4. WATER QUALITY IMPACT

4.1 Introduction

4.1.1 Water quality impact assessment has been conducted as part of the EIA study, as required in the EIA Study Brief (ESB-0010/1998). Marine works for the proposed YTB reclamation such as sand filling and mud dredging may adversely affect the water quality of the neighbouring waters. Key water quality issues to be addressed for the construction phase include the potential cumulative impacts on water quality due to concurrent construction activities in Victoria Harbour and Junk Bay around YTB and the impact of the temporary diversion of the stormwater culvert in YTB. During the operation phase, the key water quality issues include the effect of the proposed YTB reclamation on tidal flows through Victoria Harbour and the potential water quality deterioration under the concrete decking section proposed near the northern part of YTB.

4.1.2 The objective of the present study is to evaluate the potential water quality impacts as a result of the construction and operation of the YTB reclamation. The environmental acceptability of these potential water quality impacts is assessed, with a view to identifying appropriate mitigation measures to reduce any identified adverse impacts to acceptable levels. The site layout plan for the project is shown in Figure 4.1.

4.2 Environmental Legislation, Standards and Criteria

4.2.1 Statutory and guideline criteria relevant to the water quality impact assessment of the proposed YTB reclamation are described below.

Environmental Impact Assessment Ordinance (EIAO), Cap.499, S16

4.2.2 YTB reclamation is a Designated Project under Schedule 2 of the EIAO. The “Technical Memorandum on Environmental Impact Assessment Process (TM on EIA Process)” was issued by Environmental Protection Department (EPD) under Section 16 of the EIAO. The TM on EIA Process specifies the assessment method and criteria that will be followed in this study. Sections in the TM on EIA Process relevant to the water quality impact assessment are:

· Annex 6 - Criteria for Evaluating Water Pollution; and

· Annex 14 - Guidelines for Assessment of Water Pollution.

Water Quality Objectives (WQOs)

4.2.3 The Water Pollution Control Ordinance (WPCO) (Cap.358) provides the major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, the whole Hong Kong waters are divided into ten Water Control Zones (WCZs). The WCZ boundaries in the vicinity of YTB are shown in Figure 4.2. Corresponding statements of Water Quality Objectives (WQO) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZ based on their beneficial uses. The proposed YTB reclamation site is located within the Victoria Harbour (Phase One) WCZ and the corresponding WQOs, implemented since November 1994, are listed in Table 4.1.

Table 4.1 Summary of Water Quality Objectives for the Victoria Harbour Water Control Zone

Parameters	Objectives	Sub-Zone
Offensive Odour, Tints	Not to be present	Whole zone
Colour	Not to exceed 50 Hazen units, due to human activity	Inland waters
Visible foam, oil scum, litter	Not to be present	Whole zone
E. coli	Not to exceed 1000 counts per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Inland waters
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2.0 mgL^-1 for 90% of samples	Marine waters
Depth averaged DO	Not less than 4.0 mgL^-1 for 90% of samples	Marine waters
Dissolved Oxygen	Not less than 4.0 mgL^-1	Inland waters
pH	To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2	Marine waters
	Not to exceed the range of 6.0 - 9.0 due to human activity	Inland waters
Salinity	Change due to human activity not to exceed 10% of ambient	Whole zone
Temperature	Change due to human activity not to exceed 2^oC	Whole zone
Suspended solids	Not to raise the ambient level by 30% caused by human activity	Marine waters
	Annual median not to exceed 25 mgL^-1 due to human activity	Inland waters
Ammonia	Annual mean not to exceed 0.021 mg L^-1 as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
	Annual mean depth averaged inorganic nitrogen not to exceed 0.4 mgL^-1	Marine waters
BOD₅	Not to exceed 5 mgL^-1	Inland waters
Chemical Oxygen Demand	Not to exceed 30 mgL^-1	Inland waters
Toxic substances	Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.	Whole zone
	Human activity should not cause a risk to any beneficial use of the aquatic environment.	Whole zone

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

Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM on Effluent Standards)

4.2.4 Besides setting the WQOs, the WPCO controls effluent discharging into the WCZ through a licensing system. The TM on Effluent Standards was issued under the WPCO which gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, stormwater drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluents, discharging into the marine waters of Victoria Harbour. Relevant effluent standards are reproduced in Table 4.2.

Table 4.2 Standards for Effluent Discharged into the inshore waters of the Victoria Harbour Water Control Zone

Flow rate (m³ day^-1) Determinand	<=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	>3000 and <4000	>4000 and <5000	>5000 and <6000
pH (pH units)	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9	6 - 9
Temperature (^oC)	40	40	40	40	40	40	40	40	40	40	40	40
Colour (lovibond units) (25 mm cell length)	1	1	1	1	1	1	1	1	1	1	1	1
Suspended solids	50	30	30	30	30	30	30	30	30	30	30	30
BOD	50	20	20	20	20	20	20	20	20	20	20	20
COD	100	80	80	80	80	80	80	80	80	80	80	80
Oil & Grease	30	20	20	20	20	20	20	20	20	20	20	20
Iron	15	10	10	7	5	4	2.7	2	1.3	1	0.8	0.6
Boron	5	4	3	2.7	2	1.6	1.1	0.8	0.5	0.4	0.3	0.2
Barium	5	4	3	2.7	2	1.6	1.1	0.8	0.5	0.4	0.3	0.2
Mercury	0.1	0.001	0.001	0.001	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	0.001	0.001	0.001
Other toxic metals individually	1	1	0.8	0.7	0.5	0.4	0.25	0.2	0.15	0.1	0.1	0.1
Total toxic metals	2	2	1.6	1.4	1	0.8	0.5	0.4	0.3	0.2	0.14	0.1
Cyanide	0.2	0.1	0.1	0.1	0.1	0.1	0.05	0.05	0.03	0.02	0.02	0.01
Phenols	0.5	0.5	0.5	0.3	0.25	0.2	0.13	0.1	0.1	0.1	0.1	0.1
Sulphide	5	5	5	5	5	5	2.5	2.5	1.5	1	1	0.5
Total residual chlorine	1	1	1	1	1	1	1	1	1	1	1	1
Total nitrogen	100	100	100	100	100	100	80	80	50	50	50	50
Total phosphorus	10	10	10	10	10	10	8	8	5	5	5	5
Surfactants (total)	20	15	15	15	15	15	10	10	10	10	10	10
E. coli (count per 100mL)	5000	5000	5000	5000	5000	5000	5000	5000	5000	5000	5000	5000

Notes

1. All units are in mgL-1 unless otherwise stated.

2. All figures are upper limits unless otherwise indicated.

Source: EPD Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters, Table 9a.

ProPECC Practice Notes

4.2.5 Practice notes (PN) for professional persons were issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with ten types of discharge from a construction site. These include surface runoff, groundwater, boring and drilling water, bentonite slurry, water for testing and sterilization of water retaining structures and water pipes, wastewater from building constructions, acid cleaning, etching and pickling wastewater, and wastewater from site facilities. Practices given in the PN should be followed as far as practicable during construction to minimize the water quality impact due to construction site drainage.

Hong Kong Planning Standards and Guidelines (HKPSG)

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

Water Supplies Department (WSD) Sea Water Quality Standards

4.2.7 The Water Supplies Department (WSD) has also specified a set of seawater quality standards to be maintained at their saltwater intakes for flushing purposes (Table 4.3). For suspended solids concentration (SS), there is also a tolerable limit of 20 mgL^-1. WSD have indicated in the EIA study for the SEKD [1] that the tolerable limit should be met at all times while aiming to achieve the target limit of 10 mgL^-1.

Table 4.3 WSD Standards at Sea Water Intake Point

Parameter (in mg L^-1 unless otherwise stated)	WSD Target Limit
Colour (HU)	< 20
Turbidity (NTU)	< 10
Threshold Odour Number (odour unit)	< 100
Ammoniacal Nitrogen	< 1
Suspended Solids	< 10
Dissolved Oxygen	> 2
Biochemical Oxygen Demand	< 10
Synthetic Detergents	< 5
E. coli (count per 100 mL)	< 20,000

Sea Water Quality Standard for the Dairy Farm Ice Factory Saltwater Intake (DFSI)

4.2.8 The Dairy Farm Ice Factory on Cha Kwo Ling Road, next to the WSD Cha Kwo Ling Pumping Station, extracts sea water for cooling purposes. The sea water quality standard to be maintained at this intake is specified for SS which should be kept below 20 mgL^-1. This is less stringent than the target limit for SS at the WSD saltwater intakes.

4.3 Baseline Conditions

Existing Water Quality in Victoria Harbour

4.3.1 EPD has been conducting routine monitoring of the quality of Hong Kong waters for a long period of time. Figure 4.3 shows the location of marine water quality monitoring stations near YTB. Based on the EPD marine water quality data for the year 1997, statistics of the selected parameters are calculated and shown in Table 4.4 at the two monitoring stations near YTB:

· VM1 – to the south of YTB, near Lei Yue Mun.

· VM2 – to the west of YTB, near Quarry Bay.

Table 4.4 Summary statistics of EPD marine water quality data in Victoria Harbour WCZ for 1999

Determinand		Victoria Harbour East
		VM1	VM2
Number of samples		12	12
Temperature (^°C)		23.1 (17.7-27.3)	23.3 (17.7-27.3)
Salinity (ppt)		32.1 (31.1-33.9)	31.8 (30.8-33.7)
Dissolved Oxygen (mg L^-1)	Surface	4.7 (3.6-6.2)	4.4 (2.9-5.9)
	Bottom	4.8 (3.7-6.4)	4.5 (3.2-5.9)
Dissolved Oxygen (% Saturation)	Surface	65 (52-81)	62 (43-77)
	Bottom	67 (53-82)	62 (48-77)
pH		8.0 (7.7-8.5)	8.0 (7.7-8.4)
Secchi Disc Depth (m)		2.6 (2.0-3.0)	2.3 (1.9-3.5)
Turbidity (NTU)		8.8 (3.7-21.7)	7.8 (3.8-19.2)
Suspended Solids (mg L^-1)		5.8 (1.8-14.5)	4.7 (1.6-8.3)
5-day Biochemical Oxygen Demand (mg L^-1)		0.7 (0.4-1.1)	0.9 (0.5-1.6)
Ammoniacal Nitrogen (mg L^-1)		0.19 (0.01-0.34)	0.23 (0.03-0.37)
Unionized Ammonia (mg L^-1)		0.007 (0.001-0.013)	0.008 (0.003-0.015)
Nitrite Nitrogen (mg L^-1)		0.02 (0.01-0.04)	0.02 (0.01-0.04)
Nitrate Nitrogen (mg L^-1)		0.08 (0.03-0.14)	0.10 (0.03-0.18)
Total Inorganic Nitrogen (mg L^-1)		0.30 (0.15-0.45)	0.35 (0.20-0.46)
Total Kjeldahl Nitrogen (mg L^-1)		0.48 (0.22-0.71)	0.53 (0.33-0.74)
Total Nitrogen (mg L^-1)		0.59 (0.35-0.83)	0.65 (0.51-0.83)
Ortho-phosphate Phosphorus (mg L^-1)		0.04 (0.02-0.06)	0.04 (0.03-0.07)
Total Phosphorus (mg L^-1)		0.06 (0.03-0.09)	0.07 (0.04-0.09)
Silica (as SiO2) (mg L^-1)		0.9 (0.3-1.3)	1.0 (0.5-1.5)
Chlorophyll-a (mg L^-1)		2.6 (1.2-5.2)	2.3 (1.1-5.2)
Phaeo-pigment (mg L^-1)		1.0 (0.2-3.8)	0.8 (0.2-3.2)
E.coli. (cfu/100mL)		8900 (2400-26000)	11000 (1900-93000)
Faecal Coliforms (cfu/100mL)		16000 (3700-45000)	22000 (4500-150000)

Notes:

1. Data presented are depth-averaged data, unless specified otherwise.

2. Data presented are annual arithmetic means except for E.coli. and faecal coliform data which are geometric means.

3. Data enclosed in brackets indicate the ranges.

4.3.2 For mud dredging and sand filling during the construction phase, the suspended solid (SS) concentration is the most crucial parameter pertinent to the water quality assessment. The depth averaged SS reading between the period 1/1996 to 8/1998 at VM1 and VM2 are shown in Table 4.5. The variance at station VM1 is higher than that in VM2 which may be attributed to reclamation activities, such as Aldrich Bay, within this period. However, the 90 percentile depth averaged SS concentrations of the two stations are in close agreement. Hence, the 90 percentile SS concentration of 10.68 mgL^-1 (depth-averaged) at station VM1, which is close to YTB, is taken to represent the ambient SS level in the study area.

Table 4.5 Depth averaged suspended solids concentration for stations VM1 and VM2

Depth averaged SS [mgL^-1]	1996	1997	1998⁽¹⁾	Overall average⁽²⁾
Monitoring station VM1
Mean⁽²⁾	8.63 (5.7)	5.64 (3.26)	4.64 (3.89)	6.51 (4.33)
Range	3.9-17.1	2.63-10.8	1.77-7	1.77-17.1
90 percentile	15.87 (8.22)	7.95 (4.35)	6.7 (5.93)	10.68 (6.6)
Monitoring station VM2
Mean⁽²⁾	7.19 (6.68)	5.48 (4.26)	5.03 (4.83)	6.01 (5.31)
Range	3.4-11.5	2.23-10.43	2.6-13	2.23-13
90 percentile	9.91 (9.45)	9.48 (4.97)	7.54 (7.64)	9.98 (9.27)

Notes:

1. Average is obtained for the first 8 months, i.e. between 1/98 – 8/98.

2. Surface layer values are shown in brackets.

Data source: EPD routine marine water quality monitoring program.

Future Water Quality in Victoria Harbour

4.3.3 Under the YTB reclamation, the existing ship building and repairing facilities at all marine lots in the site will be decommissioned, thus removing direct sources of pollution to the bay. The demolition of industries and workshops along the waterfront will also remove potential sources of effluent discharge into the bay and the neighbouring water body.

4.3.4 With the increased enforcement exerted over industrial effluents to comply with the TM on Effluent Standards for the VHWCZ under the WPCO, the water quality in Victoria Harbour is anticipated to improve in the future. The implementation of the Strategic Sewage Disposal Scheme (SSDS) Stage 1 would provide the necessary infrastructure for sewage collection and treatment to minimize the pollution load discharging into Victoria Harbour and thus the water quality is expected to improve further.

4.4 Assessment Methodology and Criteria

Hydrodynamic and Water Quality Modelling

4.4.1 In the present study, computer modelling is employed to assess the potential water quality impacts on the harbour waters and the beneficial uses as described in Section 4.5 for different tidal conditions (dry and wet seasons, spring and neap tides). The hydrodynamic and water quality models were developed by the Danish Hydraulic Institute (DHI) and the program runs are performed by MEMCL. The DHI models, namely the MIKE 21 and MIKE 3, have been calibrated and accepted by EPD for many EIA studies. Particularly relevant applications included the South East Kowloon Development (SEKD) Feasibility Study and Tseung Kwan O (TKO) Area 131 Cargo Working Area EIA Study, which are adjacent to the present study area.

4.4.2 The main objective of the modelling was to determine whether the proposed YTB reclamation would result in non-compliance with the WQOs of the Victoria Harbour WCZ as stipulated in the WPCO, during both the construction and operation phases. In addition, the potential impact on the neighbouring sensitive receivers due to the dredging and filling activities will also be assessed. As highlighted in Section 2, the Full Reclamation option is expected to have a greater effect on the flow and water quality in Victoria Harbour than the Minimized Reclamation option. The Full Reclamation option is therefore taken to represent the worst case scenario of the YTB reclamation and is quantitatively assessed in the present study. Due to the similar construction approach of the two reclamation options and a smaller reclamation area in the Minimized Reclamation, an environmentally acceptable Full Reclamation would suggest that the minimized reclamation is also environmentally acceptable.

Model Setup

4.4.3 DHI’s 2D model, namely MIKE 21, was used to simulate the dry season hydrodynamic condition of the Hong Kong waters. To account for the effect of stratification in the water column, the 3D model, MIKE 3, is employed for the wet season simulation.

4.4.4 The model setup consists of a set of dynamically nested grids, distributed in a way to resolve the high resolution required in the harbour and narrow channels, while providing a total coverage of the whole of Hong Kong. Two sets of model grids are used:

· Large grid (3 levels) (Figure 4.4a):

Grid size ranges from 675m down to 225m and 75m, covering the whole of Hong Kong and the Pearl Estuary. The resolution in the Victoria Harbour region is enhanced using the small grid size of 75m.

· Local grid (2 levels) (Figure 4.4b)

Grid size ranges from 75m down to 25m, covering the Victoria Harbour with emphasis placed in the vicinity of YTB.

4.4.5 The different levels of the large and local grids are dynamically nested which enable the exchange of boundary conditions. The large grid is mainly used for the hydrodynamic (HD) simulation and the water level or tidal variation is extracted as boundary input to the local grid. The HD simulation is then re-run using the local grid to resolve the finer details in the proximity of YTB. Based on the local grid HD results, particle tracking or sediment plume (PA) modelling is performed to assess the impact of the dredging and filling activities during construction.

The model were run for the following simulation periods:

· Dry season, spring and neap tides: 1990/2/7 – 1990/2/21 (14 days)

· Wet season, spring tide: 1990/6/19 – 1990/6/24 (4.5 days)

· Wet season, neap tide: 1990/6/26 – 1990/7/1 (4.5 days)

4.4.6 To ensure convergence of the model, a warm up period of 1.5 days was added to the beginning of the above periods in the nested HD simulations using the large grid and the local grids. Typical time series plot of the SS elevation at the WSRs during the YTB reclamation are shown in Appendix 4D.

4.4.7 Parameters used in the nested sediment plume model are summarized in Table 4.6. These were adopted in the previous SEKD Feasibility Study.

Table 4.6 Summary of parameters for the nested sediment plume model (NPA)

Nested sediment plume (NPA) model
Longitudinal dispersion factor I_L	15 m	Minimum dispersion 1 m² s^-1
Transversal dispersion factor I_T	15 m	Minimum dispersion 1 m² s^-1
Neutral dispersion D₀	0.03 m² s^-1
Vertical dispersion of suspended solids (SS) D_v	0.0001 m² s^-1
Particle settling velocity	0.0001 m s^-1	Grain size diameter of 10 mm

Modelling Scenarios

4.4.8 The year 2006 Scenario A2 in the SEKD Feasibility Study will be used as the basis of the present study. The bathymetry or coastline of the model is modified to reflect changes for each scenario as described in the following paragraphs. The scenarios can be divided into two main classes, namely, operation phase and construction phase impacts.

Operation phase impact in year 2007

4.4.9 The long term implication of the YTB reclamation (Full Reclamation Option), representing the worst case impact with respect to the extent of reclamation, is assessed in the following scenarios:

· Scenario 1A – Baseline scenario excluding YTB reclamation

The latest coastline is updated to include the recent modifications in the SEKD study as at March 1999 and the reclamation for the Western Coast Road (WCR-Coastal option) when the modelling study was performed, while excluding the YTB reclamation in year 2007.

· Scenario 1B – Development scenario with YTB reclaimed

This is the same as Scenario 1A with the inclusion of the YTB reclamation (Full Reclamation option).

· Scenario 1C – Impact of the new Kwun Tong nullah, proposed in the SEKD Feasibility Study, and the proposed stormwater culvert in YTB on the water quality under the proposed concrete decking (Figure 4.5a).

