6 WATER QUALITY IMPACT

6.1 Introduction

This chapter presents the assessment of potential water quality impacts which may arise during the construction and operation of the Central Kowloon Route. Construction runoff, sediment dredging, sewage from site workforce, drainage diversion and temporary reclamation are potential water pollution sources during the construction phase. Operational water quality impact would mainly include road run-off and wastewater discharge from ventilation buildings.

Mitigation measures have been proposed to alleviate the potential water quality impact. With the implementation of the recommended mitigation measures, adverse residual impacts during the construction and operational phases are not anticipated.

6.2 Legislation and Standards

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

The “Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO)” specifies the assessment methods and criteria for impact assessment. This Study follows the TM-EIAO to assess the potential water quality impact that may arise during the construction and operational phases of the Project. Sections in the TM-EIAO relevant to the water quality impact assessment are:

· Annex 6 - Criteria for Evaluating Water Pollution; and

· Annex 14 - Guidelines for Assessment of Water Pollution

6.2.2 Water Quality Objectives (WQOs)

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 WPCO and its subsidiary legislation, the whole Hong Kong waters are divided into ten Water Control Zones (WCZs). Water Quality Objectives (WQOs) were established to protect the beneficial uses of water quality in each WCZ.

The proposed CKR is located within the Victoria Harbour WCZ. The WQO in Victoria Harbour WCZ is summarized in the following Table 6.1.

Table 6.1: 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

Notes:

[1] Statement of Water Quality Objectives (Victoria Harbour (Phases One, Two and Three) Water Control Zone).

6.2.3 Technical Memorandum on Effluent Discharge Standards

Discharges of effluents are subject to control under the WPCO. The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) specifies limits for effluent discharges in different water control zones.

6.2.4 Practice Note for Professional Persons on Construction Site Drainage

The Practice Note for Professional Persons (ProPECC Note PN1/94) on Construction Site Drainage provides guidelines for the handling and disposal of construction discharges. This note is applicable to this study in controlling the site runoff and wastewater generated during the construction phase. The types of discharges from construction sites outlined in the ProPECC Note PN1/94 include:

· Surface run-off;

· Groundwater;

· Boring and drilling water;

· Wastewater from concrete batching;

· Wheel washing water;

· Bentonite slurries;

· Water for testing and sterilization of water retaining structures and water pipes;

· Wastewater from building construction and site facilities; and

· Acid cleaning, etching and pickling wastewater.

6.2.5 WSD Water Quality Criteria for Salt Water Intakes

The criteria for assessing the water quality impact on the Water Supplies Department (WSD) seawater intakes are based on the Water Quality Criteria of Seawater for Flushing Supply (at intake point) issued by the Water Supplies Department (WSD) and are summarized in the following Table 6.2.

Table 6.2: WSD Water Quality Criteria for Salt Water Intakes

Parameter	Concentration
Colour	< 20 H.U.
Turbidity	< 10 N.T.U.
Threshold Odour No.	< 100
Ammonia Nitrogen	< 1 mg/l
Suspended Solids	< 10 mg/l
Dissolved Oxygen	> 2 mg/l
Biochemical Oxygen Demand	< 10 mg/l
Synthetic Detergents	< 5 mg/l
E. coli.	< 20,000 cfu/100 ml

6.2.6 Assessment Criteria for Heavy Metals and Trace Organics

There is no existing legislation or guideline for individual heavy metals and trace organics (PCBs, PAHs and TBT) in Hong Kong waters. According to the common practices in the past EIA studies, a conservative selection was made by comparing the standards of EU, Japan, USA, UK, Australia and Singapore. The lowest values from various international standards will be adopted as the assessment criteria. The adopted criteria for heavy metals and trace organics are presented in the following Table 6.3.

Table 6.3: Proposed Assessment Criteria for Heavy Metal and Trace Organics

Heavy Metal/Trace Organics	Proposed Criteria (mg/l)	Reference
Arsenic	10	1
Cadmium	2.5	2
Chromium	15	2
Copper	5	7
Lead	8.1	3
Mercury	0.16	4
Nickel	8.2	3
Silver	1.9	3
Zinc	40	2
Total PAHs	3.0	6
PCBs	0.03	3
TBT	0.1	3

References:

[1] Environment Agency, Government of Japan

[2] EC Dangerous Substances Directive (76/464/EEC), Environmental Quality Standards for List 1 and List 2 dangerous substances

[3] USEPA National Recommended Water Quality Criteria, Criterion Continuous Concentration

[4] United Nations Economic and Social Commission for Asia and the Pacific, ASEAN Marine Water

[5] Australian Water Quality Guidelines for Fresh and Marine Waters

[6] Total PAH consist of the combination of individual components including acenaphthene, acenaphthylene, anthracene, fluorene, naphthalene, phenanthrene, benzo[a]anthracene, benzo[a]pyrene, chrysene, dibenzo]a,h]anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k] fluoranthen, indeno[1,2,3-c,d]pyrene and benzo[g,h,i]perylene. According to Australian Water Quality Guidelines for Fresh and Marine Waters, the criterion of naphthalene is 3.0 µg/L for fresh water aquatic ecosystem conservations. Nevertheless, since all the WSRs are typhoon shelters and industrial use, the functions of these WSRs are neither ecological importance nor portable use. Hence, the tolerant levels should be much higher. Adoption of 3.0 µg/L as proposed criterion for total PAH is in much conservative side.

[7] According to Australian Water Quality Guidelines for Fresh and Marine Waters, the criterion of copper is 5.0 µg/L for irrigation and aquaculture purpose. Nevertheless, since all the WSRs are typhoon shelters and industrial use, the functions of these WSRs are neither for irrigation nor aquaculture purpose. Adoption of 5.0 µg/L as proposed criterion for copper is in much conservative side.

6.3 General Methodology and Principles

In accordance with Clause 3.4.8.3 of the EIA Study Brief, the area for water quality impact assessment included all areas within a distance of 300m from either side and along the full length of the project boundary.

The design of CKR has made due consideration to the Protection of Harbour Ordinance (PHO), which states that “(1) The harbour is to be protected an preserved as a special public asset and a natural heritage of Hong Kong people, and for that purpose there shall be a presumption against reclamation in the harbor. All public officers and public bodies shall have regard to the principle stated in subsection (1) for guidance in the exercise of a powers vested in them”.

While permanent reclamation requires careful consideration under the PHO, temporary reclamation is still required as the key marine works, and thus, it will be the major source of water quality impact nearby WSR such as To Kwan Wan Typhoon Shelter and the seawater intakes in Kowloon Bay. A 3 dimensional mathematical model is conducted to simulate the water quality impact due to marine works.

