5.1.1.1
This section presents the assessment on potential
water quality impacts arising from construction and operation of the Project,
which has been conducted in accordance with the criteria and guidelines as
stated in Annexes 6 and 14 of the Technical Memorandum on Environmental
Impact Assessment Process (EIAO-TM) as well as the requirements given in
Clause 3.4.6 and Appendix D of the EIA Study Brief (No. ESB-320/2019).
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 (WQOs)
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
cfu 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
cfu 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 ℃ 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)
|
Not less than 4 mg/L
or 40% saturation at any time.
|
Whole Zone
|
|
5-day biochemical oxygen
demand (BOD5)
|
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
|
|
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)
|
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.
|
|
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
|
|
Ammoniacal nitrogen
|
The un-ionised
ammoniacal nitrogen level should not be more than 0.5 milligram per litre at
any time.
|
Whole Zone
|
|
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 for
Watercourses (Tolo Harbour and Channel Water Control Zone)
5.2.3.1
The Water Supplies Department (WSD) has
specified a set of target seawater quality objectives for their flushing water
intakes. The list is shown in Table 5.2
below. These target objectives will be
applied at the points of seawater abstraction along the coastlines of Tolo
Harbour for flushing purpose.
Table 5.2 WSD’s
Target Seawater Quality Objectives at Flushing Water Intakes
|
Parameter
(in
mg/L unless otherwise stated)
|
WSD’s
Target Water Quality Limit at Flushing Water Intake
|
|
Colour
(Hazen Unit)
|
< 20
|
|
Turbidity
(NTU)
|
< 10
|
|
Threshold
Odour Number (odour unit)
|
< 100
|
|
Ammonia
Nitrogen (NH3-N)
|
< 1
|
|
Suspended
Solids (SS)
|
< 10
|
|
Dissolved
Oxygen (DO)
|
> 2
|
|
Biochemical
Oxygen Demand (BOD)
|
< 10
|
|
Synthetic
Detergents
|
< 5
|
|
E. coli (no./100mL)
|
<
20,000
|
5.2.4
Technical Memorandum on Effluent Discharge
Standard (TM-DSS)
5.2.4.1
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.
5.2.5
Professional Persons Environmental Consultative
Committee Practice Notes (ProPECC PNs)
5.2.5.1
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 in
order to control site runoff and wastewater generated during the construction
phase of the Project. 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. The ProPECC PN 1/94 provides good practice
guidelines for dealing with various types of discharge from construction sites.
5.2.5.2
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.
5.2.6
Hong Kong Planning Standards and Guidelines
(HKPSG)
5.2.6.1
The Hong Kong Planning Standards and Guidelines (HKPSG),
Chapter 9 (Environment), provides additional guidelines against water pollution
for sensitive uses such as aquaculture and fisheries zones, bathing waters and
other contact recreational waters.
5.2.7
ETWB Technical Circular (Works) No. 5/2005
Protection of Natural Streams/Rivers from Adverse Impacts Arising from
Construction Works
5.2.7.1
Environment, Transport and Works Bureau (ETWB)
Technical Circular (Works) [ETWB TC(Works)] No. 5/2005 "Protection of
natural streams / rivers from adverse impacts arising from construction
works" 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.
5.2.8
Drainage Services Department Practice Note No.
3/2021 Guidelines on Design for Revitalisation of River Channel
5.2.8.1
Drainage Services Department (DSD) Practice Note
(PN) No. 3/2021 “Guidelines on Design for Revitalisation of River Channel”
presents the essential environmental, ecological, and social considerations
that should be taken into account in the design of river channels. It presents
the Water Quality Goals for the designated water uses of the revitalised water bodies,
which are classified into 3 types of designated uses (Table 5.3
refers). The revitalised TWN belongs to
Type 1 of designated use as the water body would not be opened for public
access or physical contact due to safety reasons as described in Section 2. Water Quality Goals (WQGs) for Type 3 designated
use is applicable for the proposed water play features in the riparian amenity
area. A more stringent treatment standard for E. coli will be adopted, i.e. non-detectable in cfu/100 mL, calculated as
the geometric mean of all samples collected in one calendar year) in the
treated water (Section 5.7.2.7
refers) for the proposed water play features that in addition to fulfilling
the relevant WQGs for Type 3 designated water uses to enhance the environmental
performance of the revitalisation design .
Grey water reuse or rainwater harvesting has not been proposed under
this Project.
Table 5.3 DSD’s Water Quality Goals for Revitalisation
of Water Bodies based on Designated Water Uses
|
Type
|
Designated Use
|
Description
|
Example of
Water Friendly Activities
|
Water Quality
Goals
|
|
1
|
Aquatic Life and Aesthetic Value (including public access to the river
but primary / secondary contact to river water is not allowed)
|
Water provides a suitable condition for propagation of aquatic life.
Also, the water quality shall be of acceptable odour and appearance to
the public who participate in water friendliness activities
|
Riverside walkway
Public is allowed to access riverbed and stay close to the water body,
but direct contact of the water is not recommended
|
1) WQOs of the corresponding
WCZ
2) No objectionable odour
|
|
2
|
Secondary Contact Recreation
|
Water supports recreational activities, such as boating and paddling,
that may involve limited contact with water with no significant risk of water
ingestion
|
Boating, canoeing, rowing
|
1)
WQOs of the corresponding WCZ
2)
Geometric mean E.coli** ≤ 610 counts/100mL
3)
No objectionable odour
|
|
3
|
Primary Contact Recreation
|
Water is likely come in full body contact and/or incidental water
ingestion
|
Water play zone, interactive fountains, splash pad
|
1)
WQOs of the corresponding WCZ
2)
Geometric mean E.coli **≤ 180 counts/100mL
3)
No objectionable odour
|
Notes:
* For
types 1 and 2, if treated grey water/harvested rainwater (from sources like
roofs of buildings, permeable/non-permeable road pavement and surface runoff
from hard/soft landscaped areas) is used to replenish the river, reference
might may be made to Technical Specifications on Grey Water Reuse and Rainwater
Harvesting to specify the water quality.
** WQO of E.coli under
WPCO is calculated as annual geometric mean.
5.3.1
Assessment Area
5.3.1.1
In accordance with Clause 3.4.6.2 of the EIA
Study Brief (No. ESB-320/2019), the assessment area for this water quality
impact assessment includes areas within 500 m from the boundary of the Project
and covers Shing Mun River, Tolo Harbour and Channel Water Control Zone (WCZ)
as designated under the Water Pollution Control Ordinance (WPCO).
