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.
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,
and
20m in width and 8m in height. The size of reprovisioned Pui O Raw Water Pumping Station is
32m in length and
and
16.5.375m
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.
2.2.1 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;
·
Construction
of the proposed Siu Ho Wan Raw Water Booster Pumping Station together with the
associated raw water mains, E&M plants 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.
2.3.1
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 and for the inactivation of
Cryptosporidium and Giardia (C&G)
•
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.
2.4.1 In accordance with the Project Profile for the Siu Ho Wan WTW Extension submitted in 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 works; · Require less stabilization works for the surrounding natural slope compared to alternative location; · Maintenance and manual operation can rely on Siu Ho Wan Water Treatment Works staff resources; · Further extension of the station is possible for the relatively larger site. |
· Location is close to the raw water main and connection piping works can be minimized; · More space is available for future expansion as the space adjacent to the proposed location is still unallocated. · The land is virgin ground. No underground utilities diversion would be necessary. |
|
Constraints |
· The required minimum water level at Tai Lam Chung Reservoir would be higher than that for Alternative location as the suction pipe for this option would be longer; · The Police vehicle pounding yard next to the site may be disturbed during the construction. |
· The site is close to the MTRC protection zone and continuous monitoring of the construction work would need to be carried out; · The site is close to the seafront and would have a high water table. Special measures would be required to prevent the infiltration of underground water; · Part of the proposed site is on natural slope and slope protection works would be required for the site formation works. |
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 formation works & may require less stabilization works for the surrounding natural slope. Less impact since the pumping station site is on low value disturbed land with grass or shrub. |
Part of the alternative site would be on natural slope and slope protection works would be required for the site formation works. Significant ecological impact as the entire affected slope is tall scrubland. |
|
Landscape and Visual Impact |
The Proposed Option is near the Siu Ho Wan WTW site formation mainly covered by grass and scrubs and the loss of which during construction would have slight landscape impact. The new pumping station in an existing developed area would have low visual impact. |
Vegetation on amenity strips and natural vegetation along the site boundary would be removed, ranging from grassland to scrubland. Low to moderate landscape impact is expected. Visual impact would be higher given that the structure would be constructed in a more natural setting. |
|
Air Quality |
No adverse impact would be expected due to limitation of size of the work during construction. Potential operational air quality would not be expected. |
No adverse impact would be expected due to limitation of size of the work during construction. Potential operational air quality would not be expected. |
|
Noise |
No construction and operation noise impact would be expected as no noise sensitive receiver is identified in the area. |
No construction and operation noise impact would be expected as no noise sensitive receiver is identified in the area. |
|
Water & Waste Impact |
No significant impacts to the surrounding during construction and operation phases. |
No significant impacts to the surrounding during construction and operation phases. |
|
Cultural & Heritage Impact |
No records of archaeological findings or potential built heritage in Siu Ho Wan study area. |
No records of archaeological findings or potential built heritage in Siu Ho Wan study 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, 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.
2.5.1 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 limited to along South Lantau Road of low ecological
concern. However, clearance of
vegetation would be required at either end of the water mains alignment with
direct impact to woodland of ecological value. The length
of the proposed alignment at the eastern end passing through woodland habitat
would be about |
It would
have substantially greater direct and indirect impacts to habitats including
habitats of particular ecological interest (abandoned agricultural land and
woodland) compared to the Proposed Alignment. It would
have direct impacts across approximately 400m of abandoned agricultural land,
about 200m of plantation and about 500m of woodland. In addition, part of the alignment
(eastern end) may disturb area zoned “Country Park”. |
|
Landscape and Visual Impact |
Generally low impact given the proposed underground construction along South Lantau Road, except at either ends in woodland areas where some natural vegetation may need to be removed. |
High impact
as excavation works would go straight through agricultural field, natural
vegetation and fresh water streams.
