2 Consideration of Alternatives

2.1 Introduction

In accordance with the requirements of Section 3.3 of the EIA Study Brief, this Section describes the need for the Extension and the consideration of design options. The consideration of alternatives also includes alternative construction methods and work sequences.

2.2 Justification for the Need of the Extension

Hong Kong is facing an imminent waste problem as the existing landfills will be filled up in the next decade. In December 2005, the Government published the waste policy document “A Policy Framework for the Management of Municipal Solid Waste (2005-2014)” (hereafter referred to as “the Policy Framework”). This document sets out a comprehensive strategy for the management of municipal solid waste (MSW) in Hong Kong with clear targets and a timetable for ten years, from 2005 to 2014. The strategy embraces the concepts of sustainable waste management and the 3-tiered waste hierarchy with avoidance and minimization as the top priorities, followed by reuse, recovery and recycling, and the bulk waste reduction and landfill disposal.

The Government is therefore actively promoting initiatives to reduce waste generation and promote waste recycling. When comparing the waste statistics for 2006 with those of previous years, the amount of MSW disposed of at the three strategic landfills (WENT, NENT and SENT) dropped by 1% against an economic growth of 6.8% in 2006. Equally encouraging is the increase in the recovery rate of domestic waste from 16% in 2005 to 20% in 2006. At the same time, the overall recovery of MSW has also increased from 43% in 2005 (2.59 million tonnes) to 45% in 2006 (2.84 million tonnes), three years ahead of the target stated in the Policy Framework. There are however areas of concern. Even though the amount of MSW landfilled was reduced by 1% in 2006, there is still a long way to go in achieving the Policy Framework’s target of reducing the total MSW landfilled to less than 25%. In addition, despite EPD’s efforts in waste reduction and recovery, the amount of MSW generated remains on an increasing trend. This is likely to be the result of growth in commercial, industrial and tourism-related activities in 2006 which has led to an increase of about 4% in commercial and industrial waste generation. Therefore, despite the progress achieved for source separation and waste recycling, it is important to press ahead with the other initiatives in the Policy Framework such as Producer Responsibility Schemes (PRSs), MSW charging, integrated waste management facilities (IWMF) and landfill extensions.

At the same time, the Government is also looking into building modern large scale integrated waste management facilities that would employ thermal treatment as a core technology as it is clearly not sustainable to continue to rely on landfilling alone for the disposal of untreated MSW. The integrated waste management facilities are planned to be commissioned in the mid 2010s, assuming that good progress is made. As mentioned in the Policy Framework, landfills will still be required as the final repositories for non-recyclable waste, inert waste and waste residues after treatment. It has been estimated that the demand for landfill space from 2006 to 2025 is around 200 million tonnes, while the remaining landfill capacity, at the end of 2004 was 90 million tonnes. The provision of sufficient landfill space by extending the capacity of the three existing landfills is an important and integral part of the waste management strategy in Hong Kong and is necessary to meet the shortfall of landfill capacity. Indeed, the Policy Framework recommended that commissioning of these extensions will be required in the early 2010s to mid-2010s.

In addition to the need for landfill capacity on a territory-wide basis, there is a need to meet the regional demand for waste disposal outlets. The three landfills are at strategic locations in Hong Kong and the extension of all three is necessary to maintain the overall waste disposal plan which is based on bulk waste transfer to avoid excessive number of waste collection vehicles travelling in the urban areas ([1]). Due to its close proximity to the urban areas, the SENT Landfill is the most highly used waste disposal facility amongst the three landfills, particularly by private waste collectors for commercial, industrial as well as construction wastes. It receives about 6,200 tonnes of municipal, construction and special wastes every day. If the SENT Landfill is closed, waste will have to be diverted to the NENT and WENT Landfills. This will require vehicles collecting waste from the catchments of the SENT Landfill to travel an additional hundred thousand kilometres per day in total through the built-up areas to the remotely located NENT and WENT Landfills, thus resulting in additional environmental impacts such as increased traffic movements, vehicular emissions and noise impacts on many more sensitive receivers en-route. To reduce these impacts, we would need a succession plan by developing new waste transfer and/or handling facilities in the south-east region of the territory, such as new handling facility for construction waste (ie the Construction Waste Handling Facility (CWHF)) and refuse transfer station for MSW (ie the South East Kowloon Transfer Station (SEKTS)). As the planning (including the site search), feasibility study, statutory environmental impact assessment process, tendering and contract arrangement, detailed design, construction and commissioning of these facilities would take equally long time as the landfill extension scheme, it further strengthens the importance of maximising the capacity of Extension where feasible in order to minimize those impacts as far as we could manage.

