5.7              Mitigation of Environmental Impacts - Construction Phase

5.7.1        The description of mitigation measures to prevent adverse impacts to water quality during the construction phase has been divided into two aspects, formation of the reclamation and land based construction activities, including those for the developments on the reclaimed land and for the Chok Ko Wan Link Road.

Reclamation Formation

5.7.2        Suitable mitigation measures to prevent adverse impacts to water quality during reclamation formation are discussed here for the Siu Ho Wan, Northshore, Fa Peng and Theme Park Extension reclamations in terms of operational constraints and ‘best practice’ methods of working.

Operational Constraints

5.7.3        The following operational constraints shall be placed on the construction of the reclamations for the Northshore Lantau Development.

·                      dredging should be undertaken using grab dredgers with a maximum rate of working of 2,000 m3 day-1; and

 

·                      filling should be undertaken behind seawalls which have been constructed above the water surface.

 

5.7.4        The following maximum numbers of grab dredgers will be allowed on each of the reclamations for the Northshore Lantau Development.

·                      Siu Ho Wan - 2 grab dredgers;

·                      Northshore - 1 grab dredger;

·                      Fa Peng - 3 grab dredgers; and

·                      Theme Park Extension - 3 grab dredgers.

 

5.7.5        In the assessment of the impacts to water quality it was predicted that there may be the potential for adverse impacts in terms of the release of TBT to the surrounding marine waters.  However, the assessment was based on a very conservative assumption regarding the release of TBT to the water column from the sediment suspended during dredging.  It was recommended that elutriate testing of representative samples be carried out to better determine the proportion of TBT which could be released to the water column.  If a revised assessment based on this testing still indicates that there was the potential for adverse impacts then mitigation measures would need to be considered.  Such measures could potentially include reductions in the rate of dredging and adopting alternative methods of dredging.  The need for and magnitude of such mitigation measures could only be confirmed following further, more detailed studies, but at this time the possibility of such mitigation measures means that it may be concluded that there would be no insurmountable impacts in terms of the release of TBT.

5.7.6        The assessment of the impacts of backfilling the seawall trenches specified that two alternative measures should be employed to minimise/prevent the loss of fine sediment to suspension, which are summarised as follows.

·                      the use of rockfill containing no soil or organic debris will prevent the loss of fine sediment; and

 

·                      if the trenches are to be backfilled with sandfill then the fill should be placed by pumping down the arm of a trailing suction hopper dredger, which is positioned within the trench below the level of the surrounding seabed.

 

5.7.7        Any proposal to use alternate methods of filling the seawall trenches, such as bottom dumping sandfill, would necessitate further sediment plume modelling during detailed, further studies for the reclamation to determine whether such an operation would lead to adverse impacts to water quality.

5.7.8        The above described operational constraints are sufficient to prevent adverse impacts to water quality.  However, to supplement the operational constraints the general methods of working described below should be applied to the construction of the reclamations for the Northshore Lantau Development.

Methods of Working

5.7.9        The following general working methods shall be applied to supplement the operational constraints described above for dredging and filling to further minimise the loss of fine sediment to suspension.

·                      fully-enclosed grabs should be used when dredging contaminated sediments to minimise the loss of sediment during the raising of the loaded grabs through the water column;

 

·                      tightly closing grabs should be used when dredging uncontaminated sediments to restrict the losses of sediment to suspension;

 

·                      the descent speed of grabs should be controlled to minimise the seabed impact speed;

 

·                      barges should be loaded carefully to avoid splashing of material;

 

·                      all barges used for the transport of dredged materials should be fitted with tight bottom seals in order to prevent leakage of material during loading and transport;

 

·                      all barges should be filled to a level which ensures that material does not spill over during loading and transport to the disposal site and that adequate freeboard is maintained to ensure that the decks are not washed by wave action;

 

·                      the speed of vessels should be controlled within the works area to prevent propeller wash from stirring up the sea bed sediments;

 

·                      “rainbowing” sand fill will not be permitted; and

 

·                      the works shall cause no visible foam, oil, grease or litter or other objectionable matter to be present in the water within and adjacent to the reclamation site and along the route to and from the marine borrow area and disposal site.

 

Land Based Construction Activities

5.7.10    In this section appropriate on-site measures are defined to minimise potential impacts, which will be sufficient to prevent adverse impacts to water quality from land based construction activities, including those for the developments on reclaimed land and for the Chok Ko Wan Link Road.

Surface Run-off

5.7.11    Surface run-off from the construction sites should be directed into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sediment basins.  Channels, earth bunds or sand bag barriers should be provided on site to properly direct stormwater to such silt removal facilities.  Catchpits and perimeter channels should be constructed in advance of site formation works and earthworks.

5.7.12    Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly, at the onset of and after each rainstorm to ensure that these facilities are functioning properly at all times.

5.7.13    If excavation cannot be avoided during rainy seasons, temporarily exposed soil surfaces should be covered e.g. by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds.  Intercepting channels should be provided (e.g. along the crest/edge of the excavation) to prevent storm runoff from washing across exposed soil surfaces.  Arrangements should always be in place to ensure that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm.

5.7.14    Earthworks final surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out as soon as practical after the final surfaces are formed to prevent erosion caused by rainstorms.  Appropriate intercepting channels should be provided where necessary.  Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.

5.7.15    Open stockpiles of construction materials (e.g. aggregates and sand) on site should be covered with tarpaulin or similar fabric during rainstorms.  Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

5.7.16    Manholes (including any newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris from getting into the drainage system, and to prevent storm run-off from getting into foul sewers.  Discharges of surface run-off into foul sewers must always be prevented in order not to unduly overload the foul sewerage system.

