Agreement No. CE 75/2002 (WS) EIA Report Extension of Siu Ho Wan Water Treatment Works - Investigation 2. PROJECT DESCRIPTION 2.1 Project Location Siu Ho Wan 2.1.1 The proposed Siu Ho Wan WTW extension is within the existing WTW site boundary (location refers to Figure 2.1). The site area is approximately 5.8 hectares, located at the foot of the Tai Che Tung hill in an area designated for “Other Specified Uses” annotated (Water Treatment Works) on the Siu Ho Wan Layout Plan No. L/I-SHW/1, with a Sewage Treatment Plant to the west, North Lantau Service Road to the north and North Lantau Highway about 100 m away. The layout plan of the Siu Ho Wan WTW is shown in Figure 2.2. 2.1.2 A Siu Ho Wan Raw Water Booster Pumping Station is proposed. The proposed site and alternative site locations refer to Figure 2.1. Pui O 2.1.3 The existing Pui O Raw Water Pumping Station and Pui O No. 2 Raw Water Pumping Station are located next to the South Lantau Road, about 0.5 and 0.7 hectares in size, respectively. The demolition and reprovision of Pui O Raw Water Pumping Station and uprating of Pui O No. 2 Raw Water Pumping Station would take place within its existing boundary. The size of the existing Pui O Raw Water Pumping Station is 30.5m in length, 20m in width and 8m in height. The size of reprovisioned Pui O Raw Water Pumping Station is 32m in length and 16.5m in width. The reconstructed Pui O Raw Water Pumping Station would be of similar height. The uprating of Pui O No. 2 Raw Water Pumping Station would involve internal modification works only. 2.1.4 There are two alignment options for the duplication of two sections of the existing raw water mains (about 2 km in length) at Pui O. A Proposed Alignment is along the existing South Lantau Road while an Alternative Alignment cuts through cultivated land, as shown in Figure 2.3. 2.2 Project Requirement and Scope 2.2.1 The existing Siu Ho Wan WTW is a conventional water treatment plant which adopts coagulation, flocculation, sedimentation and filtration, followed by the addition of chlorine for disinfection. It provides treated water to the Hong Kong International Airport at Chek Lap Kok and the initial phases of North Lantau New Town. In order to cope with the anticipated increase in water demand generated from the existing and proposed developments in North Lantau New Town, Discovery Bay, Northshore Lantau, Ngong Ping and the International Theme Park at Penny’s Bay, it is necessary to complete the extension work to Siu Ho Wan WTW by the end of 2011. 2.2.2 The Project comprises the extension of Siu Ho Wan WTW from a capacity of 150,000 m3/day to 300,000 m3/day together with the associated works as follows: • Uprating of treated/fresh water pumping capacity in the existing Siu Ho Wan Raw Water and Fresh Water Pumping Station within the existing Siu Ho Wan WTW compound from a capacity of 150,000 m3/day to 300,000 m3/day; Metcalf & Eddy Ltd. 2-1 October 2004 Agreement No. CE 75/2002 (WS) EIA Report Extension of Siu Ho Wan Water Treatment Works - Investigation • Construction of the proposed Siu Ho Wan Raw Water Booster Pumping Station together with the associated raw water mains, E&M plant and access road to increase the raw water transfer capacity from Tai Lam Chung Reservoir to Siu Ho Wan Water Treatment Works; • Demolition and reprovisioning of the Pui O Raw Water Pumping Station; • Uprating of the Pui O No. 2 Raw Water Pumping Station; • Laying of two sections, approximately 2 km long, of 1200 mm diameter raw water mains at Pui O; and • All other associated civil, building, structural, pipeworks, mechanical and electrical works, plant and equipment including pumping plant, power supply plant, and water treatment plant and equipment, site formation, geotechnical, landscaping, environmental assessment, surge protection facilities, control and monitoring works, Supervisory Control and Data Acquisition System, Distributed Control System, energy management system, permanent and temporary land issues necessary for completion and commissioning of the works element as listed in the above. 2.3 Water Treatment Process for Siu Ho Wan WTW Extension 2.3.1 The existing water treatment process in Siu Ho Wan WTW consists of the Powdered Activated Carbon (PAC) addition for pre-treatment (although it is not currently in use), conventional sedimentation with triple decks, filtration and disinfection using chlorine. The proposed water treatment process for the WTW Extension would be similar to that of the process adopted in the existing WTW, except with the following modifications: • Potassium permanganate, instead of PAC (which is not in use currently due to the acceptable raw water quality), will be added in the pre-treatment contact tanks for manganese removal; • Conventional sedimentation with triple decks is replaced by sedimentation using lamella settlers to increase the surface loading rate and hence the capacity of individual sedimentation tanks, and to increase the ease of maintenance; • Intermediate ozonation, instead of chlorine, will be used for primary disinfection; • GAC or GAC/sand filter media will be used, instead of existing anthracite/sand, for filtration to remove the ozone related byproduct, produce a biologically stable filter effluent, as well as to remove ammonia; and • Washwater will be treated before being discharged to the Inlet for C & G removal. 