Apart from the marine works in To Kwa Wan, other sections of CKR will involve land-based work. In considering the anticipated small scale water quality impact, a qualitative assessment approach was adopted to all land-based works. The assessment approach is referred to Annex 6 – Criteria for Evaluating Water Pollution and Annex 14 – Guidelines for Assessment of Water Pollution under the TM-EIAO.

6.4 Baseline Conditions

To Kwa Wan is an elongated bay of Victoria Harbour between Kowloon Peninsula and Hong Kong Island. Current directions are in line with the coastline of Ma Tao Wai and the streamlines are generally parabolic.

In the Victoria Harbour WCZ, the 2010 compliance rate was 77% as compared with 80% in 2008 and 93% in 2009 which was the second highest recorded since the commissioning of HATS stage 1. It is noted that Harbour Area Treatment Scheme (HATs) stage 1 was fully commissioned at the end of 2001 and dredging works for Wan Chai Reclamation II started from 2009 while Cruise Terminal commenced in 2010. These major dredging works might affect the ambient water quality. Therefore, water quality monitoring data of 2002 to 2008 was adopted to determine the ambient water quality. The average water quality of closest monitoring stations VM2 and VT11 between 2002 and 2008 is presented in Table 6.4. Details of the annual monitoring data at each station are given in Appendix 6.1.

Table 6.4: Average Water Quality of VM2 and VT11 from 2002 to 2008

Parameters		VM2	VT11
Temperature (°C)		23.2	23.2
Salinity		32.1	31.5
Dissolved Oxygen (mg/L)	Depth Average	5.6	5.5
	Bottom	5.5	5.5
Dissolved Oxygen (% Saturation)	Depth Average	79	76
	Bottom	76	76
pH		8.0	8.0
Secchi Disc Depth (m)		2.3	1.9
Turbidity (NTU)		9.4	10.1
Suspended Solids (mg/L)		4.4	5.3
5-day Biochemical Oxygen Demand (mg/L)		0.9	1.0
Ammonia Nitrogen (mg/L)		0.124	0.157
Unionised Ammonia (mg/L)		0.005	0.007
Nitrite Nitrogen (mg/L)		0.023	0.027
Nitrate Nitrogen (mg/L)		0.099	0.130
Total Inorganic Nitrogen (mg/L)		0.25	0.31
Total Kjeldahl Nitrogen (mg/L)		0.29	0.34
Total Nitrogen (mg/L)		0.41	0.50
Orthophosphate Phosphorus (mg/L)		0.03	0.03
Total Phosphorus (mg/L)		0.04	0.05
Silica (as SiO2) (mg/L)		0.8	0.8
Chlorophyll-a (μg/L)		3.6	4.7
E.coli (count/100mL)		1077	777
Faecal Coliforms (count/100mL)		2357	1990

6.5 Water Sensitive Receivers

6.5.1 Selection of Indicator Points

Indicator points will be selected in the water quality model to provide hydrodynamic and water quality outputs to evaluate water quality impact. The selected indicator points include water quality sensitive receivers (WSR) and EPD marine water sampling stations.

The WSRs^[1] in the vicinity will include the followings:

· WSR 1 – Tai Wan Salt Water Intake (~900m from works area)

· WSR 2 – Planned Kai Tak Cooling Water Intake (~500m from works area)

· WSR 3 – To Kwa Wan Typhoon Shelter (~200m from works area)

Figure 6.1 shows the locations of these water quality sensitive receivers. The location of EPD marine water and sediment sampling stations VM2, VM4, VT11 and VS3 in Victoria Harbour WCZ are also shown in the figure for reference.

6.5.2 Proposed SS Criteria for Indicator Points

According to WQO, SS is defined as “waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities”. It is expected that the Victoria Harbour WCZ will be affected from the construction works. In order to determine the ambient SS concentrations in the waters likely to be affected by the construction works, water quality monitoring data from 2002 to 2008 EPD’s routine monitoring station VM2 and VT11 in the WCZ have been selected for analysis due to other dredging works in WCZ as discussed in Section 6.4.

The WQO for SS specifies that human activity or waste discharges shall not raise the ambient SS level by 30% and shall not affect communities. In this study, rather than averaging the 90th percentile SS concentrations over the whole area which could be affected by the construction works, it is proposed to assign each sensitive receiver to nearest EPD water quality monitoring station and to set the WQO at each station as 30% of the 90th percentile at the stations as presented in the following Table 6.5. Additionally, 10 percentile of dissolved oxygen (DO) from 2002 to 2008 at VM2 and VT11 monitoring stations are also given in the following table.

Table 6.5: 90 Percentile of Suspended Solids

Monitoring Stations	Season	Depth	90 Percentile of SS (mg/L)	30% of 90 Percentile of SS (mg/L)	10 percentile of DO (mg/L)
VM2	Dry Season ^[1]	Surface	5.4	1.6	4.3
		Middle	6.8	2.0	4.3
		Bottom	8.3	2.5	4.5
		Depth Averaged	6.6	2.0	4.4
	Wet Season ^[2]	Surface	6.4	1.9	4.1
		Middle	7.2	2.2	3.9
		Bottom	9.0	2.7	3.0
		Depth Averaged	7.7	2.3	4.0
VT11	Dry Season^[1]	Surface	5.2	1.6	4.9
		Middle	7.6	2.3	4.9
		Bottom	7.7	2.3	5.2
		Depth Averaged	6.5	2.0	5.0
	Wet Season ^[2]	Surface	7.8	2.3	4.0
		Middle	11.0	3.3	4.0
		Bottom	17.0	5.1	3.8
		Depth Averaged	12.5	3.8	4.0

Notes:

[1] Dry season starts from October to March.

[2] Wet season lasts from April to September.

Taking the WSD Water Quality Objectives for salt water intake into account, the proposed SS assessment criteria at WSRs are summarized in the following Table 6.6.

