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 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 International Airport at and the initial phases of . In order to cope with the anticipated increase in water demand generated from the existing and proposed developments in North Lantau New Town, , 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;

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• 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

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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.

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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.

Water & Waste Impact No significant impacts to the No significant impacts to the surrounding during construction surrounding during construction and operation phases. and operation phases.

Cultural & Heritage No records of archaeological No records of archaeological Impact findings or potential built findings or potential built heritage in Siu Ho Wan study heritage in Siu Ho Wan study area. area.

2.4.3 Based on the above evaluation, the Proposed Site Option is the preferred option, with less site formation work and slope stabilization works, no restrictions on future extension of the Siu Ho Wan Raw Water Booster Pumping Station, more convenient in operation and maintenance,

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and lower ecological and landscape impacts. Therefore, the Proposed Option for Siu Ho Wan Raw Water Booster Pumping Station was recommended and detailed environmental impact assessment has been focused on this Option in the later chapters.

2.5 Alternative Alignments for Duplication Pipeline at Pui O 2.5.1 With reference to the Final Study Report of the PPFS, two options of raw water mains alignments at Pui O, Proposed Alignment and Alternative Alignment as shown in Figure 2.3, were recommended. The comparison of key environmental impacts of the two raw water mains alignments is presented in Table 2.3.

Table 2.3 Environmental Considerations of Alternative Raw Water Main Alignments at Pui O

Parameter Proposed Alignment Alternative Alignment Ecology Direct impacts would be largely It would have substantially limited to along South Lantau greater direct and indirect Road of low ecological concern. impacts to habitats including However, clearance of habitats of particular ecological vegetation would be required at interest (abandoned agricultural either end of the water mains land and woodland) compared to alignment with direct impact to the Proposed Alignment. woodland of ecological value. It would have direct impacts The length of the proposed across approximately 400m of alignment at the eastern end abandoned agricultural land, passing through woodland about 200m of plantation and habitat would be about 100m about 500m of woodland. In while the western end would addition, part of the alignment pass through about 300m of (eastern end) may disturb area woodland. zoned “Country Park”.

Landscape and Visual Generally low impact given the High impact as excavation Impact proposed underground works would go straight through construction along South Lantau agricultural field, natural Road, except at either ends in vegetation and fresh water woodland areas where some streams. . natural vegetation may need to be removed.

Air Quality Potential construction dust Potential construction dust impact would be expected at impact would be slightly less some air sensitive receivers in than that of Proposed Alignment the vicinity of the site. as the work areas are located further away from air sensitive receivers.

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Parameter Proposed Alignment Alternative Alignment Noise Potential construction noise Potential construction noise impact would be expected at impact would be less than that of some noise sensitive receivers in Proposed Alignment as the work the vicinity of the site. areas are located further away from noise sensitive receivers.

Water & Waste Impact No significant impacts to the No significant impacts to the surrounding during construction surrounding during construction and operation phases. and operation phases.

Cultural Heritage Low impact as the Proposed High impact as an area of Impact Alignment would not impinge potential archaeological interest, on an area of archaeological i.e. a sandbar, would be potential. impacted during construction phase.

2.5.2 It is clear from the above discussion that Proposed Alignment would have much lower ecological, landscape and visual, and cultural heritage impacts. In view of engineering feasibility, no private land resumption or public land rezoning would be required for the Proposed Alignment. Significant number of power cables including those 11 kV cables Associated with the Pui O pumping stations were laid along the sides of South Lantau Road. Diversions of these cables would not be necessary, if the proposed duplicate watermains could be laid along one lane of South Lantau Road. As the traffic in South Lantau Road is not heavy, the work is unlikely to cause significant disturbance to the traffic flow. However, a traffic management scheme would be required to minimize disruption and there may be restriction to the hours of open trenching. Therefore, the Proposed Alignment was considered engineering feasible and an environmentally better option and has been adopted as the preferred alignment for the duplication pipelines, based on which detailed environmental impact assessment has been conducted and presented in the following sections.

2.6 Proposed Water Treatment Process 2.6.1 As mentioned in Section 2.3, there would be two major chemicals-involved changes in the recommended water treatment process in the extended Siu Ho Wan WTW. The changes of water treatment process are shown in Table 2.4.

Table 2.4 Changes of Water Treatment Process for Extended Siu Ho Wan WTW

Water Treatment Existing Process in Siu Ho Recommended Process in Process Wan WTW Extended Siu Ho Wan WTW Manganese Removal Using chlorine for Using potassium permanganate manganese removal (KMnO4) for manganese removal Primary Disinfection Using chlorine as the Using ozone as the disinfectant disinfectant

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Benefits and Potential Disadvantages of Proposed Water Treatment Process

Manganese Removal

2.6.2 The benefits and potential disadvantages of the proposed water treatment process for manganese removal are shown in Table 2.5.

Table 2.5 Benefits and Potential Disadvantages of the Proposed Water Treatment Process for Manganese Removal

Benefits Potential Disadvantages • Low capital and operation cost • When the dosage of KMnO4 is not • Very effective in manganese correct, pink or brown coloured water will oxidation without creating any DBP result (pink colour from KMnO4 for and has been used extensively over-dosage, and brown colour from overseas manganese for under-dosage) • No need to construct additional contact tanks and the existing PAC contact tanks can be used

2.6.3 However, it should be noted that as far as Siu Ho Wan WTW is concerned, the potential disadvantage would not be significant because the main source of raw water is from Tai Lam Chung Reservoir, with the buffer effect of Tai Lam Chung Reservoir, the manganese concentration fluctuating impact on the raw water to be treated at Siu Ho Wan WTW would be minimal.

