TABLE OF CONTENTS

5.    WATER QUALITY.. 5-1

5.1         Introduction. 5-1

5.2         Environmental Legislation, Standards and Guidelines. 5-1

5.3         Description of Environment 5-11

5.4         Water Sensitive Receivers. 5-22

5.5         Identification of Potential Impacts. 5-24

5.6         Assessment Methodology. 5-25

5.7         Prediction and Evaluation of Environmental Impacts. 5-33

5.8         Mitigation of Environmental Impacts. 5-58

5.9         Residual Water Quality Impacts. 5-73

5.10       Environmental Monitoring and Audit Requirements. 5-73

5.11       Conclusions. 5-73

 

List of Tables

Table 5.1      Summary of WQOs for Western Buffer WCZ

Table 5.2      Summary of Water Quality Objectives for North Western WCZ

Table 5.3      Summary of WSD’s Water Quality Criteria for Flushing Water Intakes

Table 5.4      Proposed Assessment Criteria for Heavy Metal and Trace Organics

Table 5.5      Summary EPD’s Routine Marine Water Quality Data for Western Buffer and Victoria Harbour Phase 1 WCZs in Year 2023

Table 5.6      Summary EPD’s Routine Marine Water Quality Data for North Western WCZ in Year 2023

Table 5.7      Summary of Water Quality Monitoring Data for Inland Watercourses (Dry Season)

Table 5.8      Summary of Water Quality Monitoring Data for Inland Watercourses (Wet Season)

Table 5.9      Annual Geometric Mean E. coli Levels in Tsuen Wan District

Table 5.10    Identified WSRs

Table 5.11    Projects Incorporated into Modelling for Coastline Configurations

Table 5.12    Validation and Verification Matrix for the Local Refined Model

Table 5.13    Level of Fitness Summary between the Local Refined Model and HK-DFM Model at Observation Points

Table 5.14    Level of Fitness Summary between the Local Refined Model and HK-DFM Model at Cross-sections

Table 5.15    Model Performance of the Local Refined Model

Table 5.16    90th Percentile SS from EPD Routine Monitoring Programme (2014-2023)

Table 5.17    Suspended Solids Elevation Criteria (mg/L) for the Construction Phase Impacts

Table 5.18    Allowable Suspended Solids Elevation Criteria (mg/L) for The Modelling Observation Points

Table 5.19    Predicted Maximum Suspended Solids (mg/L) Elevations during Dredging Activities (Run C1a – With Project, Unmitigated)

Table 5.20    Predicted Maximum Suspended Solids (mg/L) Elevations during Reclamation Filling Activities (Run C1b – With Project, Unmitigated)

Table 5.21    Predicted Maximum Sedimentation Rate (g/m2/day) during Dredging Activities (Run C1a – With Project, Unmitigated)

Table 5.22    Predicted Maximum Sedimentation Rate (g/m2/day) during Reclamation Filling Activities (Run C1b – With Project, Unmitigated)

Table 5.23    10th Percentile DO Concentration from EPD Routine Monitoring Programme (2014-2023)

Table 5.24    Corresponding Ambient DO Concentration (mg/L) for The Modelling Observation Points

Table 5.25    Predicted DO Depletion (mg/L) under Dredging Activities (Run C1a – With Project and Concurrent Projects, Unmitigated)

Table 5.26    Predicted Resultant DO Depletion (mg/L) under Dredging Activities (Run C1a – With Project and Concurrent Projects, Unmitigated)

Table 5.27    Predicted DO Depletion (mg/L) under Reclamation Filling Activities (Run C1b – With Project and Concurrent Projects, Unmitigated)

Table 5.28    Predicted Resultant Dissolved Oxygen Depletion (mg/L) under Reclamation Filling Activities (Run C1b – With Project and Concurrent Projects, Unmitigated)

Table 5.29    Hydrodynamic Modelling Comparison between the With and Without Project Scenarios

Table 5.30    Comparison of Ebb/Flood Tidal Flow Volume at Concerned Channels

Table 5.31    Predicted Maximum Suspended Solids (mg/L) Elevations during Dredging Activities (Run C2a – With Project, Mitigated)

Table 5.32    Predicted Maximum Suspended Solids (mg/L) Elevations during Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Table 5.33    Predicted Maximum Sedimentation Rate (g/m2/day) during Dredging Activities (Run C2a – With Project, Mitigated)

Table 5.34    Predicted Maximum Sedimentation Rate (g/m2/day) during Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Table 5.35    Predicted DO Depletion (mg/L) under Dredging Activities (Run C2a – With Project, Mitigated)

Table 5.36    Predicted Resultant DO Depletion (mg/L) under Dredging Activities (Run C2a – With Project, Mitigated)

Table 5.37    Predicted DO Depletion (mg/L) under Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Table 5.38    Predicted Resultant Dissolved Oxygen Depletion (mg/L) under Reclamation Filling Activities (Run C2b – With Project, Mitigated)

 

 

List of Figures

Figure 5.1        Locations of Identified Water Sensitive Receivers

 

 

List of Appendices

Appendix 5.1   Model Validation and Verification

Appendix 5.2   Reclamation Construction Sequence and Sediment Release Estimation

Appendix 5.3   Water Quality Modelling Results (Construction Phase)

Appendix 5.4   Hydrodynamic Modelling Results (Operational Phase)

Appendix 5.5   Elutriate and Porewater Testing Results

Appendix 5.6   Water Quality Modelling Results (Sensitivities Analysis)

Appendix 5.7   Assessment of Contaminant Release from Elutriate/Porewater Testing


5.                   WATER QUALITY

5.1               Introduction

5.1.1.1      This section presents an assessment of the potential water quality impacts associated with the construction and operation of the Project.  The assessment was conducted in accordance with the criteria and guidelines set out in Annexes 6 and 14 of the Technical Memorandum on Environmental Impact Assessment (EIAO-TM) and the requirements set out in Clause 3.4.6 of the EIA Study Brief (No. ESB-359/2023).

5.2               Environmental Legislation, Standards and Guidelines

Technical Memorandum on Environmental Impact Assessment Ordinance

5.2.1.1      The Technical Memorandum on Environmental Impact Assessment Ordinance (EIAO-TM), which was issued by EPD under Section 16 of the EIAO.  Reference sections in the EIAO-TM provide the details of assessment criteria and guidelines that are relevant to the water quality assessment, including:

·         Annex 6 - Criteria for Evaluating Water Pollution; and

·         Annex 14 - Guidelines for Assessment of Water Pollution.

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

5.2.1.2      The Water Pollution Control Ordinance (WPCO) (Cap. 358) provides the major statutory framework for the protection and control of water quality in Hong Kong.  According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs).  Corresponding statements of Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZs based on their beneficial uses.

5.2.1.3      According to Clause 3.4.6.2 of the EIA Study Brief (No. ESB-359/2023), the assessment area for this water quality impact assessment includes areas within 500 meters from the boundary of the Project and shall cover the Western Buffer WCZ and other affected WCZs as designated under the WPCO.  The WQOs for the Western Buffer WCZ and North Western WCZ are listed in Table 5.1 and Table 5.2, respectively.  These WQOs will be used as the water quality assessment criteria for the Project.

Table 5.1      Summary of WQOs for Western Buffer WCZ

Parameters

Objectives

Sub-Zone

Aesthetic appearance

There should be no objectionable odours or discolouration of the water.

Whole zone

Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.

Mineral oil should not be visible on the surface.  Surfactants should not give rise to a lasting foam.

There should be no recognisable sewage-derived debris.

Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent.

The water should not contain substances which settle to form objectionable deposits.

Bacteria

The level of Escherichia coli (E. coli) should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in a calendar year.

Secondary Contact Recreation Subzones and Fish Culture Subzones

The level of E. coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in 1 calendar year. Samples should be taken at least 3 times in 1 calendar month at intervals of between 3 and 14 days.

Recreation Subzones

The level of E. coli should be less than 1 per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Water Gathering Ground Subzones

The level of E. coli should not exceed 1000 per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Other inland waters

Colour

Human activity should not cause the colour of water to exceed 30 Hazen units.

Water Gathering Ground Subzones

Human activity should not cause the colour of water to exceed 50 Hazen units.

Other inland waters

Dissolved Oxygen (DO)

The level of dissolved oxygen should not fall below 4 mg per litre for 90% of the sampling occasions during the whole year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 m of the seabed for 90% of the sampling occasions during the whole year.

Marine waters excepting Fish Culture Subzones

The level of dissolved oxygen should not be less than 5 mg per litre for 90% of the sampling occasions during the year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 m of the seabed for 90% of the sampling occasions during the whole year.

Fish Culture Subzones

The level of dissolved oxygen should not be less than 4 mg per litre.

Water Gathering Ground Subzones and other inland waters

pH

The pH of the water should be within the range of 6.5–8.5 units. In addition, human activity should not cause the natural pH range to be extended by more than 0.2 unit.

Marine waters

Human activity should not cause the pH of the water to exceed the range of 6.5–8.5 units.

Water Gathering Ground Subzones

Human activity should not cause the pH of the water to exceed the range of 6.0–9.0 units.

Other inland waters

Temperature

Human activity should not cause the natural daily temperature range to change by more than 2.0ºC.

Whole zone

Salinity

Human activity should not cause the natural ambient salinity level to change by more than 10%.

Whole zone

Suspended Solids (SS)

Human activity should neither cause the natural ambient level to be raised by more than 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities.

Marine waters

Human activity should not cause the annual median of suspended solids to exceed 20 mg per litre.

Water Gathering Ground Subzones

Human activity should not cause the annual median of suspended solids to exceed 25 mg per litre.

Other inland waters

Ammonia

The unionised ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean).

Whole zone

Nutrients

Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.

Marine waters

Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.4 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed).

Marine waters

5-Day Biochemical Oxygen Demand (BOD5)

The 5-day biochemical oxygen demand should not exceed 3 mg per litre.

Water Gathering Ground Subzones

The 5-day biochemical oxygen demand should not exceed 5 mg per litre.

Other inland waters

Chemical Oxygen Demand (COD)

The chemical oxygen demand should not exceed 15 mg per litre.

Water Gathering Ground Subzones

The chemical oxygen demand should not exceed 30 mg per litre.

Other inland waters

Toxic Substances

Toxic substances in the water should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to interactions of toxic substances with each other.

Whole zone

Human activity should not cause a risk to any beneficial use of the aquatic environment.

Turbidity

Waste discharges shall not reduce light transmission substantially from the normal level.

Bathing Beach Subzones

Source: Statement of Water Quality Objectives (Western Buffer Water Control Zone), (Cap. 358, section 5)

 

Table 5.2      Summary of Water Quality Objectives for North Western WCZ

Parameters

Objectives

Sub-Zone

Aesthetic appearance

Waste discharges shall cause no objectionable odours or discolouration of the water.

Whole Zone

Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.

Mineral oil should not be visible on the surface. Surfactants should not give rise to lasting foam.

There should be no recognisable sewage-derived debris.

Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent.

Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.

Bacteria

The level of Escherichia coli (E. coli) should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in a calendar year.

Secondary Contact Recreation Subzones

The level of E. coli should be less than 1 per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones

The level of E. coli should not exceed 1 000 per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Tuen Mun (C) Subzone and other inland waters

The level of E. coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive. Samples should be taken at least 3 times in one calendar month at intervals of between 3 and 14 days.

Bathing Beach Subzones

Colour

Waste discharges shall not cause the colour of water to exceed 30 Hazen units.

Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones

Waste discharges shall not cause the colour of water to exceed 50 Hazen units.

Tuen Mun (C) Subzone and other inland waters

Dissolved Oxygen (DO)

Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the whole year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 m of the seabed for 90% of the sampling occasions during the whole year.

Marine waters

Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg per litre.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones, Water Gathering Ground Subzones and other inland waters

pH

The pH of the water should be within the range of 6.5–8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 unit.

Marine waters excepting Bathing Beach Subzones

Waste discharges shall not cause the pH of the water to exceed the range of 6.5–8.5 units.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

The pH of the water should be within the range of 6.0–9.0 units.

Other inland waters

The pH of the water should be within the range of 6.0–9.0 units for 95% of samples collected during the whole year. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 unit.

Bathing Beach Subzones

Temperature

Waste discharges shall not cause the natural daily temperature range to change by more than 2.0℃.

Whole Zone

Salinity

Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.

Whole Zone

Suspended Solids (SS)

Waste discharges shall neither cause the natural ambient level to be raised by more than 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities.

Marine waters

Waste discharges shall not cause the annual median of suspended solids to exceed 20 mg per litre.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

Waste discharges shall not cause the annual median of suspended solids to exceed 25 mg per litre.

Other inland waters

Ammonia

The unionised ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean).

Whole Zone

Nutrients

Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.

Marine waters

Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed).

Castle Peak Bay Subzone

Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed).

Marine waters except Castle Peak Bay Subzone

5-Day Biochemical Oxygen Demand (BOD5)

Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 mg per litre.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 mg per litre.

Other inland waters

Chemical Oxygen Demand (COD)

Waste discharges shall not cause the chemical oxygen demand to exceed 15 mg per litre.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

Waste discharges shall not cause the chemical oxygen demand to exceed 30 mg per litre.

Other inland waters

Toxins

Waste discharges shall not cause the toxins in water to attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other.

Whole Zone

Waste discharges shall not cause a risk to any beneficial use of the aquatic environment.

Phenol

Phenols shall not be present in such quantities as to produce a specific odour, or in concentration greater than 0.05 mg per litre as C6H5OH.

Bathing Beach Subzones

Turbidity

Waste discharges shall not reduce light transmission substantially from the normal level.

Bathing Beach Subzones

Source: Statement of Water Quality Objectives (North Western Water Control Zone), (Cap. 358, section 5)

Water Supplies Department Water Quality Criteria

5.2.1.4      The Water Supplies Department (WSD) has specified a set of seawater quality objectives for their flushing water intakes.  The list is shown in Table 5.3.  These target objectives will be applied at the points of seawater abstraction for flushing purpose.

Table 5.3      Summary of WSD’s Water Quality Criteria for Flushing Water Intakes

Parameters

(in mg/L unless otherwise stated)

WSD Target Limit

Colour (Hazen Unit)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammoniacal Nitrogen (NH3-N)

< 1

Suspended Solids (SS)

< 10

Dissolved Oxygen (DO)

> 2

Biochemical Oxygen Demand (BOD)

< 10

Synthetic Detergents

< 5

E. coli (count/100 mL)

< 20,000

Assessment Criteria for Heavy Metals and Trace Organics

5.2.1.5      There are no existing legislations or guidelines for heavy metals, metalloids, trace organics (i.e. polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB)), and organotin (i.e. tributyltin (TBT)) at water sensitive receivers (WSRs) in Hong Kong waters.  With reference to the approved EIA studies ([1],[2],[3]), the criteria adopted are based on international standards, including those from Mainland China, Europe, the USA, Australia, and New Zealand. The adopted criteria for heavy metals and trace organics are presented in Table 5.4.

 

Table 5.4      Proposed Assessment Criteria for Heavy Metal and Trace Organics

Heavy Metal/Metalloids/Trace Organics

Proposed Criteria

(µg/L)

Reference

Cadmium (Cd)

0.45

3

Chromium (Cr)

4.4

1

Copper (Cu)

3.1

5

Nickel (Ni)

5.0

4

Lead (Pb)

1.0

4

Zinc (Zn)

8.0

1

Mercury (Hg)

0.05

4

Arsenic (As)

13

1

Silver (Ag)

1.4

1

Total PAHs

0.1

3

Total PCBs

0.03

2

Tributyltin (TBT)

0.0015

3

References:

[1]    Australian and New Zealand Guidelines for Fresh and Marine Water Quality.  Default guideline value for protection for 95% Species in Marine water.  Available at: https://www.waterquality.gov.au/anz-guidelines/guideline-values/default/water-quality-toxicants/search.  For chromium, the more stringent standard for Cr(VI) is adopted.  For arsenic, there is no standard for marine water, standard for freshwater for As(V) was thus adopted which is more conservative than that for As(III).

[2]    U.S. Environmental Protection Agency, National Recommended Water Quality Criteria, 2009. (https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table). The Criteria Continuous Concentration (CCC) is an estimate of the highest concentration of a material in surface water (i.e. saltwater) to which an aquatic community can be exposed indefinitely without resulting in an unacceptable effect.  CCC is used as the criterion of the respective compounds in this study.

[3]     DIRECTIVE 2008/105/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 16 December 2008 on environmental quality standards in the field of water policy, amending and subsequently repealing Council Directives 82/176/EEC, 83/513/EEC, 84/156/EEC, 84/491/EEC, 86/280/EEC and amending Directive 2000/60/EC of the European Parliament and of the Council. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32008L0105

[4]       China Sea Water Quality Standard (GB 3097-1997).

https://www.mee.gov.cn/ywgz/fgbz/bz/bzwb/shjbh/shjzlbz/199807/W020061027511546974673.pdf

                       [5]     The USEPA Criterion Continuous Concentration (CCC), 

                                 http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm#Z2, 13 June 2013

Reference Suspended Solids (SS) Criterion for Cooling Water Intake

5.2.1.6      The suspended solids (SS) criterion for cooling water intakes is different from that for the WSD's intakes as their beneficial uses are different (the former is used for cooling water system and the latter for flushing purpose).  There are a number of cooling water intakes identified in the Western Buffer WCZ and North Western WCZ, including the ones for Sha Wan Drive, Wah Fu Estate, Castle Peak Power Station, China Cement Plant, ASD Tuen Mun Hospital, EMSD Sam Shing Estate and Shiu Wing Steel Mills.

5.2.1.7      The SS limit is 40mg/L for cooling water intake according to the Mass Transit Railway Corporation (MTRC) and is 100mg/L for HK Electric Power Station according to the HK Electric.  There are no other criteria for cooling water intakes within the area of influence of this Project.  Thus, a more rigid number of 40mg/L will be used in this report.  This criterion had been confirmed by telephone survey conducted under the approved EIA for the Hong Kong Convention and Exhibition Centre (HKCEC) Atrium Link Extension (ALE), and approved EIA for the Dredging Works for Proposed Cruise Terminal at Kai Tak ([4],[5]).

Assessment Criterion for Sediment Deposition (Applicable to Ecological Subtidal Habitats Only)

5.2.1.8      There is no existing legislative standard on sedimentation rate available.  Soft corals typical of the western coastal waters where the sediment regime is more dynamic than in other parts of Hong Kong's coastal waters are expected to be more tolerant of deposition.  The daily sediment deposition rate of 200 g/m2/day is generally considered as tolerable in the western waters.  The sediment deposition rate of 200 g/m2/day has been adopted as the reference criterion for this study following the approach adopted under other approved EIA studies ([6],[7] ,[8] ,[9]). 

5.2.1.9      The sedimentation criterion was derived for protection of subtidal coral habitats only and hence it is not applicable to other water sensitive receivers such as bathing beach users and seawater intakes where the main concern would be on the surface / mid-depth water quality.  No sedimentation criterion specific to bathing beach users and seawater intakes is available and therefore the sedimentation rates are not presented for these sensitive receivers under this assessment.

Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters

5.2.1.10   Discharge of effluents is subject to control under the WPCO.  The "Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters" (TM-DSS) was issued under Section 21 of the WPCO.   It sets the discharge limits vary with the effluent flow rates and the effluent should comply with the standards for effluent discharged into different type of receiving waters (foul sewers, stormwater drains, inland and coastal waters).  The standards control the physical, chemical and microbial quality of effluents.

Practice Notes

5.2.1.11   The "Professional Persons Environmental Consultative Committee Practice Note 2/24" (ProPECC PN 2/24) was issued by the EPD to provide guidelines for handling and disposal of construction site discharges.  The ProPECC PN 2/24 provides some basic environmental guidelines for handling discharge from construction sites, so as to prevent and minimise some of the pollution problems generally associated with construction activities. These include surface run-off, groundwater, boring and drilling water, wastewater from concrete batching and/or precast concrete casting, wheel washing water, bentonite slurries, water for testing and/or sterilisation of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities.  Practices given in the ProPECC PN 2/24 should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage.

