5.1.1
This Section provides an evaluation of the
potential water quality impacts arising from the construction and operation of
the proposed Project. Mitigation measures have been proposed if considered
necessary to minimise the identified water quality impacts.
Water Pollution Control Ordinance (Cap. 358)
5.2.1
The Water Pollution Control Ordinance (WPCO) is
the principal legislation controlling water quality in Hong Kong along with
Annexes 6 and 14 of the EIAO-TM. Under the WPCO, Hong Kong waters are
classified into Water Control Zones (WCZs) and Water Quality Objectives (WQOs)
are specified for each WCZ. This Project falls within Victoria Harbour (Phase 2)
WCZ. The corresponding WQOs are listed in Table 5‑1.
Table 5‑1 Summary of Water Quality Objectives for Victoria Harbour (Phase 2)
WCZ
|
Parameters
|
Objectives
|
Sub-Zone
|
|
Offensive odour, tints
|
Not to be present
|
Whole zone
|
|
Colour
|
Not to exceed 50 Hazen units, due to
human activity
|
Inland waters
|
|
Visible foam, oil scum, litter
|
Not to be present
|
Whole zone
|
|
Escherichia coli (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
the sampling occasions during the whole year
|
Marine waters
|
|
Depth-averaged DO
|
Not less than 4.0 mg/l for 90% of the
sampling occasions during the whole year; values should be calculated as the
annual water column average (expressed normally as the arithmetic mean of at
least 3 measurements at 1m below surface, mid depth and 1m above the seabed.
However in water of a depth of 5m of less the mean shall be that of 2
measurements – 1m below surface and 1m above seabed, and in water of less
than 3m the 1m below surface sample only shall apply.)
|
Marine waters
|
|
Dissolved Oxygen
(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 median not to exceed 25 mg/l
due to human activity
|
Inland waters
|
|
Unionised ammonia (UIA)
|
Annual mean not to exceed 0.021
mg(N)/l as unionised form
|
Whole zone
|
|
Nutrients
|
Shall not cause excessive algal
growth
|
Marine waters
|
|
Total inorganic nitrogen (TIN)
|
Annual mean depth-averaged inorganic
nitrogen not to exceed 0.4 mg(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
|
Technical Memorandum on Standards for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-
DSS)
5.2.2
All effluent discharges during both the
construction and operation phases of the proposed development are required to
comply with the Technical Memorandum on Standards for Effluents Discharged into
Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) issued under
Section 21 of the WPCO. The TM-DSS
defines acceptable discharge limits to different types of receiving
waters. Under the TM-DSS, effluents
discharged into the drainage and sewerage systems, inland and coastal waters of
the WCZs are subject to pollutant concentration standards for specified
discharge volumes. These are defined by the
Environmental Protection Department (EPD) and are specified in licence
conditions for any new discharge within a WCZ.
Professional Persons Environmental Consultative
Committee Practice Notes (ProPECC PNs)
5.2.3
Professional Persons Environmental Consultative
Committee Practice Note (ProPECC PN) 1/94 – “Construction Site Drainage”
provides guidelines for the handling and disposal of construction discharges.
This ProPECC Practice Note is generally applicable for control of site runoff
and wastewater generated during the construction phase of the Project.
5.2.4
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 during the operation phase of
the Project.
EIAO-TM
5.2.5
Annex 6 of the EIAO-TM provides the criteria for
evaluating water pollution while Annex 14 provides the guidelines for
assessment of water pollution.
ETWB TC(W) No. 5/2005 “Protection of Natural
Streams/Rivers from Adverse Impacts Arising from Construction Works
5.2.6
This circular provides an administrative
framework to better protect all natural streams/rivers from the impacts of
construction works and outlines practices to minimise the water quality impacts
upon watercourses.
5.3.1
Any discharge from the Project works during the
construction and operation phases would potentially affect the inland waters
within the Victoria Harbour (Phase 2) WCZ.
5.3.2
As defined in Clause 3.4.5.2 of the EIA Study Brief, the Study Area is a distance of 500 m from
boundary of the Project. The identified water sensitive receivers (WSRs)
are shown in Table 5‑2 and their locations are indicated in Figure
5.1.
Table 5‑2 Representative Water Sensitive Receivers
|
WSR ID
|
Description
|
Closest
Distance from Project Site
|
|
WSR
1a
|
Inland Watercourse in
the Vicinity 1
(Modified
channel, seasonal)
|
10m
|
|
WSR
1b
|
Inland Watercourse in
the Vicinity 2
(Modified channel,
seasonal)
|
5m
|
|
WSR
1c
|
Inland Watercourse in
the Vicinity 3
(modified channel,
seasonal)
|
92m
|
|
WSR
1d
|
Inland Watercourse in
the Vicinity 4
(Modified channel,
seasonal)
|
138m
|
|
WSR
1e
|
Inland Watercourse in
the Vicinity 5
(Modified channel,
seasonal)
|
57m
|
|
WSR
1f
|
Inland Watercourse in
the Vicinity 6
(Semi-natural stream,
seasonal)
|
38m
|
|
WSR
2a
|
Inland Watercourse
Potentially Subject to Groundwater Drawdown Impact 1
(Natural stream,
seasonal)
|
Overlapping with the
proposed cavern [1]
|
|
WSR
2b
|
Inland Watercourse
Potentially Subject to Groundwater Drawdown Impact 2
(Natural stream,
seasonal)
|
38m
|
|
WSR
2c
|
Inland Watercourse
Potentially Subject to Groundwater Drawdown Impact 3
(Natural stream,
seasonal)
|
Overlapping with the
proposed cavern [1]
|
|
WSR
2d
|
Inland Watercourse
Potentially Subject to Groundwater Drawdown Impact 4
(Natural stream,
seasonal)
|
26m
|
|
WSR
3a
|
Inland Watercourse
Assessed in Ecological Impact Assessment 1
(Partly natural/semi-natural/modified,
slow water flow)
|
Overlapping with the
proposed tunnel [1]
|
|
WSR
3b
|
Inland Watercourse
Assessed in Ecological Impact Assessment 2
(Natural for upper
section and semi-natural for lower section, slow water flow)
|
137m
|
|
WSR
3c
|
Inland Watercourse
Assessed in Ecological Impact Assessment 3
(Natural stream, slow
water flow)
|
413m
|
|
WSR
4
|
Other
Inland Watercourses (such as natural streams and modified channels; most of them
are seasonal)
|
156m
|
|
WSR
5
|
Lion Rock Country Park
|
Adjacent to the proposed
cavern
|
|
WSR
6
|
Water Gathering Ground
|
Over 300m from the
proposed cavern
|
|
Remarks:
[1] There are no
interface between the construction activities and the watercourse as the
construction of the proposed cavern/tunnel are at underground level.
