH model) was used to predict the SS elevations in the Victoria Harbour from the exact same concurrent dredging activities considered under Scenario 1A. The grid mesh of the refined detailed VH model has a higher resolution within the WDII reclamation site aiming to provide a more detailed prediction on the water quality impact generated from the WDII activities. The refined detailed VH model can therefore give a more detailed SS elevation profile within the WDII reclamation site where the WSD Wan Chai flushing water intake is located. Therefore, the predicted SS concentrations for Wan Chai flushing water intake as shown in the above table are directly extracted from the model results available under the WDII Planning and Engineering Review for the exact same concurrent dredging scenario. No other WSD flushing water intake is located within the dredging site.

^{Table 5.32a Predicted SS Concentrations at Seawater Intakes for Scenario 1A – Mitigated (Sensitivity Test using Higher Dredging Rate for Gas Main Construction)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.3	10.1	100.0%	5.5	10.1	100.0%
China H.K. City (C15)	-	8.3	9.4	-	5.5	6.9	-
Harbour City (C16)	-	8.3	9.6	-	5.3	5.4	-
Ocean Centre (C17)	-	8.3	9.6	-	5.3	5.4	-
Ocean Terminal (C18)	-	8.7	14.5	-	6.0	9.6	-
Government Premises (C19)	-	9.7	17.0	-	6.0	8.6	-
New World Centre (C20)	-	9.8	14.8	-	5.8	7.2	-
East Rail Extension (C21)	-	9.6	13.9	-	5.5	7.1	-
Dairy Farm Ice Plant (C22)	-	11.3	21.2	-	5.4	13.0	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	7.0	8.2	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	11.5	29.3	-	6.8	10.2	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.5	7.6	100.0%	2.1	4.6	100.0%
Tseung Kwan O (WSD12)	< 10	7.5	8.1	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.4	8.0	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	3.7	8.5	100.0%	1.9	3.3	100.0%
Quarry Bay (WSD17)	< 10	3.8	9.0	100.0%	2.0	4.5	100.0%
Sheung Wan (WSD19)	< 10	3.7	5.1	100.0%	2.5	3.3	100.0%
Wan Chai (WSD21) ^See Note 1	< 10	3.2	9.7	100.0%	2.1	6.2	100.0%
Tai Wan (WSD9)	< 10	3.9	8.3	100.0%	2.6	5.8	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

Note 1: The dredging activities for WDII are included in Scenario 1A only. As the WSD Wan Chai flushing water intake is located within the WDII reclamation site boundary, the SS elevation at this flushing water intake should mainly be caused by the WDII dredging activities. Under the WDII Planning and Engineering Review, a different model (namely the refined detailed VH model) was used to predict the SS elevations in the Victoria Harbour from the exact same concurrent dredging activities considered under Scenario 1A. The grid mesh of the refined detailed VH model has a higher resolution within the WDII reclamation site aiming to provide a more detailed prediction on the water quality impact generated from the WDII activities. The refined detailed VH model can therefore give a more detailed SS elevation profile within the WDII reclamation site where the WSD Wan Chai flushing water intake is located. Therefore, the predicted SS concentrations for Wan Chai flushing water intake as shown in the above table are directly extracted from the model results available under the WDII Planning and Engineering Review for the exact same concurrent dredging scenario. No other WSD flushing water intake is located within the dredging site.