5.2.1.12   The ProPECC PN 1/23 "Drainage Plans subject to Comments by Environmental Protection Department" provides guidelines and practices for handling, treatment and disposal of various effluent discharges to stormwater drains and foul sewers.  The design of site draina ge and disposal of various site effluents generated within the new development area should follow the relevant guidelines and practices as given in the ProPECC PN 1/23.

Technical Circular

5.2.1.13   Environment, Transport and Works Bureau Technical Circular (ETWB TC) (Works) No. 5/2005 provides an administrative framework to better protect all natural streams/rivers from the impacts of construction works.  The procedures promulgated under this Circular aim to clarify and strengthen existing measures for protection of natural streams/rivers from government projects and private developments.  The guidelines and precautionary mitigation measures given in the ETWB TC (Works) No. 5/2005 should be followed as far as possible to protect the inland watercourses at or near the Project area during the construction phase.

Hong Kong Planning Standards and Guidelines (HKPSG)

5.2.1.14   Chapter 9 of the HKPSG outlines environmental requirements that need to be considered in land use planning.  The recommended guidelines, standards and guidance cover the selection of suitable locations for the developments and sensitive uses, provision of environmental facilities, and design, layout, phasing and operational controls to minimise adverse environmental impacts.  It also lists out environmental factors that influence land use planning and recommends buffer distances for land uses.

5.3               Description of Environment

5.3.1           Assessment Area

5.3.1.1      According to Clause 3.4.6.2 of the EIA Study Brief (No. ESB-359/2023), the Assessment Area for this water quality impact assessment includes areas within 500m from the boundary of the Project and shall cover Western Buffer WCZ and other affected WCZs as designated under the WPCO and the WSRs in the vicinity of the Project.

5.3.2           Marine Water Quality

5.3.2.1      The marine water quality in vicinity of the Project area has been regularly monitored by EPD on a monthly basis.  Locations of EPD’s Marine Water Quality Monitoring Stations (NM1/WM4/VM12/VM14) are shown in Figure 5.1.  The baseline water quality condition of marine water was established from the marine water quality monitoring data routinely collected by EPD in the Western Buffer, North Western and Victoria Harbour WCZs.  A summary of EPD monitoring data collected in 2023 for Western Buffer, North Western and Victoria Harbour Phase 1 WCZs are presented in Table 5.5 and Table 5.6.

5.3.2.2      According to the EPD’s “Marine Water Quality in Hong Kong 2023”, the Western Buffer WCZ fully achieved the WQOs in 2023. Since the commissioning of the Harbour Area Treatment Scheme Advance Disinfection Facilities (HATS ADF) in 2010, the E. coli level in the WCZ decreased substantially.  Similar to other WCZs in the central waters, significant improvement of water quality as reflected in reduction in terms of E. coli and PO4-P has been observed.

5.3.2.3      The overall WQO compliance rate of the North Western WCZ was 89%, with the DO and NH3-N WQOs fully met.  Under the influence of high seasonal background level in the Pearl River Estuary, the compliance rate for Total Inorganic Nitrogen (TIN) WQO was 67%.

Table 5.5      Summary EPD’s Routine Marine Water Quality Data for Western Buffer and Victoria Harbour Phase 1 WCZs in Year 2023

Parameters

Hong Kong Island

(West)

Tsing Yi

(South)

Tsing Yi

(West)

Rambler Channel

WPCO WQO

(in marine waters)

WM1

WM2

WM3

WM4

VM12

VM14

Temperature (°C)

23.5

23.9

23.7

23.7

23.9

24.1

Not more than 2℃ in daily temperature range

(17.4 – 27.5)

(17.4 – 28.2)

(17.4 – 27.8)

(17.5 – 28.0)

(17.6 - 28.0)

(17.6 - 28.7)

Salinity (ppt)

32.6

31.5

32.1

31.7

31.4

29.5

Not to cause more than 10% change

(30.9 – 33.8)

(28.6 – 33.2)

(29.2 – 33.2)

(29.1 – 33.0)

(28.0 - 32.9)

(24.4 - 32.9)

Dissolved Oxygen

(mg/L)

Depth Average

6.0

6.4

5.8

5.8

5.8

6.3

Not less than 4 mg/L for 90% of samples

(4.4 - 8.7)

(4.8 - 8.6)

(3.5 - 7.7)

(3.9 - 8.0)

(3.5 - 8.4)

(3.7 - 8.2)

Bottom

5.7

5.8

5.4

5.4

5.1

5.5

Not less than 2 mg/L for 90% of samples

(3.0 - 9.0)

(4.1 - 7.9)

(2.8 - 8.0)

(3.0 - 7.9)

(3.0 - 7.8)

(3.1 - 8.1)

Dissolved Oxygen

(% Saturation)

Depth Average

85

91

82

81

81

88

Not available

(64 - 110)

(73 - 119)

(52 - 97)

(56 - 101)

(51 - 121)

(54 - 115)

Bottom

79

82

75

76

72

77

Not available

(42 - 114)

(59 - 100)

(41 - 101)

(43 - 100)

 (44 - 99)

 (44 - 104)

pH

 

7.7

7.7

7.7

7.7

7.6

7.6

6.5 - 8.5 (±0.2 from natural range)

(7.1 - 8.2)

(7.2 – 8.2)

(7.2 – 8.2)

(7.2 – 8.2)

 (7.1 - 8.0)

 (7.1 - 8.1)

Secchi Disc Depth

(m)

2.8

2.6

2.5

2.5

2.6

2.7

Not available

(1.7 - 3.8)

(1.4 - 3.9)

(1.8 - 2.9))

(1.8 - 3.1)

 (1.7 - 4.1)

 (1.5 - 3.8)

Turbidity

(NTU)

5.0

3.4

5.3

4.5

6.6

5.5

Not available

(1.9 - 13.4)

(0.9 - 10.1)

(0.6 - 13.1)

(1.0 - 11.1)

 (2.5 - 13.9)

 (2.7 - 12.4)

Suspended Solids (SS)

(mg/L)

5.4

5.0

5.9

6.4

9.1

7.8

Not more than 30% increase

(1.9 - 11.6)

(1.9 - 9.6)

(3.0 - 11.7)

(2.6 - 13.6)

 (4.3 - 20.0)

 (2.9 - 22.0)

5-day Biochemical Oxygen Demand (BOD5)

(mg/L)

0.6

0.6

0.7

0.6

0.5

0.6

Not available

(<0.1 - 1.2)

(0.1 - 1.2)

(<0.1 - 1.8)

(<0.1 - 1.2)

 (<0.1 - 1.2)

 (<0.1 - 1.1)

Ammonia Nitrogen (NH3-N)

(mg/L)

0.059

0.110

0.131

0.102

0.137

0.099

Not available

(0.019 - 0.187)

(0.037 - 0.233)

(0.051 - 0.223)

(0.028 - 0.163)

 (0.067 - 0.203)

 (0.053 - 0.143)

Unionised Ammonia

(mg/L)

0.001

0.003

0.003

0.002

0.003

0.002

Not more than annual average of 0.021mg/L

(<0.001 - 0.005)

(<0.001 - 0.008)

(<0.001 - 0.009)

(<0.001 - 0.008)

 (<0.001 - 0.007)

 (<0.001 - 0.006)

Nitrite Nitrogen

(NO2-N) (mg/L)

0.025

0.032

0.031

0.032

0.034

0.039

Not available

(0.003 - 0.054)

(0.007 - 0.070)

(0.008 - 0.067)

(0.007 - 0.070)

 (0.008 - 0.077)

 (0.007 - 0.089)

Nitrate Nitrogen

(NO3-N) (mg/L)

0.082

0.135

0.128

0.154

0.175

0.221

Not available

(0.023 - 0.156)

(0.037 - 0.210)

(0.045 - 0.180)

(0.054 - 0.253)

 (0.040 - 0.390)

 (0.048 - 0.507)

Total Inorganic Nitrogen (TIN) (mg/L)

0.17

0.28

0.29

0.29

0.35

0.36

Not more than annual average of 0.4mg/L

(0.09 - 0.36)

(0.19 - 0.38)

(0.17 - 0.43)

(0.17 - 0.39)

 (0.15 - 0.58)

 (0.14 - 0.66)

Total Kjeldahl Nitrogen (TKN) (mg/L)

0.45

0.48

                0.51

0.45

0.52

0.46

Not available

(0.13 - 0.79)

(0.24 - 0.81)

(0.21 - 0.88)

(0.17 - 0.78)

 (0.12 - 0.85)

 (0.14 - 0.85)

Total Nitrogen (TN)

(mg/L)

0.55

0.64

0.67

0.64

0.72

0.72

Not available

(0.19 - 0.97)

(0.32 - 1.02)

(0.30 - 1.08)

(0.24 - 0.97)

 (0.28 - 1.19)

 (0.26 - 1.22)

Orthophosphate Phosphorus (PO4) (mg/L)

0.009

0.012

0.014

0.013

0.016

0.013

Not available

(<0.002 - 0.016)

(<0.002 - 0.022)

(<0.002 - 0.022)

(<0.002 - 0.018)

 (0.008 - 0.026)

 (0.005 - 0.023)

Total Phosphorus (TP)

(mg/L)

0.06

0.07

0.08

0.07

0.08

0.07

Not available

(0.04 - 0.10)

(0.05 - 0.13)

(0.05 - 0.15)

(0.05 - 0.11)

 (0.05 - 0.14)

 (0.05 - 0.11)

Silica (as SiO2)

(mg/L)

0.77

0.82

0.85

0.90

1.09

1.26

Not available

(0.14 - 1.70)

(0.18 - 1.50)

(0.18 - 1.87)

(0.20 - 1.93)

 (0.35 - 2.30)

 (0.15 - 3.47)

Chlorophyll-a

(μg/L)

3.3

3.5

3.2

3.3

2.4

3.2

Not available 

(0.3 - 13.7)

(0.4 - 14.9)

(0.4 - 16.7)

(0.3 - 16.7)

(0.6 - 10.6)

(0.6 - 12.3)

E. coli

(count/100mL)

18

150

1300

160

1000

360

Not available

(1 - 2300)

(3 - 4800)

(120 - 7100)

(12 - 2500)

 (190 - 3300)

 (85 - 21000)

Faecal Coliforms

(count/100mL)

31

270

2200

280

2200

780

Not available

(1 - 4400)

(4 - 8200)

(200 - 14000)

(24 - 4200)

 (410 - 12000)

 (160 - 43000)

Notes:

1. Statement of Water Quality Objectives (Western Buffer Water Control Zone)

2. Data source: EPD Marine Water Quality in Hong Kong in 2023

3. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, Mid-depth, Bottom.

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

5. Data in brackets indicate the ranges.

 

 

 

 

 

 

Table 5.6      Summary EPD’s Routine Marine Water Quality Data for North Western WCZ in Year 2023

Parameters

Lantau Island (North)

Pearl Island

Pillar Point

Urmston Road

Chek Lap Kok

(North)

Chek Lap Kok

(West)

WPCO WQO

(in marine waters)

NM1

NM2

NM3

NM5

NM6

NM8

Temperature (°C)

24.0

24.3

24.3

24.4

24.7

24.5

Not more than 2℃ in daily temperature range

(18.3 - 28.2)

(18.4 - 28.8)

(18.3 - 28.8)

(18.3 - 29.2)

(18.2 - 29.7)

(18.2 - 29.9)

Salinity (ppt)

30.4

29.3

29.2

28.3

27.1

28.4

Not to cause more than 10% change

(26.5 - 33.0)

(23.3 - 33.0)

(23.8 - 33.1)

(22.2 - 32.9)

(17.9 - 33.0)

(16.0 - 33.1)

Dissolved Oxygen

(mg/L)

Depth Average

5.8

6.1

6.1

6.0

6.6

6.9

Not less than 4 mg/L for 90% of samples

(4.4 - 8.2)

(4.7 - 7.9)

(4.7 - 8.4)

(4.4 - 8.3)

(4.5 - 9.5)

(5.2 - 9.9)

Bottom

5.5

5.8

5.8

5.7

6.7

6.8

Not less than 2 mg/L for 90% of samples

(3.4 - 8.3)

(4.0 - 8.6)

(3.7 - 8.5)

(3.5 - 8.7)

(4.4 - 11.2)

(3.7 - 11.9)

Dissolved Oxygen

(% Saturation)

Depth Average

82

86

85

83

92

97

Not available

(64 - 106)

(69 - 118)

(69 - 108)

(65 - 106)

(66 - 141)

(76 - 143)

Bottom

77

82

81

80

94

96

Not available

(50 - 107)

(59 - 110)

(54 - 109)

(52 - 111)

(64 - 167)

(55 - 174)

pH

 

7.7

7.7

7.7

7.6

7.7

7.8

6.5 - 8.5 (±0.2 from natural range)

(7.2 - 8.1)

(7.1 - 8.2)

(7.1 - 8.2)

(7.0 - 8.1)

(7.0 - 8.2)

(7.2 - 8.4)

Secchi Disc Depth

(m)

2.4

2.3

2.1

2.2

2.2

1.9

Not available

(1.8 - 3.7)

(1.7 - 3.0)

(1.6 - 2.6)

(1.6 - 3.6)

(1.5 - 2.8)

(1.6 - 2.6)

Turbidity

(NTU)

6.0

5.3

6.8

5.2

4.4

6.4

Not available

(0.5 - 22.9)

(1.0 - 27.7)

(1.2 - 36.7)

(1.3 - 12.3)

(1.2 - 13.1)

(1.3 - 12.4)

Suspended Solids (SS)

(mg/L)

8.0

5.7

7.6

7.9

5.9

11.2

Not more than 30% increase

(3.3 - 14.0)

(3.2 - 7.4)

(3.4 - 17.3)

(4.5 - 13.2)

(3.9 - 13.0)

(5.2 - 20.7)

5-day Biochemical Oxygen Demand (BOD5)

(mg/L)

0.7

0.6

0.6

0.7

0.6

0.7

Not available

(<0.1 - 2.5)

(<0.1 - 1.9)

(0.2 - 2.3)

(0.2 - 2.3)

(0.1 - 2.0)

(0.1 - 2.4)

Ammonia Nitrogen (NH3-N)

(mg/L)

0.088

0.078

0.073

0.076

0.066

0.033

Not available

(0.046 - 0.137)

(0.050 - 0.137)

(0.049 - 0.120)

(0.042 - 0.133)

(0.039 - 0.098)

(0.012 - 0.063)

Unionised Ammonia

(mg/L)

0.002

0.002

0.002

0.002

0.002

0.001

Not more than annual average of 0.021mg/L

(<0.001 - 0.005)

(<0.001 - 0.004)

(<0.001 - 0.004)

(<0.001 - 0.004)

(<0.001 - 0.004)

(<0.001 - 0.006)

Nitrite Nitrogen

(NO2-N) (mg/L)

0.044

0.049

0.050

0.057

0.055

0.046

Not available

(0.010 - 0.085)

(0.011 - 0.099)

(0.011 - 0.106)

(0.016 - 0.129)

(0.016 - 0.133)

(0.010 - 0.113)

Nitrate Nitrogen

(NO3-N) (mg/L)

0.245

0.307

0.323

0.403

0.439

0.351

Not available

(0.075 - 0.467)

(0.067 - 0.693)

(0.070 - 0.703)

(0.096 - 0.867)

(0.084 - 1.010)

(0.025 - 0.893)

Total Inorganic Nitrogen (TIN) (mg/L)

0.38

0.43

0.45

0.54

0.56

0.43

Not more than annual average of 0.5mg/L

(0.20 - 0.57)

(0.17 - 0.79)

(0.16 - 0.81)

(0.20 - 1.05)

(0.18 - 1.08)

(0.07 - 1.01)

Total Kjeldahl Nitrogen (TKN) (mg/L)

0.44

0.39

0.39

0.37

0.34

0.35

Not available

(0.17 - 0.82)

(0.19 - 0.77)

(0.18 - 0.78)

(0.19 - 0.71)

(0.20 - 0.62)

(0.15 - 0.60)

Total Nitrogen (TN)

(mg/L)

0.73

0.75

0.77

0.83

0.84

0.74

Not available

(0.35 - 1.14)

(0.32 - 1.27)

(0.31 - 1.23)

(0.35 - 1.33)

(0.38 - 1.36)

(0.21 - 1.37)

Orthophosphate Phosphorus (PO4) (mg/L)

0.014

0.014

0.018

0.017

0.017

0.012

Not available

(0.002 - 0.021)

(0.003 - 0.024)

(0.008 - 0.026)

(<0.002 - 0.036)

(<0.002 - 0.035)

(<0.002 - 0.026)

Total Phosphorus (TP) (mg/L)

0.07

0.07

0.06

0.07

0.07

0.06

Not available

(0.03 - 0.11)

(0.04 - 0.11)

(0.04 - 0.10)

(0.04 - 0.10)

(0.04 - 0.11)

(0.04 - 0.12)

Silica (as SiO2)

(mg/L)

1.41

1.75

1.76

2.13

2.37

1.92

Not available

(0.09 - 3.27)

(0.08 - 5.17)

(0.08 - 5.07)

(0.10 - 5.80)

(0.09 - 6.57)

(0.06 - 5.60)

Chlorophyll-a

(μg/L)

2.8

2.0

1.9

1.6

2.7

5.7

Not available 

(0.4 - 17.2)

(0.5 - 9.3)

(0.7 - 7.1)

(0.5 - 5.2)

(0.6 - 14.3)

(0.5 - 27.7)

E. coli

(count/100mL)

130

33

13

11

4

2

Not available

(10 - 1900)

(4 - 130)

(3 - 80)

(1 - 63)

(<1 - 20)

(1 - 4)

Faecal Coliforms

(count/100mL)

270

66

33

27

8

4

Not available

(28 - 3200)

(6 - 250)

(5 - 130)

(5 - 110)

(1 - 71)

(1 - 34)

Notes:

1. Statement of Water Quality Objectives (North Western Water Control Zone)

2. Data source: EPD Marine Water Quality in Hong Kong in 2023

3. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, Mid-depth, Bottom.

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

5. Data in brackets indicate the ranges.

 

 

5.3.3           River Water Quality

5.3.3.1      Upon reviewing the latest available EIA reports for existing baseline water quality information, it was found that there are no recent EIA reports with baseline water quality data from previous projects available.  Additionally, the current routine river water quality monitoring locations established by the EPD do not cover the water streams near the project site.  Therefore, additional water quality survey was conducted to gather background information on the water systems in the vicinity of the project site (as shown in Figure 5.1).  The technical requirement for the additional River Water Quality Survey including survey locations, methodology, and duration has been submitted and approved by EPD.

5.3.3.2      Since there is lack of detailed characteristics of water quality of the watercourses between Tsing Yi and North Lantau Island, inland water quality survey of 3 sampling stations was proposed to collect watercourse information in areas within the proposed 500m boundary alignment.  Locations of the proposed sampling stations are shown in Figure 5.1, water sampling location 1 (W1) and 2 (W2) are located at Tsing Yi Island, and water sampling location 3 (W3) is at North Lantau Island.

5.3.3.3      Water sampling was conducted between December 2023 and January 2024 as dry season sampling and in April 2024 as wet season sampling. In each season, 3 sampling events with duplicate were conducted for each sampling location.  Since no water at W1 can be collected during dry season, there were a total of 30 sampling events at 3 sampling locations in 2 seasons.

5.3.3.4      For each survey station, field measurement on temperature, pH, DO, conductivity, turbidity and salinity were taken. Analysis of SS, BOD5, COD, oil and grease, E. coli, faecal coliforms, ammonia-nitrogen, nitrate-nitrogen, total kjeldahl nitrogen, reactive phosphorus, total phosphorus, sulphide and metals were carried out in laboratory determinations.  A summary of water sampling results is listed below in Table 5.7 for dry season and in Table 5.8 for wet season respectively.