|
5.4.1
Site visits were carried out on 22 March 2020
(dry season) and 22 September 2020 (wet season). The proposed cavern is located
outside but close to the Lion Rock Country Park. A number of stream courses are
found within the Study Area with some near the relocation site and some above
the proposed underground tunnel and rock caverns. The streams are
natural/semi-natural and the water source is from undeveloped upland hillslopes
with no major pollution source. It is observed that the water quality of the
streams is generally clean and non-odorous in both seasons.
5.4.2
There are some modified channels within the
Study Area and some of them are near the aboveground works area. Most of them
are concrete channel with no or low flow of water. The water source is mainly
from upland hillslope, residential/urban areas nearby. It is observed that the
modified channels are non-odorous with some sand/leaves in both seasons.
5.4.3
All watercourses identified within the Study
Area are within the catchment area of Kai Tai River (previously named as Kai
Tak Nullah) and generally run from the north to south. All these watercourses
flow into underground drains and discharge to Kai Tak River and ultimately to
Victoria Harbour about 3 km away from the Project Site.
Baseline River Water Quality
5.4.4
In 2019, a total of 6 river water quality
monitoring stations were monitored in the Kai Tak River all along from upstream
(KN7) to downstream (KN1) while KN7 was the closest monitoring station to the
Project. The locations of these river quality monitoring stations are indicated
in Figure 5.2. Data of key water quality parameters measured in
2019 at the six monitoring stations as reported in the annual River Water
Quality in Hong Kong are presented in Table 5‑3.
Table 5‑3 Summary of River Water Quality Monitoring Data collected by EPD for
Stations in Kai Tak River
|
Parameter
|
KN1
|
KN2
|
KN3
|
KN4
|
KN5
|
KN7
|
WPCO WQO
(Inland Waters)
|
|
Dissolved Oxygen (DO) (mg/L)
|
4.8
(1.5-6.0)
|
6.1
(5.6-7.5)
|
6.6
(5.9-7.6)
|
6.6
(5.7-7.6)
|
7.2
(7.0-8.0)
|
7.4
(6.8-8.0)
|
≥
4
|
|
pH
|
7.3
(7.2-7.5)
|
7.3
(7.1-7.6)
|
7.3
(7.1-7.5)
|
7.3
(7.1-7.5)
|
7.3
(7.1-7.5)
|
7.1
(7.0-7.3)
|
6.0
– 9.0
|
|
Suspended Solids (SS) (mg/L)
|
4.2
(1.4-7.8)
|
4.9
(2.6-13.0)
|
6.3
(1.5-10.0)
|
6.9
(4.4-13.0)
|
6.8
(4.9-16.0)
|
7.3
(3.6-13.0)
|
≤ 25
|
|
5-day Biochemical Oxygen Demand (BOD5)
(mg/L)
|
2.5
(1.4-5.0)
|
3.6
(1.8-6.4)
|
4.0
(2.3-6.8)
|
4.5
(2.8-9.8)
|
5.3
(3.1-13.0)
|
5.4
(3.0-10.0)
|
≤ 5
|
|
Chemical Oxygen
Demand (COD) (mg/L)
|
21
(11-35)
|
28
(13-36)
|
26
(14-36)
|
30
(18-36)
|
26
(14-48)
|
24
(13-42)
|
≤ 30
|
|
E. coli
(cfu/ 100mL)
|
30,000
(1,100–670,000)
|
7,200
(2,100–220,000)
|
5,100
(2,000–20,000)
|
4,900
(1,400-35,000)
|
4,100
(2,100-19,000)
|
2,100
(520-25,000)
|
≤ 1,000
|
|
Ammonia Nitrogen (NH3-N)
(mg/L)
|
1.850
(0.700-4.500)
|
1.750
(0.360-4.400)
|
1.650
(0.610-3.800)
|
1.450
(0.540-3.500)
|
1.070
(0.350-3.100)
|
1.005
(0.220-2.800)
|
Not available
|
|
Total Kjeldahl Nitrogen (TKN) (mg/L)
|
3.15
(1.80-7.40)
|
2.85
(1.80-6.70)
|
3.35
(1.50-6.10)
|
2.85
(1.40-5.50)
|
2.70
(1.20-5.50)
|
2.75
(1.10-5.10)
|
Not available
|
|
Total phosphorus
(mg/L)
|
1.15
(0.35-1.60)
|
1.35
(0.24-1.90)
|
1.25
(1.00-2.10)
|
1.20
(1.00-1.90)
|
1.30
(0.91-1.70)
|
1.20
(0.91-1.70)
|
Not available
|
|
Notes:
·
Data source: River Water Quality
in Hong Kong in 2019 (EPD)
·
Data presented are in annual medians of monthly samples; except those
for E. coli which are in annual geometric means.