Projecting the time at which these new facilities will be available is very uncertain as the site for the CWHF will unlikely be available in the early 2010s and the site selection for the SEKTS has not yet been started. It will be a long planning and public consultation process to secure suitable waterfront sites at the Tseung Kwan O and South East Kowloon areas which are acceptable to the public for the development of these waste transfer/handlling facilities, but without compromising the overall planning and development of these two areas. In addition, the funding for developing these facilities has not been secured. Under an optimistic set of conditions to form a target programme at the present stage, they could possibly be in place by 2017. With SENT expected to be full by 2012, at least six years of additional void space is necessary. It is important to extend the lifespan of the SENT Landfill so that the Government can have time to plan and develop these new waste handling facilities.

2.2.1 Extension of the SENT Landfill

In 2000, the potential to extend the SENT Landfill was examined in a study entitled the “Extension of Existing Landfills and Identification of Potential New Waste Disposal Sites”. The recommendations of this study was presented to the Advisory Council on Environment (ACE) and supported by the ACE members. The possibility of locating extensions to the west, north and east of the existing SENT Landfill was investigated, but sites in these locations were ruled out for the following reasons:

· Extension to the west: this area is already occupied by the Tseung Kwan O Industrial Estate (TKOIE);

· Extension to the north: extensive excavation into the headland that separates the existing landfill from the TKO Stage II/III Landfill would be required and could significantly interfere with the completed and restored TKO Stage II/III Landfill and works yet to be carried out at the SENT Landfill; and

· Extension to the east: this will result in a major encroachment into the CWBCP, destroy the ridge line and sever the High Junk Peak Hiking Trail.

The only feasible option is to extend the landfill southward into TKO Area 137.

EPD identified 15 hectares of land in TKO Area 137 together with an adjoining narrow strip of land within the CWBCP as a potential site for the extension of the SENT Landfill (see Figure 2.2a).

2.3 Consideration of Different Extension Options

2.3.1 Extension Options

The Assignment has identified and examined five options for the extension of the SENT Landfill. They include:

· Option 1a – a standalone landfill with no incursion into the CWBCP. This option would have completely separate infrastructure, to ensure minimal contractual interfaces with the existing SENT Landfill (see Figure 2.3a).

· Option 1b – a standalone landfill with no incursion into the CWBCP. The area available for landfilling would be maximised and the cost reduced by sharing certain items of infrastructure (eg leachate and landfill gas treatment facilities) with the existing SENT Landfill. A smaller area would therefore be required for the Extension infrastructure (see Figure 2.3b).

· Option 2 – the landfill area “piggybacks” over the existing SENT Landfill and its present infrastructure area, but does not require any land within the CWBCP. A new infrastructure area would be provided to the south of the proposed Extension, which would be utilised by both landfills (see Figure 2.3c).

· Option 3a – the landfill area piggybacks over the existing SENT Landfill and its infrastructure area, and makes a small incursion (3 ha) into the CWBCP in order provide more void capacity. A new infrastructure area would be provided to the south of the proposed Extension, which would be utilised by both landfills (see Figure 2.3d).

· Option 3b – the landfill area piggybacks over the existing SENT Landfill and its infrastructure area, and makes a slightly larger incursion (5 ha) into the CWBCP in order to maximise available void capacity. A new infrastructure area would be provided to the south of the proposed Extension, which would be utilised by both landfills (see Figure 2.3e).

Table 2.3a summarises the key information for each option.

Table 2.3a Key Information of Extension Options

Options	Characteristics	Net Void Space (million m^3)	Encroachment into CWBCP (hectares)	Estimated Construction Cost (HK$ per tonne of waste)	Additional Lifespan (years)
Option 1a	· Stand-alone landfill · No sharing of Infrastructure	1.3	0	350	<1
Option 1b	· Stand-alone landfill · Sharing of infrastructure with existing landfill	1.6	0	200	<1
Option 2	· Piggy-back landfill · Sharing of infrastructure with existing landfill	10.0	0	80	4
Option 3a	· Piggy-back landfill · Sharing of infrastructure with existing landfill	15.0	3	60	5
Option 3b	· Piggy-back landfill · Sharing of infrastructure with existing landfill	17.0	5	50	6
Note: (a) Construction cost of existing strategic landfill is about HK$60 per tonne.

2.3.2 Options Evaluation

In assessing whether an alternative is practical and reasonable, the circumstances have been taken into account and a balanced judgement reached. Hence, five criteria relevant to the evaluation of the Extension were used to evaluate the five identified options:

· Landfill capacity;

· Efficient use of land;

· Cost effectiveness;

· Encroachment into Country Park; and

· Environmental impacts.

In addition, engineering measures and additional landtake in TKO Area 137 have also been considered.

Landfill Capacity

The stand-alone options provide very low void capacity, 1.3 Mm³ for Option 1a and 1.6 Mm³ for Option 1b. This is equivalent to an extended lifetime for the SENT Landfill of less than one year. The piggyback options provide significantly higher void capacity, 10 Mm³ for Option 2, 15 Mm³ for Option 3a and 17 Mm³ for Option 3b. Option 3b provides the highest void capacity of all the options evaluated (see Table 2.3a) and provides sufficient time for the new generation of waste management facilities (see Section 2.2) to come into operation.

