(Ref. 113-03)

 

TABLE OF CONTENTs

5.......... Water Quality Impacts. 5-1

5.1          Introduction. 5-1

5.2          Environmental Legislation, Policies, Plans, Standards and Criteria. 5-1

5.3          Water Sensitive Receivers for the Project 5-8

5.4          Water Sensitive Receivers for Sewage Pumping Stations (DP9) 5-16

5.5          Baseline Conditions – River Water Quality in Deep Bay WCZ. 5-16

5.6          Baseline Conditions – River Water Quality in North Western WCZ. 5-22

5.7          Baseline Conditions – Marine Water Quality in Deep Bay WCZ. 5-25

5.8          Baseline Conditions – Marine Water Quality in North Western Water 5-25

5.9          Assessment Approach and Methodology. 5-29

5.10        Identification and Evaluation of Environmental Impacts – Construction Phase. 5-29

5.11        Identification and Evaluation of Environmental Impacts – Operational Phase. 5-38

5.12        Cumulative Impacts from Concurrent Projects. 5-55

5.13        Mitigation Measures – Construction Phase. 5-56

5.14        Mitigation Measures – Operational Phase. 5-64

5.15        Evaluation of Residual Environmental Impacts. 5-68

5.16        EM&A Requirements. 5-69

5.17        Environmental Acceptability of Schedule 2 Designated Projects. 5-69

5.18        Conclusion. 5-70

 

 

APPENDICES

Appendix 5.1    Key Assumptions for Quantification of Construction Site Run-off

Appendix 5.2    Key Assumptions for Compiling Pollution Loading of Point Source Discharge to North Western WCZ

Appendix 5.3    Key Assumptions for Compiling Pollution Loading to Deep Bay WCZ from Unsewered Developments

Appendix 5.4    Key Assumptions for Compiling Non-Point Source Pollution from Surface Run-off

FIGURES

Figure 5.1         Key Water Bodies Within Study Area and Water Quality Monitoring Stations

Figure 5.2         Locations of Inland Water Bodies – Key Plan

Figure 5.2.1      Locations of Inland Water Bodies – Sheet 1 of 14

Figure 5.2.2      Locations of Inland Water Bodies – Sheet 2 of 14

Figure 5.2.3      Locations of Inland Water Bodies – Sheet 3 of 14

Figure 5.2.4      Locations of Inland Water Bodies – Sheet 4 of 14

Figure 5.2.5      Locations of Inland Water Bodies – Sheet 5 of 14

Figure 5.2.6      Locations of Inland Water Bodies – Sheet 6 of 14

Figure 5.2.7      Locations of Inland Water Bodies – Sheet 7 of 14

Figure 5.2.8      Locations of Inland Water Bodies – Sheet 8 of 14

Figure 5.2.9      Locations of Inland Water Bodies – Sheet 9 of 14

Figure 5.2.10    Locations of Inland Water Bodies – Sheet 10 of 14

Figure 5.2.11    Locations of Inland Water Bodies – Sheet 11 of 14

Figure 5.2.12    Locations of Inland Water Bodies – Sheet 12 of 14

Figure 5.2.13    Locations of Inland Water Bodies – Sheet 13 of 14

Figure 5.2.14    Locations of Inland Water Bodies – Sheet 14 of 14

Figure 5.3         Proposed Locations of Flood Retention Facilities

Figure 5.4         Indicative Locations of Marine Water Sensitive Receivers and Observation Points

Figure 5.5         Location of DP8 and DP9 in Relation to Water Bodies within Study Area and Indicative Emergency Bypass Alignment

Figure 5.6         Locations of Footbridges and Cycle Bridges

Figure 5.7         Locations of Foundations for the Proposed Viaduct of DP12

 

5                 Water Quality Impacts

5.1                   Introduction

5.1.1                This section presents an assessment of the potential water quality impacts associated with the construction and operation phases of the Hung Shui Kui New Development Area (HSK NDA) (herein referred to as the “Project”).  Recommendations for mitigation measures have been provided, where necessary, to minimise the identified water quality impacts to an acceptable level.

