This EIA has provided an assessment of potential
environmental impacts associated with the dredging works in
¡ The assessment has been conducted in accordance with the EIA Study Brief (no. ESB-198/2008) under the Environmental Impact Assessment Ordinance (EIAO) for the Project, covering evaluation of alternatives, comparison of benefits and disbenefits of alternatives, and the following environmental aspects:
¡ Water Quality Impact
¡ Waste Management Implications
¡ Marine Ecological impact
¡ Fisheries Impact
¡ Hazard to Life
¡ Landscape, Visual and Glare Impact
¡ Cultural Heritage Impact
¡ Noise Impact
¡ Air Quality Impact
The findings of this EIA study have determined the likely nature and extent of environmental impacts predicted to arise from the construction and during the operation of the Project. During the EIA process, environmental control measures have been identified and incorporated into the planning and design of the Project to ensure compliance with environmental legislation and standards. The implementation schedule detailing the recommended mitigation measures are presented in Chapter 13.
The EIA study has predicted that the Project, with the
implementation of the mitigation measures, will be environmentally acceptable with no adverse residual
impacts on population or environmental
sensitive receivers. The environmental outcomes/benefits that have accrued from
the environmental considerations and analysis during the EIA process and the implementation of environmental control
measures of the Project are summarized in the following sections. Environmental
monitoring and audit requirements have been recommended, where necessary, to
check on project compliance of environmental legislation and standards and also on the effectiveness of mitigation
measures and remedial actions, should these be necessary.
14.1 Summary of Environmental Outcomes
14.1.1 The Project
The Project involves deepening the seabed of KTCB and
portions of Northern Fairway and Western Fairway from the existing average of
about -16.0 mCD to the depth of -17.5 mCD to ensure adequate depth of water for
the new generation of the ULCSs (Chapter
2). It is quoted in the Study Brief that the
Project involved dredging of 5.5Mm3 of sediment under this
Project. This volume has been reduced to
around 4.4Mm3 as part of the ongoing engineering assessments and
following the analysis of data pertaining to seabed levels. This reduction in volume has a significant
benefit in terms of reducing material to be disposed of and impacts on the
receiving water column during dredging.
14.1.2 Consideration of Preferred Dredging Option and Environmental Benefits
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. Different dredging options have been considered with regard to their engineering feasibility and
environmental effects as well as the
options for treating the dredged material in order to avoid dredging. In-situ treatment is not practical as the
objective of the Project is to increase the depth of water in the KTCB and the
Northern and Western Fairways. Treatment of spoil including various in-situ,
ex-situ treatments and reuse options to avoid disposal was also examined and
found to be impractical in terms of Project programme, need to minimise
disturbance to the KTCP operations as far as possible, land-take requirements,
environmental consequences of treatment methods, and viability of reuse
options. So the dredging and disposal of
sediment were thus assessed in terms of environmental acceptability and associated
impacts.
Combinations of dredging scenarios and the associated effects were studied. Options were considered which minimised the impacts to the receiving environment and avoided direct impacts to water quality, ecologically sensitive habitats and Fish Culture Zones (FCZ).
The equipment which 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.
Trailer suction hopper dredgers, cutter suction dredgers and grab
dredgers were all assessed.
Given the findings from marine traffic impact assessment and consideration of 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
and alternative equipment such
as a CSD or a modified grab dredger, or other type of ripping equipment may be
required. Since this harder material only amounts to approximately 2% of the
overall dredged material the use of either a CSD or a modified grab dredger
will not materially affect the assessment of the impacts associated with this
Project. This has been confirmed as part of the water
quality assessments.
The number of grab dredgers has been limited to a maximum of 3 taking into account marine traffic considerations and the anticipated amount of sediment to be removed within about 24 months.
On the basis of the plant requirements and environmental
criteria, each of the specific environmental aspects of the Project is given
below.
The water quality impact during both construction and operational phases of the Project has been assessed. The impacts of the proposed dredging works have been quantitatively assessed using the Delft3D Model. Suspended solids (SS) were identified as one of the most critical water quality parameter during the dredging operations. The worst-case scenarios for the dredging works in terms of SS have been assessed. No adverse water quality impacts were predicted for the identified WSRs, which included gazetted bathing beaches, coral communities and Fish Culture Zones (FCZ).
At the WSD flushing
water intakes, the predicted increases in suspended solids (SS) concentrations due to
this Project exceed the relevant water quality standard when the results are combined
with background SS concentrations.
However with the provision of mitigation measures such as the installation of a frame type silt screen at the grab dredger and silt screens at the intake location, the WSD criterion can be
achieved.
