Table of Contents

5 Water Quality Impact.. 5-1

5.1 Introduction.. 5-1

5.2 Environmental Guidelines, Standards and Criteria.. 5-1

5.3 Water Quality Sensitive Receivers.. 5-7

5.4 Description of the Environment.. 5-7

5.5 Identification of Potential Impacts.. 5-13

5.6 Assessment Methodology.. 5-13

5.7 Prediction and Evaluation of Environmental Impacts.. 5-18

5.8 Mitigation of Environmental Impacts.. 5-29

5.9 Evaluation of Residual Impacts.. 5-32

5.10 Environmental Monitoring and Audit.. 5-33

5.11 Conclusion.. 5-33

List of Tables

Table 5.1 Summary of Water Quality Objectives for Junk Bay WCZ.. 5-1

Table 5.2 Summary of Water Quality Objectives for Eastern Buffer WCZ.. 5-2

Table 5.3 Summary of Water Quality Objectives for Victoria Harbour (Phase I) WCZ.. 5-3

Table 5.4 Water Quality Criteria of Sea Water for Flushing Supply.. 5-4

Table 5.5 Proposed Assessment Objectives for Dissolved Metals and Micro-Pollutants with Reference to Standards in Other Countries.. 5-5

Table 5.6 Sediment Quality Criteria for the Classification of Sediment.. 5-6

Table 5.7 Water Sensitive Receivers (WSRs) in the Vicinity of the Project Site.. 5-7

Table 5.8 Summary Statistics of 2016 Marine Water Quality in Junk Bay WCZ.. 5-8

Table 5.9 Summary Statistics of 2016 Marine Water Quality in Victoria Harbour WCZ.. 5-9

Table 5.10 Summary Statistics of 2016 Marine Water Quality in Eastern Buffer WCZ.. 5-10

Table 5.11 Summary Statistics of 2016 Marine Water Quality in Sam Ka Tsuen Typhoon Shelter 5-11

Table 5.12 Summary of Suspended Solids Concentrations and Allowable SS Elevation at VM1 (from 2010 to 2015) 5-16

Table 5.13 Predicted Maximum Suspended Solids Elevation at Selected Observation Points during Construction Phase (Unmitigated) 5-19

Table 5.14 Predicted Maximum Sedimentation Rates at Identified Coral Sensitive Receivers during Construction Phase (Unmitigated) 5-20

Table 5.15 Marine Site Investigation Sediment Elutriate Test Results.. 5-21

Table 5.16 Predicted Maximum Elevation of Sediment Bounded Contaminants at Selected Observation Points during Construction Phase.. 5-21

Table 5.17 Summary of Changes to DO Levels due to Elevated SS Release during Construction Phase (Unmitigated) 5-22

Table 5.18 Peak Flood and Ebb Tidal Discharges through Lei Yue Mun Narrows.. 5-25

Table 5.19 Non-Point Source Pollution from Area to be Developed under the Project.. 5-26

Table 5.20 Predicted Maximum Suspended Solids Elevation at Selected Observation Points during Maintenance Dredging (Unmitigated) 5-27

Table 5.21 Predicted Maximum Sedimentation Rate Elevation at Selected Observation Points during Maintenance Dredging (Unmitigated) 5-27

Table 5.22 Predicted Maximum Elevation of Sediment Bounded Contaminants at Selected Observation Points during Maintenance Dredging.. 5-28

Table 5.23 Summary of Changes to DO Levels due to Elevated SS Release during Maintenance Dredging (Unmitigated) 5-28

Table 5.24 Predicted Maximum Suspended Solid Elevation during Construction Phase (Mitigated) 5-30

Table 5.25 Predicted Maximum Sedimentation Rates at Identified Coral Sensitive Receivers during Construction Phase (Mitigated) 5-30

Figures

Figure 5.1 LOCATIONS OF WATER SENSITIVE RECEIVERS

Appendices

Appendix 5.1 Coverage and Grid Layout of Updated Model and Refined LYM Model

Appendix 5.2 Locations of Observation & Sediment Release Points

Appendix 5.3 Contour Plots of SS Elevation and Sediment Deposition under Construction, Dry Season

Appendix 5.4 Contour Plots of SS Elevation and Sediment Deposition under Construction, Wet Season

Appendix 5.5 SS Elevation at C1 over 15-day Spring-Neap Cycle, Dry Season

Appendix 5.6 SS Elevation at C1 over 15-day Spring-Neap Cycle, Wet Season

Appendix 5.7 SS Elevation at C2 over 15-day Spring-Neap Cycle, Dry Season

Appendix 5.8 SS Elevation at C2 over 15-day Spring-Neap Cycle, Wet Season

Appendix 5.9 SS Elevation at C3 over 15-day Spring-Neap Cycle, Dry Season

Appendix 5.10 SS Elevation at C3 over 15-day Spring-Neap Cycle, Wet Season

Appendix 5.11 SS Elevation at W1 over 15-day Spring-Neap Cycle, Dry Season

Appendix 5.12 SS Elevation at W1 over 15-day Spring-Neap Cycle, Wet Season

Appendix 5.13 Total Sediment Deposition (g/m2) over 15-day Simulation Period, Dry Season

Appendix 5.14 Total Sediment Deposition (g/m2) over 15-day Simulation Period, Wet Season

Appendix 5.15 Contour Plots of Maximum Contaminant Concentrations Predicted over the Entire Simulation Period under Construction

Appendix 5.16 Comparison of the Simulated Near Surface Peak Ebb & Flood Tide Velocity Vectors, Dry Season

Appendix 5.17 Comparison of the Simulated Near Surface Peak Ebb & Flood Tide Velocity Vectors, Wet Season

Appendix 5.18 Comparison of the Simulated Water Speeds at H1, Dry Season

Appendix 5.19 Comparison of the Simulated Water Speeds at H1, Wet Season

Appendix 5.20 Comparison of the Instantaneous Discharge Through LYM Narrows

Appendix 5.21 Key Assumptions for Compiling Non-Point Source Pollution from Surface Runoff

Appendix 5.22 Contour Plots of SS Elevation and Sediment Deposition under Maintenance Dredging, Dry Season

Appendix 5.23 Contour Plots of SS Elevation and Sediment Deposition under Maintenance Dredging, Wet Season

Appendix 5.24 Contour Plots of Maximum Contaminant Concentrations Predicted over the Entire Simulation Period under Maintenance Dredging

5 Water Quality Impact

5.1 Introduction

5.1.1.1 This section presents an assessment on the associated potential hydrodynamic and water quality impacts in construction and operation phase of the proposed Project. Corresponding mitigation measures are provided to minimise the identified water quality impacts.

5.2 Environmental Guidelines, Standards and Criteria

5.2.1.1 The guidelines and criteria for evaluating water quality impacts include the following:

· Environmental Impact Assessment Ordinance (EIAO) Cap. 499;

· Water Pollution Control Ordinance (WPCO) Cap. 358;

· Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS);

· Practice Note for Professional Persons on Construction Site Drainage (ProPECC Note PN 1/94);

· Water Supplies Department (WSD) Water Quality Criteria for Flushing Water Intake;

· Hong Kong Planning Standards and Guidelines;

· Assessment Criteria for Coral;

· Metals and Micro-pollutants; and

· Sediment Quality Assessment Criteria

Environmental Impact Assessment Ordinance (EIAO) (Cap. 499)

5.2.1.2 Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) was issued by Environmental Protection Department (EPD) under Section 16 of the EIAO. It specifies the requirements in methodology and criteria for the EIA assessment. Details of assessment criteria and guidelines for water quality impact assessment are further elaborated under the reference sections in the EIAO-TM, including:

· Annex 6 – Criteria for Evaluating Water Pollution

· Annex 14 – Guidelines for Assessment of Water Pollution

Water Pollution Control Ordinance (WPCO) (Cap. 358)

5.2.1.3 The WPCO provides a statutory framework for the protection and control of water quality in Hong Kong. Water Quality Objectives (WQOs) have been specified for the Water Control Zones (WCZs) defined in WPCO. WQOs are stipulated for different water regimes in each WCZ based on beneficial uses (marine waters, inland water, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones). The study area for this water quality impact assessment covers the Junk Bay, Eastern Buffer and Victoria Harbour (Phase one) WCZ. The corresponding WQOs are summarized in Table 5.1, Table 5.2, and Table 5.3 respectively.

Table 5.1 Summary of Water Quality Objectives for Junk Bay WCZ

Parameter	Water Quality Objectives	Subzones
Offensive Odour, Tint	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolve oxygen (DO) (within 2m of the seabed)	Not less than 2.0 mg/L for 90% of samples	Marine waters
DO (Depth-averaged)	Not less than 4.0 mg/L for 90% of samples	Marine waters excepting fish culture subzones
	Not less than 5.0 mg/L for 90% of samples	Fish culture subzones
	Not less than 4.0 mg/L	Inland waters
Nutrients	Annual mean depth-averaged total inorganic nitrogen not to exceed 0.3 mg/L	Marine waters
E. coli	Annual geometric mean not to exceed 610 cfu/100mL	Secondary contact recreation subzone and fish culture subzones
	Geometric mean of the most recent 5 consecutive samples taken not exceed 1000 cfu/100mL	Inland waters
Unionised ammonia (UIA)	Annual mean not to exceed 0.021 mg/L	Whole zone
pH	In the range of 6.5 – 8.5, change due to waste discharge not to exceed 0.2	Marine waters
	In the range of 6.0-9.0	Inland waters
Salinity	Change due to waste discharge not to exceed 10% natural ambient level	Whole zone
Temperature	Change due to waste discharge not to exceed 2 ^0C	Whole zone
Suspended solids (SS)	Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities	Marine waters
	Change due to waste discharge not to exceed 25 mg/L of annual median	Inland waters
Toxicants	Not to be present at levels producing significant toxic 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

Table 5.2 Summary of Water Quality Objectives for Eastern Buffer WCZ

Parameter	Water Quality Objectives	Subzones
Offensive Odour, Tint	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolve oxygen (DO) (within 2m of the seabed)	Not less than 2.0 mg/L for 90% of samples	Marine waters
DO (Depth-averaged)	Not less than 4.0 mg/L for 90% of samples	Marine waters excepting Fish Culture Subzones
	Not less than 5.0 mg/L for 90% of samples	Fish Culture Subzones
	Not less than 4.0 mg/L	Water Gathering Ground Subzones and other inland waters
Nutrients	Annual mean depth-averaged total inorganic nitrogen not to exceed 0.4mg/L	Marine waters
E. coli	Annual geometric mean not to exceed 610 cfu/100mL	Fish culture subzones
	Geometric mean of the most recent 5 consecutive samples taken less than 1cfu/100mL	Water Gathering Ground Subzones
	Geometric mean of the most recent 5 consecutive samples taken not exceed 1000 cfu/100mL	Other inland waters
Unionised ammonia (UIA)	Annual mean not to exceed 0.021 mg/L	Whole zone
pH	In the range of 6.5 – 8.5, change due to waste discharge not to exceed 0.2	Marine waters
	Not to exceed the range of 6.5-8.5 due to human activity	Water Gathering Ground Subzones
	Not to exceed the range of 6.0-9.0 due to human activity	Other inland waters
Salinity	Change due to waste discharge not to exceed 10% natural ambient level	Whole zone
Temperature	Change due to waste discharge not to exceed 2 ^0C	Whole zone
Suspended solids (SS)	Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities	Marine waters
	Annual median not to exceed 20mg / L due to human activity	Water Gathering Ground Subzones
	Annual median not to exceed 25mg / L due to human activity	Other inland waters
Toxicants	Not to be present at levels producing significant toxic 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

