This Section
presents an evaluation of the potential water quality impacts from the
construction and operation of the Project.
Mathematical modelling has been used to predict potential impacts to hydrodynamics,
sediment transportation and water quality, the results of which have then been
assessed with reference to the relevant environmental legislation, standards
and tolerance criteria.
6.2
Relevant
Legislation and Guidelines
The following legislation and relevant guidance or
non-statutory guidelines are applicable to the evaluation of water quality
impacts associated with the construction and operation of the Project.
·
Water Pollution Control Ordinance (WPCO);
·
Technical Memorandum for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-
ICW);
·
Environmental Impact Assessment Ordinance
(Cap. 499. S.16) and the Technical Memorandum on EIA Process
(EIAO-TM), Annexes 6 and 14; and
·
Practice Note for Professional Persons,
Construction Site Drainage (ProPECC PN1/94).
6.2.1
Water Pollution Control Ordinance (WPCO)
The Water
Pollution Control Ordinance (WPCO) is the primary legislation for the
control of water pollution and water quality in Hong Kong. Under the WPCO, Hong Kong waters are divided
into 10 Water Control Zones (WCZs). Each WCZ has a designated set of statutory
Water Quality Objectives (WQOs). The proposed Project
is located within the Deep Bay WCZ. The WQOs designated for this zone are thus relevant for
assessing the water quality impacts from the construction and operation of the
Project.
6.2.2
Technical Memorandum for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-
ICW)
All discharges during both the construction and
operation phases of the proposed development are required to comply with the Technical Memorandum Standards for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
(TM-ICW) issued under Section 21 of the WPCO.
The TM-ICW
defines acceptable discharge limits to different types of receiving
waters. Under the TM-ICW, effluents discharged into the drainage and sewerage
systems, inshore and coastal waters of the WCZs are
subject to pollutant concentration standards for specified discharge
volumes. These are defined by the
Environmental Protection Department (EPD) and are specified in licence
conditions for any new discharge within a WCZ.
6.2.3
Technical Memorandum on EIA Process
(EIAO-TM)
Annexes 6 and
14 of the EIAO-TM provide general
guidelines and criteria to be used in assessing water quality impacts.
6.2.4
Practice Note for Professional Persons,
Construction Site Drainage
Apart from the above statutory requirements, the Practice Note for Professional Persons,
Construction Site Drainage (ProPECC PN 1/94),
issued by EPD in 1994, also provide useful non-statutory guidelines on water
pollution associated with construction activities.
6.3.1
Hydrology and Hydrodynamics
The
mouth of Shenzhen River is located near the Pearl River estuary. Shenzhen River originates from Wutong Mountain at an elevation of 214 m above sea
level. The river of total length 33 km
is flowing west to Deep Bay.
Shenzhen
River is located within the subtropical region with distinct wet and dry
seasons. The average annual rainfall is
around 1,900 mm. The wet season from
April to October contributes about 90% of the total annual rainfall. Rainfall is the main supply of freshwater to
Shenzhen River and the amount of run-off is closely related to rainfall. Run-off during the wet season accounts for
more than 87% of the total annual run-off.
For the section of Shenzhen River within the Project
Site, the average annual run-off volume from Qiannian
Drainage is approximately 16,480,000 m3 and the average flow rate is
about 0.522 m3 s-1, while the average annual run-off
volume and flow rate from River Ganges (Ping Yuen River) are 32,550,000 m3
and 1.032 m3 s-1, respectively. This section of the Shenzhen River comprises
a “fan-shaped” system which is short and steep with faster flow rate. Large flow from this section can converge
into the downstream section within a short period of time.
The
river section downstream of the Ping Yuen River confluence is regarded as the
downstream area of Shenzhen River. In
this area, the river course is winding on flat alluvial coastal plain. After the Stage III regulation, the Ping Yuen
River confluence and the mouth of Shenzhen River are almost at the same
elevation. According to the results of
two hydrology surveys in 2004 and 2005, the maximum water level at high tide is
decreasing downstream. The difference in
maximum water levels between Ng Tung River and Shenzhen River mouth is about 20
cm during high tide, while the difference during the low tide is small. During periods of spring and neap tide, the
flow rate of
6.3.2
River Water Quality
The proposed Project starts from Pak Fu
Shan down to the confluence of
Table 6.1 Key
Water Quality Objectives of the Deep Bay WCZ for Shenzhen River, Kong Yiu Drainage Channel and Ping Yuen River
|
Water Course within the
Study area |
pH Range |
Maximum 5-day Biochemical
Oxygen Demand (BOD5) |
Maximum Chemical Oxygen
Demand (COD) |
Maximum Annual Median
Suspended Solids (SS) |
Minimum Dissolved Oxygen (DO) |
Maximum Annual Mean
Unionised Ammoniacal Nitrogen |
|
Shenzhen River and Kong Yiu
Drainage Channel |
6.5 – 8.5 |
5 mg L-1 |
30 mg L-1 |
20 mg L-1 |
4 mg L-1 |
0.021 mg L-1 |
|
Ping Yuen River |
6.5 – 8.5 |
3 mg L-1 |
15 mg L-1 |
20 mg L-1 |
4 mg L-1 |
0.021 mg L-1 |
Water Quality of the
Shenzhen River
Routine river water quality monitoring along the
Shenzhen River has been conducted by the Shenzhen Environmental Monitoring
Centre. Data of key water quality
parameters measured during the period of 2007 to 2009 are extracted from six
monitoring stations and presented in Tables
6.2 to 6.4. These monitoring stations are located within
as well as downstream of the Study area (see Figure 6.2).
Measurements were taken once per month from Jing Du and Quarry and twice
per month from the other stations.
The monitoring data indicates that river
water quality at the upstream area is better than that at the downstream area
of the Shenzhen River (Tables 6.2 to 6.4).
The levels of nutrients, Chemical Oxygen Demand (COD), 5-day Biochemical
Oxygen Demand (BOD5) and faecal coliforms
are increasing from Jing Du to Ludang Village, after
which the levels drop sharply which is probably as a result of tidal influence
in the area when approaching the Shenzhen River mouth. For dissolved oxygen (DO), the values were
generally higher at the upstream area (ie Jing Du and
Quarry) and dropped sharply after reaching the monitoring station at Lo
Wu. Generally, DO, COD and BOD5
show non-compliances with the WQOs at downstream
stations including Lo Wu,
Table 6.2 Annual
Mean of Key Water Quality Parameters at the Shenzhen River Routine Water
Quality Monitoring Stations in 2007
|
Station / Parameter |
River WQOs |
Jing Du |
Quarry |
Lo Wu |
Ludang Village |
Pier |
Shenzhen River Mouth |
|
Water Temperature (ºC) |
n.a. |
22.8 |
25.1 |
24.9 |
25.0 |
25.0 |
25.0 |
|
pH |
6.5 – 8.5 |
7.63 |
7.34 |
7.22 |
7.21 |
7.23 |
7.23 |
|
DO (mg L-1) |
≥ 4 |
7.171 |
6.402 |
0.955 |
0.930 |
1.075 |
1.164 |
|
COD (mg L-1) |
≤30 |
4.4 |
11.8 |
22.8 |
35.7 |
25.9 |
34.5 |
|
BOD5 (mg L-1) |
≤5 |
1.01 |
3.21 |
5.38 |
12.26 |
9.05 |
13.15 |
|
Ammoniacal Nitrogen (mg L-1) |
n.a. |
0.30 |
8.47 |
14.05 |
21.13 |
18.42 |
19.39 |
|
Total Phosphorus (mg L-1) |
n.a. |
0.054 |
0.425 |
1.122 |
1.687 |
1.577 |
1.814 |
|
Total Nitrogen (mg L-1) |
n.a. |
1.06 |
11.15 |
16.07 |
24.02 |
20.03 |
22.36 |
|
Faecal Coliforms (104
cfu L-1) |
n.a. |
1 |
173 |
5,697 |
17,593 |
12,659 |
9,369 |
|
Notes: (a)
Bold
and underlined figures indicate non-compliance with the WQOs. (b)
See
Figure 6.2 for locations of the
monitoring station. (c)
n.a. indicates the absence of applicable WQOs. |
|||||||
Table 6.3 Annual
Mean of Key Water Quality Parameters at the Shenzhen River Routine Water
Quality Monitoring Stations in 2008
|
Station / Parameter |
River WQOs |
Jing Du |
Quarry |
Lo Wu |
Ludang Village |
Pier |
Shenzhen River Mouth |
|
Water Temperature (ºC) |
n.a. |
22.5 |
24.1 |
24.0 |
24.2 |
24.2 |
24.3 |
|
pH |
6.5 – 8.5 |
7.45 |
7.29 |
7.08 |
7.14 |
7.16 |
7.22 |
|
DO (mg L-1) |
≥ 4 |
7.6 |
6.61 |
1.64 |
1.00 |
1.32 |
1.42 |
|
COD (mg L-1) |
≤30 |
9.7 |
17.4 |
24.3 |
47.4 |
35.9 |
41.9 |
|
BOD5 (mg L-1) |
≤5 |
1.1 |
3.8 |
8.1 |
17.2 |
14.4 |
16.7 |
|
Ammoniacal Nitrogen (mg L-1) |
n.a. |
0.11 |
6.44 |
12.47 |
19.00 |
16.68 |
15.64 |
|
Total Phosphorus (mg L-1) |
n.a. |
0.051 |
0.367 |
0.971 |
1.563 |
1.259 |
1.271 |
|
Total Nitrogen (mg L-1) |
n.a. |
1.10 |
12.45 |
15.18 |
21.93 |
18.94 |
17.73 |
|
Faecal Coliforms (104
cfu L-1) |
n.a. |
2 |
30 |
540 |
2800 |
1500 |
1300 |
|
Notes: (a)
Bold
and underlined figures indicate non-compliance with the WQOs. (b)
See
Figure
6.2 for locations of the monitoring station. (c)
n.a. indicates the absence of applicable WQOs. |
|||||||
Table 6.4 Annual
Mean of Key Water Quality Parameters at the Shenzhen River Routine Water
Quality Monitoring Stations in 2009
|
Station / Parameter |
River WQOs |
Jing Du |
Quarry |
Lo Wu |
Ludang Village |
Pier |
Shenzhen River Mouth |
|
Water Temperature (ºC) |
n.a. |
21.1 |
22.7 |
23.1 |
23.3 |
22.8 |
23.1 |
|
pH |
6.5 – 8.5 |
7.64 |
7.33 |
7.03 |
7.10 |
7.08 |
7.08 |
|
DO (mg L-1) |
≥ 4 |
6.933 |
5.373 |
0.728 |
0.457 |
0.480 |
0.616 |
|
COD (mg L-1) |
≤30 |
4.6 |
12.9 |
45.2 |
74.2 |
55.1 |
59.5 |
|
BOD5 (mg L-1) |
≤5 |
0.64 |
2.61 |
17.04 |
26.32 |
19.17 |
20.03 |
|
Ammoniacal Nitrogen (mg L-1) |
n.a. |
0.06 |
6.64 |
18.32 |
30.00 |
21.70 |
19.93 |
|
Total Phosphorus (mg L-1) |
n.a. |
0.013 |
0.435 |
1.224 |
2.216 |
1.587 |
1.569 |
|
Total Nitrogen (mg L-1) |
n.a. |
0.39 |
13.23 |
20.96 |
33.54 |
25.00 |
23.50 |
|
Faecal Coliforms
(104 cfu L-1) |
n.a. |
1 |
39 |
2783 |
15842 |
2933 |
2311 |
|
Notes: (a)
Bold
and underlined figures indicate non-compliance with the WQOs. (b)
See
Figure
6.2 for locations of the monitoring station. (c)
n.a. indicates the absence of applicable WQOs. |
|||||||
EPD has also undertaken routine river water quality
monitoring in Hong Kong and one of the monitoring stations in
River Water Quality within
the Study Area
As part of the EIA Study, a more focussed baseline
water quality survey was carried out within the Study Area in the wet and dry
seasons of 2009. The locations of
monitoring stations are illustrated in Figure
6.3 which cover the sections of
6.3.3
Discharges into the Shenzhen River
Direct discharge of domestic sewages from
the households of Shenzhen is the main source of pollution to the river section
of the Project Site. Twenty-one sewage
outlets from Shenzhen are identified as the source of major pollutants
including BOD5, COD, ammoniacal nitrogen,
total phosphorus and total nitrogen.
