Content |
Chapter Title Page
1.1 Environmental Impact Assessment (EIA) Study
Brief______________________________________ 1
2.1 Project Requirements & Programme__________________________________________________ 2
2.2 The Study Area and Surrounding Environment___________________________________________ 3
2.3 Need for the Project and Consequences of not
Proceeding with the Project_____________________ 3
2.4 Consideration of Alternative Construction
Methods and Sequence of Work_____________________ 4
2.5 Selection of Preferred Option________________________________________________________ 7
2.6 Existing Submarine Outfall within Kwai Tsing
Container Basin______________________________ 9
2.7 Need for Maintenance Dredging_____________________________________________________ 10
2.8 Interface with Planned Projects_____________________________________________________ 10
3.1 Water_________________________________________________________________________ 12
3.2 Waste________________________________________________________________________ 18
3.3 Marine Ecology__________________________________________________________________ 20
3.4 Fisheries______________________________________________________________________ 22
3.5 Hazard to Life___________________________________________________________________ 25
3.6 Landscape, Visual and Glare_______________________________________________________ 26
3.7 Cultural Heritage________________________________________________________________ 28
3.8 Noise_________________________________________________________________________ 29
3.9 Air___________________________________________________________________________ 31
List of Figures
Figure 3.1 Location of
Water Sensitive Receivers and Water and Sediment Quality Monitoring Stations
Figure 3.3 Location of
Representative Air and Noise Sensitive Receivers
Figure 3.4 Current
Location of the QE1
1.1 Environmental Impact Assessment (EIA) Study Brief
The Project is a designated project
under item C.12 of Schedule 2 of the Environmental Impact Assessment Ordinance
(EIAO), which encompasses ”a dredging
operation exceeding 500 000 m3 or a dredging operation which
a. is less than 500m from the nearest boundary of an existing or planned
i. Site of special scientific interest;
ii. Site of cultural heritage;
iii. Bathing beach;
iv. Marine park or marine reserve;
v. Fish culture zone;
vi. Wild animal protection area;
vii. Coastal protection area; or
viii. Conservation area; or
b. Is less than 100m from a seawater intake point.”
An Environmental Impact Assessment (EIA) Study has been undertaken to provide information on the nature and extent of environmental impacts arising from the construction (and future maintenance) of this proposed designated project and related activities taking place concurrently, and to contribute to the decisions on the overall environmental acceptability of the Project.
This Executive Summary provides the key findings contained in the EIA Report, which included the assessment of potential water quality, waste, marine ecology, fisheries, landscape, cultural heritage, noise and construction dust impacts from the construction and operation of the Project, and the recommendations for mitigation measures to ensure compliance with environmental legislation and guidelines.
2.1 Project Requirements & Programme
The southern portion of Rambler Channel between Tsing Yi and
Kwai Chung has been developed into
Developments within the container shipping industry have seen
the introduction of ultra-large container ships (ULCS) to the main
intercontinental shipping routes. These vessels have a maximum draft of 15.5m.
The current average seabed level within the KTCB is approximately -15.6mCD,
while depth in parts of the approaches to the KTCB is shallower. Therefore, under this Project it is proposed
to deepen the seabed level of the KTCB and its marine access route to provide
adequate depth of water to enable the new generation of ULCS to call at the
KTCP. The Project layout is shown in Figure
2.1.
The Project’s
objective is to lower the seabed in the KTCB and its access fairways and
channels so as to maintain an adequate clearance for ULCS at all times. For the
purpose of determining the functional least depth of dredging, the maximum
draft of an ULCS is taken to be 15.5m. It is recommended in Marine Department’s “The Complete Berthing Guidelines for
In order to determine the appropriate maintained seabed level, an assessment of the sedimentation rates within the Project area since 1990 has been carried out. The assessment concludes that the potential for sedimentation within the Project area is low. However, it is not known with certainty that the conditions which existed in the period covered by the assessment will prevail for the service life of the KTCP. In order to account for possible increases in the sediment load in the Pearl River Estuary, yet still achieving a sensible balance between capital and maintenance dredging works, a target seabed level of -17.5mCD has been adopted.
In Section 2.2.1 of Port Works Design Manual Part 1, the Chart Datum (CD) is 0.146m below the Principal Datum (PD). As such, the target seabed level will be -17.646mPD.
In addition to the
foregoing, modification of the Tsing Yi Submarine Sewage Outfall and
demolition of the Kwai Chung Submarine Sewage
Outfall are included as
part of the scope of works. For the Tsing Yi Submarine Sewage Outfall
modification works, this will involve removal of the rock armour, replacement
of the existing riser pipes and non-return valves, and followed by
re-application of rock armour. Demolition of the Kwai Chung Submarine Sewage Outfall will only involve the
dismantling of the pipe section that is above the dredge level. The
dredged volume quoted in the Study Brief was 5.5Mm3; however, as the
engineering design has progressed in parallel with this EIA, the dredged volume
has been refined to be 4.4Mm3.
This provides environmental benefit through the reduction in the volume
of material to be dredged and disposed of as well as reducing the extent of
potential impacts on the receiving water column.
According to the latest estimate, the Project is tentatively scheduled to commence works in the second half of 2011, to be substantially completed within 2 years except for a small area near Container Terminal no. 1 and 5.
2.2 The Study Area and Surrounding Environment
The Kwai Tsing Container Port (KTCP), located in the
north-western part of the harbour in
the reclamation along Rambler Channel between Kwai Chung and Tsing Yi Island,
comprises nine container terminals with 24 berths of 7,804m of deep sea
frontage and is operated by five companies, each responsible for maintaining a
strip of seabed of approximately 50m wide along the terminals. The Project area
includes also a portion of Northern Fairway to the south of Tsing Yi Island and
a section of Western Fairway on the west side of
2.3 Need for the Project and Consequences of not Proceeding with the Project
The Hong Kong Container Port is the third busiest container
port in the world after
In the short term, with the trend of the increasing size of container vessels, current container ships occasionally have to wait for high tide to depart from Kwai Tsing Container Port due to insufficient depth of KTCB. Such limitations reduce the efficiency in cargo-handling operations, potentially harm the reputation of Kwai Tsing Container Port and conceivably could encourage vessels to make alternative arrangements including the diversion of traffic to Shenzhen and other Regional ports.
The execution of this Project is therefore necessary to keep
the container basin deep enough to maintain current efficiencies and to
facilitate the growing size of container ships in the short term. In addition, it is also needed to meet the
draft requirement of ULCSs and to maintain the competitiveness of the Kwai Tsing
Container Port and
In the absence of this Project, the insufficient depth of
KTCB and its approach channel will cause Kwai Tsing Container Port to become
less efficient given increased vessel sizes, including the inability to
physically berth and accommodate the ULCSs. The long-term development potential
of the Kwai Tsing Container Port will inevitably be constrained by the depth of
KTCB and its approach channel. International shipping lines will no longer
continue to call the
2.4 Consideration of Alternative Construction Methods and Sequence of Work
The do-nothing scenario is described in the
preceding section 2.3. The current depth
of the KTCB limits the efficiency of KTCP and threatens the long term position
of
The
new generation of ULCS is expected to have a draft of 15.5m. This means that in
order for these ULCS to access the container terminals at KTCP, a minimum water
depth of about 17m would be required. Current seabed levels thus constrain
access by ULCS to tides higher than +1.5mCD. Such restrictions on the
permissible access time for ULCS would severely hinder the operational flexibility
and efficiency of these container ships, and would be an impractical option for
both shipping lines and terminal operators. Consequently, a “do nothing” option is not
considered viable
for the long term economy of
2.4.2 Alternative Location
Currently, KTCP is the only port in
2.4.3 Alternatives to Treatment and Disposal of Dredged Sediment
Other than conventional dredging and
disposal of dredged material, consideration has been given to the potential for
reuse of the dredged material
in order to minimise the volumes of sediment requiring disposal, based on the nature of sediment
including moisture content and level of contamination. Reuse of the sediment as
landfill cover is not possible as sediment is not accepted at landfill sites in
Treatment options which have been considered include mechanical dewatering, physical separation, brick making, bioremediation, chemical treatment, stabilisation and thermal treatment. The viability of these treatment methods are summarised below, with further details of these methods provided in Chapter 4 of the EIA Report.
Mechanical dewatering - considered inappropriate for this project due to the slow nature of the process and the additional implications resulting from the generation of contaminated water. Disposal of remaining residual sediment still has to be resolved.
Physical separation - effective only for sandy material and would not be suited to the clay based nature of the sediment arising from the Project.
Brick making – similar to physical separation, the nature of the dredged sediment would be unsuitable for brick making.
Bioremediation – this method would be effective for organic contaminants, but not for heavy metal contaminants, hence its applicability would be restricted.
