Environmental Legislation, Standards and Guidelines
Environmental
Impact Assessment Ordinance (EIAO)
8.2
The Technical Memorandum on Environmental
Impact Assessment Process (EIAO-TM) is issued by the EPD under Section 16 of
the EIAO. It specifies the assessment
method and criteria that need to be followed in the EIA. Reference sections in the EIAO-TM provide the
details of the assessment criteria and guidelines that are relevant to the
water quality impact assessment, including:
Ÿ Annex 6 Criteria for Evaluating Water Pollution
Ÿ Annex 14 Guidelines for Assessment of Water Pollution
Water
Pollution Control Ordinance (WPCO)
8.3
The Water Pollution Control Ordinance (Cap.
358) is the major legislation relating to the protection and control of water
quality in
Table 8.1 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 |
|
E coli |
Not
to exceed 1000 per 100 mL, calculated as the
geometric mean of the most recent 5 consecutive samples taken at intervals
between 7 and 21 days |
Inland
waters |
|
Dissolved
oxygen (DO) within 2 m of the seabed |
Not
less than 2.0 mg/l for 90% of samples |
Marine
waters |
|
Depth-averaged
DO |
Not
less than 4.0 mg/l for 90% of samples |
Marine
waters |
|
DO |
Not
less than 4.0 mg/l |
Inland
waters |
|
pH |
To
be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2 |
Marine
waters |
|
Not
to exceed the range of 6.0 - 9.0 due to human activity |
Inland
waters |
|
|
Salinity |
Change
due to human activity not to exceed 10% of ambient |
Whole
zone |
|
Temperature |
Change
due to human activity not to exceed 2oC |
Whole
zone |
|
Suspended
solids (SS) |
Not
to raise the ambient level by 30% caused by human activity |
Marine
waters |
|
Annual
med |
Inland
waters |
|
|
Unionized
ammonia (UIA) |
Annual
mean not to exceed 0.021 mg(N)/l as unionized form |
Whole
zone |
|
Nutrients |
Shall
not cause excessive algal growth |
Marine
waters |
|
Total
inorganic nitrogen (TIN) |
Annual
mean depth-averaged inorganic nitrogen not to exceed 0.4 mg(N)/l |
Marine
waters |
|
5-Day
biochemical oxygen demand (BOD5) |
Not
to exceed 5 mg/l |
Inland
waters |
|
Chemical
Oxygen Demand (COD) |
Not
to exceed 30 mg/l |
Inland
waters |
|
Toxic
substances |
Should
not attain such levels as to produce significant toxic, carcinogenic, mutagenic
or teratogenic effects in humans, fish or any other
aquatic organisms. |
Whole
zone |
|
Human
activity should not cause a risk to any beneficial use of the aquatic
environment. |
Whole
zone |
Source: Statement of Water Quality Objectives (
Technical
Memorandum on Effluent Discharge Standard
8.4
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 on
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM-DSS). 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
Practice
Notes
8.5
The Practice Note (PN) 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 outlined in the PN should be followed as far as possible
during construction to minimize the water quality impact due to construction
site drainage. Other Practice Notes including the ProPECC
PN 5/93 Drainage Plan (subject to Comment by the Environmental Protection
Department) would also be considered.
