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.
Table 3.26: Elutriate Test Results of Sediment Samples
|
|
Metals
(µg/l) |
Total
PCBs (µg/l) |
Total
PAHs (µg/l) |
TBT
(ng/l) |
||||||||
Vibrocore |
Sampling
Depth |
As |
Cd |
Cr |
Cu |
Pb |
Hg |
Ni |
Ag |
Zn |
|
|
|
Water Quality Standards |
25(1) |
2.5(1) |
15(1) |
5(1) |
25(1) |
0.3(1) |
30(1) |
1.9(2) |
40(1) |
0.03(2) |
3.0(3) |
100(4) |
|
S1-2 |
0-0.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S1-2 |
0.9-1.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S1-2 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
S2 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S2 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S2 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
1 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S2 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
3 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S3 |
0-0.9M |
21 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S3 |
0.9-1.9M |
27 |
<0.2 |
<10 |
1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S3 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S3 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
2 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S4 |
0-0.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
S4 |
0.9-1.9M |
22 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S4 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S4 |
Elutriate Blank |
<10 |
0.4 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S5-2 |
0-0.9M |
17 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S5-2 |
0.9-1.9M |
21 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S5-2 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S6 |
0-0.9M |
23 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S6 |
0.9-1.9M |
33 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S6 |
1.9-2.9M |
30 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
21 |
S6 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S7 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S7 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S7 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S7 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S8 |
0-0.9M |
12 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S8 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S8 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
2 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S9 |
0-0.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S9 |
0.9-1.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S9 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S10 |
0-0.9M |
21 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S10 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S10 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S10 |
Elutriate Blank |
<10 |
0.2 |
<10 |
3 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S11 |
0-0.9M |
28 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S11 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S11 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S12 |
0-0.9M |
31 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S12 |
0.9-1.9M |
32 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
S12 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
S12 |
Elutriate Blank |
<10 |
0.3 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S13 |
Grab Sample |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S13 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
3 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S14 |
0-0.9M |
13 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S14 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S15 |
0-0.9M |
31 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
63 |
S15 |
0.9-1.9M |
11 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S15 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S15 |
Elutriate Blank |
<10 |
0.3 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S17 |
0-0.9M |
11 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S17 |
0.9-1.9M |
23 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S17 |
Elutriate Blank |
<10 |
0.3 |
<10 |
2 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S18 |
Grab Sample |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S18 |
Elutriate Blank |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S19 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S19 |
0.9-1.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S19 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S19 |
Elutriate Blank |
<10 |
0.7 |
<10 |
1 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
S21 |
0-0.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S21 |
0.9-1.9M |
15 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S21 |
1.9-2.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S21 |
Elutriate Blank |
<10 |
0.5 |
<10 |
1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D174 |
0-0.9M |
31 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D174 |
0.9-1.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D174 |
1.9-2.9M |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D174 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D196 |
0-0.9M |
31 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
D196 |
0.9-1.9M |
24 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
30 |
D196 |
1.9-2.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D196 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
D202 |
0-0.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D202 |
0.9-1.9M |
12 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D202 |
1.9-2.9M |
13 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D202 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D214 |
0-0.9M |
15 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D214 |
0.9-1.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<14 |
D214 |
1.9-2.9M |
22 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
12 |
D214 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<14 |
D221 |
0-0.9M |
17 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D221 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D221 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D234 |
0-0.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D234 |
0.9-1.9M |
24 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D234 |
1.9-2.9M |
32 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D234 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D238 |
0-0.9M |
13 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D238 |
0.9-1.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D238 |
1.9-2.9M |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D238 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S29 |
Grab Sample |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S29 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S30 |
0-0.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S30 |
0.9-1.9M |
17 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S30 |
1.9-2.9M |
23 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S30 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D272 |
Grab Sample |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D272 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S32 |
0-0.9M |
32 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S32 |
0.9-1.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S32 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S32 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D298 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D298 |
0.9-1.9M |
19 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D298 |
1.9-2.9M |
21 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D298 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S34 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<13 |
S34 |
0.9-1.9M |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S34 |
1.9-2.9M |
12 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S34 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<13 |
S35 |
0-0.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S35 |
0.9-1.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S35 |
1.9-2.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S35 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D320 |
0-0.9M |
11 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D320 |
0.9-1.9M |
13 |
<0.2 |
<10 |
2 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<9 |
D320 |
1.9-2.9M |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D320 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D330 |
0.9-1.9M |
15 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D330 |
1.9-2.9M |
12 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
2 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D330 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D337 |
0-0.9M |
14 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D337 |
0.9-1.9M |
16 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D337 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D337 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<8 |
S40 |
0-0.9M |
18 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S40 |
0.9-1.9M |
15 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S40 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D355 |
0-0.9M |
12 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D355 |
0.9-1.9M |
13 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D355 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D362 |
0-0.9M |
10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D362 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<13 |
D362 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<13 |
S44 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S44 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S44 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<14 |
D374 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
36 |
D374 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
D374 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<10 |
S47 |
0-0.9M |
17 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S47 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
S47 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D378 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D378 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D378 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<15 |
D381 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D381 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D381 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
D381 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S50 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S50 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<11 |
S50 |
1.9-2.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
S50 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D386 |
0-0.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D386 |
0.9-1.9M |
<10 |
<0.2 |
<10 |
<1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
D386 |
Elutriate Blank |
<10 |
<0.2 |
<10 |
1 |
<1 |
<0.5 |
<1 |
<1 |
<10 |
<0.05 |
<0.2 |
<12 |
(1) Value
in Bold indicate exceedance of
relevant criteria
(2)
(3) USEPA, Criteria Maximum Concentration (CMC) of the USEPA Water Quality Criteria (Saltwater)
(4)
Australian
and
(5)
Michael
H. Salazar and Sandra M. Salazar (1996).
“Mussels as Bioindicators:
Effects of TBT on Survival, Bioaccumulation, and Growth under Natural
Conditions” in Organotin, edited by M. A. Champ and P. F. Seligman. Chapman & Hall,
(6) WSD Water Quality Objectives of Sea Water for Flushing Supply (at intake point)
Ammoniacal
Nitrogen (NH3-N) and Unionised
Ammonia (UIA)
Background: The depth-averaged background TIN (which includes NH3-N and
UIA) for dry and wet seasons are summarized in Table 3.11, as derived from EPD’s routine marine
water quality monitoring data using the methodology described in Section 3.5.2. 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, while the depth-averaged UIA values show compliance
with the WQO criteria of 0.021 mg/l
annual average.
Elutriate Test Results: The first batch of sediment samples results were provided in February 2010, which included a mixture of grab and vibrocore samples. Based on a review of these test results, a small number of samples were observed to be suspect (for example, samples with lower than expected pH values), which gave concerns that these samples may have been contaminated during the sampling process. After a detailed analysis, further sampling at selected stations as shown in Figure 4.1 was undertaken in May 2010. Based on the two sets of field sampling data, all those data which exhibit consistent parameters (e.g., with pH greater than 7.8) were subsequently used for the analysis of ammoniacal-nitrogen and unionised ammonia, as shown in Table 3.27. In this table, the ammoniacal-nitrogen values were measured directly from the elutriate tests on the collected sediment samples collected, whilst the UIA values were derived using the formulae as detailed in Section 3.5.2.
Table 3.27: Elutriate Test Results
Site |
Sampling Depth |
NH3-N concentration (mg L-1) |
(NH3-N
– blank) concentration (mg L-1) |
UIA
concentration (mg L-1) |
(UIA
– blank) concentration (mg L-1) |
S1-2 |
GRAB |
2.23 |
2.08 |
0.135 |
0.126 |
S1-2 |
ELUTRIATE BLANK |
0.15 |
|
0.009 |
|
S2 |
GRAB |
13.20 |
13.06 |
0.969 |
0.959 |
S2 |
ELUTRIATE BLANK |
0.14 |
|
0.010 |
|
S2 |
0-0.9m |
20.06 |
19.88 |
1.472 |
1.459 |
S2 |
ELUTRIATE BLANK |
0.18 |
|
0.013 |
|
S2 |
0.9-1.9m |
20.84 |
20.66 |
1.530 |
1.516 |
S2 |
ELUTRIATE BLANK |
0.18 |
|
0.013 |
|
S2 |
1.9-2.9m |
3.21 |
3.03 |
0.236 |
0.222 |
S2 |
ELUTRIATE BLANK |
0.18 |
|
0.013 |
|
S3 |
GRAB |
3.03 |
2.90 |
0.230 |
0.220 |
S3 |
ELUTRIATE BLANK |
0.13 |
|
0.010 |
|
S4 |
GRAB |
4.85 |
4.74 |
0.358 |
0.350 |
S4 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S4 |
0-0.9m |
6.93 |
6.79 |
0.512 |
0.502 |
S4 |
ELUTRIATE BLANK |
0.14 |
|
0.010 |
|
S4 |
0.9-1.9m |
2.24 |
2.11 |
0.166 |
0.156 |
S4 |
ELUTRIATE BLANK |
0.13 |
|
0.010 |
|
S4 |
1.9-2.9m |
2.06 |
1.93 |
0.152 |
0.143 |
S4 |
ELUTRIATE BLANK |
0.13 |
|
0.010 |
|
S5-2 |
GRAB |
2.96 |
2.81 |
0.222 |
0.211 |
S5-2 |
ELUTRIATE BLANK |
0.15 |
|
0.011 |
|
S6 |
GRAB |
8.24 |
8.13 |
0.610 |
0.601 |
S6 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S7 |
GRAB |
4.02 |
3.92 |
0.308 |
0.301 |
S7 |
ELUTRIATE BLANK |
0.10 |
|
0.008 |