5.1.2                An application for an Environmental Permit (EP) would be submitted for the following Schedule 2 Designated Projects (DPs) (refer to Figure 1.3) and these DPs have been included in this water quality impact assessment during construction and operational phases:

·             Construction of new primary distributor road (Road P1) (DP1)

·             Construction of eight new distributor roads (Roads D1 to D8) (DP2)

·             Construction of slip roads between: Road D8 Junction and existing Castle Peak Road; Junction of D8/P1 and Junction of D7/P1; and KSWH connection to Road D3 (DP5)

·             Construction of partly depressed and partly decked-over roads located at Road D2, Road D4 and Road D6 (DP6)

·             Construction of four new SPSs (Sites 2-34, 3-41, 3-48 and 4-35) (DP9)

·             Construction of Road P1 and slip-road from KSWH to Road D3 partly located within the “CA” of Yuen Tau Shan (DP12)

 

5.2                   Environmental Legislation, Policies, Plans, Standards and Criteria

Environmental Impact Assessment Ordinance (EIAO)

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

·             Annex 6 – Criteria for Evaluating Water Pollution; and

·             Annex 14 – Guidelines for Assessment of Water Pollution.

Water Quality Objectives

5.2.2                The Water Pollution Control Ordinance (WPCO) provides the major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs). Corresponding statements of Water Quality Objectives (WQO) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZ based on their beneficial uses. The Project area is located within both Deep Bay and North Western WCZs. The boundaries of Deep Bay and North Western WCZs in relation to the Project area are shown on Figure 5.1 and Figure 5.4.  The water quality assessment area for the proposed Project shall cover Deep Bay and North Western WCZs and the corresponding WQOs are listed in Table 5.1 and Table 5.2 respectively. 


Table 5.1          Summary of Water Quality Objectives for Deep Bay WCZ

Parameters

Criteria

Subzone

Aesthetic appearance

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

Whole Zone

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

Whole Zone

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

Whole Zone

(d) There should be no recognisable sewage-derived debris.

Whole Zone

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

Whole Zone

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

Whole Zone

Bacteria

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

Secondary Contact Recreation Subzone and Mariculture Subzone (L.N. 455 of 1991)

(b) The level of Escherichia coli should be zero per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

(c) The level of Escherichia coli should not exceed 1000 per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

(d) The level of Escherichia 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. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days.

Yuen Long Bathing Beach Subzone (L.N. 455 of 1991)

Colour

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

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

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

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Dissolved oxygen (DO)

(a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.

Inner Marine Subzone excepting Mariculture Subzone

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

 

Outer Marine Subzone excepting Mariculture Subzone

(c) The dissolved oxygen level should not be less than 5 milligrams per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.

Mariculture Subzone

(d) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre.

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters of the Zone

pH

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

Marine waters excepting Yung Long Bathing Beach Subzone

(b) Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 units.

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

(c) The pH of the water should be within the range of 6.0-9.0 units.

Other inland waters

(d) The pH of the water should be within the range of 6.0-9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units.

Yung Long Bathing Beach Subzone

Temperature

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

Whole Zone

Salinity

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

Whole Zone

Suspended solids (SS)

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

Marine waters

(b) Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Ganges Subzone, Indus Subzone, Water Gathering Ground Subzones and other inland waters

Ammonia

The un-ionised ammoniacal nitrogen level should not be more than 0.021 milligram per litre, calculated as the annual average (arithmetic mean).

Whole Zone

Nutrients

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

Inner and Other Marine Subzone

(b) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.7 milligram per litre, expressed as annual mean.

Inner Marine Subzone

(c) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 milligram per litre, expressed as annual water column average (arithmetic mean of at least 2 measurements at 1 metre below surface and 1 metre above seabed).

 

Outer Marine Subzones

5-day biochemical oxygen demand (BOD)

(a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

(b) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Chemical oxygen demand (COD)

(a) Waste discharges shall not cause the chemical oxygen demand to exceed 15 milligrams per litre.

Yuen Long & Kam Tin (Upper)

Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

(b) Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Toxins

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

Whole Zone

(b) Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.

Whole Zone

Phenol

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

Yung Long Bathing Beach Subzone

Turbidity

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

Yung Long Bathing Beach Subzone

 

Table 5.2          Summary of Water Quality Objectives for North Western WCZ

Parameters

Criteria

Subzone

Aesthetic appearance

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

Whole Zone

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

Whole Zone

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

Whole Zone

(d) There should be no recognisable sewage-derived debris.

