6                     WATER QUALITY

 

Introduction

 

6.1               Stage 1 of HATS, comprising the Stonecutters Island Sewage Treatment Works (SCISTW) and the deep tunnels, was commissioned in late 2001 to bring early improvement to the harbour water quality.  The deep tunnels collect sewage from Kwai Chung, Tsing Yi, Tseung Kwan O, parts of eastern Hong Kong Island and all of Kowloon and deliver it to SCISTW for chemically enhanced primary treatment (CEPT).  Stage 2 of HATS would be implemented in two phases, namely Stage 2A and Stage 2B.  Under Stage 2A, deep tunnels would be built to bring sewage from the northern and western areas of Hong Kong Island to SCISTW and the treatment works would be expanded to meet the demands of both existing and future developments.  Stage 2B of HATS involves the provision of secondary treatment at the SCISTW to improve the effluent quality.

 

6.2               This Project involves the construction and operation of Stage 2A. Construction of the Project (i.e. Stage 2A) is tentatively scheduled to commence in 2009 for commissioning the Stage 2A scheme by  2014.The scope of Stage 2A includes the following:

 

·               Upgrading of existing preliminary treatment works (PTW) at North Point, Wan Chai East, Central, Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau on Hong Kong Island;

·               Extension of the deep tunnel network to collect and transfer sewage from the above mentioned PTWs to SCISTW for treatment and disposal;

·               Expansion of the existing CEPT capacity at SCISTW to meet the demands of both existing and future developments; and

·               Provision of disinfection to all HATS effluent before discharging into the harbour.

 

6.3               Based on the technical review of disinfection technologies and option evaluation as well as the technical environmental assessment conducted under the EIA study for “Provision of Disinfection Facilities at Stonecutters Island STW – Investigation (ADF)”, the purchase of sodium hypochlorite solution for chlorination and sodium bisulphite for dechlorination was recommended as the disinfection technology for SCISTW.  Based on the current programme, construction of the chlorination plant would commence in April 2008 for commissioning the advance disinfection facilities (ADF) in October 2009. As for the dechlorination plant, construction would commence in September 2008 for completion in September 2009.

 

6.4               During the ADF stage, use of the existing effluent culvert as the chlorine contact tank is proposed. At Stage 2A, the permanent disinfection facilities of SCISTW (including a new chlorine contact tank) will be available for the HATS effluent to increase the chlorine contact time so as to further improve the effectiveness of the chlorination and minimize the chlorine dosage.

 

6.5               This Section evaluates the potential water quality impacts that are likely to be generated during the construction and operation of Stage 2A.  The water quality impacts of Stage 1, Stage 2A and Stage 2B of the HATS have also been taken into consideration in this water quality impact assessment.  Appropriate mitigation measures were identified, where necessary, to mitigate the potential water quality impacts.

 

Water Sensitive Receivers

 

6.6               To evaluate the potential water quality impacts from the Project, water sensitive receivers within the North Western, Western Buffer, Victoria Harbour, Eastern Buffer, Junk Bay and Southern Water Control Zones (WCZ) were considered.  Major water sensitive receivers identified within the Study Area include:

 

·               Cooling Water Intakes;

·               WSD Flushing Water Intakes;

·               Fish Culture Zones (FCZ);

·               Beaches;

·               Sites of Special Scientific Interest (SSSI);

·               Marine Parks and Marine Reserves;

·               Seagrass Beds;

·               Artificial Reefs;

·               Corals;

·               Chinese White Dolphins; and

·               Green Turtle Nesting Grounds

 

6.7               Figure 6.1 shows the locations of the ecological resources and water sensitive receivers.

 

Identification of Environmental Impacts

 

Operational Phase

 

6.8               During the operational phase, the potential water quality impacts will be mainly related to the treated effluent discharge from the HATS Stage 2A.  Key concerns are:

 

·               Effects on marine water quality and sediment quality due to the discharge of disinfected CEPT effluent from SCISTW at different time horizons under normal plant operation.

·               Water quality effects of occasional overflow of screened (or untreated) effluent at individual PTW during extreme storm event under normal plant operation.

·               Water quality impacts of emergency sewage discharges due to the failure of equipment or power supply or as a result of treatment process failure.

 

6.9               The water quality parameters considered for the assessment of water quality impact from the HATS Stage 2A effluent include pH, temperature, dissolved oxygen (DO), salinity, suspended solids (SS), biochemical oxygen demand (BOD), nutrients, chlorophyll, E.coli, sedimentation rates, chlorination by-products (CBP) and toxic chemicals such as metals, total residual chlorine (TRC) and unionized ammonia etc. 

 

6.10            A comprehensive review and identification of toxic contaminants of concern (COC) in the HATS effluent and their respective assessment criteria and detailed assessment of the toxic effects of the identified COC were conducted under the human health and marine ecological risk assessment in Section 7 and Section 8.

 

Construction Phase

 

6.11            No dredging and filling activity would be anticipated for the tunnel construction.  The general construction activities that will be undertaken for the upgrading works will be primarily land-based.  Key water quality issues associated with land-based construction would include the impacts from site run-off, sewage from workforce, accidental spillage and discharges of wastewater from various construction activities. 

 

6.12            Based on the preliminary engineering design, the proposed upgrading works at one of the PTWs, Aberdeen PTW, would require seawall re-construction. Seawall re-construction would involve excavation of existing seawall.  Fine content in the filling materials in the seawall would be negligible and loss of fill material during seawall excavation is not expected.  No dredging would be required for the seawall re-construction works.

 

6.13            Temporary bypass of sewage effluent via seawall or submarine outfalls of SCISTW and individual PTW would be required during the construction stage.  The temporary sewage bypass would cause transient increase of pollution level in the receiving marine water.

 

Environmental Impacts from the Provision of Disinfection at SCISTW

 

6.14            Key water quality impacts related to the provision of disinfection facilities at the SCISTW include:

 

·               The reduction of faecal bacteria in the effluent after disinfection.

·               The potential generation of low-level total residual chlorine (TRC) and chlorination by-products (CBP) in the effluent due to chlorination of the sewage effluent.

·               The potential impact of TRC in the event of dechlorination plant failure.

·               The potential impact of faecal pollution in the event of chlorination plant failure.

·               The potential minor oxygen depletion impact due to addition of dechlorination chemical.

 

6.15            Total residual chlorine (TRC) and chlorination by-products (CBP) are major concerns of chlorination. TRC includes free chlorine residuals such as hypochlorous acid (HOCl) and dissolved hypochlorite ion (OCl-) after chlorine is added to water, plus combined chlorine residuals such as chloramines formed by the reaction of free residuals with ammonia present in the sewage. CBP refer to chlorinated organic compounds (or total organic halogen) formed by the reaction of chlorine (mainly free chlorine residuals) with some specific organic compounds such as humic substances, which generally are not present in any large quantity in CEPT effluent. CBP consist of a whole range of halogenated organic compounds, and are generally considered of concern to human health. Examples of CBP formed during chlorination include trihalomethanes (THM) and haloacetic acids (HAA). THM are suspected as being carcinogens and are strictly monitored in drinking water.  CBP concentrations may vary in orders of magnitude during different chlorination processes.  Typical concentrations of THM and HAA in chlorinated drinking water are usually in the range 1-100 mg/l ([1]).  Range of concentrations in chlorinated sewage effluent for specific CBP compounds has been identified under the EIA study for ADF and is also presented in this EIA report for completeness.