Description of the Environment
8.6
The EPD water quality monitoring stations VM4
and VM5 in
8.7
According to the “2009 Marine Water Quality
in Hong Kong”, which is the latest information published on the
EPD website at the
moment of preparing this Report, full compl
Table 8.2 Baseline
Marine Water Quality Condition for
|
Parameter |
|
WPCO WQO (in marine waters) |
||
|
VM4 |
VM5 |
|||
|
Temperature
(oC) |
23.8 (18.6 – 28.6) |
24.0 (18.7 – 28.6) |
Not more than 2 oC
in daily temperature range |
|
|
Salinity |
31.8 (24.9 –
33.6) |
31.2 (21.4 –
33.4) |
Not to cause more than 10% change |
|
|
Dissolved
Oxygen (DO) (mg/L) |
Depth average |
5.3 (4.1 –
6.7) |
5.2 (4.5 –
6.8) |
Not less than 4 mg/L for 90% of the samples |
|
Bottom |
5.1 (2.6 –
6.8) |
5.2 (4.4 –
6.8) |
Not less than 2 mg/L for 90% of the samples |
|
|
Dissolved
Oxygen (DO) (%
Saturation) |
Depth
average |
76 (60 – 98) |
74 (64 – 100) |
Not
Available |
|
Bottom |
72 (39 – 100) |
74 (64 – 99) |
Not
Available |
|
|
pH |
8.0 (7.6 – 8.4) |
7.9 (7.6 – 8.3) |
6.5 - 8.5 (± 0.2 from
natural range) |
|
|
Secchi disc Depth (m) |
2.4 (1.6 – 3.0) |
2.2 (1.2 – 3.0) |
Not
Available |
|
|
Turbidity
(NTU) |
5.1 (2.5 – 10.0) |
5.4 (2.3 – 10.2) |
Not
Available |
|
|
Suspended
Solids (SS) (mg/L) |
5.8 (3.5 – 7.5) |
5.7 (3.3 – 9.1) |
Not more than 30% increase |
|
|
5-day
Biochemical Oxygen Demand (BOD5) (mg/L) |
0.7 (0.2 – 1.2) |
0.8 (0.3 – 1.5) |
Not
Available |
|
|
Ammonia
Nitrogen (NH3-N) (mg/L) |
0.10 (0.049 – 0.203) |
0.12 (0.062 – 0.203) |
Not
Available |
|
|
Unionised
Ammonia (UIA) (mg/L) |
0.004 (0.001 – 0.007) |
0.005 (0.002 – 0.011) |
Not more than 0.021 mg/L for annual mean |
|
|
Nitrite
Nitrogen (NO2-N) (mg/L) |
0.029 (0.005 – 0.152) |
0.036 (0.008 – 0.197) |
Not
Available |
|
|
Nitrate
Nitrogen (NO3-N) (mg/L) |
0.112 (0.026 – 0.360) |
0.134 (0.043 – 0.370) |
Not
Available |
|
|
Total
Inorganic Nitrogen (TIN) (mg/L) |
0.24 (0.08 – 0.57) |
0.29 (0.12 – 0.63) |
Not more than 0.4 mg/L for annual mean |
|
|
Total Kjeldahl Nitrogen (mg/L) |
0.24 (0.15 – 0.38) |
0.28 (0.17 – 0.37) |
Not
Available |
|
|
Total
Nitrogen (TN) (mg/L) |
0.38 (0.22 – 0.69) |
0.45 (0.29 – 0.79) |
Not
Available |
|
|
Orthophosphate
Phosphorus (OrthoP) (mg/L) |
0.021 (0.011 – 0.032) |
0.025 (0.014 – 0.037) |
Not
Available |
|
|
Total
Phosphorus (TP) (mg/L) |
0.04 (0.02 – 0.05) |
0.04 (0.03 – 0.05) |
Not
Available |
|
|
Silica
(as SiO2) (mg/L) |
0.74 (0.20 – 2.47) |
0.85 (0.19 – 3.30) |
Not
Available |
|
|
Chlorophyll-a (µg/L) |
3.3 (0.7 – 8.3) |
3.9 (0.7 – 10.1) |
Not
Available |
|
|
E coli (cfu/100 mL) |
2000 (510 – 8700) |
3900 (160 – 19000) |
Not
Available |
|
|
Faecal
Coliforms (cfu/100 mL) |
4000 (760 – 12000) |
8900 (360 – 46000) |
Not
Available |
|
Notes:
1.
Data source: Marine Water Quality In Hong
Kong in 2009.
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.
Identification of Water Sensitive
Receivers
8.8
This Project is located in the Hung Hom area adjacent to the
Assessment
Approach and Methodology
8.9
The Study Area includes all areas within 300m
from the Project boundary, and covers relevant water sensitive receivers that may have a bearing on the environmental
acceptability of the Project within the
8.10
The water sensitive receivers that may be
affected by the land-based construction activities for the Project have been
identified. Potential sources of water
quality impact that may arise during the land-based construction works were
described. 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 water quality impact were then evaluated
and their impact significance was determined.
The need for mitigation measures to reduce any identified adverse
impacts on water quality to acceptable levels was determined.