Table 5.3 Summary of Water Quality Objectives for Victoria Harbour (Phase I) WCZ

Parameter	Water Quality Objectives	Sub-zone
Offensive Odour, Tint	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolve oxygen (DO) (within 2m of the seabed)	Not less than 2.0 mg/L for 90% of samples	Marine waters
DO (Depth-averaged)	Not less than 4.0 mg/L for 90% of samples	Marine waters
	Not less than 4.0mg/L	Inland waters
Nutrients	Annual mean depth-averaged total inorganic nitrogen not to exceed 0.4mg/L	Marine waters
E. coli	Geometric mean of the most recent 5 consecutive samples taken not exceed 1000 cfu/100mL	Inland waters
Unionised ammonia (UIA)	Annual mean not to exceed 0.021 mg/L	Whole zone
pH	In the range 6.5 – 8.5, change due to waste discharge not to exceed 0.2	Marine waters
	Not to exceed the range of 6.0-9.0 due to human activity	Inland waters
Salinity	Change due to waste discharge not to exceed 10% natural ambient level	Whole zone
Temperature	Change due to waste discharge not to exceed 2 ^0C	Whole zone
Suspended solids (SS)	Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities	Marine waters
	Annual median not to exceed 25 mg/L due to human activity	Inland waters
Toxicants	Not to be present at levels producing significant toxic effects in human, 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

Technical Memorandum on Effluent Discharge Standard (TM- DSS)

5.2.1.4 Under Section 21 of the WPCO, Technical Memorandum on Standards for Effluent Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters was issued to regulate the physical, chemical and microbial quality of effluents. Any effluent discharge into the foul sewers, stormwater drains, inland and coastal waters during the construction and operation phases of the proposed Project should comply with the stipulated standards in the TM-DSS.

Practice Note for Professional Persons on Construction Site Drainage

5.2.1.5 The Environmental Protection Department (EPD) has issued a Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) to control site runoff and wastewater generated during the construction stage of the proposed Project. Guidelines for handling and disposal of construction discharges are provided. Practices outlined in ProPECC PN 1/94 shall be closely followed during the construction phase to minimise potential water quality impacts associated with construction site drainage.

WSD Water Quality Criteria for Flushing Water Intakes

5.2.1.6 Water Supplies Department (WSD) has established a set of criteria for seawater uptake at flushing water intake points. Respective requirements are listed in Table 5.4.

Table 5.4 Water Quality Criteria of Sea Water for Flushing Supply

Parameter	Water Quality Criteria
Colour (H.U.)	<20 mg/L
Turbidity (N.T.U.)	<10 mg/L
Threshold Odour No. (T.O.N.)	<100 mg/L
Ammoniacal Nitrogen	<1 mg/L
Suspended Solids	<10 mg/L
Dissolved Oxygen	>2 mg/L
Biochemical Oxygen Demand	<10 mg/L
Synthetic Detergents	<5 mg/L
E. coli / 100mL	<20, 000 mg/L

Hong Kong Planning Standards and Guidelines (HKPSG)

5.2.1.7 The HKPSG, Chapter 9 (Environment), provides additional information on regulatory guidelines against water pollution for sensitive uses such as aquaculture and fisheries zones, bathing waters and other contact recreational waters.

Assessment Criteria for Coral

5.2.1.8 Excessive sediment deposition may create potential impacts on benthic organisms, including corals. Magnitude of impacts on marine ecological sensitive receivers was assessed based on the predicted sedimentation rate and Suspended Solids (SS) elevation.

5.2.1.9 There are no established legislative criteria for assessing water quality impact on corals, however, according to the studies from Pastorok and Bilyard and Hawker and Connell, a sedimentation rate higher than 100 g/m²/day was predicted to create moderate to severe impact on corals. This prediction has been adopted in other approved EIAs such as Tseung Kwan O – Lam Tin Tunnel and Associated Works EIA and Wan Chai Reclamation Phase II EIA. This threshold is believed to provide sufficient protection on marine ecological sensitive receivers and is anticipated to guard against undesirable impacts. This assessment criterion is approved by the EM&A reports of previously mentioned EIA studies, as no adverse impacts on corals are found with its adoption.

5.2.1.10 For the protection of corals from elevation of SS concentration, a threshold of 10 mg/L above the ambient level is adopted, this criterion has been adopted in other EIA reports, i.e. The Proposed Submarine Gas Pipelines from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant EIA and was adopted as the limit level in the EM&A programme of Sand Dredging at West Po Toi Marine Borrow Area.

5.2.1.11 The potential impacts on corals were also assessed with reference to the WQO for SS established under the WPCO, i.e. human activities or waste discharges shall not raise the ambient SS level by 30% and shall not affect aquatic communities. The WQO for SS has been adopted under the approved Upgrading of Pillar Point Sewage Treatment Works EIA and Tai Po Sewage Treatment Works Stage 5 EIA as one of the assessment criteria for evaluating water quality impact of sewage effluent on corals.

Metals and Micro-pollutants

5.2.1.12 The amount of potential released pollutants during dredging was estimated by elutriate test. However, there are no relevant standards in Hong Kong for assessing acceptable concentration of heavy metal and micro-pollutants such as total polychlorinated biphenyls (PCBs) and total polyaromatic hydrocarbons (PAHs) in marine water. It is proposed to make reference to the relevant water quality standards in the EU, Australia and USEPA. The proposed assessment objectives for metals and organic micro pollutants are summarized in Table 5.5. This set of assessment objectives have been adopted under the approved Sha Tin to Central Link Protection Works at Causeway Bay Typhoon Shelter EIA, Laying of Western Cross Harbour Main and Associated Land Mains from West Kowloon to Sai Ying Pun EIA, Wan Chai Development Phase II & Central – Wan Chai Bypass EIA and Dredging Works for Proposed Cruise Terminal at Kai Tak EIA.

Table 5.5 Proposed Assessment Objectives for Dissolved Metals and Micro-Pollutants with Reference to Standards in Other Countries

Parameter	Assessment Objective (µg/L)
Arsenic	25^1
Cadmium	2.5^1
Chromium	15^1
Copper	5^1
Lead	25^1
Mercury	0.3^1
Nickel	30^1
Silver	2.3^1
Zinc	40^1
PCBs	0.03^2
PAHs	3^3
Tributyltin (TBT)^4	0.1^5

Notes:

1. European Union (EU) Environmental Quality Standard (EQS) Values to Protect Marine Life.

2. The Criterion Continuous Concentration (CCC) of National Recommended Water Quality Criteria for Saltwater of the USEPA (2006).

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

4. TBT analysis was only performed for the reference sample but not the sediment samples due to insufficient amount of interstitial water.

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.

Sediment Quality Assessment Criteria

5.2.1.13 Environmental, 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:

· 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.

· Category M – Sediment with any one or more contaminant levels exceeding the LCEL and not 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.

· 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.

5.2.1.14 The sediment quality criteria for the classification of sediment are presented in Table 5.6.

Table 5.6 Sediment Quality Criteria for the Classification of Sediment

Contaminants	LCEL^1	UCEL^2
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

Notes:

1. LCEL – Low Chemical Exceedance Level

2. UCEL – Upper Chemical Exceedance Level

5.3 Water Quality Sensitive Receivers

5.3.1.1 As the proposed Project site is located in between Victoria Harbour (Phase I) WCZ, Eastern Buffer WCZ and Junk Bay WCZ, any discharge from the Project works during the construction and operation phases would potentially affect the marine water quality.

5.3.1.2 Water sensitive receivers (WSRs) within 500m of the Project site boundary are identified and listed below. According to Section 9.3.4, dive surveys were conducted to identify the coral communities. The C1, C2 and C3 are representative locations of WSRs for the coral communities to identify potential water quality impacts on corals within the site boundary and for the subtidal areas outside the site boundary. These locations fall into the survey areas of Rapid Ecological Assemment (i.e. REA2, REA4 and REA6). No main freshwater WSRs (such as natural streams and rivers) were identified. These WSRs are illustrated in Figure 5.1 and listed in Table 5.7.

Table 5.7 Water Sensitive Receivers (WSRs) in the Vicinity of the Project Site

Water Sensitive Receiver (WSR)	ID
Coral Community	C1
	C2
	C3
Sam Ka Tsuen Typhoon Shelter	VT3
Yau Tong Flushing Water Intake	W1
Heng Fa Chuen Flushing Water Intake	W2
Secondary Recreation Zone at Tseung Kwan O
Tung Lung Chau Fish Culture Zone
Potential Watersports Activity (e.g. Annual Cross Harbour Swim)

5.3.1.3 Although a Coastal Protective Area (CPA) is within the vicinity (~10m away) of the Project, there is no specific sensitive use of the area with respect to water quality. As the designated area of the CPA comprises the above high tide section only and any sub-tidal land is excluded from zoning, the CPA is not considered as a WSR.

5.4 Description of the Environment

5.4.1 Marine Water Quality

5.4.1.1 The baseline water quality condition of marine water was established from the marine water quality monitoring data routinely collected by EPD in the Junk Bay, Victoria Harbour (Phase 1), Eastern Buffer WCZs and Sam Ka Tsuen Typhoon Shelter. A summary of EPD monitoring data collected in 2016 is tabulated in Table 5.8 – Table 5.11 for EPD monitoring stations in Junk Bay (JM3 and JM4), Victoria Harbour (VM1), Eastern Buffer WCZs (EM1) and Sam Ka Tsuen Typhoon Shelter (VT3) respectively. As the Harbour Area Treatment Scheme (HATS) Stage 1 was commissioned in late 2001, the data shown in Table 5.8 – Table 5.11 represent the situation after operation of the HATS Stage 1.

5.4.1.2 In general, the compliance rate for Victoria Harbour WCZ had increased from 90% in 2015 to 93% in 2016, while the compliance rates for Eastern Buffer and Junk Bay WCZs maintained at 100% in 2015. Because sewage generated from Junk Bay (Tseung Kwan O), the Kowloon Peninsula and east of Hong Kong Island (Chai Wan) was diverted and treated at the Stonecutters Island Sewage Treatment Works (SCISTW) under the operation of HATS Stage 1, water quality of Eastern Buffer and Junk Bay WCZs has improved markedly with increasing DO and decreasing nutrient and bacterial levels. Prior to the complete establishment of HATS Stage 2A, Total Inorganic Nitrogen (TIN) level of Victoria Harbour WCZ is still subjected to change due to the influence of Pearl River discharge, Tolo Harbour Effluent Export Scheme discharge and surface run-off and effluent discharged from the remaining preliminary treatment plants located between North Point and Central.

