9.                              Water Quality Assessment

9.1                          Introduction

9.1.1.1              This section presents a water quality impact assessment of the Project, identifying the water quality issues, assessing the potential impacts and recommending mitigation measures where required.

9.2                          Project Background

9.2.1.1              A description of the KTE project can be found in Section 3 of this EIA report with the layout of the proposed railway alignment, stations, and the associated structures.  During the construction phase, water quality issues may arise due to the following potential sources (with respect to the works items in Table 3.1):

·               Site run off due to erosion of exposed surfaces, chemical accidental spillage from plant maintenance, materials handling and general site construction activities (all works sites/works areas including barging point and temporary magazine site);

·               Wastewater due to retaining wall, piling works, tunnelling works and underground construction works (all works sites/works areas);

·               Groundwater extracted during underground construction (particularly works sites for Items 2B, 2C, 2E, 3A, 3D, 3J, 4A, 4B, 5A, 5C and 5E); and

·               Sewage effluent from construction workforce (all works sites/works areas, mainly works areas for Items 3H and 5F).

9.2.1.2              During the operational phase, only limited quantities of runoff from rail track and operational tunnel drainage may cause potential impacts.  HOM and WHA Stations may also have runoff issues.  Wastewater from sewage generated at the stations may also lead to minor water quality issues.  Spent coolant discharge to marine water is not anticipated as there will be no sea water-cooled chiller plant proposed in the design.  The ‘bleed off’ of fresh water from cooling towers will be re-cycled back into the flushing water system so as to reduce the flushing water demand, with excess bleed off discharged into the foul main.  Any potential water quality issues would be properly managed.

9.3                          Environmental Legislation, Policies, Plans, Standards and Criteria

9.3.1                    Environmental Impact Assessment Ordinance

9.3.1.1              Reference to the EIAO and the associated EIAO-TM would be made for the assessment of the waste impacts.  Annexes 6 and 14 of the EIAO-TM set out the criteria and guidelines for evaluating water quality impacts.

9.3.2                    Water Pollution Control Ordinance

9.3.2.1              The Water Pollution Control Ordinance (WPCO) (Cap 358) enacted in 1980 is the principal legislation to protect the water quality in Hong Kong.  Under the WPCO, Hong Kong waters are classified into 10 Water Control Zones (WCZs), within which the Water Quality Objectives (WQOs) are specified.  WQOs establish limits for different parameters to be achieved in order to maintain the water quality inside the WCZs. The KTE project area is adjacent to the Victoria Harbour WCZ, with its WQOs as summarised in Table 9.1.

Table 9.1:   Summary of Water Quality Objectives for Victoria Harbour WCZ

Parameters

WQOs

Sub-Zone

Offensive odour, tints

Not to be present

Whole zone

Visible foam, oil scum, litter

Not to be present

Whole zone

Colour

Human activity should not cause the colour of water to exceed 50 Hazen units

Inland water

E. coli

Not exceed 1000 per 100ml

Inland waters

Dissolved oxygen (DO) within 2 m of the seabed

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

Marine waters

The level of dissolved oxygen should not be less than 4 mg per litre.

Inland waters

Depth-averaged DO

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

Marine waters

pH

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

Marine waters

To be in the range of 6.0 – 9.0

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°C

Whole zone

Suspended solids (SS)

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

Marine waters

Annual mean not to exceed 25mg/L due to human activity

Inland water

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

5-day Biochemical Oxygen Demand (BOD5)

Should not exceed 5mg/L

Inland waters

Chemical Oxygen Demand (COD)

Should not exceed 30mg/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

 

9.3.3                    Water Supplies Department (WSD) Water Quality Criteria

9.3.3.1              Besides the WQO set under the WPCO, the WSD has also specified a set of seawater quality objectives for water quality at their flushing water intakes (Table 9.2).

Table 9.2:   WSD Standards at Flushing Water Intakes

Parameter (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. / 100 ml)

< 20,000

 

9.3.4                    Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters

9.3.4.1              Besides setting the WQOs, the WPCO controls effluent discharge into the WCZs through a licensing system.  The guidance on permissible effluent discharges based on the type of receiving waters (foul sewers, stormwater drains, inland and coastal waters) is provided in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (DSS-TM).  The limits given in this TM cover the physical, chemical and microbial quality of effluents.  Any effluent discharge during the construction and operational phases should comply with the standards for effluents discharged into the inshore waters or marine waters of the Victoria Harbour WCZ.

