2.1. Nature, Scope and
Benefits of the Project
2.2. Size, shape and
design of the Project
2.3. Background and
History of the Project
2.4. Need of the
Project
2.5. Project Programme
2.6. Construction
Activity
2.7. Consideration of
Alternative Decommissioning Methods
2.8. Any Related
Projects
2.9. Description of
Scenarios With or Without the Proposed Project
2.1.1. The purpose of the Project is to decommission the PFA lagoon at the west portion of the Middle Ash Lagoon at Tsang Tsui, Tun Mun. Decommissioning is defined as the process in which the PFA lagoon, under conditions of potential adverse environmental effects, is deactivated through various constructions means. As a result, the decommissioning will provide buildable land for future developments.
2.1.2. The Project consists of the Subject Site with a total area of about 30,000m2 (3.0 hectares). It comprises 2.7ha of dry PFA platform and 0.3ha of low zone along the northern boundary, which generally contain water. In accordance with the latest available information, there is no plan that the 0.3ha low zone will be filled up. The area is considered as a man-made water channel and will be left intact. Thus, decommissioning work would include construction of retaining structure to stabilise the PFA slope along this man-made water channel.
2.1.3. Besides, a surface drainage outfall system of approximately 300m2 (0.03 hectare), as depicted in Figure 1.1, will be installed to discharge the surface runoff from the buildable land created after the completion of the decommissioning. The installation of surface drainage outfall system will not require decommissioning, whereas details of outfall system are illustrated in Appendix 2.2.
2.1.4. As the decommissioning of the Subject Site will need quite a number of to-and-fros of heavy construction vehicles and there is no proper vehicular access roads connecting the Subject Site to the public road at present, formation of construction access road will then be prerequisite for the decommissioning project. Two construction access roads are proposed, namely, North and South, which areas are about 3,000m2 and 10,000m2 respectively. A portion of the Construction Access Road Area (South) will be formed by repairing the existing paved access road only and thus not involve decommissioning works, as depicted in Figure 1.1.
2.2.1. The Subject Site includes a PFA platform with area of about 27,000m2 and a man-made water channel of around 3,000m2 in area. The Site is of trapezoidal-shape in plan. The lengths of its north and south sides are about 145m and 106m respectively, while that of the east and west sides are around 239m and 244m respectively. Upon the latest development of the Middle Ash Lagoon, the man-made water channel shall be remained at the northern part of the Subject Site. Facing south is a mountain view of Castle Peak while to the north is an existing sea wall facing Shenzhen Bay.
2.2.2. The total project area involved will be approximately 4.33 hectare, of which about 3.8 hectare of area will be decommissioned.
2.3.1. The Subject Site is located in the western part of the Middle Ash Lagoon. The site has been operated by Castle Peak Power Company Limited (CAPCO, a joint venture of CLP Power HK Ltd. and China Southern Power Grid Company) for the placement of water and pulverised fuel ash (PFA), a by-product of burned coal from Castle Peak Power Station. The ash lagoons at Tsang Tsui was formed by reclamation in the 1980s and used by CAPCO exclusively. According to the current programme, CAPCO will surrender the middle lagoon to the government by the first quarter of 2015.
2.3.2. Upon the latest development of the Middle Ash Lagoon, the majority of the Subject Site is a PFA platform with a level of about +10.5mPD. A man-made water channel of approximately 30m wide is located to the north of the Subject Site, with part of the water channel falling into the Subject Site. In accordance with the latest available information, CAPCP has no plan to remove any PFA from the Middle Lagoon up to their surrendering of this lagoon. It is reasonable to assume the 30m water channel will remain its location and width, when the subject site is handed over to the government.
2.3.3. Other than the Subject Site, the remaining portion of the Middle Ash Lagoon area will be taken over by the Environmental Protection Department (EPD) as part of an extension of WENT Landfill (WLES) and an Integrated Waste Management Facilities (IWMF). According to the approved EIA report (application EIA 201/2011) for the Development of the Integrated Waste Management Facilities (IWMF) Phase 1 by EPD, the area directly to the east of the Subject Site is one of the potential sites for the IWMF Phase 1. Further to the east in the East Lagoon, a Sludge Treatment Facilities (STF) development is currently under construction and expected to be in operation by 2015.