Chemical treatment – this method is contaminant-specific, and would not be suitable if a wide range of contaminants is identified.
Stabilisation treatment - involves binding the contaminants to prevent their release, however, this type of treatment may not be sufficient to ensure the sediment acceptable for reuse, nor will this method reduce the volume of sediment that requires disposal, therefore this option is not considered appropriate for this Project.
Thermal treatment – this option would lead to other adverse environmental impacts as well as requiring extensive pilot testing and an additional environmental impact assessment to be conducted.
The above summary shows that it is difficult to identify a practical treatment method for the dredged material that would be generated by this Project. Other constraints include limitation of the Project programme, need to minimise disturbance to the KTCP operations as far as possible, land-take requirements, environmental consequences of treatment methods, disposal of residual material and viability of reuse options. It was concluded after detailed study that these options would not be feasible especially given the volume of material to be treated.
An alternative option involving the creation of an artificial island to dispose of the dredged material would have been considered if there was reclamation associated with this Project. The practicalities of coordinating with other reclamation projects, unrelated to this Project, may still be considered by the future Contractor if timing, programme, contractual and environmental management arrangements could be coordinated. However, the risks associated with such arrangements are high. To ensure a secure outcome for the project, disposal of the dredged material is therefore the recommended option.
2.4.4 Dredging Programme
The current dredging programme is tentatively stated as being between 2011 and 2013 to allow the KTCP to receive ULCSs by 2013. In order to meet this deadline, it is envisaged that 24-hour dredging operations will be required. In order to avoid disruption to the operation of the KTCP and to maintain safe marine access, dredging operations have to take into account movements of marine traffic as well as environmental considerations. On the environmental side, the dredging programme has considered the effect of other concurrent projects in the vicinity of the Project as well as projects involving dredging which are farther away but which could potentially have a “cumulative effect” on this Project.
It is currently envisaged that
implementation of the dredging works will involve the simultaneous use of
dredgers in the Western Fairway, Northern Fairway and the KTCB i.e. a maximum
of 3 dredgers at any one time. Consideration has been given to ensure that potentially conflicting
demands of vessel traffic and dredging works are resolved through
deliberation of, inter alia, marine
traffic, types of dredgers and environmental factors.
It was also seen that within the Project area, a hot spot was found near Container Terminal no. 1 and 5 (S2). As such, it would be prudent to isolate S2 to a later stage such that the majority (c. 99%) of the navigational (i.e. capital work) dredging can proceed without affecting the overall construction programme. Scientific research indicates that dredging in the dry season where the sea water temperature is relatively lower compared to the wet season can help in controlling the release of unionized ammonia (UIA) as this is temperature dependent. This approach is especially appropriate for dredging at the hotspot area to minimize the impact in terms of UIA on water sensitive receivers.
2.4.5 Conventional Dredging Method
As part of the detailed engineering studies associated with this Project, it has been identified that equipment which could be deployed is constrained by a number of factors including: the layout and seabed composition (material to be dredged) of the KTCB; need to maintain undisrupted operation of the KTCP during the dredging works; programme; and need to avoid adverse environmental impacts.
The nature of the material is one of the key factors determining the equipment to be used for dredging. Initial ground investigations indicated the presence of soft marine deposits over the majority of the Project area. Subsequently, additional detailed investigations revealed some harder materials at a small area in the north-eastern (NE) corner of the KTCB.
Characteristics of the materials to be
dredged define the options available for dredging plant, such as, trailer
suction hopper dredger, or cutter suction dredgers or grab dredgers. The most commonly used types of dredger in
The GD generally results in smaller environmental impact compared to the other types of dredger, especially when fitted with a frame-type silt curtain. However, a GD operates in a stationary mode and is slower to manoeuvre, when compared to TSHD.
In
Findings of the Marine Traffic Impact Assessment (MTIA) (completed under Agreement No. CE 63/2008) indicate that dredging works within the KTCB and its approaches using either multiple grab dredgers or TSHDs will not result in unacceptable marine traffic impacts. However, the busy nature of the marine environment at KTCB requires that appropriate management measures be implemented and that in-field conformance to high standards of safety management be maintained.
As mentioned earlier, some hard material was
found within the NE corner
of the KTCB. Such material may not be readily removed by GD, and
may require the use of a cutter
suction dredger (CSD). The potential environmental impacts of
a CSD are
limited to the generation of sediment plume in the immediate vicinity of the
stationary CSD whilst
in operation. A CSD’s operation is very localized when engaged in the
removal of hard
materials with large particle size, and therefore, associated
environmental effect will be limited to a small area.
Other types of dredger, such as bucket
ladder dredgers and backhoe dredgers, have not been commonly used in
2.4.6 Keyhole Dredging Method
2.4.6.1 Dredging Methodology
This innovative technique was investigated
in
Keyhole dredging has not been proven to be successful on the scale demanded by this Project and adverse environmental impacts are likely. The method would have a greater impact on marine traffic in the basin and fairway than conventional grab dredging, with increased risks of collision and loss-of-life potential. In the light of the foregoing discussion, the use of keyhole dredging is considered to be not feasible for this Project and was not recommended for further consideration. As such, convention dredging is selected as the preferred option for this Project.
2.5 Selection of Preferred Option
2.5.1 Dredging Equipment
In selecting the preferred dredging option, consideration has been given to aspects including technical feasibility, environmental
acceptability, public interest and the findings from the Marine Traffic Impact
Assessment (MTIA). The benefits and
disbenefits of different dredging options which are relevant to this Project
are summarised as follow:
Table 2.1: Benefits and
Disbenefits of Dredgers which could be used for this Project
Dredging options |
Benefits |
Disadvantages |
Using grab dredger (Typical dredging rate: 4000 m3 / 24 hours) |
· Least amount of sediment release, therefore have a lesser environmental impact · Fixed position so other vessels can plan movements around the working area · Silt curtain can be applied around the dredging area to reduce the dispersion of the sediment plume · Relatively small operating area · Accurate dredging |
· Slower rate of production |
Using cutter suction dredger (Typical dredging rate: 700 m3/hour) |
·
Enables excavation of hard materials · Faster production rate than grab dredger (if overflowing is not a constraint) · More maneuverability than grab dredger |
· More marine sediment produced by volume due to high water content · Silt curtain cannot be applied in this Project due adverse impact on shipping in the KTCB and its approaches. Frame type silt curtain cannot be used |
Using trailer suction hopper dredger (Typical dredging rate: 7200 m3/24 hrs) |
· Easy to manoeuvre as the dredger is self-propelled · Potentially higher rate of production |
· More marine sediment produced by volume due to high water content · Movement of suction pipe and draghead causes turbidity and resuspension of sediment, resulting in more significant environmental impact · Overflow will not be permitted from hopper during loading to avoid causing sediment resuspension; this will have a major negative impact on the productivity of the TSHD and could render the method not feasible in terms of programming · Silt curtain cannot be applied for this Project due to constraints including those of marine traffic · Operation interferes with other marine traffic |
Table 2.2 below provides a summary of the aspect considered in identifying the preferred dredging option
Table 2.2: Selection of Preferred Dredging Option
|
Dredging Method |
||
Aspects Considered |
GD |
CSD |
TSHD |
Disturbance to marine traffic |
Moderate |
Least |
Least |
Loss Rate of SS |
Least |
Moderate |
Most |
Manoeuvrability |
Least |
Moderate |
Moderate |
Accuracy |
Most |
Moderate |
Least |
Speed of Work (production rate) |
Slow |
Slow1 |
Slow[1] |
Ease of mitigation of impact of elevated SS in the KTCB |
ü |
x |
x |
Removal of hard material |
X |
ü |
x |
Removal of Contaminated sediment |
ü |
x |
x |
Removal of Uncontaminated sediment |
ü |
ü |
ü |
Protection of water quality at Fish Culture Zones |
ü |
ü |
x |
Protection of water quality at Bathing Beaches |
ü |
ü |
x |
Public Option and perception |
ü |
x |
x |
Preferred Dredging Option |
ü |
ü |
x |
Given the aforementioned findings and considerations, the
grab dredger has been identified
as the preferred equipment for
dredging, as it is able to meet the technical requirements while
limiting the environmental
impacts. Since grab
dredgers are not effective in the removal of hard material, a CSD is likely to be needed to carry out dredging at the NE corner of KTCB dredging area. The
estimated volume of hard material
that will require excavation is approximately 92,000 m3. Since the hard material forms a very small
component of the entire dredging operation (accounting for approximately 2% of the dredged material), the
choice of CSD is not likely to significantly alter the overall environmental impacts associated with the
Project. Nonetheless the impacts
associated with both dredgers have been assessed in the subsequent sections of
the EIA.