Groundwater

5.7.17    Groundwater pumped out of wells, etc. for the lowering of ground water level in foundation construction, such as that required for new buildings, should be discharged into storm drains after being passed through appropriate silt removal facilities.

Wheel Washing Water

5.7.18    All vehicles and plant should be cleaned before they leave the construction site to ensure that no earth, mud or debris is deposited by them on roads.  A wheel washing bay should be provided at every site exit, if practicable, and wash-water should have sand and silt settled out or removed before being discharged into the storm drains.  The section of construction road between the wheel washing bay and the public road should be paved with backfall to reduce vehicle tracking of soil and to prevent site run-off from entering public road drains.

Wastewater from Building Construction

5.7.19    Wastewater generated from concreting, plastering, internal decoration, cleaning work and other similar activities, should undergo large object removal by installing bar traps at the drain inlets.  It is not considered necessary to carry out silt removal due to the small quantities of water involved.  Similarly, pH adjustment of such water is not considered necessary due to the small quantities and the fact that the water is only likely to be mildly alkaline.

Wastewater from Site Facilities

5.7.20    Sewage from toilets, kitchens and similar facilities should be discharged into a foul sewer or chemical toilets should be provided.  Should the use of chemical toilets be necessary then these should be provided by a licensed contractor, who will be responsible for appropriate disposal and maintenance of these facilities.  Wastewater collected from canteen kitchens, including that from basins, sinks and floor drains, should be discharged into foul sewers via grease traps.

5.7.21    Vehicle and plant servicing areas, vehicle wash bays and lubrication bays should, as far as possible, be located within roofed areas.  The drainage in these covered areas should be connected to foul sewers via a petrol interceptor.  Oil leakage or spillage should be contained and cleaned up immediately.  Waste oil should be collected and stored for recycling or disposal,  in accordance with the Waste Disposal Ordinance.

Storage and Handling of Oil, Other Petroleum Products and Chemicals

5.7.22    All fuel tanks and chemical storage areas should be provided with locks and be sited on sealed areas.  The storage areas should be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.  The Contractors should prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

5.8              Assessment Methodology - Operation

5.8.1        The assessment of the impacts to water quality from the operation of the Northshore Lantau Development is split into two main aspects.

·                      The surrounding marine waters; and

·                      The Chok Ko Wan Link Road.

 

Marine Waters

5.8.2        The operation of the Northshore Lantau Development will have the potential to affect the water quality of the surrounding marine waters in two ways, by changing the hydrodynamics and through the discharges of pollutants from the developments on the reclaimed land.  The impacts to hydrodynamics and the discharge of sewage effluents and stormwater from the developments have been assessed through computational modelling.

Hydrodynamics

5.8.3        The formation of the reclamations for the Northshore Lantau Development have the potential to affect tidal current patterns and tidal discharges, which could affect water quality over a wide area and local sediment erosion/deposition patterns in the vicinity of the reclamations.  In order to assess the effects of the reclamations on tidal current patterns and discharges computational hydraulic modelling has been undertaken using the Delft 3D-FLOW hydrodynamic model.  This model which calculates flow and transport phenomena resulting from tidal and meteorological forcing  by solving the unsteady shallow water equations of continuity and momentum.  The main application of Delft3D-FLOW is the three-dimensional simulation of tidal and wind driven flows, including the effect of density differences due to non-uniform temperature and salinity distributions in shallow seas, coastal areas, estuaries, rivers and lakes.  The model aims to simulate flow phenomena where the horizontal length scales are significantly larger then the vertical scales.  This model is , therefore, suited to simulating the complex hydrodynamic conditions in the Hong Kong SAR waters and the Pearl River estuary.

5.8.4        The hydrodynamic modelling for this Study was based on the model which was originally set up, calibrated and validated for the Hong Kong SAR Government ([20]).  This model, known as the Upgrade Model, covers the whole of the Hong Kong SAR waters, the Pearl River estuary, Mirs Bay, the Lema Channel and stretches of the South China coastline to the west of Macau and to the east of Mirs Bay.  This model has recently been updated using an extensive new field data set ([21]) , which has resulted in an improved representation of the hydraulics of the Hong Kong SAR waters.

5.8.5        The grid of the updated model was refined in the vicinity of the reclamations to provide an improved representation of the features of the reclamations.  The overall model grid is shown in Figure 5.8a and the detail of the model grid around Lantau Island is shown in Figure 5.8b .  The hydrodynamic model has been used to simulate three scenarios, which are defined below.  Each of the scenarios was simulated for 15 day spring-neap tidal cycles in the wet and dry seasons.

·                      Baseline, corresponding to all planned reclamations in 2012;

·                      Completed Northshore Lantau Development (including the Theme Park in Penny’s Bay); and

·                      Completed Northshore Lantau Development and Container Terminals.

 

5.8.6        The reclamations in the Baseline Scenario were defined with reference to those adopted for the study Update on Cumulative Water Quality and Hydrological Effect of Coastal Development and Upgrading of Assessment Tool ([22]) .  Major future reclamations and developments, which are included in the baseline are as follows.

·                      Tuen Mun Port;

·                      Tung Chung and Tai Ho reclamations;

·                      Siu Lam Typhoon Shelter;

·                      Tang Lung Chau Dangerous Goods Anchorage;

·                      Container Terminal 9;

·                      Tsuen Wan Bay Further Reclamation, including the reclamation for the KCRC West Rail;

·                      Sham Tseng Further Reclamation;

·                      Peng Chau Typhoon Shelter;

·                      Kowloon Point Reclamation;

·                      Green Island Reclamation;

·                      Central-Wanchai reclamations;

·                      South East Kowloon Reclamation;

·                      Tseung Kwan O reclamations;

·                      Hongkong Electric Lamma Extension on western Lamma Island; and

·                      The bridges for Crosslinks and Route 10.

