Installation of Submarine Gas Pipelines 配合舊啟德機場發展計劃之土瓜灣至北角 海底煤氣管道及相關設施之建造工程 可行性及詳細設計顧問服務 |
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Environmental Impact Assessment – Executive Summary 環境影響評估-行政摘要
文件編號:237926/51/C |
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June 2010 二零一零年六月 |
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The 香港中華煤氣有限公司 |
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Mott MacDonald Hong Kong Limited莫特麥克唐納香港有限公司
in association with合作機構:
BMT Asia Pacific Ltd.
SDA Marine Ltd.
Wilson Taylor Far East Limited
17th Floor, 香港北角渣華道363號17樓 Mott MacDonald, 20/F, Two Landmark East, T +852 2828 5757 F +852 2827 1823 W www.mottmac.com.hk |
This document is issued for the party which commissioned it and for specific purposes connected with the above-captioned project only. It should not be relied upon by any other party or used for any other purpose.
This document contains confidential information and proprietary intellectual property. It should not be shown to other parties without consent from us and from the party which commissioned it. |
Content
Chapter Title Page
2.3 Consideration
of Alternatives 2.4 Selection
of the Preferred Option |
Table 3.1 Summary of Predicted SS for all Scenarios 7
Table 3.2 Summary of Predicted DO Exceedance for
all Scenarios 8
Table 3.3 Summary of Classification of Vibrocore
Samples 9
Table 3.4 Summary of Waste Handling Procedures and
Disposal Routes 10
Table 3.5 Risk Assessment of Different Failure
Causes of the Submarine Pipelines during Operation 14
Table 3.6 Unmitigated Noise Impact due to the
Laying of Submarine Gas Main 17
Table 3.7 Unmitigated Noise Impact due to Landfall
Site Construction 17
Table 3.8 Unmitigated Noise Impact due to the
Construction of Pigging Station 18
Table 3.9 Mitigated Noise Impact due to the
Landfall Construction 18
Table 3.10 Construction Activities and Potential Dust
Emission Sources 19
Figures
Figure 2.1 Physical Constraints to the Proposed Submarine Gas Pipelines
An existing twin 400mm diameter submarine gas pipelines across the Victoria Harbour were constructed by Hong Kong China Gas Company Limited in the early 1970s to supply town gas from Kowloon to the Hong Kong Island. The existing twin 400mm diameter submarine gas pipelines are currently aligned 200m west of and parallel to the Former Kai Tak Airport (KTA) runway between a pigging station at the existing seawall at To Kwa Wan (TKW) and a pigging station at North Point (NP). The submarine gas pipelines are buried in a trench beneath the seabed and protected with rockfill. Owing to the proposed Cruise Terminal Development (CTD) and Central Kowloon Route (CKR) projects, the existing twin 400mm diameter submarine gas pipelines were requested to be diverted.
The “submarine gas pipeline” component of the Project is classified as Designated Project under item H.2 of Part I of Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO) (Cap. 499). The dredging operation associated with the formation of trench for installation of submarine gas pipelines is classified as Designated Project under item C.12(b) of Part I of Schedule 2 of the Environmental Impact Assessment Ordinance (Cap. 499) as it is less than 100m from a seawater intake point. An Environmental Permit (EP) issued under the EIAO is required for the construction and operation of the designated project.
An Environmental Impact Assessment (EIA) Study has been
undertaken to provide information on the nature and extent of environmental
impacts arising from the construction of the proposed designated project and
related activities taking place concurrently and to contribute to decisions on
the overall environmental acceptability of the Project.
This Executive Summary provides the key findings of the EIA
Report, including an 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 recommendations for mitigation measures
to comply with environmental legislations and guidelines.
The Project comprises construction of a new gas pipeline
network from To Kwa Wan to North Point so as to replace the existing one
affected by the proposed Cruise Terminal dredging works adjacent to the
existing Kai Tak runway and the proposed
¡
twin submarine gas pipelines across the
¡ two land gas pipelines at To Kwa Wan and North Point respectively (non designated project under EIA Ordinance); and
¡ two pigging stations for pigging operation at To Kwa Wan and North Point respectively (non designated project under EIA Ordinance).
The site boundary of
the proposed Project covers three main areas, namely:
The Project will ensure that the replacement of the existing
gas facilities from To Kwa Wan to North Point are completed in 2014 and the new
facilities are in service before the de-commissioning of the existing
facilities. The decommissioning / removal works of the existing
cross-harbour submarine pipelines and gas pigging stations are not included in
the scope of the proposed Project.
The construction of the proposed Project is scheduled to
commence in January 2012 for completion by June 2014.
The existing twin 400mm diameter
submarine gas pipelines from To Kwa Wan to North Point were laid below the
existing seabed. They were crucial for the supply of town gas to the
2.3
Consideration of Alternatives
2.3.1 Alignment Options
There are several major installations and underground
structures within the study area which are considered to be physical
constraints to the alignment of the proposed submarine gas pipelines. These
include To Kwa Wan and Kwun
Tong Typhoon Shelters, Small
Craft Mooring Buoys, Government
Mooring Buoys, Eastern
Quarantine and Immigration Anchorage, Hung
Hom and Eastern Fairways, To
Kwa Wan, North Point and Kwun Tong Sewage Outfalls, and Island
Eastern Corridor. The choice of
landing points of the submarine gas pipelines is limited by foundations/pier
structures of the Island Eastern Corridor and utilities and infrastructure
along the coast of
As shown in Figure 2.1,
the proposed submarine gas pipelines are bounded by To Kwa Wan and North Point
Sewage Outfall and the Eastern Quarantine and Immigration Anchorage, the existing To Kwa Wan Typhoon Shelter, sewage outfall for To
Kwa Wan Sewage Treatment Works, seawater intake for Quarry Bay Salt Water
Pumping Station, foundations/pier structures of Island Eastern Corridor while
the proposed pigging stations and land gas pipelines are bounded by proposed
extension of To Kwa Wan Sewage Treatment Works and proposed extension of Man
Hong Street Playground.
