Singapore Public Utilities Board’s (PUB) Deep Tunnel Sewerage System (DTSS) is a two-stage
US$7.3 billion project designed to meet the country’s needs for used water collection, treatment, reclamation and disposal.
Trenchless International speaks to Yong Wei Hin, Project Director of DTSS Phase 2, about the challenges of delivering the system.
DTSS is a cost-effective and sustainable solution from PUB to meet the country’s long-term wastewater needs. The scheme is key to Singapore’s wastewater future, and comprises a network of deep tunnel gravity sewers leading to two major tunnels, a number of water reclamation plants (WRPs) in the north, east and west of the city, and a network of ocean outfall pipes.
Completed in 2008, Phase 1 of the project cost US$2.5 billion and consisted of the construction of a 48 km tunnel from Kranji to Changi, where a WRP was constructed, along with two 5 km long deep sea outfall pipes and 60 km of link sewers.
Mr Hin, who is trained as a civil engineer, was involved in Phase 1 of the DTSS before being appointed as the Project Director of Phase 2 in 2013. He says “I was involved in DTSS Phase 1, specifically in the design, construction, management and commissioning of Changi Water Reclamation Plant (CWRP). I subsequently became the Head of Installation for CWRP in charge of its operations and maintenance.”
The Changi WRP is a state-of-the-art wastewater plant capable of treating 800,000 m3, or 320 Olympic-sized swimming pools, of wastewater a day. After treatment the wastewater, dubbed ‘NEWater’, is released into the ocean through deep sea outfall pipes, or channelled to the Changi NEWater factory on the rooftop of the reclamation plant, for further purification.
Delivering DTSS Phase 2
DTSS Phase 2 will extend the existing deep tunnel system to collect wastewater from the western and southern parts of Singapore. The system will be made up of 60 km of link sewers and 40 km of deep tunnels. Works will also include construction of the Tuas WRP.
Mr Hin says the project will use multiple tunnel boring machines (TBMs) for the construction of the tunnels, which will range from 3-6 m in diameter. He says that the DTSS is integral to Singapore’s water conservation plans of the future.
“As the backbone of NEWater production, DTSS contributes to the goal of increasing Singapore’s overall water recycling rate from 30 per cent to 55 per cent of total water demand in the long term, ensuring water sustainability and resilience for generations
“The DTSS optimises land use for used water infrastructure. For a densely populated city state with limited land, the DTSS is a more strategic and cost-effective solution than the conventional approach of renewing and expanding the existing used water infrastructure.”
The Tuas WRP will be able to treat two streams of wastewater separately, with a total treatment capacity of 800,000 m3. The facility will also be capable of recycling wastewater to produce NEWater. It will feature advanced technologies to enhance energy recovery from wastewater and improve water efficiency, using more biogas for power and consuming lesser energy than conventional plants. Tuas WRP will be located alongside the National Environment Agency’s Integrated Waste Management Facility (IWMF) to maximise energy and resource recovery. The two facilities will work in unison to efficiently break down food waste, in the process producing biogas that will power the IWMF’s incinerators.
Existing WRPs at Ulu Pandan and Jurong, as well as intermediate pumping stations, will be progressively phased out in the finals stages of DTSS, which is expected to be completed by 2025.
Mr Hin explains “The implementation of the entire DTSS will result in a 50 per cent reduction in the land taken up by used water infrastructure, as existing conventional water reclamation plants and intermediate pumping stations will be progressively phased out, freeing up the land for higher value development.”
He says careful planning is going into the technical design of the US$4.8 billion project. Construction of the tunnel system is expected to start next year, before work begins on the Tuas WRP in 2018.
Project challenges and trenchless benefits
As with all major infrastructure project, delivery the DTSS is not without its challenges. Mr Hin says that some of the major hurdles for the projects is coordinating the multiple components needed for successful project delivery.
“One of the main challenges of this project is ensuring that each component, the link sewer, tunnel sewer and the WRP is designed to work as a system. The overall conceptual planning and implementation strategy needs to be thought through meticulously to ensure the smooth execution of the project. In addition, varying ground conditions and limited land area for shafts also pose challenges for tunnel construction.
“There will be both planning and technical challenges in delivering the project. Therefore there is a need to have a strong project delivery team consisting of competent engineers and technical staff to ensure the successful delivery of this project,” he explains.
Project challenges aside, Mr Hin says that Trenchless Technology has been key to minimising the impacts of the project on the community.
“We anticipate minimal impact to the public as the tunnel alignment runs along major expressways and roads, and construction of the deep tunnel and associated link sewers will be largely underground, except at shaft and manhole locations.
“Adequate engagement with the communities located near construction sites will be carried out in advance, to communicate the need for the project and appropriate safety, noise, dust and pollution reduction measures will be put in place,”
In addition to this, the project is expected to stimulate the Singapore’s economy by creating many job opportunities.
For more information visit the DTSS website.
This article was featured in the September edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
If you have a project you would like covered in Trenchless International contact Assistant Editor Nick Lovering at firstname.lastname@example.org