Whole Zone

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

Whole Zone

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

Whole Zone

Bacteria

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

Secondary Contact Recreation

Subzones

(b) The level of Escherichia 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

(c) The level of Escherichia coli should not exceed 1000 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

(d) The level of Escherichia 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

(a) 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

(b) 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)

(a) 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

(b) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre.

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

pH

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

Marine waters excepting Bathing Beach Subzones

(b) 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

(c) The pH of the water should be within the range of 6.0-9.0 units.

Other inland waters

(d) The pH of the water should be within the range of 6.0-9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units.

Bathing Beach Subzones

Temperature

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

Whole Zone

Salinity

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

Whole Zone

Suspended solids (SS)

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

Marine waters’

 

 

(b) Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.

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

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

Other inland waters

Ammonia

The un-ionised ammoniacal nitrogen level should not be more than 0.021 milligram per litre, calculated as the annual average (arithmetic mean).

Whole Zone

Nutrients

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

Marine waters

(b) 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

(c) 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 excepting Castle Peak Bay Subzone

5-day biochemical oxygen demand (BOD)

(a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.

 

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

(b) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.

Other inland waters

Chemical oxygen demand (COD)

(a) Waste discharges shall not cause the chemical oxygen demand to exceed 15 milligrams per litre.

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

(b) Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.

Other inland waters

Toxins

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

Whole Zone

(b) Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.

Whole Zone

Phenol

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

Bathing Beach Subzones

Turbidity

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

Bathing Beach Subzones

 

Technical Memorandum

5.2.3                Discharge of effluents are subject to control under the WPCO. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, stormwater drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluents. Any sewage from the proposed construction and operation activities must comply with the standards for effluents discharged into the foul sewers, inland waters and coastal waters of Deep Bay WCZ and North Western WCZ, as given in the TM-DSS.

Practice Note

5.2.4                A Professional Persons Environmental Consultative Committee Practice Note (ProPECC PN) was issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with 10 types of discharge from construction sites. These include surface run-off, groundwater, boring and drilling water, bentonite slurry, water for testing and sterilisation of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities. Practices given in the ProPECC PN 1/94 should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage.

5.2.5                The ProPECC PN 5/93 “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 drainage 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 5/93. 

Technical Circular

5.2.6                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.

5.2.7                For maintenance of stormwater drainage system during operational phase, reference should be made to ETWB TC (Works) No. 14/2004 “Maintenance of Stormwater Drainage Systems and Natural Watercourses” where applicable.  The circular sets out the departmental responsibilities for the maintenance of stormwater drainage systems and natural watercourses in government and private lands.

5.3                   Water Sensitive Receivers for the Project

Existing Inland Watercourses

5.3.1                Major existing watercourses identified within and near the Project area are summarised in Table 5.3 below and include:

·             Tin Shui Wai Main Channel and its tributaries (TSW);

·             Hang Hau Tsuen Channel and its tributaries (HTT);

·             Small watercourses along Deep Bay (DB);

·             Upstream / tributaries of Shan Pui River (SPR); and

·             Upstream / tributaries of Tuen Mun River (TMR).

5.3.2                The existing natural and modified watercourses are presented in Figure 9.1.  In addition to the watercourses presented in Figure 9.1, Figure 5.1 also presents the channelized drainage systems, storm drains, and seasonal or temporary streams observed only under heavy rainfall, in order to provide an overview of existing watercourses([1]). The zoom-in maps of these watercourses are provided in Figures 5.2, 5.2.1 to 5.2.14. 

Tin Shui Wai Main Channel and its Tributaries (TSW)

5.3.3                Tin Shui Wai (TSW) Main Channel and its tributaries are located in the Deep Bay WCZ and are a major fresh water system, which spreads across the majority of the Project area. This channel system generally runs from south to north and eventually enters the marine water at inner Deep Bay. This fresh water system consists of a core channel along the north-eastern Project boundary (namely TSW Main Channel) and three key tributaries (namely Lo Uk Tsuen tributaries, Hung Shiu Kiu Main Street Channel and Tin Sam Channel respectively) as described in Table 5.3 below and also shown in Figure 5.1.