 

6.16            Water quality impacts in relation to the chlorination and dechlorination of the HATS effluent have been quantitatively assessed by mathematical modelling under the EIA study for the ADF. Details of the assessment results are presented in the separate EIA report for ADF.  Under the ADF study, water quality model simulations were performed for 30 days (excluding the spin-up time) each under the typical wet and dry seasons for normal operation scenarios and 15 days (excluding the spin-up time) each under the typical wet and dry seasons for emergency situations (due to temporary failure of chlorination or dechlorination plant) in accordance with the EIA Study Brief for ADF. 

 

6.17            The EIA Study Brief for this Project (i.e. Stage 2A) requires that the model simulations shall be performed for at least one complete calendar year under normal operation scenarios.  As such, the water quality impacts in relation to the normal operation of the disinfection facilities for HATS have been re-examined under this EIA based on a series of 1-year model simulations incorporating monthly variations in Pearl River discharges, solar radiation, water temperature and wind velocity to confirm the findings of the ADF study. 

 

6.18            According to the EIA Study Brief for this Project, assessment of temporary or emergency discharges as well as the short-term construction phase impacts may be assessed by simulating typical spring-neap cycles (at least 15 days) in the dry and wet seasons. Furthermore, the HATS flow rates adopted in the EIA study for ADF were more conservative as compared to the latest flow projections adopted in this EIA. It is considered that the water quality impacts in relation to the temporary failure of chlorination or dechlorination plant have been fully quantified and assessed under the ADF study. 

 

Environmental Legislation, Policies, Plans, Standards and Criteria

 

Environmental Impact Assessment Ordinance (EIAO)

 

6.19            The Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) is issued by the EPD under Section 16 of the EIAO.  It specifies the assessment method and criteria that need to be followed in the EIA.  Reference sections in the EIAO-TM provide the details of the assessment criteria and guidelines that are relevant to the water quality impact assessment, including:

 

·               Annex 6 Criteria for Evaluating Water Pollution

·               Annex 14 Guidelines for Assessment of Water Pollution

 

Marine Water Quality Objectives under WPCO

 

6.20            The Water Pollution Control Ordinance (WPCO) provides the major statutory framework for the protection and control of water quality in Hong Kong.  According to the WPCO and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZ).  Corresponding statements of Water Quality Objectives (WQO) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in the WCZ based on their beneficial uses.  With reference to the EIA Study Brief, the Study Area for this water quality assessment covers the North Western, Western Buffer, Victoria Harbour, Eastern Buffer, Junk Bay and Southern WCZ (see Figure 6.2). Their corresponding WQO are listed in Table 6.1 to Table 6.6 respectively.

 

Table 6.1      Summary of Water Quality Objectives for North Western WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) subzones, water gathering ground subzones and other inland waters

Not less than 4.0 mg/l for 90 % sample

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 excepting bathing beach subzones

To be in the range of 6.5 – 8.5

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) subzones and water gathering ground subzones

To be in the range of 6.0 –9.0

Other inland waters

To be in the range of 6.0 –9.0 for 95% samples

Bathing beach subzones

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

Change due to waste discharges not to exceed 20 mg/l of annual median

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) subzones and water gathering ground subzones

Change due to waste discharges not to exceed 25 mg/l of annual median

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l  as unionized form

Whole zone

Nutrients

Shall not cause excessive algal growth

Marine waters

Total inorganic nitrogen (TIN)

Annual mean depth-averaged inorganic nitrogen not to exceed 0.3 mg(N)/l

Castle peak bay subzone

Annual mean depth-averaged inorganic nitrogen not to exceed 0.5 mg(N)/l

Marine waters excepting castle peak bay subzone

E.coli

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

Secondary contact recreation subzones

Should be less than 1 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken between 7 and 21 days.

Tuen Mun (A) and Tuen Mun (B) subzones and water gathering ground subzones

Not exceed 1000 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken between 7 and 21 days

Tuen Mun (C) subzone and other inland waters

Not exceed 180 per 100 ml, calculated as the geometric mean of all samples collected from March to October inclusive.

Bathing beach subzones

Colour

Change due to waste discharges not to exceed 30 Hazen units

Tuen Mun (A) and Tuen Mun (B) subzones and water gathering ground subzones

Change due to waste discharges not to exceed 50 Hazen units

Tuen Mun (C) subzone and other inland waters

5-Day biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 3 mg/l

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) subzones and water gathering ground subzones

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 15 mg/l

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) subzones and water gathering ground subzones

Change due to waste discharges not to exceed 30 mg/l

Inland waters

Toxins

Should not cause a risk to any beneficial uses of the aquatic environment

Whole zone

Waste discharge shall not cause the toxins in water significant to produce toxic carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.

Whole zone

Phenol

Quantities shall not sufficient to produce a specific odour or more than 0.05 mg/l as C6 H5OH

Bathing beach subzones

 

Turbidity

Shall not reduce light transmission substantially from the normal level

Bathing beach subzones

Source:    Statement of Water Quality Objectives (North Western Water Control Zone).

 

Table 6.2      Summary of Water Quality Objectives for Western Buffer WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters excepting fish culture subzones

Not less than 5.0 mg/l for 90% of samples

Fish culture subzones

Not less than 4.0 mg/l

Water gathering ground subzone and other Inland waters

5-Day biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 3 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 15 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 30 mg/l

Inland waters

pH

To be in the range of 6.5 – 8.5, change due to waste discharges not to exceed 0.2

Marine waters

To be in the range of 6.5 – 8.5

Water gathering ground subzones

To be in the range of 6.0 – 9.0

Inland waters

Salinity

Change due to waste discharges not to exceed 10% of ambient

Whole zone

Temperature

Change due to waste discharges not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities

Marine waters

Change due to waste discharges not to exceed 20 mg/l of annual median

Water gathering ground subzones

Change due to waste discharges not to exceed 25 mg/l of annual median

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized 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(N)/l

Marine waters

Toxic substances

Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms

Whole zone

Waste discharges should not cause a risk to any beneficial use of the aquatic environment

Whole zone

E.coli

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

Secondary contact recreation subzones and fish culture subzones

Not exceed 180 per 100 ml, calculated as the geometric mean of all samples collected from March to October inclusive in 1 calendar year. Samples should be taken at least 3 times in 1 calendar month at intervals of between 3 and 14 days

Bathing beach subzones




Less than 1 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Water gathering ground subzones

Not exceed 1000 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Inland waters

Colour

Change due to waste discharges not to exceed 30 Hazen units

Water gathering round

Change due to waste discharges not to exceed 50 Hazen units

Inland waters

Turbidity

Shall not reduce light transmission substantially from the normal level

Bathing beach subzones

 

Source:    Statement of Water Quality Objectives (Western Buffer Water Control Zone).

 

Table 6.3      Summary of Water Quality Objectives for Victoria Harbour WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

E coli

Not to exceed 1000 per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals between 7 and 21 days

Inland waters

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters

DO

Not less than 4.0 mg/l

Inland waters

pH

To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2

Marine waters

Not to exceed the range of 6.0 - 9.0 due to human activity

Inland waters

Salinity

Change due to human activity not to exceed 10% of ambient

Whole zone

Temperature

Change due to human activity not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by human activity

Marine waters

Annual median not to exceed 25 mg/l due to human activity

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized 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(N)/l

Marine waters

5-Day biochemical oxygen demand (BOD5)

Not to exceed 5 mg/l

Inland waters

Chemical Oxygen Demand (COD)

Not to exceed 30 mg/l

Inland waters

Toxic substances

Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.

