TABLE OF CONTENTS

 

Page

 

4... WATER QUALITY IMPACT.. 4-1

4.1   Introduction   4-1

4.2   Environmental Legislation, Policies, Plans, Standards and Criteria   4-1

4.3   Description of the Environment   4-74-74-8

4.4   Water Sensitive Receiver   4-11

4.5   Assessment Methodology   4-13

4.6   Identification of Environmental Impact   4-264-264-27

4.7   Prediction and Evaluation of Environmental Impact   4-274-274-28

4.8   Mitigation of Adverse Environmental Impact   4-674-664-67

4.9   Evaluation of Residual Impact   4-704-69

4.10   Environmental Monitoring and Audit   4-704-694-70

4.11   Conclusions   4-714-70

 

 

List of Tables

 

Table 4.1   Summary of Water Quality Objectives for Victoria Harbour WCZ

Table 4.2   Summary of Water Quality Objectives for Tolo Harbour and Channel WCZ

Table 4.3   WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes

Table 4.4   Assessment Criteria for Local Marine Biota and Fisheries Resources

Table 4.5   Summary Statistics of 2002 Marine Water Quality in the Vicinity of the outfall of Kai Tak Nullah

Table 4.6   Summary Statistics of 2002 Marine Water Quality in the Vicinity of Sha Tin and Tai Po Effluent Pumping Station Emergency Bypass outfalls

Table 4.7   Current and New Effluent Standards upon commissioning

Table 4.8   Proposed Baseline and Operation Phase Water Quality Modelling Scenarios

Table 4.9   Modelling Scenarios for Option 1 and Option 2

Table 4.10a    Projected Dry Weather Diurnal Flow Pattern of TPSTW in 2006

Table 4.10b   Volume of Overflow Discharges

Table 4.10c   Key Modelling Parameters

Table 4.11   Pollution Loading from Stonecutters, Sandy Bay and North Point Sewage Treatment Works under HATS (Option 5d)

Table 4.12   Predicted Water Quality at Indicator Points for Scenario 1 – Year 2003 (annual average)

Table 4.13   Predicted Water Quality at Water Intakes for Scenario 1 – Year 2003 (annual average)

Table 4.14   Predicted Water Quality at Indicator Points for Scenario 2a (without the Project) and Scenario 2b (with the Project) in Year 2010 (annual average)

Table 4.15   Predicted Water Quality at Water Intakes for Scenario 2a (without the Project) and Scenario 2b (with the Project) in Year 2010 (annual average)

Table 4.16   Predicted Water Quality at Indicator Points for Scenario 3a (without the Project) and Scenario 3b (with the Project) in Year 2016 (annual average)

Table 4.17   Predicted Water Quality at Water Intakes for Scenario 3a (without the Project) and Scenario 3b (with the Project) in Year 2016 (annual average)

Table 4.18   Predicted Water Quality for Scenarios 4 (Baseline), 5 (Operational) and 6 (Maintenance Discharge)

Table 4.19   Predicted Water Quality at Water Intakes for Scenario 4 (Baseline) and Scenario 5 (Operational Phase) (annual average)

Table 4.20   Key Coral Sites in Tolo Harbour and Victoria Harbour

Table 4.21   Predicted Annual Average Suspended Solids and Maximum Daily Sedimentation Rates at Corals in Tolo Harbour

Table 4.22   Predicted Maximum Daily Sedimentation Rates at Corals in Victoria Harbour

 

 

List of Figures

 

Figure 4.1    Locations of EPD’s Marine Water Quality Monitoring Stations in Victoria Harbour

Figure 4.2   Locations of EPD Marine Water Quality Monitoring Stations in the Tolo Harbour and Channel WCZ

Figure 4.3   Locations of Water Intakes and Coral Sites in Victoria Harbour

Figure 4.4   Key Water and Marine Ecological Sensitive Receivers in Tolo Harbour and Channel

Figure 4.5   Coastline Configuration in 2010

Figure 4.6a   Coastline Configuration in 2016

Figure 4.6b   Alternative Coastline Configuration in 2016

Figure 4.7   Locations of the Outfalls for the Emergency Bypasses of Shatin Effluent Pumping Station and Tai Po Effluent Pumping Station

Figure 4.8   Locations of Fish Culture Zones, Beaches and Typhoon Shelters within the Water Quality Modelling Area under Scenario 1 (2003)

Figure 4.9   Locations of Fish Culture Zones, Beaches, Typhoon Shelters, and Marinas within the Water Quality Modelling Area under Scenarios 2A and 2B (2010)

Figure 4.10   Locations of Fish Culture Zones, Beaches, Typhoon Shelters, and Marinas within the Water Quality Modelling Area under Scenarios 3A and 3B (2016)

 

 

Appendices

 

Appendix 4.1   Pollution Loading Inventories for the HKSAR in 2003, 2010 and 2016

Appendix 4.2   Contour and Time Series Plots of Water Quality Modelling Results

Appendix 4.3   Environmental Protection Department, Professional Persons Environmental Consultative Committee Practice Note (ProPECC PN) 1/94 – Construction Site Drainage

Appendix 4.4a   Assessment of Water Quality Impact due to Possible Change in the HATS Treatment for 2016

Appendix 4.4b   Assessment of Water Quality Impact due to Possible Change in Coastline Configuration for 2016

Appendix 4.5   Emergency Contingency Plan

Appendix 4.6   Figures for Overflow Discharges

Appendix 4.7   Comparison of Historic Water Quality Data with Closure Periods of THEES


4.                  WATER QUALITY IMPACT

 

4.1              Introduction

 

4.1.1The Project aims to upgrade the existing Tai Po Sewage Treatment Works (TPSTW) to provide additional sewage treatment capacity to meet the demands of both existing and future development and population growth in Tai Po.  In addition, a more stringent discharge standard will be adopted for the future upgraded TPSTW to further improve the environmental conditions. This Project wouldtherefore yield high benefits for water quality by reducing the amount of raw sewage from directly discharging into the Tolo Harbour.

 

4.1.1        This section presents the findings of the assessment of potential water quality impacts associated with the construction and operation of the Project. Suitable mitigation measures have been recommended to minimise potential adverse impacts and to ensure the acceptability of any residual impact (that is, after mitigation).

 

4.1.2        Under the Tolo Harbour Effluent Export Scheme (THEES), the treated sewage effluent from Tai Po Sewage Treatment Works (TPSTW) is collected in the Tai Po effluent pumping station and pumped to the effluent pumping station at Sha Tin Sewage Treatment Works (STSTW). Then, together with the treated effluent of STSTW, the combined effluent is pumped into Kai Tak Nullah for discharge into Victoria Harbour.  In addition, treated, partially treated or untreated sewage effluent may be discharged into Tolo Harbour under emergency condition or during the THEES maintenance period.  Treated effluent may also be occasionally overflowed into the Tolo Harbour during storm events under normal operation of the Project. The discharge locations of the Project within Tolo Harbour are shown in Figure 4.7. They are the outfalls for emergency bypass of sewage effluent pumping stations at Sha Tin and Tai Po.  As such, the Project would have potential impact on both Victoria Harbour and Tolo Harbour.

 

4.2              Environmental Legislation, Policies, Plans, Standards and Criteria

 

4.2.1        The criteria for evaluating water quality impacts in this EIA Study include:

 

·        Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM);

·        Water Pollution Control Ordinance (WPCO);

·        Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS);

·        Hong Kong Planning Standards and Guidelines (HKPSG);

·        Water Supplies Department (WSD) Water Quality Criteria; and

·        Practice Note for Professional Persons (ProPECC), Construction Site Drainage (PN 1/94).

 

Environmental Impact Assessment Ordinance (EIAO)

 

4.2.2        This Project is a Designated Project (DP) under Schedule 2, Part I, F.1 of the EIAO. The EIAO-TM was issued by the Environmental Protection Department (EPD) under Section 16 of the EIAO. It specifies the assessment method and criteria that have been 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; and

·         Annex 14 Guidelines for Assessment of Water Pollution.

Water Quality Objectives (WQOs)

 

4.2.3        The WPCO provides the statutory framework for the protection and control of water quality in Hong Kong. According to the ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs).  Corresponding statements of Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches, secondary contact recreation subzones and fish culture subzones) based on their beneficial uses.  The effluent from TPSTW would impact the marine water quality within Victoria Harbour and Tolo Harbour and Channel.  Their corresponding WQOs are listed in Table 4.1 and Table 4.2.

 

Table 4.1         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 (DA) 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 4.2         Summary of Water Quality Objectives for Tolo Harbour and Channel WCZ

Parameters

Objectives

Sub-Zone

Offensive Odour, Tints

Not to be present

Harbour subzone, Buffer subzone, Channel subzone

Visible foam, oil, grease, scum, litter

Not to be present

Harbour subzone, Buffer subzone, Channel subzone

Dissolved Oxygen (DO)

Not less than 2 mg/L within two metres of the bottom, or not less than 4 mg/L in the remainder of the water column

Harbour subzone

Not less than 3 mg/L within two metres of the bottom, or not less than 4 mg/L in the remainder of the water column

Buffer subzone

Not less than 4 mg/L at any point in the water column

Channel subzone

pH

Not to cause the normal pH range to be extended by more than ± 0.5 pH units at any time.

Harbour subzone

Not to cause the normal pH range to be extended by more than ± 0.3 pH units at any time.

Buffer subzone

Not to cause the normal pH range to be extended by more than ± 0.1 pH units at any time.

Channel subzone

Light Penetration

Should not reduce light transmission by more than 20% of the normal level at any location or any time.

Harbour subzone

Should not reduce light transmission by more than 15% of the normal level at any location or any time.

Buffer subzone

Should not reduce light transmission by more than 10% of the normal level at any location or any time.

Channel subzone

Salinity

Not to cause the normal salinity range to be extended by more than ± 3 parts per thousand at any time.

Harbour subzone, Buffer subzone, Channel subzone

Temperature

Not to cause the natural daily temperature range to be extended by greater than ± 1.0 oC at any location or time.  The rate of temperature change shall not exceed 0.5 oC per hour at any location, unless due to natural phenomena.

Harbour subzone, Buffer subzone, Channel subzone

Settleable Material

Bottom deposits or submerged objects should not adversely influence bottom-living communities, alter the basic Harbour geometry or shipping channels, present any hazard to shipping or diving activities, or affect any other beneficial use of the waters.

Harbour subzone, Buffer subzone, Channel subzone

Bacteria

Not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in one calendar year.

Secondary contact recreation subzone and fish culture zone

Chlorophyll-a

Not to cause the level of chlorophyll-a in waters of the subzone to exceed 20 mg m-3, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth

Harbour subzone

 

Not to cause the level of chlorophyll-a in waters of the subzone to exceed 10 mg m-3, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth

Buffer subzone

Not to cause the level of chlorophyll-a in waters of the subzone to exceed 6 mg m-3, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth

Channel subzone

Toxic substances

Should not attain such a level as to produce significant toxic effects in humans, fish or any other aquatic organism.

Harbour subzone, Buffer subzone, Channel subzone

Source: Statement of Water Quality Objectives (Tolo Harbour and Channel Water Control Zone).

Hong Kong Planning Standards and Guidelines (HKPSG)

 

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

 

Water Supplies Department (WSD) Water Quality Criteria

 

4.2.5        Besides the WQOs set under the WPCO, WSD have also specified a set of water quality criteria for flushing water at seawater intakes shown in Table 4.3.

 

Table 4.3         WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes

Parameter (in mg/L unless otherwise stated)

Target Limit

Colour (HU)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammonia Nitrogen (NH3-N)

< 1

Suspended Solids (SS)

< 10

Dissolved Oxygen (DO)

> 2

5-day Biochemical Oxygen Demand (BOD5)

< 10

Synthetic Detergents

< 5

E. coli (no/100 mL)

< 20,000

Cooling Water Intake Standards

 

4.2.6        Based on the WDII EIA([1]), a SS limit of 40 mg/L has been adopted as the assessment criterion for Admiralty Centre intake and MTRC South intake (Point 9 and Point 8 respectively in Figure 4.3) .  No information on the SS limit is available for other cooling water intakes.