9.3.5                    ProPECC Notes

9.3.5.1              The Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges.  It provides good practice guidelines for dealing with various types of discharge from a construction site.  Practices as outlined in the ProPECC PN 1/94 should be followed during the construction phase in order to minimise the water quality impact due to construction site drainage.  Moreover, other ProPECC Notes including the ProPECC PN 5/93 Drainage Plan (subject to Comment by the Environmental Protection Department) and the Guidance Note for Contaminated Land Assessment and Remediation would also be considered.

9.4                          Existing Water Quality

9.4.1.1              Victoria Harbour is a major tidal channel with considerable assimilative capacity.  According to the EPD’s Marine Water Quality 2008, with the implementation of the Stonecutter Island Sewage Treatment Works (SCISTW) under the Harbour Area Treatment Scheme (HATS) Stage 1, about 75% of the sewage around the Victoria Harbour has undergone chemically enhanced primary treatment, resulting in a substantial improvement of water quality.  The SCISTW will also implement disinfection treatment and the E. coli level would be expected to be further lowered.

9.4.1.2              The EPD’s marine water quality monitoring stations within the Victoria Harbour WCZ nearest to the KTE project area include VM1, VM2, VM4, VM5, VM6, VM7, VM15, VT10 (inside Yau Ma Tei Typhoon Shelter) and VT11 (inside To Kwa Wan Typhoon Shelter).  The monitoring data of these stations are summarised in Tables 9.3 and 9.4 below.

Table 9.3:    Marine Water Quality for Victoria Harbour WCZ in 2008 at VM1, VM2, VM4 and VM5

Parameters

EPD Monitoring Station

VM1

VM2

VM4

VM5

Temperature (°C)

23.1

(16.1 – 27.2)

23.4

(16.2 – 27.3)

23.4

(16.2 – 27.1)

23.5

(16.3 – 27.2)

Salinity (ppt)

32.0

(29.3 – 33.5)

31.4

(26.3 – 33.2)

31.3

(26.2 – 33.2)

30.9

(25.7 – 32.7)

Dissolved Oxygen (mg/L)

5.5

(3.1 – 7.1)

5.4

(3.2 – 7.1)

5.3

(3.0 – 7.0)

5.0

(3.0 – 6.2)

BOD5 (mg/L)

0.6

(0.3 – 0.8)

0.7

(0.3 – 1.1)

0.8

(0.3 – 1.4)

1.2

(0.3 – 3.5)

SS (mg/L)

6.2

(1.7 – 13.7)

3.9

(1.9 – 7.5)

5.1

(2.9 – 8.6)

5.0

(2.8 – 8.7)

TIN (mg/L)

0.22

(0.11 – 0.42)

0.30

(0.14 – 0.71)

0.32

(0.15 – 0.73)

0.39

(0.22 – 0.71)

NH3-N (mg/L)

0.08

(0.03 – 0.13)

0.12

(0.03 – 0.18)

0.13

(0.03 – 0.22)

0.17

(0.05 – 0.27)

Chlorophyll-a (mg/L)

2.7

(0.4 – 11.3)

3.7

(0.4 – 18.3)

3.5

(0.2 – 18.3)

3.9

(0.3 – 19.3)

E. coli (cfu/100mL)

330

(76 – 3800)

1100

(76 – 14000)

2900

(370 – 12000)

4200

(840 – 23000)

Notes:

[1]     Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E. coli (geometric mean)

[2]     Data in brackets indicate ranges

[3]     Underlined indicates occurrence of non-compliance with that parameter of WQO

Table 9.4:    Marine Water Quality for Victoria Harbour WCZ in 2008 at VM6, VM7, VM15, VT10 and VT11

Parameters

EPD Monitoring Station

VM6

VM7

VM15

VT10 (Yau Ma Tei Typhoon Shelter)

VT11 (To Kwa Wan Typhoon Shelter)

Temperature (°C)

23.5

(16.3 – 27.2)

22.7

(14.8 – 27.8)

23.6

(16.5 – 27.2)

23.6

(15.7 – 27.2)

23.1

(15.4 – 26.8)

Salinity (ppt)

30.9

(27.1 – 32.7)

31.0

(26.8 – 33.2)

30.6

(24.0 – 32.8)

29.9

(27.1 – 31.3)

31.2

(29.8 – 32.2)

Dissolved Oxygen (mg/L)

5.1

(2.8 – 7.1)

5.4

(3.0 – 7.8)

5.2

(2.9 – 6.3)