By considering the constraints discussed above, the most feasible submarine gas pipelines alignment and landing points are as follows:
For the submarine portion, the shortest and the most feasible route for this portion is an alignment between the dictated landing points at the open space near Hoi Shum Park and at the waterfront area next to North Point Police Station in a manner as shown in Figure 2.1 such that the impact on water quality, coral communities, sediment management and marine archaeology be minimized and impact on underwater infrastructure and marine traffic is minimal.
For To Kwa Wan, the most feasible landing point is at the
area to the north of existing DSD To Kwa Wan Sewage Treatment Works and then
connected to a new pigging station located at adjacent to the future
For North Point, the most feasible landing point inside the North Point Police Station and then connected to a new pigging station located at the same area.
2.3.2 Pigging Station Locations
Thirteen options were considered for the selection of site on
the
Seventeen options were considered for the selection of site
on the
2.3.3 Construction Methods
The methods commonly used to install submarine gas pipelines include “jetting (trenching)”, “jetting (injection)”, “horizontal directional drilling”, and dredging to form the trench followed by “float and sink”, “bottom pull” or “lay barge” followed by backfilling to protect the pipeline. For this project the jetting technique is not feasible.
Jetting installation involves the use of water jets to loosen the seabed material sufficiently to allow the pipe to be pulled into the seabed with significant disturbance to the seabed. Horizontal directional drilling involves taking the pipelines directly from the start to end point by underground drilling with no surface disturbance being necessary. Dredging involves the removal of marine sediments from the seabed to form the trench, into which the submarine gas pipelines are laid by possible methods including Bottom Pull, Lay Barge or the Float and Sink Method. Backfill material would be placed on top to protect the pipeline and minimize the cross section of dredging and backfilling works. A typical cross section of the submarine gas pipelines are provided in Figure 2.2. Design of the cross section and the resulting amount of marine sediments to be dredged from the seabed to form the trench will be depending on the required minimum cover and the existing seabed level for the Bottom Pull, Lay Barge or the Float and Sink Method is adopted for submarine gas pipelines installation.
An analysis of different construction methods and techniques to minimise impacts on water quality, marine ecology, fisheries and waste was carried out. Details of the analysis are presented in the EIA report.
2.3.4 Best Practical Method
By comparing the pros and cons of the various construction methods, grab dredging, followed by pipe laying i.e. “Bottom Pull” method across the fairway, “Float and Sink” method near the landing point and either “Bottom Pull” or “Lay Barge” for other sections of the submarine gas pipelines followed by protection of the submarine gas pipelines by backfilling are the most practical construction method for the installation of the proposed submarine gas pipelines.
Based on the ground investigation
and laboratory testing data, the
seabed material within the works area of the project consist of about 30% of
contaminated sediment. The contamination level of the sediment along the
dredging area at
The identified very soft clay would require a slope gradient of about 1 in 3 on the sides of the trench for stability. Additional and repeated passes would be required to achieve the required trench width and depths. This would increase the volume of contaminated marine sediment being ploughed up and thus increase the spread of highly contaminated substances. This also indicates that the jetting method would not be effective in the soft mud and slurry ground conditions. Furthermore, the contaminated slurry on the sides of the trench at the top layer of the seabed would tend to collapse into the trench formed by jetting with steep gradient and the required armour rock protection cover cannot be achieved accordingly.
The jetting method
would result in extensive pollution in heavily contaminated ground. The jetting
force would cause transportation/movement of contaminated sediment and fine
particle of contaminants from its original locations to other parts of the
The proposed submarine gas pipelines should be laid at a minimum depth of 3m incorporating a rock armour protection layer or at a minimum depth of 5m should the trench be back-filled with original seabed material in accordance with the requirement of CEDD/Port Works. Trench of minimum 3m covered with armour rock would be adopted in the design in order to provide adequate protection to the pipelines and to ensure safety. At the fairway, the designed minimum cover is at least 4m, with rock armour protection. The dredging quantity is kept to a minimum of about 300,000m3 while the filling level at the seabed would match to the existing seabed level. Hydrographical surveys of seabed levels would be conducted before and after construction to ensure the original seabed level is restored.
The assessment results, recommendations and conclusions have been addressed in this EIA report based on the proposed construction techniques or methods.
2.4 Selection of the Preferred Option
The discussions presented in the EIA report have examined the rationale behind the selection of the preferred alignment and pigging stations locations, the preferred construction method and the issue of timing. The environmental and physical constraints have been presented along with the preferred alignment and pigging stations locations for the Project. The submarine gas pipelines alignment avoids direct impacts to the coral areas while the pigging stations avoids the use of open space and direct impacts to plantings and trees. The alignment presented on Figure 2.1, therefore, represents the preferred alignment for the gas pipelines and pigging stations taking into account ecological, water quality and marine traffic constraints.
By comparing the pros and cons of the various construction methods, the preferred construction method is grab dredging, followed by pipelaying i.e. “Bottom Pull” method across the fairway, “Float and Sink” method near the landing point and either “Bottom Pull” or “Lay Barge” for other sections of the submarine gas pipelines followed by protection of the submarine gas pipelines by backfilling of armour rock.
This proposed alignment and construction methods for the gas pipelines have been studied in detail as part of the EIA Report. The selection of this position was taken after a holistic review of the environmental constraints (corals, plantings and trees), physical constraints (navigation channel), the results of the water quality modelling and noise assessment exercise and the form and appearance of the proposed above ground structures with visual mitigation measures.
The environmental impacts associated with
the construction and operation of the submarine gas pipelines are summarised in the
following sections.
The water quality impact during the proposed dredging works for installation of submarine gas pipelines has been quantitatively assessed using the Delft3D Model. Suspended solids are identified as the most critical water quality parameter during the dredging operations. The worst-case scenarios for the dredging works have been assessed and adverse water quality impact was not predicted. The implementation of the appropriate mitigation measures could effectively minimize any potential water quality impacts upon seawater and cooling water intakes.