 

Technical Memorandum

 

4.2.7        Besides setting the WQOs, the WPCO controls effluent discharging into any WCZ through a licensing system.  The 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 and coastal waters of the Tolo WCZ, as shown in Table 1 and Table 7, respectively, of the TM-DSS.

 

Practice Note

 

4.2.8        A practice note for professional persons was issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The ProPECC PN 1/94 “Construction Site Drainage” provides good practice guidelines for dealing with 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 (Appendix 4.3) should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage.

 

Assessment Criteria for Coral Impact

 

4.2.9        Possible indirect impact on subtidal habitat may arise due to water quality deterioration.  Hard corals are known to be at particular risk of deleterious impacts from sedimentation through smothering and clogging of their respiratory and feeding apparatus. Similarly, more turbid water may reduce the amount of light reaching beneath the water surface which may also be detrimental to hard corals. With less light, growth rates of hermatypic hard corals (the only type of coral to possess photosynthetic algae called zooanthellae) may be reduced. The effects of increased sediment levels in the water column also extend to other marine groups apart from the corals. For instance, fauna inhabiting soft substrata may also be smothered if sedimentation rates are very high.

 

4.2.10    Corals possess mechanisms for rejecting sediment from their surfaces, but employment of these mechanisms expend energy and may cause stress ultimately leading to bleaching (expulsion of zooxanthellae) or tissue necrosis.  The vulnerability of different corals to sedimentation effects is not the same.  Corals with horizontal plate-like or massive growth forms are more vulnerable than corals that grow with plates arranged vertically or with upright branches.  Coral with convex surfaces or possessing tall polyps are also less sensitive.  Sensitivity to sediment loading also varies markedly between species of the same genus (Hawker and Connell 1992) and may even vary between individual colonies of the same species as individual colonies change their growth form to best cope with different sedimentation regimes where they live (Pastorok and Bilyard 1985).  Hawker and Connell (1992) indicated that a 30% increase in long-term background SS levels may lead to a 20% reduction in annual growth rate in hard corals.

 

4.2.11    Since potential impacts on corals may arise through increased turbidity (i.e. elevation in SS) and excessive sediment deposition, the magnitude of impacts on corals was assessed based on both of these water quality parameters.

 

4.2.12    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 such as Eastern Waters MBA Study([4]), West Po Toi MBA Study([5]) and Tai Po Gas Pipeline Study([6])This sedimentation rate criterion is considered to offer sufficient protection to corals and is anticipated to guard against unacceptable impacts. This protection has been confirmed by previous EM&A results which have indicated no adverse impacts to corals have occurred when this assessment criterion has been adopted.

 

4.2.13    The WQO for suspended solids in the Victoria Harbour WCZ states that waste discharges shall not raise the ambient level by 30%.  This was adopted in this Study as the criterion for assessing the SS impacts on corals in Victoria Harbour.

 

4.2.14    There is no marine WQO for suspended solids within the Tolo Harbour and Channel WCZ.  To assess impacts associated with SS in the Tolo Harbour, a criterion of 10 mg/L has been adopted and is considered suitable for use in this EIA Study.  Using this criterion, if SS levels exceed 10 mg/L at coral sites, adverse impacts would be predicted (and suitable mitigation pursued).  This criterion was adopted in the approved Submarine Gas Pipeline EIA (6) as well as This criterion was previously adopted in several other studies ([7]) which have discussed potential impacts of construction works on corals in Hong Kong.  Moreover, based on previous EM&A monitoring results where this assessment criterion has been adopted, no adverse impacts on corals have occurred.  In summary, the SS criterion of 10 mg/L would be sufficiently protective to guard against unacceptable impacts on corals within the Tolo Harbour.

 

Assessment Criteria for Fish Cultural Zone

 

4.2.15    Literature reviews indicate that lethal responses had not been reported in adult fish at a SS concentration of below 125 mg/L ([8]).  The AFCD consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment ([9])provides the guideline values for different parameters for protection of local marine fisheries resources.  The guideline values for relevant parameters are given in Table 4.43a below.

Table 4.4     Assessment Criteria for Local Marine Biota and Fisheries Resources

Parameter

Continuous Concentration (mg/L)

Maximum Concentration (mg/L)

Minimum Concentration (mg/L)

Ammonia, at pH 8.0 (Total ammonia as NH3-N)

0.7

1.2

-

Dissolved Oxygen

5

-

2

Total Suspended Solids

Site Specific

50

-

 

4.2.16    The guidelines derived for Hong Kong above were compared with those established for other countries, as well as tolerance and responses of marine species reported in the literature.

 

4.2.17    The continuous concentration values derived for each of the water quality parameters are required to protect local marine biota from chronic effects of pollution.  Thus, these continuous concentration values should be maintained throughout the operational phase of any development projects.  The maximum concentration (minimum concentration for DO) values, which aim at a lower level of protection, offer protection to short-term acute effects, and thus should be complied with during both the construction and operational phases.

 

 

4.3              Description of the Environment

 

Water Quality at Victoria Harbour

 

4.3.1        The marine water quality monitoring data routinely collected by EPD were used to establish the baseline condition.  The EPD monitoring stations in Victoria Harbour include VM1, VM2, VM4, VM5, VM6, VM7 (Figure 4.1).  A summary of EPD monitoring data collected in 2002 is presented in Table 4.5 for VM1, VM2 and VM4 that are closest to the outfall of Kai Tak Nullah. As the Harbour Area Treatment Scheme (HATS) Stage I was commissioned in late 2001, the data shown in Table 4.5 represent the situation after the commissioning of HATS Stage 1.

Table 4.5     Summary Statistics of 2002 Marine Water Quality in the Vicinity of the outfall of Kai Tak Nullah

Parameter

 

EPD Monitoring Station

WPCO WQOs (in marine waters)

VM1

VM2

VM4

Temperature (oC)

 

22.8

(16.2 - 27.2)

22.9

(16.2 - 27.4)

23.0

(16.2 - 27.3)

Not more than 2 oC in daily temperature range

Salinity (ppt)

 

32.7

(31.4 - 33.4)

32.4

(30.4 - 33.4)

32.2

(30 - 33.4)

Not to cause more than 10% change

Dissolved Oxygen (DO)

(% saturation)

 

81.7

(60.1 - 96.5)

83.8

(62.1 - 107.1)

80.6

(64.3 - 100.4)

-

Bottom

76.4

(29 - 96.2)

77.6

(30.3 - 105.6)

73.6

(29.9 - 99.8)

-

DO (mg/L)

 

5.8

(4.2 - 7.2)

6.0

(4.2 - 7.1)

5.7

(4.4 - 6.8)

Not below 4 mg/L for 90% of the samples

Bottom

5.5

(2.1 - 7.4)

5.6

(2.2 - 7.1)

5.3

(2.1 - 6.9)

Not below 2 mg/L for 90% of the samples

pH value

 

8.0

(7.6 - 8.2)

8.0

(7.8 - 8.2)

8.0

(7.7 - 8.2)

6.5 - 8.5 (± 0.2 from natural range)

Secchi disc (m)

 

2.2

(1.0 - 3.5)

2.1

(1.0 - 3.1)

2.0

(1.0 - 2.5)

-

Turbidity (NTU)

 

10.5

(6.3 - 14.2)

9.6

(6.4 – 14.0)

10.4

(6.7 – 15.0)

-

Suspended Solids (SS) (mg/L)

 

7.0

(3.1 - 15.2)

5.8

(2.4 - 9.9)

7.1

(2.6 - 13.8)

Not more than 30% increase

Silica (as SiO2)

(mg/L)

 

0.7

(0.2 - 1.1)

0.6

(0.1 - 1.2)

0.6

(0.2 - 1.2)

-

5-day Biochemical Oxygen Demand (BOD5) (mg/L)

 

0.8

(0.4 - 2.1)

1.1

(0.5 - 2.3)

1.0

(0.5 – 2.0)

-

Nitrite Nitrogen (NO2-N)  (mg/L)

 

0.02

(0.01 - 0.04)

0.02

(0.01 - 0.04)

0.02

(0.01 - 0.05)

-

Nitrate Nitrogen (NO3-N) (mg/L)

 

0.06

(0.03 - 0.11)

0.07

(0.03 - 0.13)

0.08

(0.03 - 0.15)

-

Ammonia Nitrogen (NH3-N) (mg/L)

 

0.10

(0.01 - 0.22)

0.13

(0.02 - 0.26)

0.15

(0.04 - 0.33)

-

Unionised Ammonia (UIA) (mg/L)

 

0.003

(0.000 - 0.009)

0.004

(0.001 - 0.010)

0.005

(0.002 - 0.01)

Not more than annual average of  0.021 mg/L

Total Inorganic Nitrogen (TIN) (mg/L)

 

0.18

(0.08 - 0.35)

0.23

(0.09 - 0.40)

0.25

(0.12 - 0.51)

Not more than annual water column average of  0.4 mg/L

Total Nitrogen (Total-N) (mg/L)

 

 

0.32

(0.20 - 0.49)

0.38

(0.19 - 0.55)

0.42

(0.25 - 0.71)

-

Ortho-Phosphate (Ortho-P) (mg/L)

 

0.01

(0.00 - 0.03)

0.02

(0.00 - 0.04)

0.02

(0.00 - 0.04)

-

Total Phosphorus (Total-P) (mg/L)

 

0.04

(0.03 - 0.06)

0.04

(0.02 - 0.06)

0.04

(0.02 - 0.07)

-

Chlorophyll-a

(µg/L)

 

2.8

(0.7 - 12.7)

3.6

(0.7 - 11.3)

4.2

(0.7 - 16.8)

-

E. coli

(cfu/100 mL)

 

 

436

(28 – 4,310)

664

(33 – 8,033)

3612

(1,361 – 6,023)

-

Faecal Coliform

(cfu/100 mL)

 

2283

(79 – 8,005)

5758

(90 – 26,930)

8222

(33,42 – 15,212)

-

Note:   1.   Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2.        Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3.        Data in brackets indicate the ranges.

4.3.2        Full compliance with the WQO for depth-averaged (DA) and bottom dissolved oxygen (DO), depth-averaged (DA) total inorganic nitrogen (TIN) and unionised ammonia (UIA) was achieved at VM1, VM2 and VM4 in 2002.

 

Trend of Water Quality in Victoria Harbour

 

4.3.3        As reported in the “Marine Water Quality in Hong Kong in 2001” issued by the EPD, there was an increasing trend of E. coli at VM1, VM2 and VM4. These findings reflect widespread and marked increase in faecal pollution in Victoria Harbour at the time before the commissioning of HATS Stage I.

 

4.3.4        A significant long-term increase in seawater temperature was also observed at VM1, VM2, and VM4. It was estimated that the temperature (surface and depth-averaged) at these stations experienced an average rise of 1 oC in the past 14 to 16 years.

 

4.3.5        As reported in the “Marine Water Quality in Hong Kong in 2002” issued by the EPD, the implementation of HATS Stage I in late 2001 has resulted in a very substantial water quality improvement at the eastern end of the harbour (VM1 and VM2) and moderate improvements in mid harbour station (VM4).  In 2002, there was a very significant reduction of E.coli at Stations VM1 and VM2 by more than 90% while VM4 experienced an E.coli reduction of 40%.  The level of ammonia nitrogen (NH3-N) at VM1 and VM2 also substantially decreased by about 50%.

 

Water Quality at Tolo Harbour and Channel

 

4.3.6        The EPD monitoring stations closest to the Sha Tin and Tai Po effluent pumping station emergency bypasses are TM2 and TM3 respectively (Figure 4.2a), that are located within the Harbour Subzone. A summary of the EPD monitoring data collected at TM2 and TM3 in 2002 is presented in Table 4.6 ([10]).


