6.　　　　 WATER QUALITY.. 3

6.1　　　 Introduction. 3

6.2　　　 Environmental Legislation. 5

6.3　　　 Existing Environment 14

6.4　　　 Assessment Criteria. 28

6.5　　　 Key Issues. 34

6.6　　　 Concurrent Projects. 37

6.7　　　 Assessment Methodology. 39

6.8　　　 Operational Phase Assessment 58

6.9　　　 Construction Phase Assessment 75

6.10　　 Mitigation Measures. 114

6.11　　 Residual Impacts. 121

6.12　　 Cumulative Impacts. 122

6.13　　 Model Sensitivity Test 123

6.14　　 Environmental Monitoring and Audit 125

6.15　　 References. 126

6. WATER QUALITY

6.1 Introduction

6.1.1.1 As described in Sections 2 and 3, the selected alignment of the TM-CLKL comprises a dual two-lane highway connecting the proposed TMWB at the southern coast of Tuen Mun in the north with the Hong Kong-Zhuhai-Macao Bridge (HZMB) Boundary Crossing Facilities (HKBCF) on an island east of the Hong Kong International Airport and then subsequently linking with the North Lantau Highway at Tai Ho Wan in north Lantau.　 The alignment comprises the following basis elements (Figure 6.1):

· a northern landfall at Pillar Point, adjacent to the River Trade Terminal of 21.1ha of land for the footprint area to the bottom of the seawall where it intersects the seabed;

· a southern landfall section of 25.4ha of land for the footprint area to the bottom of the seawall where it intersects the seabed, now connected to the HKBCF reclamation island;

· a tunnel section between the two landfalls to be constructed using TBM;

· an elevated marine viaduct connecting the southern landfall to the North Lantau Highway at Tai Ho Wan and the total footprint of the viaduct piers is about 0.2 ha; and

· various land elements including connecting slip roads and a toll plaza are Area 46 in Tuen Mun.　

6.1.1.2 The indicative construction programme for the TM-CLKL is provided in Section 3 and indicates that the construction of the TM-CLKL will commence in October 2011 and be completed for its commissioning in 2016.　 However, as the TM-CLKL reclamation is now joined to the HKBCF reclamation and the southern viaduct of the TM-CLKL now forms a key link for the operation of the HKBCF, it is necessary that these projects, in association with the HZMB Hong Kong Link Road (HKLR), which connects the HZMB to the HKBCF, will need to constructed concurrently, effectively as one project.　 Thus, as the HKBCF is proposed for a Phase I interim opening at 2014, all the marine works for all three projects, with the exception of the connecting tunnel for the TM-CLKL, will need to be completed at this time.　

6.1.1.3 Notwithstanding the targeted Phase 1 commissioning of HKBCF in 2014 assumed in this EIA report, it should be noted that two construction options, referred to as Sequence A and Sequence B, have been formulated for the reclamation works for HKBCF.　 Sequence A which adopts a series of interim/temporary seawalls and the full-dredging around local programme critical areas, will enable Phase 1 to be completed by 2014, as noted above.　 Sequence B, however, involves no interim seawalls and adopts the non-dredge method for reclamation together with more extensive surcharging and will have a target interim commissioning date for Phase 1 of 2015.　 Based upon environmental considerations, Sequence A involves more dredging and more reclamation filling, and would potentially result in larger water quality impacts.　 Sequence B, in comparison, involves less dredging and reclamation filling, and would be expected to potentially result in less water quality impacts.

6.1.1.4 Section 6.1.2 below provides a detailed comparison of the two construction sequences. However, as the programming is not fixed, in order to assess the worst case situation, the Sequence A programme has been assumed for the water quality assessment.　 The overall programme of marine works based upon Sequence A for all three projects is provided in Figure 6.2a.

6.1.1.5 As noted above, it is proposed that the TM-CLKL, HKBCF and HKLR will be constructed concurrently and the completed reclamations and road connections associated with each development could impact on local and large scale tidal flows with adverse impacts on marine water quality and the marine environment.　 With respect to construction impacts on the marine environment, all three projects could result in the loss of fine sediment to suspension during the reclamation and related construction works.　

6.1.1.6 Therefore, an assessment of impacts to the marine environment of any one of these projects individually would not be relevant and would not reflect the potential impacts that could occur from their concurrent construction and implementation.　 As such, in order to fully assess the impacts from the three projects, this water quality assessment comprises a tidal hydraulic and marine water quality study during both the construction and operational phases of all three project combined (TM-CLKL+HKBCF+HKLR).　 In terms of any land based impacts to water quality associated with construction run-off, only the TM-CLKL project is covered in this report.

6.1.1.7 Both the HKBCF and HLKR are effectively marine projects with little terrestrial sections and as such are very relevant to the water quality assessment.　 The main elements of these projects that have been taken into account in this Water Quality assessment are detailed in Figure 6.1, together the with TM-CLKL alignment, and are summarised below.

Outline Scope of HKBCF

6.1.1.8 The HKBCF largely comprises a large newly formed island which connects tot the airport island.　 However, in order to achieve synergy with the airport operations and allow existing airport operations to be maintained, other elements are, also, required.　 The outline scope and description of the elements of the HKBCF project at the northeast waters off the Chek Lap Kok Island is as follows:

· a reclamation of about 130ha (or 138ha to bottom of the seawall), to provide land for the development of the HKBCF, and to connect to the Airport (such as) and integrate with the TM-CLKL;

· a tunnel between the new HKBCF island and the airport for extension of the Automated People Mover (APM) from the Airport to the HKBCF; and

· a reprovisioned jetty for the airport fire boat station.　

Outline Scope of HKLR

6.1.1.9 The HKLR will comprise a mainline carriageway that will connect the HZMB Main Section at the HKSAR boundary to the BCF and this is achieved through a combination of marine viaduct through the airport channel, short tunnel section through Scenic Hill and then viaduct and at grade road on reclaimed land before connecting to the HKBCF.　 The outline scope and description of the elements of the HKLR project comprises the follow:

· the construction of a carriageway of about 12.5km long, largely on elevated marine viaduct, carrying a dual 3-lane expressway from the HZMB Main Section at the HKSAR boundary to the HKBCF and resulting in about 3ha of seabed loss; and

· a reclamation of about 23ha (or 27ha to the bottom of the seawalls) on the south-eastern coast of the airport island to provided land for the HKLR road tunnel section portal and connecting road (both at-grade and viaduct) to the HKBCF.

6.1.1.10 With respect to operational impacts on tidal and seasonal flows and the marine environment, the principal relevant features of the TM-CLKL are the reclamations for the northern and southern landfalls and, to a lesser extent, the marine viaduct from the southern landfall to Lantau.　 The tunnel will be below the existing seabed levels and would, therefore, not have any impact on tidal and seasonal flows.　 For the HKBCF and HLKR, the principal features that could cause operational impacts are the respective reclamations and, to a lesser extent, the bridge piers for the HKLR elevated marine viaduct and the APM tunnel and reprovisioned jetty for the HKBCF.

6.1.1.11 Construction of all the marine elements have the ability to cause impacts during the construction stage associated with the release of suspended solids into the marine environment which could affect water quality and have secondary affects on marine ecology.　 However, the reclamations, particularly for the HKBCF, are likely to be the main sources of impacts as a result if their scale.

6.1.1.12 Therefore, detailed hydraulic and water quality modelling has been carried out to ensure that the preferred layout for the TM-CLKL+HKBCF+HKLR, including all road connections, does not generate any unacceptable impacts on the marine environment during either the construction or operational phases.　 It should also be noted that other projects may be implemented in the study area at the same time as the TM-CLKL+HKBCF+HKLR, and as such it is also necessary to consider any cumulative impacts from these concurrent projects.

6.1.2 Alternative Construction Sequences (TM-CLKL+HKBCF)

6.1.2.1 As briefly described above, there are two construction sequences being considered which would mainly affect the programme of the TM-CLKL southern reclamation and the main reclamation of HKBCF but not the construction of the HKLR.　 The layout and anticipated construction progress for Sequence A (HKBCF interim opening in 2014) has been presented in Appendix D5a and the details for Sequence B (HKBCF interim opening in 2015) are presented in Appendix D5b.　 In simple terms, Sequence A involves the construction of a series of interim/temporary seawalls within the main reclamation site to enable early commencement of reclamation filling works while the entire peripheral seawall of HKBCF and TM-CLKL (southern reclamation) are constructed first before the main reclamation filling works.　 A comparison of the key features of the two sequences are presented in Table 6.1a below.

Table 6.1a　 Key Feature of Construction Sequences A and B of HKBCF

	Sequence A(HKBCF interim opening in 2014)	Sequence B (HKBCF interim opening in 2015)
Key Features	· Adopts a series of interim/temporary seawalls around the proposed locations of the Passengers Clearance Building (PCB) and the Government buildings –– With these interim seawalls, the reclamation extent needed in order to start construction of the PCB and Government buildings is minimised.　 This is advantageous from a programming point of view, as the construction time of PCB and Government buildings would be much longer than other Land Works and thus these two activities are more critical. · Owing again to the acute criticality of the construction of the PCB and Government buildings, full-dredging is adopted locally for that portion of reclamation at/around the PCB and Government buildings.	· No interim seawalls: As a result, the reclamation extent in order to start construction of the PCB and Government buildings becomes larger than that in the case of Sequence A. · Full-dredging is adopted for the seawalls only, i.e. the entire reclamation behind the seawalls will adopt the non-dredge option (with consolidation measures).
Programme	· Sequence A will enable the 1^st phase of HKBCF to be completed by 2014.	· Sequence B will involve more extensive surcharging which is time consuming, but the target date of 2015 for completion of the 1^st phase of HKCBF will just be met.
Environmental Performance	· Involves more dredging and hence more reclamation filling. · Hence will result in larger water quality impacts.	· Involves less dredging and hence less reclamation filling. · Hence will result in less water quality impacts.

6.1.2.2 The estimated volumes of dredging and filling materials for Sequence A and Sequence B programmes for the HKBCF are summarised in Table 6.1b below. As shown in Table 6.1b, Sequence A would involve more dredging and more reclamation filling due to the need for interim/temporary seawalls and the adoption of a fully dredge method at some critical areas of the HKBCF reclamation.　 In addition, Sequence A aims for a shorter construction time to enable completion of the first phase of the HKBCF by late 2014, whilst Sequence B allows for a longer construction time with the Phase I of the HKBCF being completed by the end 2015.　 Therefore, the dredging and filling works of the HKBCF in Sequence A are more intensive than those in Sequence B, thus potentially resulting in larger water quality impacts.

Table 6.1b　 Key Features of Construction Sequences A and B (HKBCF)

Option	Bulk Volume of Marine Deposit　 to be Dredged (million m³) ^[1] [2]	Bulk volume of filling (million m³) ^[1], [3]
Sequence A	29.90	52.0
Sequence B	18.70	40.8
% Reduction	37%	22%

Notes:

1. A bulk factor of 1.3 is applied to the in-situ volume.

2. The volume of dredging includes dredging to form the pits for Mf sediment and excavation of sediment in bored pile excavation after the land is reclaimed.　　　　

3. The filling includes sandfill and public fill (excluding rockfill) for seawalls and reclamation.

6.1.2.3 With respect to potential water quality impacts, the sediment loss rate is more relevant than the total volume of the material to be dredged/filled. The overall programme and sediment loss rates of Sequence A has been presented in Figure 6.2a and a similar programme with sediment loss rates for Sequence B is presented in Figure 6.2b and a comparison of the two sequences is presented in Figure 6.2c.　 It is clear from Figure 6.2c that sediment loss rates for Sequence B is substantially less than Sequence A.　 While Sequence B would be preferred and is proposed to be adopted as it is environmentally more advantageous, for such a large scale and complicated project as TM-CLKL+HKBCF+HKLR, there may be the need to change to Sequence A should, for instance, any unforeseen delay in earlier tasks occur.　 A change from Sequence B to Sequence A will enable the project to gain back time to compensate for any earlier delays.　 In view of the potential programme uncertainties, for the purposes of the EIA, it is more conservative to adopt the worse case scenario for assessment and, therefore, the water quality impact assessment has focused on Sequence A.　 However, in order to demonstrate that potential water quality impacts of Sequence B would not be larger than Sequence A, additional modelling of the worse construction scenario of Sequence B has been carried out and a comparison of the water quality impacts due to Sequence A and Sequence B has been presented in the relevant sections below.

6.2 Environmental Legislation

6.2.1 Environmental Impact Assessment Ordinance (Cap. 499)

6.2.1.1 The TM-CLKL+HKBCF+HKLR are Designated Projects under Schedule 2 of the EIAO.　 Under Section 16 of the Ordinance, the Environmental Protection Department (EPD) issued the Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO) which specifies the assessment methods and criteria for the EIA.　 Annexes 6 and 14 of the TM-EIAO stipulate the “Criteria for Evaluating Water Pollution” and “Guidelines for the Assessment of Water Pollution” respectively.

6.2.2 Water Pollution Control Ordinance (Cap. 358)

6.2.2.1 The Water Pollution Control Ordinance (WPCO) is the principal legislation governing the marine water quality in Hong Kong.　 Under the provision of the WPCO, Hong Kong’s waters have been divided into a series of Water Control Zones (WCZs).　 Water Quality Objectives (WQOs) have been declared to protect the specific beneficial uses and conservation goals of each of the zones.　 The proposed TM-CLKL+HKBCF+HKLR projects are situated within the North- western Water Control Zone (WCZ), which is identified with the following beneficial uses:

· Source of food for human consumption;

· Commercial fisheries resource;

· Habitat for marine organisms generally;

· Recreational bathing beach;

· Secondary contact recreation including diving, sailing and windsurfing;

· Domestic and industrial supply;

· Navigation and shipping; and

· Aesthetic enjoyment.

6.2.2.2 Subsequent to the gazettal of the North Western WCZ, the waters around Lung Kwu Chau and Sha Chau have been declared a Marine Park primarily to protect marine mammals which are prevalent in this part of Hong Kong.　 Also the North-western WCZ is known to support a small coral population.　 Protection of these species represents the key conservation goal for the HKSAR Government.　 The relevant Water Quality Objectives (WQOs) applicable to the North Western WCZ are summarised in Table 6.1c.　

Table 6.1c　　 WQOs of North Western WCZ

Water Quality Objectives

Aesthetic Appearance

· There should be no objectionable odours or discolouration of the water;

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

· Mineral oil should not be visible on the surface;

· There should be no recognisable sewage derived debris; and

· 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.　

Bacteria

· The levels of E coli should not exceed 180 counts per 100 ml at bathing beaches, calculated as the geometric mean of all samples collected from March to October inclusive. Samples have to be taken at least 3 times a month at intervals of between 3 and 14 days;

· The levels of E coli should not exceed 610 counts per 100 ml at secondary contact recreation sub-zones, calculated as the geometric annual mean; and

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

Dissolved Oxygen

· The depth averaged concentration of dissolved oxygen should not fall below 4 mg/l for 90% of the sampling occasions during the whole year

· The concentration of dissolved oxygen should not be less than 2 mg/l within 2m of the seabed for 90% of the sampling occasions during the whole year.

pH

· The pH of the water should be within the range 6.5-8.5 units.

· Human activity should not cause the natural pH range to be extended by more than 0.2 units.

Temperature

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

Salinity

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

Suspended Solids

· 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.

Ammonia

· The un-ionised ammoniacal nitrogen level should not be more than 0.021 mg/l calculated as the annual average (arithmetic mean).

Nutrients

· Nutrients should not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants; and

· Without limiting the generality of the above point, the level of inorganic nitrogen should not exceed 0.5 mg/l, or 0.3 mg/l within Castle Peak sub-zone, expressed as the annual water column average.

Toxins

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

6.2.3 Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems

6.2.3.1 Discharges of effluents are subject to control under the WPCO.　 The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM) sets limits for effluent discharges.　 Specific limits apply for different areas and are different between surface waters and sewers.　 The limits vary with the rate of effluent flow.　 Standards for effluent discharged into the inshore waters and marine waters of North-western WCZ are summarised in Tables 6.2 and 6.3.

Table 6.2　　 Standards for Effluents Discharged into the Inshore Waters of North Western Control Zones

Flow rate (m^3/day)	≤10	>10 and ≤200	>200 and ≤400	>400 and ≤600	>600 and ≤800	>800 and ≤1000	>1000 and ≤1500	>1500 and ≤2000	>2000 and ≤3000
Determinant
pH (pH units)	6-9	6-9	6-9	6-9	6-9	6-9	6-9	6-9	6-9
Temperature (°C)	40	40	40	40	40	40	40	40	40
Colour (lovibond units) (25mm cell length)	1	1	1	1	1	1	1	1	1
Suspended solids	50	30	30	30	30	30	30	30	30
BOD	50	20	20	20	20	20	20	20	20
COD	100	80	80	80	80	80	80	80	80
Oil & Grease	30	20	20	20	20	20	20	20	20
Iron	15	10	10	7	5	4	3	2	1
Boron	5	4	3	2	2	1.5	1.1	0.8	0.5
Barium	5	4	3	2	2	1.5	1.1	0.8	0.5
Mercury	0.1	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Cadmium	0.1	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Other toxic metals individually	1	1	0.8	0.7	0.5	0.4	0.3	0.2	0.15
Total toxic metals	2	2	1.6	1.4	1	0.8	0.6	0.4	0.3
Cyanide	0.2	0.1	0.1	0.1	0.1	0.1	0.05	0.05	0.03
Phenols	0.5	0.5	0.5	0.3	0.25	0.2	0.1	0.1	0.1
Sulphide	5	5	5	5	5	5	2.5	2.5	1.5
Total residual chlorine	1	1	1	1	1	1	1	1	1
Total nitrogen	100	100	80	80	80	80	50	50	50
Total phosphorus	10	10	8	8	8	8	5	5	5
Surfactants (total)	20	15	15	15	15	15	10	10	10
E. coli (count/100ml)	1000	1000	1000	1000	1000	1000	1000	1000	1000

All units in mg/L unless otherwise stated; all figures are upper limits unless otherwise indicated

Table 6.3　　 Standards for Effluents Discharged into the Marine Waters of North Western Control Zones

Flow rate (m^3/day)	≤10	>10 and ≤200	>200 and ≤400	>400 and ≤600	>600 and ≤800	>800 and ≤1000	>1000 and ≤1500	>1500 and ≤2000	>2000 and ≤3000
Determinant
pH (pH units)	6-10	6-10	6-10	6-10	6-10	6-10	6-10	6-10	6-10
Temperature (°C)	45	45	45	45	45	45	45	45	45
Colour (lovibond units) (25mm cell length)	4	1	1	1	1	1	1	1	1
Suspended solids	500	500	500	300	200	200	100	100	50
BOD	500	500	500	300	200	200	100	100	50
COD	1000	1000	1000	700	500	400	300	200	150
Oil & Grease	50	50	50	30	25	20	20	20	20
Iron	20	15	13	10	7	6	4	3	2
Boron	6	5	4	3.5	2.5	2	1.5	1	0.7
Barium	6	5	4	3.5	2.5	2	1.5	1	0.7
Mercury	0.1	0.1	0.1	0.001	0.001	0.001	0.001	0.001	0.001
Cadmium	0.1	0.1	0.1	0.001	0.001	0.001	0.001	0.001	0.001
Other toxic metals individually	2	1.5	1.2	0.8	0.6	0.5	0.32	0.24	0.16
Total toxic metals	4	3	2.4	1.6	1.2	1	0.64	0.48	0.32
Cyanide	1	0.5	0.5	0.5	0.4	0.3	0.2	0.15	0.1
Phenols	0.5	0.5	0.5	0.3	0.25	0.2	0.13	0.1	0.1
Sulphide	5	5	5	5	5	5	2.5	2.5	1.5
Total residual chlorine	1	1	1	1	1	1	1	1	1
Total nitrogen	100	100	80	80	80	80	50	50	50
Total phosphorus	10	10	8	8	8	8	5	5	5
Surfactants (total)	30	20	20	20	15	15	15	15	15
E. coli(count/100ml)	4000	4000	4000	4000	4000	4000	4000	4000	4000

All units in mg/L unless otherwise stated; all figures are upper limits unless otherwise indicated

6.2.4 Practice Note for Professional Persons on Construction Site Drainage

6.2.4.1 The Practice Note for Professional Persons on Construction Site Drainage (ProPECC Note PN1/94) provides guidelines for the handling and disposal of construction discharges. This note is applicable for control of site runoff and wastewater generated during the construction phase of the TM-CLKL.　 The types of discharges from construction sites outlined in the ProPECC Note PN1/94 that are relevant would include:

· Surface run-off;

· Boring and drilling water;

· Wastewater from concrete batching and precast concrete casting;

· Wheel washing water; and

· Wastewater from construction activities and site facilities.

6.2.5 Legislation for Marine Sediment Disposal

6.2.5.1 The relevant legislation and guidelines for the disposal of contaminated sediment at marine disposal sites are listed below.　

· Dumping at Sea Ordinance (Cap.466);

· Environment, Transport and Works Bureau Technical Circular (Works) No.34/2002 Management of Dredged /Excavated Sediment; and

· Works Bureau Technical Circular (WBTC) No. 12/2000 Fill Management.

6.2.5.2 The Dumping at Sea Ordinance (DASO) is the major statutory legislation to control dumping of sediment at sea and safeguards the water quality and ecology of the Hong Kong waters.

6.2.5.3 The ETWB TC(W) No.34/2002 was adopted in August 2002 to supersede Work Bureau Technical Circular (WBTC) 3/2000 which was promulgated for the purpose of assessing the disposal requirements for dredged sediment.　 The ETWB TC(W) No.34/2002 sets out the procedures for seeking approval from the EPD to dredge/excavate sediment and the management framework for marine disposal of such sediment.　 It covers the approval of the dredging/excavation proposals and marine disposal of the dredged/excavated sediment.　 It does not cover the use of dredged/excavated sediment to form land, but such dredging and reclamation works must satisfy the requirements of the EIAO.　 Application for the approval of dredging/excavation proposals and allocation of the marine disposal space shall be made to the Secretary of Marine Fill Committee (MFC).　 The allocation of sediment disposal sites would not be considered until the need for removal of such sediment has been satisfactorily demonstrated.　 The rationale for sediment removal should, therefore, be provided to the Secretary of MFC for agreement.

6.2.5.4 The ETWB TC(W) No. 34/2002 also establishes guidelines for the classification of sediment based on their contaminant levels, including:

· Metals (cadmium, chromium, copper, mercury, nickel, lead, silver and zinc);

· Metalloid (arsenic); and

· Organic micro-pollutants (polycyclic aromatic hydrocarbons, Polychlorinated biphenyls, and tributyltin).　

6.2.5.5 Currently there are two sets of chemical criteria for assessing the contamination levels of sediment:

· Lower Chemical Exceedance Level (LCEL); and

· Upper Chemical Exceedance Level (UCEL).

6.2.5.6 The LCEL is intended to represent levels below which adverse biological effects (or ecotoxicity) are considered to be unlikely.　 The UCEL, on the other hand, is intended to represent a level beyond which adverse biological effects are considered likely to occur.　 These criteria therefore represent a convenient means to broadly characterise sediment quality and identify potentially polluted sediments that might be of concern if they are disturbed in the course of the Project.　 The LCEL and UCEL for the contaminants of interest are presented in Table 6.4 below.

Table 6.4　　 Sediment Quality Criteria for Classification of Sediment under ETWB TC(W) No.34/2002

Contaminants	Lower Chemical Exceedance Level (LCEL)	Upper Chemical Exceedance Level (UCEL)
Metals (mg/kg dry wt.)
Cadmium (Cd) Chromium (Cr) Copper (Cu) Mercury (Hg) Nickel (Ni)* Lead (Pb) Silver (Ag) Zinc (Zn)	1.5 80 65 0.5 40 75 1 200	4 160 110 1 40 110 2 270
Metalloid (mg/kg dry wt.)
Arsenic (As)	12	42
Organic-PAHs (μg/kg dry wt.)
Low Molecular Weight PAHs High Molecular Weight PAHs	550 1700	3160 9600
Organic-non-PAHs (μg/kg dry wt.)
Total PCBs	23	180
Organometallics (μg TBT/l in Interstitial water)
Tributyltin*	0.15	0.15

* Contaminant level is considered to exceed UCEL if it is greater than the value shown.

6.2.5.7 Based on these criteria, the sediment is classified into Category L (low contamination level), Category M (medium contamination level) or Category H (high contamination level).　 The ETWB TC(W) No.34/2002, also, stipulates a three-tiered screening for sediment assessment for determining the disposal options as shown in Figure 6.3.　

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

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

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

6.2.5.8 The detailed description of the 3-tier approach is described as follows:

· Tier I screening is a desktop screening process to review the available information and determine whether the sediment of concern belongs to Category L material suitable for open sea disposal.　 If there is insufficient information to arrive at such conclusion, Tier II chemical screening shall proceed directly.

· Tier II screening is a chemical screening process to categorise sediment based on its chemical contaminant levels and to determine whether the sediment is suitable for open sea disposal without further testing.　 Upon Type II screening, the sediment shall be classified as Category L, M or H material.　 There are three types of disposal options: Types 1, 2 and 3 disposal represent open sea disposal, confined marine disposal and special treatment/disposal respectively.　 Category L material is suitable for open sea disposal, but Categories M and H will require Tier III screening to further determine the disposal option.

· Tier III screening is a biological screening process to identify the most appropriate disposal option for Category M (either Type 1 or 2) and certain Category H sediment (either Type 2 or 3).　 Sediment classified as Category M shall be subjected to the following three toxicity tests: (i) 10-day burrowing amphipod toxicity test; (ii) 20-day burrowing polychaete toxicity test; and (iii) 48-96 hour larvae (bivalve or echinoderm) toxicity test.

6.2.5.9 The WBTC No. 12/2000 defines the responsibilities of the MFC and Public Fill Committee (PFC).　 It also sets out the terms of reference and membership of the two committees and provides explanation on the management of fill resources, construction and demolition material, and dredged/excavated sediment disposal.

6.3 Existing Environment

6.3.1 Background

6.3.1.1 The North-western waters are situated at the mouth of the Pearl River Estuary and as such are heavily influenced by the massive freshwater flows from the hinterland.　 The area shows a distinct seasonality as a result of the seasonal influx of freshwater from the Pearl River.　 The estuarine influence is especially pronounced in the wet summer months when the freshwater flows are greatest and a strong salinity and temperature stratification is evident.　 During winter months water conditions are more typically marine and the salinity and other parameters vary less with depth. Ebb tide currents are towards the southeast where the flood tide currents move to the northwest.　 Current velocities in areas near to the project area have been predicted in previous studies to be less than 2.0 m/s on the surface and rarely exceeding 0.25 m/s near seabed (ERM, 1997, 2005)

6.3.1.2 Water temperature ranges between about 15°C and 30°C over an annual cycle with a mean of about 22-23°C.　 Salinity typically varies within the range 10-32ppt.

6.3.1.3 The Pearl River carries very heavy loads of suspended sediment and nitrates and as a consequence concentrations of these parameters within North-western waters are variable but generally far higher than in the more oceanic influenced waters to the south and east of Hong Kong.　

6.3.2 Pollution Sources

6.3.2.1 The North Western WCZ contains several significant sewage outfalls (Pillar Point, Northwest New Territories and Siu Ho Wan) and cooling water discharges from a number of users including Castle Peak Power Station, Hong Kong International Airport (HKIA) and Shiu Wing Steelworks.

6.3.2.2 In the past, dredging of marine mud and sand extraction has been extensive in the North-western Waters coastal area for reclamation projects including the land to be occupied by the Permanent Aviation Fuel Facility site (PAFF) at Tuen Mun Area 38, River Trade Terminal, Tin Shui Wai New Town and Hong Kong International Airport platform at Chek Lap Kok.　 Mud dredging to construct and maintain the navigation channel in Urmston Road and the berthing area at Castle Peak Power Station is periodic and on-going and the present temporary Aviation Fuel Receiving Facility (AFRF) at Sha Chau required the construction of a navigation channel and berthing area, which is, also, subject to maintenance dredging.　 The recently constructed Tonggu Channel just outside the HKSAR boundary, will also require periodic maintenance dredging.　 To date, no adverse environmental impacts have been reported for any of these previous dredging exercises.

6.3.2.3 Disposal of contaminated dredged material, which began in 1992, is also on-going at the Contaminated Mud Pits (CMP) at East of Sha Chau.　 The capacity of the existing pits were predicted to be exhausted by early 2009 and two potential sites for future CMPs near the HKIA have been identified (Figures 6.4 and 6.5a) and the EIA for the tentative sites have been approved by the Director of Environmental Protection (DEP). 　Disposal of Category M material that passes biological screening/uncontaminated dredged material continues intermittently at the North Brothers which has a remaining capacity of about 5 Mm³.　 The operation of the open sea disposal ground at North Lantau Borrow pit has been suspended since 2000 and there is currently no schedule for the reopening of the facility.

6.3.2.4 Commercial trawling is undertaken over much of the North-western waters and the Urmston Road is a very busy shipping channel for river trade vessels, high speed ferries, large coal vessels servicing Castle Peak Power Station and the existing temporary Aviation Fuel Receiving Facility delivery vessels.

6.3.2.5 The locations of the principal areas of seabed disturbance and the major sewage outfalls in the study area are indicated in Figure 6.4.

6.3.3 Sensitive Receivers and Modelling Output Points

6.3.3.1 There are a number of important water sensitive receivers (WSRs) within the study area as shown in Figure 6.5a.　 They include areas of ecological sensitivity and conservation importance, commercial fishing resources, areas of direct human contact, e.g. bathing beaches, and various points where seawater is abstracted for domestic, commercial or industrial purposes.　 Notwithstanding the importance of protecting the water quality generally throughout the North Western WCZ in accordance with the statutory WQOs, it is especially important to maintain the integrity of the water quality at these specific sites.

6.3.3.2 The Chinese White dolphin (Sousa chinensis) is frequently observed within the study area and in and around Sha Chau and Lung Kwu Chau Marine Park, with the areas close to the Brothers Islands being shown to be a recent key site for the dolphins (see Section 8).　 The North-western waters of Hong Kong actually represent the eastern range of the Pearl River Estuary dolphin population which extends far into the mainland Chinese waters.　

6.3.3.3 Tuen Mun is the home to a large offshore fishing fleet and the North-western waters support an important spawning ground and commercial fishery industry for a variety of fish species and Penaeid shrimps.

6.3.3.4 Other features of conservation concern in the wider study area include the mangrove stands and seagrasses (Zostera japonica, Halophilia ovata and Halopila beccarii) at Tai Ho and along the Tung Chung Channel south of the HKIA at Sha Lo Wan and San Tau.　 This area also provides the preferred habitat for horseshoe crab (Tachypleus tridentatus and Carcinoscorpius rotundicauda) which have been also observed near the beaches of Lung Kwu Tan, Lung Kwu Chau, the Brothers, San Tau and Tai Ho Wan.　 Previous surveys near Sha Chau have identified the presence of the stone coral Faviidea as well as gorgonians and sea pens which are of ecological interest.

6.3.3.5 The study area contains two ungazetted bathing beaches at Lung Kwu Tan as well as a number of gazetted bathing beaches in Tuen Mun and along Castle Peak Road.　 The Butterfly Beach is the nearest to the study area, which is located about 1 km to the east of the proposed northern landing in Tuen Mun.　 Further east towards Castle Peak Road are the Castle Peak Beach, Kadoorie Beach, Cafeteria Old and New Beaches and Golden Beach.　 These beaches have historically suffered from high sewage derived bacterial loads.　 However, as a result of recent pollution enforcement activities and sewerage infrastructure improvements, the water quality at all the gazetted beaches in the North West WCZ is now deemed ‘fair’ according to the EPD’s criteria and suitable for bathing.　

6.3.3.6 As part of the mitigation for the temporary aviation fuel line at Sha Chau, artificial reefs have been deployed in the Sha Chau and Lung Kwu Chau Marine Park. These reefs are designed to enhance fisheries resources and promote feeding opportunities for the Chinese White Dolphins which frequent the area.　 In addition, the Hong Kong Jockey Club, with the support from the AAHK, financed a project to deploy artificial reefs in the Chek Lap Kok Marine Exclusion Zone off the north eastern corner of the HKIA.　

6.3.3.7 There are a number of major seawater intakes in the study area serving the airport and industrial users, particularly the Castle Peak Power Station and Shiu Wing Steelworks immediately to the west of Tuen Mun Area 38 and the Black Point Power Station further west.　 For the Castle Peak Power Station and Black Point Power Station seawater intakes, the acceptable suspended solids levels is below 764 mg/L (ERM, 2006).

6.3.3.8 A series of specific points and sensitive receivers for inclusion in the water quality modelling have been defined based upon the above, in addition for some far field points for the operational phase assessment.　 The observation points defined in the model and their main application are summarised in Table 6.5 below and the location of the observation points are shown in Figure 6.5b.

Table 6.5　　 Nature of Water Quality Modelling Output Point and Their Usage

No	Output Points	Name / Nature	EPD Station ^(1)	Construction Assessment	Operational Assessment
1	WSR 7	Black Point Cooling Water Intake ^(2) / Far Field station	-		
2	WSR 8	Lung Kwu Sheung Tan (non-gazetted beach)	NM(5,6,8)	
3	WSR 9a	Urmston Road (Main Channel)	NM(5,6,8)		
4	WSR 10	Sha Chau and Lung Kwu Chau Marine Park	NM(5,6,8)		
5	WSR 11	Castle Peak Power Station Cooling Water Intake ^(2)	-	
6	WSR 12	Butterfly Beach (gazetted beach)	NM(1,2,3)		
7	WSR 13	WSD Seawater Intake at Tuen Mun	NM(1,2,3)	
8	WSR 15	Gazetted Beaches at Tuen Mun	NM(1,2,3)	
9	WSR 18	Gazetted Beaches along Castle Peak Road	NM(1,2,3)	
10	WSR 19	Gazetted Beach at Ma Wan	WM4	
11	WSR 20	Ma Wan Fish Culture Zone ^(3)	-		
12	WSR 21	Ta Pang Po (near Sunny Bay Mangrove)	NM(1,2,3)	
13	WSR 22a	Tai Ho Wan Outlet (inside)	NM(1,2,3)	
14	WSR 22b	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM(1,2,3)		
15	WSR 22c	Tai Ho Wan Outlet (outside) / Near coral site	NM(1,2,3)		
16	WSR 24	Tung Chung Fairway	-		
17	WSR 25	Airport Cooling Water Intake (NE)	NM(1,2,3)		
18	WSR 26	HKBCF South (open water)	-		^(4)
19	WSR 27	San Tau Beach SSSI	NM(5,6,8)		
20	WSR 28	Airport Channel / Airport Cooling Water Intake ^(2)	NM(1,2,3)		
21	WSR 29	Hau Hok Wan (Horseshoe Crab Habitat)	NM(5,6,8)		
22	WSR 30	Sha Lo Wan (Horseshoe Crab Habitat)	NM(5,6,8)		
23	WSR 31	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM(5,6,8)	
24	WSR 32	Tai O (Mangrove Habitat)	NM(5,6,8)		
25	WSR 34	Yi O (Mangrove and Horseshoe Crab Habitat)	NM(5,6,8)		
26	WSR 40	Cheung Sha Wan Fish Culture Zone ^(3) / Far Field station	-		
27	WSR 41	Artificial Reef at NE Airport	NM(1,2,3)		
28	WSR 42	Artificial Reef at Sha Chau	NM(5,6,8)	
29	WSR 43	Tung Chung Waterfront	-		
30	WSR 44	Future HKBCF Intake	-		^(4)
31	WSR 45c	Sham Shui Kok (CWD habitat range)	NM(1,2,3)	
32	WSR 46	Tai Mo To (near coral / CWD habitat range)	NM(1,2,3)	
33	WSR 47a	River Trade Terminal	NM(1,2,3)	
34	WSR 47b	River Trade Terminal (near coral site)	NM(1,2,3)	
35	WSR 48	Airport Channel Western End	NM(5,6,8)	
36	WSR 49	Tai Mo To (deep channel / CWD habitat range)	NM(1,2,3)		
37	WSR 50	Future HKBCF Embayed Area / Sky Pier	-		
38	WSR 23	Future LLP Seawater Intake	-		

Note:

1　　 EPD Station refer to the cluster of EPD routine water quality monitoring stations where relevant WQO for SS are derived for construction phase assessment.

2.　　 The cooling water intake for power stations has its own specific criteria for SS.

3.　　 Fish culture zone has its own specific criteria for SS.

4.　　 Points added after flow modelling and, hence, flow modelling results not available for these points.

6.3.4 Baseline Water Quality

6.3.4.1 The existing water quality in the North Western waters have been monitored for many years as part of the EPD’s routine monitoring programme.　 The water quality is monitored monthly at six stations within the North-western WCZ as shown in Figure 6.5b.　 A summary of the EPD’s Routine Water Quality Data for the North-western WCZ (2006 and 2007) is given in Tables 6.6a and 6.6b below.