5.3.1.2
The baseline conditions of the water bodies in
the assessment area were established with reference to the 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 2020” and “Marine Water Quality in Hong
Kong in 2020”.
5.3.2
Marine Water
5.3.2.1
The water quality monitoring results at station
closest to the Project, namely TM2 within Harbour Subzone in Tolo Harbour &
Channel WCZ, is shown in Table 5.4. Full compliances with the WQO was recorded at
the selected EPD station TM2 for DO (depth average and bottom), chlorophyll-a
and E. coli in 2020.
Table 5.4 Baseline Water Quality Condition for
Tolo Harbour and Channel WCZ in 2020
|
Parameters
|
Harbour Subzone
|
WPCO WQO
(in marine waters)
|
|
TM2
|
|
Temperature
(℃)
|
26.3
(20.6 - 29.8)
|
Change
due to waste discharge not to exceed ±1℃ and not to exceed 0.5℃ per hour at any location
|
|
Salinity
(ppt)
|
29.9
(24.8 - 32.8)
|
Change
due to waste discharge not to be greater than ±3 ppt
|
|
Dissolved
Oxygen (DO)
(mg/L)
|
Depth
Average
|
6.1
(5.1 - 7.9)
|
Not
less than 4 mg/L in the water column (except for the bottom water within 2 m
from the seabed)
|
|
Bottom
|
6.2
(4.5 - 8.3)
|
Not
less than 2 mg/L within 2 m from the seabed
|
|
Dissolved
Oxygen
(%
Saturation)
|
Depth
Average
|
89
(73 - 112)
|
Not
available
|
|
Bottom
|
90
(70 - 120)
|
Not
available
|
|
pH
|
8.0
(7.7 - 8.3)
|
Change
due to waste discharge not to be greater than ±0.5 from natural range pH
units at any time
|
|
Secchi
Disc Depth
(m)
|
2.4
(1.6 - 3.4)
|
Not
available
|
|
Turbidity
(NTU)
|
3.1
(1.5 - 5.5)
|
Not
available
|
|
Suspended
Solids (SS)
(mg/L)
|
8.1
(1.4 - 17.0)
|
Not available
|
|
5-day
Biochemical Oxygen Demand
(BOD5)
(mg/L)
|
1.7
(0.8 - 2.6)
|
Not
available
|
|
Ammonia
Nitrogen
(mg/L)
|
0.045
(0.022 - 0.076)
|
Not
available
|
|
Unionised
Ammonia (UIA)
(mg/L)
|
0.003
(<0.001 - 0.005)
|
Not
available
|
|
Nitrite
Nitrogen
(mg/L)
|
0.004
(<0.002 - 0.010)
|
Not
available
|
|
Nitrate
Nitrogen
(mg/L)
|
0.039
(<0.002 - 0.215)
|
Not
available
|
|
Total
Inorganic Nitrogen (TIN)
(mg/L)
|
0.09
(0.03 - 0.27)
|
Not
available
|
|
Total
Kjeldahl Nitrogen
(mg/L)
|
0.50
(0.22 - 0.81)
|
Not
available
|
|
Total
Nitrogen
(mg/L)
|
0.54
(0.29 - 0.82)
|
Not
available
|
|
Orthophosphate
Phosphorus
(PO4-P)
(mg/L)
|
0.008
(0.002 - 0.026)
|
Not
available
|
|
Total
Phosphorus
(mg/L)
|
0.04
(<0.02 - 0.06)
|
Not
available
|
|
Silica
(as SiO2)
(mg/L)
|
1.48
(0.50 - 4.15)
|
Not
available
|
|
Chlorophyll-a
(µg/L)
|
5.8
(1.4 - 9.2)
|
Harbour Subzone: Not to exceed 20µg/L, calculated as a running
arithmetic mean of 5 daily measurements for any single location and depth
|
|
E.
coli
(cfu/100mL)
|
13
(<1 - 4500)
|
Not to
exceed 610 cfu/100mL for geometric mean of all
samples collected in one calendar year
|
|
Faecal
Coliforms
(cfu/100mL)
|
76
(6 - 32000)
|
Not
available
|
Notes:
1. Data source: EPD Marine Water Quality in
Hong Kong in 2020
2. Unless otherwise specified, data presented
are depth-averaged values calculated by taking the means of three depths:
Surface, Mid-depth, Bottom.
3. Data presented are annual arithmetic means
of depth-averaged results except for E.
coli and faecal coliforms that are annual geometric means.
4. Data in brackets indicate the ranges.
5. cfu – colony forming unit.
5.3.2.2
The monitoring results of key water quality
parameters indicate that the overall WQO compliance rate of the Tolo Harbour
and Channel WCZ in 2020 was 93%, markedly improved compared to 79% in
2019. Tolo Harbour consistently complied
with the bacteriological WQO for the secondary contact recreation subzone. Tolo Channel, however, was subject to a
natural hydrological phenomenon of water column stratification and associated
lower bottom DO level due to restricted water exchange with the open waters.
5.3.2.3
In the mid-1980s, with the implementation of the
Tolo Harbour Action Plan, which includes the control of livestock waste, the
provision and improvement of sewerage infrastructure, the export of treated
sewage effluent from Sha Tin and Tai Po Sewage Treatment Works outside Tolo
Harbour for discharging into Victoria Harbour via Kai Tak River, as well as the
extension of village sewerage in the catchment area, there has been a steady
improvement in water quality in Tolo Harbour in the past three decades.
5.3.3
Inland Water
5.3.3.1
Section of Shing Mun River, and its tributaries
including Tai Wai Nullah and Tin Sum Nullah are located within the assessment
area, the corresponding water quality monitoring results at stations, namely
TR19I, TR19A, TR19C, TR19 and TR20B, are shown in Table
5.5.
5.3.3.2
The water quality at Shing Mun River, a major river
which has three main tributaries and runs through the densely populated Sha Tin
urban area, showed marked improvement in the past three decades. The WQO compliance rate of Shing Mun River
was 90% in 2020.
5.3.3.3
The E. coli level at Shing Mun River Main
Channel (TR19I), the only watercourse currently used for secondary contact
recreation activities in Hong Kong, was rated "Low" (i.e. ≤610
counts/100mL) in 2020. And the
Annual Water Quality Index (WQI) was rated “Excellent” in 2020, while it was
rated “Good” in 2019.