Table 5.8 Summary Statistics of 2016 Marine Water Quality in Junk Bay WCZ

Parameter		Junk Bay		WPCO WQO
		JM3	JM4
Temperature (°C)		22.9	22.7	Change due to water discharges not to exceed 2℃
		(15.4 - 28.2)	(15.4 - 27.6)
Salinity		31.6	31.7	Change due to water discharges not to exceed 10% of ambient
		(29.7 - 33.0)	(29.7 - 33.3)
Dissolved Oxygen (mg/L)	Depth Average	6.5	6.2	Marine waters: Not less than 4mg/L for 90% of samples Fish Culture Subzones: Not less than 5mg/L for 90% of samples
		(4.4 - 9.1)	(4.0 - 9.2)
	Bottom	6.4	6.0	Not less than 2mg/L for 90% of samples
		(3.7 - 8.9)	(3.6 - 8.9)
Dissolved Oxygen (% Saturation)	Depth Average	89	85	Not available
		(64 - 113)	(58 - 114)
	Bottom	89	83	Not available
		(54 - 111)	(51 - 110)
pH		7.9	7.9	6.5 - 8.5 (±0.2 from natural range)
		(7.6 - 8.3)	(7.6 - 8.2)
Secchi Disc Depth (m)		2.9	3.1	Not available
		(2.0 - 6.0)	(2.3 - 5.0)
Turbidity (NTU)		2.2	2.6	Not available
		(0.5 - 4.6)	(0.5 - 5.3)
Suspended Solids (SS) (mg/L)		4.5	4.3	Not more than 30% increase
		(0.6 - 16.7)	(0.8 - 13.7)
5-day Biochemical Oxygen Demand (BOD5) (mg/L)		1.1	0.8	Not available
		(0.2 - 2.2)	(0.2 - 1.4)
Ammonia Nitrogen (NH3-N) (mg/L)		0.052	0.051	Not available
		(0.008 - 0.105)	(0.010 - 0.121)
Unionised Ammonia (mg/L)		0.001	0.002	Not more than annual average of 0.021mg/L
		(<0.001 - 0.003)	(<0.001 - 0.004)
Nitrite Nitrogen (NO2-N) (mg/L)		0.020	0.023	Not available
		(0.002 - 0.060)	(0.002 - 0.085)
Nitrate Nitrogen (NO3-N) (mg/L)		0.082	0.091	Not available
		(0.015 - 0.163)	(0.022 - 0.187)
Total Inorganic Nitrogen (TIN) (mg/L)		0.15	0.16	Not more than annual water column average of 0.3mg/L
		(0.05 - 0.25)	(0.06 - 0.24)
Total Kjeldahl Nitrogen (mg/L)		0.45	0.44	Not available
		(0.19 - 0.71)	(0.15 - 1.01)
Total Nitrogen (TN) (mg/L)		0.55	0.56	Not available
		(0.22 - 0.89)	(0.19 - 1.19)
Orthophosphate Phosphorus (PO4) (mg/L)		0.010	0.012	Not available
		(0.003 - 0.019)	(0.005 - 0.019)
Total Phosphorus (TP) (mg/L)		0.04	0.04	Not available
		(<0.02 - 0.10)	(<0.02 - 0.06)
Silica (as SiO2) (mg/L)		0.71	0.86	Not available
		(0.22 - 1.13)	(0.36 - 1.43)
Chlorophyll-a (μg/L)		4.6	2.8	Not available
		(0.7 - 9.8)	(0.3 - 7.3)
E. coli (count/100mL)		22	55	Not to exceed 610 count/100mL for geometric mean (Secondary Contact Recreation Subzone and Fish Culture Subzones)
		(3 - 140)	(7 - 200)
Faecal Coliforms (count/100mL)		56	130	Not available
		(12 - 300)	(15 - 480)

Note:   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 5.9 Summary Statistics of 2016 Marine Water Quality in Victoria Harbour WCZ

Parameter		Victoria Harbour (East)	WPCO WQO
		VM1
Temperature (°C)		22.7	Change due to water discharges not to exceed 2℃
		(15.6 - 28.2)
Salinity		31.7	Change due to water discharges not to exceed 10% of ambient
		(29.5 - 33.4)
Dissolved Oxygen (mg/L)	Depth Average	5.9	Marine waters: Not less than 4mg/L for 90% of samples Inland waters: Not less than 4mg/L
		(4.0 - 8.1)
	Bottom	5.7	Marine waters: Not less than 2mg/L for 90% of samples
		(2.7 - 8.3)
Dissolved Oxygen (% Saturation)	Depth Average	81	Not available
		(57 - 100)
	Bottom	78	Not available
		(38 - 105)
pH		7.8	6.5 - 8.5 (±0.2 from natural range)
		(7.1 - 8.2)
Secchi Disc Depth (m)		3.5	Not available
		(2.4 - 5.2)
Turbidity (NTU)		3.4	Not available
		(1.0 - 6.1)
Suspended Solids (SS) (mg/L)		4.4	Not more than 30% increase
		(1.2 - 9.6)
5-day Biochemical Oxygen Demand (BOD5) (mg/L)		0.8	Not available
		(0.1 - 1.4)
Ammonia Nitrogen (NH3-N) (mg/L)		0.072	Not available
		(0.016 - 0.133)
Unionised Ammonia (mg/L)		0.002	Not more than annual average of 0.021mg/L
		(<0.001 - 0.004)
Nitrite Nitrogen (NO2-N) (mg/L)		0.022	Not available
		(0.007 - 0.051)
Nitrate Nitrogen (NO3-N) (mg/L)		0.106	Not available
		(0.036 - 0.273)
Total Inorganic Nitrogen (TIN) (mg/L)		0.20	Not more than annual water column average of 0.4mg/L
		(0.12 - 0.38)
Total Kjeldahl Nitrogen (mg/L)		0.41	Not available
		(0.18 - 0.82)
Total Nitrogen (TN) (mg/L)		0.54	Not available
		(0.35 - 0.91)
Orthophosphate Phosphorus (PO4) (mg/L)		0.015	Not available
		(0.003 - 0.028)
Total Phosphorus (TP) (mg/L)		0.04	Not available
		(0.02 - 0.07)
Silica (as SiO2) (mg/L)		0.97	Not available
		(0.37 - 1.53)
Chlorophyll-a (μg/L)		2.1	Not available
		(0.5 - 5.4)
E. coli (count/100mL)		200	Not to exceed 610 count/100mL for geometric mean (Secondary Contact Recreation Subzone and Fish Culture Subzones)
		(95 - 720)
Faecal Coliforms (count/100mL)		410	Not available
		(150 - 1900)

Note:   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 5.10 Summary Statistics of 2016 Marine Water Quality in Eastern Buffer WCZ

Parameter		Chai Wan Subzone	WPCO WQO
		EM1
Temperature (°C)		22.7	Change due to water discharges not to exceed 2℃
		(15.4 - 27.6)
Salinity		31.6	Change due to water discharges not to exceed 10% of ambient
		(29.5 - 32.9)
Dissolved Oxygen (mg/L)	Depth Average	6.2	Marine waters, water gathering ground subzones and inland waters: Not less than 4mg/L for 90% of samples Fish Culture Subzones: Not less than 5mg/L for 90% of samples
		(4.1 - 8.9)
	Bottom	6.0	Not less than 2mg/L for 90% of samples
		(3.5 - 8.6)
Dissolved Oxygen (% Saturation)	Depth Average	86	Not available
		(60 - 110)
	Bottom	82	Not available
		(50 - 107)
pH		7.9	6.5 - 8.5 (±0.2 from natural range)
		(7.6 - 8.2)
Secchi Disc Depth (m)		3.3	Not available
		(2.0 - 5.0)
Turbidity (NTU)		2.5	Not available
		(0.5 - 4.6)
Suspended Solids (SS) (mg/L)		6.7	Marine Water: Not more than 30% increase Water Gathering Ground: Not more than 20mg/L annual median increase
		(0.7 - 21.3)
5-day Biochemical Oxygen Demand (BOD5) (mg/L)		0.8	Not exceed 3mg/L (Water Gathering Ground)
		(<0.1 - 1.6)
Ammonia Nitrogen (NH3-N) (mg/L)		0.049	Not available
		(0.017 – 0.084)
Unionised Ammonia (mg/L)		0.001	Not more than annual average of 0.021mg/L
		(<0.001 - 0.003)
Nitrite Nitrogen (NO2-N) (mg/L)		0.023	Not available
		(<0.002 – 0.089)
Nitrate Nitrogen (NO3-N) (mg/L)		0.090	Not available
		(0.022 - 0.200)
Total Inorganic Nitrogen (TIN) (mg/L)		0.16	Not more than annual water column average of 0.4mg/L
		(0.06 - 0.24)
Total Kjeldahl Nitrogen (mg/L)		0.44	Not available
		(0.18 - 0.93)
Total Nitrogen (TN) (mg/L)		0.55	Not available
		(0.38 - 1.07)
Orthophosphate Phosphorus (PO4) (mg/L)		0.011	Not available
		(<0.002 - 0.021)
Total Phosphorus (TP) (mg/L)		0.04	Not available
		(0.02 - 0.09)
Silica (as SiO2) (mg/L)		0.89	Not available
		(0.36 - 1.57)
Chlorophyll-a (μg/L)		2.7	Not available
		(0.6 - 6.2)
E. coli (count/100mL)		65	Not to exceed 610 count/100mL for geometric mean
		(6 - 270)
Faecal Coliforms (count/100mL)		140	Not available
		(11 - 650)

Note:   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.JM4

Table 5.11 Summary Statistics of 2016 Marine Water Quality in Sam Ka Tsuen Typhoon Shelter

Parameter		Sam Ka Tsuen	WPCO WQO
		VT3
Temperature (°C)		23.5	Change due to water discharges not to exceed 2°C
		(17.0 - 27.9)
Salinity		31.2	Change due to water discharges not to exceed 10% of ambient
		(29.5 - 32.5)
Dissolved Oxygen (mg/L)	Depth Average	5.0 (3.5 - 7.4)	Marine waters: Not less than 4mg/L for 90% of samples Inland waters: Not less than 4mg/L
	Bottom	5.3 (3.6 - 8.5)	Marine waters: Not less than 2mg/L for 90% of samples
Dissolved Oxygen (% Saturation)	Depth Average	70 (50 - 92)	Not available
	Bottom	73 (51 - 106)	Not available
pH		7.8	6.5 - 8.5 (±0.2 from natural range)
		(7.4 - 8.2)
Secchi Disc Depth (m)		2.7	Not available
		(2.0 - 3.4)
Turbidity (NTU)		7.0	Not available
		(1.0 - 30.0)
Suspended Solids (SS) (mg/L)		9.3	Not more than 30% increase (Marine Water)
		(1.1 - 22.0)
5-day Biochemical Oxygen Demand (BOD5) (mg/L)		1.0	Not available
		(0.2 - 2.3)
Ammonia Nitrogen (NH3-N) (mg/L)		0.116	Not available
		(0.077 – 0.131)
Unionised Ammonia (mg/L)		0.003	Not more than annual average of 0.021mg/L
		(<0.001 - 0.006)
Nitrite Nitrogen (NO2-N) (mg/L)		0.029	Not available
		(0.008 - 0.069)
Nitrate Nitrogen (NO3-N) (mg/L)		0.143	Not available
		(0.092 - 0.200)
Total Inorganic Nitrogen (TIN) (mg/L)		0.29	Not more than annual water column average of 0.4mg/L
		(0.22 - 0.36)
Total Kjeldahl Nitrogen (mg/L)		0.45	Not available
		(0.33 - 0.62)
Total Nitrogen (TN) (mg/L)		0.62	Not available
		(0.47 - 0.85)
Orthophosphate Phosphorus (PO4) (mg/L)		0.021	Not available
		(0.011 - 0.033)
Total Phosphorus (TP) (mg/L)		0.05	Not available
		(0.03 - 0.08)
Silica (as SiO2) (mg/L)		1.11	Not available
		(1.01 - 1.25)
Chlorophyll-a (μg/L)		3.2	Not available
		(1.1 - 8.9)
E. coli (count/100mL)		870	Not to exceed 610 count/100mL for geometric mean (Secondary Contact Recreation Subzone and Fish Culture Subzones)
		(220 - 5300)
Faecal Coliforms (count/100mL)		2100	Not available
		(520 - 18000)

Note:   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.JM4

5.4.2 Sediment Quality

5.4.2.1 Site investigation (SI) was conducted in September 2006 to determine the contamination level of the sediments within the proposed dredging areas under ETWB TCW No. 34/2002. A Sediment Quality Report (SQR-2007) was submitted to EPD for agreement under Dumping at Sea Ordinance (DASO) in March 2007 to report the findings of the SI works. A Sediment Sampling and Testing Plan (SSTP) was submitted to serve the purpose of fulfilling this EIA Study and was approved by EPD in July 2016. Re-sampling and testing works were hence conducted in October 2016 and justified the validity of the SQR-2007 for this EIA Study.

