5
Water Quality
5.1.1 This Section presents an evaluation of the potential water quality
impacts from the construction and operation of the Project, and the results
were assessed with reference to the relevant environmental legislation,
standards and criteria.
5.2
Relevant Legislation and Guidelines
5.2.1 Relevant legislations, standards and guidelines governing water
quality in Hong Kong include the followings:
·
Water Pollution Control Ordinance (WPCO) (CAP.358);
·
Technical Memorandum on Standards for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters;
·
Annexes 6 and 14 of the Technical Memorandum on the
Environmental Impact Assessment Ordinance (EIAO-TM);
·
Professional Persons Environmental Consultative
Committee Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94);
·
Hong Kong Planning Standards and Guidelines (HKPSG);
·
Professional Persons Environmental Consultative
Committee Practice Note for Professional Persons on Drainage Plans subject to
Comment by the Environmental Protection Department (ProPECC
PN 5/93); and
·
DSD Technical Circular No. 1/2017 Temporary Flow Diversions and Temporary Works Affecting Capacity
in Stormwater Drainage Systems.
Water Pollution Control Ordinance
5.2.2 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. This Project is located in the
Deep Bay WCZ. WQOs for the Deep Bay WCZ relevant to this assessment are
listed in Table 5.1.
Table 5.1 Summary of Water
Quality Objectives for the Deep Bay WCZ
|
Parameters
|
Criteria
|
Sub-zone
|
|
Aesthetic Appearance
|
(a) Waste discharges
shall cause no objectionable odours or discolouration of the water.
|
Whole zone
|
|
|
(b) Tarry residues,
floating wood, articles made of glass, plastic, rubber or of any other
substances should be absent.
|
Whole zone
|
|
|
(c) Mineral oil should
not be visible on the surface. Surfactants should not give rise to a lasting
foam.
|
Whole zone
|
|
|
(d) There should be no
recognisable sewage derived debris.
|
Whole zone
|
|
|
(e) Floating, submerged
and semi-submerged objects of a size likely to interfere with the free
movement of vessels, or cause damage to vessels, should be absent.
|
Whole zone
|
|
|
(f) Waste discharges
shall not cause the water to contain substances which settle to form
objectionable deposits.
|
Whole zone
|
|
Bacteria
|
(a) The level of
Escherichia coli should not exceed 610 per 100 mL, calculated as the
geometric mean of all samples collected in a calendar year.
|
Secondary Contact
Recreation Subzone and Mariculture Subzone (L.N. 455 of 1991)
|
|
|
(b) The level of
Escherichia coli should be zero per 100 ml, calculated as the running median
of the most recent 5 consecutive samples taken at intervals of between 7 and
21 days.
|
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones
|
|
|
(c) The level of
Escherichia coli should not exceed 1000 per 100 ml, calculated as the running
median of the most recent 5 consecutive samples taken at intervals of between
7 and 21 days.
|
Yuen Long & Kam Tin
(Lower) Subzone and other inland waters
|
|
|
(d) The level of
Escherichia coli should not exceed 180 per 100 mL, calculated as the
geometric mean of all samples 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 14 days.
|
Yung Long Bathing
Beach Subzone
(L.N. 455 of 1991)
|
|
Colour
|
(a) Waste discharges
shall not cause the
colour of water to exceed
30 Hazen units.
|
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering
Ground Subzones
|
|
|
(b) Waste discharges
shall not cause the
colour of water to exceed
50 Hazen units.
|
Yuen Long & Kam Tin
(Lower) Subzone and other inland waters
|
|
Dissolved Oxygen
|
(a) Waste discharges
shall not cause the level of dissolved oxygen to fall below 4 milligrams per
litre for 90% of the sampling occasions during the year; values should be
taken at 1 metre below surface.
|
Inner Marine Subzone
excepting Mariculture Subzone
|
|
|
(b) Waste discharges
shall not cause the level of dissolved oxygen to fall below 4 milligrams per
litre for 90% of the sampling occasions during the year; values should be
calculated as water column average (arithmetic mean of at least 2
measurements at 1 metre below surface and 1 metre above seabed). In addition,
the concentration of dissolved oxygen should not be less than 2 milligrams
per litre within 2 metres of the seabed for 90% of the sampling occasions
during the year.
