EXECUTIVE SUMMARY

1.0 INTRODUCTION

1.1 Background of Project

The existing treatment facilities at Ngong Ping include grease traps and septic tanks, with discharge locally to soakaways. Following the opening of the Statue of Buddha in December 1993, the number of visitors to Ngong Ping increased significantly. The existing treatment and disposal facilities were found to be inadequate, with significant quantities of sewage being directly discharged into the local stream. It was under this setting that the recommendation to provide a local sewerage system and a centralised treatment system for Ngong Ping was put forward in the Outlying Island Sewerage Master Plan in 1994.

The cable car system linking Tung Chung and Ngong Ping is being planned for commissioning in August 2005. It will certainly further increase the number of visitors in Ngong Ping. This sewerage project will be completed to tie in with the commissioning of the Cable Car Project.

The general layout plan of the project is shown in Drawing No. 23400/R/G/001. The project is a designated project under Part I in Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO).

1.2 Description of Project

Details of the project are as follows:

Ngong Ping Sewage Treatment Works (STW)

The SBR is considered to be suitable for tertiary treatment of sewage including nutrient removal process.
Sludge treatment includes sludge thickening by gravity and sludge dewatering by plate filter press for optimising the space utilization, operating cost and effectiveness.

In odour control, wet scrubber system is used since the performance is reliable regardless the variation of gas composition. Drawing No. 23400/R/ST/013 shows the layout plan of Ngong Ping STW.

The following minimum standards of effluent discharged from Ngong Ping STW as specified in the Consultancy Brief by Drainage Services Department shall be met:

Table 1.1 Minimum Effluent Quality Standards

2.0 OPTION CONSIDERATIONS

2.1 Potential Treatment and Disposal Options

The Ngong Ping area lies in the water gathering ground subzone of the North Western Water Control Zone (WCZ). The section of the stream within the water gathering ground (Drawing No. 23400/EN/029) or country parks is stipulated as Group A inland waters in the Water Pollution Control Regulations. The section beyond the water gathering ground and country parks is classified as Group B inland waters. Five potential treatment and disposal options for the Ngong Ping sewerage system were considered:

1. Treatment at Ngong Ping and discharge locally to soakaways;
2. Treatment at Ngong Ping and disposal at Group A inland waters within the water gathering ground subzone or country park;
3. Export of untreated sewage to existing or planned treatment facilities outside the water gathering ground;
4. Treatment at Ngong Ping and discharge to marine waters of the North Western or Southern WCZ; and
5. Treatment at Ngong Ping and discharge at Group B inland waters and at the shoreline of bays or coastal waters of North Western or Southern WCZ.

Option (a) was not feasible as it would require 8,000 m2 of land and induce groundwater pollution.
Option (b) was rejected due to the uncertainty about the impacts of residual pollutants on human health.

For Option (c), two possible disposal routes were considered: (1) export of raw sewage to the planned Tung Chung New Town sewerage network for transfer to Siu Ho Wan STW and (2) transport raw sewage to the existing Tai O sewerage system for treatment at Tai O STW. These options were rejected because of concerns over potential leakage from the foul sewage pipeline in particular the route from Ngong Ping to Tai O would run through water gathering ground and Country Park which are highly environmental sensitive areas. The disposal route from Ngong Ping to Tung Chung is also not considered environmentally acceptable due to the reasons discussed in Section 2.2 below.

For discharge to marine waters of North Western or Southern WCZ, Option (d), a somewhat lower level of treatment could be considered. It was however not favoured due to the similar concerns as described in the above paragraph about the potential leakage of pipeline through the water gathering ground and country park and a higher level of treatment would have to be incorporated irrespective of the discharge location. Furthermore, discharge of effluent to marine waters of North Western or Southern WCZ would require the construction of extended outfall. Construction of extended outfall would cause significant water quality impact due to the required dredging and filling operations.

It was concluded that local treatment was necessary due to the potential environmental impacts arising from export of raw sewage through the water gathering ground and country parks, i.e. potential pollution to the Shek Pik Reservoir and adverse impacts on important habitats and breeding grounds of rare species. Option (e) for treatment at Ngong Ping followed by disposal of effluent to Group B inland waters and at the shoreline of bays or coastal waters of North Western or Southern WCZ was selected for further assessment.