5.4.1.1
In accordance with Clause 3.4.6.2 of the EIA
Study Brief (No. ESB-320/2019), the assessment area for this water quality
impact assessment includes areas within 500 m from the boundary of the Project
and covers Shing Mun River, Tolo Harbour and Channel WCZ as designated under
the WPCO and the water sensitive receivers (WSRs) in the vicinity of the
Project. WSRs within the assessment area
were identified with reference to Annex 14 of the EIAO-TM.
5.4.1.2
Key inland WSRs within 500 m from the boundary
of the Project and representative marine WSR in Tolo Harbour and Channel WCZ
were identified and are summarised in Table 5.6
below. Locations of the identified WSRs
are illustrated in Figure
5.1.
Table 5.6 Summary of Representative Water Sensitive Receivers
|
ID
|
Location
|
Nature
|
Description
|
|
Key Inland
WSR within 500 m from the boundary of the Project
|
|
WSR1
|
Shing Mun River
|
Channelised watercourse
|
Trapezoidal
channel with concrete bank and experienced tidal influence.
|
|
WSR2
|
Tai Wai Nullah
|
Channelised watercourse
|
Trapezoidal
channel with concrete bank and experienced tidal influence.
|
|
WSR3
|
Tin Sum Nullah
|
Channelised watercourse
|
Trapezoidal
channel with concrete bank and experienced tidal influence.
|
|
WSR4 / S1[1]
|
Heung Fan Liu, upstream of Tai Wai Nullah
|
Natural watercourse
|
Fairly
natural with rocky substrate with muddy bottom at its downstream. Litter were commonly found along
downstream.
|
|
WSR5 / S2[1]
|
Hillside adjacent to Shatin 400 kV substation
|
Natural watercourse
|
Fairly
natural with rocky substrate with occasional sandy bottom, and a clear and
small water flow.
|
|
WSR6 / S3[1]
|
Hillsdie west to Mei Chung Court
|
Natural watercourse
|
Relatively
natural substrate, its downstream is partly modified, and relatively fast
water flow rate.
|
|
WSR7 / S4[1]
|
Hillside north to Mei Chung Court
|
Natural watercourse
|
Relatively
natural substrate, its upstream is partly modified, and relatively fast water
flow rate.
|
|
WSR8 / S5[1]
|
Hillside north to Peak One
|
Natural watercourse
|
Relatively
natural substrate and relatively fast water flow rate.
Discharge into the existing drainage outlet of TWN
via underground drainage network, which is proposed to be partially
intercepted and be treated for the proposed water play features (Section 5.5.2.3 refers).
|
|
WSR9
|
Water gathering ground located upstream of Tai Wai Nullah
|
Water gathering ground
|
-
|
|
WSR10
|
Lower Shing Mun Reservoir located upstream of Tai Wai Nullah
|
Reservoir
|
-
|
|
Representative
marine WSR in Tolo Harbour and Channel WCZ
|
|
W1
|
WSD Flushing Water Intakes at Shatin
|
Water abstraction for flushing purpose
|
-
|
Note:
[1] Refer to Section 9.5 on full descriptions and locations of the natural
watercourses S1 – S5, i.e. WSR4 – WSR8.
5.4.1.3
The existing water gathering grounds are located
outside the boundary of the Project and upstream to the Project site. That is, the watercourses identified at or
near the Project site are running from the water gathering grounds towards the
Project site. No aboveground structure
would be constructed within the water gathering grounds. Thus, the water source of the existing water
gathering grounds is not expected to be affected during both construction and
operation phases of the Project.
5.4.1.4
The inland water in Shing Mun River and the
marine water in Tolo Harbour and Channel WCZ are designated under the WPCO as
secondary contact recreation subzone, which can be used for water sports and
water recreational activities (e.g. dragon boating, sailing, rowing etc.). The E. coli bacteria would be the
principle parameter for assessing the acceptability of using the inland and
marine water for water sports or secondary contact recreation activities with a
WQO of not exceeding 610 cfu/100 mL (calculated as the geometric mean of all
samples collected in one calendar year).
Apart
from the secondary contact recreation subzone, E. coli should not exceed
0 cfu per 100ml for inland waters in Shing Mun (B, F, G) subzones.
5.5.1.1
As detailed in Section 2, the
proposed revitalisation works involves mainly channel bed modification,
improvement of existing walkways and riparian public open spaces (which also
involves demolition and revamp of existing footbridge), construction of dry
weather flow interceptor (DWFI) system, landscaping and miscellaneous, as well
as construction of underground water
pumps near mid-stream of TWN for ecological enhancement associated water
retention and supplement. Desilting works at downstream tidal zone of TWN would be carried out at
the commencement and prior to the completion of the construction works to remove the silt
accumulated at the nullah, in addition to the routine maintenance desilting
works of smaller scale undertaken by DSD along TWN and by CEDD along Shing Mun
River under existing arrangement. The
Contractor should communicate and coordinate with DSD and CEDD to avoid
overlapping of the proposed desilting works at downstream tidal zone of TWN
during construction phase with DSD’s or CEDD’s routine maintenance desilting
works as far as practicable to minimise the potential water quality
impacts. The potential sources of
water quality impact associated with the construction works would include:
·
Wastewater from general construction activities;
·
Construction site run-off;
·
Construction works in close proximity to inland
water;
·
Construction works at TWN;
·
Sewage from construction workforce; and
·
Accidental spillage of chemicals.
5.5.1.2
Except for the flow diversion required for the
construction works within Tai Wai Nullah as detailed in Section 5.8.1.16, no alteration of
watercourses would be required.
5.5.2.1
The Project would not change the path of any existing flow or catchment of TWN. Due to ageing drainage systems and possible
expedient connection made in the past, polluted discharges from the existing
drainage outlets along TWN were observed.
The proposed DWFI system and specifc treatment wetlands under the
Project are expected to improve the water quality of the TWN by using the DWFI
system to intercept all of the
heavily polluted dry weather flows from the drainage outlets along the nullah
and discharging the dry weather flows to the existing sewerage system that
would eventually reach the relocated Sha Tin Sewage Treatment Works for treatment,
as well as by using the treatment wetlands to polish the remaining
comparatively less polluted and not-intercepted in-situ with TWN. As detailed in Section 2, the
introduction of general constructed wetland systems and provision of emergent
wetland planting (e.g. reed and other aquatic herbs) / mangroves to the channel
bed as greening and ecological enhancement measures are also expected to be
beneficial to the water quality of TWN.
