5
water quality Impact
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 3.4.6 of the Study Brief.
5.2
Environmental Legislation,
Standards and Criteria
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
5.2.2.1
The Water Pollution Control
Ordinance (WPCO) provides the 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 each
WCZ based on their beneficial uses. WQOs
for the watercourses in Tolo Harbour and Channel WCZ relevant to this
assessment are listed in Table
5.1.
Table 5.1 Summary
of Water Quality Objectives for Watercourses in Tolo Harbour and Channel WCZ
|
Parameters
|
Criteria
|
Subzone
|
|
Aesthetic Appearance
|
Waste discharges shall not cause the
water to contain substances that settle to form objectionable deposits;
|
Whole Zone
|
|
Waste discharges shall not cause the water to contain substances
that float as debris, scum, oil or other matter to form nuisances;
|
|
Waste discharges shall not cause water to contain substances
that produce objectionable colour, odours, taste or turbidity;
|
|
Waste discharges shall not cause water to contain substances
that injure or are toxic or produce adverse physiological responses in
humans, animals or plants; or
|
|
Waste discharges shall not cause water to contain substances
that are conductive to undesirable aquatic life or a nuisance to aquatic
life.
|
|
E.coli
|
Should not exceed 1000 per 100 mL, calculated as the running
median of the most recent 5 consecutive samples taken at intervals of between
7 and 21 days.
|
Inland
Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and
other watercourses.
|
|
Should not exceed 0 per 100 mL, calculated as the running median
of the most recent 5 consecutive samples taken at intervals of between 7 and
21 days.
|
Inland
Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po
subzone A.
|
|
Colour
|
Waste discharge shall not cause the colour of water to exceed 30
Hazen units.
|
Inland Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D)
subzones and Tai Po subzone A.
|
|
Waste discharge shall not cause the colour of water to exceed 50
Hazen units.
|
Inland
Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and
other watercourses.
|
|
pH
|
To be in the range of 6.0 – 9.0
|
Inland Waters in Shing Mun (D, E, I) subzones and other
watercourses.
|
|
To be in the range of 6.5 – 8.5
|
Inland
Waters in Shing Mun (A, B, C, F, G, H) subzones, Lam Tsuen (C, D) subzones
and Tai Po (A, B,C) subzones.
|
|
Temperature
|
Not to exceed ± 2 0C daily temperature range due to
waste discharge
|
Whole
Zone
|
|
Suspended
solids (SS)
|
Waste discharges shall not cause the annual median of suspended
solids to exceed 25 milligrams per litre.
|
Inland
Waters in Shing Mun (D, E, I) subzones and other watercourses.
|
|
Waste discharges shall not cause the annual median of suspended
solids to exceed 20 milligrams per litre.
|
Inland
Waters in Shing Mun (A, B, C, F, G, H) subzones, Lam Tsuen (C, D) subzones
and Tai Po (A, B,C) subzones.
|
|
Dissolve
Oxygen (DO) within 2 m of the seabed
|
Not less than 4 mg/L or 40% saturation at any time.
|
Whole
Zone
|
|
5-day
biochemical oxygen demand (BOD5)
|
(a) Waste discharges shall not cause the 5-day biochemical
oxygen demand to exceed 5 milligrams per litre.
|
Inland
Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and
other watercourses
|
|
(b) Waste discharges shall not cause the 5-day biochemical
oxygen demand to exceed 3 milligrams per litre.
|
Inland
Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po
subzone A.
|
|
Chemical
oxygen demand (COD)
|
(a) Waste discharges shall not cause the chemical oxygen demand
to exceed 15 milligrams per litre.
|
Inland
Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po
subzone A.
|
|
(b) Waste discharges shall not cause the chemical oxygen demand
to exceed 30 milligrams per litre.
|
Inland
Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and
other watercourses
|
|
Ammonia
|
Waste discharges shall not cause the ammoniacal nitrogen in
waters of the subzone to exceed 0.5 milligram per litre at any time.