·
Data in brackets indicate the ranges.
·
cfu - colony forming unit.
·
The WQO for Nitrogen under the WPCO refers to level of Un-ionised Ammoniacal
Nitrogen. As such, there is no
applicable WQO to Ammonia-Nitrogen.
|
5.4.5
The river water quality monitoring data in 2019 indicate
that the levels of SS, BOD5 and COD were higher at the upstream
stations of the Kai Tak River than the downstream stations while the levels of E.coli,
Ammonia Nitrogen (NH3-N) and Total
Kjeldahl Nitrogen (TKN) at the downstream stations were higher than the
upstream stations. It is also noted that generally high levels of E. coli
and exceedance of the WQO were recorded at all stations.
5.4.6
In terms of WQO compliance rate, overall
compliance rate of the six monitoring stations in 2019 was 88%. In 2019, the
Water Quality Index (WQI) was graded as “good” for all six monitoring stations.
Baseline Marine Water Quality
5.4.7
This Project is located within Victoria Harbour
(Phase 2) WCZ. Stations at Victoria Harbour (East) (VM1 & VM2), Kwun Tong
Typhoon Shelter (KTTS) (VT4) and To Kwa Wan Typhoon Shelter (TKWTS) (VT11) are
the closest marine water quality monitoring stations to the Project Site. Their
locations are indicated in Figure 5.2. Data of key water
quality parameters measured in 2019 at these four monitoring stations as
reported in the annual Marine Water Quality in Hong Kong are presented in Table 5‑4.
Table 5‑4 Summary of Marine Water Quality Monitoring Data collected by EPD
for VM1, VM2, VT4 and VT11
|
Parameter
|
VM1
|
VM2
|
VT11
|
VT4
|
WPCO WQO (Marine
Waters)
|
|
Temperature (oC)
|
24.0
(19.2 - 29.3)
|
24.3
(19.2 - 29.2)
|
24.2
(19.0 - 29.3)
|
24.4
(18.7 - 29.5)
|
Change ≤ 2oC
|
|
Salinity
|
32.6
(31.0 - 33.4)
|
32.1
(30.1 - 33.3)
|
32.1
(31.1 - 33.0)
|
29.6
(24.8 - 32.7)
|
Change ≤ 10% of ambient
|
|
Dissolved Oxygen (DO) (mg/L)
|
Depth Average
|
5.9
(4.3 - 7.4)
|
5.8
(4.4 - 7.3)
|
4.6
(3.2 - 6.6)
|
4.4
(2.3 - 6.9)
|
≥ 4.0 mg/L for 90% of the samples
|
|
Bottom
|
5.8
(3.3 - 7.6)
|
5.9
(4.3 - 7.3)
|
4.6
(2.6 - 6.7)
|
4.7
(2.1 - 7.2)
|
≥ 2.0 mg/L for 90% of the samples
|
|
Dissolved Oxygen (DO)
(% Saturation)
|
Depth Average
|
84
(64 - 97)
|
83
(64 - 97)
|
65
(46 - 86)
|
62
(33 - 90)
|
Not available
|
|
Bottom
|
82
(46 - 100)
|
84
(63 - 97)
|
66
(38 - 89)
|
66
(30 - 94)
|
Not available
|
|
pH
|
7.9
(7.6 - 8.1)
|
8.0
(7.6 - 8.2)
|
7.8
(7.4 - 8.1)
|
7.8
(7.5 - 8.1)
|
6.5 – 8.5 (Change not to exceed 0.2)
|
|
Suspended Solids (SS)
(mg/L)
|
6.8
(1.4 - 15.0)
|
6.5
(2.7 - 13.7)
|
6.9
(1.9 - 13.7)
|
6.7
(1.6 - 13.0)
|
≤ 30% increase
|
|
5-day Biochemical Oxygen Demand (BOD5) (mg/L)
|
0.6
(0.2 - 2.5)
|
0.6
(0.2 - 2.0)
|
0.5
(0.4 - 0.8)
|
0.8
(0.5 - 1.0)
|
Not available
|
|
Ammonia Nitrogen (NH3-N)
(mg/L)
|
0.062
(0.018 - 0.147)
|
0.091
(0.017 - 0.153)
|
0.148
(0.091 - 0.277)
|
0.201
(0.038 - 0.320)
|
Not available
|
|
Unionised Ammonia (UIA)
(mg/L)
|
0.002
(<0.001 - 0.005)
|
0.004
(<0.001 - 0.009)
|
0.005
(0.001 - 0.011)
|
0.006
(<0.001 - 0.019)
|
≤ 0.021 mg/L
for annual mean
|
|
Nitrite Nitrogen (NO2-N)
(mg/L)
|
0.018
(0.004 - 0.054)
|
0.021
(0.008 - 0.053)
|
0.018
(0.012 - 0.023)
|
0.081
(0.018 - 0.192)
|
Not available
|
|
Nitrate Nitrogen (NO3-N)
(mg/L)
|
0.070
(0.040 - 0.140)
|
0.102
(0.044 - 0.143)
|
0.112
(0.063 - 0.147)
|
0.290
(0.130 - 0.530)
|
Not available
|
|
Total Inorganic Nitrogen (TIN) (mg/L)
|
0.15
(0.09 - 0.31)
|
0.22
(0.09 - 0.33)
|
0.28
(0.20 - 0.41)
|
0.57
(0.19 - 1.04)
|
≤ 0.4 mg/L for
annual mean
|
|
Total Kjeldahl Nitrogen (TKN) (mg/L)
|
0.40
(0.12 - 1.40)
|
0.45
(0.19 - 1.37)
|
0.46
(0.25 - 0.76)
|
0.58
(0.26 - 0.95)
|
Not available
|
|
Total Nitrogen (TN)
(mg/L)
|
0.49
(0.17 - 1.49)
|
0.57
(0.27 - 1.50)
|
0.59
(0.32 - 0.88)
|
0.95
(0.41 - 1.45)
|
Not available
|
|
Orthophosphate Phosphorus (PO4) (mg/L)
|
0.011
(<0.002 - 0.017)
|
0.016
(<0.002 - 0.027)
|
0.021
(0.010 - 0.040)
|
0.078
(0.020 - 0.136)
|
Not available
|
|
Total Phosphorus (TP)
(mg/L)
|
0.04
(<0.02 - 0.11)
|
0.04
(<0.02 - 0.06)
|
0.05
(0.03 - 0.10)
|
0.11
(0.04 - 0.17)
|
Not available
|
|
Chlorophyll-a
(µg/L)
|
3.3
(0.4 - 19.9)
|
4.3
(0.6 - 21.0)
|
1.7
(0.5 - 5.8)
|
3.7
(0.5 - 11.2)
|
Not available
|
|
E. coli
(cfu/100 mL)
|
140
(32 - 350)
|
240
(56 - 470)
|
560
(67 - 2500)
|
780
(79 - 50000)
|
Not available
|
|
Faecal Coliforms
