Building underground tunnels for wastewater management very costly

Underground tunnels. Photo courtesy of SSD.

KUCHING, Sept 4: Two-thirds of the RM750 million allocation for Package 2 of the Kuching City Wastewater Management System in Petra Jaya will be spent on making underground tunnels with depths of up to 35m.

Sewerage Services Department (SSD) Sarawak director Lau Hieng Ung said the massive underground work required RM500 million because it comprised 7km of major trunk sewer (of between 4-5 feet in diameter) and about 30km of secondary (2 feet in diameter) and tertiary sewers (1 foot in diameter).

“It’s a very specialised work. In addition, the tunneling machine is also very expensive,” Lau told DayakDaily in an exclusive interview here today.


He disclosed that the technology deployed was based on an advanced Japanese tunneling technology used by the Kumpulan-Nishimatsu-Hock Seng Lee Consortium, which successfully completed Phase I at a cost of RM530 million in 2015.

The tunneling process starts from major manholes. Photo courtesy of SSD.

Work on Package 2 started in Sept 15 last year and is now 3.9 per cent completed. Overall, there would be 45 major manholes, where seven have been completed.

Package 2 is part of the Kuching Centralised Sewerage System, which commenced with the commissioning of a master plan in 2003 followed by the implementation of Phase 1 in 2008. The total cost of the sewerage master plan will cost RM4 billion.

Lau said the state government would continue to bid for more funds to complete the master plan in order to protect the environment and to improve the quality of water in Sarawak River.

“The main objective of the sewerage master plan is to ensure that all used water must be collected before being discharged into the environment. This way we can have a better quality environment and source of water supply,” Lau explained.

He added that once the whole sewerage master plan was completed, it would be able to provide sewerage services to 800,000 population equivalent (PE), which covers Kuching City right up to 5th Mile.

At the initial stage of construction, the progress would be rather slow due to many factors, including carrying out soil investigation/test and to carry out ‘pilot trenching’ to find the most suitable locations for the major manholes for the main trunk in the area, which will be covered under Phase 2, he said.

‘Pilot trenching’ is a process where the contractor scouts for the best locations for the major manholes so as to avoid cables and water mains.

“We need to avoid disrupting public utility cables and water mains so as to prevent public inconveniences,” he stressed.

Lau believed the project should be completed as scheduled — in 2023.

A photo of a major manhole. Photo courtesy of SSD.

Package 2 will provide sewerage services to 40,000 PE in Petra Jaya areas, such as Jalan Astana and Kampung Gita.

Package 1 covers the densely populated area of Kuching City from Satok and Wisma Saberkas right up to Padungan area, including housing areas, commercial centres and hotels. The tunnels covered a massive distance of 64.1km and with a depth of between 6m-27m. It has been able to provide sewerage services to up to 100,000 PE. The areas covered under Package 1 are mostly commercial and hotels in the city’s golden triangle area.

The sewerage service process both the black and grey water from the city’s main centre which is treated at a sewerage plant near the former Zecon Plaza. The treatment plant has an operational capacity of up to 100,000 PE.

Tertiary tunnels connecting residential areas. Photo courtesy of SSD.

Black water refers to the waste water from the septic tanks, while grey water refers to water discharge from kitchens, bathrooms and washing areas.

The sewerage system will collect and treat both the black and grey water to standard A, which would then be released to the Sarawak River. This ensures that Sarawak River will remain healthy. — DayakDaily