2.2 Effluent Disposal Routes

Five routes (Drawing No. 23400/EN/031) were considered for the export of effluent out of the Ngong Ping area:

In principal, those routes along existing roads without the need to construct new access roads to the effluent pipeline are preferable as it would cause less disturbance to the environment as compared to those routes where no road exists currently.

Tung Chung route would pass through Ngong Ping SSSI (highly ecologically sensitive areas) and would require resumption of private lands. Although it is on existing footpath, the route is difficult for construction as the path is narrow which crosses outcrops of rock and several other obstacles such as stream and hills. This route would also require the construction of new access roads if selected.

The cable car route would require the construction of new road as there is currently no existing road or footpath in the lower part of the route. The route would have larger disturbance to the environment as compared to other routes where the effluent pipe will be laid on existing roads.

The route to Sham Wat was not preferred as the Sham Wat stream and valley, downstream of the water intake point, is one of the most ecologically diverse in Lantau and is more environmentally sensitive as compared to the Tung Wan Route. In addition, Sham Wat Road, the only land access to villages in Sham Wat Wan, is mostly a single-lane road. Although special traffic arrangements may meet the needs of local villagers, strong objections were received from Fire Services Department over any closure of Sham Wat Road and the route was thus rejected.

Both Tai O and Tung Wan routes are all the way on two-lane existing roads and was therefore considered more favourable as compared to the other three options. Tung Wan route, which runs along Keung San Road, was comparatively less preferable than the Tai O route in view of its close proximity to Shek Pik Reservoir (the whole section of Keung Shan Road is within the water gathering ground and is situated to the immediate west of Shek Pik Reservoir). Tai O option was therefore selected as the preferred option. Tung Wan route can be considered as the second choice subject to further assessment as and when necessary. Although there may be concern about the Tung Wan route on the effect of any leakage of the pipe on the water of the reservoir, the chance of such occurrence is extremely small because the pipe would be fully concrete surrounded. The effluent will be treated to high quality (tertiary treatment) such that the impact would be small in case of pipe leakage.

2.3 Discharge Options at Tai O

The selected option is to:

1. discharge adjacent to the existing stormwater pumping station near the bus terminus on the Western side of Tai O (Location 1 on Drawing No. 23400/EN/032).

The other options at Tai O were considered to be less favourable for the following reasons:

2. Discharge to the creek at the bridge next to the fire station at a location influenced by tidal effects (Location 2 on Drawing No. 23400/EN/032), via the existing storm drain outfall or a new separate outfall, would be inferior to the selected site as it would provide less dispersion;

3. Options for discharge to the tidal creek further upstream (e.g. Location 3 Drawing No. 23400/EN/032) were rejected for reasons similar to Option 2 above. It should be noted that the locations recommended in Options 2 and 3 were further upstream in comparison with the selected option and the water at these areas was much shallower which would provide less dispersion. Options for discharge to the stream were also rejected because of the seasonal nature of the flow in the stream;

4. Discharge to marine waters at the Western end of Tai O Island outside the old Tai O police station (Drawing No. 23400/EN/031) would require a crossing of Tai O creek, construction work through Shek Tsai Po village and a much longer length of effluent pipeline;

5. Discharge to marine waters to the west of Fan Kwai Tong (Drawing No. 23400/EN/031) would require construction work alongside the salt pans and through Nam Chung Tsuen and Fan Kwai Tong villages and a longer length of effluent pipeline. The discharge would be close to secondary contact recreation zones and close to the proposed breakwater of the sheltered boat anchorage. This option also suffered from a lack of good existing access to the discharge point;

6. Discharge close to the existing sewage outfall location at the north end of Tai O island though:

7. Discharge to the Tai O sewerage system would require mixing of treated Ngong Ping effluent with Tai O raw sewage. This would lead to inefficiencies in pumping and sewage treatment. It would also require either an effluent overflow for peak flow conditions or an upgrade of the trunk sewerage system through Tai O, which as noted above would be undesirable due to construction constraints in the congested village paths within Tai O Town.