According to the Planning and Feasibility Study of the Project, the sewage discharge volume to the
Shenzhen River is estimated to be 27,000 m3 per day ([5]).
The predicted discharge concentrations of BOD5, COD, ammoniacal nitrogen, total phosphorus and total nitrogen
are 200, 300, 30, 4.5 and 35 mg L-1, while the daily discharge
volume are 15.6, 23.4, 2.34, 0.35 and 2.73 tonnes, respectively.
A total of eight main discharge sources to the
Shenzhen River are identified within and downstream of the Project Site,
including Luofang Sewage Treatment Plant, Ping Yuen
River, Shawan River, Ng Tung River, Buji River, Binhe Sewage Treatment Plant, Futian River and Huanggong
River. Water quality at these sources
and the volume and quantities of pollutants from them have been monitored in 2009 as part of the
EIA Study (see Figure
6.4) and presented in Tables 6.8 and
6.9, respectively.
Table 6.5 Values
of Key Water Quality Parameters at Station GR1 of Ping Yuen River from 2006 to
2008 (Data
extracted from EPD Annual River Water Quality Reports)
|
Parameter |
Unit |
River WQOs |
2006 |
2007 |
2008 |
|
Dissolved Oxygen |
mg L-1 |
≥ 4 |
6.2 |
6.6 |
6.1 |
|
(1.7 – 8.0) |
(3.4 – 11.1) |
(3.0 – 8.4) |
|||
|
pH |
|
6.5 – 8.5 |
7.6 |
7.4 |
7.2 |
|
(6.8 – 8.1) |
(7.2 – 8.0) |
(6.6 – 7.4) |
|||
|
Suspended solids |
mg L-1 |
≤20 |
50 |
14 |
22 |
|
(23 – 660) |
(1 – 110) |
(13 – 450) |
|||
|
BOD5 |
mg L-1 |
≤3 |
38 |
7 |
8 |
|
(4 – 170) |
(3 – 160) |
(2 – 52) |
|||
|
COD |
mg L-1 |
≤15 |
60 |
26 |
25 |
|
(7 – 1,100) |
(9 – 220) |
(8 – 250) |
|||
|
Oil and Grease |
mg L-1 |
n.a. |
1.0 |
0.5 |
0.6 |
|
(0.5 – 26.0) |
(0.5 – 12.0) |
(<0.5 – 5.3) |
|||
|
Faecal coliforms |
cfu/100ml |
n.a. |
320,000 |
160,000 |
160,000 |
|
(60,000 – 1,700,000) |
(32,000 – 1,200,000) |
(16,000 – 35,000,000) |
|||
|
E. coli |
cfu/100ml |
n.a. |
230,000 |
67,000 |
35,000 |
|
(34,000 – 1,700,000) |
(14,000 – 770,000) |
(5,000 – 800,000) |
|||
|
Ammonia -Nitrogen |
mg L-1 |
n.a. |
36.00 |
4.70 |
6.05 |
|
(3.10 – 210.00) |
(1.20 – 45.00) |
(0.41 – 24.00) |
|||
|
Nitrate-nitrogen |
mg L-1 |
n.a. |
0.28 |
0.80 |
0.61 |
|
(0.01 – 1.30) |
(0.01 – 1.90) |
(<0.01 – 1.20) |
|||
|
Total Kjeldahl nitrogen |
mg L-1 |
n.a. |
44.00 |
6.20 |
7.70 |
|
(3.50 – 300.00) |
(2.30 – 59.00) |
(0.81 – 28.00) |
|||
|
Ortho-phosphate |
mg L-1 |
n.a. |
7.15 |
1.4 |
1.8 |
|
(0.77 – 28.00) |
(0.19 – 8.90) |
(0.22 – 6.60) |
|||
|
Total phosphorus |
mg L-1 |
n.a. |
8.60 |
1.8 |
2.25 |
|
(0.98 – 51.00) |
(0.52 – 11.00) |
(0.39 – 11.00) |
|||
|
Total sulphide |
mg L-1 |
n.a. |
0.06 |
0.02 |
0.02 |
|
(0.02 – 0.22) |
(0.02 – 0.31) |
(<0.02 – 2.00) |
|||
|
Aluminium |
μg L-1 |
n.a. |
155 |
115 |
120 |
|
(70 – 900) |
(50 – 380) |
(<50 – 380) |
|||
|
Cadmium |
μg L-1 |
n.a. |
0.1 |
0.1 |
<0.1 |
|
(0.1 – 0.2) |
(0.1 – 0.2) |
(<0.1 – <0.1) |
|||
|
Chromium |
μg L-1 |
n.a. |
1 |
1 |
<1 |
|
(1 – 6) |
(1 – 1) |
(<1 – 2) |
|||
|
Copper |
μg L-1 |
n.a. |
13 |
5 |
4 |
|
(4 – 23) |
(3 – 41) |
(2 – 9) |
|||
|
Lead |
μg L-1 |
n.a. |
2 |
2 |
3 |
|
(1 – 6) |
(1 – 6) |
(<1 – 10) |
|||
|
Zinc |
μg L-1 |
n.a. |
40 |
40 |
25 |
|
(20 – 350) |
(10 – 1,600) |
(10 – 170) |
|||
|
Notes: (a)
Data
presented are in annual medians of monthly samples; except those for faecal coliforms and E.