2.5.2
Dredging
Rationale
Owing to the distinctive nature of this Project, considerations have been given to balancing the Construction Programme, Marine Traffic Impact and Environmental aspects to determine which is the most favourable dredging rationale for this Project. In achieving this balance, the first principle is ensure the outcome fulfils the needs of the Project, i.e. that the dredging operation can be undertaken within the anticipated programme. At the same time, the environmental and marine traffic issues have been taken into account such that proposed activities will not result in unacceptable levels of environmental impact and will minimise obstruction to the operation of the container terminals.
Taking into account the foregoing, it was calculated that a maximum of three grab dredgers would be able to complete the dredging operation within the programme of this Project without compromising the environment and marine traffic (a separate report has been prepared under this Project relating to the Marine Traffic Impact Assessment). Due to the presence of hard material in the NE corner of the container basin, a CSD is likely to be deployed to remove hard material in that area.
2.6
Existing Submarine Outfall within
The Project will also involve modification of the Tsing Yi Submarine Sewage Outfall and dismantling of the abandoned Kwai Chung Submarine Sewage Outfall, such that these outfalls will not pose any hazard to future marine traffic after the lowering of KTCB’s seabed.
In order to conform to the target seabed level, the existing riser pipes for the Tsing Yi Submarine Sewage Outfall will be cut down to a level below -18.9mCD. Tailor-made collars will be adopted to connect the existing riser pipes to the new non-return valves. Immediately after the modification works, the outfall and riser pipes will be protected by rock fill and rock armour. It is understood from DSD that the Tsing Yi Submarine Sewage Outfall was originally designed for continuous screened sewage discharge to the sea. Upon the commissioning of HATS Stage 1 system in 2001, the outfall changed to serve as an emergency by-pass just in case of the failure of HATS's tunnelling system.
The Kwai Chung Submarine Sewage Outfall will be demolished by chiselling, which is localised in terms of the resulting impact and is unlikely to release suspended solids (SS) or other materials to the receiving environment. As only approximately half of the outfall is above the target seabed level of -17.5mCD, this top half of the concrete pipe will be demolished, and material will fall into the bottom half of the pipe rather than being removed.
Based on the above, there is insignificant environmental impact in terms of water quality or waste management associated with the modification and dismantling of the two submarine sewage outfalls. Particular on the Tsing Yi Submarine Sewage Outfall, the modification works do not in any way modify its performance and result in addition of pollution loading to the environment.
2.7 Need for Maintenance Dredging
The following information has been used to
identify the changes in seabed levels for assessing the sedimentation rate
within the works area in the
a. Hydrographic data provided by the Marine Department for bathymetric surveys carried out in the Study Area as follows:-
i. Northern Fairway and
ii. Western Fairway – 1999, 2002, 2004, 2006 and 2008.
b. Dredging histories obtained from the Port Works (previously Technical Services) Division of the Civil Engineering Department and Marine Department on removal of high spots in local locations during development of the Container Terminal CT9.
c. Bathymetric survey completed in November 2009 under this Project.
The computer software “Surfer” was used to
analyse the changes in seabed levels through the generation of “sedimentation
isopachytes” by subtracting contours of successive survey data to identify
zones of sediment accumulation within the Study Area.
Additionally, the Container Terminal Operators (CTOs) are reported to have been undertaking maintenance dredging within the berth boxes. From the information provided, a “worst credible” maintenance scenario has been developed, based on the highest annual maintenance dredging volumes attained by each of the operators over the past ten years. In arriving at an annual maintenance dredging volume of 225,000m3, volumes of capital dredging to lower the sea bed within berth boxes have been ignored, as these are not considered to be maintenance dredging. Furthermore, where dredging intervals at particular terminals exceed one year, the dredged volume is divided by the interval to provide an estimate of the annual volume. The value includes an allowance of 30,000m3, being the estimated annual volume of maintenance dredging undertaken by the Port Works Division (PWD) of CEDD and as notified by PWD accordingly. It is considered that the aggregate volume of maintenance dredging thus derived is conservative, yet appropriate for inclusion in the assessment of Water Quality and Waste in Sections 3 and 4 of the EIA Report.
2.8 Interface with Planned Projects
This Project is tentatively scheduled to commence in the
second half of 2011, to be substantially completed within 2 years except for a
small area near Container Terminal no. 1 and 5. The following projects
have been identified as potentially concurrent projects. Some of the projects
described below could have dredging activities which overlap with this Project
and could thus cause cumulative effects. Details of the construction programmes
and descriptions of the Project works were investigated from which relevant
projects were selected for inclusion in the assessments under this EIA. Details
of the overlapping projects and activities are contained in Section 2.8 of the
EIA Report.
Table 2.3: Potential Interface with Planned Projects
Interface with Planned Projects |
1. Construction of Container Terminal No.10 (CT10) in Southwest Tsing Yi |
2. Proposed dredging for marine sand at South of Tsing Yi |
3. Marine borrow and dumping areas at South Tsing Yi |
4.
Proposed laying of submarine cable between |
5. Proposed submarine cable from Tong Fuk to Chung Hom Kok |
6. Dredging operations and seawalls modification works carried out by the container terminal’s operators |
7. Wan Chai Development Phase II and Central – Wan Chai Bypass |
8. Shatin to Central Link – Cross Harbour Section (Phase II – Hung Hom to Admiralty) |
9. Installation of Submarine Gas Pipelines and Associated Facilities from To Kwa Wan to North Point for former Kai Tak Airport Development |
10. Tuen Mun – Chek Lap Kok Link (TM-CLKL) |
11. Hong Kong – Zhuhai – |
12. HZMB |
13. |
14. Backfilling North Brothers Marine Borrow Area |
15. Existing Dredging/ Filling of the Contaminated Mud
Pits in |
16. Proposed Dredging works of the Contaminated Mud Pits in South of Brothers |
3.1.1 Assessment Scope and Criteria
The water quality assessment has been conducted in accordance
with the requirements of the Study Brief and Annexes 6 and 14 of the
EIAO-TM. The criteria used for
evaluating the water quality impacts include: the EIAO-TM; Water Quality
Objectives for the
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 |
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) No E.coli. has been detected in sediment samples taken for the Project. Insignificant E.coli impact is therefore anticipated
3.1.2 Impact Assessment
Water quality assessments were undertaken to assess the effects of dredging on the receiving environment in terms of SS, and other water quality parameters of significance to water sensitive receivers. Key water sensitive receivers identified include fish culture zones, beaches, coral communities, Water Supplies Department’s (WSD’s) flushing water intakes and the Electrical and Mechanical Services Department (EMSD’s) cooling and flushing water intakes (Figure 3.1). The water quality impact during the proposed dredging works was quantitatively assessed using the Delft3D Model.
The water quality impact during construction and operational
phase of the Project has been assessed. The impacts of the proposed dredging
works have been quantitatively assessed using the Delft3D Model. Suspended solids were identified as the most
critical water quality parameter during the dredging works. Different scenarios
including worst-case scenarios and a scenario with concurrent projects for
dredging works have been assessed and
their acceptability in terms of comparing the predicted results with various standards is provided in Table 3.3. No adverse water quality impacts were
predicted at any identified
WSRs, including bathing beaches, coral communities and Fish Culture Zones
(FCZ). At the seawater intakes the standards were exceeded due to elevated
background levels of Suspended Solids (SS) concentrations. The background
levels, without the effects of this Project, already exceeded the standards and
thus any additional SS concentration from this Project would only exacerbate
the issue.
Table 3.3: Summary of Predicted SS for all Scenarios
|
Gazetted Beaches |
Corals |
Fish Culture Zone |
Cooling Water Intakes |
|
Subject Project Only |
|
|
|
|
|
Dry Season |
|
|
|
|
|
Maximum SS elevation (mg L-1) |
1.1 |
0.9 |
0.8 |
12.7 |
13.5 |
Exceedance |
No |
No |
No |
No |
Yes |
Wet Season |
|
|
|
|
|
Maximum SS elevation (mg L-1) |
0.9 |
2.9 |
0.5 |
11.3 |
11.4 |
Exceedance |
No |
No |
No |
No |
Yes |
Concurrent Projects included |
|
|
|
|
|
Dry Season |
|
|
|
|
|
Maximum SS elevation (mg L-1) |
1.8 |
1.0 |
2.6 |
12.7 |
13.5 |
Exceedance |
No |
No |
No |
No |
Yes |
Wet Season |
|
|
|
|
|
Maximum SS elevation (mg L-1) |
1.6 |
3.7 |
2.0 |
11.3 |
11.4 |
Exceedance |
No |
No |
No |
No |
Yes |
* For cooling water and flushing water intakes, maximum SS levels are shown
Based on the predicted results, increases in Suspended Solids (SS) concentrations at some WSD flushing water intakes are anticipated. However, provided suitable mitigation measures are applied e.g. installation of a frame type silt curtain around the grab dredger and a silt screen at seawater intake locations, compliance with the WSD criterion can be achieved.