 

5.8.7        Based on the most recently available information the following modifications were made to the reclamations and developments included in the study Update on Cumulative Water Quality and Hydrological Effect of Coastal Development and Upgrading of Assessment Tool.

·                      The layouts of the Tseung Kwan O reclamations were modified to account for a revised Area 131 and an extension of reclamations up to the cross bay bridge;

·                      The island reclamation in Tung Chung Bay was deleted;

 

·                      The layout of the South East Kowloon reclamation was reduced to account for the new planning proposals for the area;

 

·                      A reclamation was introduced on the western side of Lamma Island for a proposed Waste to Energy Incineration Facility; and

 

·                      The West Lamma Breakwater was deleted from the Baseline scenario, which would only be necessary once any proposed container terminals were constructed in the vicinity of Kau Yi Chau.

 

5.8.8        The layouts for the Northshore Lantau Development reclamations were defined as part of this Study.  It should be noted that the impacts of the reclamations for the International Theme Park on hydrodynamics were tested as part of the EIA for the Theme Park alone.  The layout for the Container Terminal development was also defined for this study.  The Container Terminal development consisted of a reclamation for a 4 berth container terminal and a breakwater to the east at Kau Yi Chau.  This layout was determined in consultation with the Port and Maritime Board and represented only a partial development scenario for the Container Terminal Development, there being the possibility of the construction of a further reclamation at Kau Yi Chau to include additional berths.  However, in terms of the potential impacts to hydrodynamics the scenario simulated would be representative of the development of two container terminals.  Also included in the final scenario was the West Lamma Breakwater, which will only be constructed in the event that container terminals are developed.

Water Quality

5.8.9        During the operation of the Northshore Lantau Development discharges of waste water will incur in the form of sewage effluents and storm water.  The sewage effluent will be transported to the Siu Ho Wan Sewage Treatment Works (STW) for treatment and subsequent disposal to the marine waters via a submarine outfall.  Storm water will be discharged to the marine waters along the waterfront of the reclamations via a number of culverts.  Both of these discharges will increase the pollutant loads to the receiving marine waters and have the potential to cause adverse impacts to water quality.  Also, the changes in hydrodynamics associated with the formation of the reclamation may have the potential to affect water quality.

5.8.10    In order to study the above described impacts computational modelling has been carried out using the Delft3D-WAQ water quality model.  The model simulates water quality processes in three dimensions.  The model includes such parameters as dissolved oxygen, bacteria, nutrients, phytoplankton and suspended sediments.  Physical processes, such as the exchange of oxygen with the atmosphere and the setting of suspended substances, are included.  Biochemical processes simulated in the model include nitrification, algal growth and decay and the decay of organic matter, which affect dissolved oxygen concentrations.  Hydrodynamic data for the water quality model is provided by the Delft3D-Flow hydrodynamic model.

5.8.11    The water quality model used in this Study is based on the model which was originally set up, calibrated and validated for the Hong Kong SAR Government ([23]).  This model has the same coverage as the hydrodynamic model, which includes the whole of the Hong Kong SAR marine waters, the Pearl River estuary, Mirs Bay and the Lema Channel.   Like the hydrodynamic model, the water quality model has recently been updated during the study Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool.

5.8.12    The water quality model uses the grid of the hydrodynamic model as a basis, as shown in Figures 5.8a and 5.8b, but in order to make the simulations more efficient the grid is aggregated by a factor of 2 in the both dimensions of the horizontal plane for the areas remote from the Northshore Lantau Development reclamations.  In the vicinity of the Northshore Lantau Development reclamations the hydrodynamic grid remains unaggregated so that the a good representation of the reclamations is achieved.  The grid for the water quality model is shown in Figures 5.8c and 5.8d.  In the vertical there is an aggregation of the ten layers used in the hydrodynamic model to five layers with relative thicknesses of 10%-20%-20%-30%-20% of the water depth from the surface to the bed.

5.8.13    The water quality model has been used to simulate a complete year so that long term temporal variations in various water quality parameters may be determined.  Input hydrodynamic data has been provided by aggregating the results from the Delft 3D-Flow model for the 15 day spring-neap tidal cycles in the wet and dry seasons.

5.8.14    The water quality model has been used to simulate the same three scenarios as the hydrodynamic modelling, as follows.

·                      Baseline, corresponding to all pollutant discharges in 2012; and

·                      Completed Northshore Lantau Development, including the International Theme Park; and

·                      Completed Northshore Lantau Development and Container Terminal development.

 

5.8.15    A comparison between the first two scenarios will enable the effects of the operation of the Northshore Lantau Development on water quality to be determined, while a comparison of all three scenarios will enable the cumulative effect of the Northshore Lantau Development and Container Terminal development to be determined.

Uncertainties in Assessment Methodology

5.8.16    Quantitative uncertainties in the hydrodynamic and water quality modelling should be considered when making an evaluation of the modelling predictions.  For the hydrodynamic modelling these are considered to be negligible for the following reasons.

·                      The computational grid is sufficiently refined to provide representative simulations results;

 

·                      The model has been calibrated and validated to provide reliable predictions of hydrodynamics in the areas affected by the Northshore Lantau Development reclamations; and

 

·                      The simulations comprise a sufficient spin up period of 8 days so that the initial conditions do not affect the results.