Construction phase impact in year 2004

4.4.10 The YTB reclamation works for the Full Reclamation option will be conducted in stages, namely seawall construction, Phase 1 and Phase 2 reclamations and Phase 3 construction of concrete decking at the mouth of YTB (Figure 2.1). The water quality impacts associated with these interim construction stages and methods are assessed in the following scenarios using the particle model (PA):

· Scenario 2A – Construction impact of YTB reclamation alone (worst-case scenario)

To assess the worst case scenario of the YTB reclamation (Full Reclamation), the three interim construction stages were considered:

1. Scenario 2A_SW – Seawall construction

This involves mud dredging and sand filling for the seawall foundation.

2. Scenario 2A_P1 – Phase 1 reclamation

The area to be reclaimed is approximately 13.8 hectares (Figure 2.1). Taking a conservative approach, the maximum production rate of 10,000 m³day^-1 is assumed for sand filling in the Phase 1 reclamation and will be incorporated in the sediment plume model to test its environmental acceptability.

3. Scenario 2A_P2 – Phase 2 reclamation

The area of Phase 2 reclamation is approximately 4 times smaller than the Phase 1 reclamation. The maximum production rate of 10,000 m³day^-1 is assumed in the sediment plume model, similar to that in Scenario 2A_P1.

· Scenario 2B – Cumulative impacts from neighbouring construction activities

Two cases were considered:

1. Scenario 2B_BK – Cumulative Impacts of Other Projects

Based on the latest information as at March, 1999, the concurrent construction activities in Victoria Harbour and Junk Bay between Jan 2001 and Dec 2011 are incorporated into the sediment plume model, excluding the YTB reclamation.

2. Scenario 2B_CI – Cumulative Impact including YTB reclamation

In addition to the concurrent projects included in Scenario 2B_BK, sand filling for the Phase 1 reclamation, with the highest production rate, is taken into account in the sediment plume model.

· Scenario 2C – Impact of the temporary diversion of stormwater culvert in YTB.

The stormwater culvert in YTB will be temporarily diverted along the southern seawall of YTB to the proposed water front before the main reclamation begins. The proposed discharge location is assessed for possible water quality deterioration in Victoria Harbour and at the water sensitive receivers (Figure 4.5b).

4.4.11 The proposed Phase 3 construction works for the Full Reclamation option involve the construction of 155 uniformly spaced piles of approximately 0.9m in diameter to support the concrete decking at the mouth of YTB. The works will not involve marine works like dredging or filling that will generate significant elevations of suspended solids. Marine sediment that may be disrupted by the piling activities at the seabed will essentially be re-suspended near the seabed (about 5m from sea surface) and will subsequently re-deposit at the seabed. It is therefore considered that the associated water quality (SS)_ impact upon the existing WSD intakes that are close to the sea surface will be minor. The impact will be further minimised after the implementation of silt screens recommended in Section 4.8. The effect of the concrete piles on the flow under the decking has been taken into account in the hydrodynamic simulation for the operation phase scenario. Furthermore, the concrete decking for the Minimized Reclamation option will be reduced proportionately and thus reducing the size of the embayment. Tidal flushing of the smaller embayment and thus the water quality under the concrete decking is expected to be better than those for the Full Reclamation option. Hence, the above simulations scenarios will be sufficient for the purpose of environmental impact assessment.

General Notes and Assumptions

4.4.12 Hydrodynamic (HD) simulation using the large grid is performed for Scenario 1A. The variation of water level is then extracted as boundary input to the local grid HD simulations for all the scenarios. With the local grid HD results, sediment plume modellings are conducted for Scenarios 1C, 2A, 2B and 2C.

4.4.13 For Scenarios 1C and 2C, a conservative source for the sediment plume or particle model is used to simulate the pollutant dispersion of the new Kwun Tong nullah, the new and the temporary stormwater culvert in YTB, with an arbitrary discharge rate of 1 kg s^-1 (86400 kg day^-1). The discharge locations are shown in Figure 4.5.

4.4.14 With reference to the preliminary construction program for YTB reclamation, assuming an average production rate of 4,000 m³day^-1, the dredging and filling activities will take place between February 2004 and March 2007 (Appendix 2A). If the maximum production rate of 10,000 m³day^-1, as assumed in the sediment plume model, is maintained through out the whole construction period, the program may be shortened accordingly.

4.4.15 Based on the latest construction program as at March 1999 for the South East Kowloon Development (SEKD), the Western Coast Road (WCR-Coastal option), the Tseung Kwan O (TKO) New Town Intensification and Extension (NTIE) and the TKO Cargo Working Area (CWA), the potentially concurrent activities in the vicinity of YTB between Jan 2001 and Dec 2011 were identified for cumulative impact assessment (Scenario 2B). The construction activities which correspond to the highest production rates for each project are listed in Table 4.7 and the corresponding locations are shown in Figure 4.6a. These construction activities with the highest production rate only occur for a short period of time and, in reality, these activities are unlikely to take place simultaneously or at least not at the highest production rate. Hence, the present assessment which assumes concurrent construction for the different projects in Victoria Harbour at their highest production rates, provides a conservative estimate of the cumulative water quality impacts.

4.4.16 Since the daily production rates for the WCR - Coastal Option reclamation during the seawall construction for the YT and TKO sections are higher than those during the main reclamations, the former is taken to represent the worst case of WCR construction. This is further supported by the fact that the main reclamations for the WCR will commence after the seawall construction and the sediment plume is effectively contained within the seawall minimizing the impact on the sensitive receivers.

4.4.17 According to the EIA studies of the concurrent projects, mitigation measures were proposed to be implemented during the construction phase. Hence, the proposed mitigation measures are also included in the sediment plume modelling, giving a more realistic view of the pollution level at the time when YTB reclamation takes place. The main mitigation measure proposed in the SEKD, WCR-Coastal option and TKO CWA EIA studies is to use close grab dredgers with silt curtains for both the dredging and filling operations, which gives a sediment loss reduction of 5 times lower than that using open grab alone.

4.4.18 Since the TKO New Town intensification and extension EIA study was in progress when the modelling study was performed, mitigation measure had not been proposed. Hence, the corresponding spill loss rates for the dredging and filling works shown in Table 4.7 were unmitigated. The present cumulative impact study (Scenario 2B) serves as conservative assessment of the potential impact of the concurrent activities around YTB.

4.4.19 In the YTB reclamation, the daily production rate for the main reclamation is much higher than that during the seawall construction. Hence, the Phase 1 main reclamation is used to represent the worst case scenario of YTB reclamation in the cumulative impact study (Scenario 2B). This will be further justified by comparing the impacts associated with the different construction phases of YTB reclamation in Scenario 2A.

4.4.20 The dry densities of filling sand and harbour mud are 1800 kg m^-3 and 1400 kg m^-3 respectively except for those in the YTB reclamation. Based on the geotechnical site investigation, the dry densities of filling sand and harbour mud involved in the YTB reclamation are 1835 kg m^-3 and 1750 kg m^-3 respectively.

4.4.21 The dredging and filling works are assumed to take place 10 hours per day, 7 days per week while those of the SEKD and the TKO CWA will operate for 24 hours per day and 16 hours per day respectively.

4.4.22 The spill amount will be 1.8% and 3.7% of the mud dredged and sand filled respectively. Spilling is assumed to take place uniformly over the working hours.

4.4.23 With respect to rate of sediment loss during dredging, the Contaminated Spoil Management Study (Mott MacDonald, 1991; Table 6.12) reviewed relevant literature and concluded that losses from open-grab dredgers were estimated at 12‑25 kg m^-3 of mud removed. Taking the upper figure of 25 kg m^-3, and assuming an in-situ mud density of 1400 kg m^-3, this represents a loss to the water column of 1.8%. This rate of loss represents a conservative or worst case estimate.

4.4.24 According to the PSD test results reported in the Technical Note 3/93 – Review of Specifications for Marine Fill Material for Reclamation prepared by GEO, CED in October, 1993, the average fines content of the filling sand from the marine borrow areas, e.g. South Tatong and East Tung Lung Chau, ranges from 2% to 7% with an average value of 3.5%. As a conservative assumption, the spill loss rate of 3.7% for sand filling is assumed for the present study. Similar assumptions have been made in the SEKD study.

4.4.25 According to the information provided by the Planning Department on 9 December 1999, the “Study on Village Improvement and Upgrading of Lei Yue Mun Area” involves the assessment of a number of improvement options for the Lei Yue Mun area. Mud dredging and cleaning at the Sam Ka Tsuen Typhoon Shelter and the construction of a tidal barrier along the Lei Yue Mun Villages are the proposed marine works which might have potential water quality impact on the neighbouring water. The study is in the preliminary engineering feasibility assessment stage and no detailed dredge and fill volumes are available at present. Moreover, the proposed marine works are relatively minor as compared to the neighbouring reclamation works and are not expected to have major impact on the water sensitive receivers near YTB. Hence, these proposed works will not be included in the present assessment.

Table 4.7 Details of Dredging and Filling Activities between Jan 2001 and Dec 2011

Location/Source ID		Activity	Production Rate (m³ day^-1)	Sediment Loss Rate (kg s^-1)
South East Kowloon Development ^{(1, 3, 6)}			Feb 2003–Mar 2003 ⁽¹¹⁾
A	Mud dredging for Cha Kwo Ling PCWA reclamation work package WP31: KTNCRC6800		4187	0.24
B	Mud dredging for KBR1A reclamation work package WP04: KB1CRC1001		2101	0.12
C	Sand filling for Kai Tak nullah (KTN) reclamation, stage 2 work package WP07: KTNCRC6322		5265	0.81
D	Sand filling for the Kwun Tong Typhoon Shelter (KTTS) Reclamation (north) work package WP29: KTNCRC6350		4744	0.73
E	Sand filling for Cha Kwo Ling PCWA Reclamation work package WP31: KTNCRC6800		5895	0.91
F	Sand filling for KBR1A and KBR1B Reclamations work package WP04: KB1CRC1001, KB1CRC1003		8507	1.31
G	Sand filling for KBR south seawall foundation works work package WP13: KB1PTT1315		5000	0.77
Western Coast Road (WCR) – Yau Tong Section ^{(1, 3, 5)}			Sept 2002–Oct 2002 ⁽¹¹⁾
H		Mud Dredging for seawall foundation	1892	0.26
I		Sand filling for construction of seawall foundation	900	0.33
-		Main Reclamation	2322	0.86
Western Coast Road (WCR) – Tseung Kwan O Section ^{(1, 3, 5)}			Jun 2002–Sept 2002 ⁽¹¹⁾
J		Mud Dredging for seawall foundation	1662	0.23
K		Sand filling for construction of seawall foundation	2202	0.81
-		Main Reclamation	1787	0.66
Tseung Kwan O New Town Intensification and Extension – Area 138 ^(1,4,5)			Apr 2004–Jun 2004 ⁽¹¹⁾
L		Mud dredging for southern seawall foundations	6000	4.2
M		Sand filling for the main reclamation and eastern seawall	26000	48.1
Tseung Kwan O Cargo Working Area (CWA) – Area 131 ^{(1, 3, 7)}			Apr 2003–Mar 2004 ⁽¹¹⁾
P		Mud dredging for CWA outer arm	6358	0.56
Q		Sand filling for CWA outer arm	5694	1.32
Yau Tong Bay Reclamation ^{(2, 4, 5, 8)}			May 2004–July 2006 ⁽¹¹⁾
R1		Sand filling for Phase 1 main reclamation	10000	18.86

Notes:

1. The dry densities of filling sand and harbour mud are 1800 kg m^-3 and 1400 kg m^-3 respectively unless specified otherwise.

2. Based on the geotechnical site investigation, the dry densities of filling sand and harbour mud involved in the YTB reclamation are 1835 kg m^-3 and 1750 kg m^-3 respectively.

3. Close grab with silt curtain was adopted as a mitigation measure for sand filling and mud dredging in the EIA studies for SEKD, WCR-Coastal option and TKO CWA. Spilling is assumed to occur uniformly over the working hours with a sediment loss reduction factor of 5 times lower than that using open grab alone.

4. No mitigation measure is applied in the model for the TKO New Town intensification and extension and YTB reclamation

5. The dredging and filling works are assumed to take place 10 hrs per day, 7 days per week, except for the SEKD and the TKO CWA.

6. Operations for SEKD are carried out continuously 24 hrs per day, 7 days per week.

7. Operations for TKO CWA are carried out continuously 16 hrs per day, 7 days per week.

8. Source R1 is incorporated into the model to represent the YTB reclamation.

9. The spill amount will be 1.8% and 3.7% for mud dredging and sand filling respectively.

10. Spilling is assumed to take place at the mid water depth.

11. The period corresponds to the time when the highest production rate for each project will occur with reference to their latest construction programs as at March 1999.

Yau Tong Sewage Pumping Station Emergency Outfall

4.4.26 As part of the proposed YTB reclamation (Full Reclamation option), land provision has been considered and identified at the new waterfront of the reclaimed land for potential relocation or upgrading of the existing WSD Cha Kwo Ling saltwater pumping station and its intake. The potential intake point may be located at approximately 360m from the Yau Tong sewage PS emergency outfall. The potential water quality impact from the emergency discharge on the potential site for a new WSD intake has been assessed using the Cornell Mixing Zone Expert System (CORMIX). The CORMIX3 model, in particular, was designed to assess the near field mixing of a surface buoyant discharge which is most relevant to the present study. The CORMIX models were developed by the USEPA and have been used to assess near field water quality impacts within the mixing zone for other EIA studies in Hong Kong[2].

Assessment Criteria

4.4.27 A sediment plume model was used to predict the elevations in SS concentration above the ambient levels in Victoria Harbour and at the identified water sensitive receivers (WSRs). The predicted SS concentrations in Victoria Harbour will be compared against the relevant assessment criteria for SS to indicate compliance or non-compliance with the WQO.

4.4.28 The criteria for evaluating impacts on marine water quality are given in Annex 6 of the TM on EIA Process and have been adopted in this project. The WQO for SS states that the marine activities during the construction works must not cause the natural ambient level to be raised by more than 30% nor give rise to accumulation of suspended solids. As discussed in Section 4.3.2, the 90 percentile depth-averaged SS concentration is taken to represent the ambient SS concentrations in the study area and, in accordance with the WQO for SS, an increase in SS concentrations of not greater than 3.2 mg L^-1 in the marine waters will deemed to be acceptable.

4.4.29 For the assessment of SS concentration at the WSRs, the 90 percentile surface SS concentration of 6.6 mgL^-1 will be added to the predicted surface SS elevation from the sediment plume model to give the absolute SS concentration (Table 4.5). The absolute SS concentration will be used for comparison with the WSD’s target and tolerable SS limits for saltwater intakes.

4.5 Sensitive Receivers

4.5.1 Yau Tong Bay is situated in the Victoria Harbour WCZ (VHWCZ) (Figure 4.2) which is bounded by the Junk Bay WCZ to the east and the Eastern Buffer WCZ to the west. Water sensitive receivers in the study area most likely to be affected by the YTB reclamation are identified below (Figure 4.7):

Existing water sensitive receivers (WSRs)

· Two WSD saltwater pumping stations, namely the Cha Kwo Ling Saltwater Pumping Station (CKLSPS) and Yau Tong Saltwater Pumping Station (YTSPS), which supply flushing water to the neighbouring areas;

· The Dairy Farm Factory Saltwater Cooling Intake (DFSI);

Planned sensitive receivers

· The potential sites for future reprovisioning of the Cha Kwo Ling (NCKLSPS) and Yau Tong (NYTSPS) saltwater pumping stations after the completion of the YTB reclamation (Full Reclamation option) and the Western Coast Road (WCR-Coastal option), Yau Tong Section reclamation.

4.5.2 The nearest WSD saltwater intake on Hong Kong Island is the Sai Wan Ho saltwater intake which is located more than 1 km from YTB. Hence, no major water quality impact arising from the YTB reclamation is expected at the WSD intakes on Hong Kong Island.

4.5.3 The nearest fish culture zone (FCZ) to the study area is located at Tung Lung Chau, approximately 7 km from YTB. The Tung Lung Chau FCZ has an area of 80,000 m², with 55 licensees as on 24 December 1998, occupying a licensed raft area of 12,795 m². Half of the total area is used for fish culture and the species commonly reared include Groupers, Seabreams, Snapper, Pampano, Cobia etc.

4.6 Operation Phase Impact Assessment

Potential Sources of Impact

4.6.1 The major concern is the effect of the proposed YTB reclamation on Victoria Harbour. A reduction in tidal exchange in Victoria Harbour may lead to the accumulation of pollutants from sewerage and storm culvert discharges, and thus, adversely affecting the water quality. Since YTB lies close to Lei Yue Mun, it is important to ensure that the flow through Lei Yue Mun as well as other major channels is not significantly affected. The cumulative effects from other reclamations and developments in Hong Kong SAR are also considered.

4.6.2 A concrete decking over the two submarine pipelines was proposed to the north of YTB as part of the reclamation project (Phase 3). The water flow under the decking may be relatively low and may lead to deterioration of water quality. Hence, the water quality under the proposed decking will be assessed in this section.

4.6.3 Raw sewage from the Yau Tong area is currently conveyed to the Kwun Tong Sewage Treatment Plant via the Yau Tong Pumping Station (PS) located at Ko Fai Road. There is an existing emergency outfall from the Yau Tong PS which discharges into Victoria Harbour at the seawall. Under the WCR-Coastal option reclamation, the existing WSD Yau Tong Saltwater Pumping Station (YTSPS) as well as the emergency outfall from the Yau Tong PS will be relocated to the new water front of the reclaimed land, while land provision has been made on the YTB reclamation (Full Reclamation option) for potential reprovisioning of the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS) (Figure 4.7). The potential water quality impact in the event of an emergency discharge from the Yau Tong PS on the potential sites for reprovisioning of the WSD saltwater intakes will be assessed.

Prediction and Evaluation of Impact

Impact in Victoria Harbour

Hydrodynamic Impact in Victoria Harbour – Scenarios 1A and 1B

4.6.4 The hydrodynamic impact arising from the YTB reclamation was assessed by comparing the modelling results of Scenarios 1A and 1B. A detailed discussion of the findings are presented in this section.

4.6.5 Predicted wet and dry seasons, flood and ebb tides flow patterns in Victoria Harbour without the YTB reclamation (Scenario 1A) are shown in Figures 4.8–4.11, while those of with YTB reclaimed (Scenario 1B) are shown in Figures 4.12–4.15. The instantaneous flow patterns correspond to the maximum flow discharges across the Victoria Harbour between Tsim Sha Tsui and Wan Chai, namely the peak ebb and peak flood tidal flows.

4.6.6 Based on the peak ebb and peak flood tidal flow patterns (Figures 4.8–4.15), the following observations are made:

· The flow patterns in Victoria Harbour with or without YTB reclamation (Full Reclamation option) (Scenarios 1A and 1B) are similar with minor deviation near YTB. The maximum flow speeds for the two scenarios are roughly the same for each of the different tidal conditions, namely the wet and dry seasons, spring and neap tides.

· As observed in the flow speed contours, the wet season flow speed in Victoria Harbour is generally higher than that in the dry season. The maximum flood tide flow speed of 1.11 ms^–1 in the wet season is higher than that of 0.71 ms^–1 in the dry season (Table 4.8). Similar observation is made for the ebb tide flow.