. |
|
Air Quality |
Potential construction dust impact would be expected at some air sensitive receivers in the vicinity of the site. |
Potential
construction dust impact would be slightly less than that of Proposed
Alignment as the work areas are located further away from air sensitive
receivers. |
|
Noise |
Potential construction noise impact would be expected at some noise sensitive receivers in the vicinity of the site. |
Potential
construction noise impact would be less than that of Proposed Alignment as
the work areas are located further away from noise sensitive receivers. |
|
Water & Waste Impact |
No significant impacts to the surrounding during construction and operation phases. |
No significant impacts to the surrounding during construction and operation phases. |
|
Cultural Heritage Impact |
Low impact
as the Proposed Alignment would not impinge on an area of archaeological
potential. |
High impact
as an area of potential archaeological interest, i.e. a sandbar, would be
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.
2.6.1 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 Process |
Existing
Process in Siu Ho Wan WTW |
Recommended
Process in Extended Siu Ho Wan WTW |
|
Manganese Removal |
Using chlorine for manganese removal |
Using potassium permanganate (KMnO4) for manganese removal |
|
|
Using chlorine as the disinfectant |
Using ozone as the disinfectant |
Benefits and Potential
Disadvantages of Alternative Proposed Water Treatment Process
Manganese Removal
2.6.2
The benefits and potential
disadvantages of the alternative process proposed water treatment
process for manganese removal are shown in Table 2.5.
Table 2.5 Benefits and Potential
Disadvantages of the AlternativeProposed Water Treatment
Process for Manganese Removal
|
Benefits |
Potential
Disadvantages |
|
· Low capital and operation cost · Very effective in manganese oxidation without creating any DBP and has been used extensively overseas · No need to construct additional contact tanks and the existing PAC contact tanks can be used |
· When the dosage of KMnO4 is not correct, pink or brown coloured water will result (pink colour from KMnO4 for over-dosage, and brown colour from manganese for under-dosage) |
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.
Disinfection for C&GpPrimary Disinfection
2.6.4
The benefits and potential
disadvantages of the alternative process for C&G disinfection proposed water treatment
process for primary disinfection are shown in Table 2.6.
Table 2.6 Benefits and Potential
Disadvantages of the Alternative Process for C&G DisinfectionProposed Water Treatment Process
for Primary Disinfection
|
Benefits |
Potential Disadvantages |
|
§ Ozone is able to achieve disinfection with less contact time and concentration than chlorine § Ozone does not form halogenated Disinfection By-products (DBPs) including THMs and HAA5s ·
Allows free chlorine to be applied at a later stage in the treatment
process after precursors have been removed and at lower doses, thereby
reducing formation potential of DBPs ·
If ozonation is followed by GAC filters, 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 |
·
The operating cost is higher than using chlorine as disinfectant · Ozone would form a variety of organic and inorganic byproducts. If bromide ion is present in the raw water, halogenated DBPs (brominated by-products) may be formed ·
Shock cleaning by chlorinated water is necessary occasionally. Backwash frequency may also need to
be increased at times |
Implications of the AlternativeProposed 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 Hazard |
·
Poison gas, NIOSH considers 25ppm as the IDLH |
·
Poison gas, NIOSH considers 5ppm as the IDLH |
·
Excessive inhalation of KMnO4 is harmful 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 Explosion Hazards |
·
Not flammable ·
Oxidizer: may explode or accelerate combustion if contacting reducing
agents |
·
Not flammable ·
Strong oxidizer: incompatible with all oxidizable materials; will
accelerate combustion when involved in a fire situation |
·
Not flammable ·
Strong oxidizer: contact with incompatible material may cause fire or
explosion |
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 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 of C&G
2.6.7
In the recommended C&Gprimary disinfection
process for the extended Siu Ho Wan WTW, ozone would be used as the C&Gprimary disinfectant
rather than chlorine in the existing process. Although ozone is more poisonous than chlorine, it is
considered that the recommended C&G 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 C&Gprimary disinfection
respectively. Therefore, chlorine consumptiondose in the
extended Siu Ho Wan WTW (and also storage and delivery) would not increase decrease 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 recommended proposed water treatment
process) would not be higher than that of the existing Siu Ho Wan WTW, due to no incraseincrease in the expected decreased
chlorine consumptiondose.
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.
2.1.1
There are no other major
projects undertaken within the study area of this Project concurrently.
2.8.1