(cfu/100mL)
|
330
(67 - 850)
|
580
(110 - 1300)
|
1400
(270 - 3600)
|
1900
(130 - 160000)
|
Not available
|
|
Note :
·
Data source: Marine Water Quality in Hong Kong in 2019 (EPD)
·
Unless otherwise specified, data presented are depth-averaged (A)
values calculated by taking the means of three depths: Surface (S), Mid-depth
(M), Bottom (B).
·
Data presented are annual arithmetic means of the depth-averaged
results except for E. coli and faecal coliforms which are annual
geometric means.
·
Data in brackets indicate the ranges.
·
cfu - colony forming unit.
|
5.4.8
The marine water quality monitoring data in 2019
indicate that the water quality at Victoria Harbour (East) (VM1 & VM2) in
general meets the WQOs for Victoria Harbour. It is also noted that exceedance
of the WQOs were recorded for DO (depth average) at TKWTS (VT11) and for DO
(depth average) and TIN at KTTS (VT4).
5.5
Potential
Sources of Impacts
Construction Phase
5.5.1
Relocation of DHSRs to caverns mainly involves the
site formation, construction of caverns and tunnel, construction of ancillary
building and tunnel portal, structural works for relocated DHSRs, watermain
laying, E&M installation and other associated works (slope, landscaping works
and reinstatement for the access tunnel portal).
5.5.2
Potential
sources of water quality impact associated with the Project during construction
phase include:
·
Construction site run-off;
·
General construction activities;
·
Sewage generated by construction workforce;
·
Potential accidental spillage of chemicals;
·
Potential groundwater infiltration; and
·
Construction works in close proximity of inland
watercourses
5.5.3
This Project falls within Victoria Harbour
(Phase 2) WCZ. Considering most of the works area are underground (except
tunnel portal and ancillary building) or will be reinstated after construction
phase, the change of catchment types or areas would not be expected. There is no direct encroachment of
water bodies, alteration of water courses, natural streams, ponds, wetlands, change
of water holding/flow regimes of water bodies, erosion or sedimentation due to
the Project, hydrological changes in the assessment area would not be
anticipated.
Operation Phase
5.5.5
As the relocated DHSRs and associated pumping
stations are mainly for the storage and pumping of fresh water and flushing
water, no major associated polluting sources are identified.
5.5.6
Annual cleansing and maintenance of service
reservoirs are conducted by WSD. Effluents from cleaning of service reservoir
are subject to EPD’s control under the WPCO and a valid discharge license is
required before commencing any of the discharges. WSD will sample the discharge at the sampling
points and carry out analyses to ensure that the quantity and composition of
any discharge effluent comply with the requirements of discharge license.
5.5.7
Potential sources of water quality impact associated
with the Project during operation phase include:
·
Effluents from cleaning of service reservoir;
·
Non-point source surface run-off from new
impervious areas; and
·
Sewage from the development.
5.6.1
The assessment area includes all areas within 500m
from the Project Boundary. The WSRs that may be affected during the
construction and operation phases of the Project have been identified. Potential sources of water quality impact arising
from the construction works and operation of the Project are identified. Pollutants from point discharges and
non-point sources that could affect the quality of surface and ground water are
identified. All the identified sources
of potential water quality impact are evaluated, and their impact significance are
determined. The mitigation measures to
reduce any identified adverse impacts on water quality to acceptable levels for
both construction and operation phases are determined.
Construction Phase
Construction Site Run-off
5.7.1
Site runoff can be generated from erosion of
exposed surfaces, stockpiles and material storage areas for foundation,
excavation, concreting work, structural and mechanical works associated with
the construction of tunnel, caverns and ancillary building as well as the
watermain laying. During a rainstorm event, storm runoff can also be generated
from the construction sites.