5.4.2.2 The results of marine sediment quality analysis from the sediment testing works are presented in Section 7. The sediment testing results indicate that all marine sediments to be dredged at the Project area were classified as Category L. However, since only surface grab samples were collected because of site constraints, findings from the SQR-2007 were adopted in the quantities estimation to provide a conservative assessment. Based on the findings in SQR-2007, Category H sediment was identified at deeper depth. Details of the sediment quality criteria and estimated volumes of contaminated sediments to be generated from the Project are given in Section 7.

5.5 Identification of Potential Impacts

5.5.1.1 As presented in Section 2.12, a DSD project “Lei Yue Mun Village Sewerage project”, would be constructed concurrently with the Project. Cumulative water quality impact maybe presented under construction and operation phase and would be discussed in Section 5.7.

5.5.2 Construction Phase Impacts

5.5.2.1 The major construction works of the Project would be the construction of public landing facility and breakwater, aligning with the development of waterfront promenade and other related improvement works. Dredging would be required for constructing public landing facility, sloping seawall and breakwater while excavation and filling works would be needed for and improvement works at lookout points 1 and 5 and viewing platform respectively. Potential sources of water quality impacts under construction phase of the Project are identified as follows:

· Dredging and filling works;

· Drainage and construction site run-off during site formation;

· Wastewater discharges from general construction activities;

· Seawall modification works;

· Accidental spillage; and

· Sewage effluent produced by on-site workforce.

5.5.3 Operation Phase Impacts

5.5.3.1 The key sources of potential water quality issues associated with the operation of Project are as follows:

· Change in hydrodynamic regime;

· Sewage from visitors and operators;

· Surface runoff and drainage; and

· Maintenance dredging.

5.6 Assessment Methodology

5.6.1 Land-based Impacts

5.6.1.1 The study area for the water quality impact assessment covers all areas within 500m from the Project boundary in Victoria Harbour (Phase One), Eastern Buffer and Junky Bay WCZ designated under the WPCO and other areas that may have a bearing on the environmental acceptability of the Project. The assessment area will be extended to include other areas such as stream courses and associated water systems, existing and planned drainage system if they are found being impacted during the course of the EIA study and have a bearing on the environmental acceptability of the Project.

5.6.1.2 The WSRs that may be affected by the Project have been identified. Potential sources of water quality impacts that may arise during the construction works and operation activities were described. This task included identifying pollutants from point sources and non-point sources discharges that could affect the quality of surface water runoff. All the identified sources would then be evaluated and their impact significance would be determined. The necessity for mitigation measures to reduce any identified adverse impacts on water quality to acceptable levels would also be determined.

5.6.2 Marine-based Impacts

Modelling Tools

5.6.2.1 The hydrodynamic and sediment plume modelling platforms were developed by Delft Hydraulics, namely the Delft3D-FLOW and Delft3D-WAQ.

5.6.2.2 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.

5.6.2.3 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 computations grid and for a wide range of model substances.

5.6.2.4 Lei Yue Mun Model (hereinafter referred to the ‘LYM Model’) was adopted from the Updated Model and used as the basis for hydrodynamic and sediment plume modelling. LYM Model covers the Hong Kong waters, the Pearl Estuary and the Dangan Channel to incorporate all major influences on hydrodynamic and water quality. Additionally, this detailed model was fully calibrated and verified by comparing computational results with field measurements.

5.6.2.5 In this Project, the gird mesh of LYM Model near the Project site has been refined to increase resolution to give better representation of the local hydrodynamics and water quality conditions while the grid in the wider area remains unchanged. Appendix 5.1 shows the coverage and grid layout of the Updated and refined LYM Model. The grid quality at the refined area can also be seen in Appendix 5.1 for orthogonality and smoothness.

5.6.2.6 The grid quality in the modified area is generally good except in some areas at or close to the land boundary, however, the flow velocities were assumed to be small at or near the land boundary of the modified area. Numerical errors associated with the change of orthogonality and smoothness are therefore anticipated to be small. As a result, it is considered appropriate to adjust the grid line to represent the coastal features (instead of keeping these closed grid cells orthogonal or smooth). Orthogonality and smoothness at open grid cells had been checked for adequacy.

5.6.2.7 After refining the model grid, the model was then run initially to simulate the Baseline Scenario for the same series of tides in the dry and wet season for which the LYM Model has been calibrated and validated. Before the simulations were begun, a number of observation points were selected at which the model results could be stored and assessed in detail (Appendix 5.2). The observation points were selected to coincide with the sensitive receivers which might be impacted by the Project and the EPD routine water quality monitoring stations that are in the vicinity of the development to allow water quality assessment. In addition, a section running across Lei Yue Mun Narrows was set up for detailed discharge calculations. An observation point was selected at the center of this section (H1 in Appendix 5.2) for storing model results to facilitate a more detailed assessment on the possible large scale tidal flows impact of the proposed development.

Hydrodynamic Model

5.6.2.8 The hydrodynamic model of the LYM Model is three dimensional with a total of 10 vertical water layers. The thickness of each water layer is defined in the model as percentage of the water depth where the total sum of all the vertical layers should be 100%. The computational timestep was set to 0.1 minute. The LYM Model covers a 7-day spin-up period before the actual model simulations to maintain the simulation convergence. The actual simulation period (excluding the spin-up period) of the hydrodynamic model covers two typical 15-day full spring-neap cycles for dry and wet seasons respectively.

Sediment Plume Model

5.6.2.9 Delf3D-WAQ module was used to model dispersion of sediment during dredging activities. This module has been used for sediment plume modelling in other approved EIA, including Cross Bay Link EIA[1]and Wan Chai Development Phase II EIA[2].

5.6.2.10 The hydrodynamic conditions generated from the Delft3D-FLOW module provided basic hydrodynamic information for modelling of sediment plume dispersion. The process of settling sediment particles and exchanging sediment particles between the water column and the seabed govern the sediment transport. Sediment deposition and erosion occur when the bed shear stress is below or above the critical shear stress. The deposition and erosion rate were calculated using the following equation:

i. Bed Shear Stress (t) < Critical Shear Stress for Deposition (td = 0.2Pascal)

Deposition rate = Vs Cb ( 1 – t / td )

where: Vs = settling velocity (0.5mm/s = 43.2m/d); and

Cb = bottom layer SS concentration.

ii. Bed Shear Stress (t) > Critical Shear Stress for Erosion (te = 0.3Pascal)

Erosion rate = Re ( t / te -1 )

where: Re = erosion coefficient (=0.0002kg/m2/s).

iii. Water depth of 0.2m has been selected as the minimum depth in which deposition can take place.

5.6.2.11 Two full spring-neap cycles were adopted as spin-up period. After performing the spin-up, the hydrodynamics and water quality conditions at the end of the simulation were adopted as the initial conditions for the actual simulation. Similar to the hydrodynamic model, the actual simulation period (excluding the spin-up period) of the sediment plume model covers two 15-day full spring-neap cycles for dry and wet seasons respectively.

Sediment Loss Rate

5.6.2.12 The Project is assumed to perform dredging activities at a rate of 100 m^3/hr. It is estimated that a sediment loss rate of 25kg/m³ would be resulted from the incomplete grab closure during dredging and maximally there would be 6% of fines (<63µm) in the materials to be dredged. Therefore, a sediment loss rate of 0.0417 kg/s (100 m^3/hr x 25kg/m³ x 6%) was used in the model simulation.

5.6.2.13 Limited filling of sand would also be required for constructing the sloping seawall underneath the landing facility. It is estimated that a filling rate of 62.5m³/hr would be needed for the filling activity. Loss rate of fines due to filling activity was calculated based on the approach used in the approved Wanchai Development Phase II EIA study. The adopted parameters are listed below:

· Dry density of the sand fill is 1,680kg/m³.

· Based on a series of trial uncontaminated marine mud disposal event carried out at the East Tung Lung Chau Marine Borrow Area[3], the loss rate of fines to suspension from bottom dumping is 5% for material that consists of approximately 60% fines.

· Fines content of the sand fill material is 5% (a design requirement for reclamation is to specify a fines content for marine fill material not greater than 5%).

5.6.2.14 As such, the filling rate for this Project will be 29.17kg/s (62.5m³/hr x 1,680kg/ m³). By taking the fines content of the bottom dumping material and using a pro-rata basis, the percentage loss rate from sand filling for this Project is estimated as:

5.6.2.15 Therefore, the loss rate for fines will be 0.417% (5% x (5%/60%)). Adopting above information, a sediment loss rate of 0.122kg/s (29.17kg/s x 0.417%) for the sand filling activity was used in the model simulation.

5.6.2.16 Dredging and filling activity were assumed to be conducted concurrently from 7:00–19:00 each day over the whole 15-day spring-neap cycle. Release of sediment fines from dredging and filling were assumed to be distributed over the whole water column at 2 different locations within the Project area as shown in the inset of Appendix 5.2.

Ambient and Allowable Elevation of SS

5.6.2.17 The sediment plumes passing over a sensitive receiver will cause the ambient suspended solids concentrations to be elevated. The elevation level can determine the extent of adverse impact. The WQO for SS established under the WPCO has been adopted as the assessment criterion. It is proposed to represent the ambient SS value by the SS concentrations measured under the EPD routine marine water quality monitoring programme at Station VM1. The allowable elevation of SS in the WQO is less than 30% of the ambient condition. To assess the water quality impacts from SS due to sediment loss from dredging and filling activities, this study adopted the criterion of 30% elevation over 90^th percentiles of the ambient SS concentration, above which impacts are considered unacceptable. A summary of monitoring data collected in the period from 2010 to 2015 and the relevant allowable SS elevation at VM1 are presented in Table 5.12 below.

Table 5.12 Summary of Suspended Solids Concentrations and Allowable SS Elevation at VM1 (from 2010 to 2015)

Item	Suspended Solids Concentration (mg/L)
	Surface		Middle		Bottom		Depth Averaged
	Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
Monitoring Record	3.3	2.8	3.1	4.4	3.5	7.8	3.3	5.0
	(0.8 – 13)	(0.5 – 7.4)	(1.0 – 8.8)	(1.1 – 24)	(0.7 – 9.5)	(2.2 – 20)	(0.87 – 9.77)	(1.6 -12.2)
90% Percentile	6.3	5.1	6.3	6.8	7.0	12.0	5.9	7.9
Allowable Elevation	1.9	1.5	1.9	2.0	2.1	3.6	1.8	2.4

Note:   The data are presented as the arithmetic mean and range (Min. – Max.) of the suspended solids concentrations at each station at the three monitoring levels and as the depth-averaged concentrations.

5.6.2.18 It is proposed to assign each sensitive receiver to the nearest EPD water quality monitoring stations and to set the WQO at each station as 30% of the 90^th percentiles at that station. As such, all sensitive receivers located within the Project area would adopt VM1 WQO for assessment.

5.6.2.19 Corals are also sensitive to elevation in SS concentration and sediment deposition. To protect corals from SS concentration elevation, a threshold of 10 mg/L above the ambient level was adopted as justified in Section 5.2.1.10 above.