3.1.1
Impact
Assessment
Major
water quality impact associated with dredging activities is the elevation of suspended
solids (SS)
within the marine water column. With reference to the construction programme
and likely concurrent projects, representative worst case scenarios has been
selected for modelling and assessment. Their acceptabilities in
terms of comparing the predicted SS results with various standards are provided
in Table
3.1. Provided the recommended mitigation
measures are implemented, no unacceptable water quality impact due to
construction of the submarine gas pipelines as well as the other concurrent
marine works is expected.
Table 3.1: Summary of Predicted SS for all Scenarios
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Corals |
Fish Culture Zone |
Cooling
Water Intakes |
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Installation of Submarine Gas Pipeline Only |
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Dry Season |
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Maximum
SS (mg L-1) * |
0.1 |
0.0 |
7.7 |
7.5 |
Exceedance |
No |
No |
No |
No |
Wet Season |
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Maximum
SS (mg L-1)
* |
0.2 |
0.0 |
5.9 |
6.7 |
Exceedance |
No |
No |
No |
No |
Installation of Submarine Gas Pipeline with Concurrent Projects |
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Dry Season |
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Maximum
SS (mg L-1) * |
0.6 |
0.6 |
49.8† |
8.9 |
Exceedance |
No |
No |
No |
No |
Wet Season |
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Maximum
SS (mg L-1)
* |
0.9 |
0.6 |
39.3† |
8.2 |
Exceedance |
No |
No |
No |
No |
* For corals and Fish Culture Zones, maximum
depth-averaged SS elevations are shown; for cooling water and flushing
water intakes, maximum surface SS concentrations
are shown
† The Project (installation of submarine gas
pipeline) only contribute insignificantly to the high SS concentrations at WSR
C15. No water quality criterion was found for the
cooling water intake. Nevertheless, silt screen was recommended by the
concurrent project Wan Chai Development Phase II and Central-Wan Chai Bypass to
reduce the SS impacts on the WSR.
Dissolved oxygen (DO) exceedances were predicted in wet season. The level of DO depletion and minimum predicted depth-averaged DO for water sensitive receivers with DO exceedances are provided in Table 3.2. Predicted changes for DO by the subject Project are small (maximum depletion of 0.1 mgL-1) and within the ranges of natural variations experienced in the study area. However, as ambient depth-averaged DO levels in wet season recorded did not comply with the water quality objectives (WQO) criteria, this inevitably resulted that the predicted minimum DO values for the subject Project in wet season at various WSRs would not be able to meet the WQO criteria. As the predicted changes for DO by the subject project are small, no adverse residual water quality impact is expected.
Table 3.2: Summary of Predicted DO Exceedance for all Scenarios
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Water Quality Sensitive Receivers with Exceedance of Depth-averaged DO level |
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Fish Culture Zone (F1 and F2) |
Cooling
Water Intakes (C2 to C28) |
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Installation of Submarine Gas Pipeline Only |
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Wet Season |
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DO Depletion (mg L-1) |
0 |
0 |
0 |
Minimum
Depth-Averaged DO (mg L-1)
* |
3.6 – 4.5 |
3.3 |
3.3 |
Exceedance |
Yes* |
Yes* |
Yes* |
Installation of Submarine Gas Pipeline with Concurrent Projects |
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Wet Season |
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DO Depletion (mg L-1) |
0 |
0.1 – 0.7† |
0 – 0.1 |
Minimum
Depth-Averaged DO (mg L-1)
* |
3.6 – 4.5 |
3.3 |
3.3 |
Exceedance |
Yes* |
Yes* |
Yes* |
* Please refer to discussion in second paragraph in Section 3.1.1.
† The Project (installation of submarine gas
pipeline) only contribute insignificantly to the low Depth-averaged DO
concentrations at WSR C15. No water quality
criterion was found for the cooling water intake. Nevertheless, silt screen was
recommended by the concurrent project Wan Chai Development Phase II and
Central-Wan Chai Bypass to reduce the DO impacts on the WSR.
Hydrostatic test of the gas pipeline system will lead to effluent containing elevated concentrations of SS that will enter into the surrounding water. It was however expected that the above water quality impact will be temporary and localised during construction only. Provided the recommended mitigation measure is implemented and the effluent discharge complied with the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS) standards, no unacceptable water quality impact due to effluent arising from hydrostatic test is expected.
General
construction activities associated with the construction of the submarine gas
pipelines will lead to construction site runoff containing elevated
concentrations of SS and associated contaminants that will enter into the
marine water. It was however expected that the above water quality impacts will
be temporary and localised during construction only. Provided the recommended
mitigation measures are implemented and all construction site/works area
discharges complied with the TM-DSS standards, no unacceptable water quality
impact due to construction of the submarine gas pipelines is expected.
3.1.2
Mitigation
Measures
Implementation of the following mitigation measures is recommended during dredging to minimise the potential SS impact:
¡ Dredging shall be carried out by closed grab dredger to minimize release of sediment and other contaminants during dredging;
¡ The maximum production rate for dredging from the seabed for installation of the submarine gas pipelines shall not be more than 4,000m3 per day (and no more than 1 closed grab dredger);
¡ Deployment of frame type silt curtain to fully enclose the grab while dredging works are in progress. The frame type silt curtain shall be extended to the seabed to cover the entire water column to minimize the potential SS impact;
¡ all vessels should be sized so that adequate clearance is maintained between vessels and the seabed in all tide conditions, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;
¡ the speed of all vessels shall be controlled within the works area to prevent propeller wash from stirring up the seabed sediments;
¡ all barges / dredgers used shall be fitted with tight fitting seals to their bottom openings to prevent leakage of material;
¡ construction activities shall not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site or dumping grounds;
¡ barges or hopper shall not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation; and
¡ before commencement of dredging works, the holder of the Environmental Permit shall submit detailed proposal of the design and arrangement of the frame type silt curtain to EPD for approval.