As detailed in sewerage impact assessment in Section 8, the existing sewerage
system has enough capacity to cater for the additional dry weather flow
intercepted by the DWFI system. No
adverse water quality impact would be expected from operation of the proposed
DWFI system and ecological enhancement works.
5.5.2.2
After the revitalisation works, the nullah bed of
the engineering channel of TWN would be dry most of the time during non-rainy
days, except for the low flow channel in the middle (which is similar to the
existing condition), and the main water body of TWN, i.e. the low flow channel,
would not be opened for public access or physical contact due to safety reasons
as detailed in Section
2. Taking advantage of the
improved water qaulity of the revitalised TWN, the riparian area (nullah bed of
the engineering channel of TWN outside of the low flow channel) of midstream
TWN near Pok Ngar Villa would be opened for public access and be transformed
into a public open space that can provide communal spaces for recreation and
leisure activities to promote water friendliness (e.g. riparian walkway,
sightseeing of greening and ecological enhancement features, water play features equipped with UV
disinfection system). An additional
permanant public toilet facility (which would be operated and maintained by
Food and Environmental Hygiene Department like the existing public toilets in
Tai Wai) for the visitors to TWN is also proposed near Pok Ngar Villa. As detailed in sewerage impact assessment in Section 8, the existing sewerage
system has enough capacity to cater for the additional dry weather flow
intercepted by the DWFI system and additional sewage flow from the proposed
toilet. No water quality impact would be
expected from the operation of the additional toilet.
·
Non-point source surface run-off / irrigation
runoff from the proposed greening elements and landscaping;
·
Routine maintenance works for the drainage and
sewerage systems along TWN, including desilting along the nullah and minor
maintenance to the DWFI system, by the DSD to remove
excessive / accumulated silt, vegetation, debris and obstructions within the
channel (similar to the ones undertaken by DSD along TWN under existing
arrangement), which may lead to disturbance and re-suspension of river
sediments and thereby affecting water quality;
·
Potential changes in hydrodynamics properties
and hydrology; and
·
Water quality impact from riparian public open space
(including operation of UV disinfection system and water play features in
amenity area).
5.6
Assessment
Methodology
5.7.1
Construction Phase
Wastewater from
General Construction Activities
5.7.1.1
Wastewater generated from construction
activities, including general cleaning and polishing, wheel washing, dust
suppression and utility installation may contain high SS concentrations, as
well as a certain amount of grease and oil.
Potential water quality impacts due to uncontrolled wastewater discharge
can be avoided if construction and site management practices are implemented to
ensure that litter, fuels, and solvents do not enter the water
environment. 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
5.7.1.2
Potential pollution sources of site run-off may
include:
· Run-off
and erosion of exposed bare soil and earth, drainage channels, earth working
areas and stockpiles;
· Wash
water from dust suppression sprays and wheel washing facilities; and
· Fuel,
oil and lubricants from maintenance of construction vehicles and equipment.
5.7.1.3
During rainstorms, site run-off would wash away
the soil particles on unpaved lands and areas with topsoil exposed, if
any. The run-off is generally
characterised by high concentrations of SS.
Release of uncontrolled site run-off would increase the SS levels and
turbidity in the nearby water environment.
Site run-off may also wash away soil particles that were contaminated by
the construction activities and therefore cause water pollution.
5.7.1.4
Wind-blown dust would be generated from exposed
soil surfaces in works areas. It is
possible that wind-blown dust would fall directly onto the nearby water bodies
when a strong wind occurs. Dispersion of
dust within the works areas may increase the SS levels in surface run-off
causing a potential impact to the nearby sensitive receivers.
5.7.1.5
It is important that proper site practice and
good site management should be followed to prevent run-off with high level of
SS from entering the surrounding waters.
Best Management Practices (BMPs) in controlling construction site
discharges are recommended in Section
5.8 for
this Project. With the implementation of
BMPs to control run-off and drainage from the construction site, disturbance of
water bodies would be avoided and deterioration in water quality would be
minimal.
Construction
Works in Close Proximity to Inland Water
5.7.1.6
Landscaping
/ greening of the bankside as well as improvement of existing walkways
along TWN by the bankside (which also involves demolition and revamp of
existing footbridge) will be provided along TWN. Construction activities in close vicinity to
the inland watercourses may impact water quality due to the potential
uncontrolled release of construction waste and wastewater. Construction waste and wastewater are
generally characterised by high SS concentration and elevated pH. The implementation of adequate construction
site drainage and BMPs as described in Section
5.8 and
provision of precautionary measures / practices 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.
Construction
Works at Tai Wai Nullah
5.7.1.7
Construction
within TWN would involve channel bed modification (including
construction of energy dissipation structures), construction of DWFI system
along the nullah, construction of mid-stream underground water pipes along the nullah for water
supplement, construction of riparian walkway and amenity areas, and
desilting works at downstream tidal zone. The
existing concrete nullah of TWN will be modified and resurfaced with layer of
vegetation while the channel bed downstream of TWN’s broad-crested weir at its
confluence with Shing Mun River near Man Lai Court will be modifieid, with an
aim to improve the existing excessive accumulation of silts brought by tidal
influence due to uneven surface and flat gradient of the existing channel in
front of the broad-crested weir. Riparian walkway and amenity facilities will
also be constructed within TWN near its midstream section. Potential water quality impacts may be
generated by uncontrolled discharge of excavated materials, wastewater,
spillage and contaminants to the downstream receiving waters. Construction works within TWN would be divided
into sections and constructed in sequence starting from downstream TWN
first. For each section, these
construction works within the nullah, would be scheduled in dry season when the
flow is low. Site demarcation and flow
diversion will be implemented prior
to the construction works within channel to ensure that all the
construction works would be undertaken in dry conditions and physically separated
from the watercourses downstream to avoid potential water quality impacts upon
the downstream water quality. Together
with the implementation of precautionary and pollution control measures as
detailed in Section 5.8, the potential water
quality impacts would be well controlled.
Sewage
from Construction Workforce
5.7.1.8
During the construction of the Project, the
workforce on site will generate sewage effluent, which is characterised by high
levels of BOD, ammonia and E. coli counts. Based on the DSD Sewerage Manual, the sewage
production rate for construction workers is estimated at 0.35 m3 per
worker per day. Potential water quality
impacts upon the local drainage and freshwater system may arise from these
sewage effluents, if uncontrolled.