Tracer Model

5.6.2.20 Delft-WAQ was also used to simulate the discharge of various constituents in marine sediment from the dredging activities. An indication of the likelihood of release of contaminants (including heavy metals, PCBs, PAHs and nutrients) from the sediment during dredging is given by the results of the elutriation tests from the 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 hence increase the pollutant concentrations in the solution. The laboratory testing was to analyse the pollutant concentrations in the solution (elutriate). As there is no existing legislative standard or guideline for these contaminant contents in marine waters, relevant overseas standards (Section 5.2.1.12) are adopted as the assessment criteria.

5.6.2.21 The elutriate tests conducted in the SI works provided information on the release of contaminants from the marine mud during dredging and sand filling. An inactive tracer is defined in the model at the dredging locations to determine the dilution in the vicinity of the dredging site and to determine the size of the mixing zone for the contaminants. 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.

5.6.2.22 The maximum dimension of mixing zone for each susceptible contaminants was determined by a tracer simulation. The simulation covered two model runs for dry and wet seasons respectively.

Potential Oxygen Depletion

5.6.2.23 The degree of oxygen depletion exerted by a sediment plume is a function of the sediment oxygen demand of the sediment, its concentration in the water column and the rate of oxygen replenishment. For the purpose of this assessment, the impact of the sediment oxygen demand on dissolved oxygen concentrations is calculated based on the following equation:

DO_Dep = C * SOD * K * 0.001

Where:

DO_Dep = Dissolved Oxygen Depletion (mg/L)

C = Suspended Solids Concentration (kg/m³)

SOD = Sediment Oxygen Demand

K = Daily Oxygen Uptake Factor (set a 1.0/day for worse case estimation)

5.6.2.24 An SOD of 17,300 mg/kg was used for the calculation with reference to the EPD Summary Statistics for Bottom Sediment Quality in 2011-2015 at East Victoria Harbour (VS3).

5.6.2.25 The extent of DO depletion will not be underestimated by the analysis because the above equation does not allow re-aeration, which would tend to reduce potential impact of the suspended sediment on the water column DO concentrations. It should be noted that sediment in suspension takes time to exert oxygen demand on the water column as the sediment will be transported and mixed / dispersed with oxygenated water. As a result, the decrease in the suspended sediment concentrations will diminish the concentration of dissolved oxygen.

5.6.2.26 Oxygen depletion is not instantaneous and thus some studies have assumed that the impact of suspended sediment on dissolved oxygen will depend on tidally averaged suspended sediment concentrations. For the purposes of this study, the maximum increase in suspended sediment has been used as the basis for the calculation in order to identify the hypothetical worst case. As such, the daily update factor, K, in above equation was set to be 1.0 to indicate instantaneous oxidation of the sediment oxygen demand and represent the worst case. The resulting calculated dissolved oxygen deficit is thus anticipated to be much larger than that would be experienced in reality.

Modelling Scenario

Construction Phase

5.6.2.27 Sediment plume, hydrodynamic and tracer modelling were conducted to assess the potential water quality impacts of the construction works. It was assumed that all sediment loss resulted from the dredging and filling activities would only create near field impacts. The modelling scenario assumed that the dredging and sand filling activities would take place concurrently.

5.6.2.28 The maximum dredging and sand filing rates (adopted as the worst-case scenario) for the designated Project were assumed to be 100m³/hr and 62.5m³/hr, respectively. Construction works were assumed to be carried out from 07:00 – 19:00 per day, with no night time work because of close proximity to residential areas.

5.6.2.29 Sediments at the designated dredging area composed of only 6% of fines (<63µm). With reference to the approved Project Profile for ‘Lei Yue Mun Waterfront Enhancement Project – Dredging Works for Public Landing Facility at Lei Yue Mun’ (PW 1/2006), the sediment loss from dredging and sand filling works were estimated to be 0.0417 kg/s and 0.122 kg/s respectively. Since there is no alteration in the assumed dredging and sand filling rates, therefore, the same assumptions on sediment loss rates were made for both dredging and sand filling works in this assessment.

Operation Phase

5.6.2.30 Hydrodynamic modelling was conducted to evaluate the change in the hydrodynamic regime due to the implementation of landing facility and breakwater. The proposed layout of the landing facility and breakwater is presented in Figure 2.1. Modelling was carried out for with- and without- project scenario respectively.

5.6.2.31 The presence of breakwater and landing facility, as well as the increased water depth due to dredging may reduce the main flows in Lei Yue Mun Narrow and thus pose water quality impact. The with-project scenario, with completion of breakwater and landing facility implementation, represents the worst case in terms of tidal flushing impact. Additional scenario for addressing the hydrodynamic impact under different interim construction stages is considered unnecessary.

5.6.2.32 For modelling the impacts of maintenance dredging, the assumptions made are the same as those mentioned for the dredging activities.

5.7 Prediction and Evaluation of Environmental Impacts

5.7.1 Construction Phase

Dredging and Filling Works

5.7.1.1 Dredging would be required for constructing public landing facility, while filling works would be needed for constructing the sloping seawall. It is expected that a 3-month dredging activity would be carried out with a maximum dredging rate of 100m³ per hour. About 10,875m³ of soil are required to be dredged from a 3,820m² dredging area. Limited filling works with a maximum filling rate of 62.5m³/hr would take place for the sloping seawall. The dredging operation would be properly scheduled such that no dredging works will be carried out during the period of the Annual Cross Harbour Swim Race to be held.

Potential Suspended Solids and Sedimentation Elevation

5.7.1.2 Water quality impacts during the Project construction will be principally related to sediment losses and release of contaminant to suspension upon dredging and filling activities. This can increase the suspended sediment concentration and may bring potential impacts on below areas:

· Exceed Water Quality Objective (WQOs) for the WCZs;

· Adversely affect corals due to the alteration in deposition rates; and

· Exceed water quality criteria for specific utility, for example, flushing water intakes.

5.7.1.3 Dredging works will disturb the marine bottom sediment. Therefore, fine sediment (<63 µm) will be lost to suspension, causing an increase in SS concentrations in the water bodies. SS will be transported by currents to form sediment plumes along the tidal flows and resettle gradually. Potential water quality impacts of dredging vary in response to the contamination quantities and level, as well as the nature and locations of WSRs correlate with the dredging sites. The potential impacts are summarized as follows:

· 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;

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

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

5.7.1.4 According to the modelling result, it is predicted that the plume created resulting from dredging and filling activities would be highly localized. The mixing zones showed in Appendix 5.3 and 5.4 indicate that only area within 100m of the Project site is expected to be affected. Only the nearest WSR, namely C1 would have SS elevation exceeded the WQO and would be affected regardless tidal conditions, while other WSRs, including Sam Ka Tsuen typhoon shelter, Yau Tong and Heng Fa Chuen flushing water intakes, secondary recreation zone at Tseung Kwan O, Tung Lung Chau Fish Culture Zone and the potential watersports activity, would remain unaffected. Exceedance of the SS elevation threshold for coral protection (10mg/L) are not expected at all WSRs in all tidal conditions regardless monsoon seasons.

5.7.1.5 Time history plots of SS elevation at the surface, middle and bottom layer are presented for WSRs C1, C2 and C3 (Appendix 5.5 – 5.12). From the time history plots of SS elevation for C1, it shows that spikes of high SS levels at particular times over the whole simulation period occurred.

5.7.1.6 The predicted maximum elevation in SS at selected observation points are summarized in Table 5.13 below. Full compliance of WQO for SS elevation at all identified WSRs, except C1, are expected under dredging and filling activities.

Table 5.13 Predicted Maximum Suspended Solids Elevation at Selected Observation Points during Construction Phase (Unmitigated)

WSR	Maximum Suspended Solid Elevation (mg/L)
	Surface	Middle	Bottom	Depth Averaged	Compliance with WQO
Dry Season
WQO	1.9	1.9	2.1	1.8	N/A
C1	3.1	3.0	4.6	3.1	No
C2	1.8	1.7	1.6	1.6	Yes
C3	1.4	1.3	1.2	1.2	Yes
W1	0.1	0.1	0.2	0.1	Yes
Wet Season
WQO	1.5	2.0	3.6	2.4	N/A
C1	2.5	4.3	4.2	2.9	No
C2	1.0	1.9	1.8	1.3	Yes
C3	0.8	1.2	1.3	0.8	Yes
W1	0.0	0.1	0.1	0.1	Yes

Note:   

1. WQO – Water Quality Objectives

2. Value in bold indicates exceedance in WQO

5.7.1.7 For W1, the maximum depth averaged SS elevation is 0.1mg/L and the baseline condition for SS levels at VM1 is 1.6 - 9.8. Hence, the assessment criteria for WSD’s salt water intakes for flushing water (10mg/L) is not expected to be exceeded under Project construction.

5.7.1.8 Sediment deposition has also been simulated in the model for assessing potential detrimental effects on coral communities. Appendix 5.13 and Appendix 5.14 present the total deposition over the whole spring-neap cycles in dry and wet seasons as well as illustrate the general extents of the sediment depositions caused by filling and dredging activities. Similar to the SS elevation, the plume of daily sedimentation rates due to filling and dredging activities is highly localized, only the closest WSR, C1 would be affected, while other WSRs, including Sam Ka Tsuen typhoon shelter, Yau Tong and Heng Fa Chuen flushing water intakes, secondary recreation zone at Tseung Kwan O, Tung Lung Chau Fish Culture Zone and the potential watersports activity would not be affected.

5.7.1.9 The predicted maximum daily sedimentation rates at selected known coral sensitive receivers (confirmed by recent dive survey conducted under this study) are summarized in Table 5.14. It shows that exceedances of the threshold (100 g/m²/day) only occur as spikes of higher deposition rates at C1. Over the whole 15 days simulation period, the percentages of exceedance times would be 0.5% (maximum continuous duration of exceedance <2 hours) and 1.2% (maximum continuous duration of exceedance <5 hours) for dry and wet season respectively. To minimise the impact on coral colonies, translocation and/or other best practicable mitigation measures will be implemented before the commencement of capital dredging and filling works. The details of potential ecological impacts on corals related to elevated SS level and sedimentation rate are discussed in Section 9. The duration of exceedance can be minimised if measures recommended in Section 5.8 are followed as far as practicable. No exceedance in term of sedimentation rate was predicted at other sensitive receivers.

Table 5.14 Predicted Maximum Sedimentation Rates at Identified Coral Sensitive Receivers during Construction Phase (Unmitigated)

Known Coral Sites	Maximum Sedimentation Rate (g/m^2/d)
	Dry Season	Wet Season
C1	153	135
C2	67	74
C3	48	50

Note:   

1. Value in bold indicates exceedance in assessment criterion

Potential Contaminant Release

5.7.1.10 Likelihood of the release of contaminants from the marine sediment during dredging is indicated by the elutriate test results from the laboratory testing conducted under the marine SI for the selected sediment sampling stations as shown in Table 5.15. Description of the marine SI is given in Section 5.4.2. If the contaminant levels in the elutriate test results are higher than 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 by dredging activities. As there is no existing legislative standard or guideline for individual heavy metal contents in marine waters, the relevant water quality standards in the EU, Australia and USEPA as specified in Section 5.2.1.12 are adopted as the assessment criteria.

5.7.1.11 The elutriate samples were analysed for heavy metals, total PCBs, total PAHs, NH₃-N and Total Inorganic Nitrogen (TIN). The measured NH₃-N released from the sediment will result in a concentration of total HN₃-N were converted to unionized NH₃-N, which is a more critical parameter of concern. The estimated amount of Unionised Ammonia (UIA) was based on the nitrogen (ammonia) content, temperature, salinity and pH level. Table 5.15 shows the elutriate test results for heavy metals, total PCBs, total PAHs, UIA and TIN and Table 5.16 records the predicted maximum elevation of sediment bounded contaminants at selected observation points. The corresponding monitoring data at Station VM1 in 2015 Marine Water Quality Report was adopted in the simulation as the ambient condition.