There will be no unacceptable residual water quality impact due to the proposed dredging works. An environmental monitoring and audit programme is proposed to ensure that all the recommended mitigation measures are implemented properly.
A review of the sediment
quality data from the marine site investigation indicated that the majority (74%)
of the marine sediments to be dredged along the proposed submarine gas
pipelines were classified as Category L.
A summary of classification of the vibrocore
samples is provided in Table 3.3.
Table 3.3: Summary of Classification of Vibrocore Samples
Category |
Number of Samples |
Category L |
93 |
Category M |
5 |
Category H |
25 |
Category H (10 x > LCEL) |
2 |
3.2.1
Impact
Assessment
The
total volume of dredged sediment from the construction of the submarine gas
pipelines requiring marine disposal was
estimated in the engineering design study to be 267,603m3.
The volume of dredged sediment suitable for open sea disposal (Type 1) was
estimated to be approximately 187,179m3.
The volume of contaminated sediment requiring confined marine disposal (Type 2)
was estimated to be approximately 76,936m3.
The volume of contaminated sediment requiring special treatment or disposal
(Type 3) was estimated to be approximately 3,488m3.
Allocation of marine disposal sites and all necessary permits would be applied
from relevant authorities for disposal of dredged sediment. Project Proponent
would obtain confirmation from CEDD/Marine Fill Committee (MFC) on the disposal
options before commencement of the Project. With the implementation of the
recommended mitigation measures and management procedures in accordance with
the requirements of ETWB TCW No. 34/2002, no adverse
residual impact was predicted.
Waste
types generated by the construction activities are likely to include C&D
material (from excavation works for construction
of the landing points), general refuse from the workforce, and chemical waste
from the maintenance of construction plant and equipment. Table 3.4 provides a summary of the various waste
types likely to be generated during the construction activities for the
proposed submarine gas pipelines, together with the recommended handling and
disposal methods.
Table 3.4: Summary of Waste Handling Procedures and Disposal Routes
Waste
Material Type* |
Total Quantity Generated |
Quantity to be disposed off-site |
Disposal |
Handling |
Marine
Dredged Sediment (Uncontaminated, Type 1),
Category L |
187,179 m3 |
187,179 m3 |
MFC gazetted marine disposal ground – open sea disposal site |
Minimise resuspension by use of closed grab, controlled loading and transfer |
Marine
Dredged Sediment (Contaminated, Type 2),
Category Mf and H |
76,936 m3 |
76,936 m3 |
East Sha Chau contaminated mud pit |
Minimise resuspension by use of closed grab, tight seal on barges, controlled loading and transfer |
Marine
Dredged Sediment (Contaminated, Type 3)
Category Hf |
3,488 m3 |
3,488 m3 |
By
containment of the sediments in geosynthetic containers
and disposal at East Sha Chau contaminated mud pit |
Minimise resuspension by use of closed grab, tight seal on barges, controlled loading and transfer |
C&D Material |
900 cubic meters (preliminary estimate) |
Few hundred cubic meters (preliminary estimate) |
To be reused on-site for construction of the associated landmain gas pipelines or To be disposed to public fill reception points for other beneficial uses or To be disposed to landfill |
Segregate inert C&D material to avoid contamination from other waste arising |
General Refuse |
65 kg per day (preliminary estimate based on workforce of 100) |
65 kg per day |
Refuse station for compaction and containerisation and then to landfill |
Provide on-site refuse collection points |
Chemical Waste |
Few cubic metres per month (preliminary estimate) |
Few cubic metres per month (preliminary estimate) |
Chemical Waste Treatment Centre |
Recycle on-site or by licensed companies. Stored on-site within suitably designed containers |
* In accordance with ETWBTC (Works) No.
34/2002, 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, Hf
means Category H Material, >Upper
Chemical Exceedance Level & >10 x Lower Chemical
Exceedance Level and has failed biological screening test
3.2.2
Mitigation
Measures
Recommendations for good site practices during the construction activities include:
¡ 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
¡ Training of site personnel in proper waste management and chemical handling procedures, separation of chemical wastes with appropriate treatment
¡ Provision of sufficient waste disposal points and regular collection of waste
¡ Barges filled with dredged sediment shall be towed away immediately for disposal. In doing so, odour is not anticipated to be an issue to distant sensitive receivers
¡ Well planned delivery programme for offsite disposal such that adverse impact from transporting sediment material is not anticipated
¡ Well maintained PME should be operated on site
¡ Regular cleaning and maintenance of the drainage systems for construction of the landing points
¡ Appropriate measures to minimise windblown litter and dust during transportation of waste by either covering trucks or by transporting wastes in enclosed containers
Provided that these wastes are handled, transported and disposed of using approved methods and that the recommended good site practices are strictly followed, adverse environmental impacts is not expected during the construction phase.
The
ecological value of the marine ecological resource was evaluated based on the
results of literatures review and field surveys. It was found that the marine
benthic organisms
found within the
dredging area consist of pollution tolerant soft benthos which are in low diversity and is typical to benthos recorded in
poor quality sediments. The
inter-tidal survey confirmed that the inter-tidal communities colonizing the artificial seawall and
concrete embanked wharf piles at To Kwa Wan and North Point landing points
are common fouling organisms. Inter-tidal
surveys were also conducted at the rocky shore at
Benthic
infauna were studied and all the species found in Victoria Harbour Water Control
Zone were widely distributed along the coast of China and considered as the
indicators of the presence of high organic loading in sediment. For the hard
coral communities, low coverage of species Oulastrea
crispata was found on sub-tidal habitat of To Kwa Wan breakwaters. Coral
communities of varied coverage and species diversity were recorded in the coral
sites
3.3.1
Impact
Assessment
Habitat
loss in seabed and artificial seawall are both regarded as temporary since the
dredged area will be backfilled and the seawall will be reinstated. The
temporary loss of marine benthic and inter-tidal communities is regarded as of
low significance owing to the low diversity and abundance of marine fauna
species found in the project area. Given the high commonness of the marine
benthos and their capability of recolonization, the ecological impact in
respect of the loss of marine benthic community and their habitat is considered
as minor. Moreover, the potential impact of loss of inter-tidal communities is
also regarded as minor given their low ecological value. Further, though two
small colonies of hard coral (scleractinains) species Oulastrea crispata were found in the North Point seawall, the
impact of potential loss of the two small colonies of hard coral is regarded as
minor given the high commonness of the species and very small size of the
colonies.