Table 6.6: Proposed Assessment Criteria for SS

WSR	Season	Depth	SS Elevation (mg/L)	SS Absolute^[1] (mg/L)
WSR 1 – Tai Wan Salt Water Intake (refer to VM2)	Dry Season	Surface	1.6	10
		Middle	2.0	10
		Bottom	2.5	10
		Depth Averaged	2.0	10
	Wet Season	Surface	1.9	10
		Middle	2.2	10
		Bottom	2.7	10
		Depth Averaged	2.3	10
WSR 2 – Planned Kai Tak Cooling Water Intake (refer toVM2)	Dry Season	Surface	1.6	-
		Middle	2.0	-
		Bottom	2.5	-
		Depth Averaged	2.0	-
	Wet Season	Surface	1.9	-
		Middle	2.2	-
		Bottom	2.7	-
		Depth Averaged	2.3	-
WSR 3 – To Kwa Wan Typhoon Shelter (refer to VT11)	Dry Season	Surface	1.6	-
		Middle	2.3	-
		Bottom	2.3	-
		Depth Averaged	2.0	-
	Wet Season	Surface	2.3	-
		Middle	3.3	-
		Bottom	5.1	-
		Depth Averaged	3.8	-

Notes:

[1] Applicable to WSD Salt Water Intakes only

6.6 Potential Concurrent Projects

As discussed in Section 1.8, a number of concurrent projects have been identified. The major existing / planned marine works that might potentially affect the water quality during the construction phase of CKR are listed in the following Table 6.6a.

Table 6.6a: Potential Concurrent Projects Related to Water Quality

Project with Marine Works	Programme	Cumulative Impact
Kai Tak Runway Opening (KTRO)	Land-based construction: 2015 to 2018 Opening and dredging: 2018 (to be reviewed by Development Bureau in end 2013)	Construction Phase: Hydrodynamic impact due to Stage 2 Reclamation
Trunk Road T2 (T2)	Construction: 2015 to 2019	Construction Phase: Water quality
Kai Tak Approach Channel (KTAC) and Kwan Tong Typhoon Shelter (KTTS) Improvement Works (Phase 1)	To be completed by Sept 2014	Not anticipated
Cruise Terminal	Berth No.1 to be completed before 2013 Berth No.2 to be completed before 2015	Not anticipated
Submarine Gas Pipeline	To be completed before 2015	Not anticipated
Shatin to Central Link- Tai Wai to Hung Hom Section (SCL-Tai Wai To Hung Hom)	Dredging works required in SCL-Tai Wai To Hung Hom will start from mid 2012 to end 2012	Not anticipated

Notes:

[1] Projects of SCL IMT, Wan Chai Reclamation, Central-Wan Chai Bypass and other projects in Victoria Harbour, Junk Bay or Eastern Buffer are considered far away from the site and are not taken into the cumulative impact assessment.

6.7 Construction Phase Water Quality Assessment

6.7.1 Land-based Works

6.7.1.1 Construction Runoff

Construction site runoff comprises:

· Runoff and erosion from site surfaces, earth working areas and stockpiles;

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

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

Construction runoff may cause physical, biological and chemical effects. The physical effects include potential blockage of drainage channels and increase of Suspended Solid (SS) levels in Victoria Harbour WCZ.

Local flooding may also occur in heavy rainfall situations. The chemical and biological effects caused by the construction runoff are highly dependent upon its chemical and nutrient content.

Runoff containing significant amounts of concrete and cement-derived material may cause primary chemical effects such as increasing turbidity and discoloration, elevation in pH, and accretion of solids. A number of secondary effects may also result in toxic effects to water biota due to elevated pH values, and reduced decay rates of faecal micro-organisms and photosynthetic rate due to the decreased light penetration.

6.7.1.2 Runoff from Tunnelling Activities and Underground Works

During tunnelling work, rainfall, surface runoff and groundwater seepage pumped out from the tunnel would have high SS content. The situation would be worse during wet seasons.

Surface runoff may also be contaminated by bentonite and grouting chemicals that would be required for the tunneling works and diaphragm walls for cut-and-cover tunnel sections. In addition, wastewater from tunnelling works will also contain a high concentration of SS.

6.7.1.3 Sewage from Workforce

Sewage effluents will arise from the amenity facilities used by the construction workforce and site office’s sanitary facilities. The characteristics of sewage would include high levels of BOD₅, Ammonia and E. coli counts.

Overnight sewage from chemical toilets will also be generated. The sludge needs to be properly managed to minimize odour and potential health risks to the workforce by attracting pests and other disease vectors.

As the workers will be scattered within the construction sites, the most effective solution will be to provide adequate number of portable toilets within the site to ensure that sewage from site staff is properly collected. Depending on site conditions, land availability and site activities, the locations and number of portable toilets will be determined in the Environmental Management Plan (EMP) to be submitted by the Contractor. No adverse waste impact is envisaged provided that maintenance by licensed contractors is conducted regularly.

6.7.1.4 Groundwater Seepage

Some of the tunnel sections will be constructed by cut-and-cover method. Construction methodology using diaphragm wall techniques can minimise the intrusion of groundwater during excavation. It involves excavation of a narrow trench that is kept full of slurry, which exerts hydraulic pressure against the trench walls and acts as a shoring to prevent collapse. Slurry trench excavations can be performed in all types of soil, even below the ground water table.

The construction usually begins with the excavation of discontinuous primary panels of typically up to 6m long and down to the rockhead. In order to provide an effective cut-off to ground water flow, the walls will need to be toe grouted. Once the excavation of a panel is completed, a steel reinforcement cage will be placed in the centre of the panel. Concrete is then poured in one continuous operation. Once the primary panels are set, secondary panels will be constructed between the primary panels and the process then repeats to create a continuous wall. It should be noted that this slurry trench method will reduce the gap between the panels to the practicable minimum. After this, soil excavation will be commenced. The intrusion of groundwater through D-wall panels during soil excavation is therefore considered insignificant.

For those sections that may require bored tunnelling and / or drill-and-blast, some ground treatment (e.g. grouting) will be carried out prior to bored tunnelling. The intrusion of groundwater during bored tunnelling would therefore be insignificant.

6.7.1.5 Discharge of Groundwater Pumped out from Potential Contaminated Area

According to the 2008 survey results, there is no contaminated area identified within areas requesting excavation. Hence, adverse water quality impact due to discharge of groundwater is not anticipated.

Nevertheless, due to constraints in site access, further site investigation (SI) works at Ma Tau Kok will be required to further investigate the potential of land contamination prior to construction which would need to be carried out after possession of site by the contractor (see Chapter 8). If contaminated site found, discharge/ recharge of groundwater generated from this area may affect the groundwater quality, if uncontrolled.

6.7.1.6 Accidental Spillage

The site coverage would be rather large during the construction phase. The soil of site area may be potentially contaminated by accidental spillage of grouting materials, surplus adhesives, lubrication oil, grease, acidic/alkaline solutions, petroleum products, chemical solvents, etc. Site runoff may wash the contaminated soil into stormwater drains or watercourses and cause water quality impact.