^{Table 5.33 Predicted SS Concentrations at Seawater Intakes for Scenario 1B – Mitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.0	8.6	100.0%	5.1	5.9	100.0%
China H.K. City (C15)	-	8.1	8.5	-	5.4	5.7	-
Harbour City (C16)	-	8.1	8.5	-	5.3	5.3	-
Ocean Centre (C17)	-	8.1	8.5	-	5.3	5.3	-
Ocean Terminal (C18)	-	8.1	10.1	-	5.5	6.5	-
Government Premises (C19)	-	8.5	10.8	-	5.5	6.4	-
New World Centre (C20)	-	8.5	10.4	-	5.5	6.4	-
East Rail Extension (C21)	-	8.4	9.7	-	5.1	5.8	-
Dairy Farm Ice Plant (C22)	-	10.5	14.2	-	5.1	6.8	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	6.4	6.8	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	8.6	9.9	-	5.3	6.0	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.2	5.3	100.0%	2.0	2.8	100.0%
Tseung Kwan O (WSD12)	< 10	7.5	7.7	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.2	6.7	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	7.6	9.8	100.0%	4.4	5.3	100.0%
Quarry Bay (WSD17)	< 10	3.2	9.6	100.0%	1.8	2.3	100.0%
Sheung Wan (WSD19)	< 10	8.9	9.2	100.0%	5.6	6.1	100.0%
Wan Chai (WSD21)	< 10	8.1	9.3	100.0%	4.9	5.0	100.0%
Tai Wan (WSD9)	< 10	3.4	4.9	100.0%	2.0	2.7	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.33a Predicted SS Concentrations at Seawater Intakes for Scenario 1B – Mitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	8.0	8.6	100.0%	5.1	5.9	100.0%
China H.K. City (C15)	-	8.1	8.5	-	5.4	5.7	-
Harbour City (C16)	-	8.1	8.5	-	5.3	5.3	-
Ocean Centre (C17)	-	8.1	8.5	-	5.3	5.3	-
Ocean Terminal (C18)	-	8.2	10.1	-	5.5	6.5	-
Government Premises (C19)	-	8.5	10.8	-	5.5	6.4	-
New World Centre (C20)	-	8.5	10.4	-	5.5	6.4	-
East Rail Extension (C21)	-	8.5	9.7	-	5.1	5.8	-
Dairy Farm Ice Plant (C22)	-	10.5	14.2	-	5.1	6.8	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	6.4	6.8	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	8.6	9.9	-	5.3	6.0	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.2	5.3	100.0%	2.0	2.8	100.0%
Tseung Kwan O (WSD12)	< 10	7.5	7.7	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	6.2	6.7	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	7.6	9.8	100.0%	4.4	5.3	100.0%
Quarry Bay (WSD17)	< 10	3.2	9.6	100.0%	1.8	2.3	100.0%
Sheung Wan (WSD19)	< 10	8.9	9.2	100.0%	5.6	6.1	100.0%
Wan Chai (WSD21)	< 10	8.1	9.4	100.0%	4.9	5.0	100.0%
Tai Wan (WSD9)	< 10	3.4	4.9	100.0%	2.0	2.7	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.34 Predicted SS Concentrations at Seawater Intakes for Scenario 1C – Mitigated (Base Case Scenario)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	9.6	10.8	100.0%	5.5	6.0	100.0%
China H.K. City (C15)	-	9.5	10.6	-	5.4	5.6	-
Harbour City (C16)	-	9.5	10.1	-	5.4	5.4	-
Ocean Centre (C17)	-	9.5	10.1	-	5.4	5.4	-
Ocean Terminal (C18)	-	9.7	11.7	-	5.5	6.0	-
Government Premises (C19)	-	9.9	12.2	-	5.5	6.0	-
New World Centre (C20)	-	10.0	11.4	-	5.5	5.7	-
East Rail Extension (C21)	-	9.9	11.1	-	5.1	5.3	-
Dairy Farm Ice Plant (C22)	-	11.4	16.0	-	5.4	8.8	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	8.0	8.5	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	10.0	11.6	-	5.4	6.1	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.6	6.4	100.0%	2.1	3.2	100.0%
Tseung Kwan O (WSD12)	< 10	8.4	8.8	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	7.7	8.5	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	3.7	4.1	100.0%	1.8	2.0	100.0%
Quarry Bay (WSD17)	< 10	3.9	5.1	100.0%	1.8	2.5	100.0%
Sheung Wan (WSD19)	< 10	3.8	4.5	100.0%	2.2	2.5	100.0%
Wan Chai (WSD21)	< 10	3.9	5.0	100.0%	2.0	2.0	100.0%
Tai Wan (WSD9)	< 10	4.3	5.7	100.0%	2.0	2.5	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.34a Predicted SS Concentrations at Seawater Intakes for Scenario 1C – Mitigated (Sensitivity Test using Higher Dredging Rate for CKR)}