Efficient Use of Land

All options make use of the 15 hectares of land in TKO Area 137 that adjoins the southern end of the existing SENT Landfill. Option 3a requires an additional 3 hectares of land from the CWBCP area, whereas Option 3b requires an additional 5 hectares. As Option 3b will deliver the greatest void capacity per unit site area, it presents the most efficient use of land.

Cost Effectiveness

The estimated capital costs for the stand-alone options at HK$350 per tonne for Option 1a and HK$200 for Option 1b are 6 and 3 times more expensive than the capital cost for the existing landfills (approximately HK$60 per tonne). The capital cost for Option 2 at HK$80 per tonne is 25% higher than that for the existing landfills, whereas Option 3a has the same capital cost per tonne (i.e. around HK$60 per tonne). Option 3b at HK$50 per tonne has the lowest capital cost and thus is the most cost effective option (see Table 2.3a).

Encroachment into Country Park

The Country Parks serve three functions, namely conservation, recreation and education. There is a general presumption against development in Country Parks.

Options 1a, 1b and 2 will not encroach into the CWBCP and hence no direct impact on the CWBCP is envisaged. Option 3a and Option 3b will encroach into approximately 3 ha and 5 ha, respectively, of the CWBCP and will have a direct impact. The potential ecological and landscape impacts are discussed in the next sub-section.

It is noted that the potential encroachment area is a cliff face dominated by shrubland and grassland. At present, there are no hiking trails nor formal footpaths in the area. The area can only be accessed from the existing SENT Landfill or the fill bank in TKO Area 137. The area has not been used for recreational and educational purposes. Hence, it is considered that encroachment into the CWBCP will not adversely affect the conservation, education and recreation uses. On the other hand, the Extension encroached area can be developed for useful education and recreational uses following closure and restoration of the Extension, thus providing a chance to improve the public enjoyment of the area.

Key Environmental Impacts

Local Air Quality Impact: The nearest existing sensitive receiver for air quality is TVB City in the TKOIE. Options 1a and 1b, being standalone landfills in TKO Area 137, are located further away from the TKOIE (> 300m) when compared with Options 2, 3a and 3b, where the piggyback portion is approximately 100m from the TKOIE. The life span of the Extension will also determine the extent of the environmental impacts. Hence, a longer impact period will be associated with Option 3b while Option 1a will pose only a short impact duration. Any air quality impact would decrease significantly following completion of landfill operation.

Local Ecological Impact: Options 1a and 1b will utilise the developed land in TKO Area 137, currently occupied by the fill bank operation. No natural habitat will be directly affected. Option 2 will occupy the developed land in TKO Area 137 plus piggybacking onto the slope of the existing SENT Landfill which will affect some plantations on the restored area of the existing SENT Landfill. The ecological value of the plantations is low and no natural habitat will be directly affected. Options 3a and 3b will encroach into the CWBCP. A 9-months ecological baseline survey identified that the habitats within the encroachment area comprise shrubland and grassland, neither of which is of high ecological value. While some species of conservation interest were recorded within the directly impact area, all of these species were found to be of high mobility and were found to have access to an abundant number of similar habitats close by and within the CWBCP area. Upon completion of the landfill operation, the landfill will be completely restored and landscaped. By planting a mixture of indigenous species, the ecological value of the restored landfill could be enhanced. .

Local Landscape and Visual Impact: The landforms of Options 1a and 1b are small and will be screened or partially screened by the restored SENT Landfill and future development in the TKO Area 137 when viewed from most of the visual sensitive receivers. However, it would be difficult to integrate these landforms into the surrounding landscape. The landforms and footprint of Options 2, 3a and 3b are larger and will be visible by the sensitive receivers. Options 3a and 3b will have direct impact on the landscape within the CWBCP. The landscape and visual impact during the operation phase of the Extension will be temporary and can be reverted by appropriate landscaping during progressive restoration. Once restored, the landform of Option 3b should provide the most harmonic visual and landscape quality to the visual sensitive receivers. It is not anticipated that any of the identified extension options will cause adverse landscape and visual impacts in the long term.

General Environmental Impact at Territorial Level: As there are no waste disposal facilities for MSW, construction waste and special waste in the south-east region of the SAR, the closure of the SENT Landfill would mean that waste currently disposed of at the SENT Landfill will have to be transported to other disposal sites, e.g. the NENT Landfill and the WENT Landfill, located further away. This will lead to the waste collection vehicles travelling an extra of several tens of thousands of kilometres per day resulting in additional environmental impacts such as increased traffic movements, vehicular emissions and noise impacts on many more sensitive receivers en-route. Providing additional landfill void space to serve the SENT catchment area fro as long as practicable would defer such impacts. In view of this consideration, Option 3b will be more preferable since it has the longest lifespan. In the longer term, EPD will develop a new waste transfer/ handling facility in the south-east region of the SAR.

