11.1 This section presents an assessment of the potential water quality impacts associated with the construction and operation phases of the Project. Recommendations for mitigation measures have been provided, where necessary, to minimise the identified water quality impacts to an acceptable level.
11.2 Potential impacts of contaminated groundwater from restored Ngau Tam Mei Landfill have been assessed and presented in Section 15.
Environmental
Legislation, Standards and
Guidelines
Environmental Impact Assessment Ordinance (EIAO)
11.3 The Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) is issued by the EPD under Section 16 of the EIAO. It specifies the assessment method and criteria that need to be followed in the EIA. Reference sections in the EIAO-TM provide the details of the assessment criteria and guidelines that are relevant to the water quality impact assessment, including:
l
Annex 6 Criteria for Evaluating Water Pollution
l
Annex 14 Guidelines for Assessment of Water Pollution
Water Pollution Control Ordinance (WPCO)
11.4
The Water Pollution Control
Ordinance (Cap. 358) is the major legislation relating to the protection and
control of water quality in
Table 11.1 Summary of Water Quality Objectives for
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive odour, tints |
Not to be present |
Whole zone |
|
Visible foam, oil scum, litter |
Not to be present |
Whole zone |
|
E coli |
Not to exceed 1000 per 100 mL,
calculated as the geometric mean of the most recent 5 consecutive samples
taken at intervals between 7 and 21 days |
Inland waters |
|
Dissolved oxygen (DO) within 2 m of
the seabed |
Not less than 2.0 mg/l for 90% of
samples |
Marine waters |
|
Depth-averaged DO |
Not less than 4.0 mg/l for 90% of
samples |
Marine waters |
|
DO |
Not less than 4.0 mg/l |
Inland waters |
|
pH |
To be in the range of 6.5 - 8.5, change
due to human activity not to exceed 0.2 |
Marine waters |
|
Not to exceed the range of 6.0 -
9.0 due to human activity |
Inland waters |
|
|
Salinity |
Change due to human activity not to
exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to human activity not to
exceed 2 oC |
Whole zone |
|
Suspended solids (SS) |
Not to raise the ambient level by
30% caused by human activity |
Marine waters |
|
Annual med |
Inland waters |
|
|
Unionized ammonia (UIA) |
Annual mean not to exceed 0.021
mg(N)/l as unionized form |
Whole zone |
|
Nutrients |
Shall not cause excessive algal
growth |
Marine waters |
|
Total inorganic nitrogen (TIN) |
Annual mean depth-averaged inorganic
nitrogen not to exceed 0.4 mg(N)/l |
Marine waters |
|
5-Day biochemical oxygen demand
(BOD5) |
Not to exceed 5 mg/l |
Inland waters |
|
Chemical Oxygen Demand (COD) |
Not to exceed 30 mg/l |
Inland waters |
|
Toxic substances |
Should not attain such levels as to
produce significant toxic, carcinogenic, mutagenic or teratogenic effects in
humans, fish or any other aquatic organisms. |
Whole zone |
|
Human activity should not cause a
risk to any beneficial use of the aquatic environment. |
Whole zone |
Source: Statement of Water Quality Objectives (
Table 11.2 Summary of Water Quality Objectives for
Western Buffer 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 2.0 mg/l for 90% of
samples |
Marine waters |
|
Depth-averaged DO |
Not less than 4.0 mg/l for 90% of
samples |
Marine waters excepting fish
culture subzones |
|
Not less than 5.0 mg/l for 90% of
samples |
Fish culture subzones |
|
|
Not less than 4.0 mg/l |
Water gathering ground subzone and
other Inland waters |
|
|
5-Day biochemical oxygen demand
(BOD5) |
Change due to waste discharges not
to exceed 3 mg/l |
Water gathering ground subzones |
|
Change due to waste discharges not
to exceed 5 mg/l |
Inland waters |
|
|
Chemical oxygen demand (COD) |
Change due to waste discharges not
to exceed 15 mg/l |
Water gathering ground subzones |
|
Change due to waste discharges not
to exceed 30 mg/l |
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 |
|
To be in the range of 6.5 – 8.5 |
Water gathering ground subzones |
|
|
To be in the range of 6.0 – 9.0 |
Inland waters |
|
|
Salinity |
Change due to waste discharges not
to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to waste discharges not
to exceed 2 oC |
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 |
|
Change due to waste discharges not
to exceed 20 mg/l of annual med |
Water gathering ground subzones |
|
|
Change due to waste discharges not
to exceed 25 mg/l of annual med |
Inland waters |
|
|
Unionized ammonia (UIA) |
Annual mean not to exceed 0.021
mg(N)/l as unionized form |
Whole zone |
|
Nutrients |
Shall not cause excessive algal
growth |
Marine waters |
|
Total inorganic nitrogen (TIN) |
Annual mean depth-averaged
inorganic nitrogen not to exceed 0.4 mg(N)/l |
Marine waters |
|
Toxic substances |
Should not attain such levels as to
produce significant toxic effects in humans, fish or any other aquatic
organisms |
Whole zone |
|
Waste discharges should not cause a
risk to any beneficial use of the aquatic environment |
Whole zone |
|
|
E.coli |
Not exceed 610 per 100 ml, calculated
as the geometric mean of all samples collected in one calendar year |
Secondary contact recreation
subzones and fish culture subzones |
|
Not exceed 180 per 100 ml,
calculated as the geometric mean of all samples collected from March to
October inclusive in 1 calendar year. Samples should be taken at least 3
times in 1 calendar month at intervals of between 3 and 14 days |
Bathing beach subzones |
|
|
Less than 1 per 100 ml, calculated
as the geometric mean of the most recent 5 consecutive samples taken at
intervals of between 7 and 21 days |
Water gathering ground subzones |
|
|
Not exceed 1000 per 100 ml,
calculated as the geometric mean of the most recent 5 consecutive samples
taken at intervals of between 7 and 21 days |
Inland waters |
|
|
Colour |
Change due to waste discharges not
to exceed 30 Hazen units |
Water gathering round |
|
Change due to waste discharges not
to exceed 50 Hazen units |
Inland waters |
|
|
Turbidity |
Shall not reduce light transmission
substantially from the normal level |
Bathing beach subzones |
Source: Statement of Water Quality Objectives
(Western Buffer Water Control Zone).
Table 11.3 Summary of Water Quality Objectives for North
|
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 2.0 mg/L
for 90% of samples |
Marine waters |
|
Depth-averaged DO |
Not less than 4.0 mg/L |
Tuen Mun (A), Tuen Mun
(B) and |
|
Not less than 4.0 mg/L
for 90 % sample |
Marine waters |
|
|
pH |
To be in the range of 6.5
- 8.5, change due to human activity not to exceed 0.2 |
Marine waters excepting
Bathing Beach Subzones |
|
To be in the range of
6.5 – 8.5 |
Tuen Mun (A), Tuen Mun
(B) and |
|
|
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 |
Bathing Beach Subzones |
|
|
Salinity |
Change due to human
activity not to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to human
activity not to exceed 2 oC |
Whole zone |
|
Suspended solids (SS) |
Not to raise the ambient
level by 30% caused by human activity |
Marine waters |
|
Not to cause the annual
med |
Tuen Mun (A), Tuen Mun
(B) and |
|
|
Not to cause the annual
med |
Inland waters |
|
|
Unionized Ammonia (UIA) |
Annual mean not to
exceed 0.021 mg/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 0.3 mg/L |
|
|
Annual mean depth-averaged
inorganic nitrogen not to exceed 0.5 mg/L |
Marine waters excepting |
|
|
Bacteria |
Not exceed 610 per
100ml, calculated as the geometric mean of all samples collected in one
calendar year |
Secondary Contact
Recreation Subzones |
|
Should be less than 1
per 100 ml, calculated as the running med |
Tuen Mun (A) and |
|
|
Not exceed 1000 per 100 ml,
calculated as the running med |
Tuen Mun (C) Subzone and
other inland waters |
|
|
Not exceed 180 per 100
ml, calculated as the geometric mean of all samples collected from March to October
inclusive. Samples should be taken at least 3 times in one calendar month at
intervals of between 3 and 14 days. |
Bathing Beach Subzones |
|
|
Colour |
Not to exceed 30 Hazen
units |
Tuen Mun (A) and |
|
Not to exceed 50 Hazen
units |
Tuen Mun (C) Subzone and
other inland waters |
|
|
5-Day Biochemical Oxygen
Demand (BOD5) |
Not to exceed 3 mg/L |
Tuen Mun (A), Tuen Mun
(B) and |
|
Not to exceed 5 mg/L |
Inland waters |
|
|
Chemical Oxygen Demand
(COD) |
Not to exceed 15 mg/L |
Tuen Mun (A), Tuen Mun
(B) and |
|
Not to exceed 30 mg/L |
Inland waters |
|
|
Toxins |
Should not cause a risk
to any beneficial uses of the aquatic environment |
Whole zone |
|
Waste discharge shall
not cause the toxins in water significant to produce toxic carcinogenic,
mutagenic or teratogenic effects in humans, fish or any other aquatic organisms. |
Whole zone |
|
|
Phenol |
Quantities shall not
sufficient to produce a specific odour or more than 0.05 mg/L as C6 H5OH |
Bathing Beach Subzones |
|
Turbidity |
Shall not reduce light
transmission substantially from the normal level |
Bathing Beach Subzones |
Source: Statement of Water Quality Objectives (North Western Water Control
Zone).
Table 11.4 Summary of 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 2.0 mg/L for 90% of samples |
|
|
Dissolved Oxygen (DO)
within 1 m below surface |
Not less
than 4.0 mg/L for 90% of samples |
|
|
Not less
than 5.0 mg/L for 90% of samples |
|
|
|
Depth-averaged DO |
Not less
than 4.0 mg/L for 90% of samples |
|
|
Not less
than 4.0 mg/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 3 mg/L |
Yuen Long
& Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones |
|
Not to exceed 5 mg/L |
Yuen Long
& Kam Tin (Lower) Subzone and other inland waters |
|
|
Chemical Oxygen Demand
(COD) |
Not to exceed 15 mg/L |
Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering
Ground |
|
Not to exceed 30 mg/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 |
|
To be in the range of
6.5 – 8.5 |
Yuen Long & Kam Tin
(Upper and Lower) 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 |
|
|
|
Salinity |
Change due to waste
discharges not to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to waste
discharges not to exceed 2 oC |
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
med |
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 0.021 mg/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 0.7 mg/L |
|
|
Annual mean
depth-averaged inorganic nitrogen not to exceed 0.5 mg/L |
Outer |
|
|
Bacteria |
Not exceed 610 per
100ml, calculated as the geometric mean of all samples collected in one
calendar year |
|
|
Should be zero per 100
ml, calculated as the running med |
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. |
|
|
|
Not exceed 1000 per 100ml,
calculated as the running med |
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 |
|
|
Phenol |
Quantities shall not
sufficient to produce a specific odour or more than 0.05 mg/L as C6 H5OH |
|
|
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 |
Source: Statement of Water Quality Objectives (Deep
Bay Water Control Zone).
Technical Memorandum on Effluent Discharge Standard
11.5
Besides setting the WQOs, the
WPCO controls effluent discharging into the WCZs through a licensing
system. Guidance on the permissible
effluent discharges based on the type of receiving waters (foul sewers,
stormwater drains, inland and coastal waters) is provided in the Technical Memorandum on Standards for
Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (TM-DSS). The limits given in the TM cover the physical, chemical
and microbial quality of effluents. Any
effluent discharge during the construction and operational stages should comply
with the standards for effluents discharged into the inshore waters or marine
waters of the
Practice Notes
11.6 A practice note (PN) for professional persons was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges. The Practice Note (PN) for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) issued by EPD provides good practice guidelines for dealing with various types of discharge from a construction site. Practices outlined in the PN should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.
Water Supplies Department (WSD) Water Quality Criteria
11.7 Besides the WQO set under the WPCO, the WSD has also specified a set of seawater quality objectives for water quality at their flushing water intakes (Table 11.5).
Table 11.5 WSD Standards at
|
Parameter (in mg/L unless otherwise stated) |
WSD
Target Limit |
|
Colour (Hazen Unit) |
< 20 |
|
Turbidity (NTU) |
< 10 |
|
Threshold Odour Number
(odour unit) |
< 100 |
|
Ammoniacal Nitrogen |
< 1 |
|
Suspended Solids |
< 10 |
|
Dissolved Oxygen |
> 2 |
|
Biochemical Oxygen
Demand |
< 10 |
|
Synthetic Detergents |
< 5 |
|
E.coli (no. / 100 ml) |
< 20,000 |
Sediment Quality Assessment Criteria
11.8 Environment, Transport and Works Bureau (ETWB) Technical Circular Works (TCW) No. 34/2002 “Management of dredged/excavated sediment” sets out the procedure for seeking approval to dredge / excavate sediment and the management framework for marine disposal of dredged / excavated sediment. This Technical Circular outlines the requirements to be followed in assessing and classifying the sediment. Sediments are categorized with reference to the Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL). Detailed classification of sediment quality has been presented in Section 10.
Potential Water Quality Impacts Related to Cooling Water Discharges
11.9 Thermal plumes associated with the outfalls for cooling water discharges will lead to a temperature rise in the receiving water. The WQO for the Victoria Harbour WCZ stipulated that the temperature rise in the water column due to human activity should not exceed 2 oC (Table 11.1).