· Furthermore, the ebb tide flow speed is higher than that of the flood tide with the corresponding maxima of 0.79 ms^–1 and 0.71 ms^–1 in the dry season (Table 4.8). Similar observation is made in the wet season.

· The flow rates in the decked region under ebb and flood tides during the dry and wet seasons will be in the order of 0.1ms^-1.

Table 4.8 Maximum Flow Speed in Scenarios 1A and 1B

Maximum flow speed [ms^-1]		Scenario 1A	Scenario 1B
Dry Season	Flood Tide	0.71	0.69
	Ebb Tide	0.79	0.79
Wet Season	Flood Tide	1.11	1.11
	Ebb Tide	1.24	1.24

4.6.7 The above observations suggested that the maximum flow speeds and the flow patterns in Victoria Harbour are rather insensitive to the YTB reclamation (Full Reclamation option). With a reduction in the reclamation area and a more streamlined water front in the Minimized Reclamation option, it is expected that the effect of the Minimized Reclamation on the hydrodynamics in Victoria Harbour will be minimal and unacceptable impact is not anticipated.

4.6.8 To assess further the changes in flow speed due to the YTB reclamation (Full Reclamation option), the maximum flow discharge rates across the two major channels to the east and west of YTB are shown in Table 4.9. The cross section locations are shown in Figure 4.16. Positive discharge indicates an ebb tide flow in a direction pointing eastwards towards Lei Yue Mun and vice versa.

Table 4.9 Change in Ebb and Flood Discharges with and without YTB reclamation

Cross section	Current	Scenario 1A (Without YTB Reclamation)		Scenario 1B (With YTB Reclaimed)		% Change
		Discharge Rate [m³s^-1]
		Peak	Tidal Average	Peak	Tidal Average	Peak	Tidal Average
Dry Season
Tsim Sha Tsui / Wan Chai	Flood	-6506	-3108	-6447	-3114	-0.9%	0.2%
	Ebb	8113	3193	8194	3189	1.0%	-0.1%
Lei Yue Mun	Flood	-7262	-3372	-7358	-3358	1.3%	-0.4%
	Ebb	9417	3615	9456	3623	0.4%	0.2%
Wet Season
Tsim Sha Tsui / Wan Chai	Flood	-8074	-2731	-8079	-2733	0.1%	0.1%
	Ebb	9167	1921	9176	1924	0.1%	0.2%
Lei Yue Mun	Flood	-9037	-3021	-9029	-3019	-0.1%	-0.1%
	Ebb	10874	2201	10859	2200	-0.1%	0%
Annual (Dry and Wet) Average
Tsim Sha Tsui / Wan Chai	Flood	-7290	-2920	-7263	-2923	-0.4%	0.1%
	Ebb	8640	2557	8685	2556	0.5%	0%
Lei Yue Mun	Flood	-8149	-3197	-8193	-3189	0.5%	-0.3%
	Ebb	10145	2908	10158	2912	0.1%	0.1%

Note: The simulation results are based on the Full Reclamation option. With the reduction in reclamation area for the Minimized YTB Reclamation, the difference in flow discharges with and without the minimized reclamation is expected to be smaller than that of the Full Reclamation option.

4.6.9 Due to the smaller channel cross section area at Lei Yue Mun, the corresponding discharge rate is approximately 15 % higher than that between Tsim Sha Tsui and Wan Chai (Table 4.9). The maximum flow discharges in ebb tide, for both the wet and dry seasons, are generally higher than those in flood tide (Table 4.9). The percentage change before and after the YTB reclamation (Full Reclamation option) (i.e. Scenarios 1A and 1B respectively) is very small with a change in annual average discharge rate of less than 0.5%. This further confirms that the YTB reclamation is likely to have negligible effect on the tidal flow in Victoria Harbour. As explained in the previous paragraphs, the effect of the Minimized Reclamation option on the tidal flow is expected to be even smaller.

Water Quality Impact in Victoria Harbour

4.6.10 Raw sewage from the Yau Tong Area is currently diverted to the Kwun Tong Screening Plant. By the year 2002 it is expected that all screened sewage from the Kwun Tong Screening Plant would be diverted to the Stonecutters Island STW and discharged via the interim outfall under Stage 1 of the SSDS[3]. The sewage arising from the YTB Comprehensive Development Area (CDA) will be conveyed to the Kwun Tong Screening Plant and discharge through the SSDS Stage I outfall. In view of the negligible change in flow regime in Victoria Harbour, it is concluded that the YTB reclamation is unlikely to have any adverse impact on the water quality in Victoria Harbour.

Impacts of the New Kwun Tong Nullah and the New Storm Culvert in YTB– Scenario 1C

4.6.11 As part of the YTB development, a concrete decking is proposed to be built over the existing submarine pipelines near the northern part of YTB. Since polluted stormwater may be discharged through the new Kwun Tong nullah (NKTN) and the new YTB stormwater culvert (NYTBSC) near the decking, the low flow speed under the decking may result in a potential accumulation of pollutants. In Scenario 1C, the potential water quality impact is assessed using a tracer particle method (Appendix 4A). The dispersion and dilution of pollutants under the tidal influence is modelled using the 2D model, MIKE 21. The impact on the planned WSRs, namely, the potential sites for future reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) and the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS), will be presented.

The New Kwun Tong Nullah (KTN)

4.6.12 With the implementation of the Sewerage Master Plans (SMPs) and remedial measures to reduce loads from expedient sewerage connections, only 5% of the sewage flow in the catchment area is assumed to remain in the stormwater system in the SEKD¹, including the new Kwun Tong nullah. Based on the East Kowloon SMP, the flow and loads into the new KTN in year 2011 have been estimated in the SEKD Feasibility Study² and are shown in Table 4.10.

Table 4.10 Flow and loads into the new Kwun Tong Nullah in year 2011

Parameter	5% residual flows from expedient connections	1% residual flows from expedient connections
Flow ⁽¹⁾ (m³ d^-1)	10,121	2,024
BOD₅ (kg d^-1)	2,305	461
SS (kg d^-1)	2,029	406
Ammoniacal Nitrogen (kg d^-1)	178.4	35.7
E. coli (count per day)	1.48 x 10¹⁵	2.97 x 10¹⁴

Note: 1) A dissolved oxygen level of 2 mgL^-1, as adopted in the SEKD Feasibility Study^2, is assumed

4.6.13 A simple one dimensional segmented steady state water quality model, similar to the Kai Tak Nullah model adopted in the SEKD Feasibility Study², which takes into account the tidal mixing and decay within the nullah decking of approximately 1 km in length, was used to assess the effluent quality at the outfall of the new KTN. In the previous study², a dissolved oxygen (DO) level of 2 mgL^-1 was considered adequate in maintaining the WQOs in terms of aesthetic appearance in the open channel of the new KTN. Since the effluent DO level of the new KTN is unavailable, the same DO level of 2 mgL^-1 was assumed in the steady state water quality model for the new KTN impact.

4.6.14 The modelled effluent quality at the outfall of the new Kwun Tong nullah is shown in Table 4.11. The effluent dissolved oxygen (DO) content of 3.78 mgL^-1 at the outfall is above the WSD target limit at saltwater intake of 2 mgL^-1 but slightly lower than the WQO of 4 mgL^-1. With further mixing in Victoria Harbour, it is anticipated that the dissolved oxygen will increase to the ambient depth averaged level of 4.85mgL^-1 (Table 4.4), satisfying the WQO.

Table 4.11 Predicted Effluent Quality at the outfall of the new Kwun Tong Nullah

Assumption

Flow Rate ⁽³⁾

[m³ d^-1]

DO [mgL^-1]

BOD₅ [mgL^-1]

SS [mgL^-1]

Ammoniacal Nitrogen [mgL^-1]

E. coli [count per 100 mL]

With 5% residual flows from expedient connections

77000

3.78

0.83

31.2

0.15

2404

With 1% residual flows from expedient connections

68900

4.73

0.04

11.3

0.01

106

Notes:

1. Calculations were based on EPD routine monitoring data at station VM1 in year 1997.

2. Depth averaged values were assumed.

3. Flow rate include the tidal flow within the new Kwun Tong nullah.

4.6.15 The effective pollution load at the outfall of the new Kwun Tong nullah is estimated in Table 4.12 by multiplying the effluent pollutant concentration and the discharge flow rate, which included the tidal flow within the nullah (Table 4.11). Significant reductions in loadings of BOD₅ and ammoniacal nitrogen at the outfall are predicted, which are the results of continuous mixing by large volume of tidal flow and the rapid decay rates of parameters within the well-mixed effluent.

Table 4.12 Effective load at the outfall of the new Kwun Tong Nullah in year 2011

Parameter	5% residual flows from expedient connections	1% residual flows from expedient connections
BOD₅ (kg d^-1)	64	3
SS (kg d^-1)	2404	780
Ammoniacal Nitrogen (kg d^-1)	11.6	0.6
E. coli (count per day)	1.85 x 10¹²	7.32 x 10¹⁰

Water Quality in Victoria Harbour Water Control Zone (VHWCZ)

4.6.16 Dilution and dispersion in the vicinity of the outfall for the Full Reclamation option is simulated using the 2D particle model and the details are given in Appendix 4A. In general, the particle model result suggests that the pollutant concentration will be diluted by more than 10 times within 500 m from the outfall of the new KTN.

4.6.17 Based on the effective loading at the new KTN outfall (Table 4.12) and the particle model results (Appendix 4A), the predicted increase in biochemical oxygen demand (BOD₅), SS, Ammoniacal Nitrogen and E. coli in Victoria Habour and at the WSRs are shown in Table 4.13 . No decay factor was incorporated in the particle model giving a conservative prediction. Comparing the predicted and ambient values, obtained from EPD routine monitoring data at station VM1 in year 1997 (Table 4.4), only slight increase in the above parameters is observed in the Victoria Harbour WCZ, satisfying the WQOs (Table 4.13). Typically, SS in the VHWCZ increases by 0.14 mgL^-1 (3%) above the ambient of 5.6 mgL^-1, which is lower than the WQO requirement. Neither secondary contact recreation zone nor bathing beach zone has been identified in the study area, therefore the predicted increase in E. coli of 11 counts per 100mL, over the ambient of 5780 counts per 100mL (Table 4.13), is considered acceptable. From the particle model results (Appendix 4A), the pollutant concentration will be diluted by more than 10 times within 500 m from the outfall of the new Kwun Tong nullah. Assuming the ambient DO level of 4.85 mgL^-1 from EPD’s routine monitoring data at station VM1 (Table 4.4), the 10 times dilution corresponds to an increase in the DO level from 3.78 mgL^-1 to 4.74 mgL^-1. Taking into account the BOD₅ of less than 0.71 mgL^-1, the DO level in the VHWCZ is expected to meet the WQO.

Table 4.13 Impact of the New Kwun Tong Nullah - Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes

Description	BOD₅ [mgL^-1]	SS [mgL^-1]	Ammoniacal Nitrogen [mgL^-1]	*E. coli* [count per 100mL]
Victoria Harbour Water Control Zone (VHWCZ)
Ambient level ⁽¹⁾	0.7	5.6	0.22	5780
Predicted increase in VHWCZ	< 0.01	< 0.14	< 6.71 x 10^-4	< 11
Predicted increase under the proposed concrete decking	< 0.01	< 0.56	< 2.68 x 10^-3	< 43
WQO	N/A ⁽⁶⁾	< 30% over ambient and median < 25 mgL^-1	< 0.44 ⁽⁵⁾	N/A ⁽⁴⁾
Existing Water Sensitive Receivers (WSRs)
Maximum increase at CKLSPS ⁽²⁾	0.01	0.54	2.6 x 10^-3	41
Maximum increase at YTSPS ⁽²⁾	0.01 ⁽⁷⁾	0.31 ⁽⁷⁾	1.48 x 10^-3 ⁽⁷⁾	24 ⁽⁷⁾
Planned Water Sensitive Receivers (WSRs)
Maximum increase at NCKLSPS ⁽²⁾	0.02	0.68	3.3 x 10^-3	53
Maximum increase at NYTSPS ⁽²⁾	0.01	0.31	1.48 x 10^-3	24
WSD target limit at saltwater intake	< 10	< 10	<1	< 20000

Notes:

1. Data source: EPD routine monitoring data at station VM1 in year 1997.

2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively, while NCKLSPS and NYTSPS represent the potential sites for reprovisioning of the CKLSPS and the reprovisioned YTSPS on the WCR-Coastal option reclamation respectively.

3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.

4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.

5. With reference to the WQO of 0.021 mgL^-1 for unionized ammonia, the total ammonia present at 23^oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.

6. No WQO standards for BOD₅ in marine waters.

7. The existing YTSPS intake location will be reclaimed by the WCR-Coastal option development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the Kwun Tong Nullah as the YTSPS, similar impact is expected.

8. The results presented are based on the Full Reclamation option.

Water Quality under the Proposed Concrete Decking

4.6.18 For the Full Reclamation option, the water quality under the proposed concrete decking also satisfies the WQOs with small increase in BOD₅, SS, Ammoniacal Nitrogen and E. coli (Table 4.13). Based on the predicted pollutant dilution of 2.85 times from the outfall to under the decking, the DO level is estimated to be approximately 4.5 mgL^-1. Considering the low level of predicted BOD₅ and ammoniacal nitrogen from the new Kwun Tong nullah, no odour problem is expected.

4.6.19 The particle model result also revealed that the pollutants discharged from the new Kwun Tong nullah will take an average time of less than 4 hours to be flushed out of the decking section and into Victoria Harbour (Appendix 4A). This suggests that tidal flushing will prevent the accumulation of pollutants under the decking and thus, unacceptable water quality is not expected.

4.6.20 With a smaller reclamation area and concrete decking at the mouth of YTB, and a more streamline water front in the Minimized Reclamation option, the tidal flushing under the proposed concrete decking is expected to improve as the inner part of the embayment is more exposed to the flow current in Victoria Harbour than that in the Full Reclamation option. Hence, water quality under the proposed concrete decking is likely to be better in the Minimized Reclamation option than that predicted in Table 4.13.

Water Quality at the WSD Saltwater Pumping Stations

4.6.21 In the Full Reclamation option, the BOD₅, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS), taking into account the predicted maximum increases associated with the NKTN and the ambient levels, are well within the WSD target limit (Table 4.13), and thus, unacceptable impact is not expected. For the two planned water sensitive receivers, namely the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS) under the WCR-Coastal option reclamation and the potential site reserved for the reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) under the YTB reclamation (Full Reclamation option), the relevant water quality parameters is also expected to satisfy the WSD target limit (Table 4.13).

4.6.22 Despite of the compliance of the WSD target limit at the existing and the potential site for future reprovisioning of the CKLSPS, the predicted results suggested that the water quality at the existing CKLSPS intake will be slightly better than that at the potential site for its reprovisioning. Hence, reprovisioning of the existing CKLSPS intake will not be required in the YTB reclamation (Full Reclamation option).

4.6.23 The existing Yau Tong saltwater intake location will be reclaimed by the WCR-Coastal option development and the Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of the uncertainties in the programme of various projects, the YTSPS may continue to operate at the existing location during the YTB reclamation. Considering that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS) are located at approximately the same distance from the new Kwun Tong Nullah outfalls, it is expected that the water quality at the existing YTSPS will be similar to those predicted at the reprovisioned YTSPS. In light of the large margin between the predicted water quality and the WSD target limit at saltwater intake, unacceptable impact is not expected at the existing YTSPS.

4.6.24 For the Minimized Reclamation option, the more streamline flow in the vicinity of YTB favours the dispersion and dilution of pollutants from the NKTN and thus the water quality at the existing YTSPS intake is expected to be similar to, if not better than, that at the reprovisioned location in the Full Reclamation option, satisfying the WSD’s target limit at saltwater intakes. As discussed in the previous paragraphs, the water quality at the existing CKLSPS under the proposed concrete decking is expected to improve in the Minimized Reclamation option for YTB, as compared to that in the Full reclamation option, satifying the WSD’s target limit at saltwater intakes. Hence, no reprovisioning of the existing CKLSPS and the YTSPS intakes will be required in the Minimized Reclamation for YTB.

The new YTB Stormwater Culvert

4.6.25 The existing stormwater culvert in YTB will be extended to the new waterfront of the YTB reclamation (Full Reclamation option). Based on the population estimates in year 2011 and the load factors (Appendices 4B-1 and 4B-2), obtained from the Kowloon District Office of Planning Department and DSD Sewerage Manual, the total pollution load in the Yau Tong sewage catchment is estimated (Table 4.14). Despite the fact that new sewerage network will be built for the new developments in the YT area, it is conservatively assumed that 5% of the total load in the YT sewage catchment will enter the new YTB stormwater culvert through expedient connections. This is a conservative assumption as all the future developments in the Yau Tong area will be connected to public sewers which minimizes the pollution load to the stormwater culvert through expedient connections, and the % load interception by the storm system is expected to lower. With the increase in impermeable area due to the YTB reclamation, surface runoff and the associated pollution load will also increase. Hence, the pollution load from surface runoff is also taken into account in the total load of the new YTB stormwater culvert (Table 4.14). It is observed that the pollution load in the new stormwater culvert in YTB is much lower than that in the new KTN (Tables 4.10 and 4.14). Similar to the SEKD Feasibility Study, the effluent DO level is assumed to be 2 mgL^-1. Tidal mixing and decay within the new stormwater culvert has not been taken into account at present to provide a conservative worst case assessment.

Table 4.14 Estimated Pollution Loads in the New Stormwater Culvert in YTB in Year 2011

Parameter	Total Load in Yau Tong Sewage Catchment⁽¹⁾	Load from Surface Runoff	Total Load in the New YTB Stormwater Culvert ⁽²⁾
Flow (m³ d^-1)	50717	6677	9213
BOD₅ (kg d^-1)	11761	150	738
SS (kg d^-1)	10056	289	792
Ammoniacal Nitrogen (kg d^-1)	961	1	49
E. coli (count per day)	8.19 x 10¹⁵	0	4.09 x 10¹⁴

Notes:

1. Calculations are based on the population estimate in year 2011 obtained from the Kowloon District Office of Planning Department and the per capita load factor from DSD Sewerage Manual, Part I, 1995 (Appendices 4B-1 and 4B-2).

2. It is assumed that 5% of the total load in Yau Tong sewage catchment, together with the load from surface runoff, will enter the stormwater system and discharged through the new YTB stormwater culvert into Victoria Harbour. This is a conservative assumption as all the future developments in the Yau Tong area will be connected to public sewers which minimizes the pollution load to the stormwater culvert through expedient connections, and the % load interception by the storm system is expected to lower.

Water Quality in Victoria Harbour Water Control Zone (VHWCZ)

4.6.26 Using the 2D particle model, similar to that used in the study of the new KTN (Appendix 4A), the pollutant dilution and dispersion near the outfall of the new YTB storm culvert in the Full Reclamation option is simulated (Appendix 4C). In general, the particle model result indicated that the pollutant concentration will be diluted by more than 6 times within 100 m from the new water front near the new YTB stormwater culvert outfall (Appendix 4C).

