2 PROJECT DESCRIPTION
2.1 LOCATION AND SCALE OF THE PROJECT
The project site for the Gas Receiver Station is within the Tai Po Industrial Estate and will be located within the boundary of the existing Gas Production Plant run by Towngas (Figure 2.1a). The submarine pipelines will be laid through the Tolo Harbour, Tolo Channel and Mirs Bay (Figure 2.1b).
The proposed landing point at Tai Po is located towards the eastern end of the Tai Po Waterfront Park seawall. Two routes were identified to take the pipelines from the landing point to the Gas Receiver Station.
* Route Option 1 is located along the sea front walkway. The route is parallel to the seawall and cuts into the Towngas complex at the southeast point. The total length is approximately 1,040 m (Figure 2.1a).
* Route Option 2 cuts into the industrial estate travelling north beside the Motorola factory and turns west towards Dai Hei Street after 300 m. At the end of Dai Hei Street, it turns north again, into a car park area and eventually turns west and enters the Towngas complex at the northeast side of the tank farm. The total length is approximately 1,564 m (Figure 2.1a).
An assessment of the engineering, environmental and risk considerations of the alternative route options has been examined and both were deemed acceptable. A decision as to which route option will be pursued will be made during the detailed design stage.
2.2 CONSTRUCTION AND OPERATIONAL ACTIVITIES
The major activities involved during the construction stage of the Project are jetting, dredging, pipelaying and backfilling rock dumping, for installation of the submarine pipelines (Figure 2.1b), excavation of onshore trenches and construction of the Gas Receiver Station.
The pipelines are designed to be maintenance free and should they require inspection during the operational phase of the Project this will be done using a remotely operated intelligent pipe inspection gauge (PIG). This type of maintenance will occur once every ten years and will be within the gas pipes. The only operational impacts from the gas pipelines would be if repairs were required. Operational impacts are principally related to the potential hazard to life presented by the pipelines. Measures have been incorporated into the Project design to reduce levels of risk to acceptable levels.
2.3 PROJECT PROGRAMME
The construction of the Project is scheduled to commence in the final quarter of 2004 with completion due by the end of 2005. The entire construction period is around 12 months, in which dredging, pipelaying and jetting will be conducted in sequential stages (Figure 2.3a). It is expected that this Project has no major interactions with other projects.
2.4 PREFERRED ALTERNATIVE
2.4.1 Environmentally Sensitive Areas Protected
The EIA process has facilitated the integration of environmental considerations into the design process for the Project. The principal measures identified are those achieved through the careful routing of the pipelines and the pipelines installation methodology. In addition, a number of mitigation measures have been identified to minimise the potential for adverse environmental impacts to occur. The mitigation measures are detailed in full in the Implementation Schedule of the EIA Report. These measures will be implemented by Towngas and enforced by the EPD.
Towngas has undertaken a detailed assessment of alternatives for routing the pipelines, which has included consultations will local fishers, green groups and Government Departments. A number of alternative pipeline routes were studied and the preferred alignment avoids direct impacts to ecologically sensitive habitats and species. The key sensitive receivers avoided include the following (Figure 2.4a):
* Corals fringing Tolo Channel and Mirs Bay;
* Marine Parks at Tung Ping Chau, Yan Chau Tong and Hoi Ha Wan;
* Artificial Reef Deployment sites in the Marine Parks and Long Harbour;
* Fish Culture Zones in Tolo Harbour and Channel; and,
* Sites of Special Scientific Interest (SSSIs) at Ting Kok and Kei Ling Ha.
2.4.2 Environmentally Friendly Designs
In developing the design and installation method for the submarine pipelines, a key concern was to take steps so that indirect impacts to water quality sensitive receivers were avoided or minimised. Consequently, the following approaches were adopted.
* Bundle Configuration: The pipelines were designed in a bundle configuration so they can be laid in the same trench. Consequently the area of direct impact was reduced and hence the magnitude of potential impacts to ecological resources was reduced.
* Reduction in Indirect Impacts: The alignment chosen for the two pipelines was located at a sufficient distance from ecological sensitive receivers so that the short term dispersion of sediment from the installation works was not predicted to affect the receivers at levels of concern (as defined by the WQO and tolerance criteria). By laying the pipelines in the same trench, the horizontal spread of suspended sediment was predicted to be restricted to a confined area in the centre of the Tolo Channel. Should the pipelines have been laid in separate trenches the horizontal spread of suspended sediment would have been much larger, thereby posing a greater potential risk to sensitive receivers.
* Installation Equipment: The pipelines will be installed using two methods:
o dredging trenches in the Yantian Fairway and the Shenzhen approach (outside HKSAR waters); and
o jetting for the majority of the pipelines route.
The use of injection jetting along the majority of the route has minimised the severity of perturbations to water quality and hence allowed compliance with the WQOs at the sensitive receivers. The dredging of a trench in the Yantian Fairway and the Shenzhen approaches was assessed and it was determined that the impacts from the works would comply with the WQOs and coral tolerance criteria. This careful selection of installation equipment has helped avoid impacts to sensitive ecological receivers.
* Adoption of Acceptable Working Rates: The modelling work has demonstrated that the selected working rates for the dredging (11,880 m3 hr-1) and jetting works (1.08 km day-1 in Tolo Harbour and Channel with a working rate of 16 hours per day, ie 67.5 m hr-1; and 1.62 km day-1 in Mirs Bay with a working rate of 24 hours per day, ie 67.5 m hr-1) will not cause unacceptable impacts to water quality. Consequent elevations of suspended sediment are predicted to be compliant with the WQO and coral tolerance criterion. Consequently, unacceptable indirect impacts to marine ecological resources have been avoided.