5.7.1.9
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 control
measures as recommended in Section
5.8 are
adopted as far as practicable, it is unlikely that sewage generated from
construction workforce would have a significant water quality impact.
Accidental
Spillage of Chemicals
5.7.1.10
The use of chemicals such as engine oil and
lubricants, and their storage as waste materials has the potential to impact
water quality if spillage occurs and enters adjacent water environment. Waste oil may infiltrate into the surface
soil layer, or runoff into the nearby water environment, increasing hydrocarbon
levels. The potential impacts could
however be avoided by practical precautionary measures and good site practices
(as given in Section 5.8).
5.7.2
Operational Phase
Surface Run-off /
Irrigation Run-off
Routine Maintenance Works
5.7.2.2
During the operational phase, similar to the
existing practices, regular maintenance works for the drainage and sewerage
systems along TWN, including desilting along the nullah and minor maintenance
to the DWFI system, would be carried out by the DSD to remove excessive silts,
debris and any obstructions to safeguard the hydraulic capacity of the
nullah. The
maintenance practices and frequency would be similar to the existing
maintenance works undertaken by the DSD.
Such small-scale routine maintenance works would require only light
mechanical equipment such as a small loader and/or a small crane truck. Hand-held equipment will be used for
vegetation removal along the nullah.
5.7.2.3
Maintenance desilting of the nullah should be
carried out on an annual basis during dry season (November to March) when the
water flow is low, except during emergency situations where the accumulated
silt would adversely affect the hydraulic capacity of the nullah or where
flooding risk is imminent, or when complaints on environmental nuisance
associated with the accumulated silt are received. Whilst possible changes to water quality may
be expected during the removal of excessive silt, vegetation, debris and
obstructions within the nullah, such as increases in SS due to disturbance of
nullah bed material and subsequently increased sedimentation onto the nullah
bed, it is expected that these changes will be short-term and localised within
the area of maintenance works and for a short distance downstream due to rapid
settling out of any disturbed nullah bed material that no unacceptable adverse
water quality impacts to WSRs downstream would be anticipated. Changes in SS concentrations would be
expected to be within the typical ranges experienced under ambient conditions
following heavy storms and increased sediment run-off. Therefore, no unacceptable water quality
impacts are anticipated to occur as a result of the small-scale maintenance
desilting works.
5.7.2.4
For the minor maintenance works for the DWFI
system, it is expected that any maintenance will only be undertaken on an
as-needed basis and frequent maintenance (i.e. monthly) will not be
required. Diversion
of the dry weather flow to the nearby sewerage system can be adopted during
maintenance of DWFI system so that the water quality at TWN would not be
adversely affected. Given the
infrequent maintenance requirements and the collected solid wastes will be
collected and disposed off-site properly, unacceptable water quality impact is
not expected.
Potential Changes in
Hydrodynamics Properties and Hydrology
5.7.2.5
During operation of the Project, DWFI system
will be in place along the nullah to intercept and convey the flow with heavily
polluted discharges from some of the drainage outlets along the nullah to Sha
Tin Sewage Treatment Works for treatment, which would inevitably lead to
reduced flowrate and amount of freshwater input into TWN and downstream
receiving water (Shing Mun River Main Channel).
With
the provision of treatment wetland for in-situ polishing of non-intercepted
flow with less polluted discharges as discussed in Section 2, the polished flow could serve as a part of
the environmental flow to sustain the ecological function of the flora and
fauna and habitat processes present within the revitalised TWN. Furthermore, with the incorporation of
water retention and replenish designs and ecological enhancement features (e.g.
wetland habitats created) within the nullah (see Section 2),
average flow rate will remain similar to baseline condition and no unacceptable impacts on hydrodynamics properties
and hydrology are anticipated.
Furthermore, with the modification of channel bed and realignment of low
flow channel at downstream TWN near its confluence with Shing Mun River near
Man Lai Court, the sedimentation in front of the broad-crested weir caused by
tidal influence and uneven surface and flat gradient of the existing channel in
front of the broad-crested weir, as well as the associated water quality issues
and environmental nuisance, would be greatly reduced.
5.7.2.6
In addition, as all the identified natural
watercourses within the assessment area are located at the upper catchment of
TWN (see Section
8), no changes in
hydrodynamic properties or hydrology are anticipated for the watercourses
during operational phase of the Project.
Riparian Public Open Space
5.7.2.7
Relatively clean freshwater discharge from
an existing drainage outlet of the nullah near Pok Ngar Villa, which receives
mainly clean river flow from upstream natural hillside
catchment north to Peak One (i.e. WSR8 / S5 in
Figure 5.1),
were identified through the pollution source
identification survey conducted under this Project. The clean freshwater discharge will be
partially intercepted and directed to the proposed UV disinfection system for
treatment and be used in the water play features (e.g. water spouts and
fountains) in the riparian amenity area (fully seperated from the water body of
the revitalised TWN). Based on
preliminary design, no additional stormwater collection facilities would be
required for the conveyance of freshwater for the proposed water play
features. A more stringent treatment
standard will be adopted for the proposed water play features that in addition
to fulfilling the relevant WQGs for primary contact recreation (type 3
designated use) as stipulated in DSD PN No. 3/2021 (Table
5.3 refers), E. coli
bacteria should be non-detectable (in cfu/100 mL, calculated as the geometric
mean of all samples collected in one calendar year) in the treated water. When the disinfection system is not under
normal operation, under maintenance or when the treatment standard as specified
in the post-revitalisation water quality monitoring
programme established and implemented by DSD is not compiled with (detailed in Section 5.8.3), the water play features will be
closed and the water will be directly discharged into the low flow
channel. Since UV treatment is a physical
treatment process and the intercepted freshwater discharge would be relatively
clean, no wastewater would be generated and no secondary water quality impact
would be anticipated from its overall operation.
5.7.2.8
The riparian walkway and amenity areas would be properly
designed to restrict public access / physical contact to the water body, i.e.
the low flow channel, and to ensure safe and appropriate usage of the riparian
public space and water play features (e.g.
elevated walkway design, fencing, provision of warnings / signage, deployment
of management personnel etc.). In
particular, it should be noted that neither the water from the revitalised
nullah with improved water quality or the water play features utilising treated
freshwater shall be used for human or animal
consumption, bathing or showering, food preparation / washing. As detailed in Section 2,
access to the riparian walkway and amenity areas [provided with water play
features] will be closed and evacuated in case of foreseeable flooding at the
nullah bed or under extreme weather conditions.