5.8.17    For the water quality modelling realistic worst case assumptions were made in deriving the input data for the model in order to provide conservative predictions of impacts.  It is therefore possible that the input data for the relevant parameters may cause an overestimation of the water quality impacts.  Some examples of the conservative nature of the input parameters are given below.

·                      The upper bound estimates were used for the sewage effluent flows and pollutant concentrations from the Northshore Lantau Development and from other developments on Lantau Island; and

 

·                      The background pollutant loads have been derived from conservative population estimates, and may therefore over-predict the loads.

 

Chok Ko Wan Link Road

5.8.18    The operation design of the Chok Ko Wan Link Road has been reviewed to determine where there may the potential for water quality impacts to occur and suitable measures devised to mitigate the potential impacts. 

5.9              Identification of Environmental Impacts - Operation

5.9.1        The identification of potential impacts to water quality from the operation of the Northshore Lantau Development is split into two main aspects.

·                      the surrounding marine waters; and

·                      the Chok Ko Wan Link Road.

 

Marine Waters

5.9.2        The operation of the Northshore Lantau Development will have the potential to affect the water quality of the surrounding marine waters in two ways, by changing the hydrodynamics and through the discharges of pollutants from the Northshore Lantau Development.

Hydrodynamics

5.9.3        Impacts to the hydrodynamic regime of the waters surrounding the Northshore Lantau Development reclamations may be caused by the presence of the reclamations altering tidal currents.  These changes may be in the form of increased current speeds in some areas and decreased speeds in others.  Impacts may also occur to the discharge rates in the region surrounding the reclamations, which include the flow channel into and out of the Western Harbour and Victoria Harbour.  Any changes in tidal discharge would be important as they would indicate changes in the flushing capacity of the region, which could in turn affect water quality.  An indicator of the effects on water quality of any changes to flushing capacity is salinity, which effectively acts as a conservative tracer and changes in concentration of salinity could be represent of changes in other water quality parameters.

5.9.4        A cause for concern in terms of changes to flushing would be the areas to the west of the Penny’s Bay reclamation, including Discovery bay and Sz Pak Wan, becoming poorly flushed because of a sheltering effect of the reclamation and thus leading to a deterioration in water quality.  Such an impact would be undesirable due to the recreational uses of this area.  Also, the entrance to the small bay at Yam O will become much narrower following the completion of the Northshore reclamation, which could alter the exchange of water within the bay with that of the outside.  This could lead to the potential for stagnation within the bay and consequential deterioration in water quality.

5.9.5        In order to address the above described potential impacts the following analyses have been carried out.

·                      Calculation of instantaneous, residual and average discharges through major flow channels;

·                      Presentation of tidal current vectors; and

·                      Presentation of contours of salinity.

 

5.9.6        The model results have been processed to calculate residual and average flood and ebb discharges through major flow channels for each of the wet and dry season simulations.  The locations of the flow channels are shown on Figure 5.9a and have been selected to represent the flows into and out the areas where the Theme Park reclamations at Penny’s Bay and Yam O may affect global hydrodynamics.  At these same cross section graphs of instantaneous and accumulated discharges have been plotted for each of the wet and dry seasons.  A comparison of the discharges for the Baseline and two scenarios for the Northshore Lantau Development and Container Terminal determines the effects of the reclamations on tidal discharges.  This is an important factor as the rate at which pollutants are transported out of a particular body of water is related to the discharge rate.

5.9.7        Tidal current vectors have been plotted for each of the scenarios to determine the effects of the reclamations on tidal current speeds and directions.  The vectors have been plotted for two instances during the tidal cycle, a falling (ebb) tide and a rising (flood) tide.  The vectors have been produced for a spring tide only because the current speeds will be higher than those on a neap tide and any changes in speed and direction will therefore be most noticeable.  For the wet season spring tide the vectors have been produced for the surface and bed layers as the wet season stratification results in differences in current speeds and directions between the surface and bed.  In addition, contours of salinity are included on the wet season vector plots. The vectors for the dry season spring tide have been produced for the surface only as the waters are well mixed and there is little vertical difference in the tidal currents.  No contours of salinity have been produced for the dry season tide as there is not expected to be significant spatial or vertical variations in salinity.

Water Quality

5.9.8        During the operation of the Northshore Lantau Development and Container Terminal pollutants derived from sewage effluent and storm water will be discharged to the marine waters.  Sewage effluents from the Northshore Lantau Development and Container Terminal will be collected and transported to the Siu Ho Wan Sewage Treatment Works (STW) via sub-surface sewerage pipelines.  The effluents will be treated at the Siu Ho Wan STW and discharged to the marine waters to the north of the STW via a submarine outfall.  In the future, during the operation of the Northshore Lantau Development, the Siu Ho Wan STW will treat also effluents from the Chek Lap Kok airport, the Tung Chung and Tai Ho developments, Discovery Bay and South Lantau.  The increase in the treated effluent flows and loads due to the additional influent from the Northshore Lantau Development will have the potential to cause adverse impacts to water quality.

5.9.9        Stormwater run-off from the Northshore Lantau Development and Container Terminal areas will be discharged to the marine waters via culverts along the seawalls.  The stormwater may contain contaminants, which would have the potential to cause adverse impacts to water quality, most likely in the immediate vicinity of the discharge points due to the relatively low flow rates from these culverts.  In order to determine the impacts on water quality from the increased discharges treated sewage effluents and storm water detailed water quality modelling has been carried out for the three scenarios described above.

