6.1.1
This section presents an
assessment of the potential water quality impacts associated with construction
and operation of the Project. Recommendations for mitigation measures have been
provided to minimize the identified water quality impacts.
Environmental Impact
Assessment Ordinance (EIAO)
6.2.1
The Technical Memorandum on
Environmental Impact Assessment Process (EIAO-TM) was issued by Environmental Protection
Department (EPD) under Section 16 of the EIAO. It specifies the assessment
method and criteria that are to be followed in an EIA Study. Reference sections
in the EIAO-TM provide the details of assessment criteria and guidelines that
are relevant to the water quality impact assessment, including:
Ÿ
Annex 6 – Criteria for Evaluating Water Pollution
Ÿ
Annex 14 – Guidelines for Assessment of Water Pollution
Water Quality
Objectives
6.2.2
The Water Pollution Control
Ordinance (WPCO) provides 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 the WCZs based on their beneficial uses.
The study area for this water quality impact assessment
covers the Victoria Harbour (Phase one) WCZ. The corresponding WQOs are listed in Table 6.1.
Table 6.1 Summary of Water Quality
Objectives for Victoria Harbour WCZ
|
Parameters
|
Objectives
|
Sub-Zone
|
|
Offensive odour, tints
|
Not to be present
|
Whole zone
|
|
Visible foam, oil scum, litter
|
Not to be present
|
Whole zone
|
|
E coli
|
Not to exceed 1000 per 100 mL,
calculated as the geometric mean of the most recent 5 consecutive samples
taken at intervals between 7 and 21 days
|
Inland waters
|
|
Dissolved oxygen (DO) within 2 m of the seabed
|
Not less than 2.0 mg/L for 90% of
samples
|
Marine waters
|
|
Depth-averaged DO
|
Not less than 4.0 mg/L for 90% of
samples
|
Marine waters
|
|
DO
|
Not less than 4.0 mg/L
|
Inland waters
|
|
pH
|
To be in the range of 6.5 - 8.5, change
due to human activity not to exceed 0.2
|
Marine waters
|
|
Not to exceed the range of 6.0 - 9.0 due
to human activity
|
Inland waters
|
|
Salinity
|
Change due to human activity not to
exceed 10% of ambient
|
Whole zone
|
|
Temperature
|
Change due to human activity not to
exceed 2oC
|
Whole zone
|
|
Suspended solids (SS)
|
Not to raise the ambient level by 30%
caused by human activity
|
Marine waters
|
|
Annual median not to exceed 25 mg/L due
to human activity
|
Inland waters
|
|
Unionized ammonia (UIA)
|
Annual mean not to exceed 0.021 mg(N)/l
as unionized form
|
Whole zone
|
|
Nutrients
|
Shall not cause excessive algal growth
|
Marine waters
|
|
Total inorganic nitrogen (TIN)
|
Annual mean depth-averaged inorganic
nitrogen not to exceed 0.4 mg(N)/l
|
Marine waters
|
|
5-Day biochemical oxygen demand (BOD5)
|
Not to exceed 5 mg/L
|
Inland waters
|
|
Chemical Oxygen Demand (COD)
|
Not to exceed 30 mg/L
|
Inland waters
|
|
Toxic substances
|
Should not attain such levels as to
produce significant toxic, carcinogenic, mutagenic or teratogenic effects in
humans, fish or any other aquatic organisms.
|
Whole zone
|
|
Human activity should not cause a risk
to any beneficial use of the aquatic environment.
|
Whole zone
|
Source: Statement of Water Quality Objectives
(Victoria Harbour (Phases One, Two and Three) Water Control Zone).
Technical Memorandum on Effluent Discharge
Standard
6.2.3
Besides setting the WQOs, the
WPCO controls effluent discharging into the WCZs through a licensing system.
Guidance on the permissible effluent discharges based on the type of receiving
waters (foul sewers, stormwater drains, inland and coastal waters) is provided
in the Technical Memorandum on Standards for Effluents Discharged into Drainage
and Sewerage Systems, Inland and Coastal Waters (TM-DSS). The limits given in
the TM-DSS cover the physical, chemical and microbial qualities of the effluents.