The impact on bathing beaches was analysed and the conclusion drawn was that the beach water quality would be unaffected by this Project. The effects of dredging on the HATS outfall were assessed and was found to be negligible. The changes to the dispersion and dilution characteristics of the Tsing Yi Submarine Sewage Outfall were confirmed to be negligible. During the operation phase maintenance dredging will be required. The scale of this work is significantly less than for capital dredging works and this will be acceptable in terms of water quality at all WSR’s except the seawater intakes. The non-compliance at these intakes is due to elevated SS concentrations in the marine waters. However suitable mitigation measures will ensure compliance.
It was also seen that within the Project area, a hot spot was found at location near Container Terminal no. 1 and 5 (S2), where its ammoniacal nitrogen value in elutriate 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.
From the assessment of S2 alone, in terms of UIA the
annual average UIA values are exceeded at the beaches at Approach, Ting
Kau,
3.1.3
Mitigation
Measures
3.1.3.1 Construction Phase
Dredging
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 screens 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 studies. The surface SS levels at the
seawater intakes WSD1, WSD8, WSD9 and EMSD1 after the implementation of silt
screen were presented in Table
3.4. The SS concentrations at these WSRs comply with the WSD’s SS
criterion.
Table 3.4: Maximum Surface 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 can 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 was 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:
1. 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;
2. only two types of dredgers will be allowed for this Project: (a) grab dredger with closed grab, and (b) cutter suction dredger;
3. the allowed maximum number of grab dredgers or cutter suction dredger operating simultaneously within the Project area shall follow the requirement listed in Table 3.5 below;
4. to minimize the potential SS impact from dredging, deployment of silt curtains around the grab dredgers is recommended (please refer to Figure 3.7 attached to the EIA Report for the schematic design);
5. either
one cutter suction dredger or one grab dredger shall be working in Zone 2
(including subzones) of the
6. 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
7. Project
dredging works within Zone 1-6 (including subzones) of the
8. 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;
9. the dredging pump of cutter suction dredger shall be operated during cutting to reduce the sediment loss to water body;
10. 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;
11. 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;
12. the speed of all construction vessels will be controlled within the works area to prevent propeller wash from stirring up the seabed sediments;
13. all barges / dredgers used should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;
14. 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;
15. 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;
16. the speed of any construction vessels shall not exceed 10 knots when passing through the Project Site Boundary as shown in Figure 2.1 attached to this Executive Summary.
Table 3.5: 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 |
Treating Hotspot
Sediment from ground investigation S2 location 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 (c. 99%) of the navigational (i.e. capital work) dredging can proceed without affecting the overall construction programme. To address the high levels of NH3-N and hence UIA issue at S2, 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 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.
As discussed in Section 3.7.1.6 of the EIA report, the removal of 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 water column. An outline dredging plan is also included in EIA Report, which indicates the dredging sub-zone where S2 is located is to be isolated and with dredging works to be carried out towards the end of the construction programme. The said plan provides a mitigation strategy in which the control of dredging rate is employed as the strategy to control the release of contaminants during dredging.
Operation Phase
Maintenance Dredging
Although SS impacts on the WSRs during the maintenance dredging were expected to be much lesser than the impacts during construction phase, silt screens at the flushing water intakes WSD1 and EMSD1 should be provided. In addition, silt curtain around 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 operation phase water quality monitoring and audit programme.
Other mitigation measures that should be undertaken during maintenance dredging include:
1. only grab dredger with closed grab will be allowed with a maximum rate of 4000m3/day (in-situ volume);
2. no overflow of dredged material 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;
3. all barges used should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;
4. 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;
5. 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
6. no maintenance dredging will be carried out concurrently with other maintenance dredging works by container terminal operators.
3.1.4
Environmental
Monitoring and Auditing
An environmental monitoring and audit programme including
water quality monitoring at specific WSRs e.g. FCZ, seawater intakes, gazetted
beaches, coral communities, has been proposed to ensure that all the recommended
mitigation measures will be
implemented properly.
3.2.1 Assessment Scope and Criteria
The waste management implications have been undertaken in accordance with the requirements of the Study Brief and Annexes 7 and 15 of the EIAO-TM. This section identifies the types of wastes arising as a result of the construction and operation of the Project in accordance with the detailed requirements outlined in Condition 3.4.6 of the EIA Study Brief. The major waste will be dredged marine sediment from the Kwai Tsing Container Basin (KTCB) and portions of Western Fairway and Northern Fairway and construction and demolition (C&D) materials resulting from the modification and dismantling works for Kwai Chung and Tsing Yi Submarine Sewage Outfalls.
3.2.2 Impact Assessment
The proposed
dredging activities are anticipated to generate a variety of wastes that
could be divided into distinct
categories based on their composition and ultimate method of disposal. Mitigation measures and good site practices,
including waste handling, collection,
transportation and disposal are recommended with reference to the
applicable waste legislation and guidelines. With the implementation of the
recommended mitigation measures, no adverse
residual impact is expected to
arise during the proposed dredging
works.
Major waste generated is dredged marine sediment from the
Kwai Tsing Container Basin (KTCB) and portions of Western Fairway and Northern
Fairway. A review of the sediment quality data from the marine site
investigation indicated that the majority of the marine sediments to be dredged
along the proposed dredging area
were classified as Category L. The total volume of dredged sediment requiring
marine disposal is estimated to be 4,420,384
m3. The volume of dredged sediment suitable for Type 1, Open
Sea Disposal (Category L sediment)
is estimated to be 1,816,560 m3.
The volume of dredged sediment suitable for Type 1, Open Sea Disposal
(Dedicated Sites) (Category Mp
sediment) is estimated to be 1,102,148
m3. The volume of contaminated sediment requiring Type 2,
Confined Marine Disposal (Category Mf
and H sediment) was estimated to be 1,501,676 m3
Table 3.6: Summary
of Dredging
Rate, Manoeuvring of Dredgers and Disposal Routings
Sediment Type |
Dredging Rate |
Manoeuvring of
Dredgers |
Proposed Routing for
Disposals |
Type
1, (Category
L sediment) |
Up to maximum 12,000 m3 per day |
Maximum 3 dredgers will operate at any one time across all works areas per day |
South Cheung Chau Open Sea Disposal Area, East Ninepin Open Sea Disposal Area or other designated locations |
Type
1, (Category
Mp Sediment) |
South of Brothers Confined Marine Disposal Facility Or Cross boundary disposal arrangement (alternative option) |
||
Type
2, Confined Marine Disposal) (Category
Mf and Category H Sediment) |
South of Brothers Confined Marine Disposal Facilities |
# In
accordance with ETWB TC(W) No. 34/2002,
sediment with the following category:
L means Category
L Material, ≤Lower
Chemical Exceedance Level
Mf means Category M Material, >Lower & ≤Upper Chemical Exceedance Level and has
failed biological screening test
H means Category H Material, >Upper Chemical Exceedance Level & <10 x Lower Chemical Exceedance Level and biological
screening test is not required
Hp means Category H Material, >Upper Chemical Exceedance Level & >10 x Lower Chemical Exceedance Level and has passed biological screening test
Hf means Category H Material, >Upper Chemical Exceedance Level & >10 x Lower Chemical Exceedance Level and has failed biological screening test
* In accordance with
ETWB TC(W) No. 34/2002, no biological screening test is required for those Cat
H with chemical screening results >Upper Chemical Exceedance Level & <10 x Lower Chemical
Exceedance Level. By definition, this material belong to Type 2 Confined Marine
Disposal
The sediment would be dredged and transferred to barges for subsequent disposal as allocated by Marine Fill Committee (MFC) depending on the level of contamination. Under the current disposal planning, Category Mp sediment is to be dredged and disposed of at South of Brothers Confined Marine Disposal Facilities or alternatively cross boundary disposal facility. While Category Mf and H sediments will go to the confined marine disposal facilities at South of Brothers Confined Marine Disposal Facility which is the designated disposal site for this Project for accepting this type of dredged material.
For Category L material, which is suitable for open sea disposal in accordance with ETWB TCW no. 34/2002, disposal locations such as South Cheung Chau Open Sea Disposal Area, East Ninepin Open Sea Disposal Area or other designated locations will be allocated by MFC.