Seawater Intake (ID)	SS Concentration (Absolute Value) in Mid-depth Layer (mg/l)
	Criteria	Wet Season			Dry Season
		Mean	Maximum	% time in compliance	Mean	Maximum	% time in compliance
Cooling Water Intakes
MTRC Kowloon Station (C14)	< 40	9.6	10.8	100.0%	5.5	6.0	100.0%
China H.K. City (C15)	-	9.5	10.6	-	5.4	5.6	-
Harbour City (C16)	-	9.5	10.2	-	5.4	5.4	-
Ocean Centre (C17)	-	9.5	10.2	-	5.4	5.4	-
Ocean Terminal (C18)	-	9.7	11.7	-	5.5	6.0	-
Government Premises (C19)	-	9.9	12.2	-	5.5	6.0	-
New World Centre (C20)	-	10.1	11.4	-	5.5	5.7	-
East Rail Extension (C21)	-	9.9	11.2	-	5.1	5.3	-
Dairy Farm Ice Plant (C22)	-	11.4	16.0	-	5.4	8.8	-
Pamela Youde Nethersole Eastern Hospital (C23)	-	8.0	8.5	-	4.0	4.0	-
Hong Kong Convention and Exhibition Centre Extension / Hong Kong Academy for Performing Arts /MTRC South Intake / Telecom House (C24)	-	10.0	11.6	-	5.4	6.1	-
WSD Flushing Water Intakes
Cha Kwo Ling (WSD10)	< 10	4.6	6.4	100.0%	2.1	3.2	100.0%
Tseung Kwan O (WSD12)	< 10	8.4	8.8	100.0%	3.9	3.9	100.0%
Siu Sai Wan (WSD13)	< 10	7.7	8.5	100.0%	4.0	4.0	100.0%
Sai Wan Ho (WSD15)	< 10	3.7	4.1	100.0%	1.8	2.0	100.0%
Quarry Bay (WSD17)	< 10	3.9	5.1	100.0%	1.8	2.5	100.0%
Sheung Wan (WSD19)	< 10	3.8	4.5	100.0%	2.2	2.5	100.0%
Wan Chai (WSD21)	< 10	3.9	5.0	100.0%	2.0	2.0	100.0%
Tai Wan (WSD9)	< 10	4.3	5.7	100.0%	2.0	2.5	100.0%

Remark: Other seawater intakes, including WSD Cheung Sha Wan intake, WSD Kowloon South intake and WSD Kennedy Town intake were found not be impacted by marine works from Kai Tak Development

^{Table 5.35 Predicted SS Elevations and Sedimentation Rates at Corals for Scenario 1A - Mitigated (Sensitivity Test using Higher Dredging Rate for Gas Main Construction)}

Corals (ID)	Background SS Level (mg/l)	SS Elevation in Bottom Layer (mg/l)				Sedimentation Rate (g/m^2/day)
		Criterion (30% of Mean SS Level)	Mean	Maximum	% time in compliance	Criterion	Mean	Maximum	% time in compliance
Wet Season
Junk Bay ( CR27 )	7.19	< 2.09	0.26	0.88	100.0%	< 100	6.55	13.45	100.0%
Junk Bay - Junk Island (CR28)	5.95	< 1.76	0.34	0.92	100.0%	< 100	6.38	18.62	100.0%
Cape Collinson (CR44)	5.46	< 1.54	0.40	1.34	100.0%	< 100	3.91	15.73	100.0%
Dry Season
Junk Bay ( CR27 )	3.93	< 1.07	0.00	0.00	100.0%	< 100	2.44	2.52	100.0%
Junk Bay - Junk Island (CR28)	3.96	< 1.11	0.00	0.04	100.0%	< 100	3.21	5.07	100.0%
Cape Collinson (CR44)	3.95	< 1.10	0.00	0.05	100.0%	< 100	3.18	5.80	100.0%

Remark: The coral site at Green Island was found not be impacted by marine works from Kai Tak Development

Residual Impact of Maintenance Dredging

5.9.20 Provided that the works can be programmed to avoid dredging in wet seasons (April to September), no residual impact is expected from the maintenance dredging.

Other Good Site Practices for Capital and Maintenance Dredging

5.9.21 Other good site practices that should be undertaken during capital and maintenance dredging include:

l all vessels should be sized so that adequate clearance is maintained between vessels and the seabed in all tide conditions, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;

l all barges / dredgers should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;

l construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site or dumping grounds;

l barges or hoppers should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation.