Any effluent discharge during the construction and operational stages should
comply with the relevant standards as stipulated in the TM-DSS.
Practice Notes
6.2.4
The Practice Note (PN) for
Professional Persons on Construction Site Drainage (ProPECC PN 1/94) issued by
EPD provides good practice guidelines for dealing with various types of
discharge from a construction site. Practices outlined in the PN should be
followed as far as possible during construction to minimize the water quality
impact due to construction site drainage.
6.3.1
Any discharge from the Project
works during the construction and operational phases would potentially affect
the inland waters within the Victoria Harbour (Phase One) WCZ.
6.3.2
Major inland water bodies
within 500m from the Project site boundaries were identified and their
indicative locations are shown in Figure 6.1. These inland water bodies
include Ma Yau Tong Streams (in the vicinity of the southern Project site) as
well as the streams and channelized nullahs near Clear Water Bay Road in the
north. Descriptions of these inland waters are provided in Table
6.2.
Table 6.2 Descriptions of
Inland Waters
|
Inland
Waters (refer to Figure 6.1)
|
Closest
Distance from Project Site
|
Generalized
Flow Direction
|
Height
Relative to Project Site
|
|
Ma Yau Tong Streams near the southern
Project site
(Part natural streams / part channelized)
|
About 100 m
|
Water generally flows from the northeast or
southeast towards the Project site in the west and discharges to the drainage
network underneath the Project site and eventually flows to the Victoria
Harbour.
|
Range from about ±200 mPD in the upstream
to about ±80 mPD in the downstream as compared to the height of Project site
at about ±80 mPD
|
|
Channelized
nullahs near the northern Project site at Clear Water Bay Road
|
Immediate
vicinity
|
Water
generally flows from the north towards the south (some nullahs flow across
the Project site via underground drainage) and eventually discharges to the
Victoria Harbour.
|
Range
from over 250 mPD in the upstream to about ±170 mPD in the downstream as
compared to the height of Project site at about ±170 mPD
|
Ma Yau Tong Streams
6.4.1
Water quality monitoring data
for Ma Yau Tong Streams (close to the southern Project site) are available from
the approved Schedule 3 EIA Report for Development of Anderson Road Quarry (EIAO
Register No. AEIAR-183/2014). Monitoring data at Ma Yau Tong Stream are
available in terms of suspended solids (SS), dissolved oxygen (DO), temperature,
pH, flow rate, nutrients (ammonia and unionized ammonia), biochemical oxygen
demand (BOD) and chemical oxygen demand (COD), salinity and E. coli.
These monitoring data were collected at 4 monitoring locations, namely A, B, C
and D, as shown in Figure 6.1. The measurement was carried out three
times a week within two consecutive weeks for both dry season (i.e. March 2013)
and wet season (i.e. June 2013). The monitoring results as extracted from the
Schedule 3 EIA Report are presented in Table 6.3 and Table 6.4.