Whole zone

Human activity should not cause a risk to any beneficial use of the aquatic environment.

Whole zone

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

 

Table 6.4      Summary of Water Quality Objectives for Eastern Buffer WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters excepting fish culture subzones

Not less than 5.0 mg/l for 90% of samples

Fish culture subzones

Not less than 4.0 mg/l

Water gathering ground subzone and other Inland waters

5-Bay biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 3 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 15 mg/l

Water gathering ground subzones

Change due to waste discharges not to exceed 30 mg/l

Inland waters

pH

To be in the range of 6.5 – 8.5, change due to waste discharges not to exceed 0.2

Marine waters

To be in the range of 6.5 – 8.5

Water gathering ground subzones

To be in the range of 6.0 – 9.0

Inland waters

Salinity

Change due to waste discharges not to exceed 10% of ambient

Whole zone

Temperature

Change due to waste discharges not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities

Marine waters

Change due to waste discharges not to exceed 20 mg/l of annual median

Water gathering ground subzones

Change due to waste discharges not to exceed 25 mg/l of annual median

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized 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(N)/l

Marine waters

Dangerous substances

Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms

Whole zone

Waste discharges should not cause a risk to any beneficial use of the aquatic environment

Whole zone

E.coli

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

Fish culture subzones

Less than 1 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Water gathering ground subzones

Not exceed 1000 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Inland waters

Colour

Change due to waste discharges not to exceed 30 Hazen units

Water gathering ground

Change due to waste discharges not to exceed 50 Hazen units

Inland waters

Source:    Statement of Water Quality Objectives (Eastern Buffer Water Control Zone).

 

Table 6.5      Summary of Water Quality Objectives for Junk Bay WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90% of samples

Marine waters excepting fish culture subzones

Not less than 5.0 mg/l for 90% of samples

Fish culture subzones

Not less than 4.0 mg/l

Inland waters

5-Bay biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 30 mg/l

Inland waters

pH

To be in the range of 6.5 - 8.5, change due to waste discharges not to exceed 0.2

Marine waters

To be in the range of 6.0 –9.0

Inland waters

Salinity

Change due to waste discharges not to exceed 10% of ambient

Whole zone

Temperature

Change due to waste discharges not to exceed 2 oC

Whole zone

Suspended solids (SS)

Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities

Marine waters

Change due to waste discharges not to exceed 25 mg/l of annual median

Inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized form

Whole zone

Nutrients

Shall not cause excessive algal growth

Marine waters

Total inorganic nitrogen (TIN)

Annual mean depth-averaged inorganic nitrogen not to exceed 0.3 mg(N)/l

Marine waters

Dangerous substances

Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms

Whole zone

Waste discharges should not cause a risk to any beneficial use of the aquatic environment

Whole zone

E.coli

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

Secondary contact recreation subzones and fish culture subzones

Not exceed 1000 per 100 ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days

Inland waters

Colour

Change due to waste discharges not to exceed 50 Hazen units

Inland waters

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

 

Table 6.6      Summary of Water Quality Objectives for Southern WCZ

 

Parameters

Objectives

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Dissolved oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg/l for 90% of samples

Marine waters

Depth-averaged DO

Not less than 4.0 mg/l for 90 % sample

Marine waters excepting fish culture subzones

Not less than 5.0 mg/l for 90% of samples

Fish culture subzones

Not less than 4.0 mg/l

Inland waters

pH

To be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2

Marine waters excepting bathing beach subzones; Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) subzones

To be in the range of 6.0 – 9.0

Mui Wo (D) sub-zone and other inland waters.

To be in the range of 6.0 –9.0 for 95% of samples, change due to human activity not to exceed 0.5

Bathing beach subzones

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

Change due to waste discharges not to exceed 20 mg/l of annual median

Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) subzones

Change due to waste discharges not to exceed 25 mg/l of annual median

Mui Wo (D) subzone and other inland waters

Unionized ammonia (UIA)

Annual mean not to exceed 0.021 mg(N)/l as unionized 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 0.1 mg(N)/l

Marine waters

E.coli

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

Secondary contact recreation subzones

and fish culture subzones

Not exceed 180 per 100 ml, calculated as the geometric mean of all samples collected from March to October inclusive in 1 calendar year. Samples should be taken at least 3 times in 1 calendar month at intervals of between 3 and 14 days.

Bathing beach subzones

5-Day biochemical oxygen demand (BOD5)

Change due to waste discharges not to exceed 5 mg/l

Inland waters

Chemical oxygen demand (COD)

Change due to waste discharges not to exceed 30 mg/l

Inland waters

Dangerous substances

Should not attain such levels as to produce significant toxic effects in humans, fish or any other aquatic organisms

Whole zone

Waste discharges should not cause a risk to any beneficial use of the aquatic environment

Whole zone

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

 

Water Supplies Department (WSD) Water Quality Criteria

 

6.21            Besides the WQO set under the WPCO, the WSD has specified a set of objectives for water quality at flushing water intakes as listed in Table 6.7. 

 

Table 6.7      WSD Standards at Flushing Water Intakes

 

Parameter (in mg/l unless otherwise stated)

WSD Target Limit

Colour (Hazen Unit)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammoniacal Nitrogen

< 1

Suspended Solids

< 10

Dissolved Oxygen

> 2

Biochemical Oxygen Demand

< 10

Synthetic Detergents

< 5

E.coli (no. per 100 ml)

< 20000

 

Practice Note

 

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

 

Technical Memorandum on Effluents Discharge Standard

 

6.23            Discharges of effluents are subject to control under the WPCO.  The Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) 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 effluent discharge from the proposed construction activities must comply with the standards for effluent discharged into the foul sewers, inshore waters and marine waters of the Victoria Harbour WCZ and Western Buffer WCZ, as given in the TM-DSS.

 

Assessment Criteria for Corals

 

6.24            Potential impacts on benthic organisms, including corals, may arise through excessive sediment deposition.  The magnitude of impacts on marine ecological sensitive receivers was assessed based on the predicted sedimentation rate. 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 for protecting the corals in Hong Kong under other approved EIAs such as Tai Po Sewage Treatment Works Stage 5 EIA ([4]), Further Development of Tseung Kwan O Feasibility Study EIA, Wan Chai Reclamation Phase II EIA, Eastern Waters MBA Study ([5]), West Po Toi MBA Study ([6]) and Tai Po Gas Pipeline Study ([7]).  This sedimentation rate was used as the assessment criterion to guard against unacceptable impacts on marine ecological sensitive receivers.

 

6.25            The potential impacts on corals were also assessed with reference to the WQO of 30% from the ambient levels. However, in Eastern Buffer, Junk Bay and Southern WCZ with low baseline SS levels, it is proposed to adopt a SS criteria value of 10 mg/L for assessing the impacts upon corals. The SS value of 10 mg/L has been adopted as the SS criterion under many other EIA studies in Hong Kong ([8]) for protection of sensitive coral sites in the eastern and southern waters of Hong Kong where the baseline SS levels were low. Based on previous EM&A monitoring results where this SS criterion of 10 mg/L has been adopted, no adverse impacts on corals have occurred. 

