6.1
Legislation,
Standards and Guidelines
6.1.1.1
The following relevant
legislation, standards and guidelines are applicable to the evaluation of water
quality impacts associated with the construction and operation of the project.
·
Water
Pollution Control Ordinance (WPCO) CAP 358;
·
Technical
Memorandum for Effluents Discharged into Drainage and Sewerage Systems Inland
and Coastal Waters (TM-DSS);
·
Environmental
Impact Assessment Ordinance (EIAO) (CAP. 499), Technical Memorandum on
Environmental Impact Assessment Process (TM-EIAO);
·
No Net
Increase in Pollution Loads Requirement in Deep Bay;
·
Hong Kong
Planning Standards and Guidelines; and
·
ProPECC PN
1/94 “Construction Site Drainage.
6.1.2
Water Pollution Control
Ordinance, CAP 358
6.1.2.1
The entire Hong Kong waters
are divided into Water Control Zones (WCZs) and supplementary WCZs under the
Water Pollution Control Ordinance (WPCO) (CAP 358). Each WCZ has a designated
set of statutory Water Quality Objectives (WQOs) designed to protect the inland
and/or marine environment and its users. The proposed C&C facilities are
located within the Deep Bay WCZ and the applicable WQOs for the Deep Bay WCZ
for assessing compliance of any effects from the construction and operational
phases are presented in Table 6.1.
Table 6.1 Water Quality Objectives
for Deep Bay 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
|
|
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
|
|
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 Subzones
|
|
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
|
Shall not cause excessive algal growth
|
Marine waters
|
|
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 610 per 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 180 per 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 14 days.
|
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 21 days
|
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
|
Yuen Long Bathing Beach Subzone
|
|
Phenol
|
Quantities shall not sufficient to produce a
specific odour or more than 0.05mg/L as C6H5OH
|
Yuen 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
|
6.1.3
Technical Memorandum on
Standards for Effluents Discharged into Drainage and Sewerage Systems Inland
and Coastal Waters (TM-DSS)
6.1.3.1
Apart from the WQOs,
Section 21 of the WPCO also specifies the limits to control the physical,
chemical and microbial parameters for effluent discharges into drainage and
sewerage system at both inland and coastal waters under the Technical
Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM-DSS). The discharge limits vary with the effluent flow
rates. Groups B and C inland water standards in TM-DSS are adopted and the
effluent discharge standards are presented in Tables 6.2 and 6.3
respectively.
Table
6.2
Standards for effluents discharged into Group B inland waters
|
Parameter[1]
|
Flow Rate(m³/day)
|
|
£
200
|
＞200
and
£400
|
＞400
and
£600
|
＞600
and
£800
|
＞800
and
£1000
|
＞1000
and
£1500
|
＞1500
and
£2000
|
＞2000
and
£3000
|
|
pH (pH
units)
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
6.5-8.5
|
|
Temperature
(°C)
|
35
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
|
Colour
(lovibond units)(25mm cell length)
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
|
Suspended
solids (mg/L)
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
30
|
|
BOD (mg/L)
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
20
|
|
COD (mg/L)
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
80
|
|
Oil &
Grease (mg/L)
|
10
|
10
|
10
|
10
|
10
|
10
|
10
|
10
|
|
Iron (mg/L)
|
10
|
8
|
7
|
5
|
4
|
3
|
2
|
1
|
|
Boron (mg/L)
|
5
|
4
|
3
|
2.5
|
2
|
1.5
|
1
|
0.5
|
|
Barium (mg/L)
|
5
|
4
|
3
|
2.5
|
2
|
1.5
|
1
|
0.5
|
|
Mercury (mg/L)
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Cadmium (mg/L)
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Selenium (mg/L)
|
0.2
|
0.2
|
0.2
|
0.2
|
0.2
|
0.1
|
0.1
|
0.1
|
|
Other toxic
metals individually (mg/L)
|
0.5
|
0.5
|
0.2
|
0.2
|
0.2
|
0.1
|
0.1
|
0.1
|
|
Total Toxic
metals (mg/L)
|
2
|
1.5
|
1
|
0.5
|
0.5
|
0.2
|
0.2
|
0.2
|
|
Cyanide (mg/L)
|
0.1
|
0.1
|
0.1
|
0.08
|
0.08
|
0.05
|
0.05
|
0.03
|
|
Phenols (mg/L)
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
0.1
|
|
Sulphide (mg/L)
|
0.2
|
0.2
|
0.2
|
0.2
|
0.2
|
0.2
|
0.2
|
0.2
|
|
Fluoride (mg/L)
|
10
|
10
|
8
|
8
|
8
|
5
|
5
|
3
|
|
Sulphate (mg/L)
|
800
|
800
|
600
|
600
|
600
|
400
|
400
|
400
|
|
Chloride (mg/L)
|
1000
|
1000
|
800
|
800
|
800
|
600
|
600
|
400
|
|
Total
phosphorus (mg/L)
|
10
|
10
|
10
|
8
|
8
|
8
|
5
|
5
|
|
Ammonia
nitrogen (mg/L)
|
5
|
5
|
5
|
5
|
5
|
5
|
5
|
5
|
|
Nitrate +
nitrite nitrogen (mg/L)
|
30
|
30
|
30
|
20
|
20
|
20
|
10
|
10
|
|
Surfactants
(total) (mg/L)
|
5
|
5
|
5
|
5
|
5
|
5
|
5
|
5
|
|
E. coli (count/100mL)
|
100
|
100
|
100
|
100
|
100
|
100
|
100
|
100
|
Note:
[1] All units in mg/L unless otherwise stated.
Table
6.3 Standards for effluents discharged into Group C inland waters
|
Parameter[1]
|
Flow Rate (m3/day)
|
|
≤ 100
|
> 100 and ≤ 500
|
> 500 and ≤ 1000
|
> 1000 and ≤ 2000
|
|
pH (pH
units)
|
6-9
|
6-9
|
6-9
|
6-9
|
|
Temperature
(˚C)
|
30
|
30
|
30
|
30
|
|
Colour
(lovibond units)
(25mm cell length)
|
1
|
1
|
1
|
1
|
|
Suspended
solids (mg/L)
|
20
|
10
|
10
|
5
|
|
BOD (mg/L)
|
20
|
15
|
10
|
5
|
|
COD (mg/L)
|
80
|
60
|
40
|
20
|
|
Oil &
Grease (mg/L)
|
1
|
1
|
1
|
1
|
|
Boron (mg/L)
|
10
|
5
|
4
|
2
|
|
Barium (mg/L)
|
1
|
1
|
1
|
0.5
|
|
Iron (mg/L)
|
0.5
|
0.4
|
0.3
|
0.2
|
|
Mercury (mg/L)
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Cadmium (mg/L)
|
0.001
|
0.001
|
0.001
|
0.001
|
|
Silver (mg/L)
|
0.1
|
0.1
|
0.1
|
0.1
|
|
Copper (mg/L)
|
0.1
|
0.1
|
0.05
|
0.05
|
|
Selenium (mg/L)
|
0.1
|
0.1
|
0.05
|
0.05
|
|
Lead (mg/L)
|
0.2
|
0.2
|
0.2
|
0.1
|
|
Nickel (mg/L)
|
0.2
|
0.2
|
0.2
|
0.1
|
|
Other toxic
metals individually (mg/L)
|
0.5
|
0.4
|
0.3
|
0.2
|
|
Total toxic
metals (mg/L)
|
0.5
|
0.4
|
0.3
|
0.2
|
|
Cyanide (mg/L)
|
0.05
|
0.05
|
0.05
|
0.01
|
|
Phenols (mg/L)
|
0.1
|
0.1
|
0.1
|
0.1
|
|
Sulphide (mg/L)
|
0.2
|
0.2
|
0.2
|
0.1
|
|
Fluoride (mg/L)
|
10
|
7
|
5
|
4
|
|
Sulphate (mg/L)
|
800
|
600
|
400
|
200
|
|
Chloride (mg/L)
|
1000
|
1000
|
1000
|
1000
|
|
Total
phosphorus (mg/L)
|
10
|
10
|
8
|
8
|
|
Ammonia
nitrogen (mg/L)
|
2
|
2
|
2
|
1
|
|
Nitrate +
nitrite nitrogen (mg/L)
|
30
|
30
|
20
|
20
|
|
Surfactants
(total) (mg/L)
|
2
|
2
|
2
|
1
|
|
E. coli (count/100mL)
|
1000
|
1000
|
1000
|
1000
|
Note:
[1] All units in mg/L unless otherwise stated.
6.1.4
Environmental Impact Assessment
Ordinance (EIAO) (Cap. 499), Technical Memorandum on Environmental Impact
Assessment Process (TM-EIAO)
6.1.4.1
The general criteria and
guidelines for evaluating and assessing water quality impacts are listed in
Annexes 6 and 14 of the TM-EIAO.
6.1.5
No Net Increase in Pollution
Loads Requirement in Deep Bay
6.1.5.1
In addition to the
provisions of the TM, the ‘No Net Increase in Pollution Loads Requirement’ aims
to provide protection to the inland and marine water quality of the Deep Bay
WCZ. According to EPD “Deep Bay Water Quality Regional Control Strategy Study”,
the pollutions entering into Deep Bay have exceeded the assimilative capacity
of the water body [6-1].
Further increasing the pollution loads to the water body is therefore
environmentally undesirable.