The environmental benefits and dis-benefits of the five options are summarised in Table 2.3b.

Table 2.3b Summary of Environmental Benefits and Dis-benefits of the Extension Options

Criteria	Environmental Benefits	Environmental Dis-benefits	Can Environmental Dis-benefit be avoided/ mitigated?	Conclusion
Option 1a	· Small impact at local scale because the development scale is the smallest and the tipping area is located more than 300m from the existing development · No need to encroach into CWBCP · Less visible from most of the existing sensitive receivers	· Very short lifespan meaning earlier diversion of waste collection vehicles to more remote landfills, generating additional environmental impact at territorial scale · Standalone feature which makes it difficult to integrate with the surrounding landforms	· Additional environmental impact at territorial scale cannot be avoided because there are no other similar waste facilities in the south-east region of the SAR · The landscape impact can be minimised by careful restoration landscaping but the shape of the landfill cannot be integrated with the surrounding landform	· Least environmental impact at local scale because of its small scale of development · Relatively larger environmental impact at territorial scale because diversion of waste collection vehicles will be required for a longer period after the relatively short duration of landfilling operation at the Extension · No unacceptable environmental impact anticipated
Option 1b	· Small impact at local scale because the development scale is the second smallest and the tipping area is located more than 300m from the existing development · No need to encroach into CWBCP · Less visible from most of the existing sensitive receivers	· Very short lifespan meaning earlier diversion of waste collection vehicles to more remote landfills, generating additional environmental impact at territorial scale · Standalone feature which makes it difficult to integrate with the surrounding landforms	· Additional environmental impact at territorial scale cannot be avoided because there are no other similar waste facilities in the south-east region of the SAR · The landscape impact can be minimised by careful restoration landscaping but the shape of the landfill cannot be integrated with the surrounding landform	· Minor environmental impact at local scale because of its small scale of development · Relatively larger environmental impact at territorial scale because diversion of waste collection vehicles will be required for a longer period after the relatively short duration of landfilling operation at the Extension · No unacceptable environmental impact anticipated
Option 2	· No need to encroach into CWBCP	· Development scale is larger than Options 1a and 1b with the tipping area is located at around 100m from the existing development · Some diversion of waste collection vehicles to more remote landfills will be required (for less duration than Options 1a and 1b), generating additional environmental impact at territorial scale · Visible from most of the existing sensitive receivers and difficult to integrate with the surrounding landforms	· Environmental impacts at local scale can be mitigated by careful design, good site operation management and restoration arrangement · Additional environmental impact at territorial scale cannot be avoided because there are no other similar waste facilities in the south-east region of the SAR · The landscape impact can be minimised by careful restoration landscaping but the shape of the landfill will create a narrow valley between the landfill and the surrounding landform	· Relatively greater environmental impacts at local scale but lower impacts at territorial scale when compared with Options 1a and 1b · Impacts at local scale can be mitigated · Some environmental impact at territorial scale because diversion of waste collection vehicles will be required after the medium duration of landfilling operation at the Extension · No unacceptable environmental impact anticipated
Option 3a	· Some diversion of waste collection vehicles to more remote landfills may be required (for shorter duration than Options 1a, 1b and 2), generating relatively minor additional environmental impact at territorial scale · Visible by most sensitive receivers but able to integrate with the surrounding landform with appropriate landscape treatment	· Need to encroach approximately 3 ha into CWBCP comprising habitats of low to moderate ecological value · Development scale is the second largest with the tipping area is located at around 100m from the existing development	· Environmental impacts at local scale can be mitigated by careful design, good site management and progressive restoration arrangement · Impact on the natural habitats of low to moderate ecological value within the CWBCP can be compensated by woodland planting as part of the restoration thus enhancing the ecological value in the area · The encroached area within the CWBCP can also be developed for useful afteruse for education and recreational purposes following closure of the Extension and can provide direct linkage to the CWBCP, which is currently not accessible from the TKO area	· Relatively greater environmental impact at local scale but can be mitigated · Will encroach into CWBCP with low to moderate ecological value but can be mitigated by compensatory woodland plantation · Provide chance to develop useful afteruse of the encroached area of CWBCP for education and recreational purposes · No unacceptable environmental impact anticipated
Option 3b	· Least chance for diversion of waste collection vehicles to more remote landfills to be required · Visible by most visual sensitive receivers but able to integrate with the surrounding landform with appropriate landscape treatment	· Need to encroach approximately 5 ha into CWBCP comprising habitats of low to moderate ecological value · Development scale is the largest of all options with the tipping area is located at around 100m from the existing development	· Environmental impacts at local scale can be mitigated by careful design, good site management and progressive restoration arrangement · Impact on the natural habitats of low to moderate ecological value within the CWBCP can be compensated by woodland planting as part of the restoration thus enhancing the ecological value in the area · The encroached area within the CWBCP can also be developed for useful afteruse for education and recreational purposes following closure of the Extension and can provide direct linkage to the CWBCP, which is currently not accessible from the TKO area	· Relatively greater environmental impact at local scale of all options considered but can be mitigated · Will encroach into CWBCP with low to moderate ecological value but can be mitigated by compensatory woodland plantation · Provide chance to develop useful afteruse of the encroached area of CWBCP for education and recreational purposes · No unacceptable environmental impact anticipated