5.3.4                The TSW Main Channel and majority of its key tributary streams would be retained during the operational phase.  Revitalisation and greening of some sections including TSW Main Channel, HSK Channel and Tin Sam Channel are proposed (details refer to Section 5.10.14).  Several minor water sections of this fresh water system will be removed under the Project and their water flow would be diverted to the new covered drainage network within the new development area as summarised in Table 5.3 below.  These minor sections include four small watercourses that drain into Tin Sam Channel (namely TSW1A, TSW1B, TSW1C and TSW1D as shown in Figure 5.2.9), 4 minor watercourses near TSW Main Channel (namely TSW2, TSW2A, TSW2B as shown in Figure 5.2.7 and TSW5 as shown in Figures 5.2.12 and 5.2.13) as well as a small section of Lo Uk Tsuen tributaries (namely TSW3 as shown in Figure 5.2.8).  In addition, a small section (namely TSW4) of Tin Sam Channel will be realigned under this Project as indicated in Figure 5.2.9.

Hang Hau Tsuen Channel and its Tributaries (HTT)

5.3.5                Hang Hau Tsuen Channel and its tributaries are comparatively smaller river system found at the northern tip of the Project area as shown in Figure 5.1. This fresh water system is also located in the Deep Bay WCZ and it generally runs from south to north and finally enters the marine water at inner Deep Bay.

5.3.6                The main stream of Hang Hau Tsuen Channel will be retained during the operational phase. A side branch (namely HHT1) of Hang Hau Channel as shown in Figure 5.2.1 and the most upstream part (namely HHT2) of Hang Hau Tsuen Channel as shown in Figure 5.2.7 will be removed under the Project.  The water flow of these two affected sections would be diverted to the new covered drainage system within the Project.

Table 5.3          Summary of Major Watercourses at or Near the Project Area

ID (See Figure 5.1)

Existing Fresh Water System

Description

Water Sections to be Removed or Realigned

General

Major Sub-sections of the Fresh Water System

Figure Reference

(Fig. Ref.)

Name

Description

Fig. Ref.

Name

Description

Watercourses Discharging to Deep Bay WCZ

TSW

TSW Main Channel and its tributaries

A large fresh water system, which spreads across the majority of the Project area and generally runs from south to north and finally enters the marine water of Deep Bay WCZ

TSW Main Channel

Core channel of the fresh water system, which generally runs along the north-eastern boundary of the Project area from south to north and eventually joins the marine water of Deep Bay WCZ in the north.

Overview:  Figure 5.1

Close up maps: Figure 5.2.6, Figure 5.2.7 (see upper right) and Figure 5.2.11 (see bottom left)

N/A - The whole section of the Tin Shui Wan Main Channel will be retained under the Project

Lo Uk Tsuen tributaries

Upstream tributaries of the fresh water system, which generally run across the middle portion of the Project area from west to east and eventually enters the TSW Main Channel; Some small watercourses (originate from the hill side in the west) also enter these Lo Uk Tsuen tributaries.

Overview: Figure 5.1

Close up maps: Figure 5.2.7 (see bottom right) and Figure 5.2.8 (see upper part)

TSW3

A small upstream section of Lo Uk Tsuen Tributaries to be removed under the Project

Figure 5.2.8

Hung Shiu Kiu (HSK) Main Street Channel

An upstream tributary of the fresh water system, which originates from a water channel near Wo Ping San Tsuen in the south and then runs towards the north and eventually enters the TSW Main Channel

Overview: Figure 5.1

Close up maps: Figure 5.2.8 (see bottom right) and Figure 5.2.9 (see right hand side)

N/A -The whole section of HSK Main Street Channel will be retained under the Project

Tin Sam Channel tributaries

Upstream tributaries of the fresh water system, which originates from a watercourse in the south and then runs near Tin Sam towards the north and eventually joins the HSK Main Street Channel.  Some small watercourses (originate from the hillside in the west) also run across the Project area towards the east and then enter Tin Sam Channel

Overview: Figure 5.1

Close up maps: Figure 5.2.4, Figure 5.2.8 (see bottom right) and Figure 5.2.9 (see left hand side)

TSW1A,

TSW1B,

TSW1C, TSW1D

4 minor sections that finally drain into Tin Sam Channel to be removed under the Project

Figure 5.2.9

TSW4

A section of Tin Sam Channel to be realigned under the Project

Figure 5.2.9

Others small tributaries

Small watercourses near Tin Wah Road in the northern Project area, which finally discharge to the TSW Main Channel

