5.
WATER
QUALITY IMPACT ASSESSMENT
5.1
Introduction
5.1.1
This Section presents the water quality impact assessment
for the construction and operational phases of the Project. Potential impacts have been identified
and their significance on the Water Sensitive Receivers (WSRs) evaluated. Mitigation measures are recommended,
where necessary, to reduce the potential water quality impacts in order to
control the residual impacts to acceptable levels.
5.2
Environmental Legislation, Policies, Standards and Criteria
5.2.1
The following legislation and relevant guidance or
non-statutory guidelines are applicable to the evaluation of water quality
impacts associated with the construction and operation of the Project:
·
Water Pollution Control Ordinance (WPCO);
·
Technical Memorandum for Effluents Discharged
into Drainage and Sewerage Systems, Inland and Coastal Waters (TM- ICW);
·
Environmental Impact Assessment Ordinance
(Cap. 499. S.16) and the Technical Memorandum on EIA Process (EIAO-TM), Annexes
6 and 14;
·
Practice Note for Professional Persons,
Construction Site Drainage (ProPECC PN1/94);
·
ETWB
Technical Circular (Works) No. 5/2005 Protection of Natural Streams/Rivers from
Adverse Impacts Arising from Construction Works
·
Drainage Services Department Practice Note
No. 3/2021: Guidelines on Design for Revitalisation
of River Channel; and
·
Hong Kong Planning Standards and Guidelines
(HKPSG)
Water Pollution Control Ordinance (WPCO)
5.2.2
The Water Pollution Control
Ordinance (WPCO) (Cap. 358) is the primary legislation for the control of
water pollution and water quality in Hong Kong. Under the WPCO, Hong Kong waters are
divided into 10 Water Control Zones (WCZs). Each WCZ has a designated set of
statutory Water Quality Objectives (WQOs).
The proposed Project is located within the Deep Bay WCZ. The WQOs designated for this zone are
thus relevant for assessing the water quality impacts from the construction and
operation of the Project (Table 5.1).
Table 5.1 Water Quality Objectives for Deep Bay Water Control Zones
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive Odour, Tints |
Not to be present |
Whole zone |
|
Visible foam, oil scum, litter |
Not
to be present |
Whole
zone |
|
Dissolved Oxygen (DO) within 2 m of the
seabed |
Not less than 2.0mg/L for 90% of samples |
Outer Marine Subzone excepting Mariculture Subzone |
|
DO within 1 m below surface |
Not less than 4.0mg/L for 90% of samples |
Inner Marine Subzone excepting Mariculture Subzone |
|
Not less than 5.0mg/L for 90% of samples |
Mariculture Subzone |
|
|
Depth-averaged DO |
Not less than 4.0mg/L for 90% of samples |
Outer Marine Subzone excepting Mariculture Subzone |
|
Not less than 4.0mg/L |
Yuen Long & Kam Tin (Upper and Lower)
Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground
Subzones and other inland waters of the Zone |
|
|
5-Day Biochemical Oxygen Demand (BOD5) |
Not to exceed 3mg/L |
Yuen Long & Kam Tin (Upper) Subzone, Beas
Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones |
|
Not to exceed 5mg/L |
Yuen Long & Kam Tin (Lower) Subzone and
other inland waters |
|
|
Chemical Oxygen Demand (COD) |
Not to exceed 15mg/L |
Yuen Long & Kam Tin (Upper) Subzone, Beas
Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground |
|
Not to exceed 30mg/L |
Yuen Long & Kam Tin (Lower) Subzone and
other inland waters |
|
|
pH |
To be in the range of 6.5 – 8.5, change due
to waste discharges not to exceed 0.2 |
Marine waters excepting Yung Long Bathing
Beach Subzone |
|
To be in the range of 6.5 – 8.5 |
Yuen Long & Kam Tin (Upper and Lower)
Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering
Ground Subzones |
|
|
To be in the range of 6.0 –9.0 |
Other inland waters |
|
|
To be in the range of 6.0 – 9.0 for 95%
samples, change due to waste discharges not to exceed 0.5 |
Yung Long Bathing Beach Subzone |
|
|
Salinity |
Change due to waste discharges not to exceed
10% of ambient |
Whole zone |
|
Temperature |
Change due to waste discharges not to exceed
2°C |
Whole zone |
|
Suspended solids (SS) |
Not to raise the ambient level by 30% caused
by waste discharges and shall not affect aquatic communities |
Marine waters |
|
Not to cause the annual median to exceed
20mg/L |
Yuen Long & Kam Tin (Upper and Lower)
Subzones, Beas Subzone, Ganges Subzone, Indus Subzone, Water Gathering Ground
Subzones and other inland waters |
|
|
Unionized Ammonia (UIA) |
Annual mean not to exceed 0.021mg/L as
unionized form |
Whole zone |
|
Nutrients |
Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae
or other aquatic plants. |
Inner and Outer Marine Subzones |
|
Total Inorganic Nitrogen (TIN) |
Annual mean depth-averaged inorganic nitrogen
not to exceed 0.7mg/L |
Inner Marine Subzone |
|
Annual mean depth-averaged inorganic nitrogen
not to exceed 0.5mg/L |
Outer Marine Subzone |
|
|
Bacteria |
Not exceed 610per 100ml, calculated as the
geometric mean of all samples collected in one calendar year |
Secondary Contact Recreation Subzones and Mariculture Subzones |
|
Should be zero per 100 ml, calculated as the
running median of the most recent 5 consecutive samples taken between 7 and
21 days. |
Yuen Long & Kam Tin (Upper) Subzone, Beas
Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones |
|
|
Not exceed 180per 100ml, calculated as the
geometric mean of the collected from March to October inclusive in one
calendar year. Samples should be taken at least 3 times in a calendar month
at intervals of between 3 and 14days. |
Yung Long Bathing Beach Subzone |
|
|
Not exceed 1000 per 100ml, calculated as the
running median of the most recent 5 consecutive samples taken at intervals of
between 7 and 21days |
Yuen Long & Kam Tin (Lower) Subzone and
other inland waters |
|
|
Colour |
Not to exceed 30 Hazen units |
Yuen Long & Kam Tin (Upper) Subzone, Beas
Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones |
|
Not to exceed 50 Hazen units |
Yuen Long & KamTin
(Lower) Subzone and other inland waters |
|
|
Turbidity |
Shall not reduce light transmission
substantially from the normal level |
Yung Long Bathing Beach Subzone |
|
Phenol |
Quantities shall not sufficient
to produce a specific odour or more than 0.05mg/L as C6H5OH |
Yung
Long Bathing Beach Subzone |
|
Toxins |
Should not cause a risk to any beneficial
uses of the aquatic environment |
Whole Zone |
|
Should not attain such levels as to produce
toxic carcinogenic, mutagenic or teratogenic effects in humans, fish or any
other aquatic organisms. |
Whole
Zone |
Technical
Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM- ICW)
5.2.3
All discharges during both the construction and operation
phases of the proposed development are required to comply with the Technical Memorandum for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
(TM-ICW) issued under Section 21
of the WPCO. The TM-ICW
defines acceptable discharge limits to different types of receiving
waters. Under the TM-ICW, effluents discharged into the
drainage and sewerage systems, inland and coastal waters of the WCZs are
subject to pollutant concentration standards for specified discharge volumes.