Identification of Pollution Sources
Construction
Phase
8.11
Major construction works include cut and
cover works for tunnel and surface works, construction of superstructures
including ventilation shafts, modification work to Hung Hom Station podium structures as well as loading
and unloading at barging point and rock crushing plant. Details of the
construction works are described in Section 3. No marine work including
dredging was required for this Project. Potential sources of water quality
impact associated with the land-based construction of the Project have been
identified and described as follow:
Construction Site
Run-off
8.12
Construction site run-off would cause
potential water quality impacts.
Potential pollution sources of site run-off may include:
Ÿ Run-off and erosion of exposed bare soil and earth, drainage channel, earth working area, stockpiles, C&D materials at barging point at Hung Hom Frieght Pier.
Ÿ Release of any bentonite slurries, concrete washings and other grouting materials with construction run-off, storm water or ground water dewatering process.
Ÿ Wash water from dust suppression sprays and wheel washing facilities.
Ÿ Fuel, oil and lubricants from maintenance of construction vehicles and equipment.
8.13
During rainstorms, site run-off would wash
away the soil particles on unpaved lands and areas with the topsoil
exposed. The run-off is generally
characterized by high concentrations of SS.
Release of uncontrolled site run-off would increase the SS levels and
turbidity in the nearby water environment.
Site run-off may also wash away contaminated soil particles and
therefore cause water pollution.
8.14
Wind blown dust
would be generated from exposed soil surfaces in the works areas. It is possible that wind
blown dust would fall directly onto the nearby water bodies when a
strong wind occurs. Dispersion of dust
within the works areas may increase the SS levels in surface run-off causing a
potential impact to the nearby sensitive receivers.
General
Construction Activities
8.15
The land-based construction works could have
the potential to cause water pollution.
Various types of construction activities may generate wastewater. These include general cleaning and polishing,
wheel washing, and dust suppression.
These types of wastewater would contain high concentrations of SS. If
uncontrolled, these effluents could lead to deterioration in water quality.
Accidental Spillage
8.16
A large variety of chemicals may be used
during construction activities. These
chemicals may include petroleum products, surplus adhesives, spent lubrication
oil, grease and mineral oil, spent acid and alkaline solutions/solvent and
other chemicals. Accidental spillage of
chemicals in the works areas may contaminate the surface soils. The contaminated soil particles may be washed
away by construction site run-off or stormwater
drainage which in turn causes water pollution.
Sewage Effluent
from Construction Workforce
8.17
During the construction of the Project, the
workforce on site will contribute to the local population of the area, although
the number of workers will vary over the construction period. Potential impacts
may arise from wastewater generated from eating areas, temporary sanitary
facilities and waste disposal areas.
Excavation
Activities
8.18
The construction of the Project involves
excavation of soil materials for the tunnel, station and ventilation
shafts. Excavated materials may have to
be stored on-site before being sorted, reused or transported to disposal
sites. If stored as open air stockpiles
with no cover during rainfall, excavated materials would have a potential risk
to be washed away and thereby causing sudden increase of SS and oxygen demand
in the receiving water.
8.19 As cut and cover construction is required, diaphragm walls are used as retaining wall for excavation and serve as either temporary or permanent support for the tunnel. Potential impacts from any required diaphragm walling include turbid site run-off from the works, and bentonite and concrete washings entering water environment. Bentonite is a highly turbid material and will cause damage to aquatic organisms in receiving waters. Run-off may arise during extraction of the bentonite or during preparation for recycling or disposal. Concrete washings are potentially toxic to aquatic organisms, raising pH of receiving water bodies. Concrete washings also increase turbidity in a waterbody.
Groundwater Seepage
8.20
During excavation works, groundwater would be
required to be pumped out from works areas in case seepage of groundwater
occurs. Groundwater pumped out or from
dewatering activities as a potential source of site run-off may wash away
exposed soil at construction site and therefore would cause potential water
quality impacts by increasing the SS levels and turbidity in the nearby water
environment. Moreover, uncontrolled discharge of the groundwater from
contaminated areas may affect the surface or groundwater quality. Nonetheless, site investigation (SI)
involving sampling and testing of soil and groundwater from works areas having
potential land contamination issue have been undertaken that no contaminated
groundwater is expected. Details of the
SI are presented in Section 10 of
the EIA Study.
Change of Hydrology
and Groundwater Level
8.21
The excavation works for the tunnel, station
and ventilation shafts could have
potential impacts on groundwater system.
The major concern would be the change of hydrology and the potential
groundwater drawdown in any soil and aquifer layers. Any potential drawdown
could result in different degrees of settlement.
