5.1.1.1
This section presents an
assessment of the potential water quality impacts associated with the
construction and operation of the Project.
The assessment was conducted in accordance with set out under Clause
3.4.5 of the Study Brief.
5.2.1
Environmental Impact Assessment
Ordinance (EIAO)
5.2.1.1
Technical Memorandum on
Environmental Impact Assessment Process (EIAO-TM) was issued by EPD under
Section 16 of the EIAO. The EIAO-TM
specifies assessment methodologies and criteria that are to be followed in an
EIA Study. Sections relevant to
water quality impact assessment comprise:
·
Annex 6 – Criteria for
Evaluating Water Pollution
·
Annex 14 – Guidelines for
Assessment of Water Pollution
5.2.2
Water Quality Objectives
Table 5.1 Summary of Water Quality Objectives for Victoria Harbour (Phase Two) WCZ
|
Parameters
|
Criteria
|
Subzone
|
|
Aesthetic Appearance
|
There should be no objectionable odours or discolouration of the
water.
|
Whole Zone
|
|
Tarry residues, floating wood, articles made of glass, plastic, rubber
or of any other substances should be absent.
|
|
Mineral oil should not be visible on the surface. Surfactants
should not give rise to a lasting foam.
|
|
There should be no recognisable sewage-derived debris.
|
|
Floating, submerged and semi-submerged objects of a size likely
to interfere with the free movement of vessels, or cause damage to vessels,
should be absent.
|
|
Should not contain substances which settle to form objectionable
deposits.
|
|
Colour
|
Human activity should not cause the colour of water to exceed 50
Hazen units.
|
Inland waters
|
|
E.coli
|
Should not exceed 1000 per 100 mL, calculated as the geometric
mean of the most recent 5 consecutive samples taken at intervals of between 7
and 21 days.
|
Inland waters
|
|
Dissolve Oxygen (DO) within 2 m of the seabed
|
Not less than 2 mg/L for 90% of the sample
|
Marine waters
|
|
Dissolved Oxygen (DO)
|
Not less than 4 mg/L for 90% of the sample
|
Marine waters
|
|
Temperature
|
Not to exceed 2 0C due to human activity
|
Whole Zone
|
|
Salinity
|
Not to exceed 10% ambient change due to human activity
|
Whole Zone
|
|
pH
|
To be in the range of 6.5 – 8.5, change due to human activity
not to exceed 0.2 units
|
Marine waters
|
|
To be in the range of 6.0 – 9.0
|
Inland waters
|
|
Suspended solids (SS)
|
Human activity should neither cause the suspended solids
concentration to be raised more than 30% nor give rise to accumulation of
suspended solids which may adversely affect aquatic communities.
|
Marine waters
|
|
Human activity should not cause the annual median of suspended
solids to exceed 25 milligrams per litre.
|
Inland waters
|
|
Ammonia
|
The un-ionised ammoniacal nitrogen level should not be more than
0.021 milligram per litre, calculated as the annual average (arithmetic
mean).
|
Whole Zone
|
|
Nutrients
|
(a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae
or other aquatic plants.
|
Marine waters
|
|
(b) Without limiting the generality of objective (a) above, the
level of inorganic nitrogen should not exceed 0.4 milligram per litre, expressed
as annual mean.
|
Marine waters
|
|
5-day biochemical oxygen demand (BOD5)
|
Should not exceed 5 milligrams per litre.
|
Inland waters
|
|
Chemical oxygen demand (COD)
|
Should not exceed 30 milligrams per litre.
|
Inland waters
|
|
Toxins
|
Toxic substances in the water should not attain such levels as
to produce significant toxic, carcinogenic, mutagenic or teratogenic effects
in humans, fish or any other aquatic organisms, with due regard to
biologically cumulative effects in food chains and to toxicant interactions
with each other.
|
Whole Zone
|
|
Waste discharges shall not cause a risk to any beneficial uses
of the aquatic environment.
|
Whole Zone
|
Note: Statement of Water Quality Objectives
(Victoria Harbour (Phase Two) Water Control Zone).
