9.1 This section presents an assessment of the potential water quality impacts associated with the construction and operation phases of the proposed West Island Line (WIL). Recommendations for mitigation measures have been made, where necessary, to reduce the identified water quality impacts to an acceptable level.
9.2
The Water Pollution Control
Ordinance (Cap. 358), in existence since 1980, is the major legislation
relating to the protection and control of water quality in
Table 9.1 Summary
of Water Quality Objectives for
Parameters |
Objectives |
Sub-Zone |
Offensive odour, tints |
Not to be present |
Whole zone |
Visible foam, oil scum,
litter |
Not to be present |
Whole zone |
Dissolved oxygen (DO)
within 2 m of the seabed |
Not less than 2.0 mg/L for
90% of samples |
Marine waters |
Depth-averaged DO |
Not less than 4.0 mg/L for 90%
of samples |
Marine waters |
PH |
To be in the range of 6.5 -
8.5, change due to human activity not to exceed 0.2 |
Marine waters |
Salinity |
Change due to human
activity not to exceed 10% of ambient |
Whole zone |
Temperature |
Change due to human
activity not to exceed 2 oC |
Whole zone |
Suspended solids (SS) |
Not to raise the ambient
level by 30% caused by human activity |
Marine waters |
Unionised ammonia (UIA) |
Annual mean not to exceed
0.021 mg/L as unionised form |
Whole zone |
Nutrients |
Shall not cause excessive
algal growth |
Marine waters |
Total inorganic nitrogen
(TIN) |
Annual mean depth-averaged
inorganic nitrogen not to exceed 0.4 mg/L |
Marine waters |
Toxic substances |
Should not attain such
levels as to produce significant toxic, carcinogenic, mutagenic or
teratogenic effects in humans, fish or any other aquatic organisms. |
Whole zone |
Human activity should not
cause a risk to any beneficial use of the aquatic environment. |
Whole zone |
Source: Statement
of Water Quality Objectives (
Table 9.2 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/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/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 |
|
Bacteria |
Not
exceed 610 per 100ml, calculated as the geometric mean of all samples
collected in one calendar year |
Secondary
contact recreation subzones and fish culture subzones |
Not
exceed 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. |
Recreation
subzones |
|
Less
than 1 per 100ml, calculated as the geometric mean of the most recent 5
consecutive samples taken at intervals of between 7 and 21 days |
Water
gathering ground subzones |
|
Not
exceed 1000 per 100ml, calculated as the geometric mean of the most recent 5
consecutive samples taken at intervals of between 7 and 21 days |
Inland
waters |
|
Colour |
Change
due to waste discharges not to exceed 30 Hazen units |
Water
gathering 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).
9.3
Besides setting the WQOs, the
WPCO controls effluent discharging into the WCZs through a licensing
system. Guidance on the permissible
effluent discharges based on the type of receiving waters (foul sewers, stormwater
drains, inland and coastal waters) is provided in the Technical Memorandum (TM) on Standards for Effluents Discharged into
Drainage and Sewerage Systems, Inland and Coastal Waters. The limits given
in the TM cover the physical, chemical and microbial quality of effluents. Any effluent discharge during the
construction and operational stages should comply with the standards for
effluents discharged into the inshore waters or marine waters of the Western
Buffer and
9.4 A practice note (PN) for professional persons was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges. The Practice Note (PN) for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) issued by EPD provides good practice guidelines for dealing with various types of discharge from a construction site. Practices outlined in the PN should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.
9.5 The EPD water quality monitoring stations VM7 and VM8 in the Victoria Harbour WCZ and station WM2 in the Western Buffer WCZ are located in the vicinity of the Project area (Figure 9.1). A summary of the most recently published monitoring data (in 2006) for these stations are presented in Table 9.3. Stations VM7, VM8 and WM2 are considered to be representative of the water quality in the marine waters of the assessment area.