Table 6.3 Summary of Water
Quality Monitoring Data for Ma Yau Tong Streams
(Dry Season)
|
Parameter
|
Unit
|
Monitoring Data During Dry Season
|
|
Location
A
|
Location
B
|
Location
C
|
Location
D
|
|
Suspended Solids (SS)
|
mg/L
|
6.6
|
96.1
|
1.9
|
2.6
|
|
(1.2-11.0)
|
(0.7-358.5)
|
(0.6-3.8)
|
(0.8-6.3)
|
|
Ammonia as N
|
mg/L
|
0.02
|
0.73
|
8.53
|
8.57
|
|
(0.01-0.02)
|
(<0.01-1.67)
|
(5.95-10.45)
|
(5.45-13.35)
|
|
Unionized Ammonia (as N)
|
mg/L
|
<0.01
|
0.1
|
0.3
|
0.2
|
|
(<0.01-<0.01)
|
(<0.01-0.2)
|
(0.2-0.4)
|
(0.1-0.4)
|
|
Chemical Oxygen Demand (COD)
|
mg/L
|
6.5
|
24.4
|
15.8
|
16.6
|
|
(3.0-11.5)
|
(3.0-89.5)
|
(14.0-19.5)
|
(11.0-23.5)
|
|
Biochemical Oxygen Demand (BOD)
|
mg/L
|
1.5
|
15.1
|
5.7
|
5.4
|
|
(<1-1.5)
|
(<1-52.5)
|
(5.0-6.5)
|
(4.0-9.0)
|
|
pH Value
|
-
|
7.8
|
8.2
|
7.9
|
7.8
|
|
(7.2-8.3)
|
(7.4-8.7)
|
(7.8-8.0)
|
(7.7-8.0)
|
|
Temperature
|
°C
|
20.3
|
20.8
|
21.4
|
21.4
|
|
(19.3-21.8)
|
(19.2-23.6)
|
(19.4-23.5)
|
(19.1-23.8)
|
|
Salinity
|
g/L
|
0.1
|
<0.1
|
0.2
|
0.2
|
|
(<0.1-0.1)
|
(<0.1-0.2)
|
(0.1-0.2)
|
(<0.1-0.2)
|
|
Turbidity
|
NTU
|
9.3
|
220.3
|
4.4
|
4.4
|
|
(3.0-19.0)
|
(3.5-758.0)
|
(3.0-7.0)
|
(2.5-7.0)
|
|
Water Flow
|
L/s
|
3
|
<1
|
16
|
15
|
|
(2-4)
|
(<1-<1)
|
(12-25)
|
(12-20)
|
|
Dissolved
Oxygen
|
mg/L
|
7.6
|
8.3
|
7.7
|
7.6
|
|
(5.0-9.7)
|
(5.8-10.0)
|
(6.5-9.3)
|
(6.9-8.6)
|
|
Dissolved Oxygen - % Saturation
|
%
|
84.2
(54.9-106.0)
|
83.2
(68.1-95.4)
|
83.6
(73.5-92.9)
|
85.6
(79.5-96.4)
|
|
E. coli
|
cfu/
100mL
|
450
|
1,200
|
31,000
|
23,000
|
|
(40-2,700)
|
(N.D.-20,000)
|
(11,000-110,000)
|
(6,000-72,000)
|
Note: N.D. indicates not
detected.
Table 6.4 Summary of Water Quality
Monitoring Data for Ma Yau Tong Stream (Wet Season)
|
Parameter
|
Unit
|
Monitoring
Data During Wet Season
|
|
Location
A
|
Location
B
|
Location
C
|
Location
D
|
|
Suspended Solids (SS)
|
mg/L
|
15.5
|
227.7
|
39.6
|
104.4
|
|
(2.8-37.5)
|
(18.6-492.0)
|
(2.5-143.5)
|
(4.8-201.5)
|
|
Ammonia as N
|
mg/L
|
0.01
|
0.03
|
0.86
|
0.69
|
|
(<0.01-0.02)
|
(<0.01-0.07)
|
(0.01-2.18)
|
(0.03-1.26)
|
|
Unionized Ammonia (as N)
|
mg/L
|
<0.01
|
<0.01
|
0.03
|
<0.01
|
|
(<0.01-<0.01)
|
(<0.01-<0.01)
|
(<0.01-0.1)
|
(<0.01-0.1)
|
|
Chemical Oxygen Demand
|
mg/L
|
6.4
|
8.0
|
7.9
|
10.1
|
|
(<2-8.5)
|
(3.0-18.5)
|
(2.0-14.0)
|
(4.0-15.5)
|
|
Biochemical Oxygen Demand
|
mg/L
|
1.0
|
1.5
|
3.5
|
2.2
|
|
(<1-1.0)
|
(<1-2.0)
|
(<1-5.0)
|
(1.0-4.0)
|
|
pH Value
|
-
|
7.4
|
8.1
|
7.8
|
7.9
|
|
(6.7-7.8)
|
(8.0-8.6)
|
(7.7-7.9)
|
(7.8-8.0)
|
|
Temperature
|
°C
|
23.6
|
24.6
|
24.9
|
24.7
|
|
(23.1-24.4)
|
(24.0-26.0)
|
(23.5-27.3)
|
(23.5-27.0)
|
|
Salinity
|
g/L
|
<0.1
|
<0.1
|
<0.1
|
<0.1
|
|
(<0.1-<0.1)
|
(<0.1-<0.1)
|
(<0.1-<0.1)
|
(<0.1-<0.1)
|
|
Turbidity
|
NTU
|
20.9
|
308.6
|
48.1
|
129.4
|
|
(4.5-57.5)
|
(32.0-576.5)
|
(5.0-168.0)
|
(6.0-255.5)
|
|
Water Flow
|
L/s
|
88
|
15
|
38
|
102
|
|
(55-225)
|
(5-30)
|
(20-90)
|
(48-195)
|
|
Dissolved Oxygen
|
mg/L
|
8.3
|
8.1
|
7.9
|
8.0
|
|
(6.9-8.8)
|
(8.0-8.3)
|
(6.7-8.4)
|
(7.6-8.6)
|
|
Dissolved Oxygen - % Saturation
