PUB completes tunnelling works for Phase 2 of DTSS to convey used water via gravity in Singapore

PUB, Singapore’s National Water Agency, has concluded tunnelling works for the second phase of the Deep Tunnel Sewerage System (DTSS), which involves the construction of a 98km-long network of deep tunnels and link sewers, and the future Tuas Water Reclamation Plant (WRP).

Costing around S$10bn and designed to last for 100 years, the implementation of the entire DTSS will allow PUB to reduce the overall land footprint of the used water system across Singapore by half, freeing up to 150 hectares of land, nearly twice the size of Singapore Botanic Gardens.

Over two phases, the DTSS comprises a 206km-long network of deep tunnels and link sewers that will convey used water entirely via gravity to three centralised water reclamation plants located in Changi, Kranji and Tuas. Phase 1 of the DTSS serves the eastern half of Singapore and was completed in 2008.

The DTSS Phase 2 project, which commenced in 2019, involved over 5,000 workers at the peak of its construction works. These new infrastructure components extend the DTSS network to serve the western half of Singapore, including the downtown area and upcoming developments such as Tengah Town and Jurong Lake District.

The future Tuas WRP will be able to treat 650,000m3 of domestic used water per day, and 150,000m3 of industrial used water per day. Tuas WRP will be co-located with NEA Integrated Waste Management Facility to form Tuas Nexus, which is said to be Singapore’s first integrated used water and solid waste treatment facility that will be fully energy self-sufficient.

Further, the conveyance of used water via gravity instead of pumping stations reportedly enhances the robustness of the used water collection system. It is said to enable PUB to reclaim and recycle water in an endless cycle, boosting the capacity to produce NEWater, Singapore’s third National Tap. This also eliminates the risk of pollution in rainwater catchments.

The Phase 2 project also implemented new features such as the use of concrete resistant to microbiological-influenced corrosion, isolation gates to allow for flow diversion, fibre optic cables for remote monitoring of a tunnel’s structural integrity, and the use of air jumpers to control air flow within the tunnels.

Tunnelling work for Phase 2 had to be carried out by five different contractors, using pioneering construction methods and smart technologies for safe operations which served to reduce disruption to above-ground infrastructure and the public.

On 21 Aug 2023, a ceremony to mark this milestone was attended by Ms Grace Fu, Minister for Sustainability and the Environment, and more than 300 guests including pioneer engineers who started the DTSS project which was conceived in the 1990s to transform the country’s used water management system.

In a statement, PUB CEO Goh Si Hou said DTSS is a “engineering feat” “in strengthening Singapore’s water resilience to meet the long-term challenges of climate change and growing water needs.”

“This has been made possible through the vision of our pioneers, and decades of planning by our engineers and contractors,” he added. “We look forward to the upcoming completion of our water reclamation and NEWater plants, which will realise the full potential of DTSS in the years to come.”

Images: PUB