(WS) In-Situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report
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Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report 12 HAZARD TO LIFE Introduction 12.1 Background 12.1.1 ERM-Hong Kong Ltd (ERM) has been commissioned to conduct a Hazard to Life Assessment (HA) for the In-Situ Reprovisioning of Sha Tin Water Treatment Works (Sha Tin WTW) South Works Project (hereinafter referred to as “the Project”). The hazard assessment is a part of the Environmental Impact Assessment for the Project conducted under the EIAO. The EIA Study Brief is registered as "In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works” (Reference No. ESB-220/2011) and was issued on 9 March 2011. 12.1.1 Requirements for assessment of hazards to life are presented in Section 3.4.3 of the Study Brief. Section 3.4.3.2 stipulates that: The Applicant shall investigate alternative construction methods to avoid the use of explosives. If there is use of explosives for the construction activities and the storage or blasting location is in close proximity to populated areas and/or Potentially Hazardous Installation site (i.e. STWTW), the Applicant shall carry out hazard assessment as follows: (i) Identify hazardous scenarios associated with the transport, storage and use of explosives (including possible damage scenarios to gas and chlorine facilities) and then determine a set of relevant scenarios to be included in a Quantitative Risk Assessment (QRA); (ii) Execute a QRA of the set of hazardous scenarios determined in (i), expressing population risks in both individual and societal terms; (iii) Compare individual and societal risks with the criteria for evaluating hazard to life stipulated in Annex 4 of the TM; and (iv) Identify and assess practicable and cost-effective risk mitigation measures. The methodology to be used in the hazard assessment should be consistent with previous studies having similar issues (e.g. Shatin-to-Central Link (Tai Wai to Hung Hom Section) (ESB-191/2008), and Central Kowloon Route (ESB-156/2006). 12.1.2 Section 3.4.3.3 of the Study Brief stipulates that: The Applicant shall investigate methods to avoid and/or minimize chlorine risks. The Applicant shall carry out hazard assessment to evaluate potential hazard to life during construction and operation stages of the Project due to STWTW. The hazard assessment shall include the following: (i) Identify hazardous scenarios associated with the transport, storage and use of chlorine at STWTW (including possible damage scenarios associated with construction activities, storage of liquid oxygen) and then determine a set of relevant scenarios to be included in a QRA; (ii) Execute a QRA of the set of hazardous scenarios determined in (i), expressing population risks in both individual and societal terms; (iii) Compare individual and societal risks with the criteria for evaluating hazard to life stipulated in Annex 4 of the TM; and (iv) Identify and assess practicable and cost-effective risk mitigation measures. The methodology to be used in the hazard assessment should be consistent with previous studies having similar issues (e.g. Shatin-to-Central Link (Tai Wai to Hung Hom Section) (ESB-191/2008), and Integration of Siu Ho Wan and Silver Mine Bay Water Treatment Works (ESB-150/2006)). 12.1.3 The scope section of the Study Brief also states (Section 3.2.2 (vi)): Potential hazard to life on construction workers, operational staff and other sensitive receivers to be identified, with STWTW is Potentially Hazardous Installations (PHI) due to the use of liquid chlorine on site and the Beacon Hill North Offtake Station and its associated 750mm diameter high pressure gas 12-1 December 2014 Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report pipeline that runs through the old Beacon Hill Tunnel, and the possible use of explosives for blasting if applicable. 12.1.4 As required by the Study Brief, this assessment concerns hazards related to transport, storage and use of chlorine at Sha Tin WTW (STWTW) during the Construction Phase (South Works reprovisioning works) and Operational Phase of the Project (after the project completion). The approach adopted follows that of previous studies having similar issues. 12.1.5 Hazards relating to liquid oxygen are not included in the assessment as it has been confirmed that there will be no storage of liquid oxygen at Sha Tin WTW. Also, there will be no use of explosives and hence this is not considered further in the assessment. Further, it has been confirmed by HKCG that there are no high pressure gas pipelines running through the old Beacon Hill Tunnel. 