Table 4.6     Summary Statistics of 2002 Marine Water Quality in the Vicinity of the Sha Tin and Tai Po Effluent Pumping Station Emergency Bypass outfalls

Parameter

 

EPD Monitoring Station

WPCO WQOs (in marine waters)

TM2

TM3

Temperature (oC)

 

24.8

(16.8 - 29.7)

24.8

(16.9 - 29.7)

Not more than 1 oC change from natural daily range

Salinity (ppt)

 

30.7

(25.4 - 32.5)

31.3

(27.5 - 32.8)

Not to cause more than 3 ppt change from the normal range

Dissolved Oxygen (DO)

(% saturation)

 

97.1

(75.7 - 126.4)

109.3

(80.3 - 158)

-

Bottom

99.7

(71.7 - 126.3)

95.4

(55.5 - 132.8)

-

DO (mg/L)

 

6.8

(5 - 8.6)

7.6

(5.5 - 10.6)

Harbour and Buffer subzones: not less than 4 mg/L other than within 2 m of the bottom; Channel subzone: not less than 4 mg/L

 

Bottom

6.8

(4.7 - 8.6)

6.7

(3.8 - 9.7)

Harbour subzone:  not less than 2 mg/L within 2 m of the bottom; Buffer subzone: not less than 3 mg/L within 2 m of the bottom

pH value

 

8.2

(7.8 - 8.5)

8.2

(7.9 - 8.6)

Harbour subzone: not to exceed by ± 0.5 pH units; Buffer subzone: not to exceed by ± 0.3 pH units; Channel subzone: not to exceed by ± 0.1 pH units

Secchi disc (m)

 

1.2

(1 - 2)

1.5

(1 - 2.5)

-

Turbidity (NTU)

 

8.3

(6.3 - 14.1)

7.7

(4.7 - 12.9)

-

Suspended Solids (SS) (mg/L)

 

4.0

(1.7 - 8.1)

4.8

(1.2 - 28.6)

-

Silica (as SiO2)

(mg/L)

 

0.9

(0.1 - 2.4)

0.7

(0.1 - 1.5)

-

5-day Biochemical Oxygen Demand (BOD5) (mg/L)

 

2.2

(1.3 - 2.8)

2.0

(1.1 - 2.6)

-

Nitrite Nitrogen (NO2-N) (mg/L)

 

0.01

(0.00 - 0.04)

0.01

(0.00- 0.04)

-

Nitrate Nitrogen (NO3-N) (mg/L)

 

0.07

(0.00 - 0.3)

0.02

(0.00 - 0.14)

-

Ammonia Nitrogen (NH3-N) (mg/L)

 

0.07

(0.01 - 0.16)

0.05

(0.01 - 0.11)

-

Unionised Ammonia (UIA) (mg/L)

 

0.005

(0.000 - 0.013)

0.004

(0.001 - 0.010)

-

Total Inorganic Nitrogen (TIN) (mg/L)

 

0.15

(0.01 - 0.42)

0.08

(0.02 - 0.29)

-

Total Nitrogen (Total-N)

(mg/L)

 

0.39

(0.23 - 0.62)

0.30

(0.21 - 0.48)

-

Ortho-Phosphate (Ortho-P) (mg/L)

 

0.01

(0.00 - 0.01)

0.01

(0.00 - 0.02)

-

Total Phosphorus (Total-P) (mg/L)

 

0.03

(0.02 - 0.05)

0.03

(0.02 - 0.04)

-

Chlorophyll-a

(µg/L)

 

11.15

(2.7 - 29)

11.22

(2.5 - 37)

Harbour subzone:  not to exceed 20 µg/L; Buffer subzone:  not to exceed 10 µg/L; Channel subzone: not to exceed 6 µg/L 

E. coli

(cfu/100 mL)

 

 

70

(6 - 490)

173

(1 - 1669)

Geometric mean not to exceed 610 per 100 mL at the secondary contact recreation subzone and fish culture zones

Faecal Coliform

(cfu/100 mL)

 

439

(35 - 1878)

838

(10 - 6155)

-

Note:    1.   Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2.   Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3.   Data in brackets indicate the ranges.

4.   Chlorophyll-a level is calculated as a running arithmetic mean of five daily measurements for any single location and depth.

 

4.3.7        Full compliance with WQO for chlorophyll a, depth-averaged (DA) and bottom DO was achieved at TM2 and TM3 in 2002.

 

Trend of Water Quality in Tolo Harbour and Channel

 

4.3.8        The levels of nitrogen nutrients, orthophosphate phosphorus and total phosphorus, silica and chlorophyll-a in Tolo Harbour continued to decline in 2002.

 

4.3.9        As reported in “Marine Water Quality in Hong Kong in 2001” issued by EPD, there was a general decline in 5-day biochemical oxygen demand (BOD5) and significant decrease in nitrate nitrogen (NO3-N), total inorganic nitrogen (TIN) and orthophosphate phosphorus (Ortho-P) nutrients in the inner Tolo Harbour after the implementation of the Tolo Harbour Action Plan in 1986, following a series of measures taken by the Government to reduce pollution and improve water quality in Tolo Harbour.

 

4.4              Water Sensitive Receivers

 

4.4.1        The water sensitive receivers (WSRs) within Victoria Harbour and Tolo Harbour have been identified in accordance with the HKPSG and the EIAO-TM.

 

Sea Water Intakes

 

4.4.2        There are 15 WSD saltwater intakes at the waterfront of Victoria Harbour that may be impacted by the Project.  Their locations are shown in Figure 4.3.

 

4.4.3        There are 2 WSD saltwater intakes within Tolo Harbour, namely Tai Po and Shatin (Figure 4.4).

 

4.4.4        Saltwater is also extracted from Tolo Harbour by the Marine Laboratory of the Hong Kong Chinese University (CUHK) to provide “fresh” seawater for aquatic life within the laboratory.  The location of this intake point is shown in Figure 4.4.

 

Cooling Water Intakes

 

4.4.5        A number of existing and planned cooling water intakes are / will be located along the waterfront of Central, Wan Chai and Causeway Bay.  These intakes supply cooling water to the air conditioning systems of certain commercial buildings in Central, Wan Chai and Causeway Bay.  Their locations are shown in Figure 4.3.

 

Fish Culture Zone

 

4.4.6        There are several fish culture zones (FCZ) within Tolo Harbour and Channel, including:

·    Yim Tin Tsai FCZ;

·    Yim Tin Tsai (East) FCZ;

·    Lo Fu Wat FCZ; and

·    Yung Shue Au FCZ.

 

4.4.7        The locations of these FCZs are shown in Figure 4.4.

 

Beaches

 

4.4.8        There are several non-gazetted beaches within Tolo Harbour and Channel (Figure 4.4), namely:

 

·    Lung Mei

·    Sha Lan

·    Hoi Ha

·    Wu Kai Sha

 

4.4.9        There is also a water sport centre at Tai Mei Tuk next to Plover Cove Reservoir (Figure 4.4).

 

Marine Ecological Sensitive Receivers

 

4.4.10    Key marine ecological sensitive receivers within the Victoria Harbour include Green Island and Junk Bay coral communities (as shown in Figure 4.3) which are located more than 9 km west and 4.7 km east of the outfall of Kai Tak Nullah, respectively.

 

4.4.11    There are several marine ecological sensitive receivers and SSSIs within Tolo Harbour and Channel, including:

·    Hoi Ha Wan Marine Park;

·    Mangroves;

·    Corals; and

·    Ting Kok SSSI

 

4.4.12    The locations of these marine ecological sensitive receivers and SSSIs are shown in Figure 4.4.

 

4.5              Assessment Methodology

 

4.5.1        To assess the potential water quality impacts due to the construction and operation of the Project, the sources and nature of effluent to be generated during construction and operation were identified and their impacts were quantified where practicable.

 

Construction Phase Impact

 

4.5.2        The construction of the Project would be land-based and would not involve marine works such as dredging or filling. The construction works would be designed not to affect normal operation of the TPSTW and the sewage effluent quality. Thus, it is expected that potential water quality impact associated with the Project would be mainly from the on-site construction activities, construction runoff and drainage discharges from the construction site.  The potential impact from these activities was reviewed. Practical water pollution control measures / mitigation proposals were recommended to ensure that any effluent discharged from the construction site would comply with the criteria of WPCO.

 

Operation Phase Impact

 

4.5.3        The key water quality issue of this Project is the impact of sewage effluent discharged from TPSTW after commissioning of the Project. The impact was assessed by computer modelling.

 

4.5.4        Upon completion of the Project, the capacity of TPSTW will be increased from the present design flow of 88,000 m3 per day to 130,000 m3 per day. The current and the proposed new effluent standards upon commissioning of the Project are summarised in Table 4.7.

 

Table 4.7         Current and New Effluent Standards upon commissioning

Parameters

Current Standards

New Standards

95 percentile

Maximum

95 percentile

Maximum

Annual Average

Monthly Geometric Mean

BOD5 (mg/L)

20

40

20

40

-

-

SS (mg/L)

30

60

30

60

-

-

Total-N (mg/L)

25

50

-

35

20

-

NH3-N (mg/L)

-

-

-

10

5

-

E. coli (no/100 mL)

-

-

15,000

-

-

1,000

 

4.5.5        Based on population and flow projection as shown in paragraph 2.4.1, the projected baseflow of TPSTW has been estimated for use in the water quality modelling as shown below:

 

Year

Projected Baseflow of TPSTW

(m3/day)

Effluent Standard

(refer to Table 4.7)

2003

80,178

Current

2010 (Phase 1)

99,021

Current (for E.coli); New (for the rest)

2016 (Phase 2)

130,000

New

 

Summary of Modelling Scenarios

 

4.5.6        As discussed in Section 4.1.2, the Project would have potential impact on both Victoria Harbour and Tolo Harbour.  Two Delft3D models, namely (1) Victoria Harbour (VH) Fine Grid Model and (2) Tolo Harbour and Mirs Bay (THMB) Fine Grid Model were used to simulate the impacts within Victoria Harbour and Tolo Harbour respectively.  Table 4.8 summarises the details of water quality modelling scenarios.  Scenarios 1, 2a, 2b, 3a and 3b refer to the water quality simulation for Victoria Harbour.  Scenarios 4a, 4b, 4c, 5a, 5b, 5c, 5d, 6a, 6b, 7a and 7b refer to the water quality simulation for Tolo Harbour and Channel.  The set-up of these two models is described in Sections 4.5.8 to 4.5.40.

 


Table 4.8 Proposed Baseline and Operation Phase Water Quality Modelling Scenarios

 

 

Scenario

Phase

Flow

(m3 per day)

Location of Discharge

Effluent

Standard

BOD5

(mg/L)

TSS

(mg/L)

TKN

(mg/L)

Total N

(mg/L)

NH3-N

(mg/L)

E. coli (no/100mL)

Victoria Harbour Model

1 (Year 2003)

Baseline (normal, with HATS Phase I only, without the Project)

80,178 (TPSTW) + 240,000 (STSTW) + Peak flow (1)

Kai Tak Nullah (through the THEES)

TPSTW: Current

STSTW:  Current

20 (2)

30 (2)

14.75 (3)

25 (2)

9.95 (4)

296,500 (5)

20 (2)

30 (2)

16.53 (6)

25 (2)

11.74 (7)

296,500 (8)

2a (Year 2010)

Baseline (normal, without the Project and with HATS Stage I only)

88,000 (TPSTW) + 283,773 (STSTW) (9) + Peak flow(1)

Kai Tak Nullah (through the THEES)

TPSTW:  Current

20 (2)

30 (2)

14.75 (3)

25 (2)

9.95 (4)

296,500 (5)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

2b (Year 2010)

 

Operation (normal, after Project commission and with HATS Stage I only)

99,021 (TPSTW) (12) + 283,773 (STSTW) (9) + Peak flow(1)

Kai Tak Nullah (through the THEES)

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

296,500 (5)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

3a (Year 2016)

Baseline (normal, without Project but with HATS fully commissioned)

88,000 (TPSTW) + 340,000 (STSTW) (13) + Peak flow(1)

Kai Tak Nullah (through the THEES)

TPSTW:  Current

20 (2)

30 (2)

14.75 (3)

25 (2)

9.95 (4)

296,500 (5)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

3b (Year 2016)

 

Operation (normal, after Project commission and with HATS fully commissioned)

130,000 (TPSTW) (14) + 340,000 (STSTW) (13) + Peak flow(1)

Kai Tak Nullah (through the THEES)

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

15,000 (2)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

Tolo Harbour Model

4a (Year 2016)

Baseline condition of Tolo Harbour

No sewage/ effluent  discharge into Tolo Harbour(26)

