Water quality impacts arising from the construction and operational phases of the Project were assessed in accordance with Condition 3.4.3 of the EIA Study Brief No. ESB-198/2008 and the specific sub-conditions of the Study Brief, which are referred to in the following sub-sections where appropriate.
This section presents the findings of the assessment of potential water quality impacts of the proposed Project in the vicinity of sensitive receivers, primarily in terms of the effects of dredging as well as other related works necessary to provide sufficient water depth for the KTCB and its Approach Channel, and is structured as follows:
Section 3.2: Provides discussions on existing environmental legislation, standards, guidelines and criteria;
Section 3.3: Provides a description on the existing environmental conditions;
Section 3.4: Identifies the water sensitive receivers for this Project;
Section 3.5: Describes the assessment methodology adopted for this EIA;
Section 3.6: Provides discussions on the identification of associated environmental impacts of this Project;
Section 3.7: Describes the prediction and evaluation of environmental impacts due to the Project;
Section 3.8: Proposes potential mitigation measures to address the identified impacts;
Section 3.9: Evaluates the residual impacts;
Section 3.10: Proposes appropriate environmental monitoring and auditing programme; and
Section 3.11: Summarises the key findings of this section.
Assessments have been conducted in accordance with the requirements of the Study Brief and Annexes 6 and 14 of the Technical Memorandum on the Environmental Impact Assessment Process. Water quality impacts in terms of Suspended Solids (SS), Dissolved Oxygen (DO), Heavy Metals, TBT, PCB, PAH, Chlorinated Pesticides, Ammoniacal Nitrogen (NH3-N), and Unionised Ammonia (UIA) have been assessed and their impacts due to the project works predicted. Based on the assessment, the parameters NH3-N and UIA were found to be of concern in certain parts of the Project Area, details of which are further elaborated in the following subsections.
Appropriate mitigation measures have been recommended to minimise the potential adverse impacts and to ensure the acceptability of any residual impact, i.e., after mitigation. For the concerned areas with high NH3-N and UIA values, further confirmatory trials have been proposed to ensure works within these areas do not contribute to adverse impacts to the receiving environment. In addition, cumulative impacts of concurrent projects have also been considered in the assessment in order to assess the overall impacts of the works on the surrounding environment.
3.2 Environmental Legislation, Standards, Guidelines and Criteria
The criteria for evaluating water quality impacts in this EIA Study include the following:
¡ Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM);
¡ Water Pollution Control Ordinance (WPCO);
¡ Water Supplies Department (WSD) Water Quality Criteria;
¡ Electrical and Mechanical Services Department (EMSD) Code of Practice for Water-cooled Air Conditioning Systems Part 2: Operation and Maintenance of Cooling Towers; and
¡ Other miscellaneous criteria (as described below)
3.2.1 Environmental Impact Assessment Ordinance (EIAO)
The EIAO-TM was issued by the EPD under Section 16 of the EIAO. It specifies the assessment method and criteria that have been followed in this EIA Study. Reference sections in the EIAO-TM providing details of the assessment criteria and guidelines that are relevant to the water quality impact assessment include the following:
¡ Annex 6: Criteria for Evaluating Water Pollution; and
¡ Annex 14: Guidelines for Assessment of Water Pollution.
3.2.2 Water Quality Objectives (WQOs)
The Water Pollution Control Ordinance (Cap. 358) provides the
statutory framework for the protection and control of water quality in
Table 3.1: Summary of Water Quality Objectives
|
Parameters |
|
Western Buffer WCZ |
|
|
Dissolved Oxygen (DO) (bottom) |
Not less than 2.0 mg L-1 for 90% of samples |
Not less than 2.0 mg L-1 for 90% of samples |
Not less than 2.0 mg L-1 for 90% of samples |
|
Depth-averaged DO |
Not less than 4.0 mg L-1
for 90% of samples |
Not less than 4.0 mg L-1 for 90% of samples (Not less than 5.0 mgL-1 for 90% of samples for fish culture subzones) |
Not less than 4.0 mg L-1 for 90% of samples (Not less than 5.0 mgL-1 for 90% of samples for fish culture subzones) |
|
pH |
To be in the range of 6.5 - 8.5, change due to waste discharge not to exceed 0.2 |
To be in the range of 6.5 - 8.5, change due to waste discharge not to exceed 0.2 |
To be in the range of 6.5 - 8.5, change due to waste discharge not to exceed 0.2 |
|
Salinity |
Change due to waste discharge not to exceed 10% of natural ambient level |
Change due to waste discharge not to exceed 10% of natural ambient level |
Change due to waste discharge not to exceed 10% of natural ambient level |
|
Unionised ammonia |
Annual mean not to exceed 0.021 mg L-1 |
Annual mean not to exceed 0.021 mg L-1 |
Annual mean not to exceed 0.021 mg L-1 |
|
Temperature |
Change due to waste discharge not to exceed 2oC |
Change due to waste discharge not to exceed 2oC |
Change due to waste discharge not to exceed 2oC |
|
Suspended solids |
Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities |
Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities |
Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities |
|
Nutrients |
Annual mean depth-averaged total inorganic nitrogen not to exceed 0.4 mg L-1 |
Annual mean depth-averaged total inorganic nitrogen not to exceed 0.4 mg L-1 |
Annual mean depth-averaged total inorganic nitrogen not to exceed 0.1 mg L-1 |
|
Toxicants |
Not to be present at the levels producing significant toxic effect |
Not to be present at the levels producing significant toxic effect |
Not to be present at the levels producing significant toxic effect |
Source: Statement of Water Quality Objectives.
3.2.3 Water Supplies Department (WSD) Water Quality Criteria
Besides the WQOs set under the WPCO, WSD has specified a set of objectives for water quality at flushing water intakes as shown in Table 3.2.
Table 3.2: WSD’s Water Quality Criteria for Flushing Water at Sea Water Intakes
|
Parameter (in mg L-1 unless otherwise stated) |
Target Limit |
|
Colour (HU) |
< 20 |
|
Turbidity (NTU) |
< 10 |
|
Threshold Odour Number (odour unit) |
< 100 |
|
Ammonia Nitrogen (NH3-N) |
< 1 |
|
Suspended Solids (SS) |
< 10 |
|
Dissolved Oxygen (DO) |
> 2 |
|
5-day Biochemical Oxygen Demand (BOD5) |
< 10 |
|
Synthetic Detergents |
< 5 |
|
E. coli (no. per 100 mL) |
< 20,000 |
Note:
(1) This criteria has been taken as reference when assessing water quality at flushing water intakes. Note that not all parameters were taken for the assessment.
(2) The WSD criteria has been used as it more stringent than EMSD Code of Practice for Water-cooled Air Conditioning System in terms of suspended solids
(3) Insignificant impact due to the presence of E.coli is anticipated due to the fact that E.coli is not detected in sediment samples taken for the Project.
3.2.4 Water Quality Criteria for Cooling Water Intakes
The Mass Transit Railway Corporation (MTRC) stipulates a
limit on SS at its cooling water intakes. For the MTRC South intake the SS limit
is 40 mg L-1. According to the recently approved EIA for the
Hong Kong Convention and Exhibition Centre Atrium Link Extension (EIA 120/2006)
there are no other criteria for cooling water intakes within the area of
influence of this project, however reference
should be made to Section 3.2.5 in
connection with the
3.2.5 Water Quality Criteria for Water-Cooled Air Conditioning Systems
EMSD’s Code of
Practice for Water-Cooled Air Conditioning Systems “Part 2: Operational and
Maintenance of Cooling Tower”, sets a series of standards associated with
intake water. The pertinent standard is
SS for which the criterion is <180 mg L-1.
This criterion could be applied to the
3.2.6 Suspended Solids Criterion for Benthic Organisms
It is acknowledged that benthic organisms, including corals, may suffer damage to their respiratory function as a result of sediment deposition blocking the respiratory and feeding organs of these organisms. According to Hawker and Connell[1], a sedimentation rate higher than 0.1 kg m-2 per day would introduce moderate to severe impact upon corals. As such, this limit was adopted as the assessment criterion for protecting the marine ecological sensitive receivers in this Study. While there are no established legislative criteria for water quality for corals, an elevation criterion of SS levels less than 30% of ambient baseline conditions1 has been adopted as the critical value, above which impacts to the habitat may occur. This criterion is based on that given in a previously approved EIA[2] for assessing SS impacts on corals.
3.2.7 Suspended Solids Criterion for Fish Culture Zones
In the fish culture zones the WQO for SS applies, i.e.,
elevation of SS should be less than 30% of ambient baseline conditions. In
addition, it is noted that the criterion for maximum SS concentration as recommended by
AFCD at the fish culture zones,
based on international marine water quality guidelines for the protection of
ecosystems (based on half of
the “no observable effect concentrations”), is 50 mg L-1
(CityU’s CCPC 2001).
3.2.8
Unionised
Ammonia and Ammonia-nitrogen Criteria for Fisheries and Marine Ecology in
The unionised portion of total ammonia is an important
environmental parameter that may cause toxicity to fish and marine biota and this relates to pH and temperature.
The guidelines for protection of marine ecology follow the Water Quality
Objective (WQO) under the Water Pollution Control Ordinance (Cap. 358). The WQO
for unionised ammonia (UIA) is 0.021 mg L-1 and this is the prevailing requirement to
be met. In addition to the WQO for unionised ammonia, the lethal
concentrations of ammonia in the form
of ammoniacal-nitrogen (NH3-N)
on fisheries and marine ecology may
also be derived based on the
3.2.9 Sediment Quality
Marine disposal of dredged materials is controlled under the Dumping at Sea Ordinance (DASO). The requirements for marine disposal of sediment are specified in ETWB TCW No. 34/2002: Management of Dredged/Excavated Sediment. Dredged sediment is classified according to a set of regulatory guidelines with sediment quality criteria, which include organic pollutants and other toxic substances. Details on marine dredged sediment quality are presented in Chapter 4.
3.1 Description of the Environment
3.1.1 Marine Water Quality Monitored by EPD
Marine water quality monitoring data routinely collected by EPD was used to establish the baseline conditions for this Project. A summary of water quality data for the selected and relevant EPD monitoring stations is presented in Table 3.3 and Table 3.4 for the Victoria Harbour (VM6, 8, 12, 14 and 15), Western Buffer (WM1 and 4) and Southern (SM3, 5 and 9) WCZs. Locations of these monitoring stations are shown in Figure 3.1.
Table 3.3: Marine Water Quality in Victoria Harbour Water Control Zone at Selected Stations in 2008
|
Parameter |
Rambler Channel |
|
|
|
|
|||||||
|
|
VM12 |
VM14 |
VM8 |
VM6 |
VM15 |
|
||||||
|
Temperature (°C) |
22.7 (14.9 –
27.7) |
23.0 (14.8 -
28.5) |
22.6 (14.7 -
27.6) |
23.5 (16.3
-27.2) |
23.6 (16.5 -
27.2) |
||||||
|
Salinity |
30.8 (26.8 –
32.9) |
29.6 (22.5 –
32.7) |
31.1 (27.1 -
33.2) |
30.9 (27.1 –
32.7) |
30.6 (24.0 –
32.8) |
||||||
|
Dissolved
Oxygen (DO) (mg L-1) |
Depth
average |
5.4
(3.2 – 8.0) |
5.6
(3.9 – 7.9) |
5.8
(3.9 – 7.7) |
5.1
(2.8 -7.1) |
5.2
(2.9 – 6.3) |
|||||
|
Bottom |
5.4
(2.8 – 8.0) |
5.6
(3.4 – 8.0) |
5.7
(3.5-8.1) |
4.8
(2.5 – 6.6) |
4.9
(2.3 – 6.2) |
||||||
|
Suspended
Solids (SS) (mg L-1) |
10.2 (6.2 –
16.5) |
5.7 (3.0 –
8.2) |
5.0 (2.7 –
8.6) |
5.3 (2.7 –
7.3) |
6.1 (2.8 –
9.2) |
||||||
|
Unionised
Ammonia (UIA) (mg L-1) |
0.007 (0.003
- 0.009) |
0.006 (0.002
- 0.009) |
0.007 (0.001
- 0.013) |
0.007 (0.002
- 0.011) |
0.008 (0.003
- 0.014) |
||||||
|
Total Inorganic Nitrogen (TIN) (mg L-1) |
0.40 (0.27 -
0.53) |
0.46 (0.30 - 0.80) |
0.35 (0.22 – 0.51) |
0.38 (0.21-0.62) |
0.42 (0.25 -
0.87) |
||||||
Note:
1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: surface, mid-depth, bottom.