Table 6.6a Summary of EPD’s Routine Water Quality Data (NM1, 2, 3) for North Western WCZ (2006 – 2007)

Parameters	Monitoring Station
	NM1		NM2		NM3
	2006	2007	2006	2007	2006	2007
Temperature (°C)	23.7 (17.6 – 27.4)	23.0 (17.2 – 27.8)	23.8 (17.5 – 27.6)	23.4 (17.3 – 28.4)	23.7 (17.7 – 27.6)	23.2 (17.3 – 28.2)
Salinity (ppt)	29.6 (22.2 – 33.1	30.9 (26.1 – 33.1)	28.6 (19.0 – 33.1)	29.5 (18.8 – 33.1)	29.4 (23.7 – 33.1)	30.1 (24.9 – 33.1)
Dissolved Oxygen (mg/L)	6.3 (4.4 – 8.0)	5.7 (3.5 – 9.2)	6.5 (4.9 – 8.4)	6.0 (3.3 – 9.7)	6.3 (4.4 – 8.3)	5.8 (3.2 – 9.6)
BOD5 (mg/L)	0.6 (0.4 – 1.1)	1.0 (0.4 – 1.9)	0.6 (0.2 – 1.0)	1.0 (0.4 – 2.5)	0.7 (0.4 – 1.2)	1.1 (0.5 – 2.5)
SS (mg/L)	7.4 (2.5 – 17.4)	8.2 (2.3 – 14.7)	6.4 (2.9 – 21.3)	5.8 (1.8 – 9.3)	8.1 (3.0 – 14.0)	7.4 (3.9 – 11.7)
TIN (mg/L)	0.43 (0.17 – 0.75)	0.39 (0.09 – 0.70)	0.49 (0.18 – 0.85)	0.48 (0.09 – 1.05)	0.50 (0.22 – 0.80)	0.47 (0.13 – 0.87)
Unionised NH3 (mg/L)	0.005 (<0.001 – 0.010)	0.005 (0.001 – 0.007)	0.005 (0.001 – 0.011)	0.006 (0.001 – 0.010)	0.005 (0.001 – 0.011)	0.006 (0.001 – 0.012)
Ortho-P (mg/L)	0.03 (0.01 – 0.04)	0.025 (0.009 – 0.039)	0.03 (0.01 – 0.04)	0.024 (0.006 – 0.040)	0.03 (0.01 – 0.04)	0.026 (0.007 – 0.044)
Total P (mg/L)	0.05 (0.03 – 0.06)	0.05 (0.03 – 0.08)	0.04 (0.03 – 0.06)	0.05 (0.03 – 0.07)	0.05 (0.04 – 0.06)	0.05 (0.04 – 0.08)
Chlorophyll-a (mg/L)	3.6 (0.8 – 19.2)	5.4 (0.7 – 17.7)	2.8 (0.8 – 10.6)	6 (0.7 – 20.7)	3.3 (1.0 – 7.7)	5.9 (1.0 – 22.0)
E. coli (cfu/100mL)	1100 (340 – 2600)	670 (56 – 3100)	470 (280 – 1900)	360 (49 – 1900)	500 (140 – 2100)	430 (45 – 2400)

Notes:

[1]　　 Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E coli (geometric mean)

[2]　　 Data in brackets indicate ranges

[3]　　 Underlined indicates occurrence of non-compliance with that parameter of WQO

Table 6.6b Summary of EPD’s Routine Water Quality Data (NM5, 6, 8) for North Western WCZ (2006 – 2007)

Parameters	Monitoring Station
	NM5		NM6		NM8
	2006	2007	2006	2007	2006	2007
Temperature (°C)	24.0 (17.9 – 27.8)	23.4 (17.3 – 28.3)	24.0 (17.7 – 29.2)	23.8 (17.3 – 30.3)	23.8 (17.5 – 28.3)	23.6 (17.1 – 30.6)
Salinity (ppt)	27.2 (16.4 – 32.8)	28.6 (23.0 – 33.0)	26.0 (10.5 – 33.3)	27.5 (12.0 – 33.0)	27.6 (11.9 – 33.4)	28.9 (9.7 – 33.5)
Dissolved Oxygen (mg/L)	6.3 (4.3 – 8.2)	5.7 (3.0 – 9.3)	6.7 (4.8 – 8.7)	6.4 (3.2 – 10.0)	6.8 (4.8 – 8.2)	6.8 (3.7 – 9.8)
BOD5 (mg/L)	0.7 (0.5 – 0.9)	1.1 (0.5 – 2.7)	0.7 (0.3 – 1.3)	1.1 (0.5 – 2.7)	0.7 (0.3 – 1.9)	1.1 (0.4 – 2.1)
SS (mg/L)	15.7 (3.8 – 53.8)	11.1 (4.3 – 18.7)	12.6 (4.1 – 35.9)	10.0 (3.5 – 27.7)	15.8 (2.7 – 56.7)	11.6 (3.5 – 27.7)
TIN (mg/L)	0.67 (0.29 – 1.07)	0.64 (0.22 – 1.06)	0.66 (0.09 – 1.40)	0.58 (0.12 – 1.40)	0.44 (0.06 – 1.20)	0.44 (0.07 – 1.48)
Unionised NH3 (mg/L)	0.008 (0.03 – 0.017)	0.008 (0.001 – 0.014)	0.006 (0.002 – 0.022)	0.006 (0.001 – 0.012)	0.004 (0.001 – 0.019)	0.004 (<0.001 – 0.009)
Ortho-P (mg/L)	0.03 (0.01 – 0.05)	0.031 (0.013 – 0.053)	0.02 (<0.01 – 0.05)	0.021 (0.002 – 0.059)	0.02 (<0.01 – 0.04)	0.016 (0.003 – 0.036)
Total P (mg/L)	0.07 (0.05 – 0.11)	0.06 (0.04 – 0.08)	0.05 (0.03 – 0.08)	0.05 (0.04 – 0.09)	0.04 (0.02 – 0.06)	0.04 (0.03 – 0.07)
Chlorophyll-a (mg/L)	4.2 (1.3 – 17.4)	5.5 (1.3 – 23.0)	3.9 (1.1 – 12.0)	7.4 (1.2 – 26.3)	3.5 (1.3　 -14.7)	8.3 (0.8–20.7)
E. coli (cfu/100mL)	900 (220 – 2600)	1300 (160- 3600)	64 (2 – 1900)	46 (2 – 2400)	5 (1 – 420)	12 (1 – 240)

Notes:

[1]　　 Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E. coli (geometric mean)

[2]　　 Data in brackets indicate ranges

[3]　　 Underlined indicates occurrence of non-compliance with that parameter of WQO

6.3.4.2 Some temporal and spatial variability is evident in this dataset, but compliance is usually observed with the key WQOs for unionised ammonia notwithstanding generally eutrophic conditions resulting from the heavy nutrient load carried by the Pearl River.　 Compliance with the total inorganic nitrogen objective was remained the same during 2006 and 2007.　 In general, the water quality parameters recorded in 2007 were largely stable compared with 2006.

6.3.4.3 A drop in the compliance with the dissolved oxygen objective was noted.　 EPD suggested that the drop was related to the general occurrence of low DO starting June 2007 in Marine Water Quality in Hong Kong 2007.

6.3.4.4 Of particular relevance to this assessment, the EPD for these two years indicate that suspended solid concentrations demonstrated a drop for all station from 2006 to 2007.　 Suspended solid concentrations typically lie in the range of 2.5 to 57 mg/l with the highest recorded value being 56.7 mg/l at the Chek Lap Kok West station NM8 in 2006 while the range drops to of 1.8 to 28 mg/l with the highest recorded value being 27.7 mg/l at the Chek Lap Kok North and West stations NM6 and NM8 in 2007.

6.3.4.5 Compliance with the WQO for dissolved oxygen was not achieved at NM1, NM3 and NM5.　 Occasional dips in depth average measurements below the compliance value of 4 mg/l was also observed at stations for all monitoring stations. Oxygen super-saturation is, also, observed, particularly at the south-western most stations NM8, again indicative of eutrophication predominantly influenced by the Pearl River discharge.

6.3.4.6 In addition to EPD’s long term programme, comprehensive water quality data sets have been obtained from various construction related environmental monitoring programmes, the most significant ongoing programme being that for the management of the Contaminated Mud Pits at East of Sha Chau.　 These data are essentially comparable with the longer-term EPD dataset and show general compliance with the WQOs in the region of the mud dumping operations.　 Data obtained to date from this programme support the hypothesis that the disposal activities have not had any significant adverse effect on water quality beyond the immediate confines of the pit areas during dumping.　 Suspended sediment concentrations are again observed to range from less than 10 mg/L to over 80 mg/L although mean values tend to be a bit higher than reported by EPD.　 Over the period 1994 to 1997, for example, annual mean depth averaged suspended sediment concentrations ranged from about 18 to 40 mg/L illustrating the considerable variability for this parameter.　 Depth averaged dissolved oxygen varies at East Sha Chau within the range from 4 to 10 mg/L with a mean value of about 6.7 mg/L.

6.3.4.7 The AAHK has also conducted a serious of non-statutory water quality monitoring for the periods 1999-2000, 2002-2003 and 2005-2006 and the average concentrations of suspended sediment recorded at mid-depth was 11.3 mg/L and the values ranged between 3 to 40 mg/l (Meinhardt, 2006b). The concentrations of dissolved oxygen recorded mid-depth ranged between 2.9 to 15.8 mg/L with an average of 7.0 mg/L.

6.3.4.8 The statutory WQO for suspended sediments is not defined in absolute numerical terms but instead is worded to require that human activities should not result in an elevation of more than 30% above ambient levels (Table 6.1).　 This in part reflects the difficulty in trying to apply a single numerical value for environmental management purposes in the context of the naturally highly variable characteristics of Hong Kong’s marine waters.　 Previous workers assessing the environmental impacts associated with the temporary AFRF at Sha Chau adopted a value of up to 34 mg/L to represent ambient suspended solid concentrations in essentially the same study area as is being considered in this assessment.　

6.3.4.9 However, for the purposes of this assessment, the WQO for suspended solids at each sensitive receiver will be based on an analysis of the EPD routine monitoring data from 1998 to 2007 at the nearest EPD monitoring station, as described in Section 6.4 below.

6.3.5 Baseline Sediment Quality

6.3.5.1 There is a wealth of sediment quality data for the study area, from EPD’s routine monitoring, previous project surveys and, also, from project specific investigation undertaken for both the TM-CLKL and HKBCF.　 Details of the findings from the various sources are presented in the sections below.

EPD Routine Sediment Quality Monitoring

6.3.5.2 Some existing sediment quality data from the EPD in the North Western WCZ are available within the study area, which are monitored by the EPD every six months at four stations: NS2, NS3, NS4 and NS6 as shown in Figure 6.5b.　 NS5 is not included in this evaluation as it is located in Tuen Mun Typhoon Shelter which is not relevant to this evaluation.　 The locations of the EPD stations are as follows:

· NS2 is located to the north of Siu Mo To at ~2.5km east of the preferred alignment;

· NS3 is located in the waters off the tip of River Trade Terminal in Tuen Mun and is about 500m from the proposed north reclamation landing at Tuen Mun;

· NS4 is located between Lung Kwu Chau and Lung Kwu Tan; and

· NS6 is near the western end of the airport runway. As both are far (>5km) from the Project site, they are not considered relevant to this project.

6.3.5.3 The monitoring results of NS2, NS3 in 2003-2007 are summarised in Tables 6.7a and 6.7b below, with reference to the ETWB TC(W) 34/2002 criteria, as well as nitrogen and phosphorus nutrient contents.

Table 6.7a　 EPD’s Sediment Quality Monitoring Data for NS2 and NS3 within North Western Waters (2003-2007)

Contaminants^1	Unit	NS2^2	NS3^2	LCEL	UCEL
Arsenic	mg/kg dry wt	7.2 – 14	8.3 – 14	12	42
Cadmium	mg/kg dry wt	<0.1 – 0.1	<0.1 – 0.1	1.5	4
Chromium	mg/kg dry wt	24 – 43	20 – 42	80	160
Copper	mg/kg dry wt	28 – 42	18 – 48	65	110
Mercury	mg/kg dry wt	0.07 – 0.13	0.06 – 0.15	0.5	1
Nickel	mg/kg dry wt	15 – 27	11 – 24	40	40
Lead	mg/kg dry wt	31 – 50	27 – 45	75	110
Silver	mg/kg dry wt	0 – 1	0 – <1	1	2
Zinc	mg/kg dry wt	77 – 130	62 – 120	200	270
Low Molecular Weight PAH^3	mg/kg dry wt	14 – 67	18 – 64.5	550	3,160
High Molecular Weight PAH^3	mg/kg dry wt	35.5 – 123.5	38 – 113.5	1,700	9,600
Total PCBs	mg/kg dry wt	18 – 18	18 – 18	23	180
Particle Size Fraction <63mm	%	35 – 63	23 – 87	--	--
Total Kjeldahl Nitrogen (TKN)	mg/kg dry wt	120 – 520	120 – 440	--	--
Ammonia Nitrogen	mg/kg dry wt	0.12 – 8.2	<0.05 – 16	--	--
Total Phosphorus	mg/kg dry wt	84 – 290	86 – 250	--	--

¹　 Based on bulk samples;

²　 The presented results are in range (min-max) and values exceeding the LCELs are shown in underlined; and

³　 Mostly below analytical reporting limits and numeric values shown are calculated from the available components with <RL substituted with ½RL.　

Table 6.7b　 EPD’s Sediment Quality Monitoring Data for NS4 and NS6 within North Western Waters (2003-2007)

Contaminants^1	Unit	NS4^2	NS6^2	LCEL	UCEL
Arsenic	mg/kg dry wt	9.1 – 11	7.1 – 16	12	42
Cadmium	mg/kg dry wt	<0.1 – 0.1	<0.1 - 0.1	1.5	4
Chromium	mg/kg dry wt	26 – 36	18 – 37	80	160
Copper	mg/kg dry wt	18 – 42	8 – 27	65	110
Mercury	mg/kg dry wt	0.06 – 0.23	<0.05– 0.1	0.5	1
Nickel	mg/kg dry wt	16 – 22	10 – 24	40	40
Lead	mg/kg dry wt	29 – 46	20 – 46	75	110
Silver	mg/kg dry wt	<1 – 0	<1 – 0	1	2
Zinc	mg/kg dry wt	99 – 110	42 – 100	200	270
Low Molecular Weight PAH^3	mg/kg dry wt	90 – 99	90 – 94	550	3,160
High Molecular Weight PAH^3	mg/kg dry wt	35 – 120	16 – 49	1,700	9,600
Total PCBs	mg/kg dry wt	18 – 18	18 – 18	23	180
Particle Size Fraction <63mm	%	12 – 61	10 – 81	--	--
Total Kjeldahl Nitrogen (TKN)	mg/kg dry wt	160 – 350	130 – 400	--	--
Ammonia Nitrogen	mg/kg dry wt	0.19 – 30	0.05 – 13	--	--
Total Phosphorus	mg/kg dry wt	92 – 230	100 – 260	--	--

¹　 Based on bulk samples;

²　 The presented results are in range (min-max) and values exceeding the LCELs are shown in underlined; and

³　 Mostly below analytical reporting limits and numeric values shown are calculated from the available components with <RL substituted with ½RL.　

6.3.5.4 It is observed that of all parameters except arsenic are lower than the LCELs. Only the upper range arsenic concentrations were observed to exceed the LCEL. Based on the EPD’s Marine Water Quality in Hong Kong 2000, the arsenic concentrations might be due to the high natural arsenic levels in the soil of some areas of the northern New Territories (e.g. Lok Ma Chau, Ngau Tam Mei and Pat Heung) which could have been transported to the marine environment through river discharges and storm runoff.　

6.3.5.5 There were 6 occasions over the past 5 years have EPD detected arsenic concentrations in the North-western waters marine sediment above the UCEL criterion adopted to define a level above which adverse biological toxicological effects would be expected.　 Given that the arsenic concentrations in this region are likely to represent the result of gradual natural erosive processes over geologic timescales, it seems reasonable to assume that the existing ecosystem is tolerant to the widespread presence of this element.

East Sha Chau Contaminated Mud Disposal Pit

6.3.5.6 In addition to the EPD’s routine monitoring programme, comprehensive water quality data sets have been obtained from various environmental monitoring programmes, with the most significant on-going one being that for the management of Contaminated Mud Pits at East of Sha Chau.　 Figure 6.6 shows the locations of the monitoring stations used.　 These data are essentially comparable to the EPD’s routine monitoring dataset and show a general compliance with WQOs in the area near the mud dumping operations.　 Data obtained to date support the hypothesis that disposal activities have not had any significant adverse effects on the water quality beyond the immediate confines of the mud pit areas during dumping.　 Suspended sediment concentrations are observed to range from <10 mg/l to >80 mg/l, although mean values tend to be higher than those reported by the EPD.　 For examples, over the period of 1994-1997, the annual mean depth averaged suspended sediment concentrations ranged ~18-40 mg/l, illustrating the variability of this parameter.　 The depth averaged dissolved oxygen concentration at East Sha Chau varies within the range of 4-10 mg/l, with a mean value of ~6.7 mg/l.

HKLR (EIA Study in 2004: Former Hong Kong Section of HZMB and Connection with North Lantau Highway)

6.3.5.7 A review of previous environmental marine ground investigation (GI) of the airport east conducted in 2004 of the HKLR has been conducted under the HyD’s Agreement No. CE26/2003 (HY) former Hong Kong Section of Hong Kong-Zhuhai-Macao Bridge and Connection with North Lantau Highway – Investigation.　 Vibrocores and grab samples were collected at 11 locations and surface grab samples were collected at another 2 locations along the proposed route alignment of the Hong Kong Section of the HZMB in the western waters to the airport island, within the airport channel, and in northern waters of Tung Chung as shown in Figure 6.7.　 Elutriate testing of the surface grab samples was also carried out.　

6.3.5.8 Sediment samples were tested for the suite of metals, metalloids and organic pollutants (PAHs, PCBs and TBT) as specified in the ETWB TC(W) No.34/2002.　 Chlorinated pesticides (11 components: a-BHC, b- & g-BHC, d-BHC, aldrin, endosulfan 1, endosulfan sulfate, heptachlor, heptachlor-epoxide, p,p’-DDE, p,p’-DDD, p,p’-DDT) were also tested for the 0-1m (surface) sub-samples.　 In addition to these parameters, elutriate testing of sediment samples was also conducted for nitrogen and phosphorus (total phosphorus and reactive phosphorus) nutrients.

6.3.5.9 There were 23 Category M samples (out of 52 samples), which showed slight exceedance of arsenic concentration for the LCEL (maximum: 23 mg/kg dry weight).　 It should be noted that all tested samples had their total PAHs, total PCBs, TBT in interstitial water, and chlorinated pesticides below their respective analytical reporting limit (total PAHs: low molecular weight PAHs <55 μg/kg dry weight and high molecular weight PAH <170 μg/kg dry weight; total PCBs: <2 μg/kg dry weight; TBT in interstitial water: <0.015 μg/l; and chlorinated pesticides: <0.2 mg/kg dry weight).　 The 23 Category M samples were further tested for the biological screening in accordance with the ETWB TC(W) No.34/2002, in which 11 composite samples were formed.　 Four of the samples failed the biological screening.　

AAHK – Non-Statutory Marine Environmental Monitoring

6.3.5.10 The AAHK has undertaken a programme of non-statutory marine environmental monitoring to verify the environmental performance of the airport platform.　 The programme included the collection of sediments using surface grab and three rounds of non-statutory monitoring have been conducted so far.　 The first round was conducted in 1999-2000 which included two sampling events.　 The second round was conducted in 2002-2003 which included 1 sampling event.　 The third round was conducted in 2005-2006 which also included 1 sampling event.　 The sediment monitoring stations were the same over the 3 rounds of monitoring although less stations were monitored in the second and third rounds.　 The locations of the latest monitoring stations are shown in Figure 6.7.

6.3.5.11 Sediment samples were analysed for the same suite of contaminants as listed in the ETWB TC(W) No.34/2002 including metals, metalloid, total PAHs and total PCBs, but there was no TBT.　 Chlorinated pesticides (15 components) were also analysed.

6.3.5.12 The monitoring results are summarised in Table 6.8 for the ETWB TC(W) No.34/2002 criteria on metals and metalloid.　 The total PAHs, total PCBs and chlorinated pesticides were below the analytical reporting limits (comparable to the requirement of ETWB TC(W) No.34/2002) and the results are not presented.　

Table 6.8　　 Summary of AAHK Non-statutory Sediment Quality Monitoring Results (1999-2006)

Contaminant	Unit	Range	LCEL	UCEL
As	mg/kg dry weight	6.4 - 24.7	12	42
Cd	mg/kg dry weight	<0.05 - 0.29	1.5	4
Cr	mg/kg dry weight	16 - 60	80	160
Cu	mg/kg dry weight	16 - 52	65	110
Hg	mg/kg dry weight	<0.05 - 0.21	0.5	1
Ni	mg/kg dry weight	10 - 39	40	40
Pb	mg/kg dry weight	26 - 62	75	110
Ag	mg/kg dry weight	0.1 - <1	1	2
Zn	mg/kg dry weight	63 - 157	200	270

Study for New Contaminated Mud Disposal Facility (East of Sha Chau Pit V)

6.3.5.13 Sediment quality analyses were conducted under the Agreement No. CE 12/2002(EP) Detailed Site Selection Study for a Proposed Contaminated Mud Disposal Facility within the Airport East/East of Sha Chau area.　 There were 12 vibrocores collected (Figure 6.7), yielding 68 sub-samples with a maximum depth of 20m investigated.　 The results suggested that most of the sediment samples were uncontaminated, but 2 sub-samples (10.9-11.9m of V10 and 14.9-15.9m of V11) indicated the exceedance of UCEL for nickel and zinc concentrations.　 Some sub-samples of V2 (15-16m), V7 (0.9-1.9m), V8 (9.9-10.9m, 18.8-19.8m) and V9 (0-0.9m, 0.19-1.9m and 1.9-2.9m) also exhibited marginal exceedance of the LCEL for arsenic, except a sub-sample of V2 (15-16m, exceeding LCEL of silver) and V9 (0-0.9m, marginal exceedance of LCEL for arsenic and mercury).　 Concentrations of total PAHs and total PCBs of all samples were determined to be below the analytical report limits.　 There were 4 out of 8 composite Category M samples have failed the subsequent biological test.　 Based on the test results, 84% of samples were uncontaminated (Category L), 13% were moderately contaminated (Category M) and 3% were highly contaminated (Category H).

HKBCF and HKLR (EIA Studies in 2008 and 2009)

6.3.5.14 The site specific sediment sampling and testing for HKBCF and HKLR were conducted in 2004 and further updated in 2008 and 2009 when the preferred alignment of the HKBCF and HKLR were more well defined. There were 169 sub-samples from 27 vibrocores and 2 grab samples undertaken in the marine investigation for the HKBCF and HKLR EIAs, and the sampling locations are as depicted in Figure 6.7.　 Details of the test results are further presented in Appendix D1 and a brief summary of the testing results are presented below.

6.3.5.15 With reference to the chemical tests under the ETWB TC(W) No.34/2002, 119 subsamples exhibited compliance with the LCEL, but 50 samples showed exceedance of LCEL, which required biological tests to confirm their disposal options.　 All chemical exceedances were due to the metalloid arsenic (As) concentrations, except one case which was due to lead (Pb).　 Biological screening results for the samples showed that all samples passed the biological tests except the samples A01 (9.9 -10.8m), A5 (8.0-9.0m & 14.0-15.0m), B9 (0.9-1.0m, 5.0-6.0m & 7.0-8.0m), B15 (0.45-1.00m, 1.0-2.0m & 8.0-9.0m), G14, C11 (7.9-8.9m, 9.9-10.8m) and C14 (7.9-8.9m) and disposed of at the confined mud pit would be required, whilst the rest of them could be considered for Open Sea Disposal (Dedicated Sites). 　　

6.3.5.16 Elutriate tests and porewater tests of sediment samples were carried out for the purpose of assessing the potential extent of contaminant release when dredging activities take place.　 The testing parameters for both tests included heavy metals (cadmium, chromium, copper, mercury, nickel, lead, zinc and silver), metalloid (arsenic) and organic micro-pollutants (PCB, PAHs and TBT), chlorinated pesticides and nutrients including ammonia, PO₄-P and total phosphorus.　 In respect of the elutriate test results, in general, the levels of cadmium, chromium, mercury, silver, TBT, PAHs, PCBs and Pesticides were mostly below the reporting limits, whereas other metals and metalloid including copper, nickel, zinc and arsenic, and nutrients including ammonia, PO₄-P and total phosphorus in elutriates varied among sediment samples from different locations.　 For porewater, the levels of the tested parameters exhibited similar pattern as those for the elutriate samples.　 The details of the test results are presented in Appendix D1.　

TM-CLKL

6.3.5.17 Sampling works were conducted by the Term Contractor of Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD) between September to October 2008.　 Vibrocoring at 10 locations was undertaken for the TM-CLKL, as shown in Figure 6.7 to reflect the areas of the preferred reclamation landfalls and marine viaduct alignment.　 The details for the sediments sampling and results are presented in Appendix D1 and a summary provided below.

6.3.5.18 There were 23 sediment sub-samples at the 10 vibrocore locations near the proposed route alignment and reclamation landfalls of the TM-CLKL.　 With reference to the chemical tests under the ETWB TC(W) No.34/2002, 18 samples exhibited compliance with the LCEL, but 5 samples showed exceedance of LCEL, which required biological tests to confirm their disposal options.　 The chemical exceedance included metal (Pb), metalloid (As) and micro-organic pollutants (high molecular weight PAHs) concentrations.　 However, all of these 5 samples with exceedances of the LCEL passed the biological test.　 In summary, two classifications of sediment material has been identified, comprising Category L and Category M, that passes the biological testing (M_p).　 The materials are suitable for disposal in Type 1 open sea and Type 1 Open Sea (Dedicated) disposal, respectively.　

6.3.5.19 Elutriate tests and porewater tests of the grab sediment samples were, also, carried out for the purpose of assessing the potential extent of contaminant release when dredging activities take place.　 The testing parameters for both tests included heavy metals (cadmium, chromium, copper, mercury, nickel, lead, zinc and silver), metalloid (arsenic) and organic micro-pollutants (PCB, PAHs and TBT), chlorinated pesticides and nutrients including TKN, NO₃-N, NO₂-N, NH₄-N, PO₄-P and total phosphorus.　 In respect of the 30 elutriate samples test results, in general, the levels of cadmium, silver, TBT, PAHs, PCBs and pesticides were all below the reporting limits, whereas other metals and metalloid including chromium, copper, mercury, nickel, lead, zinc and arsenic, and nutrients including NH₄-N, NO₂-N, NO₃-N, TKN, PO₄-P and total phosphorus in elutriates varied among sediment samples from different locations.　 However, the metals in elutriate were only detected in a few samples at low level. For nutrients in elutriate, only nitrate were more often (73% of samples) detected while the other nutrient parameters were detected in no more than half of the samples (30-50% of samples). For porewater, the levels of cadmium, lead, mercury, silver, PAHs, PCBs and TBT were all below the reporting limits, whereas other metals and metalloid including chromium, copper, nickel, zinc and arsenic, nutrients including NH₄-N, NO₂-N, NO₃-N, TKN, PO₄-P and total phosphorus in porewater samples varied among sediment samples from different locations.　

Summary of Sediment Quality

6.3.5.20 In conclusion, there is an abundance of sediment quality data pertaining to the study area for this assessment which indicates that the sediments are overall not contaminated with only a few exceptions. With respect to the present project, however, since site specific ground investigation and sediment quality data has been collected during the course of the EIA studies, assessment will be based on these site specific data rather than the general area-wide data collected for other purposes. 　

6.3.5.21 There may be concern, however, that the loss of moderately contaminated material to suspension could adversely affect water quality.　 The data obtained from the previous and on-going monitoring programmes for the disposal operation at East Sha Chau Contaminated Mud Pits, however, does not indicate that sediment contamination is having an impact on marine water quality and there is a weight of evidence to indicate that the sediments to be dredged for the TM-CLKL project are not contaminated such that they might reasonably be expected to exert any significant ecotoxicological impact if disturbed during the course of the Project.　 This issue, however, is addressed further below in the impact assessment.

6.4 Assessment Criteria

6.4.1 Water Quality Objectives

6.4.1.1 For the WCZs of interest, the WQO for suspended solids is defined as “waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities”.　 It is expected that the North Western WCZ will experience the largest impact from the construction works but the Western Buffer WCZ could also be impacted to some extent.　 As a result, in order to determine the ambient suspended solids concentrations in the waters likely to be impacted by the construction works, data in the North Western and Western Buffer WCZs from EPD’s routine water quality monitoring programme from 1998 to 2007 at Stations NM1, NM2, NM3, NM5, NM6, NM8 and WM4 (see Figure 6.5b) have been analysed.　

6.4.1.2 The EPD data is obtained near the sea surface, mid-depth and near the seabed and a summary of the statistics are presented below in Tables 6.9a and 6.9b, where the wet season has been taken to be from mid-April until the end of September each year.

Table 6.9a 　　　 Suspended solids concentrations from EPD Routine Monitoring Programme (1998-2007)

Station	Suspended Solids Concentrations (mg/L) 1998 - 2007
	Surface		Middle		Bed		Depth Averaged
	Dry Season	Wet Season	Dry Season	Wet Season	Dry Season	Wet Season	Dry Season	Wet Season
NM1	7.3	5.4	9.8	6.5	13.4	12.3	10.2	7.9
	(43-1)	(25-0.7)	(43-1.1)	(21-1.3)	(53-1.4)	(45-1.2)	(41-1.5)	(20.5-3.1)
NM2	6.7	4.4	8.7	4.9	12.1	7.7	9.1	5.6
	(21-1.1)	(9.7-1.2)	(28-1.6)	(14-1)	(47-2.2)	(32-1.7)	(30-1.7)	(17.3-2.4)
NM3	7.1	5.3	9.3	7.2	15.4	13.8	10.6	8.8
	(16-1.6)	(15-1.2)	(21-1.2)	(20-1.4)	(71-2.3)	(46-2.1)	(32.3-1.9)	(23-2.7)
NM5	8.4	6.5	10.4	7.9	20.8	27.7	13.2	14
	(19-1.6)	(17-1.2)	(29-1.6)	(44-2.3)	(81-2.3)	(210-3.2)	(37.7-2)	(86.9-3.3)
NM6	10.2	5.4	11.4	6.2	16.0	12.4	12.5	8.3
	(32-2.9)	(12-0.9)	(40-2.1)	(12-1.8)	(60-3.2)	(84-2.4)	(42.7-2.8)	(35.7-2.6)
NM8	11.6	5.9	14.7	8.8	21.9	16.5	16	10.3
	(48-1.3)	(17-2.4)	(63-2.6)	(25-2.0)	(73-3.6)	(63-2.4)	(56.7-2.7)	(30.5-4.5)
WM4	6.9	3.9	11.1	6.2	14.8	12.7	10.9	7.6
	(21-0.8)	(7.9–0.9)	(52-0.6)	17-1.2	(80-1.5)	(110-1.2)	(49-1.3)	(40-1.2)

Notes　　 The data are presented as the arithmetic mean and range (max. – min.) of the suspended solids concentrations at each station at the three monitoring levels and as the depth averaged concentrations.

Table 6.9b 　　　 90th Percentile Suspended solids from EPD Routine Monitoring Programme (1998-2007)

Station	90th Percentile Suspended solids Concentrations (mg/L)
	Surface		Middle		Bed		Depth Averaged
	Dry Season	Wet Season	Dry Season	Wet Season	Dry Season	Wet Season	Dry Season	Wet Season
NM1	14.6	8.1	17.6	11.2	34.0	21.0	20.4	12.4
NM2	11.1	6.9	17.5	8.2	20.2	13.0	15.5	9.4
NM3	12.0	8.2	16.0	12.5	27.0	23.2	17.9	13.5
NM(1,2,3)	12.0	7.7	17.0	10.9	27.0	20.0	18.5	12.2
NM5	15.2	11.6	18.4	11.0	46.2	46.2*	26.9	21.0*
NM6	21.0	8.4	22.8	9.6	31.0	23.6	25.8	13.0
NM8	21.5	10.2	28.0	18.1	43.2	28.8	30.6	18.8
NM(5,6,8)	19.0	10.0	25.8	12.0	39.4	34.4	27.7	18.7
WM4	13.0	5.7	20.0	9.5	30.0	20.0*	20.2	11.3*

Notes　　 * = outliers (unusual high SS removed) before statistical calculation.

　　　　　　　 NM(1,2,3) = pooled results by combing the data set from NM1, NM2 and NM3.

　　　　　　　 NM(5,6,8) = pooled results by combing the data set from NM5, NM6 and NM8.

6.4.1.3 The construction impacts which could arise during the dredging and filling works for the TM-CLKL+HKBCF+HKLR, also, bearing in mind the potential cumulative impacts with other concurrent construction works including the HZMB, could cover the coastal waters in the North West WCZ and the Western Buffer WCZ.　 From Table 6.9b above, it can be seen that the 90^th%ile concentrations for suspended solids varies significantly among the EPD monitoring stations.　

6.4.1.4 As a result, in the current study, rather than average the 90^th%ile concentrations over the whole area which could be impacted by the construction works, it is proposed to assign each sensitive receiver to the nearest EPD water quality monitoring station and to set the WQO at each station as 30% of the 90^th%ile at that station. As indicated in Table 6.9a, monitoring results at NM1, NM2 and NM3 in the eastern half of the NWWCZ are fairly homogenous and reasonably distinct from those recorded at NM5, NM6 and NM8 on the western side of NWWCZ. Based on the hydrodynamics of the NWWCZ, major flows on the western side are mainly north-south and more heavily influenced by the Pearl River discharge and this would, also, account for the higher ambient SS levels recorded. 　Based on the data pattern, it is proposed to group the stations of similar characteristics with respect to SS into two parts, the eastern (NM 1,2,3) and western (NM 5,6,8) portions. This serves to rationalise the WQO assessment exercise, although the calculated 90%ile for each individual station has, also, been included in Table 6.9b as reference. 　The delineation of the eastern and western parts and, also, the EPD stations are presented in Figure 6.5b. 　The WQO are usually interpreted as applying to the depth averaged suspended solids concentrations.　 However, near bed suspended solids concentrations, especially when impacted by dredging and filling works, can be significantly larger than the depth averaged suspended solids concentrations.　 As a result, when assessing the impacts of the dredging and filling works on the suspended solids concentrations, it is proposed that while the principal assessment criteria shall be the depth averaged 90^th%ile concentrations in Table 6.9b, a secondary WQO criteria for each depth has, also, be referenced in the assessment, especially when a higher SS elevation at the bottom level occurred and when the SS levels in the bottom level are naturally higher than the water column.　 The WQO for each EPD monitoring station derived in this way are presented in Table 6.10 below.

Table 6.10　 Water Quality Objectives for the Assessment of Elevations in Suspended Solids Concentrations (mg/L) due to Construction Impacts

Station	WQO for Suspended Solids (mg/L)**
	Surface			Middle		Bed		Depth Averaged
	Dry Season	Wet Season	Dry Season		Wet Season	Dry Season	Wet Season	Dry Season	Wet Season
NM1	4.4	2.4	5.3		3.4	10.2	6.3	6.1	3.7
NM2	3.3	2.1	5.3		2.5	6.1	3.9	4.6	2.8
NM3	3.6	2.4	4.8		3.8	8.1	7.0	5.4	4.1
NM(1,2,3)	3.6	2.3	5.1		3.3	8.1	6.0	5.5	3.7
NM5	4.6	3.5	5.5		3.3	13.9	13.9*	8.1	6.3*
NM6	6.3	2.5	6.8		2.9	9.3	7.1	7.8	3.9
NM8	6.5	3.1	8.4		5.4	13.0	8.6	9.2	5.7
NM(5,6,8)	5.7	3.0	7.7		3.6	11.8	10.3	8.3	5.6
WM4	3.9	1.7	6.0		2.8	9.0	6.0*	6.1	3.4*
WM4 (FCZ)	-	-	-		-	-	-	39.1	43.0*

Notes　　 * based on outliers adjusted 90%ile; ** denotes an elevated in SS not an absolute value.

　　　　　　　 NM(1,2,3) = pooled results by combing the data set from NM1, NM2 and NM3.

　　　　　　　 NM(5,6,8) = pooled results by combing the data set from NM5, NM6 and NM8.

6.4.1.5 Based upon the values detailed in Table 6.10 above, each specific point / sensitive receiver that will be included in the water quality model has been assigned a specific WQO for suspended solids, as detailed in Table 6.11 below.

Table 6.11　 Water Quality Objectives for Observation Points and Water Sensitive Receivers

Output　 Points	Name	Associated EPD Station	Dry Season WQO/WQC				Wet Season WQO/WQC
			S	N	B	DA	S	M	B	DA
WSR 8	Lung Kwu Sheung Tan (non-gazetted beach)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 9a	Urmston Road (Main Channel)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Sha Chau and Lung Kwu Chau Marine Park	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Castle Peak Power Station Cooling Water Intake (Note 1)	-	764	764	764	764	764	764	764	764
WSR 12	Butterfly Beach (gazetted beach)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	WSD Seawater Intake at Tuen Mun	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Gazetted Beaches at Tuen Mun	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Gazetted Beaches along Castle Peak Road	WM4	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 19	Gazetted Beaches at Ma Wan	WM4	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Ma Wan Fish Culture Zone (Note 2)	-	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Ta Pang Po (near Sunny Bay Mangrove)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	Tai Ho Wan Outlet (inside)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Tai Ho Wan Outlet (outside) / Near coral site	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Airport Cooling Water Intake (NE)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	San Tau Beach SSSI	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Airport Channel / Airport Cooling Water Intake (S)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Hau Hok Wan (Horseshoe Crab Habitat)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Sha Lo Wan (Horseshoe Crab Habitat)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Tai O (Mangrove Habitat)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yi O (Mangrove and Horseshoe Crab Habitat)	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Artificial Reef at NE Airport	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Artificial Reef at Sha Chau	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	Sham Shui Kok (CWD habitat range)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	Tai Mo To (near coral / CWD habitat range)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	River Trade Terminal	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	River Trade Terminal (near coral site)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	Airport Channel western end	NM(5,6,8)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	Tai Mo To (Deep Channel / CWD habitat range)	NM(1,2,3)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:

“-“　 the criteria for construction plumes are not based on ambient level but on specific information as noted below.

1. 　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764 mg/L (ERM, 2006)

2. 　 Allowable increase based on general water quality protection guideline for FCZ (CityU, 2001) and long-term average of EPD monitoring results.

6.4.2 Others

6.4.2.1 In addition to the general WQO described above, other beneficial users of the coastal waters, for example, fish culture zones and seawater abstraction pumping stations, may also set specific limit levels on the absolute maximum suspended solids concentrations at the intake points.　

6.4.2.2 The limit levels set for seawater abstractions are generally much larger than are found naturally in the coastal waters (for example, 764 mg/L for the Castle Peak and Black Point Power Station (ERM, 2006)) and, in the current studies, it will be assumed that if the general WQO governing suspended solids concentrations is satisfied, then the requirements for any pumping stations will also be satisfied.

6.4.2.3 The Ma Wan fish culture zone could be impacted by the dredging and filling works and an additional limit level of 50mg/L will be set for the fish culture zone as local study has indicated that general tolerance of fishes to high suspended solids (CityU, 2001). Since the model predicts the anticipated elevation rather than the absolute value, the allowable increase has been calculated as the difference between the criterion value and the annual mean values of the nearest EPD station. The Ma Wan FCZ is in the Western Buffer WCZ and the nearest EPD station is WM4 and the wet and dry season means have been calculated and also presented in Table 6.9b. The proposed allowable elevations are shown in Table 6.10.

6.4.2.4 Deposition of fine sediment in ecologically sensitive areas including coral sites could also have an adverse impact on the marine ecosystem.　 In previous studies (Binnie 1996, Meinhardt 2007, Mouchel 2002), an indicator level above which sustained deposition could harm sediment sensitive hermatypic corals of 200 g/m²/day has been used.　 Soft corals typical of the north western coastal waters where the sediment regime is more dynamic than in other parts of Hong Kong’s coastal waters are expected to be even more tolerant of deposition.　 In a recent study in Tolo Harbour and north eastern waters (ERM 2003), however, an impact criterion of 100g/m²/day has been used but this may be overly conservative in the North-western waters.　 In the current study, it is proposed that an upper limit of 200g/m²/day is set but that any areas subject to deposition rates of over 100g/m²/day are, also, assessed to ensure any particularly sensitive areas are protected.