|
Outer Marine Subzone
excepting Mariculture Subzone
|
|
|
(c) The dissolved oxygen
level should not be less than 5 milligrams per litre for 90% of the sampling
occasions during the year; values should be taken at 1 metre below surface.
|
Mariculture Subzone
|
|
|
(d) Waste discharges
shall not cause the level of dissolved oxygen to be less than 4 mg per litre.
|
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
|
|
pH
|
(a) The pH of the water
should be within the range of 6.5-8.5 units. In addition, waste discharges
shall not cause the natural pH range to be extended by more than 0.2 unit.
|
Marine waters excepting
Yung Long Bathing Beach Subzone
|
|
|
(b) Waste discharges
shall not cause the pH of the water to exceed the range of 6.5-8.5 units.
|
Yuen Long & Kam Tin
(Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and
Water Gathering Ground Subzones
|
|
|
(c) The pH of the water
should be within the range of 6.0-9.0 units.
|
Other inland waters
|
|
|
(d) The pH of the water
should be within the range of 6.0-9.0 units for 95% of samples collected
during the whole year. In addition, waste discharges shall not cause the
natural pH range to be extended by more than 0.5 unit.
|
Yung Long Bathing Beach
Subzone
|
|
Temperature
|
Waste discharges shall
not cause the natural daily temperature range to change by more than 2.0°C.
|
Whole zone
|
|
Salinity
|
Waste discharges shall
not cause the natural ambient salinity level to change by more than 10%.
|
Whole zone
|
|
Suspended Solids
|
(a) Waste discharges
shall neither cause the natural ambient level to be raised by more than 30%
nor give rise to accumulation of suspended solids which may adversely affect
aquatic communities.
|
Marine waters
|
|
|
(b) Waste discharges
shall not cause the annual median of suspended solids to exceed 20 mg per
litre.
|
Yuen Long & Kam Tin
(Upper and Lower) Subzones, Beas Subzone, Ganges Subzone, Indus Subzone,
Water Gathering Ground Subzones and other inland waters
|
|
Ammonia
|
The un-ionized ammoniacal
nitrogen level should not be more than 0.021 mg per litre, calculated as the
annual average (arithmetic mean).
|
Whole zone
|
|
Nutrients
|
(a) Nutrients shall not
be present in quantities sufficient to cause excessive or nuisance growth of
algae or other aquatic plants.
|
Inner and Outer Marine
Subzones
|
|
|
(b) Without limiting the
generality of objective (a) above, the level of inorganic nitrogen should not
exceed 0.7 mg per litre, expressed as annual mean.
|
Inner Marine Subzone
|
|
|
(c) Without limiting the
generality of objective (a) above, the level of inorganic nitrogen should not
exceed 0.5 mg per litre, expressed as annual water column average (arithmetic
mean of at least 2 measurements at 1m below surface and 1m above seabed).
|
Outer Marine Subzone
|
|
5-day Biochemical Oxygen Demand
|
(a) Waste discharges
shall not cause the 5-day biochemical oxygen demand to exceed 3 mg per litre.
|
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones
|
|
|
(b) Waste discharges
shall not cause the 5-day biochemical oxygen demand to exceed 5 mg per litre.
|
Yuen Long & Kam
Tin (Lower) Subzone
and other inland
waters
|
|
Chemical Oxygen Demand
|
(a) Waste discharges
shall not cause the chemical oxygen demand to exceed 15 mg per litre.
|
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones
|
|
|
(b) Waste discharges
shall not cause the chemical oxygen demand to exceed 30 mg per litre.
|
Yuen Long & Kam
Tin (Lower) Subzone
and other inland
waters
|
|
Toxins
|
(a) Waste discharges
shall not cause the toxins in water to attain such levels as to produce
significant toxic carcinogenic, mutagenic or teratogenic effects in humans,
fish or any other aquatic organisms, with due regard to biologically
cumulative effects in food chains and to toxicant interactions with each
other
|
Whole zone
|
|
(b) Waste discharges
shall not cause a risk to any beneficial uses of the aquatic environment
|
Whole zone
|
|
Phenol
|
Phenols shall not be
present in such quantities
as to produce a specific odour,
or in concentration greater than 0.05 mg per litre as C6H5OH.
|
Yung Long Bathing Beach
Subzone
|
|
Turbidity
|
Waste discharges shall
not reduce light transmission substantially from the normal level.
|
Yung Long Bathing Beach
Subzone
|
Technical Memorandum on Standards for Effluents Discharged into
Drainage and Sewerage Systems, Inland and Coastal Waters
5.2.3 All discharges from the construction and operation phases of the
proposed Project are required to comply with the Technical Memorandum
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM-DSS) issued under Section 21 of the WPCO.