Figure 5.2.7 (see upper right)

TSW2, TSW2A, TSW2B

Minor watercourses near Tin Wah Road to be removed under the Project

Figure 5.2.7 (see upper right)

Small watercourse near Hung Uk Tsuen in the eastern portion of the Project area, which finally discharges to the TSW Main Channel

Figure 5.2.12, Figure 5.2.13

TSW5

A water section (west of Hung Uk Tsuen) to be removed under the Project

Figures 5.2.12, 5.2.13

HHT

Hang Hau Tsuen Channel and its tributaries

A relatively small stormwater system at the northern tip of the Project area, which generally runs from south to north and finally discharges to the marine water of Deep Bay WCZ.

Overview: Figure 5.1

Close up maps: Figure 5.2.1 and Figure 5.2.7 (see upper middle)

HHT1

A side branch of the Channel to be removed

Figure 5.2.1

HHT2

An upstream section of the Channel to be removed

Figure 5.2.7

DB

Small water-courses along Deep Bay

These small watercourses are located at the north-western boundary of the Project area, generally running from south to north and finally enters the marine water of Deep Bay WCZ.

Overview: Figure 5.1

Close up map:  Figure 5.2.2

N/A – All of these minor watercourses will be retained under the Project

SBR

Upstream tributaries of Shan Pui River

These small watercourses are located around the proposed combined flushing water service reservoir (FLWSR) and fresh water service reservoir (FWSR) in the south, within the catchment of Shan Pui River, which would eventually discharge to the marine water of Deep Bay WCZ.

Overview: Figure 5.1

Close up map: Figure 5.2.14

N/A – All these minor watercourses will be retained under the Project

Watercourses discharging to North Western WCZ

TMR

Upstream tributaries of Tuen Mun River

These watercourses are the upstream tributaries of Tuen Mun River found at the southern tip of the Project area.  They are running generally from north to south and eventually enters the marine water of North Western WCZ

Overview: Figure 5.1

Close up map: Figure 5.2.5

TMR1

An upstream section of this tributary to be removed under the Project

Figure 5.2.5

N/A – Not Applicable

Small Watercourses Along Deep Bay (DB)

5.3.7                There are some small watercourses in the northern Project area along the coastline of Deep Bay to the south of Hang Hau Tsuen Channel as shown in Figure 5.1 and also summarised in Table 5.3 above.  These watercourses generally run from the south to north and finally enter the marine water of Deep Bay WCZ.  There will be no change to these minor watercourses during the operational phase.

Upstream Tributaries of Shan Pui River (SMR)

5.3.8                There are also some small watercourses identified around the proposed combined FLWSR and FWSR in the south as shown in Figure 5.1 and also summarised in Table 5.3 above. These minor watercourses are actually located within the catchment of Shan Pui River and thus would eventually enter Shan Pui River and discharge into the marine water of Deep Bay WCZ. There will be no change to these minor watercourses during the operational phase.

Upstream Tributaries of Tuen Mun River (TMR)

5.3.9                The watercourses found at the southern tip of the Project area (as shown in Figure 5.1) are actually the upstream tributaries of Tuen Mun River. These watercourses are located within the North Western WCZ and they generally run from north to south and eventually to the main channel of Tuen Mun River and discharges to the marine water of the North Western WCZ as indicated in Table 5.3 above.

5.3.10              The most upstream part (namely TMR1) of the Tuen Mun tributaries, located within the new development area as shown in Figure 5.2.5, will be removed under the Project. The original catchment area of this small watercourse (namely TMR1) would form part of the Project. The stormwater originally collected by TMR1 would be collected by the new covered drainage system of the Project.  All the remaining downstream sections of the Tuen Mun River will be retained during the operational phase.