 

Table 5.7      Summary of Water Quality Monitoring Data for Inland Watercourses (Dry Season)

Parameters

Unit

Criteria

W2-

2023 Day 1

W2-

2023 Day 2

W2-

2024 Day 3

W2-

Avg

W3-

2023 Day 1

W3-

2023 Day 2

W3-

2023 Day 3

W3-

Avg

Temperature

°C

NA

17.30

21.20

21.50

20.00

13.05

11.50

19.70

14.75

pH

-

6.0~9.0

8.11

8.09

7.93

8.04

8.35

8.58

7.80

8.24

Dissolved Oxygen

% Saturation

NA

95.70

93.25

93.95

94.30

95.15

97.45

99.85

97.48

Dissolved Oxygen

mg/L

≥4

9.30

9.16

8.29

8.91

10.02

10.62

9.14

9.92

Turbidity

NTU

NA

0.36

0.38

0.44

0.39

3.80

3.37

5.09

4.08

Salinity

ppt

NA

0.21

0.22

0.22

0.22

0.11

0.22

0.06

0.13

Conductivity

μs

NA

376.00

374.80

411.65

387.48

0.19

0.35

0.09

0.21

Secchi Disc Depth

cm

NA

2.00

2.00

2.00

2.00

10.00

10.00

8.00

9.33

Suspended Solids (SS)

mg/L

≤25

6.20

0.65

<0.5

3.43

17.15

36.40

56.25

36.60

Ammonia as N

mg/L

≤0.021

<0.005

<0.005

<0.005

<0.005

0.03

<0.005

<0.005

0.03

Nitrate as N

mg/L

NA

0.44

0.46

0.44

0.45

0.08

0.07

0.07

0.07

Total Kjeldahl Nitrogen as N

mg/L

NA

0.20

0.08

0.11

0.13

0.16

0.23

0.22

0.20

Total Phosphorus as P

mg/L

NA

0.02

<0.01

0.01

0.01

0.02

0.03

0.03

0.03

Reactive Phosphorus as P

mg/L

NA

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

Sulphide as S2-

mg/L

NA

 <0.05

 <0.05

 <0.05

 <0.05

 <0.05

 <0.05

 <0.05

 <0.05

Cadmium (Cd)

µg/L

≤5.5

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

Chromium (Cr)

µg/L

≤4.4

7.10

6.90

6.80

6.93

<1

<1

<1

<1

Copper (Cu)

µg/L

≤3.1

<1

<1

<1

<1

1.00

2.15

2.05

1.73

Lead (Pb)

µg/L

≤4.4

<1

<1

<1

<1

1.70

1.30

4.40

2.47

Zinc (Zn)

µg/L

≤8

7.50

6.00

4.00

5.83

20.00

17.50

17.00

18.17

Total Organic Carbon

mg/L

NA

1.00

1.00

<1

1.00

<1

<1

<1

<1

Oil & Grease

mg/L

NA

<1

<1

<1

<1

<1

<1

<1

<1

Chemical Oxygen Demand

mg/L

≤30

3.50

4.00

4.00

3.83

7.50

4.50

10.00

7.33

Biochemical Oxygen Demand

mg/L

≤5

<0.1

0.15

0.20

0.18

1.45

0.45

0.60

0.83

Aluminium

µg/L

NA

40.00

35.00

30.00

35.00

280.00

220.00

895.00

250.00

E. coli

CFU/100mL

≤1000

\

1

\

1

19

21

\

20

Faecal Coliforms

CFU/100mL

NA

4

4

6

5

23

25

\

24

Notes:  (1) Values in bold and underlined indicates non-compliance with criteria.

(2) The World Geodetic System 1984 coordinates of sampling locations are: W1: 22°21'06.0"N 114°05'05.0"E; W2: 22°21'15.0"N 114°04'55.0"E; W3: 22°20'03.0"N 114°03'16.0"E.

(3) No water was found at W1 during the survey.

(4) EPD use five key parameters, including pH, suspended solids(SS), dissolved oxygen (DO), 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand (COD), are used to assess compliance with the WQOs applicable for individual monitoring stations for Inland Water.

(5) The data presented in Day 1/2/3 are the average of the duplicated water sampling results.

(6) “\” indicates no data available or "not detected". The average data didn’t count the “\” data and averaged the rest valid data.

(7) The data presented in Day 1, Day 2, and Day 3 are the average of the duplicated water sampling results.

 

Table 5.8        Summary of Water Quality Monitoring Data for Inland Watercourses (Wet Season)

Parameters

Unit

Criteria

W1-2024 Day 1

W1-2024 Day 2

W1-2024 Day 3

W1-Avg

W2-2024 Day 1

W2-2024 Day 2

W2-2024 Day 3

W2-Avg

W3-2024 Day 1

W3-2024 Day 2

W3-2024 Day 3

W3-Avg

Temperature

°C

NA

25.00

25.00

26.70

25.57

25.20

24.50

26.30

25.33

23.90

24.20

25.10

24.40

pH

-

6.0~9.0

7.86

7.42

8.42

7.90

7.90

7.85

8.30

8.02

7.50

7.68

7.65

7.61

Dissolved Oxygen

% Saturation

NA

77.30

76.90

73.45

75.88

82.15

73.20

77.20

77.52

97.15

90.35

96.40

94.63

Dissolved Oxygen

mg/L

≥4

6.38

6.22

5.79

6.13

6.67

6.10

6.14

6.30

8.18

7.56

7.93

7.89

Turbidity

NTU

NA

2.72

31.30

1.47

11.83

2.57

11.25

1.23

5.01

12.43

4.64

6.72

7.93

Salinity

ppt

NA

0.10

0.10

0.18

0.13

0.10

0.06

0.17

0.11

0.25

0.28

0.62

0.38

Conductivity

μs

NA

199.00

198.35

377.35

258.23

197.55

119.65

368.20

228.47

0.53

0.58

1.25

0.78

Secchi Disc Depth

cm

NA

\

\

\

\

2.00

2.00

2.00

2.00

14.00

6.00

8.00

9.33

Suspended Solids (SS)

mg/L

≤25

2.40

10.75

1.65

4.93

1.55

33.20

0.95

11.90

15.25

28.25

13.35

18.95

Ammonia as N

mg/L

≤0.021

0.02

0.11

0.01

0.05

0.02

0.05

0.01

0.03

0.04

0.01

0.04

0.03

Nitrate as N

mg/L

NA

2.13

1.82

2.77

2.24

2.23

1.04

2.77

2.01

0.77

0.15

0.32

0.41

Total Kjeldahl Nitrogen as N

mg/L

NA

0.65

0.94

0.44

0.67

0.68

0.54

0.48

0.56

0.41

0.22

0.23

0.28

Total Phosphorus as P

mg/L

NA

<0.01

0.05

<0.01

0.05

<0.01

0.02

<0.01

0.01

0.04

0.03

0.02

0.03

Reactive Phosphorus as P

mg/L

NA

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

0.02

<0.01

0.01

0.01

Sulphide as S2-

mg/L

NA

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

<0.05

Cadmium (Cd)

µg/L

≤5.5

<0.1

0.10

<0.1

0.10

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

Chromium (Cr)

µg/L

≤4.4

<1

3.30

<1

1.77

<1

1.30

<1

1.10

<1

<1

<1

<1

Copper (Cu)

µg/L

≤3.1

6.65

22.15

3.50

10.77

5.70

9.65

5.25

6.87

2.25

<1

1.15

1.47

Lead (Pb)

µg/L

≤4.4

<1

8.25

<1

3.42

<1

2.20

<1

1.40

2.15

<1

1.20

1.45

Zinc (Zn)

µg/L

≤8

26.00

118.50

13.50

52.67

21.00

106.50

125.00

84.17

20.00

235.50

65.00

106.83

Total Organic Carbon

mg/L

NA

4.00

6.50

3.50

4.67

4.00

6.00

3.50

4.50

4.00

2.00

2.00

2.67

Oil & Grease

mg/L

NA

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

Chemical Oxygen Demand

mg/L

≤30

13.50

41.00

10.50

21.67

13.00

18.00

9.50

13.50

20.00

7.50

28.50

18.67

Biochemical Oxygen Demand

mg/L

≤5

0.50

3.10

0.95

1.52

0.45

2.20

0.50

1.05

0.85

0.70

1.00

0.85

Aluminium

µg/L

NA

185.00

715.00

30.00

310.00

75.00

200.00

30.00

101.67

380.00

145.00

230.00

251.67

E. coli

CFU/100mL

≤1000

500

7600

205

2768

480

2750

\

1615

2000

220

810

1010

Faecal Coliforms

CFU/100mL

NA

850

8400

500

3250

1060

4650

\

2855

2550

315

1250

1371.67

Notes:  (1) Values in bold and underlined indicates non-compliance with criteria.

          (2) The World Geodetic System 1984 coordinates of sampling locations are: W1: 22°21'06.0"N 114°05'05.0"E; W2: 22°21'15.0"N 114°04'55.0"E; W3: 22°20'03.0"N 114°03'16.0"E.

 (3) WQO for Inland water was adopted.

 (4) EPD use five key parameters, including pH, suspended solids(SS), dissolved oxygen (DO), 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand (COD), are used to assess compliance with the WQOs applicable for individual monitoring stations for Inland Water.

(5) The data presented in Day 1/2/3 are the average of the duplicated water sampling results.

(6) “\” indicates no data available or "not detected". The average data didn’t count the “\” data and averaged the rest valid data.

(7) The data presented in Day 1, Day 2, and Day 3 are the average of the duplicated water sampling results.

 

 

 

5.3.3.5      Due to the prolonged absence of rainfall during the monitoring period, water samples could not be collected at water sampling location 1 (W1) in dry season. The characteristics of water quality from available data at the 3 water sampling locations are discussed below:

·        Dissolved Oxygen: DO levels varied between 8.29mg/L to 10.62mg/L in dry season and between 5.79 mg/L to 8.18mg/L in wet season. The DO WQO for inland water in the Western Buffer and North Western WCZs is set at not less than 4mg/L. The DO is slightly higher in W3 of North Lantau Island than in W2 of Tsing Yi Island, but both high and comply with the WQO in both seasons.

·        Salinity: Salinity ranged between 0.06 ppt and 0.22 ppt in dry season but slightly higher in wet season from a range of 0.06 ppt to 0.62 ppt. The water salinity at W1 and W2 are all below 0.3 ppt but only shown a higher number of 0.62 ppt at W3 in wet season. The monitored waterbodies are generally within a freshwater environment.

·        Suspended Solids: SS concentrations at W2 in dry season varied between less than the detection limit of 0.5 mg/L and 6.2 mg/L, indicating that the upstream of this watershed has minimal anthropogenic interference. SS at W3 in dry season is relatively higher, primarily due to the presence of a few residential areas upstream, indicating anthropogenic influences. In wet season, the SS ranged between 0.95 mg/L and 15.25 mg/L for the 3 locations generally but only has a high number greater than 25 mg/L at W2 and W3 on the same sample day (Day 2), which indicates there might be anthropogenic influences on that day.

·        Nutrients: The nutrient levels for the 3 locations are lower in dry season than in wet season. Ammonia-nitrogen was not detected for most of the time at 3 locations (detection limit of < 0.005 mg/L) in dry season and ranged between 0.01 mg/L and 0.11 mg/L in wet season. Ammonia-nitrogen has the highest number shown at W1 in wet season (0.11 mg/L). Nitrate-nitrogen levels varied between 0.07 mg/L and 0.46 mg/L in dry season and increased to a range from 0.15 mg/L to 2.77 mg/L in wet season. Total Kjeldahl nitrogen ranged from 0.08 mg/L to 0.23 mg/L in dry season and increased to 0.22-0.94 mg/L in wet season with the highest number shown at W1. The nitrogen level is higher at W1 and W2 than W3. Reactive Phosphorus was not detected (detection limit of < 0.01 mg/L) in dry season and only shows a above detection limit number of 0.02 mg/L at W3 in wet season. Total phosphorus varied between 0.01 mg/L and 0.03 mg/L in dry season and the upper limit increased to 0.05 mg/L in wet season. The phosphorus level is not high at all 3 monitoring locations in both seasons. The water quality monitoring results indicate that there are no significant inputs from domestic or industrial pollution sources at these 3 locations.

·        Heavy Metals: In dry season, most of the concentrations of cadmium, chromium, and lead metals were below the assessment criteria (as shown in Table 5.4), except for chromium at W2 ranged between 6.8 µg/L and 7.1 µg/L, copper at W3 varied between 1 µg/L and 2.15 µg/L, and zinc at W3 exceeded the criteria of 8 µg/L. In wet season, the level of sulphide, cadmium and chromium were below the assessment criteria at all 3 locations, while lead only has one above assessment criteria number at W1. The level of copper and Zinc were detected to exceed the criteria for all 3 locations in wet season. The concentration of aluminium was higher in W1 and W3 than in W2, and all levels were relatively elevated in both seasons. Heavy Metals are relatively higher in wet season than in dry season and the detection of elevated metal levels at the 3 locations may be attributed to temporary construction effluent located upstream of the water sampling locations.

·        Carbon: Total organic carbon was detected to be 1mg/L at W2 and was not detected (detection limit of <1mg/L) at W3 in dry season, with most of the carbon present being in the inorganic form. However, the number increased in wet season for all the locations in a range between 2 mg/L and 6.5 mg/L, indicating the carbon present being in the organic form in wet season.

·        COD/BOD: COD levels varied between 3.5mg/L and 10mg/L in dry season and increased to 7.5 mg/L to 41 mg/L in wet season with the highest exceeded criteria number at W1. BOD levels varied between 0.15mg/L and 0.6mg/L in dry season and increased to between 0.45 mg/L and 3.1 mg/L in wet season with the highest number shown at W1 as well.

·        E. coli: In dry season, E. coli level was only 1 CFU/100mL at W2, and between 19 CFU/100mL and 21 CFU/100mL at W3. However, E. coli levels slightly exceed the assessment criteria limit most of the time at all 3 locations during the wet season. This indicates potential non-point source pollution from upstream, such as first flush due to rainfall (that is, initial surface run-off of a rainstorm. Water pollution entering storm drains in areas with high proportions of impervious surfaces is typically more concentrated compared to the remainder of the storm).

 

5.3.4           Beach Water Quality

5.3.4.1      The beach water quality baseline conditions were established using data from routine monitoring conducted by the EPD at Ma Wan Tung Wan Beach.  According to the 2024 Annual Beach Water Quality Reports published by the EPD, Ma Wan Tung Wan Beach received a "Fair" ranking based on the annual ranking and the geometric mean of E. coli levels during the bathing season.

Table 5.9      Annual Geometric Mean E. coli Levels in Tsuen Wan District

Beach

E. coli counts per 100mL

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

Anglers'

27*

69*

133

130

77

76

45

143

88

105

135

142

162

83

Approach

59

83

106

121

143

78

114

92

97

133

71

84

92

107

Casam

21

50

71

63

52

42

43

94

79

84

74

109

59

62

Gemini

19*

40*

135*

110*

56*

40*

39*

120*

79*

101*

127*

139*

107*

108*

Hoi Mei Wan

23

51

86

58

90

65

63

92

112

84

76

75

85

44

Lido

21

32

53

57

52

39

34

76

65

66

98

111

56

54

Ma Wan

Tung Wan

10

24

41

31

20

32

29

74

46

84

93

54

133

46

Ting Kau

58*

88*

107*

89

151

140

75

101

102

93

85

96

113

76

Note: (1) * Beach had not opened for swimming that year.

          (2)  E.coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year.

 

5.4               Water Sensitive Receivers

5.4.1.1      The WSRs within the Assessment Area were identified with reference to Annex 14 of the EIAO-TM.  Major WSRs identified in the Western Buffer and North Western WCZs are listed below in Table 5.10 and their indicative locations are given in Figure 5.1.

Table 5.10    Identified WSRs

Category

ID

Description

Seawater Intakes

C1

Seawater Intake for Future Sunny Bay Development

C2

Tsuen Wan Seawater Intake

C3

MTR Tsing Yi Station Seawater Intake

C4

Kwai Chung Hospital

Water Pumping Stations/Flushing Water Intakes

WSD1

Intake of Sunny Bay Salt Water Pumping Station

WSD2

Intake of Tsuen Wan Salt Water Pumping Station

WSD3

Intake of Tsing Yi Salt Water Pumping Station

Typhoon Shelter/Sheltered Anchorages

SA1

Ting Kau Sheltered Anchorage

SA2

Tsuen Wan Sheltered Anchorage

TS1

Rambler Channel Typhoon Shelter

Beaches

B1

Anglers' Beach

B2

Gemini Beach

B3

Hoi Mei Wan Beach

B4

Casam Beach

B5

Lido Beach

B6

Ting Kau Beach

B7

Approach Beach

B8

Ma Wan Tung Wan Beach

Corals

CR1

Corals at To Kau Wan

CR2

Corals at Sunny Bay

Horseshoe Crabs

H1

Horseshoe Crabs Area at Yam O

Mangroves

MG1

Mangrove near Ma Wan

MG2

Mangrove near Yam O

Seagrass Beds

SG1

Seagrass Beds near Yam O

Fish Culture Zone

F1

Ma Wan Fish Culture Zone

5.5               Identification of Potential Impacts

5.5.1           Construction Phase

5.5.1.1      The key construction elements of the Project include tunnels, cable supported bridges crossing Ma Wan Fairway and Kap Shui Mun Fairway, reclamation area for the proposed bridge towers and anchorages, viaducts and at-grade roads.

5.5.1.2      Marine construction works of the Project would mainly involve long-span bridges construction crossing the Ma Wan Fairway between Ma Wan and Tsing Yi and crossing the Kap Shui Mun Fairway between Ma Wan and North Lantau. Construction work also includes reclamation at Tsing Yi and Ma Wan, and construction of pile-supported Vessels Impact Protection System (VIPS) North Lantau for the protection of bridge towers and anchorages.

5.5.1.3      To address site constraints, a combination of ground treatment methods for reclamation including Deep Cement Mixing (DCM) and dredging will be adopted.  In order to minimise environmental impact, non-dredged reclamation techniques particularly DCM, will be employed wherever feasible for the construction of seawalls and the new land. The tentative construction schedule would be 2027 to 2033 for land-based and marine-based works. Additionally, a comprehensive set of mitigation measures will be implemented to mitigate potential adverse effects on water quality in the proximity of WSRs.  Details of the reclamation method and work sequences are presented in Section 2.9 and Appendix 5.2.

5.5.1.4      The major land-based construction works include site clearance, earthworks, foundation works (including piling), drill-and-blast works for tunnels, along with other related activities involving slope modifications and the construction of retaining structures.

5.5.1.5      The key sources of potential water quality issues associated with the construction phase are as follows:

Marine-based Construction Works

·       Wastewater / sewage effluent, from the construction activities and workforce and the accidental chemical spillage into the marine environment;

·       Reclamation at different locations between North Lantau and Tsing Yi Island depending on geotechnical and environmental constraints; and

·       Potential dredging in case where it is unavoidable due to the presence of thin layer and soft marine deposits, or when the soils beneath the marine clay are excessively stiff, making it challenging or impractical to achieve the desired embedment condition using the DCM method.

Land-based Construction Works

·       Construction site run-off;

·       Wastewater discharges from general construction activities;

·       Accidental spillage of chemical; and

·       Sewage effluent produced by on-site workforce.

 

 

5.5.2           Operational Phase

5.5.2.1      The key sources of potential water quality issues associated with the operation of the Project include:

·        Change in hydrodynamic regime and local flow pattern in the vicinity of reclamation areas at Tsing Yi, Ma Wan and North Lantau; and

·        Non-point source surface run-off from the Project.

5.6               Assessment Methodology

5.6.1           General

5.6.1.1      The WSRs in the vicinity of the Project are presented in Figure 5.1.

5.6.2           Land-based Water Quality Impacts

5.6.2.1      All the identified sources of potential water quality impacts from the land-based construction works and operational phase water quality impacts (including non-point source surface run-off) were evaluated and their impact significance determined.  Practical water pollution control measures / mitigation proposals were recommended to minimise the potential water quality impacts.

5.6.3           Marine-based Water Quality Impacts

Water Quality Modelling Tools

5.6.3.1      The modules, D-Flow Flexible Mesh and D-Water Quality, from the Delft3D Flexible Mesh (DFM) Suite modelling software, was employed to simulate the hydrodynamic and water quality conditions of the waterbodies under various representative scenarios in this study.

5.6.3.2      DFM Model employs an unstructured grid system that allows for adaptive mesh refinement, making it versatile for modelling complex geometries.  The D-Flow module simulates water flow, including tides, currents, and wave propagation, with high accuracy.