The
potential indirect impact to the identified marine ecological sensitive receivers due to degradation of water quality was predicted by using water
quality modelling. As mentioned and summarized in Table 3.1, the results indicated that the elevation
of SS concentration and sedimentation rate are all within acceptable level
around the identified
marine ecological sensitive receivers. On the other hand, during the marine dive
survey for this Project, low coverage of hard coral species Oulastrea crispata were found at the
hard boulder in To Kwa Wan breakwaters. Given to the close proximity to the
dredging area, the hard coral species O.
crispata colonies attaching on the breakwaters hard boulder will have no
adverse impact with proper mitigation measures implemented.
The
dredging works to create a temporary trench at the seabed is considered as
rather small in scale which would unlikely constitute significant effect on the
water velocity and pressure of the
As the
design of the proposed submarine gas pipelines would minimize the frequency for
maintenance or repair due to accidental breakage, no maintenance dredging is
expected for the future operation of the proposed submarine gas pipelines.
Therefore, no operation impact on marine organism is expected. Since the affected seabed would be
backfilled, recolonization of benthic fauna is expected, and no maintenance dredging
is required for the submarine gas pipelines, no unacceptable residual impact is
expected.
3.3.2
Mitigation
Measures
General
mitigation measures proposed in Section
3.1.2 to control the water quality level during construction period will
also apply for marine ecology. In order to minimize the potential indirect impact
to the coral community on the To Kwa Wan breakwater, it is recommended to
deploy specific silt curtains to protect the identified coral colonies. Aside
from the general frame type silt curtain, a second silt curtain is recommended
to be installed between the dredger and the breakwater for protection of hard
coral communities. Detailed design of this silt curtain shall be submitted to
EPD and AFCD for
agreement at least two weeks prior to project commencement. Recommendations for the silt curtain are
listed below:
¡
The silt curtain shall be fabricated from permeable,
durable, abrasion resistant membrane like geotextiles.
¡
The silt curtain shall be mounted on a floating boom
structure surrounding the grab and should extend to the sea bottom.
¡
The
curtain shall be 75m long and moved along with the dredger as the works
progresses.
¡
The
curtain shall be arranged so that at least 15m of the curtain shall extend past
the dredger in each direction.
¡
The curtain
shall remain in a suitable position between the dredger and the corals until
the dredger is 250m from the corals.
With
the implementation of the recommended mitigation measures, the potential impact
to the coral communities colonizing the To Kwa Wan breakwaters would be minimized
to an acceptable level. With
the implementation of the recommended mitigation measures, it is anticipated
that the potential ecological impact arising from the Project is anticipated to
be acceptable.
3.4.1
Impact
Assessment
During construction phase, the construction
barges would occupy a small working area on sea and restrict access of marine
vessels. However, marine traffic impact assessment revealed that it was
acceptable, the occupied works area will be mobilised as the works in progress,
so the restricted marine area will be localised and implement in stages. Impact
to the marine traffic in general is acceptable. Since there was no
records of fish fry production and operation of trawlers within the proposed
works area of the project, impact to fishing activities in the area are not
expected owing to the small affected
area and short period of disturbance
during the phasing of works for dredging and installation
of the submarine pipeline. Impact on future fishing operation is not
anticipated as the rock armour will not protrude above
the original seabed level.
Ma
Wan Fish Culture Zone (approximately 16km apart) and Tung Lung
Chau Fish Culture Zone (approximately 9km apart) are
not predicted to be impacted by either suspended solids elevation, dissolved
oxygen depletion or nutrient elevation as a result of the Project. Impact
to the Fish Culture Zones and fisheries due to water quality in construction
phase is not anticipated.
As
potential impacts to fisheries resources and fishing operations arising from the
formation of the submarine gas pipelines trench at the seabed are
predicted to be temporary and localised, they are not expected to cause significant
adverse impacts to any fishing grounds or species of importance to the
fishery.
Since no maintenance dredging is required in
operation phase, no operation phase impact is predicted.
3.4.2
Mitigation
Measures
Significant Impacts to fisheries
resources and fishing operations have largely been avoided during construction
through constraints on the works operations for installation of the submarine gas
pipelines. The confinement of works area for dredging
works and pipelines installation will be in phases to minimize the impact on
marine traffic as well as fishing activities in the
To
avoid accidental breakage of pipelines during the operation phase,
precautionary measure will be implemented by backfilling of the pipeline trench
with rock armour to the seabed level. This measure not only protects the
pipelines from frequent maintenance and repairing, it also allows the
recolonization of benthic fauna to the region to support the local fisheries.
A risk assessment study has been conducted
for the relocation of the existing submarine gas pipeline and the associated
facilities. The assessment has considered various failure causes for town gas
leakage. Based on the evaluation of potential safety impacts, the risk
associated with the proposed realigned gas facilities is considered low.
Notwithstanding the low level of risk, risk minimisation measures have been
incorporated into the design to further lower the risk and safeguard population
in vicinity.
3.5.2
Mitigation
Measures
Risk control and mitigation measures will be
adopted to reduce the risk due to marine traffic, including:
¡ Proper general traffic management measures.
¡ Minimisation of works activity footprint – dredging and backfilling.
