5. Hydrodynamics and water quality impacts

5.1 Introduction

Brief Project Description

5.1.1 The key elements of the Tseung Kwan O (TKO) further development comprise the Western Coast Road (WCR), the Cross Bay Link (CBL), and the land-based developments at Town Centre South (TCS) and Pak Shing Kok (PSK). A strip of land would be reclaimed under the Project for the WCR along the western shoreline of Junk Bay (Figure 2.35). The CBL bridge alignment is shown in Figure 2.38.

5.1.2 The proposed population in PSK and TCS is around 5,000 and 33,000 including some 9,200 existing population in Bauhina Garden respectively. The population intake for PSK and TCS would commence upon completion of infrastructure around Oct 2010 and May 2010 respectively. WCR and CBL are assumed to be in place around 2016. The construction programme is shown in Appendix 2.2.

5.1.3 It is also proposed under the present Study to use part of the Eastern Channel (EDC) and Junk Bay for recreation uses such as dragon boating, sailing and rowing etc. Figure 5.1 shows the existing drainage systems of the TKO catchment. The boundary of the proposed water recreation zone is shown in Figure 5.1a.

5.1.4 According to the current TKO Outline Zoning Plan (OZP), the existing and currently planned developments would bring the ultimate population up to around 480,000. The further developments proposed under the present Study would trim down the ultimate population at TKO to around 453,000. Table 5.1Table 5.1Table 5.1Table 5.1 summarises the ultimate population for TKO envisaged in the current OZP and in the current development scenario. The ultimate population has taken into account the planned population at TCS and PSK assuming all proposed developments and infrastructures at TKO would be fully utilized.

Table 5.1 Ultimate Population for TKO

Scenario	Residential Population	Commercial Employed Population	Industrial Employed Population	School Place
Ultimate population at TKO under current OZP	484,318	99,629	10,716	67,861
Ultimate population at TKO proposed under the present Study	453,318	99,629	10,716	67,861

Other Project Components with Water Quality Issue

Construction of Northern Cycle Track Footbridge and Southern Footbridge across EDC

5.1.5 The northern footbridge is a cycle track footpath bridge of about 110m long across EDC which also serve as an emergency vehicular access in the event of blockage of Wan Po Road due to serious traffic accident. The southern footbridge will only carry a footway which is also about 110m long. Both bridges are designed without bridge piers locating in the EDC.

Service Reservoir and Pumping Station

5.1.6 A new fresh water supply system comprising a new Pak Shing Kok fresh water pumping station, a new Pak Shing Kok high level fresh water service reservoir and the associated supply and distribution mains, will be constructed under the Project.

Culvert Realignment and Piled Deck at Western Drainage Box Culvert

5.1.7 A section of culvert in Tiu Keng Leng Area 72 would be clashed by the proposed depressed Road P2. This section of culvert will be realigned to avoid such conflict. A piled deck will be constructed at the downstream section of the western drainage box culvert which replaces the existing temporary box culvert to protect the existing tidal gates.

Sewage Pumping Station and Rising Mains

5.1.8 A new sewage pumping station and rising mains are proposed to carry the sewage arising from the recreational development at TKO landfill to the TKO preliminary treatment works. The emergency outfall of the pumping station will be located 500 m away from the TKO saltwater intake. The locations of the emergency bypass and TKO saltwater intake are shown in Figure 5.1b. A standby pump will be provided to minimize the potential water quality impact from sewage overflow.

Key Water Quality Issues

Operational Phase

5.1.9 The change in coastline configuration due to the reclamation for construction of the WCR and the placement of bridge structures for the CBL may change the hydrodynamic regime and water quality in Junk Bay and Victoria Harbour and thus, may adversely affect the nearby water quality and ecological sensitive receivers.

5.1.10 The acceptability of the EDC and Junk Bay for secondary contact recreation have been addressed, in particular the cumulative impact from the potential release of landfill leachate together with other pollutant discharges within the TKO catchment as well as the potential impact in the event of any sewage overflow or emergency bypass from the TKO Preliminary Treatment Works (PTW).

Construction Phase

5.1.11 Key water quality issues associated with the land-based construction would include the impacts from site run-off, sewage from workforce, accidental spillage and discharges of wastewater from various construction activities.