These are defined by the Environmental Protection Department (EPD) and are
specified in licence conditions for any new discharge within a WCZ
Environmental
Impact Assessment Ordinance (Cap. 499. S.16) and the Technical Memorandum on EIA Process (EIAO-TM), Annexes 6 and 14
5.2.4 The EIAO-TM was issued by EPD under Section 16 of the EIAO. Annexes 6 and 14 of the EIAO-TM provide general criteria and guidelines to be used in assessing water quality issues.
Practice Note for Professional Persons, Construction Site Drainage
5.2.5 The Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94) issued by EPD in 1994, also provide useful non-statutory guidelines on the management of construction site drainage and prevention of water pollution associated with the construction activities.
ETWB
Technical Circular (Works) No. 5/2005 Protection of Natural Streams/Rivers from
Adverse Impacts Arising from Construction Works
5.2.6
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
Drainage Services
Department Practice Note No. 3/2021: Guidelines on Design for Revitalisation of
River Channel
5.2.7
The Practice Note presents the essential environmental and
ecological considerations that should be taken into account
in the design of river channels.
Hong Kong Planning Standards and
Guidelines (HKPSG)
5.2.8
The Chapter 9 (Environment) of HKPSG, provides additional
guidelines against water pollution for sensitive uses such as aquaculture and
fisheries zones, bathing waters and other contact recreational waters.
5.3
Baseline
Water Quality Conditions
Hydrology
and Hydrodynamics
5.3.1
The existing watercourse TKL04 and TKL05 are located
at Ping Che/Ta Kwu Ling areas and within the Ganges
drainage basin which is part of the Shenzhen River catchment. TKL04 runs from east to west across
agricultural lands to the north of Ping Yeung Mural Village while TKL05 is a meandering
channel which runs from Ping Che Road at the upstream to the trained Ping Yuen
River at the downstream. TKL04 and
TKL05 are not subjected to tidal influence from the Deep Bay.
5.3.2
At present, stormwater runoff collected within Ping
Che catchment is discharged to Ping Yuen River via the existing watercourse
TKL04 and TKL05 which is eventually discharged to Deep Bay through Shenzhen
River. The surface runoff collected
by three channels/watercourses namely TKL02, TKL04 and TKL07 are discharged to
TKL05. The current flood protection standard of existing channel TKL04 and
TKL05 is less than 1 in 5 years return period. Areas around Ping Che are susceptible to
flooding during severe rainstorms due to inadequate capacity of existing
channel TKL04 and TKL05.
5.3.3
The upgraded Drainage Channels TKL02 and TKL07 have
flood protection standard of 1 in 10 years return period. As stated in Section
1.2, it is anticipated that the flood problem in Ping Che could be worsened
subsequent to the completion of the drainage
improvement works at Drainage Channel TKL02 and TKL07 as more surface runoff
will be conveyed to the existing TKL05. However, the situation will be improved
under this Project.
Baseline
River Water Quality
5.3.4
The proposed Project starts from Ping Che Road and
ends at the trained section of the Ping Yuen River (Figure 5.1). Water courses identified within the
Study Area (defined as 500 m from the boundary of the Project Site) include the
Shenzhen River, and Ping Yuen River.
Water Quality of Ping Yuen River
5.3.5
A routine river water quality monitoring programme has been undertaking in Hong Kong by the EPD
since 1986. Two monitoring
stations, GR1 and GR2, are located within and downstream of the Project site,
respectively (Figure 5.1).
5.3.6
A summary of river water quality data collected at stations
GR1 and GR2 of Ping Yuen River by EPD from 2018 to 2020 ([1])([2])([3]) is shown in Table 5.2.
Table
5.2 Summary of River Water Quality Monitoring Data collected by EPD River Water
Quality Monitoring Programme for Stations GR1 and GR2 of Ping Yuen River (2018
- 2020)
|
Parameter |
Unit |
WQO |
GR1 |
GR2 |
||||
|
2018 |
2019 |
2020 |
2018 |
2019 |
2020 |
|||
|
Dissolved oxygen (DO) |
mg/L |
≥4 |
8.4 (6.8-14.0) |
7.6 (4.7 - 8.7) |
6.7 (5.2 - 9.2) |
5.5 (3.1-7.4) |
5.4 (2.6 - 7.0) |
4.7 (3.2 - 6.6) |
|
pH |
- |
6.5-8.5 |
7.4 (6.9-8.6) |
7.2 (7.1 - 7.5) |
7.5 (7.2 - 7.7) |
6.8 (6.5-7.3) |
7.3 (7.0 - 7.7) |
7.3 (6.7 - 7.6) |
|
Suspended solids (SS) |
mg/L |
≤20 |
11 (5.4-69) |
12.0 (6.8 - 19.0) |
16.0 (6.4 - 22.0) |
9.5 (3.8-29.0) |
10.0 (8.0 - 25.0) |
9.7 (3.9 - 22.0) |
|
5-Day Biochemical Oxygen
Demand (BOD5) |
mg/L |
≤3 |
6.6 (1.6-26.0) |
5.4 (0.4 - 12.0) |
7.3 (2.8 - 20.0) |
4.2 (1.5-7.5) |
3.5 (0.2 - 9.5) |
3.8 (1.9 - 5.3) |
|
Chemical Oxygen Demand
(COD) |
mg/L |
≤15 |
16 (11-34) |
17 (13 - 25) |
20 (11 - 30) |
12 (7-21) |
16 (11 - 25) |
18 (9 - 23) |
|
Oil & Grease |
mg/L |
- |
<0.5 (<0.5-<0.5) |
<0.5 (<0.5 - <0.5) |
<0.5 (<0.5 - <0.5) |
<0.5 (<0.5-0.6) |
<0.5 (<0.5 - 2.1) |
<0.5 (<0.5 - <0.5) |
|
Faecal coliforms |
cfu/100mL |
- |
11,100 (1,300-81,000) |
12,000 (4,900 – 25,000) |
5,700 (570 – 21,000) |
13,000 (930-74,000) |
23,000 (3,600 – 330,000) |
4,300 (1,000 – 53,000) |