 

EEFS Water Quality Criteria (WQC)

 

6.26            In addition to the statutory WQO stipulated under the WPCO, a set of water quality criteria (WQC) established under the “Environmental and Engineering Feasibility Assessment Studies in relation to the Way Forward of the HATS (EEFS)” was used as reference guidelines to assess the water quality impacts as per the requirement in Section 3.4.3.5 (iv) of the EIA Study Brief.

 

Background

 

6.27            The HATS is an overall sewage collection and treatment scheme for areas on both sides of Victoria Harbour. Stage 1 of HATS, fully commissioned in December 2001, collects sewage from the urban areas of Kowloon, Tsuen Wan, Kwai Tsing, Tseung Kwan O and the north-eastern part of Hong Kong Island and conveys it to SCISTW for CEPT treatment which has brought early water quality improvements especially in eastern Victoria Harbour, Eastern Buffer WCZ and Junk Bay WCZ.  As the population grows and with further development on both sides of the harbour, deterioration of water quality in Victoria Harbour may occur if the full HATS is not completed.

 

6.28            In 2004, the Government of the Hong Kong SAR completed trials and studies on environmental impacts and engineering feasibility to assist in deciding the best way forward for the remaining stages of HATS.  Detailed marine water quality, ecological and fisheries assessments were performed as part of the EEFS with the objective of assessing the potential impacts of different treatment and disposal schemes proposed for the remaining stages of HATS and the associated construction activities.  The recommended option for HATS Stage 2 is to convey all sewage from the harbour area to SCISTW for centralized treatment.  The EEFS recommended that biological treatment plus disinfection should be provided for the HATS on a long-term basis. The marine water quality, ecological and fisheries assessment conducted as part of the EEFS followed the guidelines set forth in the EIAO-TM.  The potential water quality impacts were quantitatively assessed using various WQC outlined for the EEFS with a further qualitative assessment based on the collective professional opinion of a team of local and international experts in marine sciences and water quality management.

 

 

6.29            Setting of WQC has been recognized from the start of the EEFS as a key to assessing the acceptability and performance of different HATS options.  In support of criteria setting, an extensive public consultation exercise on the proposed WQC for HATS was conducted in 2002 as part of the EEFS.  These WQC were based on the statutory WQO stipulated under the WPCO, originally developed in the late 1980’s, and further refined by the consultant of the EEFS using the results of the Environmental Impact Assessment of the Strategic Sewage Disposal Scheme (SSDS EIA) and other recently completed studies.  The set of HATS specific WQC, developed as a part of the EEFS, has integrated the concerns of various interested stakeholders and the general public through a presentation and briefing with the Advisory Council on the Environment and the Monitoring Group for HATS, public view-sharing workshops and receipt of public comments. 

 

6.30            The findings of this consultation exercise and a full set of the proposed final WQC are documented in the “Report on Community Consultation for the Proposed Water Quality Criteria (October 2002)” prepared under the EEFS.  

 

Water Quality Criteria (WQC)

 

6.31            The WQC as shown in Table 6.8 and Table 6.9 were used as reference guidelines for far field and near field impact assessment respectively. The far field water quality impact assessment and far field modelling performed under this EIA covered the North Western, Western Buffer, Victoria Harbour, Eastern Buffer, Junk Bay and Southern WCZ as well as the adjacent outer water to take into account all the major pollution sources (including the Pearl River) that may have a bearing on the environmental acceptability of the Project as required by the EIA Study Brief.  The near field impact assessment was conducted by mathematical modelling to simulate the characteristics of the sewage plume in the vicinity of the submarine outfall to determine the zone of initial dilution (ZID), plume dimensions, rise height, merging and trapping in various flow and ambient conditions.

 

6.32            Relevant WQC were derived under the EEFS for Western Buffer, Eastern Buffer, Junk Bay, Southern and Victoria Harbour WCZ. Different WQC were provided for different zones or locations to protect marine resources and uses of the water bodies. EEFS did not derive WQC for the North Western WCZ. Various marine resources and water sensitive uses identified within the Study Area are shown in Figure 6.1.

 

Table 6.8      Reference Marine Water Quality Criteria for Far Field Water Quality Assessment

 

Parameter

Value

Type / Period

Applicable Zones / Uses (1)

E.coli

≤ 180/100ml

Geometric mean for bathing season (March to October)

Bathing waters

≤ 610/100ml

Annual geometric mean

Secondary contact recreation zones and mariculture zones

≤ 20,000/100ml

90% of occasions

Sea water intakes for flushing and industrial use

Dissolved oxygen (DO)

≥ 4 mg/l (water column average)

90% of occasions

Western Buffer, Eastern Buffer, Junk Bay and Victoria Harbour WCZ (except mariculture zones and fish spawning ground) (Figure 6.2)

≥ 2 mg/l

at all times

All WCZ (except mariculture zones)

≥ 5 mg/l (water column average)

Monthly average

Southern WCZ and fish spawning ground (Figure 6.2)

≥ 5 mg/l (water column average)

90% of occasions

Mariculture zones only

≥ 2 mg/l (bottom DO within 2 m from the seabed)

90% of occasions

Mariculture zones only

Depth-averaged total inorganic nitrogen (TIN)

≤ 0.2 mg(N)/l

Annual mean

Southern WCZ and fish spawning ground (Figure 6.2)

≤ 0.4 mg(N)/l

Annual mean

Western Buffer, Eastern Buffer and Victoria Harbour WCZ (except fish spawning ground) (Figure 6.2)

≤ 0.3 mg(N)/l

Annual mean

Junk Bay WCZ (Figure 6.2)

≤ 0.1 mg(N)/l

Annual mean

Semi-enclosed bays (Figure 6.3)

Depth-averaged Unionized Ammonia (UIA)

≤ 0.021 mg(N)/l

Annual mean

All WCZ

Depth-averaged total inorganic phosphorus (PO4)

≤ 0.02 mg(P)/l

Annual mean

Southern WCZ and fish spawning ground (Figure 6.2)

≤ 0.04 mg(P)/l

Annual mean

Western Buffer, Eastern Buffer and Victoria Harbour WCZ (except fish spawning ground) (Figure 6.2)

≤ 0.03 mg(P)/l

Annual mean

Junk Bay WCZ (Figure 6.2)

≤ 0.01 mg(P)/l

Annual mean

Semi-enclosed bays (Figure 6.3)

Total residual chlorine (TRC)

≤ 0.008 mg/l

Daily maximum

All WCZ

Chronic toxicity

≤ one chronic toxicity unit (TUc), (derived from NOEC values based on whole effluent toxicity tests) (2)

4-day average chronic toxicity exposure

All WCZ

(Source: EEFS Report on Community Consultation for the Proposed Water Quality Criteria)

(1) EEFS did not derive WQC for the North Western WCZ.

(2) USEPA Technical Support Document for Water Quality-Based Toxics Control (March 1991), from which one chronic Toxicity Unit (TUc) is defined TUc = 100/NOEC, where NOEC = % of effluent which gives no observed effect on the most sensitive of the range of species tested.