5.2.3
Technical Memorandum on
Effluent Discharge Standard (TM-DSS)
5.2.3.1
Discharge of effluents is
subject to control under the WPCO.
The “Technical Memorandum on Standards for Effluents Discharged into
Drainage and Sewerage Systems, Inland and Coastal Waters” (TM-DSS) gives
guidance on the permissible effluent discharges based on the type of receiving
waters (foul sewers, storm water drains, inland and coastal waters). The standards control the physical,
chemical and microbial quality of effluents. Any sewage from the proposed
construction and operation activities must comply with the standards for
effluents discharged into the foul sewers, inland waters and coastal waters of
Victoria Harbour WCZ, as stipulated in the TM-DSS.
5.2.4
Practice Notes for Professional
Persons on Construction Site Drainage
5.2.4.1
A “Professional Persons
Environmental Consultative Committee Practice Note” (ProPECC
PN) was issued by the EPD to provide guidelines for handling and disposal of
construction site discharges. The ProPECC PN 1/94 "Construction Site Drainage"
provides good practice guidelines for dealing with 10 types of discharge from
construction sites. These include
surface run-off, groundwater, boring and drilling water, bentonite slurry,
water for testing and sterilization of water retaining structures and water
pipes, wastewater from building constructions, acid cleaning, etching and
pickling wastewater, and wastewater from site facilities. Practices given in the ProPECC PN 1/94 should be followed as far as possible
during construction to minimize the water quality impact due to construction
site drainage.
5.2.4.2
The ProPECC
PN 5/93 "Drainage Plans subject to Comments by Environmental Protection
Department" provides guidelines and practices for handling, treatment
and disposal of various effluent discharges to stormwater drains and foul
sewers. The design of site drainage
and disposal of various site effluents generated within the new development
area should follow the relevant guidelines and practices as given in the ProPECC PN 5/93.
5.2.5
WSD Water Quality Criteria for
Flushing Water Intakes
5.2.5.1
Water Supplies Department (WSD)
has established a set of criteria for seawater uptake at flushing water intake
points. Respective requirements are listed in Table
5.2.
Table 5.2 Water
Quality Criteria of Sea Water for Flushing Supply
|
Parameters
|
Water Quality Criteria
|
|
Colour
|
<20 H.U.
|
|
Turbidity
|
<10 N.T.U.
|
|
Threshold Odour No.
|
<100 T.O.N.
|
|
Ammoniacal Nitrogen
|
<1 mg/L
|
|
Suspended Solids
|
<10 mg/L
|
|
Dissolved Oxygen
|
>2 mg/L
|
|
Biochemical Oxygen Demand
|
<10 mg/L
|
|
Synthetic Detergents
|
<5 mg/L
|
|
E.coli
|
<20, 000 cfu/100mL
|
5.2.6
Water Quality Criteria for
Cooling Water Intakes
5.2.6.1
Based on the approved EIA
Report for Agreement No. CE44/2011(HY) Proposed Road Improvement Works in West
Kowloon Reclamation Development – Phase 1- Investigation, Design and
Construction, Mass Transit Railway
Corporation (MTRC) stipulates a SS limit of 40 mg/L at its cooling water
intakes and the limit will be adopted for the cooling water intakes of Kowloon
Station and will also be applied to the intakes of commercial buildings
potentially affected by this Project.
5.3.1
Study Area
5.3.1.1
According to Clause 3.4.5.2 of
the Study Brief, the Study Area for this water quality impact assessment
include the Victoria Harbour Water Control Zone as
designated under the WPCO and water sensitive receivers in the vicinity of the
Project. The proposed assessment
area covers areas within 500 meters from the boundary of the Project site. The baseline condition of water bodies in
the Study Area have been established with reference to routine marine water
quality monitoring data collected by EPD.