6.7.2 Marine-based Works

Temporary reclamation and re-location of navigation channels at To Kwa Wan will include dredging activities. As discussed in Section 3.5, a pipepile seawall method will be applied for the temporary reclamation. This will avoid the need for open dredging and subsequent filling. Compared with traditional fully dredged method, the total in-situ dredging volume for marine channel outside pipepile walls could be reduced from 357,500 m³ to 19,700 m³ (~95% reduction). With the adoption of pipepile seawall method, excavation and filling activities will be carried out within pipepile walls. Thus no contact of marine water with the works is anticipated for temporary reclamation. However, dredging activities will still be occurred during the re-location of navigation channels, as shown in Appendix 3.3. The brief procedures of marine-based works are listed in follows:-

Stage 1 Reclamation: Jan 2015 to Dec 2016 (Tentative)

- Step 1: Installation of stone columns

- Step 2: Stage 1 Reclamation – Installation of pipepile seawall

- Step 3: Stage 1 Reclamation – Excavation, filling activities and all tunneling works within the pipepile seawall

- Step 4: Stage 1 Reclamation – Excavation of filled materials and sediment to the required depth for navigation within the pipepile seawall

- Step 5: Demolition of Stage 1 pipepile seawall (except the interfacing part) by trimming of sheet pipes at top of seabed.

Dredging of Navigation Channel: Jan 2017 to Feb 2017 (Tentative)

- Step 6: Dredging of navigation channel

Stage 2 Reclamation: Mar 2017 to Apr 2019 (Tentative)

- Step 7: Stage 2 Reclamation (repeat Step 2 to 5)

The following potential water quality impacts were identified:

· Change of hydrodynamic regime due to temporary reclamation

· Sediments loss due to dredging

· Contaminant release due to dredging

· Stone Column Installation

· Seawall Demolition

Apart from temporary reclamation and their associated works, there will be a proposed barging point at Kwai Chung (see Figure 3.2.1). Since, the existing land use of this barging point is already barging activities occupied by other projects. Thus, there will be basically no additional construction works on the proposed barging point, except minor facilities might be erected on land base.

6.7.2.1 Change of Hydrodynamic Regime due to Temporary Reclamation

The 3-dimensional modeling tool, Delft3D, is adopted to simulate the hydrodynamic and water quality impact due to the construction and operation of CKR. The Delft3D-FLOW module was used for hydrodynamic simulations.

The approved SEK Model was nested from the Update Model, which is a regional model developed and calibrated under the Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool (1998). The SEK Model was also validated for hydrodynamic and water quality modeling under EIA – Kai Tak Development (EIA-157/2008). The model was therefore be adopted for hydrodynamic and so as the water quality modeling (see Section 6.7.2 below) in the present study.

Despite that SEK Model has been calibrated in that EIA study, calibration or validation of the model was required in this Study as coarse grids used in SEK Model are not suitable for the Project. Therefore, the refinement of grids will be made by either domain-decomposition or nesting process. Moreover, the pollution load inventory inside the model will be updated according to the latest information. Details of modeling parameters and calibration are attached in Appendix 6.2.

The temporary reclamation will be divided into two phases. The construction of Stage 1 temporary reclamation platform will be erected at the eastern part of Kowloon Bay during January 2015 to December 2016 while Stage 2 temporary reclamation platform will be erected at western part of Kowloon Bay near Ma Tau Kok Public Pier and will stay from March 2017 to April 2019. The graphical presentation on reclamation sequence is presented in Appendix 3.3. The following modeling scenarios were therefore identified^[2]:

· Scenario H0 – Base Scenario

· Scenario H2a – Stage 1 Reclamation

· Scenario H1a – Stage 2 Reclamation

· Scenario H1b – Stage 2 Reclamation (with Kai Tak Runway Opening)

The modeling results were presented in Appendix 6.3 and the results are summarized in Table 6.7 below.

Table 6.7: Summary of Hydrodynamic Impact due to Temporary Reclamation

Indicators	Season	Base Case	Stage 1 Reclamation	Stage 2 Reclamation	Stage 2 Reclamation (with Kai Tak Runway Opening)
Accumulated Flow (×10^8m^3)
Victoria – TST to WC	Dry	14.8	14.8	14.8	14.8
	Wet	3.4	3.4	3.4	2.8
Lei Yue Mun	Dry	14.7	14.7	14.7	14.8
	Wet	3.3	3.3	3.3	2.7
Average Velocity (m/s)
WSR 1	Dry	0.076 (0.003-0.180)	0.076 (0.004-0.180)	0.076 (0.004-0.180)	0.084 (0.012-0.194)
	Wet	0.127 (0.025-0.312)	0.126 (0.028-0.310)	0.126 (0.027-0.310)	0.138 (0.020-0.332)
WSR 2	Dry	0.046 (0.002-0.110)	0.046 (0.002-0.110)	0.046 (0.002-0.109)	0.037 (0.004-0.103)
	Wet	0.141 (0.020-0.497)	0.138 (0.020-0.477)	0.138 (0.020-0.478)	0.154 (0.020-0.523)
WSR 3	Dry	0.034 (0.003-0.066)	0.034 (0.003-0.067)	0.034 (0.003-0.067)	0.041 (0.006-0.092)
	Wet	0.059 (0.010-0.168)	0.059 (0.009-0.158)	0.059 (0.010-0.159)	0.068 (0.014-0.161)
Embayed Area	Dry	0.008 (0.001-0.060)	0.006 (0.000-0.055)	0.007 (0.000-0.052)	0.012 (0.002-0.048)
	Wet	0.030 (0.006-0.064)	0.023 (0.003-0.056)	0.031 (0.004-0.067)	0.028 (0.008-0.064)

According to the modeling results, it is observed that the change of average velocity due to the temporary reclamation is less than 0.007m/s (refer Base Case and Stage 1 Reclamation).

In the embayed area formed by the temporary reclamation, it is observed that the current directions will be changed due to the semi-enclosed opening. The velocity variations at the embayed area are less than 0.007m/s and 0.001 m/s due to the Stage 1 and 2 Reclamations (project only) respectively. Nevertheless, the water circulation at this embayed area is already in a low side (0.001 to 0.060 m/s and 0.006 to 0.064 m/s for dry and wet season respectively) compared to that typhoon shelter and outer Kowloon Bay (WSR 1 to WSR 3). The change of hydrodynamic regime due to temporary reclamation will only last for less than 5 years (around Jan 2015 to Apr 2019). Thus, hydrodynamic impact is insignificant and the associated water quality impact including dissolved oxygen profile (which the re-aeration rate is a function of velocity) would be negligible.