5.2.4 The TM-DSS defines acceptable discharge limits to different
types of receiving waters. Under the TM-DSS, effluents discharged into
the drainage and sewerage systems, inshore 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.
Technical Memorandum of Environmental Impact Assessment Process
(EIAO-TM)
5.2.5 Annexes 6 and 14 of the EIAO-TM provide general guidelines
and criteria to be used in assessing water quality impacts. Annex 6 of
the EIAO-TM stipulates criteria for evaluating water pollution and Annex
14 specifies guidelines for assessment of water pollution.
Practice Note for Professional Persons on Construction Site Drainage
(ProPECC PN 1/94)
5.2.6 A practice note for professional persons was issued by the EPD to
provide guidelines for handling and disposal of construction site discharges. The
Practice Note for Professional Persons on Construction Site Drainage (ProPECC
PN 1/94) provides good practice guidelines for dealing with various types
of discharge from a construction site. Practices outlined in ProPECC PN 1/94
should be followed as far as possible during construction to minimise the water
quality impact due to construction site drainage.
Hong Kong Planning Standards and Guidelines (HKPSG)
5.2.7 Chapter 9 of the HKPSG provides environmental considerations for
land use planning. Site selection for development, sensitive uses,
provision of environmental facilities, and design, layout, phasing and
operational controls to minimise adverse environmental impacts, etc., are
covered in the chapter. Other factors affecting land use planning to be
taken into account are listed and suitable buffer distances for land uses are
recommended.
Practice Note for Professional Persons, Drainage Plans subject to
Comment by the Environmental Protection Department (ProPECC PN 5/93)
5.2.8 This practical note provided guidelines and recommendations for
handling, treatment and disposal of various effluent discharges to stormwater
drains and foul sewers. Design considerations and disposal arrangements
of various site effluents from project operation in ProPECC PN 5/93
should be followed.
DSD Technical Circular No. 1/2017 Temporary Flow Diversions and
Temporary Works Affecting Capacity in Stormwater Drainage Systems
5.2.9 This circular provides guidance on the basic principles to be
applied when assessments are made on the adequacy of proposed temporary flow
diversions and / or temporary works design applicable to various periods
throughout the year. This circular suggests that for the purpose of works
related to temporary flow diversion and other temporary works related to
drainage, wet season should typically be from 1 April to 31 October, and dry
season should be from 1 November to 31 March. With proper analysis of
risk and justification, the designated period of wet and dry seasons can be
adjusted to suit the need for a specific project. This circular also
layout considerations and precautions to be taken for managing such works in
view of the seasonality.
5.3
Description of the Environment
Study Area
5.3.1 According to Clause 3.4.6.2 of the EIA Study Brief, the Assessment
Area shall include areas within 500m from the boundary of the Project and shall
cover the Deep Bay Water Control Zone (DBWCZ) under the WPCO.
River Water Quality
5.3.2 The Project site is located at least 8 km from marine water in any
direction. Notable body of water in the vicinity is a channelised
tributary of River Indus at over 500m to the north, as well as the mid-stream
of River Indus at about 900m northeast. Water at the mid-stream section
of River Indus flows in the northwestern direction, merges with River Beas and
then turns north. It then flows into the Shenzhen River and flows west
into the Deep Bay. According to River Water Quality in Hong Kong in
2021 (EPD, 2022), River Indus showed marked water quality improvement in
the last three decades, with its WQO compliance rate rising significantly from
24% in 1991 to 84% in 2021 overall for the river. River water quality at
River Indus was graded as “Good” to “Excellent” in 2021. The monitoring
results from the nearest monitoring stations IN1 to IN3 are summarised in Table
5.2.