Descriptions of the baseline conditions provided in the subsequent
sections are extracted from the EPD's reports “Marine Water Quality in Hong
Kong in 2018” which contains the latest information published by EPD on
marine water quality.
5.3.2
Marine Water
5.3.2.1
The EPD monitoring data
collected in 2018 are summarized in Table
5.3 for Victoria Harbour (Station VM6 and VM7)
and Table 5.4 for New Yau Ma Tei Typhoon Shelter (VT10). Indicative locations of the monitoring
stations are shown in Figure 5.1.
5.3.2.2
The overall WQO compliance rate
of the Victoria Harbour WCZ in 2018 was 97%. The WQO
compliance rates for DO and NH3-N in 2018 were both 100%. The WQO compliance rates for TIN was 90%
with only one among the ten monitoring stations not meeting standard.
5.3.2.3
The TIN compliance rate is
affected by the year-to-year natural fluctuation of the discharge from surface
run-off, Stonecutters Island Sewage Treatment Works, as well as the higher
background TIN level under the influence of Pearl River catchment are also
reflected in the North Western, Southern and Western Buffer WCZs. On the other hand, NH3-N, E.coli, PO4-P and BOD5 showed
improvement trend over the past 30 years.
Table 5.3 Summary
Statistics of Marine Water Quality of Victoria Harbour
WCZ Collected by EPD in 2018
|
Parameters
|
Victoria
Harbour (Central)
|
Victoria
Harbour (West)
|
WPCO WQO
(in Marine Waters)
|
|
VM6
|
VM7
|
|
Temperature
(℃)
|
23.4
(16.1
– 27.9)
|
23.6
(16.1 - 28.0)
|
Not more than 2℃ in daily temperature range
|
|
Salinity
|
31.4
(28.9
– 33.1)
|
31
(27.6 - 33.0)
|
Not to cause more than 10% change
|
|
Dissolved Oxygen
(mg/L)
|
Depth Average
|
5.5
(4.2 –
7.3)
|
5.6
(4.6 - 7.1)
|
Not less than 4 mg/L for 90% of the samples
|
|
Bottom
|
5.3
(2.4 – 7.4)
|
5.3
(3.3 - 7.1)
|
Not less than 2 mg/L for 90% of the samples
|
|
Dissolved Oxygen
(% Saturation)
|
Depth Average
|
77
(61 –
90)
|
78
(69 - 93)
|
-
|
|
Bottom
|
74
(35 – 94)
|
74
(49 - 96)
|
|
Turbidity (NTU)
|
3
(1.5 -
7.1)
|
3.4
(1.8 - 7.5)
|
-
|
|
pH
|
7.9
(7.6 –
8.2)
|
7.9
(7.6 - 8.2)
|
6.5 - 8.5 (±0.2 from natural range)
|
|
Suspended Solids
(mg/L)
|
6.7
(2.4 –
13.0)
|
6.9
(2.7 - 11.7)
|
Not more than 30% increase
|
|
Ammonia-nitrogen
(mg/L)
|
0.143
(0.069
– 0.227)
|
0.17
(0.060 - 0.237)
|
-
|
|
Unionised Ammonia
(mg/L)
|
0.005
(<0.001
– 0.010)
|
0.007
(0.001 - 0.014)
|
Not more than 0.021 mg/L
|
|
Nitrite-nitrogen
(mg/L)
|
0.029
(0.007
– 0.080)
|
0.034
(0.010 - 0.105)
|
-
|
|
Nitrate-nitrogen
(mg/L)
|
0.159
(0.061
– 0.287)
|
0.185
(0.059 - 0.383)
|
-
|
|
Total Inorganic Nitrogen
(mg/L)
|
0.33
(0.15
– 0.47)
|
0.39
(0.14 - 0.58)
|
Not more than 0.4 mg/L
|
|
Total Nitrogen
(mg/L)
|
0.65
(0.31
– 1.12)
|
0.69
(0.30 - 0.87)
|
-
|
|
Ortho-phosphate
(mg/L)
|
0.025
(0.010
– 0.038)
|
0.028
(0.013 - 0.040)
|
-
|
|
Total phosphorus
(mg/L)
|
0.04
(0.03
– 0.05)
|
0.04
(0.03 - 0.05)
|
-
|
|
Chlorophyll-a
(µg/L)
|
3.3
(0.7 –
14.2)
|
3.8
(0.5 - 14.8)
|
-
|
|
E. coli
(cfu/100mL)
|
700
(14 –
5,000)
|
1200
(83 - 11000)
|
Not available
|
Note:
[1] Data source:
EPD Marine Water Quality in Hong Kong in 2018.