Amongst the five options, Options 1a and 1b will have the least environmental impacts at local level due to their small scale of development. However, their shorter lifespan will imply that diversion of waste collection vehicles to the other landfills will be required for a longer period, thus generating more environmental impacts at a territorial level. Options 2 and 3a will have greater environmental impacts at both a local scale when compared with Options 1a and 1b but have lower environmental impacts at territorial level since their scale of development and lifespan provided are in the medium term. It is understood that with careful design and good site management and progressive restoration, the local environmental impacts can be mitigated. Option 3b being the largest extension option will generate greater environmental impacts at the local scale and will impact upon the natural habitats within the CWBCP. However, it is noted that the impacts on the CWBCP can be mitigated by compensatory planting and the educational and recreational value of the encroached area, which is currently not used for educational or recreational purpose, can be enhanced with appropriate afteruse development.

Engineering Measures Considered

Engineering measures have been considered to maximize the void space of the Extension while not encroaching into CWBCP. One of the measures considered include building a retaining wall around the waste mound at TKO Area 137, ie creating a “bunker” type landfill. However, to make this measure effective, the retaining wall will need to be very tall (more than 40m) and the construction cost will be very high. The standalone feature will also be difficult to integrate with the surrounding landscape and visually difficult to accept. Notwithstanding these particulars, the void space provided would still be far less than Option 3b. To soften the landscape impact, the retaining wall could be replaced by earth bunds. However, to make the earth bund strong enough to support the weight of the waste, the structure of the earth bund will be massive, which in turn will consume a significant portion of the landfill void space. Hence, the use of engineering measures to maximize the capacity of the Extension in order to avoid encroaching the CWBCP was not put forward for further consideration.

Additional Land take in TKO Area 137

An option to increase landtake within TKO Area 137 has been investigated. To develop an extension with a capacity equivalent to that in Option 3b without encroachment into the CWBCP will require more than double the size of the identified site in TKO Area 137 to be used, i.e. an increase from 15 to approximately 34 hectares. However, allocation of approximately 19 hectares of land in this area is not considered feasible.

2.3.3 Consideration of Alternative Construction Methods and Sequences of Works

Construction Methods

The construction methods that could be used for the different Extension options are summarised in Table 2.3c.

In general, the construction methods to be used for all Extension options at TKO Area 137 and the existing SENT Landfill Infrastructure Area will be the same. The Extension Site will be formed by filling, instead of excavation in the SENT Landfill Infrastructure Area and the TKO Area 137. This method will ensure smaller amount of excavated material to be generated and avoid the base of the landfill intercepting the groundwater level, which is relatively shallow in TKO Area 137. The other construction activities which involve construction and demolition of infrastructure and construction of base liner and leachate and landfill gas collection systems. Typical construction practices in Hong Kong will be adopted. With the implementation of standard pollution control measures, no adverse environmental impacts are anticipated. Hence, alternative construction methods for works in the TKO Area 137 and the existing SENT Landfill Infrastructure Area were not identified.

Table 2.3c Construction Methods for Each Extension Options

Location	Option 1a	Option 1b	Option 2	Option 3a	Option 3b
At TKO Area 137	· Site formation by filling rather than excavation · Construct new infrastructure area by typical method, including the assembly of pre-fabricated plant equipment	· Site formation by filling rather than excavation	· Site formation by filling rather than excavation · Construct new infrastructure area by typical method, including the assembly of pre-fabricated plant equipment	· Site formation by filling rather than excavation · Construct new infrastructure area by typical method, including the assembly of pre-fabricated plant equipment	· Site formation by filling rather than excavation · Construct new infrastructure area by typical method, including the assembly of pre-fabricated plant equipment
At Existing SENT Landfill Infrastructure Area	· No construction work required	· Minor construction work with typical method to connect the Extension to the existing treatment facilities	· Demolish the existing structure using typical method to dissemble the tanks, plant and equipment	· Demolish the existing structure using typical method to dissemble the tanks, plant and equipment	· Demolish the existing structure using typical method to dissemble the tanks, plant and equipment
At CWBCP	· No construction work required	· No construction work required	· No construction work required	· Slope formation	· Slope formation · Tunnel excavation
Alternative construction method identified	Alternatives not identified as the typical construction method is the simplest, most commonly used and will not create adverse environmental impact with standard pollution control measures	Alternatives not identified as the typical construction method is the simplest, most commonly used and will not create adverse environmental impact with standard pollution control measures	Alternatives not identified as the typical construction method is the simplest, most commonly used and will not create adverse environmental impact with standard pollution control measures	Alternatives not identified for works in TKO Area 137 and the existing SENT Landfill Infrastructure area as the typical construction method is the simplest, most commonly used and will not create adverse environmental impact with standard pollution control measures Alternatives are identified for the slope formation work: · Blasting using explosives · Excavation using hydraulic rock breakers · Use of non-explosive demolition agent	Alternatives not identified for works in TKO Area 137 and the existing SENT Landfill Infrastructure area as the typical construction method is the simplest, most commonly used and will not create adverse environmental impact with standard pollution control measures Alternatives are identified for the slope formation work: · Blasting using explosives · Excavation using hydraulic rock breakers · Use of non-explosive demolition agent Alternatives are identified for the tunnel construction work: · Tunnel boring · Drill and blast