Table 5.15 Marine Site Investigation Sediment Elutriate Test Results

Sediment Sampling Stations	Metal Content (µg/L)									Organic Compounds Content (µg/L)		Nutrients (mg/L)
	Cd	Cr	Cu	Hg	Ni	Pb	Ag	Zn	As	Total PCBs	Total PAHs	UIA ^(2)(3)	TIN^(3)
DH-1	<0.5	4.6	18	<1	3.6	14	<1	34	6.9	<0.02	<0.1	0.030	1.52
DH-1 (Blank)	<0.5	<1	7.9	<1	<1	1.1	<1	15	2.4	<0.02	<0.1	<0.01	0.14
DH-2	<0.5	3.5	14	<1	3.2	9.7	<1	33	6.2	<0.02	<0.1	0.019	0.78
DH-2 (Blank)	<0.5	<1	6.8	<1	<1	1.2	<1	16	2.4	<0.02	<0.1	<0.01	<0.12
DH-3	<0.5	4.4	16	<1	6.2	9.8	<1	40	6.1	<0.02	<0.1	0.021	0.81
DH-3 (Blank)	<0.5	<1	2.4	<1	<1	1.7	<1	35	3.5	<0.02	<0.1	<0.01	<0.15

Note:   

1. Value in bold indicates exceedance in assessment criteria.

2. Based on maximum concentration of ammonia sampled during SI marine sampling and converted to unionised ammonia by conversion factor of 2.5% (22.9℃, 32.7ppt and a pH of 7.8) and divided by 0.822 to convert from N to NH_3.

3. Ambient condition has been taken into account.

Table 5.16 Predicted Maximum Elevation of Sediment Bounded Contaminants at Selected Observation Points during Construction Phase

WSR	Maximum Sediment Bounded Contaminant Elevation
	Copper (µg/L)	Mercury (µg/L)	UIA (mg/L)	TIN (mg/L)
Criterion	5	0.3	0.021	0.4
Dry Season
C1	5.18	0.29	0.010	0.57
C2	1.35	0.08	0.004	0.29
C3	1.06	0.06	0.004	0.27
W1	0.27	0.02	0.002	0.21
Wet Season
C1	5.03	0.28	0.010	0.56
C2	1.17	0.06	0.004	0.28
C3	0.83	0.05	0.003	0.25
W1	0.14	0.01	0.002	0.20

Note:   

1. Value in bold indicates exceedance in assessment criteria

5.7.1.12 Table 5.15 shows that the concentrations of copper, mercury, UIA and TIN in the elutriate samples exceeded the assessment criteria. The highest concentration of copper (18 µg/L), UIA (0.03 mg/L) and TIN (1.52 mg/L) were recorded at Stations DH-1. Modelling results presented in Table 5.16 indicates that the dredging activities will cause copper and TIN level at C1 to exceed the relevant criteria despite monsoon seasons. The exceedance of copper level at C1 is considered to be marginal since it only exceeded 3.6% of the relevant criterion. Since C1 is located in the vicinity of the dredging area, the elevated amount of copper and TIN are considered reasonable. Given that corals are evidently sensitive to the sedimentation rate and elevated SS level, and the exceedances of copper and TIN levels would be marginal and localized, the potential impact due to the elevated contaminant levels on corals is expected to minimal.

5.7.1.13 An assessment of contaminant release for copper, mercury, UIA and TIN has been made in relation to the sediment quality results obtained from the marine SI. Inert tracers (with zero decay) were introduced into the Delft3D-WAQ model 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 to be over-estimated the potential impacts. The calculation was performed using the highest level of nutrient and heavy metals measured in the sediment samples collected during the marine SI for predicting conservatively. The contour plots of maximum contaminant concentrations predicted over the entire simulation period for the dry and wet seasons are shown in Appendix 5.15. As shown in the contour plots, the mixing zone would be highly localized and confined within100m from the dredging location, other WSRs, including Sam Ka Tsuen typhoon shelter, Yau Tong and Heng Fa Chuen flushing water intakes, secondary recreation zone at Tseung Kwan O, Tung Lung Chau Fish Culture Zone and the potential watersports activity would not be affected.

5.7.1.14 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 present 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 plum size. They are considered as the areas which envelop the moving plumes over the entire simulation period. The maximum instantaneous coverage of the mixing zones for contaminants should be much smaller in the actual situation.

5.7.1.15 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 minimised using closed grab dredger. Thus, long-term off-site marine water quality impact is not anticipated.

Potential Oxygen Depletion

5.7.1.16 An assessment of dissolved oxygen (DO) depleting during dredging has been made in relation to the results of the sediment plume modelling of dredging activities and the sediment quality data for the study area. The predicted maximum elevation at WSRs were used to estimate the effects of increased SS concentrations on DO.

5.7.1.17 The oxygen depletion exerted by the SS elevation is calculated and shown in Table 5.17. To determine compliance with the water quality criteria, the background water quality data are referred. The DO monitoring data from the closest EPD monitoring station, Victoria Harbour (East) in 2015 is adopted as baseline. No significant DO depletion was predicted at all WSRs. The dredging activities would cause a maximum DO depletion of less than 0.1mg/L at all WSRs. Full compliance with the WQO for depth-averaged and bottom DO of 4 mg/L and 2 mg/L respectively in the East Victoria Harbour under dredging activities is expected. No mixing zone for DO can be identified, therefore, no adverse impacts on the DO levels at WSRs would be expected from the dredging works.

Table 5.17 Summary of Changes to DO Levels due to Elevated SS Release during Construction Phase (Unmitigated)

WSR	Max. DO Depletion (mg/L)		Baseline DO (mg/L)		Resultant DO (mg/L)
	Bottom	Depth-Averaged	Bottom	Depth-Averaged	Bottom	Depth-Averaged
WQO Criteria					>2	>4
Dry Season
C1	0.079	0.054	6.52	6.39	6.44	6.34
C2	0.028	0.027			6.49	6.36
C3	0.022	0.021			6.50	6.37
W1	0.003	0.002			6.52	6.39
Wet Season
C1	0.073	0.050	4.44	4.77	4.37	4.72
C2	0.032	0.023			4.41	4.75
C3	0.023	0.016			4.42	4.75
W1	0.002	<0.001			4.44	4.77

Drainage and Construction Site Run-off

5.7.1.18 Run-off from the construction works area may contain increased loads of sediments, other suspended solids and contaminants. The concurrent land-based construction activities from the Lei Yue Mun Village Sewerage project may worsen the situation. Potential sources of pollution form site drainage include:

· Run-off and erosion from exposed soil surfaces, earth working areas and stockpiles;

· Release of grouting and cement materials with rain wash;

· Concrete production washout and drainage from dust suppression sprays; and

· Fuel and lubricants from maintenance of construction vehicles and mechanical equipment

5.7.1.19 Sediment laden run-off during site formation works, if uncontrolled, may carry pollutants (absorbed onto the particle surfaces) into the nearby marine waters. Proper site practice and good site management should be followed to prevent run-off with high level of SS from entering the surrounding waters. With the implementation of appropriate measures to control run-off and drainage from the site, disturbance of water bodies would be avoided and deterioration in water quality would be minimal, if not negligible. Recommended measures to control site run-off and drainage are described in Section 5.8.

General Construction Activities

5.7.1.20 The general construction works may have potential to cause water pollution. Various types of construction activities would generate wastewater. These include general cleaning and polishing, dust suppression and utility installation. These types of wastewater would contain high concentration of SS. Wastewater would also be generated from the accumulation of solid waste such as debris, rubbish, plastic package and construction materials. If uncontrolled, these would lead to deterioration in water quality. Adoption of the guidelines and good site practices for handling and disposal of discharges as part of the site management practices (as presented in Section 5.8) would minimise the potential impacts.

Seawall Modification Works

5.7.1.21 The improvement works for the existing lookout points and viewing platform would be undertaken within the existing seawall footprint, while minor modification of the existing seawalls would be required for lookout points 1 and 5 as well as the viewing platform. No dredging works is required for the improvement works. In view of the minor scale and nature of the modification works, the potential water quality impact due to potential SS release during the seawall modification is anticipated to be minimal. Nonetheless, mitigation measures for the modification works are proposed in Section 5.8 to further minimise the potential water quality impact.

Accidental Spillage

5.7.1.22 Variety of chemicals would be used for carrying out construction activities. These chemicals may include petroleum products, spent lubrication oil, grease, mineral oil, solvent and other chemicals. Accidental spillages of chemicals in the works area may contaminate the surface soil. Waste oil may infiltrate into the surface soil layer, or run-off into marine water environment to increase hydrocarbon level. The potential impacts could be mitigated by practical mitigation measures and good site practices (as presented in Section 5.8).

Sewage Effluent from Construction Workforce

5.7.1.23 During Project construction, workforce on-site will generate sewage effluents, which are characterized by high level of BOD, ammonia and E. coli counts. Potential water quality impacts upon the local drainage and fresh water system may arise from these sewage effluents, if uncontrolled. However, this temporary sewage can be adequately treated by interim sewage treatment facilities, such as portable chemical toilets. Provided that sewage is not discharged directly into stormwater drains or adjacent marine waters, and temporary sanitary facilities would be used and properly maintained, it is unlikely that sewage generate from the site would have a significant water quality impact. Mitigation measures and good site practices presented in Section 5.8 should be followed as close as applicable.

5.7.2 Operation Phase

5.7.2.1 Potential sources of water quality impact associated with the operation of the Project include:

· Change in hydrodynamic regime;

· Sewage effluent;

· Surface runoff and drainage; and

· Maintenance dredging.

Change in Hydrodynamic Regime

5.7.2.2 The establishment of landing facility and breakwater may cause change in hydrodynamic regime. Appendix 5.16 and 5.17 illustrate peak flood and ebb tide near surface velocity vectors in the dry and wet seasons for the simulation of the completed development superimposed with the results from the Baseline simulation. The figures illustrate that the proposed development has negligible impact on tidal water velocities remote from the development but a minor change in current direction in the vicinity of Project site is anticipated.

5.7.2.3 To assess the potential impacts on tidal water velocities comprehensively, a station was selected at the center of discharge section at Lei Yue Mun Narrows (H1). The predicted water speeds at this location in the dry and wet season in both Baseline and With-project scenario are presented in Appendix 5.18 – 5.19. Water speeds at water surface, middle and bottom layer are presented separately in the appendices. In dry season, it is appeared that the proposed development would slightly reduce the peak amplitude tides throughout the simulation period. However, the peak amplitude tides in wet season is predicted to be slightly strengthened by the proposed development. All these changes are expected to be small and the predicted changes in water speeds are not expected to affect existing siltation patterns just offshore of the proposed development or have an adverse impact on navigation for the small vessels using the proposed landing facility.

5.7.2.4 The instantaneous and total cumulative discharge in Baseline and With-project scenario at Lei Yue Mun Narrows section were also calculated. According to Appendix 5.20, it shows that the established breakwater and landing facility have insignificant impact on the instantaneous discharge at the Lei Yue Mun Narrows.

5.7.2.5 Peak flood and ebb tidal discharges on selected representative small and large amplitude tides in the dry and wet seasons at Lei Yue Mun Narrows are tabulated in Table 5.18.