5.9.10    The pollution loads for the baseline scenario, including sewage effluents and storm water discharges were derived from the pollution load inventory produced as part of the study Update on Cumulative water quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment Tool.  This data was used because it provides the most up to date information on pollution loads to the whole of the Hong Kong SAR marine waters and the Pearl River Estuary.  The key features of the pollution load inventory, which affect the water quality in the vicinity of the Theme Park reclamations are the assumptions that the Peng Chau STW continues to discharge off Tai Lei and that the Strategic Sewage Disposal Scheme Phases I-IV, including the long sea outfall, have been implemented.

5.9.11    As part of this Study the flows and loads from the Siu Ho Wan STW have been examined and modified to better reflect the expected conditions in 2012 without the additional flows from the Northshore Lantau Development.  At this time the Siu Ho Wan STW is expected to be receiving flows from the Chek Lap Kok airport, the Tung Chung and Tai Ho developments and Discovery Bay.  Data on the influent flows and quality from the Chek Lap Kok airport, the Tung Chung and Tai Ho developments and South Lantau have been obtained from the Final Design Memorandum for the Siu Ho Wan STW.  The influent flows and loads from Discovery Bay have been estimated assuming a population of 25,000 ([24]) , which is the expected ultimate development for the area and are based on the unit flow factors for domestic sewage in the Drainage Services Department Sewerage Design Manual ([25]).  The treated effluent quality from the Siu Ho Wan STW has been calculated assuming removal efficiencies of 70% for suspended solids and 55% for biochemical oxygen demand and a discharge concentration of E. coli of 20,000 cfu 100mL-1 ([26]).  The influent flows and loads to the Siu Ho Wan STW for the Baseline scenario are shown in Table 5.9a and the resulting treated effluent flows and loads are shown in Table 5.9b.

Table 5.9a         Influent Flows and Loads to the Siu Ho Wan STW for the Baseline Scenario

Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

Source

(m3 day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(cfu day-1)

Airport

16,596

4,979

4,979

10,757

769.0

429.0

31.0

3.3E+15

Tung Chung/Tai Ho

130,860

25,877

31,877

68,871

4,920.0

2,751.0

201.0

2.04E+16

Discovery Bay

9,250

1,000

1,050

2,250

212.5

125.0

14.8

1.08E+15

Total

156,706

31,856

37,906

81,878

5,901.5

3,305.0

246.8

2.48E+16

 

 

Table 5.9b         Treated Effluent Quality from the Siu Ho Wan STW for the Baseline Scenario

 Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

 

(m3 day-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(cfu 100mL-1)

Effluent Quality

156,706

60.99

108.85

522.49

37.66

21.09

1.57

20,000

 

 

5.9.12    Data on the expected sewage flows from the Northshore Lantau Development have been divided into the component phases of the development as follows.

·                      International Theme Park at Penny’s Bay;

·                      Theme Park Extension;

·                      Eco Park (Luk Keng headland);

·                      Theme Park Gateway (Northshore reclamation);

·                      Tourist and Convention Village (Northshore reclamation);

·                      Technodrome (Northshore reclamation);

·                      Residential (Siu Ho Wan reclamation);

·                      Education (Siu Ho Wan Reclamation);

·                      Fa Peng; and

·                      Tai Ho Wan Areas 2 and 5.

 

5.9.13    Flows from the International Theme Park at Penny’s Bay were provided by the Theme Park operator, based on data from similar facilities in other parts of the world.  The Theme Park Extension was assumed to be 50% the size of the Theme Park and the flows were factored accordingly.  For other tourist developments (Eco Park, Tourist and Convention Village, Technodrome and Fa Peng) the flows were calculated on a pro-rata basis from those for the Theme Park in Penny’s Bay, based on the ratio of the expected numbers of visitors.  The flows from the other areas were calculated from Table 4 (Global UCF’s) in the Drainage Services Department’s Sewerage Manual based on the expected populations.  The land usage for the Fa Peng reclamation has yet to be finalised and a number of options are currently being considered, including recreational uses and residential developments.  The potential sewage effluent flows and loads for each of the development options were examined in order to determine which of them would be the worst case in order to provide conservative estimates of the input data for the water quality modelling.   It was found that the worst case was represented by the development of a racecourse, assuming 8 racing days per month.

5.9.14    The operator for the International Theme Park in Penny’s Bay also provided data on the expected quality of the sewage effluents generated by the Theme Park, which are as follows.

·                      Suspended Solids - 120 to 250 mg L-1;

·                      Chemical Oxygen Demand - 500 to 600 mg L-1;

·                      Biochemical Oxygen Demand - 250 to 450 mg L-1;

·                      Total Kjeldahl Nitrogen - 28 to 32 mg L-1; and

·                      Ammoniacal Nitrogen - 24 to 26 mg L-1.

 

5.9.15    In order to ensure that the water quality modelling was suitably conservative the upper bound concentrations for each of the above pollutants have been used to determine the input data for the water quality modelling.  No data, however, were provided for Total Toxic Metals (TTM) and E. coli.  In order to estimate the loads for these parameters worst case factors were derived from the data contained in Table 5.9a and applied to the flows from the Theme Park.  It should be noted that the lack of data on E. coli is not critical because it is assumed that the Siu Ho Wan STW will still be able to meet the discharge standard of 20,000 cfu 100mL-1 with the additional flows from the Theme Park.  Concentrations of pollutants in the effluent from the Theme Park Extension, Eco Park, Tourist and Convention Village, Technodrome and Fa Peng were assumed to be the same as those for the International Theme Park in Penny’s Bay, which is reasonable as these developments are all tourist based.  The effluent quality from the other developments were derived from Table 4 (Global UCF’s) in the Drainage Services Department’s Sewerage Manual based on the expected populations.