|
All
inland watercourses
|
|
Toxins
|
Waste discharges shall not cause the toxicants in water to
attain such a level as to produce significant toxic 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
|
Source: Statement
of Water Quality Objectives (Tolo Harbour and Channel 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 Tolo Harbour and Channel 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, wastewater from concrete batching and precast
concrete casting, wheel washing water, bentonite slurry, water for testing and
sterilisation 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 minimise 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
ETWB Technical Circular (Works)
No. 5/2005 Protection of Natural Streams/Rivers from Adverse Impacts Arising
from Construction Works
5.2.5.1
ETWB Technical Circular (Works)
No. 5/2005 provides an administrative framework to better protect all natural
streams/rivers from the impacts of construction works. The procedures
promulgated under this Circular aim to clarify and strengthen existing measures
for protection of natural streams/rivers from government projects and private
developments. The guidelines and precautionary mitigation measures given in the
ETWB TC (Works) No. 5/2005 should be followed as far as possible to protect the
inland watercourse at or near the Project area during the construction phase
5.2.6
Hong Kong Planning Standards
and Guidelines
5.2.6.1
The Hong Kong Planning
Standards and Guidelines (HKPSG), Chapter 9 (Environment), provides additional
guidelines against water pollution for sensitive use such as aquaculture and
fisheries zones, bathing waters and other contact recreational waters.
5.3.1
Study Area
5.3.1.1
According to Item 3.4.6.2 of
the Study Brief, the Study Area for this water quality impact assessment include
areas within 500 metres from the boundary of the Project and has included the Tolo
Harbour and Channel WCZ as designated under the WPCO (Cap. 358) and the water
sensitive receivers in the vicinity of the Project. The baseline condition of water bodies in the
Study Area have been established with reference to routine river and 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 “River
Water Quality in Hong Kong in 2019” and “Marine Water Quality in Hong
Kong in 2019” which contains the latest information published by EPD on
river and marine water quality.
5.3.2
Marine Water
5.3.2.1
The EPD monitoring data collected
in 2019 is summarised in Table
5.2 for Harbour
Subzone (Station TM2). Indicative
location of this monitoring station is shown in Figure 5.1. Descriptions of the baseline water quality
conditions provided in the subsequent section are based on the EPD’s report “Marine
Water Quality in Hong Kong in 2019”.
5.3.2.2
The overall WQO compliance rate
of the Tolo Harbour and Channel WCZ in 2019 was 79%, same as 2018. The compliance
rate for the DO WQO maintained at 57%, same as the last three years.
Furthermore, the Tolo Harbour and Channel WCZ also complied with the
bacteriological WQO for the secondary contact recreation subzone.
5.3.2.3
Tolo Harbour is a shallow and
semi-enclosed water body which is essentially landlocked. Such hydrological
setting often leads to natural stratification of the water column and the
associated lower bottom DO levels, particularly during the hot summer months
with heavy rainfall. As such, occasional non-compliance with the DO WQO may
take place during summer.
Table 5.2 Summary
Statistics of Marine Water Quality of Tolo Harbour and Channel WCZ Collected by
EPD in 2019
|
Parameters
|
Harbour Subzone
|
WPCO WQO
(in marine waters)
|
|
TM2
|
|
Temperature
(℃)
|
25.2
(17.8 - 32.0)
|
Not more than ±1℃ in daily temperature range
|
|
Salinity
|
30.0
(22.2 - 32.1)
|
Not to cause more
than ±3ppt change
|
|
Dissolved Oxygen
(mg/L)
|
Depth Average
|
6.4
(4.7 - 7.7)
|
Not less than 4 mg/L
|
|
Bottom
|
6.2
(4.3 - 8.0)
|
Harbour Subzone: Not less than 2 mg/L
Buffer Subzone: Not less than 3 mg/L
Channel Subzone: Not less than 4 mg/L
|
|