2.3.2 Figure 2.4 shows the process flow diagram for the proposed water treatment process. 2.4 Alternative Sites for Siu Ho Wan Raw Water Booster Pumping Station 2.4.1 In accordance with the Project Profile for the Siu Ho Wan WTW Extension submitted in Metcalf & Eddy Ltd. 2-2 October 2004 Agreement No. CE 75/2002 (WS) EIA Report Extension of Siu Ho Wan Water Treatment Works - Investigation January 2000, two options of the proposed locations for the Siu Ho Wan Raw Water Booster Water Pumping Station were considered. One proposed site option was located adjacent to the Siu Ho Wan WTW and the other alternative option sited between the raw water main landfall at Tai Pang Po and Siu Ho Wan WTW. Both locations are illustrated in Figure 2.1. 2.4.2 Table 2.1 presents the engineering considerations of the two site options and Table 2.2 evaluates the environmental implications. Table 2.1 Engineering Considerations of Siu Ho Wan Raw Water Booster Pumping Station Alternative Site Options Site Option Proposed Site Option Alternative Site Option Advantages • Require least site formation • Location is close to the raw works; water main and connection • Require less stabilization piping works can be works for the surrounding minimized; natural slope compared to • More space is available for alternative location; future expansion as the space • Maintenance and manual adjacent to the proposed operation can rely on Siu Ho location is still unallocated. Wan Water Treatment Works • The land is virgin ground. No staff resources; underground utilities • Further extension of the diversion would be necessary. station is possible for the relatively larger site. Constraints • The required minimum water • The site is close to the MTRC level at Tai Lam Chung protection zone and Reservoir would be higher continuous monitoring of the than that for Alternative construction work would need location as the suction pipe to be carried out; for this option would be • The site is close to the seafront longer; and would have a high water • The Police vehicle pounding table. Special measures yard next to the site may be would be required to prevent disturbed during the the infiltration of underground construction. water; • Part of the proposed site is on natural slope and slope protection works would be required for the site formation works. Metcalf & Eddy Ltd. 2-3 October 2004 Agreement No. CE 75/2002 (WS) EIA Report Extension of Siu Ho Wan Water Treatment Works - Investigation Table 2.2 Environmental Considerations of Siu Ho Wan Raw Water Booster Pumping Station Alternative Site Options Parameter Proposed Site Option Alternative Site Option Ecology It would require the least site Part of the alternative site would formation works & may require be on natural slope and slope less stabilization works for the protection works would be surrounding natural slope. Less required for the site formation impact since the pumping station works. Significant ecological site is on low value disturbed impact as the entire affected land with grass or shrub. slope is tall scrubland. Landscape and Visual The Proposed Option is near the Vegetation on amenity strips and Impact Siu Ho Wan WTW site natural vegetation along the site formation mainly covered by boundary would be removed, grass and scrubs and the loss of ranging from grassland to which during construction would scrubland. Low to moderate have slight landscape impact. landscape impact is expected. The new pumping station in an Visual impact would be higher existing developed area would given that the structure would be have low visual impact. constructed in a more natural setting. Air Quality No adverse impact would be No adverse impact would be expected due to limitation of size expected due to limitation of size of the work during construction. of the work during construction. Potential operational air quality Potential operational air quality would not be expected. would not be expected. Noise No construction and operation No construction and operation noise impact would be expected noise impact would be expected as no noise sensitive receiver is as no noise sensitive receiver is identified in the area. identified in the area.