5.9.22 Appropriate numbers of portable chemical toilets shall be provided by a licensed contractor to serve the construction workers over the construction site. The Contractor shall also be responsible for waste disposal and maintenance practices.

5.9.23 Floating refuse and debris may arise from illegal dumping and littering from marine vessels and runoff from the coastal areas. It is recommended that collection and removal of floating refuse should be performed at regular intervals on a daily basis. The Contractor should be responsible for keeping the water within the site boundary and the neighbouring water free from rubbish during the dredging works. On-site waste management requirements are described further in Section 6 of this Report.

5.9.24 Silt screens are recommended to be deployed at six selected WSD flushing water intakes during the capital dredging period. The operation of the flushing water intakes would not be adversely affected by the silt screens provided that the silt screens are properly designed and maintained. Installation of silt screens at the selected flushing water intake points shall be implemented by the contractor for capital dredging. The contractor for capital dredging shall demonstrate and ensure that the design of the silt screen will not affect the normal operation of flushing water intake. The contractor shall obtain consensus from all relevant parties, including WSD and Marine Department, on the design of the silt screen at each of the six selected flushing water intake points before installation of the silt screen and commencement of the proposed dredging works. A water quality monitoring and audit programme and an Event and Action Plan as stipulated in the stand-alone Environmental Monitoring and Audit (EM&A) Manual shall be implemented by the contractor to ensure that the proposed works do not result in unacceptable impacts at the WSD flushing water intakes. As a mitigation measure to avoid the pollutant and refuse entrapment problems and to ensure that the impact monitoring results are representative, regular maintenance of the silt screens and refuse collection should be performed by the contractor at the silt screens at regular intervals on a daily basis. The Contractor should be responsible for keeping the water behind the silt screen free from floating rubbish and debris during the impact monitoring period.

Additional Precautionary Measure

5.9.25 Based on the above assessment of the water quality impact, an environmental monitoring and audit (EM&A) programme is considered necessary to obtain a database of baseline information of water quality before the dredging works, and thereafter, to monitor any variation of water quality from the baseline conditions and exceedances of WQOs at sensitive receivers during the dredging works. Details of the EM&A programme are given in the stand-alone EM&A Manual. If the water quality monitoring data indicate that the proposed dredging works result in unacceptable water quality impacts in the receiving water, appropriate actions should be taken to review the dredging operation and additional measures such as use of frame-type silt curtain ^([20]), deployment of double silt curtains ^([21]), slowing down, or rescheduling of works should be implemented as necessary.

5.10 Evaluation of Residual Environmental Impacts

5.10.1 The major water quality impact associated with capital and maintenance dredging activities is the elevation of SS within the marine water column. Provided that the recommended mitigation measures are implemented, including the control of dredging rates and programme, use of closed grab dredger, deployment of silt curtains at the appropriate dredging areas, and installation of silt screens at selected seawater intakes, there would be no unacceptable residual water quality impact due to the proposed dredging works.

5.11 Environmental Monitoring and Audit

5.11.1 There would be potential impacts of suspended solids upon the flushing water intakes due to the proposed dredging works. Appropriate mitigation measures are recommended in order to minimize the potential impacts. Water quality monitoring and audit will need to be carried out for the proposed capital and maintenance dredging works to ensure that the recommended mitigation measures are implemented properly. If the water quality monitoring data indicate that the proposed dredging works result in unacceptable water quality impacts in the receiving water, appropriate actions should be taken to review the dredging operation and additional measures such as use of frame-type silt curtain, deployment of double silt curtains, slowing down, or rescheduling of works should be implemented as necessary. Details of the water quality monitoring programme and the Event and Action Plan are provided in the stand-alone EM&A Manual.

5.12 Summary

5.12.1 The water quality impact during the proposed dredging works has been quantitatively assessed using the Delft3D Model. Suspended solids are identified as the most critical water quality parameter during the dredging operations. The worst-case scenarios for the dredging works have been assessed and it is predicted that potential water quality impacts could occur at the flushing water intakes identified within the Victoria Harbour. However, the water quality impacts upon the flushing water intakes could be effectively minimized with the implementation of the appropriate mitigation measures. There would be no unacceptable residual water quality impact due to the proposed capital and maintenance dredging works. An environmental monitoring and audit programme is required to ensure that all the recommended mitigation measures are implemented properly.