Dissolved Oxygen
(% Saturation)
|
Depth Average
|
91
(64 - 113)
|
-
|
|
Bottom
|
90
(65 - 123)
|
|
pH
|
8.1
(7.7 - 8.7)
|
Harbour Subzone: Not greater than ±0.5
from natural range
Buffer Subzone: Not greater than ±0.3 from natural range
Channel Subzone: Not greater than ±0.1
from natural range
|
|
Suspended Solids
(mg/L)
|
6.1
(2.0 - 14.0)
|
-
|
|
Ammonia-nitrogen
(mg/L)
|
0.042
(0.017 - 0.072)
|
-
|
|
Unionised Ammonia
(mg/L)
|
0.004
(<0.001 - 0.020)
|
-
|
|
Nitrite-nitrogen
(mg/L)
|
0.004
(<0.002 - 0.013)
|
-
|
|
Nitrate-nitrogen
(mg/L)
|
0.009
(<0.002 - 0.034)
|
-
|
|
Total Inorganic Nitrogen
(mg/L)
|
0.06
(0.03 - 0.12)
|
-
|
|
Total Nitrogen
(mg/L)
|
0.43
(0.15 - 0.64)
|
-
|
|
Ortho-phosphate
(mg/L)
|
0.005
(<0.002 - 0.014)
|
-
|
|
Total phosphorus
(mg/L)
|
0.03
(0.02 - 0.07)
|
-
|
|
Chlorophyll-a
(µg/L)
|
7.2
(2.2 - 12.0)
|
Harbour Subzone: Arithmetic mean not
to exceed 20µg/L
Buffer Subzone: Arithmetic mean not to
exceed 10µg/L
Channel Subzone: Arithmetic mean not
to exceed 6µg/L
|
|
E. coli
(cfu/100mL)
|
7
(<1 - 250)
|
Secondary Contact Recreation and Fish
Culture Subzones: Annual geometric mean not to exceed 610 cfu/100L
|
|
Faecal
Coliforms
(cfu/100mL)
|
38
(1 - 520)
|
-
|
Notes:
1.
Data source: EPD Marine Water
Quality in Hong Kong in 2019
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.
5.3.3
Inland Water
5.3.3.1
The water quality monitoring
results at stations in Shing Mun River, namely TR19 and TR19C, are shown in Table
5.3, and the
locations of the river water quality monitoring stations are shown in Figure 5.1. According to the EPD’s publication “River
Water Quality in Hong Kong in 2019”, the compliance rate of Shing Mun River
was 95% in 2019.
5.3.3.2
Shing Mun River, a major river
which has three main tributaries and runs through the densely populated Sha Tin
urban area, showed marked improvement during the past three decades because
factory discharges are controlled under the WPCO. Most of the domestic and
commercial premises in the urbanized town centre are connected to government
sewers. Under the Livestock Waste Control Scheme, livestock farms have ceased
operation. But the river is still affected by polluted discharges from a small
number of unsewered villages and expedient connections.
Table 5.3 Summary
Statistics of River Water Quality of Shing Mun River Collected by EPD in 2019
|
Parameters
|
Tai Wai Nullah
|
WPCO WQO
(in inland waters)
|
|
TR19C
|
TR19
|
|
Dissolved oxygen
(mg/L)
|
9.4
(8.4 – 11.1)
|
10.5
(8.7 – 13.0)
|
Waste discharges
shall not cause the level of dissolved oxygen to be less than 4 mg/L
|
|
pH
|
7.5
(7.2 – 7.8)
|
7.5
(7.1 - 8.3)
|
Inland Waters in Shing Mun (D, E, I)
subzones and other watercourses: 6.0 – 9.0
Inland Waters in Shing Mun (A, B, C,
F, G, H) subzones, Lam Tsuen (C, D) subzones and Tai Po (A, B,C) subzones:
6.5 – 8.5
|
|
Suspended solids
(mg/L)
|
1.9
(1.0 - 13.0)
|
2.8
(1.1 - 7.7)
|
Inland Waters in
Shing Mun (D, E, I) subzones and other watercourses: Annual median not to
exceed 25mg/L
Inland Waters in
Shing Mun (A, B, C, F, G, H) subzones, Lam Tsuen (C, D) subzones and Tai Po
(A, B,C) subzones: Annual median not to exceed 20mg/L
|
|
5-day Biochemical Oxygen Demand
(mg/L)
|
1.0
(0.6 - 6.8)
|
2.1
(0.9 - 5.9)
|
Inland Waters in Shing Mun (A, C, D,
E, H, I) subzones, Tai Po (B, C) subzones and other watercourses: 5-day
biochemical oxygen demand not to exceed 5mg/L
Inland Waters in Shing Mun (B, F, G)
subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A: 5-day biochemical
oxygen demand not to exceed 3mg/L
|
|
Chemical Oxygen Demand (mg/L)
|
6
(3 - 18)
|
8
(4 - 12)
|
Inland Waters in Shing Mun (B, F, G)
subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A: Not to exceed
15mg/L
Inland Waters in Shing Mun (A, C, D,
E, H, I) subzones, Tai Po (B, C) subzones and other watercourses: Not to
exceed 30mg/L
|
|
Oil & grease
(mg/L)
|
<0.5
(<0.5 – <0.5)
|
<0.5
(<0.5 - 0.6)
|
Not available
|
|
Faecal coliforms
(cfu/100mL)
|
14,000
(4,400 – 84,000)
|
82,000
(13,000 – 280,000)
|
Not available
|
|
E.