[2] Except as
specified, data presented are depth-averaged values calculated by taking the
means of three depths: surface, mid-depth and 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.
Table 5.4 Summary
Statistics of Marine Water Quality of New Yau Ma Tei Typhoon Shelter Collected by EPD in 2018
|
Parameters
|
New Yau Ma Tei
|
WPCO WQO
(in Marine Waters)
|
|
VT10
|
|
Temperature
(℃)
|
24.1
(18.2
– 27.8)
|
Not more than 2℃ in daily temperature range
|
|
Salinity
|
30.6
(29.2
– 32.3)
|
Not to cause more than 10% change
|
|
Dissolved Oxygen
(mg/L)
|
Depth Average
|
4.0
(2.4 –
7.0)
|
Not less than 4 mg/L for 90% of the samples
|
|
Bottom
|
4.0
(2.4 – 7.2)
|
Not less than 2 mg/L for 90% of the samples
|
|
Dissolved Oxygen
(% Saturation)
|
Depth Average
|
56
(36 –
90)
|
-
|
|
Bottom
|
55
(34 – 92)
|
|
pH
|
7.7
(7.4 –
8.2)
|
6.5 - 8.5 (±0.2 from natural range)
|
|
Turbidity (NTU)
|
3.3
(1.3 –
5.0)
|
-
|
|
Suspended Solids
(mg/L)
|
9.5
(2.8 –
19.0)
|
Not more than 30% increase
|
|
Ammonia-nitrogen
(mg/L)
|
0.304
(0.215
– 0.430)
|
-
|
|
Unionised Ammonia
(mg/L)
|
0.008
(0.003
– 0.018)
|
Not more than 0.021 mg/L
|
|
Nitrite-nitrogen
(mg/L)
|
0.034
(0.021
– 0.058)
|
-
|
|
Nitrate-nitrogen
(mg/L)
|
0.179
(0.096
– 0.280)
|
-
|
|
Total Inorganic Nitrogen
(mg/L)
|
0.52
(0.39
– 0.75)
|
Not more than 0.4 mg/L
|
|
Total Nitrogen
(mg/L)
|
0.85
(0.69
– 1.00)
|
-
|
|
Ortho-phosphate
(mg/L)
|
0.038
(0.028
– 0.049)
|
-
|
|
Total phosphorus
(mg/L)
|
0.06
(0.05
– 0.09)
|
-
|
|
Chlorophyll-a
(µg/L)
|
3.2
(0.6 –
13.5)
|
-
|
|
E. coli
(cfu/100mL)
|
3,100
(830 –
12,000)
|
Not available
|
Note:
[1] Data source:
EPD Marine Water Quality in Hong Kong in 2018.
[2]
Except as specified, data presented are depth-averaged values
calculated by taking the means of three depths: surface, mid-depth and 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.
5.4.1.1
Water Sensitive Receivers
(WSRs) in Victoria Harbour were identified with
reference to Annex 14 of the EIAO-TM. The developments and uses earmarked on
the South West Kowloon Outline Zoning Plan (No. S/K20/30), WKCD Development
Plan (No. S/K20/WKCD/2), other Outline Zoning Plans, Outline Development Plans,
Layout Plans and any other relevant published land use plans had been reviewed
and considered when identifying the WSRs.