It is anticipated maintenance dredging is to be carried out in the operation phase on an irregular basis. Based on the record of Port Works Division, Dredged sediment is expected to be suitable for Type 1, Open Sea Disposal and Type 2 Confined Marine Disposal. The estimated quantity (maximum of 30,000 m3 per annum for this Project, and an estimated total of 225,000m3 for KTCP which includes this Project) is anticipated. Compared to the quantity of sediment generated under the capital dredging works, the associated effect of maintenance dredging in terms of handling and disposal is considered insignificant.
The disposal options as identified in this Project will be
subject to confirmation from MFC. The Project will not be carried out before
obtaining confirmation from MFC on the disposal option.
The Project also includes the removal of portions
of outfall/diffusers of the Kwai Chung
and Tsing Yi submarine sewage outfalls above the proposed dredging level, i.e. -17.5mCD. The existing material above the proposed dredging level surrounding
the submarine outfall will also
be removed. These materials would amount to less than 500 m3. It is
anticipated that the rock and rubble generated from the removal of the submarine outfalls will not be dredged during the
dredging process and all these material
will remain below the sea bed.
Under the Dumping at
Sea Ordinance (DASO), a Sediment Quality Report (SQR) is to be prepared for
EPD’s approval under DASO before dumping permit is granted. The disposal
arrangement as identified for this Project will be subject to procedural
agreement from MFC. The Project works will not be carried out before obtaining
confirmation from MFC on the disposal option.
3.2.3
Mitigation
Measures
Adverse impacts relating to waste management such as odour, noise and wastewater discharge are not expected to arise, provided that good site practices are strictly followed. Recommendations for good site practices during the construction activities include:
1. obtain the profile of different sediment categories and careful planning of sediment removal;
2. strictly follow various mitigation measures for protecting water quality as described in the water quality section of the EIA;
3. nomination of an approved person, such as a site manager, to be responsible for good site practices, arrangements for collection and effective disposal to an appropriate facility, of all wastes generated at the site;
4. training of site personnel in proper waste management and chemical handling procedures;
5. provision of sufficient waste disposal points and regular collection of waste;
6. barges filled with dredged sediment shall be towed away immediately for disposal. In so doing, odour is not anticipated to be an issue to distant sensitive receivers;
7. well planned delivery programme for offsite disposal such that adverse environmental impact from transporting sediment material is not anticipated; and
8. use any well maintained PME on site.
3.2.4
Environmental
Monitoring and Auditing
An environmental monitoring and audit programme in terms of regular site audit and checking of various disposal records has been proposed to ensure that all the recommended mitigation measures will be implemented properly.
3.3.1 Scope and Criteria
The potential marine
ecological impacts arising from the dredging works have been
assessed in accordance with the
criteria stipulated in Annexes 8 and 16 of the EIAO-TM and Study Brief. The assessment criterion for protecting the
marine ecological sensitive receivers in this Study was based on the fact that
a sedimentation rate higher than 0.1 kg m-2 per day would introduce
moderate to severe impact upon corals. While there are no established
legislative criteria for water quality for corals, an elevation criterion of SS
levels less than 30% of ambient baseline conditions has been adopted as the
critical value above which impacts to the habitat may occur. In the fish
culture zones, the elevation of SS should be less than 30% of ambient baseline
conditions at the fish culture zones
based on international marine water quality guidelines for the protection of
ecosystems.
The guidelines for protection of marine ecology follow the
Water Quality Objectives (WQO)
under the Water Pollution Control Ordinance (Cap. 358). The WQO for unionised
ammonia (UIA) is 0.021mg/L. In addition to the WQO for unionised ammonia, the recommended maximum concentration to protect 80% marine
biota according to the water quality assessment guidelines (WQAG) for ammoniacal nitrogen (NH3-N) within
3.3.2
Impact
Assessment
The marine ecological resources within or around the dredging
area have been studied through literature review and field survey. Marine
ecology field surveys for inter-tidal, sub-tidal hard-bottom and soft-bottom
benthic habitats were conducted between September 2009 and January 2010. The
evaluation of the ecological importance of the marine habitats was conducted
through the review of the ecological resources in inter-tidal, sub-tidal
hard-bottom and soft-bottom marine benthic communities and the marine mammals
in open waters within the four Water Control Zones (WCZs) (Victoria Harbour,
Western Buffer, North Western and Southern WCZs). It was found that the
ecological resources in
Potential impact of loss of soft-bottom seabed habitat due to
the dredging works is considered to be minor, owing to the high re-colonizing
ability of the marine benthic communities on similar seabed substrates after
construction. According to the water quality modelling results, the predicted
sediment plume is confined to the dredging area such that the elevation of
suspended solid levels around the coral sites is within acceptable levels.
Therefore the indirect impacts to off-site habitats induced by the elevation of
suspended solid concentration in the water column and the increase in
sedimentation rate is expected to be minor. The predicted unionised ammonia (UIA) concentration at all sensitive
corals community indicated no exceedance of Water Quality Objective (WQO) will
occur during construction phase. Exceedances of WQO for UIA at coastal waters
around Rambler Channel are predicted to cause insignificant impact on the
dominant marine biota along the modified artificial seawall of low ecological
value. The predicted ammoniacal nitrogen concentrations at the coastal waters
around Rambler Channel are all within the recommended water quality assessment
guideline (i.e. maximum NH3-N concentration) for the protection of
80% fisheries and marine biota. Thus the potential toxicity effect on marine
ecology at coastal waters surrounding the proposed dredging area is anticipated
to be of low impact. Anticipated impacts to marine mammals relating to
direct collision and indirect disturbance due to dredging activities is
negligible as the Project area is outside the distribution range of both the
Chinese White Dolphin (Sousa chinensis)
and Finless Porpoise (Neophocaena
phocaenoides). Besides, anticipated indirect impact to recognized sites of
conservation importance namely Cape D’Aguilar Marine Reserve, Sha Chau and
During operation phase, direct collision and acoustic disturbance to Chinese White Dolphins and Finless Porpoises due to the incurred marine traffic are considered unlikely and there have been very few sightings of marine mammals recorded in the Project area and its vicinity in the last 10 years. The affected seabed habitat is expected to be recolonized by benthic organisms and no residual impact on marine ecology is predicted. Even though maintenance dredging is to be carried out, it will be of a much smaller scale than capital dredging works. In view of the fact that the Project area is of low ecological value and not the prime habitat for marine mammals, potential impact on marine ecology is considered negligible.
With the use of grab dredgers and by limiting the number of dredgers working simultaneously to three, potential impacts due to SS elevations will be minimised. To further reduce potential impacts, the release of dredged sediment into surrounding waters should be avoided and barges should work as closely as possible to the dredger. Frame type silt curtains will be deployed to reduce the migration of sediment plumes. Other water quality mitigation measures will also help to minimize the impact on marine ecology.
The potential cumulative impact of the increase in suspended
solids at marine ecology sensitive receivers including coral communities at
3.3.3
Mitigation
Measures
To minimize any potential adverse impacts arising from dredged marine sediment, the release of dredged sediment into surrounding water should be avoided. Barges should work as close as possible to the point of dredging to minimise release of sediment into the receiving waters. Frame type silt curtains will be deployed to reduce the migration of sediment plumes. Additionally, dredged sediment will be transferred to barges for subsequent disposal at the designated disposal site(s) as allocated by MFC.
3.3.4
Environmental
Monitoring and Auditing
An environmental monitoring and audit programme has been proposed in term of water
quality monitoring at designated locations to monitor the effect of dredging
activities to marine ecological environment. The intention of such EM&A
programme is to ensure that all recommended mitigation measures will be
implemented properly.
3.4.1 Scope and Criteria
An assessment of the potential
impacts of the dredging works on existing fisheries resources, fishing
operations and marine culture activities has been
undertaken in accordance with the Study Brief and EIAO–TM Annexes 9 and 17, Fisheries
Protection Ordinance (Cap 171), Marine Fish Culture Ordinance (Cap 353) and
Water Pollution Control Ordinance (Cap 358). Special attention was given to
the fishing activities and fishing, spawning and nursery grounds within the
Study Area; although it is noted that the dredging area is situated within the
Principal Fairways and the
3.4.2
Impact
Assessment
Reviews of existing information[2] on capture and culture fisheries showed that both capture and culture fisheries resources are relatively low and the fisheries activities are infrequent within the area to be dredged.