coli
(cfu/100mL)
|
1,400
(180 – 14,000)
|
3,400
(150 – 81,000)
|
Inland Waters in Shing Mun (A, C, D, E,
H, I) subzones, Tai Po (B, C) subzones and other watercourses: Not exceed
1000 per 100 mL
Inland Waters in Shing Mun (B, F, G)
subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A: Not exceed 0 per
100 mL
|
|
Ammonia-nitrogen
(mg/L)
|
0.042
(0.012 - 0.530)
|
0.037
(0.010 - 0.530)
|
Not more than 0.5 mg/L
|
|
Nitrate-nitrogen
(mg/L)
|
0.665
(0.470 - 1.600)
|
0.635
(0.520 - 1.100)
|
Not available
|
|
Total Kjeldahl Nitrogen (mg/L)
|
0.40
(0.18 - 1.20)
|
0.45
(0.31 - 0.88)
|
Not available
|
|
Ortho-phosphate
(mg/L)
|
0.016
(0.004 - 0.170)
|
0.007
(<0.002 - 0.130)
|
Not available
|
|
Total phosphorus
(mg/L)
|
0.03
(0.02 - 0.22)
|
0.03
(0.02 – 0.16)
|
Not available
|
|
Total sulphide
(mg/L)
|
<0.02
(<0.02 - <0.02)
|
<0.02
(<0.02 - <0.02)
|
Not available
|
|
Aluminium
(µg/L)
|
69
(<50 - 210)
|
61
(<50 - 122)
|
Not available
|
|
Cadmium
(µg/L)
|
<0.1
(<0.1 - 0.1)
|
<0.1
(<0.1 - 0.1)
|
Not available
|
|
Chromium
(µg/L)
|
<1
(<1 - 1)
|
<1
(<1 - 2)
|
Not available
|
|
Copper
(µg/L)
|
3
(<1 - 7)
|
3
(<1 - 4)
|
Not available
|
|
Lead
(µg/L)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
Not available
|
|
Zinc
(µg/L)
|
19
(<10 - 39)
|
17
(<10 - 31)
|
Not available
|
|
Flow
(L/s)
|
0.060
(0.024 – 0.180)
|
0.150
(0.045 – 0.384)
|
Not available
|
Notes:
1.
Data source: EPD River Water Quality in Hong Kong in 2019
2.
Data presented are in annual medians of monthly
samples; except those for faecal coliforms and E. coli which are in annual geometric means
3.
Figures in brackets are annual ranges
4.
cfu – colony forming unit
5. Values at or below
laboratory reporting limits are presented as laboratory reporting limits
6. Equal values for
annual medians (or geometric means) and ranges indicate that all data are the
same as or below laboratory reporting limits.
5.4.1.1
The Project is an inland
development, water sensitive receivers (WSRs) within 500m of the Project site
boundary and has been extended to include other areas that has a bearing on
water quality in the vicinity, are identified and listed at Table 5.4. Their indicative locations are shown in Figure 5.1.