|
S8 |
GRAB |
3.67 |
3.56 |
0.283 |
0.274 |
S8 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S9 |
0-0.9M |
13.43 |
13.14 |
0.070 |
0.068 |
S9 |
0.9-1.9M |
0.70 |
0.41 |
0.004 |
0.002 |
S9 |
ELUTRIATE BLANK |
0.29 |
|
0.002 |
|
S10 |
GRAB |
1.22 |
1.10 |
0.089 |
0.081 |
S10 |
ELUTRIATE BLANK |
0.12 |
|
0.009 |
|
S10 |
0-0.9m |
2.14 |
2.03 |
0.157 |
0.149 |
S10 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S10 |
0.9-1.9m |
2.63 |
2.52 |
0.193 |
0.185 |
S10 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S10 |
1.9-2.9m |
2.77 |
2.65 |
0.203 |
0.194 |
S10 |
ELUTRIATE BLANK |
0.12 |
|
0.009 |
|
S11 |
0-0.9M |
1.11 |
1.06 |
0.056 |
0.053 |
S11 |
0.9-1.9M |
1.42 |
1.37 |
0.071 |
0.069 |
S11 |
ELUTRIATE BLANK |
0.05 |
|
0.003 |
|
S12 |
0-0.9M |
7.82 |
7.60 |
0.054 |
0.052 |
S12 |
0.9-1.9M |
4.88 |
4.66 |
0.034 |
0.032 |
S12 |
1.9-2.9M |
5.02 |
4.80 |
0.035 |
0.033 |
S12 |
ELUTRIATE BLANK |
0.22 |
|
0.002 |
|
S13 |
GRAB |
3.24 |
2.62 |
0.092 |
0.074 |
S13 |
ELUTRIATE BLANK |
0.62 |
|
0.018 |
|
S14 |
GRAB |
2.54 |
2.49 |
0.060 |
0.059 |
S14 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
S15 |
0-0.9M |
9.00 |
8.78 |
0.058 |
0.057 |
S15 |
0.9-1.9M |
4.89 |
4.67 |
0.032 |
0.030 |
S15 |
1.9-2.9M |
4.50 |
4.28 |
0.029 |
0.028 |
S15 |
ELUTRIATE BLANK |
0.22 |
|
0.001 |
|
S17 |
0-0.9M |
5.07 |
5.02 |
0.029 |
0.028 |
S17 |
0.9-1.9M |
9.09 |
9.04 |
0.051 |
0.051 |
S17 |
ELUTRIATE BLANK |
0.05 |
|
0.000 |
|
S18 |
-- |
6.07 |
6.02 |
0.146 |
0.144 |
S18 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
S19 |
GRAB |
4.31 |
4.17 |
0.305 |
0.295 |
S19 |
ELUTRIATE BLANK |
0.14 |
|
0.010 |
|
S21 |
GRAB |
1.21 |
1.03 |
0.087 |
0.074 |
S21 |
ELUTRIATE BLANK |
0.18 |
|
0.013 |
|
D174 |
GRAB |
1.63 |
1.39 |
0.117 |
0.100 |
D174 |
ELUTRIATE BLANK |
0.24 |
|
0.017 |
|
D196 |
GRAB |
3.23 |
3.00 |
0.219 |
0.203 |
D196 |
ELUTRIATE BLANK |
0.23 |
|
0.016 |
|
D202 |
GRAB |
2.01 |
1.87 |
0.149 |
0.138 |
D202 |
ELUTRIATE BLANK |
0.14 |
|
0.010 |
|
S29 |
|
1.22 |
1.17 |
0.035 |
0.033 |
S29 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
D214 |
GRAB |
4.34 |
4.14 |
0.311 |
0.296 |
D214 |
ELUTRIATE BLANK |
0.20 |
|
0.014 |
|
D221 |
0-0.9M |
1.24 |
0.99 |
0.077 |
0.062 |
D221 |
0.9-1.9M |
1.66 |
1.41 |
0.103 |
0.088 |
D221 |
ELUTRIATE BLANK |
0.25 |
|
0.016 |
|
D234 |
GRAB |
1.04 |
0.81 |
0.071 |
0.056 |
D234 |
ELUTRIATE BLANK |
0.23 |
|
0.016 |
|
D238 |
GRAB |
3.02 |
2.74 |
0.210 |
0.190 |
D238 |
ELUTRIATE BLANK |
0.28 |
|
0.019 |
|
D238 |
0-0.9m |
9.23 |
9.03 |
0.640 |
0.627 |
D238 |
ELUTRIATE BLANK |
0.20 |
|
0.014 |
|
D238 |
0.9-1.9m |
12.06 |
11.83 |
0.837 |
0.821 |
D238 |
ELUTRIATE BLANK |
0.23 |
|
0.016 |
|
D238 |
1.9-2.9m |
13.61 |
13.40 |
0.944 |
0.930 |
D238 |
ELUTRIATE BLANK |
0.21 |
|
0.015 |
|
S30 |
GRAB |
3.43 |
3.19 |
0.243 |
0.226 |
S30 |
ELUTRIATE BLANK |
0.24 |
|
0.017 |
|
S30 |
0-0.9m |
7.40 |
7.29 |
0.525 |
0.517 |
S30 |
ELUTRIATE BLANK |
0.11 |
|
0.008 |
|
S30 |
0.9-1.9m |
8.22 |
8.10 |
0.583 |
0.575 |
S30 |
ELUTRIATE BLANK |
0.12 |
|
0.009 |
|
S30 |
1.9-2.9m |
8.44 |
8.31 |
0.599 |
0.590 |
S30 |
ELUTRIATE BLANK |
0.13 |
|
0.009 |
|
D272 |
GRAB |
1.19 |
1.14 |
0.030 |
0.029 |
D272 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
S32 |
GRAB |
3.39 |
3.19 |
0.240 |
0.226 |
S32 |
ELUTRIATE BLANK |
0.20 |
|
0.014 |
|
D298 |
GRAB |
0.25 |
0.13 |
0.019 |
0.010 |
D298 |
ELUTRIATE BLANK |
0.12 |
|
0.009 |
|
S34 |
GRAB |
3.00 |
2.90 |
0.235 |
0.228 |
S34 |
ELUTRIATE BLANK |
0.10 |
|
0.008 |
|
S35 |
GRAB |
0.56 |
0.47 |
0.044 |
0.037 |
S35 |
ELUTRIATE BLANK |
0.09 |
|
0.007 |
|
S35 |
0-0.9m |
1.48 |
1.32 |
0.116 |
0.103 |
S35 |
ELUTRIATE BLANK |
0.16 |
|
0.013 |
|
S35 |
0.9-1.9m |
0.78 |
0.62 |
0.061 |
0.049 |
S35 |
ELUTRIATE BLANK |
0.16 |
|
0.013 |
|
S35 |
1.9-2.9m |
1.49 |
1.32 |
0.117 |
0.103 |
S35 |
ELUTRIATE BLANK |
0.17 |
|
0.013 |
|
D320 |
GRAB |
2.59 |
2.48 |
0.210 |
0.201 |
D320 |
ELUTRIATE BLANK |
0.11 |
|
0.009 |
|
D330 |
0-0.9M |
0.38 |
0.33 |
0.009 |
0.008 |
D330 |
0.9-1.9M |
0.11 |
0.06 |
0.003 |
0.001 |
D330 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
D337 |
0-0.9M |
0.35 |
0.30 |
0.008 |
0.007 |
D337 |
0.9-1.9M |
0.44 |
0.39 |
0.011 |
0.009 |
D337 |
1.9-2.9M |
0.67 |
0.62 |
0.016 |
0.015 |
D337 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
S40 |
0-0.9M |
0.44 |
0.39 |
0.009 |
0.008 |
S40 |
0.9-1.9M |
1.45 |
1.40 |
0.029 |
0.028 |
S40 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
D355 |
0-0.9M |
1.01 |
0.96 |
0.020 |
0.019 |
D355 |
0.9-1.9M |
0.49 |
0.44 |
0.010 |
0.009 |
D355 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
D362 |
0-0.9M |
2.66 |
2.61 |
0.058 |
0.057 |
D362 |
0.9-1.9M |
8.66 |
8.61 |
0.188 |
0.187 |
D362 |
ELUTRIATE BLANK |
0.05 |
|
0.001 |
|
S44 |
GRAB |
1.37 |
1.30 |
0.115 |
0.109 |
S44 |
ELUTRIATE BLANK |
0.07 |
|
0.006 |
|
D374 |
GRAB |
0.62 |
0.55 |
0.051 |
0.045 |
D374 |
ELUTRIATE BLANK |
0.07 |
|
0.006 |
|
S47 |
GRAB |
0.66 |
0.61 |
0.053 |
0.049 |
S47 |
ELUTRIATE BLANK |
0.05 |
|
0.004 |
|
D378 |
GRAB |
0.82 |
0.71 |
0.070 |
0.060 |
D378 |
ELUTRIATE BLANK |
0.11 |
|
0.009 |
|
D381 |
GRAB |
2.19 |
2.14 |
0.182 |
0.178 |
D381 |
ELUTRIATE BLANK |
0.05 |
|
0.004 |
|
S50 |
GRAB |
1.84 |
1.80 |
0.157 |
0.153 |
S50 |
ELUTRIATE BLANK |
0.04 |
|
0.003 |
|
D386 |
GRAB |
1.85 |
1.81 |
0.157 |
0.153 |
D386 |
ELUTRIATE BLANK |
0.04 |
|
0.003 |
|
Based on the above results, it was observed that the majority of the measured ammoniacal nitrogen values were less than 5 mg L-1, with some data in the range of 5 mg L-1 to 13.6 mg L-1. It was also seen that within the Project area, a hot spot was found at location S2, where its ammoniacal nitrogen value was recorded at more than 20 mg L-1. Upon examination it was surmised that the high reading could be due to historically deposited contaminants from activities in the immediate area. Based on the above table, a worst case scenario was presented for the assessment of ammoniacal nitrogen and UIA.
In addition to the worst case scenario mentioned above, a two-phase approach has also been adopted: firstly, to assess impacts of the above elutriate test results by “surgically” removing S2 from the overall data, and secondly, to assess the impacts contributed by the S2 sediment data on its own. The rationale for adopting such an approach is to allow an assessment of the impacts of the “less contaminated” area i.e. almost 99% of the dredging area to determine if compliance of the WQO’s and standards can be met during the main portion of capital works dredging. If compliance cannot be met then mitigation measures would need to be proposed and residual impacts assessed. The S2 portion of dredging works area has thus been treated as a separate part of the overall dredging plan, and a highly specific approach to address the impacts of S2 independently and thus determine a discrete package of mitigation measures for this particular part of the overall dredging has been proposed.
Ammoniacal Nitrogen (worst case scenario i.e. with all samples including S2 considered, unmitigated scenario): To assess the impact of ammoniacal nitrogen on the sensitive receivers, the results from the sampling locations as indicated in Table 3.27 were grouped based on the different dredger locations (or “source”) as shown in Figure 3.5a and summarised in Table 3.29 making reference to the overall zonings for the dredging works as discussed in the Marine Traffic Impact Assessment prepared as part of this Assignment. Table 3.28 below shows the averaged NH3-N values used in the assessment for each source location.
Table 3.28: Ammoniacal Nitrogen Concentrations at
Sediment Sources (All sampling locations included)
Sediment Source |
Sampling
Locations |
Average NH3-N concentration (mg L-1) |
A |
S1-2, S2, S3,
S4, S5-2, S6, S7, S8, S10, S11 |
4.47 |
B |
S13, S14,
S18, S19, S21, D174, D196, D202 |
2.82 |
C |
D272, S32,
D298, S34, S35, D320, S29, S30, D234, D238, D221, D214 |
2.84 |
D |
D330, D337, S40,
D355, D362, S44 |
1.52 |
E |
D374, S47,
D378, D381, S50, D386 |
1.27 |
Table 3.29: Combination of Scenarios
Scenario |
Grouping of Sediment Source |
1 |
A + C + D |
2 |
A + C + E |
3 |
C + D + E |
4 |
A + B + D |
5 |
A + B + C |
Note: Please refer to Figure 3.5a
for various source locations
Based on the above table as well as dilution factors from the
tracer model, the assessment of NH3-N has been undertaken and full details of the analyses are contained in Appendix 3.12. From the predicted results it is noted
that full compliance is achieved at the corals, fish culture zones and
beaches. Some non-compliance has been
identified at two of the WSD intakes based on the guideline of 1
mg L-1 NH3-N. The
following analysis therefore focuses on the seawater intakes and the results in
Table 3.30 below show the predicted concentrations at
the various WSD seawater intakes for the worst case scenario.
Table 3.30: Predicted Elutriate
Ammoniacal Nitrogen Concentrations at
WSD Flushing Water Intakes (all sampling locations included)
Sensitive
Receivers |
Assess-ment
Point |
Scenario 1 Elutriate NH3-N concentration (mg L-1) |
Scenario 2 Elutriate NH3-N concentration (mg L-1) |
Scenario 3 Elutriate NH3-N concentration (mg L-1) |
Scenario 4 Elutriate NH3-N concentration (mg L-1) |
Scenario 5 Elutriate NH3-N concentration (mg L-1) |
|||||
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
||
WSD |
|||||||||||
Tsing Yi |
WSD1 |
1.24 |
1.14 |
1.23 |
1.12 |
0.09 |
0.10 |
1.48 |
1.28 |
1.52 |
1.32 |
|
WSD2 |
0.10 |
0.17 |
0.10 |
0.16 |
0.07 |
0.13 |
0.10 |
0.14 |
0.14 |
0.19 |
Sheung Wan |
WSD3 |
0.06 |
0.20 |
0.06 |
0.18 |
0.02 |
0.11 |
0.10 |
0.23 |
0.12 |
0.26 |
Central Water Front |
WSD4 |
0.04 |
0.18 |
0.04 |
0.16 |
0.01 |
0.10 |
0.09 |
0.19 |
0.10 |
0.21 |
Ap Lei Chau |
WSD5 |
0.04 |
0.09 |
0.04 |
0.08 |
0.03 |
0.07 |
0.03 |
0.07 |
0.04 |
0.09 |
|
WSD6 |
0.08 |
0.19 |
0.08 |
0.16 |
0.01 |
0.10 |
0.24 |
0.24 |
0.24 |
0.25 |
Cheung Sha Wan |
WSD7 |
0.05 |
0.16 |
0.05 |
0.13 |
0.01 |
0.09 |
0.14 |
0.18 |
0.14 |
0.19 |
Tsuen Wan |
WSD8 |
0.93 |
0.35 |
0.92 |
0.33 |
0.10 |
0.08 |
1.08 |
0.39 |
1.13 |
0.41 |
Near |
WSD9 |
0.18 |
0.12 |
0.17 |
0.10 |
0.10 |
0.08 |
0.17 |
0.10 |
0.22 |
0.12 |
Lamma Power Station |
WSD10 |
0.01 |
0.06 |
0.01 |
0.05 |
0.01 |
0.05 |
0.01 |
0.05 |
0.01 |
0.06 |
|
EMSD1 |
0.47 |
0.56 |
0.47 |
0.54 |
0.06 |
0.09 |
0.77 |
0.72 |
0.80 |
0.74 |
- Value in Bold indicates exceedance of relevant WSD’s Water Quality Criteria.
The guideline for NH3-N
for WSD seawater water intakes is 1 mg L-1.
From the results presented above it is noted that NH3-N
levels exceed the guideline with predicted results of 1.52 mg L-1 and 1.32 mg L-1 at WSD1 in the dry and wet seasons respectively. WSD8 is also predicted
to have an exceedance of the NH3-N
value of 1.13 mg L-1
in dry season for most scenarios except scenario 3. Full compliance is however
predicted for the wet season at WSD8.
The concerns
relating to exceedance of NH3-N at WSD’s seawater intakes are due to
the possible use of chemical treatment or physical reductions of the potential
contaminant release. Addition of
chemicals would require modifications to current practices at the seawater
pumping stations and thus alternatives such as a physical reduction in the
release of contaminants was preferred to address this issue. There is evidence from work undertaken by the
USEPA to support the view that by reducing the release rate of materials (i.e.
SS reduction through control of dredging rate) the contaminant releases can be
commensurately reduced. This mitigation
measure is favoured over the addition of chemicals to seawater at the intakes
as it treats the problem at source without creating an additional concern of
the use of chemicals and appropriate (and possibly variable) dosing rates.
In this case the mitigation measures required to reduce the impacts on the WSD1 seawater intake would however be significant if S2 were retained in the overall dredging plan. This would adversely impact the dredging programme and the duration of dredging and could also prolong the impacts if dredging rates were dramatically reduced. To address these exceedances in a more pragmatic manner, the two-phase approach mentioned earlier has been developed.
Ammoniacal Nitrogen (with excision of hotspot S2, unmitigated): With this approach, Table 3.31 below indicates the averaged NH3-N values to be used in the assessment for each source location.
Table 3.31: Ammoniacal Nitrogen Concentrations at Sediment Sources (with excision of hotspot S2)
Source |
Sampling
Locations |
Average NH3-N, mg L-1 |
A |
S1-2, S3, S4,
S5-2, S6, S7, S8, S10, S11 |
3.40 |
B |
S13, S14,
S18, S19, S21, D174, D196, D202 |
2.82 |
C |
D272, S32,
D298, S34, S35, D320, S29, S30, D234, D238, D221, D214 |
2.84 |
D |
D330, D337,
S40, D355, D362, S44 |
1.52 |
E |
D374, S47,
D378, D381, S50, D386 |
1.27 |
Based on the above table as well as dilution factors from the tracer model, the assessment of NH3-N at the various WSD seawater intakes for this scenario is shown in Table 3.32.
Table 3.32: Predicted Elutriate
Ammoniacal Nitrogen Concentrations at WSD
Flushing Water Intakes (with the excision of hotspot S2)
Sensitive
Receivers |
Assess-ment
Point |
Scenario 1 Elutriate NH3-N concentration (mg L-1) |
Scenario 2 Elutriate NH3-N concentration (mg L-1) |
Scenario 3 Elutriate NH3-N concentration (mg L-1) |
Scenario 4 Elutriate NH3-N concentration (mg L-1) |
Scenario 5 Elutriate NH3-N concentration (mg L-1) |
|||||
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
||
WSD |
|
|
|
|
|
|
|
|
|
|
|
Tsing Yi |
WSD1 |
0.96 |
0.88 |
0.96 |
0.87 |
0.09 |
0.10 |
1.20 |
1.03 |
1.24 |
1.06 |
|
WSD2 |
0.09 |
0.16 |
0.09 |
0.14 |
0.07 |
0.13 |
0.09 |
0.13 |
0.13 |
0.17 |
Sheung Wan |
WSD3 |
0.05 |
0.18 |
0.05 |
0.15 |
0.02 |
0.11 |
0.10 |
0.20 |
0.11 |
0.24 |
Central Water Front |
WSD4 |
0.03 |
0.16 |
0.03 |
0.14 |
0.01 |
0.10 |
0.08 |
0.17 |
0.09 |
0.19 |
Ap Lei Chau |
WSD5 |
0.03 |
0.08 |
0.04 |
0.07 |
0.03 |
0.07 |
0.03 |
0.07 |
0.04 |
0.08 |
|
WSD6 |
0.07 |
0.17 |
0.07 |
0.14 |
0.01 |
0.10 |
0.22 |
0.21 |
0.22 |
0.23 |
Cheung Sha Wan |
WSD7 |
0.04 |
0.14 |
0.04 |
0.11 |
0.01 |
0.09 |
0.13 |
0.16 |
0.13 |
0.17 |
Tsuen Wan |
WSD8 |
0.73 |
0.28 |
0.72 |
0.27 |
0.10 |
0.08 |
0.87 |
0.32 |
0.92 |
0.34 |
Near |
WSD9 |
0.16 |
0.11 |
0.15 |
0.09 |
0.10 |
0.08 |
0.15 |
0.09 |
0.20 |
0.11 |
Lamma Power Station |
WSD10 |
0.01 |
0.06 |
0.01 |
0.04 |
0.01 |
0.05 |
0.01 |
0.05 |
0.01 |
0.05 |
|
EMSD1 |
0.37 |
0.45 |
0.37 |
0.43 |
0.06 |
0.09 |
0.67 |
0.60 |
0.70 |
0.63 |
- Value in Bold indicates exceedance of relevant WSD’s Water Quality Criteria.