¡ Safety provision during dredging and backfilling.
¡ Liaison with relevant Government Departments before and during construction stage.
¡ Requirements during the submarine pipe pulling.
With the implementation of the above
mitigation measures, the risk during the construction phase is expected to be
low.
Risk mitigation measures to prevent the
damage of submarine pipeline during operation which will be adopted are listed
as follows:
¡ The submarine gas pipeline will be covered by armour rock, damage from marine vessels could be prevented.
¡ After the submarine pipeline is installed and will be tested to the design standards.
¡ According to HKCG's past record, pigging operation will normally be carried out once in every ten years.
The qualitative risk assessment of failure
of the submarine pipe based on different failure causes is shown in Table 3.5.
According to the risk matrix, for any high risk item, further risk mitigation
measures should be considered as necessary to reduce the risk; for moderate
risk item, further risk mitigation measures should be considered to reduce the
risk to as low as reasonably practicable; and low risk item, further risk
mitigation measures are not considered necessary since the risk is considered
broadly acceptable.
Table 3.5: Risk Assessment of Different Failure Causes of the Submarine Pipelines during Operation
Scenario |
Likelihood of Occurrence |
Consequence to Public |
Risk Level |
|
External Causes |
||||
Natural Event |
|
|||
· Earthquake |
Rare |
Minor |
Low |
|
· Severe Environmental Event |
Rare |
Minor |
Low |
|
Third Party Damage |
Rare |
Minor |
Low |
|
Anchor Drop/ Drag |
Unlikely |
Minor |
Low |
|
Vessel Sinking |
Unlikely |
Minor |
Low |
|
Fishing |
Rare |
Minor |
Low |
|
Dredging Activity |
Unlikely |
Minor |
Low |
|
Internal Causes |
||||
Corrosion |
Unlikely |
Insignificant |
Low |
|
Material Defect |
Rare |
Minor |
Low |
|
Though it can be concluded that there are no
insurmountable risks associated with the construction and operation of the
proposed submarine pipelines and gas pigging stations based on the risk ranking
analysis, a quantitative risk assessment has been conducted by HKCG. Both the offsite individual risk and societal
risk results for the submarine gas pipelines and the two gas pigging stations
have been found “Acceptable” as per risk guidelines in
Two landscape resources, LR1 – Marine Area of To Kwa Wan, LR2 – Marine Area of North Point; and four landscape character areas, LCA1 – To Kwa Wan Plain, LCA2 – To Kwa Wan Waterfront Area, LCA3 – North Point Waterfront Area, LCA4 – North Point Urban Group were identified within the landscape assessment area.
3.6.1
Impact
Assessment
As
the proposed Project will be implemented in the urban areas and have no
conflict with the existing landscape resources, potential adverse impacts on
either landscape resources or landscape character areas are therefore not
anticipated.
The To Kwa Wan Pigging Station and
North Point pigging station are proposed on the existing concrete bare ground
and car park respectively. Therefore,
all the identified landscape resources will not be impacted by the proposed
project during the construction period.
As dredging works will not require
any operation such as reclamation and building cofferdam which would cause loss
of water surface, no impacts on the marine areas are anticipated. As
such, the proposed dredging works will not cause any impact on the
existing landscape resources or landscape
character areas.
Before
implementation of mitigation measures, there could be a temporary and
reversible impact on the character of the landscape character areas resulting
from the construction works of pigging stations. However due to
the urbanised nature of the landscape baseline,
small scale of the proposed facilities and the
simple nature of the installation works, the unmitigated magnitude of the
landscape impact is negligible.
3.6.2
Mitigation
Measures
Mitigation
measures for reducing, offsetting and compensating for impacts during
construction phase which have been designed into the
project include:
¡ Screening of construction works by hoardings/noise barriers around Works area in visually unobtrusive colours, to screen Works.
¡ Hydroseeding or sheeting of stockpiles with visually unobtrusive material (in earth tone).
¡ Ensure no run-off into the harbour adjacent to the site.
Mitigation
measures for the two pigging stations during the operational phase are
identified for implementation in the approved planning permission applications
for the two pigging stations under Section 16 of the Town Planning Ordinance.
The operation mitigation measures identified in the approved planning
permission applications are listed below:
¡ The design and finish of the gas pigging station will be aesthetically compatible with the surroundings
¡ Trellises will be constructed to screen the exposed pipes inside the proposed pigging stations
¡ A planting strip of 1.5m width will be reserved in front of the boundary wall of the proposed To Kwa Wan pigging station
¡ A 300mm wide planting strip will be provided at the seafront side along the boundary fence within the proposed North Point pigging station
¡ A
300mm wide planting strip together with a 2m high visual barrier inside the
existing fence will be provided on the east boundary along
As discussed, there will be no unacceptable
landscape impacts due to the small scale of the works proposed in the Project
and also the existing poor quality of the landscape character of the affected
areas. Hence there will also be no unaccpetable
residual landscape impacts during construction and operation phases on the
Landscape Resources and Landscape Character
Areas. In fact, some slight beneficial
landscape impacts due to the introduction of green elements (i.e. screen
plantings) through the implementation of operation mitigation measures
identified in the approved planning permission applications for the two pigging
stations under Section 16 of the Town Planning Ordinance into the existing
urbanised environments are anticipated.
A baseline review identified no submerged cultural heritage sites within the Study Area. A geophysical survey which covered a 200m corridor along the length of the proposed route of the submarine gas pipelines was conducted. The survey revealed 3 significant sonar contacts located less than 50m from the centre line. However, gas blanking is present across some sections of the study area. At these locations no geophysical survey was obtained and therefore no assessment could be made.
3.7.1
Impact
Assessment
An underwater inspection of the 3 significant sonar contacts located less than 50m from the centre line and an additional 2 between 50 and 60m was conducted. All of the sonar contacts were identified as modern debris. Therefore, there was no indication of submerged cultural heritage. Therefore, no cultural heritage impact arising from marine works of the Project is anticipated at the areas where there is full geophysical survey coverage.