The Kai Tak runway opening will be operated in 2018, where will have about 16-month concurrent period. With the operation of Kai Tak runway opening during Stage 2 Reclamation, pollutant from Kai Tak Nullah and Approach Channel may be diluted and dispersed to Kowloon Bay and the embayed area^[6-8]. These pollutants are dominated by the implementation of Tolo Harbour Effluent Export Scheme (THEES), which diverts the secondary treated effluent from the Tai Po and Sha Tin sewage treatment works, and also the existing pollutants from Kai Tak Nullah and Kai Tak Approach Channel. According to the modelling prediction under in the EIA Report of Kai Tak Development (EIA-157/2008), the annual mean ammonia nitrogen and unionised ammonia levels would exceed the existing WQO^[6-8] at the embayed area. This pollutant plume may further trapped inside the embayed area if Stage 2 Reclamation occurred. This phenomenon is also shown in the salinity plot in Appendix 6.3 (H1b-D-SL-ET, H1b-D-SL-FT, H1b-W-SL-ET, H1b-W-SL-FT).

Additional scenario, Scenario H2b-DN, representing a do-nothing scenario with Kai Tak Runway Opening was modelled for comparison. The comparison of salinity levels with and without Stage 2 Reclamation was presented in Appendix 6.3A. Marginal change in salinity levels is observed with and without Stage 2 Reclamation. In general speaking salinity levels will be reduced at surface layer but increase in bottom layer with the presence of Stage 2 Reclamation. These changes are considered to be minor and will not further deteriorate the water quality and the impact were mainly due to the Kai Tak runway opening, which is a not related to CKR project.

According to the model result, the velocity variations at the embayed area is +0.004 m/s and -0.002 m/s in dry and wet season respectively during Stage 2 Reclamation with Kai Tak runway opening. Similar to the above, given the embayed area is already under a low flow condition, major change of water circulation due to the Project is not anticipated. There are also no WSR within the embayed area. Thus, the associated water quality impact is considered to be minor. In addition, according to the latest programme, Environmental Bureau will further review the tentative operation date of Kai Tak runway opening in end 2013 and the actual operation date is likely to be further delayed. Thus, cumulative impact from Stage 2 Reclamation and Kai Tak runway opening might not exist if programme changed. For conservative consideration, the maximum overlapping period of Stage 2 Reclamation and Kai Tak runway opening will only last for about 16 months. Thus, such minor impact is reversible after demolishment of Stage 2 Reclamation. Once the Stage 2 Reclamation is demolished, the water quality regime will remain as that predicted in the EIA for Kai Tak Development.

Given the insignificant hydrodynamic and water quality impact due to temporary reclamation, generic mitigation measure is recommended as follows:

· Illegal discharges to the embayed marine water is strictly prohibited; and

· Regular litter/rubbish clearance in the embayed marine water should be implemented.

6.7.2.2 Sediment Loss due to Dredging

With the adoption of pipepile seawall approach using double-layer seawall method, excavation and filling activities will be carried out within the temporary reclamation area enclosed by double-layer seawall. Thus no contact of marine water with the works is anticipated for temporary reclamation.

Demolition of temporary reclamation will involve excavation of bulk fill. The proposed construction method adopts an approach where the double-layer seawall not be removed until completion of all excavation works within the temporary reclamation area enclosed by the double-layer seawall. The double-layer seawall will then be demolished by first removing the soil infill within the double-layer steel pipepile/sheetpiles, followed by the removal of the steel pipepile/sheetpiles. Thus, excavation of bulk fill will be carried out within the area enclosed by the double-layer seawall and the sediment plume can be effectively contained within the works area. The last stage of demolition of double-layer seawall will involve trimming of pipe piles/sheet piles only, which would not create significant SS impact. No additional dredging will be required. Fines content in the filling materials in the seawall would be negligible and loss of fill material during temporary reclamation demolition is not expected.

In addition, as the project will not cause any additional marine traffic except the dredgers/barges operation. Good site practices are proposed and included in Section 6.9.

The main potential impact on water quality will be arisen from 2-month dredging activities (as shown in activities 14a and 14b in Appendix 6.10) for navigation channels immediately after demolition of Stage 1 Reclamation but prior to the construction of Stage 2 Reclamation starting from January 2017 to February 2017. The dredging location will be outside pipepile walls for Stage 1 temporary reclamation. Potential water quality impact will be related to disturbances to the water column and seabed, which will lead to the potential for physio-chemical changes in the water column. Grab dredgers will be utilized and it may release sediment into suspension by the following activities:

· Impact of the grab on the seabed as it is lowered;

· Washing of sediment off the outside of the grab as it is raised through the water column and when it is lowered again after being emptied;

· Leakage of water from the grab as it is hauled above the water surface;

· Spillage of sediment from over-full grabs;

· Loss from grabs which cannot be fully closed due to the presence of debris; and

· Disturbance of the seabed as the closed grab is removed.

The sediment loss rate for dredging activities will be calculated by the multiplication of volumetric dredging rate. The sediment loss per volumetric dredging rates closed grab dredgers will be 17 to 20 kg/m³. As a conservative approach, sediment loss of 25 kg/m³ was adopted.

Silt curtain will normally be adopted to mitigate the potential water quality impact during dredging. The effectiveness of mitigation measures is summarized in the following Table 6.8.

Table 6.8: Summary Table of Loss Reductions from Silt Curtain Configurations

Silt Curtain Type	Loss Reduction Factor	Remark
Dredging Activities
Cage type for Grab Dredger (Figure 6.2)	80%	EIA – HZMB HKLR
Floating Single Silt Curtain	75%	EIA – Cruise Terminal
Receiver Control
Silt Screen at Seawater Intakes	60%	EIA – Cruise Terminal

Water Quality Model

The hydrodynamic outputs from the model will provide inputs for water quality simulation. The hydrodynamic forcing including averaged fresh water flow, wind, initial conditions and boundary conditions for the dry season and wet seasons will be applied separately in the corresponding hydrodynamic simulation. Similarly, the dry and wet season pollution loads will be applied in the corresponding dry and wet season water quality simulations.