4.0

(2.9 – 5.9)

5.4

(4.1 – 7.5)

BOD5 (mg/L)

0.8

(0.3 – 1.3)

0.8

(0.2 – 1.5)

0.8

(0.3 – 1.3)

1.4

(0.6 – 3.1)

0.8

(0.3 – 1.3)

SS (mg/L)

5.3

(2.7 – 7.3)

4.6

(2.1 – 6.8)

6.1

(2.8 – 9.2)

6.7

(3.6 – 17.7)

4.5

(1.7 – 8.3)

TIN (mg/L)

0.38

(0.21 – 0.62)

0.40

(0.21 – 0.57)

0.42

(0.25 – 0.87)

0.56

(0.50 – 0.61)

0.36

(0.30 – 0.43)

NH3-N (mg/L)

0.17

(0.07 – 0.29)

0.19

(0.12 – 0.28)

0.19

(0.12 – 0.31)

0.31

(0.24 – 0.40)

0.15

(0.08 – 0.21)

Chlorophyll-a (mg/L)

3.8

(0.5 – 24.0)

1.8

(0.6 – 3.2)

4.2

(0.4 – 20.7)

2.5

(1.4 – 5.1)

3.5

(1.1 – 6.1)

E. coli (cfu/100mL)

4500

(990 – 12000)

5100

(290 – 41000)

2300

(440 – 9000)

1700

(480 – 33000)

510

(160 – 1600)

Notes:

[1]     Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E. coli (geometric mean)

[2]     Data in brackets indicate ranges

[3]     Underlined indicates occurrence of non-compliance with that parameter of WQO

 

9.5                          Water Sensitive Receivers

9.5.1.1              The study area for the water quality impact assessment is delineated within 300m from the proposed KTE alignment; site boundary and barging point, which would cover the relevant existing and potential water sensitive receivers (WSRs) as shown in Table 9.5 and Figure 9.1 that have a bearing on the environmental acceptability of the project.  Due to the highly urbanised nature of Kowloon Peninsula, there are no natural streams located within 300m from the alignment.  There are also no marine biological sensitive receivers such as fish culture zone, shellfish culture ground, marine park/reserve and commercial fishing ground identified within the Victoria Harbour WCZ.  However, a number of seawater abstraction points for flushing and cooling are also identified (Figure 9.1).

Table 9.5:    Nearest Water Sensitive Receivers in the Study Area

WSR No.

Water Sensitive Receivers

WSR 1

East Rail Extension Cooling Water Intake

WSR 2

Tai Wan WSD Flushing Water Intake

WSR 3

Victoria Harbour Water Control Zone

WSR 4

To Kwa Wan Typhoon Shelter

WSR 5

King’s Park High Level Service Reservoir

WSR 6

Ho Man Tin East Service Reservoir

 

9.6                          Assessment Methodology

9.6.1.1              The assessment approach was based on the requirements as specified in the EIA Study Brief (ESB-188/2008).  The criteria and guidelines for assessing water quality impacts as stated in Annexes 6 and 14 of the EIAO-TM were followed.

9.6.1.2              Specific construction methods and configurations, and operation of the KTE project were reviewed to identify if any alteration of the adjacent water courses, drainage systems, groundwater hydrology and catchment types or areas would be affected.

9.6.1.3              Pollution sources including point discharges and non-point sources to surface water runoff, sewage and polluted discharge generated from the Project have been identified. The identified pollution sources were evaluated to determine the significance of impact.

9.6.1.4              The cumulative impacts due to the other related concurrent and planned projects activities or pollution sources within the boundary around the alignment have been assessed and mitigation measures proposed where required to ensure that any water quality impacts would be controlled to acceptable levels.  The following concurrent projects are identified from a water quality perspective:

·               Reprovisioning of Gascoigne Road substation and associated cable diversion works;

·               Central Kowloon Route and Widening of Gascoigne Road Flyover Investigation;

·               Shatin to Central Link – Mongkok East to Hung Hom Section;

·               Shatin to Central Link – Tai Wai to Hung Hom Section;

·               EPIW for HOM Station; and

·               Planned dormitory of Hong Kong Polytechnic University.