5.7.2
Site runoff will contain high suspended solids level
which could be a source of water pollution contain suspended solids. Wastewater
with high pH value may be generated by concreting works for reinstatement of
the tunnel portal. Uncontrolled site
runoff can cause blockage of drainage channels. Release of the runoff would
increase the suspended solid levels, pH value, oil & grease levels in WSRs
nearby. Provided the surface runoff is effectively managed and controlled over
the site by the mitigation measures recommended in Section 5.8, adverse water
quality impacts are not anticipated.
General Construction Activities
5.7.3
Wastewater may be generated from various
construction activities such as general cleaning, wheel washing and dust
suppression. Wash water from dust suppression sprays and wheel washing
facilities of the construction site contain high levels of suspended solids
that need to be properly treated and discharged. Mitigation measures should be
in place to control construction runoff and polluted water sources, minimizing
the pollution to nearby WSRs. With proper implementation of mitigation measures
specified in Section 5.8, no adverse water quality impacts are expected.
5.7.4
Sewage will be generated from construction
workforce during the construction phase of the Project. Different from the
construction runoff and chemical spills, sewage is characterised by high levels
of biochemical oxygen demand, ammonia and E.
coli. Collection and disposal of sewage generated from workforce is
required. With provision of portable chemical toilets and proper disposal of
sewage, no adverse water quality impact is anticipated.
Potential Accidental Spillage of Chemicals
5.7.5
Chemicals, including fuel, solvents, oils and
lubricants for use by construction mechanical machinery and equipment, if not
properly stored or chemicals accidentally spilled on ground surfaces from
construction activities may potentially be carried away by construction and
storm runoff, causing pollution to the nearby aquatic environment. With the
implementation of mitigation measures for accidental spillage of chemicals
recommended in Section 5.8, adverse water quality impact is not anticipated.
Potential Groundwater
Infiltration
5.7.6
Cavern and tunnel excavation may result in groundwater
infiltration. The proposed cavern development is located on the hillside of the
Project Site, which is currently hilly terrain covered by vegetation, and no land
contamination issue is expected according to the findings in Chapter 7 of EIA
on land contamination. Thus, infiltration of contaminated groundwater is not
anticipated. Groundwater infiltration may cause increase in site run-off and
potential groundwater table drawdown. The major concern from cavern
construction activities would be the potential drawdown in any soil and aquifer
layers and the associated increase in site runoff. Any potential drawdown could
result in different degrees of settlement and dewatering of surface water
features. Groundwater in the surrounding area may be depleted by draining into tunnel/cavern.
Suspended solids would also be a key concern as infiltrated water could carry
away silt from site to the site drainage. Considerations should be taken in
cavern design to minimise the potential impacts from the change in groundwater
level. Appropriate measures during the cavern construction would also be
proposed to minimise the potential impact from groundwater drawdown. With
proper implementation of groundwater control measures recommended in Section
5.8, no adverse water quality impact is anticipated.
Construction
Works in Close Proximity of Inland Watercourses
5.7.7
Construction activities in close proximity of the
inland watercourses may pollute the inland water bodies due to the potential
release of construction wastes as well as construction wastewater and the site
runoff which are generally characterised by high concentration of SS and
elevated pH. Mitigation measures should be implemented to control the release
of construction wastes, construction wastewater and site runoff into the adjacent
inland watercourses. With proper
implementation of mitigation measures recommended in Section 5.8, adverse water
quality impact is not anticipated
Cleansing
Effluent Generated from Washing of Interior of Structures
5.7.8
Upon completion of construction and prior to
operation of the service reservoirs, the interior of the structures will be
washed and brushed down with water, added with chlorine
solution as sterilizing agent. The cleansing effluent would contain SS and
residual chlorine. Water quality impact
may arise if the cleansing effluent is not properly treated before being
discharged into storm water drainage system. With proper treatment of cleansing
effluent prior discharge, no significant water quality impact is expected.
Evaluation of Impacts on Water
Sensitive Receivers
5.7.9
The water quality of inland watercourses in the
vicinity of the works area for tunnel portal and ancillary building as well as
the watermain laying (WSR1a to WSR1f) would be
potentially affected by the construction site run-off, general construction
activities, sewage generated by construction workforce and potential accidental
spillage of chemicals. Most of the inland watercourses in the vicinity are modified
channels (WSR1a to WSR1e) while one is semi-natural stream (WSR1f) located at a
higher elevation from the proposed water mainlaying works. All of them are with
no or low flow of water during both site visits. With implementation of proper
site practice and good site management specified in the ProPECC PN 1/94 and
ETWB TC(W) No. 5/2005 as recommended in Section
5.8, no unacceptable water quality impact is anticipated.
5.7.10
For the stream courses above or near the proposed
cavern and tunnel (WSR2a to WSR2d), as tunnelling and excavation works will be
conducted underground, water quality impact to these stream courses from site
effluent is not expected. On the other hand, the stream courses may be subject
to the groundwater drawdown impact. Such potential impact can be mitigated by
practical groundwater control measures given in Section 5.8.
5.7.11
Three inland watercourses (WSR3a to WSR3c) within
the Study Area have been assessed in the ecological impact assessment in Chapter 8 of EIA. One of them, WSR3a
(named as S1 in Section 8) located
above the proposed access tunnel would be potentially subject to groundwater
drawdown impact that can be mitigated by the recommended groundwater control
measures as mentioned in Section 5.8.
For WSR3b and WSR3c (named as S2 and S3 respectively, in Chapter 8 of EIA), considering locating at least 130m away and at
higher elevation from the proposed works, water quality impact to these two
WSRs is not anticipated.
