6.1.1
This section presents an
assessment of the potential water quality impacts associated with construction
and operation of the Project. Recommendations for mitigation measures have been
provided to minimise the identified water quality impacts.
Environmental Impact Assessment Ordinance (EIAO)
6.2.1
The Technical Memorandum on
Environmental Impact Assessment Process (EIAO-TM) was issued by EPD under
Section 16 of the EIAO. It specifies the assessment method and criteria that
are to be followed in an EIA Study. Reference sections in the EIAO-TM provide
the details of 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 Quality Objectives
6.2.2 The Water Pollution Control Ordinance (WPCO) provides major
statutory framework for the protection and control of water quality in Hong
Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones
(WCZs). Corresponding statements of Water Quality Objectives (WQOs) are
stipulated for different water regimes (marine waters, inland waters, bathing
beaches subzones, secondary contact recreation subzones and fish culture
subzones) in the WCZs based on their beneficial uses. The study area for this
water quality impact assessment covers the Victoria Harbour (Phase one) WCZ and
Junk Bay WCZ. The corresponding WQOs are listed in Table 6.1
and Table
6.2.
Table 6.1 Summary
of Water Quality Objectives for Victoria Harbour WCZ
|
Parameters
|
Objectives
|
Sub-Zone
|
|
Offensive odour,
tints
|
Not to be
present
|
Whole zone
|
|
Visible foam,
oil scum, litter
|
Not to be
present
|
Whole zone
|
|
E coli
|
Not to exceed
1000 per 100 mL, calculated as the geometric mean of the most recent 5
consecutive samples taken at intervals between 7 and 21 days
|
Inland waters
|
|
Dissolved oxygen
(DO) within 2 m of
the seabed
|
Not less than
2.0 mg/l for 90% of samples
|
Marine waters
|
|
Depth-averaged
DO
|
Not less than
4.0 mg/l for 90% of samples
|
Marine waters
|
|
DO
|
Not less than
4.0 mg/l
|
Inland waters
|
|
pH
|
To be in the
range of 6.5 - 8.5, change due to human activity not to exceed 0.2
|
Marine waters
|
|
Not to exceed
the range of 6.0 - 9.0 due to human activity
|
Inland waters
|
|
Salinity
|
Change due to
human activity not to exceed 10% of ambient
|
Whole zone
|
|
Temperature
|
Change due to
human activity not to exceed 2°C
|
Whole zone
|
|
Suspended solids
(SS)
|
Not to raise the
ambient level by 30% caused by human activity
|
Marine waters
|
|
Annual median
not to exceed 25 mg/l due to human activity
|
Inland waters
|
|
Unionized
ammonia (UIA)
|
Annual mean not
to exceed 0.021 mg(N)/l as unionized form
|
Whole zone
|
|
Nutrients
|
Shall not cause
excessive algal growth
|
Marine waters
|
|
Total inorganic
nitrogen (TIN)
|
Annual mean
depth-averaged inorganic nitrogen not to exceed 0.4 mg(N)/l
|
Marine waters
|
|
5-Day
biochemical oxygen demand (BOD5)
|
Not to exceed 5
mg/l
|
Inland waters
|
|
Chemical Oxygen
Demand (COD)
|
Not to exceed 30
mg/l
|
Inland waters
|
|
Toxic substances
|
Should not
attain such levels as to produce significant toxic, carcinogenic, mutagenic
or teratogenic effects in humans, fish or any other aquatic organisms.
|
Whole zone
|
|
Human activity
should not cause a risk to any beneficial use of the aquatic environment.
|
Whole zone
|
Source: Statement of
Water Quality Objectives (Victoria Harbour (Phases One, Two and Three) Water
Control Zone).