coli which are in annual geometric means; (b)
Figures
in brackets are annual ranges. (c)
NM
indicates no measurement taken. (d)
Values
at or below laboratory reporting limits are presented as laboratory reporting
limits. (e)
Equal
values for annual medians (or geometric means) and ranges indicate that all
data are the same as or below laboratory reporting limits. (f)
Bold
and underlined figures indicate non-compliance with the WQOs. (g)
n.a. indicates the absence of applicable WQOs. |
|||||
Table 6.6 Results
of Baseline Water Quality Monitoring Conducted in the Wet and Dry Seasons,
2009, for Sections of Shenzhen River within the Study Area
|
Parameters |
WQOs |
Jing Du (S1) |
Near the Mouth of Qiannian Drainage (S2) |
Quarry (S3) |
||||||
|
|
|
Wet Season |
Dry Season |
Annual Mean |
Wet Season |
Dry Season |
Annual Mean |
Wet Season |
Dry Season |
Annual Mean |
|
Water Temperature (℃) |
n.a. |
27.85 |
21.5 |
24.68 |
29.5 |
20.6 |
25.05 |
29.7 |
23.6 |
26.65 |
|
DO (mgL-1) |
≥ 4 |
7.86 |
7.00 |
7.43 |
4.30 |
3.64 |
3.97 |
5.55 |
6.4 |
5.98 |
|
pH |
6.5 – 8.5 |
7.57 |
8 |
7.79 |
7.3 |
7.39 |
7.35 |
7.29 |
7.3 |
7.3 |
|
COD (mgL-1) |
≤30 |
6.58 |
10.3 |
8.44 |
13.1 |
6.73 |
9.92 |
13.4 |
13.2 |
13.3 |
|
Permanganate index (mgL-1) |
n.a. |
0.93 |
2 |
1.47 |
3.3 |
2.12 |
2.71 |
3.75 |
4.8 |
4.27 |
|
BOD5 (mgL-1) |
≤5 |
0.84 |
1.5 |
1.17 |
3.2 |
0.6 |
1.9 |
3.36 |
4.4 |
3.88 |
|
Ammoniacal Nitrogen (mgL-1) |
n.a. |
0.047 |
0.02 |
0.034 |
5 |
4.93 |
4.965 |
2.813 |
2.2 |
2.507 |
|
Total Nitrogen (mgL-1) |
n.a. |
0.148 |
0.3 |
0.224 |
5.7 |
8.27 |
6.985 |
7.836 |
10.7 |
9.268 |
|
Total Phosphorus (mgL-1) |
n.a. |
0.057 |
0.035 |
0.046 |
0.2 |
0.34 |
0.27 |
0.259 |
0.4 |
0.33 |
|
Fluoride (mgL-1) |
n.a. |
0.085 |
0.09 |
0.088 |
0.3 |
0.21 |
0.255 |
0.71 |
0.6 |
0.655 |
|
Hexavalent chromium (mgL-1) |
n.a. |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
|
Mercury (mgL-1) |
n.a. |
0.04 |
0.04 |
0.04 |
0.04 |
0.04 |
0.04 |
0.04 |
0.04 |
0.04 |
|
Cyanide (mgL-1) |
n.a. |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
|
Phenol (mgL-1) |
n.a. |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
|
Anionic Surfactants (mgL-1) |
n.a. |
0.024 |
0.024 |
0.024 |
0.0337 |
0.146 |
0.08985 |
0.052 |
0.1 |
0.076 |
|
Sulphide (mgL-1) |
n.a. |
0.02 |
0.02 |
0.02 |
0.02 |
0.02 |
0.02 |
0.02 |
0.02 |
0.02 |
|
Copper (mgL-1) |
n.a. |
0.013 |
0.006 |
0.01 |
0.006 |
0.006 |
0.006 |
0.05 |
0.006 |
0.028 |
|
Zinc (mgL-1) |
n.a. |
0.007 |
0.04 |
0.024 |
0.007 |
0.005 |
0.006 |
0.022 |
0.014 |
0.018 |
|
Total Lead (mgL-1) |
n.a. |
0.8 |
0.0002 |
0.4001 |
0.8 |
0.0004 |
0.4002 |
0.8 |
0.0002 |
0.4001 |
|
Total Cadmium (mgL-1) |
n.a. |
0.1 |
0.00008 |
0.05004 |
0.07 |
0.00008 |
0.03504 |
0.148 |
0.00008 |
0.074 |
|
Selenium (mgL-1) |
n.a. |
0.44 |
0.0004 |
0.2202 |
0.47 |
0.004 |
0.237 |
0.625 |
0.004 |
0.3145 |
|
Total Arsenic (mgL-1) |
n.a. |
1.65 |
0.007 |
0.8285 |
1.27 |
0.003 |
0.6365 |
0.863 |
0.0031 |
0.433 |
|
Oil and Grease (mgL-1) |
n.a. |
0.02 |
0.02 |
0.02 |
0.03 |
0.02 |
0.025 |
0.02 |
0.02 |
0.02 |
|
Faecal coliforms (104/L) |
n.a. |
3.2 |
20.0 |
11.6 |
300.0 |
71.6 |
185.8 |
25.7 |
13.3 |
19.5 |
|
Notes: (a)
Bold
and underlined figures indicate non-compliance with the WQOs. (b)
See
Figure
6.3 for locations of the monitoring station. (c)
n.a. indicates the absence of applicable WQOs. |
||||||||||
Table 6.7 Results
of Baseline Water Quality Monitoring Conducted in the Wet and Dry Seasons,
2009, for the Kong Yiu Drainage Channel and Ping Yuen
River
|
Parameter |
Kong Yiu Drainage Channel (S4) |
Ping Yuen River (S5) |
||||
|
Season |
River WQOs |
Wet Season |
Dry Season |
River WQOs |
Wet Season |
Dry Season |
|
Water Temperature (℃) |
n.a. |
n.a. |
20 |
n.a. |
n.a. |
21 |
|
pH |
6.5 – 8.5 |
7.2 |
7.3 |
6.5 – 8.5 |
7.5 |
7.2 |
|
Permanganate index (mgL-1) |
n.a. |
3.1 |
n.a. |
n.a. |
5.17 |
n.a. |
|
COD (mgL-1) |
≤30 |
8.7 |
19.3 |
≤15 |
30.5 |
21.1 |
|
BOD5 (mgL-1) |
≤5 |
2.60 |
3.72 |
≤3 |
4.30 |
3.62 |
|
Ammoniacal Nitrogen (mgL-1) |
n.a. |
0.33 |
0.13 |
n.a. |
3.09 |
13 |
|
Total Phosphorus (mgL-1) |
n.a. |
0.28 |
0.12 |
n.a. |
0.27 |
2.57 |
|
Total Nitrogen (mgL-1) |
n.a. |
1.33 |
2.47 |
n.a. |
4.94 |
22.8 |
|
Copper (mgL-1) |
n.a. |
<0.006 |
<0.006 |
n.a. |
<0.006 |
0.01 |
|
Zinc (mgL-1) |
n.a. |
0.01 |
n.a. |
n.a. |
0.01 |
n.a. |
|
Notes: (a)
Data
presented are season mean. (b)
n.a. indicates that no measurement was
being taken. (c)
Bold
and underlined figures indicate non-compliance with WQOs. (d)
n.a. indicates the absence of applicable WQOs. |
||||||
Table 6.8 Water
Quality Data Measured at the Sources of Discharge
|
Sources of Discharge |
Season |
Water Temperature (℃) |
pH |
Permanganate index (mgL-1) |
COD (mgL-1) |
BOD5 (mgL-1) |
Ammoniacal Nitrogen (mgL-1) |
Total Phosphorus (mgL-1) |
Total Nitrogen (mgL-1) |
Copper (mgL-1) |
Zinc (mgL-1) |
|
Kong Yiu Drainage Channel |
Wet |
|
7.2 |
3.1 |
8.7 |
2.6 |
0.33 |
0.28 |
1.33 |
<0.006 |
0.01 |
|
Dry |
20 |
7.3 |
|
19.3 |
3.72 |
0.13 |
0.12 |
2.47 |
<0.006 |
|
|
|
Ping Yuen
River |
Wet |
|
7.5 |
5.17 |
30.5 |
4.3 |
3.09 |
0.27 |
4.94 |
<0.006 |
0.01 |
|
Dry |
21 |
7.2 |
|
21.1 |
3.62 |
13 |
2.57 |
22.8 |
0.01 |
|
|
|
Shawan River |
Wet |
31 |
7.3 |
3.64 |
8.8 |
3.5 |
0.75 |
0.15 |
9.6 |
<0.006 |
0.01 |
|
Dry |
|
7.5 |
|
29.9 |
6.2 |
4.54 |
0.54 |
16.3 |
<0.006 |
|
|
|
Ng Tung River |
Wet |
30 |
7.2 |
3.42 |
9.4 |
2.36 |
1.85 |
0.26 |
3.72 |
0.007 |
0.01 |
|
Dry |
|
7.1 |
|
19.3 |
9.35 |
6.9 |
0.49 |
13.7 |
<0.006 |
|
|
|
Buji River |
Wet |
31 |
7.4 |
17.9 |
90.1 |
45.6 |
32.4 |
0.94 |
35.3 |
<0.006 |
0.03 |
|
Dry |
|
7.2 |
|
102 |
56.7 |
36.9 |
1.06 |
47.3 |
0.006 |
|
|
|
Futian River |
Wet |
31 |
7.2 |
17.7 |
112 |
57.4 |
16.6 |
1.46 |
19.7 |
<0.006 |
0.01 |
|
Dry |
|
7.2 |
|
61.1 |
28.7 |
18.5 |
1.95 |
35 |
<0.006 |
|
|
|
Huanggong
River |
Wet |
31 |
7.3 |
11.8 |
61 |
30.8 |
15.8 |
0.91 |
17.3 |
<0.006 |
0.01 |
|
Dry |
|
7.1 |
|
43.8 |
27.6 |
18.6 |
0.6 |
22.3 |
<0.006 |
|
Table 6.9 Quantities
of Pollutants and Discharge Volume from the Sources of Discharge
|
Source of Discharge |
Discharge Volume（m3 d-1） |
Quantities of Pollutants（kg d-1） |
||||||||
|
|
|
Total
Suspended Solids |
COD |
BOD5 |
Ammoniacal Nitrogen |
Total
Nitrogen |
Total
Phosphorus |
Oil and
Grease |
Copper |
|
|
Luofang
Sewage Treatment Plant |
350,000 |
3,850.00 |
7,700.00 |
350.00 |
108.50 |
1.19 |
126.35 |
28.00 |
0.21 |
|
|
Ping Yuen
River |
19,094 |
305.51 |
582.38 |
82.11 |
59.00 |
9.43 |
5.10 |
3.82 |
0.01 |
|
|
Shawan River |
35,942 |
1,653.35 |
316.29 |
125.80 |
26.96 |
345.05 |
5.43 |
7.19 |
0.02 |
|
|
Ng Tung River |
372,902 |
7,458.05 |
3,505.28 |
880.05 |
689.87 |
1,387.20 |
96.95 |
74.58 |
0.22 |
|
|
Buji River |
48,7296 |
68,221.40 |
43,905.37 |
22,230.44 |
15,798.10 |
17,221 |
456.60 |
97.46 |
0.29 |
|
|
Binhe Sewage Treatment Plant |
218,400 |
114.57 |
8,736.00 |
1,310.4 |
1,917.60 |
1.010 |
107.90 |
34.94 |
0.13 |
|
|
Futian River |
777 |
44.32 |
87.17 |
44.63 |
12.89 |
15.33 |
1.13 |
0.16 |
0.00 |
|
|
Huanggong
River |
31,104 |
777.60 |
1,897.34 |
956.76 |
491.44 |
539.34 |
28.18 |
6.22 |
0.02 |
|
6.3.4
Sediment Quality
The construction of the Project will
require excavation and disposal of river sediments. Under the Planning
and Feasibility Study for Training of Upstream Section of Shenzhen River,
twenty (20) river sediment samples were collected at five (5) locations within
the Study Area and tested in accordance with the requirements stipulated in the
ETWB TC(W) No. 34/2002 for an initial
assessment of the nature of contaminated materials in the river sediment and
the locations of the contaminated sediments (see Figure 6.5). In
addition, a sediment sampling programme has been undertaken as part of this EIA
Study to delineate the locations of the contaminated sediment and enable
subsequent estimation of different types of sediments (ie
contaminated and uncontaminated sediments) to be disposed of for the purpose of
the EIA. River bed sediment samples have been collected at eight (8) locations
(see Figure
6.5).
Detailed methodology and sediment quality
results for the two sediment sampling programmes are presented in the Land Contamination and Waste Management
Assessment Report while brief descriptions of the data are provided in Table 6.10. The sediment quality data is compared against
the sediment quality criteria specified in ETWB
TC(W) No. 34/2002.