6.1.5.2
In accordance with Town
Planning Board Guideline No.12C, the pollution loads of concern should be
offset by equivalent reduction of current loads for new discharge into Deep
Bay. The policy ensures that developments within the Deep Bay catchment areas
do not result in an increase in pollution loads to both the inland and marine
waters.
6.1.6
Hong Kong Planning Standards
and Guidelines
6.1.6.1
Chapter 9 of the Hong Kong
Planning Standards and Guidelines (HKPSG) outlines environmental requirements
that need to be considered in land use planning. The recommended guidelines,
standards and guidance cover the selection of suitable locations for the
developments and sensitive uses, provision of environmental facilities, and
design, layout, phasing and operational controls to minimise the adverse
environmental impacts. It also lists out environmental factors influencing land
use planning and recommended buffer distances for land uses.
6.1.7
ProPECC PN 1/94 “Construction
Site Drainage”
6.1.7.1
Professional Persons
Environmental Consultative Committee Practice Notes (ProPECC PN1/94) on
Construction Site Drainage provides guidelines for the handling and disposal of
construction discharges. It is applicable to this Study for control of site
runoff and wastewater generated during the construction phase. The types of
discharges from construction sites outlined in the ProPECC PN1/94
include:
·
Surface runoff;
·
Groundwater;
·
Boring and drilling water;
·
Wastewater from concrete
batching;
·
Wheel washing water;
·
Bentonite slurries;
·
Water for testing and
sterilization of water retaining structures and water pipes;
·
Wastewater from building
construction and site facilities; and
·
Acid cleaning, etching and
pickling wastewater.
6.2
Description of the Environment
6.2.1
Existing Environment
6.2.1.1
The project site adjoins Ng
Tung River and Shenzhen River to the west and north respectively. Ng Tung
River, also known as River Indus, is a major river in the northern New
Territories. Shenzhen River is the boundary river between the Hong Kong Special
Administration Region (HKSAR) and the Shenzhen Special Economic Zone. Ping Yuen
River, also known as River Ganges, is located at the upstream of Shenzhen River
and about 1.7 km northeast from the project site. Both Ng Tung River and Ping
Yuen River will discharge into Shenzhen River which would eventually discharge
to Inner Deep Bay. Within Inner Deep Bay area, EPD has been operating a total
of 3 marine water quality monitoring stations. Figure
6.2.1 illustrates the location of the monitoring stations.
6.2.2
Baseline Conditions
Water Quality of River Indus and River Ganges
6.2.2.1
EPD’s River Water Quality Monitoring
Stations IN1 and GR1 are the closest monitoring stations to the project site
for River Indus and River Ganges respectively. According to the EPD Reports
‘River Water Quality in Hong Kong’ in 2014[6-2],
the WQO compliance rate of River Indus and River Ganges were 82% and 85% in
2014, 84% and 91% in 2013, 46% and 41% in 1997 respectively.
6.2.2.2
For River
Indus, the River Water Quality Index (WQI) in 2014 were “Excellent” and “Good”
at upstreams and midstreams while “Good” at downstream IN1 due to the backflow
from Shenzhen River. For River Ganges, the River WQIs in 2014 were “Excellent”
and “Good” at upstreams while “Fair” at downstream GR1. River Ganges is still
affected by pollution from livestock farms, unsewered villages and small
industrial establishments in the catchment.
6.2.2.3
The latest
environmental monitoring data are presented in Table 6.4 and the locations of these monitoring stations are
presented in Figure 6.2.1.
Table 6.4 Summary of river water
quality monitoring data for the Ng Tung River (River Indus) at station IN1 and
Ping Yuen River (River Ganges) at station GR1 (2010-2014)
|
Parameter
|
Monitoring Station
|
Concentration [1]
|
|
2010
|
2011
|
2012
|
2013
|
2014
|
|
DO (mg/L)
|
IN1
|
5.1
|
3.7
|
5.0
|
6.0
|
6.1
|
|
GR1
|
6.1
|
7.4
|
7.4
|
7.5
|
6.9
|
|
pH
|
IN1
|
7.4
|
7.3
|
7.3
|
7.2
|
7.2
|
|
GR1
|
7.4
|
7.5
|
7.4
|
7.3
|
7.4
|
|
Suspended Solid (SS) (mg/L)
|
IN1
|
20
|
36
|
33
|
26
|
21
|
|
GR1
|
17
|
16
|
6
|
8
|
7
|
|
BOD5 (mg/L)
|
IN1
|
8
|
7
|
5
|
4
|
4
|
|
GR1
|
6
|
7
|
7
|
9
|
6
|
|
COD (mg/L)
|
IN1
|
18
|
15
|
17
|
14
|
16
|
|
GR1
|
22
|
20
|
18
|
14
|
16
|
Note:
[1] Data
presented are in annual medians of monthly samples.
Water Quality of
Shenzhen River
6.2.2.4
The water quality of
Shenzhen River is monitored by Shenzhen Environmental Monitoring Centre. As
shown in Figure 6.2.1, monitoring stations Quarry, Lo Wu and Ludang
Village for Shenzhen River are the closest reference stations to the project
site. The water quality for 2007-2009 extracted from approved EIA report ‘Regulation
of Shenzhen River Stage IV’ (AEIAR-160/2011) [6-3] is presented in Table 6.5. It can be seen that the water
quality at the upstream station Quarry is much better than that in middle
stream at Lo Wu and Ludang Village stations. The level of nutrients, Chemical
Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5) and faecal coliforms increases
from Quarry to Ludang Village, while Dissolved Oxygen (DO) decreases from
upstream to middle stream. Generally, the COD, BOD5 and DO show non-compliance with
the WQOs at stations Lo Wu and Ludang Village.
Table 6.5 Summary of river water
quality monitoring data for Shenzhen River at Quarry, Lo Wu and Ludang Village stations
(2007-2009)
|
Parameter
|
Monitoring Station
|
Concentration [1], [2]
|
|
2007
|
2008
|
2009
|
|
Temperature (˚C)
|
Quarry
|
25.1
|
24.1
|
22.7
|
|
Lo Wu
|
24.9
|
24.0
|
23.1
|
|
Ludang Village
|
25.0
|
24.2
|
23.3
|
|
pH
|
Quarry
|
7.34
|
7.29
|
7.33
|
|
Lo Wu
|
7.22
|
7.08
|
7.03
|
|
Ludang Village
|
7.21
|
7.14
|
7.10
|
|
DO (mg/L)
|
Quarry
|
6.402
|
6.61
|
5.373
|
|
Lo Wu
|
0.955
|
1.64
|
0.728
|
|
Ludang Village
|
0.930
|
1.00
|
0.457
|
|
COD (mg/L)
|
Quarry
|
11.8
|
17.4
|
12.9
|
|
Lo Wu
|
22.8
|
24.3
|
45.2
|
|
Ludang Village
|
35.7
|
47.4
|
74.2
|
|
BOD5 (mg/L)
|
Quarry
|
3.21
|
3.8
|
2.61
|
|
Lo Wu
|
5.38
|
8.1
|
17.04
|
|
Ludang Village
|
12.26
|
17.2
|
26.32
|
|
Ammonia nitrogen (mg/L)
|
Quarry
|
8.47
|
6.44
|
6.64
|
|
Lo Wu
|
14.05
|
12.47
|
18.32
|
|
Ludang Village
|
21.13
|
19.00
|
30.00
|
|
Total phosphorus (mg/L)
|
Quarry
|
0.425
|
0.367
|
0.435
|
|
Lo Wu
|
1.122
|
0.971
|
1.224
|
|
Ludang Village
|
1.687
|
1.563
|
2.216
|
|
Total nitrogen (mg/L)
|
Quarry
|
11.15
|
12.45
|
13.23
|
|
Lo Wu
|
16.07
|
15.18
|
20.96
|
|
Ludang Village
|
24.02
|
21.93
|
33.54
|
|
Faecal Coliforms (104 cfu/l)
|
Quarry
|
173
|
30
|
39
|
|
Lo Wu
|
5697
|
540
|
2783
|
|
Ludang Village
|
17593
|
2800
|
15842
|
Note:
[1] Data presented are in annual mean of
monthly samples in Quarry station, twice per month samples in Lo Wu and Ludang
Village stations.
[2] Bold and underlined figures indicate
non-compliance with the WQOs.
Water Quality of other
Streams/Ponds within the Study Area
6.2.2.5
The water quality of Nam
Hang Stream (Water Sensitive Receiver WSR 9 in this Study) and fish pond (WSR
10) located in the southeast of the Project was measured by the previous EIA
study for ‘Development of Organic Waste Treatment Facilities, Phase 2’
(AEIAR-180/2013) [6-4]. Three monitoring stations at locations A, B
and C are shown in Figure 6.2.2 and the
results are presented in Table 6.6. It is shown that the water quality was
compliance with WQOs for the tested parameters at upstream location A and
middle stream location B of Nam Hang Stream WSR9, but exceeds in BOD5
for fish pond WSR10 at location C.
Table 6.6 Summary of water quality
monitoring data for watercourse WSR9 and fish pond WSR10 on 15 April 2013
|
Parameter
|
Monitoring Station [1], [2]
|
|
A
|
B
|
C
|
|
pH
|
6.8
|
6.8
|
8.2
|
|
Turbidity (NTU)
|
19
|
2
|
23
|
|
DO (mg/L)
|
5.9
|
4.3
|
12.8
|
|
DO (%)
|
72
|
50
|
154
|
|
Suspended Solids (mg/L)
|
4
|
<2
|
16
|
|
BOD5 (mg/L)
|
<2
|
<2
|
10
|
Note:
[1] Mean value of the sampling.