Table 5.2
Summary of EPD River Water Quality Monitoring Data from the River Indus in Year
2021
|
Parameters
|
Lower Reach
IN1
|
Mid-stream
IN2
|
Upper Reach
IN3
|
|
Dissolved
Oxygen (mg/L)
|
6.0
|
6.7
|
8.1
|
|
(4.3 - 7.6)
|
(3.1 - 9.3)
|
(6.9 - 9.3)
|
|
pH
|
6.9
|
7.4
|
7.6
|
|
(6.7 - 7.2)
|
(6.9 - 7.9)
|
(7.1 - 7.8)
|
|
Suspended
solids (mg/L)
|
16.5
|
6.4
|
3.0
|
|
(5.2 - 65.0)
|
(2.8 - 15.0)
|
(1.4 - 13.0)
|
|
5-Day
Biochemical Oxygen Demand (mg/L)
|
3.1
|
2.6
|
1.1
|
|
(1.1 - 12.0)
|
(0.7 - 7.3)
|
(0.5 - 5.1)
|
|
Chemical
Oxygen Demand (mg/L)
|
26
|
11
|
8
|
|
(15 - 36)
|
(7 - 21)
|
(5 - 13)
|
|
Oil and
Grease (mg/L)
|
<0.5
|
<0.5
|
<0.5
|
|
(<0.5 - 0.5)
|
(<0.5 - <0.5)
|
(<0.5 - <0.5)
|
|
E. coli (counts/100mL)
|
23,000
|
3,100
|
3 100
|
|
(3,700 – 520,000)
|
(430 – 15,000)
|
(270 – 29,000)
|
|
Faecal
Coliforms (counts/100mL)
|
82 000
|
18,000
|
9 900
|
|
(10 000 - 3 800 000)
|
(3,000 – 210,000)
|
(1,600 – 42,000)
|
|
Ammonia-Nitrogen
(mg/L)
|
0.880
|
0.810
|
0.092
|
|
(0.220 - 3.100)
|
(0.180 - 1.500)
|
(0.032 - 0.220)
|
|
Nitrate-Nitrogen
(mg/L)
|
2.650
|
0.980
|
0.670
|
|
(1.000 - 4.800)
|
(0.770 - 1.600)
|
(0.460 - 0.900)
|
|
Total
Kjeldahl Nitrogen (mg/L)
|
2.70
|
1.80
|
0.47
|
|
(2.00 - 5.80)
|
(1.50 - 2.40)
|
(0.35 - 0.84)
|
|
Orthophosphate
Phosphorus (mg/L)
|
0.290
|
0.079
|
0.094
|
|
(0.052 - 0.910)
|
(0.018 - 0.170)
|
(0.038 - 0.140)
|
|
Total
Phosphorus (mg/L)
|
0.48
|
0.16
|
0.13
|
|
(0.33 - 0.87)
|
(0.15 - 0.22)
|
(0.08 - 0.14)
|
|
Sulphide
(mg/L)
|
<0.02
|
<0.02
|
<0.02
|
|
(<0.02 - 0.02)
|
(<0.02 - <0.02)
|
(<0.02 - <0.02)
|
|
Aluminium
(μg/L)
|
<50
|
<50
|
<50
|
|
(<50 - <50)
|
(<50 - 57)
|
(<50 - 65)
|
|
Cadmium
(μg/L)
|
<0.1
|
<0.1
|
<0.1
|
|
(<0.1 - <0.1)
|
(<0.1 - <0.1)
|
(<0.1 - <0.1)
|
|
Chromium
(μg/L)
|
1
|
<1
|
<1
|
|
(<1 - 3)
|
(<1 - <1)
|
(<1 - <1)
|
|
Copper
(μg/L)
|
2
|
1
|
<1
|
|
(1 - 3)
|
(1 - 3)
|
(<1 - 2)
|
|
Lead
(μg/L)
|
<1
|
<1
|
<1
|
|
(<1 - <1)
|
(<1 - <1)
|
(<1 - <1)
|
|
Zinc
(μg/L)
|
14
|
<10
|
<10
|
|
(<10 - 20)
|
(<10 - 19)
|
(<10 - 15)
|
|
Flow (m³/s)
|
9.416
|
NM
|
0.046
|
|
(4.264 - 18.411)
|
(0.021 - 0.364)
|
|
Notes:
(a)
Data
presented are annual median except for faecal coliform and E. coli,
which are geometric means.
(b)
Figures in
brackets are annual ranges.
(c)
NM indicates
no measurement taken.
(d)
Values at or
below laboratory reporting limits are presented as laboratory reporting
limits.