Planned Inland Watercourses

5.3.11              No new inland watercourse is proposed under the Project.

Existing Ponds and Wet Agricultural Areas

5.3.12              Other inland water bodies identified at or near the Project area are relatively minor, which include small ponds and wet agricultural areas.  A summary of all ponds and wet agricultural areas identified within the assessment area is provided in Table 5.4 below. A total of 13 ponds (namely P8A, P8B, P8C, P9A, P9B, P9C, P9D, P9E, P9F, P9G, P10, P10C and P12 respectively, which included flood protection, inactive fishponds, wetland mitigation ponds) and five wet agricultural areas (namely A2A, A2B, A2C, A2D and A3A respectively) are located within the Project area.  Four ponds found within the existing “Village Type Development” (“V”) areas (namely P8A, P9A, P9B and P10C respectively), which form part of the polder schemes ([2]) for flood protection of the villages, and one reinforced concrete flood storage pond (namely P12) found to the immediate west of KSWH are connected to nearby drainage system / watercourses. All the remaining ponds and wet agricultural areas are isolated from the nearby watercourses and could dry up occasionally after periods of no rain. No particular geographical clustering of these ponds was observed.

Table 5.4          Ponds and Agricultural Wet Areas within Assessment Area

ID

Description

Location

Within Project Area? (Yes/No)

Figure Reference

Remarks

P1A

Inactive fish pond

North of Project Area to the south of Hang Hau Tsuen Channel

No

Figure 5.2.1

 

P1B

Inactive fish pond

North of Project Area to the south of Hang Hau Tsuen Channel

No

Figure 5.2.1

 

P1C

Inactive fish pond

North of Project Area to the south of Hang Hau Tsuen Channel

No

Figure 5.2.1

 

P3A

Active fish pond

North of Project area along the coastline of Deep Bay

No

Figure 5.2.2

 

P3B

Active fish pond

North of Project area along the coastline of Deep Bay

No

Figure 5.2.2

 

P3C

Inactive fish pond

North of Project area along the coastline of Deep Bay

No

Figure 5.2.2

 

P3D

Active fish pond

North of Project area along the coastline of Deep Bay

No

Figure 5.2.2

 

P6A

Inactive fish pond

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

P6B

Inactive fish pond

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

P6C

Inactive fish pond

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

P6D

Inactive fish pond

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

P7

Inactive fish pond

North of Project Area to the west of TSW Main Channel

No

Figure 5.2.6

 

P7A

Recreational pond

North of Project Area to the west of TSW Main Channel

No

Figure 5.2.6

 

P8A

Flood protection pond

At the “Village Type Development” (“V”) near Sik Kong Tsuen

Yes

Figure 5.2.7

 

P8B

Inactive fish pond

At the northern part of Project area near San Wai

Yes

Figure 5.2.7

P8B will be removed under the Project

P8C

Inactive fish pond

At the northern part of Project area near San Wai

Yes

Figure 5.2.7

P8C will be removed under the Project

P9A

Flood protection pond

At the “V” in middle portion of the Project area

Yes

Figure 5.2.8

 

P9B

Flood protection pond

At the “V” in middle portion of the Project area

Yes

Figure 5.2.8

 

P9C

Flood protection pond

At the “V” in middle portion of the Project area

Yes

Figure 5.2.8

 

P9D

Wetland mitigation pond

Near the western boundary of Project area underneath KSWH

Yes

Figure 5.2.8

 

P9E

Wetland mitigation pond

Near the western boundary of Project area underneath KSWH

Yes

Figure 5.2.8

 

P9F

Wetland mitigation pond

West of Project area underneath KSWH

Yes

Figure 5.2.8

 

P9G

Wetland mitigation pond

West of Project area underneath KSWH

Yes

Figure 5.2.8

 

P9H

Inactive fish pond

West of Project area and to the west of KSWH

No

Figure 5.2.8

 

P9I

Inactive fish pond

West of Project area and to the west of KSWH

No

Figure 5.2.8

 

P9J

Inactive fish pond

West of Project area and to the west of KSWH

No

Figure 5.2.8

 

P10

Inactive fish pond

At the southern portion of Project area near San Sang San Tsuen

Yes

Figure 5.2.9

P10 will be removed under the Project

P10A

Recreational pond

At “V” east of Project area

No

Figure 5.2.12

 

P10B

Recreational pond

At “V” east of Project area

No

Figure 5.2.12

 

P10C

Flood protection pond

At the “V” in the eastern portion of the Project area

Yes

Figure 5.2.12

 

P11A

Inactive fish pond

North of Yuen Long Highway and to the south of Project area

No

Figure 5.2.13

 

P11B

Inactive fish pond

North of Yuen Long Highway and to the south of Project area

No

Figure 5.2.13

 

P12

Reinforced concrete flood storage pond

To the immediate west of KSWH

Yes

Figure 5.2.8

 