[2] Bold and underlined figures indicate
non-compliance with the WQOs.
6.2.2.6
An additional baseline
water quality monitoring has been conducted in both wet season and dry season
for Nam Hang Stream WSR 9, between the midstream and downstream section which
is along the eastern boundary of the Project. The monitoring was conducted at 2
locations (M1 and M2) in midstream and downstream of Nam Hang Stream and the
monitoring locations are shown in Figure 6.2.3. A total of 6 sampling
events for wet season were carried out on 22, 24, 26, 29 September and 3, 6
October 2014, and 6 sampling events for dry season were carried out on 17, 19,
21, 24, 26 and 28 November 2014. The monitoring data is summarised in Table 6.7 below. It is noted that the
water quality at M1 and M2, indicating the midstream and downstream of Nam Hang
Stream, was compliance with the WQOs.
Table 6.7 Summary of water quality
monitoring data for Nam Hang Stream WSR 9
|
Parameter
|
Wet Season[1]
|
Dry Season[1]
|
|
M1
|
M2
|
M1
|
M2
|
|
Temperature (oC)
|
27.1 (24.5 – 28.1)
|
27.9 (25.1 – 29.1)
|
22.5 (21.5 – 23.5)
|
20.5 (13.1 – 23.0)
|
|
Flow rate (L/min)
|
1.5 (1.3 – 1.8)
|
3.2 (2.0 – 4.1)
|
1.5 (1.4 – 1.6)
|
2.4 (2.2 – 2.7)
|
|
pH
|
7.1 (6.7 – 7.7)
|
6.9 (6.6 – 7.2)
|
7.2 (7.0 – 7.5)
|
7.0 (6.3 – 7.3)
|
|
Turbidity (NTU)
|
1.9 (1.4 – 2.1)
|
7.6 (4.7 – 13.4)
|
4.5 (2.1 – 11.4)
|
7.4 (2.9 – 13.0)
|
|
DO (mg/L)
|
6.1 (5.5 – 6.6)
|
6.8 (6.5 – 7.1)
|
8.7 (7.5 – 9.2)
|
9.6 (8.6 – 11.8)
|
|
DO (%)
|
75.8 (70.2 – 82.3)
|
86.0 (82.2 – 88.8)
|
103.1 (99.3 – 107.8)
|
107.9 (96.8 – 115.2)
|
|
Suspended Solids (mg/L)
|
2.0 (1.4 – 2.7)
|
8.9 (5.7 – 17.0)
|
2.3 (0.6 – 4.9)
|
9.1 (1.6 – 25.4)
|
|
BOD5 (mg/L)
|
< 2
|
< 2
|
< 2
|
< 2
|
|
COD (mg/L)
|
5 (3.5 – 6)
|
7.2 (5.5 – 8.5)
|
6.8 (4.5 – 9.5)
|
6.3 (5.0 – 8.5)
|
|
E.coli (cfu/100ml)
|
340 (212 – 612)
|
364 (128 – 590)
|
571 (214 – 1010)
|
864 (345 – 2121)
|
|
Ammonia-nitrogen (mg/L)
|
0.06 (0.04 – 0.09)
|
0.09 (0.08 – 0.1)
|
0.05 (0.04 – 0.07)
|
0.09 (0.06 – 0.15)
|
|
Nitrate (mg/L)
|
0.64 (0.6 – 0.7)
|
0.94 (0.91 – 0.97)
|
0.71 (0.66 – 0.77)
|
0.85 (0.81 – 0.90)
|
|
Total Kjedahl Nitrogen (TKN) (mg/L)
|
0.24 (0.2 – 0.4)
|
0.3 (0.2 – 0.4)
|
0.33 (0.2 – 0.8)
|
0.33 (0.2 – 0.4)
|
|
Orthophosphate (mg/L)
|
0.05 (0.03 – 0.06)
|
0.04 (0.02 – 0.05)
|
0.04 (0.04 – 0.05)
|
0.05 (0.04 – 0.06)
|
|
Total phosphrous (mg/L)
|
0.07 (0.05 – 0.1)
|
0.08 (0.06 – 0.12)
|
0.06 (0.06 – 0.08)
|
0.10 (0.08 – 0.11)
|
Note:
[1] Mean
value of the sampling is presented, while the range of data is stated in the
brackets.
6.2.2.7
There is no historical data
available for the Conservation Area (CA) near Yuen Leng Chai (WSR 3) located at
the north of the Project site and the watercourse in the east of San Uk Ling crossing
Lin Ma Hang Road (WSR 12). Therefore, baseline monitoring has been conducted in
both dry season and wet season at 2 locations M3 and M4 and the monitoring
locations are shown in Figure 6.2.3. A total of 6 sampling
events for wet season were carried out on 22, 24, 26, 29 September and 3, 6
October 2014, and 6 sampling events for dry season were carried out on 17, 19,
21, 24, 26 and 28 November 2014. The
monitoring data is summarised in Table
6.8 below.
Table
6.8 Summary
of water monitoring data for Conservation Area M3 and watercourse near Lin Ma
Hang Road M4
|
Parameter
|
Wet Season[1]
|
Dry Season[1]
|
|
M3
|
M4
|
M3
|
M4
|
|
Temperature (oC)
|
28.7 (27.1 – 30.9)
|
25.4 (22.8 – 26.8)
|
22.9 (21.3 – 24.8)
|
21.7 (20.9 – 22.8)
|
|
Flow rate (L/min)
|
1.6 (1.3 – 2.8)
|
5.1 (0.5 – 7)
|
1.3 (1.0 – 1.5)
|
5.1 (4.4 – 5.7)
|
|
pH
|
7.1 (6.9 – 7.6)
|
7.0 (6.5 – 7.4)
|
7.0 (6.8 – 7.2)
|
6.8 (6.4 – 7.1)
|
|
Turbidity (NTU)
|
6.4 (4.4 – 10.6)
|
3.3 (2.4 – 4.0)
|
8.4 (2.7 – 23.2)
|
3.1 (1.2 – 5.7)
|
|
DO (mg/L)
|
4.2 (3.6 – 5.5)
|
7.5 (6.8 – 8.2)
|
8.4 (6.9 – 9.5)
|
8.0 (7.6 – 8.7)
|
|
DO (%)
|
56.3 (44.8 – 74.2)
|
90.3 (82.9 – 98.9)
|
101.8 (89.5 – 107.0)
|
93.9 (88.4 – 112.6)
|
|
Suspended Solids (mg/L)
|
6.8 (5.5 – 10.2)
|
1.8 (0.7 – 2.4)
|
4.1 (2.7 – 6.0)
|
2.6 (0.5 – 4.3)
|
|
BOD5 (mg/L)
|
≤ 2.2 (2 – 3) [3]
|
< 2
|
< 2
|
< 2
|
|
COD (mg/L)
|
8.1 (6 – 11)
|
3.7 (2 – 5)
|
8.3 (6.0 – 10.5)
|
3.7 (3 – 5)
|
|
E.coli (cfu/100ml)
|
110.7 (1 – 259)
|
1864.1 (332 – 9022)
|
88.9 (5 – 260)
|
375.4 (130 – 782)
|
|
Ammonia-nitrogen (mg/L)
|
0.04 (0.01 – 0.11)
|
0.07 (0.03 – 0.15)
|
0.03 (0.01 – 0.05)
|
0.04 (0.03 – 0.06)
|
|
Nitrate (mg/L)
|
< 0.01
|
< 0.01
|
≤ 0.02 (0.01 –
0.05) [3]
|
0.69 (0.28 – 1.09)
|
|
Total Kjedahl Nitrogen (TKN) (mg/L)
|
0.26 (0.2 – 0.3)
|
0.18 (0.1 – 0.3)
|
0.23 (0.2 – 0.35)
|
0.17 (0.1 – 0.25)
|
|
Orthophosphate (mg/L)
|
≤ 0.02 (0.01 –
0.04) [3]
|
0.03 (0.02 – 0.04)
|
≤ 0.02 (0.01 –
0.04) [3]
|
0.02 (0.01 – 0.03)
|
|
Total phosphrous (mg/L)
|
0.02 (0.01 – 0.08)
|
0.05 (0.05-0.06)
|
0.02 (0.01 – 0.02)
|
0.03 (0.02-0.04)
|
Note:
[1] Mean
value of the sampling is presented, while the range of data is stated in the
brackets.
[2] Bold and
underlined figures indicate non-compliance with the WQOs.
[3] One or
more sampling result is below reporting limit.
6.2.2.8
As shown in the above table,
the water quality at M3 and M4 generally comply with the WQOs, except the E.coli count in M4 has exceeded the WQO
in wet season. This may be attributable from the discharge in the vicinity of
the village houses of San Uk Ling and the favourable warm condition for E. coli growth in wet season.
Water
Quality of Deep Bay
6.2.2.9
As discussed in Section 6.2.1, the project site is
located within the Deep Bay WCZ and EPD has been operating 3 monitoring
stations (Stations DM1 to DM3) within the Inner Deep Bay area, where Station
DM1 is more than 12km downstream of Shenzhen River from the project site.
