2 AIR QUALITY IMPACT

12.1.1 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.

12.1.2 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 Section 3.6, it is predicted that there would not be any adverse dust impact from the construction activities of the Project.

12.1.3 In order to mitigate the potential odour impacts from the proposed Ngong Ping STW to an acceptable level, it is recommended that all the major odour sources within the proposed STW namely the inlet work, the activated sludge treatment system, the sludge thickener, the aerobic digester building, the sludge dewatering and storage building, and the emergency storage tank should all be either contained by building structures or constructed as underground tanks to minimise direct emission of odour to the atmosphere. Besides, all odour emissions from the above odour sources should be 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. A backup deodorization unit should be provided to cater for the situation during maintenance or breakdown of the deodorization unit.

12.1.4 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.

12.2 Noise

12.2.1 The noise levels from the construction of the proposed Ngong Ping STW predicted at NSRs were within construction noise limits for the unmitigated scenario. The noise levels could be further lowered by using quiet plant. Cumulative noise impact due to the construction of the Ngong Ping Cable Car Terminal has been considered with reference to the Final Feasibility Study Report in March 1999 under the MTR Corporation's Consultancy Agreement NEX/034 Tung Chung Cable Car Feasibility Study (TCCCFS). The TCCCFS identified compliance with noise criteria would be able to be achieved for construction phase impact from the proposed cable car system. NSRs are generally located far away from the proposed Ngong Ping STW. Three nearest NSRs are Lin Chi Monastery, Tin Tan Buddha and village house on Ngong Ping Road near bus terminal which are more than 441m, 276m and 240m away respectively. No adverse impacts would be expected on these distant areas.

12.2.2 Construction phase noise impact could be controlled within acceptable levels for Package 2 Ngong Ping main trunk sewer and effluent export pipeline under the proposed mitigation measures. For Package 3 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.

12.2.3 Operation phase would require the proposed mitigation measures to be in place in order to bring the noise level to the acceptable limits. In the current engineering design, all the potential noise sources at the STW are enclosed in buildings and all the local pump chambers will be constructed as underground facilities. No further residual impacts were identified.

12.3 Water Quality

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

	Ductile iron pipe will be used for all the Ngong Ping village sewers and effluent pipeline for its robustness, because the area is within the water gathering ground. Sealed pipe joints with hatchboxes along the pipeline will also be adopted;
	The maximum distance between manholes would be limited to 60 m to facilitate over-pumping operations during sewer inspection or maintenance. This would also facilitate flow diversion in case of emergency situation during pipe leakage;
	Standby units, emergency power generation and emergency storage facilities will be provided at Ngong Ping STW to avoid the need for emergency discharges. It is proposed to construct an emergency storage tank to temporary store both the raw sewage from Ngong Ping sewerage catchment and the effluent of STW to cater for the STW breakdown and bursting of effluent pipe. Furthermore, it is also proposed that the size of the emergency storage tank will be large enough to store 72hr. Sewage/effluent flow (i.e. 48 hours peak day and 24 hours average day i.e. 2 x 2956 + 1524 = 7436m3) in ultimate stage. Thus, the volume of the emergency storage tank is about 7600m3 and the size is about 50m(L) x 40m(W) x 3.8m (D).
	The effluent will be treated to standards listed in Table 1.2 such that the impact to local water quality in the unlikely event of pipe leakage would be small. As a result of the high quality effluent and steep gradient, there would minimal chance of effluent pipeline blockage.
	Installation of 150mm diameter borehole with 100mm diameter slotted iron sleeve for water pollution monitoring, around the STW site at suitable location.
	The drainage of any high contamination risk areas such as the DG store will be physically separated from the drainage system of the STW site.

12.3.2 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 and country park 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 should be 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.

12.3.3 Water quality modelling has been performed to evaluate the impact on Tai O creek and Tai O waters due to the Ngong Ping exported effluent. The predicted water quality results for the exported effluent scenario complied very well with the WQO within the study area. 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 is anticipated as the natural pollution tolerance (or pollution exclusion) displayed by mangroves is well documented. Recent studies of mangals in Hong Kong and the Futien Nature Reserve in Shenzhen firmly concluded that the mangrove habitats are not adversely affected by high pollution loads, including concentrated sewage effluent (Tam et al, 1995; Tam & Wong, 1995; Wong et al, 1995; Wong, 1996(a) and 1996(b)). The increases in pollutant concentrations caused by the discharge of Ngong Ping exported effluent are considered minimal. No adverse effect would be expected upon the Tai O creek and Tai O bay waters. Marine water quality monitoring is recommended to verify the findings of the water quality modelling.