11.10 Chlorine, in the form of sodium hypochlorite solution or produced through electrolysis of sea water, is commonly used as an anti-fouling agent or biocide for the treatment of cooling water within the cooling systems. No other anti-fouling agent (such as C-treat-6) will be used for the proposed seawater cooling system. Residual chlorine discharging to the receiving water is potentially harmful to marine organisms. A previous study ([1]) indicated that a residual chlorine level of 0.02 mg/l would have an adverse impact on marine organisms. EPD had commissioned an ecotoxicity study ([2]) on total residual chlorine (TRC) using local species. The lowest No Observable Effect Concentration (NOEC) value from that study was 0.02 mg/L. However, based on the review of the relevant recent approved EIA studies, the TRC limit of 0.01 mg/L (for average value) will be used as the assessment criterion.
Description of the Environment
and Baseline Conditions
Marine Water Quality
11.11
Marine water quality monitoring
data routinely collected by EPD were used to establish the baseline
condition. The EPD monitoring data
collected in 2007 were summarised in Tables
11.6 to 11.9 for Victoria
Harbour WCZ (VM5, VM6, VM7 and VM15), Western Buffer WCZ (WM2, WM3 and WM4),
North Western WCZ (NM1, NM2, NM3, NM5 and NM6) and Deep Bay WCZ (DM1, DM2, DM3,
DM4 and DM5) respectively. The locations of these monitoring stations are shown
in Figure No.
NOL/ERL/300/C/XRL/ENS/M59/002.
Descriptions of the baseline conditions for individual WCZ provided in
the subsequent sections are extracted from the EPD’s report “2007 Marine Water
Quality in
11.12
In the past, wastewater from
both sides of the
Table 11.6 Baseline
Marine Water Quality Condition for
|
Parameter |
|
|
|
WPCO WQO (in marine waters) |
||
|
VM5 |
VM6 |
VM7 |
VM15 |
|||
|
Temperature (oC) |
23.0 (17.2 – 28.0) |
23.0 |
23.3 |
23.2 |
Not more than 2 oC
in daily temperature range |
|
|
Salinity |
31.9 (29.3 – 33.5) |
32.0 |
31.5 |
31.7 |
Not to cause more than
10% change |
|
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
5.1 (3.8 – 6.9) |
5.0 |
5.0 |
5.3 |
Not less than 4 mg/L for
90% of the samples |
|
Bottom |
4.6 (2.1 – 7.4) |
4.8 |
4.7 |
4.9 |
Not less than 2 mg/L for
90% of the samples |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
71 (57 – 87) |
70 |
71 |
74 |
Not Available |
|
Bottom |
64 (30 – 96) |
67 |
66 |
68 |
Not Available |
|
|
pH |
8.0 (7.1 – 8.2) |
8.0 |
8.0 |
8.0 |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc
Depth (m) |
1.9 (1.5 – 2.4) |
2.0 |
1.9 |
2.0 |
Not Available |
|
|
Turbidity (NTU) |
11.1 (4.2 – 23.4) |
10.9 |
10.8 |
11.9 |
Not Available |
|
|
Suspended Solids (SS) (mg/L) |
4.1 (1.5 – 11.1) |
4.8 |
4.7 |
6.7 (2.8 – 15.3) |
Not more than 30%
increase |
|
|
5-day Biochemical Oxygen Demand
(BOD5) (mg/L) |
1.5 (0.2 – 2.3) |
1.3 |
1.0 |
1.3 |
Not Available |
|
|
Ammonia Nitrogen (NH3-N)
(mg/L) |
0.18 (0.07 – 0.29) |
0.20 |
0.21 |
0.20 |
Not Available |
|
|
Unionised
Ammonia (UIA) (mg/L) |
0.007 (0.001 – 0.012) |
0.007 |
0.009 |
0.008 |
Not more than 0.021 mg/L
for annual mean |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.035 (0.015 – 0.108) |
0.034 |
0.037 |
0.039 |
Not Available |
|
|
Nitrate Nitrogen (NO3-N)
(mg/L) |
0.141 (0.060 – 0.333) |
0.133 |
0.154 |
0.146 |
Not Available |
|
|
Total Inorganic Nitrogen (TIN)
(mg/L) |
0.36 (0.14 – 0.60) |
0.36 |
0.41 |
0.38 |
Not more than 0.4 mg/L
for annual mean |
|
|
Total
Kjeldahl Nitrogen (mg/L) |
0.42 (0.29 – 0.56) |
0.41 |
0.41 |
0.41 |
Not Available |
|
|
Total Nitrogen (TN) (mg/L) |
0.59 (0.42 – 0.80) |
0.58 |
0.61 |
0.60 |
Not Available |
|
|
Orthophosphate Phosphorus (OrthoP)
(mg/L) |
0.04 (0.015 – 0.062) |
0.04 |
0.040 |
0.038 |
Not Available |
|
|
Total Phosphorus (TP) (mg/L) |
0.06 (0.05 – 0.09) |
0.06 |
0.07 |
0.06 |
Not Available |
|
|
Silica (as SiO2) (mg/L) |
1.0 (0.4 – 2.2) |
1.0 |
1.1 |
1.0 |
Not Available |
|
|
Chlorophyll-a (µg/L) |
5.9 (0.7 – 30.8) |
4.8 |
2.8 |
6.2 |
Not Available |
|
|
E coli (cfu/100 mL) |
6000 (640 – 29000) |
4600 |
6000 |
1600 |
Not Available |
|
|
Faecal Coliforms (cfu/100 mL) |
16000 (2600 – 61000) |
12000 |
19000 |
4500 |
Not Available |
|
Notes:
1.
Data source: Marine Water Quality In Hong Kong in 2007.
2.
Except as specified, data presented are depth-averaged
values calculated by taking the means of three depths: Surface, mid-depth,
bottom.
3.
Data presented are annual arithmetic means of depth-averaged
results except for E. coli and faecal
coliforms that are annual geometric means.
4.
Data in brackets indicate the ranges.
Western Buffer
11.13
The water quality in Western
Buffer WCZ was largely stable in 2007 as compared to that in 2006. The E.coli
level in the zone was high due to the effluent from SCISTW which is not yet to
be equipped with disinfection facilities.
Full compl
Table 11.7 Baseline
Marine Water Quality Condition for Western Buffer WCZ
|
Parameter |
|
Tsing Yi (West) |
WPCO WQO (in marine waters) |
||
|
WM2 |
WM3 |
WM4 |
|||
|
Temperature (oC) |
23.3 |
23.1 |
23.1 |
Not more than 2 oC in
daily temperature range |
|
|
Salinity |
31.6 |
32.2 |
31.8 |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
5.73 (4.4 – 8.9) |
5.42 |
5.53 |
Not less than 4 mg/L for 90%
of the samples |
|
Bottom |
5.5 |
5.39 |
5.37 |
Not less than 2 mg/L for 90%
of the samples |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
80 |
76 |
77 |
Not Available |
|
Bottom |
76 |
75 |
75 |
Not Available |
|
|
pH |
8.0 (7.5 – 8.5) |
7.0 |
8.1 |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc Depth (m) |
1.9 |
1.8 |
1.7 |
Not Available |
|
|
Turbidity (NTU) |
14.5 |
12.1 |
12.1 |
Not Available |
|
|
Suspended Solids (SS) (mg/L) |
5.9 |
6.0 |
6.6 |
Not more than 30% increase |
|
|
5-day Biochemical Oxygen Demand
(BOD5) (mg/L) |
0.69 |
0.8 |
0.7 (0.1 – 2.0) |
Not Available |
|
|
Ammonia Nitrogen (NH3-N) (mg/L) |
0.13 |
0.16 |
0.13 |
Not Available |
|
|
Unionised Ammonia (UIA) (mg/L) |
0.006 |
0.006 |
0.006 |
Not more than 0.021 mg/L for annual
mean |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.045 |
0.037 |
0.043 |
Not Available |
|
|
Nitrate Nitrogen (NO3-N) (mg/L) |
0.152 |
0.123 |
0.147 |
Not Available |
|
|
Total Inorganic Nitrogen (TIN)
(mg/L) |
0.32 |
0.32 |
0.32 |
Not more than 0.4 mg/L for annual
mean |
|
|
Total Kjeldahl Nitrogen (mg/L) |
0.29 |
0.31 |
0.27 |
Not Available |
|
|
Total Nitrogen (TN) (mg/L) |
0.48 |
0.47 (0.31 – 0.67) |
0.46 |
Not Available |
|
|
Orthophosphate Phosphorus (OrthoP)
(mg/L) |
0.025 |
0.028 |
0.026 |
Not Available |
|
|
Total Phosphorus (TP) (mg/L) |
0.04 |
0.05 |
0.04 |
Not Available |
|
|
Silica (as SiO2) (mg/L) |
1.1 |
1.02 |
1.1 |
Not Available |
|
|
Chlorophyll-a (µg/L) |
3.0 |
2.3 |
2.9 (0.3 – 14.0) |
Not Available |
|
|
E coli (cfu/100 (mL) |
960 |
3800 |
1300 |
Not Available |
|
|
Faecal Coliforms (cfu/100 mL) |
2100 |
11000 |
3100 |
Not Available |
|
Notes:
1.
Data source: Marine Water Quality In Hong Kong in 2007.
2.
Except as specified, data presented are depth-averaged
values calculated by taking the means of three depths: Surface, mid-depth,
bottom.
3.
Data presented are annual arithmetic means of depth-averaged
results except for E. coli and faecal
coliforms that are annual geometric means.
4.
Data in brackets indicate the ranges.
North Western
11.14
Due to the effect of the Pearl
River, the North Western WCZ has historically experienced higher levels of TIN,
particularly to the west closest to the
Table 11.8 Baseline
Marine Water Quality Condition for North
|
Parameter |
Lantau Island (North) |
|
Pillar Point |
|
Chek Lap Kok |
WPCO WQO (in marine waters) |
|
|
NM1 |
NM2 |
NM3 |
NM5 |
NM6 |
|||
|
Temperature (oC) |
23.0 |
23.4 |
23.2 |
23.4 |
23.8 |
Not more than 2 oC in daily temperature range |
|
|
Salinity |
30.9 |
29.5 |
30.1 |
28.6 |
27.5 |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
5.7 |
6.0 |
5.8 |
5.7 |
6.4 |
Not less than 4 mg/L for 90% of the samples |
|
Bottom |
5.4 |
5.7 |
5.5 |
5.4 |
6.4 |
Not less than 2 mg/L for 90% of the samples |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
79 |
83 |
80 |
78 |
89 |
Not Available |
|
Bottom |
75 |
79 |
76 |
74 |
88 |
Not Available |
|
|
pH |
8.0 |
8.0 |
8.0 |
8.0 |
8.0 |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc
Depth (m) |
1.8 |
1.6 |
1.6 |
1.4 |
1.4 |
Not Available |
|
|
Turbidity (NTU) |
14.9 |
12.5 |
13.5 |
19.2 |
15.4 |
Not Available |
|
|
Suspended Solids (SS) (mg/L) |
8.2 |
5.8 |
7.4 |
11.1 |
10.0 |
Not more than 30%
increase |
|
|
5-day Biochemical Oxygen Demand
(BOD5) (mg/L) |
1.0 |
1.0 |
1.1 |
1.1 |
1.1 |
Not Available |
|
|
Ammonia Nitrogen (NH3-N)
(mg/L) |
0.13 |
0.13 |
0.15 |
0.19 |
0.11 |
Not Available |
|
|
Unionised Ammonia
(UIA) (mg/L) |
0.005 |
0.006 |
0.008 |
0.008 |
0.006 |
Not more than 0.021 mg/L
for annual mean |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.05 |
0.063 |
0.064 |
0.09 |
0.087 |
Not Available |
|
|
Nitrate Nitrogen (NO3-N)
(mg/L) |
0.207 |
0.281 |
0.26 |
0.36 |
0.379 |
Not Available |
|
|
Total Inorganic Nitrogen (TIN)
(mg/L) |
0.39 |
0.48 |
0.47 |
0.64 |
0.58 |
Not more than 0.5 mg/L
for annual mean |
|
|
Total Kjeldahl Nitrogen (mg/L) |
0.30 |
0.31 |
0.35 |
0.40 |
0.33 |
Not Available |
|
|
Total Nitrogen (TN) (mg/L) |
0.56 |
0.657 |
0.669 |
0.852 |
0.792 |
Not Available |
|
|
Orthophosphate Phosphorus (OrthoP)
(mg/L) |
0.025 |
0.024 |
0.026 |
0.031 |
0.021 |
Not Available |
|
|
Total Phosphorus (TP) (mg/L) |
0.05 |
0.05 |
0.05 |
0.06 |
0.05 |
Not Available |
|
|
Silica (as SiO2) (mg/L) |
1.3 |
1.5 |
1.4 |
1.9 |
1.9 |
Not Available |
|
|
Chlorophyll-a (µg/L) |
5.4 |
6 |
5.9 (1.0-22.0) |
5.5 |
7.4 |
Not Available |
|
|
E coli (cfu/100 mL) |
670 |
360 |
430 |
590 |
18 |
Not Available |
|
|
Faecal Coliforms (cfu/100 mL) |
1500 |
820 |
1100 |
1300 |
46 |
Not Available |
|
Notes:
1.
Data source: Marine Water Quality In Hong Kong in 2007.
2.
Except as specified, data presented are depth-averaged
values calculated by taking the means of three depths: Surface, mid-depth,
bottom.
3.
Data presented are annual arithmetic means of depth-averaged
results except for E. coli and faecal
coliforms that are annual geometric means.
4.
Data in brackets indicate the ranges.