Table 5.4 Water
Sensitive Receivers
|
ID
|
Location
|
Nature
|
Description
|
|
S1
|
From Needle Hill
|
Natural watercourse
|
Moderate to
fast flow rate. Relatively natural and undisturbed, with a short section near
Shing Mun Tunnel Road channelised.
|
|
S2
|
From Grassy Hill
|
Natural watercourse
|
Moderate to
fast flow rate.
|
|
S3
|
From Temple Hill, at the west of Shui
Chuen O Estate
|
Natural watercourse
|
Moderate flow
rate. Middle and upper sections were relatively natural and semi-shaded.
|
|
S4
|
Kwun Yam Shan Stream running from Temple
Hill, at the east of Shui Chuen O Estate
|
Natural watercourse
|
Moderate flow
rate.
|
|
S5
|
Sha Tin Tau Village
|
Channelised watercourse
|
Concrete
nullah with slow water flow.
|
|
S6
|
From Unicorn Ridge
|
Natural watercourse
|
Limited water
flow.
|
|
S7
|
Near Shui Chuen O Estate
|
Channelised watercourse
|
Concrete
nullah with shallow water
|
|
S8
|
Shing Mun Main River Channel
|
Channelised watercourse
|
Trapezoidal
channel with concrete bank and experienced tidal influence.
|
|
S9
|
Lion Rock Country Park
|
Country Park
|
-
|
5.4.1.2
Lower Shing Mun Reservoir is
located outside the 500m Project site boundary and is located at the upstream
of the Project. Hence, no water quality impacts are expected on the reservoir
and it is not identified as a WSR.
5.5.1
Construction Impacts
5.5.1.1
The potential sources of water
quality impact associated with the construction works would include:
·
Construction works at Shing Mun
Main River Channel;
·
Wastewater from general
construction activities;
·
Construction site run-off;
·
Construction works in close
proximity to inland water;
·
Sewage from construction
workforce;
·
Accidental spillage of
chemicals; and
·
Diversion of Sha Tin Tau Nullah.
5.5.2
Operation Impacts
5.5.2.1
Potential water quality impacts
associated with the operation phase would include:
·
Non-point source surface
run-off from new impervious areas; and
·
Hydrodynamic and water quality impact
on Shing Mun River.
5.6.1
General
5.6.1.1
As discussed previously, 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 and the
operation phase 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
Construction works at Shing Mun Main River
Channel
5.7.1.1
The construction of bridge
structures across Shing Mun River Channel would require the installation of new
bridge piers in Shing Mun Main River. The bridge piers installation would
involve pilling and excavation activities in Shing Mun Main River, which may
lead to elevated suspended solids (SS) levels and dispersion of SS to the
downstream section of the river if in contact with river water. However,
according to the proposed design, watertight steel casing and concrete block cofferdam
would be used to enclose all the piling and excavation works in river to
isolate the working area from the water. The piling works in river and any
associated river excavation works would be fully enclosed by the watertight
steel casing and cofferdam as discussed in Section 2.4.2. Concrete block cofferdam will be removed before the coming wet
season to allow river flow underneath the temporary steel platform avoiding
potential overflow onto the riverbanks of SMRC during wet season. The watertight steel casing will be lifted up
gradually from the riverbed during the concreting process of pile foundations,
which will be completely removed once the concrete piles have been hardened for
casting the pile cap on top in subsequent construction stage. Water pumps would
be used to collect any construction site runoff and ingress/seepage water
within the cofferdam/watertight steel casing. The collected construction site
runoff and ingress/seepage water would be diverted to the on-site wastewater
treatment facilities for treatment to satisfactory levels before discharge. The temporary steel platform will be
demolished, and riverbed will be reinstated during dry season upon completion
of pier construction and bridge deck.
Silt curtains should be deployed to completely enclose the
cofferdam/watertight steel casing/temporary steel platform prior to setting up
piling works, installation of cofferdam/watertight steel casing and demolition
of temporary steel platform. Silt
curtains should only be removed after completion of pilling works, removal of
cofferdam/watertight steel casing and demolition of temporary steel platform.
5.7.1.2
The construction activities for
bridge piers would be conducted by phases and only one cofferdam and watertight
steel casing would be installed in each period (refer to Figure 2.4.1 & Figure 2.4.2). Since the cross-section area of the river channel to be blocked
by the pier installation was anticipated localized and temporary, the change in
flow regime would be localized and any local water quality impact would expect
to be transient. As a result, the potential impact on water quality and
hydrology of Shing Mun River would be insignificant, no unacceptable water
quality would be expected if the mitigation measures detailed in Section 5.8 are implemented properly.