5.6.3.3      The D-Water Quality module provides a sophisticated framework for studying the distribution and transformation of constituents within aquatic systems.  It facilitates assessments of water quality parameters, including temperature, salinity, nutrients, and contaminants, while considering various factors such as sediment interactions and biological processes.

Sediment Plume Modelling

5.6.3.4      The D-Water Quality module was utilised to simulate sediment transport processes, including erosion, deposition, and sediment suspension.  These simulations are essential for comprehending the evolution of the reclamation and potential dredging activities. 

5.6.3.5      The hydrodynamic conditions generated from the D-FLOW module provided basic hydrodynamic information for modelling of sediment plume dispersion.  The processes of settling of sediment particles and exchange of 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 rate and erosion rate were calculated using the following equations:

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5.6.3.6      The above parameters have been used to simulate the impacts from sediment plumes in Hong Kong associated with uncontaminated mud disposal into the Brothers MBA([10]), dredging for the Permanent Aviation Fuel Facility at Sha Chau([11]), dredging and jetting for the Development of an Offshore Wind Farm in Hong Kong([12]) and the Additional Gas-fired Generation Units Project([13]).   The same settling velocity of 0.5 mm/s was adopted in multiple approved EIAs in the vicinity which involved sediment dispersion modelling, including Hong Kong Offshore LNG Terminal (EIAO Register No. AEIAR-218/2018), Improvement Dredging for Lamma Power Station Navigation Channel (EIAO Register No.: AEIAR-212/2017) and Development of a 100MW Offshore Wind Farm in Hong Kong (EIAO Register No.: AEIAR-152/2010).

Model Grid Layout and Properties

5.6.3.7      The development of the detailed model for this study is based on the HK-DFM model of version 202210, which was accessed from the Environmental Protection Department's Centralised Environment Database (CED).  The HK-DFM model domain, encompasses the northern region of the South China Sea, spanning from Hainan Island to Taiwan, including all of Hong Kong's waters and the Pearl River Delta.  The northern boundary is restricted to the coastlines of China and the Special Administrative Regions (SARs) of Macau and Hong Kong.

5.6.3.8      For this EIA study, a detailed model has been setup by refining the existing HK-DFM model in the vicinity of the Project area.  Specifically, the resolution of the model grid in the marine waters near the Project site was initially set at 140 meters in the HK-DFM Model.  The model grid was refined in the Assessment Area to less than 70 meters to give a better representation of the hydrodynamic condition.

5.6.3.9      In general, as shown in pages 2 and 3 of the Appendix 5.1, the refinement of the HK-DFM model grid in the area of interest involves several steps, with each step refining the grid by a factor of 2 by 2. In the Project area, a local refinement of the model grid was applied within a 3-kilometer radius, which involved grid refinement of the HK-DFM model from its initial 140-meter resolution to a more detailed 70-meter resolution.  This finer grid resolution is essential for capturing the hydrodynamic characteristics more accurately and simulating the dispersion of suspended sediments within the plume.

5.6.3.10   The smoothness is defined as the ratio between the areas of two adjacent grid cells. As required in the Deltares’ model technical manual, it should preferably be less than 1.2 in the area of interest, and the ideal orthogonality is less than 0.02.  The orthogonality of the locally refined grid is generally less than 0.02. The grid quality of the detailed model is generally good, except in some areas near the land boundary and the transition between different grid sizes.  Considering that the flow velocity at the land boundary is small, numerical errors associated with changes in orthogonality is minimal.

Model Bathymetry

5.6.3.11   The bathymetry schematisation of the detailed model relies on the original bathymetry data extracted from the HK-DFM model.  In the local refinement of the model grid in the vicinity of the Project area, depth data from the 'Charts for Local Vessels 2018' provided by the Hydrographic Office of the Marine Department of the HKSAR, was used for updates.  The hydrodynamic impact of the Contaminated Mud Pit (CMP) at East Sha Chau and The Brothers has also been considered, and the final CMP depth after capping was assumed in the modelling scenarios.

Boundary Conditions

5.6.3.12   The detailed model for this Project is based on the original HK-DFM grid with local refinements and no modifications were made to other offshore grid, the model's open boundary conditions continue to rely on the original HK-DFM forcing conditions.

5.6.3.13   The HK-DFM Model is influenced by boundary conditions at its three open boundaries.   The tidal water levels at these open boundaries are determined through harmonic expansion using the amplitudes and phases of 32 tidal components.  These data were sourced from the global tide model FES2012, which provides amplitudes and phases of the harmonic constituents on a 1/16° grid.  As for the salinity and temperature open boundary conditions, they are driven by WOA2013 data. The river discharge in the Pearl River Delta is derived from the global database EartH2Observe.

Meteorological Conditions

5.6.3.14   The HK-DFM Model use spatially- and time-varying meteorological data obtained from the ERA5 dataset.  ERA5 is the latest climate reanalysis developed by the European Centre for Medium-Range Weather Forecasts (ECMWF).  This dataset offers hourly estimates of various atmospheric variables at a resolution of 0.25º by 0.25º and can be downloaded in NetCDF or GRIB format.

5.6.3.15   For meteorological surface forcing of the model, the time- and spatially varying wind speed (in u- and v-direction), the atmospheric pressure and the Charnock coefficient (required to translate wind speed to surface stresses) are derived from ECMWF’s ERA5 dataset.

Simulation Periods

5.6.3.16   As required in clause 5 (iii) Appendix D-1 of the EIA Study Brief, for construction stage impacts, model simulations should be conducted for both dry and wet seasons.  The simulation period should cover at least a 15-day full spring-neap cycle, excluding the spin-up period, for each of the dry and wet seasons. Thus, in the model setup, the typical dry season ran from 1 December 2015 to 1 February 2016, while typical wet season ran from 1 July 2016 to 1 September 2016. 

5.6.3.17   As required in clause 5 (vi) of the EIA Study Brief, the changes in hydrodynamic regime should be assessed with the model run for at least a 15-day spring-neap tidal cycle in both the dry and wet seasons.   Daily erosion/sedimentation rate on identified WSR should be computed and assessed against with relevant criteria.

5.6.3.18   Prior to undertaking any model validation and assessment, a thorough model spin-up has been conducted to ascertain the stability of the model results.  Specifically, the model has undergone a spin-up period encompassing year 2015-2016.  Subsequently, the results from the typical dry and wet seasons of 2016 were extracted for further assessment.

Modelling Scenario

Construction Phase Sediment Plume Model 

5.6.3.19   In order to navigate site constraints effectively, a hybrid approach involving DCM and dredging ground treatment methods will be implemented.  The assessment of potential water quality impacts stemming from marine-based construction activities will focus on quantifying the sources and characteristics of sediment release during both dredging and DCM processes, as detailed in the following sections.  Based on the tentative construction programme in Appendix 5.2 and the best available information from other concurrent projects as detailed in Section 5.7.2.15 to 5.7.2.16 , the following assessment scenarios were modelled:

·       Run C1a – With Project and concurrent projects (Unmitigated): Simulate sediment plume dispersion during Dredging with the highest release rate of suspended solids;

·       Run C1b – With Project and concurrent projects (Unmitigated): Simulate sediment plume dispersion during Filling with the highest release rate of suspended solids;

·       Run C2a – With Project and concurrent projects (Mitigated): Simulate sediment plume dispersion during Dredging with the highest release rate of suspended solids;

·       Run C2b – With Project and concurrent projects (Mitigated): Simulate sediment plume dispersion during Filling with the highest release rate of suspended solids.

Operational Phase Hydrodynamic Model

5.6.3.20   The operational phase hydrodynamic model is to evaluate the potential change in hydrodynamic regime and local flow pattern in the vicinity of reclamation areas upon completion of the Project. The following two assessment scenarios have been evaluated in this study:

·       Scenario 1: Base Scenario – “Without Project” condition; and

·       Scenario 2: Development Scenario – With proposed reclamation.

Coastline Configuration and Cumulative Assessment

5.6.3.21   Major factors that would affect the water quality simulation would be (i) the change in pollution loading discharged to marine waters; and (ii) the change in coastline configurations.

5.6.3.22   The coastline configurations for construction and operational phases incorporate the coastal developments that might potentially affect the hydrodynamic regime and water quality in the assessment area due to the major existing projects and planned projects anticipated to be completed by the assessment year based on best available information.

5.6.3.23   Table 5.11 shows the coastal development projects incorporated in the coastline configurations for modelling.  However, it should be noted that some of these projects are still under study and their layouts may be subjected to further modifications.  Further details regarding the programme overlap between the Project and concurrent projects will be updated in the EIA report wherever feasible.

Table 5.11    Projects Incorporated into Modelling for Coastline Configurations

Project

Source of Information on Project Layout

Development of Integrated Waste Management Facilities Phase 1

EIA Report for “Development of IWMF Phase 1” (EIAO Register No.: AEIAR – 163/2012)

 

Harbour Area Treatment Scheme Stage 2A

EIA Report for “HATS Stage 2A” (EIAO Register No.: AEIAR – 121/2008)

Hong Kong – Zhuhai – Macao Bridge Hong Kong Boundary Crossing Facilities 

EIA Report for “HZMB Hong Kong BCF” (EIAO Register No.: AEIAR – 145/2009)

 

Hong Kong Link Road

EIA Report for “HZMB – Hong Kong Link Road” (EIAO Register No.: AEIAR – 144/2009)

New Contaminated Mud Marine Disposal Facility at Airport East / East Sha Chau Area

EIA Report for “New Contaminated Mud MDF at Airport East / East Sha Chau Area” (EIAO Register No.: AEIAR – 089/2005)

 

Expansion of Hong Kong International Airport into a Three-Runway System 

EIA Report for “3RS” (EIAO Register No.: AEIAR – 185/2014)

 

Sha Tin to Central Link

EIA Report for “SCL Protection Works at Causeway Bay Typhoon Shelter: (EIAO Register No.: AEIAR – 159/2011), EIA Report for “SCL – Hung Hom to Admiralty Section” (EIAO Register No.: AEIAR – 166/2012) and EIA Report for “SCL – Tai Wai to Hung Hom Section” (EIAO Register No.: AEIAR – 167/2012)

Kai Tak Cruise Terminal

EIA Report for “Dredging, Works for Proposed Cruise Terminal at Kai Tak” (EIAO Register No.: AEIAR – 115/2007)

Tuen Mun – Chek Lap Kok Link

EIA Report for “TM-CLKL” (EIAO Register No.: AEIAR – 146/2009)

Tung Chung New Town Extension

EIA Report for “TCNTE” (EIAO Register No.: AEIAR – 196/2016)

Contaminated Mud Pit at South Brothers

 

EIA Report for “New Contaminated Mud Marine Disposal Facility at Airport East / East Sha Chau Area” (EIAO Register No. AEIAR-089/2005)

 

(Remark: The hydrodynamic effect of the capped CMP has been incorporated into the hydrodynamic model.  The final level after capping of the CMP is assumed in the model under all modelling scenarios)

CMP at East Sha Chau

Sunny Bay Reclamation

PWP Item No. 751CL - Planning and Engineering Study on Sunny Bay Reclamation

Road P1 (Tai Ho – Sunny Bay Section)

Project Profile submitted for Application for EIA Study Brief (EIAO Register No.: PP-615/2020)

Reclamation at Lung Kwu Tan #

Project Profile submitted for Application for EIA Study Brief (EIAO Register No.: PP-668/2024)

Route 11 (section between Yuen Long and North Lantau)

EIA Report (EIAO Register No.: AEIAR-255/2023)

 

Reclamation for Kau Yi Chau Artificial Islands #

Project Profile submitted for Application for EIA Study Brief (EIAO Register No.: PP-633/2021)

Reclamation at Tuen Mun West #

Public Works Subcommittee (PWSC) (Papers) No. PWSC(2023-24)25 – Planning and Engineering Study for Lung Kwu Tan Reclamation and the Re-planning of Tuen Mun West Area

Water Recreation and Yacht Bay Development #

Project Profile submitted for Application for EIA Study Brief (EIAO Register No.: PP-677/2024)

Development of Integrated Waste Management Facilities Phase 2 (I·PARK2) #

EIA Report (EIAO Register No.: AEIAR-263/2024)

Development of Tseung Kwan O Area 137 and Associated Reclamation Sites #

EIA Report (EIAO Register No.: AEIAR-265/2025)

Note:

#    Only the coastline configurations of these projects that might potentially affect the hydrodynamic regime and water quality were included in the water quality impact assessment for operational phase.  As these projects are very far away from the project boundary of TYLL, the cumulative impacts due to these projects would be negligible and hence they were not included in the list of concurrent projects in Section 2 of this EIA report.

Model Validation and Verification

5.6.3.24   As shown in Appendix 5.1, the detailed model refined for this EIA study has been properly calibrated and validated against the HK-DFM Model before its application.  A comparison was conducted between the timeseries data of water level, salinity, and current velocity at specified locations, as well as the momentary/accumulated flow at cross-sections, between the detailed model and the HK-DFM model.

5.6.3.25   Velocity vector plots and salinity contour plots were generated and compared to verify that the detailed model aligns with the HK-DFM Model.  This process supported that the refinement of the HK-DFM model grid does not compromise the model's accuracy.

5.6.3.26   The Root Mean Square Error (RMSE) or the standard deviation is the average of the square differences between the observed and predicted values.  The RMSE is widely used to evaluate the model performance.  The RMSE gives absolute values of observation-prediction discrepancies.  An RMSE error of zero is ideal.  To express the discrepancies in percentage to measure the model performance, the Normalised Root Mean Square Error (NRMSE in %) is used as the ratio of RMSE to the observed value change.  NRMSE in % is preferred over Relative Error (RE in %) because in modeling, certain variables may possess significantly large mean values, resulting in very small relative errors.  This could potentially create a misleading impression that the model predictions are highly accurate.

A math equations and formulas AI-generated content may be incorrect.

5.6.3.27   The water level predictions consistently exhibit NRMSE% below 0.5% at all observation points within the model domain throughout both seasons.  Minimal phase error is observed, particularly at high and low water levels.  The water level NRMSE% consistently remains well below the specified threshold of <8%, as outlined in the EIA Study Brief Appendix D-1.  For current speed, the overall NRMSE% ranges between 2.40% and 11.96%, and the direction predicted by the local refined model closely aligns with the HK-DFM Model.  The deviation in current speed meets the requirement set in the EIA Study Brief Appendix D-1, of which the requirement is less than 30%.  In addition to meeting the NRMSE% requirement, the model also ensured that the maximum phase error at peak speed is less than 20 minutes, and the maximum direction error at peak speed is less than 15 degrees. Predicted salinity also demonstrates strong agreement with the HK-DFM Model, with NRMSE% ranging from approximately 2.58% to 8.37%, and the predicted maximum salinity deviation could meet with the requirement of EIA Study Brief <2.5ppt.

5.6.3.28   The NRMSE% for momentary flow across the channel ranges from 0.39% to 1.38%.  Minor deviations observed in some hydrodynamic results can be attributed to the local refined model's grid refinement.  The validation process indicates that the local refined detailed model consistently aligns well with the HK-DFM Model, confirming that the grid refinement did not compromise the accuracy of the model.

Table 5.12    Validation and Verification Matrix for the Local Refined Model

Items

Parameters

Locations

Indicative Points

Water Level

Salinity

Current Velocity

 

Observation Point 01

KTD_SR5

KTD_G2

WM4

Cross-sections

Momentary Flow

Accumulated Flow

ADCP Pillar Point – CLK

ADCP Yam O Wan - TLK

Ma Wan Channel 1

Ma Wan Channel 2

Map Results

Velocity Vectors Plot

Salinity Contour Plot

Salinity Sectional Plot

-

 

 

 

 

Table 5.13    Level of Fitness Summary between the Local Refined Model and HK-DFM Model at Observation Points

Observation Locations

Seasons

Water Level

Salinity

Current Speed

RMSE

NRMSE (%)

RMSE

NRMSE (%)

RMSE

NRMSE (%)

Observation Point 01

Dry Season

0.0063

0.31%

0.0420

 
2.58%
 
0.0227
 
2.40%

Wet Season

0.0054

0.23%

0.3714

4.06%

0.0402

3.02%

KTD_SR5

Dry Season

0.0093

0.46%

 
0.0755
 
5.44%
 
0.0896
 
11.96%

Wet Season

0.0097

0.42%

 
0.7664
 
8.37%

0.0965

11.40%

KTD_G2

Dry Season

0.0027

0.13%

 
0.0439
 
4.05%

0.0527

7.17%

Wet Season

0.0042

0.18%

 
0.5785
 
7.00%
 
0.0650
 
4.50%

WM4

Dry Season

0.0040

0.19%

 
0.0486

5.12%

0.0396

5.96%

Wet Season

0.0041

0.17%

 
0.5088
 
8.24%

0.0638

8.97%

 

Table 5.14    Level of Fitness Summary between the Local Refined Model and HK-DFM Model at Cross-sections

Observation Cross-sections

Seasons

Momentary Flow

Accumulated Flow

RMSE

NRMSE

(%)

RMSE

NRMSE

 (%)

ADCP Pillar Point – CLK

Dry Season

 
321.1
 
0.39%
 
10052408
 
0.42%

Wet Season

 
379.9

0.43%

105873419

4.76%

ADCP Yam O Wan - TLK

Dry Season

 
329.2
 
0.35%
 
10152247
 
0.40%

Wet Season

 
389.2

0.39%

 
106340743
 
4.60%

Ma Wan Channel 1

Dry Season

 
330.9
 
0.35%
 
10161973
 
0.40%

Wet Season

 
388.9

0.39%

 
106311584
 
4.58%

Ma Wan Channel 2

Dry Season

 
1081.1

1.62%

 
152673909

3.62%

Wet Season

 
967.5
 
1.38%
 
88589535
 
4.79%

 

Table 5.15    Model Performance of the Local Refined Model

Criteria

Level of fitness

Model Performance

Tidal elevation (Root Mean Square of the Error)

< 8 %

< 1.9%

Maximum phase error at high water and low water

< 20 minutes

< 12 minutes

Maximum current speed deviation

< 30 %

< 11.9%

Maximum phase error at peak speed

< 20 minutes

< 16 minutes　

Maximum direction error at peak speed

< 15 degrees

< 15 degrees

Maximum salinity deviation

< 2.5 ppt

< 2.5 ppt

5.7               Prediction and Evaluation of Environmental Impacts

5.7.1           Land-based Construction Phase Impacts

5.7.1.1      The key construction elements of the Project include tunnels, cable supported bridges crossing Ma Wan Fairway and Kap Shui Mun Fairway, reclamation area for the proposed bridge towers and anchorages, viaducts and at-grade roads.

5.7.1.2      As described in Section 2.9, land-based construction predominantly involves tunnel excavation for the Project.  The primary construction method for the tunnels is expected to be the drill-and-blast method, which entails controlled blasting to excavate medium to hard rock.  Viaducts will be employed for the mainline crossing North Lantau Interchange and Tsing Yi Connection, as well as the associated slip roads.  The viaducts will be predominantly constructed using the precast concrete segmental erection method to minimise on-site casting work.  Excavation of the rock hills at Lantau Island near Yi Chuen and Tso Wan will be carried out as part of the site formation works for the proposed at-grade roads and tunnel portals.

Tunnelling Works

5.7.1.3      As mentioned above, the primary method of construction for the tunnel is expected to be the drill-and-blast method, it might have potential impacts on underground  water resource.  If the mitigation measures in Section 5.8 are followed as practicable, water quality impacts from tunnelling are expected to be minimal.

Wastewater from General Construction Activities

5.7.1.4      Wastewater generated from construction activities, including general cleaning and polishing, wheel washing, dust suppression and utility installation may contain high SS concentrations, as well as a certain amount of grease and oil.  Potential water quality impacts due to uncontrolled wastewater discharge can be avoided if construction and site management practices are implemented to ensure that litter, fuels, and solvents do not enter the water environment.  It is expected that if the good site practice suggested in Section 5.8 are followed as far as practicable, the potential water quality impacts associated with construction activities would be minimal.