Sediment
from 21 of the 33 samples tested are found to be uncontaminated (ie sediment with all contaminant levels not exceeding the
LCEL) and classified as Category L materials (see Table 6.10). The heavy
metals concentrations in 6 samples were found between the LCEL and UCEL and
thus classified as Category M contaminated materials. The concentrations in 6 samples were found
exceeded the UCEL and thus classified as Category H contaminated
materials.
Table 6.10 Summary
of Sediment Sampling Results
|
Sampling Location (h) |
Sampling
Depth (m below river bed) |
Metals and Metalloids (mg kg-1) |
Low M.Wt PAHs (µg
kg-1) (f) |
High M.Wt PAHs
(µg kg-1) (f) |
Total PCBs (µg kg-1) (f) |
TBT in interstitial water (µg L-1) (e) (f) (g) |
Overall Sediment Class(a),(b),(c) |
||||||||
|
As |
Cd |
Cr |
Cu |
Pb |
Hg |
Ni |
Ag |
Zn |
|||||||
|
Reporting
Limits |
|
1 |
0.2 |
1 |
1 |
1 |
0.05 |
1 |
0.1 |
1 |
< 550 |
< 1,700 |
< 3 |
0.015 |
|
|
LCEL(d) |
|
12 |
1.5 |
80 |
65 |
75 |
0.5 |
40 |
1 |
200 |
550 |
1,700 |
23 |
0.15 |
|
|
UCEL(d) |
|
42 |
4 |
160 |
110 |
110 |
1 |
40 |
2 |
270 |
3,160 |
9,600 |
180 |
0.15 |
|
|
SD1 |
Surface |
2.8 |
0.42 |
10 |
<1.0 |
46 |
<0.05 |
5.9 |
0.18 |
52 |
ND |
ND |
ND |
ND |
L |
|
SD1 |
0.9 |
3.5 |
0.21 |
<8.0 |
9.0 |
26 |
<0.05 |
<4.0 |
<0.10 |
20 |
ND |
ND |
ND |
ND |
L |
|
SD1 |
1.9 |
<1.0 |
<0.20 |
<8.0 |
<1.0 |
16 |
<0.05 |
<4.0 |
<0.10 |
<20 |
ND |
ND |
ND |
ND |
L |
|
SD1 |
2.9 |
<1.0 |
<0.20 |
<8.0 |
<1.0 |
12 |
<0.05 |
<4.0 |
<0.10 |
<20 |
ND |
ND |
ND |
ND |
L |
|
SD2 |
Surface |
1.1 |
1.3 |
52 |
82 |
120 |
0.21 |
24 |
1.3 |
430 |
ND |
ND |
ND |
ND |
H |
|
SD2 |
0.9 |
3.1 |
0.25 |
<8.0 |
12 |
52 |
<0.05 |
<4.0 |
0.23 |
40 |
ND |
ND |
ND |
ND |
L |
|
SD2 |
1.9 |
1.2 |
<0.20 |
<8.0 |
<1.0 |
22 |
<0.05 |
<4.0 |
<0.10 |
<20 |
ND |
ND |
ND |
ND |
L |
|
SD2 |
2.9 |
12 |
0.48 |
<8.0 |
9.0 |
<8.0 |
<0.05 |
5.9 |
0.12 |
91 |
ND |
ND |
ND |
ND |
L |
|
SD2 |
5.9 |
6.5 |
0.35 |
<8.0 |
8.7 |
19 |
<0.05 |
<4.0 |
<0.10 |
44 |
ND |
ND |
ND |
ND |
L |
|
SD3 |
Surface |
2.0 |
0.25 |
<8.0 |
9.9 |
37 |
<0.05 |
4.3 |
0.10 |
45 |
ND |
ND |
ND |
ND |
L |
|
SD3 |
0.9 |
2.4 |
<0.20 |
<8.0 |
8.6 |
31 |
<0.05 |
<4.0 |
<0.10 |
22 |
ND |
ND |
ND |
ND |
L |
|
SD3 |
1.9 |
8.5 |
1.7 |
26 |
14 |
50 |
<0.05 |
<4.0 |
<0.10 |
93 |
ND |
ND |
ND |
ND |
M |
|
SD3 |
2.9 |
<1.0 |
0.27 |
9.6 |
14 |
<8.0 |
<0.05 |
7.3 |
<0.10 |
21 |
ND |
ND |
ND |
ND |
L |
|
SD4 |
Surface |
2.0 |
<0.20 |
<8.0 |
<1.0 |
34 |
<0.05 |
<4.0 |
<0.10 |
28 |
ND |
ND |
ND |
ND |
L |
|
SD4 |
0.9 |
6.0 |
0.31 |
<8.0 |
11 |
50 |
<0.05 |
4.0 |
<0.10 |
48 |
ND |
ND |
ND |
ND |
L |
|
SD4 |
1.9 |
11 |
1.6 |
12 |
40 |
170 |
<0.05 |
15 |
0.34 |
180 |
ND |
ND |
ND |
ND |
H |
|
SD4 |
2.9 |
2.5 |
0.26 |
<8.0 |
42 |
62 |
<0.05 |
4.4 |
0.14 |
56 |
ND |
ND |
ND |
ND |
L |
|
SD5 |
Surface |
45 |
1.9 |
71 |
130 |
120 |
1.4 |
84 |
1.4 |
560 |
ND |
ND |
ND |
ND |
H |
|
SD5 |
0.9 |
12 |
0.71 |
<8.0 |
30 |
160 |
<0.05 |
11 |
0.20 |
72 |
ND |
ND |
ND |
ND |
H |
|
SD5 |
1.9 |
5.1 |
0.35 |
<8.0 |
14 |
120 |
<0.05 |
<4.0 |
<0.10 |
48 |
ND |
ND |
ND |
ND |
H |
|
SD5 |
2.9 |
5.3 |
0.42 |
<8.0 |
14 |
100 |
<0.05 |
<4.0 |
0.10 |
61 |
ND |
ND |
ND |
ND |
M |
|
SR1 |
Surface |
2 |
<0.2 |
4 |
6 |
37 |
<0.05 |
3 |
<0.1 |
31 |
ND |
ND |
ND |
NA |
L |
|
SR2 |
Surface |
3 |
0.2 |
6 |
9 |
57 |
<0.05 |
3 |
0.2 |
44 |
ND |
ND |
ND |
NA |
L |
|
SR3 |
Surface |
6 |
0.4 |
28 |
31 |
78 |
<0.05 |
17 |
0.3 |
122 |
ND |
ND |
ND |
NA |
M |
|
SR4 |
Surface |
6 |
0.4 |
11 |
21 |
86 |
<0.05 |
13 |
0.1 |
71 |
ND |
ND |
ND |
NA |
M |
|
SR4 |
0.9 |
3 |
0.2 |
9 |
21 |
54 |
<0.05 |
5 |
<0.1 |
45 |
ND |
ND |
ND |
NA |
L |
|
SR4 |
1.9 |
5 |
0.2 |
7 |
12 |
58 |
<0.05 |
4 |
<0.1 |
34 |
ND |
ND |
ND |
NA |
L |
|
SR4 |
2.9 |
1 |
<0.2 |
3 |
7 |
41 |
<0.05 |
2 |
<0.1 |
20 |
ND |
ND |
ND |
NA |
L |
|
SR5 |
Surface |
3 |
0.4 |
22 |
20 |
39 |
0.11 |
14 |
0.7 |
84 |
ND |
ND |
ND |
NA |
L |
|
SR5 |
Dup |
3 |
0.2 |
28 |
23 |
26 |
<0.05 |
16 |
0.2 |
92 |
ND |
ND |
ND |
NA |
L |
|
SR6 |
Surface |
7 |
0.8 |
8 |
14 |
97 |
<0.05 |
10 |
0.3 |
112 |
ND |
ND |
ND |
NA |
M |
|
SR7 |
Surface |
28 |
2.6 |
46 |
108 |
167 |
1.16 |
222 |
2.7 |
651 |
ND |
ND |
ND |
NA |
H |
|
SR8 |
Surface |
7 |
2.1 |
3 |
10 |
67 |
<0.05 |
4 |
0.1 |
228 |
ND |
ND |
ND |
NA |
M |
|
Notes: (a)
Category L = Sediment with all contaminant levels not
exceeding the LCEL. (b)
Category M = Sediment with any one or more contaminant
levels exceeding the LCEL and none exceeding the UCEL. (c)
Category H = Sediment with any one or more contaminant
levels exceeding the UCEL. (d)
CEL = Chemical Exceedance Levels
as stipulated in ETWB (TC) No. 34/2002.
These included the Lower and Upper Chemical Exceedance
Levels (LCEL, UCEL). (e)
NA = Not Available (f)
ND = Not Detected (g)
Analysis of tributyltin (TBT) in
interstitial water was cancelled for samples collected during the EIA Study
due to insufficient volume of interstitial water. (h)
Locations with ID “SR” are sampled as part of the EIA
Study while locations with ID “SD” are sampled as part of the FS Study. (i)
Underlined figures indicate exceedance
of the LCEL. (j)
Bold and underlined figures indicate exceedance
of the UCEL. |
6.4
Water Quality
Sensitive Receivers
The Water Quality Sensitive Receivers (WSRs)
that may be affected by changes in water quality arising from the Project are
identified in accordance with the EIAO-TM,
which include the following:
·
Shenzhen
River;
·
Kong Yiu Drainage Channel;
·
Ping
Yuen River;
·
Wetland
Conservation Area at Shenzhen River estuary; and
·
Mai
Po and Inner Deep Bay Ramsar Site.
Locations of the above WSRs
are shown in Figure 6.6
while the approximate shortest distance from the identified WSRs
to the Project Site are detailed in Table
6.11. Water from Shenzhen River will
not intrude into any active fish pond and therefore, no active fish pond is
identified as WSR within the Study Area.
Table 6.11 Identified Water Quality Sensitive
Receivers (WSRs)
|
WSRs |
Minimum Distance away from the Project Site Boundary (m) |
|
Shenzhen River |
Located within and
next to the Project Site |
|
Ping Yuen River |
Located next to
the Project Site |
|
Kong Yiu Drainage Channel |
Located next to
the Project Site |
|
Wetland
Conservation Area at Shenzhen River estuary |
7.8 km |
|
Mai Po and Inner
Deep Bay Ramsar Site |
11 km |
6.5
Potential Sources of Impact
Potential sources of impacts to water
quality arising from the Project may occur during both the construction and
operation phases. Each is discussed
below.