Table 6.2 Summary of Water
Quality Objectives for Junk Bay WCZ
|
Parameters
|
Objectives
|
Sub-Zone
|
|
Offensive Odour, Tints
|
Not to be present
|
Whole zone
|
|
Visible
foam, oil scum, litter
|
Not to
be present
|
Whole
zone
|
|
Dissolved
Oxygen (DO) within 2 m of the seabed
|
Not
less than 2.0 mg/L for 90% of samples
|
Marine
waters
|
|
Depth-averaged
DO
|
Not
less than 4.0 mg/L for 90% of samples
|
Marine
waters excepting fish culture subzones
|
|
Not
less than 5.0 mg/L for 90% of samples
|
Fish
culture subzones
|
|
Not
less than 4.0 mg/L
|
Inland
waters
|
|
5-Bay
Biochemical Oxygen Demand (BOD5)
|
Change
due to waste discharges not to exceed 5 mg/L
|
Inland
waters
|
|
Chemical
Oxygen Demand (COD)
|
Change
due to waste discharges not to exceed 30 mg/L
|
Inland
waters
|
|
pH
|
To be
in the range of 6.5 - 8.5, change due to waste discharges not to exceed 0.2
|
Marine
waters
|
|
To be
in the range of 6.0 - 9.0
|
Inland
waters
|
|
Salinity
|
Change
due to waste discharges not to exceed 10% of ambient
|
Whole
zone
|
|
Temperature
|
Change
due to waste discharges not to exceed 2 °C
|
Whole
zone
|
|
Suspended
solids (SS)
|
Not to
raise the ambient level by 30% caused by waste discharges and shall not
affect aquatic communities
|
Marine
waters
|
|
Change
due to waste discharges not to exceed 25 mg/L of annual median
|
Inland
waters
|
|
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 0.3 mg/L
|
Marine
waters
|
|
Dangerous
substances
|
Should
not attain such levels as to produce significant toxic effects in humans,
fish or any other aquatic organisms
|
Whole
zone
|
|
Waste
discharges should not cause a risk to any beneficial use of the aquatic
environment
|
Whole
zone
|
|
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 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 50 Hazen units
|
Inland
waters
|
Source: Statement of Water Quality Objectives (Junk
Bay Water Control Zone).
Technical Memorandum on Effluent Discharge Standard
6.2.3
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 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 relevant standards as stipulated in the TM-DSS.
Practice Notes
6.2.4
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.
6.3.1
Any discharges from the Project
works during construction and operational phase would potentially affect the
inland waters within the Junk Bay and Victoria Harbour (Phase One) WCZs.
6.3.2
Major inland water bodies
within 500m from the rock cavern site boundary include Tseng Lan Shue Stream as shown in Figure 6.1.
6.3.3
The rock cavern development site
is located at about 100m away from the upstream section of Tseng Lan Shue Stream. Other sections of Tseng Lan Shue Stream are further away from the rock cavern
development site. The rock cavern development site is located at about +200 mPD, whilst the section of Tseng Lan Shue
Stream nearest to the rock cavern development site is also located at a similar
vertical level. The section of Tseng Lan
Shue Stream nearest to the rock cavern development is
a natural stream flowing towards the northeast (see Figure 6.1). The stream then merges with the main Tseng
Lan Shue Stream, which eventually discharging the
water into Junk Bay.
6.4
Description of the
Environment
6.4.1 The baseline conditions of the Tseng Lan Shue Stream have been established with reference to the EPD’s
report “River Water Quality Monitoring in Hong Kong 2013” which contains the
latest information published by EPD on river water quality at the moment of preparing
this Report. The water quality monitoring results at
stations in Tseng Lan Shue
Stream, namely JR3, JR6 and JR11 are shown in Table 6.3 below.
In general,
the compliance rate for Tseng Lan Shue Stream
improved from 79% in 1997 to 90% in 2013. The water quality at JR11 and JR6
were graded as “Excellent” and “Good” and the water quality at downstream (JR3)
improved to “Fair” category due to the continued enforcement of the pollution
control legislation, the implementation of Sewerage Master Plans and the extended
village sewerage in the catchments.