According to the construction programme, the construction period of CKR under water tunnel will be Year 2015 to 2019 tentatively and the dredging period will be tentatively about 2 months. While the Kai Tak Runway Opening will be operated in 2018, the hydrodynamic conditions were therefore based on Base Case (Scenario H0). In considering the cumulative impact with other nearby marine works, the following modeling scenarios are identified:

· Scenario C3 – Dredging of marine channel for CKR

· Scenario C4 – Dredging of marine channel for CKR + T2

The sediment loss rates during dredging/filling activities are presented in Appendix 6.4 and summarized in Table 6.9 below and Figure 6.3.

Table 6.9: Sediment Loss Rate

Loading Point	Production Rate	Sediment Loss Rate
Scenario C3
CKR – Dredging	1500 m^3/day^[1]	0.87 kg/s for 2 dredgers^[2] (Unmitigated)
Scenario C4
CKR – Dredging	1500 m^3/day^[1]	0.87 kg/s for 2 dredgers^[2] (Unmitigated)
T2 – Dredging^[3]	8000 m^3/day	0.93 kg/s (Mitigated)
T2 – Filling^[3]	2000 m^3/day	0.19 kg/s (Mitigated)

Notes:

[1] Dredging rate of 1500 m³/day refers to unmitigated scenario. Silt curtain and 50% dredging rate reduction in wet season will be adopted as a mitigation measure (see below sections)

[2] Assume 12 working hours per day. Calculations refer to Appendix 6.4.

[3] According to the latest information, TBM method will be adopted for T2 project and thus no dredging/filling work is required. However, the actual construction method for T2 project is still under investigation, traditional dredging/filling works were assumed as a conservative approach.

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

DO_Dep = C * SOD * K * 0.001

where,

DO_Dep = Dissolved Oxygen depletion (mg/l)

C = Suspended Solids concentration (kg/m³)

SOD = Sediment Oxygen Demand

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

There is no monitoring data for SOD. As a conservative approach, the average Chemical Oxygen Demand (COD) of 22,000 mg/kg from 2002 to 2008 has been taken with reference to the closest EPD marine monitoring station – VS3 as a suitably representative value for sediments in the Victoria Harbour.

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

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

The modeling results were presented in Appendix 6.5 and the results are summarized in the tables below. It is noted that the predicted SS elevations, SS and DO were well within the criteria during dry season.

Exceedances of SS elevations were anticipated in WSR 2 (Planned Kai Tak Cooling Water Intake) and WSR 3 (To Kwa Wan Typhoon Shelter) during CKR dredging works of temporary marine channel outside pipepile walls (Scenario C3) during wet season without any mitigation measure. The percentage of exceedance time is up to 12%, i.e. around 8 days for the 2-month dredging period.

When considering the cumulative impacts from the potential concurrent project such as T2, exceedances at WSR 2 and WSR 3 are still anticipated during wet season. The percentage of exceedance time is around 12%, around 8 days of the 2-month dredging period. The exceedance of total SS was also anticipated at WSR1 when taking T2 into account while the percentage of exceedance time is around 1%, i.e. around 1 day of the dredging period.

Table 6.10a: Summary of Water Quality Impact due to Dredging/Filling Activities (Scenario C3) – Unmitigated

Indicators	Season	Modeling Result			Criteria
		WSR 1	WSR 2	WSR 3	WSR 1	WSR 2	WSR 3
Suspended Solid Elevation (mg/L)
Surface	Dry	0.0	0.5	0.5	1.6	1.6	1.6
	Wet	0.0	1.8	0.0	1.9	1.9	2.3
Middle	Dry	0.0	0.5	0.0	2.0	2.0	2.3
	Wet	0.2	15.3 (12%)	6.1(1%)	2.2	2.2	3.3
Bottom	Dry	0.0	0.0	0.0	2.5	2.5	2.3
	Wet	0.4	10.9 (8%)	19.6 (2%)	2.7	2.7	5.1
Depth Averaged	Dry	0.0	0.2	0.2	2.0	2.0	2.0
	Wet	0.1	7.4 (8%)	6.5 (1%)	2.3	2.3	3.8
Suspended Solid (mg/L)^[3]
Surface	Dry	5.4	5.9	5.9	≤10	-	-
	Wet	6.4	8.2	6.4	≤ 10	-	-
Middle	Dry	6.8	7.3	6.8	≤ 10	-	-
	Wet	7.4	22.5	13.3	≤ 10	-	-
Bottom	Dry	8.3	8.3	8.3	≤ 10	-	-
	Wet	9.4	19.9	28.6	≤ 10	-	-
Depth Averaged	Dry	6.6	6.8	6.8	≤ 10	-	-
	Wet	7.8	15.1	14.2	≤ 10	-	-
Dissolved Oxygen Depletion (mg/L)
Bottom	Dry	0.0	0.0	0.0	-	-	-
	Wet	0.0	0.2	0.4	-	-	-
Depth Averaged	Dry	0.0	0.0	0.0	-	-	-
	Wet	0.0	0.2	0.1	-	-	-
Dissolved Oxygen (mg/L)
Bottom ^[4]	Dry	4.5	4.5	5.2	³2	³2	³2
	Wet	3.0	2.8	3.4	³ 2	³ 2	³ 2
Depth Averaged ^[4]	Dry	4.4	4.4	5.0	³ 4	³ 4	³ 4
	Wet	4.0	3.8	3.9	³ 4	³ 4	³ 4

Notes:

[1] The dredging period will be 2 months, from January 2017 to February 2017.

[2] Grey cell represents exceedance records and the bracket shows the percentage of exceedance period.

[3] Baseline SS levels of WSRs 1 and 2 refer to VM2 and WSR 3 refer to VT11 during dry and wet seasons, separately. (Refer to Table 6.5)

[4] Baseline Bottom and depth-averaged DO levels of WSRs 1 and 2 refer to VM2 and WSR 3 refer to VT 11 during dry and wet seasons, separately. (Refer to Table 6.5)

Table 6.10b: Summary of Water Quality Impact due to Dredging/Filling Activities (Scenario C4) – Unmitigated