9.7                          Construction Phase Impacts

9.7.1                    Identification of Pollution Sources

9.7.1.1              During the construction phase there would be no dredging works, construction of marine working platform or reclamation for barging point anticipated.  Potential water pollution sources during the construction phase would mainly originate from land-based activities including drill-and-blast, cut-and-cover, soft ground tunnelling and mechanical excavation works for tunnels and station boxes construction.  The main water quality related issues will be to prevent erosion on site and minimise suspended sediment loads washed out in stormwater or dewatering activities, as well as the need to control waste water streams such as temporary sewerage facilities, cementitious waters and general construction refuse.  In summary, the key construction phase issues will be as follows:

·               Construction runoff from general construction activities and loading/unloading of C&D materials at barging point (all works sites/works areas);

·               Wastewater discharge from tunnelling and excavation (works sites for Items 2B, 2C, 2E, 3A, 3D, 3J, 4A, 4B, 5A, 5C and 5E in Table 3.1);

·               Potential impacts on the groundwater hydrology through pumping and tunnelling, e.g. drawdown and settlement; and

·               Sewage effluent from construction workforce (all works sites/works areas, mainly works areas for Items 3H and 5F in Table 3.1).

9.7.2                    Construction Runoff

9.7.2.1              Construction runoff may cause physical, biological and chemical effects. The physical effects include potential blockage of drainage channels and increase of SS levels in the Victoria Harbour WCZ.  Local flooding may also occur in heavy rainfall situations. The chemical and biological effects caused by the construction runoff are highly dependent upon its SS level and pH value.  Runoff containing significant amounts of concrete and cement-derived material may cause primary chemical effects such as increasing turbidity and discoloration, elevation in pH, and accretion of solids. A number of secondary effects may also result in toxic effects to water biota due to elevated pH values, and reduced decay rates of faecal micro-organisms and photosynthetic rate due to the decreased light penetration.  The construction site runoff comprises:

·               Surface run-off may be contaminated and turbid water may enter adjacent watercourses, drainage system and downstream as excavated material is conveyed to above ground surface;

·               Runoff and erosion from site surfaces, drainage channels, earth working areas and stockpiles, release of bentonite slurries, concrete washing and chemical grouting with construction runoff and stormwater.  Effluent discharge from temporary site facilities should be controlled to prevent direct discharge to the neighbouring water courses, marine waters and storm drains.  Such wastewater may include wastewater resulting from dust suppression sprays and wheel washing of site vehicles at site entrances; and

·               Fuel, oil, solvents and lubricants from maintenance of construction machinery and equipment: The use of engine oil and lubricants, and their storage as waste materials has the potential to create impacts on the water quality of adjacent water courses if spillage occurs and enters watercourses.  Waste oil may infiltrate into the surface soil layer, or run-off into local water courses, increasing hydrocarbon levels. 

9.7.2.2              Adoption of the relevant guidelines and good site practices for construction runoff above would minimise the potential water quality impacts.  As such, adverse water quality impacts on the WSRs as listed in Table 9.5 would not be anticipated. 

9.7.3                    Wastewater Discharge from Tunnelling and Excavation

9.7.3.1              The underground tunnel of the KTE Project would mainly be constructed by drill-and-blast technique, although some soft ground tunnelling and mechanical excavation will be undertaken throughout the rail alignment.  Potential source of water quality impact from these tunnelling works would be the discharge of tunnelling wastewater from drilling and wash-down.  Wastewater from these tunnelling works would also contain a high content of suspended solids, and the wastewater is proposed for treatment and reuse after sedimentation .  When there is a need for final disposal, the wastewater would be discharged into storm drains with after treatment with silt removal facilities.  Wastewater discharging into storm drains should comply with the standards stipulated in the DSS-TM. 

9.7.3.2              As excavation is required for the construction of the HOM and WHA Stations, diaphragm walls would be used as the retaining wall for the excavation and serve as the temporary or permanent support for stations and tunnels. Potential impacts from the required diaphragm walling include the turbid groundwater pumped out from the works sites which may be contaminated by bentonite slurries, concrete washings and chemical grouting.  Bentonite is highly turbid and will cause damage to aquatic organisms in receiving waters, e.g. arising during the extraction of the bentonite or preparation for recycling or disposal.  Concrete washings are potentially toxic to aquatic organisms, raising pH of the receiving water bodies.  Concrete washings also increase the turbidity in a waterbody.  Proper treatment of the bentonite wastewater by chemically-enhanced sedimentation and concrete washings by optimising the pH will be required to prior to disposal if required. 

9.7.3.3              Wastewater would also be generated from groundwater pumping from tunnelling works and excavation.  The quantity of wastewater produced daily would depend on the volume and type of excavation carried out.  The estimated maximum rate of wastewater discharged from tunnelling works and excavation during construction for treatment (e.g. chemically enhanced sedimentation, etc) before discharge into stormwater drains have been estimated and are shown in Table 9.6 for the various works sites.  With implementation of the mitigation measures, adverse water quality impacts on the WSRs as listed in Table 9.5 would not be anticipated. 