Table 6.3 Summary of Water Quality Monitoring Data for Tseng Lan Shue Stream in 2013
|
Parameter
|
Unit
|
Tseng
Lan Shue Stream
|
|
JR3
|
JR6
|
JR11
|
|
Dissolved
Oxygen (DO)
|
mg/L
|
6.7
(4.1-7.8)
|
7.9
(7.3-8.4)
|
9.3
(8.1-10.2)
|
|
pH
|
-
|
7.4
(6.6-8.3)
|
7.6
(7.2-7.8)
|
7.8
(7.3-8.1)
|
|
Suspended
Solids (SS)
|
mg/L
|
7
(2 - 29)
|
8
(4 - 19)
|
2
(1 - 4)
|
|
5-day
Biochemical Oxygen Demand (BOD5)
|
mg/L
|
9
(2 - 25)
|
9
(3 - 29)
|
<1
(<1 - 25)
|
|
Chemical
Oxygen Demand (COD)
|
mg/L
|
16
(6 - 28)
|
14
(7 - 27)
|
5
(3 - 36)
|
|
Oil
& grease
|
mg/L
|
<0.5
(<0.5 – 1.2)
|
0.6
(<0.5 - 1.2)
|
<0.5
(<0.5 – 0.8)
|
|
Faecal coliforms
|
cfu/
100ml
|
85,000
(27,000 - 170,000)
|
130,000
(35,000 - 580,000)
|
3,000
(510 - 13,000)
|
|
E. coli
|
cfu/
100ml
|
51,000
(11,000 - 140,000)
|
45,000
(11,000 - 170,000)
|
1,000
(240 – 7,100)
|
|
Ammonia-nitrogen
|
mg/L
|
3.45
(1.50 - 13.00)
|
0.35
(0.06 – 1.50)
|
0.09
(0.03 – 0.28)
|
|
Nitrate-nitrogen
|
mg/L
|
1.35
(0.74 – 2.10)
|
2.15
(1.80 – 2.80)
|
2.80
(1.60 – 6.80)
|
|
Total Kjeldahl nitrogen
|
mg/L
|
4.90
(1.90 - 14.00)
|
1.50
(0.30 – 3.30)
|
0.42
(0.06 – 2.00)
|
|
Ortho-phosphate
|
mg/L
|
0.57
(0.18 – 1.10)
|
0.57
(0.30 – 0.91)
|
0.34
(0.14 – 0.77)
|
|
Total
phosphorus, SP
|
mg/L
|
0.66
(0.24 - 1.70)
|
0.77
(0.41 - 1.30)
|
0.38
(0.15 – 0.96)
|
|
Total sulphide
|
mg/L
|
<0.02
(<0.02 - 0.04)
|
<0.02
(<0.02 - <0.02)
|
<0.02
(<0.02 - <0.02)
|
|
Aluminium
|
μg/L
|
165
(<50 - 279)
|
140
(70 - 240)
|
71
(<50 - 200)
|
|
Cadmium
|
μg/L
|
<0.1
(<0.1- 1.0)
|
<0.1
(<0.1- 1.0)
|
<0.1
(<0.1- 1.0)
|
|
Chromium
|
μg/L
|
<1
(<1- <1)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
|
Copper
|
μg/L
|
3
(2 - 6)
|
3
(2 - 7)
|
2
(<1 - 3)
|
|
Lead
|
μg/L
|
1
(<1 - 3)
|
1
(<1 - 3)
|
<1
(<1 - <1)
|
|
Zinc
|
μg/L
|
30
(11 - 48)
|
48
(20 - 72)
|
20
(<10 - 43)
|
|
Flow
|
L/s
|
NM
|
NM
|
104
(20 - 204)
|
Notes:
(1)
NM indicates no
measurement taken.
(2)
Figures in
brackets are annual ranges.
6.5
Assessment Methodologies
6.5.1
The study area for the water
quality impact assessment covers all areas within 500m from the Project
boundary in Victoria Harbour (Phase One) Water Control Zone (WCZ) and Junk Bay
WCZ designated under the Water Pollution Control Ordinance (WPCO) and other
areas that may have a bearing on the environmental acceptability of the Project.
6.5.2
The Water Sensitive Receivers
(WSRs) that may be affected by the Project have been identified.
Potential sources of water quality impact that may arise during the
construction and operational stage of the Project were described. This
task included identifying pollutants from point discharges and non-point
sources that could affect the quality of surface water bodies. 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.
Construction
Phase
6.6.1
The proposed construction works
would not alter the streams
and water courses identified in the study area. Potential
sources of water quality impact associated with the land-based construction of
the Project have been identified and include:
Ÿ
General
construction activities
Ÿ
Construction
site run-off;
Ÿ
Accidental
spillage and potential contamination of surface water and groundwater;
Ÿ
Sewage
effluent from construction workforce;
Ÿ
Construction
works in close proximity of inland water; and
Ÿ
Infiltration
of groundwater.