3.0 INFLUENCE FROM OTHER MAJOR PROJECTS IN THE VICINITY

There are several major projects in the vicinity that would have influence on the proposed sewerage system and its surrounding receivers:

Cumulative impacts have been assessed in this EIA Study. The results of various assessments indicate that the cumulative environmental impacts identified were within acceptable environmental standards and residual impacts were not expected.

4.0 KEY FINDINGS IN THIS EIA

4.1 Air Quality

Major air quality concerns would be the cumulative dust impact due to the construction of the Ngong Ping STW and the Tung Chung Cable Car Terminal as well as the potential odour impact on the Cable Car Terminal during the operation of Ngong Ping STW.

For the construction of the proposed STW at Ngong Ping, quantitative dust impact assessment was carried out. Potential cumulative dust impacts would be related to the concurrent construction activities associated with the proposed Tung Chung Cable Car Terminal located immediately to the northeast of the proposed STW. With the implementation of proper dust control and suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and described in EIA Report, it was predicted that there would not be any adverse dust impact from the construction activities of the Project. Table 4.1 shows the predicted dust levels at the nearest Air Sensitive Receiver (ASR) which is the village house on Ngong Ping Road near the bus terminal (Drawing No. 23400/EN/010). It can be seen that the dust levels could be brought down to below the compliance limits with the proposed mitigation measures in place.

In order to mitigate the potential odour impacts from the proposed Ngong Ping STW to an acceptable level, all the major odour sources within the proposed STW namely the inlet work, the sequencing batch reactors, the sludge thickeners, and the emergency storage tank will all be constructed as underground facilities to minimise direct emission of odour to the atmosphere. Other components of the STW will be constructed as above ground structures. All odour emissions from the underground/above ground facilities will be contained by building structures and ventilated to a centralised deodourisation unit. Based on the findings of the odour dispersion modelling, the H2S removal efficiency of the deodourisation unit should be 99.5% or better and the H2S emission rate at the exhaust end of the deodourisation unit should not be more than 50 µg/s. The exhaust height and exit velocity of the treated air should not be less than 5m and 10m/s respectively. Table 4.2 shows the predicted odour levels at the nearest ASR which is the site boundary of the cable car terminal, namely A17 as shown on Drawing No. 23400/EN/035. It can be seen that with the proposed mitigation measures in place, the predicted odour levels at the ARS were low and complied with the limit of 5 odour unit. A backup deodorization unit will be provided to cater for the situation during maintenance or breakdown of the deodorization unit.

Table 4.2 Predicted Operational Phase Odour Impacts at the Nearest ASR

All the sludge generated from the STW will be dewatered onsite to more than 30% dry solids content before transporting to the designated landfill site for disposal and will be stored in covered container along the transporting route to avoid the possible odour impact on nearby sensitive receivers. The transportation of the sludge by sea to the disposal location is recommended, as far as practicable, in order to reduce potential air quality impacts from road transportation.

4.2 Noise Impact

Cumulative noise impact due to the construction of the Ngong Ping Cable Car Terminal has been considered with reference to the Tung Chung Cable Car Feasibility Study (TCCCFS). The TCCCFS identified compliance with noise criteria would be able to be achieved for impact from construction works of the proposed cable car system. Noise Sensitive Receivers (NSRs) are generally located far away from the proposed Ngong Ping STW. Three nearest NSRs are Lin Chi Monastery, Tin Tan Buddha Statue and village house on Ngong Ping Road near bus terminal which are more than 441m, 276m and 240m away respectively (see Drawing No. 23400/EN/010). The predicted construction noise levels at the village house on Ngong Ping Road near the bus terminal are shown in Table 4.3. The construction noise was within the limit of 75dB(A) for the unmitigated scenario. The noise levels could be further lowered by using quiet plant. No adverse impacts were therefore expected.