6.2.2.10 According to EPD Reports ‘Marine Water Quality in Hong Kong’ in 2014
[6-5], the compliance level of WQOs at Deep Bay was 40% compared
with 40% in Year 2013. The total inorganic nitrogen at three Stations DM1, DM2
and DM3 were 3.48, 2.61 and 1.48 mg/L respectively and exceeded the WQOs of 0.7
mg/L in Deep Bay Water Control Zone. The inner bay was mostly affected by the
discharges from Shenzhen River as well as Kam Tin River, Yuen Long Creek and
Tin Shui Wai Nullah from the Hong Kong side. Details of EPD’s marine water
quality monitoring at Inner Deep Bay are presented in Table 6.9 and the locations of monitoring stations are presented in
Figure
6.2.1.
Table 6.9 Summary of marine water
quality of Inner Deep Bay (2010-2014)
|
Parameter
|
Monitoring Station
|
Concentration
|
|
2010
|
2011
|
2012
|
2013
|
2014
|
|
Dissolved Oxygen (mg/L)
|
DM1
|
4.2
|
4.8
|
4.9
|
4.3
|
3.7
|
|
DM2
|
4.9
|
5.4
|
5.6
|
5.0
|
4.6
|
|
DM3
|
6.2
|
6.8
|
6.1
|
6.7
|
5.5
|
|
Ammonia Nitrogen (mg/L)
|
DM1
|
2.830
|
2.520
|
1.942
|
2.517
|
2.080
|
|
DM2
|
1.930
|
1.640
|
1.643
|
1.953
|
1.410
|
|
DM3
|
0.436
|
0.438
|
0.433
|
0.382
|
0.536
|
|
Unionised Ammonia, mg/L
(Annual mean)
|
DM1
|
0.025
|
0.024
|
0.014
|
0.026
|
0.026
|
|
DM2
|
0.025
|
0.024
|
0.017
|
0.028
|
0.025
|
|
DM3
|
0.009
|
0.009
|
0.006
|
0.009
|
0.014
|
|
Nitrite Nitrogen, mg/L
|
DM1
|
0.348
|
0.348
|
0.489
|
0.350
|
0.367
|
|
DM2
|
0.348
|
0.308
|
0.420
|
0.296
|
0.291
|
|
DM3
|
0.218
|
0.187
|
0.243
|
0.157
|
0.184
|
|
Nitrate Nitrogen (mg/L)
|
DM1
|
0.628
|
0.735
|
1.193
|
0.913
|
1.030
|
|
DM2
|
0.687
|
0.734
|
1.166
|
0.815
|
0.918
|
|
DM3
|
0.803
|
1.010
|
1.135
|
0.828
|
0.759
|
|
Total Inorganic Nitrogen, mg/L
(Annual mean)
|
DM1
|
3.81
|
3.60
|
3.62
|
3.78
|
3.48
|
|
DM2
|
2.97
|
2.68
|
3.23
|
3.06
|
2.61
|
|
DM3
|
1.46
|
1.63
|
1.81
|
1.37
|
1.48
|
|
Total Kjeldahl Nitrogen (mg/L)
|
DM1
|
3.24
|
3.13
|
2.78
|
3.34
|
2.78
|
|
DM2
|
2.33
|
2.14
|
2.15
|
2.67
|
1.94
|
|
DM3
|
0.65
|
0.79
|
0.70
|
0.69
|
0.85
|
|
Total Nitrogen, mg/L
|
DM1
|
4.22
|
4.22
|
4.47
|
4.60
|
4.17
|
|
DM2
|
3.36
|
3.18
|
3.73
|
3.78
|
3.15
|
|
DM3
|
1.68
|
1.99
|
2.07
|
1.67
|
1.79
|
|
Orthophosphate Phosphorus (mg/L)
|
DM1
|
0.301
|
0.276
|
0.238
|
0.224
|
0.213
|
|
DM2
|
0.236
|
0.227
|
0.206
|
0.185
|
0.183
|
|
DM3
|
0.079
|
0.080
|
0.099
|
0.079
|
0.093
|
|
Total Phosphorous (mg/L)
|
DM1
|
0.38
|
0.38
|
0.34
|
0.36
|
0.31
|
|
DM2
|
0.30
|
0.29
|
0.26
|
0.29
|
0.27
|
|
DM3
|
0.11
|
0.13
|
0.13
|
0.11
|
0.13
|
|
E.coli (cfu/100ml)
(Annual geometric mean)
|
DM1
|
1300
|
1000
|
6100
|
4200
|
1300
|
|
DM2
|
480
|
270
|
2600
|
2000
|
380
|
|
DM3
|
26
|
19
|
36
|
58
|
37
|
|
pH
|
DM1
|
7.3
|
7.3
|
7.1
|
7.3
|
7.4
|
|
DM2
|
7.5
|
7.5
|
7.3
|
7.5
|
7.5
|
|
DM3
|
7.7
|
7.7
|
7.4
|
7.7
|
7.7
|
|
Suspended Solids (mg/L)
|
DM1
|
34.3
|
26.7
|
49.8
|
51.3
|
46.2
|
|
DM2
|
23.8
|
16.2
|
24.9
|
32.2
|
23.0
|
|
DM3
|
10.0
|
10.6
|
8.9
|
11.8
|
15.5
|
|
Salinity (psu)
|
DM1
|
17.2
|
16.9
|
15.5
|
13.7
|
15.5
|
|
DM2
|
19.0
|
19.0
|
16.9
|
15.6
|
17.5
|
|
DM3
|
21.4
|
23.6
|
19.8
|
20.6
|
21.2
|
Water
Quality of Siu Lam
6.2.2.11 As shown in Figure 1.3, a barging point in Siu Lam will be used for the
transport of surplus inert construction and demolition (C&D) materials. The
barging point is located within the North Western WCZ and EPD there are 3 EPD
water quality monitoring stations (Stations NM1 to NM3) near the barging point
(see Figure 6.2.1a).
6.2.2.12 According to EPD Reports ‘Marine Water Quality in Hong Kong’ in 2014
[6-5], the compliance level of WQOs at North Western WCZ was 61%
compared with 72% in Year 2013 due to a lower compliance rate with the TIN
objective. The total inorganic nitrogen at three stations NM1, NM2 and NM3 were
0.42, 0.58 and 0.63 mg/L respectively and exceeded the WQOs of 0.3 mg/L in
North Western WCZ. The North Western WCZ was mostly affected by the discharges
from the Pearl River. Details of EPD’s marine water quality monitoring at North
Western WCZ are presented in Table 6.9a below.
Table
6.9a Summary of marine water quality of North Western WCZ (2010-2014)
|
Parameter
|
Monitoring Station
|
Concentration
|
|
2010
|
2011
|
2012
|
2013
|
2014
|
|
Dissolved Oxygen (mg/L)
|
NM1
|
6.1
|
5.7
|
6.1
|
5.9
|
5.6
|
|
NM2
|
6.4
|
5.8
|
6.8
|
6.1
|
5.8
|
|
NM3
|
6.2
|
6.0
|
6.3
|
6.1
|
5.8
|
|
Ammonia Nitrogen (mg/L)
|
NM1
|
0.116
|
0.114
|
0.122
|
0.104
|
0.093
|
|
NM2
|
0.113
|
0.119
|
0.140
|
0.108
|
0.107
|
|
NM3
|
0.113
|
0.116
|
0.145
|
0.107
|
0.108
|
|
Unionised Ammonia, mg/L
(Annual mean)
|
NM1
|
0.004
|
0.003
|
0.003
|
0.003
|
0.003
|
|
NM2
|
0.004
|
0.004
|
0.003
|
0.003
|
0.003
|
|
NM3
|
0.004
|
0.003
|
0.003
|
0.003
|
0.003
|
|
Nitrite Nitrogen, mg/L
|
NM1
|
0.054
|
0.047
|
0.058
|
0.072
|
0.058
|
|
NM2
|
0.073
|
0.065
|
0.073
|
0.080
|
0.081
|
|
NM3
|
0.064
|
0.074
|
0.078
|
0.081
|
0.091
|
|
Nitrate Nitrogen (mg/L)
|
NM1
|
0.243
|
0.227
|
0.319
|
0.317
|
0.268
|
|
NM2
|
0.318
|
0.324
|
0.484
|
0.408
|
0.394
|
|
NM3
|
0.275
|
0.351
|
0.493
|
0.382
|
0.426
|
|
Total Inorganic Nitrogen, mg/L
(Annual mean)
|
NM1
|
0.41
|
0.39
|
0.50
|
0.49
|
0.42
|
|
NM2
|
0.50
|
0.51
|
0.70
|
0.60
|
0.58
|
|
NM3
|
0.45
|
0.54
|
0.72
|
0.57
|
0.63
|
|
Total Kjeldahl Nitrogen (mg/L)
|
NM1
|
0.28
|
0.23
|
0.29
|
0.26
|
0.27
|
|
NM2
|
0.27
|
0.25
|
0.32
|
0.27
|
0.30
|
|
NM3
|
0.26
|
0.25
|
0.34
|
0.27
|
0.29
|
|
Total Nitrogen, mg/L
|
NM1
|
0.58
|
0.51
|
0.67
|
0.65
|
0.59
|
|
NM2
|
0.66
|
0.64
|
0.87
|
0.76
|
0.78
|
|
NM3
|
0.60
|
0.68
|
0.91
|
0.73
|
0.81
|
|
Orthophosphate Phosphorus (mg/L)
|
NM1
|
0.021
|
0.022
|
0.024
|
0.025
|
0.021
|
|
NM2
|
0.021
|
0.025
|
0.025
|
0.026
|
0.023
|
|
NM3
|
0.021
|
0.025
|
0.026
|
0.027
|
0.025
|
|
Total Phosphorous (mg/L)
|
NM1
|
0.04
|
0.04
|
0.04
|
0.04
|
0.04
|
|
NM2
|
0.04
|
0.04
|
0.04
|
0.04
|
0.04
|
|
NM3
|
0.04
|
0.05
|
0.05
|
0.04
|
0.04
|
|
E.coli (cfu/100ml)
(Annual geometric mean)
|
NM1
|
90
|
42
|
34
|
160
|
300
|
|
NM2
|
65
|
55
|
69
|
140
|
71
|
|
NM3
|
250
|
100
|
180
|
380
|
110
|
|
pH
|
NM1
|
7.9
|
7.8
|
7.7
|
7.9
|
7.9
|
|
NM2
|
7.9
|
7.8
|
7.7
|
7.9
|
7.9
|
|
NM3
|
7.9
|
7.9
|
7.7
|
7.9
|
7.9
|
|
Suspended Solids (mg/L)
|
NM1
|
8.0
|
8.1
|
5.1
|
6.8
|
6.6
|
|
NM2
|
5.6
|
5.9
|
4.0
|
6.6
|
4.3
|
|
NM3
|
6.6
|
6.8
|
5.5
|
6.6
|
7.6
|
|
Salinity (psu)
|
NM1
|
30.0
|
31.0
|
29.2
|
29.0
|
30.2
|
|
NM2
|
28.8
|
29.8
|
26.8
|
27.2
|
28.3
|
|
NM3
|
29.5
|
29.3
|
27.5
|
27.7
|
28.0
|
6.3
Water Sensitive Receivers
6.3.1.1
The Water Sensitive
Receivers (WSRs) within the 500m assessment area are indicated in Figure
6.2.2. They include channelized rivers, wetlands in Conservation Area,
a number of fish ponds or ponds and watercourses. The detailed and approximate
distances are given in Table 6.10.