Wastewater from General Construction
Activities
5.7.1.3
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 minimised 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 5.8 are followed as far as practicable, the
potential water quality impacts associated with construction activities would
be minimal.
Construction Site Run-off
5.7.1.4
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.
5.7.1.5
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 inland waters. Site run-off may also wash away soil particles
that were contaminated by the construction activities and therefore cause water
pollution. Mitigation measures provided
in Section 5.8 can minimise potential impacts of site
run-off.
Construction Works in Close Proximity to
Inland Water
5.7.1.6
Construction activities in
close vicinity to the inland water courses may impact water quality due to the
potential release of construction wastewater. Construction wastewater are generally
characterized by high SS concentration and elevated pH. The implementation of adequate construction
site drainage and Best Management Practices as described Section 5.8 and provision of mitigation measures as
specified in ETWB TC(Works) No. 5/2005 “Protection of natural streams /
rivers from adverse impacts arising from construction works” as detailed in
Section 5.8,
it is anticipated that water quality impacts would be minimal.
Sewage from Construction Workforce
5.7.1.7
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. Potential water quality impacts upon the local drainage and
fresh water system may arise from these sewage effluents, if uncontrolled.
5.7.1.8
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 5.8 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
5.7.1.9
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. Groundwater
pollution may also arise from the improper use and storage of chemicals and
petroleum products within the site area 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 potential impacts could however be
mitigated by practical mitigation measures and good site practices (as given in
Section 5.8).
Water Pollution during Diversion of Sha Tin
Tau Nullah
5.7.1.10
The channelized watercourse Sha
Tin Tau Nullah would be diverted. The diversion of watercourses would involve excavation
and construction works. If not properly controlled, the excavated materials,
wastewater, chemicals or other construction materials may enter the watercourse
and give rise to water quality impact at the downstream area. To prevent
adverse water quality impact, the nullah diversion works should be scheduled in
dry season as far as practicable when the flow is low. Sequencing of works
should be duly planned to minimize water quality impacts. A temporary drainage
or permanent drainage at most downstream should first be established to
intercept and divert the upstream flow. Precautionary measures in Appendix D of
ETWB TC No. 5/2005, such as temporary isolation to other connected watercourse
using sandbags and silt curtains, shall be applied to prevent pollutants
running into the neighboring watercourse. Dewatering of the construction works
area shall be conducted prior to the construction works. Silt removal
facilities should be adopted to treat the wastewater from dewatering operations
prior to discharge. After completion of the construction works, the works area
shall be cleaned up before receiving any water flow or connecting to any
existing watercourse. Detailed mitigation measures are giving in Section 5.8.
5.7.2
Operation Phase
Surface Run-off
5.7.2.1
Potential water quality impact
may also arise from surface runoff discharge 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 upon
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. It is anticipated that with proper implementation of best
management practices as recommended in Section 5.8,
no adverse water quality impact from non-point source surface run-off is expected.
Hydrodynamic and Water Quality Impact on
Shing Mun River
5.7.2.2
The permanent bridge pier structure
in Shing Mun River has potential to obstruct the river flow. However, considering
that the bridge pier will be oriented in parallel with the existing bridge pier
of Lion Rock Tunnel Road, the cross-section area of the river channel to be
blocked by the pier installation was anticipated small, the change in flow
regime would be insignificant and any local water quality impact would expect
to be acceptable.
5.8.1
Construction Phase
5.8.1.1
Measures as listed below are
recommended to mitigate the potential water quality impacts from the land-based
construction works.
Bridge Piers in Shing Mun River
5.8.1.2
The pilling works should be
conducted by phases. The method and sequence of the proposed pier works in
Shing Mun River should be carefully designed so that wastewater and sediment
laden water generated from the pilling works would be confined and physically
separated from the watercourse.