Mitigated Scenario Use of quiet plant

Construction phase noise impact could be controlled within acceptable levels for Ngong Ping main trunk sewer and effluent export pipeline under the proposed mitigation measures such as the use of quiet plant and the use of temporary and movable noise barriers. Table 4.4 presents the predicted construction noise levels at the village house on Tai O Road, which is the nearest NSR to the effluent pipeline (see Drawing No. 23400/EN/015). The construction noise was brought down to comply with the limit of 75dB(A) with mitigation measures in place.

Note:

Mitigated scenario Use of quiet plant and use of movable and temporary noise barriers

For Ngong Ping sewerage, some disturbance to the local residents may be expected due to construction of sewerage pipes inside the village. The noise impact would be transient and localized originated from breaking up of footpath surface.  It would take only 1 day to break up the concrete surface for individual NSRs.

Operation phase would require the proposed mitigation measure to be in place in order to bring the noise level to the acceptable limits. The proposed mitigation measure will be to enclose all the local pump chambers as underground facilities and all equipment at the STW in an indoor building envelope. No residual impacts were identified.

4.3 Water Quality Impact

In view of the sensitivity of the area, several special precautionary measures will be adopted:

Nevertheless, careful monitoring of the export pipeline would still be necessary to protect the highly sensitive environment at Ngong Ping. Routine flow monitoring will be carried out at both the upstream end (STW) and downstream of the water gathering ground to ensure early detection of any major leakage. A flow monitoring chamber will be provided east of Tai O for this purpose. An Action Plan has been prepared and should be followed in the event that pipe leakage is suspected or identified. Temporary diversion of effluent to the emergency storage tank at the STW could be arranged to provide no-flow condition for the repair of the effluent pipeline.

Water quality modelling has been performed to evaluate the impact on Tai O Creek and Tai O Bay waters due to the Ngong Ping exported effluent. The modelling exercises have taken into account the cumulative impacts from the existing background pollution discharges and the direct discharge of pollutants from the future boat anchorage development. The predicted water quality results for the exported effluent scenario complied very well with the WQO within the study area. Nevertheless, relatively higher E. coli levels were predicted at the mangrove stands along Tai O Creek. The higher E. coli concentrations at Tai O Creek were assessed to be contributed by the pollution input from existing unsewered developments. The contributions from the discharge of Ngong Ping exported effluent were considered minimal. No adverse effect was therefore expected upon the Tai O creek and Tai O bay waters.

Marine water quality monitoring was recommended to verify the findings of the water quality modelling.
It was anticipated that both construction and operational phases of the project would not cause water pollution problem after undertaking all required measures proposed in the EIA. It should be stressed that all necessary mitigation measures will be implemented to ensure that all the runoff and wastewater generated from the construction sites within the water gathering ground will comply with all the standards listed in the Technical Memorandum for Group A inland waters.

4.4 Waste Management

If appropriate mitigation measures are implemented during the handling, collection, and disposal of construction waste material, the residual environmental impacts would be reduced to acceptable levels. These mitigation measures can be enforced by incorporating them into a waste management plan as part of the contract document. Environmental monitoring and audit will be necessary to ensure the implementation of correct disposal requirements for the various wastes generated from construction works.

The sludge generated during the operation of Ngong Ping STW should be dewatered to more than 30% dry solids and transported to the landfills. The operators of future UV disinfection plant should work with the supplier/manufacturer on recycling and reuse of the defective UV lamps as far as possible. Should the disposal of UV lamps be unavoidable, the operators should identify the content of the UV lamp and confirm with EPD whether the UV lamps should be disposed of as chemical waste. If so, the handling and disposal should follow the Chemical Waste (General) Regulation. In handling the UV lamps, cautions should be exerted to avoid breakage of lamps and release of contaminants.

Unless the spent fluids from the wet scrubber system are treated on-site to meet the discharge standards stipulated in the Technical Memorandum under Water pollution Control Ordinance, they should be handled and disposed of according to the requirements under the Chemical Waste (General) Regulation. Committee

4.5 Landscape and Visual

Landscape

The proposed STW development would result in impacts on the existing landscape resources of the site, notably existing rock formations and topography, agricultural soils, woodland trees, shrubland and grassland. In terms of the surrounding landscape context the loss of these features would represent only a slight impact.
Extensive planting is proposed to the perimeter of the site, and with key elements of the STW located underground grass can be established on cover slabs to increase the overall greenery on site. In the long term, with the growth of the proposed vegetation, the impact on landscape resources should be negligible. Drawing No. 23400/EN/044 shows the operational landscape plan.

