11. Summary of Environmental Outcomes

11.1. Introduction

This section presents the summary of key environmental issues regarding the project decommissioning and construction works at the west portion of the Middle Ash Lagoon at Tsang Tsui, Tuen Mun.

11.2. Air Quality Impact

11.2.1. Air quality impact during the decommissioning and construction stage involve construction dust generated from vehicles emission, material handling, construction access roads, filling activities, wind erosion of open sites and stockpiling areas. Apart from levelling and filling operations, majority of the ash stored at the Subject Site would be left in-situ. Extensive excavation and transportation of ash would not be required and there will be no off-site disposal of PFA in this Project.

11.2.2. As such, with proper implementation of practicable dust suppression measures as mentioned in Section 3.8 and as stipulated in the Air Pollution Control (Construction Dust) Regulation, adverse construction dust impact at the ASRs are not expected during the construction of the Project.

11.2.3. It is anticipated that all areas located within 500m distance from the site boundary shall be protected. 100% of the population identified at the ASRs (including Site offices in WENT Landfill, Sludge Treatment Facilities (STF) and proposed Integrated Waste Management Facilities (IWMF)) shall be protected. The ASRs and its respective estimated population protected are tabulated in Table 11.1.

Table 11.1 Estimated Protected Population through adoption of air quality protection measures

ASR	Sensitive receiver	Distance from Site Boundary (m)	Occupancy Type	Estimated Population
ASR 1	WENT Landfill Site Office ^[1]	217	Office Workers	1823
ASR 2	STF Site Office^[2]	290	Office Workers	152
Total Population				1975

Remarks:

^[1] Site Office calculated from Figure 2.1 of WENT Approved EIA Report (EIA-171/2009)

^[2] Site Office calculated from Figure 2.4 of STF Approved EIA Report (EIA-155/2008)

^[³^] It is assumed that the site offices are 2-storey high. With reference to Table 8 of “Commercial and Industrial floor Space Utilization Survey” by Planning Department, a worker density of 3.4/100m² was used to estimate the worker population

11.3. Health Impact

11.3.1. The possible health risk of Chemicals of Potential Concern (COPCs) was evaluated. The approach of Human Health Risk Assessment from the US Environmental Protection Agency was adopted for identification of potential COPCs. Possible human exposures to COPCs scenarios for the Project mainly involve the inhalations of fugitive dust emissions caused by levelling and filling works. Assessment indicates that the carcinogenic hazard/non carcinogenic hazard all comply with health risk level with reference to the adopted values/levels with the implementation of mitigated measures. Adverse health effects are unlikely to be anticipated.

11.3.2. The potential health risk induced by radon emissions associated with PFA arising from the decommissioning and construction was evaluated through a quantitative assessment, literature review and site measurements. The results indicated that the health impact associated with PFA due to radon emissions would be minimal. Through implementation of mitigation measures, the health effects of radon would be minimal.

11.3.3. The provision of 1m thick general fill will further reduce the human exposures to radon emission and COPCs, adverse health impact after completion of decommissioning work is unlikely to be anticipated.

11.4. Noise Impact

11.4.1. Potential construction noise impacts are likely caused by various construction activities on site, such as, formation of temporary soil embankments, installation of temporary surface drainage system and deposition of the excavated PFA material. Extensive use of powered mechanical equipment use is not anticipated.

11.4.2. Construction noise assessment (Appendix 5.1) concluded that the construction noise impacts associated with the construction activities on the Subject Site would not exceed the noise criteria as specified in the EIAO-TM.

11.4.3. No adverse construction noise impact is anticipated. Nevertheless, good site practices and noise management techniques as detailed in Section 5.4 shall be implemented to minimize noise at source.

11.4.4. No noise sensitive receivers were identified within 300m of the Study Area. Hence, it is anticipated that all areas located within 300m distance from the site boundary and 100% of the population located within the 300m Study Area shall be protected.

11.5. Water Quality Impact

11.5.1. Sources of water quality impact throughout the decommissioning and construction phase include drainage and construction site-runoff, sewage effluent produced by workforce, wastewater generated from general construction activities, and PFA leachate.