Operation
Phase
8.22
Major water quality impacts from the Project
operation would include:
Ÿ Tunnel run-off and drainage;
Ÿ Sewerage and storm effluents; and
Ÿ Station run-off.
Tunnel Run-off and
Drainage
8.23
The proposed
railway alignment under the SCL – Mong Kok East to Hung Hom Section
would be initially open and at-grade for the section connecting to the existing
EAL at Portal 1A near Oi Man Estate. It would gradually descend and be within
tunnel to the south of the Chatham Road Interchange. During rainstorm,
rainwater on the train surface and run-off from the open section may generate
tunnel run-off. Seepage of groundwater into the tunnel may also generate tunnel
run-off. Such run-off may contain
limited amount of lubricants, SS, iron, oil and grease. Directly discharge of
tunnel run-off may cause adverse water quality impact on nearby water
environment.
Sewage Effluents
8.24
Sewage and wastewater effluents would be
generated from staffs and customers at the Hung Hom station. Sources of sewage may include the
toilet sanitary wastewater and floor drainage.
Station Run-off
Prediction and Evaluation of
Impacts
Construction
Phase
Construction Site
Run-off
8.27
It is important that proper site practice and
good site management be followed to prevent run-off with high level of SS from
entering the surrounding waters. With
the implementation of appropriate measures to control run-off and drainage from
the construction site, disturbance of water bodies would be avoided and
deterioration in water quality would be minimal. Thus, unacceptable impacts on
the water quality are not expected, provided that the recommended measures
described in Sections 8.41 to 8.49 are properly implemented.
General
Construction Activities
8.28
Effluent discharged from temporary site
facilities should be controlled to prevent direct discharge to the neighbouring
marine waters and storm drains. Adoption
of the guidelines and good site practices for handling and disposal of
construction discharges as part of the construction site management practices
(as given in Sections 8.50 to 8.56) would minimize the potential impacts. Barging
point is proposed to be operated at the Hung Hom
Freight Pier for transportation of the spoil generated from the Project during
construction phase. No dredging works, construction of marine working platform
or reclamation would be required for barging point. Adoption of mitigation measures as outlined
in Sections 8.42 to 8.49 would minimize water quality impacts from
site runoff where appropriate. Good site practices as outlined in Section 8.68 will also be needed to minimize the disturbance
of seabed from vessel berthing at the barging point as well as the potential
release of the spoils or contaminants from loading of barges and transportation
of construction spoils.
Accidental Spillage
8.29
The use of engine oil and lubricants, and
their storage as waste materials has the potential to create impacts on the
water quality if spillage occurs and enters adjacent water environment. Waste oil may infiltrate into the surface
soil layer, or run-off into nearby water environment, increasing hydrocarbon
levels. The potential impacts could
however be mitigated by practical mitigation measures and good site practices
(as given in Sections 8.57 to 8.59).
Sewage Effluent
from Construction Workforce
8.30
Domestic sewage would be generated from the
workforce during the construction phase. Provided that sewage is not discharged
directly into stormwater drains or marine waters
adjacent to the construction site, and this temporary sewage will be properly
discharged to the public foul sewers, it is unlikely that sewage generated from
the site would have a significant water quality impact. Mitigation measures and good site practices
given in Sections 8.60 to 8.61 should be implemented.
Excavation
Activities
8.31
Excavation will be carried out for the
construction of the tunnel, station and ventilation shafts. Some of the
proposed works areas would be close to existing drainage system. Potential impacts
may occur if rain falls during the excavation works, or silt and sand material
and run-off from the excavation areas enters the marine waters, increasing
turbidity. Other pollutants, such as oil
and grease, chemicals, as well as bentonite and grouting
materials, may be present in the run-off where it flows over storage or
maintenance areas for the works. Erosion
of soil enriched in organic matter may release nutrients into the adjacent
water environment. Erosion of stockpiles
may also release suspended solids into nearby water. Mitigation measures and good site practices
(as given in Section 8.62 and
Sections 8.41 to 8.49) should be implemented to control site run-off
and drainage and site effluent from the works areas, and to prevent run-off and
drainage water entering the adjacent waters.