11.15
Pollution flows into the
Table 11.9 Baseline
Marine Water Quality Condition for Western Buffer and Deep Bay WCZ
|
Parameter |
|
Outer |
WPCO WQO (in marine waters) |
||||
|
DM1 |
DM2 |
DM3 |
DM4 |
DM5 |
|||
|
Temperature (oC) |
24.7 (15.1 - 32.3) |
24.8 (15.1 - 32.4) |
24.6 (16.2 - 31.6) |
24.5 (16.7 - 30.4) |
24.4 (17.0 - 29.6) |
Not more than 2 oC in
daily temperature range |
|
|
Salinity |
17.1 (2.5 - 23.8) |
19.1 (5.8 - 26.8) |
22.9 (8.8 - 30.1) |
24.1 (11.4 - 31.4) |
26.1 (10.3 - 32.8) |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO) (mg/L) |
Depth average |
3.8 (0.2 – 7.1) |
5.3 (1.6 - 10.2) |
6.4 (2.7 - 10.4) |
6.6 (3.3 - 9.9) |
6.7 (3.5 – 11.1) |
Not less than 4 mg/L for 90%
of the samples |
|
Bottom |
Not measured |
Not measured |
Not Available |
6.2 (3.3 – 8.8) |
6.2 (3.2 - 8.8) |
Not less than 2 mg/L for 90% of
the samples |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
49 (3 - 81) |
70 (21 - 121) |
86 (39 - 127) |
90 (46 - 138) |
92 (51 – 161) |
Not Available |
|
Bottom |
Not measured |
Not measured |
Not measured |
85 (47 - 122) |
86 (46 - 122) |
Not Available |
|
|
pH |
7.1 (6.5 – 7.9) |
7.3 (6.6 - 8.3) |
7.5 (6.7 - 8.5) |
7.6 (6.8 - 8.6) |
7.8 (6.9 – 9.3) |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc Depth (m) |
0.3 (0.1 - 0.8) |
0.4 (0.1 – 0.5) |
0.5 (0.2 – 1.2) |
0.8 (0.2 – 1.5) |
0.8 (0.2 – 1.8) |
Not Available |
|
|
Turbidity (NTU) |
28.5 (15.1 – 37.2) |
25.6 (16.7 - 41.8) |
19.3 (10.6 - 35.6) |
18.5 (9.3 - 32.4) |
21.3 (10.5 – 65.2) |
Not Available |
|
|
Suspended Solids (SS) (mg/L) |
20.7 (7.4 – 32.0) |
19.7 (10.0 – 40.0) |
13.4 (4.3 - 36.0) |
8.1 (2.2 - 13.5) |
7.4 (4.3 - 11.5) |
Not more than 30% increase |
|
|
5-day Biochemical Oxygen Demand
(BOD5) (mg/L) |
3.8 (2.1 – 8.0) |
3.6 (1.7 – 6.3) |
2.3 (0.4 – 6.2) |
1.3 (0.6 - 3.9) |
1.5 (0.5 – 6.4) |
Not Available |
|
|
Ammonia Nitrogen (NH3-N) (mg/L) |
5.62 (1.90 – 10.00) |
3.74 (1.40 - 6.10) |
0.84 (0.26 - 1.90) |
0.44 (0.10 - 0.95) |
0.21 (0.04 - 0.45) |
Not Available |
|
|
Unionised Ammonia (UIA) (mg/L) |
0.057 (0.013 – 0.16) |
0.058 (0.009 - 0.231) |
0.017 (0.001 – 0.052) |
0.011 (0.002 – 0.024) |
0.007 (0.001 - 0.017) |
Not more than 0.021 mg/L for annual
mean |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.256 (0.008 – 0.73) |
0.305 (0.150 - 0.72) |
0.21 (0.11 – 0.46) |
0.163 (0.060 – 0.425) |
0.12 (0.027 – 0.343) |
Not Available |
|
|
Nitrate Nitrogen (NO3-N) (mg/L) |
0.259 (0.003 – 0.510) |
0.308 (0.100 - 0.58) |
0.539 (0.24 – 1.200) |
0.561 (0.190 - 1.250) |
0.459 (0.092 - 1.003) |
Not Available |
|
|
Total Inorganic Nitrogen (TIN)
(mg/L) |
6.13 (2.62 – 10.02) |
4.36 (2.63 - 6.41) |
1.59 (1.10 - 2.48) |
1.16 (0.63 - 1.61) |
0.79 (0.24 - 1.42) |
Not more than 0.5 mg/L for annual
mean |
|
|
Total Kjeldahl Nitrogen (mg/L) |
7.10 |
4.89 |
1.28 |
0.71 |
0.46 |
Not Available |
|
|
Total Nitrogen (TN) (mg/L) |
7.61 (3.02 - 15.02) |
5.51 (3.03 - 8.81) |
2.03 (1.36 - 3.19) |
1.43 (0.91 - 1.83) |
1.04 (0.44 - 1.70) |
Not Available |
|
|
Orthophosphate Phosphorus (OrthoP)
(mg/L) |
0.549 (0.3 - 0.88) |
0.405 (0.26 - 0.72) |
0.14 (0.037 - 0.31) |
0.068 (0.006 - 0.12) |
0.039 (0.006 - 0.08) |
Not Available |
|
|
Total Phosphorus (TP) (mg/L) |
0.73 (0.38 – 1.30) |
0.55 (0.35 - 0.95) |
0.20 (0.09 - 0.39) |
0.10 (0.07 - 0.15) |
0.07 (0.04 - 0.11) |
Not Available |
|
|
Silica (as SiO2) (mg/L) |
5.8 (1.6 - 10.0) |
4.5 (0.3 - 7.7) |
2.7 (0.1 - 5.8) |
2.6 (0.3 - 5.7) |
2.2 (0.1 - 5.9) |
Not Available |
|
|
Chlorophyll-a (µg/L) |
18.7 (1.1 – 58) |
22.6 (2.2 – 67.0) |
14.4 (1.7 - 59.0) |
8.5 (1.0 - 41.0) |
8.3 (0.9 - 42.0) |
Not Available |
|
|
E coli (cfu/100 (mL) |
5000 (80 – 220000) |
1200 (150 - 35000) |
38 (7 - 1300) |
120 (8 - 900) |
180 (10 - 2200) |
Not Available |
|
|
Faecal Coliforms (cfu/100 mL) |
8100 (200 – 330000) |
2200 (260 - 83000) |
83 (15 - 2700) |
240 (32 - 1200) |
420 (41 - 3000) |
Not Available |
|
Notes:
1.
Data source: Marine Water Quality In Hong Kong in 2007.
2.
Except as specified, data presented are depth-averaged
values calculated by taking the means of three depths: Surface, mid-depth,
bottom.
3.
Data presented are annual arithmetic means of depth-averaged
results except for E. coli and faecal
coliforms that are annual geometric means.
4.
Data in brackets indicate the ranges.
Marine Sediment Quality
11.16 Dredging would be required for construction of the barging point at Lung Kwu Sheung Tan. Sediment quality monitoring data routinely collected by EPD in Deep Bay WCZ (DS4) and North Western WCZ (NS3, NS4 and NS6) closest to the proposed barging point were used to establish the baseline condition. The selected EPD monitoring stations are shown in Figure No. NOL/ERL/300/C/XRL/ENS/M59/002. A summary of EPD monitoring data collected in 2007 is presented in Table 11.10.
11.17 Based on the monitoring data (refer to Table 11.10), the sediments collected at the four selected stations are considered contaminated in terms of metalloid (arsenic). Levels of other parameters were low at all the stations.
Table 11.10 Baseline
Marine Sediment Quality Condition
|
Parameter |
Outer |
Pillar Point |
|
Chek Lap Kok (North) |
Sediment Quality Criteria |
|
|
DS4 |
NS3 |
NS4 |
NS6 |
LCEL |
UCEL |
|
|
Heavy Metal (mg/kg dry
weight) |
||||||
|
Cadmium (Cd) |
0.1 (<0.1
– 0.2) |
0.1 (<0.1
– 0.1) |
0.1 (<0.1
– 0.1) |
0.1 (<0.1
– 0.1) |
1.5 |
4 |
|
Chromium (Cr) |
32 (16
- 47) |
31 (20
– 42) |
29 (26
– 36) |
26 (18
- 37) |
80 |
160 |
|
Copper (Cu) |
21 (9
-64) |
28 (18
– 48) |
28 (18
– 42) |
17 (8
-27) |
65 |
110 |
|
Mercury (Hg) |
0.06 (<0.05
– 0.14) |
0.11 (0.06
– 0.15) |
0.09 (0.06
– 0.20) |
0.06 (<0.05
– 0.10) |
0.5 |
1 |
|
Nickel (Ni) |
19 (15
– 31) |
20 (11
– 24) |
19 (16
– 22) |
17 (10
– 24) |
40 |
40 |
|
Lead (Pb) |
40 (31
– 58) |
37 (27
– 45) |
36 (29
– 46) |
29 (20
– 46) |
75 |
110 |
|
Silver (Ag) |
0.2 (<0.2
– 0.5) |
0.3 (<0.2
– 0.4) |
0.3 (<0.2
– 0.3) |
0.2 (<0.2
– 0.2) |
1 |
2 |
|
Zinc (Zn) |
88 (69
– 140) |
93 (62
– 120) |
100 (99
– 110) |
73 (42
– 100) |
200 |
270 |
|
Metalloid (mg/kg dry
weight) |
||||||
|
Arsenic |
12.1 (7.6
– 18.0) |
10.8 (8.3
– 14.0) |
10.1 (9.1
– 11.0) |
10.2 (7.1
– 16.0) |
12 |
42 |
|
Organic-PAHs (µg/kg dry weight) |
||||||
|
PAHs (Low Molecular Weight) |
91 (90
– 95) |
91 (90
– 95) |
92 (90
– 99) |
90 (90
– 94) |
550 |
3160 |
|
PAHs (High Molecular Weight) |
39 (16
– 82) |
60 (38
– 110) |
64 (35
– 120) |
27 (16
– 49) |
1700 |
9600 |
|
Organic-non-PAHs (µg/kg dry weight) |
||||||
|
Total PCBs |
18 (18
– 18) |
18 (18
– 18) |
18 (18
– 18) |
18 (18
– 18) |
23 |
180 |
Note: LCEL –
Lower Chemical Exceedance Level
UCEL –
Upper Chemical Exceedance Level
Shaded value – Exceed the LCEL – Lower Chemical Exceedance
Level
(Detailed classification of sediment quality can be referred
to Section 10)
Inland Water Quality
11.18
Some proposed works areas are
located close to inland water courses or natural streams. River water quality in
11.19
The water quality measured in sampling location KT2 (close to the cut and
cover tunnel section in Shek Kong and the Shek Kong Stabling Sidings) was
ranked “very bad” in 2007 with only 41% overall compl
Table 11.11
|
Parameter |
|
River WQOs |
|
|
KT1 |
KT2 |
|
|
|
DO (mg/L) |
5.2 |
2.7 |
Not less than
4 mg/L at any time |
|
pH |
7.3 |
7.4 |
6-9 |
|
SS (mg/L) |
13 |
45 |
Annual
med |
|
BOD5 (mg/L) |
15 |
47 (14 – 130) |
Not more than
5 mg/L at any time |
|
COD (mg/L) |
19 |
87 |
Not more than
30 mg/L at any time |
|
Oil & grease (mg/L) |
0.8 |
2.4 |
- |
|
Faecal coliforms (cfu/100mL) |
460,000 |
710,000 |
- |
|
E.coli (cfu/100mL) |
100,000 |
380,000 |
- |
|
NH3-N (mg/L) |
6.45 |
12.50 |
- |
|
NO3-N (mg/L) |
0.50 |
0.01 |
- |
|
TKN – soluble & particulate
fractions (mg/L) |
8.00 |
19.00 |
- |
|
Ortho-P (mg/L) |
1.45 |
2.85 |
- |
|
TP – soluble & particulate fractions
(mg/L) |
1.85 |
4.30 |
- |
|
Aluminium (µg/L) |
50 |
55 |
- |
|
Cadmium (µg/L) |
0.1 |
0.1 (0.1 – 0.1) |
- |
|
Chromium (µg/L) |
1 |
1 |
- |
|
Copper (µg/L) |
4 |
5 |
- |
|
Lead (µg/L) |
2 |
2 |
- |
|
Zinc (µg/L) |
30 |
40 |
- |
Identification of Water Sensitive Receivers
11.20
To evaluate the potential water
quality impacts from the Project, the marine water sensitive receivers (WSR)
within the
l
Cooling Water Intakes;
l
Beaches;
l
Secondary Contact Recreation Subzones;
l
WSD
l
Oyster Beds and
l
Marine Parks.
11.21 Figure No. NOL/ERL/300/C/XRL/ENS/M59/002 shows the locations of the marine water sensitive receivers.
11.22 In addition, water sensitive receivers would include all inland waters (such as natural streams and water courses) as well as the Water Gathering Ground (WGG) at or near the proposed Project sites. Location of the WGG in relation to the Project alignment is illustrated in Figure No. NOL/ERL/300/C/XRL/ENS/M59/003.
11.23 Locations of ecological resources has been separately identified and discussed in Section 3.
Identification
of Potential Impacts
Construction Phase
11.24 The potential water quality impacts arising during the construction phase of the Project are identified in the following paragraphs.
General
Construction Activities
11.25 The land-based construction works could have the potential to cause water pollution. Various types of construction activities may generate wastewater. These include general cleaning and polishing, wheel washing, dust suppression and utility installation. These types of wastewater would contain high concentrations of Suspended Solid (SS). Impacts could also result from the sewage effluent from the construction work force involved with the construction. For some of the works areas, there may be no public sewers available for wastewater discharge on-site. If uncontrolled, these effluents could lead to deterioration in water quality.