2. Data enclosed in brackets indicate the ranges.
(Source: Adopted from EPD Marine Water Quality
Table 3.4: Marine Water Quality in Southern and Western Buffer Water Control Zones at Selected Stations in 2008
|
Parameter |
|
Western Buffer WCZ |
||||
|
East Lamma Channel SM3 |
West Lamma Channel SM5 |
West Lamma Channel SM9 |
WM1 |
Tsing Yi |
||
|
Temperature (°C) |
22.5 (14.2 – 26.8) |
23.4 (14.2 – 28.9) |
22.8 (14.2 – 27.2) |
22.3 (14.7 -27.1) |
22.6 (14.8 – 27.3) |
|
|
Salinity |
31.9 (28.2 – 33.7) |
30.3 (20.8 – 33.7) |
29.8 (19.5-32.9) |
32.0 (29.9 – 33.6) |
31.2 (29.3 – 33.0) |
|
|
Dissolved Oxygen (DO) (mg L-1) |
Depth average |
6.2 (3.7 – 9.4) |
6.9 (5.2 – 9.8) |
6.3 (4.3 – 8.8) |
6.1 (2.7 – 9.1) |
5.7 (3.4 – 8.2) |
|
Bottom |
5.9 (2.8 – 9.9) |
6.2 (3.2 – 9.7) |
6.1 (3.7 – 8.7) |
5.9 (2.1 -9.3) |
5.6 (2.7 -8.3) |
|
|
Suspended Solids (SS) (mg L-1) |
4.8 (2.3 – 11.0) |
6.2 (1.9 – 17.0) |
7.6 (2.6 – 16.7) |
5.5 (1.7 – 13.1) |
6.4 (3.0 – 12.1) |
|
|
Unionised Ammonia (UIA) (mg L-1) |
0.002 (<0.001 – 0.005) |
0.002 (<0.001 – 0.006) |
0.006 (0.001 – 0.020) |
0.002 (<0.001 – 0.004) |
0.004 (0.002 – 0.008) |
|
|
Total Inorganic Nitrogen (TIN)
(mg L-1) |
0.18 (0.03 – 0.42) |
0.24 (0.04 – 0.94) |
0.37 (0.11 – 1.15) |
0.18 (0.06 – 0.29) |
0.32 (0.17 – 0.47) |
|
Note:
1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: surface, mid-depth, bottom.
2. Data enclosed in brackets indicate the ranges.
(Source: Adopted from EPD Marine Water Quality
As reported in the EPD’s “Marine Water Quality in Hong Kong 2008”, the Victoria Harbour WCZ achieved an 80% compliance with the WQOs in 2008, which was lower than that in 2007. The decrease in compliance was mainly a reflection of an increase of TIN levels in the harbour.
In contrast, the Western Buffer WCZ achieved 92% compliance
with the WQOs in 2008, higher than that in 2007 (83%), whilst the
3.1.2 Sediment Quality
Results and discussions on the sediment quality analysis from
the marine site investigation (SI) works for the Project area are detailed in Chapter 4. A
summary of sediment quality data for the selected EPD monitoring stations in
the vicinity of the Rambler Channel (VS9), Tsing Yi (South) (WS1) and
During a recent sampling exercise, sediment samples were collected and analysed for E.coli (Appendix 11.1). The sampling locations were near the Tsing Yi Submarine Sewage Outfall (Figure 3.6), in the Northern Fairway and Western Fairway. The results indicated that the E.coli concentrations are below detection limit (< 3 MPN/g) for all locations. Therefore, the dredging activities of the Project are not expected to induce any adverse impact of E.coli on the water bodies or at the gazetted beaches within the Project’s area of influence.
Table 3.5: Bottom Sediment Quality at Selected Stations in 2004 – 2008
|
Contaminants |
Rambler Channel VS9 |
Tsing Yi (South) WS1 |
WS2 |
Sediment Quality Criteria |
|
|
LCEL |
UCEL |
||||
|
Cadmium (Cd) |
0.2 (<0.1 – 0.7) |
0.1 (<0.1 – 0.2) |
<0.1 (<0.1 – <0.1) |
1.5 |
4 |
|
Chromium (Cr) |
37 (27 – 76) |
33 (17 - 41) |
36 (32 – 40) |
80 |
160 |
|
Copper (Cu) |
67 (8 – 230) |
47 (13 - 68) |
26 (22 - 29) |
65 |
110 |
|
Mercury (Hg) |
0.11 (<0.05 – 0.23) |
0.13 (0.06 – 0.160) |
0.09 (<0.05 – 0.14) |
0.5 |
1 |
|
Nickel (Ni) |
24 (19 – 43) |
19 (9 – 24) |
24 (21 – 26) |
40 |
40 |
|
Lead (Pb) |
35 (21 – 81) |
39 (24 - 53) |
38 (32 – 43) |
75 |
110 |
|
Silver (Ag) |
1.1 (<0.2 – 6.3) |
1.0 (0.2 – 1.7) |
0.4 (0.3 – 0.5) |
1 |
2 |
|
Zinc (Zn) |
100 (66 – 210) |
110 (53 – 130) |
110 (95 – 120) |
200 |
270 |
|
Metalloid
(mg/kg dry weight) |
|||||
|
Arsenic (As) |
5 (3.0 – 8.5) |
7.3 (3.8 – 9.4) |
8.7 (6.9 – 10.0) |
12 |
42 |
|
Organic-PAHs
(µg/kg dry weight) |
|||||
|
PAHs (Low Molecular Weight) |
91 (90 – 100) |
94 (90 – 100) |
91 (90 – 94) |
550 |
3160 |
|
PAHs (High Molecular Weight) |
58 (18 – 180) |
160 (68 – 420) |
59 (35 – 120) |
1700 |
9600 |
|
Organic-non-PAHs
(µg/kg dry weight) |
|||||
|
Total PCBs |
19 (18 – 23) |
18 (18 – 18) |
18 (18 – 18) |
23 |
180 |
Based on EPD’s monitoring data in
2004 - 2008, the sediment collected at the Rambler Channel VS9 are contaminated
with heavy metals which exceeded the criteria for copper, nickel, lead, silver
and zinc. However, the sediment quality was relatively better for Station WS2
located to the west of
In order to evaluate the potential water quality impacts from the Project, water quality sensitive receivers (WSRs) near the Project area were identified, which include:
¡ Gazetted Beaches;
¡ Corals;
¡ Fish Culture Zones;
¡ WSD
¡ Cooling Water Intakes.
Water quality and ecological sensitive receivers identified near the Project area are shown in Figure 3.1. These WSRs have been included in the water quality impact assessment as they may be potentially affected by the proposed dredging works (Condition 3.4.3.2 of the Study Brief).
The assessment methodology was undertaken in accordance with the requirement of Condition 3.4.3.4 of the Study Brief.
3.3.1 Hydrodynamic and Water Quality Models
3.3.1.1 Set-up of Hydrodynamic Model
Computer modelling was employed to predict the potential impact on water quality for different tidal conditions. The hydrodynamic and water quality models were developed by Delft Hydraulics, namely Delft3D-FLOW and Delft3D-WAQ respectively.
In this study, the basis for modelling of the harbour waters
was the existing, validated Western Harbour Model, with computational grid
layout presented in Figure 3.2.
This model covers the relevant parts of the
3.3.1.2 Coastlines and Bathymetry
To ensure that an accurate coastline profile was used in the modelling, the existing model was updated with the most recently available information of proposed development from sources such as designated projects under the EIAO (Figure 3.3b). The bathymetry set up was also updated based on the latest Admiralty Chart.
3.3.1.3 Simulation Periods
The simulated periods covered a complete spring-neap tidal cycle and the actual simulation period was preceded by a spin-up period. The simulation periods are specified below:
|
Dry season: |
9 February 12:00 – 24 February 12:00 |
|
Wet season: |
26 July 04:00 – 10 August 04:00 |
In order to determine if the spin-up period was sufficient
for the simulation, the model was run for one more spring-neap cycle. It was
determined that the results of the two successive model runs were similar, and
as such, a spin-up period of 15 days was
adopted for this Project.
3.3.1.4 Initial and Boundary Conditions for Water Quality Models
A spin-up period of 15 days for the sediment plume modelling described below was included. This spin-up period is considered sufficient since comparable results between two consecutive spring-neap cycle model runs were obtained. The boundary conditions were set to zero as the excess suspended solids concentrations were modelled.
3.3.1.5 Current flow
From the results of hydrodynamic model, the current flow
patterns for dry season and wet season are obtained and are shown in Figure 3.4a
and Figure 3.4b
respectively.
3.3.1.6
The
Mixing Zone Criteria
Section 1.3.1 of the
Annex 6 of the Technical Memorandum (TM) under the EIAO provides guidelines on the determination of mixing zones. According to the TM it is not always necessary to meet all water
quality criteria in all areas and the Authority under the WPCO may allow for
the receiving water quality not to meet water quality criteria in particular circumstances.
The mixing zone
defined in this project is the region of marine water where initial dilution of
a pollution input takes place and where water quality criteria will be
exceeded. These areas are subject to greater impacts from the project activity. The mixing zones for this Project are
discussed in Section 3.7.1.6.
3.3.2 Sediment Plume Modelling
3.3.2.1
General
Water quality impacts arising from dredging activities associated with the proposed Project that would disturb the marine bottom sediment include the release of SS into the water column. The impact of sediment plume dispersion during the marine works was simulated using a three-dimensional Delft3D-WAQ Model. The WAQ model simulated suspended solids (SS, in mg L-1), optionally subdivided over different fractions representing different sediment sources. The simulated SS represented the Project related discharges only. The calculated concentrations were interpreted as excess concentrations on top of the background concentrations.
The Delft3D-WAQ model takes into account the sedimentation process by means of a settling velocity, while erosion of bed sediment, causing resuspension of sediment, is governed by a function of the bed shear stress. The parameters adopted in the present study are summarised in Table 3.6.
Table 3.6: Summary of Parameters for Sediment Plume Model (Delft3D-WAQ)
|
Sediment Plume Model Parameters[3] |
|
|
Settling velocity |
0.5mm/s |
|
Critical shear stress for deposition |
0.2N/m2 |
|
Critical shear stress for erosion |
0.3N/m2 |
|
Minimum depth where deposition allowed |
0.1m |
|
Resuspension rate |
30g/m2/d |
For this Project, the impacts in terms of dissolved oxygen
(DO) depletion and total inorganic nitrogen (TIN) were not explicitly modelled, but estimated on the basis of the
calculated sediment concentrations. This leads to an estimated increase
relative to the background of the concentrations of this parameter, dependent
on the quality of the released sediment.
For NH3-N (a component of TIN) and UIA, it has been found from elutriate tests of collected sediment samples for the purpose of this Study (as discussed in Section 3.7) that some high values of ammoniacal-nitrogen (NH3-N) were found at some of the sampling stations. As these measured values implied that high UIA values (also dependent on pH, temperature and salinity of seawater) would also be expected, a more direct approach for predicting the potential UIA values resulting from the dredging works been used to assess the potential UIA impacts as discussed later in this section. However, for the purposes of indicating the background levels of TIN and UIA of the waters within the Study Area, the established methodology for estimating these ambient conditions has been adopted.
For TIN, it was
assumed that the Kjedahl-N (KN)
content of the sediment is transformed to TIN in water. For DO, it was assumed that the entire sediment
oxygen demand (SOD) content of the sediment is transformed to give a decrease in DO concentration. This can be expressed
as follows:
SOD
where
|
TIN |
concentration
of total inorganic nitrogen
(mgN/L) |
|
SS |
concentration
of suspended solids (mg L-1) |
|
CSS,Kj-N |
concentration
of Kjedahl-N in suspended matter (gN/gSS) |
|
DO |
concentration
of dissolved oxygen (mg L-1) |
|
CSS,SOD |
concentration
of SOD in suspended matter (gO/gSS) |
This approach adopts a set of the worst case assumptions. Any removal of pollutants from the water phase along with the sedimentation of SS and any replenishment of DO from the atmosphere is neglected.
The values used for the DO assessment, as well as for estimating background TIN values, are based on EPD’s routine marine sediment quality monitoring data recorded at VS9 in 2004 - 2008 near the dredging area and are summarised in Table 3.7. The DO depletion calculation was performed using the highest level of SOD measured in the sediment samples collected during the marine SI for conservative predictions. The highest SOD level was 3620 mgO2/kg.
Table 3.7: Sediment Quality near the Dredging Area
|
Parameters |
Dry season |
Wet season |
|
CSS,Kj-N |
296E-6 |
314E-6 |
For the estimation of potential UIA values for this
EIA,a more direct approach was used to calculate UIA from elutriate
test results, where the ammoniacal nitrogen values were first analyzed, and
then the following equations[4]
used to calculate UIA taking into account of the in-situ temperature, salinity
and pH of the seawater:
For salinity > 18 ppt
UIA = NH3-N x F
F = 1 /
(10pKas – pH + 1)
pKas = pKaf +
I x (0.1552 – 0.000314 x T)
pKaf =
0.09018 + 2729.92 / (T + 273.15)
I =
19.9273 x S / (1000 – 1.005109 x S)
Where,
S – Salinity (ppt)
T – Temperature (°C)
pH – Power of Hydrogen
F – Fraction of Unionized Ammonia (UIA)
NH3-N – Ammoniacal Nitrogen
UIA – Unionized Ammonia
The above
approach is deemed more appropriate for this Project as the prediction for the
potential UIA impacts would then tend to be more representative of the actual
conditions of the project site.
