1. INTRODUCTION

1.1 Background of the Project

1.1.1 The Environmental Protection Department (EPD) completed the Outlying Islands Sewerage Master Plan (OI SMP) Study in December 1994 and drew up a SMP for Lantau Island, Cheung Chau, Lamma Island, Peng Chau and other smaller and less populated islands. The SMP comprises provisions for upgrading and expanding the sewerage systems to cover unsewered areas.

1.1.2 This sewerage project is the Stage 1 works under the OI SMP and can be divided into 3 packages as follows:
Package 1 - Ngong Ping STW with tertiary treatment
Package 2 - Ngong Ping main trunk sewer and effluent export pipeline
Package 3 - Ngong Ping village sewerage system

1.1.3 The general layout plan of the project is shown in Drawing No. 23400/R/G/001.

1.1.4 The existing treatment facilities at Ngong Ping include grease traps and septic tanks, with discharge locally to soakaways. Following the opening of the Statue of Buddha in December 1993, the number of visitors to Ngong Ping increased significantly. The existing treatment and disposal facilities were found to be inadequate, with significant quantities of sewage being directly discharged into the local stream. It was under this setting that the recommendation to provide a local sewerage system and a centralised treatment system for Ngong Ping was put forward in the OI SMP in 1994.

1.1.5 The cable car system linking Tung Chung and Ngong Ping is being planned for commissioning in August 2005. It will certainly further increase the number of visitors in Ngong Ping. This sewerage project will be completed to tie in with the commissioning of the Cable Car Project. Drawing No. 23400/EN/019 shows the worst scenario of possible location of the proposed Ngong Ping cable car terminal which is close to the Ngong Ping Sewage Treatment Works (STW) and is some 50m to the proposed STW site.

1.2 Description of the Project

1.2.1 Details of the three packages of the project are as follows:

1. Package 1 – Ngong Ping STW

2. Package 2 –Ngong Ping Main Trunk Sewer and Effluent Export Pipeline

Construction of a new sewage collection network at Ngong Ping to cover the remaining unsewered area within this region. Works of the proposed sewerage system includes connections and diversions of public sewers to the new trunk sewers, connections of sewer systems of public toilets to the new trunk sewers, and tapping sewers from the new trunk sewers to adjacent private land lot boundaries. Approximately 3 km of foul sewers and two local pump chambers at Ngong Ping will be constructed.

1.2.2 The Project is a Designated Project under Part I in Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO) and thus an Environmental Impact Assessment (EIA) is required. The EIA Study Brief No. ESB-074/2001 was issued by EPD under the EIAO in May 2001.

1.3 Location and Layout of the Project

1.3.1 The proposed alignments of the effluent export pipeline, trunk sewer and the village sewers will run along existing public roads or footpaths.

1.3.2 The sewerage network, comprising the village sewers and the main trunk sewer, will serve all areas of Ngong Ping, including the village houses, youth hostel, resort hotel, monasteries, proposed cable car terminal and associated developments. Two small pump chambers will be required within the Ngong Ping village to lift the flows from a low-lying area into the main gravity sewerage network. The proposed layout of the sewerage network is shown in Drawings No. 23400/R/VS/001-002.

1.3.3 The STW will be located west of Ngong Ping on the north side of Ngong Ping Road (See Drawings No. 23400/R/VS/002 and 23400/R/ST/013). The proposed site for the STW is an undeveloped plot of land within the Water Gathering Ground (WGG) of the Shek Pik reservoir.

1.3.4 The effluent pipeline will be located within the existing two-lane road from Ngong Ping to Tai O. A flow monitoring station will be required east of Tai O. The discharge point will be near the bus terminus at Tai O. The proposed alignment of the effluent export pipeline is shown in Drawings No. 23400/R/PP/001-009 (001, 002, 003, 004, 005, 006, 007,008,009). Drawings No. 23400/EN/086 to 091 (086, 087, 088, 089, 090,091) shows the land requirements for the Project.

1.4 Work Programme

1.4.1 The works of Package 1 and Package 2 will be carried out in two separate contracts with construction completed by July 2005 and April 2005 respectively to match the scheduled opening date of Cable Car Project. For Package 3, it will be implemented as a separate contract at a later stage as it depends on the progress of land resumption process. In addition, Package 3 work is not dependent on the commissioning of Cable Car Project and is scheduled to be completed by April 2007, after commissioning of the Ngong Ping STW.

1.5 Design Flow

1.5.1 The design flow for the sewerage system was based on the flow project on 2016 and ultimate stage. Table 1.1 gives an estimate of the flow projection.