Table 9.6:    Wastewater Discharge from Tunnelling and Excavation during Construction Phase

Works Site

Maximum Rate of Wastewater Discharge

Emergency Access Point at Club de Recreio

23L/s

HOM Station

9L/s

(groundwater discharge from tunnel and open cut excavation)

Construction Shaft at Fat Kwong Street Playground

49L/s

WHA Station

15L/s

 

9.7.3.4              With reference to the findings of the site investigation for land contamination in Section 11 of this EIA report, there would be no contamination of groundwater determined within the project study area.  However, if contaminated groundwater is found during the course of the works, no direct discharge of groundwater from contaminated areas should be adopted.  Any contaminated groundwater should be properly treated in compliance with the requirements of the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (DSS-TM).   If wastewater treatment is to be deployed for treating the contaminated groundwater, the wastewater treatment unit should deploy suitable treatment processes (e.g. oil interceptor/activated carbon) to reduce the pollution level to an acceptable standard and remove any prohibited substances (such as TPH) to an undetectable range.  All treated effluent from the wastewater treatment plant shall meet the requirements of the DSS-TM and should be either discharged into the foul sewers or tankered away for proper disposal.  Such groundwater operation should be licensed by the Regional Office of the EPD.

9.7.4                    Groundwater Hydrology

9.7.4.1              Some construction activities would have potential impacts on the change of the groundwater table, such as the cut-and-cover excavations and drill-and-blast tunnelling and station works.  The major potential impact of the proposed tunnelling work constitutes the risk of groundwater drawdown instigated by uncontrolled groundwater inflows into the excavation.  The occurrence of such drawdown could result in consolidation of the soil stratum, which could in turn lead to settlement and damage of existing surface features such as buildings and utilities.  Having considered the shoreline located in the vicinity and to the east of the proposed tunnelling, the groundwater recharge from the shoreline is anticipated when the groundwater level is drawdown during the tunnelling works.  In view of these, appropriate measures as recommended below would be undertaken during the construction of the tunnel in order to ensure that only manageable groundwater inflow into the excavation occurs:

·               Toe grouting should be applied beneath the toe level of the temporary/permanent cofferdam walls as necessary to lengthen the effective flow path of groundwater from outside and thus control the amount of water inflow to the excavation.

·               Recharge wells should be installed as necessary outside the excavation areas.  Water pumped from the excavation areas should be recharge back into the ground.

9.7.5                    Sewage Effluent

9.7.5.1              Sewage effluents will arise from the sanitary facilities provided for the on-site construction workforce. The characteristics of sewage would include high levels of BOD5, ammonia and E. coli counts.  Impacts include the generation of rubbish and wastewater from eating areas, temporary sanitary facilities and waste disposal areas.  Although the impact will be temporary, the additional population may impose significant stress on the quality of water in local water courses in the absence of adequate mitigation.  Control of construction phase sewage will be an issue and toilets will need to be connected to the local sewerage system if possible during construction but if not feasible chemical toilets will be used.  As such, adverse water quality impacts would not be anticipated on the WSRs as listed in Table 9.5.

9.7.6                    Cumulative Impacts

9.7.6.1              The known concurrent projects during the construction phase as described in Section 3 of this EIA report would include Shatin to Central Link – Tai Wai to Hung Hom Section, Shatin to Central Link – Mongkok to Hung Hom Section, and EPIW (Essential Public Infrastructure Works).  Pollution sources would arise from the works activities at the following works sites:

Shatin to Central Link – Tai Wai to Hung Hom Section

·               Construction of the cut-and-cover tunnel to the south of Chatham Road North adjoining the south of HOM Station;

·               Construction of the cut-and-cover tunnel adjoining the south of Hung Hom Station; and

·               Construction of the cut-and-cover tunnel adjoining the south of Ma Tau Wai Station. 

Shatin to Central Link – Mongkok to Hung Hom Section

·               Construction of the cut-and-cover tunnel to the north of Hung Hom Station; and

·               Operation of the barging point at Hung Hom Finger Pier. 