6.4.2.5 It has already been concluded above that the sediments are, overall, of low levels of contamination and, therefore, not at a level that dredged sediment might reasonably be expected to exert any significant ecotoxicological hazard.　 However, the elutriate and pore water tests, conducted as part of the project specific testing for the TM-CLKL, do confirm that some pollutants are leaching from the sediment.　 Therefore, in order to assess this matter further, the maximum worst case increases in dissolved contaminants associated with the sediment plumes which might be generated by the project related dredging and filling works have been calculated and compared with environmental quality standards for each contaminant where such a standard has been set.　 The European Environmental Quality Standards for metals and metalloids are detailed in Table 6.12a below.

Table 6.12a　 European Union Environmental Quality Standard (EQS) Values to Protect Marine Life

Metals and Metalloid	Water Quality Standard (as dissolved metal) (µg/L)
Arsenic	25
Cadmium	2.5
Chromium	15
Copper	5
Lead	25
Mercury	0.3
Nickel	30
Silver	Not defined
Zinc	40

6.4.2.6 The Water Quality Criteria (WQC) of Sea Water for Flushing Supply (at intake point) issued by the Water Supplies Department (WSD) specify the criteria for assessing the water quality impacts on WSD’s seawater intakes.　 Table 6.12b tabulates a list of the criteria. 　It is noted that this set of criteria is more relevant to the operation stage assessment rather than construction stage.

Table 6.12b　 WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes

Parameter	Concentration (mg/L)
Colour (H.U.)	< 20
Turbidity (N.T.U)	< 10
Threshold Odour No.	< 100
Ammonia Nitrogen (NH4-N)	< 1
Suspended Solids (SS)	< 10
Dissolved Oxygen (DO)	> 2
Biological oxygen Demand (BOD5)	< 10
Synthetic Detergents	< 5
E. coli / 100 ml	< 20,000

6.5 Key Issues

6.5.1 Background

6.5.1.1 The key issues pertinent to the water pollution during the construction and operational phases are summarised below.　 As noted above, where assessment of these factors requires water quality modelling, the assessment has been based upon the combined TM-CLKL+HKBCF+HLKLR projects.　 However, other marine and land-based factors are relevant to the TM-CLKL only.　

6.5.2 Construction Phase

6.5.2.1 The principal water quality concern associated with this project relates to disturbance to the seabed during the construction period.　 There will be a need for extensive dredging and filling for both the seawalls and the reclamations for all three projects.　 These operations will inevitably result in the loss of sediments and backfilling materials into the water column where they will add to the suspended sediment load.

6.5.2.2 During dredging works fine material will be displaced and may be carried downstream of the works area.　 The extent of the suspended sediment plume will depend on the rate of release and, thus, the working methods adopted, the particle size of the dredged material and its characteristic settling velocity, the prevailing currents and hydrodynamic conditions.　 Similar disturbance may be experienced during backfilling, although the backfill material will be very much coarser grained and heavier (sand fill and public fill).　

6.5.2.3 Sediment laden plumes may directly affect marine organisms through abrasion and clogging of fish gills and other organs or possibly as a result of reduced light penetration.

6.5.2.4 From the review of sediment quality data above, it can be concluded that the dredging operations would be most unlikely to release significant levels of contaminants of potential ecotoxicological concern into the wider environment.　 In some situations dredging operations can give rise to concerns about possible release of nutrients or organically rich material which could result in water column oxygen depletion.　 However, there is very extensive experience of dredging operations for construction works similar to those intended for this project within the marine waters of Hong Kong.　 Nutrient enrichment or oxygen depletion has never been reported as a major concern for marine dredging works in Hong Kong previously and there is no reason to believe that these processes would be of concern in the well flushed North-western Waters.　 Notwithstanding, based upon the fact that some contamination is present and some of this does leach into the surrounding waters, as noted by the elutriate tests for the TM-CLKL (Appendix D1), some further analysis have been undertaken.

6.5.2.5 In addition to the marine works, the TM-CLKL project would entail significant land based works to construct the toll plaza and connecting viaducts.　 The main water quality related issues will be to prevent erosion on site and minimise suspended sediment loads washed out in stormwater and well as the need to control waste water streams such as temporary sewage facilities, cementitious waters and general construction refuse.　 Control of construction phase sewage will, also, be an issue and toilets will need to be connected to the local sewerage system if possible during construction but if not feasible chemical toilets will be used.　

6.5.2.6 In summary, the key construction phase issues will be as follows:

· Changes in the coastline configuration that may lead to short-term impacts on hydrodynamic and water quality conditions, and water sensitive receivers (WSRs) within the North Western waters and adjacent water bodies;

· Dredging and filling activities during the construction period which may release of suspended solids and generation of sediment plumes, and release of contaminants and nutrients into the water body;

· Changes in sediment deposition rate which may affect the adjacent WSRs and ecological sensitive receivers;

· Construction site runoff causing the increase in suspended solids levels and possibly oils due to erosion of exposed surfaces, stockpiles and material storage areas, fuel and oil storage and maintenance areas and dust suppression sprays;

· Wastewater and sewage generated from construction activities causing pollution of the surrounding water bodies

· Disturbance to banks and stream beds during culverting and slope reinforcement or toll plaza works;

· Litter from packaging materials and waste construction materials; and

· Construction workforce sewage.

6.5.3 Operational Phase

6.5.3.1 The key operation a phase issues are related to the effects that the proposed reclamations will have on the larger scale flows in the area and any subsequent deterioration in water quality.　 The key issues are as follows:

· significant reduction or acceleration of tidal flows resulting in siltation or erosion of seabed and scour hole formation;

· reduction in water quality;

· siltation and loss of water depth;

· poorly flushed embayments;

· accumulation of floating debris; and

· reduced dispersion of cooling water discharges and increase in seawater temperature.

6.5.3.2 There will be no routine discharge of wastewater or contaminated surface drainage to sea or surface watercourse in the operational phase but there will be some run-off from the road surfaces that could be marginally contaminated with pollution from vehicles fuel.　

6.5.3.3 Sewage from toll plaza and ventilation buildings offices will be minimal, amounting to only about 178.5m³/day for the northern end of the study area (northern landfall and toll plaza) and only 3.5m³/day for the southern landfall.　 In the north, the sewage will be discharged to the existing sewerage system and it is expected that that adequate capacity in the local system to accommodate this amount is available.　 For the southern landfall ventilation building, the estimated sewage generation is very small and will be collected and pumped to the on-site HKBCF sewage treatment works located in the south-east corner of the HKBCF reclamation which has enough spare capacity for this small amount.　

6.5.3.4 In summary, the key operational phase issues will be as follows:

· Changes in coastline configuration that may lead to long-term impacts on the hydrodynamic and water quality conditions, and WSRs within the North Western waters and adjacent water bodies;

· Changes in sedimentation and erosion patterns at San Tau SSSI, Tai Ho Bay and North Western waters;

· Surface runoff from the northern and southern reclamation landings of the TM-CLKL, the main reclamation of HKBCF and also the coastal reclamation of HKLR; and

· Sewage generated from the TM-CLKL+HKBCF+HKLR project.　

6.6 Concurrent Projects

6.6.1.1 Notwithstanding the fact that the TM-CLKL+HKBCF+HKLR would be constructed and implemented together, it is necessary to take into account other projects that may be constructed or be in place during the operational phase of the three projects and which could result in cumulative impacts.　　

6.6.1.2 As such, it will be important to ensure that all probable concurrent projects which could result in cumulative impacts during the construction and operation of the combined projects are assessed in the water quality model studies and, where detailed information is available, that the construction rates and programme data for each project are employed.　 If detailed information is not yet available on the construction programmes for possible concurrent projects, assumptions will be made to assess the worst case scenarios.

6.6.1.3 The major developments being planned for implementation in the North-western coastal waters and, further afield, in Victoria Harbour and the Western Harbour as summarised in Table 6.13 below and further details presented in Appendix A2.　 In addition, the operation of the contaminated mud pits at East of Sha Chau and the construction and operation of the proposed new contaminated mud disposal facility at South of the Brothers have the potential to result in cumulative impacts on the marine environment during the construction of the TM-CLKL+HKBCF+HKLR.

Table 6.13　　 Concurrent Projects

Proposed Development	Impacts to be Considered
For Inclusion
Kwai Tsing Container Basin Dredging	Construction and Operation
Proposed Lantau Logistics Park (LLP) and Possible LLP Extension or other compatible uses	Construction (72ha development) Operation (72ha and 40ha developments)
Tonggu Channel	Construction (annual maintenance dredging) and Operation
Hong Kong Zhuhai Macao Bridge (HZMB)	Construction and Operation
Hong Kong Zhuhai Macao Bridge (HZMB) – Hong Kong Link Road (HKLR)	Construction and Operation
HZMB Hong Kong Boundary Crossing Facilities (HKBCF) and Tuen Mun Chek Lap Kok Link (TM-CLKL)	Construction and Operation
Road P1, Sham Shui Kok to Sunny Bay	Operation (based on assumed programme to be operational in 2026)
Further Tung Chung East and West Developments	Operation (construction to begin after completion of the TM-CLKL+HKBCF)
Existing and Proposed Contaminated Mud Disposal Facility at East of Sha Chau and South of Brothers	Construction and Operation for Target Year of 2011-2013
Mud Disposal Facility at North Brothers	Operation (when disposal operations might begin is not known but it is possible this facility could be operational after 2009)
For Exclusion
Airport Master Plan 2030 (3rd Runway)	Exclude due to lack of detail
CLP 2 x 132kV submarine cables	Exclude due to lack of data
Proposed submarine gas pipe across the Urmston Road	Exclude due to lack of data
Permanent Aviation Fuel Facility (PAFF)	Exclude – will be completed in 2009
SkyPier II	Exclude – no significant marine works
Organic Waste Treatment Facility	Exclude – no marine works
Container Terminal 10	Exclude – insufficient data on reclamation layout to include in hydraulic studies

Note 1:　 Only preliminary/indicative layout or layout options are available for the proposed HKIA 3^rd runway and, further afield, CT10, which could be expected to have significant impacts on tidal flows and water quality in the Western Harbour. Therefore, it is considered that the designs for CT10/3^rd Runway are too uncertain to be included in the current study.

6.6.1.4 Cumulative construction impacts of concern are principally those associated with elevations in suspended solids concentrations in the receiving waters during dredging and filling works. 　Details of the concurrent construction works to be assessed have been discussed in Section 6.7.4 below and presented in Appendix D5a.　 Operationally, all potential project that may be in place once the TM-CLKL+HKBCF+HKLR have been completed, have been considered in the assessment.

6.7 Assessment Methodology

6.7.1 Background

6.7.1.1 The Delft3D suite of computer models of tidal flows has been set up, calibrated and validated under previous Agreements with the Government of Hong Kong and, since 1996, the models have been applied in a large number of marine environmental studies in Hong Kong’s coastal waters.　 Under these studies, the models have been applied using a number of different model grids covering different areas of Hong Kong’s coastal waters at different spatial resolutions depending on the requirements of each particular study.

6.7.1.2 For the current Investigation, it was important that the model included the coastal waters to the South of Lantau Island to ensure that, if the proposed development does have the potential to impact on tidal flows passing North Lantau Island, the applied boundary conditions do not artificially force a flow through the relatively narrow channel between North Lantau and the New Territories and that any tidal or residual circulation around Lantau Island can correctly respond to any effects from the proposed development.

6.7.1.3 One model, the Western Harbour Model (WHM) (Figure 6.8), is considered suitable for application under the current Investigation with some minor refinements.　 For the current assessment, the model grid has been refined further in the study area to ensure that the reclamations and local flow channels are resolved adequately.　 The refined model grid in the vicinity of the proposed reclamations is shown in detail in Figure 6.9, which also shows an approximate layout for the TM-CLKL+HKBCF+HKLR combined projects to illustrate the proposed resolution of the model grid in these areas (70m-100m).　 Other proposed concurrent project such as the LLP (72ha and 40ha reclamations) and the proposed remaining Tung Chung development (these are discussed further in Section 6.6 above) are, also, included for reference.　

6.7.1.4 The Government already hold the full documentation for the Delft3D models which they run on their in-house computers at present and the model satisfies the requirements of Appendix H to the EIA Study Briefs.　 The model, before the recent refinements, has also been applied in previous studies of construction impacts in the North-western coastal waters including the impacts from the dredging for the pipeline for the Permanent Aircraft Fuel Facility between Tuen Mun Area 38 and the current Aviation Fuel Receiving Facility (AFRF) at Sha Chau.

6.7.1.5 The model of tidal flows was used to simulate the same 15-day wet and dry season spring-neap tidal cycles for which it had been calibrated and a sufficient number of 15-day cycles were run in each season (spin-up) to allow any transient effects generated at the start of the simulation to dissipate.　

6.7.1.6 The marine viaducts for the TM-CLKL southern connection and HKLR marine bridge will be supported on piles where the individual piles will be of the order of 2m or less in diameter and cannot be resolved by the model grid.　 However, Delft Hydraulics have developed a method of representing the effects of individual piles and groups of piles on tidal flows which involves the calculation of additional loss coefficients to be included in each model cell containing one or more bridge piers.　 This method is discussed further below.

6.7.2 Model Validation

6.7.2.1 The Delft3D hydrodynamic model was used to simulate tidal and seasonal flows for the Year 2010 which is considered a baseline year.　 This scenario was based on the coastline and bathymetry expected to be relevant prior to the start of construction in 2010 and was required to generate the baseline hydraulic conditions which were required in order to validate the refined model grid. Representative plots of discharges across major sections, time history of water level, salinity and current speed to demonstrate this are presented in Appendix D15a.

6.7.2.2 The model validation baseline simulation for year 2010 has been completed using the new fine grid model and the results have been compared with the results from simulations of the same scenario using the original Western Harbour model grid.　 This comparison was required to ensure that the introduction of the fine grid areas in the vicinity of the proposed TM-CLKL+HKBCF+HKLR reclamations had not altered the established calibration of the Western Harbour model and that the spin-up period was sufficiently long to allow the model to reach equilibrium. Representative plots of discharges across major sections, time history of water level, salinity and current speed to demonstrate this are presented in Appendix D15b. Since the flow simulation of the 2011 scenario for Sequence B is based on the stabilised 2011 scenario of Sequence A, additional verification plots for Sequence B is presented in Appendix D15c.

6.7.2.3 The simulations were carried out for wet and dry seasons over a 15-day spring-neap tidal cycle after allowing for a suitable spin-up period.

6.7.3 Operational Phase Methodology

6.7.3.1 Operational phase assessment comprised the modelling of both tidal and seasonal flows and, also, water quality.　 The methodologies applied are detailed in the sections below.

Tidal Flow Simulations

6.7.3.2 Having refined the model grid, the Delft3D hydrodynamic model was used to simulate various tidal and seasonal flows for assessment purposes, in addition to the year 2010 scenario used for model validation as discussed above.　

6.7.3.3 The tidal flow simulations have been chosen to represent the worst case scenarios during both the construction and operational phases of the project.　 As the project works will last over some years, several interim construction stages were considered. The anticipated project progress and construction programme were reviewed and the projected monthly maximum daily sediment loss into suspension derived based on the project progress, plant inventory and the types of marine construction activities involved.

6.7.3.4 The details of derivation of worse case construction scenarios are presented in Appendix D5a and a summary of the modelling scenarios is detailed in Appendix D2 and these are briefly summarised below.

(a) Year 2011, Construction Scenario 1:　 This Scenario was based on the coastline and bathymetry expected to be relevant to February 2011 when the construction of the HKBCF and HKLR has begun and the potential sediment loss rates from dredging and filling were at their maximum (see Appendix D5a);　

　　　　　　　　　　　　　　　　　　

(b) Year 2012, Construction Scenario 2:　 This Scenario was based on the coastline and bathymetry expected to be relevant to April 2012 when the construction of the TM-CLKL, HKBCF and HKLR would be well under way and would have had the potential to modify tidal currents.　 April 2012, also, coincided with a second peak in the potential loss rates (see Appendix D5a);

(c) Year 2013, Construction Scenario 3:　 This Scenario was based on the coastline and bathymetry expected to be relevant to April 2013 when the construction of the TM-CLKL, HKBCF and HKLR would be nearing completion and would have had the potential to modify tidal currents.　 April 2013 is, also, the time after which potential sediment losses would decrease rapidly to zero (see Appendix D5a);

(d) Year 2026: The Completed Scenario. As detailed in Appendix D2, this scenario includes the completed TM-CLKL+HKBCF+HKLR reclamations and associated bridges, the HKLR and HZMB bridges and artificial islands, Road P1, the increased water depths in the Kwai Tsing Container Basin and associated fairways, the LLP completed reclamations (72ha and 40ha), the completed Tung Chung East and West Reclamations for the completion year of 2026 for all committed projects (Figure 6.10).　 It is anticipated that the TM-CLKL+HKBCF and HKLR will be completed in 2016 but, in order to assess long term operational impacts, the target year of 2026 has been selected to allow for completion of all other expected reclamations (Table 6.12);

(e) As (d) above but without the TM-CLKL+HKBCF+HKLR.　 This simulation was required to provide information on the future tidal hydraulic conditions if all other proposed works are completed but the TM-CLKL+ HKBCF+HKLR is not constructed.

6.7.3.5 All tidal flow simulations were carried out for wet and dry seasons over a 15-day spring-neap tidal cycle after allowing for a suitable spin-up period.

6.7.3.6 As noted above, the bridge piers for the marine viaducts of the TM-CLKL southern connection and HKLR cannot be resolved by the model grid.　 In order to allow for the effects of the bridge piers on tidal flows, therefore, the Delft3D-Flow model allows for the addition of a quadratic friction term in the momentum equations which is applied in each model grid cell containing a bridge pier.　 The details of the bridge piers and the calculated loss coefficients applied in the modelling are presented in Appendix D3.

6.7.3.7 The tidal flows simulations (d) and (e) above were undertaken in order to obtain results for the future condition (2026) which would arise both if the TM-CLKL+HKBCF+HKLR had been built and, also if they were not implemented.  The results were required to provide the basic hydraulic input for the model of water quality and to identify any impacts on tidal flows resulting from the three projects. By comparing the results from these simulations, the possible impacts the TM-CLKL+HKBCF+HKLR works might have on the future marine environmental condition when all other reclamations have been completed can be assessed.

6.7.3.8 Simulations for 2011, 2012 and 2013 ((a) to (c) above) have been undertaken to provide the tidal flow data required to assess construction impacts at intermediate stages of construction when potential sediment losses were at their greatest and to cover the range of changes in tidal flow patterns which might result as the construction works proceeded.

6.7.3.9 The model stored the results at regular intervals throughout the 15-day simulations at a large number of specific locations and in each of the 10 model layers over the whole area being modelled.　 The model results from all the simulations for the wet and dry season baseline and post TM-CLKL+HKBCF+HKLR construction scenarios have been be presented in graphical and/or tabular form for the 2026 simulations ((d) and (e) above) and include:

(i) Velocity vector plots at peak flood and ebb tidal flows covering the entire length of the TM-CLKL and detailed near surface, mid-depth and near bed velocity vector plots covering the southern and northern landfalls where impacts from the TM-CLKL+HKBCF+HKLR might be expected to be greatest;

(ii) Peak speed contour plots and time-history plots at stations in the Urmston Road to demonstrate any changes to large scale tidal flows are not affected or only affected slightly; 

(iii) Time history plots of instantaneous and accumulated flows through major sections near the project area where impacts are likely (Ma Wan, Airport North and the Airport sea Channel) for the with and without scenarios;

(iv) Time history plots of water levels, water speeds, salinity at selected sensitive receivers (as shown in Figure 6.5b) have been presented where the points have been selected to be located:

· in the channel between the Airport Island and Tai Mo To (WSR 49);

· in the San Tau SSSI at the Airport Sea Channel (WSR 27); 　

· in the Urmston Road offshore of the River Trade Terminal (WSR 9a);　

· at the Ma Wan Fish Culture Zone (WSR 20);　

· in the centre of East Tung Chung Bay (WSRs 26 and 43);

· in the Sha Chau and Lung Kwu Chau Marine Park (WSR 10);

· over the cooling water intakes Black Point Power stations (WSR 7); and

· at the Cheung Sha Wan Fish Culture Zone (WSR 40).

(v) Time history plots of the instantaneous and cumulative tidal discharges and salt flux across a number of sections across the main flow channels in Hong Kong’s coastal waters (Airport North, Ma Wan, Deep Bay, Victoria Harbour, East Lamma Channel, West Lamma Channel and Admasta Channel), and across the Airport Sea Channel (Figure 6.11); and

(vi) For the major sections around the project site described in (iii) above, tabulations of:

· the peak flood and ebb tide discharges through the sections on selected large and small amplitude tides within the 15-day period of each simulation; and

· the average (residual) discharge across the sections over the 15 day period and the cumulative discharge over the 15-day period for each simulation.　 The tabulations will include the differences in discharges between the baseline and scenario simulations.　 It should be noted, however, that the cumulative discharges over a 15 day period across the longer sections will be very large and any small impacts from the development may not be easily identified from these tabulations.

6.7.3.10 The modelled area included a large number of sensitive receivers and specific points (Table 6.5 and Figure 6.5b) at which time-history plots and tabulations of numerical data could be presented.　 However, to avoid the presentation of excessive model output, results have only been presented at those output points and sensitive receivers where impacts have actually been detected.

Marine Water Quality

6.7.3.11 The assessment of any impacts on the dispersion of effluent and marine water quality as a result of the implementation of the projects needs to be undertaken.　 The Delft3D model of water quality has been applied using an overall effluent loading pattern representative of anticipated future condition following completion of the works.　

6.7.3.12 The pollution loading inventory (PLI) is a compilation of all the waste water (mainly effluent from sewage treatment works, but also surface run-off/storm drains) discharges into the marine environment.　 The Western Harbour Model already has a PLI which has, also, been updated by projects utilising this model and, as such, has been updated to include the loadings projected up to 2016.　 For this study, the selected scenario year for operational assessment is 2026 and the PLI has been further updated with due consideration to the latest forecast for the 2026 population obtained from the Planning Department (PlanD, 2008) and, also, the ultimate design capacity for major sewage treatment works in Hong Kong. 　

6.7.3.13 With respect to this project, areas of potential water quality impacts during the operational phase will largely be related to the proposed on-site sewage treatment works (STW), which is expected to employ secondary treatment technology before discharges.　 The indicative site location and discharge point are shown in Figure 6.12a and 6.12b.　 The on-site STW will have an ultimate design capacity of 1,628 m³/day and the proposed discharge standards are presented in Table 6.14a below.

Table 6.14a　 Design Details of the Proposed On-site STW for TM-CLKL+HKBCF

Flow	BOD5	DO	SS	NH4N	Ortho-P	Total P	Total N	Cu	E. coli
1,628	20	1.5	30	40	2	7	50	30	1,000
m^3/d	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L	ug/L	cfu /100ml

6.7.3.14 Apart from the on-site STW, surface run-off from the paved area may contain suspended solids onto which other pollutants may become attached.　 Potential adverse impacts from runoff from the paved road surfaces (including the carriageway and toll plaza area) can result from storm water carrying dissolved and particulate material from degradation of the road surface and tyres and from normal operational fuel and oil loss from vehicles.　 Contaminants present in the normal operational runoff will, by their chemical nature, be strongly adsorbed onto particulates present.

6.7.3.15 Stormwater drainage systems will be provided to collect stormwater from the reclamation and carriageway surfaces.　 With respect to the roads on land, the stormwater will enter into gullies along the kerb lines and the gullies will be fitted with sumps to trap silt and grit prior to discharging the stormwater into the stormwater drainage systems.　 The drainage systems will eventually discharge the stormwater into the sea at discrete locations.　 A similar system will be provided along the marine viaduct, with sump traps being proposed to be built into the deck structure. The collected stormwater will discharge into the sea at the column locations. The major project related discharging points are illustrated in Figures 6.12a and 6.12b.

6.7.3.16 The storm water pollution loading was estimated based on Hong Kong’s long-term seasonal rainfall data and the EPD Pilot Study on Storm Pollution (cited in Maunsell, 2008). The assumed runoff concentrations are shown in Table 6.14b below.

Table 6.14b　 Event Mean Concentrations for Stormwater Runoff

SS	BOD5	NH4N	Cu	Total P	Ortho-P	Silicate	Total Oxidised N	TKN
43.25	22.48	0.20	0.01	0.20	0.04	3.28	0.40	1.40

Note: All units in g/m³.

6.7.3.17 The updated PLI is presented in Appendix D4. The water quality model has been used to simulate annual cycles using the wet and dry season spring-neap tidal cycles, which were simulated by the flow model, with a sufficient number of repeating cycles being carried out to ensure dynamic equilibrium had been reached.　 The model used the simulated flow fields for the year 2026, both with and without the TM-CLKL+HKBCF+HKLR projects in order to provide a comparison of any possible water quality impacts. 　

6.7.3.18 The simulations have covered annual wet and dry season conditions and the results from the simulations have been presented as:

· Plan contour plots of key water quality parameters (suspended solids in term of percentage difference, dissolved oxygen, inorganic nitrogen, unionized ammonia and E. coli) over the whole of the area affected by the works in each season at high and low water levels on both spring and neap tides;

· Time-history plots of the key water quality parameters at all relevant sensitive receivers as listed in 6.7.3.9 above and also the beaches area to allow a direct assessment of the WQO and possible adverse impacts from the proposed development; and

· Tabulations of monthly average concentrations of the selected water quality parameters at the same stations selected for the time-history plots.

6.7.3.19 When assessing the results from any water quality modelling, where appropriate, comparisons will be made principally between the model results and the WQO for the relevant WCZ for each sensitive receiver and for the receiving waters in general.

6.7.4 Construction Phase Methodology

Assessment Scenarios and Assumptions

6.7.4.1 As discussed above, the principal water quality concerns in the construction period are those associated with dredging and backfilling for the reclamations and the marine viaducts of the TM-CLKL+HKBCF+HKLR projects.　 The sub-sea tunnel for the TM-CLKL will be constructed using TBM which will not cause any seabed disturbance.　 Construction impacts on the marine environment will be related principally to sediment losses to suspension during construction.　 Sediment losses will increase suspended sediment concentrations in the receiving waters which could:

· result in exceedances of the Water Quality Objective (WQO) for the Water Control Zones (WCZs) which could be affected by the works;

· result in deposition rates which might adversely affect corals; and

· result in exceedances of specific water quality standards set for, for example, seawater intakes.　 Sediment losses could also introduce contaminants into the water column if the sediment to be removed is contaminated.

6.7.4.2 In this assessment, representative sediment plumes have been simulated using the Delft 3D tidal flow and water quality models.　 In order to ensure that the worst case conditions were simulated and while remaining consistent with the various construction and disposal programmes, the maximum rates of dredging and filling were simulated at locations and time periods which would maximise the potential for sediment losses to be transported from the works areas and, individually and cumulatively, to impact on sensitive receivers.

Sequence A

6.7.4.3 Under Sequence A, the marine works will be on-going for about 42 months (about 3.5 years), it is not possible to model all conditions throughout this time.　 As such, as noted above, based upon the overall construction programme for the three TM-CLKL+HKBCF+HKLR projects (as seen in Appendix D5a), the times for the worst case loss rates have been determined and, also, other time periods selected to represent situations where partial completion of the construction of the TM-CLKL, HKBCF and HKLR would have had the potential to modify tidal currents.　 As such the following time periods have been selected for the assessment:

· February 2011 when the construction of the HKBCF and HKLR has begun and the potential sediment loss rates from dredging and filling are at their maximum. With reference to the overall duration of marine works, this scenario occurs at around 15% into the programme;　

· April 2012 when the construction of the TM-CLKL, HKBCF and HKLR would be well under way and would have had the potential to modify tidal currents.　 April 2012, also, coincided with a second peak in the potential loss rates. With reference to the overall duration of marine works, this scenario occurs at around 50% into the programme; and

· April 2013 when the construction of the TM-CLKL, HKBCF and HKLR would be nearing completion and would have had the potential to modify tidal currents.　 April 2013 is, also, the time after which potential sediment losses would decrease rapidly to zero. With reference to the overall duration of marine works, this scenario occurs at around 75% into the programme.

6.7.4.4 The anticipated programme of marine works and calculated monthly potential sediment loss is presented in Figure 6.2a and summarised in Figure 6.2c. The assumptions on dredging and filling rates, equipment and sequencing for all three projects, together with the calculations for the overall unmitigated sediment loss rates are presented in full in Appendix D5a. Since the anticipated potential sediment losses is calculated based on the tentative construction programmes for marine works that involve the dredging and filling works below high water mark (+2.5mPD), the assumed daily production rates and number of plants involved are presented in Figures 6.2d and 6.2e and a summary at major construction stages are presented in Table 6.15a below.

Table 6.15a　 Summary of Production Rates and Plants at Major Events for Sequence A

Area	Activities	Production Rate (bulk volume, m^3/day)	No. of Plant Trips / Day	Time & Remark
TM-CLKL North	Max. Dredging	7,200	1 Grab Dredger	Throughout the works period
	Max. Filling	16,000	16 Filling Barge Trips	In 1st quarter 2012. Both seawall and reclamation filling. Leading seawall present for reclamation.
TM-CLKL South	Max. Dredging	14,400	2 Grab Dredgers	Throughout the works period
	Max. Filling	16,000	16 Filling Barge Trips	In end 2012. Seawall filling of S-a are completed and reclamation filling for S-b just begin.
HKBCF	Max. Dredging	155,700	16 grab dredgers and 3 trips of TSHD	In end 2010 - early 2011, Portion A, B, C & FSD seawall dredging concurrent
	Max. Filling	330,000	330 Filling Barge Trips	In mid 2011, Portion A, B, C and FSD reclamation concurrent
HKLR	Max. Dredging	21,600	3 Grab Dredgers	Throughout the works period
	Max. Filling	56,000	56 Filling Barge Trips	In 3rd quarter 2012, Reclamation filling for Portion 1nearly completed, and filling activities for seawall and reclamation of Portion 2 just begin.

Notes:

1. The filling rates and daily number of plant trips are only relevant for filling below +2.5mPD and does not include bored piling works for marine viaducts. Rock filing barge trips not included. The handing of Mf material is also excluded.

2. The production rates are bulk volume and a bulking factor of 1.3 assumed for filling, 1.2 for grab dredging and 1.5 for TSHD dredging.

3. Portion A temporary seawall of HKBCF completed in 2^nd quarter 2011.

Sequence B

6.7.4.5 Under Sequence B, the marine works will be on-going for about 4 years which is slightly longer than Sequence A. As discussed previously, Sequence B will involve overall less dredging and filling. The anticipated programme of marine works and calculated monthly potential sediment losses are presented in Figure 6.2b and summarised in Figure 6.2c.　 As indicated in Figure 6.2c, the monthly sediment loss rate under Sequence B is lower than Sequence A but the first worse case scenario is also predicted to happen around February/March 2011, although the worse case daily loss rate has drastically reduced from 4,394,000kg/day associated with Sequence A at this time to about 1,778,000kg/day under Sequence B. 　Since the identified worse case scenarios of Sequence A are fully modelled for assessment and the fact that potential sediment losses under Sequence B are much lower than Sequence A, it has not been considered necessary to model all the scenarios under Sequence B for the purpose of impact assessment since Sequence B is not a worse case overall. 　Nonetheless, additional water quality modelling for the mitigated scenario for the first identified worse case timeframe (i.e, early 2011) under the Sequence B has also been conducted to confirm this assumption.

6.7.4.6 The assumptions on dredging and filling rates, equipment and sequencing for all three projects, together with the calculations for the overall unmitigated sediment loss rates and the rates adopted for the modelling are presented in full in Appendix D5b for Sequence B. Similar to Sequence A, the anticipated potential sediment losses for Sequence B is calculated based on the tentative construction programmes for marine works that involve the dredging and filling works below high water mark (+2.5mPD), the assumed daily production rates and number of plants involved are presented in Figures 6.2f and 6.2g and a summary at major construction stages are presented in Table 6.15b below.

Table 6.15b　 Summary of Production Rates and Plants at Major Events for Sequence B

Area	Activities	Production Rate (bulk volume, m^3/day)	No. of Plant Trips / Day	Time & Remark
TM-CLKL North	Max. Dredging	7,200	1 Grab Dredger	Throughout the works period.
	Max. Filling	16,000	16 Filling Barge Trips	In 1st quarter 2012. Both seawall and reclamation filling. Leading seawall present for reclamation.
TM-CLKL South	Max. Dredging	64,800	9 Grab Dredgers	In 1st quarter 2011. Seawall dredging.
	Max. Filling	24,000	24 Filling Barge Trips	In 3rd quarter 2011. Seawall filling of S-a nearly completed and reclamation filling for S-a, S-b and S-c just begin
HKBCF	Max. Dredging	72,000	10 Grab Dredgers (9 at HKBCF island and 1 at FSD reclamation)	In 4th quarter 2010. Portion 1 seawall dredging and dredging for FSD concurrent.
	Max. Filling 1	80,000	80 Filling Barge Trips	In early to mid 2011, Portion 1 seawall and FSD seawall
	Max. Filling 2	190,000	190 Filling Barge Trips	In 1st quarter 2012, Seawall filling for Portion 3, reclamation filling for the main island and APM concurrent.
HKLR	Max. Dredging	21,600	3 Grab Dredgers	Throughout the works period
	Max. Filling	56,000	56 Filling Barge Trips	In 3rd quarter 2012. Reclamation filling for Portion 1 nearly completed, and filling activities for seawall and reclamation of Portion 2 just begin.

Notes:

1. The filling rates and daily number of plant trips are only relevant for filling below +2.5mPD and does not include bored piling works for marine viaducts. Rock filing barge trips not included. The handing of Mf material is also excluded.

2. The production rates are bulk volume and a bulking factor of 1.3 assumed for filling and 1.2 assumed for grab dredging.

3. Portion 1 seawall of HKBCF completed in 3^rd quarter 2012.

6.7.4.7 The Delft3D water quality model has been applied to simulate the fate of all fine material expected to be lost to suspension from the simultaneous construction works for the TM-CLKL+HKBCF+HKLR reclamations and bored piled viaduct piers at the times periods detailed above.　 The modelling simulated the same wet and dry season tidal conditions and stages of construction as simulated by the model of tidal flows.　 The modelling has, also, employed the same coefficients to describe the behaviour of fine sediment as have been used in previous studies of construction losses in Hong Kong.　

6.7.4.8 The settling velocity of suspended cohesive sediment is concentration dependent. However, the simulations were carried out using a constant settling velocity of 0.5mm/s which is typical of low suspended solids concentrations. This represents a conservative assumption in that a higher sedimentation rate would actually be expected in the dense plume close to the dredging and filling works.

6.7.4.9 Erosion and deposition in the water quality model are defined in terms of a critical stress for deposition above which no deposition can take place and a critical stress for erosion above which erosion can take place. The critical stress for deposition was set at 0.2N/m² while the water depth of 0.2m was selected as the minimum depth in which deposition can take place. The critical stress for erosion was set at 0.3N/m² which is applicable to relatively soft new deposits with a density of around 200kg/m³ (HWR, 1993) and typically applied in Hong Kong (e.g., ERM 1997, 2005; Meinhardt 2007; Mouchel 2002a, 2002b).

6.7.4.10 The results from the sediment plume simulations have been presented as below and assessed against the criteria presented in Section 6.4 above:

a) Representative plan contour plots of surface, mid-depth and near bed suspended sediment concentrations during peak ebb and peak flood flows. Contours plots have also been presented at high and low water level on selected large (spring) and small amplitude (neap) tides during each of the15-day simulations. Tidal flow speeds at high and low water levels are small and, these plots allow the identification of hot-spots with predicted high localised suspended solids which may form at times of slack water.　 These plots will also show the maximum extent of the sediment plumes on the flood and ebb tides;

b) Time history plots of suspended sediment concentrations near the surface, mid-depth and near the bed at the　 key local sensitive receivers and observation points (see Figure 6.5b for their location) where the predicted elevations in suspended sediment concentrations due to the works are in excess of 0.5mg/L;

c) Tabulations of maximum and depth averaged elevations in suspended sediment concentrations found at each sensitive receiver (surface, mid-depth, near bed and depth averaged) over each wet and dry season 15-day simulation where the maximum elevations are in excess of 0.5mg/L and the percentage of time when any WQO exceedances are predicted; and

d) Plan contour plots of total deposition (g/m²) over each of the wet and dry season simulation periods and plan contour of the daily average deposition rate (g/m²/day).

6.7.4.11 Based upon the review of the sediment quality to be dredged against the criteria stipulated in ETWB TC(W) No.34/2002 (Section 6.3 and Appendix D1), the sediment is classed to be, overall, Category L material which is suitable for open seas disposal.　　 Based upon the data, contamination of the receiving waters during dredging works is not expected.　 However, notwithstanding, the elevations in contaminant levels have been calculated and compared to relevant water quality standards for the preservation of marine life.

6.7.4.12 The maximum worst case increases in dissolved contaminants are calculated based on the predicted elevations in suspended sediment concentrations assuming that all sediment are moderately contaminated (Category M) with contaminant concentrations equal to the UCEL for each contaminant of interest.　 In carrying out these calculations, it has also been assumed that all contaminants adsorbed on the sediments on the seabed desorb and go into solution in the water column (Meinhardt, 2007; Mouchel, 2002b).　 The results for the estimated contaminant concentrations can then be compared with environmental quality standards for each contaminant where such a standard has been set. This is a highly conservative approach as the maximum concentration of suspended solids are often transient in nature and the suspended solids sourced from the filling process (sand and public fills) are not likely to be contaminated although it is assumed to be the case for this assessment.

6.7.4.13 The degree of oxygen depletion exerted by a sediment plume is a function of the sediment oxygen demand of the sediment, its concentration in the water column and the rate of oxygen replenishment.　 For the purposes of this assessment, the impact of the sediment oxygen demand on dissolved oxygen concentrations has been calculated based on the following equation (ERM, 1997):

DO_Dep = C * SOD * K * 0.001

where 　　 DO_Dep = Dissolved Oxygen depletion (mg/l)

　　　　　 C　　　　 = Suspended Solids concentration (kg/m³)

　　　　　 SOD　 = Sediment Oxygen Demand

　　　　　 K　　　　 = Daily oxygen uptake factor (set at 1.0 for worse case estimate)

6.7.4.14 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.