3.3.2.2 Concurrent Projects
Assessment of cumulative impacts due to other concurrent projects was undertaken according to the requirements of Condition 3.4.3.5 (x) of the Study Brief.
In order to assess the cumulative impacts of this Project on the receiving environment, the impacts of other dredging projects which may be implemented concurrently were also considered in the assessment. To establish the modelling scenarios it was therefore important to consider the overlap of the construction programmes for this Project and the concurrent projects.
The dredging operations for this Project are tentatively scheduled to take place between mid 2011 and 2013, and details of the concurrent projects have been identified in Section 2.8.
3.3.2.3 Modelling Scenarios
Scenarios representing the likely “worst case scenarios” for dredging operations were developed. A total of seven scenarios were derived taking into consideration all the WSRs and the potential impacts of dredging on them, and noting the large areal extent of the Project areas shown in Figure 3.5a. Scenarios 1 to 5 represent those using grab dredgers working in different parts of the Project area, Scenario 6 represents the use of two grab dredgers and one cutter suction dredger, and Scenario 7 represents the scenario for cumulative impacts, i.e., looking at the combined impacts of this Project and the concurrent projects that were previously identified. The above scenarios are described below:
Scenario 1 – Dredging at Source ID ‘A’, ‘C’ and ‘D’
Scenario 1 assumes three grab dredgers operating simultaneously within the Project area from 2011 to 2013, with the locations of the dredgers as shown in Figure 3.5b.
Scenario 2 – Dredging at Source ID ‘A’, ‘C’ and ‘E’
Scenario 2 assumes three grab dredgers operating simultaneously within the Project area from 2011 to 2013, with the locations of the dredgers as shown in Figure 3.5c.
Scenario 3 – Dredging at Source ID ‘C’, ‘D’ and ‘E’
Scenario 3 assumes three grab dredgers operating
simultaneously within the Project area from 2011 to 2013, with the locations of
the dredgers as shown in Figure 3.5d. Scenario 3 was developed to assess the potential impacts on gazetted beaches along
Tsuen Wan and
Scenario 4 – Dredging at Source ID ‘A’, ‘B’ and ‘D’
Scenario 4 assumes three grab dredgers operating simultaneously within the Project area from 2011 to 2013, with the locations of the dredgers as shown in Figure 3.5e.
Scenario 5 – Dredging at Source ID ‘A’, ‘B’ and ‘C’
Scenario 5 assumes three grab dredgers operating simultaneously within the Project area from 2011 to 2013, with the locations of the dredgers as shown in Figure 3.5f. Scenario 5 represents the worst case for the WSRs located at Tsing Yi and Tsuen Wan.
Scenario 6 – Dredging with Cutter Suction Dredger at Source ID ‘A’
Under this scenario, one cutter suction dredger (CSD) will be used for the removal of some hard material (approximately 92000 m3) in the Rambler Channel near Container Terminal No. 5, located northeast of the Project area, along with two grab dredgers elsewhere within the Project area.
Scenario 6 assumes the three dredgers to be operating simultaneously from 2011 to 2013, with the CSD located at Source ID ‘A’, and the two grab dredgers at Source ID ‘C’ and ‘E’, respectively, as shown in Figure 3.5g. The location of the other two dredgers in this scenario was decided based on the suspended solids results obtained from Scenarios 1 to 5, which suggested that grab dredgers located at Source ID ‘C’ and ‘E’ tend to produce the highest levels of suspended solid at the WSRs near Tsing Yi and Tsuen Wan.
Scenario 7 – Dredging at Concurrent Project Areas
Scenario 7 simulates the impact from concurrent projects
operating in the selected year of 2012 and Scenario 3. Although Table
2.5 indicated concurrent activities between mid 2011 to mid 2013, year 2012
was selected for this scenario because 2012 was considered to represent the
worst year, in terms of the year with the highest sediment loss rates for the
majority of the concurrent projects. In
addition, the SS impacts predicted
under Scenario 3 on the gazetted beaches along Tsuen Wan and
The locations of the sediment sources arising from the concurrent projects are shown in Figure 3.5h. The following marine works have been incorporated:
(i)
Dredging works in Wan Chai North and
(ii)
Installation
of Submarine Gas Pipelines and Associated Facilities from To Kwa Wan to North
Point for
(iii) Shatin to Central Link (Source ID: SC1, SC2)
(iv)
Marine works north of
(v) Marine works of the project ‘Proposed Dredging Works of the Contaminated Mud Pits in South of Brothers’ (Source ID: SB1, SB2)
(vi)
Dredging works near Tuen Mun and
(vii)
Dredging works east of
(viii)
Dredging works east of
The sediment source locations (Source ID: W1, W2, W3, W4) were based on the spill locations used in the Wan Chai Development Phase II and Central – Wan Chai Bypass EIA as part of their construction phase modelling.
The sediment source locations (Source ID: T1, T2, T3, T4, T5, B1, B2, B3, B4, B5, B6, L1, L2, L3, S1, S2, SB1, SB2) were based on the marine plant locations used in the EIA for HZMB as part of their concurrent projects assessment.
Alternative Scenario
The “Alternative Scenario” is a hypothetical scenario that assumes five grab dredgers operating simultaneously at Source ID: A, B, C, D and E (shown in Figure A3.2.1 in Appendix 3.2). This scenario has been assessed for comparison purposes only, as the scenario is actually considered not practical due to the busy marine traffic within the Project area. Details of this scenario are provided in Appendix 3.2.
The seven main modelling scenarios for dredging operations are summarised in Table 3.8 and Table 3.9 below.
Table 3.8: Summary of Assumptions for Scenarios 1 to 6
|
Scenario |
Locations |
Nos. of Dredgers |
Dredging Rate m3/day/dredger |
Sediment Loss Rate kg/s |
Dredging Period |
|
1 |
Source ID A, C, D |
3 grab dredgers |
4000*1 |
1.44 |
2011 to 2013 |
|
2 |
Source ID A, C, E |
3 grab dredgers |
4000*1 |
1.44 |
2011 to 2013 |
|
3 |
Source ID C, D, E |
3 grab dredgers |
4000*1 |
1.44 |
2011 to 2013 |
|
4 |
Source ID A, B, D |
3 grab dredgers |
4000*1 |
1.44 |
2011 to 2013 |
|
5 |
Source ID A, B, C |
3 grab dredgers |
4000*1 |
1.44 |
2011 to 2013 |
|
6 |
Source ID A, C, E |
2 grab dredgers and one CSD |
4000*1 for grab dredger, 700 m3/30 mins for CSD (8400 m3/day) *2 |
1.44 for grab dredger, 2.72 for CSD |
2011 to 2013 |
* Detailed description of sediment release rates in Section
3.5.2.4 refers. Closed grab dredgers
were assumed.
*1 in-situ
volume
*2
the CSD operates for 30 minutes over a 1-hr period based on 12 hours (7:00 –
19:00) operation.
Table 3.9: Summary of Assumptions
for Scenario 7
|
Project |
Source ID |
Activity (Equipment) |
Number of Dredgers |
Daily Working Hours |
Working Rate1 |
Cycle Time |
Duration of Each Operation (minutes) |
Sediment Loss Rate kg/s |
|
The current project (Scenario 3 in Table 3.8) |
C, D, E |
Dredging (Grab Dredger) |
3 |
24 |
4000 |
continuous |
- |
1.44 |
|
|
B1 |
Filling (Dump Barge) |
4 |
16 |
769 |
120 minutes2 |
5 |
60.9 |
|
|
B2 |
Filling (Pelican Barge) |
7 |
16 |
769 |
continuous2 |
- |
1.2 |
|
|
B3 |
Dredging (Grab Dredger) |
2 |
16 |
6000 |
continuous |
- |
4.2 |
|
|
B4 |
Filling (Dump Barge) |
6 |
16 |
769 |
60 minutes2 |
5 |
60.9 |
|
|
B5 |
Filling (Pelican Barge) |
14 |
16 |
769 |
continuous |
- |
1.6 |
|
|
B6 |
Dredging (Grab Dredger) |
4 |
16 |
6000 |
continuous |
- |
8.3 |
|
|
L1 |
Filling (Dump Barge) |
5 |
16 |
769 |
90 minutes2 |
5 |
12.2 |
|
L2 |
Filling (Pelican Barge) |
9 |
16 |
769 |
continuous2 |
- |
0.2 |
|
|
L3 |
Dredging (Grab Dredger) |
3 |
16 |
6000 |
continuous |
- |
6.3 |
|
|
South of Brothers3 |
SB1 |
Filling (Barge)4,5 |
33.3 |
24 |
800 |
40 minutes |
5 |
60 |
|
SB2 |
Dredging (Grab Dredger) |
2 |
24 |
7143 |
continuous |
- |
2.8 |
|
|
East of Sha Chau CMP3 |
S1 |
Dredging (Grab Dredger) |
2 |
24 |
7143 |
continuous |
- |
2.8 |
|
S2 |
Capping (Barge)5 |
33.3 |
24 |
800 |
40 minutes |
5 |
60 |
|
|
Tuen Mun Chek Lap Kok Link |
T1 |
Dredging (Grab Dredger) |
1 |
16 |
6000 |
continuous |
- |
2.1 |
|
T2 |
Filling (Dump Barge) |
6 |
16 |
769 |
60 minutes2 |
5 |
33.5 |
|
|
T3 |
Filling (Dump Barge) |
1 |
16 |
769 |
8 hours |
5 |
33.5 |
|
|
T4 |
Filling (Pelican Barge) |
2 |
16 |
769 |
4 hours |
45 |
0.7 |
|
|
T5 |
Filling (Dump Barge) |
3 |
16 |
769 |
3 hours |
5 |
60.9 |
|
|
Wan Chai Development Phase II |
W1 |
Dredging (grab) |
1 |
16 |
6000 |
continuous |
- |
0.526 |
|
W2 |
Dredging (grab) |
1 |
16 |
6000 |
continuous |
- |
0.526 |
|
|
W3 |
Dredging (grab) |
1 |
16 |
6000 |
continuous |
- |
0.526 |
|
|
W4 |
Dredging (grab) |
1 |
16 |
1500 |
continuous |
- |
0.136 |
|
|
Shatin-Central Link |
SC1 |
Dredging (grab) |
2 |
16 |
3000 |
continuous |
- |
2.08 |
|
SC2 |
Dredging (grab) |
1 |
12 |
500 |
continuous |
- |
0.23 |
|
|
Towngas Underwater Pipeline |
TO1 |
Dredging (grab) |
1 |
16 |
4000 |
continuous |
- |
1.39 |
Notes:
1. The working rate is per grab/TSHD (m3/day) or per barge/event (m3).
2. Higher frequencies have been assumed compared to the HZMB approved EIA as a conservative approach.
3. Activities in South of Brothers and East of Sha Chau Contaminated Mud Pits were according to CEDD-MFC information
4. No backfilling activities by TSHD are anticipated according to CEDD-MFC information.
5. Figures in New Contaminated Mud Marine Disposal Facility at Airport East / East Sha Chau Area (EIA - 106/2005) refers.
6. Based on values presented in Table 5.10 of Dredging Works for Proposed Cruise Terminal at Kai Tak approved EIA report
In view of the busy marine traffic in the Rambler Channel and Northern Fairway, it is not practical to assume more than three dredgers working simultaneously within the combined areas. Similarly, a maximum of two dredgers has been assumed to be operating within the Western Fairway at any one time, as heavy marine traffic would make it impractical to operate more than two dredgers simultaneously within the Western Fairway area. The sediment loss rates of the dredgers for the dredging scenarios 1 to 6 within the Project area as shown in Table 3.8 are further discussed in Section 3.5.2.4.
3.3.2.4
Sediment
Loss Rates
The loss rates have been provided according to the requirement of Condition 3.4.3.5 (vi) of the Study Brief.
In the modelling scenarios it was assumed that grab dredger (GD) with a closed grab of 8 m3 would be used on a continuous basis (i.e. 7 days per week, 24 hours per day), on the assumption of a maximum daily production rate of 4000 m3 (in-situ volume) per dredger. With respect to the rate of sediment loss during dredging, the Contaminated Spoil Management Study[5] concluded that losses from closed GDs were estimated to be in the order of 11 to 20 kg m-3 of mud removed. Taking the upper value of 20 kg m-3 to be conservative, the loss rate is then calculated to be 0.93 kg s-1 per dredger. It is noted that, however, there are areas within the Rambler Channel where debris or large boulders could hinder proper closing of the grab, which could result in higher loss rates. In view of this, and to be conservative in the assessment, a higher loss rate of 1.44 kg s-1 was used for the Project. This loss rate has also been applied in a previously approved EIA report[6] under similar circumstances. The sediment losses were assumed to be evenly distributed over the entire water column.