A1

Wet agricultural area

West of Project area and to the west of KSWH

No

Figure 5.2.8

 

A2A

Wet agricultural area

At the “V” in middle portion of the Project area

Yes

Figure 5.2.8

 

A2B

Wet agricultural area

At the border of “V” area in middle portion of the Project area

Yes

Figure 5.2.8

Part of A2B, A3C, A3D (located outside the “V” area) will be removed

A2C

Wet agricultural area

At the border of “V” area in middle portion of the Project area

Yes

Figure 5.2.8

A2D

Wet agricultural area

At the border of “V” area in middle portion of the Project area

Yes

Figure 5.2.8

A3

Wet agricultural area

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

A3A

Wet agricultural area

At the southern part of the Project area near the upstream tributaries of Tuen Mun River

Yes

Figure 5.2.5

A3A will be removed under the Project

A3C

Wet agricultural area

South of Project area near the upstream tributaries of Tuen Mun River

No

Figure 5.2.5

 

A4A

Wet agricultural area

North of Yuen Long Highway and to the south of Project area

No

Figure 5.2.13

 

A4B

Wet agricultural area

North of Yuen Long Highway and to the south of Project area

No

Figure 5.2.13

 

A4C

Wet agricultural area

North of Yuen Long Highway and to the south of Project area

No

Figure 5.2.13

 

Shaded cell:      Ponds / wet agricultural areas to be completed or partially removed under the Project

5.3.13              Due to the proposed developments, three existing ponds (namely P8B, P8C and P10 respectively as shown in Figures 5.2.7 and 5.2.9) and one wet agricultural area (namely A3A as shown in Figures 5.2.5) will be completely removed under this Project.  In addition, three wet agricultural areas (namely A2B, A2C and A2D respectively as shown in Figure 5.2.8) are located at the border of the existing “V” area in middle portion of the Project area. Part of these three wet agricultural areas that are located outside the existing “V” area will be removed under the Project.

Planned Ponds and Agricultural Wet Areas

5.3.14              No new pond / wet agricultural wet area is proposed under the Project.

Planned Flood Retention Facilities

5.3.15              Flood retention facilities which comprise of flood retention lakes and underground storage tanks are proposed under the Project as flood mitigation measures as shown in Figure 5.3.  The flood retention lakes would be open lakes which are designed for temporarily retaining stormwater run-off to avoid overflow of adjacent drainage channels.  The underground storage tanks are covered tanks would be designed for collecting run-off from the nearby drainage system through gravity flow to avoid overflow of nearby open drainage channels.  All flood retention facilities will pump the stored run-off to the adjacent drainage channels after heavy rains.

5.3.16              The locations of the flood retention facilities presented in this EIA are indicative and for illustration purpose only. The number and sizes of the flood retention facilities will be subject to further technical review.

Marine Water Sensitive Receivers

5.3.17              The key marine Water Sensitive Receivers (WSRs) within the North Western and Deep Bay WCZs have been identified as follows:

·             Existing and planned cooling water intakes along the coastlines of outer Deep Bay, Tuen Mun District and North Lantau;

·             Existing and planned flushing water intakes along the coastlines of Tuen Mun District and North Lantau;

·             Existing bathing beaches in Tuen Mun District;

·             Existing Tuen Mun typhoon shelter;

·             Existing Gold Coast marina;

·             Planned marina at Tung Chung East;

·             Existing Tai O estuary;

·             Existing Sha Chau and Lung Kwu Chau Marine Park;

·             Planned The Brothers Marine Park;

·             Existing Mai Po Inner Deep Bay Ramsar Site;

·             Existing oyster culture area at inner Deep Bay;

·             Existing fish spawning ground north of Lantau;

·             Existing artificial reefs near airport and Sha Chau;

·             Other existing ecological resources along the coastlines of Deep Bay, Sha Chau, Lung Kwu Chau, The Brothers and north Lantau including coral habitats, horseshoe crab habitats, seagrass habitats, mangrove habitats and Sites of Special Scientific Interest (SSSIs).