Table 6.10 WSRs within 500m of assessment area
|
ID
|
WSRs
|
Status
|
Approx. Dist. from
Project Boundary
|
|
WSR 1
|
Shenzhen River
|
Channelized
river
|
Adjacent
to Project Boundary
|
|
WSR 2
|
Ng Tung River (River Indus)
|
Channelized
river
|
<10m
|
|
WSR 3
|
Wetlands and
nearby wet woodland in the Conservation Area (CA) near Yuen Leng Chai
|
Ponds,
marsh and wet woodland
|
Adjacent
to Project Boundary
|
|
WSR 4
|
Fish
ponds located at northeast of Project Site
|
Active
fish ponds
|
Adjacent
to Project Boundary
|
|
WSR 5
|
Ponds
located at southeast of Project Site
|
Ponds
|
270m
|
|
WSR 6
|
Fish
ponds located at southwest of Project
Site on Lo Wu
Station Road
|
Fish
ponds
|
Adjacent
to Project Boundary
|
|
WSR 7
|
Ponds
located at southwest of Project Site
|
Ponds
|
330m
|
|
WSR 8
|
Conservation Area
(CA) located at
southwest of project Site in Fai King Road and nearby fish pond
|
Ponds and
fish pond
|
90m
|
|
WSR 9
|
Nam Hang
Stream, running from WSR5 to WSR4 and then to Shenzhen River along the
eastern boundary of the project Site
|
Natural
stream/ channelized river (about 200m before entering Shenzhen River)
|
Adjacent
to Project Boundary
|
|
WSR 10
|
Pond
located at southeast of Project Site
|
Pond
|
240m
|
|
WSR 11
|
Ponds
located at south of Project Site
|
Ponds
|
Adjacent
to Project Boundary
|
|
WSR 12
|
Watercourse
across Lin Ma Hang Road
|
Natural
stream/ channelized river (section from Man Kam To BCP to Shenzhen River)
|
Adjacent
to Project Boundary
|
|
WSR 13
|
Ping
Yuen River (River Ganges)
|
Channelized
river
|
~10m
|
|
WSR 14
|
Watercourse located south of Project Site and across Lo Wu Station
Road
|
Natural
stream
|
80m
|
|
WSR 15
|
Watercourse located south of Project Site
near Kong Nga Po Road
|
Natural stream
|
200m
|
|
WSR 16
|
Watercourse south of San Uk Ling
|
Natural stream
|
80m
|
|
WSR 17
|
Watercrouse located south of Sha Ling
Police Post near Ng Tung River
|
Natural stream
|
~1km
|
|
WSR 18
|
Watercourse at the west of Project Site
and Ng Tung River
|
Natural stream
|
330m
|
Note:
[1] Deep Bay would
be included in the Study Area if found being impacted by the Project. However,
WSRs in the Deep Bay such as Mai Po Inner Deep Bay Ramsar Site are not listed
as they are located downstream far away from the Project Site.
6.4
Construction Phase
6.4.1
Assessment Methodology
6.4.1.1
The assessment would
identify the possible pollution sources and evaluate their impact to the Water
Sensitive Receivers (WSRs) during the construction phase. The area for water
quality impact assessment includes an area within 500m from the site boundary
of the Project and covers part of the Deep Bay WCZ. The area would be extended
to include other areas such as stream courses and associated water systems,
wetlands, fish ponds in the vicinity and Deep Bay being impacted by the Project
if found justifiable. Mitigation measures would then be proposed to minimise / avoid
adverse water quality impact.
6.4.1.2
The key pollution sources
during construction of the proposed project include construction site runoff
and sewage from workforce. As there will be neither dredging nor reclamation
works, and all the works will be land-based, therefore water quality modelling
is not required.
6.4.1.3
The assessment approach is
referred to Annex 6 – Criteria for Evaluating Water Pollution and Annex 14 –
Guidelines for Assessment of Water Pollution under the TM-EIAO.
6.4.2
Identification of Environmental
Impacts
6.4.2.1
The major
pollution sources in construction phase are construction site runoff and sewage
from the workforce. Construction site runoff would come from over the works
site, roads and slopes during site formation for the development. The surface
runoff might be polluted by:
·
Runoff and erosion from site
surfaces, drainage channels, earth working areas and stockpiles;
·
Wash water from dust
suppression sprays and wheel washing facilities; and
·
Fuel, oil, solvents and
lubricants from maintenance of construction machinery and equipment.
6.4.2.2
Sewage
arising from the on-site construction work force is likely to cause water
pollution if it is discharged improperly. The sewage is characterized by high
levels of biochemical oxygen demand (BOD), ammonia, E. coli and oil/grease. The watercourses polluted by sewage would
have aesthetic and odour problem, and may become hypoxic due to decay of large
amount of oxygen demanding material.
6.4.2.3
Road widening work along a section of Lin Ma Hang Road would also span
over watercourse WSR 12. Temporary watercourse diversion and extension of
existing box culvert may be required which would have potential for water
quality impacts.
6.4.2.4
As shown in Figure 1.3,
a barging point in Siu Lam will be used for the transport of surplus inert
construction and demolition (C&D) materials. The surplus inert C&D
materials from the construction of the C&C facilities at Sandy Ridge
Cemetery and Lin Ma Hang Road will be stored at a temporary stockpile area
on-site. The surplus inert C&D materials will be transported to designated
barging point facility by lorries, and then transported by barges for the reuse
of other concurrent projects. As the current location is an existing barging
point used by the Express Rail Link project, and no maintenance dredging is
required, adverse water quality impacts are not anticipated. Minor construction
works are required for the tipping halls and new ramps. However, considered the
small scale of works and the existing barging point environment, adverse water
quality impacts are not anticipated.
6.4.3
Prediction and Evaluation of
Environmental Impacts
General Site Operation
6.4.3.1
The
construction site runoff comprises the following:
·
Runoff and erosion from site surfaces, slope works, working areas and stockpiles;
·
Wash water from dust
suppression sprays and wheel washing facilities; and
·
Fuel, oil, solvents and
lubricants from maintenance of construction machinery and equipment.
6.4.3.2
Construction runoff may cause
physical, biological and chemical effects. The physical effects include
potential blockage of drainage channels and increase of SS levels near shore of
the project site. Runoff containing significant amounts of concrete and
cement-derived material may cause primary chemical effects such as increasing
turbidity and discoloration, elevation in pH, and accretion of solids. A number
of secondary effects may also result in toxic effects to water biota due to
elevated pH values, and reduced decay rates of faecal micro-organisms and
photosynthetic rate due to the decreased light penetration. Mitigation measures will be in place to
control runoff.
Sewage from
Workforce
6.4.3.3
Sewage
effluents will arise from the sanitary facilities provided for the on-site
construction workforce. According to Table T-2 of Guidelines for Estimating
Sewage Flows for Sewage Infrastructure Planning, the unit flow is 0.23 m3/day/employed
populations. The characteristics of sewage would include high levels of BOD,
ammonia and E. coli counts. Since temporary sanitary facilities e.g. portable
chemical toilets, and sewage holding tank will be provided, no adverse water
quality impact is anticipated
6.4.3.4
Sewage
effluents will arise from the sanitary facilities provided for the on-site
construction workforce. According to Table T-2 of Guidelines for Estimating
Sewage Flows for Sewage Infrastructure Planning, the unit flow is 0.23 m3/day/employed
populations. The characteristics of sewage would include high levels of BOD,
ammonia and E. coli counts. Since temporary sanitary facilities e.g. portable
chemical toilets, and sewage holding tank will be provided, no adverse water
quality impact is anticipated.