12.3.4 It is anticipated that both the construction and operational phase of the project would not cause water pollution problem after undertaking all required measures proposed in the EIA.

12.4 Waste

12.4.1 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.

12.4.2 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 TM under WPCO, they should be handled and disposed of according to the requirements under the Chemical Waste (General) Regulation.

12.5 Landscape and Visual

Landscape

12.5.1 The proposed STW development would result impacts on the existing landscape resources of the STW site, notably existing rock formations and topography, agricultural soils, woodland trees, shrubland and grassland. These would need to be cleared to make way for the STW development. In terms of the surrounding landscape context the loss of these features would represent only a slight impact.

12.5.2 Extensive planting is proposed to the perimeter of the site, and the sinking of key elements of the SWT underground grass can be established on covering 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.

12.5.3 The proposed works would have an impact on the quality of the landscape character of the Ngong Ping Plateau, which contains the landscape sensitive Tian Tan Buddha, Columbarium, and Po Lin Monastery. During construction the removal of existing vegetation, site formation and building works would have a slight impact on the landscape character. 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

12.5.4 The Works would have an impact on several visually sensitive receiver (VSR) groups.

12.5.5 There would be moderate level visual impacts during construction on residents of Ngong Ping Village area reside high up on the slope and in the lower areas, 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.

12.5.6 There would be 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.

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

12.5.8 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 not be built later. However with the elevated nature and proximity of the system and interchange there are likely to be moderate visual impacts from the SWT in the operational phase. This impacts of the cable car system would depend on the precise alignment and configuration of the cable car approach and terminal building.

12.5.9 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.

12.5.10 Summary of the significance of the landscape and visual impacts during construction and operation stage is tabulated in Table 7.8 and Table 7.9 for landscape and visual impacts respectively.

Mitigation Measures

12.5.11 The landscape and visual impacts of the STW development have been minimised through careful design. Measures to be adopted in order to mitigate the extent of the impacts are: -

	Retention and protection of existing woodland trees
	Decorative hoarding during construction along publicly accessible boundaries of the site
	Topsoil stripped and stored for re-use in the construction of the soft landscape works
	Control of night-time lighting
	Grass hydroseeding of slopes and underground structures within the STW site as soon as they are completed
	Native shrub and tree screen planting along the perimeter of the site
	Sensitive architectural and chromatic treatment of the elevated structures

12.6 Ecology and Fisheries

12.6.1 The impact to wildlife caused by the project was predicted to be minor. The construction of the sewage treatment works and sewerage would cause a temporary loss of 0.13 ha of plantation, 0.17 ha of grass-shrubland, 0.94 ha of urbanised/disturbed habitats and a permanent loss of 0.01 ha of plantation, 0.11 ha of grass-shrubland, and 2.01 urbanised/disturbed habitat. The sewage treatment works will be built on urbanised/disturbed area and the sewerage will follow the existing road. No habitat of ecological importance would be lost to the project. There would be no significant impact to terrestrial or aquatic ecosystems.

12.6.2 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 is recommended that earthworks near this stream should not be carried out during the breeding season of Romer's Tree Frog (March to September).

12.7 Cultural Heritage

12.7.1 Field survey was conducted during March and April 2002. The survey team walked over the entire Project area, applied 50 auger drills and excavated three test pits. In the areas close to the alignment, the team identified 19 buildings, 36 stone ruins and five graves that were dated to pre-war and retrieved a large number of cultural relics. These cultural remains, however, would not be directly affected by the proposed Project.

12.7.2 The survey team however has identified a series of historic ruins at Wang Hang Tsuen, Heng Mei and Kwun Yam Shan and over 20 historic buildings at Ngong Ping. Some of these ruins and buildings are located close to the proposed alignment (see Figures 5, 8 and 9 of Appendix 10B). The entire construction workforce should be informed of the locations of these historic ruins and buildings and special attention should be given during the entire process of project construction to avoid any damage to these historical remains. Construction sites which are close to these historical structures should be posted with notices at conspicuous locations to remind the workers not to make any disturbance to the structures. It is recommended to avoid the use of powered mechanical equipment in any works area which is less then 5 m away from the boundary of the identified sites of cultural heritage. With the above mitigation measures in place, it is not anticipated that there would be any adverse effect on the identified sites of cultural heritage.