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Options Development

In working out the most desirable layout for WENT Landfill Extension, a number of layout options were formulated, evaluated and then compared for selection, based on various evaluation criteria and an evaluation framework agreed with relevant stakeholders in advance.

The key issues and constraints identified during the course of study were taken into account in formulation of landfill extension layout options. A total of 5 broad options were thoroughly evaluated and discussed at a Value Management Workshop on 12 June 2008, attended by relevant stakeholders. Key features of the various options are recapitulated below.

Option 1

Characteristics

•	WENT A + WENT B matching with existing ridgeline

•	WENT A to fill over the Tsang Kok Stream Outfall

•	WENT B keeps nearly the same as Option 1

•	WENT A further extend to the west

•	WENT B keeps nearly the same as Option 1

•	Combine WENT A & WENT B

•	Avoidance of TTAS, Temple etc.

Capacity

71 Mm³

74 Mm³

79 Mm³

81 Mm³

39 Mm³

Evaluation Criteria

These options were evaluated / assessed in accordance with the following factors and main criteria :

• Waste management needs of at least 71Mm³ target void space;

• Engineering considerations including site formation complexity, constructability, drainage impact and maintenance;

• Environmental issues such as noise, air quality, ecology, landscape and visual, waste management, cultural heritage, water quality, etc.

• Community aspects such as afteruse flexibility, cost of disposal, land resumption and graves clearance.

Options Evaluation

Criteria	Option 1	Option 2	Option 3	Option 4	Option 5
(A) Waste Management Considerations
Waste capacity	71Mm³	74Mm³	79Mm³	81Mm³ (Preferred)	39Mm³
Cost-effectiveness	Target capacity is 71Mm³ is met, no extra cost for reclamination-based landfill	saving ~ HK$0.5b	saving ~ HK$1.5b	saving ~ HK$2b (Preferred)	Extra ~ HK$7b is needed for reclamination-based landfill
Waste-to-energy potential	Proportion to waste capacity	Proportion to waste capacity	Proportion to waste capacity	Proportion to waste capacity (Preferred)	Proportion to waste capacity
(B) Engineering
Flexibility of site formation	Export fill	Import fill	Export fill	Balance cut and fill (Preferred)	Export fill
Construction Practicability	Longer retaining wall required	Retaining wall required (Preferred)	Retaining wall required (Preferred)	Retaining wall required (Preferred)	Retaining wall required (Preferred)
Drainage Impact to Downstream	Minor impact, without decking over of Tsang Kok Stream outfall (Preferred)	Decking over of Tsang Kok Stream outfall	Decking over of Tsang Kok Stream outfall	Decking over of Tsang Kok Stream outfall	Decking over of Tsang Kok Stream outfall
Operational and Maintenance	Required maintenance of longer retaining wall	No difficulty of operational and maintenance (Preferred)	No difficulty of operational and maintenance (Preferred)	No difficulty of operational and maintenance (Preferred)	No difficulty of operational and maintenance (Preferred)
(C) Environmental Issues
Air Quality	Air quality impact can be mitigated
Noise	Noise impact can be mitigated
Water Quality Impact	Similar water quality impact
Landscape & Visual	Similar visual impact
Archaeological and Heritage Impact	Encroachment to TTAS	Encroachment to TTAS	Encroachment to TTAS	Encroachment to TTAS	No impact to TTAS, (Preferred)
Ecology Impacts	Similar impact on woodland and stream				Less impact on woodland and stream
(D) Community Aspects
Flexibility for afteruse	Separate site less afteruse flexibility	Separate site less afteruse flexibility	Separate site less afteruse flexibility	Single development, more flexibility for afteruse (Preferred)	Single development, more flexibility for afteruse (Preferred)
Unit Cost per Disposal	$$	$	$	$	$$$
Need for Land Resumption	Some private lands need to be resumed	Some private lands need to be resumed	Some private lands need to be resumed	Some private lands need to be resumed	Less private lands need to be resumed (Preferred)
Need for Graves Clearance	Nine graves to be cleared	Nine graves to be cleared	Nine graves to be cleared	Nine graves to be cleared	Clan Grave is excluded from the extension (Preferred)

It is understood that there is a public need for landfill space. The loss of waste capacity 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 other landfills or at other new landfill site, generating additional environmental impact at territorial scale. As such, when balancing all the above considerations and taking account of the recommended benefits and dis-benefits of all the Options, Option 4, which gives the largest waste capacity whilst avoiding prolonged adverse environmental impacts, was evaluated as a preferred option.