5.1.12 Potential water quality impacts arising from the proposed marine construction works would include:

· Increase of suspended solids concentration due to dredging and filling activities

· Release of contaminants during dredging of marine mud

· Release of suspended solids and contaminants during deep cement mixing (DCM) treatment

· Release of contaminants through vertical band drains during consolidation of reclamation.

5.1.13 Implementation of proper pollution control measures will be important for the construction works at or near box culverts / inland waters in order to prevent construction wastes from entering the storm system.

5.1.14 Groundwater generated from construction works in close proximity to the TKO landfill site boundary may potentially be contaminated by landfill leachate. Potential water quality impacts on the nearby receiving water may arise if the contaminated groundwater is not properly handled.

5.1.15 The performance of the existing and committed sewerage infrastructure under full development condition for the ultimate scenario was assessed and results are presented in Section 6. The results indicate that there are no risks of sewage overflow under various peak flow conditions for the ultimate scenario. The TKOPTW and the Harbour Area Treatment Scheme (HATS) Stage I Tunnel section from TKO to Kwun Tong are considered to be adequate to handle the ultimate catchment flows ⁽[1]⁾. The present Study would not pose any capacity constraint on HATS, as there would be an overall reduction in ultimate population and flows as a consequence of planned further developments.

5.2 Environmental Legislation, Policies, Plans, Standards and Criteria

Environmental Impact Assessment Ordinance (EIAO), Cap.499, S.16

5.2.1 The EIAO-TM is issued by the EPD under Section 16 of the EIAO. It specifies the assessment method and criteria that need to be followed in this Study. Reference sections in the EIAO-TM provide the details of the assessment criteria and guidelines that are relevant to the water quality impact assessment, including:

· Annex 6 Criteria for Evaluating Water Pollution

· Annex 14 Guidelines for Assessment of Water Pollution.

Marine Water Quality Objectives

5.2.2 The Water Pollution Control Ordinance (Cap.358) provides the major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZ). 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. A summary of WQOs for Junk Bay, Victoria Harbour and Eastern Buffer WCZs are given in Table 5.2Table 5.2Table 5.2Table 5.2, Table 5.3Table 5.3Table 5.3Table 5.3 and Table 5.4Table 5.4Table 5.4Table 5.4 respectively.

5.2.3 Given the planning intention of the EDC and Junk Bay for water recreation, the E.coli objective of 610 per 100mL for annual geometric mean set under the WPCO for secondary contact recreation should be adopted for the proposed water recreation zone as shown in Figure 5.1a.

Table 5.2 Summary of Water Quality Objectives for Junk Bay WCZ

Parameters	Objectives	Sub-Zone
Offensive Odour, Tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2.0 mg/L for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0 mg/L for 90% of samples	Marine waters excepting fish culture subzones
	Not less than 5.0 mg/L for 90% of samples	Fish culture subzones
	Not less than 4.0 mg/L	Inland waters
5-Bay Biochemical Oxygen Demand (BOD5)	Change due to waste discharges not to exceed 5 mg/L	Inland waters
Chemical Oxygen Demand (COD)	Change due to waste discharges not to exceed 30 mg/L	Inland waters
pH	To be in the range of 6.5 - 8.5, change due to waste discharges not to exceed 0.2	Marine waters
	To be in the range of 6.0 –9.0	Inland waters
Salinity	Change due to waste discharges not to exceed 10% of ambient	Whole zone
Temperature	Change due to waste discharges not to exceed 2^oC	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities	Marine waters
	Change due to waste discharges not to exceed 25 mg/L of annual median	Inland waters
Unionised Ammonia (UIA)	Annual mean not to exceed 0.021 mg/L as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total Inorganic Nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.3 mg/L	Marine waters
Dangerous substances	Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms	Whole zone
	Waste discharges should not cause a risk to any beneficial use of the aquatic environment	Whole zone
Bacteria	Not exceed 610 per 100ml, calculated as the geometric mean of all samples collected in one calendar year	Secondary contact recreation subzones and fish culture subzones
	Not exceed 1000 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Inland waters
Colour	Change due to waste discharges not to exceed 50 Hazen units	Inland waters

Source: Statement of Water Quality Objectives (Junk Bay Water Control Zone).

