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Continue to develop our rock caverns

Under the multi-pronged approach to increasing land supply, rock cavern development will be an option other than the proposed near-shore reclamation. Back in the 1990s, public facilities such as the Stanley Sewage Treatment Works and the Island West Refuse Transfer Station were relocated to purpose-built rock caverns to satisfy the needs of the community. As a result, Hong Kong has already gained some experience in setting up facilities in rock caverns. Given the acute shortage of land in Hong Kong at present, it is a viable option to boost our land resources by relocating some facilities to rock caverns so as to release the original sites for housing development or other uses.

According to a consultancy study commissioned by the Government, about 64 per cent of land in Hong Kong is suitable for large-scale rock cavern development and all of these areas are located in or near the urban areas. In addition, the geological features of Hong Kong are also suitable for rock cavern development. However, the Government currently has only five purpose-built rock cavern development projects in operation. Unlike the underground MTR stations and retail stores which have already become part of our daily lives, the development potential of suitable land has yet to be explored.

We gained valuable experience in rock cavern development long ago with the construction of the Stanley Sewage Treatment Works in 1995. Since no suitable sites were available in Stanley then, the Government chose to build the facility inside a rock cavern, which could serve as a natural barrier to shelter the sewage treatment works and blend it with the surrounding environment and community. The Stanley Sewage Treatment Works was the first public facility ever built inside a rock cavern in Hong Kong, and was also the first of its kind in Southeast Asia. With an area of about one hectare and a capacity of 11 600 cubic metres of sewage per day, the plant serves a population of 27 000.

Also located inside rock caverns are the Island West Refuse Transfer Station and the Explosives Complex at Kau Shat Wan completed in 1997. The more recent example is the relocation of the Salt Water Service Reservoirs in Western District to a rock cavern by the University of Hong Kong in 2009 to make way for the development of its Centennial Campus. The relocated facility is also the first reservoir ever built inside a rock cavern in Hong Kong.

In the first quarter of this year, we published the paper on Stage 2 Public Engagement (PE2) on Enhancing Land Supply Strategy: Reclamation Outside Victoria Harbour and Rock Cavern Development. We have identified three potential sites for rock cavern development and suggested relocating the Diamond Hill Fresh Water and Salt Water Service Reservoirs, as well as the Sai Kung and Sham Tseng Sewage Treatment Works to rock caverns to release some 6.3 hectares of urban land. With the completion of PE2 in late June, we have commissioned the Social Sciences Research Centre of the University of Hong Kong to conduct an independent analysis of the data collected so that we can plan for the work ahead.

With reference to the successful experience of the Stanley Sewage Treatment Works, we have also commenced studies into relocating other public facilities to rock caverns. At the end of last month, the Drainage Services Department launched Stage 2 Public Engagement for the feasibility study on the relocation of the Sha Tin Sewage Treatment Works (STSTW) to caverns. It will be held until October 18 and related roving exhibitions and a public forum will be organised. We will further consult the public on the preliminary technical assessment results, as well as the latest progress and recommendations of the feasibility study.

The STSTW, with an area of some 28 hectares, is the largest secondary sewage treatment works in Hong Kong. It serves a population of about 630 000 in the Sha Tin and Ma On Shan districts. With a design capacity of 340 000 cubic metres of sewage per day, the facility currently treats 250 000 cubic metres per day.

According to the questionnaire survey conducted during Stage 1 Public Engagement, about 72 per cent of respondents agreed that relocating the STSTW to rock caverns would benefit the community and enhance the environment in Sha Tin, with particular improvements in odour reduction and visual impacts.

Our consultant has reviewed the proposed relocation site at Nui Po Shan of A Kung Kok and compared it with four other potential areas, which include Shek Mun, Ma On Shan, Kau To Shan South and Kau To Shan North. Having considered a number of major factors such as the geological features and land ownership, as well as impacts on the existing sewage system, the surrounding environment and the transport network, the consultant has decided on Nui Po Shan of A Kung Kok as the most suitable site for relocation.

In response to local residents’ concerns about the odour problem and the impacts of blasting vibration during the construction of rock caverns, the consultant has completed an odour impact simulation and selected the most suitable locations for ventilation openings. Through the implementation of appropriate odour control measures and the construction of ventilation openings in remote locations on the hill, the odour concentration in the area would be far below 5 odour units as stipulated in the Environmental Impact Assessment Ordinance. According to the findings of another assessment, blasting vibrations would be much lower than the limits of 25mm/s or 13mm/s (whichever is appropriate). With advanced blasting technology and control measures, vibrations caused to nearby buildings would be mitigated to an acceptable level.

Regarding the site released after the relocation of the STSTW, we tentatively propose to use it for housing development and other uses beneficial to the community, such as suitable community facilities, open space, a promenade, etc, to improve the district as a whole. The relocation plan, if implemented, will be completed sometime around 2027. By then, we will undertake detailed planning for the use of the site and conduct other technical and impact assessments.

4 August, 2013