Construction Site Run-off

5.7.1.5      Potential pollution sources of site run-off may include:

·        Run-off and erosion of exposed bare soil and earth, drainage channels, earth working areas and stockpiles;

·        Wash water from dust suppression sprays and wheel washing facilities; and

·        Fuel, oil and lubricants from maintenance of construction vehicles and equipment.

5.7.1.6      Site run-off would wash away the soil particles on unpaved lands and areas with topsoil exposed during rainstorms.  Release of uncontrolled site run-off, characterised by high concentrations of SS, could increase the SS levels and turbidity in the nearby water environment.  Site run-off may also wash away soil particles that were contaminated by the construction activities and therefore cause water pollution.

5.7.1.7      Wind-blown dust would be generated from exposed soil surfaces in works areas.  It is possible that wind-blown dust would fall directly onto the nearby water bodies when a strong wind occurs.  Dispersion of dust within the works areas may increase the SS levels in surface run-off causing a potential impact to the nearby sensitive receivers.

5.7.1.8      Proper site practice and good site management should be followed to prevent run-off with high level of SS from entering the surrounding waters.  Best Management Practices (BMPs) in controlling construction site discharges are recommended in Section 5.8 for this Project.   With the implementation of BMPs to control run-off and drainage from the construction site, disturbance of water bodies would be avoided and deterioration in water quality would be minimal.

Construction Works Within and in Close Proximity to Inland Water

5.7.1.9      Construction activities in close vicinity to the inland watercourses may impact water quality due to the potential uncontrolled release of construction waste and wastewater.   Construction waste and wastewater are generally characterised by high SS concentration and elevated pH.  With the implementation of adequate construction site drainage and BMPs as described in Section 5.8 and provision of precautionary measures / practices as specified in ETWB TC(Works) No. 5/2005 "Protection of natural streams / rivers from adverse impacts arising from construction works", it is anticipated that water quality impacts would be minimal.

5.7.1.10   The construction of at-grade roads, viaduct supports, tunnel portals, and associated slope works at streams W1, W2, and W3 (as shown in Figure 8.7.1) may result in a very localised and temporary diversion of these streams. Stream diversion works should be conducted in accordance with the guidelines specified in ETWB TC(W) No. 5/2005 – Protection of Natural Streams/Rivers from Adverse Impacts Arising from Construction Works (ETWB, 2005). To minimize disturbance, construction works adjacent to watercourses should preferably be carried out during the dry season where flow in the stream/river is low. Where feasible, avoidance measures should be implemented, such as establishing a work exclusion zone with a minimum 5-meter setback from the edge of the watercourse. Alternatively, elevated temporary work platforms may be used over affected watercourses for construction and access, with supporting structures positioned outside the watercourse and its banks to reduce direct impact. With the proper implementation of the mitigation measures, no unacceptable effects on water quality are anticipated.

Sewage from Construction Workforce

5.7.1.11   During the construction of the Project, the workforce on site will generate sewage effluent, which is characterised by high levels of BOD, ammonia and E. coli counts.   Based on the DSD Sewerage Manual, the sewage production rate for construction workers is estimated at 0.35 m3 per worker per day.  Potential water quality impacts upon the local drainage and freshwater system may arise from these sewage effluents, if uncontrolled.

5.7.1.12   Temporary sewage generation can be adequately treated by interim sewage treatment facilities, such as portable chemical toilets.  Provided that sewage is not discharged directly into storm drains or inland waters adjacent to the construction site, temporary sanitary facilities are used and properly maintained, and control measures as recommended in Section 5.8 are adopted as far as practicable, it is unlikely that sewage generated from construction workforce would have a significant water quality impact.

Accidental Spillage of Chemicals

5.7.1.13   The use of chemicals such as engine oil and lubricants, and their storage as waste materials has the potential to impact water quality if spillage occurs and enters adjacent water environment.  Waste oil may infiltrate into the surface soil layer, or run-off into the nearby water environment, which in turn increases the hydrocarbon levels.  The potential impacts could however be avoided by practical precautionary measures and good site practices (as given in Section 5.8).

5.7.2           Marine-based Construction Phase Impacts

Proposed Suspended Solids Criteria for Indicator Points

5.7.2.1      The assessment area of this Project covers Western Buffer and North Western WCZs.  As detailed in Section 5.2, the WQOs for SS for both WCZs stipulate that for marine waters human activity (e.g. waste discharge) should not cause the natural ambient level to be raised by 30% or cause SS accumulation that may adversely affect aquatic communities.  The respective allowable increase in SS concentrations within the corresponding WCZs was used as the assessment criterion.  To determine the ambient SS concentrations in the affected waters, the water quality monitoring data from EPD monitoring stations WM4/NM1/VM12/VM14 in the WCZ were analysed.

5.7.2.2      EPD marine water quality data in sea surface, mid-depth and the bottom were collected and analysis.  The sampling in wet season was taken from April until the end of September in each year. The 90 percentiles for each station in the recent 10 years from 2014 to 2023 are summarised in Table 5.16.

Table 5.16    90th Percentile SS from EPD Routine Monitoring Programme (2014-2023)

Station

90th Percentile Suspended Solids Concentrations (mg/L)

Surface

Middle

Bottom

Depth Averaged

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

WM4

9.70

9.24

12.00

11.60

17.00

16.00

12.90

12.28

NM1

11.90

9.96

17.80

14.60

18.00

21.80

15.90

15.45

VM12

10.80

11.00

12.60

11.70

14.80

18.70

12.73

13.80

VM14

9.67

8.99

11.70

9.22

13.00

10.70

11.46

9.64

 

5.7.2.3      In order to assess the impact of construction activities on water quality, SS were evaluated against the WQO which stipulates that waste discharge should not increase the natural ambient level by more than 30% or cause SS accumulation that may adversely affect aquatic communities. For the affected WCZs, the allowable increase in SS concentrations was determined by comparing the ambient SS concentrations in the affected waters with the SS criteria derived from 30% of the 90th Percentile SS concentration measurement at the nearest EPD’s Monitoring Stations, as summarised in Table 5.17.  The ambient level was obtained from the nearest EPD water quality monitoring station for each identified WSR and the corresponding SS criterion for each modelling observation point is presented in Table 5.18.

5.7.2.4      For seawater intake WSRs, the WSD has established standards for the quality of abstracted seawater (Table 5.3).  The water quality of identified seawater intakes in the project has been assessed against an SS criterion of <10mg/L, in addition to the WQOs.  For the adopted standards for cooling water intake have been discussed in Section 5.2.1.7, the SS limit is 40mg/L.

5.7.2.5      The AFCD has established a guideline value for the protection of water quality at Fish Culture Zones (FCZs), recommending a maximum value of 50 mg/L.  This criterion has been adopted in previously approved EIA reports ([14],[15],[16],[17]).  Therefore, the AFCD criterion, WSD standard and the WQO are deemed applicable for the assessment area.  While these criteria are considered acceptable but to be conservative, the most stringent value has been adopted for the sediment plume assessment.

5.7.2.6      The list of observation points at the WSRs and the allowable SS elevation criteria were summarised in Table 5.18.

Table 5.17    Suspended Solids Elevation Criteria (mg/L) for the Construction Phase Impacts

Station

Suspended Solids Criteria (mg/L)

Surface

Middle

Bottom

Depth Averaged

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

WM4

2.91

2.77

3.60

3.48

5.10

4.80

3.87

3.68

NM1

3.57

2.99

5.34

4.38

5.40

6.54

4.77

4.64

VM12

3.24

3.30

3.78

3.51

4.44

5.61

3.82

4.14

VM14

2.90

2.70

3.51

2.77

3.90

3.21

3.44

2.89

 

Table 5.18    Allowable Suspended Solids Elevation Criteria (mg/L) for The Modelling Observation Points

Location

 Nearest

EPD’s Station

Suspended Solids Criteria (mg/L)

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

MG2

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

H1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

SG1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

CR2

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

C1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

CR1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

MG1

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

WM4

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

C4

VM12

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

B2

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

SA2

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

C3

VM12

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

VM12

VM12

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

VM14

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

F1

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B1

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B4

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B5

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B7

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B8

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

NM1

NM1

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

WSD2

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

WSD3

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

TS1

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

B3

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

B6

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

C2

VM14

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

SA1

WM4

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Notes:  S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

 

Sediment Release due to Proposed Reclamation Works

5.7.2.7      The reclamation in Ma Wan and Tsing Yi are unavoidable, as they will be the protection to those bridge towers, marine bridge piers and marine anchorage in Ma Wan and Tsing Yi.  Holistic engineering consideration has taken to adopt the minimum clearance between the edge of reclamation and the foundation of bridge tower/pier/anchorage, so as to avoid physical contact between vessel and bridge structure in collision.  At the same time, to minimise the extent of dredging as far as practicable so as to minimise the associated water quality impacts and impacts on marine ecology.

5.7.2.8      As presented in Section 2, in consideration of the different reclamation methods, different reclamation approaches from dredging to non-dredging were investigated. It was proposed that non-dredging method using DCM should be applied as far as practicable to limit the construction time required and reduce the settlement of the reclamation.  However, it should be noted that the DCM technique may not be practical or the most cost effective in some areas of the site.  According to the geotechnical condition, rocks (potentially of varying weathering grades), boulders / cobbles / gravels, sandy materials, dumped materials and debris are present at the seabed in these areas.  In view of these seabed features and the relatively thin marine deposits in local areas, dredging of limited depths to remove thin layer of and local marine deposits as well as various boulders / cobbles / gravels / debris may be considered as a more practical method.

5.7.2.9      To avoid the need for dredging and disposal of thick layer of marine deposits especially for the reclamation of the Tsing Yi and Ma Wan South Towers of the proposed bridge crossing Ma Wan Fairway, non-dredged reclamation with the marine deposits left in place may be adopted.  DCM ground treatment can be utilised to improve the strength and stiffness of the soft marine clay to control the stability of the seawalls and long-term settlement of the reclaimed areas.

5.7.2.10   Areas of relatively thin marine deposits are also identified in areas of the proposed reclamation for the towers of proposed bridges crossing Ma Wan Fairway and Kap Shui Mun Fairway and Ma Wan South anchorage.  Removal of soft marine deposits by dredging may be considered in these areas.  For areas where thick layer of marine deposits is present, there may be seabed features of boulders / cobbles / gravels / debris which are potential obstructions for the DCM works.  Consideration should be given to the combined ground treatment method using removal of shallow obstructions followed by DCM treatment. 

5.7.2.11   Furthermore, there may be local areas where the soft marine deposit is underlain directly by in-situ soils (e.g. saprolite), which is relatively hard for the DCM rigs to penetrate and therefore embedment condition of the DCM clusters is not expected to be acceptable.  Under this circumstance, dredging of soft marine deposit may be necessary in local areas.  As dredging works would inevitably generate SS from the disturbed sediment at the seabed, quantitative water quality modelling would be conducted to assess the impacts induced by the dredging works.

5.7.2.12   Appendix 5.2 provides details on the reclamation work sequence and the potential release of SS.  The bulk density of filling materials for sand and public fill are 1,680kg/m3 and 1,900kg/m3, respectively.  The assumed sediment loss rate for the public fill and sand blanket is 5% of the fine content percentage (<63µm) in the filling materials, and the sediment reduction due to the leading seawall is assumed to be 45% based on the HZMB EIA report and TCNTE EIA report.

5.7.2.13   According to the latest design, dredging will be necessary before commencing reclamation works.  The proposed reclamation works sequence revealing that the filling works will be carried out within the seawall, meaning that once the seawall reaches above sea level, no SS will be released into the marine water. However, since dredging activities will be carried out before seawall construction, SS will inevitably be generated when dredging seabed sediments.  Although the majority of the reclamation works will be carried out within the confines of the already constructed seawall, for conservative assessment purposes, we assume a reduction rate of 45% for SS release due to the seawall.  Therefore, a quantitative water quality model was conducted to evaluate the water quality impacts resulting from both the dredging and reclamation works (filling below water).

5.7.2.14   As shown in Appendix 5.2, the estimated SS loss per workfront is 121.8 g/s during the dredging activities.  Considering three workfronts for each zone, the total SS release rate amounts to 365.5 g/s for each zoning.  In terms of reclamation filling, the highest release rate of SS under an unmitigated scenario is expected to occur in Q4 2028 to Q1 2029.  The SS release is estimated to be 34.38 tonnes/day for Tsing Yi Tower (Q4 2028 to Q1 2029), 67.66 tonnes/day for Ma Wan South Tower (Q4 2028), and 32.60 tonnes/day for Ma Wan South Anchorage (Q4 2028).  For conservative assessment, despite the Ma Wan South Tower and Anchorage's work period being in Q4 2028, the SS loading for these three locations is combined.  Additionally, the SS loading of 1.87 tonnes/day for Kap Shui Mun Tower in Q1 2028 is included in the assessment.  This scenario represents the worst condition.  Take the Ma Wan South Tower as example, the SS release rate is calculated to be 1566 g/s under the unmitigated scenario, whereas the mitigated scenarios with silt curtain are expected to result in a rate of 861 g/s.  The sediment loss during the DCM operation process, including sediment release from auger blade rotation and other associated activities, has been comprehensively considered in the modelling.

5.7.2.15   Regarding the cumulative impacts from concurrent projects, the Route 11 (section between Yuen Long and North Lantau) and Road P1 (Tai Ho – Sunny Bay Section) were considered for the construction phase. For the I-Park 2, according to the Approved EIA Report for Development of Integrated Waste Management Facilities Phase 2 (I·PARK2) (EIAO Register No.: AEIAR-263/2024), the project's construction phase is scheduled to commence in 2026 with anticipated completion in the early 2030s, with two sediment dispersion modelling scenarios from closed grab dredger operational at the Middle Ash Lagoon shoreline during 2026 sand placement operations and at the West Ash Lagoon shoreline during 2027 sand placement activities. As detailed in Section 5.7.2.14 and Appendix 5.2, Q4 2028 to Q1 2029 would be the worst-case for sedimentation impacts from this Project, demonstrating temporal separation from both I∙PARK2 construction scenarios.

5.7.2.16   For the Sunny Bay Reclamation, Reclamation at Lung Kwu Tan, Reclamation for Kau Yi Chau Artificial Islands, Reclamation at Tuen Mun West, Water Recreation and Yacht Bay Development, as of now, these projects are either in the planning stages or their EIA reports have not yet been approved. Therefore, the specific construction periods cannot be determined at the time of this EIA preparation.

Sediment Plume Modelling Results of Unmitigated Scenario

5.7.2.17   In the context of dredging activities scenario, the maximum predicted SS elevations and sedimentation rate at the WSRs and other observation points under scenario C1 are outlined in Table 5.19 and Table 5.21, with the predicted maximum extents of SS elevations and sedimentation rates detailed in Appendix 5.3.  The maximum extent of the sediment plume resulting from dredging is confined to the dredging area, and no exceedance is anticipated at any of the WSRs.  While a slight exceedance was observed near the dredging area, the exceedance zone is very small. The maximum distance of the exceedance zone from the sediment release source is around 58m. From the simulation results, it is evident that even without the implementation of any mitigation measures such as silt curtain, the relatively low SS release load from dredging is unlikely to cause exceedances at nearby WSRs. Consequently, the dredging activities are not predicted to cause significant adverse water quality impacts on nearby sensitive receivers, including bathing beaches (e.g., Ma Wan Tung Wan Bathing Beach), Fish Culture Zones (FCZs) (such as the nearest Ma Wan FCZ), and intertidal/subtidal habitats (e.g., the corals at To Kau Wan).

5.7.2.18   In the reclamation filling activities scenario, as shown in Table 5.20 and Table 5.22 due to the adoption of the worst-case assumptions, such as in Ma Wan South Tower, the SS release rate is calculated to be 1,566 g/s under reclamation filling activities, compared to only 365.5 g/s during dredging.  The higher SS release would result in short-duration exceedances observed during the wet season at observation point WM4.  Localised instances of water quality exceedances are expected in the vicinity of the reclamation filling area. However, it is crucial to emphasise that these exceedances are transient and of short duration, dissipating rapidly upon cessation of the reclamation filling works. Furthermore, even under these worst-case conditions, the reclamation filling activities are not predicted to cause adverse water quality impacts on nearby sensitive receivers. These include the closest bathing beaches (e.g., Ma Wan Tung Wan Bathing Beach), FCZs (such as the adjacent Ma Wan FCZ), and intertidal/subtidal habitats (e.g., the corals at To Kau Wan).


Table 5.19    Predicted Maximum Suspended Solids (mg/L) Elevations during Dredging Activities (Run C1a – With Project, Unmitigated)

Location

Predicted Maximum Suspended Solids (mg/L) Elevations

 Suspended Solids Criteria (mg/L)

Compliance to Criteria (mg/L)

Dry Season

Wet Season

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

S

M

B

DA

S

M

B

DA

WSD1

0.01

0.02

0.04

0.02

0.01

0.03

0.05

0.03

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

SG1

0.00

0.01

0.01

0.00

0.00

0.00

0.01

0.01

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR2

0.02

0.07

0.07

0.05

0.00

0.03

0.07

0.03

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

C1

0.13

0.15

0.15

0.14

0.01

0.10

0.14

0.09

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR1

0.37

0.26

0.14

0.25

0.02

0.04

0.06

0.04

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG1

0.21

0.64

0.65

0.50

0.15

0.74

0.78

0.56

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

WM4

0.67

0.73

0.85

0.75

0.24

1.07

1.39

0.90

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

B2

0.12

0.15

0.21

0.16

0.09

0.32

0.38

0.26

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

SA2

0.00

0.02

0.02

0.01

0.00

0.00

0.01

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

C3

0.02

0.02

0.02

0.02

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM12

0.01

0.01

0.00

0.01

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM14

0.02

0.03

0.03

0.02

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

F1

0.07

0.18

0.21

0.15

0.01

0.13

0.14

0.10

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B1

0.04

0.12

0.14

0.10

0.03

0.11

0.11

0.08

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B4

0.03

0.09

0.10

0.07

0.00

0.02

0.09

0.04

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B5

0.02

0.09

0.10

0.07

0.00

0.04

0.12

0.05

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B7

0.01

0.06

0.08

0.05

0.00

0.00

0.01

0.01

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B8

0.30

0.30

0.30

0.30

0.19

0.19

0.19

0.19

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

NM1

0.19

0.16

0.18

0.18

0.03

0.13

0.18

0.12

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

WSD2

0.00

0.01

0.01

0.00

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

WSD3

0.02

0.02

0.02

0.02

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

TS1

0.00

0.00

0.01

0.00

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

B3

0.09

0.17

0.18

0.15

0.00

0.18

0.24

0.14

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B6

0.03

0.03

0.03

0.03

0.01

0.01

0.02

0.01

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C2

0.01

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

SA1

0.01

0.01

0.01

0.01

0.00

0.06

0.14

0.07

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

Note: 

1.               S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

2.               Values in bold and underlined indicates non-compliance with WQOs.

3.               The working hours per day is assumed to be 12 hours.

 

 

 

 

 

 

 

 

 

Table 5.20    Predicted Maximum Suspended Solids (mg/L) Elevations during Reclamation Filling Activities (Run C1b – With Project, Unmitigated)

Location

Predicted Maximum Suspended Solids (mg/L) Elevations

 Suspended Solids Criteria (mg/L)

Compliance to Criteria (mg/L)

Dry Season

Wet Season

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

S

M

B

DA

S

M

B

DA

WSD1

0.01

0.06

0.07

0.04

0.02

0.07

0.16

0.08

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.01

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

SG1

0.00

0.01

0.01

0.01

0.00

0.00

0.03

0.01

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR2

0.03

0.16

0.18

0.12

0.01

0.08

0.24

0.11

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

C1

0.20

0.40

0.41

0.34

0.04

0.27

0.46

0.26

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR1

0.22

0.26

0.23

0.24

0.03

0.10

0.18

0.10

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG1

0.17

0.48

0.47

0.38

0.17

0.74

0.74

0.55

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

WM4

2.44

3.54

4.37

3.45

0.95

8.08

4.77

4.60

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

No

C4

0.01

0.01

0.01

0.01

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

B2

0.36

0.49

0.70

0.52

0.31

0.99

1.12

0.81

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

SA2

0.00

0.05

0.06

0.04

0.00

0.01

0.02

0.01

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

C3

0.05

0.07

0.08

0.07

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM12

0.03

0.02

0.01

0.02

0.00

0.00

0.01

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM14

0.05

0.09

0.09

0.08

0.00

0.01

0.02

0.01

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

F1

0.29

0.41

0.50

0.40

0.04

0.33

0.36

0.24

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B1

0.12

0.34

0.37

0.28

0.10

0.33

0.32

0.25

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B4

0.10

0.33

0.38

0.27

0.01

0.09

0.28

0.12

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B5

0.08

0.33

0.37

0.26

0.01

0.14

0.43

0.19

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B7

0.05

0.23

0.30

0.19

0.00

0.01

0.04

0.02

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B8

0.79

0.79

0.79

0.79

0.68

0.66

0.66

0.67

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

NM1

0.39

0.35

0.52

0.42

0.10

0.62

0.72

0.48

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

WSD2

0.00

0.02

0.03

0.02

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

WSD3

0.06

0.08

0.08

0.07

0.00

0.01

0.01

0.01

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

TS1

0.00

0.02

0.02

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

B3

0.32

0.58

0.63

0.51

0.01

0.59

0.83

0.48

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B6

0.09

0.09

0.10

0.09

0.05

0.05

0.05

0.05

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C2

0.02

0.04

0.04

0.03

0.00

0.00

0.01

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

SA1

0.13

0.38

0.49

0.34

0.01

0.22

0.51

0.25

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

Note: 

1.               S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

2.               Values in bold and underlined indicates non-compliance with WQOs.

3.               The working hours per day is assumed to be 12 hours.

 

 

 

Table 5.21    Predicted Maximum Sedimentation Rate (g/m2/day) during Dredging Activities (Run C1a – With Project, Unmitigated)

WSR

Predicted Maximum Sedimentation Rates (g/m2/day)

Dry Season

Wet Season

WSD1

1.6

2.2

MG2

0.0

0.1

H1

0.0

0.3

SG1

0.3

0.7

CR2

3.1

2.9

C1

6.8

6.7

CR1

4.1

2.7

MG1

30.6

42.4

WM4

37.3

68.9

C4

0.1

0.0

B2

12.0

16.3

SA2

0.8

0.3

C3

1.0

0.1

VM12

0.1

0.1

VM14

1.1

0.2

F1

9.3

6.4

B1

6.1

5.0

B4

4.5

3.9

B5

4.5

6.3

B7

3.5

0.7

B8

0.0

0.9

NM1

7.9

8.4

WSD2

0.3

0.1

WSD3

1.2

0.1

TS1

0.2

0.0

B3

8.4

11.5

B6

0.7

0.1

C2

0.6

0.1

SA1

8.2

6.7

Notes: Values in bold and underlined indicates non-compliance with criteria, which is the daily sediment deposition rate of 200 g/m2/day was adopted.