2.4.1. As mentioned, the Middle Ash Lagoon located at Tsang Tsui, Tuen Mun will be surrendered by CAPCO to the government in the first quarter of 2015. Should there be no future development planned in the Middle Ash Lagoon, it will become an idle ash storage facility.
2.4.2. The decommissioning of the not-used ash lagoon is deemed to be required to neutralise the potential effect from the idle Middle Ash Lagoon, and provide usable land for future government development.
2.4.3. The EIA shall evaluate the environmental impacts associated with the decommissioning process at the west portion of the Middle Ash Lagoon at Tsang Tsui, Tuen Mun. The potential impact after the completion of decommissioning, as well as the limitation to future developments will also be discussed
2.4.4. Given the limited land resources in Hong Kong, decommissioning is considered as a viable option to provide buildable land for future development. In order to remove potential environmental and health concerns of the Middle Ash Lagoon to the public upon site handover by CAPCO, decommissioning works at the Subject Site is required. In view that the West PFA Lagoon will be operated by CACPO as their last PFA storage location, decommissioning in the West Lagoon was not considered as an alternative site selection option. The East PFA Lagoon, on the other hand has already been decommissioned and is currently under construction of a Sludge Treatment Facility (STF). According to the approved EIA report, Development of the Integrated Waste Management Facilities (IWMF) Phase 1 (application EIA-201/2011), and West New Territories (WENT) Landfill Extensions (application EIA-171/2009) the east portion of Middle Ash lagoon will be the proposed site for IWMF, and WENT extension. Hence the west portion of the Middle Ash Lagoon is selected to be decommissioned to provide buildable land for future government development.
2.4.5. Decommissioning of the PFA lagoon is necessary to provide buildable land for future development. The only alternative will be “no decommissioning of the PFA lagoon”, which will exclude a feasible option for increasing the building land in Hong Kong. This is not preferred in view of current shortage of buildable land in the territory. Besides, an idle ash storage facility without decommissioning may cause adverse environmental impact to the neighbourhood.
2.4.6. The Subject Site and the adjacent areas are currently not covered by any Outline Zoning Plan (OZP). The Planning Department (PlanD) is now preparing a draft OZP for this area. As such, the site is deemed to be a prime location for any future developments. It has more flexibility for the government to develop here than other sites which have already been allocated a specified land use.
2.4.7. As such, the Project aims to provide buildable land for future development by the government, of which a Columbarium by FEHD has been considered, through decommissioning of the western part of the Middle Ash Lagoon at Tsang Tsui, Tuen Mun.
2.5.1. The decommissioning of the Project will commence in September 2015. The proposed completion date is tentatively scheduled for March of 2016. The tentative programme is shown in Table 2.1.
Table 2.1 Construction Programme
|
Activity Description |
Anticipated Date |
|
Commencement
of decommissioning project |
September 2015 |
|
Completion
of decommissioning project |
March 2016 |
2.5.2. Operational phase refers to the period when all construction works within the Subject Site is completed and the development is in full operation. In this Project, it shall be the period when the decommissioning works detailed in Section 2.6 are completed. Since the Project provides a flat buildable land for future development by the government, operational phase shall not be applicable in this Project.
2.6.1. The decommissioning works in the Project shall mainly involve the following:
·
Covering
of 1m thick general fill
above the final PFA surface with minor levelling
works
·
Formation
of Construction Access
Road (North) by filling and levelling followed by layering of a 1m
thick general fill above
the final PFA surface to proposed levels
·
Formation
of part of the Construction Access Road (South) by layering of a 1m thick
general fill above the final PFA surface to proposed levels, followed by
levelling and slope works along the road section approaching to the Site
2.6.2. In addition, associate works in the Project, which will not involve decommissioning, include the following:
·
Minor
reinstating works on part of the existing access road to form the Construction
Access Road (South)
·
Construction
of retaining structure for slope stabilization along the edge of existing water
channel near the north site boundary
·
Installation
of surface drainage outfall system for discharging the surface water out of the
complete buildable land at the north-west corner of the Subject Site
·
Installation
of site hoarding and temporary surface drainage system
2.6.3. The decommissioning works in the Project will mainly involve levelling works followed by the covering of general fill above the levelled final PFA surface. The PFA platform of the Subject Site is expected to have a level of around +10.5mPD upon site handover. It is anticipated to be a dry ground at the commencement of decommissioning works. In order to cater for different future developments, the PFA within the PFA platform of the Subject Site shall be evened into a generally flat surface through levelling works. After levelling the existing PFA surface, general fill will be deposited and compacted to about 1m thick above the existing PFA platform to prevent it from being significantly disturbed due to any future development. The composition of general fill material used shall follow ASD Generation Specification for Building 2012 Edition, Section 3 Excavation and Earthwork. The general fill will be delivered to the site via the Construction Access Roads located to the south of the Subject Site. About two to three backhoes will be required for performing the filling works. The general fill shall be deposited in layers by backhoe and compacted by compaction rollers as per statutory requirements. The general fill material used for filling activities shall mainly consist of natural soil material and rock. In general, about 4 gangs of machines for filling (4 backhoes and 4 vibratory rollers) and 1 dozer will be required.