During construction the removal of existing vegetation, site formation and building works would have a slight impact on the quality of the landscape character of the Ngong Ping Plateau, which contains the landscape sensitive Tian Tan Buddha, and Po Lin Monastery. The proposed planting works within and along the perimeter of the site, and the layout and architectural treatment of the building structures should reduce the scale of the impact on character, although it is considered that there would be a slight residual impact in the long term.

Visual

There would be moderate level visual impacts during construction on residents of Ngong Ping Village area at higher elevations, visitors to the Columbarium, and motorists / travellers on Ngong Ping Road. These would be reduced to slight level in the long term with the application of the proposed mitigation measures.

There would be moderate level visual impacts during construction on visitors of Buddha Statue, but only to the northWestern side of the viewing platform surrounding the statue (not the approach steps). The proposed perimeter planting, grassing of the underground structures, and the architectural treatment of the buildings should reduce the impact on these views to slight levels in the long term.

There would only be very limited views from the Po Lin Monastery and the youth hostel due to intervening topography structures and vegetation. The proposed mitigation measures would further reduce the level of impacts to negligible in the long term.

There would be impacts of the long range views on hikers in the surrounding Country Park on the Nai Lak Shan ridgeline trail and associated footpaths. In the long term, with the growth of vegetation, the impacts of these hikers should be slight.

There would be no impact on users of future cable car system and the proposed public transport interchange during construction as it is assumed that it would be built at a later date. However, with the elevated nature and proximity of the system and interchange there are likely to be moderate visual impacts from the STW in the operational phase. The impacts of the cable car system would depend on the precise alignment and configuration of the cable car approach and terminal building.

4.6 Ecology and Fisheries

The impact to wildlife caused by the project was predicted to be minor. The sewage treatment works will be built on urbanised/disturbed area and the sewerage will follow the existing road. No habitat of ecological importance will be lost to the project. There would be no significant impact to terrestrial or aquatic ecosystems.

Potential impacts to aquatic ecology and fisheries during the construction phase would mainly arise from sedimentation due to surface runoff. Site runoff should be desilted, to reduce the potential for suspended sediments, organics and other contaminants to enter stream and marine environment. Special attention should be paid to the stream in which Romer's Tree Frog has been observed breeding. It was recommended that earthworks should not be carried out near the stream south of Ngong Ping village during the breeding season of Romer's Tree Frog (March to September).

Relatively high E. coli levels were predicted at the existing mangroves along the Tai O creek.  The predicted relatively higher E. coli concentrations at Tai O creek were contributed by the pollution input from existing unsewered developments. No adverse impact on the mangrove habitats was anticipated as the natural pollution tolerance (or pollution exclusion) displayed by mangroves was well documented.  Recent studies of mangals in Hong Kong and the Futien Nature Reserve in Shenzhen firmly concluded that the mangrove habitats were not adversely affected by high pollution loads, including concentrated sewage effluent.

4.7 Cultural Heritage

The field survey conducted during March, April and August 2002 revealed that there are some cultural remains in the vicinity of the Project.  These cultural remains, however, were located outside the works boundary of the Project. In addition, no powered mechanical equipment will be used in works areas which are within 5 m away from the identified sites of cultural heritage so as to minimize the vibration generated from the construction works. It is therefore anticipated that the proposed project would not adversely affect the identified sites of cultural heritage.

5.0 OVERALL CONCLUSION

This EIA has identified potential environmental impacts of various nature including air quality, noise, water quality, waste management, landscape and visual, ecology and fisheries, culture heritage. The results of various assessments indicate that the environmental impacts identified were generally within acceptable environmental standards and residual impacts were not expected.  In addition, the potential environmental impacts during both construction and operational stages were addressed with suitable design and mitigation measures. To further ensure the implementation of recommended mitigation measures, environmental monitoring and audit requirements were specified.