6.6.2
Based on the findings of land
contamination assessment conducted for this EIA, no groundwater contamination
issue was identified within the Project works area.
General Construction Activities
6.6.3
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, dust suppression and utility installation. These types of wastewater
would contain high concentrations of suspended solids (SS). Various
construction works may also generate debris and rubbish such as packaging,
construction materials and refuse. Uncontrolled
discharge of site effluents, rubbish and refuse generated from the construction
works would lead to deterioration in water quality.
Construction Site Run-off
Ÿ
Run-off
and erosion of exposed bare soil and earth, drainage channel, earth working
area and stockpiles;
Ÿ
Release
of any bentonite slurries, concrete washings and other grouting materials with
construction run-off or storm water;
Ÿ
Wash
water from dust suppression sprays and wheel washing facilities; and
Ÿ
Fuel,
oil and lubricants from maintenance of construction vehicles and equipment.
6.6.5
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.
6.6.6
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.
Accidental Spillage and Potential Contamination of Surface Water and
Groundwater
6.6.7
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 inland water bodies or storm drains if
spillage occurs. Waste oil may infiltrate into the surface soil layer, or
run-off into local water courses, increasing hydrocarbon levels. Groundwater
pollution may also arise from the improper use of chemicals and petroleum
products within the cavern where groundwater infiltrates into the area.
Infiltration of groundwater may occur at area where there are faults and/or
fissures in the rock mass. The spillage of petroleum products and chemicals
shall be handled properly to avoid any potential surface water or groundwater
contamination.
Sewage Effluent from Construction Workforce
6.6.8
During the construction of the
Project, the workforce on site will generate sewage effluents, which are
characterized by high levels of BOD, ammonia and E. coli counts. Based on the DSD Sewerage
Manual, the sewage production rate for construction workers is estimated at
0.35 m3 per worker per day. For every 100
construction workers working simultaneously at the construction site, about
35 m3 of sewage would be generated per day. Potential water
quality impacts upon the local drainage and fresh water system may arise from these
sewage effluents, if uncontrolled.
Construction
Works in Close Proximity of Inland Water
6.6.9
Construction activities in
close vicinity to the inland water courses may pollute the inland water bodies
due to the potential release of construction wastes. Construction wastes are
generally characterized by high concentration of SS and elevated pH. Mitigation measures should be implemented to control
the release of construction waste and site effluent into the nearby inland
water bodies.
Infiltration
of Groundwater
6.6.10
Construction of the rock cavern
may result in infiltration of groundwater. The proposed cavern development is
located on the hillside of the ARQ Site, which is currently bare rock slope
surface, and therefore land contamination issue is not an issue of concern for
the development. Thus, infiltration of contaminated groundwater is not
anticipated. The major issue of the
potential groundwater infiltration would be the increase in site runoff (and
the associated potential drawdown in any soil and aquifer layers). Suspended
solids would be the key parameter of concern for the infiltrated water. Groundwater
infiltration would affect the construction works and infiltrated water could
carry away silt from site into the site drainage. Considerations should be
taken in cavern design to minimize the infiltration of groundwater and the potential
impacts from the change in groundwater level.
Operational Phase
6.6.11
Domestic and commercial
effluent from the future development within the rock cavern would be the key
potential sources of water pollution. With reference to the assessment of
sewerage and sewage treatment implications for the Project provided in Section
7, the average sewage flow for the cavern development is estimated to be
about 8.4m3 per day. Adequate
sewerage and sewage treatment facilities will be provided for the Project
development to avoid direct discharge of sewage and wastewater to the nearby
drainage system and inland water courses. Assessment on the sewerage and sewage
treatment implications for the Project is provided in Section 7.
Construction Phase
General Construction Activities
6.7.1
Effluent discharged from
temporary site facilities should be controlled to prevent direct discharge to
the neighbouring inland waters and storm drains. Such effluent may include wastewater
resulting from wheel washing of site vehicles at site entrances. Debris and rubbish such as packaging,
construction materials and refuse generated from the construction activities
should also be properly managed and controlled to avoid accidental release to
the local storm system and inland waters.
Adoption of the guidelines and good site practices for handling and
disposal of construction discharges as specified in Section 6.9 would
minimize the potential impacts.