4.6.27 The predicted increase in biochemical oxygen demand (BOD₅), SS, Ammoniacal Nitrogen and E. coli in Victoria Habour and at the WSRs are shown in Table 4.15. The predicted increases generally satisfy the WQOs in the VHWCZ (Table 4.15). Based on the ambient DO level of 4.85 mgL^-1, from EPD’s routine monitoring data at station VM1 in year 1997 (Table 4.4), and the predicted pollutant dilution of more than 6 times within 100 m from the storm culvert outfall to the new water front, it is predicted that the DO level would increase from 2 mgL^-1 at the storm culvert outfall to 4.38 mgL^-1 in the VHWCZ. Taking into account the BOD₅ of less than 0.74 mgL^-1, the DO level is expected to meet the WQO in the VHWCZ. Since mixing and decay within the new YTB stormwater culvert have not been taken into account, it is anticipated that the actual pollutant concentration will be lower than those predicted in Table 4.15. The cumulative water quality impact of the New Kwun Tong Nullah and New YTB Stormwater Culvert is shown in Table 4.15a. Non-compliance of WSD water quality criteria or WQOs within the Victoria Harbour is not expected.

Table 4.15 Impact of the New YTB Stormwater Culvert – Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes

Description		BOD₅ [mgL^-1]	SS [mgL^-1]	Ammoniacal Nitrogen [mgL^-1]	E. coli [count per 100mL]
Victoria Harbour Water Control Zone (VHWCZ)
Ambient level ⁽¹⁾		0.7	5.6	0.22	5780
Predicted increase in VHWCZ		< 0.04	< 0.05	< 2.86 x 10^-3	< 2370
Predicted increase under the proposed concrete decking		< 0.09	< 0.09	< 5.72 x 10^-3	< 4740
WQO		N/A ⁽⁶⁾	< 30% over ambient and median < 25mgL^-1	< 0.44 ⁽⁵⁾	N/A ⁽⁴⁾
Existing Water Sensitive Receivers (WSRs)
Maximum increase at CKLSPS ⁽²⁾	0.08		0.09	5.4 x 10^-3	4455
Maximum increase at YTSPS ⁽²⁾	0.12 ⁽⁷⁾		0.13 ⁽⁷⁾	8.12 x 10^-3 ⁽⁷⁾	6730 ⁽⁷⁾
Planned Water Sensitive Receivers (WSRs)
Maximum increase at NCKLSPS ⁽²⁾		0.22	0.24	1.48 x 10^-2	12228
Maximum increase at NYTSPS ⁽²⁾		0.12	0.13	8.12 x 10^-3	6730
WSD target limit at saltwater intake		< 10	< 10	< 1	< 20000

Notes:

1. Data source: EPD routine monitoring data at station VM1 in year 1997.

3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.

4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.

1. With reference to the WQO of 0.021 mgL^-1 for unionized ammonia, the total ammonia present at 23^oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.

2. No WQO standards for BOD₅ in marine waters.

3. The existing YTSPS intake location will be reclaimed by the WCR-Coastal option development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the new YTB stormwater outfall as the YTSPS, similar impact is expected.

4. The results presented are based on the Full Reclamation option.

Water Quality under the Proposed Concrete Decking

4.6.28 In the Full Reclamation option for YTB, the water quality under the proposed concrete decking due to the new YTB stormwater culvert discharge also satisfies the WQOs with small increase in BOD₅, SS, Ammoniacal Nitrogen and E. coli (Table 4.15). It is predicted that the pollutant concentration will be diluted by more than 3 times from the outfall of the new stormwater culvert to under the proposed concrete decking. Correspondingly, the DO level is estimated to be approximately 3.9 mgL^-1. Taking into account tidal mixing within the new stormwater culvert, the WQO for DO is expected to be satisfied. At low level of BOD₅ and ammoniacal nitrogen, no odour problem is expected under the decking.

4.6.29 For the Minimized Reclamation option, with a reduction in the size of the proposed concrete decking, the tidal flushing under the proposed concrete decking is expected to improve as the inner part of the embayment is more exposed to the flow current in Victoria Harbour than that in the Full Reclamation option. Hence, water quality under the proposed concrete decking is likely to be better in the Minimized Reclamation option than that predicted in Table 4.15.

Water Quality at the WSD Saltwater Pumping Stations

4.6.30 In the Full Reclamation option, the BOD₅, SS, Ammoniacal Nitrogen and E. coli at the existing Cha Kwo Ling Saltwater Pumping Station (CKLSPS), taking into account the predicted maximum increases associated with the New Yau Tong Bay Stormwater Culvert and the ambient levels, are well within the WSD target limit (Table 4.15), and thus, unacceptable impact is not expected. For the two planned WSRs, namely the reprovisioned Yau Tong Saltwater Pumping Station (NYTSPS) under the WCR-Coastal option reclamation and the potential site reserved for the reprovisioning of the Cha Kwo Ling Saltwater Pumping Station (NCKLSPS) under the YTB reclamation (Full Reclamation option), the relevant water quality parameters is also expected to satisfy the WSD target limit (Table 4.15). As noted under the discussion of the NKTN impact, the water quality at the existing CKLSPS intake will be slightly better than that at the potential site for its reprovisioning. Hence, reprovisioning of the existing CKLSPS intake will not be required in the YTB reclamation (Full Reclamation option).

4.6.31 The existing Yau Tong saltwater intake location will be reclaimed by the WCR-Coastal option development and the Yau Tong Saltwater Pumping Station (YTSPS) have to be reprovisioned. In view of the uncertainties in the programme of various projects, the YTSPS may continue to operate at the existing location during the YTB reclamation. Considering that the existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS) are located at approximately the same distance from the new YTB stormwater culvert, it is expected that the water quality at the existing YTSPS will be similar to those predicted at the reprovisioned YTSPS. In light of the large margin between the predicted water quality and the WSD target limit at saltwater intake, unacceptable impact is not expected at the existing YTSPS.

4.6.32 For the Minimized Reclamation option, the more streamline flow in the vicinity of YTB, favours the dispersion and dilution of pollutants from the new YTB stormwater culvert and thus the water quality at the existing YTSPS intake is expected to be similar to, if not better than, that at the reprovisioned location in the Full Reclamation option, satisfying the WSD’s target limit at saltwater intakes. As discussed in the previous paragraphs, the water quality at the existing CKLSPS under the proposed concrete decking is expected to improve in the Minimized Reclamation option for YTB, as compared to that in the Full reclamation option, satifying the WSD’s target limit at saltwater intakes. Hence, no reprovisioning of the existing CKLSPS and the YTSPS intakes will be required in the Minimized Reclamation for YTB.

4.6.33 Considering the minor impact of the new Kwun Tong nullah and the new YTB stormwater culvert (Tables 4.13 and 4.15), their cumulative effects are still within the WQO and WSD target limit at the saltwater intakes (Table 4.15a). Hence, no insurmountable impact is expected in the VHWCZ, at the WSRs and under the proposed concrete decking. Also, as a result of the minor impact, the effect of stratification is considered insignificant and only the 2D particle model is necessary in this scenario.

Table 4.15a Cumulative Impact of the New Kwun Tong Nullah and New YTB Stormwater Culvert – Comparison of Predicted Water Quality with WQO and WSD Standards at Saltwater Intakes

Description	BOD [mg L^-1]	SS [mg L^-1]	Ammoniacal Nitrogen [mg L^-1]	E. coli [count per 100 mL]
Victoria Harbour Water Control Zone (VHWCZ)
Ambient level ⁽¹⁾	0.7	5.6	0.22	5780
Predicted increase in VHWCZ	< 0.05	< 0.19	< 3.531 x 10^-3	< 2381
Predicted increase under the proposed concrete decking	< 0.1	< 0.65	8.40 x 10^-3	< 4783
WQO	N/A ⁽⁶⁾	< 30% over ambient and median < 25 mg L^-1	< 0.44 ⁽⁵⁾	N/A ⁽⁴⁾
Existing Water Sensitive Receivers (WSRs)
Maximum increase at CKLSPS ⁽²⁾	0.09	0.63	8.0 x 10^-3	4496
Maximum increase at YTSPS ⁽²⁾	0.13 ⁽⁷⁾	0.44 ⁽⁷⁾	9.60 x 10^{-3 (7)}	6754 ⁽⁷⁾
Planned Water Sensitive Receivers (WSRs)
Maximum increase at NCKLSPS ⁽²⁾	0.24	0.92	1.81 x 10^-2	12281
Maximum increase at NYTSPS ⁽²⁾	0.13	0.44	9.60 x 10^-3	6754
WSD target limit at saltwater intake	< 10	< 10	< 1	< 20000

Notes:

1. Data source: EPD routine monitoring data at station VM1 in year 1997.

3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.

4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.

6. No WQO standards for BOD₅ in marine waters.

7. The existing YTSPS intake location will be reclaimed by the WCR-Coastal option development and thus the YTSPS have to be reprovisioned. Since NYTSPS is located at approximately the same distance away from the new YTB stormwater outfall as the YTSPS, similar impact is expected.

8. The results presented are based on the Full Reclamation option.

Impact from the emergency discharge of the DSD Yau Tong Sewage Pumping Station

4.6.34 There is an existing emergency outfall for the Yau Tong Sewage PS located along Ko Fai Road which discharges into Victoria Harbour at the seawall. This outfall is 1.425m in diameter and the invert level is at 0.02 mPD. According to DSD records, only one emergency discharge on 30 April 1998 was recorded for repairing the rising main and no records of other bypass discharges was found before this date. Approximately 3,500 m³ of raw sewage was discharged over 12 hours (7000 m³ day^-1). According to the East Kowloon Sewerage Master Plan and the preliminary pollution loading inventory being compared under a separate study, the sewage flow in year 2002 served by the Yau Tong sewage PS is estimated as 6,683 m³ day^-1. This estimate agrees well with the discharge record by DSD given above. As population grows in the Yau Tong area, it is estimated that the sewage flow served by the Yau Tong Sewage Pumping Station (YTPS) will be increased to 50717 m³ day^-1 in year 2011.

4.6.35 As assessed in the previous sub-sections on the impact from the NKTN and the new YTB stormwater culvert at the existing WSD CKLSPS intake, reprovisioning of the CKLSPS will not be required under the YTB reclamation (Full Reclamation option). However, a potential site for future reprovisioning of the CKLSPS saltwater intake have been proposed on the new waterfront of the YTB reclamation (Full Reclamation option),which is closer to the Yau Tong Sewage PS emergency outfall than the existing case. The potential water quality impact from the emergency discharge at the potential site for reprovisioning of the CKLSPS saltwater intake in the Full Reclamation option has been assessed using the Cornell Mixing Zone Expert System (CORMIX). The CORMIX3 model has been run for the existing and future scenarios of the Yau Tong Sewage PS emergency outfall with the model parameters given in Table 4.16 below.

Table 4.16 CORMIX Modelling Parameters

Parameter	Existing ⁽¹⁾	Future ⁽¹⁾
Outfall Parameters
Outfall Invert Level	+0.02 mPD
Outfall Cross Sectional Area	1.594 m²
Effluent Density	1000 kg m^-3
Effluent Flow	6,683 m³ day^-1	50717 m³ day^-1

Environmental parameters
High Water Level	+2.35mPD
Low Water Level	+0.35mPD
Ambient Water Depth	10m
Ambient Current Speed	0.1m s^-1
Ambient Water Density	1018 kg m^-3 (wet season) and 1023 kg m^-3 (dry season)
Darcy-Weisbach Friction Factor	0.023

Note:

1. The existing and future scenarios are based on the sewage flow served by the YTPS in year 2002 and year 2011 respectively.

4.6.36 As the density difference between the effluent and the ambient receiving waters will affect the buoyancy of the sewage plume, the model was run for a range of ambient water densities representing the wet and dry season conditions. The model results are presented graphically in Figures 4.17 and 4.18 for the existing and future scenarios respectively.

4.6.37 For both the existing and future scenarios, the sewage plume will attach to the shoreline due to the relatively low effluent velocity. It will also be buoyant due to the density difference between the sewage effluent and the ambient marine water in both the wet and dry seasons. The initial dilution values shown in Figures 4.17 and 4.18 represent the average dilution within the plume at various distances. The potential site for future reprovisioning of the Cha Kwo Ling saltwater pumping station intake (NCKLSPS) will be approximately 360m from the Yau Tong Sewage PS emergency outfall. At this distance from the outfall, the sewage plume thickness range between 0.19–0.37m from the surface in the existing and future scenarios, wet and dry seasons. The existing Cha Kwo Ling saltwater intake (CKLSPS) will be approximately 250 m further away from the emergency outfall than that of the NCKLSPS and less impact is expected. Hence, the present assessment at the NCKLSPS intake represents the worst case scenario.

4.6.38 Assuming the following typical raw sewage strength of:

· BOD 250 mg L^-1

· Suspended Solids (SS) 250 mg L^-1

· E. coli 2.00E+07 counts per 100mL

· Ammoniacal Nitrogen (NH3-N) 25 mg L^-1

4.6.39 With the background mean ambient water quality concentration as given in Table 4.4, the predicted water quality levels within the sewage plume and the depth averaged values at a distance of approximately 360m from the outfall are given in Table 4.17.

Table 4.17 Predicted water quality within sewage plume

	Pollutant Concentration at 360m from Outfall				WSD Standards at Saltwater Intake
	Within the Plume		Depth Averaged ^(1,2)
	Existing	Future	Existing	Future
Wet Season Scenario
Dilution Factor	57.0	8.4	1532.3	386.3	N/A
BOD (mg L^-1)	5.1	30.3	0.9	1.3	<10
SS (mg L^-1)	10.0	35.2	5.8	6.2	<10 (target), <20 (tolerable)
NH₃-N (mg L^-1)	0.66	3.18	0.24	0.28	<1
E. coli (count per 100 mL)	3.57 x 10⁵	2.37 x 10⁶	1.88 x 10⁴	5.76 x 10⁴	<20,000
Dry Season Scenario
Dilution Factor	51.8	8.2	1626.0	431.4	N/A
BOD (mg L^-1)	5.5	31.1	0.9	1.3	<10
SS (mg L^-1)	10.4	36	5.8	6.2	<10 (target), <20 (tolerable)
NH₃-N (mg L^-1)	0.7	3.3	0.24	0.28	<1
E. coli (count per 100 mL)	3.92 x 10⁵	2.44 x 10⁶	1.81 x 10⁴	5.21 x 10⁴	<20,000

Notes:

1. The wet season plume thickness for the existing and future scenarios are 0.37 m and 0.22 m respectively, while those of the dry season are 0.32 m and 0.19 m respectively.

2. The depth averaged values are calculated based on a water depth of 10 m and the corresponding plume thickness.

3. The results presented are based on the Full Reclamation option.

Table 4.17a Cumulative Impact of the New Kwun Tong Nullah, New YTB Stormwater Culvert and Emergency Discharge from the Yau Tong Sewage Pumping Station – Comparison of Predicted Water Quality with WQO within sewage plume at the NCKLSPS Saltwater Intake

	Pollutant Concentration at 360 m from Outfall		WSD Standards at Saltwater Intake
	Depth Averaged		WSD Standards at Saltwater Intake
	Within the Plume ⁽¹⁾	Depth Averaged ⁽²⁾
Wet Season Scenario
BOD (mg L^-1)	30.54	1.54	< 10
SS (mg L^-1)	36.12	7.12	< 10 (target), < 20 (tolerable)
NH₃-N (mg L^-1)	3.20	0.30	< 1
E. coli (count per 100 mL)	2.38 x 10⁶	69881	< 20000
Dry Season Scenario
BOD (mg L^-1)	31.34	1.54	< 10
SS (mg L^-1)	36.92	7.12	< 10 (target), < 20 (tolerable)
NH₃-N (mg L^-1)	3.32	0.30	< 1
E. coli (count per 100 mL)	2.45 x 10⁶	64381	< 20000

Notes:

1. The wet season plume thickness for the existing and future scenarios are 0.37 m and 0.22 m respectively, while those of the dry season are 0.32 m and 0.19 m respectively.

2. The depth averaged values are calculated based on a water depth of 5 m and the corresponding plume thickness.

3. The results presented are based on the Full Reclamation option.

4.6.40 The depth averaged results indicated that the WSD water quality standards, in terms of BOD₅, SS and ammoniacal nitrogen, at the saltwater intake will be satisfied, while the E. coli standards will be exceeded in the future scenario (Tables 4.17 and 4.17a). However, the sewage plume is buoyant at the surface, where pollutants are concentrated with a thickness of less than 0.37m. To avoid abstracting the sewage plume water, it is therefore recommended that the saltwater intake should be located below a depth of approximately -2.0 mPD. The intake water will then be expected to meet all the WSD standards.

4.6.41 Discharge through the emergency outfall is a rare event. Should a discharge be made through the emergency outfall, it is recommended that DSD should inform WSD of the details of such discharge, e.g. volume, timing and duration, in advance if possible. It is also recommended that DSD should minimize the discharge and liaise with WSD to avoid discharge during the peak operation hours of the WSD’s saltwater pumping station.

4.6.42 In the Minimized Reclamation option, the CKLSPS saltwater intake and the Yau Tong Sewage Pumping Station emergency outfall will remain at their existing location, which are separated further apart than that in the proposed reprovisioned locations. Hence, unacceptable water quality impact at the existing CKLSPS intake is not anticipated.

4.7 Construction Phase Impact Assessment

Potential Sources of Impact

4.7.1 Potential water quality impacts during the construction phase of YTB reclamation (Full Reclamation option) are summarized below:

· Increase of SS concentration due to dredging and filling activities within the site, and the cumulative impacts from concurrent construction activities in the vicinity of YTB, such as South East Kowloon Development (SEKD), Reclamations for the Western Coast Road (WCR-Coastal option), Tseung Kwan O (TKO) Cargo Working Area (CWA) and TKO New Town intensification and extension;

· Release of contaminants during dredging of marine mud;

· Release of contaminants through vertical band drains during consolidation of reclamation; and

· Local deterioration of water quality due to temporary diversion of stormwater culvert during interim stage of the reclamation.

Prediction and Evaluation of Impact

Sediment Plume Modelling for Dredging and Filling Activities

4.7.2 One of the major concerns of the present study is to minimize the water quality impact, particularly the SS concentration, associated with the sand filling and mud dredging of the YTB reclamation. The potential release of contaminants during dredging of contaminated mud will also be addressed.

4.7.3 Numerical models, namely MIKE 21 and MIKE 3, from the Danish Hydraulic Institute (DHI) were used to simulate the dispersion and transport of sediment released during the dredging and filling activities. The modelling details are included in Section 4.4 and the results are presented in the following sections.

Worst-Case Impact of YTB reclamation (Full Reclamation option) – Scenario 2A

4.7.4 Assumptions made in the simulations for the YTB reclamation are as follows:

· The dry densities of filling sand and harbour mud are 1835 kg m^-3 and 1750 kg m^-3 respectively, based on the geotechnical site investigation for the YTB reclamation.

· Sand filling will be carried out by barges using bottom dumping. Spilling occurs during the first 10 minutes for each 1 hour dumping cycle, 10 hours per day, 7 days per week.

· Spill loss during mud dredging by 2 x 10 m³ open bucket grab dredger will be continuous, 10 hours a day, 7 days per week.

· The spill amount will be 1.8% and 3.7% of the mud dredged and sand filled respectively.

· Spilling is assumed to take place at the water surface.

4.7.5 According to the preliminary construction program (Appendix 2A), the YTB reclamation (Full Reclamation option) can be divided into 3 different phases, namely, the seawall construction, Phase 1 and Phase 2 reclamations. The highest dredging or filling rate for the different construction phases were identified (Table 4.18). The corresponding source locations are given in Figure 4.6b.