Impacts to capture fisheries due to temporary loss of fishing ground and short term disruption of fisheries operation are predicted to be minor owing to the low frequency of fishing operation in the proposed dredging area. Indirect water quality impact to the FCZs was assessed with reference to the Water Quality Modelling results, which indicated that the suspended solids (refer to below table), bottom DO and unionised ammonia concentrations are compliant with the Water Quality Objectives as well as the maximum SS criterion of 50 mg/L at FCZs. The non-compliance of depth-averaged DO during wet season and total inorganic nitrogen concentrations is due to the non-compliance of ambient levels as recorded by the routine monitoring of EPD. However the changes in total inorganic nitrogen concentration and DO level during the construction phase in the FCZs are predicted to be insignificant. The potential toxicity effect on capture fisheries operation and fisheries resources due to the potential exceedances of unionised ammonia at coastal waters around Rambler Channel is anticipated to be of low impact, due to the marginal exceedances which are seasonally dependent. The compliance of total ammoniacal nitrogen maximum concentration of 1.2 mg L-1 for protection of 80% of fisheries at coastal waters around the gazetted beaches at Rambler Channel is predicted and the area is not the major capture fisheries operation area as discussed in Chapter 6. This further indicates insignificant impact to fisheries. The potential impact due to the release of contaminants during dredging is considered to be negligible due to the rapid dilution effect and the distance of the FCZs from the nearest dredging boundaries. Therefore the potential impact to the FCZs and fisheries due to the change of water quality in construction phase is predicted to be negligible. Potential impacts on fisheries during the operation phase are negligible as maintenance dredging will only be undertaken on a small scale, compared to capital works dredging which was assessed to be acceptable in terms of water quality, marine ecology and fisheries impact.
Table 3.7: Predicted Suspended Solids Elevations at Fish Culture Zones
Fish Culture Zone |
Assessment Point |
Dry Season |
Wet season |
||
|
Maximum Depth-averaged SS elevation (mgL-1) |
SS Criterion (mgL-1) |
Maximum Depth-averaged SS elevation (mgL-1) |
SS Criterion (mgL-1) |
|
Ma Wan |
F1 |
2.6 (Scenario 7) |
3.2 |
2.0 (Scenario 7) |
2.5 |
Lo Tik Wan |
F2 |
0.2 (Scenario 3 & 7) |
1.8 |
0.1 (Scenarios 1,2,3, 4, 6,& 7) |
1.6 |
Sok Kwu Wan |
F3 |
<0.1 (all scenarios) |
1.8 |
<0.1 (all scenarios) |
1.6 |
Cheung Sha Wan |
F4 |
<0.1 (all scenarios) |
2.6 |
<0.1 (all scenarios) |
4.4 |
The potential cumulative impact of change in water quality on fisheries due to this Project and concurrent projects were assessed in the Water Quality Impact Assessment. With reference to the water quality modelling results, cumulative impact especially for the elevation of SS levels are predicted to be complying with the relevant criteria for all the FCZs. The implementation of water quality mitigation measures, e.g. installation of frame-type silt curtain for grab dredger will reduce the migration of SS from dredging site to water sensitive receivers including FCZs.
As the future maintenance dredging will be of a much smaller scale than capital dredging works, and in view of the Project area is not the prime fishery operation area, the potential impacts on fisheries resources and fishing operations are considered to be negligible during periods of maintenance dredging.
3.4.3
Mitigation
Measures
General good site practices and mitigation measures recommended for controlling water quality to acceptable levels are also expected to be effective in minimizing the impact to capture and culture fisheries during the construction phase. Measure include: control of the speed of all construction vessels within the works area to prevent propeller wash from stirring up the seabed sediments; barges / dredgers to be fitted with tight fitting seals to their bottom openings to prevent leakage of material; and barges or hopper not to be filled to a level that will cause the overflow of materials or polluted water during loading or transportation and the use of a frame type silt curtain.
3.4.4
Environmental
Monitoring and Auditing
An environmental
monitoring and audit programme has been proposed in term of water
quality monitoring at the four fish culture zones (Ma Wan, Lo Tik Wan,
Sok Kwu Wan and Cheung Sha Wan FCZs) during the course of the marine
construction works. 24 hours water quality monitoring is also suggested at the
four FCZs for continuous measurements of DO, temperature and turbidity to
supplement the routine monitoring activities. Similarly, the intention of such EM&A programme is to ensure that all
recommended mitigation measures will be implemented properly.
3.5.1
Assessment
Scope and Criteria
The hazard to life assessment has been undertaken in accordance with the requirements of the Study Brief and Annexes 4 of the EIAO-TM. Currently, there are 3 nos. of LPG/oil depots located in the vicinity of the proposed dredging area, located at the southern part of Tsing Yi, include:
N6: Exxon Mobil Tsing Yi East Terminal for LPG and oil at TYTL 46RP;
N8: Exxon Mobil Tsing Yi West Terminal for LPG and oil at TYTL 115; and
N11: China Resources Petrochemicals Co. Ltd (now SINOPEC) LPG and oil depot at TYTL 127
The Hazard to Life assessment has been undertaken to assess
the potential risk to construction workers and users during the construction
stage of the Project due to their presence within the consultation zones of the
mentioned Potentially Hazardous Installations (PHIs). The potential adverse
impacts to construction workers and personnel onboard dredgers, barges and
other supporting craft will be evaluated by considering the total capacity of
N6 and N11, of which the
3.5.2
Impact
Assessment
The hazard assessment consists of the following steps: Information Collection; Hazard Identification; Frequency Assessment; Consequence Assessment; Risk Summation and Assessment; and Risk Mitigation and Recommendations.
Hazard scenarios from the SINOPEC and ExxonMobil LPG/ oil depots are then identified for the study. Population data, including land, marine, road and dredging workers, as well as meteorological data, are obtained from relevant sources. Consequence distances and occurring frequencies are then evaluated for risk summation in the SAFETI modelling software.The results of assessment are then compared with the Hong Kong Government Risk Guidelines (HKRG) stipulated in Annex 4 of the Technical Memorandum for Environmental Impact Assessment Ordinance (EIAO-TM) to determine the acceptability, which included the criteria for Individual Risk Guideline and Societal Risk Guideline.
Individual Risk: The 1×10-5 per year risk contours extend slightly outside the PHI boundaries, but are mostly close to the site boundary and does not go into the proposed dredging works area. Further away from the depot and jetty, the risk gradually diminishes to lower risk levels. The individual risk levels of the two PHIs therefore marginally satisfy the Hong Kong Government Risk Guidelines for individual risk. It should also be noted that individual risk is solely determined by the LPG/ oil depots (N6, N11) and is not related to the actual population. Therefore, individual risk is not affected by the presence of the dredging workers of the Project.
Societal Risk: The Frequency-fatality (FN) curves for the SINOPEC and ExxonMobil Depots before, during and after the dredging works project indicated that the societal risk levels for “all neighbouring population” (including dredging workers) for both depots have only insignificant changes from Year 2009 to 2012 and then to 2014. The reason for the change is due to changes in land, road and marine population nearby the PHIs. The F-N curves of the two PHIs all lie in the ALARP region. It should be noted that the proposed dredging project does not cause the societal risk levels of the two PHIs to go into the ALARP region. As compared to the overall societal risk from the two depots, the presence of dredging workers of the proposed project is marginal. Therefore it can be concluded that with the dredging works project taking place, the societal risk levels of the LPG/ oil depots still satisfy the Hong Kong Government Risk Guidelines for societal risk.
In summary, the overall risk levels show that the two depots meet the Hong Kong Government Risk Guidelines, which is consistent with previous studies. The increase in societal risk caused by the presence of the dredging workers is minimal comparing to the overall risk level, and is not permanent. It is therefore concluded that the risks posed by two PHIs on the neighbouring population and the dredging workers satisfy the Hong Kong Government Risk Guidelines.
In spite of the negligible additional risk, mitigation measures are recommended to further reduce the risks as low as reasonably practicable. Sound communication channels shall be established with the oil companies, Marine Department, and Fire Services Department for effective notification and emergency evacuation in case of accidents. In addition, proper safety and emergency training should be given to the relevant operation staff at the dredging site. Emergency plans and procedures should be prepared and drills should be performed periodically.
3.5.4
Environmental
Monitoring and Auditing
In view of the above assessment, no requirement for environmental monitoring and auditing is envisaged.
3.6 Landscape, Visual and Glare
3.6.1
Assessment
Scope and Criteria
Landscape, Visual and Glare Impact Assessment was conducted for the Project. The proposed Project is situated in the Rambler Channel, Northern Fairway and Western Fairway. No land works are proposed within any landscape related zonings. Therefore the Project will not have any conflict with the landscape setting of the area.
The assessment of landscape impacts involved the following procedures: identification of baseline landscape resources and landscape character areas; assessment of degree of sensitivity to change of the landscape resources and character areas; identification of potential sources of landscape impacts; identification of the magnitude of landscape impacts; identification of potential landscape mitigation measure; and predicted significance of landscape impacts before and after the implementation of the mitigation measures. The landscape impacts is to be assessed in accordance to Annex 10 and 18 of the EIAO-TM and Study Brief to determine if the impacts are beneficial, acceptable, acceptable with mitigation measures, unacceptable or undetermined.