5.8.1.3
All pilling and excavation
works in river should be fully enclosed by cofferdam/watertight steel casing. Cofferdam
and watertight steel casing should be constructed to isolate the construction
activities from the river water. The detail design of the cofferdams and
watertight steel casing will be conducted by the Contractor during the
construction phase to fulfil the requirements in DSD Technical Circular No.
14/200 “Temporary Flow Diversions and Temporary Works Affecting Capacity in
Stormwater System” for DSD approval in order to formulate feasible options
of these temporary structure.
5.8.1.4
Water pumps should be used to
collect any construction site runoff and ingress/seepage water within the
cofferdam and watertight steel casing. The collected construction site surface
runoff and ingress/seepage water should be diverted to the on-site wastewater
treatment facilities for treatment to satisfactory levels before discharged. There
is a need to apply to EPD for a discharge licence for discharging effluent from
the construction site under the WPCO. The discharge quality must meet the
requirements specified in the discharge licence and follow the TM-DSS.
5.8.1.5
To further minimize any adverse
water quality impact during the pilling and excavation works, silt curtains
should be deployed to completely enclose the cofferdam/watertight steel casing/temporary
steel platform prior to setting up piling works, installation of cofferdam/watertight
steel casing and demolition of temporary steel platform. Silt curtains should
only be removed after completion of pilling works, removal of cofferdam/watertight
steel casing and demolition of temporary steel platform. The Contractor should
be responsible for the design, installation and maintenance of the silt curtain
to minimize the impacts on water quality. The design and specification of the
silt curtains should be submitted by the Contractor to the Project Manage for
approval.
General Construction Activities and
Construction Site Run-off
Boring and Drilling Water
5.8.1.6
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
5.8.1.7
All vehicles and plants should
be cleaned before they leave a construction site to minimise 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. 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
5.8.1.8
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
5.8.1.9
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. All effluent discharged from the construction
site should comply with the standards stipulated in the TM-DSS. The following measures are recommended to
protect water quality, and when properly implemented should be sufficient to
adequately control site discharges so as to avoid water quality impact.
5.8.1.10
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, 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.
5.8.1.11
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 localised 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.
5.8.1.12
Construction works should be
programmed to minimise 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.
5.8.1.13
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.
5.8.1.14
Measures should be taken to
minimise 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.
5.8.1.15
Construction materials (e.g.
aggregates, sand and fill material) on sites should be covered with tarpaulin
or similar fabric during rainstorms.
5.8.1.16
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
5.8.1.17
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.
Construction Works in Close Proximity to
Inland Water
5.8.1.18
The practices outlined in ETWB
TC (Works) No. 5/2005 “Protection of natural streams / rivers from adverse
impacts arising from construction works” should also be adopted where
applicable to minimise the water quality impacts on any natural streams or
surface water systems. Relevant
mitigation measures from the ETWB TC (Works) No. 5/2005 are listed below:
·
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.
·
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 when carrying out
of the construction works.
·
Stockpiling of construction
materials and dusty materials should be covered and located away from any water
courses.
·
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.
·
Proper shoring may need to be
erected in order to prevent soil or mud from slipping into the watercourses.
Sewage Effluent from Construction Workforce
5.8.1.19
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.
5.8.1.20
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
5.8.1.21
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.
5.8.1.22
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.
5.8.1.23
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.
Diversion of Sha Tin Tau Nullah
5.8.1.24
During diversion of
watercourse, precaution measures shall be implemented to prevent adverse water
quality impact to the surrounding environment. Good site practices as described
in ETWB TC(Works) No. 5/2005 “Protection of natural streams/rivers from
adverse impacts arising from construction works” and ProPECC PN1/94 “Construction
Site Drainage” should be adopted where applicable. The following major
measures shall be implemented:
·
Cofferdams or impermeable structures
should be installed as appropriate to isolate the water flow from the
construction works area.
·
Dewatering or flow diversion
shall be conducted prior to the construction works to prevent water overflow to
the surrounding area.
·
Watercourse removal and flow
diversion should be conducted in dry season as far as practicable when the
water flow is low.
·
Water drained from the
watercourse shall be diverted to new/temporary drainage for watercourse
diversion.