4.7.6 The reclamation phasing mentioned above is also valid for the Minimized Reclamation with the reclamation extent reduced to the mouth of YTB. Furthermore, it is envisaged that the production rate for the Minimized Reclamation option will be the same as, if not less than, that of the Full Reclamation option. Hence, the present simulation, assuming the Full Reclamation option for YTB, represents the conservative worst case construction impact. The recommended mitigation measures proposed under this section is fully applicable to both the Full and the Minimized Reclamation options. For simplicity, it will be assumed in the following discussions of construction phase impacts that “YTB reclamation” refers to the “Full Reclamation option”, unless specified otherwise.

Table 4.18 Highest Dredging and Filling Rates of YTB Reclamation (Full Reclamation Option) (Scenario 2A)

Source ID	Activity	Approx. Duration ⁽⁵⁾ [days]	Maximum Production Rate [m³ day^-1]	Sediment Loss Rate [kg s^-1]
Seawall Construction
S	Mud dredging for seawall foundation	48	1554	1.36
T	Sand filling for seawall foundation and conventional seawall construction	48	2260	4.26
Phase 1 Main Reclamation
R1	Place sand blanket (1m) and bulk filling below sea level for Phase 1 main reclamation of YTB	320	10000 ⁽⁶⁾	113.2
Phase 2 Main Reclamation
R2	Place sand blanket (1m) and bulk filling below sea level for Phase 2 main reclamation of YTB	80	10000 ⁽⁶⁾	113.2

Notes:

1. The dry densities of filling sand and harbour mud are 1835 kg m^-3 and 1750 kg m^-3 respectively.

2. For sand filling by bottom dumping, spilling will only occur during the first 10 minutes for each 1 hr dumping cycle, 10 hours per day, 7 days per week.

3. Spill loss during mud dredging by 2 x 10 m³ open bucket grab dredger will be continuous, 10 hours a day, 7 days per week.

4. The spill amount will be 1.8% and 3.7% for mud dredging and sand filling respectively.

5. The duration of each operation is based on the preliminary construction program for the Full Reclamation option (Appendix 2A). The period will be shortened accordingly if the Minimized Reclamation option is chosen instead.

6. In the preliminary construction program (Appendix 2A), an average production rate of 4000 m³ day^-1 is assumed, while the sand filling rate of 10,000 m³ day^-1 is the highest practicable rate envisaged in the YTB reclamation.

4.7.7 To determine the worst case of the YTB reclamation (Full Reclamation option), model runs were performed for the three different phases. The results are presented below.

Seawall Construction Impact – Scenario 2A_SW

4.7.8 The major source of sediment spill during the seawall construction can be associated with the mud dredging (Source S) and back filling with sand (Source T) for the seawall foundation. Open bucket grab dredgers are assumed for both dredging and filling activities.

Water Quality in Victoria Harbour Water Control Zone (VHWCZ)

4.7.9 The predicted suspended solid (SS) elevations in Victoria Harbour are shown in Figures 4.19 – 4.22 for the dry season and Figures 4.23 – 4.30 for the wet season, spring and neap tides.

4.7.10 The dry season depth averaged SS concentration indicated that the sediment plume due to the seawall construction is localized in the vicinity of YTB (Figures 4.19 – 4.20). The allowable increase in depth averaged SS concentration of 3.2mgL^-1, i.e. 30% above the ambient level as required by the WQO (Section 4.3.2), is satisfied in the VHWCZ. SS elevation of up to 9 mgL^-1, exceeding the WQO, is limited to within 100m from the waterfront extending from the Eastern Breakwater in SEKD to the mouth of Sam Ka Tsuen Typhoon Shelter. The top 5m average SS concentration indicates that the surface plume is slightly smaller than the depth average plume (Figures 4.21 – 4.22).

4.7.11 The WQO for SS in the VHWCZ is also satisfied in the wet season. The sediment plume in the wet season neap tide is similar to that in the dry season, with a slightly lower exceedance between YTB and Sam Ka Tsuen Typhoon Shelter (Figures 4.27 – 4.28). During wet season spring tide, the sediment plume is drifted towards the western side of YTB with depth averaged SS concentration of up to 15 mgL^-1 between the Eastern Breakwater and YTB, which is higher than that in the dry season.

Water Quality at the Water Sensitive Receivers (WSRs)

4.7.12 As discussed earlier in Section 4.5, three main WSRs, namely, Dairy Farm saltwater intake (DFSI), WSD’s Cha Kwo Ling (CKLSPS) and Yau Tong (YTSPS) Saltwater Pumping Stations, were identified in the present study. In general, these intakes are located within a few metres from the water surface, where the water quality is of main concern. In the sediment plume model, results are extracted for the top 5m layer for comparison. To assess the impact at the WSRs, time series of the SS elevation are extracted (Appendix 4D) and added to the ambient 90 percentile surface SS concentration of 6.6 mgL^-1, based on EPD’s routine monitoring data (Table 4.5), giving the absolute SS concentration at the WSR. The statistics of SS concentration at the WSRs are summarised in Table 4.19. The warm up period of the first 1.5 days, as shown in the time series plot in Appendix 4D, are excluded from the statistical calculations.

4.7.13 During the seawall construction (Scenario 2A_SW) in the wet and dry seasons, the mean SS concentration ranges from 8.7 mgL^-1 at the YTSPS to 21 mgL^-1 at the DFSI, while the maximum SS concentration ranges from 26.1 mgL^-1 at the YTSPS to 91 mgL^-1 at the DFSI (Table 4.19). It should be noted that the variation of SS concentration at the WSRs in the wet season is generally greater than that in the dry season (Table 4.19).

4.7.14 In general, the SS concentration at the existing WSRs is in exceedance of the WSD target (tolerable) limit of 10 mgL^-1 (20 mgL^-1) (Table 4.19). The percentage time in compliance with the WSD target (tolerable) limit at the CKLSPS and YTSPS are 42.9% (68.5%) and 51.3% (80%) respectively, while the SS standard of 20 mgL^-1 at the DFSI is satisfied for 69.6% of the time. The above suggests that the CKLSPS is the most susceptible to the impact of the dredging and filling works for the seawall foundation.

Table 4.19 A Summary of Time Series Statistics of SS concentration at the WSRs for Scenario 2A

Absolute SS concentration ⁽²⁾ [mgL^-1]	Unmitigated			Mitigated
Absolute SS concentration ⁽²⁾ [mgL^-1]	Diary Farm Saltwater Intake (DFSI)	Cha Kwo Ling Saltwater Intake (CKLSPS)	Yau Tong Saltwater Intake (YTSPS)	Diary Farm Saltwater Intake (DFSI)	Cha Kwo Ling Saltwater Intake (CKLSPS)	Yau Tong Saltwater Intake (YTSPS)
Scenario 2A_SW - YTB Seawall Construction ^5(a,b,d)
Dry Season, Spring-Neap Cycle
Mean SS conc	19.3	17.9	14.6	3.7	3.5	3.3
Maximum SS conc	79.0	74.6	63.9	8.4	8.1	7.2
Percentage time with SS < 10 mgL^-1	46.1%	42.9%	51.3%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	69.6%	68.5%	80.0%	100.0%	100.0%	100.0%
Wet Season, Spring Tide
Mean SS conc	21.0	18.6	8.7	3.8	3.6	2.8
Maximum SS conc	78.5	74.8	26.1	8.4	8.1	4.2
Percentage time with SS < 10 mgL^-1	48.4%	50.8%	77.2%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	69.5%	69.7%	98.8%	100.0%	100.0%	100.0%
Wet Season, Neap Tide
Mean SS conc	18.9	17.1	11.5	3.6	3.5	3.0
Maximum SS conc	91.0	70.9	43.1	9.4	7.8	5.6
Percentage time with SS < 10 mgL^-1	52.7%	53.2%	76.6%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	76.7%	77.7%	85.3%	100.0%	100.0%	100.0%
Scenario 2A_P1 - YTB Phase 1 Reclamation ^5(c,d)
Dry Season, Spring-Neap Cycle
Mean SS conc	19.6	20.0	15.9	1.9	1.9	1.7
Maximum SS conc	90.2	145.0	90.5	6.4	9.9	6.4
Percentage time with SS < 10 mgL^-1	26.8%	40.8%	50.6%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	62.4%	64.5%	75.0%	100.0%	100.0%	100.0%
Wet Season, Spring Tide
Mean SS conc	9.7	10.1	25.4	1.3	1.3	2.3
Maximum SS conc	56.2	52.7	183.7	4.2	4.0	12.4
Percentage time with SS < 10 mgL^-1	74.2%	75.7%	49.6%	100.0%	100.0%	99.3%
Percentage time with SS < 20 mgL^-1	95.0%	93.7%	70.1%	100.0%	100.0%	100.0%
Wet Season, Neap Tide
Mean SS conc	21.0	19.1	31.6	2.0	1.9	2.7
Maximum SS conc	99.0	145.3	177.0	7.0	9.9	12.0
Percentage time with SS < 10 mgL^-1	41.1%	52.3%	43.8%	100.0%	100.0%	96.7%
Percentage time with SS < 20 mgL^-1	63.4%	70.4%	62.0%	100.0%	100.0%	100.0%
Scenario 2A_P2 - YTB Phase 2 Reclamation 5(c,d,e)
Dry Season, Spring-Neap Cycle
Mean SS conc	69.3	67.4	25.0	3.5	3.4	1.8
Maximum SS conc	209.8	210.2	147.2	8.9	8.9	6.5
Percentage time with SS < 10 mgL^-1	1.2%	3.0%	37.5%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	8.2%	12.7%	58.5%	100.0%	100.0%	100.0%
Wet Season, Spring Tide
Mean SS conc	14.6	14.9	19.4	1.4	1.4	1.5
Maximum SS conc	43.1	83.7	153.4	2.5	4.0	6.7
Percentage time with SS < 10 mgL^-1	46.3%	61.9%	50.0%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	80.4%	78.9%	71.0%	100.0%	100.0%	100.0%
Wet Season, Neap Tide
Mean SS conc	42.3	43.5	23.5	2.4	2.5	1.7
Maximum SS conc	145.6	164.5	142.3	6.4	7.1	6.3
Percentage time with SS < 10 mgL^-1	13.3%	25.5%	54.6%	100.0%	100.0%	100.0%
Percentage time with SS < 20 mgL^-1	27.5%	39.7%	68.5%	100.0%	100.0%	100.0%

Notes:

1. Calculations are based on the top 5m layer SS elevation modelling results at the WSRs.

2. Absolute SS concentration takes into account surface mean SS concentration of 6.6 mgL^-1. (Data source: EPD Monitoring Station VM1 for period 1/96 to 8/98)

3. The WSD target and tolerable limits for SS concentration are 10 mgL^-1 and 20 mgL^-1 respectively.

4. Sand filling by bottom dumping is assumed for the main reclamation in Phases 1 and 2. The duration of spill is assumed to take place in 10 minutes per 1 hr operation cycle, 10 cycles per day.

5. Mitigation measures:

a. Closed grab with silt curtain will be used for both filling and dredging activities during the construction of seawall, which gives a sediment loss reduction factor of 5 times as compared to that using the open grab alone.

b. A single layer of silt screen will be placed around the WSRs.

c. 2 layers of silt screen will be placed around the WSRs and a single layer of silt screen will be placed across the YTB marine access to Phase 1 and Phase 2 reclamation.

d. SS reduction factor of 2.5 times can be achieved using a silt screen. (WCR Final EIA Report and Pak Shek Kok Reclamation - Public Dump EIA Study, Final Report)

e. The production rate is reduced to 6,000 m³ day^-1.

6. The results presented are based on the Full Reclamation option.

4.7.15 Non-compliances with the WQO near YTB and the WSD target (tolerable) limits at the identified WSRs, during the seawall construction (Scenario 2A_SW), necessitate the implementation of mitigation measures to minimize the impact on water quality. Hence, mitigation measures for the dredging and filling works have been devised and are described in detail in Section 4.8.3. The mitigated SS concentration is estimated and shown in Table 4.19.

4.7.16 The existing and reprovisioned Yau Tong Saltwater Pumping Stations (YTSPS) under the WCR-Coastal option reclamation are located at approximately the same distance from the YTB reclamation works. Hence, the water quality impact at the reprovisioned YTSPS is expected to be similar to those predicted at the existing YTSPS. In the unlikely event that the reprovisioned YTSPS commences operation during the YTB reclamation (Full Reclamation option), the recommended mitigation measure for the existing YTSPS should be implemented at the reprovisioned YTSPS to ensure that water quality complies with the WSD target limit at the saltwater intake.

Mitigation Measures for Stormwater Box Culvert and Seawall Construction

4.7.17 The mitigation measure proposed for the stormwater box culvert and the seawall construction in YTB include:

· Close grab with silt curtain will be used for the dredging and filling operations, which gives a SS loss reduction factor of 5 times lower that using an open grab alone (Figure 4.79);

· A single layer of silt screen will also be placed at the saltwater intakes of the WSRs giving a SS reduction of 2.5 times at the WSRs (Figures 4.79).

Mitigated Water Quality in VHWCZ

4.7.18 From the unmitigated result for the seawall construction (Scenario 2A_SW) (Section 4.7.11), the highest depth averaged SS elevation of 15 mgL^-1 in the vicinity of YTB is found in the wet season spring tide (Figures 4.27–4.28). With the implementation of the close grab with silt curtain, the maximum elevation will be reduced to 3 mgL^-1, satisfying the WQO of 3.2 mgL^-1 in the VHWCZ.

Mitigated Water Quality at the WSRs

4.7.19 With the implementation of the proposed mitigation measures during the seawall construction (Sections 4.7.17 and 4.8.3), the mean SS concentration at the WSRs is reduced and varies from 2.8 mgL^-1 at the YTSPS to 3.8 mgL^-1 at the DFSI (Table 4.19). The maximum SS concentration is also reduced correspondingly and ranges from 4.2 mgL^-1 at the YTSPS to 9.4 mgL^-1 at the DFSI. These are lower than the WSD target limit for SS at the saltwater intakes and thus, 100% compliance can be achieved at the WSRs.

Impact of Phase 1 Reclamation – Scenario 2A_P1

4.7.20 When the seawall is formed across the mouth of YTB, the main reclamation in Phase 1 will begin (Figure 2.4b). The main works involves bulk filling by bottom dumping within the partially enclosed YTB with a 50 m opening at the seawall for marine access (Figure 4.82).

4.7.21 It is estimated that the maximum possible filling rate by bottom dumping is 10000 m³ day^-1. Based on the assumptions made in Section 4.7.3, the sediment loss rate is estimated to be 113.2 kg s^-1 (Table 4.18). In Scenario 2A_P1, a single source (Source R1) is used to model the sediment plume due to bulk filling in Phase 1 reclamation (Figure 4.6b).

Water Quality in Victoria Harbour Water Control Zone (VHWCZ)

4.7.22 The predicted SS elevations in Victoria Harbour are shown in Figures 4.31–4.34 for the dry season and Figures 4.35–4.42 for the wet season, spring and neap tides.

4.7.23 In the dry season, the depth averaged sediment plume of Phase 1 reclamation (Scenario 2A_P1) is effectively contained within YTB bounded by the seawall (Figures 4.35–4.36). The depth averaged SS elevation in Victoria Harbour is generally below 3 mgL^-1, lower than allowable increase of 3.2 mgL^-1 as stipulated in the WQO of VHWCZ. Nevertheless, exceedance with depth averaged SS elevation of up to 23 mgL^-1 is observed near YTB, extending along the coastline between the reprovisioned Kwun Tong Typhoon Shelter (NKTTS) and Lei Yue Mun. The area of exceedance lies within 500 m from the existing coastline near the Eastern Breakwater in the SEKD and 100 m from the mouth of Sam Ka Tsuen Typhoon Shelter. Furthermore, the top 5m surface plume is generally smaller than the depth averaged plume (Figures 4.37-4.38).

4.7.24 The sediment plumes in the wet season, spring and neap tides are similar to the dry season plume. However, the plume in the wet season, spring tide does not extend into the reprovisioned Kwun Tong Typhoon Shelter which is different from the dry season plume. In general, the wet season plumes extend by approximately 250 m further away from the coastline at the mouth of Sam Ka Tsuen Typhoon Shelter than that of the dry season plume. Furthermore, the surface plumes in the wet season, spring and neap tides are generally smaller than the depth averaged plumes similar to that in the dry season.

Water Quality at the Water Sensitive Receivers (WSRs)

4.7.25 The time series statistics of the SS concentration at the WSRs in Scenario 2A_P1 are shown in Table 4.19. In the wet and dry seasons, the mean SS concentration during the Phase 1 reclamation, which varies between 9.7 mgL^-1 at the DFSI and 31.6 mgL^-1 at the YTSPS, is higher than that during the seawall construction. The maximum SS concentrations, ranging from 52.7 mgL^-1 at the CKLSPS to 183.7 mgL^-1 at the YTSPS, are in exceedance of the WSD target (tolerable) limit of 10 mgL^-1 (20 mgL^-1). The percentage time in compliance with the WSD target (tolerable) limit at the CKLSPS and YTSPS are 40.8% (64.5%) and 43.8% (62%) respectively, while the SS standard of 20 mgL^-1 at the DFSI is satisfied for 62.4% of the time. The above observations suggest that the YTSPS is the most susceptible to the impact of the filling works during the Phase 1 reclamation (Scenario 2A_P1).

Mitigation Measures for Phase 1 Reclamation

4.7.26 In order to minimize the water quality impact in the VHWCZ and at the WSRs, mitigation measures are proposed for the Phase 1 reclamation (Scenario 2A_P1). The mitigation measures proposed for Scenario 2A_P1 are as follows:

· A single layer of silt curtain will be placed across the 50 m opening of the seawall (Figure 4.80), giving a SS reduction factor of 2.5 times, before bottom dumping is performed;

· Double layers of silt screen will be placed at the saltwater intakes of the WSRs giving an overall SS reduction factor of 6.25 times at the WSRs (Figures 4.80).

Mitigated Water Quality in VHWCZ-

4.7.27 As discussed in Sections 4.7.22 – 4.7.24, the SS elevation in Victoria Harbour before mitigation generally satisfies the WQO for SS in the VHWCZ. With a silt curtain at the seawall opening in place, the sediment plume size is expected to be reduced and the sediment spill will be effectively contained within Phase 1 behind the seawall. It is anticipated that the SS elevation in the vicinity of YTB will also be reduced by 2.5 times. Hence, no major adverse impact in the VHWCZ is expected.

Mitigated Water Quality at the WSRs

4.7.28 With the implementation of double layers of silt screen at the WSRs and a silt curtain at the seawall opening (Sections 4.7.26 and 4.8.3), the mean SS concentration at the WSRs, which varies from 1.3 mgL^-1 at the CKLSPS to 2.7 mgL^-1 at the YTSPS, is significantly reduced as compared to the unmitigated case (Table 4.19). The maximum SS concentration is also reduced and ranges from 4 mgL^-1 at the CKLSPS to 12.4 mgL^-1 at the YTSPS. Slight exceedance of 2–2.4 mgL^-1 above the WSD target limit for SS is observed only in the wet season at the YTSPS. Nevertheless, the target limit of 10 mgL^-1 is satisfied at the YTSPS for at least 96.7% of the time in the wet season, while the tolerable limit of 20 mgL^-1 will be satisfied at all times.