Primary Disinfection

2.6.4 The benefits and potential disadvantages of the proposed water treatment process for primary disinfection are shown in Table 2.6.

Table 2.6 Benefits and Potential Disadvantages of the Proposed Water Treatment Process for Primary Disinfection

Benefits Potential Disadvantages ♣ Ozone is able to achieve disinfection with • The operating cost is higher than using less contact time and concentration than chlorine as disinfectant chlorine • Ozone would form a variety of organic ♣ Ozone does not form halogenated and inorganic byproducts. If bromide ion Disinfection By-products (DBPs) is present in the raw water, halogenated including THMs and HAA5s DBPs (brominated by-products) may be • Allows free chlorine to be applied at a formed later stage in the treatment process after • Shock cleaning by chlorinated water is precursors have been removed and at necessary occasionally. Backwash lower doses, thereby reducing formation frequency may also need to be increased potential of DBPs at times • If ozonation is followed by GAC filters, the increased biodegradable organics Metcalf & Eddwyou Ltdld. increase biological growth in th2-e7 October 2004 filters. Biologically activated GAC (BAC) will facilitate ammonia removal so that the chlorine consumption for ammonia removal will be decreased Agreement No. CE 75/2002 (WS) EIA Report Extension of Siu Ho Wan Water Treatment Works - Investigation

Benefits Potential Disadvantages the increased biodegradable organics would increase biological growth in the filters. Biologically activated GAC (BAC) will facilitate ammonia removal so that the chlorine consumption for ammonia removal will be decreased

Implications of the Proposed Water Treatment Process to Environmental Impacts & Hazard to Life

2.6.5 Negligible environmental impacts such as air quality, noise, water quality, wastes and ecology would be expected during the operation of the proposed water treatment process. The hazardous properties of the three chemicals concerned (i.e. chlorine, ozone and potassium permanganate) are listed in Table 2.7.

Table 2.7 Hazardous Properties of Chlorine, Ozone and Potassium Permanganate

Chlorine Ozone Potassium Permanganate (KMnO4) Health • Poison gas, NIOSH • Poison gas, NIOSH • Excessive inhalation Hazard considers 25ppm as the considers 5ppm as the of KMnO4 is harmful IDLH IDLH to health • Ingestion of KMnO4 can cause burns to mouth and throat and severe gastro-intestinal distress. • Lethal effect is unlikely except at high concentration Fire and • Not flammable • Not flammable • Not flammable Explosion • Oxidizer: may explode • Strong oxidizer: • Strong oxidizer: Hazards or accelerate incompatible with all contact with combustion if oxidizable materials; incompatible material contacting reducing will accelerate may cause fire or agents combustion when explosion involved in a fire situation Note: NIOSH: National Institute for Occupational Safety and Health IDLH: Immediately Dangerous to Life and Health Concentration

Manganese Removal

2.6.6 In the recommended manganese removal process for the extended Siu Ho Wan WTW, KMnO4 would be used as the manganese removal agent rather than chlorine in the existing process. It is considered that the recommended manganese removal process would be

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potentially less hazardous than the existing one, with the following reasons:

• KMnO4 is much less hazardous to health than chlorine. Lethality would be unlikely when personnel intake KMnO4 by inhalation or ingestion;

• Given that appropriate storage and handling of KMnO4 (i.e. no contact with incompatible materials), the strong oxidizing property of KMnO4 would not cause significant impact.

Primary Disinfection

2.6.7 In the recommended primary disinfection process for the extended Siu Ho Wan WTW, ozone would be used as the primary disinfectant rather than chlorine in the existing process. Although ozone is more poisonous than chlorine, it is considered that the recommended primary disinfection process would be potentially less hazardous than the existing one, with the following reasons:

• As ozone (in form of ozone-rich gas) would be generated on-site and used immediately for disinfection, no ozone would be stored on site. Unlike the chlorine (in 1-tonne drum) stored in the Chlorine Building of the WTW, instantaneous release of large amount of toxic gas (ozone), which could cause fatality over a large distance, is not expected • Long duration continuous release of stored chlorine, which could cause fatality in a large area, is possible. However, such release of ozone would not be expected as ozone generation operation could be shut down when ozone leak is detected • Ozone has a very short half-life of less than 30 minutes under normal conditions; concentration of leaked ozone would decrease with distance. In contrast, chlorine is relatively stable and is able to disperse over a long distance and cause fatality if the concentration is sufficiently high

2.6.8 In the recommended water treatment process for the extended Siu Ho Wan WTW, chlorine would be replaced by KMnO4 and ozone for manganese removal and primary disinfection respectively. Therefore, chlorine dose in the extended Siu Ho Wan WTW (and also storage and delivery) would not increase when compared to the existing scenario. As discussed above, the recommended KMnO4 and ozone-involved water treatment process would be potentially less hazardous than the existing water treatment process using chlorine. As a result, it is considered that the potential risk to the public posed by the extended Siu Ho Wan WTW (with the proposed water treatment process) would not be higher than that of the existing Siu Ho Wan WTW, due to no increase in chlorine dose.

2.7 Project Programme 2.7.1 The construction works are tentatively scheduled to commence in December 2007 for completion in December 2011. Figure 2.5 shows the preliminary construction programme of the Project.

2.8 Interaction with Other Projects 2.8.1 There are no other major projects undertaken within the study area of this Project concurrently.

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