Assessment
could not be made of the areas where there is gas masking, and
therefore no survey data to make the assessment.
3.7.2
Mitigation
Measures
Submerged
cultural heritage were not identified at the areas with 100% geophysical survey
coverage, therefore
no mitigation measures or further action are considered necessary
for these areas.
It is recommended that a monitoring brief is conducted during dredging at the locations where there is no geophysical survey due to ‘gas masking’. The detailed requirements are set out in Appendix H2 of the EIA Report.
The construction noise impact assessment has been based on a best estimate of the construction sequence and plant inventory.
3.8.1
Impact
Assessment
The potential noise impact that could arise
from daytime construction activities of the Project has been evaluated. Construction noise level is predicted at
unmitigated scenario with a range from 64 to 77 dB(A). The predicted construction noise
impacts of different construction stages for the unmitigated scenario have been
summarised in Table 3.6 to Table
3.8.
Table 3.6: Unmitigated
Noise Impact due to the Laying of Submarine Gas Main
NSR ID |
Usage |
Slant Distance (m) |
Unmitigated Noise Level, dB(A) |
Noise Criteria, dB(A) |
Mitigation Measures Required? |
To Kwa Wan |
|||||
SCH01 |
Institutional |
370 |
66 |
70 |
No |
SCH02 |
Institutional |
346 |
68 |
70 |
No |
WFM |
Residential |
449 |
64 |
75 |
No |
SUV |
Residential |
427 |
64 |
75 |
No |
North Point |
|||||
MHE |
Residential |
334 |
67 |
75 |
No |
KCM |
Residential |
325 |
66 |
75 |
No |
LKB |
Commercial/ Residential |
400 |
64 |
75 |
No |
FSQ |
Residential |
209 |
70 |
75 |
No |
Table 3.7: Unmitigated Noise Impact due to Landfall Site Construction
NSR ID |
Usage |
Slant Distance (m) |
Unmitigated Noise Level, dB(A) |
Noise Criteria, dB(A) |
Mitigation Measures Required? |
To Kwa Wan |
|||||
SCH01 |
Institutional |
176 |
73 |
70 |
Yes |
SCH02 |
Institutional |
144 |
75 |
70 |
Yes |
WFM |
Residential |
241 |
71 |
75 |
No |
SUV |
Residential |
245 |
70 |
75 |
No |
North Point |
|||||
MHE |
Residential |
159 |
74 |
75 |
No |
KCM |
Residential |
124 |
73 |
75 |
No |
LKB |
Commercial/ Residential |
246 |
70 |
75 |
No |
FSQ |
Residential |
122 |
77 |
75 |
Yes |
Note:
Bold figure denotes exceedance of
relevant noise criteria
Table 3.8: Unmitigated Noise Impact due to the
Construction of Pigging Station
NSR ID |
Usage |
Slant Distance (m) |
Unmitigated Noise Level, dB(A) |
Noise Criteria, dB(A) |
Mitigation Measures Required? |
To Kwa Wan |
|||||
SCH01 |
Institutional |
122 |
66 |
70 |
No |
SCH02 |
Institutional |
121 |
66 |
70 |
No |
WFM |
Residential |
194 |
62 |
75 |
No |
SUV |
Residential |
230 |
61 |
75 |
No |
North Point |
|||||
MHE |
Residential |
144 |
65 |
75 |
No |
KCM |
Residential |
190 |
62 |
75 |
No |
LKB |
Commercial/ Residential |
197 |
62 |
75 |
No |
FSQ |
Residential |
168 |
63 |
75 |
No |
3.8.2
Mitigation
Measures
With the use of quiet plant and the movable
noise barriers, the construction noise impact can be mitigated to a range of 54
to 71 dB(A) which comply with the relevant noise criteria. The noise
impact has been summarised in Table
3.9.
Table 3.9: Mitigated Noise Impact due to the Landfall Construction
NSR ID |
Usage |
Slant Distance (m) |
Mitigated Noise Level, dB(A) |
Noise Criteria, dB(A) |
To Kwa Wan |
||||
SCH01 |
Institutional |
176 |
60 |
70 |
SCH02 |
Institutional |
144 |
62 |
70 |
North Point |
||||
FSQ |
Residential |
122 |
63 |
75 |
It is recommended that the Contractor should also adopt good working practices in order to minimise construction noise as far as possible, e.g.:
¡ The Contractor shall adopt the Code of Practice on Good Management Practice to Prevent Violation of the Noise Control Ordinance (Chapter 400) (for Construction Industry) published by EPD;
¡ The Contractor shall observe and comply with the statutory and non-statutory requirements and guidelines;
¡ Before commencing any work, the Contractor shall submit to the Engineer Representative for approval the method of working, equipment and noise mitigation measures intended to be used at the site;
¡ The Contractor shall devise and execute working methods to minimise the noise impact on the surrounding sensitive uses, and provide experienced personnel with suitable training to ensure that those methods are implemented;
¡ Noisy equipment and noisy activities should be located as far away from the NSRs as practical;
¡ Unused equipment should be turned off. Number of operating PME should be kept to a minimum and the parallel use of noisy equipment / machinery should be avoided;
¡ Regular maintenance of all plant and equipment; and
¡ Material stockpiles and other structures should be effectively utilised as noise barriers, where practicable.
The Contractor shall, from time to time, be
aware of the noise impacts on the surrounding NSRs through adequate noise
monitoring during the works so that adjustments could be made to control the
construction noise levels. These requirements shall be triggered by an Event
and Action Plan as part of the EM&A which shall be incorporated into the
works contract in order to make it enforceable.
Potential air quality impacts arising from
the construction and operation of the submarine gas pipelines have been evaluated.
3.9.1
Imapct
Assessment
A summary of construction activities and the
potential dust
emission sources is tabulated in Table 3.10.