It has been
estimated that around 225,000m3 of maintenance dredging could be
undertaken in the KTCP (that is including the 30,000m3 of
maintenance dredging assumed for this Project and that assumed by the Container
Terminal Operators CTO) on an annual basis, compared to 4.4Mm3
capital works dredging for this Project over 24 months. Given that historically the CTO schedule
their maintenance dredging activities to minimise disturbance to overall
operations of the KTCP it is reasonable to surmise that there will be no greater
dredging activity than has been predicted for the capital works programme. Thus, it may be concluded that concurrent
maintenance dredging programmes outside the current Project time frame will not
generate increased impacts compared to those predicted for capital dredging
works.
There is negligible effect on HATS outfall as concluded by the water quality assessment.
From the results obtained from the modelling the performance of the
Tsing Yi Submarine Sewage Outfall following modification it may be noted that the predicted changes
in ambient current
flows before and after the Project are insignificant. The results show that the
outfall dilutions from one diffuser after the modification works are enhanced
by between by 4% and 10%, compared to those before the
modification works,
under different current speed conditions. The results indicate a slight improvement of
the outfall performance, in terms of effluent dilution for a single diffuser,
after the modification works. Since the conclusion for the case of using a
single diffuser for assessment should be similar to the case for multiple diffusers, it may be
surmised that the
modification of the Tsing Yi Submarine Sewage Outfall is unlikely to cause any adverse impact
on the outfall performance but rather provide a slight enhancement in
the outfall’s performance.
From
elutriate test results, it was also seen that within the Project area, a
hot spot was found at location S2, where its ammoniacal nitrogen value was
recorded at more than 20 mg L-1. From the assessment of S2 alone in
terms of UIA that annual average UIA values are exceeded for the beaches at
Approach, Ting Kau, Lido and Casam compared with WQO UIA annual mean criteria
of 0.021 mg/L. With the excision of S2, it is predicted that the ammoniacal nitrogen and UIA level at WSD
seawater intakes and gazette beaches respectively are marginally higher than
the WQO annual mean criteria. As such, mitigation measures in terms of
implementing isolation of hotspots and dredging rate control are proposed such
that majority (c. 99%) of the navigational dredging can be carried out.
An environmental monitoring and audit programme including water quality monitoring at specific WSRs including FCZ, seawater intakes, bathing beaches, and coral communities, has been proposed to ensure that all the recommended mitigation measures are properly be implemented and that compliance with the relevant criteria and standards is achieved.
A review of the sediment quality data from the marine site
investigation indicated that the majority of the marine sediment to be dredged
along the proposed dredging area
is 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 open sea disposal (Category L
sediment) is estimated to be 1,816,560
m3. The volume of dredged sediment suitable for open sea
disposal at dedicated sites (Category Mp sediment) is
estimated to be 1,102,148 m3.
The volume of contaminated sediment requiring confined marine disposal (Category Mf and Hp
sediment) is estimated
to be 1,501,676 m3.
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 are not expected, either during the construction phase or periods of maintenance dredging.
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.
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.
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 level around the
coral sites is considered to be within acceptable levels. Therefore the
indirect disturbance 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 potential impacts associated
with direct collision and indirect disturbance to the marine mammals during the
dredging activities and operation are anticipated to be negligible since the
Project area is outside the distribution range of both the Chinese White
Dolphin (Sousa chinensis) and Finless
Porpoise (Neophocaena phocaenoides) in
Hong Kong.
In conclusion, the
direct impacts on marine ecology associated with the dredging works are minor
owing to the relatively low abundance and diversity of marine organism and no
species of conservation concern recorded in the highly disturbed habitats
within the Project area. The indirect impact due to change of water quality is
predicted to be negligible in view of the limited dispersion of SS, the
acceptable level of predicted sedimentation rate at coral sites, and the rapid
dilution effect of the potential release of contaminants during dredging.
During the
operational phase, maintenance dredging will be of a much smaller scale than
capital dredging works, and due to the fact that the Project area is of low
ecological value and not a prime habitat for marine mammals, the potential
impacts on marine ecology are considered to be negligible.
The potential
cumulative impact of the increase in suspended solids at marine ecology
sensitive receivers including coral communities at
With the
implementation of water quality mitigation measures and environmental
monitoring and auditing programme during the construction phase, no mitigation
measures specific for marine ecology are required. The potential marine
ecological impacts of the proposed dredging, demolition and modification of
outfalls are considered to be environmentally acceptable.
Review of existing information on capture and culture fisheries within the proposed dredging area and Study Area
has been undertaken. The findings show
that both capture and culture fisheries resources are relatively low and the
fisheries activities are infrequent within the area to be dredged.
The dredging area is
situated within the Principal Fairways and the
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 SS elevations are compliant with the Water Quality
Objectives as well as the maximum SS criterion of 50 mg/L at FCZs. The
exceedance of total inorganic nitrogen concentration is due to the high ambient
concentration as recorded by the routine monitoring of EPD. Additionally, the
non-compliance of DO levels during wet season is due to the non-compliance of the ambient
depth-averaged DO levels with the WQO. 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 release of contaminants during
dredging is considered to be negligible due to the rapid dilution effect and
the relatively long 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 be at a much smaller
scale than the capital dredging works, and will be confined to the areas for
the removal of local high spots.