 

Table 6.9      Reference Marine Water Quality Criteria for Near Field Water Quality Assessment

 

Parameter

Value

Type / Period

Applicable Zones / Uses

Unionized ammonia (UIA)

≤ 0.021 mg/l (as N) (2)

Annual average

At edge of ZID (1)

≤ 0.035 mg/l (as NH3) (3)

4-day average

At edge of ZID (1)

≤ 0.233 mg/l (as NH3) (3)

1-hour average

At edge of ZID (1)

pH

6.5 – 8.5,

and change ≤ 0.2

90% of occasions

At edge of ZID (1)

Temperature

change ≤ 2 oC

90% of occasions

At edge of ZID (1)

Sulphide

0.02 mg/l

90% of occasions

At edge of ZID (1)

Cyanide

0.005 mg/l

90% of occasions

At edge of ZID (1)

Total residual chlorine (TRC)

≤ 0.013 mg/l

Daily Maximum

At edge of ZID (1)

Surfactants

0.03 mg/l

90% of occasions

At edge of ZID (1)

Copper

0.005 mg/l

90% of occasions

At edge of ZID (1)

Nickel

0.005 mg/l

90% of occasions

At edge of ZID (1)

Total chromium

0.05 mg/l

90% of occasions

At edge of ZID (1)

Zinc

0.02 mg/l

90% of occasions

At edge of ZID (1)

Mercury

0.00021 mg/l

90% of occasions

At edge of ZID (1)

Arsenic

0.02 mg/l

90% of occasions

At edge of ZID (1)

Phenol

0.005 mg/l

90% of occasions

At edge of ZID (1)

Acute Toxicity

0.3 acute toxicity units (TUa) (derived from LC50 values based on whole effluent toxicity tests) (4)

One hour average condition not to exceed this value

At edge of ZID (1)

(Source: EEFS Report on Community Consultation for the Proposed Water Quality Criteria)

(1) For a surface plume, initial dilution is defined as the dilution obtained at the centre line of the plume when the sewage reaches the surface.  For a trapped plume, initial dilution is defined as the dilution obtained at the center line of the plume where the plume reaches the maximum rise height when the vertical momentum / buoyancy of the plume becomes zero.

(2) The WQC for annual averaged UIA was derived with reference to the WQO under WPCO which is expressed as N.

(3) The WQC for 1-hour and 4-day averaged UIA was derived with reference to the USEPA which is expressed as NH3.

(4) USEPA Technical Support Document for Water Quality-Based Toxics Control (March 1991), from which one acute Toxicity Unit (TUa) is defined as TUa = 100/LC50, where LC50 = % of effluent which gives 50% survival of the most sensitive of the range of species tested.

 

6.33            The chronic and acute toxicity criteria as shown in Table 6.8 and Table 6.9 respectively were used to assess the toxicity of the sewage effluent with reference to the results of the whole effluent toxicity test (WETT).  Details of the WETT results are given in Table 6.33 to Table 6.36.

 

Summary of Water Quality Criteria

 

6.34            Table 6.10 compares the WQC derived under the EEFS (in Table 6.8 and Table 6.9) with the statutory requirements stipulated under the WPCO (in Table 6.1 to Table 6.6) as well as the water quality criteria specified by WSD (in Table 6.7).  It should be noted that some parameters considered under the EEFS for far field water quality assessment as listed in Table 6.8, including PO4, TRC and chronic toxicity, are not controlled under the WPCO. In addition, most of the parameters considered under the EEFS for near field water quality assessment (in Table 6.9) are not controlled under the WPCO except for pH and temperature. 


Table 6.10    Comparison of Marine Water Quality Criteria for Water Quality Assessment

 

Applicable zones/uses (1)

Parameters

EEFS WQC

WPCO WQO

WSD Criteria (2)

Value

Type/ Period

Value

Type/ Period

Value

Type/ Period

Far Field Water Quality Criteria

Bathing waters

E.coli

≤ 180/ 100ml

Geometric mean for the period from March to October

≤ 180/ 100ml

Geometric mean for the period from March to October

Not applicable

Not applicable

Secondary contact zones

E.coli

≤ 610/ 100ml

Annual Geometric mean

≤ 610/ 100ml

Annual geometric mean

Not applicable

Not applicable

WSD flushing water intakes

E.coli

20,000/ 100ml

≥ 90% of occasions

Not specified

Not specified

≤ 20,000/ 100ml

at all times

Seawater intakes for industrial use

E.coli

≤ 20,000/ 100ml

≥ 90% of occasions

Not specified

Not specified

Not applicable

Not applicable

Mariculture zones

E.coli

≤ 610/ 100ml

Geometric mean

≤ 610/ 100ml

Annual geometric mean

Not applicable

Not applicable

DO

Depth-

averaged

≥ 5 mg/l

≥90% of occasions

≥ 5 mg/l

≥ 90% of occasions

Not applicable

Not applicable

within 2m from the seabed

≥ 2 mg/l

≥ 90% of occasions

≥ 2 mg/l

≥ 90% of occasions

Not applicable

Not applicable

Semi-enclosed bays

TIN

≤0.1 mg/l (as N)

Annual mean

Not specified

Not specified

Not applicable

Not applicable

PO4

≤ 0.01 mg/l (as P)

Annual mean

Not specified

Not specified

Not applicable

Not applicable

Western Buffer, Eastern Buffer, and Victoria Harbour WCZ (except fish spawning ground)

DO

Depth-

averaged

≥ 4 mg/l

≥ 90% of occasions

≥ 4 mg/l

≥ 90% of occasions

Not applicable

Not applicable

within 2m from the seabed

Not specified

Not specified

≥ 2 mg/l

≥ 90% of occasions

Not applicable

Not applicable

TIN

≤ 0.4 mg/l (as N)

Annual mean

≤ 0.4 mg/l

Annual mean

Not applicable

Not applicable

PO4

≤ 0.04 mg/l (as P)

Annual mean

Not specified

Not specified

Not applicable

Not applicable

Southern WCZ and fish spawning ground

DO

Depth-

averaged

≥ 5 mg/l

Monthly average

≥ 4 mg/l

≥ 90% of occasions

Not applicable

Not applicable

within 2m from the seabed

Not specified

Not specified

≥ 2 mg/l

≥ 90% of occasions

Not applicable

Not applicable

TIN

≤ 0.2 mg/l (as N)

Annual mean

≤ 0.1 mg/l

Annual mean

Not applicable

Not applicable

PO4

≤ 0.02 mg/l (as P)

Annual mean

Not specified

Not specified

Not applicable

Not applicable

Junk Bay WCZ

DO

Depth-averaged

≥ 4 mg/l

≥ 90% of occasions

≥ 4 mg/l

≥ 90% of occasions

Not applicable

Not applicable

within 2m from the seabed

Not specified

Not specified

≥ 2 mg/l

≥ 90% of occasions

Not applicable

Not applicable

TIN

≤ 0.3 mg/l (as N)

Annual mean

≤ 0.3 mg/l

Annual mean

Not applicable

Not applicable

PO4

≤ 0.03 mg/l (as P)

Annual mean

Not specified

Not specified

Not applicable

Not applicable

All WCZ

DO at any depth

≥ 2 mg/l

at all times

Not specified

Not specified

Not applicable

Not applicable

All WCZ

UIA

≤ 0.021  mg/l (as N)

Annual mean

≤ 0.021  mg/l

Annual mean

Not applicable

Not applicable

All WCZ

TRC

≤ 0.008  mg/l

Daily maximum

Not specified

Not specified

Not applicable

Not applicable

Near Field Water Quality Criteria

At edge of Initial dilution zone

pH (3)

6.5 – 8.5,

and change ≤ 0.2

≥ 90% of occasions

6.5 – 8.5,

and change ≤ 0.2

at all times

Not applicable

Not applicable

Temperature (3)

change ≤ 2oC

≥ 90% of occasions

change ≤ 2oC

at all times

Not applicable

Not applicable

(1)     EEFS did not derive WQC for the North Western WCZ.