2.6.4. The Project will not involve any exportation of PFA or soil out of the Subject Site. The existing seawall and vertical seawall surrounding the lagoon will not be alternated during decommissioning and site formation works. The final site level after decommissioning works is anticipated to be about 1m higher than the adjacent areas owing to the 1m general fill cover.
2.6.5. As there is currently no public road which links to the Subject Site, temporary construction access road to connect the Subject Site and Nim Wan Road is considered necessary for the decommissioning works.
2.6.6. An existing paved access road used by CAPCO for their operation is identified. However, the existing road is only 3m in width which do not meet the standard of a normal 2-way-2-lane road, which shall be 7.3m wide. In view of the size, loading and frequency of usage by the construction vehicles during decommissioning works, there is a high risk for two vehicles hitting head-on when running on this narrow road. Therefore, for the safety concern, it is proposed to also make use of another existing vehicular access road formed by CAPCO on the PFA embankment, i.e., the Construction Access Road (North). The existing paved access road will then be construction Access Road (South). The traffic to and from the Subject Site will run on separate roads for better vehicular circulation.
2.6.7. The Construction Access Road Area (North) of approximately 5m wide and 500m long is located at the existing PFA embankment. The PFA embankment was constructed by CAPCO and is currently used by CAPCO for vehicular access to the Middle Ash Lagoon.
2.6.8. Construction Access Road (North) shall be a one-way lane for construction vehicular access, diagonally hatched in Figure 1.1, to direct inbound construction vehicles to the Subject Site. Decommissioning of the Construction Access Road (North) of approximately 0.3 hectare will be required. Levelling works shall be carried out to even the PFA surface. After levelling the existing PFA surface, general fill will be deposited and compacted to about 1m thick above the existing PFA platform to prevent it from being significantly disturbed due to traffic. The general fill material used for filling activities shall mainly consist of natural soil material and rock and it shall follow ASD Generation Specification for Building 2012 Edition, Section 3 Excavation and Earthwork. Backhoes shall be adopted for excavation and levelling works.
2.6.9. It is anticipated that two backhoes and two vibratory rollers will be used during filling and compaction works to form the Construction Access Road (North). The Construction Access Road (North) shall then remain intact upon construction completion to provide vehicular access for future developments.
2.6.10. Construction Access Road (South) will direct outbound construction vehicles away from the Subject Site to cater for the decommissioning works. The road works will comprise of reinstating works, levelling works and slope works.
2.6.11. Part of Construction Access Road (South), which is the honeycomb hatched in Figure 1.1, is an existing one-way lane. It is currently 3m wide at level of about +6.0mPD, and is composed of bitumen, granite, sand and stone. This part of existing access road shall require minor reinstating works, which involves removing of the weeds, repairing the cracked surface, filling up holes by concrete and installing gates and fence of STF boundary.
2.6.12. The existing road level is about +6.0mPD, whereas the PFA platform is about +10.5mPD to 11.5mPD. Part of existing road is therefore required to be modified to match the PFA platform level. The modification work will involve levelling and slope works. This part of access road will be filled up with general fill material and slope works along the road sections, which will include decommissioning of approximately 0.8 hectares (hatch area in Figure 1.1). The final width of The Construction Access Road (South) shall be approximately 15.5m wide. The general fill material used for filling activities shall mainly consist of natural soil material and rock and it shall follow ASD Generation Specification for Building 2012 Edition, Section 3 Excavation and Earthwork.