Construction Site Run-off
6.7.2
Construction site run-off and
drainage may cause local water quality impacts.
Increase in SS arising from the construction site could block the
drainage channels. High concentrations
of suspended degradable organic material in marine water could lead to
reduction in DO levels in the water column.
6.7.3
It is important that proper
site practice and good site management (as specified in the ProPECC PN 1/94
“Construction Site Drainage”) 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 relevant mitigation measures as specified
in the ProPECC PN 1/94 “Construction Site Drainage” are properly implemented.
Accidental Spillage and Potential Contamination of Surface Water and
Groundwater
6.7.4
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 water or
groundwater nearby. The potential impacts could however be mitigated by
practical mitigation measures and good site practices (as given in Section 6.9).
Sewage Effluent from Construction Workforce
6.7.5
Domestic sewage would be
generated from the workforce during the construction phase. However, this temporary sewage can be
adequately treated by interim sewage treatment facilities, such as portable
chemical toilets. Provided that sewage is not discharged directly into storm
drains or inland waters adjacent to the construction site, and temporary sanitary
facilities are used and properly maintained, it is unlikely that sewage
generated from the site would have a significant water quality impact.
Construction Works in Close Proximity of Inland Water
6.7.6
Construction activities in
close vicinity to the inland water courses may pollute the inland water bodies
due to the potential release of construction wastes. Construction wastes are
generally characterized by high concentration of SS and elevated pH. The implementation of measures to control runoff and drainage
will be important for the construction works adjacent to the inland water in
order to prevent runoff and drainage water with high levels of SS from entering
the water environment. With the implementation of adequate construction site
drainage as specified in the ProPECC PN 1/94 “Construction Site Drainage” and
the provision of mitigation measures as described in the ETWB TC (Works) No.
5/2005 “Protection of natural
streams/rivers from adverse impacts arising from construction works”, it
is anticipated that unacceptable water quality impacts would not arise.
Infiltration
of Groundwater
6.7.7
Construction of rock cavern and
tunnel may result in infiltration of groundwater. The major concern from these
construction activities would be the increase in site runoff (and the
associated potential drawdown in any soil and aquifer layers). Practical
groundwater control measures are given in Section 6.9 to
minimize the potential impacts.
Operational
Phase
6.7.8
The identified potential source
of impact on water quality during the operational phase of the Project would be
the domestic and commercial effluent to be generated from the future development
inside the rock cavern. However, with provision of adequate sewerage and sewage
treatment facilities for the Project development, adverse impact associated
with these operational phase discharges is not anticipated.
6.7.9
As the future development will
be fully enclosed inside the rock cavern, this Project will not generate
additional storm pollution. Hence, no
adverse impact of non-point source pollution would be induced by this Project.
6.8
Cumulative Impacts from
Concurrent Project
Construction Phase
Construction Site Run-off and General Construction
Activities
Boring and Drilling Water
6.9.1 Water
used in ground boring and drilling for site investigation or rock / soil
anchoring should as far as practicable be re-circulated after sedimentation. When there is a need
for final disposal, the wastewater should be discharged into storm drains via
silt removal facilities.
Wheel Washing Water
6.9.2
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 backfill to
reduce vehicle tracking of soil and to prevent site run-off from entering
public road drains.
Rubbish and Litter
6.9.3
Good site practices should be
adopted to remove rubbish and litter from construction sites so as to prevent
the rubbish and litter from spreading from the site area. It is recommended to
clean the construction sites on a regular basis.
Construction Site
Run-off
6.9.4 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. 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 impact:
6.9.5 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 on site
boundaries 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.
6.9.6 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 distance of 100m should be maintained between the discharge
points of construction site run-off and the existing saltwater intakes. No
effluent will be discharged into typhoon shelter.
6.9.7 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 runoff
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.
6.9.8 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.
6.9.9 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.
6.9.10 Construction
materials (e.g. aggregates, sand and fill material) on sites should be covered
with tarpaulin or similar fabric during rainstorms.
6.9.11 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.
6.9.12 Good
site practices should be adopted to remove rubbish and litter from construction
sites so as to prevent the rubbish and litter from spreading from the site
area. It is recommended to clean the construction sites on a regular basis.