5.4.1.2
There were no waterbodies
identified within the site boundary, no alteration of any water courses, change
of water holding/flow regimes of water bodies are expected. Key marine WSRs in
Victoria Harbour were identified and their indicative
locations are shown in Figure 5.1. These marine WSRs include:
·
New Yau
Ma Tei Typhoon Shelter;
·
WSD Kowloon South Flushing Water
Intake (F1);
·
WSD Yau
Ma Tei Flushing Water Intake (F2);
·
MTRC Kowloon Station Flushing
Water Intake (F3);
·
Proposed Cooling Water Intake for
Mega Performance Venue/Exhibition Center & Hotel
(C1);
·
MTRC Kowloon Station Cooling
Water Intake (C2);
·
The Elements Cooling Water
Intake (C3); and
·
West Kowloon Cultural District District Cooling System Cooling Water Intake (C4).
5.4.1.3
Excepting WSR C1, which will be
operated by West Kowloon Cultural District Authority in 2022, all other WSRs
are already under operation.
5.5.1
Construction Phase
5.5.1.1
General construction works for
the Project would be land-based only. The potential sources of water quality
impact associated with the land-based works include:
·
General construction
activities;
·
Construction site run-off;
·
Sewage effluent from
construction workforce;
·
Accidental spillage of
chemicals; and
5.5.2
Operation Phase
5.5.2.1
Potential water quality impacts
associated with the operation phase include:
·
Non-point source surface
run-off from new impervious areas
5.6.1
General
5.6.1.1
Referring to Section 5.4, the WSRs in the vicinity
of the Project are presented in Figure 5.1. The methodology employed to assess
potential water quality impacts associated with the construction and operation
of the Project followed the detailed technical requirements given in Appendix D
of the Study Brief and was based on the information presented in Section 2.
5.6.1.2
All the identified sources of
potential water quality impacts from the land-based construction works were
evaluated and their impact significance determined. Practical water pollution control
measures were recommended to mitigate identified water quality impacts.
5.7.1
Construction Phase
General Construction Activities
5.7.1.1
Wastewater generated from
construction activities, including general cleaning and polishing, wheel
washing, dust suppression and utility installation may contain high SS
concentrations. It may also contain
a certain amount of grease and oil.
Potential water quality impacts due to the wastewater discharge can be
minimized if construction and site management practices are implemented to
ensure that litter, fuels, and solvents do not enter public drainage
systems. It is expected that if the
good site practice suggested in Section 5.9 are followed as far as practicable, the potential water quality
impacts associated with construction activities would be minimal.
Construction Site Run-off
5.7.1.2
Potential pollution sources of
site run-off may include:
·
Run-off and erosion of exposed
bare soil and earth, drainage channels, earth working areas and stockpiles;
·
Wash water from dust
suppression sprays and wheel washing facilities; and
·
Fuel, oil and lubricants from
maintenance of construction vehicles and equipment.
5.7.1.3
During rainstorms, site run-off
would wash away the soil particles on unpaved lands and areas with topsoil
exposed, if any. 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 marine
environment. Site run-off may also
wash away contaminated soil particles and therefore cause water pollution. Mitigation measures provided in Section
5.9 can minimize potential impacts of site run-off.
Sewage Effluent from Construction Workforce
5.7.1.4
During the construction of the
Project, the workforce on site will generate sewage effluent, which is
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 0.35m3 per worker per day. With reference to the Census and
Statistics Department published Quarterly Report of Employment and Vacancies at
Construction Sites (Third Quarter 2019), 51 manual workers are assumed on-site
per day. It is estimated that about
18m3 sewage will be produced by the construction of project per day.
Potential water quality impacts
upon the local drainage and fresh water system may
arise from these sewage effluents, if uncontrolled.
5.7.1.5
Temporary sewage generation 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, temporary sanitary facilities are used and properly
maintained, and mitigation measures as recommended in Section 5.9 are adopted as far as
practicable, it is unlikely that sewage generated from the site would have a
significant water quality impact.