|
%
|
96.3
|
97.7
|
94.6
|
96.8
|
|
(81.5-101.0)
|
(94.5-99.0)
|
(84.0-99.0)
|
(93.0-101.5)
|
|
E. coli
|
cfu/
100 mL
|
900
|
1,600
|
6,000
|
9,000
|
|
(60-22,000)
|
(30-24,000)
|
(600-33,000)
|
(1,000-39,000)
|
6.4.2
Monitoring data shown in above
tables indicate that levels of nutrients at all monitoring locations are low.
All monitoring locations have relatively high concentrations of DO. The
comparatively higher concentrations of BOD and COD during dry season might be
due to the low runoff volume and minor wastewater discharges from nearby
villages. Generally, the water quality conditions at Ma Yau Tong Streams are
satisfactory except relatively high levels of suspended solids (SS) at Location
B and relatively high E. coli levels at Locations C and D. The relatively high
SS levels recorded at Location B was affected by the nearby construction works during
the monitoring period. Such construction works
are expected to be completed before the commencement of this Project. Locations
C and D received water flows through the village houses at Ma Yau Tong. The relatively
high E. coli levels recorded at these 2 locations could be caused by the possible
sewage discharges from the nearby village houses.
Channelized Nullahs near Clear Water Bay Road
6.4.3
The catchments of these
channelized nullahs mostly are undeveloped areas. In particular, the upstream
sections of these nullahs are mainly collecting the runoff from the country
park areas with no major pollution source. In dry season, most of these nullahs
are expected to be dry, whereas in the wet seasons, the water flows in these
nullahs mostly would be rainwater with low pollution levels. Site inspections
and water sampling at these channelized nullahs were conducted in August 2015 representing
the wet season. It was observed during
the site inspections that most of these nullahs were dried out or had a very
low flow (with water depth of less than 3 cm).
Due to the low water flow, water sampling was only practical to be
carried out at three stations (namely Stations E, F and G respectively) in the
downstream sections of these channelized nullahs as shown in Figure 6.1.
The associated sampling results are shown in Table 6.5.
Table 6.5 Water Quality Monitoring
Data for Channelized Nullahs at Clear Water Bay Road
|
Parameter
|
Unit
|
Averaged
Value of 2 Consecutive Measurements
|
|
Station
E
|
Station
F
|
Station
G
|
|
pH Value
|
-
|
|
|
|
|
7.62
|
7.01
|
6.90
|
|
Temperature
|
°C
|
|
|
|
|
25.3
|
28.6
|
24.8
|
|
Salinity
|
ppt
|
|
|
|
|
0.0
|
0.4
|
0.1
|
|
Turbidity
|
NTU
|
|
|
|
|
7.82
|
16.9
|
0.01
|
|
Dissolved Oxygen
|
mg/L
|
|
|
|
|
7.06
|
6.31
|
5.94
|
|
Dissolved Oxygen - % Saturation
|
%
|
|
|
|
|
86.6
|
80.9
|
72.7
|
6.4.4
The pH and DO levels measured
at all the three stations were good. The turbidity level measured at Station F
was however relatively high, which could be due to the site constraint that the
water depth at this station was extremely shallow, and the bottom silt was
unavoidably disturbed during the sampling event.