Construction
Site Run-off
11.26 Construction site run-off would cause potential water quality impacts. During rainstorms, site run-off would wash away the soil particles on unpaved lands and areas with the topsoil exposed. The run-off is generally characterized by high concentrations of SS. Release of uncontrolled site run-off would increase the SS levels and turbidity in the nearby water environment. Site run-off may also wash away contaminated soil particles and therefore cause water pollution.
11.27 Wind blown dust would be generated from exposed soil surfaces in the works areas. It is possible that wind blown dust would fall directly onto the nearby water bodies when a strong wind occurs. Dispersion of dust within the works areas may increase the SS levels in surface run-off causing a potential impact to the nearby sensitive receivers. Potential pollution sources of site run-off may include:
l
Run-off and erosion of exposed bare soil and earth, drainage
channel, earth working area and stockpiles.
l
Groundwater from any dewatering activities as a result of
dredging of river sediments or excavation of wet material during tunnel
construction.
l
Release of any bentonite slurries, concrete washings and
other grouting materials with construction run-off, storm water or ground water
dewatering process.
l
Wash water from dust suppression sprays and wheel washing
facilities.
l
Fuel, oil and lubricants from maintenance of construction
vehicles and equipment.
River
Training (Diversion of Watercourse)
11.28
The cut and cover tunnel at the section in Shek Kong as well as the
proposed Shek Kong Stabling Sidings (SSS) facility would directly pass through
Kam Tin River Nullah and the
Accidental
Spillage
11.29 A large variety of chemicals may be used during construction activities. These chemicals may include petroleum products, surplus adhesives, spent lubrication oil, grease and mineral oil, spent acid and alkaline solutions/solvent and other chemicals. Accidental spillage of chemicals in the works areas may contaminate the surface soils. The contaminated soil particles may be washed away by construction site run-off or storm run-off causing water pollution.
Dredging
of Marine Sediments
11.30
During dredging for construction of the proposed barging point at Lung
Kwu Sheung Tan (LKST), fine sediment would be suspended into the water column,
which may then be transported away from the works area by tidal currents to
form sediment plumes. The quantities of fine sediment lost to suspension during
dredging will primarily depend on dredging rate and methods. Impact from suspended sediment may be caused
by sediment plumes being transported to sensitive areas. The water sensitive
receivers closest to the proposed dredging area include the Sha Chau and
Groundwater from Contaminated Area
11.31 Several proposed cut-and-cover tunnel sections and ventilation buildings/Emergency Access Points (EAPs) are adjacent to or within the areas of open storages, garages, car parks, and areas occupied by industrial facilities which are potentially contaminated sites. These works areas include the cut and cover tunnel section and ventilation building in Mai Po, the cut-and-cover tunnel section in Shek Kong, the SSS, the works area in Lai Chi Kok, and the ventilation buildings in Kwai Chung and Nam Cheung. Groundwater pumped out or from dewatering process during excavation works in these areas could be potentially contaminated. Discharge / recharge of potentially contaminated groundwater generated from these areas may affect the surface / ground water quality, if uncontrolled.
Hydrogeological
Impact
11.32
The construction of the Project would have potential impacts on
groundwater system. Such construction activities include:
l
Cut & Cover excavations for tunnel, vent buildings and
emergency access/escape point
l
Bored tunnelling works
l
Drill & Blast tunnelling works.
11.33
The major concern from these
construction activities would be the potential drawdown in any soil and aquifer
layers. Any potential drawdown could
result in different degrees of settlement and dewatering of surface water
features.
Operation Phase
11.34 Major water quality impacts from the Project operation include:
l
Tunnel run-off and drainage;
l
Sewerage and storm effluents;
l
Ventilation Buildings/EAPs run-off; and
l
Spent cooling water discharged from the proposed seawater
cooling system.
11.35
The proposed SSS would be
located within the
Sewerage
Impact Assessment
11.36 Sources of sewage arising from the operation of the Project have been identified. Sewage and wastewater effluents would be generated from staffs and customers at food and beverage outlets in WKT, operation of ventilation buildings/EAPs, passengers in the train as well as the maintenance activities in SSS. Generated sewage would be disposed of to the public sewerage system and transferred to a sewage treatment works. In order to identify impacts to the existing and future capacity of the sewers due to implementation of the Project, Sewerage Master Plan (SMP) and relevant information have been reviewed to obtain the existing and future sewerage systems at the areas of WKT, southern and northern sections of Project. The sewage generated from the Project was estimated based on the guideline set out in the DSM, Sewerage Manual (SM) Part 1 (DSD, 1995) and Plumbing Engineering Services Design Guide. Details of the sewerage impact assessment are given in Appendices 11.9a – 11.9c.
Assessment Approach and Methodology
11.37 The Assessment Area for the water quality impact assessment covers Victoria Harbour WCZ, Western Buffer WCZ, North Western WCZ, Deep Bay WCZ and all areas within 500m from the Project boundary.
Spent Cooling Water Discharge
11.38 During operational phase, seawater will be utilized to carry waste heat from the air conditioning system of West Kowloon Terminus (WKT) and the seawater after being circulated through the system will return back to the sea. A new set of intake and outfall is being proposed at the seafront of the West Kowloon and the separation between the seawater intake and outfall is set at 75 m. Locations of the proposed spent cooling water discharge point and the associated seawater intake are indicated in Figure No. NOL/ERL/300/C/XRL/ENS/M59/004.
Modelling Tools
11.39
Computer modelling was used to
assess the potential impacts on water quality in
11.40 The WDII Model developed under the approved EIA for Comprehensive Feasibility Study (CFS) for Wan Chai Development Phase II (WDII) was used as the basis for hydrodynamic and water quality modelling. This detailed model was extensively calibrated and fully verified by comparing computational results with field measurements.
11.41
Under the present EIA Study,
the grid mesh of the WDII Model has been refined in the
11.42
The XRL Model is linked to the
regional Update Model, which was constructed, calibrated and verified under the
project “CE42/97 Update on Cumulative Water Quality and Hydrological Effect of Coastal
Development and Upgrading of Assessment Tool” (Update Study). Computations are first carried out using the
Update Model to provide open boundary conditions to the XRL Model. The Update model covers the whole Hong Kong
and the adjacent Mainland waters including the discharges from
Change of Coastline Configurations
11.43
Based on the information on the
planned developments from the EIA Reports registered under the EIAO, there
would not be any major changes in the coastline configuration within the
11.44
The WDII reclamation is
currently scheduled to commence in 2009 for completion by 2016. Based on the latest information available
from approved EIA for WDII and Central Wan Chai Bypass (CWB), seawall
construction for most of the WDII reclamation stages will be completed in 2013
before commissioning of the proposed seawater cooling system in 2015. As such, the coastline with WDII is adopted
under this modelling exercise. Model results conducted under the approved EIA
for WDII and CWB indicated that the net effect of WDII reclamation on the flow
regime would be small and localized. Although there would be some changes at
the coastlines of Wan Chai, and North Point as the WDII reclamation proceeds,
the change is relatively small and would not have a major effect on the flow
regime at the
11.45
A 600 m opening will be
constructed at the northern part of the former airport runway under the Kai Tak
Development (KTD). Model results
conducted under the recent EIA for KTD indicated that the runway opening would
only have an influence on the water circulation inside
Model Performance Verification Work
11.46
The performance of the XRL
Model refined under the present Study has been checked against that of the
calibrated WDII Model approved
under the CFS for WDII EIA. The results of water level, depth averaged flow
speed, depth averaged flow directions and salinity predicted by the two models
have been compared at three indicator points (namely Stations 3, 6 and 8
respectively as shown in Appendix 11.2). In addition, the results of momentary flows
and accumulated flows were compared at two selected cross sections to check for
the consistency. The eastern cross
section is located across the Lei Yue Mun Channel, while the western section is
located between Yau Ma Tei and Sheung Wan (Appendix
11.2). Momentary flow represents the
instantaneous flow rate at a specific time in m3/s whereas
accumulated flow represents the total flow accumulated at a specific time in m3.
11.47
The comparison plots for water
level, depth averaged flow speed, depth averaged flow directions momentary
flows and accumulated flows are given in
Appendix 11.3a and Appendix 11.3b
for dry and wet seasons respectively. The comparison plots for salinity for
both dry and wet seasons are given in Appendix
11.4a. The results predicted by
both models are in general consistent with each other which implied that the
model setting of the XRL model including the nesting procedure and the
derivation of the boundary conditions were carried out correctly.
11.48
It is important to realize that
the XRL model has higher resolution than the original approved WDII Model in
the
Thermal Plume Modelling
11.49 In the present study, the basis for modelling of the harbour waters is the XRL Model as discussed above.
11.50 The Excess Temperature Model within Delft3D-FLOW model was employed to simulate the thermal plume dispersion in marine water and to assess the impact on the neighbouring cooling water intakes following the same approach adopted under the recent approved EIAs for WDII and CWB. The model allows for the excess temperature distribution and decay of the thermal plume, and addresses heat transferred from the water surface to the atmosphere. While the total heat flux is proportional to the excess temperature at the surface, the heat transfer coefficient of the formulation depends mainly on water temperature and wind speed. Each hydrodynamic FLOW simulation will cover a complete spring-neap tidal cycle (about 15 days), preceded by a spin-up period (about 1.5 tidal cycles) under both dry and wet seasons.
11.51 In order to determine whether the spin-up period of 1.5 tidal cycles is adequate for the present Study, the time series plot of predicted temperature elevations were compared between the spin-up period and the actual simulation period at one indicator point (namely Point A as shown in Figure 3 of Appendix 11.1) within the marine embayment of West Kowloon. Comparison of test results of the spin-up period and the actual simulation period for water depth, salinity and temperature at Point A is provided in Appendix 11.4b. The comparison plots showed that there was no significant deviation between the 2 sets of results. The spin-up period of 1.5 tidal cycles is therefore considered acceptable.
11.52 One-minute time step was used in the thermal plume modelling following the approach adopted under the approved EIA for WDII & CWB. In order to determine whether the time step of 1 minute is acceptable for the present Study, a sensitivity hydrodynamic run was conducted using a smaller time step of 30 seconds. The sensitivity results indicated that there was no significant deviation between the 2 sets of results. The time step of 1 minute is considered acceptable.
11.53 The design excess temperature at the outfall of the proposed cooling system would be 5 oC which is a discharge licence limit. The parameters adopted for the thermal plume modelling are summarised in Table 11.12.
Table 11.12 Summary of Parameters for Thermal Plume
Model (Delft3D-FLOW)
|
Delft3D-FLOW Excess
Temperature Model Parameters |
||
|
Background (Air) Temperature (oC) |
18 28 |
Dry Season Wet Season |
|
Temperature of spent cooling
water (oC) |
23 31 (1) |
Dry Season Wet Season |
|
Wind Speed (m s-1) |
5 |
Dry Season (north-east direction) and Wet Season
(south-west direction) |
|
Ambient Water
Temperature (oC) |
18 To be computed by model (1) |
Dry Season Wet Season |
Note:
(1) Based on the XRL
model results, the predicted temperature at intake location under the baseline
scenario (without any cooling water discharges) have been checked to be lower
than 26°C for over 80% of the simulation period, the discharge temperature of 31°C
for wet season should provide a good approximation of the temperature of spent
cooling water for thermal plume modelling and assessment.
11.54 It is conservatively assumed that all cooling water discharges have an excess temperature of 5 oC with reference to the background seawater temperature. Results of the predicted temperature elevation at the intakes are factored up by [1(1-E/k)] to take into account the potential short circuit problem of the re-circulation of heated water to the cooling water intake.
Where:
E = maximum of the mean
temperature elevations predicted at the intakes
k = excess temperature of
the cooling system = 5°C
11.55 The derivation of the heat re-circulation factor [1(1-E/k)] is given in Appendix 11.5.
11.56 Table 11.13 gives the estimated seawater flow for the proposed cooling system. It is assumed that the flow rates would be equivalent for both the intake and discharge of the cooling system. For conservative assessment, the highest flow value estimated over the year (i.e. 116,566 m3/d) will be used for model simulation under both dry and wet season scenarios.
Table 11.13 Estimated Discharge Rates
|
Month |
Estimated
Seawater Flow |
|
|
Maximum
demand (l/s) |
(m3/day) |
|
|
Excess
Temperature (ΔT=
5oC) |
||
|
January |
1,460 |
86,780 |
|
February |
1,540 |
92,029 |
|
March |
1,670 |
99,453 |
|
April |
1,730 |
104,485 |
|
May |
1,780 |
109,769 |
|
June |
1,850 |
115,585 |
|
July |
1,900 |
116,474 |
|
August |
1,870 |
116,566 |
|
September |
1,800 |
110,825 |
|
October |
1,710 |
104,777 |
|
November |
1,620 |
97,619 |
|
December |
1,520 |
91,515 |
11.57 In order to provide a more realistic prediction of the potential water quality impact, the typical diurnal flow pattern estimated for the proposed cooling system as shown in Table 11.14 below was applied to the assumed daily flow (i.e. 99,453 m3/d for dry season and 116,566 m3/d for wet season) to derive the hourly diurnal flow as model inputs. The same 24-hour diurnal flow pattern was used in the model throughout the spin-up and simulation period.