 

Table 5.22    Predicted Maximum Sedimentation Rate (g/m2/day) during Reclamation Filling Activities (Run C1b – With Project, Unmitigated)

WSR

Predicted Maximum Sedimentation Rates (g/m2/day)

Dry Season

Wet Season

WSD1

2.8

7.2

MG2

0.0

0.2

H1

0.1

0.6

SG1

0.2

1.5

CR2

7.7

10.5

C1

18.3

21.3

CR1

9.1

8.5

MG1

25.1

36.8

WM4

192.5

241.2

C4

0.4

0.0

B2

45.0

48.3

SA2

2.5

1.1

C3

3.2

0.2

VM12

0.3

0.5

VM14

3.9

0.9

F1

21.6

15.8

B1

20.6

16.2

B4

16.5

13.1

B5

16.8

22.8

B7

12.9

2.6

B8

0.0

1.4

NM1

22.5

34.1

WSD2

1.2

0.2

WSD3

3.7

0.3

TS1

0.8

0.1

B3

27.3

39.7

B6

2.8

0.3

C2

1.8

0.3

SA1

22.6

24.7

Notes: Values in bold and underlined indicate non-compliance with criteria, which is the daily sediment deposition rate of 200 g/m2/day was adopted.

Dissolved Oxygen Depletion

5.7.2.19   The degree of oxygen depletion exerted by a sediment plume is a function of the sediment oxygen demand of the sediment, the concentration in the water column and the rate of oxygen replenishment.  In this assessment, the impact of sediment oxygen demand on DO concentrations has been calculated based on the following equation:

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5.7.2.20   Due to the lack of SOD20 information for the Project area, a desktop study has been conducted.  In the EIA report of Expansion of Hong Kong International Airport into a Three-Runway System, sediment sampling and testing was undertaken in December 2012 for the proposed submarine cable diversion alignment and the field joint location.  The highest SOD measured in the sediment samples collected from the 21 sampling locations along the proposed submarine cable alignment and field joint location was 2,230 mg/kg.  Quoted from EIA report of Hong Kong - Zhuhai - Macao Bridge Hong Kong Boundary Crossing Facilities, in section 9.8.4.11, an SOD of 15,000 mg/kg has been taken with reference to EPD Marine Monitoring data as a suitably representative value for sediments in the North-Western Waters region.  For conservative assessment, the SOD20 of 15,000 mg/kg was used in this EIA.

5.7.2.21   To elaborate the impact of suspended sediment on DO in water is not an instantaneous process.  Previous studies have assumed that the effect depends on tidally averaged suspended sediment concentrations.  However, in this study, the worst-case scenario was identified by using an increase in suspended sediment as the basis for the calculation.  To ensure that oxidation rates are not underestimated, the daily uptake factor, K, in the equation was set to 1.0, as was done in previous HZMB EIA studies (EIAO Register Nos.: AEIAR-145/2009, AEIAR-144/2009).  This represents instantaneous oxidation of the sediment oxygen demand and is expected to result in a much larger calculated DO deficit than what would be experienced.

5.7.2.22   To determine the ambient DO concentrations in the affected waters, the DO monitoring data from EPD monitoring stations WM4/NM1/VM12/VM14 in the WCZ were analysed.   EPD marine DO data in sea surface, mid-depth and the bottom were collected and analysis.  The sampling in wet season was taken from April until the end of September in each year. The 10 percentiles for each station in the recent 10 years from 2014 to 2023 are summarised as ambient DO concentrations as shown in Table 5.23. The corresponding ambient DO concentration for the modelling observation points is shown in Table 5.24.   Analysis of EPD monitoring data reveals that during the wet season, 10th percentile of the depth-averaged values at certain stations are relatively lower than dry season, which are below 4 mg/L.   For example, the 10th percentile value at NM1 is 3.37 mg/L, and at WM4, it is 3.23 mg/L.

5.7.2.23   In Table 5.25, the predicted DO depletion at all the observation points is presented under the dredging activities scenario.  The increase in SS level due to dredging activities results in a minimal DO depletion.  Taking the maximum SS increment at WM4 into account, the associated depletion value ranges only from 0.05 to 0.07 mg/L. The resultant DO concentration is calculated in Table 5.26.  According to the predicted results, at most of the WSR locations, even without any mitigation measures such as a silt curtain, the resulting DO concentrations are expected to be higher than the water quality objective of 4 mg/L for the depth-averaged DO WQO, and 2mg/L for the bottom layer DO WQO.   The instances of exceeding standards at some locations were observed, as indicated in Table 5.24, are attributed to relatively low baseline values during the wet season at those specific locations.  Furthermore, dredging activities are predicted to have a negligible impact on nearby sensitive receivers, including the closest bathing beaches (e.g., Ma Wan Tung Wan Bathing Beach), FCZs (such as the adjacent Ma Wan FCZ), and intertidal/subtidal habitats (e.g., the corals at To Kau Wan). For instance, the estimated DO depletion at the nearest coral community at To Kau Wan is only between 0.0006 and 0.0038 mg/L, while at the closest Ma Wan Tung Wan Bathing Beach, it ranges from 0.0028 to 0.0045 mg/L – both representing very minimal changes.

5.7.2.24   In the reclamation filling activities scenario, due to the relatively higher SS release load compared to the dredging scenario, short-duration SS exceedances are observed at monitoring point WM4.  Consequently, this leads to DO depletion ranging between 0.052 to 0.070 mg/L (Table 5.27).  This range of DO depletion is relatively consistent with that predicted for the dredging scenario.  Furthermore, the reclamation filling activities are predicted to have a negligible impact on the nearby FCZ.  For example, the estimated DO depletion at the nearest coral community at To Kau Wan is between 0.0015 and 0.0035 mg/L.

5.7.2.25   Overall, the DO depletion induced by both dredging and reclamation filling is very minimal.  Instances of exceeding standards at certain locations can be attributed to the relatively low baseline values during the wet season at those specific locations.

Table 5.23    10th Percentile DO Concentration from EPD Routine Monitoring Programme (2014-2023)

Station

10th Percentile Dissolved Oxygen Concentrations (mg/L)

Surface

Middle

Bottom

Depth Averaged

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

Dry Season

Wet Season

WM4

4.70

4.22

5.10

2.98

5.10

2.50

4.97

3.23

NM1

4.91

4.40

5.21

3.20

5.21

2.50

5.11

3.37

VM12

4.54

4.13

4.52

3.70

4.70

3.13

4.59

3.65

VM14

4.23

4.06

4.50

3.60

4.90

3.43

4.54

3.70

Notes: 

(1). 10 percentiles derived from the recent 10 years (2014 to 2023) EPD data.

(2). 10 percentiles DO values in bold and underlined indicates non-compliance with WQOs.

 

Table 5.24    Corresponding Ambient DO Concentration (mg/L) for The Modelling Observation Points

Location

Nearest

EPD’s Stations

Ambient DO Concentration (mg/L)

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG2

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

H1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

SG1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR2

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

C1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG1

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

WM4

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C4

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

B2

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

SA2

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

C3

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM12

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM14

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

F1

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B1

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B4

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B5

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B7

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B8

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

NM1

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

WSD2

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

WSD3

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

TS1

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

B3

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B6

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C2

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

SA1

WM4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

Notes:  (1) S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

(2) 10 percentiles DO values in bold and underlined indicates non-compliance with WQOs

 

Table 5.25    Predicted DO Depletion (mg/L) under Dredging Activities (Run C1a – With Project and Concurrent Projects, Unmitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR1

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG1

0.00

0.01

0.01

0.01

0.00

0.01

0.01

0.01

WM4

0.01

0.01

0.01

0.01

0.00

0.02

0.02

0.01

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B2

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

SA2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM14

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

F1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B5

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B7

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B8

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

NM1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TS1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B6

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SA1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Notes:  S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

 

 

Table 5.26    Predicted Resultant DO Depletion (mg/L) under Dredging Activities (Run C1a – With Project and Concurrent Projects, Unmitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

H1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

SG1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

C1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR1

4.90

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG1

4.70

5.09

5.09

4.96

4.22

2.97

2.49

3.22

WM4

4.69

5.09

5.09

4.96

4.22

2.96

2.48

3.22

C4

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

B2

4.70

5.10

5.10

4.96

4.22

2.98

2.49

3.23

SA2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

C3

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

F1

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B1

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B5

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B7

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B8

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.36

WSD2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

WSD3

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

TS1

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

B3

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B6

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

SA1

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

Notes: 

(1).S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

(2).10 percentiles DO values in bold and underlined indicates non-compliance with WQOs.

 

Table 5.27    Predicted DO Depletion (mg/L) under Reclamation Filling Activities (Run C1b – With Project and Concurrent Projects, Unmitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C1

0.00

0.01

0.01

0.01

0.00

0.00

0.01

0.00

CR1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG1

0.00

0.01

0.01

0.01

0.00

0.01

0.01

0.01

WM4

0.04

0.05

0.07

0.05

0.01

0.12

0.07

0.07

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B2

0.01

0.01

0.01

0.01

0.00

0.01

0.02

0.01

SA2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM14

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

F1

0.00

0.01

0.01

0.01

0.00

0.00

0.01

0.00

B1

0.00

0.01

0.01

0.00

0.00

0.00

0.00

0.00

B4

0.00

0.00

0.01

0.00

0.00

0.00

0.00

0.00

B5

0.00

0.00

0.01

0.00

0.00

0.00

0.01

0.00

B7

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B8

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

NM1

0.01

0.01

0.01

0.01

0.00

0.01

0.01

0.01

WSD2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TS1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B3

0.00

0.01

0.01

0.01

0.00

0.01

0.01

0.01

B6

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SA1

0.00

0.01

0.01

0.01

0.00

0.00

0.01

0.00

Notes:  S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

 

Table 5.28    Predicted Resultant Dissolved Oxygen Depletion (mg/L) under Reclamation Filling Activities (Run C1b – With Project and Concurrent Projects, Unmitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

H1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

SG1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

C1

4.91

5.20

5.20

5.10

4.40

3.20

2.49

3.36

CR1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG1

4.70

5.09

5.09

4.96

4.22

2.97

2.49

3.23

WM4

4.66

5.05

5.03

4.91

4.21

2.86

2.43

3.16

C4

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

B2

4.69

5.09

5.09

4.96

4.22

2.97

2.48

3.22

SA2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

C3

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

F1

4.70

5.09

5.09

4.96

4.22

2.98

2.49

3.23

B1

4.70

5.09

5.09

4.96

4.22

2.98

2.50

3.23

B4

4.70

5.10

5.09

4.96

4.22

2.98

2.50

3.23

B5

4.70

5.10

5.09

4.96

4.22

2.98

2.49

3.23

B7

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B8

4.69

5.09

5.09

4.95

4.21

2.97

2.49

3.22

NM1

4.90

5.20

5.20

5.10

4.40

3.19

2.49

3.36

WSD2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

WSD3

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

TS1

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

B3

4.70

5.09

5.09

4.96

4.22

2.97

2.49

3.23

B6

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

SA1

4.70

5.09

5.09

4.96

4.22

2.98

2.49

3.23

Notes: 

(1).S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

(2).10 percentiles DO values in bold and underlined indicates non-compliance with WQOs.

 

Contaminant Release from Elutriate/Porewater Testing

5.7.2.26   The potential consequences of releasing contaminants into the marine water during the construction phase, including DCM in reclamation and dredging activities were thoroughly investigated. To estimate the quantity of contaminants potentially discharged into the water column, laboratory tests were conducted on elutriate and porewater samples, as detailed in the Sediment Sampling and Testing Plan (SSTP) found in Chapter 6.  The testing conducted at the proposed reclamation site focused on the following parameters:

·       Heavy metals and metalloid including cadmium, chromium, copper, mercury, nickel, lead, zinc, silver and arsenic;

·       Organic micro-pollutants including PCB, PAH, Organichlorine Pesticides (OC); and

·       Inorganic non-metallic pollutants including nitrogen and phosphorous.

 

5.7.2.27   For elutriate and porewater testing, marine water samples were collected alongside grab samples and vibrocore/borehole samples from the following five locations:

·       VC-40a;

·       VC-41;

·       VC-42; 

·       VC-43; and

·       VC-44

5.7.2.28   The summary of testing results in Appendix 5.5 were checked against the criteria set in Table 5.4.  The concentrations of heavy metals and organic compounds in the elutriate and porewater tests at the five locations generally remained below the prescribed limits. However, certain locations exhibited slight elevated levels of arsenic, copper, and zinc, necessitating further assessment. The testing results in Appendix 5.5 highlighted those specific parameters, including arsenic, copper, zinc, TBT, PAHs, PCBs, TIN, and un-ionized ammonia (UIA), require additional assessment to confirm compliance at the WSRs.

5.7.2.29   The Appendix 5.7 provides the detailed assessment of contaminant release from elutriate/porewater testing. The dilution factor from the four reclamation sites to each WSR can be calculated using the following equation.

A math equations and formulas AI-generated content may be incorrect.

5.7.2.30   This equation calculates the concentration along the centreline of a plume through solving an advection-diffusion equation for a continuous line source, which is appropriate for calculating the concentrations of contaminant release for the dredging works. This is because the equation assumes a continuous line source of sediment, which is an appropriate approximation of the sediment lost to suspension during grab dredging. It is appropriate for areas where the tidal current is uni-directional for each phase of the tidal cycle (i.e. the ebb and flood phases). The similar approach has been adopted in the approved EIA studies including Route 11 (Section between Yuen Long and North Lantau), Tung Chung New Town Extension, Hong Kong – Zhuhai – Macao Bridge Hong Kong Boundary Crossing Facilities, and Cycle Track between Tsuen Wan and Tuen Mun (Tuen Mun to So Kwun Wat). The dilution factor is estimated by assuming the radius of initial release as 10m. The calculation of sediment contaminant release would only be applied to the nearby WSRs.

5.7.2.31   Based on the summarized elutriate and porewater test results for the five sampling points presented in Appendix 5.5 and Appendix 5.7, the net contaminant release for each parameter was calculated using a weighted average method. This calculation considered the maximum filling rates from the four reclamation zones — Tsing Yi Tower, Ma Wan South Tower, Ma Wan South Anchorage, and Kap Shui Mun Tower — and the corresponding maximum net increases in contaminant concentrations derived from elutriate and porewater testing at the nearest sampling stations for each area.

5.7.2.32   Subsequently, the contaminant concentrations at each WSR location were calculated based on the dilution factors determined earlier. The estimated contaminant concentrations derived from both elutriate and porewater testing are summarised in Appendix 5.7. The results indicate that the predicted contaminant concentrations comply with the applicable environmental criteria at both ecological and recreational receptor points. The dispersion and transformation processes in the receiving environment contribute to the reduction of contaminant levels, ensuring compliance with water quality requirements. According to Item f of Section S1.3.2, Annex 6 of the Technical Memorandum on Environmental Impact Assessment Process, for Total Inorganic Nitrogen (TIN), which is set to prevent undesirable algal bloom, as the level is heavily influenced by the background seasonal estuarine input, the criteria should be assessed such that the discharge will not cause any further deterioration by more than 30% of the annual average levels, if their existing levels have exceeded or are close to the established WQO. In this project, even without applying the 30% allowance, the predicted TIN concentrations remain below the 0.4 mg/L criterion, and therefore still meet the WQO. The assessment results in Appendix 5.7 show that concentrations of all contaminants at WSRs comply with the relevant criteria. This indicates that the water quality impact induced from the Project’s construction phase is insignificant, thus no adverse water quality impacts is anticipated.

5.7.2.33     The NH3 level was determined using the observed Total Ammonia as N, ambient temperature and salinity.  The calculation method could be referred to the following reference: i) Bower C.E. and Bidwell J.P. (1978), Ionisation of ammonia in seawater:  Effect of temperature, pH and salinity. J. Fish. Res. Board Can. Vol.35, pp.1012-1016; and ii) K., Russo R.C. & et. al. (1975), Aqueous ammonia equilibrium calculations: effect of pH and temperature. J. Fish. Res. Board Can. Vol.32, pp.2379-2383. According to the assessment result in Appendix 5.7, the Un-ionise Ammonia at each WSR are below the 0.021mg/L criterion, and therefore fulfill the WQO requirements.

A math equations and numbers AI-generated content may be incorrect.

5.7.2.34   Based on the assessment results, adverse impacts on water quality due to contaminants released from disturbed sediments during construction activities are not anticipated.

Wastewater / Sewage Effluent from The Construction Activities and Workforce and The Accidental Chemical Spillage into The Marine Environment

5.7.2.35   During the construction phase, an increase in marine traffic for the transportation of construction materials is anticipated, which may impact marine water quality. The potential impacts include sewage generated by the construction workforce and accidental spillage of chemicals or chemical waste into the marine environment. These potential impacts can be readily controlled; sewage will be managed by providing adequate sanitary facilities such as portable chemical toilets on vessels, and the storage and disposal of chemical waste will follow the guidelines stipulated in the Waste Disposal (Chemical Waste) (General) Regulations. Besides these operational concerns, the overflow of filling materials from barges or hoppers can also cause water pollution during loading or transportation. This potential water quality impact can be minimised through good management practices. Specifically, measures such as carefully limiting the loading capacity of barges will be implemented to avoid the overflow of fill material. With these practices for both operational waste and material handling in place, adverse water quality impacts from the increase in marine traffic are not anticipated.