5.9.16    In the completed Northshore Lantau Development scenario the flows and loads from South Lantau have also been included.  This is because in the ultimate case (ie after 2012) the flows and loads from South Lantau are proposed to be connected to the Siu Ho Wan STW.  Flow and load data was obtained from the Final Design Memorandum for the Siu Ho Wan STW.

5.9.17    The influent flows and loads to the Siu Ho Wan STW for the completed Northshore Lantau Development scenario are shown in Table 5.9c and the resulting treated effluent flows and loads are shown in Table 5.9d.

5.9.18    The sewage loadings for the Container Terminal were based on an employment population of 17,300, which was derived from the employment assumptions for Container Terminal 9 in the final report for the study South-east Tsing Yi Port Development Planning and Engineering Feasibility Study for Container Terminal 9.  The sewage loadings were also derived from this previous study.  The employment population was based on the development of two container terminals for a total of 10 berths.  This represents the full development potential of the container terminals in the vicinity of Kau Yi Chau and was used to simulate the worst case impacts from the increase in sewage effluent flows to the Siu Ho Wan STW.

5.9.19    The influent flows and loads to the Siu Ho Wan STW for the completed Northshore Lantau Development and Container Terminal scenario are shown in Table 5.9e and the resulting treated effluent flows and loads are shown in Table 5.9f.

 

Table 5.9c - Influent Flows and Loads to the Siu Ho Wan STW for the Completed Northshore Lantau Development Scenario

Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

Source

(m3 day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(cfu day-1)

Airport

27,434

8,230.00

8,230.00

17,803.00

1,267.00

713.00

51.00

5.50E+15

Tung Chung/Tai Ho

130,860

25,877.00

31,877.00

68,871.00

4,920.00

2,751.00

201.00

2.04E+16

Discovery Bay

9,250

1,000.00

1,050.00

2,250.00

212.50

125.00

14.78

1.08E+15

International Theme Park

12,140

3,035.00

5,463.00

7,284.00

388.48

315.64

77.33

4.58E+15

Theme Park Extension

6,070

1,517.50

2,731.50

3,642.00

194.24

157.82

38.66

2.29E+15

Eco Park

6

1.50

2.70

3.60

0.19

0.16

0.06

3.50E+12

Theme Park Gateway

657

285.94

196.13

446.33

79.32

34.20

3.11

1.93E+14

Tourist and Convention Village

3,405

851.29

1,532.32

2,043.09

108.96

88.53

8.72

5.16E+14

Technodrome

2,444

610.89

1,099.60

1,466.14

78.19

63.53

5.45

3.23E+14

Residential

4,526

689.26

663.48

2,188.05

216.66

104.03

9.23

6.71E+14

Education

6

3.57

3.57

7.35

0.70

0.42

0.06

3.68E+12

Fa Peng

3,251

812.00

1,582.93

1,948.80

103.94

84.45

9.34

3.10E+14

Tai Ho Wan Areas 2 & 5

11

2.86

2.86

5.88

0.56

0.34

0.06

2.94E+12

South Lantau

12,610

2,343.00

2460.00

5271.00

498.00

293.00

19.00

2.50E+15

Total

212,670

45,259.81

56,895.09

113,230.20

8,068.74

4,731.12

437.80

3.84E+16

 

Table 5.9d - Treated Effluent Quality from the Siu Ho Wan STW for the Completed Northshore Lantau Development Scenario

 Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

 

(m3 day-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(cfu 100mL-1)

Effluent Quality

212,670

63.84

120.39

532.42

37.94

22.25

2.06

20,000

 

Table 5.9e - Influent Flows and Loads to the Siu Ho Wan STW for the Completed Northshore Lantau Development and Container Terminal Scenario

Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

Source

(m3 day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(kg day-1)

(cfu day-1)

Airport

27,434

8,230.00

8,230.00

17,803.00

1,267.00

713.00

51.00

5.50E+15

Tung Chung/Tai Ho

130,860

25,877.00

31,877.00

68,871.00

4,920.00

2,751.00

201.00

2.04E+16

Discovery Bay

9,250

1,000.00

1,050.00

2,250.00

212.50

125.00

14.78

1.08E+15

International Theme Park

12,140

3,035.00

5,463.00

7,284.00

388.48

315.64

77.33

4.58E+15

Theme Park Extension

6,070

1,517.50

2,731.50

3,642.00

194.24

157.82

38.66

2.29E+15

Eco Park

6

1.50

2.70

3.60

0.19

0.16

0.06

3.50E+12

Theme Park Gateway

657

285.94

196.13

446.33

79.32

34.20

3.11

1.93E+14

Tourist and Convention Village

3,405

851.29

1,532.32

2,043.09

108.96

88.53

8.72

5.16E+14

Technodrome

2,444

610.89

1,099.60

1,466.14

78.19

63.53

5.45

3.23E+14

Residential

4,526

689.26

663.48

2,188.05

216.66

104.03

9.23

6.71E+14

Education

6

3.57

3.57

7.35

0.70

0.42

0.06

3.68E+12

Fa Peng

3,251

812.00

1,582.93

1,948.80

103.94

84.45

9.34

3.10E+14

Tai Ho Wan Areas 2 & 5

11

2.86

2.86

5.88

0.56

0.34

0.06

2.94E+12

South Lantau

12,610

2,343.00

2460.00

5271.00

498.00

293.00

19.00

2.50E+15

Container Terminal

1,038

588.00

588.00

1,211.00

116.00

69.00

10.23

6.06E+14

Total

213,708

45,847.81

57,483.09

114,441.20

8,184.74

4,800.12

448.03

3.90E+16

 

Table 5.9f - Treated Effluent Quality from the Siu Ho Wan STW for the Completed Northshore Lantau Development and Container terminal Scenario

 Parameter

Flow

SS

BOD

COD

TKN

NH3-N

TTM

E.coli

 

(m3 day-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(mg L-1)

(cfu 100mL-1)

Effluent Quality

213,708

64.36

121.04

535.50

38.30

22.46

2.10

20,000

5.9.20    In addition to the sewage effluents generated by the Northshore Lantau Development storm water discharges have also been included in the water quality modelling.  The stormwater discharges are divided into three main areas as follows.