(2)     The WSD criteria are applicable to the WSD flushing water intakes only.

(3)     The rest of the parameters listed in Table 6.9 are not presented for comparison as they are not controlled under the WPCO and the WSD criteria.


 

6.35            The key differences between the WQC and the statutory requirements for far field water quality assessment are listed below:

 

·      The TIN criterion derived under the EEFS for Southern WCZ is less stringent (0.2 mg/l for annual mean) as compared to the WQO stipulated under the WPCO (0.1 mg/l for annual mean).

·      The DO criterion derived under the EEFS for Southern WCZ is ≥ 5 mg/l for monthly average, whereas the WQO stipulated under the WPCO is ≥ 4 mg/l for 90% of occasions.

·      A new DO requirement was derived under the EEFS that the minimum DO level at any location of the water control zone should not be less than 2 mg/l at all the times which is more stringent than the WPCO requirement that only the bottom DO (within 2 m from the seabed) should meet the value of 2 mg/l for 90% of occasions.

·      New requirements were derived under the EEFS for TRC and PO4.

 

6.36            Moreover, additional requirements for UIA, metals, sulphide, TRC, surfactants and phenol etc. were derived under the EEFS for near field water quality assessment (Table 6.9).  In particular, the UIA level should not be more than 0.035 mg/l and 0.233 mg/l for 4-day average and 1-hour average respectively based on the WQC. The acceptability of the water quality impacts have also been assessed based on both the WQO stipulated under the WPCO and the WQC established under the EEFS.

 

Assessment Criteria for CBP

 

6.37            Chlorination is proposed as the disinfection technology for the HATS which would potentially lead to the formation of total residual chlorine (TRC) and chlorination by-products (CBP) in the effluent.  Dechlorination will applied to minimize the discharge of TRC into the marine environment.

 

6.38            The proposed assessment criteria for TRC are covered by the WQC derived under the EEFS.  Based on a CBP selection exercise conducted under the ADF study, 34 CBP compounds (as listed in Table 6.11 below) were identified for impact assessment.  The CBP selection process is described in Appendix 7.1 of Section 7 under the human health risk assessment. Water quality criteria/standards of USA (federal and state level), United Kingdom, Canada, Australia and China were reviewed for the 34 selected CBP compounds.  Criteria/standards for 13 CBP were not found in this review.  For the CBP with available criteria/standards, the following rules were adopted to derive the water quality assessment criteria:

 

·      Rule 1: Criteria from Hong Kong were adopted when available and suitable

·      Rule 2: Criteria/standards for protection of marine water/saltwater biota were preferred to that of freshwater or that without clear specification (e.g. protection of aquatic environment)

·      Rule 3: Chronic criteria/standards specified with averaging time period were preferred and adopted whenever possible.   

·      Rule 4: National criteria/standards were preferred to local criteria/standards

·      Rule 5: If more than one criteria/standards for the same chemical of concern (COC) satisfied the above rules, then the most stringent criterion/standard was adopted to provide conservatism

 

6.39            The relevant CBP criteria/standards reviewed are provided in Appendix 8.4 of Section 8 under the ecological risk assessment.  A summary of the adopted values are given in Table 6.11.

 

Table 6.11    Marine Water Quality Criteria for CBP

 

CBP

Water Quality Criteria (µg/l)

Bromodichloromethane

22 a (marine water, annual avg.)

Bromoform

360 a (marine water, annual avg.)

Chloroform

12b (marine water, annual avg.)

Dibromochloromethane

34 a (marine water, annual avg.)

Bromoacetic acid

See Note 1

Chloroacetic acid

See Note 1

Dibromoacetic acid

See Note 1

Dichloroacetic acid

See Note 1

Trichloroacetic acid

See Note 1

Methylene chloride

1,580 a (marine water, annual avg.)

Carbon tetrachloride

12 b (marine, annual avg.)

Chlorobenzene

25 c (marine water)

1,1-dichloroethane

See Note 1

1,2-dichloroethane

10 b (marine, annual avg.)

1,1-dichloroethylene

3.2 a (marine, annual avg.)

1,2-dichloropropane

See Note 1

Tetrachloroethylene

8.85 a (marine, annual avg.)

1,1,1-trichloroethane

100 b (marine annual avg.)

1,1,2-trichloroethane

100 b (marine annual avg.)

Trichloroethylene

10 b (marine annual avg.)

2-chlorophenol

50 b (marine annual avg.)

2,4-dichlorophenol

20 b (marine annual avg.)

p-chloro-m-cresol

40 b (marine annual avg.)

Pentachlorophenol

2 b (marine annual avg.)

2,4,6-trichlorophenol

See Note 1

Bis(2-chloroethoxy)methane

See Note 1

1,4-dichlorobenzene

See Note 1

Hexachlorobenzene

0.03 b (marine, annual avg.)

Hexachlorocyclopentadiene

See Note 1

Hexachloroethane

See Note 1

1,2,4-trichlorobenzene

5.4 c (marine water)

Alpha-BHC

See Note 1

Beta-BHC

0.046 a (marine, annual avg.)

Gamma-BHC

0.063 a (marine, annual avg.)

Notes:

1    No criteria/standard was found from literature review.

a   USEPA. www.epa.gov/waterscience/standards/states

b   Cole S., Codline I. D., Parr W. and Zabel T. (1999).  Guidelines for Managing Water Quality Impacts within UK European Marine Sites. Prepared by WRc Swindon Frankland Road Blagrove Swindon Wiltshire SN5 8YF for the UK Marine SCA Project

c   The Canadian Council of Ministers of the Environment (2005).

d   USEPA (2004).

 

Sediment Quality Assessment Criteria

 

6.40            Environment, Transport and Works Bureau (ETWB) Technical Circular Works (TCW) No. 34/2002 “Management of dredged/excavated sediment” sets out the procedure for seeking approval to dredge / excavate sediment and the management framework for marine disposal of dredged / excavated sediment. This Technical Circular outlines the requirements to be followed in assessing and classifying the sediment.  Sediments are categorized with reference to the Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL), as follows:

 

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

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

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

6.41            The sediment quality criteria for the classification of sediment are presented in Table 6.12.

 

Table 6.12    Sediment Quality Criteria for the Classification of Sediment

 

Contaminants

LCEL

UCEL

Heavy Metal (mg/kg dry weight)

Cadmium (Cd)

1.5

4

Chromium (Cr)

80

160

Copper (Cu)

65

110

Mercury (Hg)

0.5

1

Nickel (Ni)

40

40

Lead (Pb)

75

110

Silver (Ag)

1

2

Zinc (Zn)

200

270

Metalloid (mg/kg dry weight)

Arsenic

12

42

Organic-PAHs (µg/kg dry weight)

PAHs (Low Molecular Weight)

550

3160

PAHs (High Molecular Weight)

1700

9600

Organic-non-PAHs (µg/kg dry weight)

Total PCBs

23

180

Source:   Appendix A of ETWB TCW No. 34/2002 Management of Dredged / Excavated Sediment

Note:        LCEL –     Lower Chemical Exceedance Level

                                UCEL –  Upper Chemical Exceedance Level

 

Description of the Environment

 

Existing Baseline Marine Water Quality

 

EPD Routine Monitoring Data

 

6.42            The marine water quality monitoring data routinely collected by EPD were used to establish the baseline condition.  Marine water quality monitoring is conducted by EPD on a monthly basis. Water samples are taken at three water depths, namely, 1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth is less than 6 m, in which case the mid-depth station may be omitted.  A summary of water quality data for selected EPD monitoring stations is presented in Table 6.13 to Table 6.17 for North Western WCZ (NM1-NM3, NM5-NM6 and NM8), Victoria Harbour WCZ (VM1 VM2, VM4-VM8, VM12, VM14, VM15), Western Buffer WCZ (WM2-WM4), Eastern Buffer WCZ (EM1, EM2), Junk Bay WCZ (JM3, JM4) and Southern WCZ (SM7, SM9, SM10, SM11).  Locations of the monitoring stations are shown in Figure 6.1. 