6.7.4.15 The analysis using the above equation does not allow for re-aeration which would tend to reduce any impact of the suspended sediment on the water column DO concentrations.　 The analysis, therefore, errs on the conservative side so as not to underestimate the extent of DO depletion.　 Further, it should be noted that, for sediment in suspension to exert any oxygen demand on the water column will take time and, in that time, the sediment will be transported and mixed/dispersed with oxygenated water.　 As a result, the oxygen demand and the impact on dissolved oxygen concentrations will diminish as the suspended sediment concentrations decrease.

6.7.4.16 Oxygen depletion is not instantaneous and thus previous workers have assumed that the impact of suspended sediment on dissolved oxygen will depend on tidally averaged suspended sediment concentrations (ERM, 1997).　 The previous studies (ERM, 1997) assumed that the oxygen demand would be satisfied at the same rate as the biological demand which equates to a K value of 0.23/day. However for the purposes of this demonstration the maximum increase in suspended sediment has been used as the basis for the calculation in order to identify the hypothetical worst case.　 As such, the daily uptake factor, K, in the equation above was set to be equal to 1.0 (Meinhardt, 2007; Mouchel, 2002b) which indicates instantaneous oxidation of the sediment oxygen demand and represents a worst case to ensure oxidation rates are not underestimated.　 The resulting calculated dissolved oxygen deficit, therefore, is expected to be much larger than would be experienced in reality.

Integrated Protection Measures (Sequence A)

6.7.4.17 In determining the construction methods, equipment and sequencing for the reclamation works and pier construction, measures which would minimise the amount of sediment lost to suspension have been integrated as far as possible.　 Such measures include:

· minimisation of the overall footprint of the project sites and, also, combing the TM-CLKL southern landing with the HKBCF island and, thus, further reducing the overall works area.　 For TM-CLKL, the toll plaza has moved from the northern reclamation to a terrestrial site, thereby reducing the size of the reclamation. For HKBCF, the width of the land-bridge between the HKBCF island and the airport has also been reduced (however, for the purpose of the worse case assessment, a bigger HKBCF footprint is assumed in this chapter, Appendix D5a);

· for the submarine tunnel of TM-CLKL, a tunnel boring machine construction method has been adopted instead of the traditional immersed tube tunnel, thereby reducing the dredging and filling requirement;

· formation of seawalls prior to the reclamation dredging and filling.　 In order to achieve this, a temporary seawall enclosing Portion A of HKBCF has been proposed (Appendix D5a), with a 100m gap for marine access.　 With this arrangement, the reclamation dredging and filling activities will be mostly enclosed within seawalls, reducing the potential sediment loss by about 80%.　 However, to be conservative, this factor has only been applied at the reclamation filling stage when the seawalls, other than the access gap, have been completed;

· advanced seawalls before reclamation dredging and filling as far as possible.　 Where the reclamation dredging and filling activities cannot be deferred until the seawalls are completed due to programme constraints, the works will be scheduled to be at least 200m behind the formed seawalls.　 This is expected to reduce the potential sediment loss from the reclamation dredging and filling by at least 45%.　 This has generally been applied for the TM-CLKL, HKBCF and HKLR (Appendix D5a);

· for the marine viaducts of TM-CLKL and HKLR, the bored piling will be undertaken within a metal casing and, therefore, any dispersal of the sediment will be limited to the short time of sediment removal from the top;

· where public fill is proposed for filling below +2.5mPD, the fine content in the public fill will be controlled to 25% which is in line with the CEDD’s General Specification;

· where sand fill is proposed for filling below +2.5mPD, the fine content in the sand fill will be controlled to 5%;

· for HKBCF and HKLR projects, a maximum of 30% public fill to be used for all seawall and reclamation filling below +2.5mPD;

· for TM-CLKL northern and southern landfalls seawalls, a maximum of 50% public fill to be used for seawall filling below +2.5mPD;

· for TM-CLKL southern landfall reclamation, a maximum of 30% public fill to be used for reclamation filling below +2.5mPD; and

· for TM-CLKL northern landfall reclamation, a maximum of 100% public fill to be used for reclamation filling below +2.5mPD.

Integrated Protection Measures (Sequence B)

6.7.4.18 For Sequence B the integrated protection measures formulated in Sequence A are largely retained but the longer construction programme allows for these to be enhanced to further reduce the amount of sediment lost to suspension.　 Major measures include:

· minimisation of the overall footprint of the project sites and, also, combing the TM-CLKL southern landing with the HKBCF island and, thus, further reducing the overall works area (same as Sequence A);

· for the submarine tunnel of TM-CLKL, a tunnel boring machine construction method has been adopted instead of the traditional immersed tube tunnel, thereby reducing the dredging and filling requirement (same as Sequence A);

· further minimisation of dredging/filling by adopting non-dredged reclamation method for a larger portion of the reclamation site. Comparedto Sequence A, this reduces the dredging amount by 37% and filling amount by 22% for the main reclamation site at HKBCF and TM-CLKL (southern landfall) (see Table 6.1b);

· formation of peripheral seawalls prior to, except for 100m gaps for marine access, the main reclamation dredging and filling.　 Under Sequence A, this arrangement is implemented in HKBCF+TMCLKL (south landfall) as much as possible, but is fully implemented under Sequence B;

· for other parts of the reclamation works, advanced seawalls are formed before reclamation dredging and filling.　 Where the reclamation dredging and filling activities cannot be deferred until the seawalls are completed due to programme constraints, the works will be scheduled to be at least 200m behind the formed seawalls (same as Sequence A);

· installation of sheet pile wall next to the northern boundary of the HKBCF+TM-CLKL (southern landfall) to ensure floating type silt curtains can be applied effectively (See Figure 3 of Appendix D5b). The sheet pile wall is a recommended mitigation measure under Sequence A and further developed as an integrated protection measure under Sequence B.

-　　　 before the completion of the sheet pile wall next to the northern boundary of the HKBCF+TM-CLKL (southern landfall), seawall dredging at the area north of the demarcation line of the Phase 1 and 2 of HKBCF will not be carried out; and

-　　　 before the seawall within the area of Phase 2 of HKBCF is formed above +2.5mPD, except for 100m gaps for marine access, the sheet pile wall at the northern boundary of the HKBCF+TM-CLKL (southern landfall) will not be removed.

· before the whole perimeter of seawall for HKBCF+TM-CLKL (southern landfall) is formed above +2.5mPD, except for 100m gaps for marine access and portion D of HKBCF, no dredging and reclamation filling will be carried out within the seawall boundary. 　Dredging for the formation of the pits for the subsequent Mf sediment backfilling within the HKBCF boundary is an exception; and

· for HKBCF seawall filling, no soft public fill will be used for filling below +2.5mPD;

· for TM-CLKL southern landfall seawall filling, no soft public fill will be used for filling below +2.5mPD and the fill material below that level will consist of 50% sand and 50% rock; and

· The filling material for the other parts of the works are the same as Sequence A.

6.7.4.19 Details on the anticipated construction progress, works programme and construction sequences are presented in Appendix D5b for Sequence B. Notwithstanding the integrated measures above, based upon the simulations of the unmitigated scenarios, the need for mitigation measures have been determined.　 As discussed in Sections 6.9 and 6.10 below, impacts resulting from the construction activities have the potential to cause impacts to the WQOs and ecological sensitive receivers and the extensive use of silt curtains could be required. The assumed effectiveness of the cage type silt curtain for grab dredgers and the single layer of silt curtains proposed are presented in Table 6.16a below, together with the loss reductions that could be assumed for an additional layer of silt curtain if this is considered.

Table 6.16a　 Summary Table of Loss Reductions from Silt Curtain Configurations under Sequence A

Silt Curtain Type	Loss Reduction Factor	Remark
Dredging Activities
Cage type for Grab Dredger (1)	80%	Typical, also reviewed in LNG Terminal EIA
Floating Single Silt Curtain (2)	75%	Manufactures Brochure
Second layer of Floating Silt　 Curtain (3)	50%	LNG Terminal EIA
Combined Reduction (1+2)	95%	For grab dredger only. Assumed for Option 1 (i.e., 1+1 silt curtain system) presented in Table 6.16b and　 discussed in the main text.
Combined Reduction (1+2+3)	97%	For grab dredger only. Assumed for Option 2 (i.e., 2+1 silt curtain system) presented in Table 6.16b and　 discussed in the main text.
Combined Reduction (2+3)	87%	Assumed for Option 2 (i.e., 2+1 silt curtain system) presented in Table 6.16b and　 discussed in the main text.
Filling Activities
Floating Single Silt Curtain (4)	45%
Second layer of Floating Silt Curtain (5)	30%	Proportional scaling following the reduction for dredging
Combined Reduction (4+5)	61%	Assumed for Option 2 (i.e., 2+1 silt curtain system) presented in Table 6.16b and　 discussed in the main text.

6.7.4.20 The assumed effectiveness of different arrangement of silt curtains are based on existing literature / publication and also available local information including approved EIA reports and EM&A results. For multiple layers of silt curtains, however, it can be expected that suspended solids that cannot be retained by the first layer of screen should be the very fine particle which would be difficult to be retained by the subsequent layers. Therefore, the assumed reduction factor for the second layer of silt curtain is lower than the first layer as shown in Table 6.16b above. However, as there is only limited information about the actual performance of the combined system, a field trial to verify the combined reduction is recommended during the EM&A stage. The 　EM&A during the implantation stage to ensure the sensitive receivers will not be adversely affected and that the water quality impact assessment and modelling are based on worse case scenario and conservative assumptions (see Section D5.11 of Appendix D5a), a small discrepancy in the assumed silt curtain efficiency shall not adversely affect reliability of the assessment.　

6.7.4.21 Based on the above integrated protection measures, the overall total daily sediment loss rate has been calculated for the selected scenario years (see Appendix D5a) and presented in Table 6.16b below. Table 6.16b, also, illustrates the possible further reduction in sediment loss if additional mitigation measures (silt curtains systems) are applied.

Table 6.16b　 Summary of Potential Daily Sediment Loss Rate under Sequence A

Option	Silt Curtain	2011 (kg/day)	2012 (kg/day)	2013 (kg/day)	Remark
0	0	4,394,000	2,008,000	1,705,000	Base case with integrated protection measures.
1	1+1	1,220,000 (72% reduction compared to Option 0)	672,000 (67% reduction compared to Option 0)	577,000 (66% reduction compared to Option 0)	Single layer (1) of silt curtain systems around the peripheral of proposed reclamation site for the southern reclamation of TM-CLKL, HKBCF and HKLR. For grab dredgers, an extra layer of cage type silt curtain (+1) is assumed. However, for the TM-CLKL northern reclamation, this is not assumed except works at Portion N-A (works item FN4 in Appendix D5a) as the current could be too high for effective silt curtain application.
2	2+1	844,000 (31% reduction compared to Option 1)	541,000 (19% reduction compared to Option 1)	406,000 (30% reduction compared to Option 1)	Double layers (2) of silt curtain systems around the peripheral of proposed reclamation site for the southern reclamation of TM-CLKL, HKBCF and HKLR. For TM-CLKL, no silt curtain protection is assumed for northern reclamation except works at Portion N-A (works item FN4 in Appendix D5a)

Notes: Please refer to Appendix D5a for construction sequences and works item code and Appendix D6a for the deployment of silt curtain systems.

6.7.4.22 Under Sequence B, early implementation of the sheet pile wall next to the northern boundary of the HKBCF+TM-CLKL (southern landfall) is required to ensure the floating type silt curtains can be effectively deployed in this region.　 Similar to Sequence A, wet and dry season flow simulations have been conducted for the Sequence B 2011 worse case scenario with a conservative assumption that seawalls at the eastern and western side of the main reclamation would be absent, although in reality a substantial portion should have emerged based on the construction programme. The flow simulation results confirmed that the sheet pile walls at the northern boundary of the HKBCF+TM-CLKL (southern landfall) would be effective in reducing the current speed at the area immediate within the sheet pile wall to generally below 0.2m/s (vector plots presented in Appendix D6b) and would, therefore, allow the effective application of silt curtains in this area. However, it has predicted that the sheet pile wall could lead to localised increases in peak flows in the area further south of the sheet pile wall. The peak flow has been predicted to reach 0.5m/s at the eastern side of the main reclamation and over 0.5m/s at the western side. Under such a condition, to be conservative, the effectiveness of silt curtain for sediment reduction is assumed to be reduced and specially design cage type silt curtain (with steel enclosure) will be used. The assumed effectiveness of the cage type silt curtain (with steel enclosure) for grab dredgers and the single layer of silt curtains proposed are presented in Table 6.16c below.

Table 6.16c　　 Summary Table of Loss Reductions from Silt Curtain Configurations at HKBCF+TMCLKL (southern landfall) under Sequence B

Silt Curtain Type	Loss Reduction Factor	Remark
Seawall Dredging
Cage type (with steel enslosure) for Grab Dredger (1)	80%	Proven effective in Pennys’ Bay reclamation project.
Floating Single Silt Curtain (2)	0%	Assumed no further reduction.
Combined Reduction (1+2)	80%	For grab dredger at HKBCF+TM-CLKL (southern landfall) only. Assumed for Option 1 of Sequence B (i.e., 1+1 silt curtain system) presented in Table 6.16d and discussed in the main text.
Filling at the Eastern Seawall
Floating Single Silt Curtain (3)	23%	For filling at HKBCF+TM-CLKL (southern landfall) eastern seawall only. Assumed for Option 1 of Sequence B (i.e., 1+1 silt curtain system) presented in Table 6.16d and discussed in the main text.
Filling at the Western Seawall
Floating Single Silt Curtain (4)	0%	For filling at HKBCF+TM-CLKL (southern landfall) western seawall only. Assumed for Option 1 of Sequence B (i.e., 1+1 silt curtain system) presented in Table 6.16d and discussed in the main text.

Notes: For assumed silt curtain efficiency at other areas of reclamation, please refer to Table 6.16a above.

6.7.4.23 Based on the above integrated protection measures, the overall total daily sediment loss rate under Sequence B has been calculated for the selected scenario year (see Appendix D5b) and presented in Table 6.16d below.

Table 6.16d　 Summary of Potential Daily Sediment Loss Rate under Sequence B

Option	Silt Curtain	2011 (kg/day)	Remark
0	0	1,778,000	Base case with integrated protection measures.
1	1+1	560,000 (69% reduction compared to Option 0)	Single layer (1) of silt curtain systems around the peripheral of proposed reclamation site for the southern reclamation of TM-CLKL, HKBCF and HKLR. For grab dredgers, an extra layer of cage type silt curtain (+1) is assumed. However, for the TM-CLKL northern reclamation, this is not assumed except works at Portion N-A (works item FN4 in Appendix D5a) as the current could be too high for effective silt curtain application. For HKBCF+TM-CLKL (southern landfall), the cage type silt curtain shall has a steel enclosure and the overall effectiveness of the silt curtains system are assumed to be less than at other areas as presented in Table 6.16c above.

Cumulative Impacts

6.7.4.24 In addition to the three projects, construction of other concurrent project may also occur in the same period and, as such it is necessary to assess any cumulative construction phase projects.　 As detailed in Appendix A2 and Table 6.13, the following projects have been assumed to have the potential to be under-going construction at the same time as the TM-CLKL+HKBCF+HKLR projects:

· Kwai Tsing Container Basin Dredging;

· Proposed Lantau Logistics Park (LLP) Phase I (72ha);

· Tonggu Channel annual maintenance dredging;

· Hong Kong Zhuhai Macao Bridge (HZMB); and

· Existing and Proposed Contaminated Mud Disposal Facility at East of Sha Chau and South of Brothers.

6.7.4.25 The anticipated rate of working for these concurrent projects (dredging, filling and mud disposal works at the contaminated mud pits and North of the Brothers) and the potential rate of loss of fine material (<63µm) to suspension have been calculated and are presented in Appendix D5a.　 Based upon this, the simulations for the three worst case time periods (2011, 2012 and 2013) have been repeated, combining the mitigated loss rates from the TM-CLKL+HKBCF+HKLR project simulations with those of the concurrent projects.　　

6.8 Operational Phase Assessment

6.8.1 Model Validation

6.8.1.1 The Delft3D Western Harbour model of tidal flows was used to simulate 15 day spring-neap tidal cycles in the wet and dry seasons for the 2010 Baseline scenario using both the original model grid (Western Harbour Model (WHM)) and the refined model grid (termed the WHM-RG), as detailed above (Figure 6.9). 　　The results from consecutive 15 day cycles were compared to confirm that the model spin-up period had been sufficiently long to allow the model to reach equilibrium and the results from the two model grid runs were also compared to confirm that the refinement of the model grid had not affected the calibration of the model.

6.8.1.2 Having refined the model grid, it was to be expected that the higher resolution in the vicinity of the proposed reclamations would result in an improved simulation and so some differences in the simulated tidal flows were to be expected in the area where the grid had been refined.　 However, the main tidal flows over the larger model area should not have been affected by the local grid refinement.

6.8.1.3 In general, the WHM-RG simulations of the instantaneous tidal water levels, salinity and water velocities agreed well with the original WHM except in the vicinity of the Airport Sea Channel where the model grid had been refined.　 It was to be expected that some changes in the tidal flows would be simulated and that the refined grid would result in an improved simulation compared to the WHM.　 In addition, when the accumulated flows from the WHM-RG were compared with those from the WHM, some differences were found especially in the dry season.　 Some differences in the accumulated flows were, also, found between successive 15-day simulations of the WHM-RG, again, mainly in the dry season in Victoria Harbour.　 Further details on the reasons for these differences are presented below.　 It should be noted that the accumulated flows are the result of integrating the simulated tidal discharges over the simulation period and are sensitive to the model being used and the scenarios being simulated as discussed below.

Comparison of the WHM and WHM-RG

6.8.1.4 The WHM-RG was based upon the refined grid prepared under the Lantau Logistics Park project and it was subsequently found that the resolution of the model grid in Victoria Harbour had been reduced in the model.　　 Therefore, it would be expected that the accumulated flows simulated by the WHM and WHM-RG in this area would differ.　

6.8.1.5 The WHM-RG, also, differed from the WHM in the simulation of thermal discharges from the main power stations, with the WHM thermal simulations being for the wet season only.　 Thus, the simulation of water temperatures in the WHM-RG in the dry season may also contribute to the differences in the results between the two models.

Comparison of Successive 15-day Simulations in the WHM-RG

6.8.1.6 When the results from successive 15-day simulations using the WHM-RG were compared, it was found that the instantaneous tidal water levels and water speeds agreed well and it appeared that the model had reached equilibrium.　 However, some differences between successive simulations in the accumulated flows were noted which were larger in the dry season than in the wet season.　 It has been concluded that the main reason for the differences in the results for the accumulated flows from the WHM-RG for successive 15-day simulations in the dry season was the salinity specified as the initial condition.　 However, these differences in salinity are considered to be small.

Conclusions

6.8.1.7 Based on the assessment of the model results as detailed above, it was concluded that the WHM and WHM-RG model results are in agreement with each other while taking into account the salinity effects and areas with a coarse schematisation.　 With respect to the calibration of the WHM-RG, these differences do not suggest that, in the study area, the calibration of the model has been affected by the grid refinement.　

6.8.1.8 In addition, taking into account the small differences in salinity between successive 15-day simulations which were predicted in the validation simulations, it is considered that any impacts the initial condition for salinity will have on the sediment plume and water quality simulations will be equally small.　 In assessing the construction impacts associated with the TM-CLKL+HKBCF+ HKLR projects, relatively short term direct tidal impacts are of greatest concern and the changes in dry season residual flows over the simulation periods due to the changes in the salinity distribution are not expected to be significant with respect to the results of the modelling.　

6.8.1.9 With respect to the annual simulations of water quality to be carried out for the scenarios with the completed works in 2026 and without the works in 2026, both simulations will begin with the same salinity initial conditions, specified separately in the WAQ and therefore, relatively independent of the FLOW simulation, and the relative impacts of the completed works in 2026 can still, therefore, be assessed and it is considered that the residual flows which are being generated as the salinity distribution adjusts are relatively small and unlikely to have a significant impact on the outcome of the study. The results of the verification have been detailed in a standalone working document and selected representative plots are included in Appendix D15 for reference.

6.8.2 Tidal Flows and Velocities

6.8.2.1 The tidal flows simulations (d) and (e) as described in Section 6.7.3 above have been undertaken in order to obtain results for the future condition (2026) which would arise both if the TM-CLKL+HKBCF+HKLR had been built and, also if they were not implemented. 　 By comparing the results from these simulations, the possible impacts the TM-CLKL+HKBCF+HKLR works might have on the future marine environmental condition when all other reclamations have been completed can be assessed.　 The modelling results are presented in Appendix D7a and are discussed below.

6.8.2.2 Tidal discharges have been obtained from the computed velocities across the selected cross-sections and used to assess the changes in the tidal circulation in the large or regional scale. Flow velocities at selected locations are also assessed to reflect the local effects or changes due to the proposed developments.

6.8.2.3 In terms of flow velocities, at WSR 41 located north of the HKBCF reclamation, the average speed decreases by 11% (from 43 cm/s to 39 cm/s) in the wet season and 3% ( from 37 cm/s to 36 cm/s) in the dry season but at WSR 49 located to the north-east of the HKBCF, the speed increases by about 3% (from 40 cm/s to 41 cm/s) in the wet season and by 13% (from 32 cm/s 36 cm/s) in the dry season. 　In the Airport Sea Channel (WSR 28), it is found that the average speed decreases by about 4% (from about 19.0 cm/s to 18.2 cm/s) in the wet season, but increases by about 17% (from about 11.1 cm/s to 13.0 cm/s) in the dry season. At the eastern entrance to the channel, the average speed increases from around 4.8 cm/s to 6 cm/s in dry season and from 6.4 cm/s to 6.7 cm/s in wet season. In general, the induced change incurrent speed around the proposed development is at most up to 10 – 20% or a few cm/s and no extensive stagnant area is observed.　 As mentioned above, the induced changes in the tidal speeds are only up to a few cm/s and, therefore, it is not expected that such changes will cause significant differences in the deposition and erosion of sediments from the case without the new developments.

6.8.2.4 A summary of the tidal discharges and percentages of change at key areas are presented in Table 6.17 below for residual, peak flood, peak ebb for both the wet and dry seasons.

Table 6.17　　 Wet and Dry Season Tidal Discharges (m³/s)

Section	Season	Dry		Wet
	Flow direction	Baseline 2026 Other Projects	2026 TM-CLKL/HKBCF and HKLR Projects Only	Baseline 2026 Other Project	2026 TM-CLKL/HKBCF and HKLR Projects Only
North of Airport Island	Flood	43291	42328	42492	41498
	% change	-	-2.2%	-	-2.3%
	Ebb	46384	45607	46658	45927
	% change	-	-1.7%	-	-1.6%
	Residual (+ve flood)	1601	1530	1423	1359
	% Change	-	-4.4%	-	-4.5%
Ma Wan	Flood	51883	50777	51509	50413
	% change	-	-2.1%	-	-2.1%
	Ebb	56906	55915	58496	57487
	% change	-	-1.7%	-	-1.7%
	Residual (+ve flood)	1640	1582	1402	1353
	% Change	-	-3.6%	-	-3.5%
Airport Sea Channel	Flood	158	251	214	187
	% change	-	59.3%	-	-12.5%
	Ebb	203	214	280	275
	% change	-	5.6%	-	-1.9%
	Residual (+ve flood)	24	36	-36	-21
	% Change	-	50.2%	-	-41.3%
Victoria Harbour	Flood	7443	7405	7805	7811
	% change	-	-0.5%	-	0.1%
	Ebb	5847	5770	4687	4636
	% change	-	-1.3%	-	-1.1%
	Residual (+ve flood)	1438	1440	2872	2880
	% Change	-	0.2%	-	0.3%
East Lamma Channel	Flood	33634	33367	35412	35144
	% change	-	-0.8%	-	-0.8%
	Ebb	39197	38708	35817	35423
	% change	-	-1.3%	-	-1.1%
	Residual (+ve flood)	1070	1047	2086	2105
	% Change	-	-2.2%	-	0.9%
West Lamma Channel	Flood	26332	25824	25327	24836
	% change	-	-1.9%	-	-1.9%
	Ebb	33100	32733	42038	41512
	% change	-	-1.1%	-	-1.3%
	Residual (+ve ebb)	747	740	4131	4197
	% Change	-	-0.9%	-	1.6%

　

6.8.2.5 Based upon Table 6.17, it can be seen that, overall, the changes in tidal discharges, including both increases and decrease, are relatively small after implementation of the project compared to the scenario without the project.　 From the model results, it is has been found that the proposed development has very minimal impacts upon the flow regime in Hong Kong Waters.

6.8.2.6 For north of the airport island, in comparing the scenarios, it was found that, in both the wet and dry season, the peak flood and ebb flow north of the Airport Island were found to reduce by about 2.3% and 1.7% respectively, while the residual flows were reduced by about 4.5%.　 For both wet and dry season, peak flood and ebb flow across Ma Wan were found to reduce by about 2.1% and 1.7% respectively, while the residual flow is reduced by about 3.6%.　 The reduction in residual flows may indicate the reduction in flushing and assimilative capacity of a water body.　 However, with the support of the water quality model results, the minor reduction in the tidal discharges are concluded to not have a very significant adverse impacts upon project area.

6.8.2.7 However, more significantly relative changes are found for the flow through the Airport Channel.　 In wet season, the residual, peak flood and ebb flow are shown to reduce by 41.3%, 12.5% and 1.9% respectively, while in dry season, the residual, peak flood and ebb flow increase by 50.2%, 59.3% and 5.6% respectively. Implementation of the projects, therefore, are predicted to result in increased flows in the sea channel in both directions in the dry season and in general, the proposed developments would cause a more westward flow through the Airport Channel, both of which could improve the flushing of East Tung Chung Bay but with reduced flows in the wet season.　 The predicted increased tidal flows in the sea channel following construction of the TM-CLKL+HKBCF+HKLR project could have some impact on the stability of the seabed in the sea channel with some erosion of any soft marine deposits present.　 However, it is considered that any erosion would be relatively small and would take many years to develop and as further discussed in the sedimentation section below, the predicted changes are small and insignificant.

6.8.2.8 In East Tung Chung Bay, water quality in this area at present is maintained by the offshore tidal flows and the flows through the Airport Sea Channel.　 The area is generally shallow and tidal current speeds are low and below 0.5m/s.　 However, in the absence of any local effluent discharges, the tidal currents in the bay and flows from the sea channel do generate sufficient mixing with the offshore waters to maintain water quality at existing levels.

6.8.2.9 Following construction of the projects, as compared to the other projects, the modelling has predicted that, in the dry season, the peak tidal water speeds would increase in some areas of the bay but remain very similar to the existing water speeds in other areas.　 Similar results were obtained for the wet season except that there could be some reduction in the tidal flow speeds in the north west corner of the embayed area at some times during the tidal cycle.　 However, as noted above existing tidal current speeds are already low in this area and provided the tidal currents remain sufficiently strong to maintain the same level of exchange with the offshore waters as at present, there should be no reduction in water quality following construction of the projects.

6.8.2.10 Areas of increased water speeds within the embayed area and in the sea channel have been noted.　 It should be noted, however, that while peak water speeds are expected to increase in many areas following construction of the project reclamations compared to the situation with the other projects only, the water speeds are not expected to be any larger than are found at present at locations further east along the North Lantau Island shoreline.　 It should, also, be noted that the peak water speeds only persist for a short time during the tidal cycle and, for most of the tidal cycle, water speeds will remain well within the range of speeds which would be expected if the TM-CLKL+HKBCF+HKLR was not built.

6.8.2.11 Tai Ho Bay is a particularly sensitive area and it is important that any developments do not adversely affect the tidal flows and water quality within the bay.　 The tidal flows which enter and leave the bay each day are driven by the tidal water levels outside the bay and controlled by the width of the entrance to the bay.　 Considering the relatively small area to be reclaimed for the projects compared to the total water area north of Lantau Island, no impact on tidal water levels are anticipated if the TM-CLKL+HKBCF+HKLR reclamations are built.　 The model studies have, also, confirmed that tidal water levels would not be affected by the project.　 As a result, the daily tidal flows into and out of Tai Ho Bay will also remain unaffected as compared to the future 2026 other project baseline.

6.8.2.12 From the assessment of the results of the simulations of the 2026 TM-CLKL+HKBCF+HKLR project and 2026 other projects on tidal flows, it has been found that both options could have some impacts on tidal flows in the Airport Sea Channel which could impact on the flushing of East Tung Chung Bay.　 Overall, however, the TM-CLKL+HKBCF+HKLR projects are not expected to have a greater potential to result in adverse impacts on tidal flows in East Tung Chung Bay.　 The TM-CLKL+HKBCF+HKLR will result in changes to existing tidal flow patterns with increased water speeds at times in some aeras during the tidal cycle.　 Any increases in water speeds, however, will remain within the range of water speeds to be encountered should the project not go ahead and no unacceptable changes to tidal flows are expected.　 Similarly, while the TM-CLKL+HKBCF+HKLR reclamations will modify the existing tidal flow patterns, at least locally, the project are not expected to adversely affect the exchange of water between the embayed area, the Airport Sea Channel and the offshore waters.

6.8.2.13 As discussed above with respect to the peak discharges, the differences identified between the residual discharges for the TM-CLKL+HKBCF+HKLR reclamations and the future no project scenario are generally very small.　 It is fair to conclude, therefore, that the proposed development will not result in any significant change to the residual flow patterns in the wet and dry seasons.

6.8.3 Water Quality

6.8.3.1 The water quality in the water control zones of interest in the current study is determined by effluent sources, water quality in the neighbouring water control zones and the tidal and residual flows.　 The proposed TM-CLKL, HKBCF and HKLR projects will result in only minor discharges from the reclamation pavement runoff and also the discharge from the on-site sewage treatment works, as described in Section 6.7.3.　 However, these discharges together with the existing and future ones, have been included in the pollution load inventory which has been used in the simulation of water quality impacts for the 2026 TM-CLKL+HKBCF+HKLR projects and the future 2026 scenario without these projects.

6.8.3.2 The results of the tidal flow simulations have concluded that there should be no significant effects on the large scale tidal or residual flows as a result of the proposed development and areas where there are some decreases or increases in flows are not expected to affect the overall water quality.

6.8.3.3 The following water quality parameters have been assessed for the future based and 2026 TM-CLKL+HKBCF+HKLR scenarios:

· Water temperature;

· Salinity;

· Biological Oxygen Demand (BOD₅);

· E. coli;

· Ammonia;

· Total Inorganic Nitrogen;

· Dissolved Oxygen;

· Suspended Solids; and

· Sedimentation Rate

6.8.3.4 In assessing the impacts on water quality, key areas of interest have been selected for analysis both in the immediate vicinity and further afield from the project as follows:

(i) WSR 7 - Black Point Cooling Water Intake (Far Field);

(ii) WSR 9a - Urmston Road (Main Channel);

(iii) WSR 10 - Sha Chau and Lung Kwu Chau Marine Park;

(iv) WSR 20 - Ma Wan Fish Culture Zone;

(v) WSR 25 – Airport cooling water intake (North-east);

(vi) WSR 26 - HKBCF South;

(vii) WSR 27 - San Tau Beach SSSI;

(viii) WSR 28 - Airport cooling water intake (South);

(ix) WSR 40 - Cheung Sha Wan Fish Culture Zone (Far Field);

(x) WSR 41 - Artificial Reef at NE Airport;

(xi) WSR 43 - Tung Chung waterfront;

(xii) WSR 44 - Future HKBCF Intake; and

(xiii) WSR 49 - Tai Mo To (Deep channel / CWD habitat range).

6.8.3.5 Overall, the results from the water quality modelling have shown that, following construction of the 2026 reclamations for the HKBCF and associated projects, the water quality at the sensitive receivers listed changes only marginally compared to the scenario without the HKBCF, TM-CLKL and HKLR.　 The changes (small increases or decreases) differ from season to season but, overall, most changes are negligible or very small with some beneficial increases in DO and reductions in E. coli concentrations in certain areas.

6.8.3.6 A summary of the monthly averaged levels at the surface, mid-layer and bottom layer, as well as the depth averages results of water quality modelling parameters for each of the key sensitive receivers and for each of the scenarios is presented in the summary tables and contour plots in Appendix D7b and D7c.　 A description of the results for each parameter is presented below.

Temperature and Salinity

6.8.3.7 Based upon the results in Appendix D7b (Figures 112-135, 167-190, 491-559 and 629-697) and D7c (Tables 13-15 and 18-20), it can be seen that, overall, all the results for both wet and dry seasons and for all water depth layers are very similar in 2026 for both scenarios, with and without the project.　 Since there are no additional thermal discharges being introduced under the proposed developments, the predicted changes in salinity and temperature at the selected localities can be interpreted as being caused by the changes in the flow regimes due to the developments and in a regional sense. 　With the presence of the new reclamations, the flow from the Pearl River and North-western waters during the ebb tide is more confined to the region between the new reclamations and noticeable changes are found in two regions, the eastern side of the northern reclamation of TM-CLKL and the region to the south of the HKBCF. 　The former region is subjected to a greater influence by the flood flow through Ma Wan, while the flow through the Airport Sea Channel has a greater effect upon the latter zone than before. 　In general, it is found that smaller intertidal variations (the difference between the daily extremes), as well as the vertical variation in the water column, result in these regions.

6.8.3.8 The predicted water temperature and salinity for the scenario year 2026 (with and without project, and also the calculated percentage difference between the two cases) are presented in Appendix D7c (Tables 13-15, 18-20) and the predicted changes in monthly averaged salinity and temperature for representative areas of interest, that is, ecological and fisheries sensitive receivers in which the temperature and salinity are the major physiological parameters, are summarised in Tables 6.18 and 6.19a below. In general, only very small changes in depth-averaged monthly temperatures and salinity are predicted and the predicted changes are within the WQOs of ±2°C for temperature and 10% of change for salinity, although technically it should be noted that these two WQO criteria are applied to waste discharges. 　

6.8.3.9 The average changes in depth-averaged monthly temperature are generally less than 0.5°C although a slightly higher change of about 1.1°C has been predicted at Ma Wan FCZ during the summer months. 　The average changes in depth-averaged monthly salinity are virtually zero for most of the time although a slightly larger change of 3% (corresponds to a difference of about 0.5 – 0.6 ppt) are predicted around Tai Ho Wan during the summer months. 　The waters in the North-western WCZ are generally heavily influenced by the Pearl River discharges which is to some extent dictated by the level of precipitation. The natural annual fluctuation of temperature and salinity in the North-western WCZ, as indicated by the inter-year difference of EPD’s station in 2006 and 2007 (Tables 6.6a and 6.6b), were already shown to be in the range of 0.2 °C to 0.7 °C for temperature and -0.7ppt to -1.5ppt for salinity, which are comparatively larger than the predicted change related to the proposed project reclamations. 　Hence, it can be concluded that these small changes attributable to the proposed reclamation would unlikely induce significant ecological impacts to the species in the study area which are already acclimatised to such variations.

Table 6.18　　 Summary of Predicted Changes in Monthly Depth-Averaged Temperature at Ecological and Fisheries Sensitive Receivers

WSR	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec
WSR 10	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (-1%)	0.2 (2%)	0.3 (3%)	0.4 (3%)	0.3 (3%)	0.1 (1%)	0.0 (0%)	-0.1 (-1%)	0.0 (0%)
WSR 20	-0.1 (-1%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.8 (5%)	1.1 (6%)	1.1 (6%)	1.1 (6%)	0.1 (1%)	0.0 (0%)	0.0 (0%)	0.0 (0%)
WSR 22b	-0.1 (-2%)	-0.2 (-3%)	-0.1 (-2%)	-0.1 (-2%)	-0.1 (-2%)	-0.2 (-3%)	-0.1 (-1%)	-0.2 (-3%)	-0.3 (-4%)	-0.2 (-3%)	-0.1 (-2%)	-0.2 (-3%)
WSR 22c	-0.1 (-1%)	-0.2 (-3%)	-0.1 (-1%)	-0.2 (-3%)	0.0 (0%)	0.4 (4%)	0.4 (4%)	0.4 (4%)	-0.2 (-2%)	-0.2 (-2%)	-0.1 (-1%)	-0.2 (-3%)
WSR 27	0.2 (3%)	0.1 (2%)	0.2 (3%)	0.1 (2%)	-0.1 (-2%)	-0.7 (-8%)	-0.7 (-8%)	-0.8 (-9%)	-0.7 (-7%)	0.1 (1%)	0.1 (2%)	0.1 (2%)
WSR 28	0.2 (3%)	0.2 (3%)	0.2 (3%)	0.2 (3%)	-0.3 (-5%)	-0.4 (-5%)	-0.5 (-5%)	-0.5 (-5%)	-0.6 (-6%)	0.1 (1%)	0.2 (3%)	0.2 (3%)
WSR 29	0.2 (3%)	0.2 (3%)	0.2 (3%)	0.2 (3%)	-0.5 (-8%)	-0.4 (-4%)	-0.4 (-4%)	-0.4 (-4%)	-0.7 (-7%)	-0.2 (-3%)	0.1 (2%)	0.2 (3%)
WSR 30	-0.2 (-3%)	-0.2 (-3%)	-0.2 (-3%)	-0.2 (-3%)	-0.4 (-6%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.4 (-4%)	-0.5 (-6%)	-0.2 (-3%)	-0.2 (-3%)
WSR 32	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.3 (3%)	0.5 (5%)	0.5 (5%)	0.4 (4%)	0.1 (1%)	0.0 (0%)	0.0 (0%)	0.0 (0%)
WSR 34	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.3 (3%)	0.5 (5%)	0.5 (5%)	0.4 (4%)	0.2 (2%)	0.0 (0%)	0.0 (0%)	0.0 (0%)
WSR 41	0.1 (1%)	0.2 (2%)	0.2 (2%)	0.2 (2%)	0.5 (5%)	0.5 (4%)	0.5 (4%)	0.5 (4%)	0.2 (2%)	0.1 (1%)	0.2 (2%)	0.1 (1%)
WSR 43	0.0 (-1%)	0.0 (-1%)	0.0 (-1%)	0.0 (-1%)	-0.1 (-1%)	-0.7 (-7%)	-0.7 (-7%)	-0.7 (-7%)	-0.5 (-5%)	-0.1 (-1%)	0.0 (-1%)	-0.1 (-1%)
WSR 49	-0.2 (-2%)	-0.1 (-1%)	-0.1 (-1%)	-0.1 (-1%)	0.2 (2%)	0.5 (4%)	0.5 (4%)	0.5 (3%)	0.0 (0%)	-0.1 (-1%)	-0.1 (-1%)	-0.1 (-1%)

Notes:

· All values are presented as “absolute change in °C (percentage change %)” relative to the 2026 baseline case without the proposed project. Negative (–ve) value indicate reduction after project implementation.