Table 9.3 Summary Statistics of Marine Water
Quality in the
Parameter |
|
|
WPCO WQO (in marine waters) |
||
VM7 |
VM8 |
WM2 |
|||
Temperature (oC) |
23.8 (16.9-27.9) |
23.8 (16.9-27.9) |
23.8 (16.9-27.4) |
Not more than 2 oC in daily temperature range |
|
Salinity |
30.8 (24.2-33.0) |
30.7 (23.3-33.0) |
30.9 (23.9-33.2) |
Not to cause more than
10% change |
|
Dissolved Oxygen (DO) (%
Saturation) |
Depth average |
80 (60-107) |
85 (61-105) |
86 (59-113) |
Not available |
Bottom |
77 (48-98) |
82 (49-109) |
84 (52-114) |
Not available |
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
5.7 (4.0-7.3) |
6.0 (4.1-7.7) |
6.1 (4.0-8.1) |
Not less
than 4 mg/L for
90% of the samples |
Bottom |
5.5 (3.3-7.0) |
5.8 (3.3-7.8) |
6.0 (3.5-8.2) |
Not less
than 2 mg/L for
90% of the samples |
|
pH |
8.0 (7.7-8.3) |
8.0 (7.8-8.3) |
8.0 (7.7-8.3) |
6.5
- 8.5 (± 0.2 from natural range) |
|
Secchi disc Depth (m) |
2.0 (1.2-2.5) |
1.9 (1.0-2.5) |
2.0 (1.3-2.5) |
Not available |
|
Turbidity
(NTU) |
11.5 (5.8-20.5) |
11.9 (5.3-19.0) |
12.0 (6.2-20.3) |
Not available |
|
Suspended
Solids (SS) (mg/L) |
5.5 (1.8-11.6) |
5.9 (2.1-11.0) |
4.8 (1.4-10.3) |
Not
more than 30% increase |
|
5-day
Biochemical Oxygen Demand (BOD5) (mg/L) |
0.8 (0.1-1.2) |
0.7 (0.2-1.1) |
0.6 (0.1-1.2) |
Not available |
|
Nitrite
Nitrogen (NO2-N) (mg/L) |
0.033 (0.014-0.053) |
0.035 (0.009-0.060) |
0.034 (0.006-0.057) |
Not available |
|
Nitrate
Nitrogen (NO3-N) (mg/L) |
0.16 (0.06-0.38) |
0.16 (0.04-0.40) |
0.16 (0.03-0.43) |
Not available |
|
Ammonia
Nitrogen (NH3-N) (mg/L) |
0.21 (0.07-0.52) |
0.17 (0.13-0.26) |
0.10 (0.05-0.21) |
Not available |
|
Unionised Ammonia (UIA) (mg/L) |
0.008 (0.003-0.018) |
0.007 (0.004-0.016) |
0.004 (0.001-0.009) |
Not
more than 0.021 mg/L for annual mean |
|
Total
Inorganic Nitrogen (TIN) (mg/L) |
0.40 (0.24-0.67) |
0.37 (0.20-0.64) |
0.29 (0.12-0.55) |
Not
more than 0.4 mg/L for annual mean |
|
Total
Nitrogen (TN) (mg/L) |
0.58 (0.45-0.75) |
0.53 (0.38-0.86) |
0.43 (0.23-0.79) |
Not available |
|
Orthophosphate
Phosphorus (OrthoP) (mg/L) |
0.03 (0.01-0.05) |
0.03 (0.02-0.04) |
0.02 (0.01-0.03) |
Not available |
|
Total
Phosphorus (TP) (mg/L) |
0.05 (0.03-0.08) |
0.04 (0.03-0.06) |
0.04 (0.02-0.06) |
Not available |
|
Chlorophyll-a (µg/L) |
2.6 (0.6-9.0) |
2.7 (1.0-11.3) |
2.8 (0.9-10.9) |
Not available |
|
E coli (cfu/100
mL) |
9400 (2600-57000) |
6100 (350-21000) |
910 (16-5400) |
Not available |
|
Faecal
Coliforms (cfu/100
mL) |
23000 (5400-180000) |
15000 (930-55000) |
2000 (42-11000) |
Not available |
Note:
1.
Data source: Marine Water Quality In Hong Kong in 2006.
2.
Except as specified, data presented are depth-averaged
values calculated by taking the means of three depths: Surface, mid-depth,
bottom.
3.
Data presented are annual arithmetic means of depth-averaged
results except for E. coli and faecal
coliforms that are annual geometric means.
4.
Data in brackets indicate the ranges.