(e)
Equal values
for annual medians (or geometric means) and ranges indicate that all data are
the same as or below laboratory reporting limits.
|
Water Quality Sensitive
Receivers
5.3.3 There is no major body of water in the surrounding of the Project
Site. The Project site is at least 8km away from any marine water and
over 500m from any major river (nearest being River Indus). Within 500m
from the Project Site, there are two surface drains that pass through the works
area, both along the So Kwun Po Road (near North District Park), So Kwun Po
Road (near SKH Wing Chun Primary School), Other nearby surface drainage
include drainage system around So Kwun Po, and another nullah located in
between Ching Ho Estate and Kai Leng flows northeasterly toward the Project
site and turns into an underground drain / box culvert before passing
underneath the Project Site. These are also considered water sensitive
receivers. Note that within the 500m Assessment Area there are a few more
surface drainage systems, which are also considered to be WSRs in nature, but
are much further away and would less likely to be affected by this Project.
5.3.4 There are also artificial ponds within the North District Park to
the east of the Project, Tai Ping Estate to the west of the Project as well as
Sheung Shui Garden to the north of the Project. They do not serve the
beneficial uses listed as sensitive to water pollution under Section 3.1 of
EIAO-TM Annex 14, therefore the pond is not considered to be a water sensitive
receiver under this Study.
5.3.5 Identified representative WSRs within the 500m Assessment Area of
the project are presented in Figure 5.1 and listed in Table
5.3.
Table 5.3
Identified Representative WSRs within 500m Assessment Area
|
ID
|
Description
|
Nature
|
Status
|
Geodesic Distance (m)
|
|
D1
|
Surface drainage system along So
Kwun Po Road (near North District Park)
|
Surface drain
|
These are actively managed surface
drains.
|
Passes through Project footprint
|
|
D2
|
Surface drainage system along So
Kwun Po Road (near SKH Wing Chun Primary School)
|
Surface drain
|
Passes through Project footprint
|
|
D3
|
Surface drainage system around of So
Kwun Po
|
Surface drain
|
Less than 10 m
|
|
D4
|
Surface drainage system (between
Ching Ho Estate and Kai Leng)
|
Surface drain
|
Around 36 m
|
|
D5
|
Surface drainage system north to Po
Wing Road Playground
|
Surface drain
|
Passes through Project footprint
|
5.4
Approach and Methodology
5.4.1 According to Clause 3.4.6.2 of the EIA Study Brief, the Assessment
Area shall include areas within 500m from the boundary of the Project and shall
cover the DBWCZ under the WPCO. WSRs within the Assessment Area have been
identified. Potential sources of water pollution were identified based on
work nature and appropriate mitigation measures would be recommended
accordingly to minimize the potential water quality impact. Residual
impact would be evaluated. Environmental monitoring, if needed, would be
recommended.
5.5
Potential Sources of Impact
Construction Phase
5.5.1 Potential sources of water quality impact
associated with construction activities for the Project include:
·
Construction site runoff;
·
General construction activities (including the
effluents generated from dewatering associated with piling activities, grouting
and concrete washing and those specified in the ProPECC Practice Note 1/94);
·
Diversion / modification of box culvert;
·
Accidental spillage; and
·
Sewage effluent from the construction workforce.
Operation Phase
5.5.2 Potential sources of water quality impact
associated with operation of the Project include road
runoff containing oil/grease and suspended solids.
5.5.3
There will be no diversion of
surface watercourses under this Project. Two sections of existing box
culvert would be modified / realigned under this Project, but the modification
will not significantly affect the surface characteristic as well as drainage
capacity. Other than these two sections of affected box culverts, the
proposed road works would only alter existing road surface, as well as certain
road side vegetation for widening and realignment of road. No action
related to notable change in hydrology of the area is identified.
5.6
Impact Assessment
Construction Phase
Construction Site Runoff
5.6.1 Road works involving clearance of existing structures would result
in exposure surfaces, which are vulnerable towards erosion in rainstorm if
unprotected. Other sources of pollution for construction site runoff may
include:
·
Erosion from stockpiles and earth working areas;
·
Dust suppression sprays;
·
Grout, bentonite slurries and concrete washings
released; and
·
Fuel, lubricants or other chemical for construction
vehicles and equipment.