6.5.1
Construction Phase
The main construction activities associated with the
Project that have the potential to cause water quality impacts involve the
following:
·
Cofferdam
demolition (ie involves wet excavation by backhoes along
the central line of the designed river course) after river widening, formation
of flood detention pond and embankment;
·
Drainage
from foundation pit for construction of new embankment;
·
Construction
of boundary fence and boundary patrol road; and
·
Site
runoff and pollutants entering the receiving waters.
River water will
be diverted from the works area before the commencement of excavation and
construction activities by constructing a cofferdam which will be made of
hessian bags with clay. Impact to water
quality due to the river diversion is thus not expected to occur. As the excavation of river bed will be
carried out in dry condition within the cofferdam, release of suspended
sediment, and hence water quality impact is not expected.
The potential impacts to water quality arising from
operation of the Project have been identified as follows:
·
Changes
to the hydrodynamics through the river regulation and thereby affecting the
local erosion and sedimentation pattern and water quality; and
·
Maintenance
dredging which may lead to disturbance and re-suspension of river sediments and
thereby affecting water quality.
6.6.1
General Methodology
The methodology employed to assess the
above impacts is presented in the Water
Quality Modelling Method Statement (see Annex C1) and has been based on the information
presented in the Project Description.
Impacts to the concentrations of SS caused
by the demolition of cofferdam and foundation pit drainage have been assessed
using mathematic modelling. It is
planned to carry out river bed excavation during dry season. However, the impact assessment has also taken
into account excavation during both dry and wet seasons just in case if
excavation during wet season is necessary.
The release of heavy metals, nutrients and micro-organic pollutants from
the disturbed sediments caused by cofferdam demolition was also assessed. Mitigation
measures, as proposed in Section 6.9,
were assumed to be absent in the modelling so that worse case scenarios were
examined.
Operational impacts on water quality have
also been studied by means of mathematical modelling. The models have been used to simulate the
effects of operation due to river regulation, including potential effects on flows
and water levels and subsequent water quality effects due to changing
hydrodynamics and dry weather flow interception works on the Shenzhen side, and
any changes in local erosion and sedimentation.
Full details of the working conditions
examined in the modelling works are provided in Annex C1.
Figures presenting the modelling results are presented in Annex C2.
As Kong Yiu Drainage Channel and Ping Yuen
River will not be affected by tidal influence, water from Shenzhen River will
not intrude into these watercourses.
Hence, the water quality impact to Kong Yiu
Drainage Channel and Ping Yuen River will only be assessed qualitatively, if
found necessary.
6.6.2
Uncertainties in Assessment Methodology
In order to study the worst case
environmental impacts during construction and operation of the Project, it is
conservatively assumed that all sediment released will be discharged into the
receiving water. The total sediment
leaked would be treated as intensively discharging into the water body at the
same time. In reality, this would not
happen and thus will represent a worst case scenario and it is a conservative
assessment.
Suspended Sediment Dispersion
The main potential impacts to water quality arising from
this Project during the construction phase relate to the re-suspension of river
sediment caused by foundation pit drainage and cofferdam demolition. The construction of cofferdam does not
involve any excavation works and hence, will not lead to significant
disturbance of the river sediments.
Unacceptable water quality impacts are thus not anticipated. Drainage from the foundation pit will also
lead to dispersion of suspended sediment from the works area. The resulting suspended sediment dispersion will
subsequently cause potential physico-chemical changes
in the river water.
It is noted that the demolition of
cofferdam will involve the use of backhoes (1 m3) and long boom
backhoes (0.55 m3) at different locations of the Project Site. To assess the impacts of the demolition of
cofferdam and drainage of foundation pits to the SS concentrations, a total of
two working conditions have been modelled which assumed that the works are
carried out concurrently among Work Areas I (near Changling
Village) and II (near the proposed Liantang/Heung
Yuen Wai Boundary Control Point (LT/HYW BCP)) and
among Work Areas III (near Luofang Village) and IV
(near Ping Yuen River confluence), respectively, for both wet and dry seasons
(see Figure
6.1). For each working
condition, the sediment release rate of the backhoes was made reference to an
open grab. For comparison purpose, the
use of closed grab was also modelled (see Annex C1).
As a conservative approach, the estimated total excavation volume of
100,000 m3 of the Project is assumed to be generated from wet
excavation works only for calculation of the sediment release rate. In the water quality model, the daily
excavation rate adopted for each Work Area is 996 m3 day-1
for the dry season and 432 m3 day-1 for
the wet season, respectively.
Foundation pits will be excavated within
the cofferdam for the construction of the new dykes on both sides of the
Shenzhen River. Before the foundation
pits are being filled, it is required to discharge wastewater from the pits
regularly. The foundation pit drainage,
which contains certain amount of river sediment, will have the potential to
increase the SS concentration of the river water in the vicinity of the works
area during the construction phase.
According to the Guangdong
Province Discharge Limits for Water Quality Pollutants (DB44/26-201), SS concentration in the
foundation pit drainage shall not be higher than 100 mg L-1. Adequate time (48 hours) will be allowed for the
settlement of the suspended sediments to ensure that the aforementioned
standard is met before foundation pit drainage are being discharged outside the
works area. The recommended flow rate of
the foundation pit drainage is 0.17 m3 S-1. With the adoption of the maximum allowable value of 100 mg L-1,
the SS release rate from the foundation pit drainage is 0.017 kg s-1
and is adopted in the water quality model to predict the SS elevations caused
by foundation pit drainage from the works area (see Annex C1). It should be noted that foundation pit drainage and
cofferdam demolition are not concurrent activities since the foundation pit
will be filled for formation of embankment before demolition of cofferdam.
Therefore, they are not assessed as concurrent activities in the model.
The results from each working condition
have been presented as average monthly SS concentration along the length of the
modelled river section, presented as the distance from the most upstream point
of the Stage IV Project Site (see Figures
C-1 to C-4 of Annex C2). According
to the WQO for inland waters of the Deep Bay WCZ (including Ganges Subzone,
Indus Subzone and other inland waters with the Study area), effluent discharge
from the Project Site shall not cause the annual median of SS to exceed 20 mg L-1. However, results of the water quality
modelling show that baseline SS concentration within the Study area is well above 20 mgL-1 which limits the practicality to
adopt such standard (see Figures C-1 to C-4 of Annex C2). As effluent from the Project Site will
eventually flow into Deep Bay through the Shenzhen River, the WQO for marine
waters which states that effluent discharge shall not cause a 30% increase in
SS level in the natural environment is used for the assessment. This criterion is adopted to determine whether
the increase of SS concentration in river water at 500 m upstream and 1,000 m
downstream of the work area would cause unacceptable water quality impact (ie SS concentrations caused by construction activity >
130% of baseline SS concentrations). It
should be noted that the same criterion was adopted in the approved EIA study
of the Shenzhen River Regulation Project Stage III ([6]).
Mitigation measures to reduce impacts to acceptable levels, if deemed
necessary, are then recommended.
In summary, the following working conditions were set
to assess the potential water quality impacts of cofferdam demolition and
foundation pit drainage during the construction phase:
·
Condition
1: The SS concentrations with cofferdam demolition and foundation pit drainage
near Changling Village (Work Area I) and the proposed
LT/HYW BCP (Work Area II).
·
Condition
2: The SS concentrations with cofferdam demolition and foundation pit drainage
near Luofang Village (Work Area III) and Ping Yuen
River confluence (Work Area IV).
For both
the dry and wet season periods, modelling results show that SS concentrations
associated with foundation pit drainage and demolition of cofferdams using
either open grab or closed grab are compliant with the assessment criterion (ie SS
concentrations caused by construction activity at 500 m upstream and 1,000 m
downstream of the work area < 130% of baseline SS concentrations)
under the two working conditions (see Table
6.12; and Figures
C-1 to C-4 of Annex C2). According to the modelling results, foundation
pit drainage and cofferdam demolitions will only lead to localised SS
elevations downstream of the Work Areas and will not exert any impact at the
upstream areas (see Figures C-1 to C-4 of Annex C2). SS elevations associated with foundation pit drainage
show compliance with the assessment criterion along the entire river
section. For Work Area I and Work Area
II (ie Working Condition 1), SS concentrations
exceeding 130% of the baseline concentrations are anticipated in a region of
900 m and 790 m downstream of the cofferdam demolition activity near the
proposed LT/HYW BCP for
the dry and wet season, respectively.
For Work Area III and Work Area IV (ie Working
Condition 2), SS concentrations exceeding 130% of the baseline conditions are
predicted by the water quality model within a region of 660 m downstream of the
cofferdam demolition activity near
the Ping Yuen River confluence in both seasons. No WSRs are located
within the regions mentioned above.
Unacceptable water quality impacts are thus not expected to occur and
mitigation measures are considered not necessary.
It is
therefore anticipated that no adverse water quality impacts would arise from
cofferdam demolition and foundation pit drainage.
The
elevated SS caused by the construction activities is localised to the vicinity
of the Project Site (see Figures C-1 to C-4 of Annex C2). Concentrations of SS at the mouth of Shenzhen
River during the construction activities are the same as the baseline
concentrations under all working conditions (see Table 6.12). Therefore, it
is anticipated unacceptable impacts to the Wetland Conservation Area and Mai Po
and Inner Deep Bay Ramsar Site near the Shenzhen
River mouth will not occur.
Overall,
no adverse impacts to SS concentrations are anticipated to occur as a result of
the cofferdam construction and demolition and foundation pit drainage.
Heavy Metals, Nutrients and Micro-Organic Pollutants
Elutriate tests (sediment to water ratio of 1:4) were
carried out to assess the potential for the release of heavy metals (including
arsenic, cadmium, chromium, copper, lead, nickel, silver and zinc), nutrients
(including ammoniacal nitrogen, total nitrogen and
total phosphorus) and micro-organic pollutants (including PAHs,
PCBs and chlorinated pesticides) from the river sediments as they are
disturbed/agitated through wet excavation during cofferdam demolition. Sediment samples collected under the EIA
Study from five out of eight sediment sampling locations (see Figure
6.5) were tested and results are shown in Table 6.13 (please refer to Annex C3 for
the detailed laboratory analysis results).