Impact of Phase 2 Reclamation – Scenario 2A_P2

4.7.29 The Phase 2 reclamation is very similar to that in Phase 1 and will commence after the bored pile seawall, near the submarine pipelines, is constructed. The area of the Phase 2 reclamation is approximately one forth of the Phase 1 reclamation. Assuming the same production rate as for Phase 1 reclamation, the duration of bulk filling is also shortened proportionately (Table 4.18).

4.7.30 The maximum filling rate by bottom dumping for the Phase 2 reclamation (Scenario 2A_P2) is assumed to be 10,000 m^-3 day^-1, which is the same as that in Phase 1. Hence, the sediment loss rate of 113.2 kg s^-1 is also the same as that in Phase 1. In Scenario 2A_P2, a single source (Source R2) is used to model the sediment plume due to bulk filling in Phase 2 reclamation (Figure 4.6b).

Water Quality in Victoria Harbour Water Control Zone (VHWCZ)

4.7.31 The predicted SS elevations in Victoria Harbour are shown in Figures 4.43–4.46 for the dry season and Figures 4.47–4.54 for the wet season, spring and neap tides.

4.7.32 Due to the similarity of the bulk filling operations in the Phase 1 and Phase 2 reclamations, the size and extent of the sediment plumes are similar in the two cases (Figures 4.31 and 4.43). However, the sediment plumes for the Phase 2 reclamation (Scenario 2A_P2), in general, extend further into the reprovisioned Kwun Tong Typhoon Shelter than those in the Phase 1 reclamation (Scenario 2A_P1).

4.7.33 During the Phase 2 reclamation (Scenario 2A_P2), the SS elevation in Victoria Harbour are generally below 3 mgL^-1, satisfying the WQO for SS of 3.2 mgL^-1 in the VHWCZ (Figures 4.43–4.44). In the dry season, SS elevation of up to 123 mgL^-1, which is higher than that in the Phase 1 reclamation, is observed in the vicinity of YTB (Figure 4.44). The top 5m surface plume is smaller than the depth averaged plume (Figures 4.45–4.46).

4.7.34 In the wet season, spring tide, the sediment plume during the Phase 2 reclamation (Scenario 2A_P2) is similar to that in the dry season, while the plume in the wet season, neap tide extends even further into the reprovisioned Kwun Tong Typhoon Shelter. However, SS elevation of up to 83 mgL^-1 in the vicinity of YTB is lower than that in the dry season.

Water Quality at the Water Sensitive Receivers (WSRs)

4.7.35 Since the Phase 2 reclamation (Scenario 2A_P2) is closer to the DFSI and the CKLSPS than the Phase 1 reclamation, it is anticipated that the SS concentration will be higher during the Phase 2 reclamation. The mean SS concentration is between 14.6 mgL^-1 and 69.3 mgL^-1 at the DFSI, while the maximum ranges from 43.1 mgL^-1 at the DFSI to 210.2 mgL^-1 at the CKLSPS (Table 4.19). These are in exceedance of the WSD target and tolerable limits which require mitigation.

Mitigation Measures for Phase 2 Reclamation

4.7.36 In order to minimize the water quality impact in the VHWCZ and at the WSRs, mitigation measures are proposed for the Phase 2 reclamation (Scenario 2A_P2), similar to those for the Phase 1 reclamation. The mitigation measures proposed for Scenario 2A_P2 are as follows:

· A single layer of silt curtain will be placed across the 50 m opening of the seawall (Figure 4.81), giving a SS reduction factor of 2.5 times, before bottom dumping is performed;

· Double layers of silt screen will be placed at the saltwater intakes of the WSRs giving an overall SS reduction factor of 6.25 times at the WSRs (Figures 4.81);

· Since the area of the Phase 2 reclamation is smaller than that of the Phase 1 reclamation, it is envisaged that a maximum filling rate of 6,000 m³ day^-1 is more likely to be the actual case.

Mitigated Water Quality in VHWCZ

4.7.37 As discussed in Sections 4.7.31 – 4.7.34, the SS elevation in Victoria Harbour before mitigation generally satisfies the WQO in the VHWCZ. With the reduction in the production rate and the implementation of a silt curtain at the seawall opening, the size of the plume is expected to reduce significantly and thus, no major impact is expected in the VHWCZ.

Mitigated Water Quality at the WSRs

4.7.38 With the implementation of the proposed mitigation measures in the Phase 2 reclamation (Sections 4.7.36 and 4.8.3), the mean SS concentration at the WSRs is significantly reduced as compared to the unmitigated case to below 3.5 mgL^-1 (Table 4.19). Meanwhile, the maximum SS concentration at the WSRs is also reduced to below 8.9 mgL^-1. Hence, the WSD target limit for SS of 10 mgL^-1 at the WSRs is expected to be satisfied at all times.

Summary of YTB Reclamation (Full Reclamation option) Impact for Different Construction Phases – Scenario 2A

4.7.39 From the sediment plume model results for the different construction phases (Scenarios 2A_SW, 2A_P1 and 2A_P2), it is predicted that the impact of the YTB reclamation (Full Reclamation option) on Victoria Harbour is minimal and the WQO is satisfied in the VHWCZ, except in the vicinity of YTB. However, the SS concentration at the WSRs exceeds the corresponding SS requirements. Hence, mitigation measures, such as the use of silt curtain at the seawall openings, were proposed accordingly for the various construction phases. With the proposed mitigations, it is anticipated that the impact on Victoria Harbour and at the WSRs will be significantly reduced. The predicted SS concentration at the WSRs with mitigation is expected to satisfy the WSD target limit for SS of 10 mgL^-1 and the in house SS standard of 20 mgL^-1 at the DFSI. However, marginal exceedance for less than 3.3% of the time in the wet season is observed at the YTSPS during the Phase 1 reclamation which forms the worst case scenario (Scenario 2A_P1) for the YTB reclamation (Full Reclamation option).

4.7.40 With a reduction in the reclamation extent and duration of construction, together with a more streamlined new water front in the YTB reclamation (Minimized Reclamation option), it is expected that the water quality impacts, arising from the corresponding reclamation works, will be similar, and in reality less significant, than those predicted for the worst case scenario of the YTB reclamation (Full Reclamation option). Hence, with the implementation of the recommended mitigation measures as proposed in the different construction phases for the YTB reclamation (Full Reclamation option), unacceptable water quality impact is not anticipated during the construction phase of the Minimized Reclamation option.

Cumulative Impacts during Construction Phase – Scenario 2B

4.7.41 Cumulative impacts on water quality may arise during the dredging and filling works for the YTB Reclamation should other dredging and filling activities be underway near the study area. As described in Section 2, the dredging and filling works for the Yau Tong Bay Reclamation (Full Reclamation option) are estimated to commence in February, 2004 and will be completed by March, 2007. Possible concurrent construction works near the study area are indicated in Table 4.7, based on the construction programs for the South East Kowloon Development (SEKD), Western Coast Road (WCR-Coastal option), Tseung Kwan O (TKO) Cargo Working Area (CWA) and TKO New Town Intensification and Extension (NTIE). These are identified as the concurrent projects and are represented by 15 sediment sources (Sources A–M, P, Q) in the sediment plume model (Table 4.7).

4.7.42 The cumulative impacts of the concurrent construction works other than the YTB reclamation, are first simulated (Scenario 2B_BK). The impact of the YTB reclamation (Full Reclamation option) in Phase 1 (Source R1) is then added to the former giving the cumulative impact (Scenario 2B_CI). Details of the modelling assumptions in Scenario 2B are presented in Section 4.4.4 and the results are presented in the following sections.

Cumulative Impacts from Other Projects – Scenario 2B_BK

Water Quality in the VHWCZ

4.7.43 The predicted SS elevation in Victoria Harbour due to the construction activities of the concurrent projects, but without the YTB reclamation, is shown in Figures 4.55–4.58 for the dry season and Figures 4.59–4.66 for the wet season, spring and neap tides.

4.7.44 Since mitigation measures are assumed for all the concurrent projects listed in Table 4.7, except for the TKO New Town Intensification and Extension, the sediment plumes associated with the different dredging and filling activities are mainly localized in the corresponding works area, such as the Kowloon Bay (Sources B, F) and Kwun Tong Typhoon Shelters (Sources C, D) (Figures 4.55–4.56). The allowable increase in SS concentration under the WQO in the VHWCZ (i.e. 3.2mgL^-1) is generally satisfied for the wet and dry seasons. Nevertheless, the depth averaged sediment plume in the wet season, spring and neap tides are larger than that in the dry season, with slight exceedance across Victoria Harbour, towards Shau Kei Wan Typhoon Shelter (Figures 4.60 and 4.64). The wet season is, thus, the worst case scenario.

4.7.45 Without mitigation, the TKO New Town Intensification and Extension generates a large plume due to the high production rates and extends from Junk Bay into the Lei Yue Mun Channel, with SS elevation of up to 63 mgL^-1 in Junk Bay area. This explains the exceedance of the WQO for SS near the Shau Kei Wan Typhoon Shelter in the wet season.

4.7.46 Although YTB reclamation is not taken into account in the present Scenario 2B_BK, the sediment plume due to the construction works in the SEKD and the WCR-Coastal option extends across YTB with SS elevation of up to 23 mgL^-1. This suggests that the SS concentration in the vicinity of YTB due to the concurrent projects is in exceedance of the WQO. Hence, exceedance of the WQO locally around YTB is anticipated as the YTB reclamation commences.

Water Quality at the WSRs

4.7.47 A single layer of silt screen was proposed in the SEKD and WCR-Coastal option EIA studies to protect the WSRs from the construction impact. Together with the use of close grab with silt curtain for the dredging and filling activities, the SS concentration at the CKLSPS and DFSI is expected to meet the WSD target limit of 10 mgL^-1 and the in house SS standard of 20 mgL^-1 respectively at all times (Table 4.20). However, the variation of SS concentration at the YTSPS reveals that the cumulative impacts from other projects, without YTB reclamation, exceeds the WSD target (tolerable) limit of 10 mgL^-1 (20 mgL^-1) for up to 3.8% (1%) of the time. This can be attributed mainly to the unmitigated works of the TKO New Town Intensification and Extension (NTIE). With appropriate mitigation measures for the TKO NTIE, the SS concentration at the YTSPS is expected to satisfy the WSD target (tolerable) limit.

Table 4.20 A Summary of Time Series Statistics of SS concentration at the WSRs for Scenario 2B

Absolute SS concentration ⁽²⁾ [mgL^-1]	Unmitigated			Mitigated
Absolute SS concentration ⁽²⁾ [mgL^-1]	Diary Farm Saltwater Intake (DFSI)	Cha Kwo Ling Saltwater Intake (CKLSPS)	Yau Tong Saltwater Intake (YTSPS)	Diary Farm Saltwater Intake (DFSI)	Cha Kwo Ling Saltwater Intake (CKLSPS)	Yau Tong Saltwater Intake (YTSPS)
Scenario 2B_BK - Cumulative Impacts from Other Projects (excluding YTB reclamation)^7(a,b,d)
Dry Season, Spring-Neap Cycle
Mean SS conc	N/A	N/A	N/A	3.8	3.5	4.3
Maximum SS conc	N/A	N/A	N/A	14.7	7.2	17.1
Percentage time with SS < 10 mgL^-1	N/A	N/A	N/A	99.1%	100.0%	96.6%
Percentage time with SS < 20 mgL^-1	N/A	N/A	N/A	100.0%	100.0%	100.0%
Wet Season, Spring Tide
Mean SS conc	N/A	N/A	N/A	3.3	2.9	4.4
Maximum SS conc	N/A	N/A	N/A	13.0	4.5	32.0
Percentage time with SS < 10 mgL^-1	N/A	N/A	N/A	98.2%	100.0%	96.5%
Percentage time with SS < 20 mgL^-1	N/A	N/A	N/A	100.0%	100.0%	99.0%
Wet Season, Neap Tide
Mean SS conc	N/A	N/A	N/A	3.2	3.1	4.2
Maximum SS conc	N/A	N/A	N/A	7.0	4.2	21.0
Percentage time with SS < 10 mgL^-1	N/A	N/A	N/A	100.0%	100.0%	96.2%
Percentage time with SS < 20 mgL^-1	N/A	N/A	N/A	100.0%	100.0%	99.6%
Scenario 2B_CI – Cumulative impact (including YTB reclamation) ^7(a,c,d)
Dry Season, Spring-Neap Cycle
Mean SS conc	22.5	22.1	20.2	2.4	2.2	2.3
Maximum SS conc	91.7	148.5	94.7	6.7	10.5	7.1
Percentage time with SS < 10 mgL^-1	14.3%	26.4%	29.3%	100.0%	99.9%	100.0%
Percentage time with SS < 20 mgL^-1	53.0%	60.2%	65.1%	100.0%	100.0%	100.0%
Wet Season, Spring Tide
Mean SS conc	11.3	10.8	29.7	1.5	1.4	2.9
Maximum SS conc	57.5	53.4	185.8	5.2	4.1	12.9
Percentage time with SS < 10 mgL^-1	69.3%	72.2%	36.4%	100.0%	100.0%	97.7%
Percentage time with SS < 20 mgL^-1	91.7%	93.6%	63.6%	100.0%	100.0%	100.0%
Wet Season, Neap Tide
Mean SS conc	22.5	20.2	35.5	2.2	2.0	3.3
Maximum SS conc	99.7	146.5	194.1	7.1	10.1	16.7
Percentage time with SS < 10 mgL^-1	34.2%	46.6%	39.9%	100.0%	100.0%	94.8%
Percentage time with SS < 20 mgL^-1	60.0%	70.0%	59.5%	100.0%	100.0%	100.0%

Notes:

1. Calculations are based on the top 5m layer SS elevation modelling results at the WSRs.

2. Absolute SS concentration takes into account the 90 percentile surface SS concentration of 6.6 mgL^-1. (Data source: EPD Monitoring Station VM1 for period 1/96 to 8/98).

3. The WSD target and tolerable limits for SS concentration are 10 mgL^-1 and 20 mgL^-1 respectively.

4. The works for all the projects, including the WCR-Coastal option construction, TKO New Town Intensification and Extension and YTB reclamation, are assumed to take place 10 hrs daily, except for the works of the TKO CWA and the SEKD which operate 24 hrs and 16 hrs per day respectively.

5. All concurrent projects identified are assumed to be mitigated as recommended in their corresponding EIA studies, except for the TKO New Town Intensification which EIA study is in progress.

6. Sand filling by bottom dumping is assumed for the Phases 1 reclamation of YTB. The duration of spill is assumed to take place in 10 minutes per 1 hr operation cycle, 10 cycles per day.

7. Mitigation measures:

a) For all concurrent projects identified, except the YTB reclamation and TKO New Town Intensification and Extension, closed grab with silt curtain will be used for both filling and dredging activities giving a sediment loss reduction factor of 5 times as compared to that using the open grab alone.

b) A single layer of silt screen will be placed around the WSRs as recommended in other EIA studies.

c) A total of 2 layers of silt screen will be placed around the WSRs and a single layer of silt screen will be placed across the YTB marine access of Phase 1 and Phase 2 reclamation.

d) SS reduction factor of 2.5 times can be achieved using a silt screen. (WCR Final EIA Report and Pak Shek Kok Reclamation - Public Dump EIA Study, Final Report)

8. The results presented are based on the Full Reclamation option.

Cumulative Impact including YTB Reclamation (Full Reclamation option) – Scenario 2B_CI

Water Quality in the VHWCZ

4.7.48 Taking into account the Phase 1 reclamation of YTB (Source R1), without mitigation, the mean SS concentration in Victoria Harbour is shown in Figures 4.67–4.70 for the dry season and Figures 4.71–4.78 for the wet season, spring and neap tides.

4.7.49 With the contribution of the YTB reclamation (Scenario 2B_CI), the sizes of the sediment plume in the wet and dry seasons are marginally increased near YTB. Exceedance of the WQO for SS of up to 23 mgL^-1 is only observed locally. Hence, the WQO in the VHWCZ is expected to be satisfied with no major impact on Victoria Harbour.

Mitigated Water Quality in VHWCZ

4.7.50 Assuming the same mitigation measures proposed earlier for the Phase 1 reclamation of YTB (Scenario 2A_P1, Section 4.7.26), the contribution of the YTB reclamation to the sediment plume in the neighbouring waters will be reduced. It is anticipated that a SS reduction of 2.5 times across the silt curtain at the seawall opening in Phase 1 can be achieved, minimizing the impact of the YTB reclamation on Victoria Harbour.

Water Quality at the WSRs

4.7.51 Without mitigation for the YTB reclamation, the mean SS concentration at the WSRs due to the impacts of the concurrent activities varies between 10.8 mgL^-1 at the CKLSPS and 35.5 mgL^-1 at the YTSPS (Table 4.20). Meanwhile, the maximum SS concentration ranges from 53.4 mgL^-1 at the CKLSPS to 194.1 mgL^-1 at the YTSPS which are in exceedance of the WSD target and tolerable limits.

Mitigated Water Quality at the WSRs

4.7.52 Mitigation measures proposed for the Phase 1 reclamation of YTB (Scenario 2A_P1, Section 4.7.26) are also used to minimize the impact at the WSRs. SS reduction of 6.25 times can be achieved across the double layers of silt screen at the WSRs, while the silt curtain at the seawall opening of Phase 1 reclamation of YTB gives a SS reduction of 2.5 times. With the implementation of the above mitigation measures, it is anticipated that the mean and maximum SS concentration at the WSRs will be below 3.3 mgL^-1 and 16.7 mgL^-1. The WSD target limit for SS of 10 mgL^-1 is generally satisfied at the CKLSPS and YTSPS with slight exceedance at the latter for upto 5.2% of the time in the wet season, while the WSD’s in house tolerable limit for SS of 20 mgL^-1 will be satisfied at all times. The above represents the worst case cumulative impact at the YTSPS, taking into account the unmitigated works of the Tseung Kwan O New Town Intensification and Extension in Area 138 (TKO NTIE), is considered acceptable. With appropriate mitigation measures for the TKO NTIE, sediment plume dispersion of the marine works of TKO NTIE will be essentially confined within Junk Bay and the residual SS concentration at the YTSPS is expected to very similar to the mitigated water quality under the Scenario 2A_P1 (as presented in paragraph 4.7.28). That is, the residual SS level at the intake of YTSPS will comply the WSD SS tolerable limit (20 mgL^-1) all the time, but marginal exceedance of SS target limit (10 mgL^-1) (by maximum 2.4 mgL^-1) will occur for less than 3.3% of the time in the wet season.

Summary of Cumulative Impacts during Construction Phase – Scenario 2B

4.7.53 From the above discussions of the cumulative impacts due to the other concurrent activities in Victoria Harbour (Scenario 2B_BK) and the contribution from the YTB reclamation (Full Reclamation option) (Scenario 2B_CI), it is found that the YTB reclamation contributes significantly to safeguard the water quality of the harbour and only poses a minor impact to the neighbouring waters. Furthermore, by adopting the mitigation measures proposed for the Phase 1 reclamation of YTB (Scenario 2A_P1), the impact at the WSRs will be minimize with the SS concentration satisfying both the WSD target limit at the saltwater intakes and the in house standard for the DFSI. Although SS exceedance is predicted at the YTSPS as a result of the cumulative impacts from other projects (Scenario 2B_BK), the proposed mitigation measure is sufficient to reduce the overall impact, including the YTB reclamation (Full Reclamation option), to the relevant standards. In addition, it is most likely that mitigation measure will be imposed on the TKO New Town Intensification and Extension works, and thus, the present result serves as a conservative prediction.

