14.      Conclusion


14.1          General

This EIA has provided an assessment of potential environmental impacts associated with the dredging works in Kwai Tsing Container Basin and its Approach Channel, based on available information .

¡      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.    

14.2          Water Quality

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.

14.4          Waste Management

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.

14.5          Marine Ecology

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 Kwai Tsing Container Basin are relatively low in ecological importance owing to the newly installed artificial habitats colonized by low abundance of pollution tolerant marine organisms. Along the Western Fairway, the marine ecological resources at the inter-tidal and sub-tidal zones are of moderate-low importance with the more natural shores and presence of coral communities at Green Island and Kau Yi Chau.

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 Green Island and Kau Yi Chau is considered to be minor with the implementation of frame type silt curtain and water quality control measures. The loss of the soft-bottom sub-tidal habitat will be temporary and benthic fauna will be recolonized after the construction ceased. The residual impacts on marine ecology are considered to be negligible. 

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.  

14.6          Fisheries

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 Container Basin, which are not regarded as prime fishery operation areas. For the culture fisheries, four Fish Culture Zones namely Ma Wan, Lo Tik Wan, Sok Kwu Wan and Cheung Sha Wan FCZs were identified as the fisheries sensitive receivers.  

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.

14.7          Hazard to Life

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 Hong Kong risk criteria, which is consistent with previous studies. The increase in societal risk caused by the presence of dredging workers is minimal compared to the overall risk level, and is not permanent. Therefore it can be concluded that the risks posed by two PHIs on the neighbouring population and the dredging workers satisfy the Hong Kong risk guidelines.

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.

14.9          Cultural Heritage

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.

14.10    Noise

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.

14.11    Air Quality

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.

14.13    Summary

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.