Table 5.3 Summary of Water Quality Objectives for Victoria Harbour WCZ

Parameters	Objectives	Sub-Zone
Offensive Odour, Tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2.0 mg/L for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0 mg/L for 90% of samples	Marine waters
PH	To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2	Marine 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 (SS)	Not to raise the ambient level by 30% caused by human activity	Marine waters
Unionised Ammonia (UIA)	Annual mean not to exceed 0.021 mg/L as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total Inorganic Nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg/L	Marine 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).

Table 5.4 Summary of Water Quality Objectives for Eastern Buffer WCZ

Parameters	Objectives	Sub-Zone
Offensive Odour, Tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2.0 mg/L for 90% of samples	Marine waters
Depth-averaged DO	Not less than 4.0 mg/L for 90% of samples	Marine waters excepting fish culture subzones
	Not less than 5.0 mg/L for 90% of samples	Fish Culture Subzones
	Not less than 4.0 mg/L	Water Gathering Ground Subzone and other Inland waters
5-Bay Biochemical Oxygen Demand (BOD5)	Change due to waste discharges not to exceed 3 mg/L	Water Gathering Ground Subzones
	Change due to waste discharges not to exceed 5 mg/L	Inland waters
Chemical Oxygen Demand (COD)	Change due to waste discharges not to exceed 15 mg/L	Water Gathering Ground Subzones
	Change due to waste discharges not to exceed 30 mg/L	Inland waters
PH	To be in the range of 6.5 – 8.5, change due to waste discharges not to exceed 0.2	Marine waters
	To be in the range of 6.5 – 8.5	Water Gathering Ground Subzones
	To be in the range of 6.0 – 9.0	Inland waters
Salinity	Change due to waste discharges not to exceed 10% of ambient	Whole zone
Temperature	Change due to waste discharges not to exceed 2^oC	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities	Marine waters
	Change due to waste discharges not to exceed 20 mg/L of annual median	Water Gathering Ground Subzones
	Change due to waste discharges not to exceed 25 mg/L of annual median	Inland waters
Unionised Ammonia (UIA)	Annual mean not to exceed 0.021 mg/L as unionised form	Whole zone
Nutrients	Shall not cause excessive algal growth	Marine waters
Total Inorganic Nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg/L	Marine waters
Dangerous substances	Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms	Whole zone
	Waste discharges should not cause a risk to any beneficial use of the aquatic environment	Whole zone
Bacteria	Not exceed 610 per 100ml, calculated as the geometric mean of all samples collected in one calendar year	Fish Culture Subzones
	Less than 1 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Water Gathering Ground Subzones
	Not exceed 1000 per 100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days	Inland waters
Colour	Change due to waste discharges not to exceed 30 Hazen units	Water Gathering Ground
	Change due to waste discharges not to exceed 50 Hazen units	Inland waters

Hong Kong Planning Standards and Guidelines (HKPSG)

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

Water Supplies Department Water Quality Objectives

5.2.5 Besides the WQO set under the WPCO, the Water Supplies Department (WSD) has also specified a set of seawater quality objectives for water quality at seawater intakes. The list is shown in Table 5.5Table 5.5Table 5.5Table 5.5. The relevant criteria for suspended solids (SS) are the target limit of 10 mg/L.

Table 5.5 WSD Standards at Sea Water Intakes

Parameter (in mg/L 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 (no. / 100 ml)	< 20,000

Cooling Water Intake Standards

5.2.6 Based on the information provided by the individual cooling water intake operators (Dairy Farm Ice Plant and Pamela Youde Nethersole Eastern Hospital), no specific requirement on seawater quality at these two cooling water abstraction points was identified.

Technical Memorandum

5.2.7 Besides setting the WQOs, the WPCO controls effluent discharges into any WCZ through a licensing system. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS), issued under Section 21 of the WPCO, gives guidance on permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluent. Any sewage from the proposed construction activities should comply with the standards for effluent discharged into the foul sewers, inshore waters or marine waters of the Victoria Harbour WCZ and Junk Bay WCZ, shown in Table 1, Table 9a and Table 9b, Table 10a and Table 10b, respectively, of the TM-DSS.