Accidental Spillage of Chemicals
5.7.1.6
The use of chemicals such as
engine oil and lubricants, and their storage as waste materials has the
potential to impact water quality if spillage occurs and enters adjacent water
environment. Waste oil may
infiltrate into the surface soil layer, or runoff into the nearby water
environment, increasing hydrocarbon levels. The potential impacts could however
be mitigated by practical mitigation measures and good site practices (as given
in Section 5.9).
5.7.2
Operation Phase
Surface Run-off
5.7.2.1
Potential water quality impact
may also arise from surface runoff discharged during operational phase. The surface runoff may contain small amount of suspended solids that may cause water quality
impacts to the nearby receiving waters.
However, impacts on water quality would be minimal, provided that a
proper drainage system would be provided to receive surface runoff to the
drainage system at the planning and design stages.
5.7.2.2
According to the DSD "Stormwater
Drainage Manual", annual rainfall in Hong
Kong is around 2,400 mm. However,
the EPD study namely “Update on Cumulative Water Quality and Hydrological
Effect of Coastal Developments and Upgrading of Assessment Tool (Update Study)”
suggested that only rainfall events of sufficient intensity and volume would
give rise to runoff and that runoff percentage is about 44% and 82% for dry and
wet season, respectively.
Therefore, only 1,512 mm of 2,400 mm annual rainfall would be considered
as effective rainfall that would generate runoff (i.e. 1,512 mm = 2,400 mm ×
(82%+44%)/2).
5.7.2.3
The Project will create around
280 m2 additional paved area. Making reference
to the abovementioned DSD’s manual, about 0.9 as the runoff coefficient for
paved area is assumed. The
non-point source pollution from surface run-off is estimated to be 1.04 m3/day
(= 0.9 × 1,512 mm/year × 280 m2). It is anticipated that with proper
implementation of best management practices as recommended in Section 5.9.2, the adverse water quality
impact from non-point source surface run-off is not significant.
5.8.1.1
The construction of the Project
potentially overlaps with the construction programme of
other nearby projects as identified in Section 2.11. However, with incorporation of the
recommended mitigation measures outlined under Section 5.9 below, no unacceptable adverse water quality impacts would be
resulted from the Project, hence no adverse cumulative water quality impacts
are anticipated.
5.9.1
Construction Phase
5.9.1.1
Measures as listed below are recommended
to mitigate the potential water quality impacts from the land-based
construction works.
General Construction Activities and Construction Site Run-off
Boring and Drilling Water
5.9.1.2
Water used in ground boring and
drilling for site investigation or rock / soil anchoring should be
re-circulated as far as practicable after sedimentation. When there is a need for final disposal,
the wastewater should be discharged into storm drains via silt removal
facilities in compliance with the WPCO (see Section 5.9.1.13).
Wheel Washing Water
5.9.1.3
All vehicles and plants should
be cleaned before they leave a construction site to minimize the deposition of
earth, mud and debris on roads. A
wheel washing bay should be provided at every site exit if practicable and washwater should have sand and silt settled out or removed
before discharging into storm drains in compliance with the WPCO (see Section 5.9.1.13). 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
5.9.1.4
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
5.9.1.5
The site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should
be followed as far as practicable to minimize surface run-off and the chance of
erosion. The following measures are
recommended to protect water quality, and when properly implemented should be sufficient to adequately control site discharges so as to
avoid water quality impact.
5.9.1.6
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 in compliance with the WPCO (see Section 5.9.1.13). Channels, 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 as 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.
5.9.1.7
Silt removal facilities,
channels and manholes should be maintained and the
deposited silt and grit should be removed regularly (as well as at the onset of
and after each rainstorm) to prevent overflows and localized flooding. Before disposal at the public fill
reception facilities, the deposited silt and grit should be solicited in such a
way that it can be contained and delivered by dump truck instead of tanker
truck. Any practical options for
the diversion and realignment of drainage should comply with both engineering
and environmental requirements in order to provide adequate hydraulic capacity
of all drains.