-

-

-

-

-

-

-

-

4b (Year 2010)

Baseline condition of Tolo Harbour

No sewage / effluent discharge into Tolo Harbour(26)

-

-

-

-

-

-

-

-

4c (Year 2003)

Baseline condition of Tolo Harbour

No sewage / effluent discharge into Tolo Harbour(26)

-

-

-

-

-

-

-

-

5a (Year 2016)

 

Operation (normal, after project commission)

Occasional overflow of treated effluent from TPSTW and STSTW (25)

Overflow at STSTW only

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

15,000 (2)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

5b (Year 2016)

 

Operation (normal, after project commission)

Occasional overflow of treated effluent from TPSTW and STSTW (25)

Overflow at TPSTW and STSTW

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

15,000 (2)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

5c (Year 2010)

 

Operation (normal, after Phase 1 commission)

Occasional overflow of treated effluent from TPSTW and STSTW (24) treated effluent from TPSTW and STSTW (24

Overflow at STSTW only

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

296,500 (5)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

5d (Year 2010)

 

Operation (normal, after Phase 1 commission)

Occasional overflow of treated effluent from TPSTW and STSTW (24)

Overflow at TPSTW and STSTW

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

296,500 (5)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

6a (Year 2016)

 

Operation (Maintenance of THEES tunnel)

130,000 (TPSTW) (14) + 340,000 (STSTW) (13) + Peak flow(1)

Bypass at STSTW only (for about four weeks)

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

15,000 (2)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

6b (Year 2016)

 

Operation (Maintenance of THEES tunnel)

130,000 (TPSTW) (14) + 340,000 (STSTW) (13) + Peak flow(1)

Bypasses at TPSTW and STSTW (for  four weeks)

TPSTW:  New

20 (2)

30 (2)

16.51 (3)

27.99 (11)

7.66 (11)

15,000 (2)

STSTW (10)

20 (2)

30 (2)

18.59 (6)

27.99 (11)

7.66 (11)

15,000 (2)

7a (Year 2016)

Operation (emergency – complete power failure) (Dry Season)

130,000 (TPSTW) (14) + Peak flow(1)

Emergency bypass at TPSTW (for 24 hours discharge)

TPSTW:  No treatment

273 (dry) (21)

460 (dry) (21)

57 (dry) (21)

57 (dry) (22)

28 (dry) (21)

2x107 (dry) (23)

7b (Year 2016)

Operation (emergency – complete power failure) (Wet Season)

130,000 (TPSTW) (14) + Peak flow(1)

Emergency bypass at TPSTW (for 24 hours discharge)

TPSTW:  No treatment

170 (wet) (21)

297 (wet) (21)

46 (wet) (21)

46 (wet) (22)

27 (wet) (21)

2x107 (wet) (23)

Remark:

(1)     “ + Peak flow” means 4-hour storm flow will be combined with the TPSTW dry weather flow pattern.

(2)     At 95 percentile values of the effluent standards.

(3)     Estimated from the ratio of TKN : Total N of the monthly analytical data of TPSTW sewage effluent between January 2001 and December 2002.

(4)     Estimated from the ratio of NH3-N : Total N of the monthly analytical data of TPSTW sewage effluent between January 2001 and December 2002.

(5)     As there is no record of E. coli concentration of sewage effluent from TPSTW, the 95 percentile value of STSTW E. coli records is used.

(6)     Estimated from the ratio of TKN : Total N of the monthly analytical data of STSTW sewage effluent between January 2002 and December 2002.

(7)     Estimated from the ratio of NH3-N : Total N of the monthly analytical data of STSTW sewage effluent between January 2002 and December 2002.

(8)     95 percentile value of monthly analytical data of STSTW sewage effluent between January 2002 and December 2002.

(9)     Projected sewage effluent of STSTW in 2010 based on the Review of North District and Tolo Harbour SMPs Final Interim Report.

(10)   Effluent standards of STSTW (with UV disinfection) after the commission Stage III Extension.

(11)   95-percentile values of the effluent standards.

(12)   Projected sewage effluent of TPSTW in 2010 after the commission of the Project based on the Review of North District and Tolo Harbour SMPs Final Interim Report.

(13)   Design capacity (dry weather flow) of STSTW after the STSTW Stage III Extension.

(14)   Design capacity (dry weather flow) of TPSTW after full commission of the Project.

(21)   Dry season data were derived from the monthly analytical data for TPSTW between January 2001 and March 2001, while the wet season data were derived from the monthly data between June and August 2001.

(22)   According to Metcalf & Eddy, Inc (1991), Wastewater Engineering, Treatment, Disposal, and Reuse (Third Edition, McGraw-Hill, Inc.), the value of Total N is about the same as the value of TKN in untreated domestic wastewater.  The amount of inorganic nitrogen in untreated domestic wastewater is negligible.

(23)   Design load concentration of TPSTW.

(24)    Occasional overflow of effluent from TPSTW/STSTW during storm event above the capacity of the Sha Tin Effluent Pumping Station.

(25)    Occasional overflow of effluent from TPSTW/STSTW during storm event and under ultimate flow conditions above the capacity of the Sha Tin Effluent Pumping Station.

(26)    Ignoring the impact caused by diffuse pollution in the absence of the Project.t

 

 

 


4.5.7        A total of 16 modelling scenarios were proposed to address the potential impacts from the Project (see Table 4.9 below).   The projected baseflow in Section 4.5.5 and the effluent standards in Table 4.7 were used to estimate the projected pollution load discharged from the Project for different year horizons.  The background pollution loading within the Study Area was also input to the model to take into account the cumulative effect.  The background pollution load adopted for different years of assessment (i.e. 2003, 2010 and 2016) are discussed in Sections 4.5.34 to 4.5.40. A more detailed description of each modelling scenario and the detailed modelling methodology are provided in the subsequent sections.

 

Table 4.9         Summary of Modelling Scenarios

Water Quality Impact

Scenario (Refer to Table 4.8)

Baseline

Interim and Operational Phases

Impact within Victoria Harbour when treated effluent is discharged into Victoria Harbour via Kai Tak Nullah under THEES (normal operation mode which applies in all time except under exceptional conditions)

Scenario 1 (2003)

Scenario 2a (2010)

Scenario 3a (2016)

Scenario 2b (2010)

Scenario 3b (2016)

Impact within Tolo Harbour under occasional overflow of treated effluent during storm event or under ultimate flow conditions

Scenario 4a (2016)

Scenario 4b (2010)

Scenario 4c (2003)

 

Scenarios 5a&5b (2016)

Scenarios 5c&5d (2010)

Exceptional condition 1:

Impact within Tolo Harbour when all treated effluent is diverted into Tolo Harbour under the shutting down of the THEES tunnel for maintenance

Scenarios 6a&6b (2016)

Exceptional condition 2:

Impact within Tolo Harbour when untreated effluent from TPSTW is diverted into Tolo Harbour under emergency situation (complete power failure). 

Scenario 7a& 7b (2016)

Simulation Period

 

4.5.8        The simulation period of water quality models cover a spin-up period followed by the actual simulation period. A longer spin-up period was allowed for the THMB Model because of the embayed features of the Tolo Harbour that requires longer ‘warm-up’ period to achieve quasi-steady state. The same spin-up and simulation periods were used for all modelling scenarios and all assessment years.  Details are given below.

 

Victoria Harbour Model

 

4.5.9        The hydrodynamic simulations driving the water quality model consist of two 15-day full spring-neap cycles (9 to 24 February 1996 for dry season; and 26 July to 10 August 1996 for wet season).  These hydrodynamic simulation periods were selected based on the EPD Update Study (Agreement No. CE 42/97, Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool). These hydrodynamic simulation results were used repeatedly for water quality simulation for more than one complete calendar year as shown below:

 

·        Spin-up period of water quality model:       

2 December (of the 1st year) to 1 January (of the 2nd year)

·        Actual simulation period of water quality model:      

1 January (of the 2nd year) to 31 December (of the 2nd year)

Tolo Harbour and Mirs Bay Model

 

4.5.10    The Tolo Harbour and Mirs Bay (THMB) Model was developed by EPD under Agreement No. WP01-27.   The simulation period of the THMB Model cover 2 calendar years for both hydrodynamic model and water quality model as adopted in Agreement No. WP01-27.  The spin-up and actual simulation periods for THMB model are shown below. 

 

·    Spin-up period:                     1 January 2000– 1 January 2001

·    Actual simulation period:       1 January 2001 – 31 December 2001

 
Diurnal Flow Pattern

 

4.5.11    The projected diurnal flow pattern of TPSTW for 2006 is shown in Table 4.10a which is based on the Review of North District and Tolo Harbour SMPs Final Interim Report.  The percentages in Table 4.10a were applied to the projected daily baseflow in Section 4.5.5 to derive the hourly dry weather diurnal flow from the Project for different year horizons as model inputs.  The same 24-hour diurnal flow pattern was used in the model throughout the simulation year.

 

Table 4.10a     Projected Dry Weather Diurnal Flow Pattern of TPSTW in 2006

Hour

% of Daily Flow

Hour

% of Daily Flow

Hour

% of Daily Flow

Hour

% of Daily Flow

0:00

4.51%

6:00

2.71%

12:00

4.72%

18:00

4.21%

1:00

4.44%

7:00

3.08%

13:00

4.58%

19:00

4.95%

2:00

3.83%

8:00

4.72%

14:00

4.11%

20:00

4.86%

3:00

3.36%

9:00

4.35%

15:00

4.06%

21:00

5.32%

4:00

2.94%

10:00

4.44%

16:00

4.35%

22:00

5.09%

5:00

2.71%

11:00

3.97%

17:00

4.11%

23:00

4.58%

 
Scenario 1 (Victoria Harbour Year 2003 Baseline)

 

4.5.12    This scenario represents the existing condition under normal operation of the TPSTW, STSTW and THEES in 2003.  An average dry weather flow (ADWF) of 80,178 m3 per day and 240,000 m3 per day for TPSTW and STSTW, respectively, were incorporated into the model.  Scenario 1 represents the situation when all the effluent from TPSTW and STSTW is discharged into Victoria Harbour via Kai Tak Nullah.  Thus, the existing effluent quality standards (see Table 4.8) were employed together with the hourly dry weather diurnal flow to derive the hourly pollution loadings as model inputs.

 

Scenario 2a (Victoria Harbour Year 2010 Baseline without the Project)

 

4.5.13    Scenario 2a represents the baseline condition in 2010 without the Project.  All the effluent of TPSTW and STSTW would be discharged into Victoria Harbour via Kai Tak Nullah under normal operation of TPSTW, STSTW and THEES (with HATS Stage 1 commissioned only).  The ADWF of STSTW would reach 283,773 m3/day in 2010, while the TPSTW would be operating at its current design capacity (i.e. 88,000 m3/day) without the Project. Stage III Extension of STSTW with UV disinfection would be commissioned by 2010 and the corresponding new effluent standards for STSTW were adopted.  The same current effluent standards (Table 4.8) would still be applicable for TPSTW in 2010.  The coastline configuration adopted in the Victoria Harbour Model for 2010 is shown in Figure 4.5.  In 2010, the outfall of Kai Tak Nullah would be diverted from Kai Tak Nullah Approach Channel to the seafront of Kowloon Bay under the SEKD.

 

Scenario 2b (Victoria Harbour Year 2010 with the Project)

 

4.5.14    Scenario 2b represents normal operation of TPSTW and STSTW after the Project commission in 2010. The difference of Scenario 2b from Scenario 2a would be the increase of effluent flow from TPSTW.  The ADWF of TPSTW would reach 99,021 m3/day by 2010 and the new effluent standards (Table 4.7) were adopted for all parameters except for E.coli.

 

Scenario 3a (Victoria Harbour Year 2016 Baseline without the Project)

 

4.5.15    Scenario 3a represents the baseline condition in 2016 without the Project.  Major differences of Scenario 3a (2016 baseline) from Scenario 2a (2010 baseline) include (i) the increase of effluent flow from STSTW to reach its full capacity (340,000 m3/day); and (ii) the change in background pollution loading (Sections 4.5.34 to 4.5.40) and (iii) coastline configuration (Figure 4.6a) in Victoria Harbour between 2010 and 2016.  In addition, all stages of HATS would be commissioned by 2016 (see Section 4.5.37 and Table 4.11 for details).