6.5
Assessment Methodologies
6.5.1
The study area for the water
quality impact assessment covers all areas within 500m from the Project
boundary in Victoria Harbour (Phase One) Water Control Zone (WCZ) designated
under the Water Pollution Control Ordinance (WPCO) and other areas that may have
a bearing on the environmental acceptability of the Project.
6.5.2
The Water Sensitive Receivers
(WSRs) that may be affected by the Project have been identified.
Potential sources of water quality impact that may arise during the
construction and operational stages of the Project were described. This
task included identifying pollutants from point discharges and non-point
sources that could affect the quality of surface water bodies. All the
identified sources of potential water quality impact were then evaluated and
their impact significance determined. The need for mitigation measures to
reduce any identified adverse impacts on water quality to acceptable levels was
determined.
Construction Phase
6.6.1
The proposed construction works
would not alter the streams and water courses
identified in the study area. Potential sources of
water quality impact associated with the land-based construction of the Project
have been identified and include:
Ÿ
General construction activities
Ÿ
Construction site run-off;
Ÿ
Accidental spillage;
Ÿ
Sewage effluent from construction workforce; and
Ÿ
Construction works in close proximity of inland water.
6.6.2
Based on the findings from the land
contamination assessment provided in Section 8, no historical
contaminative land uses were identified within the Project sites. Thus, generation
of contaminated groundwater is not an issue of concern for this Project.
General
Construction Activities
6.6.3
The land-based construction
works could have the potential to cause water pollution. Various types of construction activities may
generate wastewater. These include general cleaning and polishing, wheel
washing, dust suppression and utility installation. These types of wastewater
would contain high concentrations of suspended solids (SS). Various
construction works may also generate debris and rubbish such as packaging,
construction materials and refuse. Uncontrolled
discharge of site effluents, rubbish and refuse generated from the construction
works would lead to deterioration in water quality.
Construction
Site Run-off
6.6.4
The total construction works
area for all the RIW sites would be approximately 0.013 km2. Assuming the works area is 100% active and a
runoff coefficient of 1 (for conservative estimation), the total peak runoff
generated from the construction site would be in the order of about 2,700 m3 per hour under a 10-year-return-period rainstorm and design duration of 5
minutes according to the Stormwater Drainage Manual of
the Drainage Services Department (DSD). Potential pollution sources of site run-off
may include:
Ÿ
Run-off and erosion of exposed bare soil and earth, drainage
channel, earth working area and stockpiles;
Ÿ
Release of any bentonite slurries, concrete washings and other
grouting materials with construction run-off or storm water;
Ÿ
Wash water from dust suppression sprays and wheel washing
facilities; and
Ÿ
Fuel, oil and lubricants from maintenance of construction
vehicles and equipment.
6.6.5
During rainstorms, site run-off
would wash away the soil particles on unpaved lands and areas with the topsoil
exposed. The run-off is generally
characterized by high concentrations of SS.
Release of uncontrolled site run-off would increase the SS levels and
turbidity in the nearby water environment.
Site run-off may also wash away contaminated soil particles and
therefore cause water pollution.
6.6.6
Wind blown dust would be generated from exposed soil surfaces in the works
areas. It is possible that wind blown dust would fall directly onto the nearby water
bodies when a strong wind occurs.
Dispersion of dust within the works areas may increase the SS levels in
surface run-off causing a potential impact to the nearby sensitive receivers.
Accidental
Spillage
6.6.7
A large variety of chemicals
may be used during construction activities.
These chemicals may include petroleum products, surplus adhesives, spent
lubrication oil, grease and mineral oil, spent acid and alkaline solutions/solvent
and other chemicals. Accidental spillage
of chemicals in the sites may contaminate the surface soils. The contaminated soil particles may be washed
away by construction site run-off or stormwater drainage which in turn causes
water pollution.
Sewage
Effluent from Construction Workforce
6.6.8
During the construction of the
Project, the workforce on site will generate sewage effluents, which are
characterized by high levels of BOD, ammonia and E. coli counts. Based on the DSD Sewerage
Manual, the sewage production rate for construction workers is estimated at
0.35 m3 per worker per day. For every 100
construction workers working simultaneously at the construction site, about
35 m3 of sewage would be generated per day. Potential water
quality impacts upon the local drainage and fresh water system may arise from these
sewage effluents, if uncontrolled.