It is anticipated that with proper implementation of BMPs and the
adoption of channel management system by the DSD as detailed in Section
5.8, no adverse water
quality impact from the operation of the riparian public open space is
expected.
5.8.1
Construction Phase
Wastewater from General Construction
Activities and Construction Site Run-off
·
prevent or minimise the likelihood of pollutants
(generated from construction activities) being in contact with rainfall or
run-off; and
·
abate pollutants in the stormwater surface
run-off prior to the discharge of surface run-off to the nearby water bodies.
5.8.1.2
These principle objectives should be achieved by
implementation of the BMPs of mitigation measures in controlling water
pollution. The guidelines for handling
and disposal of construction site discharges as detailed in the ProPECC PN 1/94
should be followed, where applicable.
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 of the
inland and coastal waters, and when properly implemented should be sufficient
to adequately control site discharges so as to avoid water quality impacts.
Construction
Site Run-off
5.8.1.3
Surface runoff from construction sites should be
discharged into storm drains via adequately designed sand/silt removal
facilities such as sand traps, silt traps and sedimentation basins. Channels or earth bunds or sandbag barriers
should be provided on site during construction works to properly direct
stormwater to such silt removal facilities.
Perimeter channels should be provided on site boundaries where necessary
to intercept storm runoff 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.
5.8.1.4
Silt removal facilities, channels and manholes
should be maintained and the deposited silt and grit should be removed
regularly, at the onset of and after each rainstorm to prevent local
flooding. Any practical options for the
diversion and re-alignment of drainage should comply with both engineering and
environmental requirements in order to provide adequate hydraulic capacity of all
drains.
5.8.1.5
Construction works should be programmed to
minimise soil excavation works in rainy seasons (April to September). If soil excavation cannot be avoided in these
months or at any time of year when rainstorms are likely, for the purpose of
preventing soil erosion, temporary exposed slope surfaces should be covered
e.g. by tarpaulin, and temporary access roads should be protected by crushed
stone or gravel, as excavation proceeds.
Intercepting channels should be provided (e.g. along the crest / edge of
excavation) to prevent storm runoff from washing across exposed soil
surfaces. Arrangements should always be
in place in such a way that adequate surface protection measures can be safely
carried out well before the arrival of a rainstorm.
5.8.1.6
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.
5.8.1.7
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.
5.8.1.8
Open stockpiles of construction materials (e.g.
aggregates, sand and fill material) on sites should be covered with tarpaulin
or similar fabric during rainstorms. Measures should
be taken to prevent the washing away of construction materials, soil, silt or
debris into any drainage system.
5.8.1.9
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 runoff from getting into foul sewers. Discharge of surface runoff into foul sewers
must always be prevented in order not to unduly overload the foul sewerage
system.
Boring and
Drilling Water
5.8.1.10
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
5.8.1.11
All vehicles and plants should be cleaned before
they leave a construction site to minimise the deposition of earth, mud, debris
on roads. A wheel washing bay should be
provided at every site exit if practicable and wash water should have sand and
silt settled out or removed before discharging into storm drains. The section of construction road between the
wheel washing bay and the public road should be paved to reduce vehicle
tracking of soil and to prevent site runoff from entering public road drains.
Rubbish
and Litter
5.8.1.12
Good site practices should be adopted to remove
rubbish and litter from construction sites so as to prevent the rubbish and
litter from spreading from the site area.
It is recommended to clean the construction sites on a regular basis.
Acid
Cleaning, Etching and Pickling Wastewater
5.8.1.13
Acidic wastewater generated from acid cleaning,
etching, pickling and similar activities should be neutralised to within the pH
range of 6 to 10 before discharging into foul sewers.
Effluent
Discharge
5.8.1.14
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
sprays, 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
5.8.1.15
The precautionary measures / 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 precautionary measures / practices
from the ETWB TC (Works) No. 5/2005 include but not limited to the following:
·
The use of less or smaller construction plants
may be specified in areas close to the watercourses 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 watercourses.
·
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.
Construction Works at Tai Wai Nullah
5.8.1.16
As detailed in Section 5.7.1.7,
construction works within TWN would be divided into sections and
constructed in sequence and all construction works within the nullah should be
be scheduled in dry season when the flow is low. All the construction works should be
undertaken in dry conditions and physically separated from the watercourses
downstream. Precautionary measures in
Appendix D of ETWB TC No. 5/2005, such as temporary isolation to other
connected watercourse using concrete blocks, sandbag barriers or other
appropriate measures, shall be applied.
Site demarcation and flow diversion with physical barriers / temporary
drainage will be implemented prior to the construction works within
channel to ensure that all the construction works would be
undertaken in dry conditions and physically separated from the watercourses
downstream to avoid potential water quality impacts upon the downstream water
quality. Physical barriers (such as
concrete blocks/sandbags or other appropriate measures) with impermeable liners
will be deployed to confine the works area to maintain a dry condition within
and to prevent pollutants running into
the downstream waters; and depending on the site conditions, physical barriers
or temporary drainage would be established to intercept and divert the upstream
flow. 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. Details
of the containment structures, flow diversion pathway and water treatment
method should be provided by the Contractor to the Engineer for approval before
commencement of construction works for the Project. After completion of the construction works,
the works area shall be cleaned up before receiving any water flow or
connecting to any existing watercourse.
5.8.1.18
The pollution control measures for construction
works in close proximity to inland water and mitigation measures for general
construction activities as recommended in Section
5.8.1.1 to 5.8.1.15 should also
be implemented to avoid and minimise any potential water quality impacts from
construction within TWN. Regular site
checks should be conducted to ensure no adverse impact to TWN are induced by
the construction activities.
Sewage from Construction Workforce
5.8.1.19
No direct discharge of sewage to the stormwater
drains and inland water will be allowed.
Adequate and sufficient portable chemical toilets should be provided in
the works areas to handle sewage from construction workforce. A licensed collector should be employed to
clean and maintain 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 should be conducted to provide an
effective control of any malpractices and achieve continual improvement of
environmental performance on site.
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. The
Contractor is also recommended to develop management procedures for chemicals
used and prepare an emergency spillage handling procedure to deal with chemical
spillage in case of accident occurs.