· WSR 10 = Sha Chau and Lung Kwu Chau Marine Park; WSR 20 = Ma Wan FCZ; WSR 22b = Tai Ho Wan (inner), Near Tai Ho Stream SSSI; WSR 22c = Tai Ho Wan near coral site; WSR 27 = San Tau Beach SSSI; WSR 28 = Airport Channel; WSR 29 = Hau Hok Wan; WSR 30 = Sha Lo Wan; WSR 32 = Tai O; WSR 34 = Yi O; WSR 41 = Artificial Reef at NE Airport; WSR 49 = Tai Mo To.

Table 6.19a　 Summary of Predicted Changes in Monthly Depth-Averaged Salinity at Ecological and Fisheries Sensitive Receivers

WSR	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec
WSR 10	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.2 (-1%)	-0.2 (-1%)	-0.2 (-1%)	-0.3 (-2%)	-0.2 (-1%)	-0.1 (-1%)	-0.1 (0%)	-0.1 (0%)
WSR 20	0.0 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)
WSR 22b	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.2 (-1%)	0.1 (0%)	0.5 (3%)	0.5 (3%)	0.5 (3%)	0.4 (2%)	-0.1 (0%)	-0.2 (-1%)	-0.2 (-1%)
WSR 22c	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	0.1 (0%)	0.6 (3%)	0.6 (3%)	0.6 (3%)	0.3 (2%)	-0.2 (-1%)	-0.2 (-1%)	-0.2 (-1%)
WSR 27	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (0%)	0.3 (1%)	0.1 (1%)	0.0 (0%)	0.0 (0%)	0.2 (1%)	0.1 (0%)	-0.1 (0%)	0.0 (0%)
WSR 28	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (0%)	0.4 (2%)	0.2 (1%)	0.1 (1%)	0.1 (1%)	0.2 (1%)	0.2 (1%)	0.0 (0%)	0.0 (0%)
WSR 29	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.5 (2%)	0.2 (1%)	0.1 (1%)	0.1 (1%)	0.2 (1%)	0.3 (1%)	0.0 (0%)	0.0 (0%)
WSR 30	0.1 (0%)	0.1 (0%)	0.1 (0%)	0.2 (1%)	0.4 (2%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.1 (1%)	0.3 (1%)	0.1 (0%)	0.1 (0%)
WSR 32	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (0%)	0.0 (0%)	-0.1 (-1%)	-0.1 (-1%)	-0.1 (-1%)	0.0 (0%)	0.0 (0%)	0.0 (0%)
WSR 34	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	0.0 (0%)	-0.1 (-1%)	-0.1 (-1%)	-0.1 (-1%)	0.0 (0%)	0.0 (0%)	0.0 (0%)
WSR 41	0.1 (0%)	0.1 (0%)	0.1 (0%)	0.0 (0%)	-0.1 (0%)	-0.3 (-2%)	-0.4 (-2%)	-0.4 (-2%)	-0.2 (-1%)	0.1 (0%)	0.0 (0%)	0.0 (0%)
WSR 43	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	-0.1 (0%)	0.2 (1%)	0.0 (0%)	-0.1 (-1%)	-0.1 (-1%)	0.1 (0%)	0.0 (0%)	-0.1 (0%)	-0.1 (0%)
WSR 49	-0.2 (-1%)	-0.2 (-1%)	-0.2 (-1%)	-0.2 (-1%)	-0.3 (-1%)	-0.4 (-2%)	-0.4 (-2%)	-0.4 (-2%)	-0.4 (-2%)	-0.4 (-2%)	-0.2 (-1%)	-0.2 (-1%)

Notes:

· All values are presented as “absolute change in ppt (percentage change %)” relative to the 2026 baseline case without the proposed project. Negative (–ve) value indicate reduction after project implementation.

· WSR 10 = Sha Chau and Lung Kwu Chau Marine Park; WSR 20 = Ma Wan FCZ; WSR 22b = Tai Ho Wan (inner), Near Tai Ho Stream SSSI; WSR 22c = Tai Ho Wan near coral site; WSR 27 = San Tau Beach SSSI; WSR 28 = Airport Channel; WSR 29 = Hau Hok Wan; WSR 30 = Sha Lo Wan; WSR 32 = Tai O; WSR 34 = Yi O; WSR 41 = Artificial Reef at NE Airport; WSR 49 = Tai Mo To.

6.8.3.10 It is noted that, as indicated in the wet season hourly salinity plots presented in Appendix D7a, there could be larger differences in the hourly salinity levels in the Airport Channel (WSR 27) and area south of the main reclamation (WSR 43), than the monthly average. The plots indicate that the differences are mainly predicted in the wet season and at the bottom level and this phenomenon was further investigated. Table 6.19b summarises the wet season salinity differences at WSR 27 and WSR 43. As indicated in Table 6.19b, the average differences at the surface level are only between -0.1 to -0.2 ppt (reduction) with a maximum difference of -2.1 ppt. At the bottom level, the average differences are between -1.4 to -1.9 ppt although the maximum difference can reach about -3.1ppt at WSR27 and -5.0 ppt at WSR 43. 　Closer analysis of the plots, however, reveals that the vertical difference (between surface and bottom) in salinity levels are predicted to be reduced with the implementation of the project. Without the project, the average vertical differences are between -2.3 ppt to -3.4ppt (the bottom level is more saline) but can reach a maximum of -7.8 ppt. With the implementation of the project, the average vertical differences are reduced to only about -1.0ppt to -1.7ppt and the maximum difference also reduced to -7.1ppt only. In order to facilitate the visualisation of the pattern, the predicted salinity level and surface and bottom level as well as the vertical differences are depicted in Figure 6.13. Overall, the changes are relatively small and extreme differences are only predicted for a small fraction of the time. However, as the vertical mixing is improved, it could be expected that this could potentially be beneficial to the ecology of the area since wet season bottom level hypoxia often develops when the water column is stratified and the reduced vertical difference can help avoid the development of stratification. 　It should also be noted that the minimum salinity in the North Western Waters at any time in the wet season is heavily dependent on the freshwater discharge from the Pearl River Estuary while, in the dry season, the salinity should be close to oceanic values in excess of 34ppt.　 As a result, the established marine ecology in this area will already tolerate large variations in salinity and the impact of the project on salinity levels is not expected to have any adverse impact on the marine ecology.

Table 6.19b　 Summary of Predicted Changes in Hourly Salinity Differences at Airport Channel and Tung Chung (Wet Season)

	Difference at Surface Level	Difference at Bottom Level	Vertical Difference Without Project	Vertical Difference With Project
WSR27	-0.1 (-2.1 – 1.6)	-1.4 (-3.1 – -0.1)	-2.3 (-6.2 – -0.4)	-1.0 (-4.8 – 0.0)
WSR43	-0.2 (-1.7 – 1.8)	-1.9 (-5.0 – -0.1)	-3.4 (-7.8 – -0.5)	-1.7 (-7.1 – 0.0)

Note:

Values are presented as average (min – max) pair wise differences (ppt).

Difference at level are calculated as 2026 (project – baseline).

Vertical difference are (surface – bottom).

BOD₅

6.8.3.11 Based upon the results in Appendix D7b (Figures 191-214 and 698-766) and D7c (Tables 21-23), it can be seen that, overall, all the results for both wet and dry seasons for all water depth layers are very similar in 2026 for both scenarios with and without the project.　 The BOD₅ levels do increase marginally (approximately 0.1-0.2mg/L) as a result of the project during the dry season but these changes represent average changes of 1-3% overall, although up to about 9% increase at mid-depth will occur at WSR 44 (HKBCF water intake) during the wet season.　 This increase is not a critical factor for this location and the depth–averaged concentration increases by only 0.1-0.3mg/L.　 Some reductions are also noted at the majority of the WSRs, specifically WSR 26, WSR 28, WSR 40, WSR 41 and WSR 49, in the wet season.　 The reductions occur mainly in the surface and middle layer and are generally small in real terms.　

E. coli

6.8.3.12 The E. coli results vary through out the study area, with the largest concentrations being recorded near Tai Mo To as a result of the Siu Ho Wan STW outfall.　 However, all the levels are well within the criteria of 610 cfu/100ml, although this WQO is specifically for secondary contact zones and not strictly relevant for the open waters.　 At WSR 28, WSR 41 and WSR 43, the E. coli levels are expected to increase in the dry season but decrease in the wet season.　 At both WSR 26, south of the HKBCF, and WSR 44, the E. coli levels are predicted to decrease through the whole year with a maximum reduction of about 58 cfu/100ml at the surface layer in the wet season. While the Butterfly Beach (WSR 12) is close to the proposed reclamation works at Tuen Mun and potentially more prone to the project related impacts, there is shown to be a reduction in E. coil with the project implementation rather than an increase. The predicted monthly average ranged between 2 – 11 cfu/100ml and well, therefore, below the 180 cf/100ml criteria for beaches during swimming season. Details of the modelling results are presented in Appendix D7b (Figures 055-078 and 353-421) and D7c (Tables 7-9).

Unionised Ammonia (NH₃)

6.8.3.13 The levels of NH₃ in the study area are very low and in the majority of cases below the limit of detection.　 There are some changes in the concentrations predicted for both with and without the projects.　 For example, at WSR41 throughout the year, and at WSR 26, WSR 28 and WSR 43, the NH₃ levels increase during the dry season and reduce during the wet season.　 In particular for WSR 28, the increases are around 10%.　 Again at WSR 49, the NH₃ levels decrease in the surface layer and increases in the lower layers, while in WSR 44, the levels are reduced for almost the duration of the entire year.　　 However, all the changes are very marginal in real terms and all values are notably factors of 10 below the 0.021 mg/L WQO criteria. Details of the modelling results are presented in Appendix D7b (Figures 082-105 and 422-490) and D7c (Tables 10-12).

Dissolved Inorganic Nitrogen (DIN)

6.8.3.14 For the WSRs in close vicinity to the works, namely WSRs 26, 27, 28 and 43 and, to a lesser extent, WSRs 44 and 49, the dissolved inorganic nitrogen (DIN) levels increase during the dry season and reduce during the wet season with the project in place.　 However, all the increases are less than 3%. Due to the change in the tidal flow patterns following construction of the proposed reclamation, the DIN levels at WSR41 (the artificial reef at the airport exclusion zone) increase throughout the year, but the increases are marginal at about 1% in both wet and dry season respectively.　 Details of the modelling results are presented in Appendix D7b (Figures 001-024 and 215-283) and D7c (Tables 1-3). 　Overall, the levels of DIN both with and with out the project are comparable and significant changes are not predicted.

Dissolved Oxygen (DO)

6.8.3.15 Based upon a comparison of the results for the two scenarios, both with and without the projects in 2026, it can be seen that levels of Dissolved oxygen (DO) do not change significantly as a result of the implementation of the project, particularly in the dry season when, overall, there are no changes or marginal increases.　 The DO levels decease in both cases in the wet season as a result of seasonal variations and the levels reflect the natural fluctuations of the Pearl River Delta.　 However, some localised decreases are predicted in the wet season, typically of less than 3%, when comparing the two scenarios, with and without project.　 Notwithstanding, all results for both the scenarios show that the DO levels will comply with the DO WQO criteria (depth average >=4 mg/L, bottom level >=2 mg/L), typically by some margin.　 As a result, it can be concluded that the implementation of the project will not significantly affect DO levels and no ecological sensitive receivers, including the CWD, corals and fisheries, will be affected by the implementation of the project.　 Details of the modelling results are presented in Appendix D7b (Figures 028-054 and 284-352) and D7c (Tables 4-6).

Suspended Solids (SS)

6.8.3.16 For the majority of the study area, there are negligible or no changes in SS levels as a result of the project.　 Notwithstanding, in certain areas changes do occur, notably at Pillar Point on the east side of the TM-CLKL northern landfall and also around the HKBCF/TM-CLKL island east of the airport.　 These are probably due to the fact that significant amount of SS has originated from the Pearl River discharges.　 With the proposed reclamation in Tuen Mun and the creation of the HKBCF and TM-CLKL southern landfall, the flow during the ebb tide will be diverted towards the Airport and HKBCF, so higher SS concentrations would result.　 On a monthly average basis, the changes are relatively small at between 2-3% either way, in general, as shown in Appendix D7 (Table 16).　 However, at certain tides, the increases can be more noticeable as shown by the plots in Appendix D7 (Figure 136-162 and 560-628).　 The SS concentrations at WSR 44 and WSR 49 increase through the year.　 For WSR 44 (the HKBCF seawater intake), the increases are around 4% in the dry season but can be up to about 15% in the lower layers of the water column during the wet season.　 In general, greater changes occur in the dry season but the maximum changes are around 10%.　 Notwithstanding, the results show that the implementation of the project would not cause any increases in SS to above 30% (that is, the WQO) of the baseline without the project scenario.

6.8.3.17 For the WSR seawater intake at future LLP (WSR 23), as a conservative scenario, they are assumed to locate near the seabed. The closest EPD water quality monitoring stations to these receivers are NM3 and NM6.　 According to EPD monitoring data from Yr 1998 to Yr 2007, the average SS in dry and wet seasons near the seabed were 15.7mg/L and 13.1mg/L, which have exceeded the WSD criteria of 10mg/L. The project will further cause an elevation in SS at this sensitive receiver by around 5 (dry season) - 10 mg/L (wet season) above the baseline level. The predicted elevated SS at the sensitive receiver are 20.7 mg/L and 23.1 mg/L during dry and wet seasons, respectively. To minimize the impact on WSD seawater intakes, installation of silt screens in the intake is necessary. With the silt screen, it can provide a further 60% reduction in the SS level. Hence, the predicted maximum SS in dry season at WSR23 will be reduced to 8.3 mg/L. The predicted maximum SS in wet season at WSR23 will be reduced to 9.2 mg/L. With the silt screen in place, the maximum SS in both dry and wet seasons would comply with the WQO.　

Sedimentation

6.8.3.18 The annual sedimentation, unlike other the water quality parameters that can be read directly from the annual water quality model, needs further calculation after the modelling. 　The model provides the mass of the sediment accumulated in the model cells and, thus, the annual sedimentation rate have been calculated as the net accumulated sediment at 1 Jan 2027 and 1 Jan 2026. 　This value has then been divided by the surface area of the model grid cells to give the net annual rate per unit area (g/m²/year). 　In long-term, the deposited sediment will consolidate and the dry density of typical marine mud (750 kg/m³) provides the estimate of net annual sedimentation rates in terms of depth changes (mm/year). The predicted annual sedimentation rate in the areas of interest (such as major flow channels, navigation channel, representative ecology sensitive receivers and also beaches in and around the project site) in both (g/m²/year) and (mm/year) have been tabulated in Appendix D7c (Table 17) and the contour plots are presented in Appendix D7b (Figures 163-166).

6.8.3.19 While it has been predicted that there could be some short-term transient changes in the pattern of suspended solids in the water columns, the project is not predicted to induce significant changes in the overall sedimentation pattern. 　The predicted changes are in general small and less than 0.5 mm/year.　 A largest change of up to about +1.07 mm/year is predicted at the more sheltered area of the River Trade Terminal (WSR 47b), adjacent to the northern reclamation of TM-CLKL, but changes at the more exposed part (WSR 47a) are only about +0.15 mm/year. 　Changes at the Butterfly Beach (WSR 12) are, again, predicted to be very small at around 0.19 mm/year and no significant impacts are expected for such a small change. 　No changes in the sedimentation of the Urmston Road main channel (WSR 9a) are predicted while a very minimal change of -0.01 mm/year in the Tung Chung Fairway (WSR 24) is predicted. 　A very minor reduction (-0.01 to -0.07 mm/year) in the sedimentation rate has, also, predicted at the north Lantau coast including the Airport Channel (WSR 28), San Tau Beach SSSI (WSR 27) and Tai Ho Wan (WSRs 22b and 22c) which is negligible.

6.8.3.20 It is noticeable that while the Sky Pier (WSR 50) will be embayed with the HKBCF reclamation, the predicted increase in sedimentation at this area is only about +0.77 mm/year and the predicted absolute magnitude is 1.57 mm/year with the proposed reclamation in place. Based on that, it is not expected that maintenance dredging at this area will be required. Alternatively, if there is already maintenance dredging planned at the Sky Pier, the proposed reclamation is not expected to affect the magnitude required.

6.8.3.21 With respect to changes at representative ecology / fisheries sensitive sites such as the Sha Chau and Lung Kwu Chau Marine Park (WSR 10), San Tau Beach SSSI and Airport Channel (WSRs 27, 28, 29 and 30), Tai Ho Wan (WSRs 22b and 22c), Tai Mo To (WSR 49), the artificial reef at the NE of the airport (WSR 41) and Ma Wan FCZ, the predicted changes are very small and range between -0.09mm/year to +0.10mm/year. These small changes indicate that the inter-tidal habitats at these soft-shores will not be impacted. 　With the project implemented (2026), the predicted annual deposition rates at these sites ranged between +0.50 mm/year to +2.28 mm/year. 　The positive results shows that the project is not expected to lead to a net erosion at the soft-shores habitats along the north Lantau coast.

Summary

6.8.3.22 In summary, on the whole, only marginal increases or decreases of the water quality parameters will occur as a result of the implementation of the project compared to if it was not constructed.　 In addition, all parameters are expected to stay within the relevant criteria and significant water quality impacts as a result of the project are not predicted.　

6.8.4 Accidental Spillage

6.8.4.1 Under normal operating circumstances, significant impacts on water quality are not predicted.　 However, while Dangerous Goods (DG) vehicles of Categories 1, 2 and 5 are prohibited from using the tunnel, oil tankers (DG Cat5) will be allowed to use the southern marine viaduct and in the event of an accident with such a tanker, there is the possibility for the spillage of a large volume of oil or chemicals.　 In this case, the integrated permanent road drainage system discharge any spilt materials into the marine environment, although the 0.8m profile barrier, which has been proposed along the marine viaduct, will prevent vehicles from leaving the road.　 However, in the event that a major spill occurs on the marine viaduct of the TM-CLKL, a defined response plan is required in order to, not only be able to reopen the road as soon as possible to minimise disruption to traffic, but also to minimise effects on the marine ecological resources and water quality. 　All methods of spill clearance, should be environmentally acceptable and should not lead to pollution of the marine environment.　 The following sections detail the procedures that would be applicable in this situation.

Chemical Spillages

6.8.4.2 For chemical spillages that do not pose fire, explosion or life risks, the spills should be contained, recovered and soaked-up for disposal as chemical waste.　 Under no circumstances should chemical spillages be washed into the natural streams, or any other natural or man-made water bodies or carrying systems.　

Oil Spillages

6.8.4.3 In respect of oil spillage, the use of chemical dispersants to break up the oil is not recommended as their use could impact on the surrounding environment and compound the pollution situation.　 In addition, the oil spill should be contained in the location of the spill wherever possible.

6.8.4.4 For all spillages, the acceptable method of control is by “absorption” and then removal of the absorbed waste for disposal by special contractors.　 Absorption of the oil should be achieved by the use of sawdust or other suitable material. Advice on how to clean-up a chemical spillage if required can be sought from EPD. Contact should be made with EPD’s Chemical Waste Treatment Centre for assistance in disposing of the contaminated sawdust. Source of sawdust for use in case of emergencies can be obtained from Highways Department.

6.8.4.5 The management and maintenance authority for the venue/roads/parts would be responsible for clearing up a spillage in their responsible area, as summarised in Table 6.20. The emergency call-out procedure in case oil/chemical spillage on roads in this area are:

a) Police

· to access the impact of incident and then immediately inform:

- FSD in case of fire hazard; and

- TD in case of road closure:

· to set up a Mobile Command Post to co-ordinate the road closure and clearing up operations.　 All parties concerned might then liaise with the Command Post for updated information; and

· to inform EPD, FEHD and other departments to render assistance if necessary after the immediate traffic and rescue operations completed.

b) Transport Department

· to inform HyD’s Emergency Co-ordination Centre;

· to liaise with the bus companies, MTRCL, relevant ferry operators on emergency public transport arrangements;

· to disseminate information of emergency public transport arrangements through GIS.

6.8.4.6 A summary of the key responsibilities of relevant authorities are provided in the following Table 6.20.

Table 6.20　　 Spill Response Key Responsibilities

Department	Area of Responsibility
FSD	To standby at scene if there is fire hazard
HyD	To be responsible for clearing up chemical spillage on public roads by supplying labour and sawdust
	To assist Police in assessing the road re-opening time.
Police	To implement road closure and direct traffic To coordinate the operations of clearing up
	To inform FSD, TD in the first instant and then other departments on an as need basis
Transport Department	To inform HyD To liaise with bus companies and MTRCL, ferry operators on emergency public transport To disseminate information of emergency public transport arrangements through GIS

6.8.4.7 These measures will reduce the magnitude of any impacts.　 Notwithstanding it is possible for some of the spilled material to be discharged into the marine environment via the viaduct drainage system.　 While oil interceptors are not feasible on the marine viaduct, the spill will decay through a variety of means including evaporation, adsorption onto suspended materials and emulsification.　 Adsorption of oils can be effective means for breaking up the spill. 　However, the natural process of the spill spreading reduces its thickness and allows the process of wind and wave action in breaking up the spill to increase as well as evaporation and dissolution.　 Dispersion of any spill will occur more rapidly in high energy waters which occur along the majority of the viaduct length but in lower flows of the waters in the bays, dispersion could take longer.　 Notwithstanding, it is likely that a spill would disperse in region of 3-4 days without any long term effects on water quality (ERM 1995).　

6.8.4.8 Based upon this, the emergency response plan would be considered to be sufficient to reduce any impacts to acceptable levels.

6.9 Construction Phase Assessment

6.9.1 Suspended Solids - Year 2011 Scenario (Sequence A)

Unmitigated Sediment Plumes

6.9.1.1 The first selected worse case scenario is early (February) 2011 which corresponds to about 15% into the overall duration of the marine works and the construction activities at this time are restricted to the HKBCF and HKLR.　 The anticipated work fronts are mainly concentrated on seawall construction at the HKBCF site although the works for re-provision FSD berth at the NE tip of the Airport Island will also be ongoing. The seawalls for HKLR construction have just begun.　 Apart from the temporary seawalls along the northern edge of the HKBCF Portions A and C, the coastline is largely the same as the pre-construction condition.

6.9.1.2 The predicted elevations in suspended solids concentrations in the sediment plumes for the selected time frames (peak ebb and flood tides, high and low water levels during spring and neap tides), time history plots of the elevations over the entire modelling timeframe and the total and daily sediment deposition are presented in Appendix D8a and D8d, and tabulated values presented in Appendix D11 (Tables 1).

6.9.1.3 As the project site is located in the relatively sheltered East Tung Chung Bay area, the sediment plumes are largely retained within the vicinity of the site. During the slack periods (high and low waters), the suspended solids (SS) at the work fronts could elevate to around 300 mg/l at the surface.　 However, during peak ebb and flood tides, the plumes could travel further east (ebb tide) or west (flood tide) directions depending on the tidal state but the surface SS rapidly drops to around 50 mg/L within a distance of about 2km.　 In general, the plumes travel a longer distance during the ebb tide and could approach Ta Pang Po (WSR 21), north Lantau, at low concentrations (<10 mg/L) but this situation only occurs rarely.

6.9.1.4 The western extent of the surface plumes (~50 mg/L) occur at about the NE tip of the Airport, close to the artificial reef deployment site (WSR 41), but such levels generally do not reach the airport intake (WSR 25).　 Lower concentration surface plumes (<10 mg/L) could, however, reach to a distance about halfway along the airport runway.　 Under no circumstances do the plumes cross the Urmston Road.　 The sediment plumes generally remain around the East Tung Chung Bay near the project site, although during spring tide flooding, the plumes from HKLR reclamation could pass the Tung Chung Channel (underneath the North Lantau Highway) and reach Ma Wan Chung at low concentrations (<10 mg/L) but would not reach the San Tau SSSI (WSR 27).　 This situation is, again, very rare and the plumes only last for around 2 hour if it does occur.

6.9.1.5 The predicted maximum elevations in SS for selected observation points around the site and comparison with the water quality objective (WQO) or water quality criteria (WQC) for selected specific sites are summarised in Table 6.21below. The principal assessment criteria (Section 6.4) is assumed to be the depth-averaged value, although secondary criteria for each depth level have, also, been presented in Table 6.21, and the following discussion refers the depth-averaged values / WQO unless specified otherwise. As indicated in Table 6.21, SS elevations exceeding the relevant WQO are limited to locations around the project site.　 While the plumes can reach Ta Pang Po (WSR 21), this is only predicted to occur during the dry season and the maximum depth- averaged concentrations is only 7.2 mg/L and exceedances are only predicted for about 3% of the dry season time.　

6.9.1.6 For key marine ecology sensitive sites around the project area, no WQO exceedances are predicted for Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (WSR 27, 28, 29, 30 and 48). Patches of hard and soft corals have been identified around the Tai Mo To and also along the outer seawall of Tai Ho Wan and the nearest modelling output points are WSR 46 and WSR 22c, respectively. Marginal WQO exeedances are predicted at WSR 46 during the wet season but at very low frequency (<1% of time) but no exceedances are predicted in the dry season, and no exceedances at WSR 22c. 　Patches of soft corals were, also, identified at the west end of airport channel (WSR 48) near the HKLR alignment although sediment plumes are not predicted in the airport channel nor the western side of the airport island and, hence, no WQO exceedances are predicted. 　The predicted maximum plumes at south of Tai Mo To (WSR 49) or Sham Shui Kok (WSR 45c) around the recently identified key dolphin habitat, however, would occasionally marginally exceed the WQOs in the wet season only (WSR 45c: 4% of dry season time; no exceedances during wet season; WSR 49; 2% of the wet season time; no exceedances during dry season) suggesting the need for mitigation measures.　 No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted elevation is less than 1 mg/L and does not exceed the WQC level.

6.9.1.7 In terms of the predicted surface maximum SS elevations at the Artificial Reef at NE Airport (WSR 41), which is very close to (about 300m from the HKBCF and about 1km from the TM-CLKL) and downstream (during the flood tide) of the project site, however, exceedances of the calculated WQO of 3.7 mg/L (wet season) and 5.5 mg/L (dry season) could occur for about 35% to 39% of the time.　 The predicted surface maximum SS elevations at the NE Airport Intake (WSR 25) would also exceed the WQO for about 33% (wet season) to 36% (dry season) of the time.

6.9.1.8 The total sediment deposition over the entire simulation period for construction (that is, 15 days) and net daily averaged sediment deposition rates are also presented in Appendix D8a (Figures 37-40). 　Tabulations of running averages of the accumulated sediment over every 24 hours period are also presented in Appendix D11 (Table 45 and 46). As the proposed site is located in a shallow sheltered bay area, the suspended solids plumes generally stay around the project site and the deposition is also the highest in the project area reaching around 10,000 g/m²/day around the site boundary. However, outside the site boundary, it rapidly reduced to less than 200 g/m²/day in about 1km. 　The daily sediment deposition rate is particular relevant to coral sites and a rate of 200 g/m²/day is generally considered as tolerable in the western waters. The predicted maximum daily sedimentation rate at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged from between 0.0 g/m²/day to 49.4 g/m²/ day which are all below the tolerable rate for corals, although corals were only identified at some of these sites. Relatively high sedimentation rate of 267.4 g/m²/day are predicted at the artificial reef (AR) at the NE of airport and specific mitigation would be required.

Mitigated Sediment Plumes ((1+1) Silt Curtain System)

6.9.1.9 Under the early (February) 2011 unmitigated scenario, the predicted maximum SS elevations could exceed the WQO for a few sensitive receivers around the project site as discussed above.　 As such, specific mitigation measures would be required to reduce the suspended solids dispersal.　 The use of a layer of floating type silt curtains surrounding each reclamation site (while taking into account the need for marine access), combined with a cage-type silt curtain around each grab dredger to be used (referred as the (1+1) silt curtain system), has been recommended and modelled.　 This (1+1) silt curtain system is expected to reduce the overall potential sediment loss to the surrounding water columns by 72% in the 2011 scenario year (Table 6.16b).　 The applicability and effectiveness of silt curtains are limited by the current speed at the site and the technical feasibility of the recommended silt curtain system has been evaluated based upon the results of the flow simulations and concluded to be acceptable given the low currents in this area.　 Further details, together with an indication of the silt curtain layout, are presented in Appendix D6a.

6.9.1.10 The predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and, also, the total and daily sediment deposition assuming the (1+1) silt curtain system is implemented are shown in Appendix D8b and D8d and tabulated values presented in Appendix D11 (Tables 2).

6.9.1.11 With these specific mitigation measures, the predicted sediment plume sizes and maximum SS elevations are much reduced compared to the unmitigated scenario.　 In general, surface plumes above 30 mg/L are predicted to be confined to within about 500m of the project site.　 The dynamic pattern of the plumes is similar to the unmitigated case but the concentrations are much reduced.　 The eastward extent of the sediment plumes are only expected to reach Sham Shui Kok (WSR 45c), which is about 1.5km west of Ta Pang Po, and only low surface concentrations of around 3 mg/L would occur.　 Again, this situation is predicted to happen only rarely.

6.9.1.12 The western extent of the surface plume around the NE tip of the airport is, also, much reduced to only around a maximum of 15 mg/L. With the mitigation, the plumes from HKLR reclamation will be confined to within only a few hundred meters from the site at low concentrations (<10 mg/L) and are not predicted to cross the Tung Chung Channel, nor would it reach the San Tau Beach SSSI.

6.9.1.13 The predicted maximum elevations in SS for selected observation points around the site and comparison with the Water Quality Objectives (WQO) or Water Quality Criteria (WQC), for selected specific sites, for the mitigated scenario are summarised in Table 6.22 below.　 As indicated in Table 6.22, SS exceedances of the relevant WQOs are limited to few areas in close vicinity to the site.　

6.9.1.14 No WQO exceedances are predicted for key ecology sensitive areas around the project area, such as Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (including WSR 27, 28, 29, 30 and 48). The predicted maximum plumes at known coral sites near Tai Mo To (WSR 46), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO. 　The predicted maximum plumes at south of Tai Mo To (WSR 49) or Sham Shui Kok (WSR 45c) around the recently identified dolphin habitat would also be controlled below the WQO and no impacts are anticipated with the mitigation. No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted elevation is <0.5 mg/L and does not exceed the WQC or WQOs.

6.9.1.15 The SS elevations at the Artificial Reef at the airport Exclusion Zone (WSR 41) are predicted to comply with the WQO during the dry season, although marginal exceedances are predicted for a small percentage (4%) of the wet season time but not during the dry season. 　The AR site has been proposed to be re-provided and, therefore, the marginal exceedances should not be a major concern. 　For the NE Airport Intake (WSR 25), while the (1+1) silt curtain systems provided significant reduction to the sediment plumes from 17.6 – 30.7 mg/L to 4.7 – 6.7 mg/L, marginal exceedances of WQO are, however, still predicted for about 2% of both wet or dry season time and it is, therefore, recommended that an additional silt curtain be deployed around this water intake to ensure full compliance with SS WQO.　 Although the effectiveness of silt curtain at a sensitive receiver cannot be modelled, the approximately equivalent (2+1) silt curtain system mitigation has been modelled and results presented in Appendix 12a. Based on the results of the (2+1) silt curtain mitigation, no SS WQO exceedances at WSR 25 are predicted.

6.9.1.16 The total sediment deposition over the simulation period and daily averaged sediment deposition rate is also presented in Appendix D8 (Figures 37-40). 　Tabulations of running averages of the accumulated sediment over every 24 hours period is also presented in Appendix D11 (Tables 51 and 52).With the mitigation measures, the deposition of suspended sediment are mainly confined to the project site and outside the site boundary, deposition rapidly reduces to less than 200 g/m²/day in about 500m. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged between 0.0 g/m²/day to 19.0 g/m²/ day which are well below the tolerable rate for corals although corals were only identified in some of these sites. 　While relatively high maximum rate of 267.4 g/m²/day are predicted at the artificial reef (AR) at the NE of airport, the maximum rate is much reduced to 69.3 g/m²/day with the (1+1) silt curtain system.

6.9.1.17 In summary, the (1+1) silt curtain system proposed is considered to reduce impacts from suspended solids to within acceptable levels and while some marginal and transient exceedances remain in very close proximity to the works site, these were not predicted to affect major ecological sensitive receivers, including marine park, coral sites and key dolphin habitat at Tai Mo To, as well as the Ma Wan FCZ, and so significant residual impacts are not expected.

6.9.1.18 Double layers of peripheral silt curtains and cage silt curtains around the grab dredgers (referred as the (2+1) silt curtain system), could further reduce the potential sediment losses by an extra reduction of about 31%.　 As such, this (2+1) double silt curtain system could be applied if the construction phase EM&A on-site showed the need for further mitigation.　 This (2+1) silt curtain system has been modelled and the predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and, also, the total and daily sediment deposition are shown in Appendix D12a for reference. In addition, if specific sensitive receivers need further protection, silt curtains around sensitive receivers could be considered.

Table 6.21　　 Predicted Maximum SS (mg/L) Elevations at Observation Points for the Scenario Year 2011 (Unmitigated) (Sequence A)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.4	0.7	0.7	0.6	0.1	0.6	1.5	0.7	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.1	0.1	0.2	0.1	0.0	0.1	0.4	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.1	0.1	0.2	0.1	0.0	0.1	0.3	0.1	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.0	0.1	0.2	0.1	0.0	0.1	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.1	0.1	0.1	0.1	0.0	0.1	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.2	0.5	0.3	0.3	0.1	0.1	0.3	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.1	0.1	0.1	0.1	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.7	0.9	0.9	0.8	0.4	0.4	0.4	0.4	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	6.4	7.1	8.0	7.2	1.5	1.7	1.8	1.7	4%	3%	0%	3%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.2	0.2	0.3	0.2	0.1	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.4	0.5	0.6	0.5	0.1	0.3	0.4	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	18.4	26.9	30.7	23.7	8.2	23.3	30.6	17.6	24%	38%	37%	36%	5%	35%	33%	33%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.7	0.9	1.0	0.9	0.1	0.6	1.4	0.6	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	14.7	26.0	65.4	29.9	16.8	38.1	70.8	24.4	20%	40%	22%	39%	18%	38%	26%	35%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.1	0.1	0.1	0.1	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	7.9	9.0	10.2	9.0	1.7	2.0	2.3	2.0	5%	5%	2%	4%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	3.2	6.6	7.8	4.2	4.7	4.4	12.9	4.4	0%	1%	0%	0%	2%	1%	1%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	0.1	0.4	0.6	0.4	0.1	0.2	0.3	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	0.1	0.1	0.2	0.1	0.0	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	2.6	6.4	7.2	4.3	1.3	3.1	18.4	6.2	0%	1%	0%	0%	0%	0%	5%	2%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

Table 6.22　　 Predicted Maximum SS (mg/L) Elevations at Observation Points for the Scenario Year 2011 (Mitigated) (Sequence A)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.1	0.2	0.2	0.2	0.0	0.2	0.3	0.2	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.0	0.0	0.1	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.0	0.0	0.1	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.0	0.0	0.1	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.1	0.2	0.1	0.1	0.0	0.0	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.3	0.3	0.3	0.3	0.1	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	2.4	2.6	2.9	2.6	0.6	0.7	0.7	0.7	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.1	0.1	0.1	0.1	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.1	0.2	0.2	0.2	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	5.6	7.2	8.2	6.7	2.3	6.4	8.3	4.7	4%	9%	1%	2%	0%	13%	2%	2%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.0	0.0	0.1	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	4.3	4.7	13.1	5.1	3.6	10.8	18.0	6.1	1%	0%	4%	0%	3%	12%	7%	4%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	2.9	3.3	3.8	3.3	0.6	0.7	0.9	0.7	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	1.0	2.0	3.9	1.4	2.4	1.8	6.6	2.3	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	0.0	0.2	0.2	0.1	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	0.0	0.0	0.1	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	0.9	2.0	2.6	1.4	0.5	1.3	6.9	2.3	0%	0%	0%	0%	0%	0%	1%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764 mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

6.9.2 Suspended Solids - Year 2012 Scenario (Sequence A)

Unmitigated Sediment Plumes

6.9.2.1 The second selected worse case scenario was early (April) 2012 which corresponds to about 50% into the overall duration of the marine works and the construction activities for TM-CLKL, HKBCF and HKLR would all be actively progressing.　 The seawalls for the Phase 1 of HKBCF would be mostly completed and seawalls for the Phase 2 HKBCF would also be partially completed and causing some localised changes to the flow patterns.　 The presence of the HKBCF seawalls will slightly increase the current speed at the gap between the Airport Island and the partially formed HKBCF, especially during the peak ebb and peak flood tides (from generally <0.2m/s to about <0.6 m/s but reaching around <0.8m/s during peak flood).　 The local flows at this area will be mainly in the north-south direction.　 The current at the south of the HKBCF will, also, slightly increase from around <0.2 m/s to about <0.4 m/s during peak ebb/flood, although the average speed stays around <0.2m/s.　 These changes could have some localised effect on the plume dispersion. 　However, the seawall for Portion 1 of the HKLR should be nearly completed at this time and would, thus, restrict the sediment loss from this part of the works area.

6.9.2.2 The anticipated work fronts are scattered around the multiple work sites.　 At the HKBCF island, works are mainly around the northern part of the Phase 1 site and, also, the construction of the southern landfall nib for the TM-CLKL is actively in progress.　 In addition, the dredging / filling works for the APM tunnel between the airport and HKBCF islands is also on-going at this time.　 Construction works at the TM-CLKL northern reclamation will be on-going with works being mainly confined to around the partially formed Portion N-C.　 There are also predicted to be small losses from the construction of the bridge viaduct piers for both the TM-CLKL and HKLR.

6.9.2.3 The predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water levels during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and the total and daily sediment deposition are presented in Appendix D9a and D9d and tabulated values are presented in Appendix D11 (Tables 4).

6.9.2.4 The total daily unmitigated sediment losses have reduced from around 4.4Mkg/day in early 2011 to about 2.0 Mkg/day at this time and as such the sediment plumes can be expected to be smaller than the 2011 scenario. During the slack periods (high and low waters), the suspended solids (SS) at the work fronts only elevate to around 30 - 50 mg/L at the surface. Surface plumes leaving the site during the slack periods are generally at low concentrations (<10 mg/L) and do not travel far from the site.　 During peak ebb and flood tides, the main direction of plume travel is still east (ebb tide) or west (flood tide).　 With directions depending on the tidal state, some components of north-south flowing plumes are predicted to travel along the gap between the Airport Island and the HKBCF. Overall, the surface SS rapidly drops to around less than (10 mg/L) at a distance of about 1km.　 The plumes may travel a longer distance during the peak ebb tide and pass over Ta Pang Po but at concentrations of less than 3 mg/L but this situation only occurs rarely.