Based on the above results, it is noted that the maximum NH3-N concentrations predicted at WSD1 are 1.24 mg L-1 (dry season) and 1.06 mg L-1 (wet season) and at WSD8 are 0.92 mg L-1 (dry season) and 0.34 (wet season) respectively (Appendix 3.12). This means that full compliance with the WSD guideline is achieved at WSD8, and marginal compliance achieved at WSD1 in the wet season. Mitigation measures are thus only required for the dry season. However, to be prudent, mitigation measures backed up by monitoring are recommended for both seasons as described in Section 3.8.
Apart from the WSD flushing water intake guideline for NH3-N, the only other guideline for this parameter in the water control zones is the published guidelines for the protection of marine biota at 0.7 mg L-1. The impacts of the predicted NH3-N based on this guideline are discussed in Chapters 5 and 6.
Ammoniacal Nitrogen (Hotspot S2 only, unmitigated): Using the same approach, i.e. with S2 sediment being the only source of dredging (source A), the averaged NH3-N values were used in the assessment for predicting impacts of dredging S2 in isolation.
Based on the results obtained and contained in Appendix 3.12 as well as dilution factors from the tracer model, the assessment of NH3-N at the various sensitive receivers also indicates non-compliance at some WSD seawater intakes for this scenario as shown in Table 3.33.
Table 3.33: Predicted Elutriate
Ammoniacal Nitrogen Concentrations at
WSD Flushing Water Intakes (for only hotspot S2 case)
Sensitive
Receivers |
Assessment
Point |
Elutriate NH3-N concentration (mg L-1) |
|
Dry Season |
Wet Season |
||
WSD
|
|
|
|
Tsing Yi |
WSD1 |
3.66 |
3.33 |
|
WSD2 |
0.13 |
0.20 |
Sheung Wan |
WSD3 |
0.12 |
0.31 |
Central Water Front |
WSD4 |
0.10 |
0.27 |
Ap Lei Chau |
WSD5 |
0.04 |
0.09 |
|
WSD6 |
0.24 |
0.31 |
Cheung Sha Wan |
WSD7 |
0.14 |
0.23 |
Tsuen Wan |
WSD8 |
2.67 |
0.87 |
Near |
WSD9 |
0.27 |
0.14 |
Lamma Power Station |
WSD10 |
0.01 |
0.06 |
|
EMSD1 |
1.34 |
1.51 |
- Value in Bold indicates exceedance of relevant WSD’s Water Quality Criteria.
Not unexpectedly given the proximity of source A (i.e. S2) to WSD1 seawater intake, the results indicate that WSD1 has the highest predicted NH3-N level of 3.66 mg L-1 and 3.33 mg L-1 in both the dry and wet season respectively. A level of 2.67 mg L-1 is predicted at WSD8 for the dry season with compliance predicted during the wet season. A value of 1.34 mg L-1 and 1.51 mg L-1 of NH3-N is anticipated at EMSD1. In order to comply with the WSD seawater intake criteria, mitigation measures would thus be required and are described in Section 3.8.
Unionized Ammonia (worst
case scenario i.e. with all samples including S2 considered, unmitigated): To assess the impact of UIA
on the sensitive receivers, the results from the sampling locations as
indicated in Table 3.27
were similarly grouped based on the dredger locations as shown in Figure 3.5a. As mentioned in Section 3.5.2, the UIA values were derived based on the measured NH3-N
values; as such, the average UIA value is 0.327 mg/L for Source A, 0.136 mg/L
for Source B, 0.195 mg/L for Source C, 0.046 mg/L for Source D and 0.107 mg/L
for Source E.
Based on the dilution factors from the tracer model, the assessment of UIA for the various sensitive receivers for the worst case scenario is shown in Table 3.34.
Table 3.34: Predicted Elutriate
UIA Concentrations at
Sensitive
Receivers |
Assessment
Point |
Scenario 1 Elutriate
UIA concentration (mg L-1) |
Scenario 2 Elutriate
UIA concentration (mg L-1) |
Scenario 3 Elutriate
UIA concentration (mg L-1) |
Scenario 4 Elutriate
UIA concentration (mg L-1) |
Scenario 5 Elutriate
UIA concentration (mg L-1) |
||||||||||
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
||
Gazetted Beaches |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.011 |
0.010 |
0.011 |
0.011 |
0.010 |
0.011 |
0.007 |
0.007 |
0.007 |
0.010 |
0.008 |
0.009 |
0.013 |
0.011 |
0.012 |
Approach |
B2 |
0.065 |
0.011 |
0.038 |
0.066 |
0.011 |
0.039 |
0.007 |
0.005 |
0.006 |
0.068 |
0.010 |
0.039 |
0.073 |
0.012 |
0.043 |
Ting Kau |
B3 |
0.051 |
0.010 |
0.031 |
0.051 |
0.010 |
0.031 |
0.006 |
0.005 |
0.006 |
0.052 |
0.009 |
0.031 |
0.056 |
0.011 |
0.034 |
|
B4 |
0.033 |
0.008 |
0.021 |
0.033 |
0.008 |
0.021 |
0.007 |
0.005 |
0.006 |
0.032 |
0.007 |
0.019 |
0.037 |
0.009 |
0.023 |
Casam |
B5 |
0.016 |
0.009 |
0.013 |
0.017 |
0.009 |
0.013 |
0.007 |
0.006 |
0.006 |
0.015 |
0.007 |
0.011 |
0.019 |
0.010 |
0.015 |
Hoi Mei Wan |
B6 |
0.015 |
0.009 |
0.012 |
0.015 |
0.009 |
0.012 |
0.007 |
0.006 |
0.006 |
0.013 |
0.007 |
0.010 |
0.018 |
0.010 |
0.014 |
Gemini |
B7 |
0.014 |
0.009 |
0.011 |
0.015 |
0.009 |
0.012 |
0.007 |
0.006 |
0.006 |
0.012 |
0.007 |
0.010 |
0.017 |
0.010 |
0.013 |
Angler’s |
B8 |
0.014 |
0.009 |
0.011 |
0.014 |
0.009 |
0.011 |
0.007 |
0.006 |
0.006 |
0.012 |
0.007 |
0.009 |
0.016 |
0.010 |
0.013 |
Lo So Shing |
B9 |
0.001 |
0.004 |
0.002 |
0.001 |
0.004 |
0.002 |
0.001 |
0.003 |
0.002 |
0.000 |
0.003 |
0.002 |
0.001 |
0.004 |
0.002 |
Hung Shing Yeh |
B10 |
0.001 |
0.004 |
0.002 |
0.001 |
0.004 |
0.002 |
0.001 |
0.003 |
0.002 |
0.000 |
0.003 |
0.002 |
0.001 |
0.004 |
0.002 |
Corals |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Pak Kok |
CR1 |
0.007 |
0.007 |
0.007 |
0.007 |
0.007 |
0.007 |
0.005 |
0.006 |
0.005 |
0.005 |
0.005 |
0.005 |
0.007 |
0.007 |
0.007 |
Shek Kok Tsui |
CR2 |
0.005 |
0.007 |
0.006 |
0.005 |
0.007 |
0.006 |
0.004 |
0.005 |
0.005 |
0.004 |
0.005 |
0.005 |
0.006 |
0.007 |
0.006 |
Luk Chau |
CR3 |
0.003 |
0.003 |
0.003 |
0.004 |
0.004 |
0.004 |
0.003 |
0.003 |
0.003 |
0.003 |
0.002 |
0.003 |
0.004 |
0.004 |
0.004 |
Wong Chuk Kok |
CR4 |
0.003 |
0.002 |
0.002 |
0.003 |
0.002 |
0.003 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.002 |
0.003 |
0.002 |
0.003 |
Ap Lei Chau |
CR5 |
0.003 |
0.004 |
0.004 |
0.004 |
0.004 |
0.004 |
0.003 |
0.003 |
0.003 |
0.002 |
0.003 |
0.003 |
0.004 |
0.004 |
0.004 |
|
CR6 |
0.004 |
0.008 |
0.006 |
0.005 |
0.010 |
0.008 |
0.003 |
0.008 |
0.006 |
0.003 |
0.006 |
0.005 |
0.005 |
0.009 |
0.007 |
|
CR7 |
0.010 |
0.008 |
0.009 |
0.010 |
0.008 |
0.009 |
0.007 |
0.006 |
0.007 |
0.006 |
0.006 |
0.006 |
0.012 |
0.009 |
0.010 |
Kau Yi Chau |
CR8 |
0.009 |
0.010 |
0.009 |
0.009 |
0.010 |
0.009 |
0.006 |
0.007 |
0.006 |
0.007 |
0.008 |
0.008 |
0.010 |
0.011 |
0.011 |
Kau Yi Chau |
CR9 |
0.009 |
0.010 |
0.009 |
0.009 |
0.010 |
0.009 |
0.006 |
0.006 |
0.006 |
0.007 |
0.008 |
0.007 |
0.010 |
0.011 |
0.011 |
Kau Yi Chau |
CR10 |
0.008 |
0.008 |
0.008 |
0.009 |
0.008 |
0.009 |
0.006 |
0.006 |
0.006 |
0.007 |
0.006 |
0.007 |
0.010 |
0.009 |
0.010 |
Siu Kau Yi Chau |
CR11 |
0.009 |
0.010 |
0.010 |
0.009 |
0.010 |
0.010 |
0.006 |
0.007 |
0.006 |
0.007 |
0.007 |
0.007 |
0.011 |
0.011 |
0.011 |
Siu Kau Yi Chau |
CR12 |
0.009 |
0.010 |
0.009 |
0.009 |
0.010 |
0.010 |
0.006 |
0.006 |
0.006 |
0.007 |
0.007 |
0.007 |
0.011 |
0.011 |
0.011 |
Siu Kau Yi Chau |
CR13 |
0.009 |
0.008 |
0.009 |
0.009 |
0.008 |
0.009 |
0.006 |
0.006 |
0.006 |
0.007 |
0.006 |
0.007 |
0.010 |
0.009 |
0.010 |
Peng Chau |
CR14 |
0.009 |
0.009 |
0.009 |
0.009 |
0.009 |
0.009 |
0.006 |
0.006 |
0.006 |
0.007 |
0.007 |
0.007 |
0.010 |
0.010 |
0.010 |
Peng Chau |
CR15 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.005 |
0.006 |
0.005 |
0.006 |
0.006 |
0.006 |
0.009 |
0.009 |
0.009 |
Peng Chau |
CR16 |
0.009 |
0.009 |
0.009 |
0.009 |
0.009 |
0.009 |
0.006 |
0.006 |
0.006 |
0.007 |
0.006 |
0.007 |
0.010 |
0.010 |
0.010 |
Peng Chau |
CR17 |
0.008 |
0.009 |
0.008 |
0.009 |
0.009 |
0.009 |
0.005 |
0.006 |
0.006 |
0.007 |
0.006 |
0.007 |
0.010 |
0.010 |
0.010 |
Peng Chau |
CR18 |
0.008 |
0.007 |
0.008 |
0.008 |
0.007 |
0.008 |
0.005 |
0.005 |
0.005 |
0.006 |
0.005 |
0.006 |
0.009 |
0.008 |
0.009 |
Fish Culture Zones |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ma Wan |
F1 |
0.010 |
0.007 |
0.009 |
0.010 |
0.007 |
0.009 |
0.006 |
0.005 |
0.006 |
0.008 |
0.006 |
0.007 |
0.012 |
0.008 |
0.010 |
Lo Tik Wan |
F2 |
0.002 |
0.006 |
0.004 |
0.003 |
0.006 |
0.004 |
0.002 |
0.005 |
0.003 |
0.002 |
0.004 |
0.003 |
0.003 |
0.006 |
0.004 |
Sok Kwu Wan |
F3 |
0.002 |
0.004 |
0.003 |
0.002 |
0.004 |
0.003 |
0.002 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.002 |
0.004 |
0.003 |
Cheung Sha Wan |
F4 |
0.005 |
0.006 |
0.006 |
0.005 |
0.006 |
0.006 |
0.003 |
0.005 |
0.004 |
0.004 |
0.005 |
0.004 |
0.006 |
0.007 |
0.006 |
- Value in Bold indicates exceedance of relevant annual mean criteria.
Based on the above results, it is observed that there are no
predicted adverse effects at any fish culture zones or
coral sites. This is also true at
the gazetted beaches, with Scenario 3 indicating full compliance of the WQO
criteria (for all dry season, wet season and annual average values), whilst all
other scenarios comply for the wet season. Exceedance of the WQO’s UIA (annual
mean) criterion of 0.021 mg L-1 is predicted for the dry season
at the Ting Kau, Approach and
In the dry season as the worst case, the predicted maximum UIA values are 0.073 mg L-1 at Approach (B2), 0.056 mg L-1 at Ting Kau (B3) and 0.037 mg L-1 at Lido (B4).
Using a
similar approach as for the
ammoniacal nitrogen assessment, a two-phase
approach for UIA was also adopted, as elaborated further below.
Unionized Ammonia (with excision of hotspot S2, unmitigated): With this approach, the average UIA values at various sources are 0.248 mg/L for Source A, 0.136 mg/L for Source B, 0.195 mg/L for Source C, 0.046 mg/L for Source D and 0.107 mg/L for Source E. Based on the dilution factors, the assessment of UIA for this scenario is shown in Table 3.35.