Diaphragm Wall
8.32
As cut and cover construction is required,
diaphragm walls are used as retaining wall for excavation and serve as either
temporary or permanent support for the tunnel. Potential impacts from any
required diaphragm walling include turbid site run-off from the works, and bentonite and concrete washings entering water
environment. As good site practice,
mitigation measures (as given in Sections
8.41 to 8.49) should be implemented to control site run-off
and drainage as well as any site effluents generated from the works areas, and
to prevent run-off and construction wastes from entering the adjacent waters.
Groundwater Seepage
8.33
Excavation works are required for various
construction activities during the construction. Different construction methods will be
employed to minimize the intrusion of groundwater into works areas. Cofferdam wall will be
required as necessary to limit groundwater
inflow. In case seepage of groundwater
occurs, groundwater would be pumped out from works areas and discharged to the stormwater system via silt trap. Uncontaminated groundwater from dewatering
process should also be discharged to the storm system via silt removal
facilities. As no groundwater would be
directly discharged into streams and drainages, no adverse water quality
impacts would be expected.
Change of Hydrology
and Groundwater Level
8.34
The major concern of the hydrology impact is
the potential groundwater drawdown in any soil and aquifer layers. The excavation works for the tunnel, station
and ventilation shafts will only require dewatering temporarily during their
construction. In the long term they are
designed to be undrained with the full hydrostatic
head. Mitigation measures as outlined in
Sections 8.65 to 8.67 will be put in place to mitigate any drawdown
effects to the groundwater table during the operation of the temporary
dewatering works. Provided that the
mitigation measures are properly followed, no unacceptable impact in relation
to the groundwater drawdown would be expected.
Operation
Phase
Tunnel Run-off and
Drainage
8.36
The tunnel wall should be equipped with
water-tight liner to avoid ground water seepage. The amount of groundwater seepage into the
tunnel would be insignificant. Any
tunnel run-off could be contaminated with limited amount of lubricants, SS,
iron, oil and grease from passing trains or from maintenance activities. The discharge quality of any tunnel run-off
should satisfy the standards listed in the TM-DSS. Standard oil/grit
interceptors/chambers should be provided to remove oil, lubricants, grease,
silt and grit from the tunnel run-off before discharging into public storm
drainage/foul sewerage systems. No adverse
water quality impacts would be expected.
Sewage Effluents
8.37
Sewage and wastewater effluents would be
generated from staffs and customers at the Hung Hom
station. Sources of sewage may include the toilet sanitary wastewater and floor
drainage. Generated sewage and
wastewater would be connected to the existing foul sewer system. Run-off from cleaning activities at the
stations which would enter floor drains would also be connected to the foul
sewer. It is expected that no adverse
water quality impact would arise from sewage and wastewater effluent generated
during the operation of the Hung Hom station.
Station Run-off
8.38
The station is likely to be completely
enclosed and therefore run-off will be limited to wash-off from the outside of
the station. Sources of potentially polluted stormwater
that may arise from station run-off include dust from the roof of the buildings
and cleaning agents used for washing building facade. Station run-off would contain low levels of
SS and surfactants used for washing.
With good washing practice, adverse impacts from station run-off would
be minimal.
8.39
For handling, treatment and disposal of other
operational stage effluent, the practices outlined in ProPECC PN 5/93 should be adopted where applicable.
Cumulative Impacts from
Concurrent Projects
8.40
Information on concurrent projects is
presented in Section 3. As all the Project works would be land-based and provided
that proper mitigation measures will be implemented by the project, the water quality impact generated from the projects would be localized
and no adverse cumulative water quality impacts
would be expected.
Recommended
Water Quality Mitigation Measures
Construction
Phase
Construction Site
Run-off and General Construction Activities
8.41
The site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should
be followed as far as practicable to minimise surface run-off and the chance of
erosion. Effluent discharged from the
construction site should comply with the standards stipulated in the TM-DSS.
The following measures are recommended to protect water quality and sensitive
uses of the coastal area, and when properly implemented should be sufficient to
adequately control site discharges so as to avoid water quality impacts:
Construction Site Run-off
8.42
Surface run-off from construction sites
should be discharged into storm drains via adequately designed sand/silt
removal facilities such as sand traps, silt traps and sedimentation
basins. Channels or earth bunds or sand
bag barriers should be provided on site to properly direct stormwater to such silt removal facilities. Perimeter channels at site boundaries should
be provided where necessary to intercept storm run-off from outside the site so
that it will not wash across the site. Catchpits and perimeter channels should be constructed in
advance of site formation works and earthworks.