Site Effluent
6.9.13
There is a need to apply to 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 TM-DSS. 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 relevant WPCO licence which is under the ambit of
regional office (RO) of EPD.
Accidental Spillage and Potential Contamination of Surface Water and
Groundwater
6.9.15
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.
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; and
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
Construction Works in Close Proximity of Inland Waters
Ÿ
Construction
works close to the inland waters should be carried out in dry season as far as
practicable where the flow in the surface channel or stream is low.
Ÿ
The
use of less or smaller construction plants may be specified in areas close to
the water courses to reduce the disturbance to the surface water.
Ÿ
Temporary
storage of materials (e.g. equipment, chemicals and fuel) and temporary
stockpile of construction materials should be located well away from any water
courses during carrying out of the construction works.
Ÿ
Stockpiling
of construction materials and dusty materials should be covered and located
away from any water courses.
Ÿ
Construction
debris and spoil should be covered up and/or disposed of as soon as possible to
avoid being washed into the nearby water receivers.
Ÿ Proper shoring may need to be erected in
order to prevent soil or mud from slipping into the watercourses.
Infiltration
of Groundwater
6.9.20
Appropriate measures during the
cavern construction should be implemented to minimize the groundwater infiltration. The water control
strategies include:
Ÿ
Probing
Ahead: As normal practice, the Contractor will undertake rigorous probing of
the ground ahead of 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 / cavern 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 / cavern advance.
Ÿ
Pre-grouting:
Where water inflow quantities are excessive, pre-grouting will be required to
reduce the water inflow into the tunnel / cavern. 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 / cavern face.
Ÿ
The
installation of waterproof lining would also be adopted after the formation of
the tunnels and caverns.
6.9.21 In the event of excessive infiltration being observed as a result of
the tunnelling or excavation works even after incorporation of the water
control strategies, post-grouting should be applied as far as practicable as
described below:
Ÿ
Post-grouting:
Groundwater drawdown will be most likely due to inflows of water into the
tunnel / cavern 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 /
cavern surround (by grouting) to limit inflow to acceptable levels.
6.9.22 The practical groundwater control measures stated above are proven
technologies and have been extensively applied in other past projects. These
measures or other similar methods, as approved by the Engineer to suit the
works condition shall be applied to minimize the groundwater infiltration.
6.9.23 In case seepage of groundwater occurs, groundwater should be pumped
out from works areas and discharged to the storm system via silt trap. Uncontaminated groundwater from dewatering
process should also be discharged to the storm system via silt removal
facilities.
Operational Phase
6.9.24
All the sewage and wastewater
generated from the future development should be properly collected and diverted
to public sewers for proper treatment and disposal. Discharge of any commercial
effluent to the public sewers will be subject to control under the WPCO and the
relevant dischargers shall apply to EPD for a discharge licence for discharge
of commercial effluent and the discharge quality must satisfy all the standards
listed in the TM-DSS and meet the requirements specified in the discharge
licence. Assessment of the sewage and
sewerage implications for this Project is presented in Section 7.
6.9.25
The practices outlined in
ProPECC PN 5/93 for handling, treatment and disposal of operational stage
effluent should also be adopted where applicable.
6.10.1 With
the full implementation of the recommended mitigation measures for the
construction and operational phases of the proposed Project, no residual impact
on water quality are anticipated.
6.11.1 Water quality monitoring is recommended to be
carried out at the Tseng Lan Shue Stream during the
site clearance and slope excavation works. Details of the recommended water
quality monitoring requirements are provided in the stand-alone EM&A Manual
for the Project. It is recommended that regular site inspections during the
construction phase should be undertaken to inspect the construction activities
and works areas in order to ensure the recommended mitigation measures are
properly implemented.
Construction
Phase
6.12.1 The key
issue from the land-based construction activities would be the potential for
release of wastewater from surface
works areas, open cut excavation and groundwater infiltration during the
formation of rock cavern. 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.
Operational
Phase
6.12.2 The key
source of potential impact on water quality during the operational phase will
be the sewage and wastewater generated from the rock cavern development.
However, no adverse water quality impact associated with the operational phase
would be anticipated, provided that adequate sewerage and sewage treatment
facilities are properly implemented to
accommodate all the sewage effluents.