Table 3.35: Predicted Elutriate
UIA Concentrations at
Sensitive
Receivers |
Assessment
Point |
Scenario 1 Elutriate
UIA concentration (mg L-1) |
Scenario 2 Elutriate
UIA concentration (mg L-1) |
Scenario 3 Elutriate
UIA concentration (mg L-1) |
Scenario 4 Elutriate
UIA concentration (mg L-1) |
Scenario 5 Elutriate
UIA concentration (mg L-1) |
||||||||||
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
Dry
Season |
Wet
Season |
Annual
Average |
||
Gazetted Beaches |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.010 |
0.009 |
0.009 |
0.010 |
0.009 |
0.010 |
0.007 |
0.007 |
0.007 |
0.008 |
0.007 |
0.007 |
0.012 |
0.010 |
0.011 |
Approach |
B2 |
0.051 |
0.009 |
0.030
|
0.051 |
0.010 |
0.030
|
0.007 |
0.005 |
0.006 |
0.054 |
0.008 |
0.031 |
0.058 |
0.011 |
0.034 |
Ting Kau |
B3 |
0.040 |
0.009 |
0.024
|
0.040 |
0.009 |
0.025
|
0.006 |
0.005 |
0.006 |
0.041 |
0.007 |
0.024 |
0.045 |
0.010 |
0.028 |
|
B4 |
0.026 |
0.007 |
0.017 |
0.027 |
0.007 |
0.017 |
0.007 |
0.005 |
0.006 |
0.026 |
0.006 |
0.016 |
0.030 |
0.008 |
0.019 |
Casam |
B5 |
0.014 |
0.008 |
0.011 |
0.014 |
0.008 |
0.011 |
0.007 |
0.006 |
0.006 |
0.012 |
0.006 |
0.009 |
0.017 |
0.009 |
0.013 |
Hoi Mei Wan |
B6 |
0.013 |
0.008 |
0.010 |
0.013 |
0.008 |
0.011 |
0.007 |
0.006 |
0.006 |
0.011 |
0.006 |
0.008 |
0.016 |
0.009 |
0.012 |
Gemini |
B7 |
0.012 |
0.008 |
0.010 |
0.013 |
0.008 |
0.010 |
0.007 |
0.006 |
0.006 |
0.010 |
0.006 |
0.008 |
0.015 |
0.009 |
0.012 |
Angler’s |
B8 |
0.012 |
0.008 |
0.010 |
0.012 |
0.008 |
0.010 |
0.007 |
0.006 |
0.006 |
0.010 |
0.006 |
0.008 |
0.014 |
0.009 |
0.012 |
Lo So Shing |
B9 |
0.001 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.000 |
0.002 |
0.001 |
0.001 |
0.004 |
0.002 |
Hung Shing Yeh |
B10 |
0.001 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.000 |
0.002 |
0.001 |
0.001 |
0.004 |
0.002 |
Corals |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Pak Kok |
CR1 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.005 |
0.006 |
0.005 |
0.004 |
0.005 |
0.005 |
0.007 |
0.007 |
0.007 |
Shek Kok Tsui |
CR2 |
0.005 |
0.006 |
0.005 |
0.005 |
0.006 |
0.006 |
0.004 |
0.005 |
0.005 |
0.004 |
0.005 |
0.004 |
0.005 |
0.006 |
0.006 |
Luk Chau |
CR3 |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
0.002 |
0.002 |
0.002 |
0.003 |
0.003 |
0.003 |
Wong Chuk Kok |
CR4 |
0.002 |
0.002 |
0.002 |
0.003 |
0.002 |
0.003 |
0.002 |
0.002 |
0.002 |
0.002 |
0.001 |
0.002 |
0.003 |
0.002 |
0.002 |
Ap Lei Chau |
CR5 |
0.003 |
0.004 |
0.003 |
0.004 |
0.004 |
0.004 |
0.003 |
0.003 |
0.003 |
0.002 |
0.003 |
0.002 |
0.004 |
0.004 |
0.004 |
|
CR6 |
0.004 |
0.008 |
0.006 |
0.004 |
0.010 |
0.007 |
0.003 |
0.008 |
0.006 |
0.003 |
0.006 |
0.004 |
0.005 |
0.008 |
0.006 |
|
CR7 |
0.009 |
0.007 |
0.008 |
0.009 |
0.008 |
0.009 |
0.007 |
0.006 |
0.007 |
0.006 |
0.005 |
0.005 |
0.011 |
0.008 |
0.010 |
Kau Yi Chau |
CR8 |
0.008 |
0.009 |
0.008 |
0.008 |
0.009 |
0.008 |
0.006 |
0.007 |
0.006 |
0.006 |
0.007 |
0.007 |
0.009 |
0.010 |
0.010 |
Kau Yi Chau |
CR9 |
0.008 |
0.009 |
0.008 |
0.008 |
0.009 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.007 |
0.006 |
0.009 |
0.010 |
0.010 |
Kau Yi Chau |
CR10 |
0.007 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.005 |
0.006 |
0.009 |
0.008 |
0.009 |
Siu Kau Yi Chau |
CR11 |
0.008 |
0.009 |
0.009 |
0.008 |
0.009 |
0.009 |
0.006 |
0.007 |
0.006 |
0.006 |
0.006 |
0.006 |
0.010 |
0.010 |
0.010 |
Siu Kau Yi Chau |
CR12 |
0.008 |
0.009 |
0.008 |
0.008 |
0.009 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.010 |
0.010 |
0.010 |
Siu Kau Yi Chau |
CR13 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.005 |
0.006 |
0.009 |
0.008 |
0.009 |
Peng Chau |
CR14 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.009 |
0.009 |
0.009 |
Peng Chau |
CR15 |
0.007 |
0.007 |
0.007 |
0.007 |
0.007 |
0.007 |
0.005 |
0.006 |
0.005 |
0.006 |
0.005 |
0.005 |
0.008 |
0.008 |
0.008 |
Peng Chau |
CR16 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.009 |
0.009 |
0.009 |
Peng Chau |
CR17 |
0.007 |
0.008 |
0.008 |
0.008 |
0.008 |
0.008 |
0.005 |
0.006 |
0.006 |
0.006 |
0.006 |
0.006 |
0.009 |
0.009 |
0.009 |
Peng Chau |
CR18 |
0.007 |
0.006 |
0.007 |
0.007 |
0.006 |
0.007 |
0.005 |
0.005 |
0.005 |
0.006 |
0.005 |
0.005 |
0.008 |
0.007 |
0.008 |
Fish Culture Zones |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ma Wan |
F1 |
0.009 |
0.007 |
0.008 |
0.009 |
0.007 |
0.008 |
0.006 |
0.005 |
0.006 |
0.007 |
0.005 |
0.006 |
0.011 |
0.007 |
0.009 |
Lo Tik Wan |
F2 |
0.002 |
0.005 |
0.004 |
0.003 |
0.006 |
0.004 |
0.002 |
0.005 |
0.003 |
0.002 |
0.004 |
0.003 |
0.002 |
0.006 |
0.004 |
Sok Kwu Wan |
F3 |
0.002 |
0.003 |
0.002 |
0.002 |
0.004 |
0.003 |
0.002 |
0.003 |
0.002 |
0.001 |
0.003 |
0.002 |
0.002 |
0.004 |
0.003 |
Cheung Sha Wan |
F4 |
0.004 |
0.006 |
0.005 |
0.004 |
0.006 |
0.005 |
0.003 |
0.005 |
0.004 |
0.003 |
0.004 |
0.004 |
0.005 |
0.006 |
0.006 |
- Value in Bold indicates exceedance of relevant annual mean criteria.
The WQO stipulates a (annual mean) criterion of 0.021
mg L-1 for the UIA. Based
on the prediction, there is no adverse impact to Fish Culture Zones (FCZ) and
Coral Sites. In addition, full compliance of the WQO criteria is also achieved
for Scenario 3 for all WSR’s.
Regarding compliance
with WQO UIA annual average criteria of 0.021 mg/L, marginal compliance
is achieved based on the annual average results for these other scenarios, with
0.034 mg L-1 at B2 (Approach Beach) and 0.028 mg L-1 at
B3 (Ting Kau). For the wet season, the results have shown no UIA value higher
than 0.021 mg/L at all beaches
and WSRs with maximum predictions of 0.058 mg L-1 at B2 (Approach Beach), 0.045 mg L-1
at B3 (Ting Kau) and 0.030 mg L-1 at B4 (Lido) during the dry season.
As noted previously, although compliance is based on annual results, the analysis indicates that it would be prudent to provide mitigation measure for the dredging operations in the dry season, whilst mitigation is not anticipated during the wet season, which is not unexpected as the dilution effects are greater in the wet season compared to the dry season. Notwithstanding the above, a robust monitoring regime will be required to be provided for both dry and wet season working for these areas, as discussed in Section 3.8.
Unionized Ammonia (hotspot S2 only, unmitigated): With this approach, the value of S2 in Table 3.27 was used in conjunction with the dilution factors to assess the UIA at the sensitive receivers. The results for this scenario are shown in Table 3.36.
Table 3.36: Predicted
Elutriate Unionized Ammonia Concentrations at
Water Sensitive Receivers (for only hotspot S2 case)
Sensitive
Receivers |
Assessment
Point |
Elutriate UIA concentration (mg L-1) |
||
Dry Season |
Wet Season |
Annual average |
||
Gazetted Beaches |
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.018 |
0.014 |
0.016 |
Approach |
B2 |
0.190 |
0.024 |
0.107 |
Ting Kau |
B3 |
0.145 |
0.020 |
0.083 |
|
B4 |
0.087 |
0.013 |
0.050 |
Casam |
B5 |
0.033 |
0.013 |
0.023 |
Hoi Mei Wan |
B6 |
0.029 |
0.013 |
0.021 |
Gemini |
B7 |
0.026 |
0.012 |
0.019 |
Angler’s |
B8 |
0.025 |
0.012 |
0.018 |
Lo So Shing |
B9 |
0.001 |
0.005 |
0.003 |
Hung Shing Yeh |
B10 |
0.001 |
0.005 |
0.003 |
Corals |
|
|
|
|
Pak Kok |
CR1 |
0.009 |
0.009 |
0.009 |
Shek Kok Tsui |
CR2 |
0.007 |
0.008 |
0.007 |
Luk Chau |
CR3 |
0.004 |
0.004 |
0.004 |
Wong Chuk Kok |
CR4 |
0.003 |
0.003 |
0.003 |
Ap Lei Chau |
CR5 |
0.004 |
0.005 |
0.004 |
|
CR6 |
0.005 |
0.011 |
0.008 |
|
CR7 |
0.010 |
0.010 |
0.010 |
Kau Yi Chau |
CR8 |
0.012 |
0.015 |
0.013 |
Kau Yi Chau |
CR9 |
0.013 |
0.014 |
0.013 |
Kau Yi Chau |
CR10 |
0.012 |
0.011 |
0.012 |
Siu Kau Yi Chau |
CR11 |
0.014 |
0.014 |
0.014 |
Siu Kau Yi Chau |
CR12 |
0.014 |
0.014 |
0.014 |
Siu Kau Yi Chau |
CR13 |
0.013 |
0.011 |
0.012 |
Peng Chau |
CR14 |
0.013 |
0.012 |
0.012 |
Peng Chau |
CR15 |
0.012 |
0.011 |
0.011 |
Peng Chau |
CR16 |
0.013 |
0.012 |
0.012 |
Peng Chau |
CR17 |
0.012 |
0.011 |
0.012 |
Peng Chau |
CR18 |
0.012 |
0.009 |
0.010 |
Fish Culture Zones |
|
|
|
|
Ma Wan |
F1 |
0.015 |
0.010 |
0.013 |
Lo Tik Wan |
F2 |
0.003 |
0.008 |
0.005 |
Sok Kwu Wan |
F3 |
0.002 |
0.005 |
0.003 |
Cheung Sha Wan |
F4 |
0.007 |
0.008 |
0.008 |
Cooling Water Intakes |
|
|
|
|
Tsuen Wan |
C1 |
0.195 |
0.067 |
0.131 |
MTRC Tsing Yi Station |
C2 |
0.227 |
0.216 |
0.221 |
MTRC |
C3 |
0.008 |
0.019 |
0.013 |
|
C4 |
0.007 |
0.021 |
0.014 |
Sha Wan Drive |
C5 |
0.005 |
0.012 |
0.009 |
|
C6 |
0.005 |
0.010 |
0.008 |
Wah Fu Estate |
C7 |
0.003 |
0.006 |
0.005 |
|
EMSD1 |
0.098 |
0.111 |
0.105 |
WSD
|
|
|
|
|
Tsing Yi |
WSD1 |
0.269 |
0.244 |
0.257 |
|
WSD2 |
0.009 |
0.014 |
0.012 |
Sheung Wan |
WSD3 |
0.008 |
0.023 |
0.016 |
Central Water Front |
WSD4 |
0.007 |
0.019 |
0.013 |
Ap Lei Chau |
WSD5 |
0.003 |
0.007 |
0.005 |
|
WSD6 |
0.017 |
0.023 |
0.020 |
Cheung Sha Wan |
WSD7 |
0.011 |
0.017 |
0.014 |
Tsuen Wan |
WSD8 |
0.196 |
0.064 |
0.130 |
Near |
WSD9 |
0.020 |
0.010 |
0.015 |
Lamma Power Station |
WSD10 |
0.001 |
0.005 |
0.003 |
|
EMSD1 |
0.098 |
0.111 |
0.105 |
- Value in Bold indicates exceedance of relevant annual mean criteria.
It is observed from the assessment of S2 alone in terms of
UIA that annual average UIA values are exceeded for the beaches at Approach,
Ting Kau,
A comparatively smaller number of the other sensitive receivers such as cooling water and flushing water intakes were also predicted to exceed the UIA criterion as shown in Table 3.36. As mentioned previously, the S2 location is considered a hotspot which needs to be dealt with separately, i.e. isolated from the rest of the Project area in order not to adversely affect the overall programme of the navigational dredging (almost 99% of the total dredging area). As such, careful planning of dredging such as carry out field trials, formulation of dredging sub-zones with the control of dredging rate together with the implementation of mitigation measures are recommended for this area and are described in Section 3.8.
Mixing Zone
Tracer simulations have been carried out for the 5 source points (i.e.
Source A to E) and under the five combinations of dredging in different zones,
referred to as scenarios, in order to determine the maximum dimensions of
mixing zones for the ammoniacal nitrogen (NH3-N) and unionized
ammonia (UIA). In each scenario there are 3 source points according to the
combinations shown in Figure
3.5b to Figure 3.5f. Both dry
and wet seasons are covered in the simulations.