Table
11.14 Estimated Diurnal Flow Pattern
|
Hour |
Percentage
of Daily Flow |
|
|
3.4% |
|
|
2.7% |
|
|
0.5% |
|
|
0.5% |
|
|
0.5% |
|
|
0.5% |
|
|
2.6% |
|
|
4.3% |
|
|
5.3% |
|
|
5.4% |
|
|
5.5% |
|
|
5.5% |
|
|
5.6% |
|
|
5.7% |
|
|
5.7% |
|
|
5.7% |
|
|
5.8% |
|
|
5.8% |
|
|
5.7% |
|
|
5.6% |
|
|
5.6% |
|
|
4.5% |
|
|
4.5% |
|
|
3.2% |
Residual Chlorine
11.58 The 3-dimensional particle tracking model (Delft3D-PART) developed by Delft Hydraulics was employed to model the residual chlorine discharged from the cooling water following the same modelling approach as adopted under the approved EIA for WDII & CWB. No other anti-fouling chemical agent (e.g. C-treat-6) will be used at the proposed seawater cooling system. The discharge of residual chlorine is represented by discrete particles released into the surface layer of the model. These discrete particles are transported with flow fields determined from the hydrodynamic simulation using the Delft3D-FLOW XRL Model, and turbulent diffusion and dispersion, based on a random walk technique. The residual chlorine elevation over the ambient level is then evaluated from the particle density in each cell of the curvilinear grid of XRL Model. Due to the high decay rate of chlorine in marine waters, the ambient chlorine level is assumed to be negligible.
11.59 The flow data adopted in Delft3D-PART model are obtained from the Delft3D-FLOW hydrodynamic model results. Each flow simulation covers a complete spring-neap tidal cycle (about 15 days). The actual simulation period is preceded by a spin-up period.
11.60
Each Delft3D-PART simulation
covers a complete spring-neap tidal cycle (about 15 days), preceded by a
spin-up period of 15 days under both dry and wet seasons. The 15-day flow simulation results are
repeated for the 30-day simulation period for Delft3D-PART with due
consideration on the continuity of the tidal level between successive 15-day
periods. In order to determine whether
the spin-up period for Delft3D-PART is adequate, the time series plot of
predicted residual chlorine is compared between the spin-up period and the
actual simulation period at one indicator point (namely Point A as shown in
Figure 3 of Appendix 11.1) within
the marine embayment at
11.61 Delft3D-PART makes use of the information on water flow derived from the Delft3D-FLOW model. One-minute time step for numerical simulation and 6 minutes (for saving model outputs and “com” files) were applied in the Delft3D-FLOW model. As the number of particles that can be used in the Delft3D-PART is limited, 6 minutes time step is used for numerical simulation in particle tracking following the approach adopted under the recent approved EIA for WDII & CWB. Based on the design information, it is assumed that the spent cooling water discharges have a residual chlorine concentration of 0.2 mg/l, which is assumed to be discharged at the discharge rates described in Sections 11.56 and 11.57.
11.62
It should be noted that the
residual chlorine concentration represents total residual chlorine as there is
no mechanism in the
Table 11.15 Summary of Parameters for Modelling of Residual Chorine
(Delft3D-PART)
|
Partical Track Model Parameters |
||
|
Horizontal Dispersion Coefficient DH (m2 s-1) |
A = 0.003 B = 0.4 |
DH = a t b, where t is the age of particle from the
instant discharge in seconds |
|
Vertical Dispersion Coefficient DV (m2 s-1) |
5 x 10-3 1 x 10-5 |
Dry Season Wet Season |
|
Residual Chlorine (mg/l) |
0.2 |
- |
|
Decay Factor for Residual Chlorine, T90
(s) |
8289 (2) |
- |
|
Flow Rate (m3s–1) |
Equivalent for Intake and Discharge |
No loss of water in the cooling system. |
|
Particle Settling Velocity (m s-1) |
-0.005 (Constant) |
Heated discharge is slightly less dense
than ambient water |
|
Critical Shear Stress(1) |
N/A |
No sedimentation or erosion |
Notes:
(1)
Sedimentation and erosion are irrelevant for chlorine modelling
(2)
Approved EIA Study for Tai
Cumulative Water Quality Impact
11.63
Other concurrent / background
spent cooling water discharges within the
l
MTRC
l
l
l
Ocean Centre; and
l
Ocean Terminal.
|
|
Approximate Distances from
Proposed WKT Outfall (m) |
|
|
Intake |
Outfall |
|
|
MTRC |
610 |
680 |
|
|
210 |
290 |
|
|
480 |
370 |
|
Ocean Centre |
550 |
640 |
|
Ocean Terminal |
690 |
640 |
Land-based Construction Works
11.64
The water sensitive receivers
that may be affected by the land-based construction activities for the Project
have been identified. Potential sources
of water quality impact that may arise during the land-based construction works
were described. This task included
identifying pollutants from point discharges and non-point sources that could
affect the quality of surface water run-off.
All the identified sources of potential water quality impact were then
evaluated and their impact significance determined. The need for mitigation measures to reduce
any identified adverse impacts on water quality to acceptable levels was
determined.
Dredging of Marine Sediment at LKST
Ambient and Tolerance Values
11.65
The sediment plumes passing
over a sensitive receiver will cause the ambient suspended solids
concentrations to be elevated. The level
of elevation will determine whether the impact is adverse. The determination of the acceptability of
elevations in suspended solids (SS) concentrations is based on the Water
Quality Objectives (WQO). The WQO for SS
is defined as being an allowable elevation of 30% above the background. It is proposed to represent the ambient SS
value by the 90th percentile of SS concentrations measured under the
EPD routine marine water quality monitoring programme at the station, namely
NM5, nearest to the sensitive receivers that would be potentially affected by
the dredging works (including the Sha Chau and Lung Kwu Chau Marine Parks as
well as the cooling water intake for Castle Peak Power Station near Tap Shek
Kok) identified at the
Urmston Road as shown in Figure No. NOL/ERL/300/C/XRL/ENS/M59/002. Other sensitive receivers such as the beaches and WSD
flushing water intake at Tuen Mun are further away from the proposed dredging
site. The relevant EPD data and allowable elevations in
suspended sediment concentration are summarised in Table 11.16a. The 90th
percentile SS values presented in Table
11.16a were calculated based on the EPD monitoring data collected in the
period from 2006 to 2007.
|
Sensitive Receiver (Relevant EPD
Monitoring Station) |
Dry Season |
Wet Season |
||
|
90th Percentile |
30 % Tolerance |
90th Percentile |
30 % Tolerance |
|
|
Sha Chau and |
17.8 mg/L |
5.4 mg/L |
20.4 mg/L |
6.1 mg/L |
11.66 The allowable elevation in SS concentration as defined by the WQO for a particular site corresponds to the 30% tolerance level. The calculated maximum SS concentrations from the dredging have been compared with the 30% tolerance values in the above table to determine the acceptability of the impacts.
Dredging Method and Sediment Loss
Rate for Unmitigated Scenario
11.67 The dredging works at LKST will be conducted at a slow production rate of 1000 m3 per day. Dredging will be carried out by a single closed grab dredger of about 8 m3 capacity working for 12 hours per day (6 days per week). The sediment loss rate was calculated to be about 0.46 kg/s under the unmitigated scenario based on the following assumptions:
l
The density of mud measured
within the dredging area was 1,040 kg/m3.
l
Dredging by closed grab
dredger is assumed to be continuous, 12 hours a day.
l
With respect to rate of sediment loss during dredging, the
Contaminated Spoil Management Study ([3])
(Mott MacDonald, 1991, Table 6.12) reviewed relevant
literature and concluded that losses from closed grab dredgers were estimated
at 11 – 20 kg/m3 of mud removed. Taking the upper figure of 20 kg/m3
to be conservative, the loss rate in kg/s was calculated based on the daily
volume rate of dredging. (Assuming a dry density for marine mud of 1040 kg/m3, the
sediment loss during dredging is equivalent to a spill amount of approximately 2.2%).
Consideration of Mitigation
Measures and Sediment Loss Rate for Mitigated Scenario
11.68
To minimise the potential impact due to SS, deployment of silt curtains
around the closed grab dredgers is recommended as an appropriate mitigation
measure.
11.69
According to the Contaminated Spoil Management Study (3),
the implementation of silt curtain around the closed grab dredgers will reduce
the dispersion of SS by a factor of 4 (or about 75%). Hence, the sediment loss rate within the
dredging area would be about 0.12 kg/s after deploying the silt curtain around
the works area.
Near Field Sediment Dispersion
Modelling
11.70
The method of calculation of the near field
concentrations of suspended sediment plumes is the same as that used in the
approved EIA study for Outlying Islands Sewerage Stage 1, Phase II Package J –
Sok Kwu Wan Sewage Collection, Treatment & Disposal Facilities ([4]). In this method, a simple model
is used to calculate the depth averaged suspended sediment concentrations along
the centreline of a plume by solving the advection-diffusion equation for a
continuous line source ([5]). This model is considered
appropriate for the calculation of suspended sediment concentrations from the
proposed dredging work because the equation is based on a continuous line
source of sediment, which is a reasonable approximation of the loss of sediment
due to suspension during grab dredging. It is appropriate for areas where the
tidal current is uni-directional for each phase of the tidal cycle (i.e. the
ebb and flood phases), which is the case at
Tidal excursion = maximum speed * period * 2 /╥
11.71
The tidal excursion is thus calculated to be approximately 7 km. Even in the near shore region where the
dredging area is located, the maximum current speed could also be up to 0.2 m/s
where the calculated tidal excursion could be up to roughly 3 km. Hence this
approach may be considered appropriate because of the low rate of dredging and
thus the expected limited extent of the plumes, which will certainly be within
the tidal excursion. The formula which is used is as follows.
C(x)
= q / (D*x*ω*√╥
)
Where C(x) = concentration at distance x from the
source
q = sediment loss rate = (0.12
kg/s after deployment of silt curtain)
D = water depth = (2 m at the
near shore region of
X = distance from source
ω = diffusion velocity =
0.01 m/s
11.72
The water sensitive areas closest to the proposed dredging site are
located in the open water at
11.73
The use of the above equation is limited to situations where the value
of γ, as defined by the following
equation, is small and where ω / u is also small.
γ
= W t / D
Where W = settling velocity of suspended
sediment
t = time
D = water depth
11.74
The sediments suspended by the dredging operations may be split into a
fine fraction and a coarse fraction. The fine fraction is assumed to remain in
suspension indefinitely, which is based on the fact that the settling velocity
for the sediment particles according to Stokes Law is offset by local
turbulence. The value of settling
velocity, W, for the coarse fraction of the sediment (based on the Stokes Law)
would depend on the sediment particle size. The value for t will be taken to be
half of the tidal period, which may be taken to be the time between the ebb and
flood phases of the tidal cycle. In
11.75
The average current speed in the vicinity of the dredging area is
conservatively taken to be 0.1 m/s, the value of ω / u (where ω is
the diffusion velocity and u is the current speed) is calculated to be 0.1,
which is considered to be small and the use of the sediment plume dispersion
formula is considered valid.
Cumulative Impacts from
Concurrent Projects
Construction Phase
11.76
Information of concurrent projects including “Proposed Comprehensive
Development at Wo Shang Wai, Yuen Long”, “Construction of Cycle Tracks and the
associated Supporting Facilities from Sha Po Tsuen to
11.77
The proposed dredging works at
LKST would be small in scale and conducted at a slow production rate. The potential water quality impacts are
expected to be localized and confined in close proximity of the Project site as
demonstrated from the sediment plume modelling conducted under this EIA. No significant cumulative water quality
impact with other concurrent marine construction works would be contributed
from this Project.
Operation Phase
11.78
With regard to the water quality impact from the proposed seawater
cooling water system at WKT, other concurrent spent cooling water discharges
identified within the
Prediction and Evaluation of
Impacts
Construction Phase
Site Effluent
11.79 Effluent discharge from temporary site facilities should be controlled to prevent direct discharge to the neighbouring water courses, marine waters and storm drains. Such wastewater may include wastewater resulting from wheel washing of site vehicles at site entrances. Adoption of the guidelines and good site practices from the handling and disposal of construction discharges as part of the construction site management practices (as given in Sections 11.137 to 11.156) would minimize the potential impacts.
Accidental Spillage
11.80 The use of engine oil and lubricants, and their storage as waste materials has the potential to create impacts on the water quality of adjacent water courses if spillage occurs and enters watercourses. Waste oil may infiltrate into the surface soil layer, or run-off into local water courses, increasing hydrocarbon levels. The potential impacts could however be mitigated by practical mitigation measures and good site practices (as given in Sections 11.162 to 11.164).
Sewage Effluent from Construction
Workforce
11.81 During construction, the increased workforce will contribute to the local population of the area, although the number of workers will vary over the construction period. Impacts include the generation of rubbish and wastewater from eating areas, temporary sanitary facilities and waste disposal areas. Although the impact will be temporary, this additional population may impose significant stress on the quality of water in local water courses in the absence of adequate mitigation. Mitigation measures and good site practices given in Sections 11.136, 11.152 and 11.153 should be implemented.
River Training (Diversion of
Watercourse)
11.82
The cut and cover tunnel at the section in Shek Kong as well as the
proposed Shek Kong Stabling Sidings (SSS) facility would directly pass through
Kam Tin River Nullah and the
11.83
Mitigation measures to be implemented during the flow diversion works
for minimizing the release of sediments and construction wastes into the
watercourses and downstream are described as follows. The excavation works at
the existing stream in Shek Kong/Kam Tin Nullah would be carried out in
sections using approved methods developed by the engineer to minimise erosion.
Should excavation works be carried out at the designated section of water
course, temporary river diversion would be conducted prior to the commencement
of works to avoid water flowing into works area. The temporarily diversion
of water flow would be performed by appropriate means, such as completion of
proposed channel section for carrying diverted flow prior to excavation works,
or other similar methods, as approved by the Engineer to suit the works
condition. This works arrangement would
provide a dry zone for excavation works within the river channel and would
prevent the conveyance of suspended sediment downstream. Dewatering at works section would also be
conducted prior to the commencement of works. Mitigation measures for
minimizing the water quality impact for surface construction works at or close
to the watercourses are provided in Section
11.165.