For Options 3a and 3b, which will encroach into the CWBCP, excavation of the natural slopes during site formation will however be unavoidable. The construction methods identified for the slope formation work, their respective environmental benefits and dis-benefits, as well as other considerations are summarised in Table 2.3d.

As described in Table 2.3d, the use of non-explosive agents will create the least environment impacts. However, it is very expensive and time consuming to use this method to form the large slope area, thereby significantly lengthening the overall construction period and delaying the opening of the Extension. As this method cannot meet the programme, it is not preferred. It should also be noted that by utilising the blasting method any impacts are confined to a far shorter duration. No adverse environmental impacts are anticipated for the blasting method. The blasting method, which avoids prolonged adverse environmental impacts to the maximum practicable extent, is the preferred option. In fact, this method had been used for slope formation work during the construction of the existing landfills and are commonly used in other construction projects in Hong Kong.

For Option 3b, in order to drain surface water from the low point at the south-eastern corner of the Extension, two small drainage tunnels (2m diameter) will be required. The construction methods identified for the tunnel construction, their respective environmental benefits and dis-benefits, as well as other considerations are summarised in Table 2.3e.

As described in Table 2.3e, the alternative methods will generate different environmental impacts: tunnel boring will have continuous but lower impacts while blasting will have relatively higher environmental impacts but at instantaneous duration. Since the majority of the environmental impacts will be confined within the tunnel, the overall environmental impacts associated with both options are comparable. However, the merit of tunnel boring is its higher productivity and a better controlled excavation profile. Residual issues requiring careful management related to safety concerns over the use of explosives in confined space in close proximity to potential sources of landfill gas. Tunnel boring is the preferred option.

Table 2.3d Construction Methods for Slope Formation Work

Construction Method	Environmental Benefits	Environmental Dis-benefits	Can Environmental Dis-benefit be avoided/ minimised/mitigated?	Other Considerations	Evaluation
Blasting Using Explosives Shotholes are drilled in the rockface, which are then filled with explosive. The blast will ensure the rock to be adequately fragmented to allow it to be removed by excavation plant.	· Impact restricted to instantaneous noise, dust and vibration (i.e. short impact duration)	· Relatively high noise, dust and vibration during the blast	The environmental dis-benefits can be minimised by appropriate design of the blasting operations and adopting the following well proven control measures: · The quantity of explosive used and the dimensions and spacings of shotholes can carefully designed to minimise air overpressure, flyrock generation and ground-borne vibration · Remove loose material and stones in the site before blasting · Wet the blasting area prior to blasting to minimise dust · Use of fine blast nets, screens and other protective covers to prevent the projection of flying fragments and material resulting from blasting	· Relatively quick and more cost effective · Can fit the tight construction programme to meet the target opening day of the Extension · Well proven method used in the construction of all three existing landfills and common large scale slope formation work	· The magnitude of environmental impacts is the highest but the duration is very short · Impact can be minimised by careful design of blasting method · Shortest construction period and can meet the target opening day of the Extension · Proven and cost effective method used in the construction of previous landfills in Hong Kong
Excavation Using Hydraulic Rock Breakers Using conventional hydraulic rock breaker to break the rock into fragment to allow it to be removed by excavation plant.	· Less noisy, dusty and lower vibration than blasting method	· Need longer construction time with continual use of noisy hydraulic breakers	· Noise can be minimised by reducing the number of hydraulic rock breakers to be used at any one time. As works will be carried out on steep slope, it is not possible to use removable noise barrier to minimise the noise impact.	· Require more time than the blasting method and less cost effective · Construction period will be much longer causing potential delay to the opening of the Extension	· Magnitude of environmental impacts is less than the blasting method but the impact duration is much longer · Impact can be minimised by controlling the number of plant working on-site at any one time mitigation measures · Longer construction period than the blasting method and will cause delay to the opening of the Extension
Use of Non-explosive Demolition Agent Introduce a mixture of inorganic powder with water into pre-drilled holes in the rock mass as a slurry. On hardening, the slurry expands and causes the rock mass to shatter. The fragmented rock will then be removed by excavation plant	· Quiet and will not generate dust and vibration	· None	· None	· Very expensive and time consuming, usually only used where explosive demolition is impractical (e.g. too close to developments) and in small-scale work · Construction period will be much longer causing delay to the opening of the Extension	· Least environmental impacts · Very expensive and time consuming which will results in the longest construction period and cause delay to the opening of the Extension