Construction
Works in Close Proximity of Inland Water
6.6.9
Construction activities in
close vicinity to the inland water courses may pollute the inland water bodies
due to the potential release of construction wastes. Construction wastes are
generally characterized by high concentration of SS and elevated pH. Mitigation measures should be implemented to control
the release of construction waste and site effluent into the nearby inland
water bodies.
Operational
Phase
6.6.10
The identified potential
sources of impact on water quality during the operational phase would be runoff
from the road surfaces. Based on the paved area of the RIW sites of
approximately 0.01 km2 and a runoff coefficient of 1, the total peak runoff generated from
the Project sites would be in the order of about 2,000 m3 per hour under a 10-year-return-period rainstorm and design duration of 5
minutes according to the Stormwater Drainage Manual of
the DSD. The road
runoff may contain small amount of oil and grit leaked from passing
vehicles. However, impacts upon water
quality will be minimal provided that the road works are designed with adequate
drainage systems and appropriate silt trap, as required.
Construction Phase
General Construction
Activities
6.7.1
Effluent discharged from
temporary site facilities should be controlled to prevent direct discharge to
the neighbouring inland waters and storm drains. Such effluent may include wastewater
resulting from wheel washing of site vehicles at site entrances. Debris and rubbish such as packaging,
construction materials and refuse generated from the construction activities
should also be properly managed and controlled to avoid accidental release to
the local storm system and inland waters.
Adoption of the guidelines and good site practices for handling and
disposal of construction discharges as specified in Section 6.9 would minimize the potential impacts.
Construction Site
Run-off
6.7.2
Construction site run-off and
drainage may impact local water quality.
Increase in SS arising from the construction site could block the
drainage channels. High concentrations of suspended degradable organic material
in marine water could lead to reduction in DO levels in the water column.
6.7.3
It is important that proper
site practice and good site management (as specified in the ProPECC PN 1/94
“Construction Site Drainage”) to be followed to prevent run-off with high level
of SS from entering the surrounding waters.
With the implementation of appropriate measures to control run-off and
drainage from the construction site, disturbance of water bodies would be avoided
and deterioration in water quality would be minimal. Thus, unacceptable impacts on the water
quality are not expected, provided that the relevant mitigation measures as specified
in the ProPECC PN 1/94 “Construction Site Drainage” are properly implemented.
Accidental Spillage
6.7.4
The use of engine oil and
lubricants, and their storage as waste materials has the potential to create
impacts on the water quality if spillage occurs and enters adjacent water
environment. Waste oil may infiltrate into
the surface soil layer, or run-off into the nearby water environment,
increasing hydrocarbon levels. The
potential impacts could however be mitigated by practical mitigation measures
and good site practices (as given in Section 6.9).
Sewage Effluent from
Construction Workforce
6.7.5
Domestic sewage would be
generated from the workforce during the construction phase. However, this temporary sewage can be adequately
treated by interim sewage treatment facilities, such as portable chemical
toilets. Provided that sewage is not discharged directly into storm drains or inland
waters adjacent to the construction site, and temporary sanitary facilities are
used and properly maintained, it is unlikely that sewage generated from the
sites would have a significant water quality impact.
Construction Works in Close Proximity of
Inland Water
6.7.6
Construction activities in
close vicinity to the inland water courses may pollute the inland water bodies
due to the potential release of construction wastes. Construction wastes are
generally characterized by high concentration of SS and elevated pH. The implementation of measures to control runoff and
drainage will be important for the construction works adjacent to the inland
water in order to prevent runoff and drainage water with high levels of SS from
entering the water environment. With the implementation of adequate
construction site drainage as specified in the ProPECC PN 1/94 “Construction
Site Drainage” and the provision of mitigation measures as described in the
ETWB TC (Works) No. 5/2005 “Protection
of natural streams/rivers from adverse impacts arising from construction works”,
it is anticipated that unacceptable water quality impacts would not arise.