The CSD will only be used for the removal of hard materials under the seabed near Container Terminal Number 5 as identified earlier. Based on the findings of the 2000 Contaminated Spoil Management Study as well as input from the Engineering Design Team for this Study, a maximum dredging rate of 700 m3 (in-situ volume) in 30 minutes over 1 hr period from 7:00 to 19:00 (8400 m3/day) and a loss rate of 7 kg/ m3 (or 2.72 kg s-1) for the CSD operation have been assumed. It should be noted that a CSD could operate at a much higher dredging rate. The value of 700 m3 in 30 minutes over 1 hr period adopted here is specified for the subject Project only. The sediment losses during the operation of the CSD (via suction of sediment by pump action during dredging) are assumed to take place in the lowest layer of the model in view of the hard material located below the existing seabed.
3.3.2.5
Contaminant Release during Dredging
The loss of sediment to suspension during dredging may have chemical effects on the receiving waters, due to the possibility of the sediment containing hitherto bound organic and chemical pollutants. As part of the marine site investigation works for this Project, laboratory testing of sediment samples were undertaken, in accordance with the requirement of Condition 3.4.3.5 (viii) of the Study Brief. A full description of the sediment quality testing and the classification of the sediment according to the levels of contaminants found i.e. category L, M and H are detailed in Chapter 4, with recommendations of appropriate mitigation measures and disposal options provided according to the requirement of Condition 3.4.3.5 (xii) of the Study Brief.
Elutriate tests were performed on sediment samples to simulate and quantify the degree of mobilization of various contaminants, such as metals and trace organic contaminants, into the water column during dredging. An indication of the likelihood of release of heavy metals and organics from the sediment during dredging can be deduced from the results of these tests. If the contaminant levels are higher in the elutriates compared to the blanks (i.e. marine water from the same site), it may be surmised that the contaminants could be released into the marine waters during dredging activities. As there is no existing legislative standard or guideline for individual heavy metal content in marine waters, the UK’s Water Quality Standards for Coastal Surface Water, the Australian and New Zealand Guidelines for Fresh and Marine Waters, Environmental Economic and Best Practical Environmental Option (BPEO) Assessment Principals for Integrated Pollution Control, and United States Environmental Protection Agency (USEPA’s) Salt Water Criterion have been adopted as the assessment criteria for this aspect.
Where there was an exceedance
of the results from the elutriate tests compared to the assessment
criteria, conservative tracers were
then introduced into the model to estimate the dilution that could be generated
by the tidal flows and the size of the mixing zone
of the contaminants. In such cases the release rate of tracers followed the sediment release rate discussed in Section 3.5.2.4 at the source (discharge location)
and a concentration of 0 g/m3 was defined at
all the boundaries. Since there is no decay of the tracer, the changes in
concentration of the tracers at different grid cells would be due to the advection and
dispersion of tidal flows. Comparing the concentration at the grid cell of the
source (C0) and the concentration at a selected grid cell located at the WSR
(C1), the dilution rate can be obtained (C0:C1). Results of the
modelling which was undertaken using this approach are presented in Appendix
3.3 and discussed in Section
3.7.1.6.
3.3.3 Outfall Dilution Modelling
Minor modification works at the Tsing Yi Submarine Sewage Outfall form part of the scope for this Project. The modification works may cause a change in the performance of the Tsing Yi Submarine Sewage Outfall, and thus, a quantitative assessment using the USEPA’s Visual Plume (UM3) model has been undertaken to predict the effluent dilution before and after the modification works. Details of the model inputs are provided in Appendix 3.6, including outfall specification, effluent characteristics, and ambient conditions in wet and dry seasons, among others.
For a
surface effluent plume, the minimum initial dilution is defined as the dilution
obtained when the effluent reaches the water surface. For a trapped plume, the
minimum initial dilution is defined as the dilution obtained when the plume reaches
the maximum rise height.
3.4 Identification of Environmental Impact
3.4.1 Construction Phase
3.4.1.1 Impact of Suspended Sediment
As a result of dredging activities during the construction phase, fine sediment (less than 63 µm) will be lost to suspension. The suspended sediment will be transported by currents to form sediment plumes, which will gradually resettle. The impact from sediment plumes is to increase the suspended sediment concentrations in the receiving water body, which could cause non-compliance with the relevant WQOs and other criteria for particular sensitive receivers.
The extent of elevation of ambient suspended sediment concentrations would determine if the impact is adverse, whilst the acceptability of any elevation would be dependent on compliance with the WQOs. The WQO for SS is defined as being an allowable elevation of 30% above the background. Taking reference from a previous study on the environmental impacts of released SS[7], the ambient value is represented by the 90th percentile of reported concentrations.
The depth-averaged and surface SS levels in 90 percentiles during dry and wet seasons are summarised in Table 3.10. These values were derived from EPD’s marine water quality monitoring results at the routine monitoring stations. The SS levels recorded from 2007 to 2008 were used in this Study. Since seawater intakes are generally located near the water surface, the ambient surface SS levels were added to the predicted SS elevations at these sensitive receivers for comparison against the relevant water quality criteria. It should be noted that the background level SS concentrations recorded at some stations do not comply with the WSD’s SS criterion of 10 mgL-1.
Table 3.10: Background Levels of Depth-averaged and Surface SS
|
Stations |
Dry Season |
Wet Season |
||
|
|
Depth-averaged |
Surface |
Depth-averaged |
Surface |
|
VM6, VM8, VM15 |
||||
|
Average SS (mg L-1) |
5.4 |
4.4 |
5.5 |
4.1 |
|
90 percentile (ambient level) |
8.5 |
7.2 |
9.2 |
6.8 |
|
30% increase above the ambient level |
2.6 |
2.2 |
2.8 |
2.0 |
|
WM1 |
||||
|
Average SS (mg L-1) |
5.0 |
3.7 |
6.8 |
3.6 |
|
90 percentile (ambient level) |
7.3 |
5.5 |
9.9 |
5.5 |
|
30% increase above the ambient level |
2.2 |
1.6 |
3.0 |
1.7 |
|
SM3 |
||||
|
Average SS (mg L-1) |
4.5 |
3.7 |
3.9 |
2.8 |
|
90 percentile (ambient level) |
6.0 |
4.9 |
5.2 |
3.9 |
|
30% increase above the ambient level |
1.8 |
1.5 |
1.6 |
1.2 |
|
SM5 |
||||
|
Average SS (mg L-1) |
6.6 |
5.3 |
3.5 |
2.8 |
|
90 percentile (ambient level) |
9.4 |
8.1 |
6.2 |
4.1 |
|
30% increase above the ambient level |
2.8 |
2.4 |
1.9 |
1.2 |
|
SM9 |
||||
|
Average SS (mg L-1) |
5.6 |
4.7 |
8.0 |
5.3 |
|
90 percentile (ambient level) |
8.8 |
6.3 |
14.6 |
10.2 |
|
30% increase above the ambient level |
2.6 |
1.9 |
4.4 |
3.1 |
|
VM14,VM12 |
||||
|
Average SS (mg L-1) |
8.3 |
7.2 |
8.0 |
5.6 |
|
90 percentile (ambient level) |
12.1 |
11.3 |
15.5 |
10.4 |
|
30% increase above the ambient level |
3.6 |
3.4 |
4.7 |
3.1 |
|
WM4 |
||||
|
Average SS (mg L-1) |
6.5 |
5.4 |
6.3 |
3.3 |
|
90 percentile (ambient level) |
10.6 |
9.9 |
8.3 |
4.3 |
|
30% increase above the ambient level |
3.2 |
3.0 |
2.5 |
1.3 |
Note: Values in Bold indicate exceedance of WSD’s SS criterion. The corresponding values for Stations VM6, VM8, VM12, VM14 and VM15 are presented in Appendix 3.4. Dry season is from November to March and wet season is from May to September.
3.4.1.2 Impact on Dissolved Oxygen, Total Inorganic Nitrogen and Unionised Ammonia
The extent of depletion of ambient DO concentration and elevation of ambient TIN and UIA will also indicate if the impact is adverse or not. The determination of the acceptability of any depletion or elevation is based on the level of compliance with the WQOs. The WQO of DO, DO bottom, TIN and UIA are defined as being larger than or equal to 4 mgL-1 (larger than or equal to 5 mgL-1 for Fish Culture Subzones), larger than or equal to 2 mgL-1, less than or equal to 0.4 mgL-1 (0.1 mgL-1 in Southern WCZ) and less than or equal to 0.021 mgL-1 respectively.
An assessment of DO depletion and nutrient release (for the purposes of estimating background levels only) during dredging was made in relation to the results of the sediment plume modelling of dredging activities and the sediment quality data of the Study Area. The predicted maximum elevations in tidal and depth-averaged SS concentrations at the construction site were used to estimate the effects of increased SS concentrations on DO and TIN. It was assumed that all SOD was exerted and that all TIN in the sediment were released to the water.
To determine compliance with the water quality criteria,
background water quality data were required.
The depth-averaged DO, TIN and UIA and bottom layer DO background levels
during dry and wet seasons are summarised in Table 3.11. The average DO, TIN and UIA values
derived from the EPD’s routine marine water quality monitoring data were used
in the assessment. It is noted that the background depth-averaged TIN
concentration recorded at some stations during dry and wet seasons do not comply with the WQO for TIN,
that is less than or equal to 0.1 mg L-1 in Southern WCZ and less
than or equal to 0.4 mg L-1 in the rest of the waters.
Table 3.11: Background Levels of DO, TIN and UIA
|
Stations (2007 & 2008) |
Dry Season |
Wet Season |
||
|
|
Depth-averaged |
Bottom |
Depth-averaged |
Bottom |
|
VM6,
VM8, VM15 |
||||
|
Dissolved Oxygen (mg L-1) |
5.0 |
5.0 |
3.6 |
2.6 |
|
Total Inorganic Nitrogen (mg L-1) |
0.32 |
- |
0.44 |
- |
|
Unionised Ammonia (mg L-1) |
0.005 |
- |
0.009 |
- |
|
WM1 |
||||
|
Dissolved Oxygen (mg L-1) |
5.9 |
6.0 |
3.9 |
2.5 |
|
Total Inorganic Nitrogen (mg L-1) |
0.17 |
- |
0.22 |
- |
|
Unionised Ammonia (mg L-1) |
0.002 |
- |
0.003 |
- |
|
SM3 |
||||
|
Dissolved Oxygen (mg L-1) |
6.2 |
6.2 |
3.7 |
2.7 |
|
Total Inorganic Nitrogen (mg L-1) |
0.14 |
- |
0.21 |
- |
|
Unionised Ammonia (mg L-1) |
0.002 |
- |
0.003 |
- |
|
SM5 |
||||
|
Dissolved Oxygen (mg L-1) |
6.1 |
6.3 |
5.3 |
3.3 |
|
Total Inorganic Nitrogen (mg L-1) |
0.11 |
- |
0.33 |
- |
|
Unionised Ammonia (mg L-1) |
0.001 |
- |
0.005 |
- |
|
SM9 |
||||
|
Dissolved Oxygen (mg L-1) |
6.0 |
6.1 |
4.4 |
4.1 |
|
Total Inorganic Nitrogen (mg L-1) |
0.25 |
- |
0.5 |
- |
|
Unionised Ammonia (mg L-1) |
0.005 |
- |
0.007 |
- |
|
VM14,VM12 |
||||
|
Dissolved Oxygen (mg L-1) |
5.3 |
5.4 |
3.9 |
3.3 |
|
Total Inorganic Nitrogen (mg L-1) |
0.35 |
- |
0.53 |
- |
|
Unionised Ammonia (mg L-1) |
0.005 |
- |
0.008 |
- |
|
WM4 |
||||
|
Dissolved Oxygen (mg L-1) |
5.5 |
5.7 |
3.6 |
2.7 |
|
Total Inorganic Nitrogen (mg L-1) |
0.29 |
- |
0.37 |
- |
|
Unionised Ammonia (mg L-1) |
0.004 |
- |
0.006 |
- |
Note: Values in Bold indicate exceedance of relevant criteria. The corresponding values for Stations VM6, VM8, VM12, VM14 and VM15 are presented in Appendix 3.4. Dry season is from November to March and wet season is from May to September.
3.4.1.3 Impact on Disturbance of Seabed Sediment due to Marine Traffic
Propeller
wash from vessels during
construction phase could lead
to potential disturbance of seabed sediment, and could generate an elevation in SS concentrations.
An assessment has been undertaken in Section 3.7.1.7 to determine whether
there is potential for cumulative impacts to be generated from this activity
and from the propeller wash from the dredgers themselves.