8.43
Silt removal facilities, channels and
manholes should be maintained and the deposited silt and grit should be removed
regularly, at the onset of and after each rainstorm to prevent local
flooding. Any practical options for the
diversion and re-alignment of drainage should comply with both engineering and
environmental requirements in order to provide adequate hydraulic capacity of
all drains. Minimum distances of 100 m should be maintained between the
discharge points of construction site run-off and the existing saltwater
intakes.
8.44
Construction works should be programmed to
minimize soil excavation works in rainy seasons (April to September). If excavation in soil cannot be avoided in
these months or at any time of year when rainstorms are likely, for the purpose
of preventing soil erosion, temporary exposed slope surfaces should be covered
e.g. by tarpaulin, and temporary access roads should be protected by crushed
stone or gravel, as excavation proceeds.
Intercepting channels should be provided (e.g. along the crest / edge of
excavation) to prevent storm run-off from washing across exposed soil
surfaces. Arrangements should always be
in place in such a way that adequate surface protection measures can be safely
carried out well before the arrival of a rainstorm.
8.45
Earthworks final surfaces should be well
compacted and the subsequent permanent work or surface protection should be
carried out immediately after the final surfaces are formed to prevent erosion
caused by rainstorms. Appropriate
drainage like intercepting channels should be provided where necessary.
8.46
Measures should be taken to minimize the
ingress of rainwater into trenches. If excavation of trenches in wet seasons is
necessary, they should be dug and backfilled in short sections. Rainwater pumped out from trenches or
foundation excavations should be discharged into storm drains via silt removal
facilities.
8.47
Open stockpiles of construction materials
(e.g. aggregates, sand and fill material) on sites should be covered with
tarpaulin or similar fabric during rainstorms.
8.48
Manholes (including newly constructed ones)
should always be adequately covered and temporarily sealed so as to prevent
silt, construction materials or debris from getting into the drainage system,
and to prevent storm run-off from getting into foul sewers. Discharge of surface run-off into foul sewers
must always be prevented in order not to unduly overload the foul sewerage
system.
Wheel Washing Water
8.50
All vehicles and plant should be cleaned before
they leave a construction site to minimize the deposition of earth, mud, debris
on roads. A wheel washing bay should be
provided at every site exit if practicable and wash-water should have sand and
silt settled out or removed before discharging into storm drains. The section of construction road between the
wheel washing bay and the public road should be paved with backfall to reduce vehicle tracking of soil and to
prevent site run-off from entering public road drains.
Bentonite Slurries
8.51
Bentonite slurries used in diaphragm wall construction
should be reconditioned and used again wherever practicable. If the disposal of a certain residual
quantity cannot be avoided, the used slurry should either be dewatered or mixed
with inert fill material for disposal to a public filling area.
8.52
If the used bentonite slurry is intended to be disposed of through
the public drainage system, it should be treated to the respective effluent
standards applicable to foul sewer, storm drains or the receiving waters as set
out in the TM-DSS.
Wastewater from Building Construction
8.53
Before commencing any demolition works, all
sewer and drainage connections should be sealed to prevent building debris,
soil, sand etc. from entering public sewers/drains.
8.54
Wastewater generated from building
construction activities including concreting, plastering, internal decoration,
cleaning of works and similar activities should not be discharged into the stormwater drainage system.
If the wastewater is to be discharged into foul sewers, it should
undergo the removal of settleable solids in a silt
removal facility, and pH adjustment as necessary.
Acid Cleaning, Etching and Pickling Wastewater
8.55
Acidic wastewater generated from acid
cleaning, etching, pickling and similar activities should be neutralized to
within the pH range of 6 to 10 before discharging into foul sewers.
Effluent Discharge
Accidental Spillage
8.58
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.
8.59
Disposal of chemical wastes should be carried
out in compl
Ÿ Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport.
Ÿ Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents.
Ÿ Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.
Sewage Effluent
from Construction Workforce
8.60
The construction workforce on site will
generate sewage. It is recommended that
all the sewage generated from the workforce should be discharged into the
public foul sewers. If disposal of sewage to public sewerage
system is not feasible, appropriate numbers of portable toilets shall be
provided by a licensed contractor to serve the construction workers over the
construction site to prevent direct disposal of sewage into the water
environment. The Contractor shall also
be responsible for waste disposal and maintenance practices.
