For discussion PWSC(96-97)44
on 10 July 1996


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, retitledentitled “Tuen Mun sewerage, stage I, phase II - trunk sewers to Siu Hong Road pumping station”, to Category A at an estimated cost of $28.9 million in money-of-the-day prices; and
  2. the retention of the remainder of 160DS in Category B.


The improper discharge of sewage generated from the Tuen Mun north area into local streamcourses is polluting the Tuen Mun River Channel and the nearby coastal waters.


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 $28.9 million in money-of-the-day (MOD) prices to construct a trunk sewer to serve the Tuen Mun north area.


3. The full scope of 160DS comprises -

  1. the laying of trunk sewers from Castle Peak Road near Nai Wai to Siu Hong Road sewage pumping station;
  2. the modification of the existing Siu Hong Road low flow interceptor;
  3. the construction of a pumping station, rising mains and gravity sewers to serve the Siu Lam area; and
  4. the provision of sewerage systems to ten villages including 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.

4. The part of the project which we now propose to upgrade to Category A comprises the works in paragraph 3(a) above. We will construct trunk sewers of 1.2 km in length with diameters ranging from 600 mm to 900 mm. The sewers will start upstream at Castle Peak Road near Nai Wai and terminate downstream at the existing Siu Hong Road sewage pumping station near Siu Hong Court. The location plan is at the Enclosure.


5. The area north of Siu Hong Court in Tuen Mun does not have adequate public sewerage facilities. This area comprises San Hing Tsuen, Tuen Tsz Wai, Tsing Chuen Wai, Lam Tei, To Yuen Wai, Nai Wai and Shun Fung Wai. At present, sewage from treatment ofprivate lots in this area is treatedis by private septic tanks. After treatment, the sewage flows into stream courses leading to the Tuen Mun River Channel. However, most private owners do not maintain their septic tanks up to the required standard and they rarely carry out regular desludging. Therefore, the tanks are not able to handle the sewage effectively and efficiently. As a result, the treated sewage has affected the water quality in the streamcourse downstream of the Yuen Long - Tuen Mun Corridor (south) area. Recently, during regular water quality monitoring, the Director of Environmental Protection (DEP) classified the water in this area as being ‘very bad’1 .

6. To prevent improperly treated sewage from entering into the streamcourse, we propose to construct new sewers to collect and convey the sewage through the existing Siu Hong Road sewage pumping station to Pillar Point sewage treatment works for proper treatment and disposal.


7. We estimate the capital cost of the works to be $28.9 million in MOD prices (see paragraph 8 below), made up as follows -

$ million

(a) Trunk sewers


(b) Contingency


(at December 1995 prices)


(c) Inflation allowance


(in MOD prices)


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


$ million
(Dec 1995)


$ million

1996 - 97




1997 - 98




1998 - 99




1999 - 00






9. We have derived the MOD estimate on the basis of the Government’s forecast of trend labour and construction prices for the period from1996 to 2000. We will tender the works as a standard re-measurement contract as it involves extensive underground works, the extent and exact quantities of which may vary during the construction stage. 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 for maintenance to be $0.3 million. We will charge this expenditure to the Sewage Services Trading Fund. Subject to resolution passed by the Legislative Council passing a Resolution on appropriation of assets to the Sewerage ServicesTrading Fund, the sewerage works under the project will, upon completion, become assets in the Fund valued at cost.


11. We presented the project under 160DS to the Environmental Improvement and District Development Committee (EIDCC) of the Tuen Mun District Board on 7 July 1994. Members of the Committee EIDCC supported 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.


12. DEP completed an environmental review in connection with the proposed works in October 1995. DEP concluded that the environmental impacts associated with the works would not exceed established standards and guidelines. The proposed sewerage when completed will improve the water quality in the Tuen Mun River Channel and the nearby coastal waters. We will control the site run-off, dust and noise impact during construction through the implementation of standard pollution control measures in the construction contract.


13. The proposed works do not require land acquisition.


14. 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 the area. We decide to implement the recommended improvement works in two stages. Stage I works under 160DS will reduce water pollution in Tuen Mun River Channel. We will implement stage II improvement works under 181DS “Tuen Mun sewerage, stage II” to reduce water pollution in Tai Lam Chung, northen Tuen Mun and Lung Kwu Tan area.

15. We upgraded 160DS to Category B in May 1994. Finance Committee approved the upgrading of part of the project to Category A on 7 July 1995 as 196DS entitled “Tuen Mun sewerage, stage I phase I” at an estimated cost of $62.4 million in MOD prices. We started the works under 196DS in August 1995 for completion in February 1999.

16. The Director of Drainage Services has completed the detailed design and tender documents for the construction of the proposed works in this paper using in-house resources. We intend to start the works in October 1996 for completion in April l998. We intend to start the remaining works under 160DS in July 1998 for completion in December 1999.

17. We upgraded 181DS to Category B in October 1994. We have tentatively scheduled the works under 181DS to start in July 1999 for completion in July 2001.

1 -- Based on the results of regular water quality measurements of dissolved oxygen, five-day biochemical oxygen demand and ammonia nitrogen, DEP classifies river water quality into five grades, namely, 'excellent', 'good', 'fair', 'bad', and 'very bad'

Last Updated on 8 December 1998