3.4.2 Operation Phase
As noted in Section
2.7 maintenance dredging cannot be ruled out. Even though these activities may be
infrequent, and involving relatively smaller volumes of material to be dredged,
this type of dredging still requires assessment in terms of its impacts on the
receiving water quality.
The Project also involves modification works to the Tsing Yi Submarine Sewage Outfall
and removal of the Kwai Tsing Submarine Sewage Outfall (Figure
3.6). Removal of the
outfall at Kwai Tsing is not expected to induce any adverse water quality
impact. The impact of the performance of the
Tsing Yi Submarine Sewage Outfall is addressed in Section
3.7.2.2. The potential impact of the deepening of seabed level in the
Rambler Channel and Northern Fairway due to the Project on the effluent
dispersion of HATS outfall of
3.5 Prediction and Evaluation of Environmental Impacts
3.5.1 Construction Phase
3.5.1.1 Impact of Suspended Solids
The models used to simulate
the dredging activities and to
consider the worst-case
scenarios were described in
the foregoing sub-sections. These model simulations covered typical
spring and neap tidal cycles during both dry and wet seasons in
The predicted SS elevations and concentrations for Scenarios
1 to 6 in the dry and wet seasons at the WSRs are detailed in Tables 3.12 to Table 3.23. The predicted SS elevations and
concentrations at the WSRs for Scenario 7 are provided in Appendix
3.8.
Table 3.12: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 1
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
Depth averaged |
Depth averaged |
|||
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.7 |
3.2 |
0.2 |
2.5 |
|
Approach |
B2 |
1.0 |
3.2 |
0.5 |
2.5 |
|
Ting Kau |
B3 |
0.4 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.3 |
3.2 |
0.8 |
2.5 |
|
Casam |
B5 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Hoi Mei Wan |
B6 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Angler’s |
B8 |
0.8 |
3.2 |
0.3 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.6 |
2.2 |
0.2 |
3.0 |
|
Shek Kok Tsui |
CR2 |
0.6 |
2.2 |
0.2 |
3.0 |
|
Luk Chau |
CR3 |
0.3 |
1.8 |
<0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.2 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.3 |
1.8 |
0.1 |
1.6 |
|
|
CR6 |
0.3 |
2.2 |
0.2 |
3.0 |
|
|
CR7 |
0.7 |
2.2 |
0.2 |
3.0 |
|
Kau Yi Chau |
CR8 |
0.5 |
2.6 |
1.0 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.5 |
2.6 |
2.3 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.4 |
2.6 |
1.3 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.5 |
2.6 |
1.7 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.5 |
2.6 |
1.6 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.4 |
2.6 |
1.1 |
4.4 |
|
Peng Chau |
CR14 |
0.3 |
2.6 |
0.6 |
4.4 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.3 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR17 |
0.3 |
2.6 |
0.8 |
4.4 |
|
Peng Chau |
CR18 |
<0.1 |
2.6 |
0.2 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.6 |
3.2 |
0.4 |
2.5 |
|
Lo Tik Wan |
F2 |
0.1 |
1.8 |
0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold indicate exceedance of relevant criteria
Table 3.13: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 1
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.0 |
10.7 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.7 |
11.3 |
|
MTRC |
C3 |
- |
7.2 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.7 |
5.6 |
|
|
C6 |
- |
5.6 |
5.6 |
|
Wah Fu Estate |
C7 |
- |
5.7 |
5.6 |
|
|
*EMSD1 |
,<180 |
11.4 |
11.1 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
13.5 |
11.4 |
|
|
WSD2 |
<10 |
7.5 |
6.9 |
|
Sheung Wan |
WSD3 |
<10 |
7.2 |
6.9 |
|
Central Water Front |
WSD4 |
<10 |
7.2 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.0 |
3.9 |
|
|
WSD6 |
<10 |
7.2 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
12.1 |
10.8 |
|
Near |
WSD9 |
<10 |
10.6 |
4.5 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.4 |
11.1 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
13.2 |
16.9 |
|
MTRC Tsing Yi Station |
C2 |
- |
14.3 |
19.0 |
|
MTRC |
C3 |
- |
8.5 |
9.2 |
|
|
C4 |
- |
8.5 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.6 |
10.1 |
|
|
C6 |
- |
7.6 |
10.1 |
|
Wah Fu Estate |
C7 |
- |
7.5 |
10.0 |
|
|
*EMSD1 |
<180 |
12.4 |
16.2 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
15.2 |
20.3 |
|
|
WSD2 |
<10 |
8.8 |
9.4 |
|
Sheung Wan |
WSD3 |
<10 |
8.5 |
9.4 |
|
Central Water Front |
WSD4 |
<10 |
8.5 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.1 |
5.3 |
|
|
WSD6 |
<10 |
8.5 |
9.3 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
13.3 |
16.8 |
|
Near |
WSD9 |
<10 |
11.8 |
8.5 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.4 |
16.2 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of SS includes
the ambient SS level presented in Table 3.10 plus the SS elevations predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai Chung Hospital is a WSR for both
cooling water and salt water flushing intakes, the more conservative criterion
has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
Table 3.14: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 2
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
|
Depth averaged |
Depth averaged |
||
|
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.8 |
3.2 |
0.2 |
2.5 |
|
Approach |
B2 |
1.0 |
3.2 |
0.5 |
2.5 |
|
Ting Kau |
B3 |
0.4 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.3 |
3.2 |
0.8 |
2.5 |
|
Casam |
B5 |
0.8 |
3.2 |
0.5 |
2.5 |
|
Hoi Mei Wan |
B6 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Angler’s |
B8 |
0.7 |
3.2 |
0.3 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.5 |
2.2 |
0.2 |
3.0 |
|
Shek Kok Tsui |
CR2 |
0.4 |
2.2 |
0.2 |
3.0 |
|
Luk Chau |
CR3 |
0.3 |
1.8 |
0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.4 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.4 |
1.8 |
0.1 |
1.6 |
|
|
CR6 |
0.5 |
2.2 |
0.3 |
3.0 |
|
|
CR7 |
0.8 |
2.2 |
0.3 |
3 |
|
Kau Yi Chau |
CR8 |
0.4 |
2.6 |
0.9 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.4 |
2.6 |
2.2 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.4 |
2.6 |
1.2 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.4 |
2.6 |
1.7 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.4 |
2.6 |
1.6 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.3 |
2.6 |
1.1 |
4.4 |
|
Peng Chau |
CR14 |
0.3 |
2.6 |
0.6 |
4.4 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR17 |
0.2 |
2.6 |
0.7 |
4.4 |
|
Peng Chau |
CR18 |
<0.1 |
2.6 |
0.2 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.6 |
3.2 |
0.4 |
2.5 |
|
Lo Tik Wan |
F2 |
0.1 |
1.8 |
0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold
indicate exceedance of relevant criteria
Table 3.15: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 2
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.0 |
10.7 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.7 |
11.3 |
|
MTRC |
C3 |
- |
7.2 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.8 |
5.7 |
|
|
C6 |
- |
5.7 |
5.7 |
|
Wah Fu Estate |
C7 |
- |
5.7 |
5.6 |
|
|
*EMSD1 |
<180 |
11.4 |
11.1 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
13.5 |
11.4 |
|
|
WSD2 |
<10 |
7.5 |
6.9 |
|
Sheung Wan |
WSD3 |
<10 |
7.2 |
6.9 |
|
Central Water Front |
WSD4 |
<10 |
7.2 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.1 |
4.0 |
|
|
WSD6 |
<10 |
7.2 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
12.1 |
10.8 |
|
Near |
WSD9 |
<10 |
10.6 |
4.5 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.4 |
11.1 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
13.2 |
16.9 |
|
MTRC Tsing Yi Station |
C2 |
- |
14.3 |
19.0 |
|
MTRC |
C3 |
- |
8.5 |
9.2 |
|
|
C4 |
- |
8.5 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.8 |
10.2 |
|
|
C6 |
- |
7.7 |
10.1 |
|
Wah Fu Estate |
C7 |
- |
7.6 |
10.0 |
|
|
*EMSD1 |
<180 |
12.4 |
16.2 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
15.2 |
20.3 |
|
|
WSD2 |
<10 |
8.9 |
9.4 |
|
Sheung Wan |
WSD3 |
<10 |
8.6 |
9.4 |
|
Central Water Front |
WSD4 |
<10 |
8.5 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.2 |
5.3 |
|
|
WSD6 |
<10 |
8.5 |
9.3 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
13.3 |
16.8 |
|
Near |
WSD9 |
<10 |
11.8 |
8.5 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.4 |
16.2 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of SS includes
the ambient SS level presented in Table 3.10 plus the SS elevations predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai
Chung Hospital is a WSR for both cooling water and salt water flushing intakes,
the more conservative criterion has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
Table 3.16: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 3
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
|
Depth averaged |
Depth averaged |
||
|
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.8 |
3.2 |
0.2 |
2.5 |
|
Approach |
B2 |
0.8 |
3.2 |
0.5 |
2.5 |
|
Ting Kau |
B3 |
0.3 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.3 |
3.2 |
0.9 |
2.5 |
|
Casam |
B5 |
1.0 |
3.2 |
0.5 |
2.5 |
|
Hoi Mei Wan |
B6 |
1.1 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
1.1 |
3.2 |
0.4 |
2.5 |
|
Angler’s |
B8 |
1.0 |
3.2 |
0.4 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.9 |
2.2 |
0.3 |
3 |
|
Shek Kok Tsui |
CR2 |
0.8 |
2.2 |
0.3 |
3 |
|
Luk Chau |
CR3 |
0.5 |
1.8 |
0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.5 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.5 |
1.8 |
0.1 |
1.6 |
|
|
CR6 |
0.6 |
2.2 |
0.3 |
3 |
|
|
CR7 |
0.9 |
2.2 |
0.4 |
3 |
|
Kau Yi Chau |
CR8 |
0.7 |
2.6 |
1.3 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.7 |
2.6 |
2.9 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.5 |
2.6 |
1.4 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.7 |
2.6 |
2.2 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.6 |
2.6 |
2.0 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.5 |
2.6 |
1.4 |
4.4 |
|
Peng Chau |
CR14 |
0.4 |
2.6 |
0.6 |
4.4 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.3 |
2.6 |
0.7 |
4.4 |
|
Peng Chau |
CR17 |
0.3 |
2.6 |
1.1 |
4.4 |
|
Peng Chau |
CR18 |
0.1 |
2.6 |
0.2 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.8 |
3.2 |
0.5 |
2.5 |
|
Lo Tik Wan |
F2 |
0.2 |
1.8 |
0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold
indicate exceedance of relevant criteria.