9.6
According to the EPD’s
publication “Marine Water Quality in Hong Kong 2006”, the water quality in the Western
Buffer WCZ was largely stable with an increase of E coli at the southern part of the WCZ. This may be related to the
increased discharges from the sewage treatment works in the western part of
9.7
Based on EPD’s publication
“Marine Water Quality in Hong Kong 2006”, the depth-averaged and bottom DO in
the
9.8
There are no natural streams or
rivers within or in close proximity to the proposed works areas. Existing small watercourses within 500m from
the Project boundary comprise streams on the hillslopes of
9.9 Water sensitive receivers (WSR) identified along the harbour front within the assessment area include WSD flushing water intakes at Kennedy Town, Sheung Wan and Central Water Front. The location of these identified WSR is shown on Figure 9.1.
Construction Phase
9.10 Potential sources of water quality impact associated with the proposed construction activities at the works areas of the Project have been identified and include:
•
construction site runoff and drainage
•
general construction activities
•
sewage effluent produced by on-site workforce
•
wastewater discharge from tunnelling and open cut
excavation.
9.11 Specific to the tunnel sections, an identified potential source of water quality impact would be the discharge of tunnelling wastewater from groundwater inflows, drilling and wash-down. Wastewater would also arise from groundwater pumping inside the open cut excavation for Kennedy Town Station.
9.12
Tree walls at
9.13 No marine-based construction work would be required for the construction of the proposed barging points.
Operation Phase
9.14 The assessment of operational stage water quality impacts of the Project has addressed the following identified potential areas of concern:
•
runoff from rail track and operational tunnel drainage
•
discharge from any
fresh water cooling facilities
•
sewage and wastewater effluents from stations
9.15 Seawater would not be used in the cooling system. Both air-cooled and water-cooled chiller schemes are considered to be technically feasible for the WIL project.
9.16 The Assessment Area for the water quality impact assessment covers the Western Buffer WCZ and the Victoria Harbour WCZ and all areas within 500m from the Project boundary.
9.17 The water sensitive receivers that may be affected by the construction activities for the Project have been identified. Potential sources of water quality impact that may arise during the construction and operation phases of the Project are as described in the above section. This task included identifying pollutants from point discharges and non-point sources that could affect the quality of surface water run-off. All the identified sources of potential water quality impact were then evaluated and their impact significance determined. The need for mitigation measures to reduce any identified adverse impacts on water quality to acceptable levels was determined.
9.18 Runoff from the surface construction works areas may contain increased loads of sediments, other suspended solids (SS) and contaminants. Potential sources of pollution from site drainage include:
•
runoff from and erosion from site surfaces, drainage
channels, earth working areas and stockpiles
•
runoff from the proposed barging facilities
•
wash water from dust suppression sprays and wheel washing
facilities
•
fuel, oil, solvents and lubricants from maintenance of
construction vehicles and mechanical equipment.
9.19
Sediment laden runoff
particularly from works areas subjected to excavation or earth works, if
uncontrolled, may carry pollutants (adsorbed onto the particle surfaces) into any
nearby stormwater drains. For the
construction of the cut and cover station at
9.20 As a good site practice, mitigation measures should be implemented to control construction site runoff and drainage from the works areas, and to prevent runoff and drainage water with high levels of SS from entering any nearby stormwater drains. With the implementation of adequate construction site drainage and provision of sediment removal facilities as described in Section 9.29, it is anticipated that unacceptable water quality impacts would not arise. The construction phase discharge would be collected by the temporary drainage system installed by the Contractor and then treated or desilted on-site before discharging to the stormwater drain. The contractor would be required to obtain a license from EPD for discharge to the public drainage system.
9.21
No adverse water quality impacts
would be expected at the WSD flushing water intakes at
9.22 On-site construction activities may cause water pollution from the following:
•
uncontrolled discharge of debris and rubbish such as
packaging, construction materials and refuse
•
spillages of liquids stored on-site, such as oil, diesel and
solvents etc.
9.23 Good construction and site management practices should be observed, as detailed in Section 9.30 - 9.31, to ensure that litter, fuels and solvents do not enter the public drainage system
9.24 Domestic sewage would be generated from the workforce during the construction phase. However, portable chemical toilets can be installed within the construction site. The Contractor will have the responsibility to ensure that chemical toilets are used and properly maintained, and that licensed Contractors are employed to collect and dispose of the waste off-site at approved locations. Therefore water quality impacts would not be expected.