5.3.18              The indicative locations of these major marine WSRs are shown in Figure 5.4.

 

5.4                   Water Sensitive Receivers for Sewage Pumping Stations (DP9)

5.4.1                Locations of the four proposed SPS and the tentative alignments of their emergency overflow bypass culverts in relation to the WSRs are shown in Figure 5.5. Table 5.5 below summarises the tentative discharge point of emergency overflow for each SPS and the downstream receiving water that would potentially be affected by the emergency overflow.  Detailed description of the receiving water is provided in Table 5.3 above. Further discussion on the emergency overflow and the receiving water are also given in Sections 5.11.16 to 5.11.25 below.

Table 5.5     Tentative Discharge Points of Emergency Overflow from SPS and Downstream Receiving Water

SPS (see Figure 5.5)

Discharge Point of Emergency Overflow and Downstream Receiving Water

(refer to Table 5.3 for detailed description of Receiving Water)

SPS No. 1

Tin Sam Channel, which would then discharge to the TSW Main Channel and finally to the marine water of Deep Bay WCZ.

SPS No. 2

A side branch of Tin Sam Channel, which would firstly drain into Tin Sam Channel and then discharge to the TSW Main Channel and finally to the marine water of Deep Bay WCZ.

SPS No. 3

Tin Sam Channel, which would then discharge to the TSW Main Channel and finally to the marine water of Deep Bay WCZ.

SPS No. 4

Lo Uk Tsuen Tributaries, which would then enter the TSW Main Channel and finally to the marine water of Deep bay WCZ.

 

5.5                   Baseline Conditions – River Water Quality in Deep Bay WCZ

Tin Shui Wai Main Channel and Its Tributaries (TSW)

5.5.1                The water quality of TSW Main Channel and its tributaries is routinely monitored by EPD. According to the EPD’s publication “River Water Quality in Hong Kong in 2014” (which contains the latest information published by EPD on river water quality at the time of writing), the upstream station of TSW Main Channel (TSR2) located near Wo Ping San Tsuen reached a 95% WQO compliance in 2014, compared with 98% in 2013. The downstream station (TSR1) was 82% in compliance in 2014 as compared with 2013’s 83%.  The two EPD stations at Tin Sui Wai Catchment (TSR1 and TSR2 as shown in Figure 5.1) received ‘Fair’ and ‘Good’ grading respectively in 2014, similar to 2013. The water quality at the two EPD monitoring stations in the TSW Catchment is summarised in Table 5.6.

Table 5.6   Summary Statistics of River Water Quality Data at Tin Shui Wai Catchment Collected by EPD in 2014

Parameters

EPD Stations (Figure 5.1)

WPCO WQO

TSR1

TSR2

Dissolved oxygen (DO)  (mg/L)

5.8

9.4

Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg/L

(3.1 – 9.3)

(8.2 – 12.0)

pH

7.6

8.2

The pH of the water should be within the range of 6.0-9.0

(7.2 – 8.0)

(7.4 – 8.7)

Suspended solids (mg/L)

5

5

Waste discharges shall not cause the annual median of suspended solids to exceed 20mg/L

(2 - 23)

(2 -8)

5-day Biochemical Oxygen Demand (BOD) (mg/L)

6

2

Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5mg/L

(4 - 40)

(<1 - 7)

Chemical Oxygen Demand (COD) (mg/L)

15

6

Waste discharges shall not cause the chemical oxygen demand to exceed 30mg/L

(6 - 48)

(<2 - 12)

Oil & grease (mg/L)

<0.5

<0.5

Not available

(<0.5 – 2.8)

(<0.5 - <0.5)

Faecal coliforms (cfu/100mL)

650,000

47,000

Not available

(75,000 - 7,000,000)

(5,300 - 200,000)

E. coli (cfu/100mL)

210,000

20,000

Not exceed 1000 per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

(15,000 – 2,500,000)

(2,800 - 88,000)

Ammonia-nitrogen (mg/L)

2.20

0.34

Not available

(0.40 – 4.30)

(0.10 – 1.50)

Nitrate-nitrogen (mg/L)

0.51

0.77

Not available

(<0.01 - 1.00)

(0.54 - 0.96)

Total Kjeldahl nitrogen (mg/L)

3.85

0.69

Not available

(0.83 - 7.20)

(0.19 – 2.20)

Ortho-phosphate (mg/L)

0.17

0.05

Not available

(0.06 - 0.38)

(<0.01 - 0.19)

Total phosphorus (mg/L)

0.34

0.08

Not available