Hydrological
impact on the watercourse encroached by Lin Ma Hang Road
6.4.3.5
The watercourse WSR 12 is
running approximately perpendicular across the existing Lin Ma Hang Road. The
intersection between the watercourse and the road is in close vicinity of the
northern east edge of San Uk Ling Village.
6.4.3.6
WSR 12 is about 1 to 2m
wide at that intersection and there is an existing box culvert to allow water
flow from one side to another side of the road. As observed in site, the
outfall of the culvert is approximate 1m from the footpath and this space is sufficient
for the local widening of the footpath / carriageway on Lin Ma Hang Road.
Therefore, the widening works will not encroach upon the watercourse and
extension of the existing culvert is not required. Hence, diversion of the
watercourse for the construction works is not required and will not cause any
adverse impacts.
6.4.4
Mitigation Measures
General Site Operation
6.4.4.1
Sewage effluents will arise
from the sanitary facilities provided for the on-site construction workforce.
According to Table T-2 of Guidelines for Estimating Sewage Flows for Sewage
Infrastructure Planning, the unit flow is 0.23 m3/day/employed
populations. The characteristics of sewage would include high levels of BOD,
ammonia and E. coli counts. Since temporary sanitary facilities e.g. portable
chemical toilets, and sewage holding tank will be provided, no adverse water
quality impact is anticipated.
6.4.4.2
Sewage
effluents will arise from the sanitary facilities provided for the on-site
construction workforce. According to Table T-2 of Guidelines for Estimating
Sewage Flows for Sewage Infrastructure Planning, the unit flow is 0.23 m3/day/employed
populations. The characteristics of sewage would include high levels of BOD,
ammonia and E. coli counts. Since temporary sanitary facilities e.g. portable
chemical toilets, and sewage holding tank will be provided, no adverse water
quality impact is anticipated.
6.4.4.3
In accordance with the Professional Persons Environmental Consultative Committee Practice
Notes on Construction Site Drainage, Environmental Protection Department,
1994 (ProPECC PN 1/94), best management practices should be implemented as far
as practicable as below:
·
At the start of site
establishment, perimeter cut-off drains to direct off-site water around the
site should be constructed with internal drainage works. Channels (both
temporary and permanent drainage pipes and culverts), earth bunds or sand bag
barriers should be provided on site to direct stormwater to silt removal facilities;
·
Diversion of natural stormwater
should be avoided as far as possible. The design of temporary on-site drainage
should prevent runoff going through site surface, construction machinery and
equipment in order to avoid or minimise polluted runoff. Sedimentation tanks
with sufficient capacity, constructed from pre-formed individual cells of
approximately 6 to 8 m3 capacities, are recommended as a general
mitigation measure which can be used for settling surface runoff prior to
disposal. The system capacity shall be flexible and able to handle multiple
inputs from a variety of sources and suited to applications where the influent
is pumped;
·
The dikes or embankments for
flood protection should be implemented around the boundaries of earthwork
areas. Temporary ditches should be provided to facilitate the runoff discharge
into an appropriate watercourse, through a silt/sediment trap. The
silt/sediment traps should be incorporated in the permanent drainage channels
to enhance deposition rates;
·
The design of efficient silt
removal facilities should be based on the guidelines in Appendix A1 of ProPECC
PN 1/94. The detailed design of the sand/silt traps should be undertaken by the
contractor prior to the commencement of construction;
·
Construction works should be
programmed to minimise surface excavation works during the rainy seasons (April
to September). All exposed earth areas should be completed and vegetated as
soon as possible after earthworks have been completed. If excavation of soil
cannot be avoided during the rainy season, or at any time of year when
rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or
other means;
·
All drainage facilities and
erosion and sediment control structures should be regularly inspected and
maintained to ensure proper and efficient operation at all times and
particularly following rainstorms. Deposited silt and grit should be removed
regularly and disposed of by spreading evenly over stable, vegetated areas;
·
If the excavation of trenches
in wet periods is necessary, it should be dug and backfilled in short sections
wherever practicable. Water pumped out from trenches or foundation excavations
should be discharged into storm drains via silt removal facilities;
·
All open stockpiles of
construction materials (for example, aggregates, sand and fill material) 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 being washed into the
drainage system and storm runoff being directed into foul sewers;
·
Precautions to be taken at any
time of year when rainstorms are likely, 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. Particular attention should
be paid to the control of silty surface runoff during storm events;
·
All vehicles and plant should
be cleaned before leaving a construction site to ensure no earth, mud, debris
and the like is deposited by them on roads. An adequately designed and sited
wheel washing facilities should be provided at every construction site exit
where practicable. Wash-water should have sand and silt settled out and removed
at least on a weekly basis to ensure the continued efficiency of the process. The
section of access road leading to, and exiting from, the wheel-wash bay to the
public road should be paved with sufficient backfall toward the wheel-wash bay
to prevent vehicle tracking of soil and silty water to public roads and drains;
·
Oil interceptors should be
provided in the drainage system downstream of any oil/fuel pollution sources.
The oil interceptors should be emptied and cleaned regularly to prevent the
release of oil and grease into the storm water drainage system after accidental
spillage. A bypass should be provided for the oil interceptors to prevent
flushing during heavy rain;
·
Construction solid waste,
debris and rubbish on site should be collected, handled and disposed of
properly to avoid water quality impacts;
·
All fuel tanks and storage
areas should be provided with locks and sited on sealed areas, within bunds of
a capacity equal to 110% of the storage capacity of the largest tank to prevent
spilled fuel oils from reaching water sensitive receivers nearby; and
·
Regular environmental audit on
the construction site should be carried out in order to prevent any
malpractices. Notices should be posted at conspicuous locations to remind the
workers not to discharge any sewage or wastewater into the water bodies, marsh
and ponds.
6.4.4.4
By adopting the best management
practices, it is anticipated that the impacts of general site operation will be
reduced to satisfactory levels before discharges. The details of best
management practices will be highly dependent to actual site condition and
Contractor shall apply for a discharge license under WPCO.
Sewage from Workforce
6.4.4.5
Portable chemical toilets and sewage holding tanks should be provided
for handling the construction sewage generated by the workforce. A licensed
contractor should be employed to provide appropriate and adequate portable toilets
to cater 0.23m3/day/employed population and be responsible for
appropriate disposal and maintenance. With reference to Section 7, the maximum number
of construction
workforce is around 190 on site and
the total sewage generated per day would be 45m3 during
construction phase (Detail refers to Section
7).
6.4.4.6
Notices should be posted at
conspicuous locations to remind the workers not to discharge any sewage or
wastewater into the nearby environment during the construction phase of the
Project. Regular environmental audit on the construction site should be
conducted in order to provide an effective control of any malpractices and
achieve continual improvement of environmental performance on site. It is
anticipated that sewage generation during the construction phase of the Project
would not cause water quality impact after undertaking all required measures.
Operation of Barging Point at Siu Lam
6.4.4.7
The following good practice shall apply
for the barging facilities operations:
·
All barges should be fitted
with tight bottom seals to prevent leakage of materials during transport;
·
Barges or hoppers should not be
filled to a level that will cause overflow of materials or polluted water
during loading or transportation;
·
All vessels should be sized so
that adequate clearance is maintained between vessels and the seabed in all
tide conditions, to ensure that undue turbidity is not generated by turbulence
from vessel movement or propeller wash; and
·
Loading of barges and hoppers
should be controlled to prevent splashing of material into the surrounding
water.
·
Mitigation measures for
land-based activities as outlined in Section
6.4.4 should be applied to minimise water quality impacts from site runoff
and open stockpile spoils at the proposed barging facilities where appropriate.
6.4.5
Residual Environmental Impacts
6.4.5.1
No adverse residual impact
is anticipated during the construction phase of the Project with the
implementation of mitigation measures.
6.5
Operational Phase
6.5.1
Assessment Methodology
6.5.1.1
The assessment would
identify the possible pollution sources and evaluate their impact to the Water
Sensitive Receivers (WSRs) during operation stage. The area for water quality
impact assessment includes area within 500m from the site boundary of the
Project and covers the Deep Bay WCZ. The area would be extended to include
other areas such as stream courses and associated water systems, wetlands, fish
ponds in the vicinity and Deep Bay being impacted by the Project if found
justifiable. Mitigation measures would then be proposed to minimise / avoid adverse
water quality impact.
6.5.1.2
The key pollution sources
during operation of the proposed project include as sewage and non-point source
pollution from the project site. The sewage from the project site could be
directed to the sewage treatment system. The non-point source pollution from
roads and project site runoff would be estimated in worst case scenario.
6.5.1.3
Beside
pollution sources, the hydrological impact to WSR3 (wet woodland nearby the Conservation Area) due to the Project would also need to be evaluated. Three
aspects would be assessed in the following Study: i) change
in groundwater hydrology from Sandy Ridge slope to WSR3 using in-situ ground
water monitoring data; ii) water quality impact due to non-point source
pollution from the proposed platform; and iii) potential erosion due to
increased runoff in high momentum from the proposed platform to WSR3 through
the seasonal watercourses.
6.5.2
Identification of Environmental
Impacts
6.5.2.1
The key pollution
sources in operational phase are sewage from the development and runoff from
the project site and roads. It is anticipated that sewage will be generated by
visitors and workers, as well as wastewater from cleaning activities in the
development.
6.5.2.2
There would
be additional pollution loading in association with the increase of runoff,
which is a non-point source pollution during operational phase. Substances such
as vehicle dust, tyre scraps and oils deposited and accumulated on the road
surfaces will be washed into nearby drainage system or watercourses during
rainfall events. Under normal condition, runoff will not be generated in low
rainfall intensity. However, the worst case scenario to water quality will take
place during the first flush under heavy rainstorm events.