Excavation Activities
11.84
Excavations will be carried out for the construction of cut and cover
tunnel section, diaphragm walling, shafts, SSS, ventilation buildings/EAPs,
West Kowloon Terminus (WKT), as well as emergency vehicular accesses and
carriageways. As mentioned before, the
proposed cut and cover tunnel at the section of Shek Kong and the SSS would
directly pass through the local streams that would drain into
11.85
Potential impacts may occur if rain falls during the excavation works,
and water from the river enters the excavated area, or silt and sand material and
run-off from the excavation enters the watercourses, increasing turbidity. Other pollutants, such as oil and grease, and
chemicals, as well as bentonite and grouting materials, may be present in the
run-off where it flows over storage or maintenance areas for the works. Erosion of soil enriched in organic matter
may release nutrients into the adjacent watercourses. Erosion of stockpiles may also release
suspended solids into nearby watercourses.
As a good site practice, mitigation measures (as
given in Sections 11.128 to 11.136) should be implemented to control site run-off and drainage from the
works areas from entering the adjacent waters.
Groundwater Seepage from
Uncontaminated Area
11.86
Excavation works are required for various construction activities during
the construction. Different construction
methods will be employed to minimize the intrusion of groundwater into works
areas. In case seepage of groundwater
occurs, groundwater would be pumped out from works areas and discharged to the
storm system via silt trap.
Uncontaminated groundwater from dewatering process should also be
discharged to the storm system via silt removal facilities. Change of groundwater table would be
minimal. As no groundwater would be
directly discharged into streams and drainages, water quality impacts would not
be expected.
11.87
As the proposed WKT is near the
Site Runoff and Groundwater from
Contaminated Areas
11.88
According to Section 9 of the EIA study, it is identified that the works
areas including the cut and cover tunnel sections in Mai Po and Shek Kong, the
ventilation buildings in Mai Po, Kwai Chung and Nam Cheung, the SSS as well as
the works area at Lai Chi Kok would have land contamination issues. Details of
the land contamination assessment are separately presented in Section 9. Any contaminated material
disturbed, or material which comes into contact with the contaminated material,
has the potential to be washed with site run-off into watercourses. Mitigation measures
(as given in Section 9) should be implemented to control site runoff from the contaminated areas, and to prevent
runoff entering the adjacent waters.
11.89
Groundwater pumped out or from dewatering process during excavation
works in these areas would be potentially contaminated.
Prior to the excavation works, the baseline
groundwater quality in these potentially contaminated areas should be reviewed with
reference to the past relevant site investigation data and any additional
groundwater quality measurement results.
The review results should be submitted to EPD for examination. If
the review indicated that the groundwater to be generated from the excavation
works would be contaminated, this contaminated groundwater will be either
properly treated or properly recharged into the ground in compl
11.90 If deployment of wastewater treatment is not feasible for handling the contaminated groundwater, groundwater recharging wells will be installed as appropriate for recharging the contaminated groundwater back into the ground. The recharging wells will be selected at places where the groundwater quality will not be affected by the recharge operation as indicated in section 2.3 of the TM-DSS. Pollution levels of groundwater to be recharged shall not be higher than pollutant levels of groundwater at the recharge well. Provided that all the mitigation measures and monitoring requirements as recommended in Sections 11.157 and 11.158 are followed properly, no adverse water quality impact would be envisaged.
11.91 Potential impact of contaminated groundwater from the Ngau Tam Mei Landfill has been provided in Section 15.
Tunnelling Activities
11.92
The underground tunnel of the Project would mainly be constructed by
Drill and Blast (D&B) and Tunnel Boring Machine (TBM)
technique. Potential source of water quality impact from
these tunnelling operations would be the discharge of tunnelling wastewater
from drilling, boring and wash-down. The
use of bentonite and grouting materials for the construction of bored tunnels
would contaminate the water pumped out from the tunnel. Surface run-off may also be contaminated and
turbid water may enter adjacent watercourses, drainage system and downstream as
excavated material is conveyed to the surface.
Wastewater from tunnelling works would also contain a high content of
SS. Water used for the tunnelling
activities should as far as practicable be re-circulated after
sedimentation. When there is a need for
final disposal, the wastewater should be discharged into storm drains via silt
removal facilities. Wastewater
discharging into storm drains should comply with the standards stipulated in
the TM-DSS.
11.93
The potential impact on groundwater system along the tunnel section
during the construction stage has been assessed with mitigation measures given
in Appendix 11.8.
Diaphragm Wall
11.94
As cut and cover construction
is required, diaphragm walls are used as retaining wall for excavation and
serve as either temporary or permanent support for the tunnel. Potential
impacts from any required diaphragm walling include turbid site run-off from
the works, and bentonite and concrete washings entering watercourses. Bentonite is a highly turbid material and
will cause damage to aquatic organisms in receiving waters. Run-off may arise during extraction of the
bentonite or during preparation for recycling or disposal. Concrete washings are potentially toxic to
aquatic organisms, raising pH of receiving water bodies. Concrete washings also increase turbidity in
a waterbody. As good site practice,
mitigation measures (as given in Sections 11.128 to 11.165) should be implemented to control site run-off
and drainage as well as any site effluents generated from the works areas, and
to prevent run-off and construction wastes from entering the adjacent waters.
Barging Point
11.95
Six barging points is proposed
to be constructed for transportation of the spoil generated from the Project to
the Mainland China for reuse/disposing of.
These barging points are located at
Construction Works near the Water
Gathering Ground
11.96
A section of D&B tunnel (between Pat Heung and Shing Mun) will be
constructed underneath the WGG (refer to Figure No.
NOL/ERL/300/C/XRL/ENS/M59/003). No
surface construction activities would be undertaken within the WGG. The proposed
Dredging of Marine Sediment at LKST
11.97
The results of the calculation of suspended sediment concentrations are
given in Table 11.16b.
Table 11.16b Calculated Suspended Sediment Concentrations
(with Deployment of Silt Curtain)
|
Distance from
Source (m) |
Suspended
Sediment Concentration (mg/L) |
|
100 |
32.4 |
|
200 |
16.2 |
|
300 |
10.8 |
|
400 |
8.1 |
|
500 |
6.5 |
|
600 |
5.4 |
|
700 |
4.6 |
|
800 |
4.1 |
11.98
The closest identified
sensitive receiver to the proposed dredging site is the
Sha Chau and
11.99 To further minimize the potential impact upon the ecological sensitive receivers (such as the coral communities identified along the coastline near the dredging site), double silt curtains are recommended to be deployed around the dredging works area as far as practicable as a precautionary measure. The model results provided in Table 11.16b has taken into account the effect of single silt curtain only. With the deployment of double silt curtains around the works area, the resulted water quality impact is expected to be much smaller than that predicted in Table 11.16b. Other precautionary measure such as avoidance of dredging works in the peak calving season of the Chinese White Dolphin (i.e. from March to August), and breeding season of horseshoe crab (i.e. April to August) is also proposed under the Ecological Impact Assessment in Section 3 to minimize the potential ecological impact. Details of the ecological sensitive receivers and ecological impact assessment are given in Section 3. Mitigation measures and good site practices for minimizing the water quality impacts from dredging activities are given in Sections 11.167 to 0.
Hydrogeological Impact
11.100
The construction of the Project would have potential impacts on change
of groundwater table. Such construction activities include:
l
Cut & Cover Excavations for vent buildings and emergency
access/escape point
l
Bored Tunnelling works
l
Drill & Blast Tunnelling works
11.101 A hydrogeological impact
assessment has been carried out to identify and assess the potential impact of
the tunnel works under the Project on the surface water and groundwater (Appendix 11.8 refers). The major
concern of the hydrogeological impact assessment is the potential drawdown in
any soil and aquifer layers. Any
potential drawdown could result in different degrees of settlement and
dewatering of surface water features. The potential
effects on the groundwater drawdown due to the tunnel works are discussed
briefly as follows.
Cut & Cover Tunnels
11.102
The cut and cover tunnels and associated excavations for ventilation
buildings and emergency access/escape points will only require dewatering
temporarily during their construction.
In the long term they are designed to be undrained with the full
hydrostatic head. Mitigation measures as
outlined in Sections 11.168 to 11.172 will be put in pace to mitigate any drawdown
effects to the groundwater table during the operation of the temporary
dewatering works. Provided that the
mitigation measures are properly followed, no unacceptable impact in relation
to the groundwater drawdown would be expected.
Bored Tunnelling
11.103
For the bored tunnelling works, the effects on the external groundwater
regime are expected to be small both during construction and in the long term
due to the method of construction and the use of undrained linings. The bored tunnels will be constructed using a
closed face tunnel boring machine to limit water inflow into the excavation
face. The cutter head for the machine
will be sealed during excavation and therefore the water inflow from the face
will be very small. Precast undrained
linings shall be installed and back grouted behind the tunnel boring machine as
it advances along the alignment and therefore the potential inflow of water
behind the cutter head will also be small.
Drill & Blast Tunnels
11.104
For the proposed tunnel sections located within the hillside areas at
Tai Mo Shan and Kai Kung Leng, drill and blast techniques are proposed to be
employed. Considering the proposed tunnel
span together with the maximum expected pressure heads in excess of 300m in
sections of the alignment, a drained tunnel is the only technically feasible
option. An undrained
lining is technically impossible under these conditions. Drained tunnels have been
commonly adopted in this situation in
11.105
In order to reduce the potential for drawdown and ensure the safety of
his works, the Contractor will initially adopt suitable water control
strategies while undertaking the excavation works. In the event that the ground water table is
observed to be lowered unacceptably even after the application of these water
control strategies then post grouting or other similar acceptable remedial
measures will be undertaken from within the tunnel as a suitable mitigation
measure.
11.106
Details of the mitigation
measures to prevent any potential groundwater drawdown associated with
different construction methods described above are described in Sections 11.168 to 11.172.
Operation Phase
Tunnel Run-off and Drainage
11.107 The railway tunnel is a confined environment and hence there would not be any rainwater run-off. The tunnel wall should be equipped with water-tight liner to avoid ground water seepage. The amount of groundwater seepage into the tunnel would be insignificant. Any tunnel run-off could be contaminated with limited amount of grease and iron from passing trains or from maintenance activities. The discharge quality of any tunnel run-off should satisfy the standards listed in the TM-DSS. Standard designed silt trap or grease trap (if necessary) and oil interceptor should be provided to remove the oil, lubricants, grease, silt and grit from the tunnel run-off before discharge into stormwater drainage. No adverse water quality impacts would be expected.
Sewage Effluents and Sewerage
Impact Assessment
11.108 Sewage and wastewater effluents would be generated from staffs and customers at food and beverage outlets in WKT, operation of ventilation building, passengers in the train as well as the maintenance activities in SSS. Generated sewage and wastewater should be connected to the foul sewerage system or properly treated before controlled discharge. All the sewage effluents will be treated as necessary to satisfy the discharge standards stipulated in the TM-DSS.
11.109
Sewerage impact assessment (SIA) has been conducted to identify impacts
to the existing and future capacity of the sewers due to implementation of the
Project. Details of the SIA for the WKT, and northern and southern
section of the XRL tunnel are provided in Appendices 11.9a – 11.9c
respectively. Assessment indicated that
the operation of the Project is considered sustainable in terms of sewerage.
11.110
All wastewater and sewage generated from the WKT will be discharged into
the foul sewers. Sewerage impact assessment for WKT concluded that the existing
sewer will still have spare capacity to receive the sewage flow generated from
other further development in the area. New gravity sewers ranging from
300mm to 375mm diameter pipe are proposed to receive the sewage flow generated
from the West Kowloon Terminus and to discharge into the existing 1350mm
diameter trunk sewer located at
11.111
For the Northern Section, as the commissioning of XRL is scheduled in
2015 whereas public sewer would be available by the end of 2014 according to
DSD’s latest programme, the intended sewerage strategy for XRL would tie in
with the proposed sewerage improvement works in Kam Tin and Ngau Tam Mei.
Additional flows from proposed XRL facilities should be considered for
the design of planned sewerage system under Public Works Programme Project
(PWP) Item No. 235DS. According to the estimated sewage flow from XRL
facilities, there would be negligible impact on the proposed sewerage system
with the addition of sewage flow from XRL facilities. Prior to the completion of proposed sewerage
system, sewage from ventilation buildings, EAPs, and SSS will be stored in a
holding tank and then tankered away by licenced collector for discharge in Yuen Long Sewage Treatment Works (YLSTW) or to San Wai
Sewage Treatment Works (SWSTW) for treatment and disposal.
Sewage generated from the train passengers will also be collected at the
SSS and then tankered away. No
additional sewage / wastewater flow would be discharged to the surface water
system within the
11.112
For the southern section of the proposed railway alignment, major
sources of sewage include the toilet sanitary wastewater and floor drainage
generated at the ventilation buildings and the foul water from the tunnel and
foul water drainage system, and all sewage effluent will be discharged into the
public foul sewers. Assessment results indicated that the existing capacities
of the sewerage systems would be adequate to convey the flows generated by the
XRL permanent works together with the existing flows. No adverse impact
would be caused on the existing sewerage systems by the proposed southern section
of XRL works, and no any improvement or mitigation works are required in
general.