5.7.12
Other inland watercourses (WSR4) would be
potentially affected by the construction site run-off, general construction
activities, sewage generated by construction workforce and potential accidental
spillage of chemicals. Considering certain distance (at least 156m) from Project
area, no significant water quality impact associated with the proposed works is
expected with proper implementation of the proposed mitigation measures.
5.7.13
Lion Rock Country Park is located at a higher
elevation from the proposed cavern works, site effluent if any will not flow to
the Country Park. Adverse water quality impact to the Lion Rock Country Park is
not expected.
5.7.14
Water
gathering grounds are located at least 300m away from the Project Site and the
majority of the water gathering grounds are at another side of the Lion Rock
Country Park. The part of water gathering ground on the same side of the Lion
Rock Country Park is at much higher elevation from the proposed cavern works.
Therefore, the water gathering grounds would not be affected by the Project.
Operation Phase
5.7.15
As the relocated DHSRs are mainly for the
storage and pumping of fresh water and flushing water, no adverse water quality
impact is envisaged during the operation of the relocated DHSRs.
Effluents from Cleaning of Service Reservoir
5.7.16
Cleansing
effluent would be generated from the regular cleansing and maintenance of the
service reservoirs with water, added with chlorine solution as sterilizing
agent. The cleansing effluent would contain SS and residual chlorine. Water quality
impact may arise if the cleansing effluent is not properly treated before being
discharged into storm water drainage system. Treatment
and disposal of cleansing water during annual cleansing and maintenance of the
service reservoirs shall follow the WSD’s current practice, and a valid
discharge licence issued by EPD under the WPCO is required before commencing
any of the discharges. No adverse water quality impact is envisaged during
operation and maintenance of the Project.
Non-point Source Surface Runoff
5.7.17
The relocated DHSRs will be fully enclosed inside
the rock cavern and hence no non-point source surface runoff will be generated
from the DHSRs. However, potential water quality impact may arise from surface
runoff from the ancillary building and access road during operation phase.
5.7.18
According to the “Stormwater Drainage Manual (5th
Edition) issued by Drainage Services Department, the average annual rainfall of
Hong Kong is about 2,400mm. The EPD study “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 (63% in average).
Therefore, only 63% of the average
annual rainfall of 2,400mm (i.e. 1,512mm) would be considered as effective
rainfall that would generate surface runoff.
5.7.19
The total footprint of the ancillary building and
access road would be 2,840m2 which is the new impervious area
created by the proposed Project. With the assumption of 0.95 as the runoff
coefficient, the non-point source surface run-off pollution is estimated to be 11
m3/day (2,840m2 x 1.512m x 0.95 / 365day). The surface
runoff may contain a small amount of suspended solids, oil, grease and grit
that may cause water quality impacts to the nearby water bodies. However, impacts upon water quality will be
minimal provided that a proper drainage system will be provided to receive
surface run-off at the planning and design stages. With proper implementation
of recommended mitigation measures and best management practices described in
Section 5.8.13, adverse water quality impact associated with the
discharge of surface runoff is not anticipated.
Sewage from the Development
5.7.20
Minimal sewage will be generated from the intermittent
use of sanitary fitments inside the proposed unmanned
ancillary building during maintenance. The toilet will not open to the public
and the ancillary building is unmanned. It is anticipated that the usage of
toilet is very limited. According to Guidelines for Estimating Sewage Flows for
Sewage Infrastructure Planning, the unit flow due to commercial activities
(electricity gas & water) and commercial employees is 0.33 m3
per day per worker. Assuming that there
would be 5 nos. of workers during maintenance, the quantity of sewage generated
would be around 1.65 m3 per day. The sewage will be properly conveyed
to the existing sewerage system in Chuk Yuen Road. The proposed manholes
to be connected is at Chuk Yuen Road near Wang King House (FMH4032902). It is
estimated that the capacity of the existing sewer is about 100L/s which is
considered sufficient to cater for the instantaneous additional flow of 2.16L/s.
Construction Phase
5.8.1
The
main potential water quality impacts from the construction stage of the Project
include an increase in suspended solids, pH value, oil & grease in general
site effluent and the nearby water bodies. The following proposed mitigation
measures should be implemented during construction of the Project.
General Construction Site Practice
5.8.2
The
Contractor should observe and comply with the Water Pollution Control Ordinance
and its subsidiary regulations and obtain a discharge license under the
Ordinance for discharge of effluent from the construction site. 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 Contractor should
carry out the Project works in such a manner as to minimise adverse impacts on
the water quality during execution of the works. In particular, the Contractor should arrange
the working method to minimise the effects on the water quality within and
outside the Project Site and on the transport routes. In addition, the management of construction
site drainage from the Project will follow guidelines provided in ProPECC PN 1/94
– “Construction Site Drainage”. The mitigation measures
described in ETWB TC(W) No. 5/2005 shall also be followed where necessary for
construction activities in close vicinity to inland watercourses.
Construction Site Runoff and General Construction Activities
5.8.3
Proper
site management measures should be implemented to control site runoff and
drainage, and thereby prevent high sediment loadings from reaching downstream
sections of the river/stream. The Contractor should follow the practices, and
be responsible for the design, construction, operation and maintenance of all
the mitigation measures. The design of
the mitigation measures should be submitted by the Contractor to the Engineer
for approval. These mitigation measures shall include the following practices
to minimise site surface runoff and the chance of erosion, and also to retain
and reduce any suspended solids prior to discharge.
·
Provision of perimeter channels to intercept
storm-runoff from outside the site.
