For discussion
on 11 February 1998


Environmental Protection - Sewerage and sewage treatment
160DS - Tuen Mun sewerage, stage I

Members are invited to recommend to Finance Committee -

  1. the upgrading of part of 160DS, entitled "Tuen Mun sewerage, stage I phase III - enhancement of Siu Hong Road low-flow interceptor", to Category A at an estimated cost of $30.1 million in money-of-the-day prices; and

  2. the retention of the remainder of 160DS in Category B.


The existing Siu Hong Road low-flow interceptor in the Tuen Mun River Channel cannot effectively intercept all the polluted flow from the streamcourses.


2. The Director of Drainage Services, with the support of the Secretary for Planning, Environment and Lands, proposes to upgrade part of 160DS to Category A at an estimated cost of $30.1 million in money-of-the-day (MOD) prices for the Tuen Mun sewerage, stage I phase III works.


3. Project 160DS aims to improve the sewerage system in Tuen Mun. The part of the project we now propose to upgrade to Category A comprises the construction of the following items to improve the performance of the Siu Hong Road low-flow interceptor -

  1. a screening house and ancillary pipework; and

  2. a desilting basin and low-flow channels.

The site plan at Enclosure 1 shows the locations of the proposed works.

4. The remainder of 160DS comprises -

  1. the construction of a pumping station, a rising main and gravity sewers to serve the Siu Lam area; and

  2. the provision of sewerage systems to ten villages, namely Yeung Siu Hang, Kau Hui San Tsuen, Lam Tei/ Tuen Mun San Tsuen, To Yuen Wai, Shun Fung Wai, Nai Wai, Tsing Chuen Wai, Tuen Tse Wai, San Hing Tsuen and Kei Lun Wai.


5. The existing low-flow interceptor in the Tuen Mun River Channel, with a manually-raked screen and a sewer pipe connected to the sewerage system, was built many years ago to intercept the polluted low flow from the streamcourses. The sewer pipe carries the polluted water into the sewerage system for proper treatment and disposal. As more houses have been built in the villages upstream, the polluted flow from the streamcourses has increased significantly. This flow contains rubbish and debris which frequently block the screen of the interceptor, despite regular and extensive cleaning. As a result, polluted water often overflows from the interceptor to the channel while rubbish and debris carried by the flow settle over a large area in the channel. These have become a source of pollution to the Tuen Mun River Channel and the nearby coastal water.

6. We propose to improve the interceptor by replacing the manually-raked screen by an automatic one to reduce the frequency of blockage. We also propose to construct a screening house to enclose the screenings, a desilting basin next to the screening house to control the deposition of rubbish and debris and low-flow channels to guide the polluted river water to the desilting basin and the screening house. After the new interceptor is completed, we will divert the low flow to the desilting basin and screening house and remove the existing screens.


7. We estimate the capital cost of the proposed works to be $30.1 million in MOD prices (see paragraph 8 below), made up as follows -

$ million

(a) Screening house and ancillary pipework


(i) Civil works


(ii) Electrical and mechanical works


(b) Desilting basin and low-flow channels


(c) Contingencies





(at December
1996 prices)

(d) Inflation allowance





(in MOD prices)


8. Subject to approval, we will phase the expenditure as follows -


$ million
(Dec 1996)


$ million

1998 - 99




1999 - 2000




2000 - 01










9. We have derived the MOD estimate on the basis of the Government's forecast of trend labour and construction prices for the period 1998 to 2001. We will tender the civil works and the electrical and mechanical works under fixed price lump sum contracts because we can clearly define the scope of the proposed works. The tender price will not be subject to subsequent adjustment for inflation because the duration of the contract period is less than 21 months.

10. We estimate the annually recurrent expenditure to be $554,310.

11. Based on the current level of water consumption and sewage charges, the annually recurrent expenditure will have negligible impact on sewage charges.


12. We presented the project under 160DS to the Environmental Improvement and District Development Committee of the Tuen Mun District Board on 7 July 1994. Members of the Committee had no objection to the implementation of the project as they have been very concerned about the water quality of the Tuen Mun River Channel and have been requesting Government to take effective measures to improve the situation.


13. The Director of Environmental Protection completed an environmental review in October 1995 and concluded that the project would have no long-term environmental impact and no environmental impact assessment would be required. We shall install forced ventilation and de-odorizers to the enclosed screening house to minimize potential odour nuisance during the operation phase. For short term construction impacts, we shall control noise, dust and site run-off nuisance to within established standards and guidelines through the implementation of mitigation measures in relevant contracts.


14. The proposed works do not require land acquisition.


15. We completed a study in October 1993 under 131DS "Tuen Mun sewerage master plan study - consultants' fees and investigation" to establish a long-term sewerage improvement plan for Tuen Mun. We plan to implement the recommended improvement works in two stages.

16. We upgraded 160DS to Category B in May 1994 for the stage I sewerage improvement in Tuen Mun. We upgraded two parts of it to Category A, one as 196DS entitled "Tuen Mun sewerage, stage I phase I" on 7 July 1995 at an estimated cost of $62.4 million in MOD prices and the other as 280DS entitled "Tuen Mun sewerage, stage I phase II - trunk sewers to Siu Hong Road pumping station" on 19 July 1996 at an estimated cost of $28.9 million in MOD prices.

17. We are ready to proceed with the stage I phase III works. We have completed the detailed design and tender documents for these works using in-house resources. We plan to start construction in July 1998 for completion in January 2000. We plan to start construction of the remaining works under 160DS in February 2000 for completion in September 2002.

18. We upgraded 181DS to Category B in October 1994 for the Tuen Mun sewerage, stage II works. These mainly involve the provision of a sewerage system to the eastern area of Tuen Mun. We plan to start the works in 2000 for completion in 2002.

Planning, Environment and Lands Bureau
January 1998