For discussion PWSC(96-97)48
on 10 July 1996

ITEM FOR PUBLIC WORKS SUBCOMMITTEE
OF FINANCE COMMITTEE

HEAD 704 - DRAINAGE
Environmental Protection - Sewerage and sewage treatment
143DS - Central, Western and Wan Chai West sewerage -
works and identification of individual improper connections

Members are invited to recommend to Finance Committee -

1. the upgrading of part of 143DS, entitled “Central, Western and Wan Chai West sewerage, stage I works”, to Category A at an estimated cost of $1,417 million in money-of-the-day prices; and
2. the retention of the remainder of 143DS, retitled “Central, Western and Wan Chai West sewerage, stage II works” in Category B.

---

PROBLEM
PROPOSAL
PROJECT SCOPE AND NATURE
JUSTIFICATION
FINANCIAL IMPLICATIONS
PUBLIC CONSULTATION
ENVIRONMENTAL IMPLICATIONS
LAND ACQUISITION
BACKGROUND INFORMATION
143DS - Central, Western and Wan Chai West sewerage - works and identification of individual improper connections

---

PROBLEM

Existing sewers in Central, Western and Wan Chai West do not have adequate capacity to serve the areas. Furthermore, expedient connections to the sewerage system have heavily polluted stormwater drains serving the areas.

PROPOSAL

2. The Director of Drainage Services (DDS), with the support of the Secretary for Planning, Environment and Lands, proposes to upgrade part of 143DS to Category A at an estimated cost of $1,417 million in money-of-the-day (MOD) prices for the construction of Central, Western and Wan Chai West sewerage, stage I works.

PROJECT SCOPE AND NATURE

3. The full scope of 143DS comprises the implementation of the sewerage improvement scheme of Central, Western and Wan Chai West and the rectification of expedient connections under two stages. A location plan is at Enclosure I.

4. The part of the project we now propose to upgrade to Category A comprises the construction of the stage I works which include -

1. construction of the Western trunk sewer (2.6 kilometre long and 1 050 mm to 1 800 mm in diameter) from Smithfield to Des Voeux Road West;
2. construction of the Central trunk sewer (0.9 kilometre long and 900 mm to 1 800 mm in diameter) from Pottinger Street to the Central sewage screening plant;
3. construction of the Wan Chai West trunk sewer (2.4 kilometre long and 1 200 mm to 1 800 mm in diameter) from Ice House Street to the Wan Chai East sewage screening plant;
4. construction of interceptor sewers (4.3 kilometre long and 400 mm to 1 500 mm in diameter) and reticulation sewers (14.7 kilometres long and 225 mm to 750 mm in diameter) in Central, Western and Wan Chai West;
5. construction of a new sewage pumping station and associated ancillary works in the existing Central sewage screening plant; and
6. construction of a new sewage pumping station, screening facilities and associated ancillary works in the existing Wan Chai East sewage screening plant.

5. The scope of the stage II works comprises -

1. construction of interceptor sewers (6.6 kilometres long and 225 mm to 1 800 mm in diameter) and reticulation sewers (9.5 kilometres long and 225 mm to 750 mm in diameter) in Central, Western and Wan Chai West;
2. rectification of improper expedient connections; and
3. decommissioning of the Wan Chai West sewage screening plant.

JUSTIFICATION

6. We designed and built the existing sewerage system in Central, Western and Wan Chai more than 50 years ago. As the estimated peak sewage flow of the system¹ has exceeded its hydraulic capacity² , the sewers are unable to meet the existing demand of the areas. Further, we have identified five kilometres of sewers in these areas reaching the end of their useful life. These sewers are in the old urban districts of Central and Western such as the area between Caine Road and Connaught Road Central, Sheung Wan and the area between Queen’s Road East and Johnston Road.

7. Due to the steep slopes, the dense development and the heavily trafficked, narrow roads of these areas, opportunities for the resewerage of the system without creating severe traffic disruption are extremely limited. In the past, we have not made extensive improvement works to the system. With the continuing rapid developments in the sewerage catchment areas, we expect further overloading of the existing sewerage system.