4.7.54 With a reduction in the reclamation extent and duration of construction, together with a more streamlined new water front in the YTB Reclamation (Minimized Reclamation option), it is expected that the water quality impacts, arising from the corresponding reclamation works, will be similar, and in reality less significant, than those predicted for the worst case scenario of the YTB reclamation (Full Reclamation option). Hence, with the implementation of the recommended mitigation measures as proposed in the different construction phases for the YTB reclamation (Full Reclamation option), unacceptable water quality impact is not anticipated during the construction phase of the Minimized Reclamation option.

Impact of the temporary YTB Stormwater Culvert - Scenario 2C

4.7.55 Before the Phase 1 reclamation of YTB, the existing YTB stormwater culverts have to be diverted to avoid discharging into an embayment formed by the seawall (Figures 2.4a-d). A temporary stormwater culvert, in the form of an open channel, will be formed along the southern seawall extending to the mouth of YTB. Potential water quality deterioration and pollutant accumulation in Victoria Harbour are evaluated using the particle model (Appendix 4E), similar to that used for the impact assessment of the new Kwun Tong nullah and the new YTB storm culvert (Appendices 4A and 4C). The impact on the two existing WSRs, namely, the Cha Kwo Ling (CKLSPS) and Yau Tong (YTSPS) saltwater pumping stations, will be addressed.

4.7.56 Based on the population estimates in year 2011 from the Kowloon District Office of the Planning Department and the per capita load factor in the DSD Sewerage Manual, the total load generated in the Yau Tong catchment are estimated and shown in Table 4.14. The details of population estimates are given in Appendices 4B-1 and 4B-2. With the implementation of the SMPs[4], it is conservatively assumed that 5% of the total load in the Yau Tong sewage catchment, as adopted in the SEKD Feasibility Study, will be discharged through the existing YTB stormwater culvert during the YTB reclamation. Dilution and dispersion are simulated using the particle model (Appendix 4E). To assess the worst case impacts, tidal mixing and decay within the channel are not taken into account at present. This is a conservative assumption as all the new developments in the Yau Tong area will be connected to public sewers which minimizes the pollution load to the stormwater culvert through expedient connections, and the % load interception by the storm system is expected to lower.

4.7.57 The increase in BOD₅, SS, Ammoniacal Nitrogen and E. coli are predicted according to the estimated pollution load for the temporary YTB stormwater culvert and the particle model results. Comparison between the predicted values and the ambient in year 1997 are shown in Table 4.21. The predicted increase in BOD₅, SS and Ammoniacal Nitrogen are very low in comparison with the WQOs for the VHWCZ. Since no secondary contact recreation zone has been identified within Victoria Harbour, the increase in E. coli of 2370 counts per 100mL as compared to the ambient level of 5780 counts per 100mL is considered acceptable. The above confirms that minor impact is expected in the VHWCZ. At the existing WSRs, the BOD₅, SS and E. coli levels, taking into account the predicted maximum increases and the ambient levels, are lower than the WSD target limits, indicating that the WSD saltwater intakes are only marginally affected by the temporary diversion of the stormwater culvert. As mentioned in the previous paragraph, decay and mixing processes in the stormwater culvert are omitted in the present calculation, which tend to reduce the pollutant concentration in the storm effluent and thus the effective pollution load discharging into Victoria Harbour. Hence, the actual water quality is expected to be better than that predicted.

Table 4.21 Impact of Temporary Stormwater Culvert in YTB (Scenario 2C) – Comparison of Predicted Water Quality with WQO in VHWCZ and WSD Standards at Saltwater Intakes

Description	BOD₅ [mgL^-1]	SS [mgL^-1]	Ammoniacal Nitrogen [mgL^-1]	E. coli [count per 100mL]
Victoria Harbour Water Control Zone (VHWCZ)
Ambient level ⁽¹⁾	0.7	5.6	0.22	5780
Predicted increase in VHWCZ	< 0.04	< 0.05	< 2.86 x 10^-3	< 2370
WQO	N/A ⁽⁶⁾	< 30% over ambient and median < 25mgL^-1	< 0.44 ⁽⁵⁾	N/A ⁽⁴⁾
Existing Water Sensitive Receivers (WSRs)
Maximum increase at CKLSPS ⁽²⁾	0.03	0.03	2.12 x 10^-3	1750
Maximum increase at YTSPS ⁽²⁾	0.2	0.21	1.32 x 10^-2	10900
WSD target limit at saltwater intake	< 10	< 10	< 1	< 20000

Notes:

1. Data source: EPD routine monitoring data at station VM1 in year 1997.

2. CKLSPS and YTSPS represent the existing Cha Kwo Ling and Yau Tong saltwater pumping stations respectively. Water quality impacts on the potential reprovisioned CKLSPS and the reprovisioned YTSPS are not anticipated during the construction phase of the YTB reclamation (see para. 4.7.12.4 and 4.7.12.5).

3. Data presented are depth averaged, except at the WSRs where top 5m layer data are considered.

4. No secondary contact recreation and bathing beach sub-zone is identified in VHWCZ.

2. No WQO standards for BOD5 in marine waters.

3. The results presented are based on the Full Reclamation option.

4.7.58 In the unlikely event that the reprovisioned YTSPS commences operation before the YTB reclamation begins, the temporary stormwater culvert in YTB will have to be extended to the new waterfront of the Western Coast Road (WCR-Coastal option) Reclamation. The relative position of the extended temporary stormwater culvert outfall and the reprovisioned YTSPS will be approximately the same as that between the proposed temporary outfall and the existing YTSPS. Considering the large margin between the predicted water quality and the WSD target limit at existing YTSPS, unacceptable impact is not expected at the reprovisioned YTSPS.

4.7.59 As discussed in the operation phase water quality impact assessment sections, reprovisioning of the CKLSPS will not be required under the proposed YTB development. An advantage of the Full Reclamation option over the Minimized Reclamation option is that land provisions can be made available at the new water front of the YTB reclamation for future reprovisioning or upgrading of the CKLSPS. However, this potential reprovisioning of the CKLSPS will not be possible before or during the YTB reclamation. Hence, no water quality impact on the reprovisioned CKLSPS is envisaged from the YTB reclamation and the temporary stormwater culvert.

Potential Release of Contaminants during Dredging and Surcharging

4.7.60 The assessment of sediment contamination were performed which included sampling and testing of mud from the seabed at 9 locations so as to quantify the extent of contamination within the proposed reclamation area (Full Reclamation option). The locations of vibrocores are shown in Figure 5.1. Sediment samples recovered from vibrocoring were laboratory tested for heavy metals. The results of the sediment testing indicate that seriously contaminated, Class C material, was found at all four vibrocore locations along the proposed seawall and at the five vibrocores within the reclamation site for the Full Reclamation option. Full details of the sediment quality analysis, the parameters tested, and the contaminated sediments classification are presented in Section 5.4.

4.7.61 During the dredging of contaminated sediments, there is a potential impact on water quality through the release of heavy metals into the surrounding water column. As stipulated in the EPD Technical Circular No. 1-1-92, Classification of Dredged Sediments for Marine Disposal, the seriously contaminated material must be dredged and transported with great care. The dredged sediment cannot be dumped in the gazetted marine disposal grounds and must be effectively isolated from the environment upon final disposal. Therefore appropriate dredging methods have been incorporated into the recommended mitigation measures and include the use of closed-grab dredgers.

4.7.62 An indication of the likelihood of release of heavy metals from the excavated marine mud is given by the results of the elutriation tests as described in Section 5.4. If the contaminant levels are higher in the elutriates in comparison with the blanks (marine water from the same site), it can be concluded that the contaminants are likely to be released into the marine waters during dredging activities. The concentrations of the metals copper, nickel, zinc and lead in the elutriate samples were higher than the background values recorded in the marine water sample. The results indicate that these four heavy metal species are likely to be released from the sediment into the marine waters when the seabed is disturbed during dredging activities. As there is no existing legislative standard or guideline for individual heavy metal contents in marine waters, the UK Water Quality Standards for Coastal Surface Water [5] is adopted as the assessment criteria. As shown in Table 4.22 below, the heavy metal concentrations (other than mercury) in the elutriate samples fall within the UK Water Quality Standards. The detection limit for mercury is higher than the UK Water Quality Standard and therefore it is not possible to draw a similar conclusion based on the elutriate test results. Hence, an alternative method is considered below.

4.7.63 A quantification of the predicted release of the metal mercury from pore water during dredging has been made based on the equation adopted from the “Water Quality Prevention, Identification and Management of Diffuse Pollution” by Vladimir Novotny & Harvey Olem, Van Nostrand Reinhold, New York, 1994. (This equation was used in the water quality assessment undertaken in the EIA Study for the South East Kowloon Development Feasibility Study). Based on the measured concentration of mercury in the marine sediment (the highest concentration of 4.5 mg/kg recorded at vibrocore V4 was used as a worst-case scenario), the predicted maximum desorbed concentration of mercury in the pore water is estimated to be 0.026mg l^-1, which is below the UK Water Quality Standard. Details of the calculation are provided in Appendix 4F. Therefore it is concluded that adverse water quality impacts arising from the release of heavy metals from the contaminated sediment are not anticipated during the dredging works.

Table 4.22 Comparison of Sediment Elutriate Test Results with UK Water Quality Standards

Metal Content (mg l^-1)	Vibrocore Location									Water Quality Standard of Receiving Water (mg l^-1)	Exceedance of Water Quality Standard
	V1	V2	V3	V4	V5	V6	V7	V8A	V9B
Cu	0.8	0.9	1.8	<0.5	<0.5	0.7	1	3.2	<0.5	5	No
Ni	<3	<3	<3	<3	7	5	3	8	12	30	No
Zn	5	8	5	7	8	5	5	5	6	40	No
Pb	<0.5	0.7	0.6	<0.5	0.6	<0.5	<0.5	<0.5	<0.5	25	No
Cd	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	2.5	No
Cr	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	15	No
Hg	<2	<2	<2	<2	<2	<2	<2	<2	<2	0.3	*

* Detection limit for Hg is higher than the UK Water Quality Standard of 0.3 mg l^-1

4.7.64 Elutriation tests were also conducted to assess the likelihood of release of organic compounds, such as total polychlorinated biphenyls (PCBs) and total polyaromatic hydrocarbons (PAHs), and tributyltin (TBT) from the marine mud during dredging activities. As there are no existing legislative standards or guidelines for the contaminants PCB, PAH and TBT in marine waters, reference is made to the recommendations and conclusions of the consultancy study Review of Marine Water Quality Objectives of Hong Kong (Final Report, January 1997, Mouchel Asia Ltd. for EPD). This study concluded that PCBs and PAHs are primarily associated with sediments and therefore WQO for these parameters are not required. For TBT, a WQO was not recommended for Beneficial Uses 6, 7 and 8. The identified water sensitive receivers in the study area comprise saltwater intakes, which represent Beneficial Use 6 i.e. domestic and industrial purposes. As described in Section 5.4.8, the measured PCB and PAH concentrations in the elutriate samples tested from each vibrocore location were not higher than the background values recorded in the seawater sample from the site. Similarly, the measured TBT concentrations in the elutriate samples were not higher than the background values recorded in the seawater sample. Therefore, it can be concluded that adverse water quality impacts due to the potential release of the contaminants PCB, PAH and TBT from the sediment are not anticipated during the dredging activities.

4.7.65 Since the nutrient levels in the sediment is not expected to be a major concern in Yau Tong Bay, testing of nutrient levels is not included in the sediment testing plan. For the assessment of nutrient release during dredging, the typhoon shelter sediment quality data extracted from “Marine Water Quality in Hong Kong in 1997” prepared by EPD is used, which is similar to that in YTB (Appendix 4G). The sediment quality in the six typhoon shelters in the vicinity of YTB, namely, To Kwa Wan (VS20), Kwun Tong (VS14), Sam Ka Tsuen (VS13), Causeway Bay (VS12), Aldrich Bay (VS18) and Chai Wan (ES3) Typhoon Shelter, between 1993 and 1997, were analysed (Appendix 4G). The maximum levels of Ammoniacal Nitrogen (NH4N), Total Kjeldahl Nitrogen (TKN) and Total Phosphorus (TP) were 140 mg kg^-1, 1400 mg kg^-1 and 540 mg kg^-1 respectively. Assuming all the nutrients in the sediment will be released into the water column and based on the SS concentration of 3 mgL^-1 at the outer edge of the sediment plume from the modelling predictions (Figure 4.20), the corresponding increase in concentration of NH4N, TKN and TP at the plume boundary will be 4.2x10^-4 mgL^-1, 4.2x10^-3 mgL^-1, 1.62 x10^-3 mgL^-1 respectively. The predicted increases of NH4N, TKN and TP are less than 2% of the ambient levels, based on EPD’s routine monitoring data (Table 4.23), and the water quality is expected to satisfy the WQOs in the VHWCZ.

Table 4.23 Predicted Maximum Elevation of Nutrients Concentration during Mud Dredging for the Seawall Foundation.

Determinand	Elevation at Plume Boundary [mgL^-1]	Ambient Concentration in VHWCZ⁽¹⁾ [mgL^-1]	WQO [mgL^-1]
Ammoniacal Nitrogen (NH4N)	4.2x10^-4(0.2%)⁽³⁾	0.22	< 0.44⁽²⁾
Total Kjeldahl Nitrogen (TKN)	4.2x10^-3(0.4%)⁽³⁾	1.05	NA
Total Phosphorus (TP)	1.62x10^-3(2%)⁽³⁾	0.1	NA
Chemical Oxygen Demand (COD)	0.15	NA	NA

Notes:

1. Data source: EPD routine monitoring data at station VM1 in year 1997.

2. With reference to the WQO of 0.021 mgL^-1 for unionized ammonia, the total ammonia present at 23^oC and pH 8 is estimated to be 0.44. Calculations are based on EPD’s monitoring data at VM1 in year 1997.

3. Numbers in bracket represent the percentage increase over the ambient levels.

4.7.66 Similarly, the maximum Chemical Oxygen Demand (COD) of 50000 mg kg^-1 is expected to be reduced to 0.15 mgL^-1 at the sediment plume boundary. Considering the dissolved oxygen (DO) level of 5 mgL^-1 in Victoria Harbour, based on EPD’s routine monitoring at station VM1 in 1997, and the low COD of 0.15 mgL^-1, the WQO for DO of 4 mgL^-1 in the VHWCZ is expected to be satisfied. The above serves as a conservative or worst case assessment of the impact of nutrients release during dredging of marine mud and the actual situation is expected to be better than those predicted.

4.7.67 The proposed seawall for the Minimized Reclamation will be shortened accordingly and thus potential water quality impacts associated with dredging works will be minimized in terms of the duration of impact and the water quality is expected to be similar to those predicted above for the Full Reclamation option.

4.7.68 During the consolidation of the reclamation, the potential release of heavy metals and other sediment constituents in the contaminated pore water, which may escape through the installed vertical band drains, may affect water quality in Victoria Harbour.

4.7.69 As shown in Table 4.22, the measured heavy metal concentrations in the elutriate samples do not exceed the UK Water Quality Standards. Furthermore, as described in the previous paragraphs, the predicted maximum desorbed concentration of mercury in the sediment pore water of 0.026mg l^-1is below the UK Water Quality Standard. The measured concentrations of PCB, PAH and TBT in the elutriate samples did not exceed the background concentrations recorded in the seawater sample taken from the site. Therefore it is concluded that adverse water quality impacts arising from the release of contaminated pore water from the sediment are not anticipated during the surcharge period.

4.7.70 With a reduction in the reclamation extent and the surcharging area in the YTB Reclamation (Minimized Reclamation option), it is expected that the potential impacts arising from the release of contaminated pore water from the sediment, will be reduced proportionately from those predicted above for the Full Reclamation option. Hence, unacceptable water quality is not anticipated.

4.8 Mitigation of Adverse Impacts

Construction Phase

4.8.1 It is important that appropriate measures be undertaken to ensure that potential impacts on water quality during construction phase of the YTB Reclamation (Full Reclamation option) can be kept to within acceptable levels as defined by the WQO. Temporary mitigation measure is necessary to protect the water sensitive receivers (WSRs), so that the WSD target limit and other in house water quality standards at saltwater intakes can be satisfied. The use of appropriate dredging and filling methods will reduce the amount of sediment suspension, and, in turn, minimize adverse impacts on the WSRs. As the Full Reclamation option represents the worst case scenario for the YTB Reclamation, the recommended mitigation measures for the Full Reclamation option will also be applicable to the Minimized Reclamation option.

Temporary Diversion of YTB Stormwater Box Culvert

4.8.2 To avoid the accumulation of the pollutants within the embayed water during construction, a temporary channel / culvert will be constructed to divert the existing culvert outfalls out of the YTB before the commencement of marine works.

Dredging / Filling Works for the Stormwater Box Culvert and the Seawall Construction

4.8.3 Based on the predicted impacts, low impact dredging techniques such as closed grab dredgers are recommended. In addition, the use of silt curtains around the barge is recommended for the dredging and filling activities to minimize the dispersion of sediment plumes (Figure 4.79). To provide further protection at the WSD saltwater pumping stations in the study area during dredging and filling works, it is recommended that silt screens (typically made from synthetic geotextile fabrics) be placed across the Dairy Farm saltwater intake and the intakes of the Yau Tong and Cha Kwo Ling saltwater pumping stations (Figures 4.79). On-site environmental team should regularly check the proper implementation and functioning of the silt screens through visual inspections and review of marine water quality at the intakes.

4.8.4 Although dredging and filling may take place simultaneously as modelled in Scenario 2A_SW, it is recommended that the maximum daily production rate, during the seawall construction, shall not exceed 1550 m³ day^-1 for dredging and 2200 m³ day^-1 for sand filling, as derived from the preliminary construction program as at January, 2001 (Appendix 2A).

Bulk Filling Works for the Phase 1 and Phase 2 Reclamations

4.8.5 Since seawall will be formed before the commencement of Phase 1 and Phase 2 reclamations, the major impact of bulk filling by bottom dumping is effectively contained behind the seawall in YTB. Nevertheless, the 50 m opening of the seawall for marine access allows tidal flushing of sediment into Victoria Harbour. In order to minimize the water quality impact in the VHWCZ, a single layer of silt curtain (made from impervious material such as coated nylon) is recommended to be placed across the seawall opening (Figures 4.80 and 4.81) before bottom dumping is performed. The WSRs, namely the Yau Tong and Cha Kwo Ling Saltwater Pumping Station and the Dairy Farm Ice Factory, should be further protected by double layers of silt screen at the saltwater intakes locations (Figures 4.80 - 4.81). On-site environmental team should regularly check the proper implementation and functioning of the silt screens and silt curtains through visual inspections and review of marine water quality at the intakes.

4.8.6 It is recommended that the maximum sand filling rate for the Phase 1 and Phase 2 reclamations shall not exceeded 10,000 m³ day^-1 and 6,000 m³ day^-1 respectively as derived from the modelling results of Phase 1 and Phase 2 reclamations (Scenarios 2A_P1 and 2A_P2).

4.8.7 The double silt screens at the WSRs should be maintained throughout the construction of the proposed concrete decking near the mouth of YTB (Phase 3). It is recommended that the developer or its representative be responsible for the inspection and maintenance of the silt screens and curtains during the construction phases of the YTB reclamation.