EPIW

·               Connections to Oi Man Estate and Ho Man Tin Estate (including the subway from HOM Station across Chung Hau Street and the covered walkway along Chung Hau Street, Chung Yi Street and Fat Kwong Street) and the associated slope stabilisation works;

·               Public transport facility and lay-bys at Chung Hau Street; and

·               Passageway and covered footbridge over Chatham Road North and connection to Wuhu Street. 

9.7.6.2              As the interfacing works of these projects with those in the KTE project would only involve land-based construction works provided that the proper mitigation measures recommended below will be implemented by each project, no adverse cumulative water quality impacts would be anticipated on the WSRs as listed in Table 9.5.

9.7.7                    Recommended Mitigation Measures

Construction Site Run-off and General Construction Activities

9.7.7.1              In accordance with the Practice Note for Professional Persons on Construction Site Drainage, Environmental Protection Department, 1994 (ProPECC PN 1/94), construction phase mitigation measures shall include the following:

·               At the establishment of works sites and works areas including barging point and temporary magazine site, perimeter cut-off drains to direct off-site water around the site should be constructed with internal drainage works and erosion and sedimentation control facilities implemented.  Channels (both temporary and permanent drainage pipes and culverts), earth bunds or sand bag barriers should be provided to divert the stormwater to silt removal facilities.  The design of the temporary on-site drainage system will be undertaken by the contractor prior to the commencement of construction; 

·               Dikes or embankments for flood protection should be implemented around the boundaries of earthwork areas. Temporary ditches should be provided to facilitate the runoff discharge into an appropriate watercourse, through a site/sediment trap. Sediment/silt traps should be incorporated in the permanent drainage channels to enhance deposition rates;

·               The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94, which states that the retention time for silt/sand traps should be 5 minutes under maximum flow conditions.  The sizes may vary depending upon the flow rate, but for a flow rate of 0.1 m3/s, a sedimentation basin of 30m3 would be required and for a flow rate of 0.5 m3/s the basin would be 150m3.  The detailed design of the sand/silt traps shall be undertaken by the contractor prior to the commencement of construction;

·               The construction works should be programmed to minimise surface excavation works during rainy seasons (April to September).  All exposed earth areas should be completed and vegetated as soon as possible after the earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks where practicable.  If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or other means;

·               The overall slope of works sites should be kept to a minimum to reduce the erosive potential of surface water flows, and all trafficked areas and access roads should be protected by coarse stone ballast.  An additional advantage accruing from the use of crushed stone is the positive traction gained during the prolonged periods of inclement weather and the reduction of surface sheet flows;

·               All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure their proper and efficient operation at all times particularly following rainstorms.  Deposited silts and grits should be removed regularly and disposed of by spreading evenly over stable, vegetated areas;

·               Measures should be taken to minimise the ingress of site drainage into excavations.  If the excavation of trenches in wet season is inevitable, they should be dug and backfilled in short sections wherever practicable.  The water pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities;

·               Open stockpiles of construction materials (for example, aggregates, sand and fill material) of more than 50m3 should be covered with tarpaulin or similar fabric during rainstorms.  Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system;

·               Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system and storm runoff being directed into foul sewers;

·               Precautions to be taken at any time of the year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted and during or after rainstorms, are summarised in Appendix A2 of ProPECC PN 1/94.  Particular attention should be paid to the control of silty surface runoff during storm events, especially for areas located near steep slopes;

·               All vehicles and plant should be cleaned before leaving a construction site to ensure no earth, mud, debris and the like is deposited by them on roads.  An adequately designed and sited wheel washing facilities should be provided at the exit of every construction site where practicable.  Wash-water should have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process.  The section of access road leading to, and exiting from, the wheel-washing bay to public roads should be paved with sufficient backfall toward the wheel-washing bay to prevent vehicle tracking of soil and silty water to public roads and drains;

·               Oil interceptors should be provided in the drainage system downstream of any oil/fuel pollution sources.  Oil interceptors should be emptied and cleaned regularly to prevent the release of oil and grease into the storm water drainage system after accidental spillage.  A bypass should be provided for oil interceptors to prevent flushing during heavy rain;

·               The construction solid waste, debris and rubbish on-site should be collected, handled and disposed of properly to avoid causing any water quality impacts.  The requirements for solid waste management are detailed in Section 10 Waste Management of this EIA report;

·               All fuel tanks and storage areas should be provided with locks and sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled fuel oils from reaching the nearby WSRs; and

·               By adopting the above mitigation measures with best management practices it is anticipated that the impacts of construction site runoff will be reduced to an acceptable level.