The potential
cumulative impact of change in water quality on fisheries due to this Project
and concurrent projects was assessed in the Water Quality Impact Assessment.
With reference to the water quality modelling results, the cumulative impact especially for the elevation of SS levels
are predicted to be minimal for all the FCZs. The implementation of water
quality mitigation measures including closed grab dredger and frame type silt
curtain will further reduce the SS level and thus the impacts to fisheries will
be minimal.
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. With the implementation of water quality
monitoring programme during the construction phase including routine monthly
water quality monitoring and 24 hours monitoring for dissolved oxygen,
temperature and turbidity at the four fish culture zones, no specific
mitigation measure for fisheries impact is required.
The QRA study
examined the effects of the proposed dredging work near Tsing Yi Island on risk
levels posed by the SINOPEC N11 and ExxonMobil N6 LPG/ oil depots. Major
hazardous incidents which could potentially impact on the dredging area were
evaluated on their hazard consequences and occurring frequencies. The overall
risk levels show that the two depots marginally meet the
14.8 Landscape, Visual and Glare
As dredging activities will not involve any land works, no conflicts with all existing landscape resources and landscape character areas during construction and operational phases are identified.
Given the proposed works only involve seabed dredging, and that only 3 dredgers will be used compared with the busy maritime traffic traversing the existing fairways, the level of landscape and visual impact is anticipated to be acceptable. There will be no adverse visual effects caused by the implementation of the Project on identified VSRs during the construction and operational phases.
The proposed dredging works will not cause any adverse glare nuisance, as no man-made light sources are directly pointing to VSRs, visa shields will be added to lights on dredgers, and no facilities and equipment are installed with mirrors or any other polished materials. Therefore neither direct nor indirect light sources potentially causing glare are anticipated.
Historical evidence indicates that the waters within the study area have been the focus of intense maritime activity which includes reclamation, utility installations and dredging. These activities would have collectively damaged or destroyed any archaeological remains, if present. However, the geophysical survey identified a total of 74 sonar contacts of which 20 cannot be accurately identified. A monitoring brief is recommended for the 20 unidentified sonar contacts and masked areas, which have low archaeological potential.
This assessment has predicted insignificant construction noise impacts associated with the Project at a representative NSR closest to the Project area. The NSR is located more than 310m from the site boundary. Based on the latest available information, there are no existing and planned NSRs identified within 300m from Project boundary.
Even without any mitigation measures, the noise predicted level at the representative residential NSR will comply with the construction noise standard during daytime working hours. Therefore no adverse noise impact is expected.
As the maintenance dredging would utilise the same type of plant as for capital works dredging but with a reduced duration and with only one dredger and one barge, the noise level predicted at the representative NSR during maintenance dredging will be no worse than during the construction phase. Full compliance with the noise criteria is predicted.
The proposed construction works will be carried out 24 hours per day. As the construction noise impact level at the representative NSR is predicted to comply with the noise standards during restricted hours, it is feasible for the construction works to be carried out 24 hours per day. It will be the Contractor’s responsibility to ensure compliance with the NCO and the relevant TMs and he will be required to submit a CNP application to the Noise Control Authority before commencing 24 hour works.
As the dredging activities are marine based, negligible dust
impacts are anticipated. According to the marine site investigation
results, the AVS levels are in the
same order of magnitude as the
AVS levels remediated sediments collected from Sam Ka Tsuen Typhoon Shelter; Given the above and the fact that
sensitive receivers are located far away from the Project area, it is expected that the potential
odour emissions from the sediment within the dredging area of this Project
would not be significant and adverse odour impact from the dredging activities
is not anticipated. Nonetheless
mitigation measures are proposed including the covering of dredged material on
barge if the material is going to stay for more than one day and prompt removal
of dredged material if it is found to be malodorous.
14.12
Environmental
Monitoring and Audit
An Environmental Monitoring and Audit (EM&A) Programme is proposed which includes various monitoring and site auditing activities for both construction and operational phases. During the course of Project, concerned parties, particular the Contractor (and in future for the maintenance dredging works, the Port Works Division of CEDD) shall follow the implementation schedule and plan their works accordingly to minimize potential impacts to the nearby environment.
Based on the assessment, no adverse impact is anticipated to be generated by the Project during either the construction or the
operational phases. In addition, no
residual effects are expected provided that the proposed mitigation
measures are implemented, e.g.
installation of silt curtain to control the migration of sediment plume from
the dredging area to the only affected
WSR’s, i.e., WSD flushing water intakes. No other sensitive receivers are adversely affected by the proposed
dredging works.