These should be constructed in advance of the construction works.
·
Temporary ditches such as channels, earth bunds
or sand bag barriers should be included to facilitate runoff discharge into the
stormwater drain, via a sand/silt basin/trap.
·
Works programme should be designed to minimise
works areas at any one time, thus minimizing exposed soil areas and reducing
the potential for increased siltation and site runoff.
·
Sand/silt removal facilities such as sand traps,
silt traps and sediment basins should be provided to remove the sand/silt
particles from run-off where necessary.
These facilities should be properly and regularly cleaned and
maintained. These facilities should be
carefully planned to ensure that they would be installed at appropriate
locations to capture all surface water generated on site.
·
Careful programming of the works to avoid
excavation works during the rainy season (April to September).
·
Temporary access roads (if any) should be
protected by crushed gravel and exposed slope surfaces shall be protected (e.g.
by tarpaulin) when rainstorms are likely;
·
Open stockpiles of construction materials
on-site should be covered with tarpaulin or similar fabric during rainstorms to
prevent erosion. Measures should be taken to prevent the washing away of
construction materials, soil, silt or debris into any drainage system.
·
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.
·
Measures should be taken to minimise 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.
·
Manholes 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.
·
Water used in ground boring and drilling for
site investigation or rock/soil anchoring should as far as practicable be
recirculated after sedimentation. When there is a need for final disposal, the
wastewater should be discharged into storm drains via silt removal facilities.
·
All vehicles and plant should be cleaned before
they leave a construction site to ensure no earth, mud, debris and the like is
deposited by them on roads. A wheel washing bay should be provided at every
site 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.
5.8.4
Reuse of treated site runoff shall be considered
as far as practicable for on-site activities such as dust suppression, wheel
washing and general cleaning, etc.
Sewage Generated by Construction Workforce
5.8.5
No discharge of sewage to the
storm drains and inland watercourse will be allowed. Domestic sewage generated by workforce
on-site should be collected in a suitable storage facility such as portable
chemical toilets. An adequate number of portable toilets will be provided
during the construction phase, with a licensed collector employed to clean the
chemical toilets on a regular basis, and be responsible for collection and
disposal of the sewage. According to the
Reference Materials on Construction
Site Welfare, Health and Safety Measures that issued by the Construction
Industry Council, the
number of toilet facilities provided on site shall be at a ratio of not less
than one for every 25 workers. These toilets should be maintained in a state
that will not deter the workers from using them. It is anticipated that the
sewage generated by construction workforce would not cause adverse water
quality impact after implementation of all recommended measures.
Accidental Spillage of Chemicals
5.8.6
The
following mitigation measures should be implemented to avoid adverse impacts of
chemical spillage:
·
Waste streams classifiable as chemical wastes
should be properly stored, collected and treated for compliance with the
requirements set out in the Waste Disposal Ordinance and its subsidiary Waste
Disposal (Chemical Waste) (General) Regulation.
·
All fuel tanks and chemical storage areas should
be provided with locks and be sited on paved areas.
·
The storage areas should be surrounded by bunds
with a capacity equal to 110% of the storage capacity of the largest tank to
prevent spilled oil, fuel and chemicals from reaching the receiving
waters.
·
Waste oil should be collected and stored for
recycling or disposal, in accordance with the Waste Disposal Ordinance.
·
Vehicle and plant servicing areas, vehicle wash
bays and lubrication bays should, as far as possible, be located within roofed and
paved areas. The drainage in these
covered areas should be connected to foul sewers via a petrol interceptor.
Groundwater infiltration and Groundwater Drawdown
5.8.7
To
minimise the groundwater infiltration, the following groundwater control
measures are recommended:
·
The Contractor shall undertake rigorous probing
of the ground ahead of excavation works to identify zones of significant water
inflow. In such zones of significant water inflow that could occur as a result
of discrete, permeable features, the overall inflow would be reduced by means
of cut-off grouting executed ahead of the tunnel/cavern advance.
·
Where water inflow quantities are excessive,
pre-grouting will be required to reduce the water inflow into the
tunnel/cavern.
·
In case of excessive infiltration being observed
as a result of the tunnelling or excavation works even after pre-grouting
measures, post-grouting should be applied as far as practicable.
·
Waterproof lining will be installed after the
formation of the tunnel and cavern.
·
In the event of seepage of groundwater occurs,
groundwater should be pumped out from works areas and discharged to the storm drains
via silt removal facilities. The discharges during construction phase shall
comply with WPCO requirements.
Construction
Works in Close Proximity of Inland Watercourses
5.8.8
The mitigation measures proposed for “General
Construction Site Practice” and “Construction Site Runoff and General
Construction Activities” in Sections 5.8.2 and 5.8.3 shall be
implemented properly to minimise the water quality impacts due to the
construction works in close proximity of inland watercourses.
5.8.9
The practices outlined in ETWB TC(W) No. 5/2005 shall
also be adopted where applicable to minimise the water quality impacts upon any
natural streams or other inland watercourses.
Relevant mitigation measures are listed below:
·
The
use of less or smaller construction plants may be specified in areas close to
the inland watercourses to reduce the disturbance to the surface water.
·
Temporary
storage of materials (e.g. equipment, chemicals and fuel) and temporary
stockpile of construction debris and spoil should be located well away from any
watercourses.
·
Stockpiling
of construction materials and dusty materials should be covered and located
away from any watercourses.
·
Construction
debris and spoil should be covered up and/or disposed of as soon as possible to
avoid being washed into the nearby inland watercourses.
·
Adequate lateral support may need to
be erected in order to prevent soil/mud from slipping into the watercourses.