Table 5.18 Peak Flood and Ebb Tidal Discharges through Lei Yue Mun Narrows

Condition		Baseline (m^3/s)	With Project (m^3/s)	% of Ebb / Flood Variability^1 (m^3/s)
Dry Season
Peak Ebb	Spring Tide	-10, 453	-10, 422	-0.1%
	Neap Tide	-5, 851	-5, 860	0.1%
Peak Flood	Spring Tide	10, 486	10, 490	0.02%
	Neap Tide	4, 979	4, 974	-0.05%
Flood - Ebb	Spring Tide	20, 939	20, 912
	Neap Tide	10, 830	10, 834
Wet Season
Peak Ebb	Spring Tide	-8, 663	-8, 696	0.2%
	Neap Tide	-3, 293	-3, 349	0.5%
Peak Flood	Spring Tide	12, 546	12, 506	-0.2%
	Neap Tide	6, 975	6, 972	-0.04%
Flood - Ebb	Spring Tide	21, 209	21, 202
	Neap Tide	10, 268	10, 321

Note:   

1. Positive change indicates an increase in peak flow in Project operation   

5.7.2.6 As shown in Table 5.18, the largest reduction in peak tidal flows is predicted to be occurred during the spring tide flood tide in the wet season. The range of predicted peak tidal change is about -0.1% to 0.1% in dry season and -0.2% to 0.5% in wet season. All predicted changes in peak tidal discharges past LYM would be less than 0.5%, which suggests that the proposed development will not have a significant impact on peak tidal discharges.

5.7.2.7 The increased water depths and the establishment of breakwater may change the local water flow and water quality pattern during the operation phase. The reduced flushing of water body between the breakwater and the existing shoreline to the west of the landing facility may cause floating debris accumulation. However, the modelling results demonstrate that the proposed development would not have a significant impact on water flow nor water quality pattern, Project area remains completely open to the main flows in the Lei Yue Mun Narrows and is in close proximity to the main navigation channel. In addition, no increased amount of jetsam is expected to enter the landing area owing to the Project operation. It is anticipated that the LYM waterfront under Project operation will maintain its relatively well flushed property despite the predicted minor change in tidal flows.

Sewage from visitors and operators

5.7.2.8 Under Project operation, sewage effluent from the increased touristic and local commercial activities would be the key potential source of water pollution and may have potential impacts on watersports activities such as the Annual Cross Harbour Swim. With reference to the assessment of sewerage and sewage treatment implications for the Project provided in Section 6, there is only limited public sewerage system in LYM; only some restaurants and shops have equipped with septic tanks and grease traps to treat the oily or greasy food wastes before discharging to the shoreline and most of the domestic sewage from the village houses is directly discharged into the existing drainage system (open channels and rains) and eventually conveyed into the sea. It is predicted that with the absence of proper management works, the increased touristic and local commercial activities would result in an elevated amount of untreated sewage, which will potentially degrade the water quality and create nuisance problems in adjacent watercourses.

5.7.2.9 Notwithstanding the above, a long-term sewerage scheme titled ‘Lei Yue Mun Village Sewerage project” is proposed to be commissioned concurrently with the Project by DSD. Additional sewerage networks involving gravity sewers, rising mains and sewage pump sumps in LYM, aligning with the upgrade works in the existing sewers and Sam Ka Tsuen pumping chamber would be provided under the sewerage scheme to cater for the estimated ultimate flow in LYM. The proposed public sewerage system within the vicinity of the Project site would be completed by Q1 2023, with no programme gap with the Project. With its implementation, adverse water quality impacts arise from the increased sewage loading due to the increased touristic and commercial activities would be minimised by having sewage conveyed to proper treatment before final discharge. Considering that only limited public sewerage is available in LYM at present and many villagers discharge sewage to surface channel directly, the deployment of the concurrent Lei Yue Mun Village Sewerage project can improve water quality in adjacent water bodies and no adverse impacts due to the operation of Project is expected ultimately.

Surface runoff and drainage

5.7.2.10 Surface runoff to be generated from the Project is known as non-point source pollution. The paved and developed areas, especially the promenade, landing facility and breakwater will increase the chance of surface runoff. The presence of oil, grease and grit on the surfaces of road within the Project site could be washed into the nearby drainage system or even directly into the marine water during rainfall event because footpath and landing facility are located in close proximity to the shoreline. Surface runoff generated from the paved or developed areas may contain debris, refuse, dust from tourisms activities. Practices that cleaning agents used for washing streets and building façade may also affect the quality of the nearby receiving water environment. Meanwhile, fuel, oil and lubricants from maintenance and operation of vessels will also be washed into adjacent marine water.

5.7.2.11 Within the area to be developed under this Project, the proposed promenade, public landing facility, as well as the breakwater will be the newly developed / paved areas. Thus, about 990m² additional paved area will be created by the Project. More surface runoff would be generated from the paved area than the unpaved area. Assuming 0.9 as the runoff coefficient for paved areas, the non-point source pollution from surface runoff is quantified in Table 5.19 below. The assumptions used for compiling the non-point source pollution are detailed in Appendix 5.21.

Table 5.19 Non-Point Source Pollution from Area to be Developed under the Project

Parameters	Approx. Loading under Likely Future Condition (kg/day)
SS (kg/day)	0.146
BOD (kg/day)	0.076
NH3-N (kg/day)	0.0007
Org-N (kg/day)	0.004
TIN (kg/day)^1	0.002
TN (kg/day)	0.006
TP (kg/day)	0.0007

Note:   

1. Total inorganic nitrogen (TIN) is equal to total nitrogen (TN) minus organic nitrogen (Org-N)

5.7.2.12 Minor non-point source pollution would be expected from the establishment of promenade, landing facility and breakwater, however, the potential water quality impacts could be mitigated by measures recommended in Section 5.8.

Maintenance dredging

5.7.2.13 To maintain sufficient water depth for vessels, maintenance dredging of seabed would be needed. The area of maintenance dredging would be the same as capital dredging under the construction phase, which is about 3,820m². With a 0.3m tolerance in maintenance dredging from practical point of view, up to 0.8m of sediment will need to be dredged in every 5 to 10 years. As such, about 3,056m³ dredged volume would be produced for each dredging exercise. Assuming a maximum dredging rate of 100m³ per hour and access is limited, the maintenance dredging would be carried out by one grab dredger and would last for not more than a week. The dredging operation would be properly scheduled such that no dredging works will be carried out during the period of the Annual Cross Harbour Swim Race to be held.

Potential Suspended Solids and Sedimentation Elevation

5.7.2.14 The predicted maximum SS and sedimentation rate elevation at selected observation points are summarized in Table 5.20 and Table 5.21respectively. Full compliance at all identified WSRs for these two parameters are expected under maintenance dredging. The contour plots of SS elevation and sediment deposition in both dry and wet seasons are presented in Appendix 5.22 and 5.23 separately, they suggest that the impacts of SS and sedimentation rate elevation would be highly localized, all WSRs would not be affected.

Table 5.20 Predicted Maximum Suspended Solids Elevation at Selected Observation Points during Maintenance Dredging (Unmitigated)

WSR	Maximum Suspended Solid Elevation (mg/L)
	Surface	Middle	Bottom	Depth Averaged	Compliance in WQO
Dry Season
WQO	1.9	1.9	2.1	1.8	N/A
C1	0.7	0.7	0.8	0.7	Yes
C2	0.5	0.4	0.4	0.4	Yes
C3	0.3	0.3	0.3	0.3	Yes
W1	0.0	0.0	0.1	0.0	Yes
Wet Season
WQO	1.5	2.0	3.6	2.4	N/A
C1	0.6	0.7	1.3	0.6	Yes
C2	0.4	0.4	0.4	0.3	Yes
C3	0.3	0.3	0.3	0.2	Yes
W1	0.0	0.0	0.0	0.0	Yes

Table 5.21 Predicted Maximum Sedimentation Rate Elevation at Selected Observation Points during Maintenance Dredging (Unmitigated)

Known Coral Sites	Maximum Sedimentation Rate (g/m^2/d)
	Dry Season	Wet Season
C1	33	54
C2	14	14
C3	10	11

Potential Contaminant Release

5.7.2.15 Modelling results for the release of contaminants bounded sediment are showed in Table 5.22. Contour plots of the predicted maximum contaminant concentrations are shown in Appendix 5.24. Owing to the predicted hydrodynamic change resulted from the proposed breakwater, the sediment bounded contaminant elevations were predicted to be lower at C1 and slightly higher at C2, C3 and W1 compared to those in capital dredging. Unlike the construction phase scenario, only TIN level at C1 would marginally exceed WQO, other WSRs, including Sam Ka Tsuen typhoon shelter, Yau tong and Heng Fa Chuen flushing water intakes, secondary recreation zone at Tseung Kwan O, Tung Lung Chau Fish Culture Zone and the potential watersports activity would not be affected. Given that corals are mainly sensitive to SS elevation and sedimentation rate, whilst and the exceedance of TIN would be minor and localized, no unacceptable water quality impact is anticipated.

Table 5.22 Predicted Maximum Elevation of Sediment Bounded Contaminants at Selected Observation Points during Maintenance Dredging

WSR	Maximum Sediment Bounded Contaminant Elevation^(1)
	Copper (µg/L)	Mercury (µg/L)	UIA (mg/L)	TIN (mg/L)
Criterion	5	0.3	0.021	0.4
Dry Season
C1	3.95	0.22	0.008	0.48
C2	2.02	0.11	0.005	0.34
C3	1.54	0.09	0.004	0.30
W1	0.37	0.02	0.003	0.22
Wet Season
C1	3.32	0.18	0.007	0.44
C2	1.85	0.10	0.005	0.33
C3	1.29	0.07	0.004	0.29
W1	0.18	0.01	0.002	0.20

Note:   

(1) Value in bold indicates exceedance in assessment criteria

Potential Oxygen Depletion

5.7.2.16 The oxygen depletion exerted by the SS elevation is calculated and showed in Table 5.23. No significant DO depletion was predicted at all WSRs. The maintenance dredging activities would cause a maximum DO depletion of less than 0.02mg/L. Same with the construction scenario, full compliance with the WQO for depth-averaged and bottom DO of 4 mg/L and 2 mg/L respectively in the East Victoria Harbour under maintenance dredging activities is expected. No mixing zone for DO and no adverse impacts on the DO levels at WSRs would be expected from the maintenance dredging.

Table 5.23 Summary of Changes to DO Levels due to Elevated SS Release during Maintenance Dredging (Unmitigated)

WSR	Max. DO Depletion (mg/L)			Baseline DO (mg/L)		Resultant DO (mg/L)
	Bottom		Depth-Averaged	Bottom	Depth-Averaged	Bottom	Depth-Averaged
WQO Criteria						>2	>4
Dry Season
C1	0.014	0.012		6.52	6.39	6.51	6.38
C2	0.006	0.006				6.51	6.38
C3	0.005	0.005				6.52	6.39
W1	<0.001	<0.001				6.52	6.39
Wet Season
C1	0.023	0.010		4.44	4.77	4.42	4.76
C2	0.006	0.006				4.43	4.76
C3	0.005	0.004				4.44	4.77
W1	<0.001	<0.001				4.44	4.77

5.7.2.17 As discussed above, no unacceptable impact with regard to the SS elevation, sediment deposition, contaminant release and oxygen depletion are expected at all identified WSRs during maintenance dredging in view of the scale of the dredging works would be much smaller than that in the Project construction phase. However, mitigation measures recommended in Section 5.8.1 for capital dredging should also be adopted during maintenance dredging to avoid unfavourable water quality impacts.

5.8 Mitigation of Environmental Impacts

5.8.1 Mitigation Measures for Marine Construction

Good Site Practices for Capital and Maintenance Dredging

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

· 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 vessels movement or propeller wash;

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

· Excess material shall be cleaned from the decks and exposed fittings of barges and hopper dredgers before the vessel is moved;

· 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;

· Construction activities should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation.