11.5.2. The construction runoff discharged from the Subject Site shall fully comply with the standards stated in Section 6.2, otherwise the discharge shall be collected and conveyed to the on-site treatment prior discharge. With proper implementation of construction site mitigation measures and good site practices described in ProPECC PN 1/94, adverse water quality impacts on the WSRs during construction phase is not anticipated.

11.5.3. It is anticipated that 100% of areas and population located within 500m distance from the site boundary shall be protected. Water sensitive receivers including Tsang Kok Stream located to the south of the Subject Site and the Coastal Waters of Deep Bay shall not be subjected to adverse water quality impacts.

11.6. Waste Management

11.6.1. The types of waste that would be generated during the decommissioning and construction phases of the Project include construction and demolition (C&D) materials from the construction activities, general refuse from the workforce and chemical wastes from maintenance of construction equipment.

11.6.2. To reduce potential adverse environmental impacts associated with handling, collection and disposal of waste arising from the Project, the Contractor shall submit a Waste Management Plan (WMP), in accordance with the ETWB TC(W) No.19/2005 so as to provide an overall framework of waste management and reduction.

11.6.3. Provided that the wastes are handled, transported and disposed of properly and good site practices and waste reduction measures are implemented accordingly, adverse environmental impact is not expected during the construction phase of the Project.

11.7. Land Contamination

11.7.1. Land contamination assessment has been conducted based on historical and current land use. Research indicated the construction of protective liners by CLP at the onset to prevent leakage of the stored water and PFA. The historical land use of Subject Site has been for the storage of water and PFA since the 1980s. Hence no impact from land contamination is expected.

11.7.2. The major construction activities at the Subject Site includes decommissioning process which will involve levelling the surface of PFA, followed by the covering of 1m thick natural soil, bringing to a final post-decommissioning level to be +11.5mpD. In order to minimize impact off-site, PFA contaminated water/soil are prevented from leaving the site.

11.7.3. Provided that good site practices are implemented accordingly, adverse environmental impact from land contamination is not expected during the construction phase of the Project. It is therefore anticipate that 100% of site area shall be protected and adverse impact is not anticipated.

11.8. Ecological (Terrestrial and Aquatic) Impact

11.8.1. Major ecological impacts of the proposed Project include loss of about 2.7 hectare of ash platform in the Middle Ash Lagoon, 0.6 hectare of grassland/shrub land and 0.7 hectare of urbanised/disturbed area. The potential impact to Little Grebe has been largely avoided by reduction of decommissioning area and leaving the 30m water channel (potential breeding habitat of Little Grebe) largely unaffected. Construction of retaining wall along the northern edge of the Subject Site for the slope stabilization area had been minimised in scale and only cause negligible loss of open water area.

11.8.2. Construction period of the retaining structure and surface drainage outfall system will be limited to non-breeding season of Little Grebe (the non-breeding season of the Little Grebe is assumed to be dry season, which is November to March in the following year, in accordance with the definition as stated in EIAO Guidance Note No. 7/2010). Moreover, if any nestling activities being observed, no works along the man-made channel should be allowed to avoid potential disturbance. In this connection, the potential adverse impacts are considered minimal and acceptable.

11.8.3. In addition, mitigation measures proposed include installation of hoarding along the boundary of the works areas to minimise disturbance to Little Grebe. Good site practices and precautionary measures should be implemented to avoid encroachment onto the nearby natural habitats, minimise disturbance to wildlife, and ensure good air and water quality. These include but are not limited to on-site treatment of site runoff before discharge, placement of sand bags at fencing near the watercourse and coverage of filled slopes and materials with tarpaulin sheet.

11.8.4. With proper implementation of good site practices and mitigation measures, it is anticipated adverse ecological impact is not anticipated.

11.9. Landfill Gas Hazard

11.9.1. The Project is located within the 250m Consultation Zone of the proposed WENT Landfill Extension. In this connection, a landfill gas hazard assessment is conducted for the Project.

11.9.2. A qualitative assessment of the potential hazards associated with landfill gas hazard has been conducted in accordance to the methodology and requirements set out in Landfill Gas Hazard Assessment (LFGHA) Guidance Note. The landfill gas hazard risk has been classified as MEDIUM for construction workers working outdoors and site office personnel.