Pile-Supported Vessels Impact Protection System (VIPS) at Lantau Deflection Pier

5.7.2.36   To meet the location of deflection pier at North Lantau, VIPS is proposed to be adopted in the area of existing shoreline.  The VIPS structure will be supported by piles with a superstructure and hanger slab to protect the piles from vessel impact, thus reclamation is no longer required at North Lantau.  The VIPS structure will be supported by piles with a reinforced concrete superstructure and hanger slab to protect the piles from vessel impact. This sea-based logistical approach eliminates the need for extensive shoreline construction sites, material stockpiling on land, or heavy vehicle traffic along coastal roads. Consequently, the VIPS construction is self-contained offshore, with its only potential land interface being a small, temporary area for logistical support. This method avoids significant land-based activities such as excavation or land reclamation, thereby preserving the integrity of the existing coastline while still providing the necessary protection for the pier.

5.7.2.37   The construction of the pier will not involve open sea dredging of the seabed. It will primarily employ in-situ bored pile foundations founded on bedrock or the seabed.  As detailed in Chapter 2.6, during construction, the piling equipment will be set up on a barge after installing a silt curtain.  Subsequently, pile construction will take place by placing a steel pile casing at the pier site, with seawater trapped inside the casing.  A funnel will be utilised at the top of the pile casing during excavation.  This construction method, creating a confined environment for excavation, minimises the release of contaminants into the water column, thereby reducing the risk of disturbance to the seabed and the adjacent marine environment.

5.7.2.38   Based on Chapter 2 - Project Description, VIPS at the Lantau Deflection Pier has some piles located in seawater. Based on the rate of constructing a pile (i.e. 5m/day) and the pile diameter (i.e. 2m), the sediment volume generation is calculated to be . To quantify the rate of sediment loss into the water column, relevant study reports were reviewed: i) Contaminated Spoil Management Study (MacDonald, 1991); ii) EIA: Dredging an Area of Kellett Bank for Reprovisioning of Six Government Mooring Buoys - Working Paper on Design Scenarios (ERM,1997); and iii) EIA: Hong Kong – Zhuhai – Macao Bridge Hong Kong Boundary Crossing Facilities (2009).  The reports indicated that sediment loss is at a rate of 20~25 kg/m3 for areas with significant amounts of debris on the seabed, and of 12~18 kg/m3 for areas where debris is less likely to hinder the operations.  For conservative assessment purpose, the highest sediment loss rate 25 kg/m3 is adopted.  Consequently, the sediment release rate into the water column was estimated to be  without mitigation measures.

5.7.2.39   Compared to the sediment loss rate estimates for reclamation in Section 5.7.2.15, the SS release is estimated to be 34.38 tonnes/day for the Tsing Yi Tower (Q4 2028 to Q1 2029), 67.66 tonnes/day for the Ma Wan South Tower (Q4 2028), and 32.60 tonnes/day for the Ma Wan South Anchorage (Q4 2028). In contrast, the sediment loss rate caused by VIPS is a maximum of only 0.39 tonnes/day, which is significantly lower than the values caused by reclamation. It should also be noted that the above VIPS SS release estimation adopts a highly conservative approach, without considering any confined environment as described in Section 5.7.2.36.

5.7.2.40   Excavation of soil and rock socket will be carried out using a mechanical grab and reverse circulation drill, respectively.  Steel reinforcement will be installed, fixed with a permanent casing for concreting.  The pile cap above high-tide level will be installed through the construction of a cofferdam, utilising permanent precast panels. Seawater trapped inside the cofferdam will be pumped out, creating a dry working environment throughout the construction process.

5.7.3           Operational Phase

Potential Changes in Hydrodynamic Regime

5.7.3.1      The hydrodynamic simulations comparing scenarios with and without reclamation are presented in Table 5.29, Table 5.30 and detailed in Appendix 5.4.  This study conducted a thorough analysis of water level, salinity, and current speed at three specified locations and five cross-sections near the reclamation area, both before and after the proposed reclamation activities.  The focus of the cross-sectional results was primarily on evaluating changes in tidal flow at the main water passage sections in the area following the implementation of the reclamation project, characterised by both instantaneous and cumulative flow rates.  Three observation points were placed in the adjacent waters of the reclamation area to assess variations in seawater flow before and after project implementation.

5.7.3.2      The findings indicate that the proposed reclamation area had a negligible impact on local hydrodynamics, with only minor alterations observed in water level, flow velocity, and salinity.  As shown in Table 5.29, the overall changes in water level are minimal, with a normalised NRMSE below 0.5%.  The NRMSE for salinity and velocity is below 5%. The NRMSE percentages for momentary flow are consistently below 1.1% at all observation cross-sections.  The comparative analysis of flow rates reveals that the flow remains stable at both cross-sections before and after the proposed reclamation, with no significant differences observed between the two scenarios.

5.7.3.3      As presented in Table 5.30 and Appendix 5.4, a comparison of ebb and flood tidal flow volumes was conducted for the key channels under both “without project” and “with project” scenarios, covering both dry and wet seasons. For the dry season, the relative differences in ebb and flood tidal flow volumes across channels such as ADCP YAM O WAN – TLK, MA WAN CHANNEL 1, and others are very small — mostly within a fraction of a percent (-1.36% to 0.45%). Similarly, during the wet season, minimal relative differences (-1.58% to 0.33%) were observed for these same channels. Overall, the Project is predicted to result in insignificant changes to the ebb and flood tidal flow volumes at all concerned channels. The relative differences across all channels and seasons range from approximately –1.58% to +0.45%, indicating that the impact on tidal flow characteristics is insignificant. This level of change confirms that the Project's influence on the hydrodynamic regime is insignificant when compared to the baseline "without project" conditions and does not alter the overall tidal behaviour in the study area.

5.7.3.4      The results affirm that the proposed reclamation activities have a negligible impact on the local hydrodynamic regime.  Although there is a slight alteration in tidal flow direction in the vicinity of the reclaimed area due to localised land reclamation projects, it is insufficient to disrupt the water dynamics characteristics in the region. This minor change in current direction is attributed to the localised nature of the reclamation and the overall stability of the hydrodynamic conditions in the area.  Given the minimal change in average velocity, there is no anticipation of a significant impact on flushing capacity.  The projected operational impacts of the Project suggest no noteworthy alterations in flow regime and water quality.  Consequently, no adverse hydrodynamic, no additional pollution source and water quality impacts are expected during the operational phase, and no mitigation measures, such as maintenance dredging, are deemed necessary.

 

 

Table 5.29    Hydrodynamic Modelling Comparison between the With and Without Project Scenarios

Locations

Season

Water Level

Surface Salinity

Bottom Salinity

Depth-average Current Speed

Momentary Flow

RMSE

NRMSE (%)

RMSE

NRMSE (%)

RMSE

NRMSE (%)

Magnitude Without Project (m/s)

Magnitude With Project (m/s)

RMSE

NRMSE (%)

RMSE

NRMSE (%)

 

F5

Dry

0.005

0.25%

0.044

3.06%

0.033

2.51%

0.066

0.065

0.11

3.26%

 

Wet

0.004

0.18%

0.148

1.59%

0.110

1.04%

0.091

0.093

0.37

1.69%

 

KTD_G2

Dry

0.004

0.23%

0.031

2.71%

0.022

2.74%

0.152

0.151

0.08

2.89%

 

Wet

0.005

0.23%

0.130

1.58%

0.193

2.14%

0.196

0.195

0.33

1.68%

 

B14

Dry

0.005

0.29%

0.020

2.74%

0.020

2.73%

0.004

0.004

0.03

2.32%

 

Wet

0.007

0.35%

0.432

3.84%

0.391

4.46%

0.005

0.005

1.08

4.09%

 

ADCP Yam O Wan - TLK

Dry

 

 

118.0

0.13%

 

Wet

176.3

0.17%

 

Ma Wan Channel 1

Dry

118.0

0.13%

 

Wet

168.4

0.16%

 

Ma Wan Channel 2

Dry

255.2

0.36%

 

Wet

326.0

0.43%

 

Kap Shui Mun

Dry

149.1

0.69%

 

Wet

250.7

1.10%

 

Rambler Channel

Dry

79.5

0.29%

 

Wet

77.8

0.58%

 

Note: the definition of RMSE and NRMSE were presented in Section 5.6.3.26.

 

 

Table 5.30    Comparison of Ebb/Flood Tidal Flow Volume at Concerned Channels

Cross-section

Tidal Flow Type

Without project (m3)

With project (m3)

Difference (m3)

Relative Difference (%)

Dry Season

ADCP YAM O WAN-TLK

Ebb Tidal Flow

4.58E+10

4.58E+10

-2.95E+07

-0.06%

Flood Tidal Flow

-5.40E+10

-5.38E+10

2.51E+08

-0.46%

MA WAN CHANNEL 1

Ebb Tidal Flow

4.63E+10

4.62E+10

-2.93E+07

-0.06%

Flood Tidal Flow

-5.45E+10

-5.42E+10

2.51E+08

-0.46%

KAP SHUI MUN

Ebb Tidal Flow

1.10E+10

1.09E+10

-8.32E+07

-0.75%

Flood Tidal Flow

-1.39E+10

-1.39E+10

-6.21E+07

0.45%

MA WAN CHANNEL 2

Ebb Tidal Flow

3.38E+10

3.40E+10

1.41E+08

0.42%

Flood Tidal Flow

-4.01E+10

-3.96E+10

4.91E+08

-1.22%

RAMBLER CHANNEL

Ebb Tidal Flow

3.81E+09

3.76E+09

-5.19E+07

-1.36%

Flood Tidal Flow

-1.48E+09

-1.48E+09

8.01E+06

-0.54%

Wet Season

ADCP YAM O WAN-TLK

Ebb Tidal Flow

5.19E+10

5.18E+10

-1.03E+08

-0.20%

Flood Tidal Flow

-5.40E+10

-5.38E+10

2.29E+08

-0.42%

MA WAN CHANNEL 1

Ebb Tidal Flow

5.24E+10

5.23E+10

-1.03E+08

-0.20%

Flood Tidal Flow

-5.45E+10

-5.43E+10

2.28E+08

-0.42%

KAP SHUI MUN

Ebb Tidal Flow

1.21E+10

1.19E+10

-1.91E+08

-1.58%

Flood Tidal Flow

-1.28E+10

-1.28E+10

4.83E+07

-0.38%

MA WAN CHANNEL 2

Ebb Tidal Flow

3.84E+10

3.85E+10

1.28E+08

0.33%

Flood Tidal Flow

-4.20E+10

-4.16E+10

3.42E+08

-0.81%

RAMBLER CHANNEL

Ebb Tidal Flow

3.77E+09

3.71E+09

-5.78E+07

-1.53%

Flood Tidal Flow

-1.53E+09

-1.51E+09

1.51E+07

-0.99%

                      Note: the sign of the values under “Without project” and “With project” represents the flow direction and the corresponding positive flow direction can be referred to Appendix 5.4.

Surface Run-off

5.7.3.5      Surface run-off to be generated from the Project is known as non-point source pollution.  The additional paved roads will increase the quantity of surface run-off. Release of uncontrolled surface run-off would increase the suspended solids levels and turbidity as well as nutrients in the nearby waterbodies.  However, impacts upon water quality would be minimal provided that proper drainage system would be incorporated into the proposed works to receive surface run-off to the drainage system at the planning and design stages. 

5.7.3.6      It should be emphasised that there will be no direct wastewater discharge during the operational phase of the project. No sewage or process wastewater will be generated from the proposed road infrastructure, and therefore, no new pollution sources will be introduced during operation. It is anticipated that with proper implementation of BMPs as recommended in Section 5.8, no adverse water quality impact from non-point source surface run-off is expected.

5.8               Mitigation of Environmental Impacts

5.8.1           Construction Phase

Reclamation Works

5.8.1.1      Based on the reclamation method and work sequences discussed in Section 2 and Appendix 5.2, a silt curtain will be installed before any dredging and reclamation activities to minimise the impact of suspended solids on marine water.  The removal efficiency of a single floating silt curtain is assumed to be 45%, in accordance with the HZMB, TCNTE and New Contaminated Sediment Disposal Facility to the West Lamma EIA reports. To ensure environmental compliance, a Silt Curtain Deployment Plan will be submitted to the EPD for approval in advance of any construction, particularly marine reclamation works.

5.8.1.2      Based on the aforementioned simulations, the dredging scenario, even without implementing any mitigation measures, can maintain full compliance at all WSR locations.  Therefore, with the additional 45% reduction in SS release through the implementation of silt curtains, both the sediment plume and sedimentation rate values are further reduced (Table 5.31, Table 5.33 and Appendix 5.3).

5.8.1.3      In the scenario of reclamation filling activities, based on the previous assessment, short-duration exceedances are projected at the observation point WM4 location if no mitigation measures are implemented.  However, with the implementation of a silt curtain, no exceedance at WM4 will be anticipated.  All other WSR locations comply with WQOs. The sediment plume closes the reclamation works area is further reduced in extent compared to the scenario without mitigation measures (Table 5.32, Table 5.34 and Appendix 5.3). Section 5.7.2.22 highlights that EPD monitoring data indicate lower 10th percentile depth-averaged values at certain stations during the wet season, in comparison to the dry season. The model predictions (Table 5.35 to Table 5.38) suggest that DO depletion resulting from the Project activities would be minimal and temporary, particularly with the implementation of the silt curtain. Consequently, no significant water quality impacts are expected.

Table 5.31    Predicted Maximum Suspended Solids (mg/L) Elevations during Dredging Activities (Run C2a – With Project, Mitigated)

Location

Predicted Maximum Suspended Solids (mg/L) Elevations

 Suspended Solids Criteria (mg/L)

Compliance to Criteria (mg/L)

Dry Season

Wet Season

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.01

0.02

0.01

0.00

0.01

0.03

0.01

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR2

0.01

0.04

0.04

0.03

0.00

0.01

0.04

0.02

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

C1

0.07

0.08

0.08

0.08

0.01

0.06

0.08

0.05

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR1

0.20

0.14

0.08

0.14

0.01

0.02

0.03

0.02

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG1

0.12

0.35

0.36

0.28

0.08

0.41

0.43

0.31

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

WM4

0.37

0.40

0.47

0.41

0.13

0.59

0.76

0.50

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

B2

0.07

0.08

0.11

0.09

0.05

0.18

0.21

0.14

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

SA2

0.00

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

C3

0.01

0.01

0.01

0.01

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM12

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM14

0.01

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

F1

0.04

0.10

0.12

0.08

0.01

0.07

0.08

0.05

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B1

0.02

0.07

0.07

0.05

0.02

0.06

0.06

0.04

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B4

0.02

0.05

0.06

0.04

0.00

0.01

0.05

0.02

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B5

0.01

0.05

0.05

0.04

0.00

0.02

0.07

0.03

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B7

0.01

0.03

0.04

0.03

0.00

0.00

0.01

0.00

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B8

0.17

0.17

0.16

0.17

0.10

0.10

0.10

0.10

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

NM1

0.10

0.09

0.10

0.10

0.02

0.07

0.10

0.06

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

WSD2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

WSD3

0.01

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

TS1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

B3

0.05

0.09

0.10

0.08

0.00

0.10

0.13

0.08

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B6

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C2

0.00

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

SA1

0.02

0.06

0.08

0.05

0.00

0.03

0.08

0.04

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

Note: 

1.               S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

2.               Values in bold and underlined indicates non-compliance with WQOs.

3.               The working hours per day is assumed to be 12 hours.

 

 

 

 

 

 

 

 

 

Table 5.32    Predicted Maximum Suspended Solids (mg/L) Elevations during Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Location

Predicted Maximum Suspended Solids (mg/L) Elevations

 Suspended Solids Criteria (mg/L)

Compliance to Criteria (mg/L)

Dry Season

Wet Season

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.03

0.04

0.02

0.01

0.04

0.09

0.05

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.00

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.02

0.01

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR2

0.02

0.09

0.10

0.07

0.00

0.05

0.13

0.06

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

C1

0.11

0.22

0.22

0.19

0.02

0.15

0.25

0.14

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

CR1

0.12

0.14

0.12

0.13

0.01

0.05

0.10

0.06

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

MG1

0.09

0.25

0.24

0.19

0.09

0.39

0.39

0.29

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

WM4

1.34

1.95

2.40

1.90

0.52

3.45

2.63

2.20

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

B2

0.20

0.27

0.38

0.28

0.17

0.55

0.62

0.45

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

SA2

0.00

0.03

0.03

0.02

0.00

0.01

0.01

0.01

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

C3

0.03

0.04

0.04

0.04

0.00

0.00

0.00

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM12

0.02

0.01

0.00

0.01

0.00

0.00

0.01

0.00

3.24

3.78

4.44

3.82

3.30

3.51

5.61

4.14

Yes

VM14

0.03

0.05

0.05

0.04

0.00

0.00

0.01

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

F1

0.16

0.23

0.27

0.22

0.02

0.18

0.19

0.13

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B1

0.07

0.19

0.20

0.15

0.05

0.18

0.18

0.14

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B4

0.05

0.18

0.21

0.15

0.00

0.05

0.15

0.07

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B5

0.05

0.18

0.20

0.14

0.01

0.08

0.23

0.11

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B7

0.03

0.12

0.16

0.10

0.00

0.00

0.02

0.01

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B8

0.43

0.43

0.43

0.43

0.37

0.36

0.36

0.37

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

NM1

0.22

0.19

0.28

0.23

0.05

0.34

0.39

0.26

3.57

5.34

5.40

4.77

2.99

4.38

6.54

4.64

Yes

WSD2

0.00

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

WSD3

0.03

0.04

0.04

0.04

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

TS1

0.00

0.01

0.01

0.01

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

B3

0.17

0.32

0.35

0.28

0.01

0.32

0.46

0.26

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

B6

0.05

0.05

0.05

0.05

0.03

0.03

0.03

0.03

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

C2

0.01

0.02

0.02

0.02

0.00

0.00

0.00

0.00

2.90

3.51

3.90

3.44

2.70

2.77

3.21

2.89

Yes

SA1

0.07

0.21

0.27

0.18

0.01

0.12

0.28

0.14

2.91

3.60

5.10

3.87

2.77

3.48

4.80

3.68

Yes

Note: 

1.               S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

2.               Values in bold and underlined indicates non-compliance with WQOs.

3.               The working hours per day is assumed to be 12 hours.

 

 

Table 5.33    Predicted Maximum Sedimentation Rate (g/m2/day) during Dredging Activities (Run C2a – With Project, Mitigated)

WSR

Predicted Maximum Sedimentation Rates (g/m2/day)

Dry Season

Wet Season

WSD1

0.9

1.2

MG2

0.0

0.1

H1

0.0

0.1

SG1

0.2

0.4

CR2

1.7

1.6

C1

3.7

3.7

CR1

2.3

1.5

MG1

17.1

23.3

WM4

20.5

37.9

C4

0.1

0.0

B2

6.6

9.0

SA2

0.5

0.2

C3

0.6

0.0

VM12

0.1

0.1

VM14

0.6

0.1

F1

5.1

3.5

B1

3.4

2.8

B4

2.5

2.2

B5

2.5

3.5

B7

1.9

0.4

B8

0.0

0.5

NM1

4.4

4.6

WSD2

0.2

0.0

WSD3

0.6

0.0

TS1

0.1

0.0

B3

4.6

6.4

B6

0.4

0.0

C2

0.3

0.0

SA1

3.4

3.7

Notes: Values in bold and underlined indicate non-compliance with WQOs.

 

Table 5.34    Predicted Maximum Sedimentation Rate (g/m2/day) during Reclamation Filling Activities (Run C2b – With Project, Mitigated)

WSR

Predicted Maximum Sedimentation Rates (g/m2/day)

Dry Season

Wet Season

WSD1

1.6

3.9

MG2

0.0

0.1

H1

0.0

0.3

SG1

0.1

0.8

CR2

4.2

5.7

C1

10.0

11.7

CR1

4.9

4.7

MG1

12.9

19.1

WM4

105.8

132.7

C4

0.2

0.0

B2

24.7

26.8

SA2

1.4

0.6

C3

1.8

0.1

VM12

0.2

0.2

VM14

2.2

0.5

F1

11.8

8.6

B1

11.3

8.9

B4

9.1

7.2

B5

9.3

12.6

B7

7.1

1.4

B8

0.0

0.8

NM1

12.3

18.8

WSD2

0.7

0.1

WSD3

2.0

0.2

TS1

0.5

0.0

B3

15.0

21.8

B6

1.6

0.1

C2

1.0

0.2

SA1

12.4

13.6

Notes: Values in bold and underlined indicate non-compliance with WQOs.