---

^([1]) Territory Development Department (July 2001). Agreement No. CE 74/98, Wan Chai Development Phase II, Comprehensive Feasibility Study, Environmental Impact Assessment Report, Volume I – Text.

^([2]) Pastorok, R.A. and Bilyard, G.R. (1985). “Effects of sewage pollution on coral-reef communities.” Marine Ecology Progress Series 21: 175-189.

^([3]) Hawker, D. W. and Connell, D. W. (1992). “Standards and Criteria for Pollution Control in Coral Reef Areas” in Connell, D. W and Hawker, D. W. (eds.), Pollution in Tropical Aquatic Systems, CRC Press, Inc.

^([4]) Maunsell Consultants Asia Limited (2003). Tai Po Sewage Treatment Works Stage 5, EIA Report, Drainage Services Department, 2003

^([5]) Hyder (1997). Sand Dredging and Backfilling of Borrow Pits at the Potential Eastern Waters Marine Borrow Area, EIA Report, CED, 1997.

^([6]) ERM-Hong Kong, Limited (2001).  Focused Cumulative Water Quality Impact Assessment of Sand Dredging at the West Po Toi Marine Borrow Area Final Report.

^([7]) ERM-Hong Kong, Limited (2003). The Proposed Submarine Gas Pipelines from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant, Hong Kong, EIA Report, The Hong Kong and China Gas Company Limited, 2003

^([8]) EPD (2005). 20 Years of Marine Water Quality in Hong Kong (1986 – 2005).

^([9]) EPD (2005). 20 Years of Marine Water Quality in Hong Kong (1986 – 2005).

^([10]) Agreement No. CE4/2004 (TP) South East Kowloon Development Comprehensive Planning and Engineering Review – Stage 1: Planning Review

^([11]) Mott MacDonald (1991). Contaminated Spoil Management Study, Final Report, Volume 1, for EPD, October 1991.

^([12]) Agreement No. CE 42/97, Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool.

^([13]) Scott Wilson (Hong Kong) Ltd. (February 2000). Northshore Lantau Development Feasibility Study (Agreement No. CE 60/96), Final Environmental Impact Assessment Report.

[14]

^([15]) The rate of oxygen consumption exerted by the sediment on the overlying water at 20^oC for a period of five days.

⁽[16]⁾ Environmental Quality Standards and Assessment Levels for Coastal Surface Water (from HMIP (1994) Environmental Economic and BPEO Assessment Principals for Integrated Pollution Control). (Source: Environmental Impact Assessment Study for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit, by ERM, January 1997).

⁽[17]⁾ Planning Department Agreement No. CE48/97 Feasibility Study for Additional Cross-border Links Stage 2: Investigations on Environment, Ecology, Land Use Planning, Land Acquisition, Economic/Financial Viability and Preliminary Project Feasibility/Preliminary Design Final Water Quality Impact Assessment Working Paper WP2 Volume 1 1999.

^([18]) ERM-Hong Kong, Ltd. (January 1997). Environmental Quality Standards and Assessment Levels for Coastal Surface Water (from HMIP (1994) Environmental Economic and BPEO Assessment Principals for Integrated Pollution Control). (Source: Environmental Impact Assessment Study for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit.)

^([19]) Mott MacDonald (1991). Contaminated Spoil Management Study, Final Report, Volume 1, for EPD, October 1991.

^([20]) The frame type silt curtain should be designed to enclose local pollution caused by the grab dredger. The silt curtain should be hung from a frame mounted on the grab dredger. The silt curtain should be of sufficient length to cover the entire water column from water surface down to the seabed. Steel chain or ballast should be attached to the bottom of the silt curtain to keep the silt curtain at its location.

^([21]) The double silt curtain system should comprise of the hanging type silt curtain in combination of the standing type silt curtain. The hanging type silt curtain would be hanged by floating buoys extending from the water surface to some distance (usually several metres) above the seabed. The standing type silt curtain should be fixed to the bottom of seabed and erects from the seabed to minimize sediment releases from the bottom water column.