Operational Phase
6.7.7
The identified potential source
of impact on water quality during the operational phase of the Project is
runoff from the road surfaces. The road run-off may contain minimal amount of
oil, grease and grit that may cause water quality impacts to the receiving
waters in Victoria Harbour WCZ. To
minimise the impacts from road run-off, a road drainage system will be properly
planned to receive road run-off at the planning and design stages. With proper implementation of recommended
mitigation measures and best management practices described in Section 6.9, adverse impact associated with the discharge of runoff is not
anticipated.
Construction
Phase
Control of Site Run-off
of Different General Construction Activities as
follows:
Boring and
Drilling Water
6.9.1 Water used in ground boring and drilling
for site investigation or rock / soil anchoring should as far as practicable be
re-circulated after sedimentation. When there
is a need for final disposal, the wastewater should be discharged into storm
drains via silt removal facilities.
Wheel
Washing Water
6.9.2 All vehicles and plant should be cleaned before they leave a
construction site to minimize the deposition of earth, mud, debris on roads. A
wheel washing bay should be provided at every site exit if practicable and
wash-water should have sand and silt settled out or removed before discharging
into storm drains. The section of construction road between the wheel washing
bay and the public road should be paved with backfall
to reduce vehicle tracking of soil and to prevent site run-off from entering
public road drains.
Rubbish
and Litter
6.9.3
Good site practices should be
adopted to remove rubbish and litter from construction sites so as to prevent
the rubbish and litter from spreading from the site area. It is recommended to
clean the construction sites on a regular basis.
Construction
Site Run-off
6.9.4 The site practices outlined in
ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as
practicable to minimise surface run-off and the chance of erosion. The following measures are
recommended to protect water quality and sensitive uses of the coastal area,
and when properly implemented should be sufficient to adequately control site
discharges so as to avoid water quality impact:
6.9.5 Surface run-off from construction
sites should be discharged into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps
and sedimentation basins. Channels 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 on site boundaries 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.
6.9.6 Silt removal facilities, channels
and manholes should be maintained and the deposited silt and grit should be
removed regularly, at the onset of and after each rainstorm to prevent local flooding. Any practical options for
the diversion and re-alignment of drainage should comply with both
engineering and environmental requirements in order to provide adequate
hydraulic capacity of all drains. Minimum distance of 100m should be maintained
between the discharge points of construction site run-off and the existing
saltwater intakes. No effluent will be discharged into typhoon shelter.
6.9.7 Construction works should be
programmed to minimize soil excavation works in rainy seasons (April to
September). If excavation in soil cannot be avoided in these months or at
any time of year when rainstorms are
likely, for the purpose of preventing soil erosion, temporary exposed slope
surfaces should be covered e.g. by tarpaulin, and temporary access roads should
be protected by crushed stone or gravel, as excavation proceeds. Intercepting
channels should be provided (e.g. along the crest / edge of excavation) to
prevent storm runoff from washing across exposed soil surfaces. Arrangements
should always be in place in such a way that adequate surface protection
measures can be safely carried out well before the arrival of a rainstorm.
6.9.8 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.
6.9.9 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.
6.9.10 Construction materials (e.g.
aggregates, sand and fill material) on sites should be covered with tarpaulin
or similar fabric during rainstorms.
6.9.11 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.
6.9.12 Good site practices should be
adopted to remove rubbish and litter from construction sites so as to prevent
the rubbish and litter from spreading from the site area. It is recommended to
clean the construction sites on a regular basis.
Site
Effluent
6.9.13
There is a need to apply to EPD
for a discharge licence for discharge of effluent from the construction site
under the WPCO. The discharge quality
must meet the requirements specified in the discharge licence. All the runoff and wastewater generated
from the works areas should be treated so that it satisfies all the standards
listed in the TM-DSS. The beneficial
uses of the treated effluent for other on-site activities such as dust
suppression, wheel washing and general cleaning etc., can minimise water
consumption and reduce the effluent discharge volume. If monitoring of the treated effluent quality
from the sites is required during the construction phase of the Project, the
monitoring should be carried out in accordance with the relevant WPCO licence
which is under the ambit of regional office (RO) of EPD.