Results of the elutriate tests show that levels of all heavy metals and
micro-organic pollutants are below the reporting limits and within the
assessment criteria (Table 6.14). Levels of total nitrogen, ammoniacal
nitrogen and total phosphorus were recorded above the reporting limits, consequently, the water quality impacts associated
with the release of these nutrients from the disturbed river sediments are
further evaluated.
Compared with the water quality data of the Shenzhen
River collected by the Shenzhen Environmental Monitoring Centre (Tables 6.2 to 6.4), it is found that the concentrations of total nitrogen, total
phosphorus and ammoniacal nitrogen from the elutriate
tests (Table 6.14) are generally
similar to the concentrations recorded by the Centre at stations downstream of
the Project Site from 2007 to 2009. It
is thus anticipated that nutrients release from the disturbed sediments as a
result of the excavation works within the Project Site will not lead to
unacceptable water quality impacts to the downstream area. In addition, the modelling results show that
during construction, SS concentrations at the WSRs
(including the Wetland Conservation Area and Mai Po and
Inner Deep Bay Ramsar Site near the Shenzhen River
mouth) will be
the same as the baseline concentrations (please refer to the assessment of suspended sediment
dispersion in Section 6.7.1). Disturbed sediments will thus
not disperse to the WSRs from the Project Site.
Therefore, the potential of release of total nitrogen, ammoniacal nitrogen and total phosphorus from the disturbed
sediments at the WSRs as a result of the construction
of the Project is considered negligible.
It is considered that the potential water quality
impacts with respect to increase of heavy metals, nutrients and micro-organic
pollutants levels in the receiving water due to release from
disturbed/re-suspended sediments are minimal and acceptable.
Table 6.12 Percentage
Increase in SS Concentrations under Different Working Conditions during the
Construction Phase of the Project
|
Locations of Construction Works |
Working Condition 1 |
Working Condition 2 |
|||||
|
Distance from Works Location |
Upstream 500 m (b) |
Downstream 1,000 m (b) |
At Shenzhen River mouth |
Upstream 500 m (c) |
Downstream 1,000 m (c) |
At Shenzhen River mouth |
|
|
% Increase in Dry Season |
Closed Grab |
0.0 |
17.6 |
0.0 |
0.0 |
2.9 |
0.0 |
|
Open Grab |
0.0 |
21.6 |
0.0 |
0.0 |
2.9 |
0.0 |
|
|
Foundation Pit Drainage |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
|
|
% Increase in Wet Season |
Closed Grab |
0.0 |
18.9 |
0.0 |
0.0 |
9.8 |
0.0 |
|
Open Grab |
0.0 |
23.0 |
0.0 |
0.0 |
11.8 |
0.0 |
|
|
Foundation Pit Drainage |
0.0 |
1.4 |
0.0 |
0.0 |
0.0 |
0.0 |
|
|
Notes: (a)
According to the WQO of the Deep Bay WCZ, effluent
discharge shall not cause a 30% increase in SS level in the natural
environment. (b)
For Working Condition 1, the % change in SS is calculated
at an area 500 m upstream of the location of construction activities at Work
Area I and an area 1,000 m downstream of the location of construction
activities at Work Area II. (c)
For Working Condition 2, the % change in SS is calculated
at an area 500 m upstream of the location of construction activities at Work
Area III and an area 1,000 m downstream of the location of construction
activities at Work Area IV. |
|||||||
Table 6.13 Results of Elutriate Test Conducted for
River Sediment
|
Sampling Location |
Total Nitrogen (mg L-1) |
Total Phosphorus (mg L-1) |
Ammoniacal Nitrogen (mg L-1) |
|
SR1 |
5.8 |
1.6 |
4.63 |
|
SR3 |
23.2 |
0.4 |
18.8 |
|
SR5 |
53.8 |
1.0 |
12.5 |
|
SR6 |
12.0 |
1.5 |
11.9 |
|
SR8 |
9.0 |
0.8 |
6.11 |
|
River Water Concentration |
7.0 |
0.6 |
6.98 |
Table 6.14 Summary of Assessment Criteria for
Dissolved Metals, Organic Compounds and Nutrients
|
Compound |
Unit |
Assessment Criteria |
|
Heavy
Metals |
|
|
|
Arsenic (As) |
ug L-1 |
340 (a) |
|
Cadmium (Cd) |
ug L-1 |
2 (a) |
|
Chromium (Cr) |
ug L-1 |
16 (a) |
|
Copper (Cu) |
mg L-1 |
1.0 (b) |
|
Lead (Pb) |
ug L-1 |
65 (a) |
|
Nickel (Ni) |
ug L-1 |
470 (a) |
|
Zinc (Zn) |
ug L-1 |
120 (a) |
|
Silver (Ag) |
ug L-1 |
3.2 (a) |
|
PAHs |
|
|
|
Naphthalene |
ug L-1 |
37 (b) |
|
PCBs |
|
|
|
Total PCBs |
ug L-1 |
0.014 (a)(c) |
|
Chlorinated
pesticides |
|
|
|
Heptachlor |
ug L-1 |
0.52 (a) |
|
Aldrin |
ug L-1 |
3 (a) |
|
Heptachlor epoxide |
ug L-1 |
0.52 (a) |
|
Alpha - Endosulfan |
ug L-1 |
0.22 (a) |
|
Beta – Endosulfan |
ug L-1 |
0.22 (a) |
|
4,4’ - DDT |
ug L-1 |
1.1 (a) |
|
|
|
|
|
Nutrients |
|
|
|
Total Nitrogen |
mg L-1 |
2 (d) |
|
Total Phosphorus |
mg L-1 |
0.4 (d) |
|
Ammoniacal Nitrogen |
mg L-1 |
2 (d) |
|
Notes: (a)
U.S.
Environmental Protection Agency (USEPA), National Recommended Water Quality
Criteria, 2009 (http://water.epa.gov/scitech/swguidance/waterquality/). Criterion Maximum Concentration (CMC)
values are adopted if not stated otherwise.
(b)
Australian
and New Zealand Environment and Conservation Council (ANXECC), Australian and
New Zealand Guidelines for Fresh and Marine Water Quality (2000) – Trigger
values for protection of 90% of species.
(http://www.mincos.gov.au/publications/australian_and_new_zealand_guidelines_for_fresh_and_marine_water_quality (c)
USEPA
(2009) Criterion Continuous Concentration (CCC) for freshwater is adopted for
total PCBs (e.g., the sum of all congener or all isomer or homolog or Aroclor analyses.) (d)
Ministry
of Environmental Protection of the People’s Republic of China, Environmental
Quality Standards for Surface Water (GB 3838 - 2002) – Class V surface Water. |
||
Sewage will be generated from the
construction workforce, site office’s sanitary facilities and from portable
toilets. If not properly managed, these
wastewaters could cause adverse water quality impacts, odour and potential
health risks to the workforce by attracting pests and other disease vectors.
It
is estimated that up to 1,350 construction workers will be involved in the
construction of the Project during the peak construction period. With a sewage generation rate of 0.15 m3/worker/day ([7]), about 203 m3 of sewage will
be generated per day. It is estimated
that about 45 portable toilets will be required ([8]).
However, the exact number of portable toilet required will be based on
the contractor practice, as well as the site condition. Nevertheless, an adequate number of portable
toilets will be provided at the Project Site to ensure that sewage from site
staff is properly collected. No adverse
environmental impacts are envisaged provided that the portable toilets are
properly maintained by a contractor and the collected sewage is disposed at the
designated sewage treatment works.
Land Based Construction Activities
(including the advanced works)
Discharges and runoff from the Project
Site during the construction phase, particularly during soil excavation,
filling of embankment foundation, slope protection, and landscaping works, will
contain SS which could be a source of water pollution. Wastewater with high pH value may be
generated by concrete washing during slope protection works and in situ concreting works. However, with proper implementation of
general good construction site practices as described in Section 6.8, it
is anticipated that the land based construction works will not cause adverse
water quality impact.
Hydrodynamic Assessment
River improvement works will be carried
out under the Project in order to rectify
the flood prevention performance of the regulated section of Shenzhen River (ie to attain the drainage capacity of a 50-year return
period) and to safeguard the livelihood of settlements along the river.
In relation to the above, changes in
hydrodynamic conditions after implementation of the Project, especially the
changes in water surface profile of the river before and after the
implementation of the Project, have been assessed by mathematical model.
In the hydraulic model calculations, the
hydraulic elements of Shenzhen River under different design conditions (ie before and during the implementation of the Project and
one year after operation) have been simulated.
The flood control standard before implementation of the Project is 1 in
2 to 20 years, and after implementation of the Project, it will achieve the 1
in 50 year standard. The working
conditions for the modelling were formulated as follows:
·
Condition
1: Before and after the implementation of
the Project, the flood surface profile when 1 in 50 years flood encounters 1 in
50 years tidal level;
·
Condition
2: Before and after the implementation of
the Project, the flood surface profile when 1 in 50 years flood encounters 1 in
10 years tidal level;
·
Condition
3: Before and after the implementation of
the Project, the flood surface profile when 1 in 10 years flood encounters 1 in
50 years tidal level;
·
Condition
4: Before and after the implementation of
the Project, the flood surface profile when 1 in 10 years flood encounters 1 in
10 years tidal level;
·
Condition
5: One year after the implementation of the
Project, the flood surface profile when 1 in 50 years flood encounters 1 in 50
years tidal level;
·
Condition
6: One year after the implementation of the
Project, the flood surface profile when 1 in 50 years flood encounters 1 in 10
years tidal level;
·
Condition
7: One year after the implementation of the
project, the flood surface profile when 1 in 10 years flood encounters 1 in 50
years tidal level; and
·
Condition
8: One year after the implementation of the
project, the flood surface profile when 1 in 10 years flood encounters 1 in 10
years tidal level.
Detailed modelling methodology is discussed in Annex C1.