 

Scenario 3b (Victoria Harbour Year 2016 with the Project)

 

4.5.16    Scenario 3b represents normal operation of TPSTW and STSTW in 2016 after Project commission. The differences of Scenario 3b from Scenario 3a would be the increase of effluent flow from TPSTW to reach its full capacity (130,000 m3/day) and the use of new effluent standards in Table 4.7.

 

Scenario 4a, 4b and 4c (Tolo Harbour Year 2016, 2010 and 2003 Baseline)

 

4.5.17    Scenarios 4a, 4b and 4c represent the baseline conditions of Tolo Harbour where no effluent from TPSTW and STSTW would be discharged into the harbour in 2016, 2010 and 2003 respectively with different background pollution loadings.

 

Scenario 5 (Tolo Harbour under Normal Operation)

 

4.5.18    Scenario 5 simulates the impact from the overflow discharges under normal operation of TPSTW and STSTW when treated effluent flow exceeds the existing capacities of the effluent pumping stations.  The overflow bypasses of Shatin and Tai Po effluent pumping stations are shown in Figure 4.7.  The assessment of overflow bypass has taken into account the effect of storm events. Based on the past discharge records for TPSTW in 2001, it is assumed that the low flow periods where storm events are rare would occur in 13 to 24 February and 15 to 27 November (Figure 1 of Appendix 4.6).  The recorded average flow of these dry periods was 77,200 m3/day. It is assumed that any days in 2001 with surplus flow above this dry flow value (77,200 m3/day) are wet days with storm events.  Figure 2 of Appendix 4.6 shows the surplus flow recorded in 2001.  The surplus flow derived from the 2001 data for each wet day was allocated to the dry weather design flow on the same day for different assessment years to take into account the effect of storm events for water quality modelling. Figure 3 of Appendix 4.6 is a sample plot showing the projected daily discharge rate (dry weather flow + surplus flow from storm events) of TPSTW for 2016.  It is also assumed that the surplus flow on each such wet day was contributed by a 4-hour storm event. The surplus flow derived from the 2001 data for each wet day was allocated to the dry weather diurnal discharge on the same day between 19:00 and 22:00 (refer to Section 4.5.11) for all the assessment years.  When the combined volume of surplus flow (if any) and dry weather diurnal discharges from the TPSTW exceeds the existing capacity of the effluent pumping station of 4752 m3/hour, the effluent would overflow into a storage tank of 6,500 m3 in size.  Overflow via the emergency bypass near TPSTW would occur only in the hours where the effluent stored in the storage tank exceeds 6,500 m3.  Figure 4 of Appendix 4.6 shows a sample plot of diurnal overflow at Tai Po effluent pumping station for 2010.  The effect of the storage tank on the total quantity of overflow discharged into the Tolo Harbour is not so significant for 2016 and was, on the conservative side, not taken into account for all 2016 modelling scenarios.  On the other hand, combined flow of effluent transported from TPSTW via the Tai Po effluent pumping station and the effluent from STSTW would also occasionally exceed the capacity of Sha Tin effluent pumping station of 21600 m3/hour, and overflow would then be discharged via the emergency bypass of the station near STSTW.  Within the same year, the total daily flow and pollution load overflowed into Tolo Harbour would vary seasonally due to the seasonal change in storm water flow.  The daily volume of overflows would also be increased with increasing year of horizon due to the increase in the projected baseflow of STSTW and TPSTW (Table 4.10b).  The overflow would occur only occasionally within a day and would be discharged intermittently.  It is assumed that the pollution levels in the storm water would be the same as those in the effluent (Table 4.8) and no dilution of the effluent would occur as conservative approach.

 

Table 4.10b     Volume of Overflow Discharges

Scenario

Discharge Location

Total Volume of Treated Effluent Overflow discharged in a year (m3/year)

5a (2016 with upgrading of Tai Po effluent pumping stationoverflow bypass at Shatin only)

Sha Tin

10,580,133

5b (2016 with NO upgrading of Tai Po effluent pumping stationoverflow bypass at both Tai Po and Shatin)

Tai Po

9,832,240

Sha Tin

4,656,300

Total

14,488,540

5c (2010 overflow bypass at Shatin onlywith upgrading of Tai Po effluent pumping station)

Sha Tin

1,946,384

5d (2010 overflow bypass at both Tai Po and Shatinwith NO upgrading of Tai Po effluent pumping station)

Tai Po

1,299,318

Sha Tin

48,837

Total

1,348,155

 

Scenarios 5a and 5b (Year 2016)

 

4.5.19    Scenarios 5a and 5b represent the situation of overflow bypass after the Project is completed in full scale.  For Scenario 5a, it was assumed that, with upgrading of the Tai Po effluent pumping station and associated facilities, all effluent from TPSTW can be exported to Sha Tin effluent pumping station.  The combined effluent flow from the TPSTW and STSTW and any storm events would occasionally exceed the existing capacity of Sha Tin effluent pumping station and overflow would be discharged via the emergency bypass of the Sha Tin effluent pumping station.  The overflow would occur only in 7 hours per day.  It was assumed that the duration of overflow (7 hours at STSTW) would be the same every day throughout the model simulation year.

 

4.5.20    Scenario 5b assumed that there would be no upgrading of the existing Tai Po effluent pumping station and effluent from TPSTW would occasionally exceed the capacity of the station.  Part of the treated effluent would then be discharged via the emergency bypass of the station near TPSTW. On the other hand, combined flow from TPSTW and STSTW would also occasionally exceed the capacity of Sha Tin effluent pumping station and overflow would then be discharged via the emergency bypass of the station at STSTW.   The overflow would occur in 19 hours per day at TPSTW and 5 hours per day at STSTW throughout the model simulation year.  It is noted that this long duration of overflow represents an overestimation owing to the assumption mentioned in 4.5.18 that the storage tank in the TPSTW is ignored.  It was assumed that the duration of overflow (19 hours at TPSTW and 5 hours at STSTW) would be the same every day throughout the model simulation year.

 

Scenarios 5c and 5d (Year 2010)

 

4.5.21    Scenarios 5c and 5d are basically the same as Scenario 5a and 5b respectively except that the modelling year was 2010 with a smaller projected baseflow from TPSTW and STSTW (Section 4.5.5).  In addition, unlike Scenarios 5a and 5b, Scenarios 5c and 5d had taken into the account the effect of the storage tank at the Tai Po effluent pumping station as discussed in Section 4.5.18 above.

 

4.5.22    For Scenario 5c, the overflow would occur at STSTW only for 4 hours per day throughout the model simulation year.  It was assumed that the duration of overflow (4 hours at STSTW) would be the same every day throughout the model simulation year.

 

4.5.23    For Scenario 5d, overflow would occur at TPSTW only during wet days with discharge up to 4 hours per day.  No overflow would occur at TPSTW during dry days.  The overflow would occur for 2 hours per day at STSTW throughout the model simulation year. It was assumed that the duration of overflow at STSTW would be the same every day throughout the model simulation year.

 

Scenario 6a and 6b (Year 2016 Four-Week Maintenance Period)

 

4.5.24    Scenarios 6a and 6b simulate the potential impact during a four-week maintenance of THEES tunnel in 2016 after Project commission.  Fully treated sewage effluent from TPSTW and STSTW would all be discharged into Tolo Harbour via the emergency bypass of Sha Tin effluent pumping station under Scenario 6a and via the emergency bypasses of Tai Po effluent pumping station and Sha Tin effluent pumping station under Scenario 6b for four weeks.  The maintenance period was assumed from 25 June to 22 July during which the estimated volume of effluent flow would be the highest.   The loading conditions not during maintenance discharges would be the same as those adopted for Scenarios 5a and 5b respectively.

 

Scenario 7a and 7b (Year 2016 24-hour Emergency Discharge of Untreated effluent from TPSTW only)

 

4.5.25    Scenarios 7a and 7b simulate the potential impact of untreated effluent discharge from TPSTW during a 24-hour emergency period after Project commission. Thesesimulationsare based on a worst-case assumptionof 24-hour discharge.  Based on the past record, emergency discharge of untreated effluent had occurred only once since 1995due to CLP power supply failure to Tai Po effluent pumping statat the TPSTW Stage IV inlet worksonnlet works.  The duration of the emergency discharge was less than 3 hours with a total discharge volume of less than 9,000 m3.  For conservative assessment, iIt was also assumed in the modelling that the emergency condition would occur on the day with the highest effluent flow of the year.  Untreated effluent would be discharged via the emergency bypass of TPSTW during the dry season on 1 March (Scenario 7a) and the wet season on 27 June (Scenario 7b). Under these scenarios, it was assumed that there would be no overflow from the Shatin effluent pumping station.  The loading conditions not during emergency bypass would be the same as those adopted in Scenarios 5a and 5b respectively.

 

Hydrodynamic and Water Quality Model

 

4.5.26    The hydrodynamic and water quality models were developed by Delft Hydraulics, namely Delft3D-FLOW (for hydrodynamic modelling) and Delft3D-WAQ (for water quality modelling).

 

4.5.27    Delft3D-FLOW is a 3-dimensional hydrodynamic simulation programme with applications for coastal, river and estuarine areas. This model calculates non-steady flow and transport phenomena that result from tidal and meteorological forcing on a curvilinear, boundary fitted grid.

 

4.5.28    Delft3D-WAQ is a water quality model framework for numerical simulation of various physical, biological and chemical processes in three dimensions. It solves the advection-diffusion-reaction equation for a predefined computational grid and for a wide range of model substances. The hydrodynamic simulation that drives the water quality model is generated from the simulation of Delft3D-FLOW model.

 

4.5.29    In this study, the Victoria Harbour (VH) Fine Grid Model was used for modelling discharges during normal operation of both the Project and the THEES. Overflows and emergency discharge at Tolo Harbour were modelled by the Tolo Harbour and Mirs Bay (THMB) Fine Grid Model.

 

4.5.30    The original Victoria Harbour Model was developed for the Sha Tin Stage III Extension EIA study under the contract CE 90/97. The model grids (Figure A4-1 in Appendix 4.2) were modified to take account of the existing coastline and the latest information on the planned reclamation layouts under Central Reclamation Phase III (CRIII), Wan Chai Development Phase II (WDII), South East Kowloon Development (SEKD), Yau Tong Bay Development (YTBD), etc.  The years of 2003, 2010 (with only HATS Stage I commissioned) and 2016 (with all stages of HATS commissioned) were selected as the time horizons for existing (baseline) and operation phase hydrodynamic and water quality modelling. The coastline configurations in 2010 and 2016 adopted for modelling are shown in Figures 4.5 and 4.6a.

 

4.5.31    The THMB Model was developed for the EPD under Agreement No. WP01-277. The model grids were modified to provide higher resolution near the overflow / emergency bypass outfalls and the nearby sensitive receivers (Figure A4-2 in Appendix 4.2). The coastline configuration of the Model was also updated, taking account of the layout of the reclamation at Pak Shek Kok.  No further major reclamation within the Tolo Harbour and Channel is expected before 2016. The THMB Model was also refined using the dispersion array function of the water quality model to allow for spatial variation of vertical dispersion in the model.  In general, the vertical dispersion of the model has been increased near the river mouths of Shing Mun River and Lam Tsuen River to 0.001 m2 s-1.  The dispersion value gradually decreases to 5 x 10-6 m2 s-1 further away from the river mouths.  These settings would enhance vertical mixing at shallow waters near the river mouths that would gradually diminish at deeper waters away from the river mouths. The performance of the refined THMB model has been checked against the EPD data collected at the TM stations and is considered acceptable for use in this EIA for model simulations.

 

4.5.32    While the boundary conditions of the Victoria Harbour Model were adopted from the Update Model developed under Agreement No. CE 42/97([11]), the boundary conditions of the THMB Model were obtained from the actual forcing of wind, rainfall and temperature. Monthly variations of river discharges, solar radiation, water temperature and wind velocity were incorporated into the models.