In practical terms the mixing zone of the contaminants released from the
dredging operation will move as the dredging proceeds. However in order to simulate the mixing zone
the model scenarios have been derived to demonstrate the worst case situation
and the maximum values of pollutant levels in the mixing zone. The area shown in the mixing zone plots do
not therefore represent the actual boundary of exceedance, rather they may be
considered to be the envelope of the extent of the mixing zone over the entire
simulation period. The mixing zone plots of contaminants (NH3-N
and UIA) for the dry and wet seasons of Scenario 1 to 5 are shown in Appendix
3.11.
From the plots of the mixing zones, it can be seen that the areas
of exceedance of NH3-N and UIA are
confined to the dredging areas for most of the source points in each of the five
scenarios. This is because contaminants released during dredging would be
quickly diluted by the large volume of marine water within the dredging zone
and the high energy i.e. dispersion forces in the Project areas. The area
of exceedance is predicted to be highly localized and confined within 200m for
most of the dredging locations. Impact on the fisheries resources from the
potential contaminant release would be limited since the boundaries of mixing
zones are remote from Fisheries Sensitive Receivers.
Cumulative Impact
The cumulative
impacts (Scenario 7) associated with the release of TIN and UIA, of both this Project and other concurrent projects were also assessed on the
basis of the mixing zone. In accordance with
the approved EIAs of the Hong Kong Boundary Crossing Facility, the
1.
Impact of Disturbance of Seabed Sediment due to
Marine Traffic
Aerial photographs
of the Project area indicate that in some cases, the large container vessels
appear to generate sediment plumes which could be due to propeller wash. In order to assess whether these plumes could
combine with SS released during the dredging operations, an assessment was
carried out which included reference to the findings of the Marine Traffic Impact
Assessment undertaken for this Project.
Dredging
Under worst case
conditions, two dredgers would
work within the KTCB area. Each dredger
setup will consist of one tugboat, one hopper barge/derrick barge and one
dredger. A typical tugboat registered in
Other marine traffic
Under the current situation, all large-sized vessels (especially ocean-going container vessels) power off their propellers and are pulled by tugboats to the berths when they navigate the KTCB area. As mentioned above, the tugboats will not have a significant impact on the seabed sediment due to their shallow drafts. However, the deep drafts of the container vessels have been shown to disturb the seabed sediment, resulting in sediment plumes. However, the increase in suspended solids in the marine water due to these vessels has been reflected in the background water quality monitoring data and is beyond the control of this Project.
The issue relating to this Project is the potential disturbance of the
area being dredged due to passing vessels and the potential combination of
sediment plumes from the dredging works and passing vessels. From the MTIA conducted under this Project it
is noted that the master of a vessel would attempt to remain a certain distance
away from other vessels, fixed objects and other potential hazards to maintain
navigation safety;
therefore, it is expected that the passing vessels will be at a reasonable distance from the dredging area. A 50m buffer also has
been allowed for a vessel’s typical manoeuvring requirements and the escorting
tugboats in the assessment of the marine traffic impact.
It is further noted
that the disturbance to the seabed due to the dredging activities is confined
to the dredging area which will be
contained within a silt curtain. This mitigation measure as described
in Section 3.8 will not only serve to prevent the
dispersion of sediment from the dredging area but also to screen off any
disturbance from other marine vessels. Furthermore, non-project-related marine
vessels are not expected to be navigating close to the dredgers for safety reasons. Therefore no impacts due to the non-project marine vessels are expected.
2. Operational Phase
3.
Impact of Suspended Solids due to Maintenance
Dredging
The need for
maintenance dredging has been described in Section 2.7 along with the
associated details and assumptions. For the water quality assessment of this particular
type of dredging, a similar approach has been adopted as for the capital
dredging works, i.e., by assessing the volume of dredged material and
considering the number of dredgers involved in the works and duration of works.
From Section
2.7 it has been identified that maintenance dredging of the KTCB and
its Approach Channel would be undertaken by Port Works Department (PWD) and would not exceed 30,000 m3 per annum. Clearly this
maintenance dredging activity would not be spread out over the entire year but
rather to a programme to suit the needs and requirements of the works. For the
purposes of this water quality assessment it was assumed that one dredger and
barge configuration would be involved in the maintenance works on a daily
basis. This would be reasonable and in accordance with previous maintenance
dredging operations. Moreover the work would not be conducted over a 24 hour
period as for the capital dredging works, but more likely over a 12-16 hour
period. Even if the same rate of dredging could be achieved for the maintenance
dredging as for the capital works, this infers that only 4,000m3 (maximum and in-situ volume) would be dredged on a
daily basis. In the event that a rate of
4,000m3 could be achieved, this
would equate to approximately 8 days of maintenance dredging compared to the 24
months for capital dredging. The duration is therefore much shorter than for the capital works programme.
In terms of the
release of suspended solids to the receiving waters, the model predictions for
the capital works programme indicate compliance with the WQOs except at WSD’s flushing water intakes. Therefore, it may be surmised that similar compliance would be achieved during periods of maintenance
dredging for this Project
except at the WSD flushing water intakes which are influenced by the ambient
levels of SS. Indeed, the SS
concentrations predicted at the WSRs could be surmised to be almost one third of those for the capital works programme given
the reduction in dredging rate on a daily basis.
Additionally, as
mentioned in Section 2.7 the Container
Terminal Operators (CTO) undertakes maintenance dredging within the berth
boxes. The Container Terminal Operators have provided their records for
maintenance dredging since year 2000 and these are extracted from Section
2.7 and copied into Table 3.37.
Table 3.37: Volume of Maintenance Dredging undertaken by Container Terminal Operators; 2000 - 2009
Terminal No. |
Operator |
Approximate Maintenance Dredge Volumes (m3) from Year 2000 to 2009 |
ANNUAL MAX |
|||||||||
2000 |
2001 |
2002 |
2003 |
2004 |
2005 |
2006 |
2007 |
2008 |
2009 |
|||
1 |
MTL |
15,667 |
-- |
53,0001 |
-- |
-- |
-- |
-- |
12,333 |
-- |
12,667 |
26,5001 |
2 |
MTL |
15,667 |
12,500 |
12,500 |
-- |
-- |
-- |
-- |
12,333 |
-- |
12,667 |
15,667 |
3 |
DPW |
-- |
-- |
9,000 |
11,000 |
1,600 |
-- |
-- |
-- |
17,000 |
-- |
17,000 |
4 |
HIT |
-- |
50,0003 |
-- |
-- |
-- |
-- |
65,0002 |
-- |
-- |
-- |
50,0003 |
5 |
MTL |
15,667 |
12,500 |
12,500 |
-- |
-- |
-- |
-- |
12,333 |
-- |
12,667 |
15,667 |
6 |
HIT |
50,0003 |
50,0003 |
10,000 |
-- |
35,000 |
-- |
65,0002 |
-- |
19,800 |
-- |
50,0003 |
7 |
HIT |
50,0003 |
-- |
10,000 |
-- |
35,000 |
-- |
-- |
-- |
19,800 |
13,000 |
50,0003 |
8 East4 |
COSCO/HIT |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
0 |
8 West4 |
ACT |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
0 |
9 |
HIT |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
4,300 |
20,000 |
20,000 |
Totals |
147,000 |
125,000 |
107,000 |
11,000 |
71,600 |
0 |
130,000 |
37,000 |
60,900 |
71,000 |
|
Notes:
1. Figure for CT1 in 2002 covers two years, so annual maximum is half of this value.
2. These figures include lowering of the seabed and are therefore not taken as maintenance dredging maxima.
3. HIT has advised that it will not undertake more than 100,000m3 maintenance dredging annually.
4. COSCO/HIT
and ACT have both advised they have no plans to undertake maintenance dredging.
It has been
estimated that around 225,000m3 of maintenance dredging could be
undertaken in the KTCP (that is including the 30,000m3 of
maintenance dredging assumed for this Project) (refer to Section 2.7) on an annual basis compared to 4.4Mm3
capital works dredging for this Project over 24 months. Given that historically the CTO’s schedule
their maintenance dredging activities to minimise disturbance to overall
operations of the KTCP it is reasonable to surmise that there will be no
greater dredging activity than has been predicted for the capital works
programme. Thus, it may be concluded
that concurrent maintenance dredging programmes will not generate increased
impacts compared to those predicted for capital dredging works.
Given the
discussions relating to maintenance dredging for the KTCB and its Approach
Channel and the acceptability of the impacts, it may similarly be surmised that
maintenance dredging works undertaken by the CTO would generate similar or
lower levels of SS at the WSRs. Selected results from the water quality monitoring
programme for dredging at Kwai Tsing Container Terminal 1-4 are included in Table 3.41 for
reference.
Sensitivity test on a Lower Dredging rate of
1,500 m3/day
A
sensitivity test has been carried out to determine the potential difference if
the dredging rate is lowered from 12,000 m3/day (with 3 dredgers) to
1,500 m3/day (only 1 dredger) and the results are shown in Appendix 3.10. Please note that Scenario
3 was chosen as the scenario for the cumulative impact assessment as described
in Table 3.9 with
other concurrent projects. As for maintenance dredging, there will only be one
grab dredger deployed for the operation instead of 3 grab dredgers, Source C of
scenario was selected as the source for this sensitive test, i.e. cumulative
impact during maintenance dredging.
Comparison
of the results for the two cases shows that the impacts of SS elevation, DO
depletion, and TIN elevation will be reduced at most of the WSRs; however, the
effects vary for each
WSRs due to influences from concurrent projects and
background pollutant concentrations.
Predicted
Suspended Solids Elevations at
The
predicted SS elevations for Gazetted Beaches differ the most at B2 in dry
season (SS dropped from 1 to 0.8 mg L-1) and B4 in wet season (SS dropped from 1.6 to
1.2 mg L-1) (refer to Table
3.38).
The
predicted SS elevations for Marine Ecology Sensitive Receivers differ the most
at CR1 in dry season (SS dropped from 1 to 0.3 mg L-1) and CR9 in wet season (SS dropped
from 3.7 to 1.8 mg L-1).
However, the
predicted SS elevations SS elevations for Fisheries Sensitive Receivers are
insignificantly changed. This is because the majority of the SS elevations at
these Sensitive Receivers are due to concurrent projects.
The WQO
requires that the SS elevations due to project works should not exceed 30% of
the ambient SS levels. Referring to the predicted values in Scenario 7, there
is no predicted exceedance of SS levels at
Table 3.38: Maximum Reduction in predicted SS
elevations at Gazetted Beaches, Marine Ecology and Fisheries Sensitive
Receivers for the Scenario of 1,500 m3/day at Source C Compared to
12,000 m3/day
|
Dry season |
Wet season |
||||
|
Reduction
in predicted SS elevations (mg L-1) |
Corresponding
WSR |
Ref.
SS criteria (mg L-1) |
Reduction
in predicted SS elevations (mg L-1) |
Corresponding
WSR |
Ref.
SS criteria (mg L-1) |
Gazetted Beaches |
0.2 |
B2 |
2.8 -
3.2 |
0.4 |
B4 |
1.9 –
2.5 |
Marine Ecology |
0.7 |
CR1 |
1.8 -
2.6 |
1.9 |
CR9 |
1.6 -
4.4 |
Fisheries Sensitive Receivers |
0 |
- |
1.8 -
3.2 |
0 |
- |
1.6 -
4.4 |
Predicted
Suspended Solids Elevations at Cooling and Sea Water Intakes for Dredging Rate
of 1,500 m3/day compared to 12,000 m3/day
In the case of
Cooling and Sea Water Intakes, the predicted surface layer Suspended Solids
elevations were lowered by a maximum of 0.3 mg L-1 at WSD2 for dry season and 0.1 mg L-1 at C6 and WSD2 for wet season. The predicted
depth averaged Suspended Solids elevations were lowered by a maximum of 0.4 mg L-1 at WSD9 for dry season and 0.5 mg L-1 at C5 for wet season (refer
to Table 3.39).
To determine
the compliance of the predicted Suspended Solids with the relevant criteria,
the values of suspended solids elevations in addition to the background SS
levels were assessed. There are still exceedances predicted at WSD1, WSD8, WSD9
and EMSD1 since the background SS levels have already breached the SS criterion
for WSD flushing water intake.
Table 3.39: Maximum Reduction in predicted SS
elevations at Cooling and Flushing Water Intakes for the Scenario of 1,500 m3/day
at Source C Compared to 12,000 m3/day
|
Dry season |
Wet season |
||||
|
Reduction in predicted SS elevations (mg L-1) |
Corresponding WSR |
Ref. SS criteria (Total SS in mg L-1) |
Reduction in predicted SS elevations (mg L-1) |
Corresponding WSR |
Ref. SS criteria (Total SS in mg L-1) |
Cooling Water
Intakes (surface layer) |
0.2 |
C5 |
- |
0.1 |
C6 |
- |
WSD |
0.3 |
WSD2 |
<10 |
0.1 |
WSD2 |
<10 |
0.2 |
WSD1 |
<10 |
0.0 |
WSD1 |
<10 |
|
0.1 |
WSD8 |
<10 |
0.0 |
WSD8 |
<10 |
|
|
||||||
Cooling Water
Intakes (depth averaged) |
0.3 |
C5 |
<180 for EMSD1 |
0.5 |
C5 |
<180 for EMSD1 |
WSD |
0.4 |
WSD9 |
<10 |
0.1 |
WSD2 |
<10 |
0.2 |
WSD1 |
<10 |
0.0 |
WSD1 |
<10 |
|
0.1 |
WSD8 |
<10 |
0.0 |
WSD8 |
<10 |
Reduction
in DO depletions for Dredging Rate of 1,500 m3/day compared to
12,000 m3/day
From the
comparison, the difference in DO depth average value of the two cases (
Table 3.40: Maximum Reduction in predicted DO
depletions at the WSRs for the Scenario of 1,500 m3/day at Source C
Compared to 12,000 m3/day
|
Reduction in predicted DO depletions (depth averaged) (mg L-1) |
Reduction in predicted DO depletions at bottom layer (mg L-1) |
||||
|
Dry season |
Wet season |
Ref. DO criteria (mg L-1) |
Dry season |
Wet season |
Ref. DO criteria (mg L-1) |
Gazetted
Beaches |
0.001 |
0.001 |
4.0 |
0.001 |
0.003 |
2.0 |
Marine Ecology |
0.003 |
0.007 |
4.0 |
0.007 |
0.012 |
2.0 |
Fisheries
Sensitive Receivers |
<0.001 |
<0.001 |
5.0 |
<0.001 |
<0.001 |
2.0 |
WSD Cooling and
|
0.001 |
0.001 |
4.0 |
0.001 |
0.001 |
2.0 |
Table 3.41: Water
Quality Monitoring Programme for dredging works in Kwai Tsing Container
Terminal 1-4.