|
Escherichia coli (E.coli) |
cfu/100mL |
- |
4,100 (700-70,000) |
4,600 (580 – 13,000) |
14,000 (810 - 170,000) |
3,400 (380-16,000) |
4,900 (800 – 51,000) |
14,000 (2,400 – 100,000) |
|
Ammonia-nitrogen (NH3-N) |
mg/L |
- |
5.50 (0.31-32.00) |
4.30 (0.44 - 21.00) |
11.00 (0.52 - 30.00) |
5.30 (0.24-26.00) |
7.40 (0.30 - 31.00) |
7.70 (0.42 - 38.00) |
|
Nitrate-nitrogen |
mg/L |
- |
1.150 (0.900-2.500) |
1.020 (0.680 - 2.300) |
1.200 (0.32 - 2.20) |
0.865 (0.027-1.700) |
0.600 (0.055 - 1.500) |
0.385 (0.065 - 1.800) |
|
Total Kjeldahl
nitrogen (TKN) |
mg/L |
- |
6.40 (1.00-36.00) |
5.40 (0.80 - 21.00) |
13.00 (0.89 - 32.00) |
6.00 (0.40-28.00) |
9.15 (1.40 - 34.00) |
10.50 (0.59 - 40.00) |
|
Ortho-phosphate |
mg/L |
- |
0.480 (0.160-3.000) |
0.555 (0.120 - 2.100) |
0.660 (0.130 - 1.100) |
0.180 (0.067-0.730) |
0.230 (<0.002 - 0.620) |
0.240 (0.120 - 0.540) |
|
Total phosphorus |
mg/L |
- |
0.66 (0.32-3.10) |
0.72 (0.39 - 2.70) |
1.10 (0.16 - 2.00) |
0.36 (0.20-1.20) |
0.47 (0.18 - 2.00) |
0.68 (0.24 - 1.30) |
|
Sulphide |
mg/L |
- |
<0.02 (<0.02-<0.02) |
<0.02 (<0.02 - 0.02) |
<0.02 (<0.02 - <0.02) |
<0.02 (<0.02-<0.02) |
<0.02 (<0.02 - 0.02) |
<0.02 (<0.02 - <0.02) |
|
Aluminum |
μg/L |
- |
52 (<50-111) |
<50 (<50 - 222) |
<50 (<50 - 103) |
51 (<50-538) |
66 (<50 - 222) |
<50 (<50 - 125) |
|
Cadmium |
μg/L |
- |
<0.1 (<0.1-<0.1) |
<0.1 (<0.1 - 0.1) |
<0.1 (<0.1 - 0.1) |
<0.1 (<0.1-0.4) |
<0.1 (<0.1 - <0.1) |
<0.1 (<0.1 - <0.1) |
|
Chromium |
μg/L |
- |
<1 (<1-<1) |
<1 (<1 - <1) |
<1 (<1 - <1) |
<1 (<1-<1) |
<1 (<1 - <1) |
<1 (<1 - <1) |
|
Copper |
μg/L |
- |
3 (1-13) |
7 (2 - 20) |
7 (1 - 31) |
3 (<1-29) |
4 (<1 - 9) |
1 (1 - 3) |
|
Lead |
μg/L |
- |
<1 (<1-2) |
<1 (<1 - 2) |
<1 (<1 - <1) |
<1 (<1-20) |
1 (<1 - 25) |
<1 (<1 - 1) |
|
Zinc |
μg/L |
- |
<10 (<10-24) |
15 (<10 - 30) |
12 (<10 - 16) |
<10 (<10-80) |
18 (<10 - 29) |
11 (<10 - 37) |
|
Flow rate |
m3/s |
- |
0.020 (0.005-0.180) |
0.067 (0.012 - 0.266) |
0.117 (0.020 - 0.422) |
0.035 (0.015-0.300) |
0.114 (0.020 - 0.289) |
0.102 (0.064 - 0.289) |
Notes:
o Data presented are in
annual medians of monthly samples; except those for faecal
coliforms and E. coli which are in annual geometric means.
o Figures in brackets are
annual ranges.
o Values at or below
laboratory reporting limits are presented as laboratory reporting limits.
o Equal values for annual
medians (or geometric means) and ranges indicate that all data are the same as
or below laboratory reporting limits.
o Shaded values indicate
non-compliance of WQO.
* GR1 and GR2 are located within Ganges Subzone of
Deep Bay Water Control Zones.
5.3.7
The overall WQO compliance for River Ganges (Ping Yuen
River) has been decreased, sharing the compliance rate of 84% ,80% and 79% in
2018, 2019 and 2020 respectively. Level of 5-day Biochemical Oxygen Demand (BOD5)
has shown non-compliances with WQO at GR1 and at GR2 from 2018 to 2020. For
Chemical Oxygen Demand (COD), non-compliance with the WQOs was recorded at GR1
in 2018 and 2019 and GR2 in 2019 and 2020. E.
Coli levels for both stations between 2018 to 2020 has obtained high values
up to 14000 cfu/100ml. These parameters indicate that
the water in Ping Yuen River is potentially affected by pollution from the
livestock farms, unsewered villages and small industrial establishments in the
catchment. From 2018 to 2020, GR1 and GR2 maintained “Fair” in the Water
Quality Index (WQI).
5.4
Assessment
Methodology
5.4.1
The assessment area covers an area within 500 m of the
Project site boundary. The assessment has be extended
to include other areas such as stream courses and associated water systems,
ponds in the vicinity being impacted by the construction and/or operation of
the Project which include all water sensitive receivers identified in Section
5.5. Potential sources of water quality impact that may arise during the
construction and operation of the Project were analysed
and discussed. All the identified potential sources of water quality impact and
their impact significance was presented in Section 5.6. Mitigation
measures was then suggested in Section 5.8 to reduce any identified
adverse water quality impact.
5.4.2
The Project is located within the Deep Bay WCZ. Latest
Outline Zoning Plan (OZP) including OZP No. S/NE-TKL/14 (Ping Che and Ta Kwu Ling) and No.S/NE-TKLN/2
(Ta Kwu Ling North). The project is mainly
improvement works to the tributary sections of Ping Yuen River (River
Ganges-TKL04 and TKL05; and drainage improvement works at Ping Yeung Village,
constructing of road drainage system at Ping Che Road.
5.4.3
Site Visit has been conducted in March 2021, site
photos are recorded in Appendix 5.1.
5.5
Water
Sensitive Receivers
5.5.1 The
Water Sensitive Receivers (WSRs) that may be affected by changes in water
quality arising from the Project are identified in accordance with the EIAO-TM.
The water sensitive receivers (WSRs) include a number of fish
ponds, water courses, channelised watercourse,
conservation area, fishing ground and oyster cultural area. These WSRs (Figures 5.1)
and their approximate distances are given in Table 5.3.