Table 3.17: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 3
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
11.5 |
10.6 |
|
MTRC Tsing Yi Station |
C2 |
- |
11.7 |
10.6 |
|
MTRC |
C3 |
- |
7.2 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.8 |
5.7 |
|
|
C6 |
- |
5.7 |
5.7 |
|
Wah Fu Estate |
C7 |
- |
5.8 |
5.6 |
|
|
*EMSD1 |
<180 |
11.3 |
10.5 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
11.8 |
10.7 |
|
|
WSD2 |
<10 |
7.6 |
7.0 |
|
Sheung Wan |
WSD3 |
<10 |
7.2 |
6.9 |
|
Central Water Front |
WSD4 |
<10 |
7.2 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.1 |
4.0 |
|
|
WSD6 |
<10 |
7.2 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
11.5 |
10.5 |
|
Near |
WSD9 |
<10 |
10.7 |
4.5 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.3 |
10.5 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.5 |
15.9 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.6 |
15.8 |
|
MTRC |
C3 |
- |
8.5 |
9.2 |
|
|
C4 |
- |
8.5 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.8 |
10.2 |
|
|
C6 |
- |
7.7 |
10.1 |
|
Wah Fu Estate |
C7 |
- |
7.6 |
10.0 |
|
|
*EMSD1 |
<180 |
12.2 |
15.6 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
12.7 |
15.8 |
|
|
WSD2 |
<10 |
8.9 |
9.4 |
|
Sheung Wan |
WSD3 |
<10 |
8.6 |
9.4 |
|
Central Water Front |
WSD4 |
<10 |
8.5 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.3 |
5.3 |
|
|
WSD6 |
<10 |
8.5 |
9.2 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
12.4 |
16.0 |
|
Near |
WSD9 |
<10 |
12.0 |
8.6 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.2 |
15.6 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of SS includes
the ambient SS level presented in Table 3.10 plus the SS elevations predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai
Chung Hospital is a WSR for both cooling water and salt water flushing intakes,
the more conservative criterion has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
Table 3.18: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 4
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
|
Depth averaged |
Depth averaged |
||
|
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.8 |
3.2 |
0.1 |
2.5 |
|
Approach |
B2 |
1.0 |
3.2 |
0.4 |
2.5 |
|
Ting Kau |
B3 |
0.4 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.2 |
3.2 |
0.7 |
2.5 |
|
Casam |
B5 |
0.5 |
3.2 |
0.4 |
2.5 |
|
Hoi Mei Wan |
B6 |
0.5 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
0.5 |
3.2 |
0.3 |
2.5 |
|
Angler’s |
B8 |
0.5 |
3.2 |
0.3 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.5 |
2.2 |
0.2 |
3.0 |
|
Shek Kok Tsui |
CR2 |
0.5 |
2.2 |
0.2 |
3.0 |
|
Luk Chau |
CR3 |
0.3 |
1.8 |
<0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.2 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.1 |
1.8 |
<0.1 |
1.6 |
|
|
CR6 |
0.2 |
2.2 |
0.1 |
3.0 |
|
|
CR7 |
0.3 |
2.2 |
0.2 |
3.0 |
|
Kau Yi Chau |
CR8 |
0.4 |
2.6 |
0.8 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.4 |
2.6 |
1.9 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.3 |
2.6 |
1.1 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.4 |
2.6 |
1.3 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.4 |
2.6 |
1.1 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.3 |
2.6 |
0.9 |
4.4 |
|
Peng Chau |
CR14 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR17 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR18 |
<0.1 |
2.6 |
0.2 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.4 |
3.2 |
0.3 |
2.5 |
|
Lo Tik Wan |
F2 |
0.1 |
1.8 |
0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold indicate exceedance of relevant criteria
Table 3.19: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 4
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.0 |
10.7 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.7 |
11.3 |
|
MTRC |
C3 |
- |
7.3 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.6 |
5.6 |
|
|
C6 |
- |
5.6 |
5.5 |
|
Wah Fu Estate |
C7 |
- |
5.6 |
5.5 |
|
|
*EMSD1 |
<180 |
11.5 |
11.2 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
13.5 |
11.4 |
|
|
WSD2 |
<10 |
7.3 |
6.9 |
|
Sheung Wan |
WSD3 |
<10 |
7.3 |
6.8 |
|
Central Water Front |
WSD4 |
<10 |
7.3 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.0 |
3.9 |
|
|
WSD6 |
<10 |
7.4 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
12.2 |
10.8 |
|
Near |
WSD9 |
<10 |
10.4 |
4.4 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.5 |
11.2 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
13.2 |
17.0 |
|
MTRC Tsing Yi Station |
C2 |
- |
14.3 |
19.1 |
|
MTRC |
C3 |
- |
8.6 |
9.2 |
|
|
C4 |
- |
8.6 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.4 |
10.0 |
|
|
C6 |
- |
7.4 |
10.0 |
|
Wah Fu Estate |
C7 |
- |
7.4 |
9.9 |
|
|
*EMSD1 |
<180 |
12.7 |
16.3 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
15.2 |
20.4 |
|
|
WSD2 |
<10 |
8.7 |
9.3 |
|
Sheung Wan |
WSD3 |
<10 |
8.6 |
9.3 |
|
Central Water Front |
WSD4 |
<10 |
8.6 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.1 |
5.2 |
|
|
WSD6 |
<10 |
8.8 |
9.3 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
13.3 |
16.9 |
|
Near |
WSD9 |
<10 |
11.4 |
8.5 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.7 |
16.3 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of SS includes
the ambient SS level presented in Table 3.10 plus the SS elevations predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai
Chung Hospital is a WSR for both cooling water and salt water flushing intakes,
the more conservative criterion has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
Table 3.20: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 5
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
|
Depth averaged |
Depth averaged |
||
|
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.8 |
3.2 |
0.1 |
2.5 |
|
Approach |
B2 |
1.0 |
3.2 |
0.4 |
2.5 |
|
Ting Kau |
B3 |
0.4 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.2 |
3.2 |
0.6 |
2.5 |
|
Casam |
B5 |
0.5 |
3.2 |
0.4 |
2.5 |
|
Hoi Mei Wan |
B6 |
0.5 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
0.5 |
3.2 |
0.3 |
2.5 |
|
Angler’s |
B8 |
0.5 |
3.2 |
0.3 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.2 |
2.2 |
0.1 |
3.0 |
|
Shek Kok Tsui |
CR2 |
0.2 |
2.2 |
0.1 |
3.0 |
|
Luk Chau |
CR3 |
0.1 |
1.8 |
<0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.1 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.2 |
1.8 |
<0.1 |
1.6 |
|
|
CR6 |
0.2 |
2.2 |
0.2 |
3.0 |
|
|
CR7 |
0.6 |
2.2 |
0.2 |
3.0 |
|
Kau Yi Chau |
CR8 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.2 |
2.6 |
1.6 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.2 |
2.6 |
1.0 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.2 |
2.6 |
1.0 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.3 |
2.6 |
0.8 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.2 |
2.6 |
0.8 |
4.4 |
|
Peng Chau |
CR14 |
0.1 |
1.8 |
0.4 |
1.6 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
<0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.1 |
2.6 |
0.4 |
4.4 |
|
Peng Chau |
CR17 |
0.1 |
2.6 |
0.4 |
4.4 |
|
Peng Chau |
CR18 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.3 |
3.2 |
0.3 |
2.5 |
|
Lo Tik Wan |
F2 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold indicate exceedance of relevant criteria
Table 3.21: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 5
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.0 |
10.7 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.7 |
11.3 |
|
MTRC |
C3 |
- |
7.3 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.6 |
5.6 |
|
|
C6 |
- |
5.6 |
5.6 |
|
Wah Fu Estate |
C7 |
- |
5.6 |
5.5 |
|
|
*EMSD1 |
<180 |
11.5 |
11.2 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
13.5 |
11.4 |
|
|
WSD2 |
<10 |
7.4 |
6.9 |
|
Sheung Wan |
WSD3 |
<10 |
7.3 |
6.9 |
|
Central Water Front |
WSD4 |
<10 |
7.3 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.0 |
3.9 |
|
|
WSD6 |
<10 |
7.4 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
12.2 |
10.8 |
|
Near |
WSD9 |
<10 |
10.3 |
4.4 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.5 |
11.2 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
13.2 |
17.0 |
|
MTRC Tsing Yi Station |
C2 |
- |
14.3 |
19.1 |
|
MTRC |
C3 |
- |
8.6 |
9.2 |
|
|
C4 |
- |
8.6 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.5 |
10.1 |
|
|
C6 |
- |
7.5 |
10.0 |
|
Wah Fu Estate |
C7 |
- |
7.4 |
9.9 |
|
|
*EMSD1 |
<180 |
12.7 |
16.3 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
15.2 |
20.4 |
|
|
WSD2 |
<10 |
8.8 |
9.4 |
|
Sheung Wan |
WSD3 |
<10 |
8.6 |
9.4 |
|
Central Water Front |
WSD4 |
<10 |
8.6 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.1 |
5.2 |
|
|
WSD6 |
<10 |
8.8 |
9.3 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
13.3 |
16.9 |
|
Near |
WSD9 |
<10 |
11.3 |
8.5 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.7 |
16.3 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of SS includes
the ambient SS level presented in Table 3.10 plus the SS elevations predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai
Chung Hospital is a WSR for both cooling water and salt water flushing intakes,
the more conservative criterion has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
Table 3.22: Predicted Suspended Solids Elevations at Gazetted Beaches, Marine Ecology, and Fisheries Sensitive Receivers for Scenario 6
|
Sensitive Receivers |
Assessment Point |
Maximum SS Elevation (Dry Season) |
Maximum SS Elevation (Wet Season) |
||
|
|
|
Depth averaged |
Depth averaged |
||
|
|
|
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
SS Elevation (mgL-1) |
SS Criteria (mgL-1) |
|
Gazetted Beaches |
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.5 |
3.2 |
0.1 |
2.5 |
|
Approach |
B2 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Ting Kau |
B3 |
0.3 |
3.2 |
0.2 |
2.5 |
|
|
B4 |
0.3 |
3.2 |
0.8 |
2.5 |
|
Casam |
B5 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Hoi Mei Wan |
B6 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Gemini |
B7 |
0.8 |
3.2 |
0.4 |
2.5 |
|
Angler’s |
B8 |
0.7 |
3.2 |
0.3 |
2.5 |
|
Lo So Shing |
B9 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Hung Shing Yeh |
B10 |
<0.1 |
2.8 |
<0.1 |
1.9 |
|
Corals |
|
|
|
|
|
|
Pak Kok |
CR1 |
0.4 |
2.2 |
0.2 |
3 |
|
Shek Kok Tsui |
CR2 |
0.4 |
2.2 |
0.2 |
3 |
|
Luk Chau |
CR3 |
0.3 |
1.8 |
0.1 |
1.6 |
|
Wong Chuk Kok |
CR4 |
0.4 |
1.8 |
<0.1 |
1.6 |
|
Ap Lei Chau |
CR5 |
0.4 |
1.8 |
0.1 |
1.6 |
|
|
CR6 |
0.5 |
2.2 |
0.2 |
3 |
|
|
CR7 |
0.8 |
2.2 |
0.3 |
3 |
|
Kau Yi Chau |
CR8 |
0.4 |
2.6 |
0.9 |
4.4 |
|
Kau Yi Chau |
CR9 |
0.4 |
2.6 |
2.1 |
4.4 |
|
Kau Yi Chau |
CR10 |
0.3 |
2.6 |
1.2 |
4.4 |
|
Siu Kau Yi Chau |
CR11 |
0.4 |
2.6 |
1.6 |
4.4 |
|
Siu Kau Yi Chau |
CR12 |
0.4 |
2.6 |
1.6 |
4.4 |
|
Siu Kau Yi Chau |
CR13 |
0.3 |
2.6 |
1.1 |
4.4 |
|
Peng Chau |
CR14 |
0.3 |
2.6 |
0.6 |
4.4 |
|
Peng Chau |
CR15 |
<0.1 |
2.6 |
0.1 |
4.4 |
|
Peng Chau |
CR16 |
0.2 |
2.6 |
0.5 |
4.4 |
|
Peng Chau |
CR17 |
0.2 |
2.6 |
0.7 |
4.4 |
|
Peng Chau |
CR18 |
<0.1 |
2.6 |
0.2 |
4.4 |
|
Fish Culture Zone |
|
|
|
|
|
|
Ma Wan |
F1 |
0.6 |
3.2 |
0.4 |
2.5 |
|
Lo Tik Wan |
F2 |
0.1 |
1.8 |
0.1 |
1.6 |
|
Sok Kwu Wan |
F3 |
<0.1 |
1.8 |
<0.1 |
1.6 |
|
Cheung Sha Wan |
F4 |
<0.1 |
2.6 |
<0.1 |
4.4 |
Values in Bold indicate exceedance of relevant criteria
Table 3.23: Predicted Suspended Solids Concentrations at Cooling and Sea Water Intakes for Scenario 6
|
Sensitive Receivers |
Maximum (1) SS concentration in surface layer (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
11.8 |
10.6 |
|
MTRC Tsing Yi Station |
C2 |
- |
12.3 |
11.3 |
|
MTRC |
C3 |
- |
7.2 |
6.8 |
|
|
C4 |
- |
7.2 |
6.8 |
|
Sha Wan Drive |
C5 |
- |
5.8 |
5.7 |
|
|
C6 |
- |
5.7 |
5.7 |
|
Wah Fu Estate |
C7 |
- |
5.7 |
5.6 |
|
|
*EMSD1 |
<180 |
11.4 |
10.9 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
12.5 |
11.4 |
|
|
WSD2 |
<10 |
7.5 |
6.9 |
|
Sheung Wan |
WSD3 |
<10 |
7.2 |
6.9 |
|
Central Water Front |
WSD4 |
<10 |
7.2 |
6.8 |
|
Ap Lei Chau |
WSD5 |
<10 |
5.1 |
4.0 |
|
|
WSD6 |
<10 |
7.2 |
6.8 |
|
Cheung Sha Wan |
WSD7 |
<10 |
7.2 |
6.8 |
|
Tsuen Wan |
WSD8 |
<10 |
11.9 |
10.7 |
|
Near |
WSD9 |
<10 |
10.5 |
4.5 |
|
Lamma Power Station |
WSD10 |
<10 |
8.1 |
4.1 |
|
|
*EMSD1 |
<10 |
11.4 |
10.9 |
|
Sensitive Receivers |
Maximum (1) depth averaged SS concentration (mgL-1) |
|||
|
|
Assessment Point |
SS Criterion (mgL-1) |
Dry Season |
Wet Season |
|
Cooling
Water Intakes |
|
|
|
|
|
Tsuen Wan |
C1 |
- |
12.9 |
16.6 |
|
MTRC Tsing Yi Station |
C2 |
- |
13.7 |
18.6 |
|
MTRC |
C3 |
- |
8.5 |
9.2 |
|
|
C4 |
- |
8.5 |
9.2 |
|
Sha Wan Drive |
C5 |
- |
7.8 |
10.2 |
|
|
C6 |
- |
7.7 |
10.1 |
|
Wah Fu Estate |
C7 |
- |
7.6 |
10.0 |
|
|
*EMSD1 |
<180 |
12.3 |
16.0 |
|
WSD |
|
|
|
|
|
Tsing Yi |
WSD1 |
<10 |
14.4 |
20.4 |
|
|
WSD2 |
<10 |
8.9 |
9.4 |
|
Sheung Wan |
WSD3 |
<10 |
8.6 |
9.4 |
|
Central Water Front |
WSD4 |
<10 |
8.5 |
9.3 |
|
Ap Lei Chau |
WSD5 |
<10 |
6.2 |
5.3 |
|
|
WSD6 |
<10 |
8.5 |
9.2 |
|
Cheung Sha Wan |
WSD7 |
<10 |
8.5 |
9.2 |
|
Tsuen Wan |
WSD8 |
<10 |
13.0 |
16.5 |
|
Near |
WSD9 |
<10 |
11.8 |
8.5 |
|
Lamma Power Station |
WSD10 |
<10 |
9.4 |
6.2 |
|
|
*EMSD1 |
<10 |
12.3 |
16.0 |
Values in Bold indicate exceedance of relevant criteria.