Station |
SS concentration (mgL-1) |
Exceedance? |
||||
|
Aug 2009 |
Sep 2009 |
Oct 2009 |
Nov 2009 |
|
|
Surface |
||||||
Station 1 |
3.5 - 22.0 |
3.0 - 15.0 |
7.0 - 16.0 |
6.0 - 11.5 |
No |
|
Station 2 |
2.5 - 14.0 |
3.5 - 15.0 |
4.0 - 17.0 |
6.0 - 9.0 |
No |
|
Station 3 |
2.5 - 14.0 |
3.0 - 15.0 |
4.0 - 17.0 |
5.0 |
No |
|
Depth-averaged |
||||||
Station 1 |
4.6 - 17.7 |
3.3 - 13.2 |
6.3 - 15.3 |
5.5 - 7.5 |
No |
|
Station 2 |
2.8 - 11.7 |
3.5 - 12.3 |
5.2 - 13.0 |
4.7 - 6.5 |
No |
|
Station 3 |
3.3 - 12.5 |
3.5 - 12.7 |
4.8 - 14.2 |
6.0 - 6.7 |
No |
|
* No
exceedance in monitoring parameter was reported under the EM&A programme
for dredging works at
Although the
monitoring data provided in Table 3.41 indicates that SS releases during previous
maintenance dredging works are compliant with the water quality standards, the
elevated background SS concentrations suggest that there should still be
mitigation measures needed for the protection of water quality at some WSD and
EMSD intakes when maintenance dredging is undertaken. Details of the mitigation
measures proposed are provided in Section
3.8.
Regarding the impact
relating to NH3-N and UIA, if maintenance dredging rate is reduced
to 12.5% of the capital dredging quantity, the sediment release due to seabed
disturbance will commensurately reduce by 12.5%. Since NH3-N and UIA release are
closely related to sediment release due to dredging, by reducing the dredging
rate, it is anticipated the release of NH3-N and UIA will also be
reduced. As such, the effect of NH3-N and UIA during maintenance
dredging is expected to be insignificant.
4. Impact on the Performance of Tsing Yi Submarine Sewage Outfall
The existing
Tsing Yi Submarine Sewage Outfall was retained under the HATS
Stage 1 Scheme (in 2001) to act as an emergency outfall in the event of failure
of HATS Stage1. Due to the proposed dredging of KTCB down to -17.5mCD, the
Tsing Yi Submarine Sewage Outfall will be affected since the
diffuser ports of the outfall needs to be modified to match the new seabed level. The performance (i.e. the
dispersion characteristics) of the modified outfall has been assessed. It should be noted that the emergency
function of this outfall has not been used since 2001.
Figure 3.6 shows the layout plan of the existing Tsing Yi
Submarine Sewage Outfall. With the existing finished level of rubble at
approximately -16.5mCD for the Tsing Yi Submarine Sewage Outfall, the seabed is required to
be lowered by about 1m
and the existing outfall is required to be modified. A typical section of
the outfall in Drawing No. 259053/CIV/2002 in Appendix
3.5a shows the difference between the existing and future
configurations of diffuser ports. The existing steel pipe riser will be cut
down and the non-return valve and concrete pipe will be removed for replacement.
Since the horizontal outfall is still under the seabed level, there will be no
change to the horizontal pipe and thus no environmental impact associated with
that modification.
During the modification works, the existing rubble layer will firstly be removed to a level below
-18.9mCD (i.e. -19.05mPD) and the existing riser pipes will then be cut down.
Tailor-made collars will be adopted to connect the existing riser pipes to the
new non-return valves. The tailor-made collar will be combined by two semi-circular
pipes and bolted together to form a circular shape surrounding the existing
riser pipe. The tail of the collar will be welded to the existing riser pipe to
prevent leakage of treated sewage. The new non-return valves, which function in
the same way as the existing non-return valves, will be connected to the
existing riser pipes through the collars by bolting. Similar to the existing
conditions, the riser pipes protected by concrete pipes will be extruded from
the proposed dredging level to avoid blockage by siltation. The surrounding
rock fill and armour will be replaced around the modified diffusers to afford
the same level of protection as existed prior to dredging.
Upon the
completion of this Project, the diffusers ports will be in the same locations
as the existing ones but will be lowered by a depth of approximately 2m. Details of the levels are provided in Appendix
3.5b.
Impact on
the Performance
of the outfall
As part of the EIA, an additional assessment has been carried out using
a Visual Plume (UM3)
model, and outputs of the
simulation are
contained in Appendix
3.6. It is noted that the model predicted effluent dilution from single
or multiple ports of a single diffuser. The results of comparison of outfall
performance before and after the modification works undertaken were for effluent
discharge from one diffuser, and not from 17 diffusers of the Tsing Yi outfall. The effects such as
plume merging due to the interaction of the plumes from multiple diffusers have
not been considered; however, given that the location of the outfall does not
change except in terms of depth, it may be surmised that the approach adopted
for a single point discharge remains valid for the current assessment.
From the results obtained from the modelling (contained in Appendix
3.5b) it may noted
that the predicted changes in ambient current flows before and after the
Project are insignificant (Appendix
3.5b). The results show that the outfall dilutions from one diffuser
after the modification works are enhanced by between by 4% and 10%, compared to those before the
modification works,
under different current speed conditions. The results indicate a slight improvement of
the outfall performance, in terms of effluent dilution for a single diffuser,
after the modification works. Since the conclusion for the case of using a
single diffuser for assessment should be similar to the case for multiple diffusers, it may be
surmised that the
modification of the Tsing Yi Submarine Sewage Outfall is unlikely to cause any adverse impact
on the outfall performance but rather provide a slight enhancement in
the outfall’s performance.
Notwithstanding the foregoing, in the “Final Report Relating to Drainage/Sewerage Matters
and Submarine Outfalls”, March 2010 under this Project, it was proposed that hydraulic performance measurements be conducted before, during and after
the modification works in order to ensure that the hydraulic performance of the
submarine outfall will not be adversely affected due to the proposed dredging
and outfall modification works. As the pipe size, pipe thickness, pipe
material, protection material and specification for non-return valve will be
the same as the
existing submarine outfalls, the hydraulic performance of the modified
submarine outfall is anticipated to be similar to the original
outfall, and dilution and dispersion characteristics are unlikely to change
appreciably.
5. Impact on the HATS Effluent Dispersion
The deepening of
the seabed level
due to the completion of the Project has been considered in connection with the potential impacts on the HATS outfall
and the potential changes to its effluent dispersion characteristics. The results of the modelling of the current speed and direction at surface and
near-bottom levels in the proximity of the HATS outfall before (results in red)
and after (results in green) the Project are contained in Appendix
3.7. No significant changes in the current speed or direction were predicted for the whole spring-neap
cycle in wet and dry seasons. As such, it is surmised that
there will be negligible effect on the HATS outfall effluent dispersion due to the Project.
6. Mitigation of Adverse Environmental Impact
Recommendation of appropriate mitigation measures is provided according to the requirement of Condition 3.4.3.5 (xii) of the Study Brief. As discussed in Section 3.7, administrative control measures were suggested based on the assessment results in NH3-N and UIA including dredging rate control, seasonal dredging, etc. In the following section, more specific measures which are considered effective in controlling the impact to water sensitive receivers are described.
7. Construction Phase
8. General Dredging Practices
The non-compliance of WSD’s SS criterion at the flushing water intakes WSD1, WSD8, WSD9 and EMSD1 is due to the non-compliance of ambient SS levels at the Rambler Channel and waters near Tsuen Wan. Deployment of silt screen at the flushing water intakes WSRs WSD1, WSD8, WSD9 and EMSD1 was recommended to minimise the predicted elevation in SS levels at the four WSRs.
The implementation of silt screens at the flushing water intakes would reduce the SS level by 60%. The SS reduction factor has been adopted in the previous approved EIA studies4,[8]. The surface SS levels at the seawater intakes WSD1, WSD8, WSD9 and EMSD1 after the implementation of silt screen were presented in Table 3.42. The SS concentrations at these WSRs comply with the WSD’s SS criterion.
Table 3.42: Maximum SS Levels (mg L-1) with
Silt Screen
WSR |
Scenario 1 |
Scenario 2 |
Scenario 3 |
Scenario 4 |
Scenario 5 |
Scenario 6 |
Scenario 7 |
|||||||
|
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
Dry |
Wet |
Surface |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
WSD1 |
5.4 |
4.6 |
5.4 |
4.6 |
4.7 |
4.3 |
5.4 |
4.6 |
5.4 |
4.6 |
5.0 |
4.6 |
4.8 |
4.4 |
WSD8 |
4.8 |
4.3 |
4.8 |
4.3 |
4.6 |
4.2 |
4.9 |
4.3 |
4.9 |
4.3 |
4.8 |
4.3 |
4.7 |
4.3 |
WSD9 |
4.2 |
1.8 |
4.2 |
1.8 |
4.3 |
1.8 |
4.2 |
1.8 |
4.1 |
1.8 |
4.2 |
1.8 |
4.5 |
2.1 |
EMSD1 |
4.6 |
4.4 |
4.6 |
4.4 |
4.5 |
4.2 |
4.6 |
4.5 |
4.6 |
4.5 |
4.6 |
4.4 |
4.5 |
4.2 |
Depth-averaged |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
WSD1 |
6.1 |
8.1 |
6.1 |
8.1 |
5.1 |
6.3 |
6.1 |
8.2 |
6.1 |
8.2 |
5.8 |
8.2 |
5.2 |
6.5 |
WSD8 |
5.3 |
6.7 |
5.3 |
6.7 |
5.0 |
6.4 |
5.3 |
6.8 |
5.3 |
6.8 |
5.2 |
6.6 |
5.1 |
6.5 |
WSD9 |
4.7 |
3.4 |
4.7 |
3.4 |
4.8 |
3.4 |
4.6 |
3.4 |
4.5 |
3.4 |
4.7 |
3.4 |
5.0 |
3.8 |
EMSD1 |
5.0 |
6.5 |
5.0 |
6.5 |
4.9 |
6.2 |
5.1 |
6.5 |
5.1 |
6.5 |
4.9 |
6.4 |
4.9 |
6.3 |
Occasionally, the near-surface current speed near the flushing water intake WSD1 could be greater than 0.5 ms-1 especially during spring tides, such that the effectiveness of the silt screen would be reduced. However, the deployment of silt screen is still recommended at WSD1 since high SS impact occurs due to poor tidal flushing when current speed is low.
Other mitigation measures that should be undertaken during dredging include:
maximum dredging rate shall be 4000 m3 (in-situ volume) per day per grab dredger and 700 m3 in 30 minutes in any given hour (max. 8400 m3/day, based on a 12-hour operation per day) per cutter suction dredger;
only two types of dredgers will be allowed for this Project: (a) grab dredger with closed grab, and (b) cutter suction dredger;;
the allowed maximum number of grab dredgers or cutter suction dredger operating simultaneously within the Project area shall follow the requirement listed in Table 3.43 below;
to minimize the potential SS impact from dredging, deployment of silt curtains around the grab dredgers is recommended (please refer to Figure 3.7 for the schematic design);
either
one cutter suction dredger or one grab dredger shall be working in Zone 2
(including subzones) of the
CSD is only to be deployed for the removal of
harder material during daytime only (07:00 to 19:00) in Zone 2 (including
subzones) of the
Project dredging works within Zone 1-6
(including subzones) of the
if further mitigation measures are required, as demonstrated by the water quality monitoring data under the EM&A programme, then consideration will be given to reducing the dredging rate, or dredging only on the state of the tide which would avoid migration of SS towards the WSD and EMSD intakes;
the dredging pump of cutter suction dredger shall be operated during cutting to reduce the sediment loss to water body;
no overflow of dredged mud will be allowed. Barges or hopper should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation;
all construction vessels should be sized so that clearance is maintained between vessels and the seabed in all tide conditions, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;
the speed of all construction vessels will be controlled within the works area to prevent propeller wash from stirring up the seabed sediments;
all barges / dredgers used should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;
construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site or dumping grounds;
before commencement of dredging works, the holder of the Environmental Permit should submit detailed proposal of the design and arrangement of the frame type silt curtain to EPD for approval; and;
the speed of any construction vessels shall not exceed 10 knots when passing through the Project Site Boundary as shown in Figure 2.1.
Table 3.43: Allowed Maximum Number of Grab Dredgers or Cutter Suction Dredger Operating Simultaneously
Locations Scenario |
Rambler Channel (A)* |
|
Northern Fairway (C)* |
Western
Fairway (D)* |
Western Fairway (E)* |
1 |
One GD |
|
One GD |
One GD |
|
2 |
One GD |
|
One GD |
|
One GD |
3 |
|
|
One GD |
One GD |
One GD |
4 |
One GD |
One GD |
|
One GD |
|
5 |
One GD |
One GD |
One GD |
|
|
6 |
One CSD |
|
One GD |
|
One GD |
* denote reference dredging
locations and working zones shown in Figure
3.5b to 3.5j.
9. Specific Dredging Activities
Sediment from
S2 has been identified, through
testing sediments and elutriates,
to be highly contaminated with ammonia. As such, the impact assessment has identified that it
would be prudent to isolate S2 such that the majority (approximately
99%) of the navigational (i.e.
capital work) dredging can proceed
without affecting the overall construction
programme.
As discussed in Section
3.7.1.6, the removal of the contaminated sediment identified at S2 from the
main dredging programme can effectively reduce the predicted level of ammoniacal nitrogen and UIA at seawater
intakes and gazetted beaches. This
is the first level of mitigation proposed.
However, since there is marginal exceedance of WSD guidelines or
WQO, a reduction in dredging
rate is still recommended as the administrative control strategy to control the
release of contaminants into the water
column. Tables
3.44, 3.45 and 3.46 below
indicate the proposed reduction in dredging
rates which would be needed to achieve compliance with various criteria.
An outline dredging plan is also included in Appendix 3.13, which indicates the sub-zone Z2B where S2 is located. This sub-zone Z2B is shown to be isolated and with dredging works to be carried out towards the end of the construction programme. The dredging plan provides a mitigation strategy for the overall dredging works i.e. the main navigational works and the specific programme for Z2B in which the control of dredging rate is employed as the key strategy to control the release of contaminants during dredging. The detailed plan will be subject to further construction programming, and in particular will be refined to reflect the specifics of the proposed field trial and monitoring confirmation together with individual subzones evaluations. It is recommended that the dredging plan and the field trial programme are submitted for agreement before the construction phase commences.
