SINGAPORE: The second phase of the Deep Tunnel Sewerage System (DTSS) will incorporate innovative features in order for the infrastructure to last 100 years, national water agency PUB said on Monday (Nov 20).

The features include embedded fibre optic cables for remote monitoring; air jumpers to prevent odorous air from escaping into the surroundings; and additional linings to protect against corrosion from bacteria and other micro-organisms.

This was announced at a groundbreaking ceremony on Monday to commemorate the beginning of construction for DTSS Phase 2, which aims to create a network of 40km of deep tunnels and 60km of link sewers.

When completed in 2025, the 100km of tunnels and sewers – equivalent to the length of about 1,100 football fields – will extend the deep tunnel system to cover the western part of Singapore, including the downtown area and major upcoming developments such as Tengah Town and Jurong Lake District.

“The construction of the conveyance system for DTSS Phase 2 will pose a new set of exciting challenges for us, as we look forward to dig deep to navigate through a variety of ground conditions in the Jurong Formation as well as tunnel beneath existing underground infrastructure and even under the sea”, said the director of DTSS Phase 2 Yong Wei Hin, at the groundbreaking ceremony.

Environment and Water Resources Minister Masagos Zulkifli said planning for DTSS started in the 1990s “with a recognition that this is a costly but critical investment that we needed to make to strengthen our long term water security to benefit Singaporeans for generations to come”. DTSS Phase 2 is a S$6.5 billion project, with deep tunnels and link sewers alone costing about S$2.3 billion. 

The DTSS Phase 2 conveyance system comprises the South Tunnel, which will transport domestic used water, the Industrial Tunnel for non-domestic used water and associated link sewers, which will largely run under the Ayer Rajah Expressway, as well as underwater.

The tunnels in phase two will connect to the existing ones in the first phase, which is currently serving eastern Singapore. When the entire project is completed in 2025, the whole island will be served by the DTSS.

The DTSS is the nation’s way of collecting and transporting used water from the whole of Singapore to three water reclamation plants – Changi, Kranji and soon, Tuas – for treatment.

The water is then treated and purified to become NEWater, or discharged into the sea.

INNOVATIVE FEATURES FOR A LONGER LIFESPAN

According to the plans, the deep tunnels will be lined with two layers to protect against corrosion, particularly from bacteria and other micro-organisms, as well as gaseous fumes in the harsh sewage environment. For underwater tunnels, there is an additional waterproof membrane to ensure water-tightness.

Fibre optic cables will also be embedded in the concrete lining so as to enable remote monitoring of the tunnels’ structural integrity without the need for physical inspection. PUB said this is especially important when there are construction works in the vicinity.

In the event a physical inspection or repairs are needed, gates will be lowered down vertical shafts to temporarily isolate that part of the tunnel. This makes it dry and safe for workers to carry out inspections. During this time, the incoming used water will be diverted to the link sewer network, before it rejoins the tunnel downstream.

The second phase of the DTSS will be the first project in Singapore to use air jumpers, whose aim is to push odorous air rising from the deep tunnel back down. The gas will then flow to Odour Control Facilities – which are located away from residential areas – treated, and then released. The air jumpers will also help cut down the number of OFCs.

Once DTSS phase 2 is completed, the existing water reclamation plants at Ulu Pandan and Jurong, as well as pumping stations, will be shut down. This will enable about 214 football fields of land to be freed up for development, PUB said.

“The DTSS is a more cost-effective and sustainable way of meeting Singapore’s used water needs and securing NEWater supply for the future, than simply renewing and expanding the existing conventional used water infrastructure”, added Mr Yong.  

It’s also one way to deal with the challenges posed by climate change, like prolonged dry seasons and unpredictable weather patterns, said Mr Masagos.

“It is therefore critical to augment our water sources by reclaiming water so that it can be used again and again, in an endless cycle”, he said, adding that Phase 2 of DTSS will further boost Singapore’s NEWater supply.