Table 5.3 Water Sensitive
Receivers
|
ID |
WSRs |
Status |
Potential Impact from the Project |
|
WSR1 |
Ping
Yuen River (River Ganges) near Shenzhen
River |
Channelized watercourse |
Construction works will be undertaken to
connections with the proposed improvement works of downstream TKL05 |
|
WSR2 |
Shenzhen
River |
Natural watercourse |
Approx. 500 m away from the Project, no
direct impact |
|
WSR3 |
TKL04
Watercourse |
Natural watercourse |
To be widened |
|
WSR4 |
TKL05
Watercourse |
Natural watercourse |
To be widened |
|
WSR5 |
TKL02
Watercourse |
Channelized watercourse |
Direct upstream of the Project, minor
impact may anticipate |
|
WSR6 |
TKL07
Watercourse |
Channelized watercourse |
Direct upstream of the Project, minor
impact may anticipate |
|
WSR7 |
Watercourse
near Sing Ping Village |
Natural watercourse |
Minor impact may anticipate at the
connection of the WSR 10 and the construction works of TKL04 |
|
WSR8 |
Ping
Yuen River |
Natural watercourse |
Minor construction works will be undertaken
to connections between Ping Yuen River (WSR 8) and the improvement works of
downstream TKL04 |
|
WSR9 |
Watercourse
near Ping Yeung |
Natural watercourse |
Close proximity
to the Project, minor impact may anticipate |
|
WSR10 |
Area
of Fish Pond |
Fish Pond |
Over 9000m, no direct impact |
|
WSR11 |
Deep
Bay Oyster Culture Area |
Oyster Culture Area |
Over 16000m, no direct impact |
|
WSR12 |
Watercourse
near Ta Kwu Ling Farm |
Natural watercourse |
Minor impact may be anticipated at the
connection o the WSR 12 and the construction works
of TKL05 |
|
WSR13 |
Yuen
Leng Chai |
Conservation Area |
Over 3000m from the Project, no direct
impact |
|
WSR14 |
Hoo
Hok Wai |
Conservation Area |
Over 4000m from the Project, no direct
impact |
|
WSR15 |
Ha
Wan Tsuen |
Conservation Area |
Over 8000m from the Project, no direct
impact |
|
WSR16 |
Sam Po Shue |
Conservation Area |
Over 9000m from the Project, no direct impact |
|
WSR17 |
Mai
Po Marsh SSSI |
SSSI |
Over 11000m from the Project, no direct
impact |
|
WSR18 |
Inner
Deep Bay Ramsar Site |
Ramsar |
Over 10000m from the Project, no direct
impact |
5.5.2
Although waters from the Project Site will eventually
be discharged into the Deep Bay through the Shenzhen River, it is considered
unlikely that the Project will lead to any adverse water quality impacts to the
Conservation Area and ponds along Shenzhen River (Yuen Leng
Chai, Hoo Hok Wai, Ha Wan
Tsuen and Sam Po Shue), Mai Po Marsh SSSI, Inner Deep
Bay Ramsar Site near the Shenzhen River estuary, area of fish pond and oyster
culture area in Deep Bay given the large separation distance from the Project
Site as presented in Table 5.3 above.
5.6
Potential Sources of Impacts
Construction Phase
5.6.1
The main construction activities associated with the
Project that have the potential to cause water quality impacts involve the
following:
·
Temporary flow diversion
and excavation works;
·
Sewage discharges from
the construction work force;
·
Widening of Drainage
Channels;
·
Construction runoff and
drainage; and
·
Pollutants entering the
receiving waters due to accidental spillage /uncontrolled discharge from the
general construction activities.
Operation Phase
5.6.2
During the operation phase of the Project, potential water
quality impacts that may arise are identified as follows:
·
Maintenance and desilting
works within the proposed drainage channel to remove excessive silt,
vegetation, debris and obstructions within the drainage channel which may lead
to disturbance and re-suspension of river sediments and thereby affecting water
quality;
· Changes in hydrodynamic conditions, water quality and local erosion and sedimentation patterns during the operation of the drainage channel; and
· Potential effect of brackish tidal influence from Inner Deep Bay or Lower Ping Yuen River.
5.7
Impact Assessment
Construction Phase
Temporary Flow
Diversion and Excavation Works of the Existing Watercourse
5.7.1
The major construction activities will include temporary flow
division, sewage discharge from the construction workforce, construction runoff
and drainage and widening drainage channel. Temporary flow division will
reroute water from the upstream flow to a designed portion of the downstream to
allow for construction activities to take place in the channel of TKL04 &
TKL05. Temporary flow diversion and excavation works for the Project along the
entire TKL04 and TKL05 will be divided by segments in dry condition. It is
anticipated that the temporary flow diversion and excavation works will be
carried out in each segment of approximate 50m in length. Temporary flow
diversion will be undertaken before any excavation works within the existing
watercourse to ensure that the flow is not affected and to provide dry
condition for excavation. As the temporary flow diversion and excavation works
will be undertaken in dry conditions with segment division, it will not lead to
disturbance of the river bed material. Unacceptable water quality impacts are
thus not anticipated.
5.7.2
Overall, no unacceptable adverse impacts to water quality are
anticipated to occur as a result of the temporary flow diversion and excavation
works within the existing watercourse TKL04 and TKL05.
Sewage
Generated from the Construction Workforce
5.7.3
Sewage will be generated from the construction workforce,
site office’s sanitary facilities and from portable toilets. If not properly managed, these
wastewaters could cause adverse water quality impacts.
5.7.4
It is estimated that about 80 to 100 construction workers
will be involved in the construction of the Project during the peak
construction period. With a sewage generation rate of 0.15 m3/worker/day
(Table T-2 of EPD’s Report No.: EPD/TP 1/05 Guidelines for Estimating Sewage
Flows for Sewage Infrastructure Planning Version 1.0.), about 15 m3
of sewage will be generated per day. The sewage is characterised by high levels
of Biochemical Oxygen Demand (BOD), ammonia, E.coli
and oil/grease. An adequate number of portable toilets will be provided at the
Project Site to ensure that sewage from site staff is properly collected. No adverse impacts are envisaged
provided that the portable toilets are properly maintained by a contractor and
the collected sewage is disposed at the designated sewage treatment works.
Construction Runoff and Drainage
5.7.5
Runoff and drainage from construction activities may contain
elevated levels of suspended solids and possibly other contaminants (e.g. oil
and grease from machinery).
Potential sources of water pollution from site runoff include the
following:
·
Runoff and erosion of
exposed bare soil and earth and temporary stockpiles;
·
Release of cement
materials with rain wash;
·
Wash water from dust
suppression sprays and vehicle wheel washing facilities; and
·
Fuel, oil, and lubricants
from maintenance of construction vehicles and mechanical equipment.
5.7.6
Potential adverse water quality impacts may arise if
construction site runoff is allowed to spill outside
the construction site area and drain into the nearby streams, storm drain or
natural drainage without treatment.
The Best Management Practices outlined in ProPECC
PN 1/94 will be implemented to control site runoff and drainage during
construction phase. Precautionary measures relating to rainstorms as stated in
Appendix A2 of ProPECC PN 1/94 will also be
implemented to avoid water pollution due to site runoff during inclement
weather. With the proper implementation of appropriate mitigation measures,
good site practices and housekeeping as discussed in Section 5.7, unacceptable water quality impacts due to construction
runoff and drainage are not expected to occur.
Widening of Drainage Channels
5.7.7
As indicated in Section 2, the area for the proposed
widening and deepening of channels will be excavated. Upon completion of
excavation, fixing of reinforcement bars and concreting would be carried out on
site for the structures of the proposed channels.
5.7.8
During construction phase, there will be potential water
quality impact due to the alternation of watercourses. The existing streams at
TKL04 and TKL05 will be upgraded/widened.
5.7.9
The channel widening will involve excavation, formation of
embankments and temporary diversion of watercourses, which would probably lead
to temporary obstruction of flows. In addition, construction activities being
carried out along the channels without adequate mitigation measures may likely
cause erosion and lead to suspended solids elevation in the waterbody.