The field trials will also determine the operation requirements of the CSD (Scenario 6) which is confined to Zone 2 (Appendix 3.13).
Table 3.44: Mitigation Proposal for Ammoniacal Nitrogen
(after excision of S2)
|
Source |
Dry Season |
Wet Season |
||||||
Scenario |
A |
B |
C |
D |
E |
% Reduction |
Dredging Rate |
% Reduction |
Dredging Rate |
1 |
* |
|
* |
* |
|
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
2 |
* |
|
* |
|
* |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
3 |
|
|
* |
* |
* |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
4 |
* |
* |
|
* |
|
16 |
3,341 |
3 |
3,877 |
5 |
* |
* |
* |
|
|
20 |
3,216 |
6 |
3,759 |
Note: Dredging rate is
indicated as volume (cubic meters) for the grab dredger at Source A per day.
To support this
proposed mitigation measure a detailed literature survey has been undertaken
and results indicate that releases of contaminants of concerned in dissolved
phase to water and releases of volatile contaminants to air are directly
related to sediment resuspension[9].
A study of contaminated sediments in
Other references
indicate that there is evidence that the actual toxicity of NH3-N may
be less than anticipated based on the oxidation of ammonia to nitrate and as a
reaction to changing pH associated with liberation of dredged material at sea.
It is important to
note that the actual area affected by this hot spot needs to be confirmed through
detailed sampling and testing; however, initial interpretation of the data
indicates that a precautionary principle has been applied to define the area
affected for the S2 effects (sub-zone Z2B), as shown in Appendix 3.13.
Table 3.45: Mitigation
Proposal for UIA (after excision of S2)
|
Source |
Dry Season |
Wet Season |
Annual Average |
|||||||
Scenario |
A |
B |
C |
D |
E |
% Reduction |
Dredging Rate |
% Reduction |
Dredging Rate |
% Reduction |
Dredging Rate |
1 |
* |
|
* |
* |
|
59 |
1,647 |
No reduction is needed |
4,000 |
31 |
2,777 |
2 |
* |
|
* |
|
* |
59 |
1,637 |
No reduction is needed |
4,000 |
31 |
2,759 |
3 |
|
|
* |
* |
* |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
4 |
* |
* |
|
* |
|
61 |
1,561 |
No reduction is needed |
4,000 |
32 |
2,700 |
5 |
* |
* |
* |
|
|
64 |
1,443 |
No reduction is needed |
4,000 |
39 |
2,439 |
Note: Dredging rate is indicated as volume
(cubic meters) for the grab dredger at Source A per day.
Only under Scenario
3 (dredging in Zones C, D, E) can dredging be carried out at a rate of
Table 3.46: Mitigation Proposal for Dry
and Wet Season for both Ammoniacal
Nitrogen and UIA
|
Dry Season |
Wet Season |
Annual Average |
|||
Scenario |
% Reduction |
Dredging Rate |
% Reduction |
Dredging Rate |
% Reduction |
Dredging Rate |
1 |
59 |
1,647 |
No reduction is needed |
4,000 |
31 |
2,777 |
2 |
59 |
1,637 |
No reduction is needed |
4,000 |
31 |
2,759 |
3 |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
No reduction is needed |
4,000 |
4 |
61 |
1,561 |
3 |
3,877 |
32 |
2,700 |
5 |
64 |
1,443 |
6 |
3,759 |
39 |
2,439 |
Note: Dredging rate is indicated as volume (cubic meters) for the grab dredger at Source A per day.
Though there is a
more mitigation in the dry
season, it should be noted that seawater temperature is lower in dry season and
thus the anticipated UIA release could
be expected to be lower compared to
the wet season as a
result of the slower release rate of
UIA at lower temperatures.
Also data suggests that release of
contaminants are less during the use of closed grab dredging method compared to
those highly aggressive methods of dredging (e.g. TSHD) and as such release
rates may also be lower than predicted from the elutriates test results.
As such it would be
prudent to consider environmental monitoring programmes including monitoring of Suspended Solids and NH3-N and UIA at seawater intakes and other monitoring locations to assess release rates against predicted
rates. In case of any anomalies, investigations should then be carried out to assess the source, degree and
extent of impact. If it is found to be works related, follow up action shall be
carried out including further reduction in dredging rate, or to dredge in
certain tidal windows, etc. If the release rates are less than predicted
then consideration could be given to reinstating the dredging rate to reduce
the duration of the works, while still ensuring compliance with the prevailing
standards.
As discussed in earlier in this section, it is proposed to isolate S2 and deal with this small part of the Project area. Since this location potentially has very high level of NH3-N release, the relationship between dredging and release of ammoniacal nitrogen was studied and is shown in the following table.
Table 3.47: Prediction
of Unmitigated and Mitigated
Ammoniacal Nitrogen Concentrations at Sensitive Receivers based on hotspot S2
case only
Sensitive
Receivers |
Assessment
Point |
0% reduction |
50% reduction |
80% reduction |
|||
|
|
Elutriate NH3-N concentration (mg L-1) |
Elutriate NH3-N concentration (mg L-1) |
Elutriate NH3-N concentration (mg L-1) |
|||
|
|
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Dry Season |
Wet Season |
Gazetted
Beaches |
|
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.25 |
0.19 |
0.12 |
0.10 |
0.05 |
0.04 |
Approach |
B2 |
2.59 |
0.32 |
1.29 |
0.16 |
0.52 |
0.06 |
Ting Kau |
B3 |
1.97 |
0.28 |
0.99 |
0.14 |
0.39 |
0.06 |
|
B4 |
1.18 |
0.18 |
0.59 |
0.09 |
0.24 |
0.04 |
Casam |
B5 |
0.45 |
0.18 |
0.23 |
0.09 |
0.09 |
0.03 |
Hoi Mei Wan |
B6 |
0.39 |
0.17 |
0.20 |
0.09 |
0.08 |
0.03 |
Gemini |
B7 |
0.36 |
0.17 |
0.18 |
0.09 |
0.07 |
0.03 |
Angler’s |
B8 |
0.36 |
0.17 |
0.17 |
0.08 |
0.07 |
0.03 |
Lo So Shing |
B9 |
0.01 |
0.06 |
0.01 |
0.03 |
0.00 |
0.01 |
Hung Shing Yeh |
B10 |
0.01 |
0.06 |
0.01 |
0.03 |
0.00 |
0.01 |
Corals |
|
|
|
|
|
|
|
Pak Kok |
CR1 |
0.12 |
0.12 |
0.06 |
0.06 |
0.02 |
0.02 |
Shek Kok Tsui |
CR2 |
0.09 |
0.11 |
0.04 |
0.06 |
0.02 |
0.02 |
Luk Chau |
CR3 |
0.06 |
0.06 |
0.03 |
0.03 |
0.01 |
0.01 |
Wong Chuk Kok |
CR4 |
0.04 |
0.04 |
0.02 |
0.02 |
0.01 |
0.01 |
Ap Lei Chau |
CR5 |
0.05 |
0.07 |
0.03 |
0.03 |
0.01 |
0.01 |
|
CR6 |
0.07 |
0.15 |
0.04 |
0.07 |
0.01 |
0.03 |
|
CR7 |
0.14 |
0.14 |
0.07 |
0.07 |
0.03 |
0.03 |
Kau Yi Chau |
CR8 |
0.17 |
0.20 |
0.08 |
0.10 |
0.03 |
0.04 |
Kau Yi Chau |
CR9 |
0.17 |
0.19 |
0.09 |
0.09 |
0.03 |
0.04 |
Kau Yi Chau |
CR10 |
0.16 |
0.15 |
0.08 |
0.08 |
0.03 |
0.03 |
Siu Kau Yi Chau |
CR11 |
0.19 |
0.19 |
0.09 |
0.09 |
0.04 |
0.04 |
Siu Kau Yi Chau |
CR12 |
0.18 |
0.19 |
0.09 |
0.09 |
0.04 |
0.04 |
Siu Kau Yi Chau |
CR13 |
0.17 |
0.15 |
0.09 |
0.08 |
0.03 |
0.03 |
Peng Chau |
CR14 |
0.18 |
0.16 |
0.09 |
0.08 |
0.04 |
0.03 |
Peng Chau |
CR15 |
0.16 |
0.15 |
0.08 |
0.07 |
0.03 |
0.03 |
Peng Chau |
CR16 |
0.17 |
0.16 |
0.09 |
0.08 |
0.03 |
0.03 |
Peng Chau |
CR17 |
0.17 |
0.16 |
0.08 |
0.08 |
0.03 |
0.03 |
Peng Chau |
CR18 |
0.16 |
0.13 |
0.08 |
0.06 |
0.03 |
0.03 |
Fish
Culture Zones |
|
|
|
|
|
|
|
Ma Wan |
F1 |
0.21 |
0.14 |
0.10 |
0.07 |
0.04 |
0.03 |
Lo Tik Wan |
F2 |
0.04 |
0.10 |
0.02 |
0.05 |
0.01 |
0.02 |
Sok Kwu Wan |
F3 |
0.03 |
0.07 |
0.01 |
0.03 |
0.01 |
0.01 |
Cheung Sha Wan |
F4 |
0.09 |
0.12 |
0.05 |
0.06 |
0.02 |
0.02 |
Cooling
Water Intakes |
|
|
|
|
|
|
|
Tsuen Wan |
C1 |
2.65 |
0.91 |
1.33 |
0.45 |
0.53 |
0.18 |
MTRC Tsing Yi Station |
C2 |
3.09 |
2.94 |
1.54 |
1.47 |
0.62 |
0.59 |
MTRC |
C3 |
0.10 |
0.25 |
0.05 |
0.13 |
0.02 |
0.05 |
|
C4 |
0.10 |
0.28 |
0.05 |
0.14 |
0.02 |
0.06 |
Sha Wan Drive |
C5 |
0.07 |
0.17 |
0.04 |
0.08 |
0.01 |
0.03 |
|
C6 |
0.07 |
0.14 |
0.03 |
0.07 |
0.01 |
0.03 |
Wah Fu Estate |
C7 |
0.05 |
0.09 |
0.02 |
0.04 |
0.01 |
0.02 |
|
EMSD1 |
1.34 |
1.51 |
0.67 |
0.75 |
0.27 |
0.30 |
WSD
|
|
|
|
|
|
|
|
Tsing Yi |
WSD1 |
3.66 |
3.33 |
1.83 |
1.66 |
0.73 |
0.67 |
|
WSD2 |
0.13 |
0.20 |
0.06 |
0.10 |
0.03 |
0.04 |
Sheung Wan |
WSD3 |
0.12 |
0.31 |
0.06 |
0.16 |
0.02 |
0.06 |
Central Water Front |
WSD4 |
0.10 |
0.27 |
0.05 |
0.13 |
0.02 |
0.05 |
Ap Lei Chau |
WSD5 |
0.04 |
0.09 |
0.02 |
0.05 |
0.01 |
0.02 |
|
WSD6 |
0.24 |
0.31 |
0.12 |
0.15 |
0.05 |
0.06 |
Cheung Sha Wan |
WSD7 |
0.14 |
0.23 |
0.07 |
0.12 |
0.03 |
0.05 |
Tsuen Wan |
WSD8 |
2.67 |
0.87 |
1.33 |
0.44 |
0.53 |
0.17 |
Near |
WSD9 |
0.27 |
0.14 |
0.13 |
0.07 |
0.05 |
0.03 |
Lamma Power Station |
WSD10 |
0.01 |
0.06 |
0.01 |
0.03 |
0.00 |
0.01 |
|
EMSD1 |
1.34 |
1.51 |
0.67 |
0.75 |
0.27 |
0.30 |
- Value in Bold indicates exceedance of relevant criteria.
- Dredging Rate is indicated as volume (cubic meters) per grab dredger per day.