 

6.43            As the HATS Stage I was commissioned in late 2001, the data shown in Table 6.13 to Table 6.17 represent the situation after the commissioning of HATS Stage I.  The relevant WQO and WQC are included in Table 6.13 to Table 6.17 for comparison.  It should be noted that WQO for E.coli is only applicable to stations SM10 and SM11 because only these two selected stations are located in secondary contact recreation subzones. Descriptions of the baseline conditions for individual WCZ provided in the subsequent sections are extracted from the EPD’s report “Marine Water Quality Monitoring in Hong Kong 2006” issued in 2007 which contains the latest information published by EPD on marine water quality at the moment of preparing this EIA report.

 

North Western Waters

 

6.44            Due to the effect of the Pearl River, the North Western WCZ has historically experienced higher levels of TIN, particularly to the west closest to the river's outflow. In addition to this, the WCZ is affected by local discharges, in particular those from the Stonecutters, Pillar Point and San Wai Sewage Treatment Works, as well as discharges from village houses in unsewered areas.

 

6.45            Over the years that the EPD has monitored this WCZ, it has recorded long-term increases in ammonia nitrogen and TIN at its stations along the Urmston Road (the water channel between Lung Kwu Chau and Tap Shek Kok), which appeared to be from a combination of local discharges and Pearl River flow. Considerable long-term increases of E.coli were observed at NM1 and NM5.  The former may be related to pollution in Victoria Harbour (including the discharges from SCISTW) and other discharges around Castle Peak Road, while the latter to effluents discharged from the San Wai Sewage Treatment Works and Pillar Point Sewage Treatment Works. Based on EPD’s long term monitoring data, the E.coli levels at NM1 appeared to increase after commissioning of HATS Stage 1 in 2001.

 

6.46            The levels of E.coli at stations NM1, NM2, NM3 and NM5 located nearer the local effluent discharges (from SCISTW, Pillar Point and San Wai Sewage Treatment Works) were generally higher compared with other stations.  Except for the two western-most stations (nearest to the Deep Bay and Pearl River) which did not meet the WQO for TIN, all other stations achieved full compliance with the WQOs (Table 6.13).  Orthophosphate (PO4) and total phosphorus (TP) were largely low and stable in recent years.

 

Central Waters

 

6.47            The Central Waters refers to the Victoria Harbour, Eastern Buffer, Western Buffer and Junk Bay WCZ. In the past, wastewater from both sides of the Victoria Harbour was discharged into it after just simple screening, leading to marine water low in DO and high in organic nutrients and sewage bacteria.

 

6.48            Commissioning of HATS Stage 1 in late 2001 has brought large and sustained improvements to the water quality of the Central Waters, especially that of the eastern Victoria Harbour, Eastern Buffer and Junk Bay WCZ. Levels of DO increased in these areas, while levels of nutrients and organic pollutants fell. Also falling have been levels of E.coli bacteria, which has led to improvements in water quality at the bathing beaches on the eastern end of Hong Kong Island. The long-term trend of increasing E.coli levels reversed in eastern Victoria Harbour from 2002, and in the mid-Harbour from 2003. Total inorganic nitrogen (TIN) levels also went into decline after 2002, particularly in the eastern part of the harbour.

 

6.49            However, water quality improvements were less noticeable in the western harbour area which was still subject to the sewage discharges from local PTW (Central, Wan Chai West and Wan Chai East).  Because the Stage 1 effluent has not been disinfected, E.coli levels rose in the vicinity of the SCISTW outfall. As a result, the western harbour (Western Buffer WCZ and northern part of the Southern WCZ), including the water around Tsing Yi and the Tsuen Wan beaches, has experienced increased E.coli counts after commissioning of HATS Stage 1.

 

6.50            In 2006, the marked water quality improvements in eastern Victoria Harbour (VM1 and VM2) and moderate improvements in the mid harbour area (VM4 and VM5) and northern part of Rambler Channel (VM14) since HATS Stage 1 was commissioned were generally sustained.  Several monitoring stations in the WCZ are located close to sewage outfalls, including VM5 (Wan Chai East and Wan Chai West PTW outfall), VM6 (Central PTW outfall), VM4 (North Point PTW outfall) and VM8 (SCISTW – HATS Stage I outfall).  The water quality at these stations was inevitably subject to the direct impact of sewage discharge from these outfalls.  Full compliance with the WQO (for DO and UIA) and WQC (for DO, UIA and PO4) was achieved in 2006 in the Victoria Harbour WCZ.  However, the WQO and WQC compliance for TIN was 80% ([9]) in 2006 (Table 6.14). The overall WQO compliance in 2006 was 90%, higher than that in 2005 (83%).

 

6.51            The water quality in Western Buffer WCZ was largely stable in 2006 as compared to that in 2005 except that there were some decreases of DO at the western-most station (WM4) causing a non-compliance with the WQO for DO at this station.  This was due to the lower DO level at the western-most station closest to the Pearl River flow and where water stratification occurred during summer.  The E.coli level in the zone was high due to the effluent from SCISTW which is yet to be equipped with disinfection facilities. However, full compliance with the WQO (TIN and UIA) and WQC (TIN, UIA and PO4) was achieved at the Western Buffer in 2006 (Table 6.15). As a result of the non-compliance for DO recorded at WM4, the overall WQO compliance for all the parameters was 92%.

 

6.52            The water quality at Junk Bay and Eastern Buffer was stable and improvements since HATS Stage 1 were generally sustained in 2006.    In 2006, the Junk Bay and Eastern Buffer WCZs had all attained 100% compliance with the WQO (for DO, TIN, and UIA) and WQC (for DO, TIN, UIA and PO4).

 

Southern Waters

 

6.53            The Southern Waters consist of one large WCZ, the Southern WCZ, which covers an area located to the south of Hong Kong Island and to the east of Lantau Island, directly open to the South China Sea. Marine water quality monitoring is conducted by EPD at 16 stations within the Southern WCZ (refer to Figure 6.1). It is a large expanse of open sea and as such enjoys good levels of DO, but the western parts of it are affected by the discharge from the Pearl River further to the west, in particular during the wet summer months when the river's fresh water flow increases. A number of parameters are affected by the Pearl River, including salinity, suspended solids (SS) and total inorganic nitrogen (TIN). Typically, higher levels of SS and TIN were found at the western stations than at those further east, while the situation was the reverse for salinity. This phenomenon became more obvious in the summer months.