6.9.2.5 The western extent of the surface plumes (~15 mg/L) occurs at about the NE tip of the Airport, close to the artificial reef deployment site (WSR 41), but not reaching the airport intake (WSR 25).　 Similar to the 2011 scenario, low concentration surface plumes could, however, reach to a distance of about half the length of the airport runway but the SS elevation reaching this area is low (<5 mg/L).　 Under no circumstances do the plumes cross the Urmston Road.　 The sediment plumes generally remain around the East Tung Chung Bay near the project site, although during the spring tide flood phase, the plumes from the HKLR could pass the North Lantau Highway and reach Ma Wan Chung at low concentrations (<3 mg/L), but not reaching the San Tau SSSI (WSR 27).　 This situation is, again, very rare and the plumes only last for around 2 hours, if it does occur.

6.9.2.6 The plumes form the northern reclamation of TM-CLKL will be rapidly dispersed by the high flow of Urmston Road.　 Small plumes of <10 mg/L elevation were only obvious during the slack tide periods and the plumes rapidly diluted within about 100m.

6.9.2.7 The predicted maximum elevations in SS for selected observation points around the site and comparison with the water quality objective (WQO) or water quality criteria (WQC) for selected specific sites are summarised in Table 6.23 below. The principal assessment criteria (Section 6.4) is the depth-averaged value, although secondary criteria for each depth level have also been presented in Table 6.23, and the following discussion refers the depth-averaged values / WQO unless specified otherwise. 　As indicated in Table 6.23, SS elevations exceeding the relevant WQO are limited to locations around the project site.　 While the plumes can reach Ta Pang Po (WSR 21), this are only predicted during the dry season and the maximum depth average concentrations is only 2.6 mg/L and below the WQO.　

6.9.2.8 For key marine ecology sensitive area around the project area, no WQO exceedances are predicted for Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (WSR 27, 28, 29, 30 and 48). The predicted maximum plumes at known coral sites near the River Trade Terminal (WSR 47b), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO, although a low frequency (1 to 3%) of WQO exceedances at low level (max. of 11.2 mg/L) is predicted at Tai Mo To (WSR 46).　 The predicted maximum plumes at the recently identified dolphin habitats close the project site, including Tai Mo To (WSR49) and at areas further away like Sham Shui Kok (WSR 45c), are below the WQO, although for WSR 49 low frequency exceedances at separate depths (1-5% of time) during wet season are predicted.　 The plumes are expected to reach Ma Wan FCZ (WSR 20) at only very low levels (less than 1 mg/L) and no WQC /WQO exceedances are predicted. At the northern TM-CLKL works site, the maximum predicted elevations at Butterfly Beach (WSR 12) and WSD intake (WSR 13) were predicted to be less than 2 mg/L and well below the WQO/WQC.　 Rare exceedances are only predicted to occur around the River Trade Terminal (WSR 47a), adjacent to the works although there are no specific sensitive uses in this location.

6.9.2.9 In terms of the predicted SS elevations, the Artificial Reef at NE Airport (WSR 41), which is very close to (about 300m from the HKBCF and about 1km from the TM-CLKL) and downstream (during flood tide) of the project site, would be subject to exceedances of the calculated WQO of 3.7 mg/L (wet season) and 5.5 mg/L (dry season) for about 24% - 25% of the time.　 The predicted surface maximum SS elevations at the NE Airport Intake (WSR 25) would, also, exceed the WQO for about 19% of the time.　 Higher levels and frequency of WQO exceedances, however, are predicted at the mid-depth for both WSR 41 and WSR 25.

6.9.2.10 The total sediment deposition over the entire simulation period and daily averaged sediment deposition rates are, also, presented in Appendix D9a (Figures 37-40). Tabulations of running averages of the accumulated sediment over 24 hours period are also presented in Appendix D11 (Tables 47 and 48). 　As the majority of the proposed works are located in a shallow sheltered bay area, the suspended solids plumes, generally, remain around the project site and the deposition is also the highest in the project area, reaching around 10,000 g/m²/day around the site boundary. 　However, outside the site boundary, the SS concentrations rapidly reduce to less than 200 g/m²/day in about 500m.　 For the northern reclamation of the TM-CLKL, the deposition rate would be less than 50 g/m²/day outside the work site. 　The daily sediment deposition rate is particular relevant to coral sites and a rate of 200 g/m²/day is generally considered as tolerable in the western waters. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged between 0.0 g/m²/day to 65.8 g/m²/ day which are below the tolerable rate for corals, although corals were only identified at some of these sites. 　Relatively high sedimentation rate of 130.6 g/m²/day are predicted at the artificial reef (AR) at the NE of airport although the AR will be re-provided.

Mitigated Sediment Plumes ((1+1) Silt Curtain System)

6.9.2.11 Under the early (April) 2012 unmitigated scenario, the predicted maximum SS elevations could exceed the WQO for only a very few sensitive receivers around the project site as discussed above.　 As such, specific mitigation measures would be required to reduce the suspended solids dispersal.　 The use of (1+1) silt curtain systems has been recommended and modelled.　 This (1+1) silt curtain system is expected to reduce the overall potential sediment loss to the surrounding water columns by 67% in the 2012 scenario year (Table 6.16b).　 The applicability and effectiveness of the use silt curtains are limited by the current speed of the site and the technical feasibility of the recommended silt curtain system has been evaluated based upon the results of the flow simulations and concluded to be acceptable given the low currents in this area. As noted in Table 6.16b, however, no silt curtain system protection is assumed at this stage for the TM-CLKL northern reclamation in which the flow is high. Further details, together with an indication of the silt curtain layout, are presented in Appendix D6a.

6.9.2.12 The predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and, also, the total and daily sediment deposition assuming the (1+1) silt curtain system is implemented are shown in Appendix D9b and D9d and tabulated values are presented in Appendix D11 (Tables 5).

6.9.2.13 With these specific mitigation measures, the predicted sediment plumes size and maximum SS elevations are much reduced.　 In general, surface plumes above 15 mg/L are predicted to be confined to within about 500m of the project site.　 The dynamic pattern of the plumes is similar to the unmitigated case, but the concentrations are much reduced.　 The eastward bound extent of the sediment plumes are not expected to reach Tai Mo To (WSR 49) or Sham Shui Kok (WSR 45c) as the predicted elevation will be less than 2mg/L.

6.9.2.14 The western extent of the surface plume around the NE tip of the airport is, also, much reduced to only around a maximum of 10 mg/L.　 With the mitigation, the plumes from the HKLR reclamation will be confined to within only a few hundred metres from the site at low concentrations (<10 mg/L) and are not predicted to cross the North Lantau Highway, nor would they reach the San Tau Beach SSSI.

6.9.2.15 The predicted maximum elevations in SS for selected observation points around the site and comparison with the Water Quality Objectives (WQO) or Water Quality Criteria (WQC), for selected specific sites, for the mitigated scenario are summarised in Table 6.24 below. The principal assessment criteria (Section 6.4) is the depth-averaged value, although secondary criteria for each depth levels are also presented in Table 6.24, and the following discussion refers the depth-averaged values / WQO unless specified otherwise.　 As indicated in Table 6.24, SS exceedances of the relevant WQOs are limited to few areas in close vicinity to the site.　

6.9.2.16 No WQO exceedances are predicted for key ecology sensitive areas around the project area, such as Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (including WSR 27, 28, 29, 30 and 48). The predicted maximum plumes at known coral sites near River Trade Terminal (WSR 47b), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO. While at Tai Mo To (WSR 46), low frequency (1%) exceedances at low levels (3.3 – 6.6 mg/L) are predicted in the wet season, the overall SS elevations will be within the WQO for both wet and dry seasons.　 The predicted maximum plumes at the recently identified dolphin habitats close to the project site, including Tai Mo To (WSR49) or the more distant areas like Sham Shui Kok (WSR 45c), are predicted to be below the WQO.　 No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted elevation is less than 1 mg/L and does not exceed the WQC /WQOs.

6.9.2.17 The maximum SS elevations at the Artificial Reef in the airport Exclusion Zone (WSR 41) are predicted to comply with the WQO.　 Similarly, WQO exceedances are not predicted for the NE Airport Intake (WSR 25) although low frequency (<4%) exceedances at low level are predicted at separate water depths for both WSRs there.　

6.9.2.18 The total sediment deposition over the simulation period and daily averaged sediment deposition rates are presented in Appendix D9b (Figures 37-40). Tabulations of running averages of the accumulated sediment over 24 hours period are also presented in Appendix D11 (Tables 53 and 54). With the mitigation measures in place, sediment deposition is mainly confined to the project site.　 Outside the site boundary, deposition rates rapidly reduce to less than 100 g/m²/day within about 500m. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged between 0.0 g/m²/day to 21.8 g/m²/ day which are below the tolerable rate for corals although corals were only identified in some of these sites.　 While relatively high sedimentation rates of 136.0 g/m²/day are predicted at the artificial reef (AR) at the NE of airport, the maximum rate is much reduced to 38.6 g/m²/day with the (1+1) silt curtain system.

6.9.2.19 In summary, the (1+1) silt curtain system proposed is considered to reduce impacts from suspended solids to within acceptable levels and while some marginal and transient exceedances remain in very close proximity to the works site, these exceedances were not predicted to affect any ecological sensitive receivers, including marine park, corals sites and key dolphin habitat at Tai Mo To, as well as the Ma Wan FCZ.　 As a result, significant residual impacts are not expected.　 Although the current speeds at the works site for the northern reclamation of TM-CLKL are too high for the effective application of silt curtain systems, no significant impacts were predicated in this area.

6.9.2.20 Notwithstanding, double layers of peripheral silt curtains and cage silt curtains around the grab dredgers (referred as the (2+1) silt curtain system), could further reduce the potential sediment losses by an extra reduction of about 19%.　 As such, this (2+1) double silt curtain system could be applied if the construction phase EM&A on-site showed the need for further mitigation.　 This (2+1) silt curtain system has been modelled and the predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and the total and daily sediment deposition are shown in Appendix D12b for reference. In addition, if specific sensitive receivers need further protection, silt curtains around sensitive receivers could be considered.

Table 6.23　　 Predicted Maximum SS (mg/L) Elevations at Observation Points for the Scenario Year 2012 (Unmitigated)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.4	0.5	0.3	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.3	0.4	0.6	0.3	0.3	0.4	0.7	0.3	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.0	0.1	0.1	0.1	0.0	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.3	0.9	1.2	0.8	0.0	0.2	2.1	0.7	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.4	1.2	1.4	0.9	0.6	1.1	1.4	0.9	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.7	0.9	1.1	0.9	0.5	0.8	1.2	0.7	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.2	0.5	0.5	0.4	0.1	0.2	0.3	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.1	0.1	0.1	0.1	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.6	0.7	0.8	0.7	0.2	0.4	0.4	0.4	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	2.4	2.6	2.9	2.6	0.8	0.9	1.1	0.9	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.1	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.2	0.2	0.2	0.2	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	9.3	13.5	18.1	10.7	5.8	13.7	16.9	10.1	9%	24%	17%	19%	4%	26%	18%	19%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.1	0.2	0.2	0.1	0.0	0.0	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	8.2	12.2	23.3	12.3	7.8	13.7	21.2	10.0	19%	29%	21%	25%	12%	31%	12%	24%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.1	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	2.2	2.6	3.0	2.6	0.7	1.0	1.4	0.8	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	5.2	8.8	27.4	11.2	8.4	14.1	22.2	7.9	1%	5%	4%	1%	14%	7%	5%	3%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	6.0	8.4	14.6	5.5	4.2	9.7	11.0	4.9	2%	1%	1%	0%	4%	6%	1%	3%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	0.6	0.7	2.3	1.0	0.7	1.7	1.7	0.8	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	2.6	6.9	6.6	4.7	4.5	6.0	10.1	3.7	0%	3%	0%	0%	1%	5%	4%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764 mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

Table 6.24　　 Predicted Maximum SS (mg/l) Elevations at Observation Points for the Scenario Year 2012 (Mitigated)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.3	0.5	0.3	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.1	0.2	0.6	0.3	0.1	0.3	0.6	0.2	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.0	0.0	0.1	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.3	0.9	1.2	0.8	0.0	0.2	2.1	0.7	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.4	1.1	1.4	0.9	0.6	1.1	1.4	0.9	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.7	0.9	1.1	0.9	0.5	0.8	1.1	0.7	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.2	0.2	0.3	0.2	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.2	0.2	0.2	0.2	0.1	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	0.6	0.7	0.8	0.7	0.2	0.3	0.3	0.3	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.0	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	2.6	3.6	5.0	3.0	1.6	3.7	4.6	2.7	0%	0%	0%	0%	0%	1%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	3.1	4.0	7.5	4.0	2.7	4.0	6.5	3.1	0%	0%	0%	0%	0%	3%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	0.6	0.7	0.8	0.7	0.2	0.3	0.4	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	1.4	2.6	7.7	3.3	3.3	4.0	6.6	2.4	0%	0%	0%	0%	1%	1%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	6.0	8.4	14.6	5.5	4.2	9.7	10.9	4.9	2%	1%	1%	0%	4%	6%	1%	3%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	0.6	0.7	2.3	1.0	0.7	1.7	1.7	0.8	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	0.8	1.8	2.0	1.3	1.2	1.6	3.0	1.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

6.9.3 Suspended Solids - Year 2013 Scenario (Sequence A)

Unmitigated Sediment Plumes

6.9.3.1 The last selected worse case scenario is early (April) 2013 which corresponds to about 75% into the overall duration of marine works and construction activities for both the TM-CLKL and HKBCF are still actively progressing. 　The reclamation works of the HKLR are expected to be complete by this time and the only HKLR marine works left would comprise piling for the viaduct piers. 　The seawalls for the Phase 2 of HKBCF would be largely completed, while Portion D of the HKBCF, connecting the Airport Island and the HKBCF, would, also, be partially formed. 　The narrowing of the channel by Portion D of HKBCF will further change the local north-south flows along Portion A of the HKBCF seawalls from peak ebb speeds of <0.4m/s to around <0.8m/s, but the peak flood flows stay around <0.8m/s. 　Significant localised change in flows around the south of the HKBCF are not anticipated. 　For the northern reclamation of TM-CLKL, the seawalls would be almost completed and, thus, shielding the works being undertaken near the shore.

6.9.3.2 The anticipated work fronts are scattered around the multiple work sites. 　At the HKBCF, works will comprise mainly reclamation filling for Phase 2. 　Works at the TM-CLKL southern reclamation would be on-going and progressing southwards along the edge of the HKBCF island. 　As noted above, seawalls for the TM-CLKL northern reclamation would be almost complete and the main works would comprise reclamation filling. 　Marine works for HKLR would be completed except the viaduct pier piling. 　Piling for the TM-CLKL southern marine viaduct pilling would, also, be expected to be completed.

6.9.3.3 The predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water levels during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and the total and daily sediment deposition are presented in Appendix D10a and D10d and tabulated values are presented in Appendix D11 (Tables 7).

6.9.3.4 As the works near completion, the total daily unmitigated sediment losses has reduced from around 2.0M kg/day in early 2012 to about 1.7 M kg/day and as such the sediment plumes can be expected to be similar to 2012 scenario, although the newly formed Phase 1 HKBCF land mass and the location of the works fronts will also affect the dynamics of the sediment plumes.　 During the slack periods (high and low waters), the suspended solids (SS) at the work fronts could elevate to around 300 mg/L at the surface. This is mainly localised around the Portion D of works in which seawall filling and reclamation dredging rates are higher than 2012 and, hence, the localised elevation is also higher than the 2012 scenario.　 As a consequence, the surface plumes leaving the site during the slack periods could elevate to around <100 mg/L within 1km of the site and only drop to <30 mg/L at a distance of 2km.　 This is mainly predicted around the low water level in which the ebb tide carried the plumes from Portion D towards East Tung Chung Bay where flow and dilution is relatively week and the plumes can build up. Plumes heading north towards the artificial reef near the NE tip of the airport will be rapidly diluted by the high flow of the main channel and as such the plumes will be small and of low elevation (<30 mg/L). Under no circumstances do the plumes cross the Urmston Road.

6.9.3.5 During peak ebb, the main direction of plumes from Portion D are southward and then eastward in East Tung Chung Bay and the surface plumes of around 30mg/L can just reach the proposed South Brothers CMP Pit B. The ebbing plumes are, also, predicted to be larger and of higher concentration during the dry season, but could be closer to the Tung Chung coastline during the wet season. During the peak flood, plumes from Portion D of the works travel northward and than westward.　 The surface plumes at the gap between the Airport Island and HKBCF would reach around 100 mg/L but rapidly diluted to <30mg/L in around 500m after leaving the gap heading west. The plumes from the Phase 2 of the HKBCF would be mainly confined by the surrounding seawalls and no surface plumes outside this working area are expected.

6.9.3.6 The surface plumes leaving the TM-CLKL southern reclamation are, generally, of low concentrations (<15 mg/L) outside the works area and, typically, they travel westward along the southern edge of the HKBCF during flood tide and eastward during the ebb tide. At the TM-CLKL northern reclamation, the plumes are highly localised to the east side of the reclamation where the marine access gap is located. The localised surface plumes at Tuen Mun, however, could become more prominent as flows are blocked by the seawalls. 　Notwithstanding, the local surface plumes outside the site are often predicted to drop to <10mg/L in 500m and would not affect the coastline.

6.9.3.7 The predicted maximum elevations in SS for selected observation points around the site and comparisons with the water quality objective (WQO) or water quality criteria (WQC) for selected specific sites are summarised in Table 6.25 below. The principal assessment criteria (Section 6.4) is the depth-averaged value, although secondary criteria for each depth level are also presented in Table 6.25, and the following discussion refers the depth-averaged values / WQO unless specified otherwise. As indicated in Table 6.25, SS elevations exceeding the relevant WQO are limited to locations around the project site.　 For plumes occasionally reaching Ta Pang Po (WSR 21), the maximum depth average concentrations are only 1.5 mg/L, which would not be detectable and are below the WQOs for all depths.　

6.9.3.8 For key marine ecology sensitive area around the project area, no WQO exceedances are predicted for Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (WSR 27, 28, 29, 30 and 48). The predicted maximum plumes at known coral sites near Tai Mo To (WSR 46), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO. 　However, for corals near the River Trade Terminal (WSR 47b), low levels of exceedances are predicted for 6% and 32% of the dry and wet season time, respectively. The predicted maximum SS elevations at the recently identified dolphin habitats close to the project site, including Tai Mo To (WSR49) and at areas further away like Sham Shui Kok (WSR 45c), are low and no WQO exceedances are predicted.　 No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted maximum elevations are 0.5 mg/L and not exceeding the WQC /WQOs.　 At the TM-CLKL northern landing, the maximum predicted elevations at Butterfly Beach (WSR 12) and WSD intake (WSR 13) will be less than 2 mg/L and well below the WQO/WQC.　

6.9.3.9 In terms of the predicted maximum SS elevations, the Artificial Reef at NE Airport (WSR 41), would be subject to exceedances of the calculated WQO of 3.7 mg/L (wet season) and 5.5 mg/L (dry season) for about 9% to 11% of the wet and dry season time, respectively.　 Similarly, the predicted maximum SS elevations at the NE Airport Intake (WSR 25) would also exceed the WQO for about 4% to 21% of the wet and dry season time, respectively.

6.9.3.10 The total sediment deposition over the entire simulation period and daily averaged sediment deposition rates are also presented in Appendix D10a (Figures 37-40). Tabulations of running averages of the accumulated sediment over 24 hours period is also presented in Appendix D11 (Tables 49 and 50). As the proposed site is located in a shallow sheltered bay area, the suspended solids plumes generally stay around the project site and the deposition is also the highest in the project area and reaching around 10,000 g/m²/day around the site boundary. However, outside the site boundary, deposition rapidly reduces to less than 200 g/m²/day within about 500m.　 For Portion D of the HKBCF, however, an area of relatively high deposition rate (~1,000 g/m²/day) could extend by about 1km southward.　 For the northern reclamation of the TM-CLKL, the deposition rate would be reduced to less than 200 g/m²/day in about 500m from the work site. The daily sediment deposition rate is particular relevant to coral sites and a rate of 200 g/m²/day is generally considered as tolerable in the western waters. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged between 0.0 g/m²/day to 16.5 g/m²/ day which are below the tolerable rate for corals although corals were only identified in these sites. Relatively high sedimentation rates of 263.1 g/m²/day are predicted near the River Trade Terminal (WSR 47a) which impacts coral colonies there if unprotected.

Mitigated Sediment Plumes ((1+1) Silt Curtain System)

6.9.3.11 Under the early (April) 2013 unmitigated scenario, the predicted maximum SS elevations could exceed the WQO for only a very few sensitive receivers around the project site as discussed above.　 As such, specific mitigation measures would be required to reduce the suspended solids dispersal.　 The use of (1+1) silt curtain systems has been recommended and modelled.　 This (1+1) silt curtain system is expected to reduce the overall potential sediment loss to the surrounding water columns by 66% in the 2013 scenario year (Table 6.16b).　 The applicability and effectiveness of the use silt curtains are limited by the current speed of the site and the technical feasibility of the recommended silt curtain system has been evaluated based upon the results of the flow simulations and concluded to be acceptable given the low currents in this area. For TM-CLKL northern reclamation, the work front would be close to the shoreline and the formed seawall would, also, provide some degree of protection against high flows and, as such, silt curtains can be applied at this stage (i.e., Portion N-C) in this location.　 Further details, together with an indication of the silt curtain layout, are presented in Appendix D6a.

6.9.3.12 The predicted elevations in suspended sediment concentrations (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and the total and daily sediment deposition assuming the (1+1) silt curtain system is implemented are shown in Appendix D10b and D10d and tabulated values are presented in Appendix D11 (Tables 8).

6.9.3.13 With these specific mitigation measures, the predicted sediment plume sizes and maximum SS elevations are much reduced.　 In general, surface plumes with concentrations above 50 mg/L are predicted to be confined to within about 500m of the project site.　 The dynamic pattern of the plumes is similar to the unmitigated case, but the concentrations are much reduced.　 The eastward extent of the sediment plumes are not expected to reach Tai Mo To (WSR 49) or Sham Shui Kok (WSR 45c) in excess of the WQO as the predicted elevation will be less than 3mg/L.

6.9.3.14 The western extent of the surface plume around the NE tip of the airport is, also, much reduced to only around a maximum of 10 mg/L.　 With the mitigation, the south-east surface plumes from Portion D of the HKBCF work, during ebbing, are predicted to reduce to around 30 mg/L within 1km.　 Similarly, the plumes from the TM-CLKL at Tuen Mun are predicted to be much reduced.

6.9.3.15 The predicted maximum elevations in SS for selected observation points around the site and comparison with the Water Quality Objectives (WQO) or Water Quality Criteria (WQC), for selected specific sites for the mitigated scenario are summarised in Table 6.26 below. The principal assessment criteria (Section 6.4) is the depth-averaged value, although secondary criteria for each depth level are also presented in Table 6.26, and the following discussion refers the depth-averaged values / WQO unless specified otherwise. As indicated in Table 6.26, SS exceedances of the relevant WQOs are limited to a few areas in close vicinity to the site.　

6.9.3.16 No WQO exceedances are predicted for key ecology sensitive areas around the project area, such as Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (including WSR 27, 28, 29, 30 and 48). 　The predicted maximum plumes at known coral sites near Tai Mo To (WSR 46), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO. For corals near the River Trade Terminal (WSR 47b), low level of exceedances are still predicted at 11% of the wet season time but not during the dry season. As corals colonies near the River Trade Terminal are recommended to be translocated prior to the works, not direct impacts are anticipated. 　The predicted maximum plumes at the recently identified dolphin habitat like Tai Mo To (WSR49) and Sham Shui Kok (WSR 45c) would not exceed the WQO. No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted elevation is <0.5 mg/L and does not exceed the WQC /WQO.

6.9.3.17 The maximum SS elevations at the Artificial Reef at the airport Exclusion Zone (WSR 41) are predicted to comply with the WQO.　 Similarly, the predicted maximum SS concentrations at the NE Airport Intake (WSR 25) will be below the WQO, although low frequency (<2%) exceedances at low levels are predicted at separate water depths for both WSRs there.　

6.9.3.18 The total sediment deposition over the simulation period and daily averaged sediment deposition rate is also presented in Appendix D10b (Figures 37-40). Tabulations of running averages of the accumulated sediment over 24 hours period are also presented in Appendix D11 (Tables 55 and 56). With the mitigation measures, the deposition of suspended sediment is mainly confined to the project site and outside the site boundary, deposition rates rapidly reduce to less than 100 g/m²/day within about 500m. For Portion D of HKBCF, however, such low levels of deposition are predicted at an area 1km away from the site. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.27 and the maximum rates ranged between 0.0 g/m²/day to 27.4 g/m²/ day which are below the tolerable rate for corals although corals were only identified in these sites. Relatively high sedimentation rates of 263.1 g/m²/day are predicted at the River Trade Terminal (WSR 47b) and the maximum rate is much reduced to 144.7 g/m²/day with the (1+1) silt curtain system.

6.9.3.19 In summary, overall, the (1+1) silt curtain system proposed is considered to reduce impacts from suspended solids to within acceptable levels and while some marginal and transient exceedances remain in very close proximity to the works site, these do not affect any ecological sensitive receivers, including marine park, corals sites and key dolphin habitat at Tai Mo To as well as the Ma Wan FCZ.　 As a result, significant residual impacts are not expected.

6.9.3.20 However, the sediment plumes from Portion D of HKBCF are predicted to be close to the Tung Chung coastline even with the (1+1) silt curtain systems in place for the 2013 scenario compared to the other scenario years, as a result of the narrowing of the channel and associated increase in flow when the construction of Portion D begins.　 In the original worse case construction programme (Sequence A), it is assumed that the northern and southern seawalls for Portion D will be constructed in parallel with the reclamation dredging and filling.　 Under this scenario, the potential sediment loss from this work front is high as minimal integrated design measures such as a leading seawall can be implemented. With the implementation of the (1+1) silt curtain system, overall, WQO exceedances and high SS plumes can be mitigated to some extent.　 However, the localised high flows could represent a challenge for effective deployment of the (1+1) silt curtain system and the effectiveness of the silt curtain systems may not be guaranteed unless the silt curtain system are specially built (as per the manufacturer specification) or some other engineering measures such as steel sheet piles (proposed on the northern part of HKBCF) is considered. A more viable alternative would be the formation of either the northern or southern seawalls for the Portion D which, once completed, would be expected to reduce the local flow speed (box culverts, however, will be provided at the operation phase to restore flows in the embayed area) and, thus, the size of the sediment plumes. This, however, would be subject to other constrains such as marine access although it is recommended that this programme change be considered should a higher level of protection to the Tung Chung coastline (southern seawall first) or to the artificial reef at the NE of airport (northern seawall first) be required.

6.9.3.21 Notwithstanding, double layers of peripheral silt curtains and cage silt curtains around the grab dredgers (referred as the (2+1) silt curtain system), could further reduce the potential sediment losses by an extra reduction of about 30%.　 As such, this (2+1) double silt curtain system could be applied if the construction phase EM&A on-site showed the need for further mitigation.　 This (2+1) silt curtain system has been modelled and the predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and, also, the total and daily sediment deposition are shown in Appendix D12c for reference.　 In addition, if specific sensitive receivers need further protection, silt curtains around sensitive receivers could be considered.

Table 6.25　　 Predicted Maximum SS (mg/L) Elevations at Observation Points for the Scenario Year 2013 (Unmitigated)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.2	0.3	0.3	0.2	0.1	0.5	0.4	0.3	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.0	0.0	0.1	0.0	0.0	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.1	0.2	0.2	0.2	0.0	0.1	0.3	0.1	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.3	0.8	0.6	0.5	0.6	1.5	1.8	0.9	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.1	0.1	0.1	0.1	0.3	0.3	0.3	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.1	0.3	0.2	0.2	0.1	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.1	0.1	0.1	0.1	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.3	0.5	0.5	0.4	0.1	0.2	0.2	0.2	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	1.3	1.5	1.6	1.5	0.2	0.3	0.4	0.3	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.1	0.2	0.2	0.2	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.3	0.4	0.4	0.4	0.1	0.2	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	14.5	18.6	21.2	16.5	3.0	15.2	8.8	8.7	10%	26%	21%	21%	2%	14%	1%	4%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.1	0.2	0.2	0.2	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	14.5	19.8	24.3	16.2	21.5	16.6	3.2	10.7	11%	17%	6%	11%	18%	10%	0%	9%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	1.7	2.2	2.0	2.0	0.4	0.5	0.5	0.4	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	4.4	7.9	3.9	3.5	4.0	3.9	5.3	1.9	1%	3%	0%	0%	1%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	0.1	0.3	0.4	0.3	0.0	0.2	0.4	0.2	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	4.6	10.7	19.1	9.4	7.2	16.1	21.0	10.7	1%	10%	9%	6%	20%	42%	23%	32%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	3.3	7.1	6.0	4.8	1.5	2.6	4.2	2.4	0%	3%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764 mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

Table 6.26　　 Predicted Maximum SS (mg/l) Elevations at Observation Points for the Scenario Year 2013 (Mitigated)

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 08	Yes	Lung Kwu Sheung Tan (non-gazetted beach)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.1	0.1	0.1	0.1	0.0	0.2	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 10	Yes	Sha Chau and Lung Kwu Chau Marine Park	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 11	Yes	Castle Peak Power Station Cooling Water Intake (Note 1)	-	0.0	0.1	0.1	0.1	0.0	0.0	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	764	764	764	764	764	764	764	764
WSR 12	Yes	Butterfly Beach (gazetted beach)	NM1,2,3	0.2	0.4	0.3	0.3	0.3	0.8	1.0	0.5	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 13	Yes	WSD Seawater Intake at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.1	0.2	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 15	Yes	Gazetted Beaches at Tuen Mun	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 18	Yes	Gazetted Beaches along Castle Peak Road	WM4	0.0	0.1	0.1	0.1	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 19	Yes	Gazetted Beaches at Ma Wan	WM4	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.9	6.0	9.0	6.1	1.7	2.8	6.0	3.4
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.1	0.2	0.2	0.1	0.0	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 21	Yes	Ta Pang Po (near Sunny Bay Mangrove)	NM1,2,3	0.4	0.5	0.5	0.5	0.1	0.1	0.1	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22a	No	Tai Ho Wan Outlet (inside)	NM1,2,3	0.0	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22b	Yes	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	NM1,2,3	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.1	0.1	0.1	0.1	0.0	0.0	0.1	0.0	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	4.8	6.0	6.8	5.5	1.0	5.2	3.0	3.0	2%	2%	0%	0%	0%	1%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.0	0.1	0.1	0.1	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 28	Yes	Airport Channel / Airport Cooling Water Intake (S)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 29	Yes	Hau Hok Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 30	Yes	Sha Lo Wan (Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 31	Yes	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 32	Yes	Tai O (Mangrove Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 34	Yes	Yi O (Mangrove and Horseshoe Crab Habitat)	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	4.5	6.2	7.8	5.1	7.1	5.3	1.2	3.4	2%	2%	0%	0%	11%	2%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 42	Yes	Artificial Reef at Sha Chau	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	0.5	0.7	0.6	0.6	0.1	0.2	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	1.4	2.5	1.2	1.1	1.3	1.3	1.9	0.7	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47a	No	River Trade Terminal	NM1,2,3	0.1	0.1	0.2	0.1	0.0	0.1	0.2	0.1	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 47b	Yes	River Trade Terminal (near coral site)	NM1,2,3	2.5	5.9	10.5	5.2	4.0	8.9	11.6	5.9	0%	1%	1%	0%	6%	18%	9%	11%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 48	No	Airport Channel western end	NM5,6,8	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0%	0%	0%	0%	0%	0%	0%	0%	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	1.1	2.3	1.9	1.5	0.5	0.8	1.3	0.8	0%	0%	0%	0%	0%	0%	0%	0%	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 There is a specific requirement for the Castle Peak Power Station intake and the SS should be maintained at below 764 mg/L (ERM, 2005)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

Table 6.27　　 Predicted Maximum Daily Sedimentation Rate at Representative Marine Ecology and Fisheries Sensitive Receivers (Sequence A)

WSR	Nature	2011 Unmitigated	2011 　Mitigated	2012 Unmitigated	2012 Mitigated	2013 Unmitigated	2013 Mitigated
WSR 10	Sha Chau and Lung Kwu Chau Marine Park	2.6	0.7	1.9	1.1	0.9	0.3
WSR 20	Ma Wan Fish Culture Zone	4.8	1.8	4.7	1.7	3.0	1.0
WSR 22b	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	0.0	0.0	0.0	0.0	0.0	0.0
WSR 22c	Tai Ho Wan Outlet (outside) / Near coral site	5.3	1.9	2.5	0.8	3.8	1.2
WSR 27	San Tau Beach SSSI	8.8	0.4	1.2	0.2	1.3	0.4
WSR 28	Airport Channel	0.3	0.0	0.1	0.1	0.1	0.0
WSR 41	Artificial Reef at NE Airport (Note 1)	267.4	69.3	130.6	38.6	85.0	27.4
WSR 46	Tai Mo To (near coral / CWD habitat range)	49.4	19.0	65.8	19.1	16.5	5.4
WSR 47b	River Trade Terminal (near coral site) (Note 2)	2.9	1.0	21.9	21.8	263.1	144.7
WSR 48	Airport Channel western end	0.0	0.0	0.1	0.1	0.1	0.1

Notes: Unit = g/m²/day;

1. The AR at NE Airport is proposed to be re-provided.

2. Coral colonies near River Trade Terminal is proposed to be trans-located before project works.

3. Mitigated refer to the (1+1) silt curtain system.

6.9.4 Suspended Solids - Sequence B Worse Case Scenario

Mitigated Sediment Plumes ((1+1) Silt Curtain System) (Sequence B)

6.9.4.1 As elaborated in Section 6.1.2, a construction Sequence B has been developed to further minimised the potential water quality impacts. The mitigation measures formulated in Sequence A are also incorporated as integrated protection measures under Sequence B and detailed in Section 6.7.4. As the potential sediment loss of the unmitigated scenario of Sequence B is substantially lower than for Sequence A (see Tables 6.16b and 6.16d), only the mitigated scenario of Sequence B has been modelled to demonstrate the effectiveness of this new construction sequence.

6.9.4.2 Under the conservative worse case scenario for Sequence B, it is assumed that only the sheet piled wall near the northern side of the HKBCF reclamation is present while the seawalls at the eastern and western sides of the main HKBCF+TM-CLKL (southern landfall) are not present. The sheet piled wall is predicted to reduce the flows in the area immediately south to <0.1 m/s while the high east-west flow north of the sheet pile wall (Urmston Road) would not be affected by the sheet piled wall. The sheet piled wall, however, is predicted to cause some localised change in the flows at the gap between the Airport Island and HKBCF and also in the area further south, including the main reclamation site. At the gap between the Airport Island and HKBCF, the north-south flow will increase to a peak of around 1.0 m/s, although it is generally below 0.5 m/s for the majority of the time. At area south of the main reclamation, the east-west flows become more obvious during the peak ebb/flood tides with flows generally reaching around <0.3 m/s to <0.4 m/s, although localised flows reaching 0.7 m/s are, also, predicted at the perimeter of the site.

6.9.4.3 As Sequence A has demonstrated that mitigation in the form of (1+1) silt curtain system is required to reduce the suspended solids dispersal, this is also assumed under Sequence B. The applicability and effectiveness of silt curtains are limited by the current speed at the site and the technical feasibility of the recommended silt curtain system has been evaluated based upon the results of the flow simulations and concluded to be acceptable given the low currents in this area. However, as the integrated sheet piled wall measure is predicted to increase localised flows to, and at times over, 0.5m/s, which is the generally 　accepted level for the application of fully efficient silt curtains, the effectiveness of silt curtains at the main HKBCF+TM-CLKL (southern landfall) reclamation site is assumed to be reduced as presented in Table 6.16c. Further details, including the vector plots during peak ebb and flood tides together with an indication of the silt curtain layout, are presented in Appendix D6b. Under this setting, the (1+1) silt curtain system is expected to reduce the overall potential sediment loss to the surrounding water columns by 69% in the 2011 scenario year from 1,778,000 kg/day to 560,000 kg/day (Table 6.16d).　

6.9.4.4 The major works assumed in this scenario is the seawall dredging and filling for the main reclamation of HKBCF+TM-CLKL (southern landfall) although there are also works at FSD berth and also coastal reclamation of HKLR. The main works is at the western seawall of the main HKBCF+TM-CLKL (southern landfall) reclamation where relative intensive seawall dredging and filling activities are on going. There are also 3 works fronts of seawall filling at the eastern seawall of the main HKBCF+TM-CLKL (southern landfall) at low intensity.

6.9.4.5 The predicted elevation in the sediment plumes (contours) for the selected time frames (peak ebb and flood tides, high and low water level during spring and neap tides), time history plots of the elevation over the entire modelling timeframe and, also, the total and daily sediment deposition assuming the (1+1) silt curtain system is implemented are shown in Appendix D14a and tabulated values presented in Appendix D14b (Tables 1).

6.9.4.6 With these specific mitigation measures, the predicted sediment plume sizes and maximum SS elevations are much reduced compared to the mitigated scenario of Sequence A.　 Generally, the plumes are highly localised and constrained within the works areas. Because of the higher working rate at the western seawall and higher fine content soft public fill is used at the FSD reclamation, plumes are mainly found around these two works areas. During the slack periods (high and low waters), the suspended solids (SS) at the work fronts would only elevate to around 30 - 50 mg/L at the surface. However, for the FSD reclamation site, surface plumes reaching 100 - 200 mg/L is predicted although this is mostly contained within the site. Surface plumes leaving the site are of low concentrations (<15 mg/L) and do not travel far from the site.

6.9.4.7 During peak ebb and flood tides, the main directions of initial plumes are north (flood tide) or south (ebb tide). The north moving plumes (during flooding) often are captured by the sheet piled wall and the newly formed FSD seawall. 　For those that pass through the gap between the Airport Island and main reclamation, they are rapidly deflected westward towards the airport intake at low concentrations (<10 mg/L) and completely dispersed at around 1km. The south moving plumes (during ebbing) are generally dispersed to around <10 mg/L at the southern boundary of the site. The remaining plumes that have not completely dispersed at the southern boundary of the site are then deflected eastward along the southern boundary. 　If this remaining eastward plume merged with the filling plumes at reclamation portion S-c of the TM-CLKL, the eastward plume could further travel for about 1km, but the concentrations leaving the eastern boundary are generally low at around <6mg/L.