Assessment of the
potential magnitude of visual and glare impacts will consider such factors
including: compatibility with the surrounding landscape; duration of the
impact, reversibility of the impact; scale of the impact and distance of the
source of impact from the viewer, and blockage of view. The magnitude of visual and glare impact is
classified as: Large; Intermediate; Small; or Negligible. The visual impact assessment covered the
areas of Ma Wan, Tsing Yi, Kwai Chung, Tsuen Wan, Northeast Lantau and
Northwestern part of
Potential glare
impacts assessment during construction covered all the nearby sensitive
receivers in Tsing Yi, Kwai Chung, Tsuen Wan,
Major Sports Stadium: 1000 to 2000 lux
e.g. Hong Kong Stadium – 1400 lux, 2008 Beijing Olympics Equestrian Venue, Shatin – 1400 lux
Sunny Day: 30,000 to 50,000 lux
(Lux is a unit used to define illustration. 1 lux is equal to 1 lumen falling on an area of 1 square metre)
3.6.2 Impact Assessment
The baseline study identified 14 landscape resources and 5 landscape character areas (LCA) within the assessment area. As the Project will not involve any land works, no conflicts with any identified landscape resources and landscape character areas were anticipated during the construction and operational phases. The impact level on existing landscape is therefore acceptable.
The proposed works only involve seabed dredging and a small number of dredgers to be used compared with the busy maritime traffic traversing the exiting fairways, and thus the level of visual impact is anticipated to be acceptable. There will be no significant visual effects caused by the implementation of the Project on identified VSRs during the construction or operational phases.
Lighting for the 24-hour dredging operation is the only man-made light source generated by the proposed Project. The proposed lighting for dredging activities of the Project will be about 250 lux, which is applicable to both day-time and night-time dredging for 24-hour operation. However, the proposed dredging works will not cause any adverse glare nuisance, as these man-made light sources will not be directly pointing to any VSRs and potential spill light will be avoided by the provided visa shields to the lights of dredgers. There will also be no facilities or equipments installed with mirrors or any other polished materials on the dredgers. The slight increase of about 5-20 lux experienced by the VSRs due to the Project will be insubstantial as this low level of lighting intensity basically is not noticeable to the VSRs. Therefore the glare impact level is considered to be acceptable.
Landscape: The proposed Project involves no land works and therefore no conflicts with all existing landscape resources and landscape character areas were anticipated. No specific mitigation measure is required.
Visual and Glare: Although no adverse visual and glare effects were identified, some precautionary measures are recommended to ensure the environmental performance in terms of visual and glare nuisance at VM1 (ID no. of visual mitigation measure). Proper site practice for works lighting shall carefully consider the following: to avoid light pollution and glare to the surroundings; visa shields to the lights of dredgers shall be provided; the light source shall not point directly to any VSRs; and lights shall be switched off if they are not in use.
3.6.4
Environmental
Monitoring and Auditing
In view of the above assessment, no requirement for environmental monitoring is envisaged.
3.7.1 Assessment Scope and Criteria
The cultural heritage impact has been undertaken in accordance with the requirements of Annexes 10 and 19 of the EIAO-TM and Study Brief. A Marine Archaeological Investigation (MAI) was completed to locate and assess the significance of any underwater cultural heritage which may be present on the seabed in the areas that will be impacted by the dredging works. In accordance with Antiquities and Monuments Office (AMO) Guidelines, the MAI comprised: Marine Archaeological Review, Baseline Review, Geophysical Survey, Assessment of Archaeological Potential and Impact Assessment.
3.7.2 Impact Assessment
There have been no previous MAI Studies in the vicinity of the current study. The two previous EIA studies in the vicinity, namely for the South-East Tsing Yi Port Development and for dredging of the Anchorage Area for Stonecutters Island Naval Base, did not contain any information relevant to the current investigation.
The Baseline Review revealed historical evidence indicating
that the waters within the Study
Area have been the focus of
intense maritime activity. The main shipping route to
In November 2009 a geophysical survey was completed to cover 100% of the Study Area. It revealed that the seabed within the Study Area is extensively disturbed with clear evidence for previous dredging, dumping and modern debris. This is particularly intense in the vicinity of the existing utilities: two submarine outfalls, one pipeline and two submarine cables.
The side scan sonar data indicated the presence of 74 sonar contacts for unidentified objects. 54 of these have been disregarded as having archaeological potential. The remaining 20 are all situated in areas where there has been extensive previous dredging. The seismic profiler data showed 36 seismic contacts for buried objects. However, most of these contacts are associated with the modern utilities. There were some sections of the Study Area for which there was no data due to gas masking.
The geophysical survey confirmed that the seabed within the Study Area has been previously disturbed. The most significant impact on the seabed across the Study Area is the extent of previous dredging. This started in 1990 with maintenance dredging and subsequently construction of the Container Terminal 9 in 1998. Regular maintenance dredging is carried out. The full MAI sets out the details of the dredging and it can be clearly seen that the entire seabed has been dredged at each of the 20 unidentified sonar contacts. Dredging would have had a negative impact on the seabed and would have served to destroy or redistribute archaeological remains, if present. It is therefore not possible that an intact archaeological site is present on the seabed within the Study Area. The 20 unidentified objects could represent isolated objects that have been exposed and moved by the dredging but it is more likely they are modern dumped materials. The objects have low archaeological potential.
3.7.3 Mitigation Measures
As the seismic profiler data was not able to provide 100% coverage due to the gas masking, it is recommended that a monitoring brief is conducted. The 20 sonar contacts have low archaeological potential and it is recommended that a monitoring brief should be conducted during the dredging. When dredging occurs in the vicinity of the sonar contacts and the masked areas, a marine archaeologist should be present to monitor the dredged spoil and provide advice. If material indicative of archaeological remains is retrieved, the AMO should be contacted as soon as possible.
3.7.4
Environmental
Monitoring and Auditing
In view of the above assessment, no particular requirement for environmental monitoring and auditing is envisaged, except that a monitoring brief shall be conducted for the 20 sonar contacts and masked areas during the dredging.
3.8.1
Assessment
Scope and Criteria
Potential noise impact arising from the construction of the Project has been evaluated, based on the criteria and guidelines for evaluation and assessing noise impact as stated in Annexes 5 and 13 of the EIAO-TM , Study Brief and Noise Control Ordinance (NCO), with the key criteria illustrated below.
Table 3.8: Noise Standards for Daytime Construction Activities
Noise Sensitive Uses |
0700 to
1900 hours on any day not being a Sunday or general holiday, Leq (30 min),
dB(A) |
All domestic premises including
temporary housing accommodation |
75 |
Hotels and hostel |
|
Educational institutions
including kindergarten, nurseries and all others where unaided voice
communication is required |
70 65 during examination |
Table 3.9: Area Sensitivity Rating
Type of Area Containing NSR |
Degree to which NSR is affected by Influencing Factors (IF) |
||
Not Affected |
Indirectly Affected |
Directly Affected |
|
(i) Rural area, including country
parks or village type developments |
A |
B |
B |
(ii) Low density residential area
consisting of low-rise or isolated high-rise developments |
A |
B |
C |
(iii) Urban area |
B |
C |
C |
(iv) Area other than those above |
B |
B |
C |
Table 3.10: Acceptable Noise Level for Construction Noise
Time Period |
ANL, Leq (30 min), dB(A) |
||
ASR A |
ASR B |
ASR C |
|
All
days during the evening (1900 to 2300 hours), and general holidays including Sundays
during the daytime and evening (0700 to 2300 hours) |
60 |
65 |
70 |
All
days during the night-time (2300 to 0700 hours) |
45 |
50 |
55 |
3.8.2 Impact Assessment
Noise Sensitive Receivers (NSRs) located
closest to the Project site boundary are selected for the assessment. They are Ching Tao House (CTH) of Cheung
Ching Estate in Tsing Yi, which is located more than 310m from the site
boundary and Cheung Ching Estate which are within 500m from the site boundaries
(Figure
3.3).
The construction noise impact assessment has been based on different work schedule scenarios. The construction noise level at the representative noise sensitive receiver (NSR) is predicted to be 43 to 54 dB(A) which complies with the construction noise standard during daytime working hours i.e. 75 dB(A). No adverse noise impact is anticipated. During periods of maintenance dredging in the operational phase, it is anticipated that a reduced plant inventory will be used on the basis of the significantly reduced dredging volumes anticipated for maintenance dredging compared to capital works dredging. Given that the use of three dredgers was acceptable for the construction phase, then it may be surmised that maintenance dredging will also be able to comply with the relevant noise criteria.
Based on the assessment, the construction noise levels predicted at the representative NSR will also comply with the noise standards during restricted hours. It is therefore considered feasible to undertake dredging works over a 24 hour period, subject to obtaining a Construction Noise Permit for works being carrying out in restricted hours.