Indicators	Season	Modeling Result			Criteria
		WSR 1	WSR 2	WSR 3	WSR 1	WSR 2	WSR 3
Suspended Solid Elevation (mg/L)
Surface	Dry	0.0	0.5	0.5	1.6	1.6	1.6
	Wet	0.5	1.8	0.0	1.9	1.9	2.3
Middle	Dry	0.0	0.5	0.0	2.0	2.0	2.3
	Wet	1.1	15.3 (12%)	6.1 (1%)	2.2	2.2	3.3
Bottom	Dry	0.0	0.0	0.0	2.5	2.5	2.3
	Wet	1.1	10.9 (8%)	19.6(2%)	2.7	2.7	5.1
Depth Averaged	Dry	0.0	0.2	0.2	2.0	2.0	2.0
	Wet	0.4	7.4 (8%)	6.5 (1%)	2.3	2.3	3.8
Suspended Solid (mg/L)^[3]
Surface	Dry	5.4	5.9	5.9	£ 10	-	-
	Wet	6.9	8.2	6.4	£ 10	-	-
Middle	Dry	6.8	7.3	6.8	£ 10	-	-
	Wet	8.3	22.5	13.3	£ 10	-	-
Bottom	Dry	8.3	8.3	8.3	£ 10	-	-
	Wet	10.1(1%)	19.9	28.6	£ 10	-	-
Depth Averaged	Dry	6.6	6.8	6.8	£ 10	-	-
	Wet	8.1	15.1	14.2	£ 10	-	-
Dissolved Oxygen Depletion (mg/L)
Bottom	Dry	0.0	0.0	0.0	-	-	-
	Wet	0.0	0.2	0.4	-	-	-
Depth Averaged	Dry	0.0	0.0	0.0	-	-	-
	Wet	0.0	0.2	0.1	-	-	-
Dissolved Oxygen (mg/L)
Bottom ^[4]	Dry	4.5	4.5	5.2	³ 2	³ 2	³ 2
	Wet	3.0	2.8	3.4	³ 2	³ 2	³ 2
Depth Averaged ^[4]	Dry	4.4	4.4	5.0	³ 4	³ 4	³ 4
	Wet	4.0	3.8	3.9	³ 4	³ 4	³ 4

Notes:

[1] The dredging period will be 2 months, from January 2017 to February 2017.

[2] Grey cell represents exceedance records and the bracket shows the percentage of exceedance period.

[3] Baseline SS levels of WSRs 1 and 2 refer to VM2 and WSR 3 refer to VT11 during dry and wet seasons, separately. (Refer to Table 6.5)

[4] Baseline Bottom and depth-averaged DO levels of WSRs 1 and 2 refer to VM2 and WSR 3 refer to VT 11 during dry and wet seasons, separately. (Refer to Table 6.5)

6.7.2.3 Contaminant Release due to Dredging

Sediment samples have been collected at the proposed site of temporary reclamation. Elutriate tests and pore water test have been conducted for the following parameters:

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

· Organic micro-pollutants including PCB, PAH, and TBT; and

· TKN, NO₃-N, NO₂-N, NH₄-N, PO₄-P, total phosphorus, reactive phosphorus and chlorinated pesticides.

The laboratory results for the sediment samples collected within the dredging area were presented in Appendix 6.6. The sediment results for other concurrent projects are also included in Appendix 6.6 for easy referencing. It is observed that the elutriate and pore water test results of most contaminant parameters complied the proposed criteria. Thus, the release of other contaminants will be well mixed locally around the dredging point without causing enlargement of mixing zones with the exception of Cu, Ni, Total PAH, UIA, TIN, PO₄ and TP. The extracted elutriate data with exceedance or higher than baseline level was incorporated in Table 6.11.

The elutriate and pore water test results provided the information on the initial concentrations of these parameters that would be released from the marine mud during the dredging operation. As a conservative approach, the contaminant loss rate (in mg/s or µg/s) for model input assumed that all of the heavy metals and nutrient concentrations in the sediment would be released to the water (i.e. sediment release rates (in kg/s) times the sediment quality (in mg/kg or µg/kg).

Similar to Section 6.7.2.2, two scenarios, Scenario C3 and C4, were identified and tracer substances is adopted in the model run.

Table 6.11: Summary of Maximum Elutriate Test Results (for those sampling points with exceedance or higher than baseline levels)

	Metal		Trace Organics	Nutrients
	Cu	Ni	Total PAHs	UIA^[1]	TIN^[2]	PO4	TP
Unit	µg/L	µg/L	µg/L	mg/L	mg/L	mg/L	mg/L
Assessment Criteria^[3]	5	8.2	3.0^[7]	0.021	0.4	N/A	N/A
Reference sample (Considered as background level if above detection limit) ^[4]	less than detection limit	less than detection limit	less than detection limit^[8]	0.008	0.3	less than detection limit	less than detection limit
Project
CKR^[5]	22	93	549	4.996	89.2	0.1	0.2
T2^[6]	<2	7	<<32	1.017	18.1	-	4.0

Note:

[1] [UIA] = 5.62 x 10^-10 x [NH₃-N] / 10^-pH, taking pH of 8.0 according to the average pH value of EPD’s monitoring stations VM2, VT11

[2] [TIN] = [NO₃-N] + [NO₂-N] + [NH₃-N]

[3] Apart from parameters of UIA and TIN, the assessment criteria are set with reference to Table 6.3 while the assessment criteria of UIA and TIN are set based on the WQO for Victoria Harbour WCZ.

[4] Concentrations of reference sample of elutriate testing results. The detection limit for Cu, Ni, TPAH, PO4 and TP are one-third of the reporting limits, i.e. 0.33µg/L, 0.33µg/L, 1.07µg/L(see footnote [8]), 0.0033µg/L and 0.033µg/L respectively.

[5] According to dredging extent and dredging depth, elutriate data from VR2, VR3, VR4, VR5, GB6 and GB7 from 0 to 2.9m were adopted.

[6] EIA Report of South East Kowloon Development, Table 4.29, 4.30

[7] According to Australian Water Quality Guidelines for Fresh and Marine Waters, the criterion of naphthalene is 3.0 µg/L for fresh water aquatic ecosystem conservations. Nevertheless, since all the WSRs are typhoon shelters and industrial use, the functions of these WSRs are neither ecological importance nor portable use. Hence, tolerant levels should be much higher. Adoption of 3.0 µg/L as proposed criterion for total PAH is in much conservative side.

[8] The detection limit of individual PAH (e.g. naphthalene) is 0.067 µg/L. The concentration of total PAH is determined by adding the concentration of individual PAH. Thus, the detection limit of total PAH is 1.07 µg/L.

Appendix 6.7 presents the mixing zones and time series contaminant levels at individual WSRs. The summary of modeling results is presented in Table 6.12a and Table 6.12b. According to the modeling results, no exceedance was predicted for any scenarios during wet season. The detail analysis are given below:-

Heavy Metals

The size of mixing zones of heavy metals will be highly localized during peak dredging periods as shown in Appendix 6.7. The maximum mixing zone of Cu during peak time is around 1.53 km², cumulating at the inner Kowloon Bay (see Drawings D-CU and D-CCU of Appendix 6.7). The predicted Cu level at WSR 3 (To Kwa Wan Typhoon Shelter) exceeds the proposed criteria of 5 µg/L at bottom layer for Scenario C3 during dry season.