2.6.13. It is anticipated that two backhoes and two vibratory rollers will be used during filling and compaction works to form the Construction Access Road (South). The Construction Access Road (South) shall then remain intact upon construction completion to provide vehicular access for future developments.
2.6.14. Slope stabilization works would be carried out to the existing slope along the edge of the water channel located along the north site boundary. As currently the slope is steep and formed by loose PFA deposition, the slope stabilization is technically necessary in order to keep the water channel intact and safe from landslide. Slope stabilization works would mainly involve construction of retaining structure, of which the reinforcement earth wall system is proposed subject to detail design. The construction of retaining structure will be located away from the man-made water channel and carried-out in non-breeding season of Little Grebe. Any PFA excavated during the construction of the retaining structure will be relocated within the PFA platform. Details of works may be referred to Appendix 2.1.
2.6.15.
A site surface water drainage
outlet pipe would be constructed at the north-west of the site for future site
storm water drainage purpose. This forms part of the surface drainage outfall
system for avoiding the surface water flowing into the existing water channel.
Its construction shall involve the construction of a 1.05m in diameter pipe
which crosses the existing water channel and connected to a sand trap located
on the existing sea wall. Anchors and pipe rack shall be erected on a strip of
newly filled aggregate across the 30m wide water channel as supporting
structure to the said drainage pipe. No decommissioning to this area is
required. The alignment of drainage pipe is design as close as practicable to
the western end of the man-made channel, whereas Appendix
2.2 details the typical section of the drainage outfall system.
2.6.16. In addition, an area of approximately 1.2 hectare in the middle of the Construction Access Road Area is currently vegetated PFA surface (dots hatched in Figure 1.1) and will not be used during the whole decommissioning period. No decommissioning works will be carried out in this area.
2.6.17.
Machines required for levelling
of general fill at Construction Access Road Area shall not be working
concurrently with the machines for filling works in the Subject Site. Table
2.2 summarizes type and number of construction plants used during
construction.
Table 2.2 Construction Site Plant Equipment Schedule
|
Location |
Equipment Type |
Number of Equipment |
Equipment
Allocation |
|
Subject Site |
Backhoes |
4 |
·
Fill
import and handling: 4 backhoes ·
Backfilling:
4 backhoes and 4 compaction rollers ·
Excavation:
4 backhoes and 1 dozer |
|
Compaction Rollers |
4 |
||
|
Dozers |
1 |
||
|
Construction Access
Road |
Backhoes |
2 |
|
|
Vibratory Roller |
2 |
2.7.1. Potential decommissioning methods are identified as (1) in-situ treatment such as hardening with cement; (2) off site treatment or storage; and (3) covering with soil.
2.7.2. In-situ treatment, such as hardening with cement could chemically and physically fix the PFA in the cement matrix, leading to the stable ground condition. However, this method is considered not feasible, due to the large quantity of cement is required to fix the PFA.
2.7.3. Another alternative method is the removal of all PFA from Subject Site. Taken into account of the relatively stable PFA and its large quantity, disposal of PFA to other storage facilities is not a favourable environmental alternative since it would generate a large amount of PFA as waste. Excavating the PFA to off-site location for recycle and treatment would involve extensive transportation. Moreover, excavation of PFA would pose possible environmental and health hazards to workers due to PFA dust emission during excavation works. In addition, transportation of large amount of PFA for disposal is not a cost-effective option. In addition, there are currently no government-specified location for the disposal of PFA.
2.7.4. Due to the large amount of PFA, exportation of PFA for reproduction of concrete might would require transportation of large quantity of PFA and also a long period of time for consumption. It may cause more environmentally adverse impacts to the public and fail to provide buildable land in the case of the shortage of territory currently.
Covering with Soil
2.7.5. Leaving the PFA in-situ is considered as the most cost and environmental viable option. As such, decommissioning of the Subject Site through covering of 1m thick general fill above the final PFA surface upon minor levelling works is adopted in this Project. Different fill materials such as broken stone, concrete, and other hard inert material, have been considered for filling of PFA areas. However, the import of general fill compared with the aforementioned alternative materials is more cost-effective. Moreover, in the long run, general fill material is easier to manage for any future developments at Subject Site.