 

4.5.33    The transport of substances and associated water quality processes were incorporated in the Delft3D-WAQ module. The model includes the physical / biochemical processes of suspended sediment, nutrients, phytoplankton and bacteria. Physical processes such as the exchange of oxygen with the atmosphere and the sedimentation of suspended substances, as well as biochemical processes such as nitrification, algal growth and decay and the decay of organic matter, are also modelled. The key hydrodynamic and water quality modelling parameters are shown in Table 4.10c below.

 

Table 4.10c Key Modelling Parameters

Parameter

Description

Velocity

Velocity

Water Level

Water Level

Salinity

Salinity

ModTemp

Water Temperature

E Coli

E. coli Bacteria

Oxy

Oxygen

CBOD5

Carbonaceous 5-day Biochemical Oxygen Demand

NO3

Nitrate

NH4

Ammonium

PO4

Ortho-Phosphorus

AAP

Adsorbed Ortho-Phosphorus

Si

Silica

Diat

Diatoms

Green

Algae

DetC

Detritus Carbon

DetN

Detritus Nitrogen

DetP

Detritus Phosphorus

DetSi

Detritus Silica

BOD5

5-day Biochemical Oxygen Demand

Chlfa

Chlorophyll a

SS

Suspended Solids

TotN

Total Nitrogen

TotP

Total Phosphorus

NH3

Unionised Ammonia **

**     The UIA levels were calculated by the water quality model based on the temperature, salinity and pH characteristics of the water.  The pH was entered into the model as a constant process parameter with the value 8.2.  This value was derived from the Update Study (Agreement No. CE 42/97) based on previous measurements (EPD monitoring).

 

 Background Pollution Loading Inventory

 

4.5.34    The years of assessment were 2003 (baseline scenario), 2010
(interim operation scenario) and 2016 (operation scenario).

 

4.5.35    For the existing baseline scenarios (1 and 4c), the 2003 pollution loading inventory presented in the Technical Note on Flow and Load Inventory (December 2000) for the EIA of Comprehensive Feasibility Study for the Revised Scheme of South East Kowloon Development (Agreement No. CE 32/99) was adopted. For pollution load within Tolo Harbour and Mirs Bay, the loading inventory derived for the original THMB Model was adopted.  Tables A4.1 and A4.2 in Appendix 4.1 show the pollution loading inventory for the Hong Kong SAR in 2003 dry and wet seasons, respectively.

 

4.5.36    According to the latest population forecast provided by the Planning Department, the projected 2010 Hong Kong residential population (7,447,700) would be similar to the population forecasts of 2007 Scenario I (7,439,679) but smaller than 2007 Scenario II (7,853,130) adopted in the Update Study.  To be consistent with the pollution loading inventory derived for 2016 operation scenario (Section 4.5.42), the pollution loading inventory of 2007 Scenario II was also adopted for the pollution loading inventory of the 2010 operation scenarios (including Scenarios 2a, 2b, 4b, 5c and 5d).  The pollution loads and discharge locations were modified to take account of the latest reclamation plans and construction schedules of CRIII, WDII and SEKD. For pollution load within Tolo Harbour, the loading inventory derived for the original THMB Model was adopted.  Tables A4.5 and A4.6 in Appendix 4.1 show the pollution loading inventory for the Hong Kong SAR in 2010 dry and wet seasons, respectively.

 

4.5.37    For the 2016 operation scenarios (including Scenarios 3a, 3b, 4a, 5a, 5b, 6a, 6b, 7a and 7b), the 2016 pollution loading inventory presented in the Technical Note on Flow and Load Inventory (December 2000) for the EIA of Comprehensive Feasibility Study for the Revised Scheme of South East Kowloon Development (Agreement No. CE 32/99), which was slightly modified from 2012 Scenario II pollution inventory of the Update Study, was adopted for water quality modelling.  To take into account of the implementation of HATS and its potential worst case impact upon Victoria Harbour, it was assumed that Option 5d of HATS proposed by the International Review Panel that includes the existing Stonecutters Island Sewage Treatment Works (SCISTW) and the planned sewage treatment works at Sandy Bay and North Point, would have been implemented by 2016.  The flows and pollution loading of the treated effluent from these three treatment works are shown in Table 4.11.

 

Table 4.11   Pollution Loading from Stonecutters, Sandy Bay and North Point Sewage Treatment Works under HATS (Option 5d)

Parameters

Stonecutters

Sandy Bay

North Point

Flow (m3 per day)

2198052

132313

456926

BOD (g per day)

35168832

2117008

7310816

SS (g per day)

52753248

3175512

10966224

Organic Nitrogen (g per day)

5495130

330782.5

1142315

NH3-N (g per day)

4396104

264626

913852

E. coli (no. per day)

7.31303 x 1014

4.40212 x 1013

1.52022 x 1014

Copper (g per day)

14995

903

3117

Total Phosphorus (g per day)

4835714

291089

1005237

Ortho-Phosphate (g per day)

3978474

239487

827036

Silicate (g per day)

18022365

1084867

3746448

Total nitrite and nitrate (g per day)

50922602

3065315

10585674

 

4.5.38    Option 5d in Table 4.11 above assumed that the discharge from HATS would receive secondary treatment with nitrification. As the HATS study is still on-going and the level of treatment is still being considered, an additional model run has been carried out to address the possible scenario of HATS with chemical enhanced primary treatment with disinfection.  The model set-up, modelling results and detailed assessment for this additional scenario are given in Appendix 4.4a.

 

4.5.39    Similar to year 2003 and 2010, the loading inventory derived for the original THMB Model was adopted for Tolo catchment for 2016 scenarios as a conservative approach. Tables A4.7 and A4.8 in Appendix 4.1 show the pollution loading inventory for Hong Kong SAR in 2016 dry and wet seasons, respectively.

 

4.5.40    It should be noted that the pollution loading inventories of 2003, 2010 and 2016 shown in Appendix 4.1 do not include the pollution loadings of the TPSTW and STSTW, which are incorporated into the water quality model separately under various scenarios.

 

Uncertainties in Assessment Methodology

 

4.5.41    Quantitative uncertainties in the water quality modelling should be considered when making an evaluation of modelling predictions. The worst case conditions were adopted as model input to indicate the maximum extent of the potential environmental impacts. The input data tended to be conservative to provide a margin of tolerance.  Some examples of the conservative nature of the input parameters are given below:

·        95 percentiles (%iles) of the treated effluent pollution loadings incorporated in the operation phase water quality modelling are considered very conservative, given that 95 %iles of the pollution loads are about twice their mean values. Thus, the water quality impacts simulated under Scenarios 1, 2a, 2b, 3a, 3b, 5a, 5b, 5c, 5d, 6a and 6b were likely to be higher than the real situation that would happen.

·        Option 5d of the HATS was adopted in modelling the water quality impact in Victoria Harbour under Scenarios 3a and 3b. This option, which included a submarine outfall close to North Point (that is near the outfall of the reprovisioned Kai Tak Nullah), was chosen as a worst-case scenario to model the possible cumulative impact of the Project and HATS.

 

4.5.42    Uncertainty in modelling the oxygen profile of the inner Tolo Harbour and Sha Tin Hoi using the original THMB Model was reported in a previous EPD study([12]).  The modified THMB Model that was adopted in the current study was adjusted with less stratification throughout the year to enhance the model performance in the inner Tolo Harbour and Sha Tin Hoi.

 

Possible Changes in Coastline Configuration in Victoria Harbour

 

4.5.43    As the reclamation limits for some planned coastal developments such as the SEKD, CRIII and WDII are not yet confirmed and still subject to change at the time when this EIA is prepared, a sensitivity test was conducted under this Study to investigate the effect of possible changes in coastline configuration in Victoria Harbour on the overall conclusion of the water quality assessment. Modelling was undertaken for Scenario 3b (Table 4.8) using an alternate coastline configuration as shown in Figure 4.6b as a sensitivity test.  The test results are attached in Appendix 4.4b.

 

Decommissioning of Wanchai West Outfall

 

4.5.44    The submarine outfall of Wanchai West sewage screening plant (WCW) has been decommissioned in 2003 and all flow originally discharged via the WCW would be diverted to that of Wan Chai East sewage screening plant (WCE).  It is assumed in the model that the sewage flow from Wanchai would be distributed to both WCW and WCE for all the assessment years except 2016 after full commissioning of the HATS.  It should be noted that the effects of such change in local distribution of flow amongst WCW and WCE should be localized and would unlikely affect the overall conclusion of the modelling results.

 

 

4.6              Identification of Environmental Impacts

 

Construction Phase

 

General Construction Activities

 

4.6.1        The general construction works would be primarily land-based but would have the potential to cause water pollution.  Various types of construction activities may generate wastewater. These include general cleaning and polishing, wheel washing, dust suppression and utility installation.  These types of wastewater would contain high concentrations of suspended solids.  Impacts could also result from the accumulation of solid and liquid waste such as packaging and construction materials, and sewage effluent from the construction work force involved with the construction.  If uncontrolled, these could lead to deterioration in water quality.  Increased nutrient level from contaminated discharges and sewage effluent could also lead to a number of secondary water quality impacts including localised increase in ammonia and nitrogen concentrations that would stimulate algal growth.

 
Construction Site Runoff

4.6.2        During a rainstorm, site runoff generated would wash away the soil particles. The runoff is generally characterised by high concentrations of suspended solids.  Release of uncontrolled site runoff would increase the SS levels and turbidity in the nearby water environment.

 

4.6.3        Wind blown dust would be generated from exposed soil surface in the works areas.  It is possible that wind blown dust would fall directly onto the nearby water bodies when a strong wind occurs.  Dispersion of dust within the works areas may increase the SS levels in surface runoff causing a potential impact to the nearby sensitive receivers.

 
Accidental Spillage

4.6.4        There would be a large variety of chemicals to be used for carrying out construction activities. These may include surplus adhesives, spent paints, petroleum products, spent lubrication oil, grease and mineral oil, spent acid and alkaline solutions/solvent and other chemicals. Accidental spillage of chemicals in the works areas may contaminate the surface soils. The contaminated soil particles may be washed away by construction site runoff or storm runoff causing water pollution.

 

Operation Phase

 

4.6.5        After commissioning of the Project, more sewage would be received by the TPSTW.  Thus, the total pollution loading of the treated effluent would be increased.  Potential impacts are listed in the first column of Table 4.9.

 

4.7              Prediction and Evaluation of Environmental Impacts

 

Construction Phase Water Quality Impact

 
General Construction Activities

 

4.7.1        The effects on water quality from general construction activities are likely to be minimal, provided that site drainage would be well maintained and good construction practices would be observed to ensure that litter, fuels, and solvents are managed, stored and handled properly.

 

4.7.2        Based on the Sewerage Manual, Part I, 1995 of the Drainage Services Department (DSD), the sewage production rate for construction workers is estimated at 0.35 m3 per worker per day. For every 100 construction workers working simultaneously at the construction site, about 35 m3 of sewage would be generated per day.  The sewage should not be allowed to discharge directly into the surrounding water body without treatment.  Sufficient chemical toilets should be provided for workers.  Existing toilets within the TPSTW could also be made available for use as necessary.

 

Construction Runoff and Drainage

 

4.7.3        Construction run-off and drainage may cause local water quality impacts.  Increase in SS arising from the construction site could block the drainage channels and may result in local flooding when heavy rainfall occurs.  High concentrations of suspended degradable organic material in marine water could lead to reduction in DO levels in the water column.

 

4.7.4        It is important that proper site practice and good site management be followed to prevent run-off with high level of SS from entering the surrounding waters.  With the implementation of appropriate measures to control run-off and drainage from the construction site, disturbance of water bodies would be avoided and deterioration in water quality would be minimal. Thus, unacceptable impacts on the water quality are not expected, provided that the recommended measures described in Sections 4.8.1 to 4.8.9 and Appendix 4.3 are properly implemented.

 

Water Quality Impact under Normal Operation (Victoria Harbour)

 

4.7.5        For assessment of the potential impact on Victoria Harbour under normal operation of the Project, the model results are presented as contour plots for DO, BOD5, UIA, TIN, E. coli, SS, sedimentation rate and salinity.  All contour plots are presented as annual arithmetic averages except for the E.coli levels which are annual geometric means.