9.7.7.2              There is a need to apply to the EPD for a discharge licence for discharge of effluent from the construction site under the WPCO.  The discharge quality must meet the requirements specified in the discharge licence.  All the runoff and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the DSS-TM.  Minimum distances of 100m should be maintained between the discharge points of construction site effluent and the existing seawater intakes.  In addition, no new eff1uent discharges in nearby Typhoon shelters should be allowed.  The beneficial uses of the treated effluent for other on-site activities such as dust suppression, wheel washing and general cleaning etc, can minimise water consumption and reduce the effluent discharge volume.  If monitoring of the treated effluent quality from the works areas is required during the construction phase of the Project, the monitoring should be carried out in accordance with the WPCO license. 

Tunneling Works

9.7.7.3              Specific mitigation measures for the tunnelling works using drill-and-blast, soft ground and mechanical excavation techniques should include the following:

·               The cut-and-cover tunnelling works should be conducted sequentially  to limit the amount of construction wastewater generated from the exposed areas during the wet season (April to September);

·               Uncontaminated discharge should pass through settlement tanks prior to discharge;

·               The wastewater with high concentrations of SS should be treated (e.g. by settlement in tanks with sufficient retention time) before discharge.  Oil interceptors would also be required to remove the oil, lubricants and grease from the wastewater; and

·               Direct discharge of the bentonite slurry (e.g. from the diaphragm-wall construction) is not allowed and it should be reconditioned and reused wherever practicable.  Temporary storage locations (typically a properly closed warehouse) should be provided on-site for any unused bentonite that needs to be transported away after all related construction activities are completed.  The requirements in ProPECC PN 1/94 should be adhered to when handling and disposal of bentonite slurries.

Barging Point

9.7.7.4              There will be no marine works like dredging, no pontoon moorings to be used and no seawall modification works for the establishment of the barging point at Hung Hom Finger Pier.  As such, adverse ecological impacts are not anticipated.  Mitigation measures as outlined above should be applied to minimise water quality impacts from site runoff and temporary open stockpile of spoils at the proposed barging point.  Other good site practices include:

·               All vessels should be sized so that adequate clearance is maintained between vessels and the seabed in all tide conditions, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;

·               All hopper barges should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;

·               Construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site; and

·               Loading of barges and hoppers should be controlled to prevent splashing of material into the surrounding water.  Barges or hoppers should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation.  

Temporary Magazine Site

9.7.7.5              There will be no piling or marine works for the establishment of the temporary magazine site at TKO Area 137.  Mitigation measures as outlined above (refer to Section 9.7.7.1) should be applied to minimise water quality impacts from construction runoff at the proposed temporary magazine site.  Other good site practices include those recommended for the establishment of the barging point above. 

Sewage and Effluent

9.7.7.6              Portable chemical toilets and sewage holding tanks are recommended for handling the construction sewage generated by the workforce.  A licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance. 

Accidental Spillage of Chemicals

9.7.7.7              Contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes. 

9.7.7.8              Any service shop and maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be provided. Maintenance of vehicles and equipment involving activities with potential for leakage and spillage should only be undertaken within the areas appropriately equipped to control these discharges. 

9.7.7.9              Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance details the requirements to deal with chemical wastes. General requirements are given as follows:

·               Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport;

·               Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents; and

·               Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area. 

9.8                          Operational Phase Impacts

9.8.1                    Identification of Pollution Sources

9.8.1.1              During the operational phase, there would be no direct discharge of wastewater into Victoria Harbour anticipated.  Therefore, quantitative water quality dispersion modelling would not be necessary.  Potential water pollution sources during the operational phase would include the following:

·               Runoff from rail track and operational tunnel drainage;

·               Station runoff; and

·               Sewage from the stations operations.

9.8.1.2              The estimated volume of the anticipated wastewater/water seepage to be discharged from the station/tunnel is summarised in Table 9.7

Table 9.7:    Wastewater Discharge during Operational Phase

Type

Source Location Discharges (L/s)

Tunnel

Station

Wastewater seepage (discharge to public sewage system), trackwash (discharge to public sewage system), foul water (e.g. from toilet)

(discharge to public sewage system)

14L/s*

28L/s**

Notes:

* The amount of discharge for the tunnel station is based upon: (1) Foul water of 5 L/s which is the design pump rate for foul water discharge at WAB; (2) wastewater of 9 L/s which includes (i) trackwash (Assuming max. 25,000 L/km/hour) and (ii) wastewater seepage (Different seepage rates have been assumed for different elements or joint types in the calculation.)