9.25 During tunnelling works, groundwater ingress water pumped out from the tunnel would have a high content of SS and on-site treatment would be required prior to off-site discharge. The water pumped out from the tunnel may be contaminated by bentonite and grouting materials that would be required for the construction of the bored tunnels (for tunnel boring and groundwater treatment) and diaphragm walls for cut-and-cover tunnel sections. Wastewater would also be generated from groundwater pumping inside the open cut excavation for Kennedy Town Station. The quantity of wastewater produced daily would depend on the volume and type of excavation carried out. The maximum wastewater quantities during construction for treatment before discharge into stormwater drains have been estimated by the Preliminary Design Consultant (PDC) and are shown in Table 9.4 for the various works sites.
Table 9.4 Maximum
Waste Water Quantities during Construction Phase
Works
Site |
Wastewater
Quantity (L/s) |
KET: turnback and station open cut |
14.0 |
KET - UNI UNI Construction adit |
20.0 |
Vent adit / access UNI - SYP SYP |
10.2 |
Excavations to adit entrances |
1.0 |
Deep ventilation / entrance shafts |
5.0 |
SYP - SHW tunnels ( |
6.0 |
9.26
Potential groundwater drawdown
resulted from tunnelling works would have impact on the tree walls at
Operation Phase
9.27 All tracks would be underground and hence there would not be any rainwater runoff. The tunnel wall would be equipped with water-tight liner and designed for no seepage. The amount of groundwater seepage into the tunnel would be insignificant. Any tunnel runoff could be contaminated with limited amount of grease from passing trains or from maintenance activities. Standard designed silt trap or grease trap (if necessary) and oil interceptor would be provided to remove the oil, lubricants, grease, silt and grit from the tunnel runoff before discharge into stormwater drainage. The waste would then be disposed of as general refuse and industrial waste as described in Section 7.42. No adverse impacts on marine waters would be expected.
9.28 According to the preliminary design, both air-cooled and water-cooled chiller scheme would be technically feasible for the WIL project. If water-cooled chiller scheme is to be adopted, the bleed off water from the chiller is recommended to be recycled for flushing use, if possible. The operation of the fresh water cooling system would not be expected to result in unacceptable impacts on water quality since there would not be any spent cooling effluent discharged into marine waters.
9.29 Sewage and wastewater effluents generated from the staff at stations and food and beverage outlets, if any, would be connected to the existing foul sewerage system. Runoff from cleaning activities at the stations which would enter floor drains would also be connected to the foul sewer. Hence, it is expected that no adverse water quality impact would arise from sewage and wastewater effluents generated during the operation of the stations.
9.30 Proposed mitigation measures for containing and minimizing water quality impacts are summarised below.
9.31 The site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as practicable in order to minimise surface runoff and the chance of erosion. The following measures are recommended to protect water quality and sensitive uses of the coastal area i.e. WSD flushing water intakes along the harbour front, and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts:
•
The 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. The sediment/silt
traps should be incorporated in the permanent drainage channels to enhance
deposition rates, if allowable.
•
Sand/silt removal facilities such as sand/silt traps and
sediment basins should be provided to remove sand/silt particles from runoff to
meet the requirements of the TM standards under the WPCO. 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. Sizes may
vary depending upon the flow rate, but for a flow rate of
•
All drainage facilities and erosion and sediment control
structures should be regularly inspected and maintained to ensure proper and
efficient operation at all times and particularly during rainstorms. Deposited silt and grit should be regularly
removed, at the onset of and after each rainstorm to ensure that these
facilities are functioning properly at all times.
•
Measures should be taken to minimize the ingress of site
drainage into excavations. If excavation
of trenches in wet periods is necessary, they should be dug and backfilled in
short sections wherever practicable. Water
pumped out from foundation excavations should be discharged into storm drains
via silt removal facilities.
•
If surface excavation works cannot be avoided during the wet
season (April to September), temporarily exposed slope/soil surfaces should be
covered by a tarpaulin or other means, as far as practicable, and temporary
access roads should be protected by crushed stone or gravel, as excavation
proceeds. Interception channels should be provided (e.g. along the crest/edge
of the excavation) to prevent storm runoff from washing across exposed soil
surfaces. Arrangements should always be
in place to ensure that adequate surface protection measures can be safely
carried out well before the arrival of a rainstorm. Other measures that need to be implemented
before, during and after rainstorms are summarized in ProPECC PN 1/94.