Table 1.1 Flow Projection at 2016 and Ultimate Stage

Notes:

A. The values of peak flow are based on intense storm and reduced diurnal peak flow due to 10% visitor reduction in such weather conditions.Bold and Italic - Design flow criteria of the sewerage system.

1.6 Effluent Quality Standard

1.6.1 The sewage treatment process of the Ngong Ping STW will be designed to meet the minimum effluent quality standard as specified in the DSD Consultancy Brief (Table 1.2). From the findings and recommendations of the EIA, the effluent with the below quality standard will meet the Water Quality Objectives of the selected receiving water bodies.

Table 1.2 Minimum Effluent Quality Standards

1.7 Preliminary Design of the Sewerage System

1.7.1 The STW incorporates the following units:

· Inlet pumping station with coarse screening
· Grit removal and fine screening
· Biological treatment by sequencing batch reactor (SBR) process
· Tertiary treatment with gravity filters
· Disinfection using ultra-violet irradiation
· Sludge thickening, digestion, dewatering and storage.

1.7.2 The preliminary assessment indicates that Sequence Batch Reactor (SBR) is considered to be suitable for tertiary treatment including nutrient removal process.

1.7.3 Sludge thickening by gravity and sludge dewatering by plate filter press are recommended in order to optimize the space utilization, operating cost and effectiveness.

1.7.4 In odour control, wet scrubber system would be used since the performance would be reliable regardless the variation of gas composition.

1.7.5 It is proposed to construct an emergency storage tank to temporary store both the raw sewage from Ngong Ping sewerage catchment and the effluent of STW to cater for the STW breakdown and bursting of effluent pipe. Furthermore, it is also proposed that the size of the emergency storage tank will be large enough to store 72hr. Sewage/effluent flow (48 hours peak day and 24 hours average day i.e. 2 x 2956 + 1524 = 7436m3) in ultimate stage. Thus, the volume of the emergency storage tank would be about 7600m3 and the size would be about 50m(L) x 40m(W) x 3.8m (D).

1.7.6 In the STW, both normal and essential power shall be supplied by means of dual power supply and emergency generator set. The normal power would be supplied by CLP substation near the site of STW in the form of dual supply system, which can minimise the maintenance and operating requirement.

1.7.7 The flow in the entire effluent pipeline will be driven by the static pressure induced by the level difference between the STW at Ngong Ping and the discharge point at Tai O. An effluent monitoring station will be constructed east of Tai O. Flows monitored at this station will be compared with those monitored at the STW to check for any possible leakage from the effluent pipeline.

1.8 Key Environmental Issues

1.8.1 The key issues associated with the various packages of the Project include:

1.9 Objectives of Environmental Impact Assessment Study

1.9.1 The objectives of the EIA for the Project as detailed in the EIA Study Brief No. ESB-074/2001 issued by the EPD under the EIAO are as follow:

1. to describe the proposed project and associated works in detail together with the requirements for carrying out the Project;

2. to identify and describe the elements of the community and environment likely to be affected by the Project and/or likely to cause adverse impacts to the Project, including natural and man-made environment and the associated environmental constraints;

3. to provide information on the consideration of alternatives to avoid and minimize the environmental impacts, in particular on the Lantau North Country Park, the Ngong Ping Site of Special Scientific Interest (SSSI), the Water Gathering Ground, the mangroves marsh at Tai O and the users of the future cable car system.

4. to identify and quantify emission sources and determine the significance of impacts on sensitive receivers and potential affected uses;

5. to identify and quantify any potential landscape and visual impacts and to propose measures to mitigate these impacts;

6. to identify and quantify any potential losses or damage to flora, fauna and natural habitats and to propose measures to mitigate these impacts;

7. to identify any negative impacts on sites of cultural heritage and to propose measures to mitigate these impacts;

8. to propose the provision of mitigation measures so as to minimize pollution, environmental disturbance and nuisance during construction and operation of the Project;

9. to investigate the feasibility, effectiveness and implications of the proposed mitigation measures;

10. to identify, predict and evaluate the residual environmental impacts (i.e. after practicable mitigation) and the cumulative effects expected to arise during the construction and operation phases of the Project in relation to the sensitive receivers and potential affected uses;

11. to identify, assess and specify methods, measures and standards, to be included in the detailed design, construction and operation of the Project which are necessary to mitigate the identified environmental impacts and cumulative effects and reduce them to acceptable levels;

12. to investigate the extent of the secondary environmental impacts that may arise from the proposed mitigation measures and to identify constraints associated with the mitigation measures recommended in the EIA study, as well as the provision of any necessary modification; and

13. to design and specify the Environmental Monitoring and Audit (EM&A) requirements to ensure the effective implementation of the recommended environmental protection and pollution control measures.