11.9.3. Mitigation measures were recommended to ensure the landfill gas hazard risks are minimized, including building protection measures and routine landfill gas monitoring. With the implementation of these measures, no adverse impact of landfill gas hazard on this Project is anticipated.

11.9.4. With proper implementation of good site practices and mitigation measures, it is anticipated that no adverse impact of landfill gas on this Project is anticipated. It is therefore anticipate that all site area and 100% of the population located within Study Area shall be protected and adverse impact is not anticipated.

11.10. Environmental Outcomes

An environmental impact assessment (covering air quality, health impact, noise impact, land contamination, waste management, ecology, landfill gas hazard, and water quality) was completed for the proposed decommissioning works of the Project. The potential environmental impacts are considered transient and minimal. No adverse environmental impacts are envisaged due to the works in accordance with relevant assessment criteria stipulated in the EIAO (TM). Therefore low to negligible adverse residual environmental impact is anticipated.

11.11. Population Protected

This project would influence populations; including on-site workers and workers in WENT Landfill, proposed STF and proposed IWMF, located within the study area. No residential users were identified within study area, the closest residential area, Ha Pak Nai is located 2 km away from the site. With the implementation of relevant mitigation measures, these people would not be significantly affected by the Project.

11.12. Environmentally Sensitive Areas Protected

The major sensitive areas within the Study Area include offices of WENT Landfill, proposed office of STF and proposed office of IWMF. Major habitat includes Middle Ash Lagoon, grassland/shrub land and urbanised/disturbed area. In view that the man-made water channel located at the north of the Subject Site has provided suitable nesting grounds to Little Grebes as breeding habitat during the wet season, the decommissioning area will exclude the man-made water channel to avoid environmental impact to the Little Grebes. 100% of sensitive area within the study area will be protected in various environmental aspects.

11.13. Environmentally Friendly Options and Designs

Environmentally friendly options and designs are summarised below:

· Method of decommissioning of ash lagoon was chosen to be provision of 1m thickness of general fill cover, in order to minimise the movement of PFA;

· The layout of decommissioning work was chosen such that no construction work to be within the man-made water channel to avoid loss of potential habitat area for Little Grebe;

· Decommissioning works near water channel will be carried out in non-breeding season of Little Grebe;

· Construction of retaining structure along the man-made water channel to prevent further soil erosion;

11.14. Key Environmental Problems Avoided

Key environmental problems include potential health impact and ecological impact. Avoidances are summarised below:

· Potential health impact to nearby sensitive receivers to be avoid by provision of 1m thickness of general fill cover;

· Loss of potential habitat area for Little Grebe as work shall be avoid by excluding decommissioning work within the man-made water channel during their breeding season.

11.15. Environmental Benefits of the Environmental Protection Measures

Environmental benefits include the reduction of potential health impact to on-site workers through limiting of PFA emission by provision of cover to non-active construction area; Little Grebe shall be able to nest on the man-made water channel during the breeding season and their potential habitat area shall be protected.

11.16. Site Constraint

After completion of decommissioning, a piece of buildable land at the west part of Middle Ash Lagoon will be created. With provision of 1m in thickness of general fill over the top of ash lagoon, the PFA will be concealed within the site. The associated environmental impacts had been assessed and showed no significant impact will occur after the decommissioning. However, further site development should be aware of PFA underneath the 1m soil layer. Future development design and construction should prevent expose or export the covered PFA with following recommendations:

· Basement design is not recommended to avoid excessive PFA generation requiring large disposal space;

· Piling method is suggested to be designed carefully to minimise disruption of 1m soil protection layer. Piling methods, such bore pile or piling requiring pre-bore should be avoid to prevent excessive exposure of covered PFA or disposal of PFA. If such piling method is deemed to be required, assessment on potential adverse impact should be carried out; and

· For any construction requiring excavation, the extent of excavation should be minimised. The excavation area should be fence-off individually to minimise PFA emission from wind erosion. Excavated area should be backfilled with at least 1m soil cover afterward.