 

6.54            In terms of WQO compliance, as the TIN levels at most stations in the WCZ were relatively high, especially in the summer, they exceeded the WQO for this parameter. In the 1990s, the WQO compliance rate for TIN was consistently below 20%, and even in 2006 the only two stations (namely SM1 and SM19 as shown in Figure 6.1) that complied with the WQO were situated in the far eastern side of the WCZ.  When compared to the less stringent WQC for TIN, about half of the stations still failed to comply with the TIN standard. Similar TIN levels have been recorded since 1991. In 2006, full compliance with WQO (for DO and UIA) and WQC (for DO, UIA and PO4) was achieved in the Southern WCZ.

 

6.55            E.coli levels were generally low and stable across the WCZ. However, in some places the bacteriological water quality was affected by coastal sewage discharges. For example, long-term increases in E.coli levels were recorded at stations (SM7 and SM9) near the discharge from the SCISTW, in connection with the implementation of HATS Stage 1.  Only four stations (SM7, SM9, SM10 and SM11) closest to the SCISTW outfall were selected for presentation in Table 6.17.

 


Table 6.13           Baseline Water Quality Condition for North Western WCZ in 2006

 

Parameter

Lantau Island (North)

Pearl Island

Pillar Point

Urmston Road

Chek Lap Kok

WPCO WQO (in marine waters)

EEFS WQC (in marine waters)

NM1

NM2

NM3

NM5

NM6

NM8

Temperature (oC)

23.7
(17.6 – 27.4)

23.8
(17.5 – 27.6)

23.7
(17.7-27.6)

24.0
(17.9 – 27.8)

24.0
(17.7 – 29.2)

23.8
(17.5 – 28.3)

Not more than 2 oC in daily temperature range

Not available

Salinity

29.6

(22.2 – 33.1)

28.6
(19.0 – 33.1)

29.4
(23.7 – 33.1)

27.2
(16.4 – 32.8)

26.0
(10.5 – 33.3)

27.6
(11.9 – 33.4)

Not to cause more than 10% change

Not available

Dissolved Oxygen  (DO)

(mg/l)

Depth average

6.3
((4.4 – 8.0)

6.5
(4.9 – 8.4)

6.3
(4.4 – 8.3)

6.3
(4.3 – 8.2)

6.7
(4.8 – 8.7)

6.8
(4.8 – 8.2)

Not less than 4 mg/l for 90% of the samples

Not available

Bottom

5.9
(2.4 – 7.9)

6.3
(3.9 – 8.4)

6.1
((3.3 – 8.0)

5.9
(3.4 – 7.9)

6.6
(4.2 – 8.6)

6.7
(4.6 – 8.3)

Not less than 2 mg/l for 90% of the samples

Not available

Dissolved Oxygen (DO) (% Saturation)

Depth average

87
(62 – 113)

90
(69 – 119)

88
(63 – 117)

87
(59 – 116)

92
(64 – 123)

94
(64 – 113)

Not available

Not available

Bottom

82
(35 – 111)

88
(56 – 118)

85
(47 – 113)

83
(49 – 108)

92
(60 – 122)

94

(63 – 118)

Not available

Not available

PH

7.9
(7.6 – 8.0)

7.9
(7.6 – 8.1)

7.9
(7.6 – 8.1)

7.9
(7.5 – 8.1)

7.9
(7.5 – 8.2)

7.9
(7.5 – 8.2)

6.5 - 8.5 (± 0.2 from natural range)

Not available

Secchi disc Depth (m)

1.6

(0.9 – 2.5)

1.7
(1.1 – 2.8)

1.5
(0.5 – 2.4)

1.4
(0.7 – 2.2)

1.2
(0.5 – 1.5)

1.3
(0.8 – 2.0)

Not available

Not available

Turbidity (NTU)

20.3
(6.8 – 78.7)

18.0

(5.8 – 75.3)

18.7

(8.1 – 55.8)

25.8
(11.0 – 75.3)

22.9
(8.0 – 47.8)

23.8
(9.3 – 45.5)

Not available

Not available

Suspended Solids (SS) (mg/l)

7.4
(2.5 – 17.4)

6.4
(2.9 – 21.3)

8.1
(3.0 – 14.0)

15.7
(3.8 – 53.8)

12.6
(4.1 – 35.9)

15.8
(2.7 – 56.7)

Not more than 30% increase

Not available

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

0.6
(0.4 – 1.1)

0.6

(0.2 – 1.0)

0.7
(0.4 – 1.2)

0.7
(0.5 – 0.9)

0.7
(0.3 – 1.3)

0.7
(0.3 – 1.9)

Not available

Not available

Ammonia Nitrogen (NH3-N) (mgN/l)

0.15
(0.04 – 0.27)

0.15
(0.05 – 0.27)

0.15
(0.04-0.27)

0.22
(0.13 – 0.37)

0.17
(0.01 – 0.50)

0.10

(0.01 – 0.35)

Not available

Not available

Unionised Ammonia (UIA) (mgN/l)

0.005
(<0.001 – 0.010)

0.005
(0.001 – 0.011)

0.005
(0.001 – 0.011)

0.008
(0.003 – 0.017)

0.006
(0.002 – 0.022)

0.004
(0.001 – 0.019)

Not more than 0.021 mg/l for annual mean

Not available

Nitrite Nitrogen (NO2-N) (mgN/l)

0.056
(0.017 – 0.150)

0.064
(0.020 – 0.170)

0.064
(0.018 – 0.187)

0.091
(0.024 – 0.250)

0.093
(0.026 – 0.200)

0.066

(0.009 – 0.150)

Not available

Not available

Nitrate Nitrogen (NO3-N) (mgN/l)

0.23
(0.04 – 0.45)

0.28
(0.04 – 0.57)

0.28
(0.06 – 0.51)

0.37
(0.08 – 0.69)

0.39
(0.03 – 1.00)

0.28
(0.01 – 0.72)

Not available

Not available

Total Inorganic Nitrogen  (TIN) (mgN/l)

0.43
(0.17 – 0.75)

0.49
(0.18 – 0.85)

0.50
(0.22 – 0.80)

0.67
(0.29 – 1.07)

0.66
(0.09 – 1.40)

0.44
(0.06 – 1.20)

Not more than 0.5 mg/l for annual mean

Not available

Total Nitrogen (TN) (mgN/l)

0.60
(0.29 – 0.92)

0.65
(0.28 – 1.05)

0.66
(0.33 – 0.94)

0.86
(0.41 – 1.31)

0.84
(0.22 – 1.66)

0.62
(0.15 – 1.39)

Not available

Not available

Orthophosphate Phosphorus (PO4) (mgP/l)

0.03
(0.01 – 0.04)

0.03
(0.01 – 0.04)

0.03
(0.01 – 0.04)

0.03
(0.01 – 0.05)

0.02
(<0.01 – 0.05)

0.02
(<0.01 – 0.04)

Not available

Not available

Total Phosphorus (TP) (mgP/l)

0.05
(0.03 – 0.06)

0.04
(0.03 – 0.06)

0.05
(0.04 – 0.06)

0.07
(0.05 – 0.11)

0.05
(0.03 – 0.08)

0.04
(0.02 – 0.06)

Not available

Not available

Chlorophyll-a

(µg/L)

3.6
(0.8 – 19.2)

2.8
(0.8 – 10.6)

3.3
(1.0 – 7.7)

4.2
(1.3 – 17.4)

3.9
(1.1 – 12.0)

3.5

(1.3 – 14.7)

Not available

Not available

E.coli

(cfu/100 ml)

1100
(340 – 2600)

470
(280 – 1900)

500
(140 – 2100)

900
(220 – 2600)

64
(2 – 1900)

5
(1 – 420)

Not available

Not available