8. In order to provide adequate capacity for the sewerage system to convey sewage to screening plants, we will construct sections of new large trunk sewers at deeper levels, associated interceptor sewers and reticulation sewers in the areas. We have carried out a traffic impact assessment under 176DS “Central, Western and Wan Chai West sewerage, consultants’ fees and investigations”. To minimize traffic disruption, we will maintain road access as far as possible. In busy road sections we will work only in non-peak hours or at night where exceptional circumstances require we do so. In addition, we will employ the “trenchless” method³ for the construction of trunk sewers.

9. The proposed Central trunk sewer will be ten metres deeper than the present one when it reaches the existing Central sewage screening plant. As the Central sewage screening plant was not designed to lift sewage from such a deep level, we propose to construct a new pumping station capable of lifting sewage from both the new, deeper Western trunk sewer and the new Central trunk sewer.

10. In addition, we will increase the capacity of the existing Wan Chai East sewage screening plant from the present 65 660 m³/day to 166 400 m³/day to cater for -

1. the diversion of an expected sewage flow of 96 680 m³/day in 2011 from the Wan Chai West catchment. As part of the Stage II works under 143DS, we will decommission the Wan Chai West sewage screening plant (commissioned in 1987) since it costs about $95 million more to upgrade the plant to meet the expected sewage flow than to divert the flow to the Wan Chai East sewage screening plant. Also, there is not enough space at the Wan Chai West plant for its further upgrading and its location will no longer be compatible with the surrounding environment on completion of the Central and Wan Chai Reclamation. On the decommissioning of the Wan Chai West sewage screening plant in late 2002, the sewage flow will be diverted to the Wan Chai East sewage screening plant;

a projected excess flow of 28 250 m³/day from the Central sewerage catchment by 2011. We expect the sewage flow generated in the Central catchment to increase to 160 250 m³/day. We do not propose to upgrade the Central sewage screening plant to increase its capacity because of site constraints. Moreover, it is more economical to centralise all upgrading works in the Wan Chai East sewage plant which, in any case, would require upgrading for its own catchment; and

an expected sewage flow of 41 470 m³/day by 2011 from the Wan Chai East catchment.

11. We will also construct a new pumping station at the Wan Chai East sewage screening plant to handle the planned increase in sewage flow and to lift the sewage from the new incoming trunk sewer.

FINANCIAL IMPLICATIONS

12. We estimate the capital cost of the proposed works to be $1,417 million in MOD prices, made up as follows -

A breakdown by man months of the estimates for consultants’ fees and resident site staff cost is at Enclosure II.

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

14. We have derived the MOD estimate on the basis of the Government’s forecasts of trend labour and construction prices for the period 1996 to 2002. We will tender the trunk sewers and sewage screening plant civil works under a lump sum contract. We will adopt this form of contract because we will construct the trunk sewers using the trenchless method and we can ascertain the scope of the major part of the works and that of the screening plant civil works. The contract will provide for inflation adjustments to the tender prices as the contract period exceeds 21 months.

15. We will tender the works for the interceptor sewers and reticulation sewers by means of measurement contracts under which we will reimburse the contractor by measuring the amount of works actually carried out on site. This will also allow us to assume more active control over the execution of the works. This contract will also provide for inflation adjustments to the tender price as the contract period exceeds 21 months.

16. We will tender the electrical and mechanical works for the sewage screening plants under a fixed-price, lump-sum contract as the major part of the works will be the supply and installation of electrical and mechanical equipment.

17. We estimate the additional annually recurrent expenditure arising from the proposed sewerage works to be $4.11 million. This expenditure will be a charge to the Sewage Services Trading Fund. Subject to the Legislative Council passing a Resolution on appropriation of assets to the Trading Fund, the sewerage works under this project will, upon completion, become assets in the Fund valued at cost.

PUBLIC CONSULTATION

18. We briefed the Wan Chai District Board on the proposed works including the general temporary traffic arrangements on 11 July 1995 and the Central and Western District Board on 13 July 1995 as well as 7 September 1995. On all these occasions, the District Boards supported the proposal. The Central and Western District Board, however, expressed concern about temporary traffic arrangements. Because of the scope, nature and duration of the project, we shall continue to brief the Boards when actual construction works take place and will carefully work out the temporary traffic arrangements in consultation with the Boards.

