Harbour Area Treatment Scheme Background
To improve the water quality of Victoria Harbour, the Harbour Area Treatment Scheme (HATS), formerly known as the Strategic Sewage Disposal Scheme, was launched in the late 1980’s. The project was implemented in stages for the collection and treatment of sewage arising from the urban areas around the Harbour. The Stage 1 Scheme was commissioned in 2001 and the Stage 2A Scheme in 2015. For more information of HATS, please click here.
Maintenance and Replacement of Electrical and Mechanical Facilities
The Drainage Services Department (DSD) will be conducting maintenance and replacement of electrical and mechanical facilities in the Stonecutters Island Sewage Treatment Works (SCISTW) in the dry seasons between February 2018 and early 2020.
The SCISTW has been in uninterrupted 24-hour operation over the past 17 years since first commissioning in December 2001. Throughout the time, DSD has been providing timely maintenance to it, while maintaining normal operation of the whole system.
Among the numerous facilities in the SCISTW, there are two large-scale penstocks located at 34 metre depth on the periphery of Main Pumping Station No.1, which constitute a uniquely complicated situation. After long and continuous operation, these penstocks are approaching the end of their normal service life and need replacement in order to ensure continued proper functioning of the HATS. The replacement works require partial bypass of preliminarily treated sewage at the upstream preliminary treatment works into Victoria Harbour for five episodes, each not exceeding two weeks in duration. The first bypass is scheduled for February 20 to March 5.
Details of Bypass
Sewage bypass involves the submarine discharge of preliminarily treated sewage at 7 of the 16 preliminary treatment works located on either side of Victoria Harbour (namely, Chai Wan, Shau Kei Wan, Tseung Kwan O, Kwun Tong, To Kwa Wan, Tsing Yi and Kwai Chung preliminary treatment works) for dilution and dispersion at deep sea level. Affected areas include the waters of Hong Kong Island East, Kowloon East and the Rambler Channel.
The sewage bypass would only involve the above-mentioned 7 preliminary treatment works of HATS Stage 1. The other parts of HATS Stage 1 and HATS Stage 2A system are not affected and will maintain normal operation. The bypassed portion constitutes around 55% of the total flows to the HATS system.
Water Quality Monitoring
DSD has employed consultants to conduct a detailed assessment of potential water quality impacts of the bypass through water quality modelling. The assessment indicated that the potential impacts would be limited and transient. DSD has devised appropriate mitigation measures and related contingency plans, and will step up water quality monitoring in Victoria Harbour during the bypass. Please click here for the monitoring results.
Potentially Affected Areas
DSD would like to advise the public not to engage in water sports, angling or seawater extraction at the potentially affected locations during the bypass periods. Notices will be put up at relevant places including Approach Beach, Ting Kau Beach, Lido Beach, Casam Beach, Hoi Mei Wan, Gemini Beach, Anglers’ Beach, Ma Wan Tung Wan, promenades along Victoria Harbour, etc. to remind the public of the potential effect of the works.
[Information Update (August 1, 2018)]
The First Bypass
The first bypass has been carried out from 20 February 2018 to 4 March 2018. The scheduled works, including detailed surveys and partial dismantling of the existing penstocks, were completed as planned.
Water Quality Monitoring Results
Water quality monitoring results of the first bypass revealed water quality in the Harbour was generally in line with that predicted in the previous modelling, and similar to the baseline level before the bypass. Water quality resumed normal quickly after the end of bypass within a few days’ time.
Next Stage of Works
DSD is planning for the next stage of maintenance and replacement works. As scheduled, two episodes of bypass would be carried out in November 2018 and March 2019, each not exceeding two weeks in duration. Same as the first bypass, DSD would implement appropriate mitigation measures to minimize the potential environmental impacts. We would keep reviewing the progress of works and strive to minimize the overall duration of bypasses.
[Information Update (20 Feburary 2019)]
The second bypass has been carried out from 5 to 16 November 2018. The schedule works including the installation of temporary bulkheads were completed as planned. Further to the installation of temporary bulkhead in the second bypass, replacement of the penstocks at Main Pumping Station No. 1 is anticipated to be completed by March 2019, and therefore the third bypass for the removal of the temporary bulkhead is scheduled to take place from 4 to 17 March 2019.
[Information Update (22 May 2019)]
The third bypass has been carried out from 4 to 17 March 2019. The penstocks replacement works were completed successfully in March 2019 and the numbers of bypass were reduced from 5 times to 3 times to minimize the nuisance to the public.