(1) Absolute value of
SS includes the ambient SS level presented in Table 3.10 plus the SS elevations
predicted.
* Note that the EMSD Code of
Practice requires <180 mg L-1 at cooling water intakes. As Kwai
Chung Hospital is a WSR for both cooling water and salt water flushing intakes,
the more conservative criterion has been applied, i.e. <10 mg L-1, as required for WSD’s salt water flushing
water intakes.
A summary of the impact arising from Scenarios 1 to 7 is presented below:
Scenario 1
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.0 mg L-1 during the dry season (worst affected location was B2) and 0.8 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.7 mg L-1 during the dry season (worst affected location was CR7) and 2.3 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.6 mg L-1 during the dry season (worst affected location was F1) and 0.4 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.7 mg L-1 during the dry season and 11.3 mg L-1 during the wet season at C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 13.5 mg L-1 during dry season and 11.4 mg L-1 during wet season at WSD1 based on the surface level result.
Scenario 2
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.0 mg L-1 during the dry season (worst affected location was B2) and 0.8 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.8 mg L-1 during the dry season (worst affected location was CR7) and 2.2 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.6 mg L-1 during the dry season (worst affected location was F1) and 0.4 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.7 mg L-1 during the dry season and 11.3 mg L-1 during the wet season at C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 13.5 mg L-1 during dry season and 11.4 mg L-1 during wet season at WSD1 based on the surface level result.
Scenario 3
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.1 mg L-1 during the dry season (worst affected locations were B6 and B7) and 0.9 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.9 mg L-1 during the dry season (worst affected locations were CR1 and CR7) and 2.9 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.8 mg L-1 during the dry season (worst affected location was F1) and 0.5 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 11.7 mg L-1 during the dry season and 10.6 mg L-1 during the wet season at C1 and C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 11.8 mg L-1 during dry season and 10.7 during wet season at WSD1 based on the surface level result.
Scenario 4
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.0 mg L-1 during the dry season (worst affected location was B2) and 0.7 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.5 mg L-1 during the dry season (worst affected locations were CR1 and CR2) and 1.9 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.4 mg L-1 during the dry season (worst affected location was F1) and 0.3 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.7 mg L-1 during the dry season and 11.3 mg L-1 during the wet season at C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 13.5 mg L-1 during dry season and 11.4 during wet season at WSD1 based on the surface level result.
Scenario 5
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.0 mg L-1 during the dry season (worst affected location was B2) and 0.6 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.6 mg L-1 during the dry season (worst affected location was CR7) and 1.6 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.3 mg L-1 during the dry season (worst affected location was F1) and 0.3 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.7 mg L-1 during the dry season and 11.3 mg L-1 during the wet season at C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 13.5 mg L-1 during dry season and 11.4 mg L-1 during wet season at WSD1 based on the surface level result.
Scenario 6
Gazetted Beaches – model results indicated the maximum SS elevations to be 0.8 mg L-1 during the dry season (worst affected locations were B2, B5, B6 and B7) and 0.8 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 0.8 mg L-1 during the dry season (worst affected location was CR7) and 2.1 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 0.6 mg L-1 during the dry season (worst affected location was F1) and 0.4 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.3 mg L-1 during the dry season and 11.3 mg L-1 during the wet season C2 based on the surface level result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 12.5 mg L-1 during dry season and 11.4 mg L-1 during wet season at WSD1 based on the surface level result.
Scenario 7
Gazetted Beaches – model results indicated the maximum SS elevations to be 1.8 mg L-1 during the dry season (worst affected location was B7 & B8) and 1.6 mg L-1 during the wet season (worst affected location was B4). No exceedance of the SS criteria occurred.
Corals – model results indicated the maximum SS elevations to be 1.0 mg L-1 during the dry season (worst affected location was CR1 & CR7) and 3.7 mg L-1 during the wet season (worst affected location was CR9). No exceedance of the SS criteria occurred.
Fish Culture Zone – model results indicated the maximum SS elevations to be 2.6 mg L-1 during the dry season (worst affected location was F1) and 2.0 mg L-1 during the wet season (worst affected location was F1). No exceedance of the SS criteria occurred.
Cooling Water Intakes – model results indicated the maximum SS concentrations to be 12.0 mg L-1 during the dry season and 10.9 mg L-1 during the wet season at C2 based on the level surface result.
WSD Flushing Water Intakes – the SS criterion (<10 mg L-1) was exceeded at four locations (WSD1, WSD8, WSD9, EMSD1) during the dry season, and at three locations (WSD1, WSD8, EMSD1) during the wet season. Model results indicated the maximum SS concentrations to be 12.0 mg L-1 during dry season and 11.0 mg L-1 during wet season at WSD1 based on the surface level result.
A summary of the results and compliance is given in Table 3.24 below.
Table 3.24: Summary of SS Results for Scenarios 1 - 7
|
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
Scenario 4 |
Scenario 5 |
Scenario 6 |
Scenario 7 |
|
Gazetted
Beaches |
|
|
|
|
|
|
|
|
Maximum SS elevation in dry season (mg L-1) / (Location) |
1.0 (B2) |
1.0 (B2) |
1.1 (B6 & B7) |
1.0 (B2) |
1.0 (B2) |
0.8 (B2, B5-B7) |
1.8 (B7 & B8) |
|
Maximum SS elevation in wet season (mg L-1) / (Location) |
0.8 (B4) |
0.8 (B4) |
0.9 (B4) |
0.7 (B4) |
0.6 (B4) |
0.8 (B4) |
1.6 (B4) |
|
Exceedance? |
No |
No |
No |
No |
No |
No |
No |
|
Corals |
|
|
|
|
|
|
|
|
Maximum SS elevation in dry season (mg L-1) / (Location) |
0.7 (CR7) |
0.8 (CR7) |
0.9 (CR1 & CR7) |
0.5 (CR1 & CR2) |
0.6 (CR7) |
0.8 (CR7) |
1.0 (CR1 & CR7) |
|
Maximum SS elevation in wet season (mg L-1) / (Location) |
2.3 (CR9) |
2.2 (CR9) |
2.9 (CR9) |
1.9 (CR9) |
1.6 (CR9) |
2.1 (CR9) |
3.7 (CR9) |
|
Exceedance? |
No |
No |
No |
No |
No |
No |
No |
|
Fish Culture
Zone |
|
|
|
|
|
|
|
|
Maximum SS elevation in dry season (mg L-1) / (Location) |
0.6 (F1) |
0.6 (F1) |
0.8 (F1) |
0.4 (F1) |
0.3 (F1) |
0.6 (F1) |
2.6 (F1) |
|
Maximum SS elevation in wet season (mg L-1) / (Location) |
0.4 (F1) |
0.4 (F1) |
0.5 (F1) |
0.3 (F1) |
0.3 (F1) |
0.4 (F1) |
2.0
(F1) |
|
Exceedance? |
No |
No |
No |
No |
No |
No |
No |
|
Cooling
Water Intakes |
|
|
|
|
|
|
|
|
Maximum SS level in dry season (mg L-1) / (Location) |
12.7 (C2) |
12.7 (C2) |
11.7 (C2) |
12.7(C2) |
12.7 (C2) |
12.3 (C2) |
12.0 (C2) |
|
Maximum SS level in wet season (mg L-1) / (Location) |
11.3 (C2) |
11.3 (C2) |
10.6 (C1 & C2) |
11.3(C2) |
11.3 (C2) |
11.3 (C2) |
10.9 (C2) |
|
Exceedance? |
No |
No |
No |
No |
No |
No |
No |
|
|
|
|
|
|
|
|
|
|
Maximum SS level in dry season (mg L-1) / (Location) |
13.5 (WSD1) |
13.5 (WSD1) |
11.8 (WSD1) |
13.5 (WSD1) |
13.5 (WSD1) |
12.5 (WSD1) |
12.0 (WSD1) |
|
Maximum SS level in wet season (mg L-1) / (Location) |
11.4 (WSD1) |
11.4 (WSD1) |
10.7 (WSD1) |
11.4 (WSD1) |
11.4 (WSD1) |
11.4 (WSD1) |
11.0 (WSD1) |
|
Exceedance? |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Depth-averaged SS elevations were reported for gazetted beaches, corals, fish culture zones while surface SS levels were reported for water intakes
Exceedance of WSD’s SS criterion of 10 mg L-1 was predicted at the seawater intakes WSD1, WSD8, WSD9 and EMSD1 due to the exceedance of ambient SS levels at the Rambler Channel and waters near Tsuen Wan (Table 3.10). Mitigation measures are proposed to protect these WSRs and details are provided in Section 3.8.
The predicted SS elevations and total concentrations for
Scenario 6 during the dry and wet seasons at WSRs are presented in Tables
3.22 and 3.23. The effects of using a CSD instead of
a GD in the Northeast of the Rambler Channel have been assessed with reference to the predicted results for Scenarios 2 (GD) and 6 (CSD). The
results indicated that there is no
significant difference between the
predicted results for these two scenarios. The WSD flushing water intake
WSD1 is the closest WSR to the working
area of the CSD. The difference in SS elevation at WSD1 is less than 0.2
mg L-1.
No non-compliance of the SS criteria was found at any gazetted beach, coral communities, fish culture zone or cooling water intake. Exceedances of the SS criterion at the WSD flushing water intake are similar to those described in Scenario 2. As such, it may be inferred that the CSD operation would not induce significant additional impact compared with those induced by the GD assumed in Scenario 2. It was also concluded that with either one GD or one CSD operating in the Rambler Channel under Scenarios 1, 2, 4 and 5, there would be no significant change in the predicted SS impacts at any of the WSRs.
As noted in Section 3.5.2.3, an alternative modelling scenario which included 5 dredgers operating concurrently has also been undertaken and is described in Appendix 3.2 which also included the impact assessment at the identified WSRs. SS elevations have been presented as colour contours and time series plots. The extent of maximum surface, bottom and depth-averaged SS elevations over the complete simulation period during dry and wet seasons, respectively are also presented in Appendix 3.2. As illustrated in the contour plots in Appendix 3.2 the SS impact would appear to be confined close to the dredging areas in the Rambler Channel, Northern Fairway and Western Fairway. Details of the temporal variations of surface, mid-depth, bottom and depth-averaged SS elevations at various WSRs in close proximity to the dredging areas during dry and wet seasons were also provided in Appendix 3.2. It must be stressed that this scenario is only included as an extreme example, because at no time will 5 dredgers operate together under this Project.
3.5.1.2 Contribution of the Suspended Solids from Potentially Concurrent Projects
The potential concurrent projects included in the cumulative impact assessments were described in Sections 2.8 and 3.5.2.2. Scenario 7 was specifically developed to examine the potential cumulative impacts. In the first instance reference was made to the HZMB approved EIAs which included the SS impact assessment of the concurrent projects of TMCLKL, HKBCF and HKLR projects and other concurrent projects including the Dredging and Backfilling of East of Sha Chau Contaminated Mud-Pits (V). Based on the contour plots presented in these EIAs, the predicted maximum SS levels during mitigated case in year 2012 (spring tide, lowest low) occurred near the proposed BCF and the Brothers. The SS levels reduced gradually from < 6 mg L-1 near Yam O Wan to < 3 mg L-1 near the Ma Wan Fish Culture Zone. The SS levels in the plume further reduced to background levels (< 2 mg L-1) in the Ma Wan Channel between Tsing Yi and Ma Wan. No noticeable plume with SS levels was observed on the Tsuen Wan coast or in the Rambler Channel.
The predicted SS elevations and total SS concentrations at
the identified WSRs due to the concurrent projects and Scenario 3 for this
Project are provided in Appendix 3.8.