5.6.2 Such runoff, as well as stormwater during a rainstorm, could carry
the above pollutants from work areas into the surrounding bodies of water,
resulting in elevated levels of turbidity, suspended solids, other chemicals /
pollutants as well as a reduction in dissolved oxygen levels. Debris
washed into drainage system could also obstruct pipes and channels.
5.6.3 However, it is anticipated that no adverse water quality impacts
would arise if proper mitigation measures, described in Section 5.7.2,
are in place to control site runoff.
General Construction Activities
5.6.4 Discharges from the site during land-based construction may contain
suspended solids which could be a source of water pollution. Other
construction works, such as concreting, dewatering for piling, grouting,
general dust suppression, cleaning, polishing, etc. could generate wastewater,
which may contain high level of suspended solids, as well as other contaminants
within site boundary. With the implementation of good site practices
described in Section 5.7.2, no unacceptable adverse water quality
impacts would be anticipated.
Diversion / Modification of Box
Culvert
5.6.5 Based on the latest available information, a section of box culvert
near the North District Park requires modification under this Project, while
another section of box culvert near Kai Leng Roundabout will be
realigned. The related construction works involve construction within
existing box culvert. Typically, these kinds of works would be arranged
during the dry season to ensure drainage flow be manageable and to allow
diversion. Before the commencement of construction works within box
culverts, diversion of channel flow (using sandbag barrier and/or other means
of temporary flow diversion) would first be conducted to ensure works can be
conducted in dry area. This avoids drainage water from encroaching in the
work area (for safety and for environmental protection) and control site runoff
and wastewater from entering the drainage flow. Excavation works for the
Project should be undertaken in a confined and dry condition to minimise the
adverse impact on water quality. All wastewater generated from the construction
works should be collected and properly stored for disposal by licensed
contractor. With the implementation of the above mitigation measures, no
unacceptable water quality impact from construction works for the diversion and
modification of box culverts would be expected.
Accidental Spillage
5.6.6 Various chemicals would be used for the proposed road works and
accordingly different chemical waste would be generated. These chemicals
and corresponding chemical wastes include:
·
Fuel;
·
(Spent) lubricants;
·
(Spent) grout;
·
(Spent) paint and adhesive;
·
(Spent) solvent; and
·
(Spent) acid and alkaline
5.6.7 Accidental spillage of these chemicals or chemical wastes would
contaminate surface or (for exposed surface) soil. The contaminated
surface and soil could be swept up by runoff / stormwater and result in
elevated level of pollutants in the receiving waters. Proper clean up
kits should be available onsite for the corresponding types of chemicals used
for various construction works. Clean up waste should be stored in marked
container as chemical wastes for proper disposal.
5.6.8 Proper control and storage of these chemicals as well as the
associated wastes should be implemented according to Waste Disposal
Ordinance (Cap 354) as well as the associated regulations including the Waste
Disposal (Chemical Waste) (General) Regulation to minimize the risk of
spillage and contamination. All chemical wastes should be stored in
secured and sheltered area(s) for collection and disposal by licensed
contractor.
Sewage Effluent from the
Construction Workforce
5.6.9 Construction workforce onsite will generate sewage effluent.
Sufficient number of chemical toilets, properly served, cleaned and emptied
regularly by licensed contractor, would be required for each work areas to
ensure hygiene and avoid nuisance.
Operation Phase
5.6.10 Operation of
the proposed road improvement works would result in slight increase to road
runoff of similar nature to existing condition. According to the separate
Drainage Impact Assessment Report, the estimated increase in runoff
(based on 1 in 50 years rainstorm) would be only 0.18 m3/s and is
considered to be negligible for the catchment. Such runoff typically
contains elevated levels of suspended solids, grits as well as trace amount of
oil and grease from vehicles, which could affect the water quality of the
receiving waters. Proper road drainage system fitted with appropriate
pollutant removal devices (such as grit traps) will be required to ensure
pollutants from road runoff be removed before entering receiving bodies of
water. Given the negligible change in terms of the nature and amount of
runoff, as well as the implementation of proposed mitigation measures and
management practices (Section 5.7.6), no significant change to pollution
loading related to road runoff would be expected. No unacceptable water
quality impact associated with road runoff is expected.
5.6.11 The modification and realignment of box culvert sections under this
Project is not expected to adversely affect the hydraulic capacity of the
drainage system, or any surface water features. No unacceptable impact on
hydrology of the area is
expected.