Nevertheless, since the proposed copper criterion (i.e. 5.0 µg/L) is for protection of irrigation and aquaculture purpose according to Australian Water Quality Guidelines for Fresh and Marine Waters, it is already in a conservative side. Since all the WSRs are typhoon shelters and industrial use, the functions of these WSRs are neither for irrigation nor aquaculture purpose. Thus, exceedance of heavy metals levels are not sensitive to these WSRs. In addition, the dredging period will occur within a short period (only 2 months). The residue impacts are likely to be temporary and will not deteriorate their existing functions.

In cumulative consideration with T2 dredging (Scenario C4), exceedance were predicted or both WSR 2 (Planned Kai Tak Cooling Water Intake) and WSR 3 (To Kwa Wan Typhoon Shelter) and the highest Cu level is 6.0 µg/L. In order to further protect the WSRs, mitigation measures are proposed as much as possible and details are presented in Section 6.9.2.2.

The mixing zones of other heavy metals are unnoticeable. The predicted peak levels of Ni at all three WSRs are lower than the respective proposed criteria of 8.2 µg/L.

Trace Organics

The initial concentration of PAH levels is rather high (549 µg/L) during dredging periods. Unlike the unnoticeable mixing zones from other trace organics, the maximum mixing zone of PAH due to the project during the peak time is around 0.78 km² at the inner Kowloon Bay as shown in Drawings D-PAH and D-CPAH of Appendix 6.7. The predicted PAH levels at WSR 3 (To Kwa Wan Typhoon Shelter) has exceeded the proposed criteria of 3.0 µg/L at bottom layer for Scenario C3 during dry season.

Nevertheless, since the proposed total PAH criterion (i.e. 3.0 µg/L) is for protection of fresh water aquatic ecosystem according to Australian Water Quality Guidelines for Fresh and Marine Waters, the tolerant levels for marine aquatic ecosystem is much higher. Since all the WSRs are typhoon shelters and industrial use, the functions of these WSRs are neither ecological importance nor for portable use. Thus, exceedance of total PAH levels are not sensitive to these WSRs. In addition, the dredging period will occur within a short period (only 2 months). The residue impacts are likely to be temporary and will not deteriorate their existing functions.

In cumulative consideration with T2 dredging (Scenario C4), exceedance were predicted or both WSR 2 (Planned Kai Tak Cooling Water Intake) and WSR 3 (To Kwa Wan Typhoon Shelter) and the highest PAH level is 12.0 µg/L. In order to further protect the WSRs, mitigation measures are proposed at much as possible and details are presented in Section 6.9.2.2.

Nutrients

The size of mixing zones of nutrient will be highly diluted during peak dredging periods. The levels of UIA and TIN at three WSRs are all far below the respective assessment criteria (0.021 and 0.4 mg/L respectively), only with marginal increase due to the dredging. And their maximum mixing zones are not noticeable during peak time. Very limited increase of PO₄ and TP are also estimated at three WSRs, as shown in Table 6.12a. The maximum mixing zones of PO₄ and TP during peak time are around 0.125 km² due to CKR while the cumulative maximum mixing zone of TP would possibly be 1 km² without reaching WSRs (see Drawings D-RP, D-CRP, D-TP and D-CTP of Appendix 6.7). No exceedance to the proposed criteria is therefore anticipated.

Table 6.12a: Model Results for Release of Contaminants (Dry Season dredging)

		Metal		Trace Organics	Nutrients
		Cu^[1]	Ni^[1]	Total PAHs^[1]	UIA^[2]	TIN^[2]	PO4^[1]	TP^[1]
Unit		µg/L	µg/L	µg/L	mg/L	mg/L	mg/L	mg/L
Assessment Criteria		5	8.2	3.0	0.021	0.4	N/A	N/A
Reference sample (Considered as background level if above detection limit)		less than detection limit	less than detection limit	less than detection limit	0.008	0.3	less than detection limit	less than detection limit
WSR 1 – Tai Wan Salt Water Intake
Scenario C3 – CKR Only	Surface	1.5	0.1	0.8	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.001	0.001
	Bottom	1.7	0.1	1.2	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.001	0.001
Scenario C4 – Cumulative	Surface	2.7	0.1	2.9	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.001
	Bottom	3.3	0.1	3.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.001
WSR 2 – Planned Kai Tak Cooling Water Intake
Scenario C3 – CKR Only	Surface	5.0	0.3	3.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.003	0.001
	Bottom	4.1	0.2	2.8	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.002	0.001
Scenario C4 – Cumulative	Surface	5.1	0.3	5.1	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.003
	Bottom	6.1	0.3	6.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.002
WSR 3 – To Kwa Wan Typhoon Shelter
Scenario C3 – CKR Only	Surface	4.6	0.3	3.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.002	0.002
	Bottom	10.0	0.6	6.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.005	0.006
Scenario C4 – Cumulative	Surface	6.3	0.4	5.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.003
	Bottom	12.3	0.7	12.0	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.006

Note:

[1] Refers to peak value.

[2] Refers to annual mean according to WQO. For 2 months dredging, Annual mean = Peak elevation x 2/12 + background

[3] Included background

Table 6.12b: Model Results for Release of Contaminants (Wet Season dredging)

		Metal		Trace Organics	Nutrients
		Cu^[1]	Ni^[1]	Total PAHs^[1]	UIA^[2]	TIN^[2]	PO4^[1]	TP^[1]
Unit		µg/L	µg/L	µg/L	mg/L	mg/L	mg/L	mg/L
Assessment Criteria		5	8.2	3.0	0.021	0.4	N/A	N/A
Reference sample (Considered as background level if above detection limit)		less than detection limit	less than detection limit	less than detection limit	0.008	0.3	less than detection limit	less than detection limit
WSR 1 – Tai Wan Salt Water Intake
Scenario C3 – CKR Only	Surface	0.4	0.0	0.3	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.000	0.000
	Bottom	0.3	0.0	0.2	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	0.000	0.000
Scenario C4 – Cumulative	Surface	1.4	0.1	0.3	0.008^[3] (Peak: 0.008)	0.3^[3] (Peak: 0.3)	N/A	0.000
	Bottom	1.7	0.1	0.2