6.9.4.8 The dynamic pattern of plumes from the HKLR are similar to the 2011 mitigated scenario for Sequence A and are confined to stay within only a few hundred meters from the site at low concentrations (<10 mg/L) and are not predicted to cross the Tung Chung Channel, nor would it reach the San Tau Beach SSSI.

6.9.4.9 The predicted maximum elevations in SS for selected observation points around the site and comparison with the Water Quality Objectives (WQO) or Water Quality Criteria (WQC), for selected specific sites, for the mitigated scenario are summarised in Table 6.28a below.　 As indicated in Table 6.28a, SS exceedances of the relevant WQOs are limited to few areas in close vicinity to the site. Table 6.28a also includes the results of Sequence A 2011 mitigated scenario and it is clear that the predicted SS elevations at sensitive receivers from Sequence B are generally lower than Sequence A.

6.9.4.10 No WQO exceedances are predicted for key ecology sensitive areas around the project area, such as Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Tai Ho Wan (WSR 22a-c) or Airport Channel (including WSR 27, 28, 29, 30 and 48). The predicted maximum plumes at known coral sites near Tai Mo To (WSR 46), Tai Ho Wan seawall (WSR 22c) and west of the Airport Channel (WSR 48) were all below the WQO.　 The predicted maximum plumes at south of Tai Mo To (WSR 49) or Sham Shui Kok (WSR 45c) around the recently identified dolphin habitat would also be controlled below the WQO and no impacts are anticipated with the mitigation. No observable plumes at Ma Wan FCZ (WSR 20) are expected as the predicted elevation is <0.5 mg/L and does not exceed the WQC or WQOs.

6.9.4.11 The predicted surface maximum SS elevations at the Artificial Reef at NE Airport (WSR 41), which is very close to (about 300m from the HKBCF and about 1km from the TM-CLKL) and downstream (during the flood tide) of the project site, however, are still predicted to exceed the calculated WQO of 3.7 mg/L (wet season) and 5.5 mg/L (dry season) for less than 1% of the time. Compared to the mitigated Sequence A 2011 scenario in which exceedances are predicted for 4% 　of the wet season but none during the dry season, the Sequence B overall have reduced the potential impacts to the AR. Nonetheless, as the AR site has been proposed to be re-provided and, therefore, the marginal exceedances would not be a major concern.　 For the NE Airport Intake (WSR 25), marginal exceedances are also predicted under the mitigated Sequence B for about 1% of the wet season time (max. SS elevation is 4.2 mg/L compared to 3.7 mg/L of the calculated WQO) but none during the dry season. This again is an improvement over the Sequence A in which exceedances are predicted for about 2% o the wet and dry season time (max. SS elevation are about 4.7 – 6.7 mg/L). While only very low frequences of low level excceedances are predicted, an additional silt curtain at around this water intake to ensure full compliance with SS WQO is recommended.

6.9.4.12 The total sediment deposition over the simulation period and daily averaged sediment deposition rates are also presented in Appendix D14a (Figures 37-40).　 Tabulations of running averages of the accumulated sediment over every 24 hours period are also presented in Appendix D14b (Tables 6 and 7). With the mitigation measures, the deposition of suspended sediment is mainly confined to the project site. Outside the site boundary, deposition is mainly predicted at the gab between the Airport Island and the HKBCF and area immediate south of the main reclamation. The averaged deposition rate higher than 100 g/m²/day is not predicted outside the site except in the gap between the Airport Island and the HKBCF. The predicted maximum daily sedimentation rates at major ecological sensitive receivers are summarised in Table 6.28b together with a comparison of the predicted rate for Sequence A under similar time frame. At all sensitive receivers, it is clear that the sedimentation is controlled within the project site and the predicted rate outside the project site are much lower compared to Sequence A. The maximum rates ranged between 0.0 g/m²/day to 7.6 g/m²/ day which are well below the tolerable rate for corals although corals were only identified in some of these sites.　 Under Sequence A, the maximum rate of 69.3 g/m²/day g/m²/day has been predicted at the artificial reef (AR) at the NE of airport and the maximum rate is much reduced to 28.8 g/m²/day under Sequence B.

6.9.4.13 In summary, Sequence B with the (1+1) silt curtain system proposed is considered to reduce impacts from suspended solids to within acceptable levels and while some marginal and transient exceedances remain in very close proximity to the works site, these were not predicted to affect major ecological sensitive receivers, including marine park, coral sites and key dolphin habitat at Tai Mo To, as well as the Ma Wan FCZ, and so significant residual impacts are not expected.

6.9.4.14 As Sequence B has a much reduced potential sediment loss by design and construction programme, double layers of peripheral silt curtains and cage silt curtains around the grab dredgers (referred as the (2+1) silt curtain system) considered under Sequence A is considered not necessary and not evaluated.

Table 6.28a　 Predicted Maximum SS (mg/L) Elevations at Observation Points for Worse Case Scenario (Year 2011) (Mitigated) (Sequence B) and Comparison with Sequence A of Similar Scenario Time

			Associated	Maximum SS (mg/L)								Percentage of Time Exceedances Predicted								WQO / WQC
Observation	Point		EPD	Dry Season				Wet Season				Dry Season				Wet Season				Dry Season				Wet Season
Points	SR	Name	Station	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA	S	M	B	DA
WSR 09a	No	Urmston Road (Main Channel)	NM5,6,8	0.1 (0.1)	0.1 (0.2)	0.1 (0.2)	0.1 (0.2)	0.0 (0.0)	0.1 (0.2)	0.1 (0.3)	0.1 (0.2)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 20	Yes	Ma Wan Fish Culture Zone (Note 2)	-	0.1 (0.3)	0.1 (0.3)	0.2 (0.3)	0.1 (0.3)	0.0 (0.1)	0.1 (0.1)	0.1 (0.1)	0.0 (0.1)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	39.1	39.1	39.1	39.1	43.0	43.0	43.0	43.0
WSR 22c	Yes	Tai Ho Wan Outlet (outside) / Near coral site	NM1,2,3	0.1 (0.1)	0.1 (0.2)	0.1 (0.2)	0.1 (0.2)	0.0 (0.0)	0.0 (0.1)	0.0 (0.1)	0.0 (0.1)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 24	No	Tung Chung Fairway	NM1,2,3	0.3 (0.2)	0.4 (0.2)	0.5 (0.2)	0.4 (0.2)	1.5 (0.1)	1.9 (0.3)	2.1 (2.9)	1.5 (1.1)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 25	Yes	Airport Cooling Water Intake (NE)	NM1,2,3	4.8 (5.6)	6.3 (7.2)	7.3 (8.2)	5.5 (6.7)	1.1 (2.3)	6.7 (6.4)	6.0 (8.3)	4.2 (4.7)	0% (4%)	2% (9%)	0% (1%)	0% (2%)	0% (0%)	7% (13%)	0% (2%)	1% (2%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 27	Yes	San Tau Beach SSSI	NM5,6,8	0.0 (0.0)	0.0 (0.0)	0.0 (0.1)	0.0 (0.0)	0.0 (0.0)	0.0 (0.0)	0.1 (0.1)	0.0 (0.0)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	5.7	7.7	11.8	8.3	3.0	3.6	10.3	5.6
WSR 41	Yes	Artificial Reef at NE Airport	NM1,2,3	6.7 (4.3)	11.0 (4.7)	10.1 (13.1)	5.7 (5.1)	4.5 (3.6)	10.5 (10.8)	3.3 (18.0)	3.8 (6.1)	4% (1%)	5% (0%)	1% (4%)	0% (0%)	2% (3%)	12% (12%)	0% (7%)	0% (4%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 45c	No	Sham Shui Kok (CWD habitat range)	NM1,2,3	0.5 (2.9)	0.7 (3.3)	0.6 (3.8)	0.5 (3.3)	0.1 (0.6)	0.2 (0.7)	0.1 (0.9)	0.1 (0.7)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 46	No	Tai Mo To (near coral / CWD habitat range)	NM1,2,3	1.5 (1.0)	3.5 (2.0)	2.2 (3.9)	1.5 (1.4)	0.9 (2.4)	1.2 (1.8)	1.7 (6.6)	0.6 (2.3)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7
WSR 49	No	Tai Mo To (Deep Channel / CWD habitat range)	NM1,2,3	1.0 (0.9)	2.2 (2.0)	2.5 (2.6)	1.7 (1.4)	0.6 (0.5)	0.6 (1.3)	1.1 (6.9)	0.5 (2.3)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (0%)	0% (1%)	0% (0%)	3.6	5.1	8.1	5.5	2.3	3.3	6.0	3.7

Notes:　　　　　　　　　

· WQO = Water Quality Objective; WQC = Water Quality Criteria; S=Surface level; M=Mid-depth; B=Bottom level; DA=Depth-averaged.

· Grey cell = Values with WQO/WQC Exceedances

1　　 The values in brackets are prediction of the Sequence A2011 mitigated scenario (see Table 6.22 for full)

2　　 General water quality protection guideline for FCZ (CityU, 2001)

3　　 The "Point SR" column indicate if the site is considered as specific stationary sensitive receiver by the nature of its use (e.g., beaches, existing intakes, SSSI or habitats for less mobile species).

Table 6.28b　 Comparison of Predicted Maximum Daily Sedimentation Rate at Representative Marine Ecology and Fisheries Sensitive Receivers (Sequence B)

WSR	Nature	Sequence A	Sequence A	Sequence B
		2011 Unmitigated	2011　 Mitigated	2011 Mitigated
WSR 10	Sha Chau and Lung Kwu Chau Marine Park	2.6	0.7	0.2
WSR 20	Ma Wan Fish Culture Zone	4.8	1.8	1.0
WSR 22b	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	0.0	0.0	0.0
WSR 22c	Tai Ho Wan Outlet (outside) / Near coral site	5.3	1.9	0.9
WSR 27	San Tau Beach SSSI	8.8	0.4	0.3
WSR 28	Airport Channel	0.3	0.0	0.0
WSR 41	Artificial Reef at NE Airport (Note 1)	267.4	69.3	28.8
WSR 46	Tai Mo To (near coral / CWD habitat range)	49.4	19.0	7.6
WSR 47b	River Trade Terminal (near coral site) (Note 2)	2.9	1.0	0.4
WSR 48	Airport Channel western end	0.0	0.0	0.0

Notes: Unit = g/m²/day;

1. The AR at NE Airport is proposed to be re-provided.

2. Coral colonies near River Trade Terminal is proposed to be trans-located before project works.

3. Mitigated refer to the (1+1) silt curtain system.

6.9.5 Sediment Contaminants

6.9.5.1 As reviewed in Section 6.3.5 and reflected in the site specific sediment quality testing (Appendix D1), organic pollutants like PAHs, PCBs, TBT and chlorinated pesticides were generally not detected in the sediment, elutriate or pore water samples and, hence, organic pollutants are not a key concern to this project. While some of the sediment samples were classified as Category M, these were mainly due to the presence of arsenic which is naturally occurring in the study area. Nonetheless, to address the potential dispersion of metallic and metalloid contaminants at the sensitivity receivers, the maximum worst case increases in dissolved contaminants have been calculated based on the predicted maximum elevations in suspended sediment concentrations assuming that all sediment are moderately contaminated (Category M) with contaminant concentrations equal to the UCEL for each contaminant of interest (Meinhardt, 2007; Mouchel, 2002b). 　The estimated maximum increases in dissolved contaminants for each modelling scenario are presented in Appendix D11 (Tables 10-13, 16-19 and 22-25) for Sequence A and Appendix D14b (Tables 2 and 3) and a summary of the highest increase for selected points/sensitive receivers over the three unmitigated scenarios (that is, 2011, 2012 and 2013) are presented in Table 6.29 below.

Table 6. 29　　 Estimated Highest Maximum Elevation in Contamination Concentrations and DO Depletion Based on the Maximum Predicted Depth-averaged SS Elevation

WSR		Maximum	Maximum Elevation (ug/L)									% of EQS									Maximum
		Elevation	Cd	Cr	Cu	Hg	Ni	Pb	Ag	Zn	As	Cd	Cr	Cu	Hg	Ni	Pb	Ag	Zn	As	depletion
	Name	SS (mg/L)	4*	160*	110*	1*	40*	110*	2*	270*	42*	2.5#	15#	5#	0.3#	30#	25#	-	40#	25#	DO　 (mg/L)
WSR 10	Sha Chau and Lung Kwu Chau Marine Park	0.1	0.00	0.02	0.01	0.00	0.00	0.01	0.00	0.03	0.00	0.0%	0.1%	0.2%	0.0%	0.0%	0.0%	-	0.1%	0.0%	0.0
WSR 12	Butterfly Beach (gazetted beach)	0.9	0.00	0.14	0.10	0.00	0.04	0.10	0.00	0.24	0.04	0.1%	1.0%	2.0%	0.3%	0.1%	0.4%	-	0.6%	0.2%	0.0
WSR 15	Gazetted Beaches at Tuen Mun	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 18	Gazetted Beaches along Castle Peak Road	0.4	0.00	0.06	0.04	0.00	0.02	0.04	0.00	0.11	0.02	0.1%	0.4%	0.9%	0.1%	0.1%	0.2%	-	0.3%	0.1%	0.0
WSR 19	Gazetted Beaches at Ma Wan	0.1	0.00	0.02	0.01	0.00	0.00	0.01	0.00	0.03	0.00	0.0%	0.1%	0.2%	0.0%	0.0%	0.0%	-	0.1%	0.0%	0.0
WSR 20	Ma Wan Fish Culture Zone	0.8	0.00	0.13	0.09	0.00	0.03	0.09	0.00	0.22	0.03	0.1%	0.9%	1.8%	0.3%	0.1%	0.4%	-	0.5%	0.1%	0.0
WSR 21	Ta Pang Po (near Sunny Bay Mangrove)	7.2	0.03	1.15	0.79	0.01	0.29	0.79	0.01	1.94	0.30	1.2%	7.7%	15.8%	2.4%	1.0%	3.2%	-	4.9%	1.2%	0.1
WSR 22b	Tai Ho Wan (inner), Near Tai Ho Stream SSSI	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 22c	Tai Ho Wan Outlet (outside) / Near coral site	0.5	0.00	0.08	0.06	0.00	0.02	0.06	0.00	0.14	0.02	0.1%	0.5%	1.1%	0.2%	0.1%	0.2%	-	0.3%	0.1%	0.0
WSR 27	San Tau Beach SSSI	0.9	0.00	0.14	0.10	0.00	0.04	0.10	0.00	0.24	0.04	0.1%	1.0%	2.0%	0.3%	0.1%	0.4%	-	0.6%	0.2%	0.0
WSR 29	Hau Hok Wan (Horseshoe Crab Habitat)	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 30	Sha Lo Wan (Horseshoe Crab Habitat)	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 31	Sham Wat Wan (Mangrove and Horseshoe Crab Habitat)	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 32	Tai O (Mangrove Habitat)	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 34	Yi O (Mangrove and Horseshoe Crab Habitat)	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 41	Artificial Reef at NE Airport	29.9	0.12	4.78	3.29	0.03	1.20	3.29	0.06	8.07	1.26	4.8%	31.9%	65.8%	10.0%	4.0%	13.2%	-	20.2%	5.0%	0.4
WSR 42	Artificial Reef at Sha Chau	0.1	0.00	0.02	0.01	0.00	0.00	0.01	0.00	0.03	0.00	0.0%	0.1%	0.2%	0.0%	0.0%	0.0%	-	0.1%	0.0%	0.0
WSR 45c	Sham Shui Kok (CWD habitat range)	9.0	0.04	1.44	0.99	0.01	0.36	0.99	0.02	2.43	0.38	1.4%	9.6%	19.8%	3.0%	1.2%	4.0%	-	6.1%	1.5%	0.1
WSR 46	Tai Mo To (near coral / CWD habitat range)	11.2	0.04	1.79	1.23	0.01	0.45	1.23	0.02	3.02	0.47	1.8%	11.9%	24.6%	3.7%	1.5%	4.9%	-	7.6%	1.9%	0.2
WSR 47b	River Trade Terminal (near coral site)	10.7	0.04	1.71	1.18	0.01	0.43	1.18	0.02	2.89	0.45	1.7%	11.4%	23.5%	3.6%	1.4%	4.7%	-	7.2%	1.8%	0.2
WSR 48	Airport Channel western end	0.0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.0%	0.0%	0.0%	0.0%	0.0%	0.0%	-	0.0%	0.0%	0.0
WSR 49	Tai Mo To (Deep Channel / CWD habitat range)	6.2	0.02	0.99	0.68	0.01	0.25	0.68	0.01	1.67	0.26	1.0%	6.6%	13.6%	2.1%	0.8%	2.7%	-	4.2%	1.0%	0.1

Notes:

* = assumed highest concentrations of pollutants (i.e., at UCEL) in the suspended solids (mg/kg dry wt.)

# = European Union Environmental Quality Standard (EQS) Values to Protect Marine Life (ug/L).

1. The above maximum SS elevations are the highest values among the three unmitigated scenario year and over both the wet and dry seasons. It is not the prediction of maximum SS elevation for a particular scenario case.

6.9.5.2 Among the selected points/sensitive receivers of concern, the predicted highest maximum depth-averaged SS elevation is noted at the Artificial Reef, north-east of the airport (WSR 41) and the predicted maximum depth-averaged SS concentration has been recorded as 39.9 mg/L (Table 6.25) in the 2011 dry season unmitigated scenario.　 Even with this level of SS elevation, the predicted maximum potential increase in the majority of the metallic contaminants will be below the European Union Environmental Quality Standard (EQS) for the protection of marine life.　 Among the metallic and metalloid contaminants, copper is estimated to closest (65.8%) to the EQS but is still well below the EQS of 5 ug/L under the unmitigated scenarios and with the (1+1) silt curtain system implemented, it will be even further below the EQS. 　It should also be noted that the degree of contamination assumed for the sediment (Category M with all contaminant concentrations equal to the UCEL) has resulted in a very conservative assessment (overestimate) of contaminant levels which may arise in the water column when the sediment is actually mostly Category L.

6.9.5.3 For sites with specific sensitive use such as beaches (for example, WSRs 12, 15 or 18) along the Tuen Mun and Castel Peak coastline, the estimated highest maximum depth-averaged SS increases under the unmitigated scenarios are in the range of 0.0 to 0.9 mg/L and only a non-significant increase in sediment borne contaminants are predicted.　 Among the ecological sensitive sites (WSRs 10, 22c, 27, 28, 29, 30, 41, 42, 45c, 46 and 49), the predicted highest depth-averaged SS elevation (29.9 mg/L in the 2011 unmitigated scenario) is at the artificial reef at the NE airport (WSR 41) close to the project area and even with this level of SS elevation, the potential maximal increase in sediment borne contaminants will only be 4.0 (Ni) – 65.8% (Cu) of the EQS.

6.9.5.4 It is clear from the above worst case assessment, based upon the assumptions that the suspended sediments from the projects would be moderately contaminated up to the threshold of the UCELs and could immediately release all contaminants into solution, that the predicted maximum increases in the sediment borne contaminants will be well within the criteria for the protection of marine life, except in the immediate vicinity of the works area. This assessment approach is highly conservative and would not underestimate the risk.　 As noted in the on-site sediment quality testing report (Appendix D1), sediment from the project sites are generally non-contaminated and below the LCELs.　 Furthermore, part of the potential suspended sediment would be sourced from fill materials which should not be contaminated at all.　 Therefore, it is concluded there will be minimal elevations of contaminants associated with the sediment plumes and they are predicted to be well within the environmental criteria for the protection of marine life.　

6.9.5.5 The elutriate / pore water results (summarised in Section 6.3.5 and detailed in Appendix D1), provide information on the potential for contaminants to be released during the dredging operations and the results have demonstrated that the metals and organic pollutants are, generally, not detected and, hence, unlikely to be a cause of concern. There were, however, some sediment bound nutrients that can be released, were detected in the elutriate/porewater samples and the potential implications are further assessed below. 　The highest nutrient levels associated with the site specific sediment samples are presented in Table 6.30a while summary statistics for the site specific marine water, sediment elutriate and sediment pore water testing results have been calculated and presented in Table 6.30b below.

Table 6. 30a　 Maximum Nutrient Concentrations Recorded in Site Specific Sediment (TM-CLKL)

Sample	TKN	NH4-N	NH3	NO3-N	NO2-N	TIN	PO4-P	TP
Maximum in Sediment	1100	58	-	2.4	4.7	-	-	680

Unit: mg/kg dry wt. Nutrient level in the sediment were not tested for sediment samples collected under HKBCF/HKLR.

Table 6.30b　 Summary Statistics of Site Specific Marine Water, Sediment Elutriate and Sediment Porewater Testing

Parmeter	TKN	NH4-N	NH3	NO3-N	NO2-N	TIN	PO4-P	TP
RL (mg/L)	0.5	0.025	-	0.025	0.025	-	0.1	0.1
WQO (mg/L)	-	-	0.021	-	-	0.5	-	-
TM-CLKL
Marine Water
Mean	0.6	0.08	0.004	0.50	0.08	0.65	<0.1	0.05
Max	1.0	0.2	0.010	0.82	0.14	1.13	<0.1	0.11
Min	<1.0	<0.025	0.001	<0.025	<0.025	0.16	<0.1	<0.1
n	14	14	14	14	14	14	14	14
%>RL	14.3%	85.7%	-	92.9%	85.7%	-	0%	7.1%
Elutriate
Mean	1.5	1.04	0.052	0.24	0.43	1.7	0.08	0.09
Max	6.5	6.1	0.305	1.80	5.40	0.75	0.67	0.62
Min	<1.0	<0.025	0.001	<0.025	<0.025	0.04	<0.1	<1.0
n	30	30	30	30	30	30	30	30
%>RL	30%	47%	-	73%	50%	-	13%	30%
Porewater
Mean	0.7	0.38	0.019	2.97	0.61	4.0	0.61	0.64
Max	1.9	1.60	0.080	18	3.40	21	2.30	2.40
Min	<1.0	<0.025	0.001	<0.025	0.03	0.12	<0.1	0.18
n	12	12	12	12	12	12	12	12
%>RL	22.2%	77.8%	-	100%	100%	100%	88.9%	100%
HKBCF/HKLR
Elutriate
Mean	4.4	3.9	0.19	0.36	0.16	4.4	0.07	0.11
Max	14.0	13.0	0.65	0.82	0.50	13.7	0.44	0.31
Min	<1.0	<0.025	0.001	0.15	0.044	0.3	<0.10	<0.10
n	50	50	50	50	50	50	50	50
%>RL	84%	96%	-	100%	100%	-	12%	52%
Porewater
Mean	1.6	1.30	0.07	0.06	0.04	1.4	0.10	0.21
Max	3.3	3.30	0.17	0.26	0.10	3.3	0.32	0.49
Min	<1.0	0.05	0.003	<0.025	<0.025	0.1	<0.10	0.12
n	10	10	10	9	10	10	10	10
%>RL	70%	100%	-	44%	60%	-	30%	100%

Notes:
‘-‘ = not applicable; Unionised ammonia (NH₃) assumed to be 5% of the ammoniacal nitrogen (NH₄-N); TIN = NH₄-N + NO₃-N + NO₂-N; RL = Reporting Limit. For samples below RL, the values are substituted with ½ RL before calculation of sample mean value.

6.9.5.6 Tables 6.30a and 6.30b indicated that the phosphorus nutrients are firmly sediment bound and are not readily released into the water column even under vigorous agitation during the elutriate process. The total inorganic nitrogen (TIN) nutrient represents the major nitrogen species, including the ammoniacal nitrogen (NH₄-N), nitrate (NO₃-N) and nitrite (NO₂-N), but it is more useful to focus on this parameter as this is the WQO parameter (WQO=0.5 mg/L) and assume that different forms of this nutrient are inter-convertible under the nitrogen-cycle. The results suggested that the TIN could be readily released into the water column during dredging and the concentrations at source (elutriate) could exceed the WQO. Among the nitrogen nutrient species, it is notable that the unionised ammonia, assumed to be 5% of the ammoniacal nitrogen (ERM, 2006), can also exceed the WQO (0.021 mg/L) at source (elutriate).

6.9.5.7 Since the release potential of nitrogen nutrients could be comparatively high, the maximum potential elevation in this nutrient species at sensitive receivers has been further evaluated using the maximum worse case approach similar to estimation of potential metal release.　 However, it is acknowledged that the sediment associated nutrient dispersion fate and characteristics, especially once they are dissociated from the sediment, could be different from the suspended solids. 　However, the dissociation kinetic process is not instant and as such the maximum worse case results would be unlikely to under-estimate the potential risk. The same approach has, also, been adopted in the recently approved EIA study for the CLP’s LNG receiving terminal and associated facilities which is in the same study area and this approach was considered as highly conservative (ERM, 2006). 　Under this approach, the highest nutrient concentrations recorded in the site specific sediment tests as shown in Table 6.30a and are assumed to be present in the suspended solids. 　In order to address the full potential of ammonia release, TKN (sum of organic nitrogen and ammonia) has been taken as the worse case surrogate instead of the measured ammoniacal nitrogen (NH₄-N) and a further conservative assumption of 5% NH₄-N has been adopted for the conversion to the unionised ammonia (NH₃). 　Tabulation of the potential nutrients release at the sensitivity receivers are presented in Appendix D11 (Tables 28-31, 34-37 and 40-43).

6.9.5.8 Nitrogen and phosphorus nutrients are generally non-toxic, however, high nutrient level in the ambient can lead to an increased risk of development of harmful algal blooms (i.e, red tides). High level of unionised ammonia can be toxic to juvenile stage of fish although toxicity test of local fish indicated a relatively high no observed effect concentration (NOEC) of 1.1 mg/L of unionised ammonia (CityU, 2001). Hence, among the observation points and sensitive receivers, the impacts of nutrients and ammonia elevations are more relevant to ecological sensitive receivers. As WSR 41 will be re-provided WSR 46 is the nearest ecological sensitive receiver of interest and the highest predicted SS elevation at this station is 11.2 mg/L (2012 unmitigated dry season). The estimated maximum potential nutrient release at this WSR is presented in Table 6.31 below.

Table 6.31　　 Estimated Maximum Nutrient Release Based on the Maximum Predicted-Depth-averaged SS Elevation at WSR 46

Parameter	Unit	TKN	NH4-N	NH3	NO3-N	NO2-N	TIN	TP
Maximum in Source Sediment	mg/kg dry wt	1100	58	-	2.4	4.7	-	680
Predicted Receiver Water	mg/L	0.01	0.001	0.001	0.000	0.000	0.01	0.01
Ambient Water Sample	mg/l	1.0	0.2	0.01	1.1	0.3	1.2	0.1
EPD 10 years depth-averaged	mg/L	0.30	0.12	0.01	0.29	0.06	0.46	0.05
WQO	mg/L	-	-	0.021	-	-	0.5	-

Notes:
‘-‘ =not applicable; TIN = NH₄-N + NO₃-N+NO₂-N; Unionised ammonia (NH₃) assumed to be 5% of the TKN.

1. The predicted receiver water concentrations is based on an assumed maximum concentration in the suspended sediment, the predicted highest SS elevation at WSR 46 is 11.2 mg/L (2012 dry season unmitigated case).

2. EPD 10 years depth-averaged is the grand average of the EPD dataset for NM1-NM8 from 1998 to 2007.

6.9.5.9 The worse case assessment indicates that the potential elevations in the nitrogen nutrient attributable to the project works is generally low and WQO exceedances are not expected for TIN nor unionised ammonia (NH₃). Similarly, elevations in phosphorus are, also, not predicted to be high even under this worse case situation.

6.9.5.10 It is noted in Table 6.30bthat the calculated highest TIN (21 mg/L) concentrations in pore water and NH₃ (0.65 mg/L) concentrations in the elutriate sample can exceed the WQO. However, as the dredging will be done by closed grab dredgers, the majority of the material will be retained within the bulk dredged spoil rather than released into environment and the above worse case estimation of release of the sediment bound contaminants has demonstrated that very low elevations is expected at the ecological sensitive receivers. Nonetheless, further assessment on the possible zone of influence has been, therefore, calculated below. If these pollutants are absent from the ambient waters, the needed dilution factor to meet the WQO for TIN and NH₃ would be 43 and 31 times, respectively. 　

6.9.5.11 The quantitative evaluation was based on a near field model which has been adopted in other local EIA reports to study of near field behaviour of sediment disturbed during the dredging operations. The　 main point of the quantitative prediction:

(a) Formula:　 C(x) = 1000×q/(D×X×w×Öp)

Where : 　 C(x) = concentration at distance X from the source (mg/L)

　　　　　　　　 q = sediment loss rate (kg/s)

　　　　　　　　 D = water depth (taken as 2m for the general area)

　　　　　　　　 X = distance from source (m)

　　　　　　　　 w = diffusion velocity. The value for diffusion velocity is taken to be 0.01 m/s, which is the same as that which was used in the previous study for the near field assessment of sediment plumes from the installation of CLP’s 132kV cable A between Tuen Mun and Chek Lap Kok airport and from the reclamations associated with the developments at Penny’s Bay.

(b) Sediment loss rate: the loss rate for a grab dredgers is 20 kg/m³ and for a daily 16 hour working with a target dredging rate of 6,000 m³/day, the instantaneously loss rate is 2.08 kg/s (unmitigated).

6.9.5.12 Based on the above equation and values, assuming a grab dredger with working radius of 10m (D=10m), the sediment concentrations at source could reach 5,868mg/L [=(1000*2.08) / (2*10*0.01*Öp)] and at WSR 46 which is about 560m (D=560m) from the site, the sediment concentrations is about 105mg/L [=(1000*2.08) / (2*560*0.01*Öp)]. These values are much higher than the sediment plumes predicted using the full water quality model suggesting that the simplified model overestimated the sediment concentrations. However, this provides a conservative estimate of the dilution factor of 55 (=5,868 / 105) at the sensitive receiver which is higher than the need minimum dilution factor of 43. Thus, the dilution calculation also suggested that there will be no excessive elevation of nutrients and ammonia at the sensitive receivers. 　Overall, both the estimation based on conservative instant release from the suspended solids (Table 31) and conservative dilution calculation indicated even if in the unlikely case that the sediment contains a high fraction of porewater or leachable nutrients and ammonia and all at the maximum concentrations as sampled, no excessive elevation of nutrient and ammonia at the sensitive receivers are predicted.

6.9.6 Dissolved Oxygen Depletion

6.9.6.1 Similar to the estimation of sediment borne contaminants, the maximum potential instant DO depletion has been estimated using the estimated maximum potential increase in suspended solids. The estimates for each modelling scenario are presented in Appendix D11 (Tables 10-13, 16-19 and 22-25) and a summary of the highest depletion for selected points/sensitive receivers over the three unmitigated scenarios (2011, 2012 and 2013) are, also, presented in Table 6.25 above.

6.9.6.2 Among the selected points/sensitive receivers, the predicted highest maximum depth-average SS elevation is in the East Tung Chung Bay immediately south of the HKBCF reclamation site (WSR 26) and the predicted maximum depth-averaged SS concentration is 80.2 mg/L (Table 6.25) in the 2013 unmitigated scenario.　 With this level of SS elevation, the predicted maximal potential DO depletion is 1.2 mg/L.　 As noted in Table 6.6, the DO of the North-western waters is generally high and on average ranges between 5.7 - 6.8 mg/L.　 Thus, 1.2 mg/L of short-term depletion will not be detrimental to the ecological systems of the area. Notwithstanding, the potential depletion at this site will be much reduced with the (1+1) silt curtain protection system implemented and there are no specific ecological receivers in this location.

6.9.6.3 For sites with specific sensitive use such as beaches (WSRs 12, 15 or 18) along the Tuen Mun coastline, the estimated maximum depth-averaged SS increases are in the range of 0.0 to 0.9 mg/L and no potential DO depletion (0.0 mg/L) are predicted. 　Among the ecological sensitive sites (WSRs 10, 22c, 27, 30, 41, 42, 45c and 49), the predicted highest depth-averaged SS elevation (29.9 mg/L in 2011 unmitigated scenario) is at the artificial reef at the NE airport (WSR 41) and with this level of SS elevation, the potential maximal DO depletion is only 0.4 mg/L which is well within the natural background fluctuation of the area.　　

6.9.6.4 Based upon the above worst case estimations, the predicted maximum DO depletion will be well within the natural background fluctuation, except at some areas in the immediate vicinity of the works area. This assessment approach is highly conservative and would not underestimate the risk as the hypothetical maximum increased in SS under the unmitigated scenarios is assumed, which if it occurs at all, is only predicted for a small percentage of the time. 　Furthermore, the suspended sediment sources from fill materials which should not be contaminated at all and are not expected to exert high DO demand as would be the dredged spoils. Therefore, it is concluded there will be minimal DO depletion associated with the sediment plumes and they are predicted to be well within the environmental range supportive of marine life.

6.9.7 Water Quality Impacts on Chinese White Dolphins

6.9.7.1 The Chinese White Dolphin (CWD) is a species of major concerns with the study area and, as discussed in the Marine Ecology (Section 8), needs special attention. There has been some consideration on the need to establish a mixing zone to protect the Chinese White Dolphin (CWD) habitats around the project site, especially for the newly identified CWD hot-spot at the area between the Brothers and Sham Shui Kok. 　Annex 6 of the EIAO-TM provided objective criteria for establishing a reasonable mixing zone within which the initial dilution of a pollution input takes places and where water quality criteria can be exceeded. The EIAO-TM has not defined a fixed acceptable mixing zone, instead performance base criteria have been suggested.

Criteria for Establishing a Mixing Zone

6.9.7.2 In general, the criteria for acceptance of a mixing zone are that:

(a) 　 it must not impair the integrity of the water body as a whole;

(b) 　 it must not interfere with the migratory pathways of important species to a degree which is damaging to the ecosystem;

(c) 　 it must not endanger sensitive uses e.g. beaches, breeding grounds, or diminish beneficial uses;

(d) it must not result in the accumulation of substances to such levels as to produce significant toxic effects in human or aquatic organisms;

(e) 　 within a mixing zone the following basic water quality criteria shall be met

- 　 materials not in such concentrations that settle to form objectionable deposits;

- 　 floating debris, oil, scum, and other matter not in such concentrations that form nuisances; and

- 　 substances not in such concentrations that produce objectionable colour, odour, taste, or turbidity.

Pollutants of Potential Concern

6.9.7.3 Prior to defining a mixing zone, the pollutants of potential concern and their characteristics should be established. As demonstrated by the on-site sediment quality testing (Appendix D1), the sediment of the project sites are generally free from the more toxic and persistent organic pollutants such PAHs, PCBs, TBT or chlorinated pesticides which are of most concern to the CWD. 　While some of the sediments within the site were classified as category M, these were mainly due to the presence of low level of arsenic (max of 23 mg/kg dry wt. and below UCEL) which, however, is known to be naturally occurring in the North-western waters of Hong Kong. 　Nonetheless, the potential release of sediment bound pollutants and potential depletion of dissolved oxygen associated with this overall non-contaminated sediment have been assessed assuming a higher level of contamination (just below UCEL). 　Even based upon such a hypothetical worst-case release as discussed above, the risk of sediment borne contaminants is predicted to be very low and within the relevant criteria for the protection of marine life at fixed ecology and fisheries sensitive receivers or local hot-spots for the more mobile CWD. 　Therefore, the prime pollutant would the impact of suspended solids (SS).

Potential Ecotoxicological Effects of SS to CWD

6.9.7.4 There are no data on the toxicity threshold of SS to CWD, as often it is the associated contaminants, such as heavy metals and organochlorines (OCs) that may be stirred up, desorbed from the sediment substrate and redistributed into the water column during dredging operations, that are of concern.　 The resuspension of these environmental contaminants may increase the bioaccumulation in Chinese White Dolphins through the intake of prey items in the vicinity of a dredging site.　 The main class of pollutants of concern are the organochlorines (also referred to as persistent organic pollutants (POPs)), although some heavy metals and organotins may also be an issue (Jefferson et al. (2006)). However, the testing results have shown that these contaminants are generally not present in the project sites.

6.9.7.5 In the influential monograph on the population biology of Chinese White Dolphin (CWD) in Hong Kong waters, Jefferson (2000) confirmed that the some 1000 individuals of CWD in Hong Kong waters belong to the wider Pearl River Estuary population. The latest highest CWD estimate for any season in Hong Kong was 193 in autumn and including dolphins in Mainland waters, the total population size was considered to be about 1300-1500 animals (Jefferson 2007). The discharges from the Pearl River are the major factor contributing to the SS loading of the CWD’s home range in PRD.

6.9.7.6 Parry (2000) undertook a detailed review of the suspended sediments in Hong Kong waters and some of the essential information about the SS of the PRE are extracted as below:

The Pearl River estuary is dominated by sedimentary accretion with the delta advancing seaward at between 50-150 m/year (Ravensrodd 1991).　 A range of annual water discharges and sediment loads for all the tributaries are quoted in the literature but are generally in the order of 320x10⁹m³ of water and 71x10⁶ tons of sediment.　 Ninety percent of runoff occurs in the wet season between May and September and it is estimated that approximately 20% of the sediment load is deposited at the river mouth, the remainder being transported out to sea (Ren, 1987).　 The four channels of the main Pearl River estuary discharge a total of approximately 170M m³ of water and some 36x10⁶ tons of sediment per year (Chen & Che, 1992).

Kot and Hu (1995) stated that the mean annual sediment content of the estuary is 100 to 300 mg/l, with a wet season depth average of 300-500 mg/l and a dry season depth average of 20-100 mg/l.　 Kirby (1992), however, reported much larger depth averaged suspended solid concentrations, with concentrations of over 1400 mg/l.　 Gu and Zu (in Kirby, 1992) reported that satellite photographs, calibrated with suspended sediment samples, showed a pronounced lateral asymmetry in suspended sediments within the estuary.　 A sharp division occurred between the eastern and western zones, which for much of its length is coincident with the western margin of the Lingding channel.　 This strong asymmetrical distribution of suspended sediment concentrations is a result of the major river inputs being located on the west side of the estuary, combined with residual tidal flows from east to west, giving rise to an anticlockwise circulation within the estuary, possibly enhanced by the Coriolis effect. These effects are also likely to result in an asymmetrical turbidity maximum within the estuary.

Turbidity maximums are a feature of all macrotidal estuaries, with the tidal flow maintaining higher concentrations of suspended sediment in the upper estuary than in the river or sea.

