Advisory Council on the Environment

The Proposed Submarine Gas Pipelines from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant, Hong Kong

(ACE-EIA Paper 02/2003)
For Advice




This paper presents the key findings and recommendations of the Environmental Impact Assessment (EIA) report for the Proposed Submarine Gas Pipelines from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant, Hong Kong (the Project) submitted under Section 6(2) of the Environmental Impact Assessment Ordinance (EIAO). The Hong Kong and China Gas Company Limited (Towngas) and their consultants will make a presentation.

Advice Sought

2. Members' views are sought on the findings and recommendations of the EIA report. The Director of Environmental Protection will take into account the comments from the ACE and the public when he makes his decision on the approval of the EIA report under the EIAO.

Need for the Project

3. Towngas is presently reviewing the reliability and flexibility of their existing system to meet expected future demand. The proposed gas pipelines system would be used to supply natural gas as an alternative feedstock to produce gas at the existing production plant.

Description of the Project

4. The Project is to construct and operate a gas receiver facility (GRF) at the existing Tai Po gas production plant within Tai Po Industrial Estate and twin submarine gas pipelines to supply gas from a liquefied natural gas receiving terminal in Cheng Tou Jaio, Shenzhen to the GRF (Figure 1 MSWORD). The submarine gas pipelines will be laid through Tolo Harbour, Tolo Channel and Mirs Bay, with a length of about 28.5 km in Hong Kong waters (whereas in Mainland waters is about 3 km). The major construction activities of installing the submarine gas pipelines are jetting, dredging, pipe-laying and backfilling rock dumping.

5. The Project is a Designated Project under Item H.1, Schedule 2 of the EIAO (i.e. a submarine gas pipelines or submarine oil pipeline). Construction of the Project is scheduled to commence in the final quarter of 2004 for completion by the end of 2005.

Alignment Selection

6. Alternative alignment options, including land based route, marine based route and combination of land and marine based route have been considered and evaluated in the EIA report, taking into account environmental, engineering and risk factors.

7. The results indicated that the land based route and the combination of land and marine based route were less preferred due to their high potential for ecological and landscape/visual impacts and would pose more risk to the public because of exposure to longer length of pipelines and more people in closer proximity. The EIA has therefore recommended the marine based route as the preferred option.

Specific Environmental Aspects to Highlight

8. The key environmental issues identified for this project are: water quality, marine ecology, fisheries, hazard to life and mud disposal.

Water Quality

9. During construction, the potential water quality impacts arise mainly from the dredging and jetting works for laying the gas pipelines. They could be effectively minimized by:

  1. allowing only one trailer suction hopper dredger to conduct dredging (dredging work is recommended for laying a 3.6km section of pipelines in Hong Kong waters, as shown in Figure 1);
  2. limiting the maximum dredging rate at 11,880m3/hour;
  3. limiting the forward speed of the jetting machine to 67.5m/hour; and
  4. installation of 200m long silt curtains close to the seawall at Tai Po, as a precautionary measure, to prevent impacts to the WSD's seawater intake.
10. With the above first three measures in place, the EIA predicted that the impacts from dredging would comply with the WQO requirements and the coral tolerance criteria. Also, marine sediments disturbed by jetting works would settle rapidly back onto seabed and the suspended solid (SS) elevations would be of short duration. Details of the assessment results are presented in "Ecology" section below.

11. The pipelines are designed to be maintenance free during the operational phase and therefore no regular disturbance to the seabed is envisaged. In the unlikely event that a pipeline rupture occurs, the damaged section could be isolated and repaired by divers with hand jets which would localize sediment disturbance, if any, and consequently avoid impacts to water quality sensitive receivers.

Marine Ecology

12. Literature reviews coupled with extensive field surveys, including dive surveys of marine ecological resources have been undertaken. The pipelines alignment has been selected to avoid and reduce direct impacts to all ecological sensitive receivers in the vicinity. The closest ecological sensitive receivers from the pipelines alignment are corals in Tolo Channel at about 380m away.

13. The EIA estimates that the maximum depth-averaged SS elevation close to the coral sites is about 3 mg/L which is within the tolerance criterion of 10 mg/L elevation. The elevated SS is predicted to occur only over very short periods, i.e. 6 to 12 hours and that SS settle rapidly for concentration to fall to levels of less than 1 to 2 mg/L. The maximum sediment deposition close to the coral sites would be about 60 g/m2/day which is well below the assessment criterion of 100 g/m2/day. Sediment deposition at marine parks (i.e. Hoi Ha Wan, Yan Chau Tong and Tung Ping Chau) and areas of high coral cover in the vicinity of the pipeline route (i.e. Chek Chau and Wong Chuk Kok) is predicted to be very small (i.e. all below 10 g/m2/day). As a result, the impacts to corals are not expected to be unacceptable.


14. The EIA estimates that water quality in the fish culture zones (FCZs) within the study area and the proposed fisheries protection areas (FPAs) in Long Harbour and Tolo Channel as a result of the pipelines installation works would reach a maximum depth-averaged SS elevation at the FCZs of less than 3 mg/L. This elevation is small and within the assessment criterion for fisheries impacts, i.e. total concentrations of SS not greater than 50 mg/L. The overall depth-averaged values at the FPAs are predicted to be less than 25 mg/L which are also below the assessment criterion. As a result, the impacts to fishing grounds or species of importance to the fishery are not expected to be unacceptable.

Hazard to Life

15. A qualitative risk assessment is conducted and identifies that no insurmountable risk is envisaged for operation of the gas pipelines. Mitigation measures to further reduce the risk levels have been recommended, such as using armour rock to cover certain sections of the pipelines under navigation channel as additional protection.

Mud Disposal

16. The EIA estimates that dredging works for laying the pipelines within Mirs Bay would generate about 220,000 m3 of marine mud requiring disposal. All the dredged marine mud is found to be uncontaminated and will be disposal of at designed marine dumping areas, i.e. at East Nine Pin or South Cheung Chau.

Environmental Monitoring & Audit (EM&A)

17. An EM&A programme is proposed in the EM&A manual submitted with the EIA report. A pilot test on water quality monitoring to verify the water quality modeling predictions of the EIA report is included in the EM&A programme. Also, a comprehensive and reactive coral monitoring programme would be undertaken to ensure that the pipelines installation works would have no adverse impact on corals. The EM&A requirements will be enforced as Environmental Permit conditions.

Public Consultation

18. Towngas has made the EIA report, EM&A manual and Executive Summary available for public comment under the EIAO on 5 March 2003. Members will be briefed about any comments received from the public at the meeting.

Environmental Protection Department. March 2003


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