·
Construction works close to the
inland watercourses should be carried out in dry season as far as practicable
where the flow in the surface channel or stream is low.
Cleansing
Effluent Generated from Washing of Interior of Structures
5.8.10
The cleaning effluent containing SS and residual
chlorine should be settled out through the sedimentation tank and dechlorinated
by the de-chlorination plant. The discharge quality of the cleansing effluent
generated from washing of interior of
structures after the construction shall meet the requirements specified in the
discharge licence and the cleaning effluent should be treated properly so that
it satisfies all the standards listed in the TM-DSS.
Operation Phase
5.8.11
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. No adverse water quality impact is identified from the sewage generated
from the unmanned ancillary building during operation. Only minimal amount of sewage will be generated
and properly conveyed to existing sewerage system, no mitigation measure is
required for this aspect.
Effluents from Cleaning of Service Reservoir
5.8.12
Treatment and disposal of cleansing water during
annual cleaning and maintenance of the service reservoirs shall follow the
WSD’s current normal practice with reference to Sections 23.24 – 23.25 of the
General Specification for Civil Engineering Works. Portable water incorporated with a
mixture of sterilizing chemicals shall be used for washing water retaining
structures. The cleansing effluent shall be settled out through the
sedimentation tank and dechlorinated by a dechlorination unit before being
discharged to drainage system. Agreement of DSD and discharge license from EPD
shall be obtained before commencing any of the discharges during operation
phase.
Non-point Source Surface Runoff
5.8.13
Best Management Practices (BMPs) to reduce
non-point source surface water pollution are proposed as follows:
Design Measures
·
Exposed surface shall be avoided within access
road and portal/ancillary building areas to minimise soil
erosion. The access road and the portal/ancillary building areas
shall be either hard paved or covered by landscaping area where appropriate.
Devices / Facilities to Control Pollution
·
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.
·
Road gullies with standard design and silt traps
should be provided to remove particles present in stormwater runoff, where
appropriate.
Administrative Measures
·
Good management measures such as regular
cleaning and sweeping of road surface/ open areas are suggested. The road
surface/ open area cleaning should also be carried out prior to occurrence of
rainstorm.
·
Manholes, as well as storm water gullies,
ditches provided at the Project site should be regularly inspected and cleaned (e.g.
monthly). Additional inspection and
cleansing should be carried out before forecast heavy rainfall.
5.9.1
There are two concurrent projects potentially
causing cumulative water quality impacts during construction phase and their
locations are shown in Figure 2.5. They include:
·
CE 28/2017 (HY) - Pedestrian Link near Chuk Yuen
North Estate – Design and Construction
·
CE 48/2018 (HY) – Improvement
of Lion Rock Tunnel
5.9.2
According to the best available information, the
project “Pedestrian Link near Chuk Yuen North Estate” will commence in mid-2023
for completion in mid-2029. The water quality impact such as construction site
run-off associated with watermain laying under the Project would have potential
cumulative impact with the concurrent project. Considering the small scale
works of section-by-section watermain laying and good implementation of
mitigation measures recommended, no unacceptable cumulative water quality impact
is anticipated.
5.9.3
EIA study brief (ESB-323/2019) of the project
“Improvement of Lion Rock Tunnel” was issued in November 2019. Based on the
latest information, the target work commencement date of the project
“Improvement of Lion Rock Tunnel” is mid of 2024, which is a concurrent project
with this Project during construction. According to the project profile of the
tunnel project, potential sources of water quality impacts including
construction site run-off, accidental spillage of chemicals, sewage effluent
from construction workforce and wastewater from general construction activities
may arise from the construction of the tunnel project. The construction works
for tunnel portal and ancillary building under this Project would cause
potential cumulative impact with the concurrent tunnel project. Considering
good implementation of mitigation measures for the projects, no unacceptable
cumulative water quality impact is anticipated.
Construction Phase
5.10.1
No adverse residual water quality impact is
anticipated from the construction of the Project with the implementation of the
recommended mitigation measures and good construction site practices.
Operation Phase
5.10.2
No adverse residual water quality impact is
anticipated during the operation of the Project with the implementation of the
recommended mitigation measures.
Construction Phase
5.11.1
With the implementation of the recommended
mitigation measures and ensuring all site effluents are properly treated before
discharge, no adverse water quality impact is envisaged during the construction
phase of the Project. Regular site inspection should also be conducted during
the construction phase in order to ensure the recommended mitigation measures
are properly implemented. Details of the EM&A programme are presented in
the standalone EM&A Manual.
Operation Phase
5.11.2
Given no adverse water quality impact is
anticipated during the operation of the Project, monitoring during operation
phase is considered not necessary.
5.12.1
The potential sources of water quality impacts
associated with the construction of the Project have been identified and the
potential impacts were evaluated. Water quality impact may arise from construction
site run-off, general construction activities, sewage from construction workforce,
potential accidental chemical spillage, potential groundwater infiltration,
construction works in close proximity of inland watercourses and cleansing effluent generated from washing of interior of structures. With
proper implementation of mitigation measures, no unacceptable water quality
impact is expected during construction phase. Regular site inspection
should be conducted during the construction phase to ensure the recommended
mitigation measures are properly implemented.
5.12.2
DHSRs and associated pumping stations are mainly
for the storage and pumping of fresh water and flushing water. Water quality impact may
arise from effluents from cleaning of service reservoir, non-point source
surface runoff and sewage from the development. With proper implementation of
mitigation measures, adverse water quality impact associated with the operation
of the Project is not envisaged.
END OF TEXT