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 for 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.
5.8.2
Operational Phase
Surface Run-off / Irrigation Run-off / Runoff from Riparian Public Open Space
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. DSD PN No. 3/2021
“Guidelines on Design for Revitalisation of River Channel” presents the
essential environmental considerations and maintenance and management
requirements for a revitalised river channel.
Design
Measures
5.8.2.2
Exposed surface shall be avoided within the site
to minimise soil erosion. The site shall
be either hard paved or covered by landscaping area and plantation where
appropriate.
5.8.2.3
The drainage system within the site should be
designed to cater for the runoff from 50 year-return-period rainstorm.
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 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 stormwater runoff.
Administrative
Measures
5.8.2.6 BMPs for storm water discharge and
management, as well as good administrative and management measures for riparian
public open spaces as detailed below are recommended for the Project to
mitigate potential adverse water quality impacts.
5.8.2.7
Good management measures such as regular
cleaning and sweeping of road surface / open areas should be followed. The road surface / open area cleaning should
also be carried out prior to occurrence of rainstorm. Sufficient
garbage collection unit / system should be established / maintained (Section 6 refers) and litters in
amenity areas or river should be regularly removed.
5.8.2.8
Good management practices should be adopted to
properly manage the water application rate and time during irrigation to minimise
chance of run-off. Use of fertilisers
and pesticides, if required, should be properly controlled, e.g. applications prior to forecasted heavy rain event should
also be avoided to minimise the potential for run-off of residual
fertiliser. Priority would be given to
remove infected/sick plantings over the use of pesticides. In addition, use of more specific, systemic and biodegradable
pesticide in low dosage is more preferred.
The use and handling of fertilisers and pesticides should follow
the Pesticide Ordinance and Code of Practice for the Safe and Proper Use of
Pesticides in Public Areas by AFCD, Food and Health Bureau (FEHD) and Leisure
and Cultural Services Department (LCSD).
5.8.2.9
Manholes, as well as storm water gullies,
ditches provided among the development areas should be regularly inspected and
cleaned (e.g. monthly). Additional
inspection and cleansing should be carried out before forecasting heavy
rainfall.
5.8.2.10
Channel that allows activities close to the
water should deploy a patrol team to identify unsafe behaviours and to
safeguard the public’s safety. The leisure facilities should also be provided
with instructions and safety warnings in conspicuous places.
5.8.2.11
The following management and maintenance
requirements on water quality control recommended in DSD PN No. 3/2021:
·
Regular sample and test water quality;
·
Facilities that allow primary contact
recreation (e.g. water play zone) should develop its standard operating
procedure in case of not meeting the Water Quality Goals (Mitigation measures during
operation phase for water play zone);
·
Regularly maintain the treatment unit to meet
its design treatment effectiveness;
·
Develop emergency response plan on how primary/secondary
contact recreation activities; and shall be suspended when water quality fails
to achieve the water quality goals i.e. mitigation measures during operation
phase for water play zone.
Routine Maintenance Works
5.8.2.12
During the operational phase, similar to the
existing practices, regular maintenance works for the drainage and sewerage
systems along TWN, including desilting along the nullah and minor maintenance
to the DWFI system, would be carried out by the DSD to remove excessive silts,
debris and any obstructions to safeguard the hydraulic capacity of the
nullah. The maintenance practices and
frequency would be similar to the existing maintenance works undertaken by the
DSD.
5.8.2.13
The following good site practices would be
included in planning for the maintenance works:
·
Maintenance desilting of the nullah should be
carried out on an annual basis during dry season (November to March) when the
water flow is low, with the exception of during emergency situations where the
accumulated silt would adversely affect the hydraulic capacity of the nullah or
where flooding risk is imminent, or when complaints on environmental nuisance
associated with the accumulated silt are received. Desilting should be carried out by hand-held
or light machinery at low tide.
·
Phasing of the works should be considered to
better control and reduce any impacts caused.
Where possible, works should be carried out along half width of the
drainage channel in short sections. A
free passage along the drainage channel is necessary to avoid forming stagnant
water in any phase of the works.
·
Containment structures (such as sandbags
barrier) should be provided for the desilting works area to facilitate a dry or
at least confined working area within the drainage channel.
·
The locations for the disposal of the removed
materials should be identified and agreement sought with the relevant
departments before commencement of the maintenance works. Temporary stockpile of waste materials should
be located away from the channel and properly covered. These waste materials should be disposed of
in a timely and appropriate manner.
·
Effective temporary flow diversion scheme should
be implemented and the generated wastes should be collected and disposed
off-site properly to avoid adversely affecting the water quality of the
drainage system.
5.8.3.1
Upon completion of revitalisation for TWN, water quality of TWN is anticipated
to be improved with the implmentation of the proposed DWFI system and treatment
wetland systems. A post-revitalisation
water quality monitoring programme, covering the water qaulity of the
revitalised TWN and the disinfected water for the proposed water play features,
would be established and implemented by the DSD, with an aim to assess the
compliance with the WQGs; to monitor long-term water quality trend; to
facilitate the emergency response plans for failing to achieve WQGs; and to
facilitate the development and implementation of operation and maintenance
plan. Maintenance and management requirements for TWN would be adjusted
accordingly based on the monitoring results following the operation and
maintenance considerations / guidelines stipulated in DSD PN No. 3/2021.
5.9
Cumulative Impacts
5.9.1
Potential Concurrent Projects
5.9.1.1
A number of potential concurrent projects have
been identified and their potential environmental cumulated impacts are
discussed in Section 2.8.
Based on the latest available information at the time of preparation of this
EIA Report, there are four projects potentially be constructed and operated
concurrently with the Project, including:
·
Box culverts along Chui Tin Street under
“Drainage Improvement Works in Sha Tin and Sai Kung;”
·
“Revitalisation of Tai Wai Nullah”;
·
“Revised Trunk Road T4”; and
·
Joint-user complex at Tsuen Nam Road, Tai
Wai.
5.9.2
Construction Phase
5.9.2.1
Based on the tentative construction programme of
potential concurrent projects as detailed in Section 2.8,
the construction phase of the Project would potentially overlap with that of
the box culvert construction under “Drainage Improvement Works in Sha Tin and
Sai Kung” during 2024 – 2029, “Revised Trunk Road T4” during 2024 – 2028; and
“Joint-user complex at Tsuen Nam Road, Tai Wai” during 2024 – 2029.