5.7.10
To minimize potential impacts on water quality during the
channel works for the proposed drainage improvements, the excavation works
would be carried out in dry condition. Construction would be strictly carried
out by land-based plant. Potential impacts on water quality would be minimised
by restricting the excavation works within an artificially enclosed dry section
of the river/stream.
5.7.11
De-watering of streams and sediment removal would be
conducted during channel widening works. Temporary access and maintenance
access along the proposed drainage channel will be constructed prior to all
construction works, and due consideration for the overland flow patterns and
the drainage connections will be given if flow diversion is necessary. As the
alignment of the proposed channel coincides with the existing stream, channel
diversions will be required to divert existing flow, in
particular when the construction coincides with the wet season (April to
September). Relevant requirements and stipulations from ETWB TCW No.5/2005 “Protection
of Natural Streams/Rivers from Adverse Impacts Arising from Construction Works"
will be complied to better protect the natural watercourses from the impacts of
construction works.
5.7.12
Works will commence from downstream
and proceed to upstream. Diversion of the channel flow is required before
excavation works start. Shallow water levels were noted in the existing
channels and dewatering will be required in trenches below channel inverts or
after heavy rainstorm. Adequate knowledge of subsurface conditions is required before
excavation. All excavated materials will be stockpiled outside the existing
stream/channel but within the defined works area, and temporarily stabilized to
prevent re-entry into the stream/channel. The stockpile should not create
adverse drainage impacts and not impede the overland flow patterns. The area
next to the proposed channel works shall be fully utilized as temporary
workplace and storage of construction plant. Where possible, the excavated
materials will be utilized in any backfilling. On balance, it is anticipated
that some fill will need to be imported to form the embankments.
5.7.13
The
proposed channel will be constructed in segments from downstream to upstream.
When the segment under construction requires stream diversion, sheet pile will
be installed both upstream and downstream of the existing stream to separate
the flow through the bypass channel so that the works area will remain dry for
later excavation and widening works. To reduce resumption of private land lots
for temporary construction works, where possible, all stream diversion and
widening works will be strictly confined within the site boundary.
5.7.14
Construction of embankment will be undertaken after
excavation works. Ramps shall also be required to provide a pathway for
machinery to utilize the excavated channel bottom for construction and
maintenance of the embankment and channel. Lining of channel bank will be
followed and the lining material to be used will be fully agreed with DSD.
5.7.15
With good implementation of appropriate working method
controls and good management practices, it is anticipated that unacceptable
water quality impacts would not arise at the identified WSRs during
construction phase. However, monitoring and audit of water quality during the
construction phase is recommended.
Accidental Spillage
5.7.16
Accidental spillage of liquid and chemicals stored on-site,
such as oil, diesel and solves etc., and illegal disposal of these chemicals
would cause soil contamination and adverse impact to the groundwater quality.
The Code of Practice on Packaging, Labelling and Storage of Chemical Wastes
released by the Waste Disposal Ordinance will be used as a guideline for
chemical waste handling. All chemicals disposal should comply with the
requirement imposed by the Waste Disposal Ordinance.
5.7.17
With proper measures to prevent accidental spillage, no
adverse impacts to water quality are anticipated due to accidental spillage of
liquid or chemicals.
Uncontrolled Discharge from
General Construction Activities
5.7.18
The following pathways of uncontrolled discharge and spillage
of contaminants from general construction activities may lead to adverse water
quality impacts to nearby WSRs:
· Uncontrolled
discharge of wastewater generated from concrete and vehicle washing;
· Uncontrolled
discharge of debris and rubbish such as packaging, construction waste and
refuse, etc.; and
5.7.19
Wastewater generated from concrete and vehicle washing may
contain elevated levels of suspended solids. Wastewater from concrete washing is also
noted with high pH value. Debris
and rubbish generated by the construction activities, if allowed to enter
nearby streams, storm drain or natural drainage, may cause blockages, water
quality impacts and hygiene issues.
5.7.20
The effects on water quality from the construction activities
are, however, likely to be minimal, provided that the site is well maintained
and that good construction practices and well
designed temporary drainage system and mitigation measures, as
described in Section 5.8, are
implemented properly.
Operation Phase
Maintenance Works
5.7.21
Regular maintenance would be necessary for the proposed
drainage channel in order to maintain the flow in the channel and its
structural integrity. Siltation
will generally be allowed to accumulate and removal of silt, vegetation growth,
debris and obstructions would only be carried out at locations where water flow
is impeded. Such small scale maintenance 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.
5.7.22
Whilst possible changes to water quality may be expected
during the removal of silt, vegetation growth, debris and obstruction, such as
increases in suspended solids due to disturbance of river bed material and
subsequently increased sedimentation onto the river bed, it is expected that
these changes will be short term and occur only within the area of maintenance
works and for a short distance downstream due to rapid settling out of any
disturbed river bed material.
Changes in suspended solids concentrations and sedimentation rate would
be expected to be similar to ambient conditions
following heavy storms and increased sediment run-off. With the implementation of the
precautionary measures in Section 5.8, no unacceptable water quality
impacts are anticipated to occur as a result of the small
scale maintenance works.
Water quality impacts to the water and ecological sensitive receivers
located downstream of the proposed drainage channel (Wetland Conservation Area
and Mai Po and Inner Deep Bay Ramsar Site near the Shenzhen River estuary) are
also not expected to occur.
Changes in Hydrodynamic Conditions
5.7.23
According to the Drainage Impact Assessment (DIA) of the
Project, by achieving the flood protection standard of 1 in 10 years after
implementation of the Project, water level within the Project Site will be
slightly lower than the water level before implementation in a 1 in 10 years
flooding event. It is thus
considered that implementation of the Project will be beneficial to the
hydrodynamics of the Project Site by improving the flood prevention
performance. Water level at the
downstream boundary of the proposed Drainage Channel TKL05 will be slightly
increased (i.e. 26mm) during the operation phase in a 1 in 10 years flooding
event. Therefore, implementation of
the Project is not expected to significantly affect the hydrodynamic conditions
downstream of the Project Site. As indicated in the DIA report, the associated
drainage sub-catchments are highlighted in red in the diagram below. Compared to
the total catchment area of the North district catchment, drainage
sub-catchments of the Project is relatively small.
Therefore, it is considered that the flow discharged from drainage
sub-catchments of the Project will have a limited impact to the hydraulic
condition. In addition, unacceptable water quality impacts to the downstream
WSRs due to the insignificant changes in hydrodynamic conditions caused by the
Project are not expected.
Changes in Water Quality
5.7.24
The operation of the proposed Drainage Channel TKL04 and 05
will not generate any new pollution load to the catchment. Instead, vegetation
re-established/planted along the gabion mattress at river bed
will help to remove dissolved and particulate contaminants through absorptive,
filtration and biological mechanisms. The water quality pollutants (e.g. SS,
BOD and COD) are expected to be reduced. In addition, it is expected that foul
odour of polluted water and river bed material during
low flow periods would be alleviated with the improved flow conditions and
removal of river bed material during channel construction and operation. Since
the Project will not induce additional discharge or pollutants from the
Project, there will not be changes on downstream salinity profile nor effect on
aquatic organisms. It is thus anticipated that the Project will not cause any
significant adverse changes to water quality thus impacts are not expected
during the operation phase.