6.5.2.3
The
platform and its associated foundation structure cover about 2ha area. There
would be hydrological change to the downstream area in both groundwater and
surface water due to the Project. For groundwater, the infiltration rate to the
ground would be reduced and the hydrological flow of underground water may also
be potentially interrupted by the foundation of the proposed platform. The
amount of surface runoff would increase as the area of slope changes from the
neutrally unpaved to artificially paved condition.
6.5.2.4
The surface runoff
collected on the platform and the associated road network will be collected by
stormwater drainage system and discharged into seasonally wet watercourses
leading to the wet woodland of WSR3 downstream. The downstream area would therefore
receive extra amount of runoff and sediment, especially during the first flush
of a strong rainstorm during which the large momentum of water flow will cause
a higher amount of erosion.
6.5.3
Prediction and Evaluation of
Environmental Impacts
Sewage and Sewerage System
6.5.3.1
The sewage would
be diverted to the upgraded Shek Wu Hui Sewage Treatment Works (SWH STW). The
proposed upgraded capacity of SWH STW for North East New Territories New
Development Areas project is from 113,000 m3/day to 190,000 m3/day
with spare capacity about 6,000 m3/day by 2031 (AEIAR: 175/2013).
6.5.3.2
According to the latest
design, the average daily sewage flow are 92.1m3/day for normal day
and 672.7m3/day for festive period respectively and the details are
shown as below:
Table
6.11a Estimated sewage flows during normal days
|
Source
of Sewage
|
Unit
Flow Factor (m³/h/d)
|
No.
of people
|
Average
Sewage Flow (m3/day)
|
Peak
Sewage Flow (l/s) [1]
|
|
Staff
|
0.080
|
140
|
11.2
|
0.8
|
|
Visitors[2]
|
0.010
|
4,980
|
34.9
|
2.5
|
|
Restaurant[3]
|
1.580
|
20
|
31.6
|
2.2
|
|
Washing facilities
|
-
|
-
|
14.4
|
1.0
|
|
Total
|
92.1
|
6.5
|
Note:
[1]: Global Peaking
factor = 6 (EPD’s GESF Table T-5, population between 1,000 and 5000 including
stormwater allowance)
[2] Reference has
been made to the sewage flow calculation from the Tai Po Tsz Shan Monastery
project, in which 50% of the total number of visitors were assumed to
contribute to sewage flow generation. Due to the remoteness of Sandy Ridge
site, a more conservative approach has been applied that we have assumed 70% of
the total number of visitors will use toilet and contribute to sewage flow
generation.
[3] The flow from
restaurant is estimated by the number of staff and the corresponding unit flow
factor for the staff. The maximum number of staff in restaurant is estimated to
be 20 which is considered as the upper bound of sewage flow from restaurant and
applicable to both normal and festive days.
Table
6.11b Estimated sewage flows during festive periods
|
Source
of Sewage
|
Unit
Flow Factor (m³/h/d)
|
No.
of people
|
Average
Sewage Flow (m3/day)
|
Peak
Sewage Flow (l/s) [1]
|
|
Staff
|
0.080
|
140
|
11.2
|
0.5
|
|
Visitors[2]
|
0.010
|
86,880
|
608.3
|
28.2
|
|
Restaurant[3]
|
1.580
|
20
|
31.6
|
1.5
|
|
Washing facilities
|
-
|
-
|
21.6
|
1.0
|
|
Total
|
672.7
|
31.2
|
Note:
[1]: Global Peaking
factor = 4 (EPD’s GESF Table T-5, population greater than 50,000 including
stormwater allowance)
[2] Reference has
been made to the sewage flow calculation from the Tai Po Tsz Shan Monastery
project, in which 50% of the total number of visitors were assumed to
contribute to sewage flow generation. Due to the remoteness of Sandy Ridge
site, a more conservative approach has been applied that we have assumed 70% of
the total number of visitors will use toilet and contribute to sewage flow
generation.
[3] The flow from
restaurant is estimated by the number of staff and the corresponding unit flow
factor for the staff. The maximum number of staff in restaurant is estimated to
be 20 which is considered as the upper bound of sewage flow from restaurant and
applicable to both normal and festive days.
6.5.3.3
As the
sewage generated from the development is mainly in Ching Ming Festival and
Chung Yeung Festival, it is anticipated that the upgraded SWH STW will have
enough capacity to handle such relatively small amount of sewage from the
development. Thus no adverse impact would be anticipated.
Non-Point Source Pollution Loading
6.5.3.4
The existing area in the
vicinity is partially rural area. With the development of the Project, there
would be an increase in the total paved area. Such change of pavement around an
addition of 8ha will reduce the infiltration rate into the ground, consequently
resulting in a higher flood risk as extra stormwater runoff may be generated
during rain events. The increase of average daily runoff would be about 300m3/day.
6.5.3.5
Nevertheless, the whole
Deep Bay Catchment covers Sheung Shui, Fanling, Kam Tin and Yuen Long with
total area of over 68,000 ha. The change of effective catchment area will only
account for less than 0.02% of the whole Deep Bay Catchment and hence it is
considered negligible.
6.5.3.6
In terms of water quality
impact, there would be additional pollution loading in association with the
increase of runoff, which is known as non-point source pollutions during
operational phase. Substances such as vehicle dust, tyre scraps and oils deposited
and accumulated on the road surfaces and parking area will be washed into
nearby drainage system or watercourses during rainfall events. Under normal
condition, runoff will not be generated in low rainfall intensity. However, the
worst scenario to water quality will take place during the first flush under
heavy rainstorm events. Proper drainage systems with silt traps should be
installed. The design of road gullies with silt traps should be incorporated in
the later detailed design.
6.5.3.7
The total loading of non-point
source pollution due to the development is compared with that of existing
condition in Appendix 6.1. According to the assessment result, the increase
of loading in terms of BOD5, TN and TP are 2.66, 0.24 and 0.02 kg/day
respectively. These additional loading generated from the increased surface
runoff due to the Project accounts for less than 0.0010% of the total pollution
loading to Deep Bay from both Hong Kong SAR and Mainland in Year 2012 (reference
to EIA report ‘Upgrading of Pillar Point Sewage Treatment Works’ AEIAR-118/2008
[6-6]). This would be a minor source in pollution loading to the Deep Bay
WCZ due to the Project development. Moreover, with the implementation of the
mitigation measures stated in Section
6.5.4, such as best management practice to remove pollutants on road or
other surface area, the pollution loading due to surface runoff would be
further reduced.
Hydrological Impact due to Viaduct Section
6.5.3.8
A viaduct is proposed as
the access road for the northeast part of the Project (Figure
6.2.2). The piers of the proposed viaduct section may alter the seasonally wet watercourses nearby. The water flow through
the seasonal watercourses to downstream in wet
season may be changed or diverted.
Hydrological Impact to the Wet Woodland
Groundwater Hydrology
6.5.3.9
Three different cross
sections showing the existing ground profiles and groundwater monitoring data
are presented in Appendix 6.2. It can be seen that the proposed platform is
approximately 40-50m above the woodland. The inferred underground water levels were
interpreted from the preliminary borehole information available.
6.5.3.10
During fine weather, the
average inferred water level is only about 1m above the rock head profile. It
implies that the groundwater aquifer from the sloping ground at Sandy Ridge is
unlikely the major water sources to the wet woodland. Indeed, the groundwater
supply of wet woodland is mainly due to the water seepages from the ponds and
marsh of WSR3 as shown in Figure 6.2.2.
6.5.3.11
During rainstorm events,
the peak inferred water levels could rise up to 15-20m from the average water
levels. This implies that the permeability of soil layer above the rock head
level is relatively high and hence the water level would vary significantly. Site
inspections also reveal that the maximum water level would drop quickly after
the heaviest rainfall period, typically within one day.
6.5.3.12
It can also be observed
from these sections that the proposed platform structure would only marginally
encroach into the maximum inferred water level but would not encroach into the
average inferred water level. As the maximum inferred water level only occurs
during very heavy rainfall, it is considered that proposed platform structure
would not significantly affect the groundwater level.
6.5.3.13
Other than proposed
platform structure, the sections also illustrate the tentative design for the
foundation of the proposed platform structure. According to the current
preliminary design, the foundation design would compose of bore piles of about
0.6m in diameter and the spacing between each pile would be approximately
3.5–5m. As compared to other foundation designs such as D-wall or pipepile
walls, the proposed small diameter bore pile system would allow a notional free
area of about 87 – 91% for groundwater to pass through.
6.5.3.14
Hence, based on the above
arguments, it is considered that the proposed platform structure and its
associated foundation design would not cause a significant change in the
groundwater hydrology connecting to the wet woodland.
Water Quality of Runoff from
the Proposed Platform
6.5.3.15
As stated in Section 6.5.3 as non-point source
pollution, the surface runoff collected on the platform and associated road
system may contain certain dusty materials and hence may cause pollution to wet
woodland in WSR3. Installation of proper silt traps in the drainage systems and
road gullies incorporated with silt traps in the design are proved to be
practical measure to reduce pollution from surface runoff. Regular cleaning are
required such that to avoid debris entering the downstream rivers during first
flush.