·
Any excavated land-based
sediment from the diversion of watercourse shall be properly stored at bunded
areas away from any watercourses and covered with tarpaulin before transporting
out of the site. Detailed management of excavated land-based sediment is
discussed in Section 6.6.
Surface Runoff
5.8.2.1
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 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 Project to mitigate potential adverse water quality impacts.
Design Measures
5.8.2.2
Exposed surface shall be
avoided within the proposed development to minimise soil erosion. Development site shall be either hard paved or
covered by landscaping area where appropriate to reduce soil erosion.
5.8.2.3
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
5.8.2.4
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.
5.8.2.5
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
5.8.2.6
Good management measures such
as regular cleaning and sweeping of road surface / open areas is suggested to
be implemented by contractors. The road
surface / open area cleaning should also be carried out prior to occurrence of
rainstorm.
5.8.2.7
Manholes, as well as storm
water gullies, ditches provided among the development areas should be regularly
inspected and cleaned (e.g. monthly) by contractors. Additional inspection and cleansing should be
carried out before forecast heavy rainfall.
Hydrodynamic and Water Quality impact on
Shing Mun River
5.8.2.8
No significant change in flow
regime and water quality associated with the operation of the revised Trunk
Road T4 is anticipated. No adverse hydrodynamic and water quality impacts would
therefore be expected during the operational phase and no mitigation measures
are considered necessary.
5.9.1.1
According to Section 1, Revitalization of Tai Wai Nullah would be constructed and operated
concurrently with the Project and Widening of Tai Po Road (Shat Tin Section) would
also be operated in conjunction with the Project.
5.9.2
Construction Phase
5.9.2.1
The construction phase of
Revitalization of Tai Wai Nullah will overlap with that of the Project during
2024 to 2028. According to the Project Profile, construction site runoff, silts
arising from earthworks, oil and lubricants from construction vehicles and
plants as well as wastewater from general construction activities would cause
impacts on water quality. With proper adoption of mitigation measures and good
site practices, potential sedimentation and other water quality impacts to
areas downstream of the proposed works areas would be minimized. No unacceptable
water quality impacts were expected.
5.9.2.2
As no significant water quality
impact was expected from the Project and Revitalization of Tai Wai Nullah
during construction phase, adverse cumulative water quality impacts were hence
not anticipated.
5.9.3
Operation Phase
5.9.3.1
Revitalization of Tai Wai
Nullah would operate in concurrent with the Project. According to the Project
Profile, no adverse water quality impact would be expected. Nevertheless, water
quality of the Tai Wai Nullah would be enhanced by the proposed dry weather
flow intercepting system.
5.9.3.2
For the operation of Widening
of Tai Po Road (Sha Tin Section), major sources of water quality impacts were
expected to be paved area runoff and accidental spillage of chemicals from
loaded vehicles. Based on the EIA Report, no unacceptable water quality impacts
were expected if the mitigation measures provided are implemented properly.
5.9.3.3
As neither the Project nor the
concurrent projects were anticipated to generate significant water quality
impact during operation phase, adverse cumulative impacts were hence not
anticipated.
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 unacceptable 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 works area to ensure the recommended mitigation
measures are properly implemented.
5.12
Conclusions
5.12.1
Construction Phase
5.12.1.1
The key issues of the
land-based construction works include construction works at Shing Mun Main
River Channel and in close proximity to inland water, wastewater generated from
general construction activities, construction site runoff, sewage from
construction workforce, accidental spillage of chemicals and diversion of
watercourse. The potential water quality impacts could be mitigated and
controlled by implementing the recommended mitigation measures. Regular site
inspections should be undertaken routinely to inspect the construction
activities and works area to ensure the recommended mitigation measures are
proper implemented.
5.12.2
Operation Phase
5.12.2.1
The key issues of the operation
phase are the surface runoff generated from the new paved areas as well as the
potential hydrodynamic and water quality impact on Shing Mun River due to the
installation of permanent structures. Provided that the recommended mitigation
measures for the drainage system are properly implemented, the associated water
quality impacts are expected to be minimal and acceptable. No significant
change in flow regime and water quality associated with the permanent
structures is predicted, therefore, no unacceptable water quality impact on
Shing Mun River is expected.