Practice Note

5.2.8 A practice note for professional persons has been 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 sterilisation of water retaining structures and water pipes, wastewater from building construction, acid cleaning, etching and pickling wastewater, and wastewater from site facilities. Practices given in the ProPECC PN 1/94 should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage. For operational stage effluent handling, treatment and disposal, reference should be made to ProPECC PN 5/93.

Assessment Criteria for Coral Impact

5.2.9 According to Pastorok and Bilyard⁽[2]⁾ and Hawker and Connell⁽[3]⁾, a sedimentation rate higher than 0.1 kg/m²/day would introduce moderate to severe impact upon corals. This criterion has been adopted in other recently approved EIA. Detailed assessment criteria for marine ecological sensitive receivers including coral and fish culture zone (FCZ) are provided in Chapters 8 and 9.

SS Criterion for Fish Cultural Zone (FCZ)

5.2.10 Literature reviews indicate that lethal responses had not been reported in adult fish at a SS concentration of below 125 mg/L ⁽[4]⁾. The AFCD consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment ⁽[5]⁾ provides the guideline value for suspended solids (SS) for protection of local marine fisheries resources as given in Table 5.6Table 5.6Table 5.6Table 5.6 below.

Table 5.6 Assessment Criterion for SS for Local Marine Biota and Fisheries Resources

Parameter	Maximum Concentration (mg/L)
Total Suspended Solids	50

5.2.11 The maximum SS concentration value offers protection to short-term acute effects, and thus should be complied with during both the construction and operational phases. A description on legislation for fish cultural zone is presented in Section 9.2.

5.3 Description of the Environment

5.3.1 The marine water quality monitoring data routinely collected by EPD were used to establish the baseline condition. The EPD monitoring stations in Junk Bay WCZ (JM3 and JM4), Eastern Buffer WCZ (EM1 and EM2) and Victoria Harbour WCZ (VM1 and VM2) are shown in Figure 5.2. A summary of EPD monitoring data collected in 2002 and 2003 is presented in Table 5.7, Table 5.8 and Table 5.9 for Junk Bay, Eastern Buffer and Victoria Harbour WCZs representatively. As the Harbour Area Treatment Scheme (HATS) Stage I was commissioned in late 2001, the data shown in Table 5.7, Table 5.8 and Table 5.9 represent the situation after the commissioning of HATS Stage 1.

Table 5.7 Summary Statistics of 2002 and 2003 Marine Water Quality in Junk Bay WCZ

Parameter		EPD Monitoring Station				WPCO WQOs for Junk Bay WCZ(in marine waters)
		JM3		JM4
		2002	2003	2002	2003
Temperature (^oC)		23.7 (17.4 – 27.8)	23.1 (17.2– 27.2)	23.5 (17.4 – 27.7)	22.9 (17.1 – 27.0)	Change due to waste discharges not to exceed 2°C
Salinity (ppt)		32.4 (29.9 – 33.8)	32.9 (30.9– 33.9)	32.6 (30.0 – 33.9)	33.1 (32.2 – 33.8)	Change due to waste discharges not to exceed 10% of ambient
Dissolved Oxygen (DO) (% saturation)		92 (74 – 126)	86 (72 – 115)	89 (72 – 104)	83 (66 – 102)	-
	Bottom	90 (75 – 111)	80 (55 – 101)	88 (71 – 109)	78 (46 – 100)	-
DO (mg/L)		6.5 (5 – 8.3)	6.1 (4.9 – 7.8)	6.3 (4.7 – 7.9)	5.9 (4.4 – 8.1)	Not less 4 mg/L for 90% of the samples
	Bottom	6.4 (4.9 – 7.7)	5.7 (3.9 – 7.9)	6.3 (4.9 – 8.2)	5.6 (3.2 – 7.9)	Not less 2 mg/L for 90% of the samples
pH value		8.0 (7.7 – 8.2)	8.1 (7.9 – 8.3)	8.0 (7.8 – 8.2)	8.1 (7.9 – 8.3)	6.5 - 8.5 (± 0.2 from natural range)
Secchi disc (m)		2.2 (1.0 – 3.5)	2.7 (1.5 – 4.0)