12.1.6 Additional hazard to life requirements are also formulated in Section 2.1 (v) of the Study Brief, which as one of the objectives of the EIA Study specifies: To identify and assess the potential risk to human life due to the construction works impact on the operation of the existing PHI (Chlorine Store), the 400kV overhead power line and other notifiable gas installations (NGIs), e.g. Beacon Hill North Offtake Station present or in the vicinity of Project site and to propose measures to mitigate these impacts. These issues are also addressed in relevant sections of this assessment. 12.2 Hong Kong Risk Guidelines and Other Relevant Legislation 12.2.1 Hong Kong Risk Guidelines (HKRG) for Designated Projects are defined in Annex 4 of the Technical Memorandum to Environmental Impact Assessment Process (EIAO-TM) in terms of individual and societal risks as follows: x Maximum level of off-site individual risk should not exceed 1 in 100000 per year, i.e. 1 × 10-5 per year; and x Societal Risk Guidelines as stipulated in EIAO-TM are shown in Figure 12.1. For definitions of the individual and societal risk measures see Section 12.12. 12-2 December 2014 Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report Figure 12.1 Societal Risk Guidelines for Acceptable Risk Levels (EIAO-TM) 12.2.2 The Sha Tin WTW is designated as a Potentially Hazardous Installation (PHI) owing to its use and storage of chlorine in 1-tonne (1t) drums. A Consultation Zone (CZ), centred at the Chlorination House, of 1000m radius but excluding the areas located at over 150 m above sea level is established around the WTW (Figure 12.2). The Hong Kong Planning Standards and Guidelines (HKPSG), Chapter 12, require that PHIs comply with Hong Kong Risk Guidelines as described above. 12-3 December 2014 Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report Figure 12.2 Sha Tin WTW Location and Consultation Zone 12.3 Sha Tin Water Treatment Works: Location and Operations Location 12.3.1 Sha Tin WTW lies at the head of a valley on Keng Hau Road, Hin Tin to the south-west of Sha Tin new town. The site is approximately rectangular in shape and measures 400 m north to south by 300 m east to west. The treatment plant comprises a South Works and a North Works. The Chlorination House is located in the south-west corner of the site. The site location is shown in Figure 12.2 and the existing site layout in Figure 12.3. 12.3.2 Sha Tin WTW is located at 30 m above the Principal Datum (PD) and is surrounded on three sides by hills rising to approximately 300 m. To the north-east the land slopes gently downwards towards the town of Sha Tin. The topography is of particular relevance; since chlorine is a dense gas, the spread of a chlorine cloud from any large release would be restricted by the neighbouring hills and directed towards the populated areas. The topography of the site is shown in Figure 12.4. 12-4 December 2014 Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report Figure 12.3 Existing Layout of Sha Tin WTW Figure 12.4 Topography of the Sha Tin WTW Area (not to scale) Sha Tin WTW Delivery, Storage and Handling of Chlorine 12.3.3 Chlorine is delivered to Sha Tin WTW in batches of up to 6×1-tonne drums. Unloading takes place inside the Chlorination House, with the doors closed, in a designated truck unloading bay. The movement of drums within the storage area and ‘drive-through’ unloading bay is carried out using a 12-5 December 2014 Agreement No. CE 13/2009 (WS) In-situ Reprovisioning of Sha Tin Water Treatment Works – South Works Water Supplies Department Environmental Impact Assessment Report hoist/monorail system with a purpose-built lifting beam. Prior to usage, the drums are stored on cradles within the chlorine storage area. 12.3.4 The on-site chlorine delivery route is shown in Figure 12.6. Chlorination System 12.3.5 The draw-off units comprise of pairs of drums, one drum on duty, the other serving as standby. The number of drums on line is subject to the raw water quality. Changeover panels automatically change the draw-off from duty to standby when the draw-off pressure falls below a preset level. The changeover is achieved by electrically-actuated isolating valves provided for each drum. 12.3.6 Liquid chlorine is drawn from the 1-tonne drums and is passed to the evaporators for conversion into the gaseous state.