Advisory Council on the Environment

Environmental Impact Assessment Ordinance (Cap. 499)


(ACE-EIA Paper 16/2002)
For advice

Environmental Impact Assessment Report
Application No. EIA-079/2002

Ngong Ping Sewage Treatment Works and Sewerage


1. This paper presents the key findings and recommendations of the Environmental Impact Assessment (EIA) Report for the Ngong Ping Sewage Treatment Works and Sewerage under section 6(2) of the Environmental Impact Assessment Ordinance (EIAO). Comments from the public and ACE will be taken into account by the Director of Environmental Protection when he makes his decision on the approval of EIA report under the EIAO.

Advice Sought

2. Members' views are sought on the findings and recommendations of the EIA report.

Need for the Project

3. At present, sewage generated in Ngong Ping area is treated by grease traps and septic tanks, and then discharged locally via soakaways. According to Drainage Services Department (DSD), with significant increase of the number of visitors to Ngong Ping since the opening of the Statue of Buddha and the forecasted further increase after operation of the Tung Chung Cable Car system, the existing sewage treatment and disposal facilities are found inadequate. The proposed project will provide a centralised sewage treatment system and a local sewerage system for Ngong Ping.

Description of the Project

4. The proposed project will consist the following elements :

  • A sewage treatment plant (STP) providing biological and tertiary treatment with disinfection to the sewage collected. The STP will be designed to meet the following minimum standards of effluent :

    Water Quality Parameter Minimum Effluent Standard
    Biochemical Oxygen Demand, mg/L 10 (95 percentile)
    Suspended Solids, mg/L 15 (95 percentile)
    Ammonia Nitrogen, mg/L 1 (annual average)
    Nitrate + Nitrite Nitrogen, mg/L 7 (annual average)
    E. Coli. count/100mL 100 (geometric mean)
  • A trunk sewer and connection sewers serving the cable car terminal, existing main public toilets at Ngong Ping and Po Lin Monastery;
  • An effluent export pipeline conveying the treated effluent from the STP to Tai O for discharge; and
  • A new sewage collection network serving the unsewered village premises in Ngong Ping area.

5. The proposed project is a Designated Project under Item Q.1, Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO) (i.e. projects partly or wholly in an existing or gazetted proposed country park or a conservation area, etc). Construction of the proposed project will start in 2003 for completion in 2005.

Characteristic of the Selected Option

6. The proposed project will involve sewage treatment at Ngong Ping followed by disposal of treated effluent to inshore waters in Tai O. Comparing with other treatment and disposal options, including discharging locally via soakaways; disposal of treated effluent to inland waters within country park or water gathering ground; export of untreated sewage and disposal of treated effluent to marine water studied in the EIA, the selected treatment and disposal option is preferred from the perspective of minimising the potential risk to human health and environmentally sensitive area.

7. The STP will be located at a site which is mainly covered with grass with occasional plantation trees. Comparing with another potential site opposite to the selected site, the selected site will entail less tree cutting and hence minimise the landscape impact.

8. The treated effluent from the STP will be exported and discharged at Tai O. The potential routes, including towards Tung Chung, towards Sham Wat and towards Tung Wan have also been assessed in the EIA report, which concluded that the selected effluent export route is environmentally preferable. The recommended route, which basically follow the existing road, will avoid the ecological impact when compared with the Tung Chung route which may impinge on the Ngong Ping Site of Special Scientific Interest (a place known to support the largest population of the protected Romer's Tree Frog) and the Sham Wat route which may affect the ecologically diverse Sham Wat stream and valley. When compared with Tung Wan route which is close to Shek Pik Reservoir, the Tai O route will have less risk in directly discharging into the reservoir in the rare event of pipe leakage.

9. The findings of various treatment and disposal options studied in the EIA report for the proposed project were presented by DSD to the ACE EIA Sub-committee in July 2002.

Specific Environmental Aspects to Highlight

10. The major environmental issues identified for the proposed project are: water quality, odour, construction noise and visual & landscape.

Water Quality

11. The major water quality concern during operation is the potential impact on Tai O water quality from discharge of treated sewage. The EIA has concluded that as the sewage will be treated to tertiary quality standard (paragraph 4 above), there would not be any adverse residual impact. The EIA has recommended a comprehensive monitoring, including monitoring of flow in effluent export pipeline, to prevent and detect any pipe leakage in order to protect the water gathering ground and the sensitive environment in Ngong Ping.


12. To mitigate the potential odour problem arising from the operation of the STP, all the major odour sources within the STP, such as inlet work, sequencing batch reactors, sludge thickeners and emergency storage tank, will be constructed as underground facilities. In addition, all odour emissions will be contained and ventilated to a centralized deodourisation unit with minimal odour removal efficiency of 99.5%. With the mitigation measures in place, there will be no adverse residual odour impact to the nearby receivers, including future cable car passengers.

Construction Noise

13. To mitigate the construction noise impact arising from the construction of the proposed project, temporary movable noise barriers and quiet construction plants will be used. There will be no adverse residual construction noise impact associated with the construction of STP and effluent export pipeline as the mitigation measures can control construction noise impact to within the day-time construction noise criterion of 75dB(A) stipulated in the EIAO Technical Memorandum. For the construction of a new sewage collection network serving the unsewered village premises in Ngong Ping area, some local villagers may be disturbed by the transient and localised noise due to the construction of local sewers. Manual construction methods will be adopted as far as practicable to further mitigate the construction noise impact. Residual construction noise impact exceeding 75dB(A) will be experienced by some local villagers but will only last for less than a day.

Visual and Landscape

14. Key elements of the STP will be constructed as underground facilities. Extensive planting along the perimeter of the STP site and sensitive architectural treatment of the elevated structures of the STP were recommended to reduce the visual impact of the STP. With the mitigation measures in place, there will be no adverse residual visual and landscape impact during operational stage.

Environmental Monitoring and Audit (EM&A)

15. An EM&A programme was proposed in the EM&A Manual submitted together with the EIA report. A detailed Implementation Schedule was included. For those elements of the proposed project that are Designated Projects, the EM&A requirements will be enforced as Environmental Permit conditions.

Comments received so far from the Public during the Public Inspection Period

16. DSD has made the EIA report, the EM&A Manual and the Executive Summary available for the public to comment under the EIAO since 30 August 2002. Members will be briefed on any comments received from the public at the meeting.

Environmental Protection Department
September 2002


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