•
The overall slope of the site should be kept to a minimum to
reduce the erosive potential of surface water flows, and all trafficked areas
and access roads protected by coarse stone ballast. An additional advantage accruing from the use
of crushed stone is the positive traction gained during prolonged periods of
inclement weather and the reduction of surface sheet flows.
•
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 facility should be provided at every construction site
exit 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-wash
bay to the public road should be paved with sufficient backfall toward the
wheel-wash bay to prevent vehicle tracking of soil and silty water to public
roads and drains.
•
Open stockpiles of construction materials or construction
wastes on-site 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 be taken at any time of year when rainstorms are
likely, actions to be taken when a rainstorm is imminent or forecasted, and
actions to be taken during or after rainstorms are summarized 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.
•
Bentonite slurries used in piling or slurry walling should
be reconditioned and reused wherever practicable. Temporary enclosed storage locations should
be provided on-site for any unused bentonite that needs to be transported away
after all the related construction activities are completed. The requirements in ProPECC PN 1/94 should be
adhered to in the handling and disposal of bentonite slurries.
9.32 Construction solid waste, debris and refuse generated on-site should be collected, handled and disposed of properly to avoid entering any nearby stormwater drain. Stockpiles of cement and other construction materials should be kept covered when not being used. Requirements for solid waste management are detailed in Section 7 of this report.
9.33 Oils and fuels should only be used and stored in designated areas which have pollution prevention facilities. To prevent spillage of fuels and solvents to any nearby stormwater drain, all fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank. The bund should be drained of rainwater after a rain event.
9.34 Temporary sanitary facilities, such as portable chemical toilets, should be employed on-site where necessary to handle sewage from the workforce. A licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance.
9.35 Wastewater with a high level of SS should be treated before discharge by settlement in tanks with sufficient retention time. Oil interceptors would also be required to remove the oil, lubricants and grease from the wastewater. In case of very high levels of SS, an on-site pre-packaged treatment plant may be required with the addition of flocculants to improve the settlement of solids. A discharge licence under the WPCO would be required for discharge to the stormwater drain. It may be a stipulation of the WPCO licence to require the Contractor to monitor the quality/quantity of the discharge to show compliance with the conditions of the licence.
9.36
Impact on tree walls at
9.37 Mitigation measures are only required to mitigate runoff from track during the operational phase. With the implementation of the following mitigation measures, no residual impact during operational phase is anticipated.
•
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.
•
The silt traps and oil interceptors should be cleaned and
maintained regularly.
•
Oily contents of the oil interceptors should be transferred
to an appropriate disposal facility, or to be collected for reuse, if possible.
9.38 With the full implementation of the recommended mitigation measures for the construction and operation phases of the proposed Project, no residual impacts on water quality are anticipated.
9.39 Given that there would not be any marine based works for the construction of the Project, water quality monitoring is not considered necessary during the construction phase. However, it is recommended that regular audit of the implementation of the recommended mitigation measures at the work areas be undertaken during the construction phase in order to ensure the recommended mitigation measures are properly implemented.
9.40
As a precautionary measure against potential impact on tree walls at
9.41 The key issue in terms of water quality during the construction phase of the Project would be the potential for release of sediment-laden water from surface works areas, open cut excavation and tunnelling works. Minimisation of water quality deterioration could be achieved through implementing adequate mitigation measures such as control measures on site runoff and drainage from the works areas to minimise construction runoff, and on-site treatment of tunnelling wastewater prior to discharge. Proper site management and good housekeeping practices would also be required to ensure that construction wastes and other construction-related materials would not enter the public drainage system and coastal waters. Sewage effluent arising from the construction workforce would also be handled through provision of portable toilets.
9.42 With the implementation of these recommended mitigation measures, the construction works for the Project would not be expected to result in unacceptable impacts on water quality. Site inspections should be undertaken routinely to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented.
9.43 The operational water quality impact for track run-off and tunnel seepage would have no adverse water quality impact provided that mitigation measures are incorporated in the design. The fresh water cooling system for the WIL would not be expected to result in unacceptable impacts on water quality. Sewage and wastewater arisings from the operation of the stations would be discharged to the foul sewer and would not cause adverse water quality impact.