ENVIRONMENTAL IMPLICATIONS

19. We completed an Environmental Impact Assessment (EIA) on the construction and operation of the project works in May 1996. The study indicated that odour from the Central and Wan Chai East sewage screening plants is a concern. In accordance with the recommendation of the EIA, we will install odour control facilities⁵ inside the plants to meet established standards and guidelines. We estimate the cost of odour control facilities to be $7 million. This amount has been included in the project estimate.

20. The proposed sewerage works will improve the nearby coastal water quality by re-diverting the sewage, currently discharged untreated into the harbour via stormwater drains, into a proper sewerage system. For short term impact during construction we will control noise, dust and site run-off nuisances through the implementation of mitigation measures in the relevant contracts.

LAND ACQUISITION

21. The proposed works do not require land acquisition

Background INFORMATION

22. We have commissioned a comprehensive study of the sewerage system in the Central, Western and Wan Chai West areas under 111DS “Central, Western and Wan Chai West sewerage masterplan study - consultants’ fees and investigations” at an estimated cost of $12 million. Based on the findings of the study, we have drawn up a sewerage improvement scheme for these areas to provide sufficient sewerage capacity to meet demand up to 2011. Most of the proposed reclamation in Central, Western and Wan Chai will be occupied by that time and the population will reach its peak before 2011.

23. We have identified the seriousness of the problem subsequent to the completion of the sewerage master plan in Central, Western and Wan Chai West areas. DDS has undertaken immediate rectification in three areas (the catchments at Smithfield, Water Street and Jubilee Street). The Director of Territory Development has also taken remedial action in five areas (the catchments at Murray Road, Pedder Street, Gilman Street, Queen Victoria Street and Fleming Road) as part of the Central and Wan Chai reclamation projects.

24. We upgraded 143DS to Category B in March 1994. In April 1994, Finance Committee approved the upgrading to Category A of part of 143DS as 176DS “Central, Western and Wan Chai West sewerage, consultants’ fees and investigations” at an estimated cost of $40.1 million for the engagement of consultants to undertake design and investigation for the works.

25. We will implement the project in two stages. The consultants have completed the detailed design and preparation of tender documents for the stage I works. We intend to start the stage I works in August 1996 for completion in October 2000. The detailed design work and preparation of the tender documents for the stage II works is in progress. We plan to start the stage II works in July 1999 for completion in late 2002.

1 -- The estimated peak flow is a function of the land use, population, water consumption pattern of the sewage catchment upstream of the sewer.
2 -- The hydraulic capacity of a sewer is a function of the pipe size, gradient and material.
3 -- The trenchless method refers to the use of micro-tunnelling or boring techniques to construct underground sewers and drain pipes without opening up the road surface. The method will greatly reduce road excavation and thus minimize disruption to the traffic and underground utilities.
4 -- Pumps and penstocks required as part of the necessary electrical and mechanica equipment are not available in the local market. After we place the order, we will need to attend precision tests at the factory overseas to ensure that the equipment is acceptable before delivery.
5 -- We installed odour control facilities in the Wan Chai West sewage plant in 1993.

---

(LL102)

Enclosure I to PWSC(96-97)48

the site plan not attached

---

Enclosure II to PWSC(96-97)48

143DS - Central, Western and Wan Chai West sewerage - works and identification of individual improper connections

Breakdown of estimates for consultants' fees -

Notes

1. A multiplier factor of 3 is applied to the average MPS point to arrive at the full staff costs including the consultants’ overheads and profit, as the staff will be employed in the consultants’ offices. (At 1.4.95, MPS pt.40 = $51,440 p.m. and MPS pt.16 = $17,270 p.m.) A multiplier factor of 2.1 is applied in the case of site staff supplied by the consultants.
2. The figures given in (a) above are based on the actual fee proposal from the consultants undertaking the investigations, design and construction supervision. The figures given in (b) above are estimates prepared by the Director of Drainage Services.

---