Turbidity maximums are formed by river sediment moving down the estuary in the freshwater discharge which rises over the denser saline layer.　 The lack of mixing due to the suspension of turbulence allows the sediment to be carried in the freshwater surface layer. In freshwater the settling is negligible.　　 However, once the salinity exceeds 1-2 ppm, flocculation can occur and settling commences from the surface seaward moving layer to the landward moving saline layer.　 As a general observation low tidal ranges tend to result in turbidity maximums with suspended solid concentrations of 100- 200 mg/l, whereas large tidal ranges result in concentrations of 1,000-10,000 mg/l (Dyer, 1986).

6.9.7.7 With the high natural fluctuation and asymmetry of the SS in the PRE, it must be assumed that these levels (that is, up to 10,000 mg/L) are the physiological tolerable range of CWD as the PRE is their prime habitat. 　For the purpose of 　impact assessment, the acceptable level shall be established and this shall be at least based on some speculated toxic effects. 　It is, however, difficult to establish a toxicological relationship between the suspended solids per se and CWD as marine mammals, who unlike other marine fauna are not filter feeders and do not depend on filamentous gill structure for gas exchange. Suspended solids per se can be a concern to fishes or other marine life that use gill structures for gaseous exchanges as high level of suspended solids can physically clog the gills, and if prolonged, can cause suffocation. 　Marine mammals, however, are air breathers and have lung structures for gas exchange. For this reason, secondary effects of depletion of water column dissolved oxygen associated with SS are, also, not a concern to CWD. For marine filter feeders (e.g., corals and some benthos), suspended solids can be a concern as the sudden high flow of SS can either overwhelm the filtering mechanism or completely block them leading to starvation. This again is not relevant to most marine mammals and CWD as they physical ingest food materials.　

Protective SS Criterion to CWD Preys

6.9.7.8 Given the high SS levels the CWD experiences in its natural habitat ranges (that is, up to 10,000 mg/L) and the relative low predicted SS elevations (generally less than 50 mg/L 500m outside the sites after mitigation) due to the project works, it can reasonably be concluded that project related SS would unlikely induce significant adverse impacts on the CWD.

6.9.7.9 As a protective and precautionary measure, however, further hypothetical worse case impact suppositions are discussed below. 　The study of the stomach contents of stranded CWD indicated that fish families accounted for over 93% of all prey consumed by CWD (Barros et al 2004) and it may, thus, be postulated that if significant adverse impacts to fishes (major preys of CWD) are not predicted, than there should be no reason to anticipate significant adverse impacts to CWD. 　AFCD has sponsored a study of local species toxicology/tolerance to some common pollutants of concern, including suspended solids and the study reported that SS levels as high as 5,000 mg/L did not elicit notable impacts to fishes (CityU, 2001).　 A protective criterion of 50 mg/L for protection of fish was subsequently proposed and this has been largely adopted as the specific criteria for the protection of marine aquaculture facilities in local EIAs studies, including this Investigation. Taking this aboard, a 50 mg/L elevation would be highly conservative to CWD.

6.9.7.10 The predicted maximum extent of sediment plumes and the potential maximum elevations are shown together with the 2002-2008 long-term CWD density grid DPSE (which indicates relatively density of dolphins within a grid) in Figures 6.14 to 6.25 for each of the modelling scenario times with and without (1+1) silt curtain mitigation under Sequence A and Figures 6.26 to 6.27 under Sequence B with (1+1) silt curtain mitigation. 　It should be cautioned that the maximum plumes envelope only indicates the potentially highest level at a place without any indication of the time or frequency that such a maximum elevation would occur. 　The frequency of the SS levels exceeding the WQO criteria (generally below 10 mg/L), and the even more conservative criteria for CWD, at representative CWD hot-spots including the Sha Chau and Lung Kwu Chau Marine Park (WSR 10), Sham Shui Kok (WSR 45c), the Tai Mo To (WSRs 46 and 49) are tabulated in Tables 6.21 to 6.28 and shall be referenced for the more exact value of predicted maximum SS elevations and frequency of WQO exceedances. 　It is clear from these tables that the predicted maximum SS elevation at these points are well below the 50 mg/L criteria even without mitigation.

6.9.7.11 With reference to Figures 6.14 to 6.27 and the CWD DPSE density grid and sediment plumes, it is clear that the prime CWD habitats are to the west of Lantau and, also, at the Sha Chau and Lung Kwu Chau Marine Park (left panel of the figures) but no project related sediment plumes are predicted in these prime CWD habitats despite the fact that there could be small sediment losses from bored piling along the HKLR alignment at west of Lantau. 　The project related sediment plumes are mainly confined to the more sheltered East Tung Chung Bay and often the majority of the plumes are confined to within the project site (right panel of the figures).　 While plumes can extend outside the project site, the maximum levels are generally constrained to less than 50 mg/L within 500m of the works site, also taking into account that high levels of elevations are not frequently predicted. Without mitigation, plumes dispersing into the Brothers/Sham Shui Kok area are generally below 10 mg/L, although a higher level of around <30 mg/L could be present in the bottom level.　

6.9.7.12 Figures 6.14 to 6.27 also demonstrate that, with the implementation of the extensive (1+1) silt curtain system which effectively encloses the entire project sites, the SS elevation band at around 500m of the site are largely reduced to <30 mg/L. 　This is well within the CWD tolerable range and establishing a SS mixing zone for CWD is not considered as being warranted. 　Notwithstanding the above, there will be a 250m CWD exclusion zone to protect the CWD from underwater noise disturbance during all dredging and reclamation works and this exclusion zone would, also, offer protection against water quality deterioration in the immediate vicinity of the works site, as has been predicted.

6.9.8 Construction Phase Runoff

6.9.8.1 Potential impacts to waters quality can occur during the construction phase as a result of construction site runoff containing elevated suspended solids and possibly oils due to erosion of exposed surfaces, stockpiles and material storage areas, fuel and oil storage and maintenance areas and dust suppression sprays.　 As all the streams and surface water courses downstream of the proposed works in both Tuen Mun and Lantau are already disturbed and channelised and as such, significant impacts to natural water courses will not occur as a result of the construction of the project.　 Therefore, construction runoff entering the marine environment via these culverts will be the main source of potential impacts.

6.9.8.2 Thus, a key issue will be the control of runoff from road and slopes works into the marine waters off Tai Ho Wan and Pillar Point.　 However, the extent of the excavation works are not substantial and the works in both north Lantau and Tuen Mun will be undertaken on land that is already disturbed and, as such, the works are not expected to significantly increase the area of impermeable surfaces which would cause an increased volume of runoff for any given rainfall event.　 In addition, the runoff from the works site will form only a small percentage of the total catchwater flows of these areas meaning that the level of dilution would be high.　 In addition, the runoff would be discharged below the catchwater, thus, making the contribution even lower.

6.9.8.3 Thus, even at elevated levels, by the time any sediment in suspension reaches the receiving waters, it can be expected to be extensively diluted.　 Notwithstanding this dilution, assuming the runoff is assimilated into the receiving waters off Tai Ho Wan within say 100m from the discharge location, the equivalent tidal volume (that is, the increase in volume between low tide and high tide) of the area inshore of this 100m line is estimated to be in the range 80,000 to 200,000m³ depending upon the tide type.　 The total runoff from construction works would be expected to be a fraction of this amount and, therefore, large levels of dilution would be expected.　 Any suspended solids would, also, be predicted to be dispersed and settle out rapidly.

6.9.8.4 Bearing in mind the dilution rates which would be achieved, the road runoff should not result in a significant increase in concentrations of contaminants.　 The total contaminant load in the road runoff will represent a small increase in the natural contaminant load and should not result in a significant detrimental impact on marine water quality especially when the small rainfall volumes with respect to the tidal volume are taken into account.　 Based upon these factors, significant effects on the water quality are not predicted.　

6.9.8.5 The implementation of good construction site practices would be recommended, however, to reduce the suspended solid concentrations to a minimum.　 These land based mitigation measures are detailed in Section 6.10 below.

6.10 Mitigation Measures

6.10.1 Construction Phase

Marine Works (Sequence A)

6.10.1.1 Mitigation during the marine works to reduce impacts to within acceptable levels have been recommended and will comprise a series of measures that restrict the method and sequencing of dredging/backfilling, as well as protection measures.　 Details of the measures are provided below and summarised in the Environmental Mitigation Implementation Schedule in Appendix A1:

· formation of temporary seawall enclosing Portion A of HKBCF (notwithstanding a 100m of marine access) to be completed prior to the main phase of reclamation dredging and filling activities;

· construction of seawalls to be advanced by at least 200m before the main reclamation dredging and filling can commence. It should be noted that the protection by advanced seawall is a dynamic process depending on the progress of the construction activities and the stage when such protection could be realised is illustrated in Figure 6.2a and detailed in Appendix D6a. 　The part of the works where such measures can be undertaken for the majority of the time includes the following locations:

- TM-CLKL northern reclamation;

- TM-CLKL southern reclamation (after formation of the nips);

- Reclamation dredging and filling for Portion B of HKBCF;

- Reclamation filling for Portion C of HKBCF;

- Reclamation filling for Portion D of HKBCF; Reclamation filling for FSD berth of HKBCF; and

- Reclamation dredging and filling for Portion 1 of HKLR;

· use of TMB for the construction of the submarine tunnel, thus, avoiding extensive dredging and backfilling of tunnel trench;

· export for dredged spoils from NWWCZ avoiding exerting high demand on the disposal facilities in the NWWCZ and, hence, minimise potential cumulative impacts;

· for the marine viaducts of TM-CLKL and HKLR, the bored piling will be undertaken within a metal casing;

· a maximum of 30% public fill to be used for all seawall and reclamation filling below +2.5mPD for the HKBCF and HKLR projects;

· a maximum of 50% public fill to be used for seawall filling below +2.5mPD for TM-CLKL northern and southern landfalls;

· a maximum of 30% public fill to be used for reclamation filling below +2.5mPD for TM-CLKL southern landfall;

· a maximum of 100% public fill to be used for reclamation filling below +2.5mPD for TM-CLKL northern landfall;

· where public fill is proposed for filling below +2.5mPD, the fine content in the public fill will be controlled to 25%;

· where sand fill is proposed for filling below +2.5mPD, the fine content in the sand fill will be controlled to 5%;

· silt curtains (cage type) will be applied round all grab dredgers during the HKBCF, HKLR and TM-CLKL southern reclamation works;

· single layer silt curtains will be applied around all works as defined in Appendix D6a;

· single layer silt curtain to be applied around the North-east airport water intake (WSR 25);

· when constructing Portion D of the HKBCF, one side of the seawall crossing the channel should be constructed first and prior to the other works. 　This would reduce the maximum flow speed across the channel and enhance the effectiveness of other mitigation measures such as silt curtain system;

· a sheet piled wall shall be constructed north of the HKBCF island (Appendix D6a), in order to allow the use of silt curtains during Phase 2 works; and

· silt curtain shall have the proofed effectiveness from the producer and shall be fully maintained throughout the works by the contractor.

6.10.1.2 To ensure the water quality impacts are controlled, apart from the above mentioned measures, it would be essential for the works to be implemented following the construction sequence, production rates and other assumptions as outlined in Appendix D5a.　 These measures shall include the following:

· The daily maximum production rates shall not exceed those assumed in the water quality assessment. A summary of these daily maximum production rates is tabulated in Table 6.15a; and

· The dredging and filling works shall be scheduled to spread the works evenly over a working day.

6.10.1.3 In addition, dredging operations should be undertaken in such a manner as to minimise resuspension of sediments. Standard good dredging practice measures should, therefore, be implemented including the following requirements which should be written into the dredging contract.　

· trailer suction hopper dredgers shall not allow mud to overflow;

· use of Lean Material Overboard (LMOB) systems shall be prohibited;

· mechanical grabs shall be designed and maintained to avoid spillage and should seal tightly while being lifted;

· barges and hopper dredgers shall have tight fitting seals to their bottom openings to prevent leakage of material;

· any pipe leakages shall be repaired quickly.　 Plant should not be operated with leaking pipes;

· loading of barges and hoppers shall be controlled to prevent splashing of dredged material to the surrounding water.　 Barges or hoppers shall not be filled to a level which will cause overflow of materials or pollution of water during loading or transportation;

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

· adequate freeboard shall be maintained on barges to reduce the likelihood of decks being washed by wave action;

· all vessels shall 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; and

· the works shall not cause foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the works site.

Marine Works (Sequence B)

6.10.1.4 In general, the recommended mitigated measures for Sequence A are also applicable to Sequence B and will comprise a series of measures that restrict the method and sequencing of dredging/backfilling, as well as protection measures.　 Details of the measures are provided below and summarised in the Environmental Mitigation Implementation Schedule in Appendix A1:

· formation of seawall enclosing the main reclamation site of TM-CLKL (southern landfall) and HKBCF (except for 100m gaps for marine access) to be completed prior to reclamation dredging and filling activities;

· installation of sheet pile wall next to the northern boundary of the HKBCF+TM-CLKL (southern landfall) to ensure floating type silt curtains can be applied effectively (See Figure 3 of Appendix D5b). The sheet piled wall is a recommended mitigation measure under Sequence A and further developed as an integrated protection measure under Sequence B:

- before the completion of the sheet pile wall next to the northern boundary of the HKBCF+TM-CLKL (southern landfall), seawall dredging at the area north of the demarcation line of the Phase 1 and 2 of HKBCF will not be carried out;

- before the seawall within the area of Phase 2 of HKBCF is formed above +2.5mPD, except for 100m gaps for marine access, the sheet pile wall at the northern boundary of the HKBCF+TM-CLKL (southern landfall) will not be removed; and

- before the whole perimeter of seawall for HKBCF+TM-CLKL (southern landfall) is formed above +2.5mPD, except for 100m gaps for marine access and portion D of HKBCF, no dredging and reclamation filling will be carried out within the seawall boundary. Dredging for the formation of the pits for the subsequent Mf sediment backfilling within the HKBCF boundary is an exception;

· for other parts of the reclamation works construction of seawalls to be advanced by at least 200m before the main reclamation dredging and filling can commence. It should be noted that the protection by advanced seawall is a dynamic process depending on the progress of the construction activities and the stage when such protection could be realised is illustrated in Figure 6.2b and detailed in Appendix D6b.　 The part of the works where such measures can be undertaken for the majority of the time includes the following locations:

- TM-CLKL northern reclamation;

- Reclamation filling for Portion D of HKBCF; Reclamation filling for FSD berth of HKBCF; and

- Reclamation dredging and filling for Portion 1 of HKLR;

· use of TMB for the construction of the submarine tunnel, thus, avoiding extensive dredging and backfilling of tunnel trench;

· export for dredged spoils from NWWCZ avoiding exerting high demand on the disposal facilities in the NWWCZ and, hence, minimise potential cumulative impacts;

· for the marine viaducts of TM-CLKL and HKLR, the bored piling will be undertaken within a metal casing;

· for HKBCF seawall filling, no soft public fill will be used for filling below +2.5mPD;

· for TM-CLKL southern landfall seawall filling, no soft public fill will be used for filling below +2.5mPD and the fill material below that level will consist of 50% sand and 50% rock;

· The filling material for the other parts of the works are the same as Sequence A;

· silt curtains (cage type) will be applied round all grab dredgers during the HKBCF, HKLR and TM-CLKL southern reclamation works. Cage type silt curtain (with steel enclosure) shall be used for grab dredgers working in the sites of HKBCF and TM-CLKL southern reclamation;

· single layer silt curtains will be applied around all works as defined in Appendix D6b;

· single layer silt curtain to be applied around the North-east airport water intake (WSR 25); and

· silt curtain shall have the proven effectiveness from the producer and shall be fully maintained throughout the works by the contractor.

6.10.1.5 For Sequence B, a key measure to control the release of the resuspended solids outside the works areas is the completion of the peripheral seawalls for HKBCF/TM-CLKL southern landfall before the main reclamation works, except the handling of Mf material which will be controlled within dedicated sheet piled walls and silt curtains. During the construction of seawalls, there would be limited protection against sediment losses except the silt curtain systems and sheet piled walls described above. Thus, it would be essential for the works to be implemented following the construction sequence, production rates and other assumptions as outlined in Appendix D5b. The other major sequences that should be followed are summarised below:

· HKBCF+TM-CLKL southern landfall:

- The construction sequence of the seawall shall commence at the southern part of Portion 1 seawall in HKBCF, and then TM-CLKL southern landfall seawall, northern part of Portion 1 seawall, Portion 2 and finally Portion 3 seawall in HKBCF;

- The seawall dredging and filling works for TM-CLKL southern landfall shall start from the south-most Portion N-c towards Portion N-a unless the northern sheet piled wall has been completed; and

- The main dredging and filling works at the reclamation areas of 　HKBCF+TM-CLKL southern landfall within the seawall boundary shall only be carried out when the whole Portion 1 seawall (except for 100m gaps for marine access) is completed above +2.5mPD.

· TM-CLKL northern landfall:

- Reclamation filling shall not proceed until at least 200m section of leading seawall at both the east and west sides of the reclamation are formed above +2.5 mPD, except for 100m gaps for marine access;

· HKLR coastal reclamation:

- Reclamation filling shall not proceed until at least 200m section of leading seawall are formed above +2.5 mPD, except for 100m gaps for marine access;

· The daily maximum production rates shall not exceed those assumed in the water quality assessment. A summary of these daily maximum production rates is tabulated in Table 6.15b; and

· The dredging and filling works shall be scheduled to spread the works evenly over a working day.

6.10.1.6 In addition, dredging operations should be undertaken in such a manner as to minimise resuspension of sediments. Standard good dredging practice measures should, therefore, be implemented including the following requirements which should be written into the dredging contract.　

· mechanical grabs shall be designed and maintained to avoid spillage and should seal tightly while being lifted;

· barges shall have tight fitting seals to their bottom openings to prevent leakage of material;

· any pipe leakages shall be repaired quickly.　 Plant should not be operated with leaking pipes;

· loading of barges and hoppers shall be controlled to prevent splashing of dredged material to the surrounding water.　 Barges or hoppers shall not be filled to a level which will cause overflow of materials or pollution of water during loading or transportation;

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

· adequate freeboard shall be maintained on barges to reduce the likelihood of decks being washed by wave action;

· all vessels shall 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; and

· the works shall not cause foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the works site.

Land Works

6.10.1.7 General construction activities on land should follows ProPECC PN 1/94 “Construction Site Drainage” and also be governed by standard good working practice.　 Specific measures to be written into the works contracts should include:

· wastewater from temporary site facilities should be controlled to prevent direct discharge to surface or marine waters;

· sewage effluent and discharges from on-site kitchen facilities shall be directed to Government sewer in accordance with the requirements of the WPCO or collected for disposal offsite.　 The use of soakaways shall be avoided;

· storm drainage shall be directed to storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sediment basins.　 Channels, earth bunds or sand bag barriers should be provided on site to properly direct stormwater to such silt removal facilities. Catchpits and perimeter channels should be constructed in advance of site formation works and earthworks;

· silt removal facilities, channels and manholes shall be maintained and any deposited silt and grit shall be removed regularly, including specifically at the onset of and after each rainstorm;

· temporary access roads should be surfaced with crushed stone or gravel;

· rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities;

· measures should be taken to prevent the washout of construction materials, soil, silt or debris into any drainage system;

· open stockpiles of construction materials (e.g. aggregates and sand) on site should be covered with tarpaulin or similar fabric during rainstorms;

· manholes (including any 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;

· discharges of surface run-off into foul sewers must always be prevented in order not to unduly overload the foul sewerage system;

· all vehicles and plant should be cleaned before they leave the construction site to ensure that no earth, mud or debris is deposited by them on roads. A wheel washing bay should be provided at every site exit;

· wheel wash overflow shall be directed to silt removal facilities before being discharged to the storm drain;

· the section of construction road between the wheel washing bay and the public road should be surfaced with crushed stone or coarse gravel;

· wastewater generated from concreting, plastering, internal decoration, cleaning work and other similar activities, shall be screened to remove large objects;

· vehicle and plant servicing areas, vehicle wash bays and lubrication facilities shall be located under roofed areas.　 The drainage in these covered areas shall be connected to foul sewers via a petrol interceptor in accordance with the requirements of the WPCO or collected for off site disposal;

· the contractors shall prepare an oil / chemical cleanup plan and ensure that leakages or spillages are contained and cleaned up immediately;

· waste oil should be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance;

· all fuel tanks and chemical storage areas should be provided with locks and be sited on sealed areas. The storage areas should be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank; and

· surface run-off from bunded areas should pass through oil/grease traps prior to discharge to the stormwater system.

6.10.2 Operational Phase

6.10.2.1 No significant impacts are predicted for the operational stage.　 Notwithstanding, as a precautionary measures roadside gullies to trap silt and grit prior to discharging the stormwater into the marine environment.　 The sumps will be maintained and cleaned at regular intervals.

6.11 Residual Impacts

6.11.1.1 The recommended mitigation measures are predicted to be sufficient to control water quality impacts to acceptable levels during both the construction and operational phases.　 Thus, no significant adverse residual water quality impacts are expected.

6.11.1.2 The model predictions for the operational phase of the project indicated that while small changes in the water quality can be expected intuitively due the large reclamation, the water quality conditions in North-western waters would not be adversely affected by the projects and the predicted changes, especially for physicochemical parameters like DO, salinity and temperature, are small and within the ranges of natural variations experienced in the study area. 　Changes in erosion and sedimentation patterns were, also, low and were not predicted to significantly increase the sedimentation at major navigation channels leading to more frequent maintenance dredging nor affect the long-term stability of the intertidal soft-shores at the major ecological sites like San Tau Beach SSSI and Tai Ho Stream SSSI. 　Residual impacts during the operational phase would be low and considered acceptable.

6.11.1.3 During the construction phases, as detailed in Section 6.9, with the application the of the integrated protection measures and also the (1+1) silt curtain system, the major zone of influence is mainly limited to areas within 500m from the reclamation sites. There is, however, generally no specific sensitive use of the waters within this radius.　 With the integrated protection measures and, also, the (1+1) silt curtain system in place during the construction stage, however, marginal SS exceedances of WQO at the airport water intake (WSR 25) are still predicted for about 2% of 2011.　 The level of potential maximum SS elevations are low at 4.7 – 6.7 mg/L and it has been recommended that additional silt curtain be deployed around this water intake to ensure full compliance with SS WQO.　 Although the effectiveness of silt curtain at a sensitive receiver cannot be modelled, the approximately equivalent (2+1) silt curtain system mitigation has been modelled and results presented in Appendix 12. Based on the results of the (2+1) silt curtain mitigation, no SS WQO exceedances at WSR 25 are predicted and residual impacts would be acceptable.

6.11.1.4 The artificial reef (AR) site at the north-east of the airport (WSR 41) is another sensitive receiver where low frequencies of SS WQO exceedances are predicted in 2011 even with the (1+1) silt curtain system mitigation in place.　 However, the effects on this AR will be compensated for by re-provision of another AR at a suitable location.　 The third sensitive receiver where SS WQO exceedances are predicted is that the recently identified coral site near the River Trade Terminal (WSR 47b) in which low frequency of SS WQO exceedance is predicted in 2013.　 However, as the corals in this area will also be directly affected by the reclamation works, it has been recommended that where practicable, the corals at this site be translocated prior to the works.　 Therefore, while low level of residual impacts are predicted at these three specific sensitive sites close to the project sites, alternative mitigation and protection measures are recommended, the residual impacts are considered as insignificant and acceptable.

6.12 Cumulative Impacts

6.12.1.1 Cumulative impacts associated with the construction of the TM-CLKL+HKBCF+HKLR together with other construction activities from other concurrent projects (Table 6.13) have been modelled and the methodology are summarised in Section 6.7.4 and detailed in Appendix D5.　 The results for the 3 scenario years are presented in Appendices D8c, D9c and D10c, respectively.

6.12.1.2 The results show that the sediment plumes from the TM-CLKL+HKBCF+HKLR are generally confined to within the sheltered East Tung Chung Bay and do not merge with sediment plumes from the other concurrent projects. 　The plumes could, however, under certain tidal conditions, slightly mix with the plumes from the (unmitigated) LLP. 　The predicted cumulative maximum SS elevation, however, is still low although it will infrequently exceed the WQO. 　It is expected that the LLP will have extensive mitigation measures in place to avoid cumulative impacts with other projects and, thus, it is not expected that the plume would merge during actual construction.

6.12.1.3 Of more concern may be the dredging / disposal operations of CMPs at East Sha Chau and the South Brothers and the Type I disposal operation at North Brothers MBA. 　The combined plumes of the worst case CMPs and MBA operations would cause high level and frequent WQO exceedances, although the contributions from the TM-CLKL+HKBCF+HKLR project are low as demonstrated in the project alone modelling scenarios. 　If it is considered that the TM-CLKL+HKBCF+HKLR would be the major driver to the operation of these Type I and II disposal facilities, these facilities could be operating to their maximum rates concurrently with the TM-CLKL+HKBCF+HKLR. 　However, major measures will be implemented to reduce the demand for these facilities from the TM-CLKL+HKBCF+HKLR projects, including the use of TBM for the TM-CLKL’s main tunnel and, also, a high proportion of the dredged spoil from the HKBCF, HKLR and the southern reclamation of the TM-CLKL is proposed to be exported outside the NWWCZ, thereby potentially reducing the operational rate of the CMPs and MBA. 　With careful scheduling of the concurrent projects and strict implementation of their respective mitigation measures (for example the CMP IVc has an operations plan that dictates that disposal should only take place in an upstream area, thus avoiding plumes outside the confines of the pits), the worst case cumulative impacts as modelled would not occur and significant cumulative impacts should be able to avoided.

6.13 Model Sensitivity Test

6.13.1.1 Trailing suction hopper dredgers (TSHD) have been proposed for the artificial islands and immersed tube tunnel dredging works for the Mainland section of HZMB works with overflows for the major part of the working time, as stated in the Ocean Environmental Impact Assessment for the HZMB (HZMB OEIA) (COES 2008). 　The TSHD is a sea-going ship equipped with a suction ladder and at the end of the ladder is a draghead which can be lowered onto the seabed while the TSHD navigates at a reduced speed. 　During the forward movement of the TSHD, the draghead agitates a thin layer of the seabed and the loosened material, together with some water, is sucked into the suction pipe by means of a centrifugal pump, which is installed in the vessel’s hull. The material is then pumped into the vessel’s hopper until it is completely filled. 　During this loading phase, excess water may flow overboard together with some of the finer material, while the coarser fraction accumulates in the hopper.

6.13.1.2 One of the major environmental constraints of the TSHD is the suspended sediment generated by the overflow of excessive transport water with a high fines content. 　Although there have been many advancements in the overflowing system of TSHDs in recent years to reduce the environmental impacts, the dredging of mud in Hong Kong cannot benefit from them as overflow is generally prohibited completely during dredging of mud. 　As such, the characteristics of sediment release during the overflowing cycle is less uncertain, especially in the local context. A set of overflowing parameters (1.31 kg/s for 45,00m³ TSHD) have been proposed in the HZMB OEIA as detailed in Appendix D5a and adopted in this EIA (scaled up to 2.82 kg/s for the larger 10,000m³ TSHD). However, given the relatively high uncertainty of potential sediment release during the overflowing cycle, a sensitivity test of the effect of varying the overflow rate of the TSHD has been considered necessary.　 While overflows for mud dredging are not allowed, it is an essential requirement for the efficient and economic operation of the TSHD when working for sand dredging. 　There are also limited results of sand dredging with overflows and, as such, the overflow rate of 491 kg/s, as applied in a local modelling study for sand dredging (e.g., ERM 2001), has, therefore, been adopted for the sensitivity test.

6.13.1.3 The 2011 mitigated scenario with concurrent projects has been chosen as the test case for the sensitivity run as, at this time, the HZMB artificial islands dredging works are assumed to be closest to Hong Kong SAR boundary. Therefore, the model set-up has been essentially the same as for the 2011 mitigated (Option 1, Table 6.16b) scenario with concurrent projects, but with an assumed higher TSHD overflow at the HZMB two artificial island. 　This setting has, also, allowed for the direct comparison of the effects of an assumed high overflow on the water quality of western waters. The results of the sensitivity test are presented in Appendix D13 and briefly discussed below.

6.13.1.4 The two ZHMB artificial islands are located at the side of major north-south running Lingding Fairway, Rongshutou Fairway and Longgu Western Fiarway. The eastern HZMB artificial island is closer to Hong Kong SAR boundary (about 150m apart) and is about 3km north-west of Tai O. The main direction of flows in these area is north-south running (HZMB OEIA). The sediment plume form the dredging works of HZMB artificial islands are also mainly north-south running. A comparison of the surface SS plumes under typical tidal conditions are summarised in Table 6.32 below.

6.13.1.5 As indicated in Table 6.32, the size of sediment plumes from the TSHD dredging and grab dredging at the HZMB artificial island is generally small and even if the plumes do cross the HKSAR boundary, they are generally at low levels and close to Hong Kong’s WQO. 　However, under the hypothetical high overflow rates, very large plumes hitting both the west and south Lantau coast are predicted. However, even under such extreme conditions, the sediment plumes from the HZMB works generally do not merge with the sediment plumes from the bulk of TM-CLKL+HKBCF+HKLR, with the plumes from these latter sources being mainly confined to the more sheltered East Tung Chung Bay. Nonetheless, as the sensitivity test results indicate extensive sediment plumes could potentially arise from the Mainland section of the HZMB crossing the Hong Kong SAR boundary and affecting the sensitive receivers at west Lantau, it is recommended that concurrent projects near the HKSAR boundary and/or west Lantau consider conducting water quality monitoring along the boundary so as to detect and differentiate the source of sediment plumes found at their own site.

Table 6.32　　 Comparison of Surface Plumes During HZMB TSHD Assumed Overflows and Sensitivity Test Overflows

Tide	Assumed Overflow		Sensitivity Test Overflow
State	Dry Season	Wet Season	Dry Season	Wet Season
Peak ebb	Time = 14:00; low level of southward SS elevation down to <3 mg/L band along the boundary	Time = 14:00; no surface plumes predicted in HKSAR	large southward plumes of down to the <30 mg/L band along the west Lantau reaching about Fan Lau Kok, but not get into Tai O or Yi O.	large southward plumes of down to <30 mg/L band along the west Lantau reaching west of Yi O, but not get into Tai O or Yi O. Plumes reaching about west of Fan Lau Kok at around down to <8 mg/L band
Peak flood	Time = 8:00; TSHD dredging just begin and no residual surface plumes predicted.	Time = 8:00; TSHD dredging just begin and no residual surface plumes predicted.	residual surface plume of around <4 mg/L band persist at west of Tai O	TSHD dredging just being and no residual surface plumes predicted.
LL, Spring	Time = 18:00; TSHD dredging stopped　 2.5 hours ago and no residual surface plumes	Time = 16:00; TSHD dredging stopped　 0.5 hours ago and no residual surface plumes	large residual plumes of about down to <30 mg/L band between west of Yi O and south of Fan Lau Kok.	residual southward plumes of down to <30 mg/L band between the AI and west of Yi O. A break off patch of down to <16 mg/L band at west of Fun Lau.
HH, Spring	Time = 10:00; small low level north-east plumes of down to <4 mg/L band along the HKSAR boundary to the north (~2.5 km) of the AI.	Time = 10:00; small low level plumes of down to <4 mg/L around the north of the AI.	large north-east plumes of down to <100 mg/L band along the HKSAR boundary to the north (~ 2.5km) of the AI. The eastern extend of down to <10 mg/L band is about 2.5km from the AI	high north-east plumes of down to <100 mg/L band along the HKSAR boundary to the north (~2.5km) of the AI. The eastern extend of down to <10 mg/L band is about 3.5km west of the AI
LL, Neap	Time = 20:00; TSHD dredging stopped at 15:30 no residual surface plumes predicted	Time = 20:00 TSHD dredging stopped at 15:30 no residual surface plumes predicted	residual plume of down to <7 mg/L band between the mouth of Tai O to about the mid-way between Yi O and Fan Lau Kok.	no residual surface plumes predicted
HH, Neap	Time = 14:00; small low level plumes of down to <7 mg/L band around the north of the AI.	Time = 14:00; small low level plumes of down to <7 mg/L band around the north of the AI.	north-east plumes of down to <100 mg/L band along the HKSAR boundary to the north (~ 2.5km) of the AI. The eastern extent of down to <10 mg/L band is about 2km of the AI	north-east plumes of down to <30 mg/L band about 2.5km north and 2.5km west of the AI.

Notes:

- AI = HZMB Eastern Artificial Island;

- LL = Lowest Low water level; HH = Highest high water level;

- The assumed HZMB TSHD working time are between 8:00 – 11:30 (first cycle) and 12:00 – 15:30 (second cycle). However, grab dredging is continuous 24 hours a day.

6.14 Environmental Monitoring and Audit

6.14.1.1 The implementation of good construction works practice and good dredging practice as well as the various specific mitigation measures identified above is important to prevent pollution of marine water in the construction phase.　 It is, therefore, recommended that construction activities both on land and offshore should be subject to a routine audit programme throughout the construction period.　 Further details on the scope of this audit are provided in the project EM&A manual.

6.14.1.2 With the implementation of the recommended mitigation measures no significant residual adverse impacts on water quality are identified.　 Nevertheless in view of the close proximity of the key sensitive receivers and the scale of the combined projects, it is considered appropriate to implement a water quality monitoring programme throughout the marine works construction period to verify that the intensity of sediment plumes caused by activities associated with dredging and backfilling are within the predicted acceptable bounds.　 The monitoring programme shall form an integral part of a management and control programme with a clearly defined Action Plan to trigger implementation of any necessary revision to works practice or provision of supplementary mitigation measures in the unlikely event that adverse impacts are identified.　 Further details of the monitoring programme and accompanying Action Plan are provided in the EM&A manual.

6.14.1.3 Since the marine works of TM-CLKL will be concurrent with HKBCF and HKLR and the southern landfall of TM-CLKL is indeed an integrated part of the HKBCF, it is recommended that the water quality monitoring works of the three concurrent projects, also by the same project proponent, be conducted as a whole to enhance the efficiency and cost-effectiveness of the monitoring programme.

6.14.1.4 An important mitigation measure to control the potential sediment loss to an acceptable level is extensive use of a combination of silt curtain systems enclosing individual grab dredgers as well as the perimeter of the works area. 　The sediment reduction efficiency of this type of silt curtain applied separately are well established. 　For multiple layers of silt curtains, however, it can be expected that suspended solids that cannot be retained by the first layer of screen should be the very fine particle which would be difficult to be retained by the subsequent layers. Although this phenomena has been taken into account in estimating the combined efficiency of the multiple silt curtain system, there are only limited information about the actual performance of the combined system. As such, a field trial to verify the reduction effect of the silt curtain system is recommended during the EM&A stage.

6.14.1.5 Furthermore, to ensure the San Tau Beach SSSI will not be adversely affected by the project as predicted, operation phase water quality monitoring at San Tau Beach SSSI is recommended. Further details of the specific EM&A requirements are detailed in Section 15 of this report and in the EM&A Manual.

6.15 References

Barros, N.B., T.A. Jefferson, and E.C.M. Parsons. (2004). Feeding habits of Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong. Aquatic Mammals (Special Issue) 30:179-188. (87)

Binnie Consultants Limited (1996). Fill Management Study - Phase IV Investigations and Development of Marine Borrow Areas: Coral Growth at High Island Dam. For The Civil Engineering Department, Hong Kong SAR Government.

CityU (City University of Hong Kong) (2001).　 Agreement No. CE 62/98, Consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment, Final Report, for the Agriculture, Fisheries and Conservation Department, HKSAR Government.

COES (China Offshore Environmental Services Ltd) (2008). 港珠澳大橋工程海洋環境影響報告書(送审稿)(2008年十月)(HZMB OEIA).

ERM Hong Kong, Ltd (1997). Environmental Impact Assessment Study for Disposal of Contaminated Mud In the East of Sha Chau Marine Borrow Pit. Prepared for Civil Engineering Department, HKSAR Government.

ERM Hong Kong, Ltd (2001). Focussed Cumulative Water Quality Impact Assessment of Sand Dredging at the West Po Toi Marine Borrow Area. Prepared for HAM Dredging and Marine Contractors, Hong Kong.

ERM Hong Kong, Ltd (2003a). The Proposed Submarine Gas Pipelines From Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant, Hong Kong – Environmental Impact Assessment Study. For The Hong Kong and China Gas Company Limited. (EIA – 089/2003)

ERM Hong Kong, Ltd (2003b). Proposed Aviation Fuel Receiving Facility at Sha Chau: Environmental Impact Assessment, Volume 1, January 1995.

ERM Hong Kong, Ltd (2005). Detailed Site Study for a Proposed Contaminated Mud Disposal Facility within the Airport East/East of Sha Chau. Prepared for Civil Engineering and Development Department, HKSAR Government.

ERM Hong Kong, Ltd (2006).　　 Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities. EIA Report. Prepared for CLP Power, Hong Kong.

HWR (1993) Disposal of Spoil at West Po Toi.　 An Assessment of the Stability and Losses of Dumped Spoil.　 Hydraulics and Water Research (Asia) Ltd Report HWR 067, July 1993 for Greiner Maunsell.

Jefferson T.A. (2007). Monitoring of Chinese white dolphins (Sousa chinensis) in Hong Kong waters – Biopsy sampling and population data analysis - Final report. Prepared for Agriculture, Fisheries and Conservation　　 Department, HKSAR Government AFCD

Maunsell (2008). Agreement No. CE 43/2005 (EP) Harbour Area Treatment Scheme (HATS) Stage 2A EIA Study – Investigation. Final Environmental Impact Assessment Report. Prepared for Drainage Service Department, HKSAR Government.

Meinhardt Infrastructure and Environment (2007). Contract P325 Environmental Assessment Services for Permanent Aviation Fuel Facility. Final Environmental Impact Assessment Report. Prepared for Airport Authority Hong Kong.

Mouchel Asia Limited (2002a). Environmental Assessment Study for Backfilling of Marine Borrow Pits at North of the Brothers (Agreement No Geo 01/2001) - Environmental Assessment Report. For The Civil Engineering Department, Hong Kong SAR Government.

Mouchel Asia Limited (2002b). Contract M811 Environmental Assessment Services for Permanent Aviation Fuel. Final Environmental Impact Assessment Report. Prepared for Airport Authority Hong Kong.

PlanD (Planning Department) (2008). Technical Notes on the Compliation of 2006-based TPDEM. Planning Department, HKSAR Government.

Parry, S. (2000). Suspended Sediment in Hong Kong Waters. GEO Report No. 106. Geotechnical Engineering Office, Civil Engineering Department, HKSAR Government.