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.
9.2.1.1
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
Table 9.1: Summary of Water Quality Objectives for
|
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
|
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.
9.4.1.1
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
|
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
|
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
9.5.1.1
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
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 |
|
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 |
9.6.1.1
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
·
Central
·
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
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.
9.7.3.3
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 |
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
·
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.
·
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
·
Passageway
and covered footbridge over
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.
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.
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.
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.
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.
9.8.1
Identification of Pollution Sources
9.8.1.1
During the operational phase, there would be no
direct discharge of wastewater into
·
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.
9.9.1.1
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.
9.11.1
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).