Design Consideration for the future reprovisioning or upgrading of Cha Kwo Ling Saltwater Intake

4.8.8 The modelling results suggested that the potential sewage plume arising from the Yau Tong Sewage Pumping Station emergency outfall at Ko Fai Road will be confined to the water surface along the new water front of the YTB reclamation. If the CKLSPS is to be reprovisioned or upgraded in the future at the potential site suggested under the Full Reclamation option, the intake level is recommended to be located below -2.0 mPD to avoid possible abstraction of the surface sewage plume discharged from Yau Tong Sewage Pumping Station. Optimal intake configuration should be reviewed and decided in the detailed design stage for the reprovisioning or upgrading of the Cha Kwo Ling Saltwater Pumping Station.

4.8.9 To avoid accumulation of floating debris at water below the decked promenade near the intake of existing CKLSPS, floating booms shall be deployed near the intake (Figure 4.82) and any floating debris detained by the floating booms should be collected and removed regularly. Air slots should be included in the detailed design of the decked promenade to enhance the air flow below.

Good Operational Practices

4.8.10 The contractor will be required to minimize potential adverse impacts on water quality resulting from dredging and dumping operations to within acceptable levels as defined by the WQO. To achieve these requirements the contractor should design and implement methods of working, to the maximum practicable extent, that:

· minimize disturbance to the seabed while dredging;

· minimize leakage of dredged material during lifting;

· prevent loss of material during transport of dredged material;

· prevent discharge of dredged material except at approved locations;

· dredging operations should involve leaving sediment in place whenever practicable; and

· ensure that the construction works will cause no visible foam, oil, grease, scum, litter or other objectionable matter to be present in the water within and adjacent to the site or dumping grounds.

4.8.11 The licensee should formulate his design and construction methods with these factors in mind, and provide specification in the tender submission.

4.8.12 The contractor should provide the work schedule of the dredging and filling activities to WSD before the construction works starts.

Disposal of Sewage from Construction Workers and Soil Remediation Works

4.8.13 There will be generation of wastewater from the construction workers for the reclamation works. The wastewater volume is expected to be less than 700 m³/d (based on about 2000 workers). Chemical toilets or other suitable facilities should be provided by the reclamation contractors to ensure work-site hygiene and proper sewage disposal. There should be minimal impact on the downstream sewers, because of the expected small volumes. Another source of possible wastewater generated from the soil remediation works will be disposed vide recharge to the ground water. Any Leachate collected from the contaminated soil remediation works shall be treated to remove all floating TPH product before recharging back to the groundwater table.

Pollution Avoidance Measures During Dredging and Dumping

4.8.14 Pollution avoidance measures shall include, but not be limited to, the following:

· mechanical grabs shall be designed and maintained to avoid spillage and shall seal tightly while being lifted (closed-grab clamshell dredgers);

· 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;

· all pipe leakages shall be repaired promptly and plant shall not be operated with leaking pipes;

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

· adequate freeboard shall be maintained on barges to ensure that decks are not washed by wave action;

· all barges shall be fitted with tight fitting seals to their bottom openings to prevent leakage of material; and

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

Contaminated Marine Sediments

4.8.15 Additional provisions will be required where marine sediments are contaminated. The results of the sediment quality analyses indicate that the marine sediments along the proposed seawall foundation are seriously contaminated (Class C). The locations and depths of areas of contaminated marine sediments shall be indicated in the construction contract. The contractor shall ensure that contaminated marine sediments are dredged, transported and placed in approved special dumping grounds in accordance with the EPD Technical Circular No. 1-1-92 Classification of Dredged Sediments for Marine Disposal, Works Branch Technical Circular (WBTC) No. 22/92 Marine Disposal of Dredged Mud and WBTC No. 6/92 Fill Management. Special EPD procedures for the avoidance of pollution during the dredging, transportation and disposal of designated contaminated marine sediment are listed below:

(a) Uncontaminated mud shall not be dumped other than in dumping grounds as may be approved for the purpose by the Director of Environmental Protection (DEP) and in accordance with the Dumping at Sea Ordinance. If the contaminated mud cannot be left in situ, it shall be dumped at East Sha Chau Contaminated Mud Disposal Pits (CMPs) or other disposal pits as may be approved for the purpose by the DEP. The Contractor shall be responsible for obtaining all necessary licences for these operations.

Notes: The Engineer shall ensure that the Contractor has access to WBTC No. 22/92; EPD TC No. 1.1.92; and Fill Management Committee General Allocation Conditions for Marine Borrow Areas and Mud Disposal Sites.

(b) When the Contractor dumps the contaminated mud at East Sha Chau CMPs, he shall place the contaminated mud at a location and in such a manner as directed by the Management Team of the Civil Engineering Department. The Contractor shall proceed with the disposal operation as instructed by the Management Team and in accordance with guidance notes which are issued by the Management Team. The Contractor shall not carry out any dumping without permission of the Management Team or when the Management Team is not in operation.

(c) The Contractor shall carry out the dumping operation in strict accordance with the method statement agreed by the DEP, any non-compliance with the agreed method shall be a breach of conditions of the relevant licence issued by the DEP and is an offence under the Dumping at Sea Ordinance.

(d) When dredging, transporting and disposing of designated contaminated marine mud, the Contractor shall implement additional special procedures for the avoidance of pollution which shall include, but not be limited to, the following:

(i) employ a grab dredger with a closed watertight grab for dredging of designated contaminated marine mud;

(ii) transport designated contaminated marine mud by split barge of not less than 750m³ capacity, well maintained and capable of rapid opening and discharge at the disposal site;

(iii) design properly and maintain carefully all operational plant so as to minimize the risk of sediments or other pollutants being released into the water column and deposited in the seabed other than designated locations. The Contractor’s work shall cause no visible foam, oil, grease, scum, litter or other objectionable matter to be present in the water within the site;

(iv) fit all barges with tight fitting seals to their bottom openings to prevent leakage of material;

(v) release the mud rapidly and close the hoppers immediately; any material adhering to the sides of the hopper shall not be washed out of the hopper and the hopper shall reclosed until the barge next returns to the disposal site. The Contractor shall ensure that the dumping vessel shall be stationary throughout the dumping operation;

(vi) size all vessels such that adequate clearance is maintained between the seabed and vessels at all states of the tide, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash. Adequate freeboard shall be maintained on barges to ensure that decks are not washed by wave action;

(vii) employ only barges equipped with automatic self-monitoring devices for the dumping operation, and shall co-operate with and facilitate the DEP to inspect the device and retrieve the record stored in the device on a regular basis;

(viii) provide experienced full time personnel on board all dumping vessels and provide suitable training to ensure that appropriate methods to minimize pollution are implemented. Records shall be maintained to satisfy the DEP that there is no short dumping or dumping outside the Designated Dumping Area. The Contractor shall also make available to the DEP and the secretary of Fill Management Committee (S/FMC), Civil Engineering Department, at any time upon the written request of the DEP, all information and records relevant to the dredging and mud disposal operation. This information shall include, but not be limited to, all data on the plant used by the Contractor, up-to-date periodic data on production rates and record copies of Notification of Dumping which have been sent to the Management Team, etc.

Operation Phase

4.8.16 In the present study, it was found that the proposed YTB reclamation (Full or Minimized Reclamation option) will have negligible effect on the flow condition within Victoria Harbour and thus, unacceptable water quality is not expected in the long run. In view of the concern expressed by WSD regarding the potential impact of the emergency sewage discharge at the Yau Tong sewage pumping station on the neighbouring WSD’s saltwater pumping station, it is proposed that a communication channel be established between WSD and DSD for dealing with this event.[6] It is recommended that this communication procedure between the two government departments be established at the detailed design stage. Should discharge of sewage be made through the emergency outfall, DSD should inform WSD of the details of such discharge, e.g. volume, timing and duration, in advance where possible. It is also recommended that DSD should minimize the discharge and liaise with WSD to avoid discharge during the peak operation hours of WSD’s saltwater pumping station. Details of the liaison mechanisms between DSD and WSD should be established for the operation stage, notably with regard to discharges through the emergency outfall and potential impacts on WSD saltwater pumping station performance, during the detail design stage of the project.

4.8.17 No other mitigation measure is recommended for the operation phase in the present study. Furthermore, the scope of the present EIA study covers mainly the environmental impact of the Yau Tong Bay reclamation during the construction phase. The impact of the subsequent development on the reclaimed land will be addressed under a separate EIA study. Hence, mitigation measures, if any, for the subsequent development will be addressed in the corresponding EIA study.

4.9 Environmental Monitoring and Audit Requirements

4.9.1 A design audit in terms of water quality impact is recommended to be carried out at the detailed design stage to review the updated information. Should any adverse water quality impacts other than those assessed in this report be identified during the detailed design stage, appropriate measures will be proposed to mitigate the adverse impacts. The EM&A manual should then be revised, where necessary, to included the recommended mitigation measures.

4.9.2 Based on the water quality impact assessment results in this report, it is recommended that environmental monitoring and auditing (EM&A) of marine water quality be carried out at the Yau Tong and Cha Kwo Ling WSD saltwater intakes and the Dairy Farm seawater intake during the construction phase. In particular, monitoring of water quality during dredging and sand filling activities for the seawall foundation, Phase I and Phase II reclamations will be required. An EM&A program will be required to ensure the implementation of the recommended water quality mitigation measures and to assess the effectiveness of these measures during the construction works. Details of the EM&A procedures are presented in Section 9.2. If monitoring results indicate that the dredging and/or sand filling works have caused an adverse impact on water quality at the above sensitive receivers, the construction program should be carefully reviewed so as to slow down the rate of dredging or sand filling accordingly, such that the water quality at these sensitive receivers is in compliance with the water quality criteria.

4.10 Definition and Evaluation of Residual Impacts

4.10.1 With the full and strict implementation of the recommended mitigation measures for the construction of the YTB reclamation, no unacceptable residual impacts on marine water quality are anticipated to arise. In addition, it is considered that no adverse environmental effects will result from the employment of the recommended water quality mitigation measures for the reclamation works, as described in Section 4.8.

4.11 Conclusions

Operation Phase

4.11.1 Detailed hydrodynamic modelling was conducted using the DHI models, MIKE 21 and MIKE 3, to determine the impact of the completed YTB reclamation (Full Reclamation option) on tidal flow patterns in Victoria Harbour. The percentage change in flow discharge rates through Victoria Harbour from the baseline scenario without the YTB reclamation to the development scenario with YTB reclaimed is very small, with a change in annual average discharge rate of less than 0.5%. The tidal flow patterns were observed to be similar for the baseline and development scenarios with minor deviation near YTB, and the maximum flow speeds for the two scenarios were also similar for the wet and dry seasons, spring and neap tides. The results of the hydrodynamic modelling indicate that the YTB reclamation (Full Reclamation option) is likely to have negligible effect on the tidal flow regime in Victoria Harbour. As the reclamation extent of the Minimized Reclamation option is smaller than that for the Full Reclamation option, the corresponding impact is expected to be less significant than that for the Full Reclamation option.

4.11.2 The potential water quality impact of an emergency discharge from the Yau Tong Sewage Pumping Station on the potential site proposed under the YTB Reclamation (Full Reclamation option) for future reprovisioning of the CKLSPS has been assessed for both wet and dry seasons. The model results indicate that the depth averaged water quality in terms of BOD₅, SS and ammoniacal nitrogen is expected to meet the WSD standards at the reprovisioned CKLSPS; however, the E. coli standards will be exceeded. The sewage plume is shown to attach to the shoreline and is buoyant at the surface with a thickness of less than 0.4m. To avoid abstracting the sewage plume water, it is recommended that the future reprovisioned CKLSPS saltwater intake should be located below -2.0 mPD. The intake water would then be expected to comply with the WSD water quality standards. The optimal intake configuration should be reviewed and decided at the detailed design stage for the reprovsioning of the CKLSPS. Under the Minimized Reclamation option, no provisions have been made for the relocation or upgrading of the CKLSPS which will remain in operation at the existing location where the water quality is expected to meet the WSD target limits at the saltwater intakes.

4.11.3 No adverse water quality impact in Victoria Harbour and, in particular, at the existing and potentially reprovisioned CKLSPS, under the YTB reclamation (Full Reclamation option), and the reprovisioned YTSPS, under the WCR-Coastal option reclamation, is expected from the polluted stormwater in the new Kwun Tong nullah and the new YTB stormwater culvert (with the conservative assumption of 5% residual flows from expedient connections). The model result suggested that tidal flushing will prevent the accumulation of pollutants under the proposed concrete decking at the mouth of YTB and the water quality is expected to comply with the WSD’s target limits at the saltwater intakes. Since the proposed concrete decking under the Minimized Reclamation will be reduced in size and is more exposed to the tidal flow in Victoria Harbour, the water quality under the concrete decking is expected to be better than that for the Full Reclamation option. Hence, it is concluded that reprovisioning of the CKLSPS will not be required under the YTB reclamation (Full or Minimized Reclamation option).

Construction Phase

4.11.4 Sediment plume modelling of the different construction phases was conducted to assess the water quality impact of the dredging and filling activities for the proposed YTB reclamation (Full Reclamation option), which represents the worst case scenario. The three main construction phases identified were the seawall construction, Phase 1 and Phase 2 reclamations. Sediment loss rates for dredging and filling were estimated based on the employment of open grab dredgers without silt curtains and bottom dumping barges. With the same construction sequence and methodology as adopted in the Full Reclamation option, the water quality impact arising from the Minimized Reclamation option is expected to similar, if not less significant, than the former. Hence, the recommended mitigation measures for the Full Reclamation option will be fully applicable to the Minimized Reclamation.

4.11.5 The predicted elevation in SS concentration in Victoria Harbour generally satisfies the stipulated WQO for SS in both the wet and dry seasons, spring and neap tides. Exceedance of the WQO for SS is only found locally within the sediment plume near YTB. High SS concentration are predicted at the WSD's Yau Tong and Cha Kwo Ling Saltwater Pumping Stations and the Dairy Farm saltwater intake for the various construction phases, which are in exceedance of the WSD target (tolerable) limit for SS at saltwater intakes. The non-compliance of the WQO and WSD standard at saltwater intakes necessitate the implementation of the proposed mitigation measures during the construction period.

4.11.6 The proposed mitigation measures include: the use of closed grab dredgers with silt curtain for the dredging and filling of seawall construction and dredging of stormwater box culvert; a silt curtain to be placed across the seawall opening for the Phase 1 and Phase 2 reclamations using bottom dumping; double layers of silt screen to be installed at the Yau Tong (YTSPS) and Cha Kwo Ling (CKLSPS) Saltwater Pumping Stations and the Dairy Farm Saltwater Intake (DFSI); and the reduction of Phase 2 reclamation filling rate to 6,000 m³day^-1. Details of the mitigation measures to be implemented are discussed in Section 4.8 and summarized in the Implementation Schedule for Water Quality Control (Table 11.2).

4.11.7 With the proposed mitigation measures fully implemented, it is anticipated that the size of the sediment plume of the YTB reclamation (Full Reclamation option) will be reduced, minimizing the impact on Victoria Harbour. It is also expected that the SS concentration at the WSRs will satisfy the WSD tolerable limit for SS (20 mgL^-1) at the CKLSPS and YTSPS, and the in-house standard of 20 mgL^-1 for SS at the DFSI at all times.

4.11.8 Based on the available information, the dredging and filling works for the South East Kowloon Development (SEKD), Western Coast Road (WCR-Coastal option), Tseung Kwan O (TKO) Cargo Working Area (CWA) and TKO New Town Intensification and Extension (NTIE), potentially concurrent to the YTB reclamation were identified.

4.11.9 An assessment of the water quality impacts due to the concurrent works in Victoria Harbour, except the YTB reclamation, was performed to establish a reference level (Scenario 2B_BK). The WQO for SS in the VHWCZ was generally satisfied with the sediment plumes associated with the different projects being localized. With the available information, mitigation measure was implemented for all the concurrent projects except for the TKO NTIE works. Hence, the plume associated with the TKO NTIE works is relatively large, extending into the Lei Yue Mun Channel and across Victoria Harbour to the Shau Kei Wan Typhoon Shelter, particularly, in the wet season. The surface SS concentration due to the cumulative impacts from other projects generally complies with the WSD target limit for SS at the CKLSPS and the in-house SS standard at the DFSI. However, exceedance of the WSD target (tolerable) limit is observed at the YTSPS, which can be attributed to the unmitigated works of the TKO NTIE.

4.11.10 The cumulative impact of the YTB reclamation is taken into account by comparing the contribution of the YTB reclamation and the concurrent works (Scenario 2B_CI). The result suggests that the YTB reclamation only contributes to a marginal increase in the size of the sediment plume around YTB. Hence, no unacceptable impact on Victoria Harbour is anticipated. With the implementation of the proposed mitigation measures for the YTB reclamation, the water quality at the WSRs is expected to improve over the reference level due to the concurrent project without the YTB reclamation (Scenario 2B_BK). Exceedance of the WSD target limit for SS concentration of 10 mgL^-1 at the YTSPS is essentially associated with the unmitigated works of the TKO NTIE mentioned earlier. With appropriate mitigation measures to be proposed by the TKO NTIE EIA study, sediment plume dispersion of the marine works of TKO NTIE will be essentially confined within Junk Bay and the residual SS concentration at the YTSPS is expected to very similar to the mitigated water quality under the Scenario 2A_P1 (as presented in paragraph 4.11.2.4). That is, the residual SS level at the intake of YTSPS will comply with the WSD SS tolerable limit (20 mgL^-1) all the time.

4.11.11 No adverse impact in Victoria Harbour and on the existing sensitive receivers are expected from polluted stormwater due to the temporary diversion of the stormwater culvert to the mouth of YTB before the reclamation starts. The diverted stormwater will be directly discharged into Victoria Harbour and thus, prevents the accumulation of pollutants in the temporary embayment. The results also suggested that pollutants from stormwater discharge is unlikely to cause unacceptable water quality impacts in the VHWCZ during the construction period.

4.11.12 Adverse impacts on water quality arising from the release of heavy metals from contaminated sediment are not anticipated during the dredging works. A quantification of the release of heavy metals from the sediment pore water indicates that the predicted heavy metal concentrations in the marine waters surrounding the dredging site will not exceed the UK Water Quality Standards for Coastal Surface Water.

4.11.13 Environmental monitoring and auditing (EM&A) program will be required to monitor and audit the implementation and efficacy of measures to mitigate any adverse impacts, arising from the YTB reclamation works, on the water quality sensitive receivers, as detailed in Section 9.2.

[1] Feasibility Study for South East Kowloon Development. Environmental Impact Assessment Report, Maunsell Consultants Asia Ltd, January 1999.

[2] EIA Study for outlying islands sewerage stage I, phase II, package J – Sok Kwu Wan sewage collection, treatment and disposal facilities, Maunsell Consultants Asia Ltd, September 1998.

[3] Preliminary Pollution Loading Inventory Report (Draft) Oct. 1998, Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool. Hyder Environmental & CES (Asia) Ltd.

[4] Pypun Group Consultants (1989), Development of a Master Plan for Sewage Disposal for East Kowloon, Final Report, vol 1.

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

[6] DSD have stated (by fax dated 25 April 2000) that they have no objection to the proposed communication channel between WSD and DSD for dealing with the emergency discharge at Yau Tong Sewage Pumping Station.