Table 2.3e Construction Methods for Drainage Tunnel

Construction Method	Environmental Benefits	Environmental Dis-benefits	Can Environmental Dis-benefit be avoided/ minimised/mitigated?	Other Considerations	Conclusion
Tunnel Boring	· Continuous low vibration and noise generation	· Longer impact period	· Environmental impacts are mostly confined to within the tunnel	· Controlled excavation profile · Higher production rates but relatively more expensive	· More efficient
Drill and Blasting	· Impact restricted to instantaneous noise and vibration	· Higher vibration and noise	· Environmental impacts are mostly confined to within the tunnel	· Safety consideration of the use of explosives in confined space of tunnels in close proximity to potential sources of landfill gas · Lower production rates but relatively cheaper	· Less efficient and have potential safety concerns

2.3.4 Construction Sequences

The construction sequence for Options 1a and 1b is relatively flexible due to the small scale of the works, i.e. site formation for landfill base and the construction/modification of the infrastructure area can be undertaken concurrently or sequentially. Undertaking the work concurrently can shorten the impact duration associated with the construction work but the magnitude of impact could be slightly higher. On the other hand undertaking the work sequentially will reduce the cumulative impacts but lengthen the impact duration. With the implementation of standard pollution control measures, neither construction sequence will cause adverse environmental impacts.

For Options 2, 3a and 3b, to ensure seamless operation of the infrastructure at the existing SENT Landfill, the new infrastructure at the Extension, which will also be designed to treat leachate and landfill gas from the existing SENT Landfill, will have to be constructed and commissioned before decommissioning and demolishing the existing infrastructure. Also, to make way for the site formation of the landfill base, the existing infrastructure will have to be demolished before the landfill base is formed. Due to the shape and size of the Extension Site, it is necessary to form and line the entire base of the landfill prior to commencement of waste placement, and to commence placement of waste against the newly-formed cut slope within the first year of landfill operation (for Options 3a and 3b). As a result, it will be necessary to form the entire cut slope at an early stage of the landfill development, i.e. completed before commencement of landfill operation. Although this may result in a greater concentration of construction activity, it also ensures that the disturbance due to the slope formation work is limited to a shorter timeframe and will ensure a safe operating condition during landfilling. Given the constraints described above and the fact that the construction work will be required to complete within 24 months to ensure timely opening of the Extension, no other practical and reasonable alternative construction sequences have been identified.

2.3.5 Work Sequence

The Extension will be developed in Phases. Applicable to all options, within each Phase, it is proposed that filling should commence on the western side (ie closest to Wan Po Road and the nearby sensitive receivers). The western perimeter of the Phase will be filled to its intended height (each Phase will comprise approximately a 20m increase in elevation of the landfill), and the outward face of the landfill will be progressively restored (ie the final cap will be placed and preliminary landscape planting will occur). This completed portion of the Phase will then act as a screen to minimise noise, visual and air quality impacts from the tipping operations within the remaining part of that Phase.

2.4 The Preferred Option

With reference to Clause 3.3.2 of the Study Brief, consideration shall be given to avoid or minimize the encroachment onto the CWBCP and the disturbance to the ecosystems in the adjacent areas including the CWBCP. Hence, Options 1a, 1b and 2, which do not encroach the CWBCP are considered first.

Of the five options examined, Options 1a and 1b would have the least impacts on CWBCP and the sensitive receivers in the vicinity in terms of both construction and operation. However, the additional landfill void capacity provided by these options is very small making them very inefficient in terms of cost and land use. The lifespan of these options is very short and thus will result in waste collection vehicles travelling to the more remote landfills in the short-term. This will result in more environmental impacts at territorial level. These options are thus not recommended.

Option 2’s void capacity is about 6 times than that of Option 1b and will not require additional land within the CWBCP. However, the void capacity will only be 10 Mm³ (i.e. still well below the target capacity), and the construction cost will be more expensive than that of the existing strategic landfills. Compared with Options 3a and 3b, the void space provided by Option 2 is 50% less than these options. Some diversion of the waste collection vehicles to the other two more distant strategic landfills will be required and hence there is potential for additional environmental impacts at a territorial level. In terms of environmental impacts at the local level during both construction and operation phases this option will be similar to Options 3a and 3b, except that no natural habitat will be directly impacted. As discussed in the previous section, engineering measures, such as the use of a large retaining wall and earth bund have been investigated but were found to create adverse visual impacts, to be very expensive and will only gain a small increase in void space.

Options 1a, 1b and 2 cannot satisfactorily fulfil the requirement of maximising landfill space to meet the landfill space demand in Hong Kong for the next 20 years and so Options 3a and 3b are considered further.