5.7.25
Long term reduction of pollution load into the channels is
necessary to improve the water quality in the proposed Drainage Channel TKL04
and TKL05. It is expected that the
water quality of the drainage channel can be improved by the continuous
enforcement of Livestock Waste Control Scheme which will regulate discharge of
livestock waste into the drainage channel.
In addition, the existing watercourse TKL05 is currently receiving some
domestic waste discharge. Provision
of sewers connecting the village households to treatment works will thus lead
to improvement of water quality of the proposed Drainage Channel TKL05. Such provision of public sewers to the
unsewered villages is being implemented under the North District Sewerage
Master Plan.
Change in Sediment Deposition and Erosion Pattern
5.7.26
The improved flow condition (i.e. higher flow rate of runoff)
in the proposed Drainage Channel TKL04 and TKL05 may alter the pattern of
sediment deposition and erosion within the drainage channel and along the
downstream section of Ping Yuen River and Shenzhen River. However, as regular maintenance works
will be undertaken within the proposed drainage channel and at the downstream
sections to remove excessive sediments (regular maintenance
works will be undertaken by DSD at these downstream sections with some
hand-held tools which are not within the scope of the Project), it
is not anticipated that the Project will lead to any adverse water quality
impacts within the Project Site and along the downstream section of Ping Yuen
River and Shenzhen River by altering sediment deposition and erosion
patterns. It is also not expected
that the Project will lead to any unacceptable water quality impacts at the
Wetland Conservation Area and Mai Po and Inner Deep Bay Ramsar Site since these
areas which are susceptible to changes in sediment deposition and erosion
pattern are in considerable distance from the proposed Drainage Channel TKL04
and TKL05 (i.e. >4, >11 and >10 km, respectively). Therefore, we
expect same/similar scale of upstream water volume (i.e. in the unit of “m3”)
discharging into the channel. After improvement works, the cross-section is
expected to be larger, hence the water flow (i.e. in the unit of “m3/s”)
shall be decreased. The drainage velocity will be slightly decreased with
implementation of drainage improvement works due to wider cross-sections.
5.7.27
Bottom sediment re-suspension will be alleviated because of
the decreased flow. Sediment erosion would be substantially reduced, which lead
to reduction of drainage maintenance desilting frequency and minimize the potential
water quality impacts which may arise from maintenance desilting
activities. Sedimentation rate is a function associated with densities
of the particle and water, effective particle diameter and dynamic
viscosity (Stokes Law). Thus, the change of flow regime will
not change the sedimentation rate significantly.
Potential effect of brackish tidal influence
5.7.28
As the invert level of the proposed channels are over 3.5m,
which is higher than the highest predicted tide level at Tsim
Bei Tsui (<3.5m) and thedownstream Invert level is
+4.8mPD. Therefore, the effect of brackish tidal influence from Inner Deep Bay
or Lower Ping Yuen River is not expected. Mitigation measures such as tidal
barriers / flow management devices are therefore considered not necessary.
5.8
Mitigation Measures
Construction
Phase
5.8.1
Potential impacts on water quality as a result of
construction activities of the Project, including temporary flow diversion,
excavation works within the existing watercourse, sewage generation from
workforce, construction runoff and drainage, unplanned accidental spillage and
uncontrolled release of pollutants have been assessed in Section 5.7 above. The
following section describes the mitigation measures proposed to alleviate water
quality impacts during construction of the Project.
5.8.2
The contractor should comply with the Water Pollution
Control Ordinance (WPCO) and its
subsidiary regulations. The
contractor should carry out works in such a manner as to minimise adverse
impacts on the water quality during execution of the works. In particular, the contractor should
arrange his method of working to minimise the effects on the water quality
within and outside the site and on the transport routes.
5.8.3
Best Management Practices should be implemented in
controlling water pollution during the construction phase. The contractor
should follow the practices, and be responsible for the design, construction, operation
and maintenance of all the mitigation measures below and as specified in ProPECC PN 1/94 – Construction Site Drainage. In particular, the contractor should
submit and implement an Water Pollution Control Plan (as part of the Environmental
Management Plan (4), thereafter called
“the Plan”) which should incorporate details of the mitigation measures
recommended below to reduce water quality impacts arising from construction
works. There is also need to apply to the EPD for a discharge licence for
discharge of effluent from the construction site under the WPCO. All discharges
during the construction phase of the Project should comply with the Technical Memorandum for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
(TM-ICW) issued under the WPCO.
5.8.4
For construction works in the vicinity of natural rivers and
streams, the contractor should follow the recommendations given in ETWB TC (Works) No. 5/2005-
Protection of Natural Streams/Rivers from Adverse Impact Arising from
Construction Works, including but not limited to:
·
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.
·
Adequate lateral support
may need to be erected in order to prevent soil or mud from slipping into the
watercourses.
Temporary
Flow Diversion and Excavation Works of the Existing Watercourse
5.8.5
The following good practices should apply
at all times during excavation works:
·
Excavation within the
existing watercourse TKL04 and TKL05 should be carried out in dry
conditions. The dry excavation
condition could be created with temporary flow diversions as described in
detail in Section 5.7.
·
The excavated material, especially
river bed material, should be temporary stored in the
stockpile areas for dewatering by natural ventilation. Runoff from these stockpile areas should
be collected for treatment by sedimentation with the addition of coagulant. The treated water should be reused on
site for water spraying or wheel washing.
·
The dried/dewatered
excavated material should be reused on-site as backfilling material, as far as
practicable.
Sewage
Generated from the Construction Workforce
5.8.6
Domestic sewage/wastewater generated by workforce on-site
should be collected in a suitable storage facility such as portable chemical
toilets. An adequate number of
portable toilets should be provided during the construction phase. These toilets should be maintained in a
state that will not deter the workers from using them. The collected sewage/wastewater should
be discharged into the foul sewer or transferred to the Government sewage
treatment works by a licensed collector. Other measures, such as providing
notices at conspicuous locations, regular site audit etc., would be conducted.
Widening of Drainage Channels
5.8.7
Due to the characteristics of narrow width and small water
flow of the existing channel, the excavation should be carried out in dry
condition (even in wet season) by diverting the stream flow from upstream by a
temporary drainage channel with a temporary sheetpiles,
earth bund or barrier; so that the works area will remain dry for later
excavation and widening works.
5.8.8
The temporary drainage channel would be removed when the
construction works are completed or the temporary
diversion is no longer required. Although flooding of the proposed contaminant
section seldom occurs in dry season, the excavation would be considered to
suspend when flood water enters the containment and causes leakage of runoffs
to stream water.
5.8.9
After dewatering of the streams, the sediments should be
allowed to dry before excavation (yet still maintain a moist state to avoid
dust nuisance). This will facilitate excavation of the sediments and also minimize the risk of drained water flowing back
into watercourses or diversion channels as the sediment is handled. Where time
or weather constraints require handling of wet sediment, care should be taken
in the removal of sediment and the storage area should be bunded to prevent
silty runoff entering watercourses. Given its small quantity, all excavated
sediment should be reused on-site as backfilling material.