Excavation
Activities
Diaphragm Wall
8.63
Mitigation measures, as given in Sections 8.41 to 8.49 should be implemented to control site run-off and
drainage as well as any site effluents generated from the works areas, and to
prevent run-off and construction wastes from entering nearby water
environment. Proper handling of bentonite slurries used in diaphragm wall construction
should refer to Sections 8.51 to 8.52.
Groundwater
Seepages
8.64
As some proposed works areas are near the
Change of Hydrology
and Groundwater Level
8.65
For the construction works for the tunnel, station and
ventilation shafts, which
will require dewatering temporarily during their construction, the following
measures should be put in place in order to mitigate any drawdown effects to
the groundwater table during the operation of the temporary dewatering works:
Ÿ 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.
Ÿ Recharge wells should be installed as necessary outside the excavation areas. Water pumped from the excavation areas should be recharge back into the ground.
8.66
In addition, the Contractor should initially
adopt suitable water control strategies as far as practicable while undertaking
the excavation works. The water control strategies are given as follow:
Ÿ Probing Ahead: The Contractor will undertake rigorous probing of the ground ahead of tunnel excavation works to identify zones of significant water inflow. The probe drilling results will be evaluated to determine specific grouting requirements in line with the tunnel advance. In such zones of significant water inflow that could occur as a result of discrete, permeable features, the intent would be to reduce overall inflow by means of cut-off grouting executed ahead of the tunnel advance.
Ÿ Pre-grouting: Where water inflow quantities are excessive, pre-grouting will be required to reduce the water inflow into the tunnel. The pre-grouting will be achieved via a systematic and carefully specified protocol of grouting.
Ÿ In principle, the grout pre-treatment would be designed on the basis of probe hole drilling ahead of the tunnel face.
Ÿ Post-grouting: Groundwater drawdown will be most likely due to inflows of water into the tunnel that have not been sufficiently controlled by the pre-grouting measures. Where this occurs post grouting will be undertaken before the lining is cast. Whilst unlikely to be required in significant measure, such a contingency should be allowed for reduction in permeability of the tunnel surround (by grouting) to limit inflow to acceptable levels.
Barging Point
Ÿ 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.
Ÿ All hopper barges should be fitted with tight fitting seals to their bottom openings to prevent leakage of material.
Ÿ Construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site.
Ÿ 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.
Operation
Phase
Tunnel Run-off and
Drainage
Ÿ Track drainage channels discharge should pass through oil/grit interceptors/chambers to remove oil, grease and sediment before discharging into the public storm drainage/foul sewerage systems.
Ÿ The silt traps and oil interceptors should be cleaned and maintained regularly.
Ÿ Oily contents of the oil interceptors should be transferred to an appropriate disposal facility, or to be collected for reuse, if possible.
Sewage Effluents
8.70
Connection of domestic sewage generated from
the Project should be diverted to the foul sewer. All the discharge should
comply with the requirements stipulated in the TM-DSS. For handling, treatment
and disposal of other operational stage effluent, the practices outlined in ProPECC PN 5/93 should be adopted where applicable.
Evaluation of Residual Impacts
8.71
With the full implementation of the
recommended mitigation measures for the construction and operation phases of
the proposed Project, no adverse residual
impacts on water quality are anticipated.
Environmental Monitoring and
Audit Requirements
Construction
Phase
8.72
Minimisation of water quality deterioration
from land-based construction activities could be achieved through implementing
adequate mitigation measures. No surface
water monitoring is proposed. However, it is recommended that regular site
inspections should be undertaken to inspect the construction activities and
works areas in order to ensure the recommended mitigation measures are properly
implemented.
Operation
Phase
8.73
No adverse water quality impact was
identified during the operational phase with proper implementation of the
recommended mitigation measures.
Operation phase water quality monitoring is considered not necessary.
Construction
Phase
8.74
The key issue from the land-based
construction activities would be the potential release of sediment-laden water
from surface works areas and open cut excavation. Minimisation of water quality deterioration
could be achieved through implementing adequate mitigation measures. Regular 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.
Operation phase
8.75
The main operational impacts from the Project
would come from tunnel/station run-off and effluent discharges from the Hung Hom Station and maintenance activities, which could also be
minimized through implementing adequate mitigation measures.