11.113 The above-ground ventilation buildings are likely to be completely enclosed and therefore run-off will be limited to wash-off from the outside of the building. Sources of potentially polluted stormwater that may arise from the ventilation building run-off include dust from the roof of the ventilation buildings and cleaning agents used for washing building facade. Run-off from the ventilation buildings would contain low levels of SS and surfactants used for washing. With good washing practise, adverse impacts from station run-off would be minimal.
Shek Kong Stabling Sidings (SSS)
11.114 The SSS facility is proposed to provide stabling, maintenance and cleaning activities as well as canteen and staff accommodation. Potential water quality impacts would be generated if accidental spillage occurs from maintenance activities. Surface or washed water runoff generated during the maintenance areas is also potentially contaminated and may pose water quality impact, if not well controlled.
11.115 It would be a required site practice not to directly discharge contaminated surface runoff into the surface channel or nearby water bodies. All the maintenance areas within the SSS will be housed to prevent generation of contaminated rainwater runoff. All contaminated surface runoff or wastewater should be collected and diverted to oil interceptor or other appropriate treatment facilities for proper treatment.
11.116
All waste oils and fuels should
be collected and handled in compl
11.117 All sewage and wastewater generated from the SSS would be properly collected. Prior to the availability of pubic sewerage system, sewage will be stored in a holding tank and then tankered away by licenced collector for discharge in YLSTW or SWSTW for treatment and disposal. There will be no direct discharge of wastewater into the storm or surface water system.
Diversion of Watercourse
11.118
The cut and cover tunnel at the section in Shek Kong as well as the
proposed Shek Kong Stabling Sidings (SSS) facility would directly pass through
Kam Tin River Nullah and the
Spent Cooling Water Discharge
11.119
Potential water quality impacts
in terms of temperature rise and residual chlorine contamination may arise from
spent cooling water discharges from the proposed seawater cooling system. Other anti-fouling chemical agent (e.g. C-treat-6) will not be used at
the proposed seawater cooling system. Mathematical
modelling was conducted to simulate and assess the potential impacts in the
11.120 The WQO for the Victoria Harbour WCZ stipulated that the temperature rise in the water column due to human activity should not exceed 2 oC (Table 11.4). Appendix 11.6a and Appendix 11.6b show the surface temperature elevations over the ambient temperature at different tidal conditions for dry and wet seasons respectively. The model results indicated that temperature rise in areas close to the outfall of the proposed seawater cooling water system was no more than 1 oC in the surface water layer under different tidal conditions, taken into account of other concurrent spent cooling water discharges in the West Kowloon area. The overall thermal plume at the surface water layer was localised and confined near the cooling water outfall.
11.121 It should be noted that the intake and outfall of the proposed seawater cooling water system would be located at -3.15 mPD which are located in a water layer much deeper than the surface water. Table 11.17 gives the mean and 90 percentile temperature rises predicted at the cooling water intake points which correspond to the mid or deeper layer of the water column. The predicted 90-percentile temperature rises ranged from 0.11 oC to 1.13 oC. Hence, no unacceptable cumulative impact of temperature elevation is anticipated at all the identified water intake points.
Table 11.17 Temperature Elevations at Cooling Water Intakes
|
Sensitive Receiver |
Temperature elevation
at Water Intakes (°C) |
|||
|
|
Dry season |
Wet season |
||
|
|
Mean |
90 percentile |
Mean |
90 percentile |
|
MTRC
Kowloon Station (mainly used by Elements) |
0.09 |
0.14 |
0.10 |
0.25 |
|
|
0.08 |
0.13 |
0.09 |
0.19 |
|
|
0.09 |
0.14 |
0.16 |
0.30 |
|
Ocean
Centre |
0.08 |
0.13 |
0.19 |
0.42 |
|
Ocean
Terminal |
0.07 |
0.11 |
0.05 |
0.12 |
|
Intake
of Seawater Cooling System proposed under the Project |
0.17 |
0.26 |
0.50 |
1.13 |
11.122 Chlorine, in the form of sodium hypochlorite solution or produced through electrolysis of sea water, is commonly used as an anti-fouling agent or biocide for the treatment of cooling water within the cooling systems. Residual chlorine discharging to the receiving water is potentially harmful to the marine organisms. However, the residual chlorine would have no adverse impacts on the cooling water intakes. The assessment criterion for chlorine was developed for protection of marine life only. Appendix 11.7a and Appendix 11.7b show the predicted tidal and depth averaged chlorine concentration for a spring-neap cycle, in the dry and wet seasons respectively.
11.123
The model results indicated
that the Project discharge would not contribute any non-compl
11.124 For cooling water where no information on the residual chlorine level is available, the maximum chlorine dose rates have been directly applied to calculate the chlorine loading for model input which, again, represents a very adverse scenario. In reality, the peak discharge flow rates would occur during a short period of time within a day and the chlorine would be decayed within the cooling water system. Therefore, the actual chlorine contents in the cooling water discharges should be significantly smaller than that assumed in the model.
11.125 The background cooling water discharges have been included in the model only for the purpose of addressing the possible worst-case cumulative impact with the Project discharge. The model results indicated that the seawater cooling system proposed under the Project would not cause any cumulative chlorine impacts with all other concurrent discharges assumed in the model.
Acceptability
of Mixing Zone
11.126
Non-compl
Table
11.18 Approximate
Dimension of Mixing Zones of Thermal from the Proposed Seawater Cooling
System
|
Parameter |
Approximate
Dimension of Mixing Zone |
Level
of Non-compl |
|
Temperature |
20
m x 20 m |
Temperature elevation of more than 2 oC
(up to a maximum level of 3.4 oC) was predicted at the outfall in
4.1% of time during wet season only |
11.127
The predicted non-compl
· The
exceedance was highly localized and would be confined close to the cooling
water outfall and would not impair the integrity of the water body and the
ecosystem in the
· The
mixing zone would not endanger sensitive uses e.g. beaches, breeding grounds,
or diminish existing beneficial uses and therefore would not cause any adverse
effects in human or aquatic organism.
Recommended Water Quality Mitigation
Measures
Construction Phase
Construction Site Run-off and
General Construction Activities
Surface
Run-off
11.129
Surface run-off from
construction sites should be discharged into storm drains via adequately
designed sand/silt removal facilities such as
sand traps, silt traps and sedimentation basins. Channels or earth bunds or sand bag barriers
should be provided on site to properly direct stormwater to such silt removal
facilities. Perimeter channels at site
boundaries should be provided where necessary to intercept storm run-off from
outside the site so that it will not wash across the site. Catchpits and perimeter channels should be
constructed in advance of site formation works and earthworks.
11.130 Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly, at the onset of and after each rainstorm to prevent local flooding. Any practical options for the diversion and re-alignment of drainage should comply with both engineering and environmental requirements in order to provide adequate hydraulic capacity of all drains. Minimum distances of 100 m should be maintained between the discharge points of construction site runoff and the existing saltwater intakes.
11.131 Construction works should be programmed to minimize soil excavation works in rainy seasons (April to September). If excavation in soil cannot be avoided in these months or at any time of year when rainstorms are likely, for the purpose of preventing soil erosion, temporary exposed slope surfaces should be covered e.g. by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds. Intercepting channels should be provided (e.g. along the crest / edge of excavation) to prevent storm runoff from washing across exposed soil surfaces. Arrangements should always be in place in such a way that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm.
11.133 Measures should be taken to minimize the ingress of rainwater into trenches. If excavation of trenches in wet seasons is necessary, they should be dug and backfilled in short sections. Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.
11.134 Open stockpiles of construction materials (e.g. aggregates, sand and fill material) on sites should be covered with tarpaulin or similar fabric during rainstorms.
11.135 Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris from getting into the drainage system, and to prevent storm run-off from getting into foul sewers. Discharge of surface run-off into foul sewers must always be prevented in order not to unduly overload the foul sewerage system.
Boring
and Drilling Water
11.137 Water used in ground boring and drilling for site investigation or
rock / soil anchoring should as far as practicable be re-circulated after
sedimentation. When there is a need for
final disposal, the wastewater should be discharged into storm drains via silt
removal facilities.
Wastewater
from Concrete Batching Plant
11.138
Wastewater generated from the
washing down of mixing trucks and drum mixers and similar equipment should
whenever practicable be used for other site
activities. The discharge of wastewater
should be kept to a minimum and should be treated to meet the appropriate
standard as specified in the TM-DSS before discharging.
11.139 To prevent pollution from wastewater overflow, the pump of any wastewater system should be provided with an on-line standby pump of adequate capacity and with automatic alternating devices.
11.140 Under normal circumstances, surplus wastewater may be discharged into foul sewers after treatment in silt removal and pH adjustment facilities (to within the pH range of 6 to 10). Disposal of wastewater into storm drains will require more elaborate treatment.
Wheel
Washing Water
11.141
All vehicles and plant should
be cleaned before they leave a construction site to minimize the deposition of
earth, mud, debris on roads. A wheel
washing bay should be provided at every site exit if practicable and wash-water
should have sand and silt settled out or removed before discharging into storm
drains. The section of construction road
between the wheel washing bay and the public road should be paved with backfall
to reduce vehicle tracking of soil and to prevent site run-off from entering
public road drains.
Bentonite
Slurries
11.142
Bentonite slurries used in
diaphragm wall and bore-pile construction should be reconditioned and used
again wherever practicable. If the
disposal of a certain residual quantity cannot be avoided, the used slurry may be
disposed of at the marine spoil grounds subject to obtaining a marine dumping
licence from EPD on a case-by-case basis.
11.143 If the used bentonite slurry is intended to be disposed of through the public drainage system, it should be treated to the respective effluent standards applicable to foul sewer, storm drains or the receiving waters as set out in the TM-DSS.
Water
for Testing & Sterilization of Water Retaining Structures and Water Pipes
11.144
Water used in water testing to check
leakage of structures and pipes should be used for other purposes as far as
practicable. Surplus unpolluted water will be discharged into storm drains.
11.145 Sterilization is commonly accomplished by chlorination. Specific advice from EPD should be sought during the design stage of the works with regard to the disposal of the sterilizing water. The sterilizing water should be used again wherever practicable.
Wastewater
from Building Construction
11.146
Before commencing any
demolition works, all sewer and drainage connections should be sealed to
prevent building debris, soil, sand etc. from entering public sewers/drains.
11.147 Wastewater generated from building construction activities including concreting, plastering, internal decoration, cleaning of works and similar activities should not be discharged into the stormwater drainage system. If the wastewater is to be discharged into foul sewers, it should undergo the removal of settleable solids in a silt removal facility, and pH adjustment as necessary.
Acid
Cleaning, Etching and Pickling Wastewater
11.148
Acidic wastewater generated
from acid cleaning, etching, pickling and similar activities should be
neutralized to within the pH range of 6 to 10 before discharging into foul
sewers. If there is no public foul sewer
in the vicinity, the neutralized wastewater should be tankered off site for
disposal into foul sewers or treated to a standard acceptable to storm drains
and the receiving waters.
Wastewater
from Site Facilities
11.149
Wastewater collected from
canteen kitchens, including that from basins, sinks and floor drains, should be
discharged into foul sewer via grease traps capable of providing at least 20
minutes retention during peak flow. In
case connection to the public foul sewer is not feasible, wastewater generated
from kitchens or canteen, if any, should be collected in a temporary storage
tank. A licensed waste collector should
be deployed to clean the temporary storage tank on a regular basis.
11.150 Drainage serving an open oil filling point should be connected to storm drains via petrol interceptors with peak storm bypass.
11.151 Vehicle and plant servicing areas, vehicle wash bays and lubrication bays should as far as possible be located within roofed areas. The drainage in these covered areas should be connected to foul sewers via a petrol interceptor. Oil leakage or spillage should be contained and cleaned up immediately. Waste oil should be collected and stored for recycling or disposal in accordance with the Waste Disposal Ordinance.
Sewage
from Workforce
Groundwater
Seepages from Uncontaminated Area
11.154
Appropriate measures will be deployed to minimize the intrusion of
groundwater into excavation works areas.
In case seepage of uncontaminated groundwater occurs, groundwater should
be pumped out from the works areas and discharged into the storm system via
silt removal facilities. Uncontaminated
groundwater from dewatering process should also be discharged into the storm
system via silt traps.
11.155
As the proposed WKT is near the
11.156 To monitor the tide and groundwater relationship, it is recommended to install groundwater level loggers at the nearest tidal areas (i.e. near Mai Po). Further groundwater monitoring and in-situ testing of hydrogeological parameters will be required along the Project alignment and the surrounding areas to provide additional data for the groundwater contour plots and to develop the groundwater model. A ground investigation programme has been developed to include a significant number of drillholes with at least one piezometer installed. The results will improve the reliability of future groundwater models. Upon receipt of more reliable and extensive data, both regional and local scale groundwater models should be developed to allow more comprehensive assessment of the impact of the project on the hydrogeological regime. Where appropriate numerical modelling (i.e. SEEP/W) should also be carried out to assess the impact of construction on the groundwater regime. Such modelling should only be attempted for areas where sufficiently reliable data exists to adequately validate the model.
Site Runoff or Groundwater from
Contaminated Areas
11.157
No directly discharge of
groundwater from contaminated areas should be adopted. Prior to any excavation works within the
potentially contaminated areas (including the cut and cover tunnel section and ventilation building in Mai Po,
the cut-and-cover tunnel section in Shek Kong, the SSS, the works area in Lai
Chi Kok, and the ventilation buildings in Kwai Chung and Nam Cheong), the baseline groundwater quality in these areas should be reviewed
based on the past relevant site investigation data and any additional
groundwater quality measurements to be performed with reference to Guidance Note for Contaminated Land
Assessment and Remediation and the review results should be submitted to
EPD for examination. If the review results indicated that the groundwater to be
generated from the excavation works would be contaminated, this contaminated
groundwater should be either properly treated or properly recharged into the
ground in compl
11.158
If deployment of wastewater
treatment is not feasible for handling the contaminated groundwater,
groundwater recharging wells should be installed as appropriate for recharging
the contaminated groundwater back into the ground. The recharging wells should
be selected at places where the groundwater quality will not be affected by the
recharge operation as indicated in section 2.3 of the TM-DSS. The baseline groundwater
quality should be determined prior to the selection of the recharge wells, and submit
a working plan to EPD for agreement.