Table 3.10: Construction Activities and Potential Dust Emission Sources
Construction Activities |
Potential Emission Sources |
No. of Plant Used* |
|
Marine Works |
Trench Dredging |
Gasesous emission from barges |
1-3 |
|
Pipe Laying (at sea) |
Gasesous emission from barges |
1-5 |
|
Pipe Laying (on land) |
Dust generated from site vehicles and gasesous emission from construction plant |
1-2 |
|
Backfilling |
Gasesous emission from barges |
1-3 |
Land Works |
Mobilizations/ Site Preparation |
Dust generated from site vehicles and gasesous emission from construction plant |
1 |
|
Seawall demolition |
Dust generated from site vehicles and gasesous emission from construction plant |
1-2 |
|
Seawall reinstatement |
Dust generated from site vehicles and gasesous emission from construction plant |
1 |
|
Construction of pigging station – Surface reinstatement |
Dust generated from site vehicles and gasesous emission from construction plant |
1 |
|
Construction of pigging station – Facilities installation |
Dust generated from site vehicles and gasesous emission from construction plant |
1 |
Note: [*] The no. of plant used is referred to
Table 10.4 and Table 10.5 of the
EIA report.
As the number of construction plant involved
in the submarine gas pipelines laying activities at anytime on site will be
limited, exceedance of AQOs emissions of gaseous pollutants from these
construction plant is not anticipated.
The number of plant required on site for the construction of the landing
points will also be limited. Dust impact
and SO2 and NO2 emissions from plants and site vehicles will
be minimal.
3.9.2
Mitigation
Measures
With the implementation of appropriate dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation, together with proper maintenance of equipment, adverse air quality impact is not anticipated. Recommended dust control measures include:
No air quality impact is anticipated at the operational phase since there will not have any operational phase emissions.
An environmental monitoring and audit
(EM&A programme) has been recommended for implementation during
construction of the Project to ensure compliance with environmental legislation
and standards during Project implementation.
Monitoring of construction noise and water
quality is recommended during construction of the Project to verify the
effectiveness of the mitigation measures and to obtain a robust, defensible
database of baseline information of noise and water quality before
construction, and thereafter, to monitor any variation of noise and water
quality from the baseline conditions and exceedances of relevant noise criteria
and water quality objectives (WQOs) at the sensitive receivers during
construction of the Project.
The EIA process has facilitated integration of environmental considerations into the design process for the Project. The principal measures identified are those achieved through careful routing of the gas mains and locating of the pigging stations and the installation methodology or gas mains design. Moreover, a number of mitigation measures have been identified to minimise the potential for adverse environmental impacts to occur. The mitigation measures are detailed in full in the Environmental Mitigation Implementation Schedule in Section 14 of the EIA Report. These measures would be implemented by Towngas and, if appropriate, enforced by EPD by means of the EIAO.
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. A detailed assessment of alternatives for routing the gas mains and locating the pigging stations was undertaken. A number of alternative gas mains routes were studied and the preferred alignment minimises impact on water quality and sediment management and avoids direct impacts to ecologically sensitive habitats and species such as corals and marine archaeology. A number of alternative pigging stations locations were studied and the preferred locations for pigging stations avoids encroach the Man Hong Street playground/open space area and proposed “Open Space”, avoids interface with the existing petrol/LPG filling stations and a waterfront promenade will be available next to the To Kwa Wan (TKW) pigging station for use by the general public which avoids direct impact on recreational uses serving the public and local residents.
In preparing the design and installation method for the gas mains, a key concern was to take steps so that indirect impacts to water quality sensitive receivers, through disturbance to the seabed, were avoided or minimised. Consequently, the following approaches were taken to achieve the above.
¡ Reduction
in Indirect Impacts - The alignment chosen for the submarine gas pipelines was
located at a sufficient distance from ecological sensitive receivers so that
the temporary dispersion of sediment from the installation works was not
predicted to affect the receivers at levels of concern (as defined by the WQO
and tolerance criteria).
¡ Installation
Equipment - The use of grab dredging, “bottom-pull” and “float and sink” along
the entire route has minimized the severity of perturbations to water quality
and hence allowed compliance with the WQOs at the sensitive receivers. This careful selection of installation
equipment has helped avoid impacts to sensitive ecological receivers.
¡
Adoption of Acceptable Working Rates - The
modelling work has demonstrated that the selected working rates for the dredging, “bottom-pull” and “float
and sink” works will not cause unacceptable impacts to water quality. Consequently, unacceptable indirect impacts
to marine ecological resources have been avoided.
In preparing
the design of the pigging stations, a key concern is to take steps so that air
quality, noise, waste management and landscape and visual impacts were
minimised. Consequently, a boundary wall will be constructed to screen
the above-ground pipeworks of TKW pigging station to minimise air quality and
noise impact and a planting strip will be reserved in front of the boundary
wall of the TKW pigging station to soften its’ visual appearance and thus
minimises visual impact. A planting strip together with a visual barrier inside
the existing fence on the east boundary along Hoi Yu Street of NP pigging
station will be constructed to soften its’ visual appearance and thus minimises
visual impact. Landscape impact assessment for the two pigging stations are
incorporated in the approved planning permission applications under Section 16
of the Town Planning Ordinance.
The primary objective of this Project is to construct a new
gas pipeline network from To Kwa Wan to North Point so as to replace the
existing one affected by the proposed Cruise Terminal dredging works adjacent
to the existing Kai Tak runway and the proposed
The new gas pipeline network would ensure the existing gas facilities from To Kwa Wan to North Point are replaced before the decommissioning of the existing facilities. With the proposed new gas pipeline network, the risk of no gas supply after the decommissioning of the existing facilities would be minimised. It would also minimise the requirement of constructing new gas production and distribution facilities in the highly congested urban areas with heavy traffic and congested underground utilities, and hence prevents associated environmental impacts arisen from those works.