** The amount of discharge for the station is based upon: (1) Foul water of 18 L/s which is summation of the design pump rates for foul water discharge at HOM and WHA; and (2) wastewater of 10 L/s which includes (i) trackwash (Assuming max. 25,000 L/km/hour) and (ii) wastewater seepage (Different seepage rates have been assumed for different elements or joint types in the calculation.)

9.8.2                    Runoff from Rail Track

9.8.2.1              Since all tracks are contained in concrete tunnel box, there will be no rainwater runoff.  The tunnel wall will be equipped with water-tight liner and designed for no seepage.  The amount of groundwater seepage into the tunnel will be insignificant.  Any tunnel run-off could be contaminated with limited amount of grease from passing trains or from maintenance activities.  Standard designs of silt traps and oil interceptors will be provided to remove the oil, lubricants, grease, silt, grit and debris from the wastewater before discharging into the stormwater drainage.  The screened solid waste will then be disposed of as general refuse and industrial wastes as described in Section 10 Waste Management of this EIA report.  No adverse impact on marine environment is anticipated. 

9.8.3                    Station Runoff

9.8.3.1              The rainwater runoff from the station structures (e.g. station building, ventilation building, entrance, etc) would be completely enclosed and therefore run-off will be limited to wash-off from the outside of the building.  Sources of potentially polluted stormwater that may arise from the ventilation building run-off include dust from the roof of the ventilation buildings and cleaning agents used for washing building facade.  Run-off from the ventilation buildings would contain low levels of SS and surfactants used for washing.  With good washing practise, adverse impacts from station run-off would be minimal.

9.8.4                    Sewage from Stations

9.8.4.1              Connection of domestic sewage generated from the Project should be diverted to the foul sewer wherever possible.  If a public sewer system is not available, sewage removal services via tanker or on-site sewage treatment facilities should be provided to prevent direct discharge of sewage to the nearby storm system and all the discharge shall comply with the requirements stipulated in the DSS-TM.  For handling, treatment and disposal of other operational stage effluent, the practices outlined in ProPECC PN 5/93 should be adopted where applicable. 

9.8.5                    Cumulative Impacts

9.8.5.1              The known concurrent project during the operational phase as described in Section 3 of this EIA report would include the railway operation of SCL – Tai Wai to Hung Hom Section at HOM Station.  Pollution sources would arise from the runoff from rail track and operational tunnel drainage, station runoff, and sewage from the station operation.  However, provided that proper mitigation measures as described below will be implemented, no adverse cumulative water quality impacts would be anticipated on the WSRs as listed in Table 9.5. 

9.8.6                    Recommended Mitigation Measures

9.8.6.1              Mitigation measures are only required to mitigate runoff from tracks during the operational phase.  With the implementation of the following mitigation measures, no residual impact during operational phase is anticipated:

·               The track drainage channels discharge should pass through oil/grit interceptors/chambers to remove oil, grease and sediment before being pumped to the public stormwater drainage system;

·               Silt traps and oil interceptors should be cleaned and maintained regularly; and

·               The oily contents of oil interceptors should be transferred to an appropriate disposal facility, or to be collected for reuse, if possible.

9.9                          Residual Impacts

9.9.1.1              Residual impacts during the construction and operational phases are not anticipated, provided that the above mitigation measures are implemented. 

9.10                      Environmental Monitoring and Audit

 

9.10.1.1          The implementation of good construction works practices as well as the various specific mitigation measures recommended above will be important to prevent the pollution of marine water during the construction phase.  It is, therefore, recommended that construction activities should be subject to a routine audit programme throughout the construction period.  Further details on the scope of this audit are provided in the EM&A Manual.  No operational phase EM&A for water quality is considered required.

9.11                      Conclusion

9.11.1                Construction Phase

9.11.1.1          Potential water pollution sources have been identified as construction runoff, sewage from workforce, wastewater discharge from tunnelling and excavation, change of the groundwater table, and groundwater contamination.  Mitigation measures including covering of excavated construction materials, carrying out excavation during dry seasons, and provision of sedimentation tanks etc are recommended to mitigate any adverse water quality impacts.  The sites should be regularly inspected and audited.   

9.11.2                Operational Phase

9.11.2.1          The track run-off and tunnel seepage during the operational phase of the project would have no adverse water quality impact anticipated, provided that mitigation measures have been incorporated in the design. The proposed mitigation measures are defined in the Environmental Mitigation Implementation Schedules (in Section 16 of this EIA report).