Modelling results showing water surface profiles before (ie before construction) and after implementation (ie during operation) of the Project under different flood
and tidal conditions (ie working conditions 1 to 4)
are illustrated in Figures C-5 to C-8 of Annex C2. By achieving the
flood control standard of 1 in 50 years after implementation of the Project,
water level of the regulated river section of the Project will be lower than
the water level before implementation under all the four working conditions of
tidal and flood levels (working conditions 1 to 4). It is thus considered that implementation of
the Project will be beneficial to the hydrodynamics of the Project Site by
improving the flood
prevention performance. However,
due to tidal influence from Deep Bay, water level during operation phase at
river section downstream of Ping Yuen River confluence (ie
downstream of the Project Site) will be similar to the original water level
before implementation of the Project under all working conditions. Therefore, implementation of the Project is
not expected to significantly affect the hydrodynamic conditions downstream of
the Project Site, and hence Wetland Conservation Area and Mai Po and Inner Deep
Bay Ramsar Site near the Shenzhen River mouth.
After one year of implementation, water level within
the Project Site under the four combinations of flood and tidal frequency (ie working conditions 5 to 8) will be lower than the
designed water level due to channel erosion (see Figure C-9 to C-12 of Annex C2).
Water level after one year of implementation will be lower than the
designed level by a maximum of 1 m.
However, due to deposition of river sediments between Ping Yuen River
confluence and Ng Tung Rive confluence, water level after one year of operation
will be higher than that of the designed water level as indicated by the
modelling results under all the four combinations of flood and tidal frequency
for working conditions 5 to 8. Detailed
discussions on the channel erosion and sediment deposition along the Shenzhen
River are provided below.
Erosion
and Sediment Deposition of Riverbed
The variations of channel erosion and
sediment deposition after the implementation (ie
during operation) of the Project have been assessed. The working conditions for the modelling were
formulated as follows:
-
Condition
1: Before implementation of the Project, erosion and deposition of riverbed
experiencing one year’s flow and sediment;
-
Condition
2: After implementation of the Project, erosion and deposition of riverbed
experiencing one year’s flow and sediment;
-
Condition
3: After implementation of the Project, erosion and deposition of riverbed
experiencing two consecutive typical water and sediment years;
-
Condition
4: After implementation of the Project, erosion and deposition of riverbed
experiencing three consecutive typical water and sediment years.
Detailed modelling methodology is
presented in Annex C1 and results of the four working
conditions are illustrated in Figures
C-13 to C-14of Annex C2.
Modelling
results presented in Table 6.17
indicate that net erosion of river bed is expected to occur within the Project
Site before and after one, two and three years of operation of the Project as a
result of steeper gradient in this river section compared with the downstream
section (see Figure C-13 of Annex C2).
Negative values for deposition thickness and volume are predicted in
this river section (see Table 6.15). The section between Ping Yuen River
confluence and Ng Tung River confluence is the main receiving body of upstream
sediments and hence net deposition of sediments is expected to occur under all
the four working conditions reflecting by the positive deposition thickness and
volume (see Table 6.15). The maximum sediment deposition is
anticipated between Ng Tung River confluence and Huanggong
River confluence due to sediments flowing from upstream section and Buji River and tidal influence from Deep Bay. Maximum sediment deposit thickness of 0.43 m
and volume of approximately 100,000 m3 are predicted by the model
after one year of Project implementation (ie working
condition 2), which is similar to those before construction of the Project (ie working condition 1).
Incoming tide from Deep Bay is the source of deposited sediments between
Huanggong River confluence and Shenzhen River mouth,
therefore, unacceptable impacts at the Wetland Conservation Area and Mai Po
Reserve as a result of sediment deposition caused by the Project implementation
is not expected.
From the modelling results, a general trend
of decreasing deposition volume and thickness with time after implementation of
the Project at river section downstream of Ping Yuen River confluence is
observed (ie working conditions 2 to 4 on Table 6.15) as the deposition soon
reaches equalibrium.
However, maintenance dredging, say 3 to 5 years, would still be required
downstream of the Project Site to remove the deposited sediment in order to
maintain the overall flood prevention performance of the Shenzhen River.
Water Quality
Levels
of key water quality parameters (DO, COD, BOD5, total nitrogen,
total phosphorus and ammoniacal nitrogen) along
Shenzhen River were modelled under working conditions of with (during
operation) or without the Project (baseline) for both wet and dry seasons. The water quality impacts were assessed by
comparing the differences in water quality parameters between the baseline and
operation conditions. Figures
illustrating the modelling results are included in Annex C2. The modelling results show that levels of
COD, BOD5, total nitrogen, total phosphorus and ammoniacal
nitrogen during the operation phase would be equal to or less than those of the
baseline situation in both wet and dry seasons (see Figures C-17 to C-26 of Annex C2).
For DO, the values during operation are equal to or higher than those of
the baseline in both seasons (see Figures
C-15 and C-16 of Annex C2).
It should be noted that the model calculations have taken account of the
effects of sewage collection and diversion works on the Shenzhen side of the
river. Overall, no unacceptable water
quality impacts are expected from operation of the Project.
Table
6.15 Thickness of Volume of Sediment
Deposition on the River Bed under different Working Conditions
|
River Section |
Most upstream point of Stage 4 to Ping
Yuen River Confluence |
Ping Yuen River Confluence to Ng Tung River Confluence |
Ng Tung River Confluence to Huanggong
River Confluence |
Huanggong River Confluence to Shenzhen River Mouth |
||||
|
|
Deposition thickness (m) |
Deposition volume (m3) |
Deposition thickness (m) |
Deposition volume (m3) |
Deposition thickness (m) |
Deposition volume (m3) |
Deposition thickness (m) |
Deposition volume (m3) |
|
Working
Condition 1 - After 1 year
under existing conditions |
-1.14 |
-45,201.66 |
0.41 |
101,793.10 |
0.44 |
397,181.10 |
0.10 |
42,236.15 |
|
Working
Condition 2 - After 1
year of Operation |
-0.29 |
-22,498.37 |
0.39 |
93,952.20 |
0.43 |
409,950.04 |
0.12 |
46,980.42 |
|
Working Condition
3 – After 2
years of Operation |
-0.17 |
-11,735.01 |
0.07 |
16,421.00 |
0.09 |
79,352.16 |
0.11 |
39,164.06 |
|
Working
Condition 4 – After 3
years of Operation |
-0.08 |
-3,196.52 |
0.07 |
16,078.40 |
0.08 |
69,436.13 |
0.11 |
39,703.51 |
|
Note:
(a)
Existing
conditions refer to the river bed before the construction of the Project. |
||||||||
Maintenance Dredging
Within
the Project Site where the river course is straightened and widened, a trend of
continuous sediment erosion is anticipated due to greater difference in
elevation of this river section.
Modelling results of sediment transport during the operation phase
presented above indicate that a total of approximately 22,500 m3 and
11,700 m3 of sediments will be eroded from the Project Site and
deposited on the river section downstream of the Ping Yuen River confluence
after one and two years of Project implementation, respectively. As such, it is anticipated that the need for
maintenance dredging within the Project Site is minimal. However, in case where maintenance dredging
is needed, it is anticipated that it will be undertaken infrequently and in
small and localised scale during dry season (October to March), with a dredging
rate less than that during the construction phase, ie 996 m3 day-1. The impact of maintenance dredging to SS
concentrations is thus expected to be insignificant.
Sedimentation at the flood retardation
pond is anticipated. Given the nature of
the flood retardation pond, river water will only be required to enter the pond
during wet season after severe rainstorm events. Hence, the frequency for maintenance dredging
required at the pond will be low. Since
the flood retardation pond is a confined area, the suspended river sediments
associated with maintenance dredging will eventually settle within the pond
without causing any SS elevations in the river.
Unacceptable river water quality impacts are thus not anticipated.
The
modelling results indicate that after one year operation of the Project, the
increase in sediment deposition in the river sections from Ng Tung River
Confluence to Huanggong River Confluence and from Huanggong River Confluence to Shenzhen River Mouth is
12,770 m3 and 4,700 m3, respectively (please refer to
Working Condition 2 of Table 6.15). Part of the increase is due to tidal
effect. After the second and third year
of operation, the amount of deposited sediment in the two river sections will
become less than that of the baseline condition. It is thus considered that the insignificant
increase in sediment deposition will not increase the scale of the routine
maintenance dredging downstream of the Project Site. No additional water quality impacts as a result of the implementation of the Project is
expected to occur.
Overall, unacceptable impacts to SS
concentrations caused by maintenance dredging are not expected to occur.
6.8.1
Construction Phase
Cofferdam Demolition
The impacts
to water quality from the loss of sediment to suspension were assessed during
the cofferdam demolition which involves wet excavation. The assessment was based on the predicted
loss rates of fine sediments to suspension from open grab and closed grab
working at different locations during the times of peak excavation rate. The highest loss rate was predicted to occur
during the time at which the maximum rate of wet excavation was occurring. The maximum loss rate was then adopted in the
Study and it was predicted that this loss rate would not give rise to adverse
water quality impacts. Nevertheless, good practices is recommended to further minimise the water
quality impact. It is therefore
recommended that the maximum loss rate during the wet excavation should be kept
at or below these limits.
The following good practices shall apply at all
times:
·
Dry
excavation will be used, as far as practicable, for cofferdam excavation.
·
Attention
will be paid to the lifting speed of the grab to minimise the loss of sediment.
·
Excavated
sediment will be disposed of in a gazetted marine disposal area in accordance
with the Dumping at Sea Ordinance (DASO) permit conditions (as discussed in
the Land Contamination and Waste
Management Assessment Report).
·
The
marine vessels ([9])
for transport of sediment to
the marine dumping ground will be fitted with tight bottom seals in order to
prevent leakage of material during transport.
The barges will be filled to a level, which ensures that material does
not spill over during transport to the disposal site and that adequate
freeboard is maintained to ensure that the decks are not washed by wave action.
·
The
contractor(s) will confirm that the works cause no visible foam, oil, grease,
litter or other objectionable matter to be present in the water within and
adjacent to the excavation site.
·
For
concurrent excavation works at adjacent work areas (ie
Work Areas I and II, and Work Areas III and IV), construction will be carried
out along the same flow direction (ie from upstream
to downstream / downstream to upstream) to minimise the overall impacts to SS
concentrations from adjacent work areas.
With the proper implementation of the
recommended mitigation measures during cofferdam demolition works, no
unacceptable water quality impacts will occur.