It is recognised that Options 3a and 3b will both have a direct impact on the CWBCP. In terms of maximising void capacity, making the most effective use of available land and achieving the highest cost effectiveness, Option 3b performs the best. The local environment impacts are similar to those associated with Option 2 and can be mitigated by careful design and good site practices. As discussed in Section 2.3.2, the encroachment area is primarily a cliff face without any hiking trail and proper access. It is unlikely that public enjoyment of the CWBCP would be affected. In terms of impacts on natural habitats, the encroachment area is of low to moderate ecological value with flora and fauna commonly found within the CWBCP. Adverse ecological impacts are not expected (refer to Section 9 of this EIA Report for details of the ecological impact assessment). When the encroached area is restored together with the fully restored landfill in the vicinity after the completion of landfill operation, it is anticipated that the restored Extension could be enriched to provide a higher amenity value.

It is understood that there is a public need for both landfill space and country parks. The loss of void space as a result of not maximising the use of this Extension Site would require void space to be provided at other landfills, resulting in a shortfall of space at the other landfills and an overall shortfall of landfill space in Hong Kong within the next 20 years. When balancing all of the above considerations and taking account of the recommended benefits and dis-benefits of all the options, Option 3b, gives the largest void space and lifespan while avoiding prolonged adverse environmental impacts to the maximum practicable extent. With proper design and mitigation, Option 3b is recommended as the preferred option for detailed environmental impact assessment.

The recommendation for adopting Option 3b as the preferred option for the SENT Landfill Extension was taken to the Country and Marine Parks Board (CMBP) on 22 May 2007 and was agreed by the CMPB subject to the following conditions:

· Government to press ahead a series of waste management strategy including the commissioning of the Integrated Waste Management Facilities by 2014;

· EIA of SENT Landfill Extension to be approved by the ACE and the EIA report to be presented to CMPB members for consideration;

· EPD to report to CMPB to update members progress of the waste management strategies; and

· Progressive restoration to be adopted for the SENT Landfill Extension. The encroachment area to be properly restored before it was returned to AFCD for country park use.

2.5 Consideration of Contractual Arrangements

The contractual options for procuring the Extension have been thoroughly assessed taking into consideration the interface with the existing SENT Landfill contract. In general, the two broad categories are:

· Design, construct and operate by one contractor (i.e. the same contractor will manage both the existing SENT Landfill and the Extension)

· Design, construct and operate by two contractors (i.e. the existing SENT Landfill and the Extension will be managed by two separate contractors)

The key difference to the design is the requirement for modifying the existing landfill gas extraction wells and the placement of liner on the piggybacked portion of the Extension. Under the “one contractor” scenario, the two landfills (ie the existing SENT Landfill and the Extension) will become one landfill. It will not be required to install a leachate containment system on top of the final cap of the existing SENT Landfill to separate the two landfills.

For the “two separate contractors” option, the piggybacked area will have to be separated by a new leachate containment system so that management of the two landfills (eg collection and treatment of leachate and landfill gas) will be completely separated. Modification of the existing landfill gas extraction wells in the piggybacked area will be required so that the liner of the leachate containment system of the Extension will not be damaged by existing gas wells as a result of differential settlement of waste mass of the existing SENT Landfill.

The environmental implications of the different contractual options are evaluated in Table 2.5a.

Table 2.5a Difference of Environmental Implications Associated With Different Contractual Options

Environmental Aspects	Differences
Air Quality	No difference as the modification and lining works for the “two contractors” option is not dusty.
Noise	“Two contractors” option is considered the worst case scenario due to the use of powered mechanical equipment for the modification and lining works.
Water Quality	No difference as the total leachate quantity will not be affected.
Waste	No difference as the modification and lining works will not generate significant amount of waste.
Landfill Gas Hazards	“Two contractors” option is considered as the worst case scenario due to the possibility of contact with landfill gas during the well modification and lining works.
Ecology	No difference to the ecological resources to be affected.
Landscape and Visual	No difference to the landscape resources to be affected.

For the purpose of assessing the worst case scenario for this EIA, the “two contractors” option, which is technical and contractual more complex, has been assumed.

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([1]) According to the White Paper “Pollution in Hong Kong – A Time to Act” issued on 5 June 1989 and the subsequent waste disposal strategy under the Waste Disposal Plan approved by the Governor in Council on 12 December 1989, there should be three new landfills in Hong Kong distributed on a regional basis for the following reasons:

· the daily quantity of MSW could not be handled by one or two landfills simply because of the strain that would be placed on the surrounding road network and on the landfill sites themselves;

· the increases in MSW were projected for the western and north-eastern New Territories and provision of disposal facility in each of these areas would help reduce transportation costs; and

· there would continue to be a need for a final disposal facility in reasonable proximity to Hong Kong Island in order to contain the transportation cost for waste arising from urban areas.

The existing 3 strategic landfills were therefore located at the western, north-eastern and south-eastern New Territories regions within the territory in the absence of other alternative site available in Kowloon and Hong Kong Island.