Closed Grab and Dredging Production Rates

5.8.1.2 To minimise the release of sediment and other contaminants during capital and maintenance dredging, only one closed grab will be used any time for the dredging works during both construction and operation phase. Moreover, in order to mitigate the potential impact of SS elevation and after consideration of the construction programme, it is recommended that the dredging production rate shall not exceed 100m³ per hour during both capital and maintenance dredging.

Deployment of Silt Curtains

5.8.1.3 To abate the potential water quality impacts in relation to the SS elevation under dredging, sand filling and seawall modification activities, floating type silt curtain is suggested to be deployed to enclose the works areas of the aforementioned construction activities. According to the Contaminated Spoil Management Study Final Report (Table 6.12)[4], implementation of silt curtains enclosing the dredging and filling operation will reduce the dispersion of SS as well as sedimentation rate by a factor of 4 (or about 75%). It is recommended that the dredging, sand filling and seawall modification activity in this Project should be enclosed by silt curtains. Under Section 10.6.31 of the Contaminated Spoil Management Study Final Report, silt curtains are defined as screens that extend over the full water depth in the dredging area to confine most of the suspended sediments. This is equivalent to the silt curtains to be adopted for the dredging, filling and seawall modification works in LYM waterfront, which involve the use of impervious sheets or filter fabrics extending over the full water depth. Regular inspection on the silt curtain condition by the contractor should be carried out to ensure the silt curtains are deployed properly and to maintain the performance of the silt curtains throughout the construction period. The reduction factor (75%) has been assumed under the approved EIAs for Dredging Works for Proposed Cruised Terminal at Kai Tak, Wan Chai Development Phase II & Central-Wan Chai Bypass and Reclamation of Yau Tong Bay. The effectiveness of silt curtains is inversely proportional to the flow velocities.

5.8.1.4 With the implementation of the above mitigation measures, the SS elevation and sedimentation rate at all WSRs would comply with the corresponding WQO and assessment criteria for coral. The results of SS elevation and sedimentation rate with mitigation are summarized in Table 5.24 and Table 5.25 respectively.

Table 5.24 Predicted Maximum Suspended Solid Elevation during Construction Phase (Mitigated)

WSR	Maximum Suspended Solid Elevation (mg/L)
	Surface	Middle	Bottom	Depth Averaged	Compliance with WQO
Dry Season
WQO	1.9	1.9	2.1	1.8	N/A
C1	0.775	0.75	1.15	0.775	Yes
C2	0.45	0.425	0.4	0.4	Yes
C3	0.35	0.325	0.3	0.3	Yes
W1	0.025	0.025	0.05	0.025	Yes
Wet Season
WQO	1.5	2.0	3.6	2.4	N/A
C1	0.625	1.075	1.05	0.725	Yes
C2	0.25	0.475	0.45	0.325	Yes
C3	0.2	0.3	0.325	0.2	Yes
W1	0.0	0.25	0.25	0.25	Yes

Note:   

1. WQO – Water Quality Objectives

Table 5.25 Predicted Maximum Sedimentation Rates at Identified Coral Sensitive Receivers during Construction Phase (Mitigated)

Known Coral Sites	Maximum Sedimentation Rate (g/m^2/d)
	Dry Season	Wet Season
C1	38.25	33.75
C2	16.75	18.5
C3	12	12.5

Seawall Modification Works

5.8.1.5 Apart from the silt curatin as recommended in Section 5.8.1.3, the seawall modification works for lookout points 1 and 5, and viewing platform are recommended to be undertaken during low tide, when the water level is low.

5.8.2 Mitigation Measures for Land-based Construction

General

5.8.2.1 Control of potential water quality impact arising from the general construction works shall be achieved based on the following principles:

· Minimisation of surface run-off;

· Prevention or minimisation of the likelihood of the identified pollutants being in contact with rain or run-off or adjacent marine waters; and

· Measures to abate pollutants at source.

5.8.2.2 The Contractor shall apply for a discharge license under the WPCO and the discharge shall comply with the terms and conditions of the license. The Contractor shall also devise an Emergency Contingency Plan for accidental leakage or spillage of chemicals during construction phase and maintenance dredging. It should detail the communication line between Contractor, relevant government and stakeholders, remediation plan for containing and cleaning of leakage, evaluation and improvement work and determine follow-up action, such as monitoring.

Site Run-off and General Activities

5.8.2.3 The Best Management Practices (BMPs) given in the ProPECC PN 1/94 shall be implemented in controlling water pollution during the whole construction phase. The main practices provided in the ProPECC PN 1/94 are also summarized below which should be implemented by the contractor during the construction phase, where practicable:

· High loading of SS in site run-off should be prevented through proper site management by the contractor;

· Sand and silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly by the contractor, and at the onset of and after each rainstorm to ensure that these facilities are functioning properly;

· The drilling operation can be fully controlled by the workers, the volume of sediment laden water and the material stockpiled in the temporary storage steel tank can be anticipated such that spillage can be prevented. The tank should be kept within the temporary working platform with surrounding concrete bund walls. The tanks should be removed to other site area located far away from the river immediately after filling up and within the same day;

· Stockpiles should be located away from any watercourses and the seafront;

· Plant workshop / maintenance areas should be bunded on a hard standing. Sediment traps and oil interceptors should be provided at appropriate locations;

· Works should be programmed to minimise soil excavation works where practicable during the rainy days;

· Vehicle wheel washing facilities should be provided at the site exit such that mud, debris, etc. attached to the vehicle wheels or body can be washed off before the vehicle leaves the work site;

· Section of the road between the wheel washing bay and the public road will be paved to reduce vehicle tracking of soil and to prevent site run-off from entering public road drains; and

· Sufficient chemical toilets should be provided in the works areas in the proximity of the riverside for the sewage generated by the workforce. A licensed waste collector should be deployed to clean the chemical toilets on a regular basis. Any sewage or wastewater discharge into the surrounding environment should not be allowed. Any chemical toilets should be located away from the river.

5.8.3 Mitigation Measures for Operation Phase

5.8.3.1 Best Management Practices (BMPs) for storm water discharges are recommended for the new development as given below:

Design Measures

5.8.3.2 Exposed surface shall be avoided within the proposed development to minimise soil erosion. Development site shall be either hard paved or covered by landscaping area where appropriate to reduce soil erosion.

5.8.3.3 The existing marine water in adjacent to the Project sites will be retained to maintain the original flow path. The drainage system will be designed to avoid any case of flooding based on the 1 in 50 year return period.

Devices / Facilities to Control Pollution

5.8.3.4 Screening facilities such as standard gully grating and trash grille, with spacing which is capable of screening off large substances such as fallen leaves and rubbish should be provided at the inlet of drainage system.

5.8.3.5 Road gullies with standard design and silt traps and oil interceptors should be incorporated during the detailed design to remove particles present in storm water runoff.

5.8.3.6 In addition to the above, subject to detailed design, standard manholes with desilting opening / sand trap designed for first flush flow (capable of providing at least 5 minutes’ detention time) can be provided at final discharge point before discharge into the existing watercourse. The feasibility of alternative measure such as Vortex grit separator would also be considered during the detailed design stage.

Administrative Measures

5.8.3.7 Good management measures such as regular cleaning and sweeping of road surface / open areas is suggested. The road surface / open area cleaning should also be carried out prior to occurrence of rainstorm.

5.8.3.8 Manholes, as well as storm water gullies, ditches provided among the development areas should be regularly inspected and cleaned (e.g. monthly). Additional inspection and cleansing should be carried out before forecast heavy rainfall.

5.9 Evaluation of Residual Impacts

5.9.1.1 It is predicted that the maximum SS elevation and sedimentation rate at all WSRs would be in compliance with the corresponding WQO and assessment criteria with the implementation of recommended mitigation measures under construction phase. Marginal exceedance of copper and TIN level at C1 is expected during dredging works. Considering corals are mainly sensitive to SS elevation and sedimentation rate, whilist the exceedance of copper and TIN would be marginal and localized, no unacceptable residue water quality impact due to marine dredging is anticipated. To further minimise the impact on coral colonies, translocation and /or other best practicable mitigation measures will be implemented before the commencement of capital dredging and filling works as detailed in Section 9.

5.9.1.2 No unacceptable residual impact is expected during operation phase since no adverse hydrodynamic and water quality impacts due to the establishment of landing facility and breakwater as well as maintenance dredging were predicted.

5.10 Environmental Monitoring and Audit

5.10.1.1 Water monitoring is recommended as a part of the Environmental Monitoring and Audit (EM&A) programme to ensure that the recommended mitigation measures are properly implemented during the construction and operation phase (maintenance dredging). If the water quality monitoring data indicates that the proposed construction activities, particularly, the dredging works result in unacceptable water quality impacts in the receiving water, appropriate actions should be taken to review the operation and additional measures such as slowing down, or rescheduling of works should be implemented as necessary. Details of the EM&A requirements are provided in the EM&A Manual.

5.11 Conclusion

5.11.1 Construction Phase

5.11.1.1 The key issues associated with the land-based construction activities would be the potential release of construction site run-off from surface work areas, wastewater from general construction activities, accidental spillage and sewage from construction workforce. Minimisation of water quality deterioration could be achieved through implementing adequate mitigation measures. Regular site inspections should be undertaken routinely to inspect the construction activities and work areas in order to ensure the recommended mitigation measures are properly implemented. For marine construction activity, the key source of potential water quality impact is associated with dredging and filling activities, which have potential to release contaminants and increase suspended solid levels in marine water. The potential water quality impacts have been quantitatively assessed using the Delft3D Model, it identified that the potential water quality impacts from suspended solids and sedimentation rate elevation as well as the contaminants release would be confined in 100m of the Project site. Therefore, only coral community C1, which located in the immediate vicinity of the Project site would be affected. No unacceptable residual water quality impact would be resulted with implementation of the recommended mitigation measures. A water quality monitoring and audit programme is nevertheless required to ensure that all the recommended mitigation measures are implemented properly during the dredging works.

5.11.2 Operation Phase

5.11.2.1 The key source of potential water quality impacts under the operation phase would be the change in hydrodynamic regime, sewage effluent from the increased touristic and commercial activities, surface run-off associated with the new paved areas and maintenance dredging. Since LYM waterfront was predicted to maintain its good flushing ability, no adverse water quality impact would be attributed to the establishment of landing facility and breakwater. Meanwhile, as Lei Yue Mun Village Sewerage project will be commissioned concurrently to provide sewerage system to LYM, including the Project area, it is expected that water quality would be improved upon the completion of this concurrent project. For the potential impacts of surface run-off, it is anticipated that with proper implementation of the recommended mitigation measures, the potential adverse water quality impact would be minimised. During maintenance dredging, C1 was predicted to encounter a marginal exceedance in TIN level. Nonetheless, given that corals are mainly sensitive to SS elevation and sedimentation rate, whilst the exceedance of TIN would be minor and localized, no unacceptable water quality impact is anticipated.

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[1] ARUP (Jan 2013). Agreement No. CE 43/2008 (HY), Cross Bay Link, Tseung Kwan O – Investigation Environmental Impact Assessment Report.

[2] Territory Development Department (2001). Agreement No. CE. 74/98, Wan Chai Development Phase II Comprehensive Feasibility Study Environmental Impact Assessment Report.

[3] Dredging Research Ltd (1996).  Measurements of Sediment Transport after Dumping from Trailing Suction Hopper Dredgers in the East Tung Lung Chau Marine Borrow Area.  Report to GEO/CED.

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