5.8.10
To further minimize the leakage and loss of sediments during
excavation, tightly sealed closed grab excavators should be employed in river
sections where material to be handled is wet. Where material is dry and in
non-river sections, conventional excavations can be used.
5.8.11
Excavated sediment will likely be temporarily stored on-site
for reuse as backfilling material. This should be stored in a bunded area and
covered at any time to avoid inadvertent release of silts and suspended solids
to nearby water bodies.
5.8.12
Regular monitoring of suspended solids, pH and turbidity
should be conducted during excavation works. Any exceedance of water quality in
the nearby water bodies caused by inadvertent release of site runoff should be
rectified in accordance with EM&A programme for this Project.
Construction
Runoff and Drainage
5.8.13 Good construction site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as practicable in order
to minimise surface runoff and the chance of erosion, and
also to retain and reduce any suspended solids in surface runoff prior
to discharge. These practices include the following:
·
Prior to discharge of
site runoff into the nearby water bodies, site runoff should be treated via
sand/silt removal facilities such as sand/silt traps or sedimentation
facilities on-site to remove sand/silt particles and to meet the discharge
standards of the TM-ICW under the WPCO. The design of sand/silt
removal facilities should be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities
and erosion and sediment control structures should be
inspected regularly and maintained to confirm proper and efficient operation at
all times during construction phase and particularly before and after
rainstorms. Deposited silt and grit
should be removed regularly.
·
Appropriate surface
drainage should be designed and provided, where necessary. In particular, surface runoff should be
collected along the river banks and be diverted to
sedimentation tank/pond before discharge into the river.
·
The precautions to be
taken at any time of year when rainstorms are likely together with the actions
to be taken when a rainstorm is imminent or forecasted and actions to be taken
during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94 and
should be followed.
·
Oil interceptors should
be provided in the drainage system where necessary and regularly emptied to
prevent the release of oil and grease into the stormwater drainage system after
accidental spillages.
·
Temporary and permanent
drainage pipes and culverts provided to facilitate runoff discharge should be
adequately designed for the controlled release of storm flows. The design of
permanent drainage pipes should follow the guidelines provided in ProPECC PN 5/93 Drainage plan subject to comment
by the Environmental Protection Department.
·
The temporary diverted
drainage should be reinstated to the original condition when the construction
work has finished or when the temporary diversion is no longer required.
·
Construction materials
stored on-site should be covered with tarpaulin sheets to prevent from being
washed away. Other measures such as
containment bunds, sand bags and temporary drainage
should also be considered, especially during wet season or heavy rainstorm
events. Such runoff could be
minimized through reduction of flat exposed open area, and through diversion
and collection via temporary drainage system on the periphery of the Project
site.
5.8.14 Site
runoff during concrete curing period should be carefully contained and diverted
to treatment facilities on-site to prevent it from entering existing
watercourses directly. Adjustment
of pH should be carried out by adding a suitable neutralising reagent to the
wastewater collected.
5.8.15 Any
exceedance of pH level against acceptable range in WQO in the nearby
watercourse should be closely monitored during the construction phase. Such situation should be rectified in
accordance with the EM&A programme for this Project. Adoption of lesser or
smaller construction plants would be proposed to reduce disturbance to the
channel bed and to the nearby sensitive receivers; and the use of concrete or
the like should be avoided or minimized.
Accidental Spillage / Uncontrolled Discharge
from General Construction Activities
General Construction Activities
5.8.16 The
following good site measures should be implemented to prevent uncontrolled
discharge or spillage from the general construction activities:
·
Site office, workshop and
depot should be located on hard standing grounds with provision of temporary
drainage channel and sedimentation tanks with oil interceptor if required. The oil interceptor should be inspected
regularly to prevent blockage and oil overflow during storm events.
·
Debris and refuse
generated on-site should be collected, handled and disposed of properly to
avoid entering the existing Ping Yuen River and Shenzhen River downstream of
the Project site. Stockpiles of cement and other construction materials
should be kept covered when not being used.
·
Good site practices
described in ProPECC PN 1/94, such as
avoidance of excavation works in rainy / wet season should be complied.
Storage and Handling of Oil, Other Petroleum
Products and Chemicals
5.8.17 The following mitigation measures should be implemented for the storage and handling of oil, other petroleum products and chemicals:
·
Waste streams
classifiable as chemical wastes should be properly stored, collected and
treated for compliance with Waste
Disposal Ordinance or Waste Disposal
(Chemical Waste) (General) Regulation requirements.
·
All fuel tanks and
chemical storage areas should be provided with locks and be sited on paved
areas.
·
The storage areas should
be surrounded by bunds with a capacity equal to 110% of the storage capacity of
the largest tank to prevent spilled oil, fuel and chemicals from reaching the
receiving waters. The storage areas should be located away from water bodies as
far as possible.
·
Waste oil should be
collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.
·
Vehicle and plant
servicing areas, vehicle wash bays and lubrication bays should, as far as
possible, be located within roofed areas.
The drainage in these covered areas should be connected to foul sewers
via a petrol interceptor.
Handling of Spillage / Leakage
5.8.18
In the event that accidental spillage or
leakage of hazardous substances / chemical wastes occur, the response
procedures as listed below should be followed. It should be noted that the procedures
below are not exhaustive and the contractor should
propose other response procedures in the Emergency Contingency Plan based on
the particular types and quantities of chemicals or hazardous substances used,
handled and stored on-site.
·
Oil leakage or spillage
should be contained and cleaned up immediately. Waste oil should be collected
and stored for recycling or disposal in accordance with the Waste Disposal Ordinance.
·
Instruct untrained
personnel to keep at a safe distance well away from the spillage area.
·
If the spillage / leakage
involves highly toxic, volatile or hazardous waste, initiate emergency
evacuation and call the emergency service.
·
Only trained persons
equipped with suitable protective clothing and equipment should be allowed to
enter and clean up the waste spillage / leakage area.
·
Where the spillage/
leakage is contained in the enclosed storage area, the waste can be transferred
back into suitable containers by suitable handheld equipment, such as hand
operated pumps, scoops or shovels.
If the spillage / leakage quantity is small, it can be covered and mixed
with suitable absorbing materials such as tissue paper, dry soft sand or
vermiculite. The resultant slurry
should be treated as chemical waste and transferred to suitable containers for
disposal.
·
For spillage / leakage in
other areas, immediate action is required to contain the spillage /
leakage. Suitable liquid absorbing
materials such as tissue paper, dry soft sand or vermiculite should be used to
cover the spill. The resultant
slurry should be treated as chemical waste and transferred to suitable
containers for disposal.
·
Areas that have been
contaminated by chemical waste spillage / leakage should be cleaned. While water is a soluble solvent for
aqueous chemical wastes and water soluble organic
waste, kerosene or turpentine should be used for organic chemical wastes that
are not soluble in water. The waste
from the cleanup operation should be treated and
disposed of as chemical waste.