 

Scenario 1 (Year 2003 baseline)

 

4.7.6        The water quality simulation results of Scenario 1 are shown in Figures 1-1 to 1-10 in Appendix 4.2Tables 4.12 and 4.13 summarise the modelling results at identified water sensitive receivers.  This scenario reflects the existing baseline condition for 2003.

 

4.7.7        Treated effluent from TPSTW and STSTW is transported to Kai Tak Nullah under THEES and discharged into the embayed Kai Tak Nullah Approach Channel adjacent to the old airport runway.  The model predicted non-compliance of the marine WQO for depth-averaged (DA) DO (4 mg/L), bottom DO (2 mg/L), TIN (0.4 mg/L) and NH3–N (0.021 mg/L) within Approach Channel and at Kwun Tong Typhoon Shelter, both of them have very weak tidal circulation and are subject to direct influence of the pollution discharges from Kai Tak Nullah (Figures 1-2, 1-3, 1-5 and 1-6).  High levels of E. coli and SS were also predicted within the channel (Figures 1-7 and 1-8).

 

4.7.8        Non-compliance with WSD criteria for SS and E. coli was also predicted at Cheung Sha Wan seawater intake (Table 4.13) which was essentially due to the pollutant discharge from nearby stormwater drains.

 

Scenarios 2a and 2b (Year 2010 “without” and “with” the Project respectively)

 

4.7.9        The water quality simulation results of Scenarios 2a and 2b are shown in Figures 2a1 to 2a10 and Figures 2b1 to 2b10 in Appendix 4.2Tables 4.14 to 4.15 summarise the modelling results of Scenarios 2a and 2b at identified water sensitive receivers.

 

4.7.10    The modelling results of Scenarios 2a and 2b indicate that, after diversion of Kai Tak Nullah outfall away from the Approach Channel to Kowloon Bay under the SEKD, water quality within Kwun Tong Typhoon Shelter would be greatly improved.  Although non-compliance of WQO for TIN and NH3-N was predicted near the waterfront of Kowloon Bay (Figures 2a5, 2a6, 2b5 and 2b6), the patches of exceedances would be very localized and would not adversely affect the identified sensitive receivers.  Full compliance with the marine WQO would be achieved at all identified sensitive receivers in 2010 (Table 4.14).  However, the predicted SS and E. coli levels at Cheung Sha Wan seawater intake would marginally exceed the WSD criteria (Table 4.15) which was essentially due to the pollutant discharge from the nearby stormwater drains.  The same levels of exceedances were predicted under both baseline (Scenario 2a) and operational phase (Scenario 2b).

 

4.7.11    The comparison between the modelling results of Scenario 2a (without the Project) and Scenario 2b (with the Project) (Tables 4.14 and 4.15) indicated that there was no obvious difference in the extent of water quality impact between the scenarios.  The Project would not contribute any WQO exceedance in 2010.


Table 4.12      Predicted Water Quality at Indicator Points for Scenario 1 – Year 2003 (annual average)

 

DA DO

(mg/L)

DA DO 10%tile

(mg/L)

 

Bottom DO

(mg/L)

 

Bottom DO 10%tile (mg/L)

DA TIN 

(mg/L)

DA UIA

(mg/L)

DA SS

(mg/L)

DA E. coli

(no/100mL)

Marine Fish Culture Zone (Figure 4.8)

Ma Wan

5.81

4.94

5.68

4.56

0.23

0.007

7.43

129

Tung Lung Chau

5.81

4.17

5.51

3.22

0.04

0.002

3.86

12

Gazetted Beach (Figure 4.8)

Tung Wan

5.82

4.83

5.61

4.38

0.20

0.006

6.89

122

Ting Kau

5.77

4.85

5.66

4.57

0.23

0.007

6.92

291

Typhoon Shelter (Figure 4.8)

Rambler Channel

5.67

4.90

5.44

4.50

0.26

0.010

7.06

4550

Yau Ma Tei

6.14

5.35

5.52

4.16

0.22

0.010

6.80

3700

To Kwa Wan

5.88

4.84

5.60

4.13

0.20

0.009

5.63

357

Kwun Tong

4.15

3.35

3.80

2.05

4.02

0.194

18.10

5750

Sam Ka Tsuen

6.03

5.00

5.73

4.23

0.13

0.005

5.03

916

Causeway Bay

6.04

5.34

5.86

4.89

0.17

0.008

5.70

5840

Sau Kei Wan

5.89

4.57

5.66

3.93

0.11

0.005

4.77

2280

EPD Monitoring Station (Figure 4.1)

EM1

5.81

4.11

5.63

3.55

0.07

0.003

4.21

174

EM2

5.76

4.03

5.57

3.42

0.05

0.002

4.00

28

EM3

5.74

3.80

5.56

3.37

0.04

0.001

3.76

16

VM1

5.85

4.44

5.68

3.93

0.11

0.005

4.69

1260

VM2

5.87

4.60

5.71

4.09

0.13

0.006

4.87

866

VM4

5.85

4.66

5.68

4.13

0.15

0.007

5.15

4890

VM5

5.84

4.83

5.66

4.31

0.18

0.009

5.57

9250

VM6

5.82

4.85

5.61

4.25

0.19

0.009

5.69

7270

VM7

5.80

4.90

5.56

4.21

0.25

0.013

6.24

33200

VM8

5.77

4.84

5.57

4.38

0.21

0.009

5.92

1380

VM12

5.60

4.66

5.34

4.00

0.24

0.010

6.41

1830

VM13

5.57

4.68

5.37

4.25

0.25

0.009

6.84

2120

VM14

5.68

4.88

5.55

4.59

0.25

0.009

6.91

1920

VM15

5.82

4.95

5.53

4.19

0.21

0.010

5.93

3400

WM1

5.84

4.46

5.63

3.89

0.09

0.003

4.67

207

WM2

5.87

4.74

5.66

4.22

0.14

0.005

5.65

82

WM3

5.61

4.64

5.37

4.14

0.28

0.013

6.35

7990

WM4

5.71

4.64

5.61

4.40

0.21

0.007

6.79

306

Note:  Numbers in bold indicated non-compliance of WQO.


Table 4.13      Predicted Water Quality at Water Intakes for Scenario 1 – Year 2003 (annual average)

 

DA DO

(mg/L)

DA DO 10%tile

(mg/L)

DA TIN 

(mg/L)

DA UIA

(mg/L)

DA SS

(mg/L)

DA E. coli

(no/100mL)

WSD Salt Water Intake (Figure 4.3)

Tsuen Wan (26)

5.79

5.08

0.26

0.009

7.00

2000

Tsing Yi (27)

5.65

4.78

0.25

0.009

6.78

733

Cheung Sha Wan (28)

5.94

4.54

0.42

0.022

10.30

33400

Yau Ma Tei (19)

6.19

5.49

0.19

0.008

6.01

1700

Tai Wan (20)

6.08

5.21

0.16

0.007

5.29

434

Cha Kwo Ling (21)

6.13

5.21

0.19

0.008

5.24

592

Yau Tong (22)

5.85

4.38

0.09

0.004

4.47

236

Kennedy Town (15)

6.03

5.23

0.19

0.008

5.62

1440

Sheung Wan (14)

5.97

5.29

0.22

0.010

5.92

2290

Central Water Front (13)

5.98

5.30

0.21

0.010

5.87

1930

Wan Chai (12a)

6.05

5.39

0.18

0.008

5.66

5030

North Point (25)

6.04

5.09

0.13

0.006

5.10

1260

Quarry Bay (16)

6.00

4.87

0.11

0.005

4.89

773

Sai Wan Ho (17)

6.02

5.05

0.13

0.005

5.06

2030

Siu Sai Wan (18)

6.10

4.78

0.07

0.003

4.47

1200

Cooling Water Intake (Figure 4.3)

Princes Building (11)

5.98

5.25

0.19

0.009

5.67

4830

HSBC Intake (10)

6.04

5.38

0.18

0.009

5.70

5310

Queensway Government Offices (9)

6.04

5.38

0.18

0.009

5.70

5310

DCS Zone 1 (23)

6.00

5.32

0.19

0.009

5.79

3740

Telecom House (7) (8) (6b)

6.00

5.32

0.19

0.009

5.79

3740

Great Eagle Centre (4) (5) (6a)

6.05

5.39

0.18

0.008

5.66

5030

Sun Hung Kai Centre (3)

6.26

5.60

0.22

0.012

6.35

21800

Windsor House (1) / Excelsior Hotel / World Trade Centre (2)

6.26

5.60

0.22

0.012

6.35

21800

Note:  Numbers in bold indicated non-compliance of WSD standard.


Table 4.14    Predicted Water Quality at Indicator Points for Scenario 2a (without the Project) and Scenario 2b (with the Project) in Year 2010 (annual average)

Indicator Point

Scenario

DA DO

(mg/L)

DA DO 10%tile

(mg/L)

 

Bottom DO

(mg/L)

 

Bottom DO 10%tile (mg/L)

DA TIN 

(mg/L)

DA UIA

(mg/L)

DA SS

(mg/L)

DA E. coli

(no/100mL)

 

Fish Culture Zone (Figure 4.9)

 

Ma Wan

Without the Project (2a)

5.77

4.9

5.64

4.5

0.24

0.007

7.44

159

 

 

With the Project (2b)

5.77

4.79

5.64

4.5

0.24

0.007

7.44

159

 

Tung Lung

Without the Project (2a)

5.82

4.21

5.51

3.23

0.05

0.002

3.91

16

 

 

With the Project (2b)

5.82

4.15

5.51

3.24

0.05

0.002

3.91

16

 

Gazetted Beach (Figure 4.9)

 

Gazetted Beach (Figure 4.9)

Tung Wan

Without the Project (2a)

5.85

4.94

5.58

4.41

0.21

0.007

6.75

167

 

 

With the Project (2b)

5.85

4.91

5.58

4.36

0.21

0.007

6.75

167

 

Ting Kau

Without the Project (2a)

5.72

4.79

5.6

4.52

0.23

0.007

6.95

316

 

 

With the Project (2b)

5.72

4.76

5.6

4.51

0.23

0.007

6.95

316

 

Typhoon Shelter (Figure 4.9)

 

Typhoon Shelter (Figure 4.9)

Rambler

Channel

 

Without the Project (2a)

5.62

4.83

5.41

4.48

0.27

0.01

7.11

3650

 

With the Project (2b)

5.62

4.71

5.41

4.46

0.27

0.01

7.11

3650

 

Yau Ma Tei

Without the Project (2a)

6.07

5.18

5.31

3.76

0.26

0.011

7.05

3270

 

 

With the Project (2b)

6.08

5.09

5.31

3.76

0.27

0.011

7.06

3270

 

Kwun Tong

Without the Project (2a)

5.96

5.18

5.63

4.29

0.25

0.009

5.59

871

 

 

With the Project (2b)

5.96

5.15

5.63

4.29

0.25

0.009

5.59

872

 

Sam Ka Tsuen

 

Without the Project (2a)

5.94

4.87

5.65

4.11

0.14

0.005

4.95

990

 

With the Project (2b)

5.95

4.86

5.65

4.14

0.15

0.005

4.96

990

 

Causeway Bay

 

Without the Project (2a)

5.93

5.22

5.7

4.58

0.2

0.008

5.56

2660

 

With the Project (2b)

5.93

5.21

5.7

4.57

0.2

0.008

5.56

2660

 

Sau Kei Wan

Without the Project (2a)

5.83

4.5

5.61

3.91

0.14

0.006

4.8

2280

 

With the Project (2b)

5.83

4.5

5.61

3.94

0.14

0.006

4.8

2290

 

Marina (Figure 4.9)

 

Marina (Figure 4.9)

Kellett Island

Without the Project (2a)

5.95

5.27

5.73

4.73

0.21

0.009

5.56

3170

 

With the Project (2b)

5.95

5.26

5.73

4.72

0.21

0.009

5.57

3170

 

EPD Monitoring Station (Figure 4.1)

 

EPD Monitoring Station (Figure 4.1)

EM1

 

Without the Project (2a)

5.77

4.07

5.6

3.52

0.08

0.003

4.22

195

 

With the Project (2b)

5.77

4.13

5.6

3.53

0.08

0.003

4.22

195

 