 

Table 5.35    Predicted DO Depletion (mg/L) under Dredging Activities (Run C2a – With Project, Mitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG1

0.00

0.01

0.01

0.00

0.00

0.01

0.01

0.00

WM4

0.01

0.01

0.01

0.01

0.00

0.01

0.01

0.01

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SA2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM14

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

F1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B5

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B7

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B8

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

NM1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TS1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B6

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SA1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Notes:  S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

 

Table 5.36    Predicted Resultant DO Depletion (mg/L) under Dredging Activities (Run C2a – With Project, Mitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

H1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

SG1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

C1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG1

4.70

5.09

5.09

4.96

4.22

2.97

2.49

3.23

WM4

4.69

5.09

5.09

4.96

4.22

2.97

2.49

3.23

C4

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

B2

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

SA2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

C3

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

F1

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B1

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B4

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B5

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B7

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B8

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

NM1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

WSD2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

WSD3

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

TS1

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

B3

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B6

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

SA1

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

Notes: 

(1).S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

(2).10 percentiles DO values in bold and underlined indicates non-compliance with WQOs.

 

Table 5.37    Predicted DO Depletion (mg/L) under Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

H1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SG1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CR1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

MG1

0.00

0.00

0.00

0.00

0.00

0.01

0.01

0.00

WM4

0.02

0.03

0.04

0.03

0.01

0.05

0.04

0.03

C4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B2

0.00

0.00

0.01

0.00

0.00

0.01

0.01

0.01

SA2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

VM14

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

F1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B4

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B5

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B7

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B8

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

NM1

0.00

0.00

0.00

0.00

0.00

0.01

0.01

0.00

WSD2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

WSD3

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TS1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

B3

0.00

0.00

0.01

0.00

0.00

0.00

0.01

0.00

B6

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

C2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

SA1

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Notes:  S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

 

 

 

Table 5.38    Predicted Resultant Dissolved Oxygen Depletion (mg/L) under Reclamation Filling Activities (Run C2b – With Project, Mitigated)

Station

Dry Season

Wet Season

S

M

B

DA

S

M

B

DA

WSD1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

H1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

SG1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

CR2

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

C1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.36

CR1

4.91

5.21

5.21

5.11

4.40

3.20

2.50

3.37

MG1

4.70

5.10

5.10

4.96

4.22

2.97

2.49

3.23

WM4

4.68

5.07

5.06

4.94

4.21

2.93

2.46

3.20

C4

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

B2

4.70

5.10

5.09

4.96

4.22

2.97

2.49

3.23

SA2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

C3

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM12

4.54

4.52

4.70

4.59

4.13

3.70

3.13

3.65

VM14

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

F1

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B1

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B4

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B5

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

B7

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

B8

4.69

5.09

5.09

4.96

4.21

2.97

2.49

3.23

NM1

4.91

5.21

5.21

5.11

4.40

3.19

2.49

3.36

WSD2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

WSD3

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

TS1

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

B3

4.70

5.10

5.09

4.96

4.22

2.98

2.49

3.23

B6

4.70

5.10

5.10

4.97

4.22

2.98

2.50

3.23

C2

4.23

4.50

4.90

4.54

4.06

3.60

3.43

3.70

SA1

4.70

5.10

5.10

4.96

4.22

2.98

2.50

3.23

Notes: 

(1). S – Surface Layer, M – Middle Layer; B – Bottom Layer; DA – Depth Averaged.

(2).10 percentiles DO values in bold and underlined indicates non-compliance with WQOs.

Construction of Piles at Deflection Pier at North Lantau

5.8.1.4      Pile casing and watertight cofferdam should be installed at the pier site and seawater trapped inside the casing and cofferdam should be pumped out to generate a dry working environment prior to carrying out sediment excavation.  During dewatering of the cofferdam, appropriate desilting or sedimentation device should be provided on site for treatment before discharge.  The Contractor should ensure discharge water from the sedimentation tank meeting the WPCO / TM-DSS requirements before discharge.

5.8.1.5      To minimise any adverse water quality impact during the excavation of sediment, a funnel should be placed at the top of pile casing during excavation and silt curtains should be deployed to completely enclose the cofferdam and steel pile casing.  Silt curtains should be deployed prior to setting up piling equipment on barge, installation of cofferdam and pile casing.  Silt curtains should only be removed after completion of pile caps and piers.  The Contractor should be responsible for the design, installation and maintenance of the silt curtain to minimise the impacts on water quality.  The design and specification of the silt curtains should be submitted by the Contractor to the Service Manager for approval.  All vessels should be sized such that adequate clearance is maintained between vessels and the sea bed at all states of the tide to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash. 

Wastewater from General Construction Activities and Construction Site Run-off

5.8.1.6      Control of potential pollution of nearby water bodies during the construction phase of the Project should be achieved by measures to:

·         prevent or minimise the likelihood of pollutants (generated from construction activities) being in contact with rainfall or run-off; and

·         abate pollutants in the stormwater surface run-off prior to the discharge of surface run-off to the nearby water bodies.

5.8.1.7      These principal objectives should be achieved by implementation of the BMPs of mitigation measures in controlling water pollution.  The guidelines for handling and disposal of construction site discharges as detailed in the ProPECC PN 2/24 should be followed, where applicable.  All effluent discharged from the construction site should comply with the standards stipulated in the TM-DSS.  The following measures are recommended to protect water quality of the inland and coastal waters, and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts.

Construction Site Run-off

5.8.1.8      Surface run-off from construction sites should be discharged into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sedimentation basins.  Channels or earth bunds or sandbag barriers should be provided on site during construction works to properly direct stormwater to such silt removal facilities.  Perimeter channels should be provided on site boundaries where necessary to intercept storm run-off from outside the site so that it will not wash across the site.  Catchpits and perimeter channels should be constructed in advance of site formation works and earthworks.

5.8.1.9      Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly, at the onset of and after each rainstorm to prevent local flooding.  Any practical options for the diversion and re-alignment of drainage should comply with both engineering and environmental requirements in order to provide adequate hydraulic capacity of all drains.

5.8.1.10   Construction works should be programmed to minimise soil excavation works in rainy seasons (April to September).  If soil excavation cannot be avoided in these months or at any time of year when rainstorms are likely, for the purpose of preventing soil erosion, temporary exposed slope surfaces should be covered e.g., by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds.  Intercepting channels should be provided (e.g., along the crest / edge of excavation) to prevent storm run-off from washing across exposed soil surfaces.  Arrangements should always be in place in such a way that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm.

5.8.1.11   Earthworks final surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out immediately after the final surfaces are formed to prevent erosion caused by rainstorms.  Appropriate drainage like intercepting channels should be provided where necessary.

5.8.1.12   Measures should be taken to minimise the ingress of rainwater into trenches.  If excavation of trenches in wet seasons is necessary, they should be dug and backfilled in short sections.  Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.

5.8.1.13   Open stockpiles of construction materials (e.g., aggregates, sand and fill material) on sites should be covered with tarpaulin or similar fabric during rainstorms.  Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

5.8.1.14   Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris from getting into the drainage system, and to prevent storm run-off from getting into foul sewers.  Discharge of surface run-off into foul sewers must always be prevented in order not to unduly overload the foul sewerage system.

Boring and Drilling Water

5.8.1.15   Water used in ground boring and drilling for site investigation or rock / soil anchoring should as far as practicable be re-circulated after sedimentation.  When there is a need for final disposal, the wastewater should be discharged into storm drains via silt removal facilities.

Wheel Washing Water

5.8.1.16   All vehicles and plants should be cleaned before they leave a construction site to minimise the deposition of earth, mud, debris on roads.   A wheel washing bay should be provided at every site exit if practicable and wash water should have sand and silt settled out or removed before discharging into storm drains.  The section of construction road between the wheel washing bay and the public road should be paved to reduce soil track-out by vehicles and to prevent site run-off from entering public road drains.

Rubbish and Litter

5.8.1.17   Good site practices should be adopted to remove rubbish and litter from construction sites so as to prevent the rubbish and litter from spreading from the site area.  It is recommended to clean the construction sites on a regular basis.

Acid Cleaning, Etching and Pickling Wastewater

5.8.1.18   Acidic wastewater generated from acid cleaning, etching, pickling and similar activities should be neutralised to within the pH range of 6 to 10 before discharging into foul sewers.

Effluent Discharge

5.8.1.19   There is a need to apply to EPD for a discharge licence for discharge of effluent from the construction site under the WPCO.  The discharge quality must meet the requirements specified in the discharge licence.  All the run-off and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS.  The beneficial uses of the treated effluent for other on-site activities such as dust suppression sprays, wheel washing and general cleaning, etc., can minimise water consumption and reduce the effluent discharge volume.  If monitoring of the treated effluent quality from the works areas is required during the construction phase of the Project, the monitoring should be carried out in accordance with the relevant WPCO licence.

Construction Works Within and in Close Proximity to Inland Water

5.8.1.20   For construction of bridge piers within the drainage channel (modified watercourse), all pilling and excavation works should be fully enclosed by cofferdam / watertight steel casing.  Cofferdam and watertight steel casing should be constructed to isolate the construction activities from the river water.  The detailed design of the cofferdams and watertight steel casing will be conducted by the Contractor during the construction phase to fulfil the requirements in DSD Technical Circular No. 1/2017 “Temporary Flow Diversions and Temporary Works Affecting Capacity in Stormwater System” for DSD approval in order to formulate feasible options of these temporary structure.

5.8.1.21   Water pumps should be used to collect any construction site run-off and ingress/seepage water within the cofferdam and watertight steel casing.  The collected construction site surface run-off and ingress/seepage water should be diverted to the on-site wastewater treatment facilities for treatment to satisfactory levels before discharged.  There is a need to apply to EPD for a discharge licence for discharging effluent from the construction site under the WPCO.  The discharge quality must meet the requirements specified in the discharge licence and follow the TM-DSS.

5.8.1.22   The precautionary measures / practices outlined in ETWB TC (Works) No. 5/2005 "Protection of natural streams / rivers from adverse impacts arising from construction works" should also be adopted where applicable to minimise the water quality impacts on any natural streams or surface water systems.  Relevant precautionary measures / practices from the ETWB TC (Works) No. 5/2005 include but not limited to the following:

·         The use of less or smaller construction plants may be specified in areas close to the watercourses to reduce the disturbance to the surface water;

·         Construction works adjacent to watercourses should preferably be carried out during the dry season where flow in the stream/river is low;

·         Temporary storage of materials (e.g., equipment, chemicals and fuel) and temporary stockpile of construction materials should be located well away from any water courses when carrying out of the construction works;

·         Stockpiling of construction materials and dusty materials should be covered and located away from any watercourses;

·         Construction debris and spoil should be covered up and / or disposed of as soon as possible to avoid being washed into the nearby water receivers; and

·         Proper shoring may need to be erected in order to prevent soil or mud from slipping into the watercourses.

Sewage from Construction Workforce

5.8.1.23   No direct discharge of sewage to the stormwater drains and inland water will be allowed.  Adequate and sufficient portable chemical toilets should be provided in the works areas to handle sewage from construction workforce.  A licensed collector should be employed to clean and maintain the chemical toilets on a regular basis. Notices should be posted at conspicuous locations to remind the workers not to discharge any sewage or wastewater into the surrounding environment.  Regular environmental audit of the construction site should be conducted to provide an effective control of any malpractices and achieve continual improvement of environmental performance on site.

Accidental Spillage of Chemicals

5.8.1.24   Contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities.  The Waste Disposal Ordinance (Cap. 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation, should be observed and complied with for control of chemical wastes.  The Contractor is also recommended to develop management procedures for chemicals used and prepare an emergency spillage handling procedure to deal with chemical spillage in case of accident occurs.

5.8.1.25   Any service shop and maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be provided.  Maintenance of vehicles and equipment involving activities with potential for leakage and spillage should only be undertaken within the areas appropriately equipped to control these discharges.

5.8.1.26   Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance.  The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance details the requirements to deal with chemical wastes.  General requirements are given as follows:

·         Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport;

·         Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents; and

·         Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.

Wastewater / Sewage Effluent from The Construction Activities and Workforce and The Accidental Chemical Spillage into The Marine Environment

5.8.1.27   The potential impact associated with sewage generated by the workforce shall be controlled by the provision of adequate sanitary facilities such as portable chemical toilets on the marine vessels. The storage and disposal of chemical waste shall follow the guidelines stipulated in the Waste Disposal (Chemical Waste) (General) Regulations. Besides, overflow of filling materials in the barges or hoppers can cause water pollution during loading or transportation. Good management practice such as limiting the capacity of a barge to avoid overflow of filling material can minimise the potential water quality impact.

Tunnelling Works

5.8.1.28   During tunnelling operations, the Contractor shall adopt appropriate water control measures to the extent practicable, including the following:

·         Ahead Probing: The Contractor shall conduct rigorous ground probing ahead of the tunnel face to identify zones with potential for significant water inflow. Probe drilling results shall be evaluated to determine the need for pre-grouting along the tunnel alignment. In areas where discrete, permeable geological features could lead to substantial inflow, grouting should be implemented to reduce groundwater ingress.

·         Pre-grouting: In cases of excessive water inflow, pre-grouting shall be carried out to minimize inflow into the tunnel. This will be achieved through a systematic and carefully designed grouting protocol, based on site-specific conditions and probe drilling data.

·         Grout Treatment Design: As a general principle, pre-grouting design shall be informed by data obtained from probe holes drilled ahead of the tunnel face.

·         If works results in potential groundwater drawdown, it is crucial to ensure that the engineers/APs are informed of the issue and its potential water quality impact if not controlled. Due consideration should be made with reference to prevailing regulations, guidelines and standards (including but not limited to CEDD’s “General Specification for Civil Engineering Works – Part 5; GEO publications such as GEO Publication No.1/2023 and Geoguide 2, BD’s PNAPs such as PNAP No.APP-24, etc.) during site investigation and actual civil works on groundwater monitoring and control.

5.8.2           Operational Phase

Surface Run-off

5.8.2.1      The ProPECC PN 1/23 “Drainage Plans subject to Comment by the Environmental Protection Department” provides guidelines and practices for handling, treatment and disposal of various effluent discharges to stormwater drains and foul sewers.  The design of site drainage should follow the relevant guidelines and practices as given in the ProPECC PN 1/23. 

Design Measures

5.8.2.2      Exposed surface shall be avoided within the site to minimise soil erosion.  The site shall be either hard paved or covered by landscaping area and plantation where appropriate.

5.8.2.3      The drainage system within the site should be designed to cater for the run-off from 50 year-return-period rainstorm.

Devices / Facilities to Control Pollution

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

5.8.2.5      Road gullies with standard design and silt traps and oil interceptors should be incorporated during the detailed design to remove particles present in stormwater run-off.

Administrative Measures

5.8.2.6      BMPs for stormwater discharge and management, as well as good administrative and management measures for riparian public open spaces as detailed below are recommended for the Project to mitigate potential adverse water quality impacts.

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

5.8.2.8      Manholes, as well as stormwater 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 forecasting heavy rainfall.

5.9               Residual Water Quality Impacts

5.9.1           Construction Phase

5.9.1.1      The water quality impacts associated with the construction of the Project would be temporary and localised.  With proper implementation of the recommended mitigation measures, no unacceptable residual water quality impact would be anticipated during the construction phase.

5.9.2           Operational Phase

5.9.2.1      As outlined in Section 5.7.3, no adverse hydrodynamic and water quality impacts are anticipated during the operation of the Project. Consequently, there will be no adverse residual impacts associated with the Project's operation.

5.10            Environmental Monitoring and Audit Requirements

5.10.1        Construction Phase

5.10.1.1   The potential water quality impact from the proposed marine works can be effectively controlled through the implementation of recommended mitigation measures.  Nevertheless, it is essential to conduct regular site inspections and water quality monitoring during the construction phase to ensure the proper implementation of the recommended mitigation measures.  Detailed environmental monitoring procedures and audit requirements are provided in the standalone EM&A manual.

5.10.2        Operational Phase

5.10.2.1   As no adverse hydrodynamic and water quality impacts would be anticipated from the Project, no monitoring programme specific for operational phase of the Project would be required.

5.11            Conclusions

5.11.1        Construction Phase

5.11.1.1   During the construction phase, the sediment plume resulting from dredging is confined to the dredging area, and no exceedance is anticipated at any of the WSRs.  Simulation results indicate that even without implementing mitigation measures such as silt curtain, the relatively low sediment release load from dredging is unlikely to cause exceedances at nearby WSRs.

5.11.1.2   In the scenario involving reclamation filling activities relatively high sedimentation rate are projected at the observation point WM4 if no mitigation measures are implemented. With the deployment of silt curtains, the sediment plume is further reduced. Furthermore, transient DO depletion resulting from the Project activities would be minimal. Overall, no adverse water quality impacts are expected.”

5.11.1.3   The key issues of the land-based construction work include wastewater generated from general construction activities, construction site run-off, sewage from construction workforce, accidental spillage of chemicals and underground water impact during tunnelling works.  The potential water quality impacts could be mitigated and controlled by implementing the recommended mitigation measures.  Regular site inspections should be undertaken routinely to inspect the construction activities and works area to ensure that the recommended mitigation measures are proper implemented.

5.11.2        Operational Phase

5.11.2.1   Potential hydrodynamic changes resulting from the proposed reclamation have been identified and evaluated through a computational modelling approach.  The hydrodynamic modelling results indicate that the proposed Project would not significantly alter the local hydrodynamic regime.  Negligible differences were observed in water level, salinity, flow velocities, flow rates, and flow fields between the without and with Project scenarios.  The potential changes in hydrodynamic regime due to the Project can be considered insignificant.

 


[1]     New Contaminated Sediment Disposal Facility to the West of Lamma Island (EIAO Register No.: AEIAR-241/2022)

[2]     Route 11 (section between Yuen Long and North Lantau) (EIAO Register No.: AEIAR-255/2023)

[3]     Expansion of Hong Kong International Airport into a Three-Runway System (EIAO Register No.: AEIAR-185/2014)

[4]     EIA-183/2010, Providing Sufficient Water Depth for Kwai Tsing Container Basin and its Approach Channel.

[5]     EIA-120/2006, Hong Kong Convention and Exhibition Centre, Atrium Link Extension.

[6]     Ove Arup & Partners Hong Kong Ltd., Agreement No. CE14/2008 (HY) Hong Kong – Zhuhai – Macao Bridge Hong Kong Boundary Crossing Facilities, Environmental Impact Assessment Report prepared for Highways Department.

[7]     ERM , Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities, Environmental Impact Assessment Report prepared for CLP.

[8]     Mouchel. Permanent Aviation Fuel Facility (PAFF) – Environmental Impact Assessment Report prepared for Airport Authority- Hong Kong.

[9]     EIA Report, Expansion of Hong Kong International Airport into a Three-Runway System.

[10] Mouchel (2002a) Environmental Assessment Study for Backfilling of Marine Borrow Pits at North of The Brothers. Environmental Assessment Report.

[11] Mouchel (2002b) Permanent Aviation Fuel Facility. EIA Report. Environmental Permit EP-139/2002.

[12] BMT Asia Pacific Ltd (2009). EIA for Hong Kong Offshore Wind Farm in Southeastern Waters. For HK Offshore Wind Limited. Register No.: AEIAR-140/2009

[13] ERM (2016). Additional Gas-fired Generation Units Project. EIA Report. Environmental Permit EP-507/2016.

[14]       ERM (2018) EIA for Hong Kong Offshore LNG Terminal. Final EIA Report. For CLP.

[15]       Mott MacDonald (2010) EIA for Providing Sufficient Water Depth for Kwai Tsing Container Basin and its Approach Channel. Final EIA Report. For CEDD.

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

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