Pollution levels of groundwater to be recharged shall not be higher than
pollutant levels of ambient groundwater at the recharge well. Groundwater
monitoring wells should be installed near the recharge points to monitor the
effectiveness of the recharge wells and to ensure that no likelihood of
increase of groundwater level and transfer of pollutants beyond the site
boundary. Prior to recharge, free
products should be removed as necessary by installing the petrol
interceptor. The Contractor should apply
for a discharge licence under the WPCO through the Regional Office of EPD for
groundwater recharge operation or discharge of treated groundwater.
11.159 Mitigation measures for the contaminated groundwater from Ngau Tam Mei Landfill are provided in Section 15.
Barging Points
·
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
·
all hopper barges should be fitted with tight fitting seals
to their bottom openings to prevent leakage of material
·
construction activities should not cause foam, oil, grease,
scum, litter or other objectionable matter to be present on the water within
the site
·
loading of barges and hoppers should be controlled to
prevent splashing of material into the surrounding water. Barges or hoppers should not be filled to a
level that will cause the overflow of materials or polluted water during
loading or transportation
Effluent Discharge
11.161 There is a need to apply to EPD for a discharge licence for discharge of effluent from the construction site under the WPCO. The discharge quality must meet the requirements specified in the discharge licence. All the runoff and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS. Minimum distances of 100 m should be maintained between the discharge points of construction site effluent and the existing seawater intakes. The beneficial uses of the treated effluent for other on-site activities such as dust suppression, wheel washing and general cleaning etc., can minimise water consumption and reduce the effluent discharge volume. If monitoring of the treated effluent quality from the works areas is required during the construction phase of the Project, the monitoring should be carried out in accordance with the WPCO license which is under the ambit of Regional Office (RO) of EPD.
Accidental Spillage of Chemicals
11.163 Any service shop and maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be provided. Maintenance of vehicles and equipment involving activities with potential for leakage and spillage should only be undertaken within the areas appropriately equipped to control these discharges.
11.164
Disposal of chemical wastes
should be carried out in compl
·
Suitable containers should be used to hold the chemical
wastes to avoid leakage or spillage during storage, handling and transport.
·
Chemical waste containers should be suitably labelled, to
notify and warn the personnel who are handling the wastes, to avoid accidents.
·
Storage area should be selected at a safe location on site
and adequate space should be allocated to the storage area.
Surface Construction Works at or in
Close Proximity of Watercourses or Seafront
11.165
Mitigation measures to minimize
water quality impacts from construction activities located at or in close
proximity of watercourses including the diversion works at
l
The proposed surface construction works should be carried
out in dry season as far as practicable where the flow in the river channel or
stream is low.
l
The use of less or smaller construction plants may be
specified to reduce the disturbance to the riverbed or pond deposits.
l
Temporary sewerage system should be designed to prevent
wastewater from entering the river, streams and sea.
l
Temporary storage of materials (e.g. equipment, filling materials,
chemicals and fuel) and temporary stockpile of construction materials should be
located well away from any water courses during carrying out of the
construction works.
l
Stockpiling of construction materials and dusty materials
should be covered and located away from any water courses.
l
Construction debris and spoil should be covered up and/or
disposed of as soon as possible to avoid being washed into the nearby water
receivers.
l
Construction activities, which generate large amount of
wastewater, should be carried out in a distance away from the waterfront, where
practicable.
l
Mitigation measures to control site run-off from entering
the nearby water environment should be implemented to minimize water quality
impacts. Surface channels should be
provided along the edge of the waterfront within the work sites to intercept
the run-off.
l
Construction effluent, site run-off and sewage should be
properly collected and/or treated.
l
Any works site inside the water courses should be
temporarily isolated. The water flow
should be temporarily diverted to downstream by using PVC pipes, steel arrays
in concrete case or similar, restricting the excavation works to be conducted
within an enclosed dry section of the channel.
This works arrangement would provide a dry zone for excavation works
within the river channel and would prevent the conveyance of suspended sediment
downstream. Dewatering at works section
should be conducted prior to the commencement of works. Further limiting or
reducing the works area inside the water courses should be considered during
wet season or rainstorm event in order to reduce the area of exposed surface.
l
Silt curtain should be installed around the construction
activities at or near the watercourses to minimize the potential impacts due to
accidental spillage of construction wastes and excavated materials.
l
Proper shoring may need to be erected in order to prevent
soil or mud from slipping into the watercourses.
l
Supervisory staff should be assigned to station on site to
closely supervise and monitor the works.
Surface Construction Works Close to
Water Gathering Grounds
11.166 For surface construction works close to the WGG, the conditions as specified in WSD guidelines on protection of WGG should be followed or observed where practicable, including:
l
All practical measures shall be taken to ensure that no
pollution or siltation occurs to the WGG.
l
Storage and discharge of flammable or toxic solvents,
petroleum oil or tar and other toxic substances shall not be allowed within the
WGG,
l
Temporary drains with silt/grease traps shall be constructed
at the boundary of the site prior to the commencement of any earthworks. The effluent from the drains shall comply
with the standards stipulated in TM-DSS.
l
For drainage and sewerage diversions within or affecting
WGG, the agreement of the Director of Water Supplies is required.
l
Regular cleaning of the silt/grease traps shall be carried
out to ensure that they function properly at all times.
l
Provision of temporary toilet facilities within the WGG
shall be subject to the approval of the Director of Water Supplies. All waste shall be cleared away daily and
disposed of outside WGG. The toilet
facilities shall not be less than 30 m from any watercourse.
Dredging of Marine Sediments at
LKST
l
Closed grab dredger should be
used to minimize the loss of sediment during the raising of the loaded grabs
through the water column.
l
No more than one closed grab
dredger should be operated at any one time.
l
Double silt curtains should be
deployed around the dredging operations as far as practicable.
l
The descent speed of grabs should
be controlled to minimize the seabed impact speed.
l
Barges should be loaded carefully
to avoid splashing of material.
l
All barges used for the transport
of dredged materials should be fitted with tight bottom seals in order to
prevent leakage of material during loading and transport.
l
All barges should be filled to a
level which ensures that material does not spill over during loading and
transport to the disposal site and that adequate freeboard is maintained to
ensure that the decks are not washed by wave action.
Hydrogeological Impact
l
Toe grouting should be applied
beneath the toe level of the temporary/permanent cofferdam walls as necessary
to lengthen the effective flow path of groundwater from outside and thus
control the amount of water inflow to the excavation.
l
Recharge wells should be
installed as necessary outside the excavation areas. Water pumped from the excavation areas should
be recharge back into the ground.
11.169
The bored tunnels should be constructed using a closed face tunnel boring
machine to limit water inflow into the excavation face. The cutter head for the machine will be
sealed during excavation and therefore the water inflow from the face will be
very small. Precast undrained linings
should be installed and back grouted behind the tunnel boring machine as it
advances along the alignment to minimize the potential inflow of water behind
the cutter head.
11.170
In addition, the Contractor should initially adopt suitable water
control strategies as far as practicable while undertaking the excavation
works. The water control strategies are given as follow:
l
Probing
Ahead: As normal practice, the Contractor will undertake rigorous probing of
the ground ahead of tunnel excavation works to identify zones of significant
water inflow. The probe drilling results will be evaluated to determine
specific grouting requirements in line with the tunnel advance. In such zones
of significant water inflow that could occur as a result of discrete, permeable
features, the intent would be to reduce overall inflow by means of cut-off
grouting executed ahead of the tunnel advance.
l
Pre-grouting:
Where water inflow quantities are excessive, pre-grouting will be required to
reduce the water inflow into the tunnel. The pre-grouting will be achieved via
a systematic and carefully specified protocol of grouting.
l
In principle, the grout
pre-treatment would be designed on the basis of probe hole drilling ahead of
the tunnel face.
l
Post-grouting: Groundwater
drawdown will be most likely due to inflows of water into the tunnel that have
not been sufficiently controlled by the pre-grouting measures. Where this
occurs post grouting will be undertaken before the lining is cast. Whilst
unlikely to be required in significant measure, such a contingency should be
allowed for reduction in permeability of the tunnel surround (by grouting) to
limit inflow to acceptable levels.
Operation Phase
Tunnel Run-off and Drainage
11.173 Mitigation measures are required to mitigate tunnel run-off from track during the operational phase as illustrated in follow:
l
Track drainage channels discharge should pass through
oil/grit interceptors/chambers to remove oil, grease and sediment before being
pumped to the foul sewer / holding tank for further disposal.
l
The silt traps and oil interceptors should be cleaned and
maintained regularly.
l
Oily contents of the oil interceptors should be transferred
to an appropriate disposal facility, or to be collected for reuse, if possible.
Sewage Effluents
11.174 Connection of domestic sewage generated from the Project should be diverted to the foul sewer wherever possible. If public sewer system is not available, sewage tankering away services or on-site sewage treatment facilities should be provided to prevent direct discharge of sewage to the nearby storm system and all the discharge shall comply with the requirements stipulated in the TM-DSS.
11.175 For handling, treatment and disposal of other operational stage effluent, the practices outlined in ProPECC PN 5/93 should be adopted where applicable.
Shek Kong Stabling Sidings
(SSS)
11.176 All the maintenance areas within the SSS should be housed or covered to prevent generation of contaminated rainwater runoff. All wastewater generated from the maintenance and cleaning activities should be collected and diverted to oil interceptor or other appropriate treatment facilities for proper treatment so that it satisfies the requirements stipulated in the TM-DSS.
11.177
In case there is no pubic sewer available for the SSS during the
operational phase, all wastewater generated or collected in the SSS should be
tankered away for proper disposal to prevent direct
discharge of any wastewater to the nearby surface water system.
11.178 Oil interceptors should be regularly inspected and cleaned to avoid wash-out of oil during storm conditions. A bypass would be provided to avoid overload of the interceptor’s capacity.
11.179
All waste oils and fuels should
be collected and handled in compl
11.180
Disposal of chemical wastes
should be carried out in compl
Diversion of Watercourse
11.181
Diversion of a small section of Kam Tin River Nullah and
Evaluation
of Residual Impacts
11.182 With the full implementation of the recommended mitigation measures for the construction and operation phases of the proposed Project, no residual impacts on water quality are anticipated.
Environmental
Monitoring and Audit Requirements
Construction Phase
Land-based
Activities
11.183 Minimisation of water quality deterioration from land-based construction activities could be achieved through implementing adequate mitigation measures. It is recommended that regular site inspections should be undertaken to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented. No surface water monitoring is proposed.
Hydrogeological
Impact
11.184 Groundwater monitoring is recommended during the construction phase as one of the precautionary measures to minimize any unacceptable groundwater drawdown. Piezometers will be installed all along the alignment and at locations associated with particular sensitive receptors such as Mai Po area to obtain the baseline condition prior to the commencement of tunnelling works. Monitoring of the groundwater table will be undertaken during the progress of the tunneling works to ensure that the groundwater levels do not deviate significantly from the baseline data or recorded historical seasonal fluctuations. A detailed groundwater monitoring programme should be developed in detailed design stage to monitor both the proposed works and the impact of those works on the adjacent area.
Dredging
of Marine Sediment
11.185 The water quality impact generated from the proposed dredging works has been assessed to be
localized and minor.
No marine water quality monitoring is considered necessary.
Operation Phase
11.186 No adverse water quality impact was identified during the operational phase with proper implementation of the recommended mitigation measures. Operational phase water quality monitoring is considered not necessary.
Construction Phase
Land-based Activities
11.187 The key issue from the land-based construction activities would be the potential for release of sediment-laden water from surface works areas, open cut excavation and tunnelling works. Minimisation of water quality deterioration could be achieved through implementing adequate mitigation measures. Regular site inspections should be undertaken routinely to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented.
Hydrogeological Impact
11.188 Hydrogeological impact assessment has been conducted for the Project. Assessment results indicated that the proposed tunnelling works would cause no unacceptable impacts to the groundwater regime with proper implementation of the recommended mitigation measures.
Dredging of Marine Sediment
11.189
The water quality impact during
the proposed dredging works has been quantitatively assessed using the near
field sediment dispersion model. The model results indicated that
the water quality impact generated from the dredging works would be localized and minor and
would unlikely contribute any significant cumulative water quality impact from
other concurrent dredging activities being proposed in the same broad area,
i.e. the North Western Water Control Zone. Mitigation measures are proposed to ensure that no
unacceptable water quality impact would be resulted from the dredging works.
Operational Phase
11.190 The main operational impacts from the Project would come from tunnel seepage and effluent discharges from terminus, ventilation buildings and maintenance activities, which could also be minimized through implementing adequate mitigation measures.
11.191 The water quality impact from the proposed seawater cooling system has been quantitatively assessed using the Delft3D Model. The water quality impact from the proposed seawater cooling system on the harbour water was predicted to be localized and minor. No unacceptable water quality impact is anticipated from the operation.
11.192 Sewerage impact assessment has been conducted for the Project. Assessment results indicated that there would be no adverse impacts to the existing sewerage systems, and therefore mitigation measures would not be required.