Table 3.48: Prediction
of Unmitigated and Mitigated UIA
Concentrations at Sensitive Receivers based on hotspot S2 case only
Sensitive
Receivers |
Assessment
Point |
0% reduction |
50% reduction |
80% reduction |
90% reduction |
||||||||
Elutriate UIA
concentration (mg L-1) |
Elutriate
UIA concentration (mg L-1) |
Elutriate
UIA concentration (mg L-1) |
Elutriate
UIA concentration (mg L-1) |
||||||||||
Dry Season |
Wet Season |
Annual Average |
Dry Season |
Wet Season |
Annual Average |
Dry Season |
Wet Season |
Annual Average |
Dry Season |
Wet Season |
Annual Average |
||
Gazetted Beaches |
|
|
|
|
|
|
|
|
|
|
|
|
|
Tung Wan, Ma Wan |
B1 |
0.018 |
0.014 |
0.016 |
0.009 |
0.007 |
0.008 |
0.004 |
0.003 |
0.003 |
0.002 |
0.001 |
0.002 |
Approach |
B2 |
0.190 |
0.024 |
0.107 |
0.095 |
0.012 |
0.053 |
0.038 |
0.005 |
0.021 |
0.019 |
0.002 |
0.011 |
Ting Kau |
B3 |
0.145 |
0.020 |
0.083 |
0.072 |
0.010 |
0.041 |
0.029 |
0.004 |
0.017 |
0.014 |
0.002 |
0.008 |
|
B4 |
0.087 |
0.013 |
0.050 |
0.043 |
0.007 |
0.025 |
0.017 |
0.003 |
0.010 |
0.009 |
0.001 |
0.005 |
Casam |
B5 |
0.033 |
0.013 |
0.023 |
0.017 |
0.006 |
0.012 |
0.007 |
0.003 |
0.005 |
0.003 |
0.001 |
0.002 |
Hoi Mei Wan |
B6 |
0.029 |
0.013 |
0.021 |
0.015 |
0.006 |
0.010 |
0.006 |
0.003 |
0.004 |
0.003 |
0.001 |
0.002 |
Gemini |
B7 |
0.026 |
0.012 |
0.019 |
0.013 |
0.006 |
0.010 |
0.005 |
0.002 |
0.004 |
0.003 |
0.001 |
0.002 |
Angler’s |
B8 |
0.025 |
0.012 |
0.018 |
0.012 |
0.006 |
0.009 |
0.005 |
0.002 |
0.004 |
0.002 |
0.001 |
0.002 |
Lo So Shing |
B9 |
0.001 |
0.005 |
0.003 |
0.000 |
0.002 |
0.001 |
0.000 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
Hung Shing Yeh |
B10 |
0.001 |
0.005 |
0.003 |
0.000 |
0.002 |
0.001 |
0.000 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
Corals |
|
|
|
|
|
|
|
|
|
|
|
|
|
Pak Kok |
CR1 |
0.009 |
0.009 |
0.009 |
0.004 |
0.004 |
0.004 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Shek Kok Tsui |
CR2 |
0.007 |
0.008 |
0.007 |
0.003 |
0.004 |
0.004 |
0.001 |
0.002 |
0.001 |
0.001 |
0.001 |
0.001 |
Luk Chau |
CR3 |
0.004 |
0.004 |
0.004 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
Wong Chuk Kok |
CR4 |
0.003 |
0.003 |
0.003 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
Ap Lei Chau |
CR5 |
0.004 |
0.005 |
0.004 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
|
CR6 |
0.005 |
0.011 |
0.008 |
0.003 |
0.005 |
0.004 |
0.001 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
|
CR7 |
0.010 |
0.010 |
0.010 |
0.005 |
0.005 |
0.005 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Kau Yi Chau |
CR8 |
0.012 |
0.015 |
0.013 |
0.006 |
0.007 |
0.007 |
0.002 |
0.003 |
0.003 |
0.001 |
0.001 |
0.001 |
Kau Yi Chau |
CR9 |
0.013 |
0.014 |
0.013 |
0.006 |
0.007 |
0.007 |
0.003 |
0.003 |
0.003 |
0.001 |
0.001 |
0.001 |
Kau Yi Chau |
CR10 |
0.012 |
0.011 |
0.012 |
0.006 |
0.006 |
0.006 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Siu Kau Yi Chau |
CR11 |
0.014 |
0.014 |
0.014 |
0.007 |
0.007 |
0.007 |
0.003 |
0.003 |
0.003 |
0.001 |
0.001 |
0.001 |
Siu Kau Yi Chau |
CR12 |
0.014 |
0.014 |
0.014 |
0.007 |
0.007 |
0.007 |
0.003 |
0.003 |
0.003 |
0.001 |
0.001 |
0.001 |
Siu Kau Yi Chau |
CR13 |
0.013 |
0.011 |
0.012 |
0.006 |
0.006 |
0.006 |
0.003 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Peng Chau |
CR14 |
0.013 |
0.012 |
0.012 |
0.007 |
0.006 |
0.006 |
0.003 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Peng Chau |
CR15 |
0.012 |
0.011 |
0.011 |
0.006 |
0.005 |
0.006 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Peng Chau |
CR16 |
0.013 |
0.012 |
0.012 |
0.006 |
0.006 |
0.006 |
0.003 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Peng Chau |
CR17 |
0.012 |
0.011 |
0.012 |
0.006 |
0.006 |
0.006 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Peng Chau |
CR18 |
0.012 |
0.009 |
0.010 |
0.006 |
0.005 |
0.005 |
0.002 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Fish Culture Zone |
|
|
|
|
|
|
|
|
|
|
|
|
|
Ma Wan |
F1 |
0.015 |
0.010 |
0.013 |
0.008 |
0.005 |
0.006 |
0.003 |
0.002 |
0.003 |
0.002 |
0.001 |
0.001 |
Lo Tik Wan |
F2 |
0.003 |
0.008 |
0.005 |
0.001 |
0.004 |
0.003 |
0.001 |
0.002 |
0.001 |
0.000 |
0.001 |
0.001 |
Sok Kwu Wan |
F3 |
0.002 |
0.005 |
0.003 |
0.001 |
0.002 |
0.002 |
0.000 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
Cheung Sha Wan |
F4 |
0.007 |
0.008 |
0.008 |
0.003 |
0.004 |
0.004 |
0.001 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Cooling Water
Intakes |
|
|
|
|
|
|
|
|
|
|
|
|
|
Tsuen Wan |
C1 |
0.195 |
0.067 |
0.131 |
0.097 |
0.033 |
0.065 |
0.039 |
0.013 |
0.026 |
0.019 |
0.007 |
0.013 |
MTRC Tsing Yi Station |
C2 |
0.227 |
0.216 |
0.221 |
0.113 |
0.108 |
0.111 |
0.045 |
0.043 |
0.044 |
0.023 |
0.022 |
0.022 |
MTRC |
C3 |
0.008 |
0.019 |
0.013 |
0.004 |
0.009 |
0.007 |
0.002 |
0.004 |
0.003 |
0.001 |
0.002 |
0.001 |
|
C4 |
0.007 |
0.021 |
0.014 |
0.004 |
0.010 |
0.007 |
0.001 |
0.004 |
0.003 |
0.001 |
0.002 |
0.001 |
Sha Wan Drive |
C5 |
0.005 |
0.012 |
0.009 |
0.003 |
0.006 |
0.004 |
0.001 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
|
C6 |
0.005 |
0.010 |
0.008 |
0.003 |
0.005 |
0.004 |
0.001 |
0.002 |
0.002 |
0.001 |
0.001 |
0.001 |
Wah Fu Estate |
C7 |
0.003 |
0.006 |
0.005 |
0.002 |
0.003 |
0.002 |
0.001 |
0.001 |
0.001 |
0.000 |
0.001 |
0.000 |
|
EMSD1 |
0.098 |
0.111 |
0.105 |
0.049 |
0.055 |
0.052 |
0.020 |
0.022 |
0.021 |
0.010 |
0.011 |
0.010 |
WSD |
|
|
|
|
|
|
|
|
|
|
|
|
|
Tsing Yi |
WSD1 |
0.269 |
0.244 |
0.257 |
0.135 |
0.122 |
0.128 |
0.054 |
0.049 |
0.051 |
0.027 |
0.024 |
0.026 |
|
WSD2 |
0.009 |
0.014 |
0.012 |
0.005 |
0.007 |
0.006 |
0.002 |
0.003 |
0.002 |
0.001 |
0.001 |
0.001 |
Sheung Wan |
WSD3 |
0.008 |
0.023 |
0.016 |
0.004 |
0.011 |
0.008 |
0.002 |
0.005 |
0.003 |
0.001 |
0.002 |
0.002 |
Central Water Front |
WSD4 |
0.007 |
0.019 |
0.013 |
0.004 |
0.010 |
0.007 |
0.001 |
0.004 |
0.003 |
0.001 |
0.002 |
0.001 |
Ap Lei Chau |
WSD5 |
0.003 |
0.007 |
0.005 |
0.001 |
0.003 |
0.002 |
0.001 |
0.001 |
0.001 |
0.000 |
0.001 |
0.000 |
|
WSD6 |
0.017 |
0.023 |
0.020 |
0.009 |
0.011 |
0.010 |
0.003 |
0.005 |
0.004 |
0.002 |
0.002 |
0.002 |
Cheung Sha Wan |
WSD7 |
0.011 |
0.017 |
0.014 |
0.005 |
0.009 |
0.007 |
0.002 |
0.003 |
0.003 |
0.001 |
0.002 |
0.001 |
Tsuen Wan |
WSD8 |
0.196 |
0.064 |
0.130 |
0.098 |
0.032 |
0.065 |
0.039 |
0.013 |
0.026 |
0.020 |
0.006 |
0.013 |
Near |
WSD9 |
0.020 |
0.010 |
0.015 |
0.010 |
0.005 |
0.007 |
0.004 |
0.002 |
0.003 |
0.002 |
0.001 |
0.001 |
Lamma Power Station |
WSD10 |
0.001 |
0.005 |
0.003 |
0.001 |
0.002 |
0.001 |
0.000 |
0.001 |
0.001 |
0.000 |
0.000 |
0.000 |
|
EMSD1 |
0.098 |
0.111 |
0.105 |
0.049 |
0.055 |
0.052 |
0.020 |
0.022 |
0.021 |
0.010 |
0.011 |
0.010 |
- Value in Bold indicates exceedance of relevant
criteria.
- Dredging Rate is
indicated as volume (cubic meters) per grab dredger per day.
From Tables
3.47 and 3.48, it can been seen that the
dredging rate has to be reduced to about 80% of the
original rate to reduce the UIA level to allow compliance with WQO at gazetted
beaches as well as compliance of NH3-N level at WSD’s seawater intake (WSD1). As the level of
contamination is high in the area of S2, it is therefore recommended that to
clearly define the area affected and thereafter to propose a field trial or
alternative confirmatory methods to be carried out before dredging works at S2 commence.
The field trials may include but are not limited to consideration of
methods or options such as hydraulically closed grab dredgers, specially
designed silt curtains, bioremediation or similar methods for treating the
specific cause of the contamination prior to removal of sediments.
The objective of the
field trial is to propose the most effective dredging process and rate to control the release of ammoniacal
nitrogen and UIA into the water
column and achieve compliance at the
WSD1 seawater intake (NH3-N) and at the beaches for UIA. Capital dredging works in the
vicinity of S2 should not therefore be carried out until the proposed method and rate are
confirmed. Having taken note of the other projects in
the vicinity, it would be appropriate to time the dredging of S2 to avoid other
capital works projects as far as possible and thus the Q3/Q4 of 2013 would
currently be favoured.
From Table 3.35, it is
shown that marginal exceedance of annual mean WQO UIA criteria of 0.021 mg L-1
at Approach, Tung Kau and
10. Operational Phase
11.
Maintenance Dredging
The
isopachytes show that there was no significant level of siltation within most of the Study Area, other than for some isolated high spots adjacent to the
berth boxes. Maintenance dredging will therefore
only be considered when the removal of
local high spots is required to maintain
the navigation depth. The scale of the maintenance dredging works is far
smaller than that of the
capital dredging. The reduction in dredging
plant (one dredger compared to three) to be
deployed and the reduced volume of
sediment to be removed (30,000m3 per
annum maximum for this Project with an estimated 225,000m3 for all
maintenance dredging associated with KTCP) during maintenance
dredging compared to the
capital dredging works programme further suggest
a reduction of impacts on receiving water quality.
The SS
impacts on the WSRs due to the maintenance dredging may be assumed to be reduced compared to the
impacts arising from the capital dredging due to
the reduction in daily production rate (maximum daily rate of 4,000m3
in-situ volume for maintenance compared to 12,000m3 in-situ volume
for capital dredging using 3 grab dredgers). To minimise the potential SS
impact from the maintenance dredging, PWD has no objection to deploy silt
screens at the flushing water intakes, i.e. at WSD1 and EMSD1. In addition,
silt curtain around the grab dredgers will be installed during maintenance
dredging. Subject to the review of environmental performance of the dredging
operations, the deployment of silt curtains may be suspended if supporting
evidence is obtained through the operational
phase water quality monitoring and audit programme.
In view of
the above discussion, the following mitigation measures are proposed when undertaking maintenance dredging:
only grab dredger with closed grab will be allowed with a maximum rate of 4000m3/day (in-situ volume);
no overflow of dredged mud will be allowed. Barges should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation;
all barges used should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;
construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site or dumping grounds,
in the event that there is an exceedance of SS at the WSD intakes other than WSD1 then further mitigation measures shall be considered including the use of silt curtains or a reduction in the dredging rate; and
no maintenance dredging will be carried out concurrently with other maintenance works by container terminal operators.
12. Evaluation of Residual Impacts
During the construction phase, the key water quality impact associated with dredging activities is the elevation of SS within the marine water column. Provided that the recommended mitigation measures are implemented, no unacceptable residual water quality impact due to dredging within the Project areas is expected.
No residual water quality impact due the operational phase of
the Project is anticipated.
13. Environmental Monitoring and Audit
Appropriate mitigation measures have been recommended to minimize potential water quality impacts during the construction phase. Water quality monitoring and audit would be required to obtain a robust, defensible database of baseline information of water quality before construction, and thereafter, to monitor any variation of water quality from the baseline conditions and exceedances of WQOs at sensitive receivers (including fish culture zones) during construction, and to ensure that the recommended mitigation measures are implemented properly. Details of the water quality monitoring and audit programme and the Event and Action Plan have been provided in the stand-alone EM&A Manual.
In addition to water quality monitoring, in order to ensure that the hydraulic performance of the Tsing Yi Submarine Sewage Outfall will not be adversely affected due to the proposed dredging and outfall modification works, hydraulic performance measurement is therefore recommended to be conducted before, during and after the proposed modification works. The stand-alone EM&A Manual contains the details for the hydraulic performance requirements.
The water quality impacts arising from the construction and operational phase of the Project have been assessed. The impacts of the proposed dredging works have been quantitatively assessed using the Delft3D Model. Suspended solids (SS) were identified as one of the critical water quality parameters during the dredging operations. The worst-case scenarios for the dredging works have been assessed, in terms of SS and adverse water quality impact has been predicted on any of the identified WSRs provided that appropriate mitigation measures are implemented.
Although high levels of ammoniacal nitrogen and UIA were found within the Project Area detected through sediment sampling for this Project, assessment showed that for the majority of the area, some 99% of the project area, navigational dredging will not cause an adverse impacts to the receiving environment through mitigation measures such as reducing the dredging rates backed up by monitoring. Due to only the marginal exceedance of the NH3-N and UIA at the sensitive receivers in the dry season, the release of suspended solids from sediment and hence the associated pollutants (e.g. NH3-N) into water column can be controlled via the reduced dredging rates. With the implementation of the effect dredging rate control, it is not considered likely there will be any residual impacts associated with the navigational dredging for this Project.
A hot spot has been found at the northeastern corner of the
Project Area (namely, at sampling station S2), which abnormally high levels of
NH3-N, and hence UIA. To
address this issue, it is recommended that before dredging works at S2 commences, a field trial or
alternative confirmatory method is to be carried out to clearly define the area
affected, and thereafter, to propose (through the field trials) an acceptable method or option such as hydraulically
closed grab dredgers, specially designed silt curtain, bioremediation or
similar methods to work at this area.
The objective of the field trial is to propose the most effective
dredging process and rate to control the release of ammoniacal
nitrogen and UIA into the water
column and achieve compliance at the
WSD1 seawater intake (NH3-N) and at the beaches for UIA. Capital
dredging works in the vicinity of S2 should
not therefore be carried
out until the proposed method and rate
are confirmed. Having taken note of the other projects in
the vicinity, it would be appropriate to time the dredging of S2 to avoid other
capital works projects as far as possible and thus the Q3/Q4 of 2013 would
currently be favoured.
An environmental monitoring and audit programme has been proposed to ensure that all the recommended mitigation measures would be implemented properly.
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[9] Source 2:
[10] Invited contribution published as, Jones-Lee, A., and Lee, G.F., “Water
Quality Aspects of Dredged Sediment Management, “Water Encyclopedia: Water Quality and Resource Development, Wiley,