EM2

Without the Project (2a)

5.75

4

5.54

3.41

0.06

0.002

4.01

33

 

 

With the Project (2b)

5.75

4.05

5.54

3.44

0.06

0.002

4.01

33

 

EM3

Without the Project (2a)

5.74

3.81

5.56

3.36

0.04

0.001

3.76

21

 

 

With the Project (2b)

5.74

3.82

5.56

3.42

0.04

0.001

3.76

21

 

VM1

Without the Project (2a)

5.79

4.4

5.63

3.9

0.14

0.005

4.73

1280

 

 

With the Project (2b)

5.79

4.37

5.63

3.91

0.14

0.005

4.73

1280

 

VM2

Without the Project (2a)

5.8

4.62

5.63

4.1

0.18

0.007

4.98

1450

 

 

With the Project (2b)

5.8

4.62

5.63

4.07

0.19

0.007

4.98

1450

 

VM4

Normal Operation (2a)

5.76

4.58

5.59

4.07

0.19

0.008

5.19

5290

 

 

Normal Operation (2b)

5.76

4.58

5.59

4.06

0.19

0.008

5.19

5290

 

VM5

Without the Project (2a)

5.73

4.74

5.54

4.16

0.22

0.01

5.6

9310

 

 

With the Project (2b)

5.73

4.72

5.54

4.14

0.23

0.01

5.61

9310

 

VM6

Without the Project (2a)

5.71

4.75

5.48

4.09

0.24

0.011

5.74

8240

 

 

With the Project (2b)

5.71

4.74

5.48

4.08

0.24

0.010

5.74

8240

 

VM7

Without the Project (2a)

5.67

4.79

5.41

4.04

0.31

0.015

6.43

41800

 

 

With the Project (2b)

5.67

4.73

5.41

4.06

0.31

0.015

6.44

41800

 

VM8

Without the Project (2a)

5.7

4.77

5.51

4.33

0.21

0.008

5.92

1140

 

 

With the Project (2b)

5.7

4.77

5.51

4.24

0.21

0.009

5.92

1140

 

VM12

Without the Project (2a)

5.49

4.54

5.21

3.86

0.27

0.011

6.47

1810

 

 

With the Project (2b)

5.49

4.52

5.21

3.87

0.27

0.011

6.48

1810

 

VM15

Without the Project (2a)

5.69

4.86

5.37

3.99

0.26

0.011

5.99

3880

 

 

With the Project (2b)

5.69

4.78

5.37

4.06

0.26

0.011

5.99

3880

 

VM13

Without the Project (2a)

5.5

4.58

5.32

4.17

0.26

0.01

6.94

1370

 

 

With the Project (2b)

5.50

4.54

5.32

4.12

0.27

0.01

6.94

1370

 

VM14

Without the Project (2a)

5.63

4.83

5.52

4.58

0.26

0.009

7

1350

 

 

With the Project (2b)

5.63

4.70

5.52

4.54

0.26

0.009

7

1350

 

WM1

Without the Project (2a)

5.82

4.45

5.62

3.88

0.09

0.003

4.67

266

 

 

With the Project (2b)

5.82

4.39

5.62

3.91

0.09

0.003

4.67

266

 

WM2

Without the Project (2a)

5.84

4.73

5.64

4.2

0.15

0.005

5.66

99

 

 

With the Project (2b)

5.84

4.74

5.64

4.1

0.15

0.005

5.66

99

 

WM3

Without the Project (2a)

5.47

4.52

5.23

4.04

0.31

0.015

6.47

8470

 

 

With the Project (2b)

5.47

4.51

5.23

4.03

0.31

0.015

6.47

8470

 

WM4

Without the Project (2a)

5.66

4.59

5.55

4.32

0.21

0.007

6.63

418

 

 

With the Project (2b)

5.66

4.61

5.55

4.21

0.21

0.007

6.63

418

 

Note:  Numbers in bold indicated non-compliance of WQO.

 


Table 4.15      Predicted Water Quality at Water Intakes for Scenario 2a (without the Project) and Scenario 2b (with the Project) in Year 2010 (annual average)

Indicator Point

Scenario

DA DO

(mg/L)

DA DO 10%tile

(mg/L)

DA TIN

(mg/L)

DA UIA

(mg/L)

DA SS

(mg/L)

DA E. coli

(no/100mL)

WSD Salt Water Intake (Figure 4.3)

Tsuen Wan (26)

Without the Project (2a)

5.74

5.02

0.26

0.009

7.07

1640

 

With the Project (2b)

5.74

4.81

0.26

0.009

7.08

1640

Tsing Yi (27)

Without the Project (2a)

5.64

4.85

0.26

0.009

6.86

1160

 

With the Project (2b)

5.64

4.71

0.26

0.009

6.86

1160

Cheung Sha Wan (28)

Without the Project (2a)

5.94

4.53

0.47

0.024

10.2

29700

 

With the Project (2b)

5.94

4.53

0.47

0.024

10.2

29700

Yau Ma Tei (19)

Without the Project (2a)

6.25

5.42

0.24

0.01

6.44

1470

 

With the Project (2b)

6.26

5.40

0.24

0.01

6.44

1470

Tai Wan (20)

Without the Project (2a)

5.9

4.99

0.29

0.011

5.44

1530

 

With the Project (2b)

5.9

4.97

0.29

0.011

5.44

1530

Cha Kwo Ling (21)

Without the Project (2a)

6.14

5.32

0.16

0.006

5.00

518

 

With the Project (2b)

6.14

5.28

0.16

0.006

5.00

518

Yau Tong (22)

Without the Project (2a)

6.04

5.13

0.15

0.006

4.91

1140

 

With the Project (2b)

6.04

5.09

0.15

0.006

4.92

1140

Kennedy Town (15)

Without the Project (2a)

5.88

5.14

0.22

0.009

5.77

1320

 

With the Project (2b)

5.89

5.03

0.22

0.009

5.78

1320

Sheung Wan (14)

Without the Project (2a)

5.86

5.16

0.25

0.011

5.88

3330

 

With the Project (2b)

5.86

5.03

0.25

0.011

5.88

3340

Central Water Front (13)

Without the Project (2a)

5.86

5.15

0.25

0.011

5.91

2520

 

With the Project (2b)

5.86

5.22

0.25

0.011

5.91

2520

Wan Chai (12a)

Without the Project (2a)

5.97

5.27

0.21

0.009

5.59

5360

 

With the Project (2b)

5.97

5.25

0.21

0.009

5.59

5360

North Point (25)

Without the Project (2a)

5.96

4.95

0.16

0.006

5.11

1180

 

With the Project (2b)

5.96

4.95

0.16

0.006

5.11

1180

Quarry Bay (16)

Without the Project (2a)

5.95

4.96

0.16

0.006

5.07

1910

 

With the Project (2b)

5.95

4.96

0.16

0.006

5.07

1910

Sai Wan Ho (17)

Without the Project (2a)

5.94

4.81

0.15

0.006

4.95

1230

 

With the Project (2b)

5.94

4.84

0.15

0.006

4.95

1230

Siu Sai Wan (18)

Without the Project (2a)

6.08

4.73

0.08

0.003

4.49

1350

 

With the Project (2b)

6.08

4.72

0.08

0.003

4.49

1350

Cooling Water Intake (Figure 4.3)

Princes Building (11)

Without the Project (2a)

5.91

5.18

0.23

0.01

5.72

4600

 

With the Project (2b)

5.91

5.13

0.23

0.01

5.72

4600

HSBC Intake (10)

Without the Project (2a)

5.93

5.23

0.23

0.01

5.77

4570

 

With the Project (2b)

5.93

5.20

0.23

0.01

5.78

4570

Queensway Government

Offices (9)

Without the Project (2a)

5.93

5.23

0.23

0.01

5.74

6000

With the Project (2b)

5.93

5.21

0.23

0.01

5.74

6000

DCS Zone 1 (23)

Without the Project (2a)

5.93

5.23

0.23

0.01

5.74

6000

 

With the Project (2b)

5.93

5.21

0.23

0.01

5.74

6000

Telecom House (7) (8) (6b)

Without the Project (2a)

5.95

5.27

0.23

0.01

5.7

5160

 

With the Project (2b)

5.96

5.26

0.23

0.01

5.7

5160

Great Eagle Centre (4) (5) (6a)

Without the Project (2a)

5.92

5.20

0.22

0.009

5.64

6390

With the Project (2b)

5.92

5.16

0.22

0.009

5.65

6390

Sun Hung Kai Centre (3)

Without the Project (2a)

5.94

5.24

0.22

0.009

5.63

4700

 

With the Project (2b)

5.95

5.24

0.22

0.009

5.63

4700

Windsor House (1) / Excelsior

Hotel / World Trade Centre (2) 

Without the Project (2a)

6.16

5.49

0.20

0.008

5.56

2400

With the Project (2b)

6.16

5.38

0.20

0.008

5.56

2400

DCS Zone 4 (24)

Without the Project (2a)

6.01

5.34

0.22

0.009

5.68

9120

With the Project (2b)

6.01

5.28

0.22

0.009

5.68

9120

Note:  Numbers in bold indicated non-compliance of WQO.

 

 

 


Scenarios 3a and 3b (Year 2016 “without” and “with” the Project respectively)

 

4.7.12    The water quality simulation results of Scenarios 3a and 3b are shown in Figures 3a1 to 3a10 and Figures 3b1 to 3b11 in Appendix 4.2.  Tables 4.16 to 4.17 summarise the modelling results of Scenarios 3a and 3b at identified water sensitive receivers.

 

4.7.13    The modelling results of Scenario 2 and Scenario 3 are similar.  Non-compliance of WQO for TIN and NH3-N was predicted near the waterfront of Kowloon Bay in 2016 (Figures 3a5, 3a6, 3b5 and 3b6) but the patches of exceedances would be very localized.  Full compliance with the marine WQO would be achieved at all identified sensitive receivers except that the TIN level marginally exceeded the WQO of 0.4 mg/L at the new Marina of SEKD where is a semi-enclosed water body with low flushing capacity (Table 4.16).  The predicted SS and E. coli levels at Cheung Sha Wan seawater intake would also marginally exceed the WSD criteria (Table 4.17) which was essentially due to the pollutant discharge from the nearby stormwater drains.  The same levels of exceedances were predicted under both baseline (Scenario 3a) and operational phase (Scenario 3b).

 

4.7.14    The comparison between the modelling results of Scenario 3a (without the Project) and Scenario 3b (with the Project) (Tables 4.16 and 4.17) indicated that there was no obvious difference in the extent of water quality impact between the scenarios.  The model predicted that the Project would not contribute any WQO exceedances in 2016.

 

 

 


Table 4.16      Predicted Water Quality at Indicator Points for Scenario 3a (without the Project) and Scenario 3b (with the Project) in Year 2016 (annual average)

Indicator

Point

Scenario

DA DO

(mg/L)

DA DO 10%tile

(mg/L)

Bottom DO

(mg/L)

Bottom DO 10%tile (mg/L)

DA TIN 

(mg/L)

DA UIA

(mg/L)

DA SS

(mg/L)

DA E. coli

(no/100mL)

Fish Culture Zone (Figure 4.10)

Ma Wan

Without the Project (3a)

5.86

4.97

5.74

4.6

0.25

0.006

7.39

44

 

With the Project (3b)

5.86

4.97

5.74

4.6

0.25

0.006

7.39

44

Tung Lung

Without the Project (3a)

5.88

4.37

5.54

3.32

0.05

0.002

3.88

9

 

With the Project (3b)

5.88

4.37

5.54

3.32

0.05

0.002

3.89

9

Gazetted Beach (Figure 4.10)

Tung Wan

Without the Project (3a)

6.02

5.06

5.76

4.54

0.24

0.005

6.66

12

 

With the Project (3b)

6.02

5.06

5.76

4.54

0.24

0.005

6.66

12

Ting Kau

Without the Project (3a)

5.86

4.9

5.76

4.63

0.25

0.006

6.86

100

 

With the Project (3b)

5.86

4.9

5.76

4.63

0.25

0.006

6.86

100

Typhoon Shelter (Figure 4.10)

Rambler

Channel