·                      the International Theme Park at Penny’s Bay;

·                      the Northshore Lantau Development (Siu Ho Wan , Northshore, Fa Peng and Theme Park Extension); and

·                      Container Terminal development.

 

5.9.21    The Theme Park at Penny’s Bay has been divided into two main areas, the Theme Park and the commercial/developed areas behind the Theme Park.  Based on an annual average rainfall of 1,756 mm at Discovery Bay the annual average flows rates from the Theme Park and commercial/developed areas has been calculated to be 2,907,930 m3 and 2,778,700 m3 respectively ([27]).  Rainfall data for Discovery Bay from the period 1980 to 1997 was analysed to determine the proportions of rainfall for the wet and dry seasons.  For the purposes of the assessment the wet season was assumed to extend from April to September and the dry season from October to March.  The analysis determined that, on average, 83.6% of the rainfall occurs in the wet season and 16.4% in the dry season.

5.9.22    The run-off from these areas are proposed to be discharged to marine waters via three culverts, two for the Theme Park and one for the commercial/developed areas.  The locations of these outfalls are shown in Figure 5.9b, which show Outfalls 1 and 2 serving Phases 1 and 2 of the Theme Park respectively and Outfall 3 serving the commercial/developed areas.  The catchment area for Outfall 1 is 99 ha and the catchment area for Outfall 2 is 81 ha.  The average wet and dry season flows for the Theme Park were split according these areas.  The resulting average wet and dry season storm water flows are shown in Table 5.9g.

Table 5.9g - Average Wet and Dry Season Stormwater Flows

Area

Flow (m3 s-1)

 

Wet Season

Dry Season

Theme Park

 

 

Outfall 1

0.0848

0.0166

Outfall 2

0.0694

0.0136

Commercial/Developed Areas

 

 

Outfall 3

0.1473

0.0289

 

5.9.23    Data on the pollutants in the stormwater were obtained from the Theme Park operator and were based on measurements made at a similar facility in Florida.  The data can be considered to be representative for the proposed Theme Park at Penny’s Bay and was used as input data for the water quality modelling.  The pollutant concentrations are presented in Table 5.9h.

Table 5.9h - Pollutant Concentrations in the Stormwater from the Theme Park

Parameter

Concentration

Suspended Solids (mg L-1)

<50

Biochemical Oxygen Demand (mg L-1)

<50

Chemical Oxygen Demand (mg L-1)

<75

Total Phosphorous (mg L-1)

0.05 - 0.5

Total Nitrogen (mg L-1)

1 - 3

E. coli (cfu 100mL-1)

<100

Total Toxic Metals (mg L-1)

<0.1

 

5.9.24    In order to maintain a degree of conservatism the upper bound estimates for each of the parameters was assumed to provide input data to the water quality modelling.

5.9.25    The quality of the stormwater from the commercial/developed areas was obtained from the Stormwater Pollution Loading Working Paper, which was prepared as part of the ongoing feasibility study for the Northshore Lantau Development([28]).  The stormwater quality for these areas is suitable to provide input data to the water quality modelling as it represents the most up to date source of information.  The stormwater quality data are presented in Table 5.9i.

Table 5.9I - Pollutant Concentrations in the Stormwater from the Commercial/ Developed Areas

Parameter

Concentration

Suspended Solids (mg L-1)

43.3

Biochemical Oxygen Demand (mg L-1)

22.8

Chemical Oxygen Demand (mg L-1)

45.8

Total Phosphorous (mg L-1)

0.2

Total Kjeldahl Nitrogen (mg L-1)

1.4

Nitrate + Nitrite (mg L-1)

0.4

Copper (mg L-1)

14.8

Lead (mg L-1)

9.6

Zinc (mg L-1)

135

 

5.9.26    The stormwater flows from the other areas of the Northshore Lantau Development were calculated based on the rainfall data presented above and the catchment areas.  The catchments were divided into urban, rural and managed areas with run-off coefficients of 1.0, 0.6 and 0.7 respectively.  The resulting average wet and dry season flows for each of the catchment areas are presented in Table 5.9j.  The locations of the catchments and stormwater discharge points are shown in Figures 5.9c to 5.9j.