·
In incidents where the
spillage / leakage may result in significant contamination of an area or risk
of pollution, the EPD should be informed immediately.
·
The Code of Practice on
Packaging, Labelling and Storage of Chemical Wastes published under the WDO
should be used as a guideline for handing chemical wastes.
Operation
Phase
Maintenance Works
5.8.19
Maintenance would be necessary for the proposed drainage
channel at regular intervals to remove excessive silts, vegetation, debris and
obstruction.
5.8.20
Before proceeding with any maintenance works, except for
emergency works, the maintenance engineer should check to ascertain if any of
the proposed works should be located in or near an
environmentally sensitive and/or ecologically important areas. In case of doubt, advice from
5.8.21
If the proposed works should be located inside or near one of
the environmentally sensitive and/or ecologically important areas, careful
consideration should be given to the proposed method of implementation so as to
minimise any adverse environmental impact.
Depending on the extent of the maintenance works,
5.8.22
The following precautionary measures should be included in
planning for the maintenance works for the proposed channels:
(a)
Maintenance of the channels should be restricted to annual
silt removal when the accumulated silt should adversely affect the hydraulic
capacity of the channel, except during emergency situations where flooding risk
is imminent. Desilting should be
carried out by hand or light machinery during the dry season (October to March)
when water flow is low.
(b)
Vegetation removal should be limited to manual cutting to be
carried out during dry season and only when growth of vegetation is very likely
to impede channel flow.
(c)
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.
(d)
Containment structures (such as sand bags barrier) should be
provided for the desilting works area to facilitate a dry or at least confined
working area within the drainage channel.
(e)
Where no maintenance access is available for the channel,
temporary access to the works site should be carefully planned and located to
reduce disturbance caused to the drainage channel, adjacent vegetation and
nearby sensitive receivers by construction plants.
(f)
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.
(g)
The use of lesser or smaller construction plants should be
considered to reduce disturbance to the channel bed where fish habitats are
located and to the nearby sensitive receivers;and
(h)
The use of concrete or the like should be avoided or minimzed.
5.9
Residual Impacts
5.9.1
With the proper implementation of the recommended mitigation
measures described in Section 5.8
above, it is expected that unacceptable residual water quality impacts would
not arise from the construction and operation of the Project.
5.10
Cumulative Impacts
5.10.1
The potential for cumulative water quality impact during the
construction phase has been checked against the following known committed/existing
projects at the time the EIA is prepared, and the project proponents of these
projects have been approached and will be closely consulted throughout this
Project:
·
Implementation
of Water Intelligent Network (WIN), Remaining District Metering Areas and
Pressure Management Areas in Yuen Long and Sheung Shui & Fanling Major Supply Zones;
·
Widening
of the Western Section and Eastern Section of Lin Ma Hang Road (Ping Yuen River
to Ping Che Road / Tsung Yuen Ha to Lin Ma Hang).
5.10.2
Implementation of WIN will fall within the Study Area while
the works will be confined into localised works area with little potential to
generate water quality impacts. In
addition, the widening of the Western Section and Eastern Section of Lin Ma
Hang Road (Ping Yuen River to Ping Che Road / Tsung Yuen Ha to Lin Ma Hang) is
not substantial and is over 500m of this Project. Therefore, the potential of causing
unacceptable cumulative water quality impacts from these projects is considered
low.
5.10.3
In addition to the above projects, there are also three
planning studies with study areas within and in the vicinity of the Project
Site, which included the following:
·
Preliminary Feasibility
Study on Developing the New Territories North (NTN);
·
Drainage Improvement
Works in Hang Tau, Kong Ha and Sha Tau Kok Town, and Lower Ping
Yuen River; and
·
North East New
Territories Sewerage System Upgrade.
5.11
Monitoring and Audit
Requirement
Construction
Phase
5.11.1
With proper implementation of the recommended mitigation
measures, adverse water quality impacts at the identified WSRs are not expected
to occur. However, a water quality
monitoring programme is recommended to verify the predictions of the EIA and
ensure compliance with the assessment criteria.
5.11.2
Detailed approach and methodology of the water quality
monitoring programme are presented in the Environmental Monitoring and Audit
Manual (EM&A Manual) under a separate cover and are briefly described
below.
5.11.3
Baseline monitoring should be undertaken for three times per
week for a period of four weeks before commencement of the construction works
to establish baseline water quality conditions of the area. Impact monitoring should be undertaken
for three times per week during the construction period to obtain updated water
quality data of the area for comparison with the baseline water quality data
and hence determine any water quality impacts from the construction
activities.
5.11.4
Monitoring should be undertaken at stations located upstream
and downstream of the Project Site.
The upstream station should serve as control station at which the water
quality is unlikely to be affected by the Project’s activities while the
downstream station will serve as impact station. Data will be compared between the
upstream and downstream station to determine any adverse water quality impacts
as a result of the construction works of the Project. Locations of the monitoring station are
recommended in the EM&A Manual.
5.11.5
The following parameters will be monitored under the water
quality monitoring programme:
·
Dissolved Oxygen (mg/L) (in situ measurement);
·
Temperature (in situ measurement);
·
pH (in situ measurement);
·
Turbidity (NTU) (in situ measurement);
·
Suspended Solids (mg/L)
(laboratory analysis);
·
Salinity (in situ measurement);
·
Water depth (in situ measurement)
5.11.6
Weekly site inspections and monthly site audits will
be conducted to ensure that the recommended mitigation measures are properly
implemented during the construction stage.
Operation
Phase
5.11.7
Adverse water quality impact is not expected during
operation phase of the Project and hence monitoring is considered not
necessary.
5.12
Conclusion
5.12.1
The potential sources of water quality impacts associated
with the construction and operation of the Project have been identified and the
potential impacts were evaluated.
5.12.2
Potential impacts arising from the proposed construction
works are predicted to be largely confined to the specific works areas. With
proper implementation of the recommended mitigation measures, in particular the
establishment of dry conditions for excavation works within the existing
watercourse and good construction site practices as recommended in relevant
regulatory guidelines, adverse water quality impacts are not expected at the
identified WSRs.
5.12.3
During the operation phase, changes to hydrodynamic regime
within the Project Site are predicted to have no adverse impacts. Adverse water quality impacts are not
expected at any identified WSRs during the operation phase as the Project will
not generate any new pollution loads and the maintenance works to remove
excessive silt, vegetation, debris and obstructions are small scale in
nature. The improved flow condition
in the proposed Drainage Channel TKL04 and 05 may alter the pattern of sediment
deposition and erosion along the downstream section of Ping Yuen River and
Shenzhen River. With regular
maintenance works at these downstream sections to remove excessive sediments,
it is not anticipated that the Project will lead to any unacceptable adverse
water quality impacts by altering their sediment deposition and erosion
pattern.
5.12.4
With the implementation of the recommended mitigation
measures, it is expected that unacceptable residual water quality impacts would
not arise from the construction and operation of the Project. Nevertheless, a monitoring programme is
recommended during construction phase to verify the predictions of the EIA and
ensure compliance with the assessment criteria.