5.9.2.2
For “Drainage Improvement Works in Sha Tin and
Sai Kung” and “Joint-user complex at Tsuen Nam Road, Tai Wai”, while no
confirmed construction programme of these concurrent projects is available at
time of the preparation of this EIA, potential water quality impacts from these
concurrent projects are expected to
be localised and land-based, including construction site runoff, wastewater
from general construction activities, accidental spillage and sewage from
construction workforce. With proper
implementation of mitigation measures and good site practices, potential water
quality impacts to downstream areas in Shing Mun River Channel would be well
controlled. No unacceptable cumulative
water quality impacts from these concurrent projects would therefore be
anticipated. Nontheless, during the
detailed design stage, the contractor of this Project should be requested to
closely liaise with the contractors of these potential concurrent projects in
planning the interfacing works properly to further minimise any potential
cumulative impacts.
5.9.2.3
For “Revised Trunk Road T4”, the water quality key issues of this
concurrent project 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, which
could be mitigated and controlled by implementing the recommended mitigation
measures that no unacceptable water quality impacts were expected based
on the approved EIA report (AEIAR-231/2021).
In view that the construction works of the concurrent project
within the site area of overlapping with this Project would be the foundation
works for the Revised Trunk Road T4 viaducts, and that the construction works
along the nullah will not be undertaken at the entire work section at the same
time (see Section
2), the tentative
construction programme and works at the interface area between the two projects
could be arranged efficiently, e.g. scheduling works to be carried out during
dry season, through close liaison between DSD’s and CEDD’s contractors of this
Project and the concurrent project respectively in order to avoid construction
works of respective works contracts to be carried out concurrently at the same
interfacing areas and CEDD has agreed to include this requirement in the
respective works contract. With such arrangement in place,
cumulative construction environmental impacts, and water quality impacts upon
the downstream water body could be minimised.
For the construction of bridge piers within Shing Mun River under “Revised
Trunk Road T4 in Sha Tin”, the construction activities for bridge piers would
be conducted by phases and all pilling and excavation works in river would be
fully enclosed by cofferdam/watertight steel casing and with deployment of silt
curtains to completely enclose the cofferdam/watertight steel casing prior to
setting up piling works, hence, the potential water quality impacts could be
mitigated and controlled by implementing the recommended mitigation
measures. As such, no unacceptable
cumulative water quality impacts from these projects would be anticipated.
5.9.2.4
Based on the tentative construction programme of
potential concurrent projects as detailed in Section 2.8,
the construction of “Revitalisation of Fo Tan Nullah” would overlap with that
of the Project during 2024 to 2029. The
concurrent projects are located over 2km from this Project. Potential water quality impacts from this
concurrent project are expected to
be similar to this Project and localised that significant cumulative water
quality impacts would not be expected given the large separation distance. With
proper implementation of mitigation measures and good site practices, potential
water quality impacts to downstream areas in Shing Mun River Channel would be
minimised.
5.9.3
Operational Phase
5.9.3.1
The operation of box culverts under “Drainage Improvement
Works in Sha Tin and Sai Kung” does not constitute any elements that would be
water pollution sources and would not generate any new pollution load to the
catchment, no cumulative water quality impact would be expected from its
operation.
5.9.3.2
The nature of “Revitalisation of Fo Tan Nullah” is similar to
the Project that no adverse water quality impact would be anticipated with the
implementation of appropriate control measures and good site practices during
the operational phase. Furthermore,
water quality and hygiene of the nullahs would be improved by the proposed DWFI
system.
5.9.3.3
For the “Revised Trunk Road T4”, major sources
of water quality impacts were expected to be non-point source surface run-off
from new impervious areas; and·hydrodynamic and water quality impact on Shing
Mun River during operational phase.
Based on the approved EIA Report (AEIAR-231/2021), no unacceptable water
quality impacts from its operation would be anticipated provided that the
recommended mitigation measures are implemented properly.
5.9.3.4
For the operation of “Joint-user complex at
Tsuen Nam Road, Tai Wai”, provided that the site drainage would be properly
designed and adequate sewerage works would be provided for the development in
accordance with relevant guidelines (e.g. ProPECC PN 5/93) to avoid direct
discharge of sewage and wastewater to the nearby drainage system and inland
watercourses. No unacceptable water quality impact would be
anticipated.
5.10.1.1
With proper implementation of mitigation
measures described in Section 5.8, no adverse residual water quality
impact to nearby WSRs or downstream areas in Shing Mun River Channel is
expected from the construction or operation of this Project.
5.11
Environmental
Monitoring and Audit
5.11.1.2
While the Project is expected to improve the
overall water quality of TWN and environmental monitoring and audit for water
quality is not considered necessary for the operational phase under this EIA
study, as detailed in Section 5.8.3.1,
a post-revitalisation water quality monitoring programme to review compliance
with the Water Quality Goals as stipulated in DSD PN No. 3/2021 will be
establised and implemeneted by the DSD.
5.12.1
Construction Phase
5.12.1.1
The key issues of the land-based construction
works include construction works at and in close proximity to TWN / inland
water, wastewater generated from general construction activities, construction
site runoff, sewage from construction workforce and accidental spillage of
chemicals. The potential water quality
impacts would be avoided and minimised
by implementing the recommended pollution control measures. No adverse water quality impact during
construction phase would therefore be anticipated. Water quality monitoring is therefore not
considered necessary. Nonetheless,
regular weekly site audit during the construction phase is proposed to inspect
the construction activities and works area to ensure the recommended pollution
control measures are properly implemented.
5.12.2
Operational Phase
5.12.2.2
Despite the reduced environmental baseflow at
the nullah due to the interception of the flow with
polluted discharges by the DWFI system, owing to the natural sloping
gradient along TWN and the water retention and
replenish designs and ecological enhancement features (e.g. wetland habitats
created) within the nullah, average flow rate would remain similar to
baseline condition and no unacceptable impacts on hydrodynamics properties and
hydrology would be anticipated. No
adverse water quality impact during the operational phase would therefore be
anticipated.
5.12.2.3
While the Project is expected to improve the
overall water quality of TWN and environmental monitoring and audit for water
quality is not considered necessary for the operational phase under this EIA
study, a post-revitalisation water quality monitoring programme to review
compliance with the Water Quality Goals as stipulated in DSD PN No. 3/2021 will
be establised and implemeneted by the DSD.