Comparison of the results of Scenario 7 (concurrent projects plus Scenario 3)
and Scenario 3 only indicated that insignificant SS elevations (< 1 mg L-1)
were predicted at all the
WSRs, except at the Ma Wan Fish
Culture Zone (WSR F1). The highest SS elevation (1.8/1.5 mg L-1 in
dry/wet seasons), due to the
contribution of concurrent projects,
was predicted at the Ma Wan
Fish Culture Zone (WSR F1). The SS elevation due to the concurrent projects is
also noticeable at the beaches along Tsuen Wan Coast and Castle Peak Road (i.e.
WSRs B5 – B8), with the maximum elevation of 0.8/0.9 mg L-1 in
dry/wet seasons. These findings were qualitatively consistent with those for
the HZMB approved EIAs. Further South of Tsing Yi Island, the predicted SS impacts due to the concurrent projects were
reduced.
From the assessment
of the predicted data, it may
be concluded that the SS impacts of the concurrent projects on the WSRs are not significant. According
to the results given in Appendix 3.8,
no SS exceedance was found at any
gazetted beach, coral communities or
fish culture zone for this scenario. The SS exceedance at WSD1, WSD8, WSD9 and EMSD1 in Scenario 7 are due to the
high SS background level as mentioned
in previous sections. The maximum contribution from the concurrent projects to these WSRs is 0.5/0.8 mg L-1,
which is not significant and could be further
reduced by the mitigation measures proposed in Section 3.8.
The maximum predicted sedimentation rate at all the coral communities for Scenario 7 was less than 23 g m-2 per day (22.2 g m-2 per day at WSR CR9). A maximum of 43 g m-2 per day was obtained when this value was added to the maximum predicted sedimentation rate given in Section 3.7.1.3 below, which is well within the criterion of 100g m-2 per day.
In the event the Container Terminal Operators need to undertake maintenance dredging when capital works for this Project are underway, one of the three dredgers located within container basin (Zone 1 to 6 (including subzones) of Appendix 3.13) for this Project (either the GD or CSD) will be temporarily suspended during the period of the CTO’s maintenance works. The replacement of one dredger in the KTCB for this Project by one dredger for the CTO maintenance works will, by interpolation, result in similar predicted SS levels at the WSRs as to the previous scenarios assumed for the capital works dredging. In other words, it can be assumed that if the CTO undertake maintenance dredging concurrently with this Project, the SS levels will be similar to those predicted for 3 dredgers operating under the capital works dredging programme.
3.5.1.3 Sedimentation Rate
The sedimentation rates at those locations where coral
communities are identified, namely, Peng Chau, Kau Yi Chau, Western Fairway,
East Lamma Channel and north of
3.5.1.4 Impacts on the Gazetted Beaches
During the
consultations for this Project, some concerns were expressed in relation to the
effects of the dredging works on the Ting Kau gazetted beaches. The modelling results indicated that no
significant SS impact due to the Project was predicted at these beaches. In addition, the sediment analysis also
indicated that no E.coli was identified in the samples collected from
nearby the sewage outfalls and as such it may be surmised that the dredging works
will not affect water quality or the health of the gazetted beaches.
3.5.1.5 Dissolved Oxygen and Total Inorganic Nitrogen
The minimum depth-averaged and bottom layer DO for all scenarios in dry and wet seasons at beaches, fish culture zones, marine ecology sensitive receivers and the cooling and seawater intakes were predicted based on the methodology in Section 3.5.2. The predicted DO and TIN at individual WSRs are presented in Appendix 3.9 and summarised in Table 3.25.
No exceedance of WQO of DO in the bottom layer WSD1 – WSD4, WSD6 – WSD8, WSD10, EMSD1, C1 – C4, B9, B10, CR1 – CR4, CR8 – CR18, and F2 – F4, especially for those in the Southern WCZ. TIN exceedance was recorded at WSRs WSD1 – WSD4, WSD6 – WSD8, WSD10, EMSD1, C1 – C4, B9, B10, CR1 – CR4, CR8 – CR18, and F2 – F4, especially for those in the Southern WCZ. The elevations are considered to be due to the non-compliance of the ambient TIN levels with the WQO recorded at the EPD monitoring stations (Table 3.11). Similarly, the DO non-compliance at WSRs WSD1 – WSD9, EMSD1, C1 – C7, B1 – B8, CR1 – CR7, and F1 – F4 in wet seasons is due to low ambient DO levels with WQO recorded at the EPD monitoring stations. The results of DO and TIN for the “Alternative Scenario” (i.e., 5 dredgers operating simultaneously) are presented in Table A3.5 in Appendix 3.2 for reference purpose only.
A summary of the results for Scenarios 1 – 7 is presented
below.
Scenario 1
As presented in Table A3.9a and Table A3.9b of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 1 is predicted to be 0.017 mgL-1 at WSR WSD1. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.002 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0015 mgL-1 at WSR WSD1.
Scenario 2
As presented in Table A3.9c and Table A3.9d of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 2 is predicted to be 0.017 mgL-1 at WSR WSD1. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.002 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0015 mgL-1 at WSR WSD1.
Scenario 3
As presented in Table A3.9e and Table A3.9f of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 3 is predicted to be 0.011 mgL-1 at WSR CR9. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.003 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0009 mgL-1 at WSR CR9.
Scenario 4
As presented in Table A3.9g and Table A3.9h of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 4 is predicted to be 0.018 mgL-1 at WSR WSD1. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.001 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0015 mgL-1 at WSR WSD1.
Scenario 5
As presented in Table A3.9i and Table A3.9j of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 5 is predicted to be 0.018 mgL-1 at WSR WSD1. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.001 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0015 mgL-1 at WSR WSD1.
Scenario 6
As presented in Table A3.9k and Table A3.9l of Appendix 3.9, the maximum decrease in depth-averaged DO for Scenario 6 is predicted to be 0.018 mgL-1 at WSR WSD1. The maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.002 mgL-1 and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0015 mgL-1 at WSR WSD1.
Scenario 7
As presented in Table
A3.9m and Table A3.9n of Appendix 3.9,
the maximum decrease in depth-averaged DO for Scenario 7 is predicted to be
0.013 mgL-1 at WSR CR9. The
maximum decrease in depth-averaged DO at WSR F1 for this scenario is 0.01 mgL-1
and there is insignificant DO depletion at WSR F2 and F3. The maximum increase in TIN for this scenario is predicted to be 0.0011 mgL-1 at WSR CR9.
Summary of impacts on DO and TIN
Although there will be decreases in DO levels, the impacts on depth-averaged DO can be surmised as being very minor which is considered to be a minimal impact on the water quality. The increase in TIN concentrations at WSRs for all scenarios was predicted to be less than 0.002 mgL-1, which is considered to be a minimal impact on the water quality. The existing water quality in some areas has already breached the WQO for depth-averaged DO and TIN.
It may be surmised that
there is no significant impact relating to dissolved oxygen and total inorganic nitrogen for all
dredging scenarios assessed.
The non-compliance of minimum depth-averaged DO levels at the beaches, corals,
water intakes and fish culture zones and maximum TIN at WSRs within
Table 3.25: Summary of Dissolved Oxygen for Scenario 1-7
|
|
Minimum Depth-averaged DO level (mgL-1) |
Minimum DO level at bottom layer (mgL-1) |
Maximum TIN concentration (mgL-1)# |
|
Scenario 1 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2903 |
|
Wet Season |
3.60 |
2.70 |
0.3702 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2502 |
|
Wet Season |
3.70 |
2.50 |
0.5007 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2902 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3507 |
|
Wet Season |
3.60 |
2.50 |
0.5311 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3509 |
|
Wet Season |
3.60 |
2.60 |
0.5315 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 2 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2903 |
|
Wet Season |
3.60 |
2.70 |
0.3702 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2501 |
|
Wet Season |
3.70 |
2.50 |
0.5007 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2902 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3507 |
|
Wet Season |
3.60 |
2.50 |
0.5311 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3509 |
|
Wet Season |
3.60 |
2.60 |
0.5315 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 3 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.69 |
0.2903 |
|
Wet Season |
3.60 |
2.69 |
0.3703 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2502 |
|
Wet Season |
3.70 |
2.50 |
0.5009 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2903 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3502 |
|
Wet Season |
3.60 |
2.50 |
0.5301 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3502 |
|
Wet Season |
3.60 |
2.60 |
0.5302 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 4 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2903 |
|
Wet Season |
3.60 |
2.70 |
0.3702 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2501 |
|
Wet Season |
3.70 |
2.50 |
0.5006 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2901 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3507 |
|
Wet Season |
3.60 |
2.50 |
0.5311 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3509 |
|
Wet Season |
3.60 |
2.60 |
0.5315 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 5 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2903 |
|
Wet Season |
3.60 |
2.70 |
0.3702 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2501 |
|
Wet Season |
3.70 |
2.50 |
0.5005 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2901 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3507 |
|
Wet Season |
3.60 |
2.50 |
0.5311 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3510 |
|
Wet Season |
3.60 |
2.60 |
0.5315 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 6 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2902 |
|
Wet Season |
3.60 |
2.70 |
0.3702 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2501 |
|
Wet Season |
3.70 |
2.50 |
0.5007 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.50 |
5.70 |
0.2902 |
|
Wet Season |
3.60 |
2.70 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3505 |
|
Wet Season |
3.60 |
2.50 |
0.5310 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3507 |
|
Wet Season |
3.60 |
2.60 |
0.5315 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Scenario 7 |
|
|
|
|
Gazetted Beaches |
|
|
|
|
Dry Season |
5.49 |
5.69 |
0.2906 |
|
Wet Season |
3.59 |
2.69 |
0.3705 |
|
Non-compliance? |
Yes† |
No |
No^ |
|
Corals |
|
|
|
|
Dry Season |
5.90 |
6.00 |
0.2502 |
|
Wet Season |
3.70 |
2.50 |
0.5011 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Fish Culture Zone |
|
|
|
|
Dry Season |
5.49 |
5.69 |
0.2908 |
|
Wet Season |
3.59 |
2.69 |
0.5000 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
Cooling Water Intakes |
|
|
|
|
Dry Season |
5.00 |
5.00 |
0.3503 |
|
Wet Season |
3.60 |
2.50 |
0.5302 |
|
Non-compliance? |
Yes† |
No |
Yes* |
|
|
|
|
|
|
Dry Season |
4.99 |
4.99 |
0.3503 |
|
Wet Season |
3.60 |
2.59 |
0.5303 |
|
Non-compliance? |
Yes† |
No |
Yes* |
# The WQO
for TIN is 0.4 mgL-1
except at
^ Except for B9 and B10, where
non-compliance of TIN levels are predicted due to the non-compliance of the
background TIN levels with the WQO. TIN levels at B9 and B10 are not the
maximum predicted TIN concentration among the gazetted beaches,
* Due to the
non-compliance of the background
TIN levels with the WQO.
† Due to the
non-compliance of the background depth-averaged DO levels with the WQO in Wet
Season.
3.5.1.6 Potential Contaminant Release During Dredging
An indication of the potential
release of contaminants from the marine sediments during dredging was determined
using the results of the elutriate tests from the laboratory testing conducted under the marine Site Investigation (SI). The locations of sediment sampling are shown in Figure 4.1 and Figure 4.2.
The description of the marine SI is contained within Chapter 4.
Heavy Metals, TBT,
PCB’s Total PAHs and Chlorinated Pesticides
Details of the elutriate test results for heavy metals, TBT, PCBs, total PAHs and chlorinated pesticides are included in Appendix 3.1, with the results summarized in Table 3.26. The measured levels of all the PCBs, PAHs and chlorinated pesticides were below the detection limits. The highest TBT concentration was 36 ngL-1 measured at D374. Similarly, the measured heavy metal concentrations at most sampling locations were below the detection limits. Non-compliance of the water quality criteria (Table 3.26) for heavy metals and organics was only observed in the arsenic concentration measured at sampling location S3, S6, S11, S12, S15, S32, D174, D196 and D234 in Rambler Channel and Northern Fairway. However, the non-compliance was considered to be minor with the maximum arsenic concentration of 33 g L-1 (at location S6) compared with the water quality criterion of 25 g L-1. Based on the maximum arsenic concentration, the dilution required to meet the relevant water quality criterion was calculated to be 1.3.
With reference to Figure 3.1 and Figure 4.1, the nearest WSRs to the sampling location S6, S11 and S12 which demonstrated exceedance of arsenic concentration were WSD1, C2 and EMSD1, which are located at least 600m away from the sampling locations. All of the WSRs are flushing water and cooling water intakes. There are no criteria for heavy metals or organics in connection with the WSD seawater intakes, thus reference has been made to the UK Water Quality Standard.
It should be stressed that any release of heavy metals during dredging will be rapidly diluted by the large volume of marine water within the dredging site and the small exceedance of arsenic at a few points is not expected to adversely affect WSD intake water quality. According to the elutriate test results, it was concluded that the potential impacts of release of heavy metals and organics due to seabed disturbance on all WSRs (in particular the nearby beaches, fish culture zones, ecological sensitive receivers) are negligible.