Construction Phase
5.7.1
A WPCO discharge license should be applied for the
disposal of effluent from the construction site. All standards, criteria
and requirements stipulated in the relevant license apply.
5.7.2 Suitable control measures stipulated in ProPECC PN 1/94
should be implemented, namely:
·
Surface run-off from construction sites should be
discharged into storm drains via adequately designed sand/silt removal
facilities such as sand traps, silt traps and sediment basins. Channels
or earth bunds or sand bag barriers should be provided on-site to properly
direct stormwater to such silt removal facilities. Perimeter channels at site
boundaries should be provided where necessary to intercept storm run-off from
outside the site so that it will not wash across the site. Catchpits and
perimeter channels should be constructed in advance of site formation works and
earthworks.
·
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 ensure that these facilities are
functioning properly at all times
·
Construction works should be programmed to minimize
soil excavation works in rainy seasons (April to September). If
excavation in soil could not be avoided in these months or at any time of year
when rainstorms are likely, for the purpose of preventing soil erosion,
temporarily exposed slope surfaces should be covered e.g. by tarpaulin.
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 to ensure that adequate
surface protection measures can be safely carried out well before the arrival
of a rainstorm.
·
Earthworks final surfaces should be well compacted and
the subsequent permanent work or surface protection should be carried out
immediately after the final surfaces are formed to prevent erosion caused by
rainstorms. Appropriate drainage like intercepting channels should be
provided where necessary
·
Measures should be taken to minimize 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.
·
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.
·
Manholes (including newly constructed ones) should
always be adequately covered and temporarily sealed so as to prevent silt,
construction materials or debris from getting into the drainage system, and to
prevent storm run-off from getting into foul sewers. Discharge of surface
run-off into foul sewers must always be prevented in order not to unduly
overload the foul sewerage system.
·
Water used in ground boring and drilling for site
investigation or rock/soil anchoring should as far as practicable be
recirculated after sedimentation. When there is a need for final
disposal, the wastewater should be discharged into storm drains via silt
removal facilities.
·
All vehicles and plant should be cleaned before they
leave a construction site to ensure no earth,
mud, debris and the like is deposited by them on roads. A wheel
washing bay should be provided at every site 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 with backfall to reduce vehicle tracking of
soil and to prevent site run-off from entering public road drains.
·
Wastewater generated from building construction
activities including concreting, cleaning of works and similar activities
should not be discharged into the stormwater drainage system. If the
wastewater is to be discharged into foul sewers, it should undergo the removal
of settleable solids in a silt removal facility, and pH adjustment as
necessary.
·
Acidic wastewater generated from acid cleaning,
etching, pickling and similar activities should be neutralized to within the pH
range of 6 to 10 before discharging into foul sewers. If there is no
public foul sewer in the vicinity, the neutralized wastewater should be
tankered off site for disposal into foul sewers or treated to a standard
acceptable to storm drains and the receiving waters.
5.7.3 Sufficient number of chemical toilets should be required for each
works area. These toilets should be regularly cleaned, maintained and
emptied by licensed contractor.
5.7.4 For construction works within box culverts, construction works
should preferably be arranged in dry season. Before the commencement of
construction works within box culverts, diversion of channel flow (using
sandbag barrier and/or other means of temporary flow diversion) would first be
conducted to ensure works can be conducted in dry area. Excavation works
for the Project should be undertaken in a confined and dry condition to
minimise the adverse impact on water quality. All wastewater generated
from the construction works should be collected and properly stored for
disposal by licensed contractor.
· 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.
Operation Phase
5.7.6
The design of the drainage system shall follow the
relevant guidelines and practices as given in the ProPECC PN 5/93 and be
fitted with appropriate design measures to control pollution of drainage water,
namely,
· Standard screening designs such as gully grating
should be provided to stop large objects from entering;
· Where appropriate, silt traps and oil interceptors
should be provided to remove pollutants from runoff / stormwater.
5.7.7 These facilities should also be cleaned, maintained and inspected
regularly and particularly before and after a rainstorm.
5.8.1 Known concurrent projects in the vicinity are listed in Table 2.5.
The potential cumulative water quality impact from the construction and
operation of these concurrent projects is discussed below.