5.9.1.8
Construction works should be
programmed to minimize soil excavation in the wet season (i.e. April to
September). If soil excavation
cannot be avoided in these months or at any time of year when rainstorms are
likely, temporarily 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 rainstorm.
5.9.1.9
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.
5.9.1.10
Measures should be taken to
minimize the ingress of rainwater into trenches. If excavation of trenches in the wet
season 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 in compliance with the WPCO (see Section 5.9.1.13).
5.9.1.11
Open stockpiles of construction
materials (e.g. aggregates, sand and fill material) on sites should be covered
with tarpaulin or similar fabric during rainstorms.
5.9.1.12
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.
Effluent Discharge
Sewage Effluent from Construction Workforce
5.9.1.14
The construction workforce on
site will generate sewage. Sufficient chemical toilets should be provided in the works
area, with a licensed waste collector employed to clean the chemical toilets on
a regular basis.
5.9.1.15
Notices should be posted at
conspicuous locations to remind the workers not to discharge any sewage or
wastewater into the surrounding environment. Regular environmental audit of the
construction site will provide an effective control of any malpractices and can
encourage continual improvement of environmental performance on site. It is anticipated that sewage generation
during the construction phase of the project would not cause water pollution
problem after undertaking all required measures.
Accidental Spillage of Chemicals
5.9.1.16
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.
5.9.1.17
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 leakage and spillage should only be undertaken within
the areas appropriately equipped to control these discharges.
5.9.1.18
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.
·
Storage area should be selected
at a safe location on site and adequate space should be allocated to the
storage area.
5.9.2.1
The ProPECC
PN 5/93 “Drainage Plans subject to Comments by Environmental Protection
Department” provides guidelines and practices for handling, treatment and
disposal of various effluent discharges to stormwater drains and foul sewers. The design of site drainage and disposal
of various site effluents generated within the development area should follow
the relevant guidelines and practices as given in the ProPECC
PN 5/93. Best Management Practices (BMPs) for storm water discharge are
recommended for the new development to mitigate potential adverse water quality
impacts.
Design Measures
5.9.2.2
Exposed surface shall be
avoided within the proposed development to minimize soil erosion. Development site shall be either hard
paved or covered by landscaping area where appropriate to reduce soil erosion.
5.9.2.3
The existing watercourses in
adjacent to the Project site will be retained to maintain the original flow path. The drainage system will be designed to
avoid any case of flooding based on the 1 in 50 year
return period.
Devices / Facilities to Control Pollution
5.9.2.4
Screening facilities such as
standard gully grating and trash grille, with spacing which is capable of
screening off large substances such as fallen leaves and rubbish should be
provided at the inlet of drainage system.
5.9.2.5
Road gullies with standard
design and silt traps and oil interceptors should be incorporated during the
detailed design to remove particles present in storm water runoff.
Administrative Measures
5.9.2.6
Good management measures such
as regular cleaning and sweeping of road surface / open areas is
suggested. The road surface / open
area cleaning should also be carried out prior to occurrence of rainstorm.
5.9.2.7
Manholes, as well as storm
water gullies, ditches provided among the development areas should be regularly
inspected and cleaned (e.g. monthly).
Additional inspection and cleansing should be carried out before forecast heavy rainfall.
5.10.1.1
With proper implementation of
mitigation measures, no adverse residual water quality impact is expected in
construction and operation phases.
5.11.1.1
The Project is not expected to
create any adverse water quality impacts in the construction and operation
phase, if the recommended mitigation measures are implemented properly. Water quality monitoring is therefore not
considered necessary. Nonetheless,
regular site inspections during the construction phase is proposed to inspect
the construction activities and work areas to ensure the recommended mitigation
measures are soundly implemented.
5.12.1
Construction Phase
5.12.2
Operation Phase
5.12.2.1
The only source of potential adverse
water quality impact in the operation phase is identified as surface runoff
from the minor additional paved areas. This is expected to be minimal and
acceptable, provided that the recommended mitigation measures for the drainage
system are properly implemented.