Accidental Spillage
6.9.15
Any service shop and
maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be
provided. Maintenance of vehicles and
equipment involving activities with potential for leakage and spillage should
only be undertaken within the areas appropriately equipped to control these
discharges.
Ÿ
Suitable containers should be used to hold the chemical wastes
to avoid leakage or spillage during storage, handling and transport;
Ÿ
Chemical waste containers should be suitably labelled, to
notify and warn the personnel who are handling the wastes, to avoid accidents;
and
Ÿ
Storage area should be selected at a safe location on site and
adequate space should be allocated to the storage area.
Sewage
Effluent from Construction Workforce
Construction
Works in Close Proximity of Inland Waters
·
Construction works close to the
inland waters should be carried out in dry season as far as practicable where
the flow in the surface channel or stream is low.
·
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 during carrying
out of the construction works.
·
Stockpiling of construction
materials and dusty materials should be covered and located away from any water
courses.
·
Construction debris and spoil
should be covered up and/or disposed of as soon as possible to avoid being
washed into the nearby water receivers.
·
Proper shoring may need to be
erected in order to prevent soil or mud from slipping into the watercourses.
Operational
Phase
6.9.20 Best Management Practices (BMPs) to reduce
storm water and non-point source pollution have been proposed for the RIW as
follows:
Design
Measures
·
Exposed
surface shall be avoided within the RIW sites to minimize soil erosion. The development site shall be either hard
paved or covered by landscaping area where appropriate.
·
The streams and channelized nullahs near the RIW sites will be
retained to maintain the original flow path. The drainage system will be designed to avoid flooding.
·
Green areas / tree / shrub planting etc. will be introduced along roadside
amenity strips and central dividers as far as possible, which can help to
reduce soil erosion.
·
Evergreen trees species, which in general generate relatively
smaller amount of fallen leaves, should be selected where possible.
Devices/
Facilities to Control Pollution
6.9.21 In addition to the above, the following devices/ facilities will be incorporated into
the design:
·
Screening
facilities such as standard gully grating and trash grille, with spacing which
is capable of screening off large substances such as fallen leaves and rubbish
should be provided at the inlet of drainage system.
·
Road
gullies with standard design and silt traps and oil interceptors should be
incorporated during the detailed design to remove particles present in
stormwater runoff, where appropriate.
Administrative Measures
6.9.22
Good
management measures such as regular cleaning and sweeping of road surface/ open
areas are suggested. The road surface/ open area cleaning should also be
carried out prior to occurrence rainstorm.
6.9.23
Manholes, as well as stormwater gullies, ditches provided at the
Project sites should be regularly inspected and cleaned (e.g. monthly). Additional inspection and cleansing should be
carried out before forecast heavy rainfall.
6.10.1 With the full implementation of the recommended
mitigation measures for the construction and operational phases of the proposed
Project, no residual impacts on water quality are anticipated.
6.11.1 Water quality monitoring is recommended
for Ma Yau Tong Stream and the channelized nullahs at Clear Water Bay Road
during the site formation works. Details of the
recommended water quality monitoring requirements are provided in the
stand-alone EM&A Manual for the Project. It is recommended that regular site inspections during the construction
phase should be undertaken to inspect the construction activities and works
areas in order to ensure the recommended mitigation measures are properly
implemented.
Construction
Phase
6.12.1 Water Sensitive Receivers (WSRs) are identified for the water
quality impact assessment. The key issue from the land-based road improvement
works construction activities would be the potential for release of wastewater
from surface works areas and open cut excavation. Minimization of water quality
deterioration could be achieved through implementing adequate mitigation
measures, such as control of site run-off of different general construction
activities. Regular site inspections should be undertaken routinely to inspect
the construction activities and works areas in order to ensure the recommended
mitigation measures are properly implemented.
Operational
Phase
6.12.2 The only source of potential impact on water quality during the
operational phase will be runoff from the road surfaces. It is anticipated that
the water quality impact associated with the operational phase would be minimal
and acceptable, provided that the recommended mitigation measures (such as
design measures to be incorporated and devices/facilities to control pollution)
and best management practices are properly implemented.