Erosion
from the Runoff from the Proposed Platform
6.5.3.16
There are in total 5 drainage
paths (P1 – P5) leading to seasonally wet watercourses which in turn lead to
the wet woodland as shown in Figure 6.5.1. These catchments and seasonally
wet watercourses serve as important pathways for the surface water to reach the
woodland, whilst portion of the surface water will infiltrate into the
groundwater system.
6.5.3.17
According to the current
platform design, the existing drainage flow path P1 to P4 will not be affected
but the catchment areas for drainage path P5 would be reduced as a result of
site formation, by an amount of 7,350m2 for P5.
6.5.3.18
However, a certain portion
of the runoff from the platforms formed in the vicinity of P5 will be diverted
to natural watercourses as well. Figure
6.5.2 illustrates the latest arrangement for the platforms formed. It
can be seen that there are a total of 3 new platforms, including Platform 1,
Platform 2a and Platform 2b. Out of these 3 platforms, part of the runoff from Platform
1 will be diverted to natural watercourse downstream of P4 and P5. The
remaining runoff from Platform 1 and those runoff from Platform 2a and 2b will
be drained to other engineering drainage system in vicinity and ultimately to
Shenzhen River.
6.5.3.19
The following table
summarises the catchment areas leading to the seasonal watercourse for both the
existing conditions and the conditions after the platforms are completed.
Table 6.12 Catchment areas before and after completion of the Project
|
Catchment
Leading to Watercourses
|
Catchment
Area (m2)
|
|
Existing
|
After
Site Formation
|
W/
New Platforms
|
Total
|
|
P1
|
5,450
|
5,450
|
0
|
5,450
|
|
P2
|
16,560
|
16,560
|
0
|
16,560
|
|
P3
|
8,910
|
8,910
|
0
|
8,910
|
|
P4
|
23,950
|
23,950
|
0
|
23,950
|
|
P5
|
22,900
|
14,300
|
1,250
|
15,550
|
Note:
[1] Only part of the runoff will be drained
into the watercourses downstream of P5.
6.5.3.20
However, it should be noted
that the catchment area within P5 are permeable and that the new platforms will
be paved and impermeable. The current
design has ensured that the total flow rate leading to the seasonal
watercourses downstream of P5 would be insignificant. However, the volumetric
flow rate and hence the maximum velocity from the first flux would inevitably
increase. According to the current design, the maximum velocity for the
seasonal watercourses downstream for P5 will be increased from 0.65m/s to
2.63m/s. The following table summarises the changes in terms of volumetric flow
rates and maximum velocity.
Table 6.13 Estimated surface runoff into seasonal watercourses before and after
completion of the Project
|
Catchment Leading to Seasonal Watercourse
|
Existing [1],
[2]
|
After Site formation [1], [2]
|
Change
|
|
Flow
(m3/s)
|
Speed
(m/s)
|
Flow
(m3/s)
|
Speed
(m/s)
|
Flow (m3/s)
|
Speed
(m/s)
|
|
P1
|
0.18
|
0.98
|
0.18
|
0.98
|
0
|
0
|
|
P2
|
0.51
|
1.05
|
0.51
|
1.05
|
0
|
0
|
|
P3
|
0.28
|
0.90
|
0.28
|
0.90
|
0
|
0
|
|
P4
|
0.71
|
1.55
|
0.71
|
1.55
|
0
|
0
|
|
P5
|
0.65
|
0.79
|
0.65
|
2.63
|
0
|
+1.84
|
Note:
[1] Flow
rate and speed connecting to the seasonal watercourse.
[2] Data
from one in 50 years design return period.
6.5.3.21 The increase in maximum velocity along the seasonal watercourse
downstream of P5 may increase the potential for soil erosion. In order to
reduce the velocity and hence the potential for soil erosion, energy
dissipaters would be installed at the seasonally wet watercourses downstream of
P5. Appendix
6.3 shows the typical configuration of the energy dissipaters which
comprises of a number of concrete steps to allow water velocity to
decelerate. The actual dimensions of the
energy dissipaters would be subject to detailed design.
Hydrological impact on the watercourse encroached by Lin
Ma Hang Road
6.5.3.22 As discussed in Section 6.4.3,
road widening work will be carried out along a section of Lin Ma Hang Road
spanning over the watercourse WSR 12. However, the drainage system would not be
affected and hence, the watercourse WSR 12 will not be affected during
operational phase of the Project.
6.5.4
Mitigation Measures
Sewage and Sewerage System
6.5.4.1
Sewage
generated by visitors and workers, as well as
wastewater from cleaning activities in the development should be connected to the foul sewerage system. Detention tank will be provided for interim stage such that emergency discharge is
generally avoided as a consequence of pause of power supply, pump failure or etc.
Change in Hydrological Flow, Drainage System and Road Runoff
6.5.4.2
According to the current
design, small bore piles of about 0.6m in diameter and pile to pile spacing
3.5–5m approximately would be adopted for foundation of the proposed platform
structure. As compared to other foundation design options such as D-wall or pipepile
walls, this proposed small diameter bore pile design would allow free passage
for groundwater to run through and would not significantly interrupt the
groundwater hydrology.
6.5.4.3
The piers of the proposed viaduct
section would span over the seasonally wet
watercourses. The alternation of water flow through the seasonal watercourses
in wet season would be minimised.
6.5.4.4
During operational phase,
vehicle dust, tyre scraps and oils might be washed away from the road surface
and parking area to the nearby watercourses by surface runoff or road surface
cleaning. Proper drainage systems with silt traps and oil interceptors should
be installed. The design of road gullies with silt traps should be incorporated
in the later detailed design especially for the catchment leading to the
existing wet woodland area located at the north of the site.
6.5.4.5
The pollution induced from
surface runoff can be controlled by best management practice. Runoff will be
intercepted by properly designed and managed silt traps at appropriate spacing,
so that the common roadside debris, refuse and fallen leaves etc. can be
captured before allowing the runoff to drain into watercourse along the east
boundary of the Project and Shenzhen River. The silt traps and oil interceptors
are recommended to clean the trapped dirt regularly, especially before peak
seasons of the visitors in Ching Ming Festival and Chung Yeung Festival, so that designed removal efficiency of the silt or oils can be achieved.
The road and parking area should be cleaned prior to the occurrence of a
tropical storm to avoid debris entering the
downstream rivers during first flush. Each of the cleaning events should
be carried out during low traffic flow period. Manual methods or mechanical
means such as vacuum sweeper/truck equipped with side broom are preferable,
which can sweep road sludge and debris into the suction nozzle to increase the
removal efficiency of pollutants. The collected pollutants would be tankered
away for off-site disposal at landfill sites. With the interception and removal
of the pollutants, the pollution loading of stormwater to the sensitive
receivers nearby would be much reduced.
6.5.4.6
The pollution induced from
surface runoff can be controlled by best management practice. Runoff will be
intercepted by properly designed and managed silt traps at appropriate spacing,
so that the common roadside debris, refuse and fallen leaves etc. can be
captured before allowing the runoff to drain into watercourse along the east
boundary of the Project and Shenzhen River. The silt traps and oil interceptors
are recommended to clean the trapped dirt regularly, especially before peak
seasons of the visitors in Ching Ming Festival and Chung Yeung Festival, so that designed removal efficiency of the silt or oils can be achieved.
The road and parking area should be cleaned prior to the occurrence of a
tropical storm to avoid debris entering the
downstream rivers during first flush. Each of the cleaning events should
be carried out during low traffic flow period. Manual methods or mechanical
means such as vacuum sweeper/truck equipped with side broom are preferable,
which can sweep road sludge and debris into the suction nozzle to increase the
removal efficiency of pollutants. The collected pollutants would be tankered
away for off-site disposal at landfill sites. With the interception and removal
of the pollutants, the pollution loading of stormwater to the sensitive
receivers nearby would be much reduced.
6.5.4.7
In
order to minimise the erosion impact to the wet woodland due to high momentum
from first flush, a by-pass drainage will be provided from the platform and the
associated road network and extra runoff amount would be diverted away from the
wet woodland and pond. Energy dissipaters would be installed at the seasonally
wet watercourses to reduce the magnitude of the first flush. Appendix 6.3 illustrates the standard design of stepped channel which is
a common practice for energy dissipation of a watercourse in steep slope. The
opportunity of undesirable erosion along the existing seasonally wet
watercourses would be minimised.
6.5.5
Residual Environmental Impacts
6.5.5.1
According to the assessment
of environment impact from sewage generated and non-point source pollution
loading due to Project in Section 6.5.3,
the increase of pollution loads to Deep Bay from sewage and surface run-off due
to the Project is relatively small. No adverse residual impact is anticipated
during the operational phase of the Project with the implementation of mitigation
measures.
6.6
Conclusion
6.6.1.1
By optimizing the design of
the platform, foundation design and the drainage system, hydrological impact
including groundwater and surface water to the wet woodland located at the
north of the site has been minimised.
6.6.1.2
With full implementation of
the mitigation measures including proper sewerage and drainage systems, adverse
water quality impact is not anticipated during both the construction and operational
phases of the Project.
6.7
References
[6-1] EPD, Deep Bay Water Quality Regional
Control Strategy Study, (ACE Paper 55/98)
[6-2] EPD, 2010-2014, River Water Quality
Reports
[6-3] AEIAR-160/2011, Regulation of
Shenzhen River Stage IV
[6-4] AEIAR-180/2013, Development
of Organic Waste Treatment Facilities, Phase 2
[6-5] EPD, 2010-2014, Marine Water Quality
Reports
[6-6] AEIAR-118/2008, Upgrading
of Pillar Point Sewage Treatment Works