3.8.3
Mitigation
Measures
No mitigation measures are required during the daytime construction, as no exceedance of the daytime noise criteria is anticipated. The construction noise level at the representative NSR is predicted to comply with the noise standards stipulated in the GW-TM. No residual impact is anticipated,
In order to further ameliorate the construction noise impacts, good site practices listed below should be adopted by all the Contractors as far as practicable. Although the noise mitigating effects are not easily quantifiable and the benefits may vary with the site conditions and operating conditions, good site practices are easy to implement and do not impact upon the works schedule.
1. Only well-maintained plant should be operated on-site and plant should be serviced regularly during the construction programme;
2. Machines and plant that may be in intermittent use should be shut down between works periods or should be throttled down to a minimum;
3. Plant known to emit noise strongly in one direction should, wherever possible, be orientated so that the noise is directed away from nearby NSRs; and
4. Should dredging be carried out during restricted hours, work locations close to NSRs shall be avoided.
3.8.4
Environmental
Monitoring and Auditing
As no existing or planned NSR have been identified within 300 m from the works areas and the predicted construction noise level at the NSR located nearest to the works areas is far below the daytime noise criteria, construction noise monitoring is not required. If there are any planned noise sensitive uses within 300m from the works area occupied during the dredging period, noise monitoring programme should then be implemented during the period(s) with predicted occurrence of noisy activities.
Notwithstanding the above, auditing of the site works to ensure proper implementation of the required mitigation measures is recommended.
3.9.1 Assessment Scope and Criteria
The air quality impact has been undertaken in accordance with the requirements of Section 1 of Annexes 4 and 12 of the EIAO-TM and Study Brief. Potential air quality impact arising from the construction of the Project has been evaluated. Assessment Criteria for aerial emission is based on the Hong Kong Air Quality Objectives (“AQO”) for air pollutants given in Chapter 9, "Environment", of the Hong Kong Planning Standards and Guidelines (HKPSG) for air pollution control and are listed below.
Table 3.11: Hong Kong Air Quality Objectives
Pollutant |
Concentration in micrograms per cubic metre |
||||
Average Time |
|||||
1 hour |
8 hours |
24 hours |
3 months |
1 year |
|
|
800 |
N.A. |
350 |
N.A. |
80 |
Total Suspended Particulates |
500* |
N.A. |
260 |
N.A. |
80 |
Respirable Suspended Particulates |
N.A. |
N.A. |
180 |
N.A. |
55 |
Nitrogen Dioxide |
300 |
N.A. |
150 |
N.A. |
80 |
Carbon Dioxide |
30,000 |
10,000 |
N.A. |
N.A. |
N.A. |
Photochemical Oxidants (as Ozone) |
240 |
N.A. |
N.A. |
N.A. |
N.A. |
Lead |
N.A. |
N.A. |
N.A. |
1.5 |
N.A. |
3.9.2 Impact Assessment
Within the 500m assessment area, 24 existing air sensitive receivers (ASRs) were identified in accordance with Annex 12 of the EIAO-TM which the main ones including Hutchison Logistics Centre, Asia Terminal Limited Logistics Centre, Mariners’ Club, Modern Terminal Limited Building, Tsing Yi Industrial Centre, Cheung Ching Estate, Hong Kong International Terminal, Rambler Oasis Hotel and Rambler Crest (Figure 3.3).
The construction activities involved in the Project are mostly marine based and without dusty activities. The dredged materials are of very high moisture content and dust emissions are not expected during the construction period.
According to the marine site investigation results, the acid
volatile sulphide (AVS) levels are of similar magnitude than those of the odour remediated sediments collected from
3.9.3
Mitigation
Measures
Negligible dust impact is expected from the proposed dredging activities. To further ensure the minimization of potential air quality impact at the ASRs, requirements of the Air Pollution Control (Construction Dust) Regulation, where relevant, shall be adhered to during the construction and any maintenance dredging activities.
Adverse odour impact during dredging is not anticipated. However, in recognition of good site practice and in order to minimize any potential odour emissions, the dredged sediment placed on barge for more than one day shall be properly covered as far as practicable to minimise the exposed area and hence the potential odour emissions during the transportation of the dredged sediment. If dredged sediment is found to be malodorous it shall be removed from site as soon as possible.
3.9.4
Environmental
Monitoring and Auditing
In view of the above assessment, no requirement for environmental monitoring is required; however, auditing of the site works to ensure proper implementation of the required mitigation measures is recommended.
An environmental monitoring and audit programme (EM&A programme) has been recommended for implementation during construction of the Project to ensure compliance with environmental legislation and standards during Project implementation.
On the basis of the assessments carried out for this EIA,
monitoring of water quality is recommended during construction and periods of
maintenance dredging for this Project. The monitoring programme has been
designed to confirm the effectiveness of the mitigation measures proposed and
the acceptability of the impacts associated with the Project. It has also been
developed to obtain a robust, defensible database of baseline information for water quality before construction, and
thereafter, to monitor any variation of water quality from the baseline
conditions and exceedances of relevant water quality objectives (WQOs) at the
sensitive receivers during construction of the Project. It should also be noted that the
monitoring of water quality also provides details on the acceptability of the
works on the marine ecology and fisheries resources as described in the EIA.
While none of the other aspects considered under this EIA require formal monitoring under the Environmental Monitoring and Audit programme for the works, it is recommended that auditing of these aspects is undertaken and this has formed the basis of the holistic EM&A programme.
In addition to dredging, 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 monitoring is proposed to be conducted before, during and after the proposed modification works. A summary of the proposed monitoring and auditing requirements is given in Table 4.1 for the construction phase.
Table 4.1: Environmental Monitoring and Audit Requirements during Construction Phase
Environmental Aspects |
Environmental Monitoring |
Site Audit |
Water |
√ |
√ |
Waste |
X |
√ |
Marine
Ecology |
X |
√ |
Fisheries |
X |
√ |
Hazard to Life |
X |
√ |
Landscape, Visual and Glare |
X |
√ |
Cultural Heritage |
√ |
√ |
Noise |
X |
√ |
Air Quality |
X |
√ |
Although the volume of dredging required for maintenance dredging is less than for the capital works dredging, the monitoring of water quality and auditing of waste handling and disposal arrangements is recommended, as part of the maintenance dredging programme.
This EIA has provided an assessment of potential
environmental impacts associated with the dredging works in
One of the key environmental outcomes has been the ability to plan, design and ultimately construct the Project so that direct impacts to sensitive receivers are avoided, as far as practically possible. Considerations of different dredging options with regard to engineering feasibility and environmental effects have been undertaken. Combinations of dredging scenarios and the associated effects were studied. Preferred options were proposed to minimise the impacts on water quality and avoid direct impacts to water quality, ecologically sensitive habitats and Fish Culture Zones (FCZ).
The equipment that can be deployed for this project is constrained by a number of factors including; the layout and seabed composition of the KTCB; the need to maintain undisrupted operation of the KTCP during the dredging works; the programme; and the need to avoid adverse environmental impacts.
Given the findings from marine traffic impact and environmental effects, the use of grab dredgers was identified as the preferred dredging method, as the grab dredger is able to meet the technical requirements while limiting environmental impacts. However, the grab dredger may not able to remove harder materials which have been identified in the NE of the KTCB. Alternative equipment such as CSD was suggested. Since this harder material only amounts to approximately 2% of the overall dredged material the use of CSD will not materially affect the assessment of the impacts associated with this Project. This has been confirmed in the assessments undertaken.
It was also seen that within the Project area, a hot spot was found at location near Container Terminal no. 1 and 5 (S2), where its ammoniacal nitrogen value in elutriate 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. As such, it would prudent to isolate S2 such that the majority (c. 99%) of the navigational (i.e. capital work) dredging can proceed without affecting the overall construction programme. To address the high levels of NH3-N and hence UIA issue at S2, 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) the most effective dredging process and rate to control the release of ammoniacal nitrogen and UIA into the water column.
Detailed impact assessments have been conducted for both construction and operational phases of the Project, and have concluded acceptable impacts for all aspects considered. With the assistance of water quality modelling, water quality impacts have been demonstrated as being acceptable, albeit with the adoption of mitigation measures for the protection of water quality at the WSD seawater intakes.
A programme of Environmental Monitoring and Audit has been developed to confirm the effectiveness of the mitigation measures associated with the Project.
[1] The prohibition of overflowing from TSHDs reduces their efficiency and effectively nullifies any dredging rate advantage over grab dredging; this effect is exacerbated with increasing separation between dredging site and disposal facility.
[2] Please refer to Section 6.12 of the EIA report for the complete list of references.