Table 5.9j - Average Wet and Dry Season Stormwater Flows from the Northshore Lantau Development

Catchment

Urban Area

(m2)

Average Wet

Season Flow

(m3 s-1)

Average Dry

Season Flow

(m3 s-1)

Rural Area

(m2)

Average Wet

Season Flow

(m3 s-1)

Average Dry

Season Flow

(m3 s-1)

Managed Area

(m2)

Average Wet

Season Flow

(m3 s-1)

Average Dry

Season Flow

(m3 s-1)

N1

460750

0.04290

0.00842

285000

0.01592

0.00312

0

0.00000

0.00000

N2

321750

0.02996

0.00588

1364500

0.07622

0.01495

0

0.00000

0.00000

N3

84500

0.00787

0.00154

23500

0.00131

0.00026

0

0.00000

0.00000

N4

218500

0.02034

0.00399

293250

0.01638

0.00321

0

0.00000

0.00000

N5

45500

0.00424

0.00083

78500

0.00439

0.00086

0

0.00000

0.00000

N6

116000

0.01080

0.00212

336000

0.01877

0.00368

45500

0.00297

0.00058

N7

56150

0.00523

0.00103

173750

0.00971

0.00190

5600

0.00036

0.00007

N8

143500

0.01336

0.00262

278150

0.01554

0.00305

23600

0.00154

0.00030

N9

85000

0.00791

0.00155

110550

0.00618

0.00121

10700

0.00070

0.00014

N10

161250

0.01501

0.00295

819600

0.04578

0.00898

57400

0.00374

0.00073

N11

150250

0.01399

0.00274

313800

0.01753

0.00344

28700

0.00187

0.00037

N12

309500

0.02881

0.00565

168350

0.00940

0.00184

30400

0.00198

0.00039

N13

111500

0.01038

0.00204

60250

0.00337

0.00066

4500

0.00029

0.00006

N14

287500

0.02677

0.00525

113200

0.00632

0.00124

20800

0.00136

0.00027

N15

237250

0.02209

0.00433

293900

0.01642

0.00322

14600

0.00095

0.00019

N16

119500

0.01113

0.00218

289500

0.01617

0.00317

20250

0.00132

0.00026

N17

34250

0.00319

0.00063

97700

0.00546

0.00107

2800

0.00018

0.00004

N18

19500

0.00182

0.00036

201750

0.01127

0.00221

22500

0.00147

0.00029

N19

102500

0.00954

0.00187

555250

0.03102

0.00608

0

0.00000

0.00000

N20

242500

0.02258

0.00443

563250

0.03146

0.00617

0

0.00000

0.00000

N21

257250

0.02395

0.00470

59250

0.00331

0.00065

0

0.00000

0.00000

N22

200000

0.01862

0.00365

300000

0.01676

0.00329

0

0.00000

0.00000

Theme Park Extension

70000

0.00600

0.00118

0

0.00000

0.00000

0

0.00000

0.00000

 

5.9.27    It should be noted that the stormwater from the urban and managed areas in Catchments N10 and N11 is diverted via a tunnel to the west of the Luk Keng headland, while the stormwater from the rural areas is discharged into the Yam O bay.

5.9.28    The Container Terminal development has an approximate land area of 1,820,000 m2 and using the same rainfall figures as above and a runoff coefficient of 1.0 gives average wet and dry season flows of 0.1694 m3 s-1 and 0.0332 m3 s-1 respectively.  It has been assumed that the stormwater from the Container Terminal will be discharged to the north east via a single culvert, the location of which is shown on Figure 5.9k.

5.9.29    The quality of the stormwater from the urban and managed areas of the Northshore Lantau Development was assumed to be the same as that for the commercial/developed areas of the International Theme Park, as presented in Table 5.9i.  The quality of the stormwater from the Theme Park Extension was taken to be the same as that for the International Theme Park, as shown in Table 5.9h.

5.9.30    The baseline scenario did not include any of the above described stormwater flows, which are specific to the developments on Northshore Lantau.  The completed Northshore Lantau Development scenario included the stormwater flows for the International Theme Park and those for the Northshore Lantau Development.  The completed Northshore Lantau Development plus Container Terminal included the stormwater flows for the International Theme Park, the Northshore Lantau Development and the Container Terminal.

5.9.31    In order to compare the results of the water quality modelling with the relevant Water Quality Objectives statistical analyses of water quality parameters were carried out for the identified sensitive receivers (see Figures 5.3a and 5.3b) and contours of water quality parameters for all three scenarios were produced.  Both the statistical analyses of the results at sensitive receivers and contours of the water quality parameters were produced for the following.

·                      Dissolved oxygen - depth averaged values which are exceeded for 90% of the simulation time;

·                      Dissolved oxygen - bottom values which are exceeded for 90% of the simulation time;

·                      5-day biochemical oxygen demand - depth averaged mean values;

·                      Total inorganic nitrogen - depth averaged mean values;

·                      Unionised ammonia - depth averaged mean values;

·                      Chlorophyll-a - depth averaged mean values;

·                      E. coli - depth averaged geometric mean values; and

·                      Suspended sediment - depth averaged maximum values.

 

5.9.32    In order to compare the results with the WSD criteria for abstracted sea water the water quality modelling results were analysed for the following parameters at the WSD sea water intakes.

·                      Dissolved oxygen - minimum surface layer concentrations;

·                      5-day biochemical oxygen demand - maximum surface layer concentrations;

·                      Ammoniacal nitrogen - maximum surface layer concentrations;

·                      E. coli - maximum surface layer concentrations; and

·                      Suspended solids - maximum surface layer concentrations.

 

5.9.33    The analysis of data for comparison with the WSD criteria was undertaken for the surface layer in the water quality model because this corresponded most closely with the vertical positioning of the intakes.

5.9.34    The above analyses were carried out for the wet and dry seasons separately.  The values were derived by assuming that the wet season could be represented by the period early June to mid September and the dry season by the period of late September to early April.

Chok Ko Wan Link Road

5.9.35    Road run-off will enter the stormwater drainage system before entering the marine waters of the Western Buffer and Southern WCZs.  The run-off may contain a number of pollutants that result from the normal wear and tear of road vehicles, including suspended solids, adsorbed pollutants such as heavy metals and PAHs.