Preferred
Decommissioning Method
2.7.6. The Project’s adopted decommissioning method of importing 1m thick general fill to cover the PFA surface aims at cost-effectiveness while minimizing impact on the environment. During the Project, mobilisation and preparation/establishment will be carried out by the Contractor. Careful design of the decommissioning works will be adopted to optimize the import of materials. No surplus construction materials/waste is to be delivered to public fill bank.
2.7.7. To the existing water channel at the north of the Subject Site, one of the options is to fill up the entire water channel to provide more land for future developments. However, in view that the water channel may provide suitable nesting grounds to Little Grebes as breeding habitat during the wet season, filling up the water channel is deemed to cause the ecological impact. In this connection, the current adopted option is considered to reduce the decommissioned area and the construction sequence is carefully phased in order to reduce the Project’s environmental impact to the Little Grebes.
2.7.8. In the current design, slope stabilization works would be carried out to the edge of the water channel to prevent soil loss of water channel through erosion as well as providing a stable habitat. A surface water drainage system would be constructed to discharge future storm water runoff from the Subject Site and prevent adverse environmental impact to the water channel. Such works would provide long-term environmental benefits as well as minimization of habitat loss
2.8.1. The Project is located in the ash lagoon areas which are currently occupied by CAPCO for uses relating to the operation of the Castle Peak Power Stations. Various projects have been proposed in the Nim Wan and Tsang Tsui areas, including the STF, WLES, and the IWMF.
2.8.2. The proposed STF is located in the northern part of East Lagoon. The STF is designed to treat 2,000 wet tonnes/day of the dewatered sludge generated after the sewage treatment process in the Stonecutters Island Sewage Treatment Works and 10 other regional sewage treatment facilities, by fluidized bed incineration technology to substantially reduce the volume of sewage sludge for disposal to landfills. It is under construction and is scheduled to be completed in 2015. In accordance with the latest reply by EPD on 4th July 2014, the construction of the structures for the main facilities and installation of the process plant equipment were substantially completed. Testing of the incineration plant with sludge has commenced since June 2014 for partial commissioning by Nov 2014.
2.8.3.
The planned WLES is also
located in the vicinity of the Subject Site. The WLES forms an integral part in
the strategic plan in maintaining the continuity of landfill capacity in the
West New Territories for the disposal of solid wastes in the next decades. It
occupies the West Lagoon and the southern part of the Middle and East Lagoons
as well as the area between the Black Point Power Station and the existing WENT
Landfill. The WENT Landfill Extension will be developed under six phases to
allow progressive use of the overall landfill area. The site formation of the
Phase 1 is tentatively scheduled to commence in 2016/17.
Integrated Waste Management
Facility (IWMF)
2.8.4. The area directly to the east of the Subject Site is one of the potential sites for the IWMF Phase 1. The purpose for the facilities will be for managing municipal solid waste (MSW). The IWMF Phase 1 will comprise of: (a) an advanced thermal incineration plant with design capacity of 3,000 tonnes per day (tpd) and (b) a mechanical sorting and recycling plant with design capacity of 200 tpd. The non-recyclables sorted from the mechanical plant will be sent to the thermal incineration plant for further treatment. Under any conditions, the total MSW feeding to the thermal incineration plant and the mechanical plant will not exceed 3,000 tpd. There is no programme for the IWMF project at the Tsang Tsui site from September 2015 to March 2016 under which the proposed decommissioning works would be carried out. Hence, it is not considered as a concurrent project under EIA.
2.9.1. The Middle Ash Lagoon has been used for water collection and conservation system since 1997. Freshwater discharged from various systems within the Castle Peak Power Station, together with rainwater from the Subject Site, are fed into the lagoon for storage through a system of pipes. The water can then be pumped back into the power station as and when needed. Upon site handover in 1st quarter of 2015, the Subject Site would become mainly a piece of land covered with PFA, unavailable for use before decommissioning.
2.9.2. A fundamental project alternative is the option to not implement the decommissioning, (including the related site formation, drainage and road works), which in environmental terms is referred to be as the “Do-nothing” option. However, the provision of buildable land is essential in order for the government to provide sufficient facilities to the public. As such, the “Do-nothing” option is not preferred.
2.9.3. Overall, the decommissioning works which consists of covering of 1m thick general fill above the final PFA platform at the Subject Site and Construction Access Road Area would provide buildable land for future developments on the Subject Site and provide environmental benefit as it prevents potential PFA exposure to the Public.