Construction Phase
Housing Development in Ching
Hiu Road
5.8.2 Based on the latest available information, this housing development
project, located at 217m southwest to the Project site, is expected to be under
construction from 2022 to 2030. The construction of the housing
development at Ching Hiu Road is considered relatively small scale according to
its site area. The site is currently flat land and the construction is
expected to mainly involve piling and superstructure works. Any potential
water quality impact from this housing development project is expected to be
limited and localised. No unacceptable cumulative water quality impact is
anticipated.
Housing Development in Fanling
Area 17
5.8.3 Based on the latest available information, this housing development
project, located at 274m east to the Project site, is expected to be under
construction from 2023 to 2031. The housing development project is
expected to involve localised construction works and minor modifications works
at the surrounding. Nevertheless, given the large separation distance
from the Project site, construction of the housing development at Fanling Area
17 is not expected to cause unacceptable cumulative water quality impact.
Expansion of North District
Hospital
5.8.4 Based on the latest available information, this expansion project,
located at 272m west to the Project site, is expected to be construction from
2021 to 2028. The site for North District Hospital Expansion has been
formed and the upcoming construction is expected to mainly involve piling and
superstructure works. Any potential water quality impact from this
housing development project is expected to be limited and localised. No
unacceptable cumulative water quality impact is anticipated.
Utilities Works and Junction
Improvement Works for Partial Development of Fanling Golf Course Site
5.8.5 Based on the latest available information, this utilities and
junction improvement project, located at 195m west to the Project site, is
expected to be under construction from 2024 to 2029. Utilities Works and
Junction Improvement Works for Partial Development of Fanling Golf Course Site
are considered as minor works. The associated water quality impact is
expected to be limited with the implementation of appropriate mitigation
measures. No unacceptable cumulative water quality impact is anticipated.
Reclaimed Water Supply to
Sheung Shui and Fanling
5.8.6 Based on the latest available information, this reclaimed water
supply project, located at north and east to the Project site (nearest section
at 18m from Project site), is expected to be under construction from 2021 to
2026. The works of the Reclaimed Water Supply to Sheung Shui and Fanling
are divided into different segments. Based on the construction programme
attached in the latest available monthly EM&A report of the Reclaimed Water
Supply to Sheung Shui and Fanling (3/WSD/20) (i.e. Report No.21 - Aug 2023)
during the preparation of this EIA Report, the works which encroach into the
500m Assessment Area will be completed by end of August 2025, whereas the
construction works of the proposed Project commences in August 2025. Hence, the
overlapping of the two projects only lasts for less than a month. In
addition, the project is considered as minor work and the associated water
quality impact is expected to be limited with the implementation of appropriate
mitigation measures. No unacceptable cumulative water quality impact is
anticipated.
Operation Phase
5.8.7 Potential water quality impact from operation of the Project is
expected to be minimal. No unacceptable cumulative water quality impact
for operation phase is expected.
5.9.1 With the implementation of the recommended mitigation measures, no
unacceptable water quality impact associated with the construction and
operation of the proposed road improvement works would be expected.
5.10
Environmental Monitoring and Audit
Construction Phase
5.10.1 With the
implementation of the recommended mitigation measures, no unacceptable water
quality impact is expected during Project construction. Environmental
monitoring is not considered necessary for water quality. Regular site
inspections should be conducted during construction to ensure the proper
implementation of the recommended mitigation measures.
Operation Phase
5.10.2 As there is
no unacceptable water quality impact expected during the operation of the
Project, water quality monitoring for operation phase is not considered
necessary.
5.11.1 The
environment and baseline condition at and around the Project Site has been
reviewed based on historic record of water quality data from nearby EPD river
water quality monitoring stations. Applicable environmental legislations
and guidelines related to construction and operation phase water quality
impacts were identified. Potential sources of water quality impact from
construction and operation phases of the proposed road improvement works have
been identified and evaluated. These sources of impacts include,
construction site runoff; general construction activities,
diversion/modification of box culvert, accidental spillage and sewage effluent
from the construction workforce for construction phase, as well as increase
road runoff for operation phase. Suitable mitigation / control measures
were recommended based on standard guidelines including ProPECC PN 1/94,
and Code of Practice on the Packaging, Labelling and Storage of
Chemical Wastes. No unacceptable residual water quality impact is
expected from the construction and operation of the Project with the
implementation of proposed mitigation measures.