Construction Site Runoff and Drainage
Good construction site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” will be followed as far as practicable
in order to minimise surface runoff and the chance of erosion, and also to
retain and reduce any suspended solids in surface runoff prior to
discharge. These practices include the following:
·
Silt
removal facilities such as silt traps or sedimentation facilities will be
provided to remove silt particles from runoff to meet the discharge standards
of the TM-ICW under the WPCO. The design of silt removal
facilities will be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities and erosion and sediment
control structures will be inspected on a regular basis and maintained to
confirm proper and efficient operation at all times and particularly during
rainstorms. Deposited silt and grit will
be removed regularly.
·
Excavation within cofferdam will be
maintained in dry condition as far as possible.
Water within the cofferdam will be discharged to the river before
excavation commences and at times when needed (eg
after heavy rain). Adequate time (48
hours) will be allowed for suspended solid to settle (potentially overnight)
before foundation pit drainage are being discharged outside the works area.
·
Non-active
area along the river bank will be covered by impermeable sheets or hydroseeding completed sections immediately whenever
possible to minimise erosion of soil by runoff particularly during heavy
rainstorms.
·
Earthworks
to form the final surfaces will be followed up with surface protection and
drainage works to prevent erosion caused by rainstorms.
·
Appropriate
surface drainage will be designed and provided, where necessary. In particular, surface runoff will be
collected along the river bank and be diverted to sedimentation tank/pond
before discharge into the river
·
The
precautions to be taken at any time of year when rainstorms are likely together
with the actions to be taken when a rainstorm is imminent or forecasted and
actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94.
·
Oil
interceptors will be provided in the drainage system where necessary and
regularly emptied to prevent the release of oil and grease into the stormwater drainage system after accidental spillages.
·
Temporary
and permanent drainage pipes and culverts provided to facilitate runoff
discharge will be adequately designed for the controlled release of storm
flows.
The
temporary diverted drainage will be reinstated to the original condition when
the construction work has finished or when the temporary diversion is no longer
required.
The
dredged sediment will be temporary stored in the stockpile areas for dewatering
by natural ventilation. Runoff from
these stockpile areas will be collected for treatment by sedimentation with the
addition of coagulant. The treated water
will be reuse on site for water spraying.
Sewage Discharge
An adequate number of portable toilets will be
provided for the on-site construction workforce ([10]).
Wastewater/sewage will be transferred to the Luofang
Sewage Treatment Works in Shenzhen (during the river modification and associated
works) or a Government sewage treatment works in HKSAR (during the advanced
works) by a reputable collector.
General Construction Activities
·
Debris
and refuse generated on-site will be collected, handled and disposed of
properly to avoid entering the nearby WSRs.
Stockpiles of cement and other construction materials will be kept covered when
not being used.
·
Oil
leakage or spillage will be contained and clean up immediately. Waste oil will be collected and stored for
recycling or disposal in accordance with the Waste Disposal Ordinance.
6.8.2
Operation Phase
Hydrodynamics
The
hydrodynamic modelling has predicted that the operation of the Project will be
beneficial to the Project Site by improving its flood prevention performance
and no adverse impacts to hydrodynamics are expected to occur at the sensitive
receivers. Mitigation measures are thus
not considered to be necessary.
Channel Erosion and Deposition
Eroded sediment flowing from the Project Site will be
deposited between Ping Yuen River confluence and Huanggong
River confluence and consequently affecting the flood prevention performance of
this section. Maintenance dredging,
which would mainly be undertaken outside the Project Site, would be required to
rectify the flood prevention performance.
Water Quality
Sewage from the Shenzhen side currently discharged to
the Project Site will be collected and diverted to the sewage treatment works,
which will effectively reduce the pollutants discharge to the river. The water quality of the Shenzhen River
during the operation of the Project will be improved and mitigation measures
are thus not considered to be necessary.
Maintenance Dredging
No adverse
water quality impact due to maintenance dredging is predicted. Mitigation
measures are not considered to be necessary.
With the proper implementation of the recommended
mitigation measures, no residual environmental impacts are envisaged from the
construction and operation of the Project.
According to publicly available information, the
following major developments in north eastern part of Hong Kong will be
constructed and/or operated concurrently with the construction and operation (ie maintenance dredging) of the Project.
·
Liantang/Heung Yuen Wai Boundary
Control Point (LT/HYW BCP) and the associated road works;
·
Construction
of a Secondary Boundary Fence (SBF) and New Sections of Primary Boundary Fence
(PBF) and Boundary Patrol Road (BPR) ([11]); and
·
Drainage
Improvement in Northern New Territories – Package C (Remaining Works) ([12]).
There are also two ongoing planning studies
with study areas within and in the vicinity of the Project Site:
·
Land
Use Planning for the Closed Area; and
·
New Development
Areas in North East New Territories (NENT NDAs).
The construction of the LT/HYW BCP and the
connecting roads is scheduled to commence in mid 2013 and be completed in mid
2018 ([13]).
With implementation of proper mitigation measures, unacceptable water
quality impacts would not be expected to occur during construction of the
BCP. During the operation phase,
additional surface runoff from the BCP will be discharged into the Shenzhen
River which constitutes approximately 2.2 % of the existing peak flow of the
Shenzhen River near the Ping Yuen River confluence. Before discharge into the Shenzhen River, stormwater and surface runoff from the BCP will be
collected by a drainage system and treated using standard silt trap (or grease
trap if necessary) and oil interceptor at the Public Transport Interchange and
vehicles holding area to remove the oil, lubricants, grease, silt and
grit. Hence, no adverse water quality
impacts are anticipated to be caused by the discharge. Sewage and wastewater effluents generated
from the staff, food and beverage outlets and passengers of the BCP will be
directed to a high level wastewater treatment plant using Membrane Bioreactor
treatment (MBR) technology, which will be designed with a treatment capacity of
387.56 m3 d-1.
About 178.75 m3 d-1 of the treated effluent will
be reused on site for irrigation and flushing and the remaining effluent will
be discharge to the Deep Bay via gravity sewers in order to meet the
requirement of no net increase in pollutants loading of the receiving water
body. As the discharge will have no net
increase in pollutants loading, unacceptable cumulative water quality impacts
are not expected to occur during the operation phase.
The construction of the SBF and new sections of PBF and
BPR only involves land-based construction works. According to the latest tentative programme,
the works from Ng Tung River to Ping Yuen River will be carried out between end
2011 and early 2013, while the works from Pak Fu Shan to Lin Ma Hang Road will
be carried out between end 2011 and end 2013.
With proper implementation of the recommended mitigation measures in the
EIA study, no residual impacts are anticipated from the construction and
operation of this project ([14]).
Moreover, the reprovisioning of a section of
the border patrol road and boundary fences within the Project area will be
incorporated into the design and construction programme of this Project (as
advanced works). The potential water
quality impacts associated with the reprovisioning of
the SBF and the associated patrol roads have been assessed in this EIA.
The construction activities for the drainage
improvement works of Package C is scheduled to commence in July 2012 and be
completed in December 2014 (ie overlapped with the
construction phase of Stage IV regulation) ([15]).
However, details regarding its water quality impact assessment are not
yet available and thus assessment of the cumulative water quality impacts is
not possible at this stage.
The development schedule and programme of the Closed
Area Study and the NENT NDAs Study are not available
at this stage. However, it is anticipated that the construction of the new developments
planned under these studies will not be carried out concurrently with the
construction of this Project.
No unacceptable cumulative water quality impacts are
expected.
6.11
Environmental
Monitoring and Audit
6.11.1
Construction Phase
With proper
implementation of the recommended mitigation measures, sediment dispersion is
not expected to cause adverse water quality impacts at the identified water
sensitive receivers. However, a monitoring programme is
recommended to verify the predictions of the EIA and ensure compliance with the
assessment criteria.
Water quality monitoring will be undertaken during the
foundation pit drainage and cofferdam demolition at the following locations:
During foundation
pit drainage and cofferdam demolition at Work Area I and Work Area II
·
500 m
upstream of Work Area I; and
·
1,000
m downstream of Work Area II.
During foundation
pit drainage and cofferdam demolition at Work Area III and Work Area IV
·
500 m
upstream of Work Area III; and
·
1,000
m downstream of Work Area IV.
There will be one monitoring station at each location
(ie a total of four monitoring stations). Monitoring will be conducted for three times
per week during the construction period.
The interval between two sampling surveys will not be less than 36
hours. During each sampling survey, water
samples for laboratory analysis and in
situ measurements will be taken at all monitoring stations for the
following water quality parameters:
·
Dissolved
Oxygen (mg L-1) (in situ);
·
pH (in situ);
·
Turbidity
(NTU) (in situ); and
·
Suspended
Solids (mg L-1) (laboratory analysis).
Monthly site inspections and audits will be
conducted to ensure that the recommended mitigation measures are properly
implemented during the construction stage.
6.11.2
Operation Phase
Adverse
water quality impact is not expected during operation phase and hence
monitoring is not considered necessary.
In fact the water quality will be monitored through the existing
monitoring programme along Shenzhen River
The
potential sources of water quality impacts associated with the construction and
operation of the Project have been identified and the potential impacts were
evaluated using proven mathematical models.
The modelling has assessed a number of scenarios (including a number of
worse case scenarios) for pollutants (including SS, heavy metal, nutrients and
micro-organic pollutants) releases from the construction activities, and
maintenance dredging and the change of the hydrodynamic conditions of the river
during the operation of the Project.
Potential
impacts arising from the proposed construction works are predicted to be
largely confined to the specific works areas.
With proper implementation of the recommended mitigation measures,
sediment dispersion is not expected to cause adverse water quality impacts at
the identified WSRs.
During the operation phase, changes to
hydrodynamic regime within the Project Site are predicted to be beneficial and
no adverse impacts are anticipated.
Adverse water quality impacts are not expected at any identified WSRs due to the operation of the Project. It is envisaged from the modelling results of
sediment erosion and deposition that maintenance dredging would be required
between the Ping Yuen River confluence and Huanggong
confluence to maintain the flood prevention performance of this section of the
Shenzhen River. Within the Project Site,
the scale and volume of the maintenance dredging activity will be significantly
smaller than that of the capital construction work. Adverse water quality impact is not expected.
With
the implementation of the recommendation mitigation measures, no residual water
quality impacts are envisaged due to the construction and operation of the
Project. Nevertheless, a monitoring programme is recommended
during construction phase to verify the predictions of the EIA and ensure
compliance with the assessment criteria.
Cumulative
water quality impacts associated with concurrent projects within the Study Area
have been considered, no adverse impact is anticipated.