Deep Tunnel Sewerage System (Phase 1), Singapore

What is it? A conceptually stunning US$2.5 billion deep tunnel sewer system to meet Singapore's needs for wastewater collection, treatment and disposal for the next 100 years. Phase 1 of the scheme was completed in 2008, and comprises a 48km-long deep tunnel, a centralised water reclamation plant, a network of link sewers and a deep-sea outfall.

Who is responsible? Singapore's PUB is the client. CH2M Hill and Parsons Brinckerhoff conducted the feasibility study. MWH provided design and construction supervision of the outfall. Phase one of the DTSS project involved 49 main contractors and consultants, and more than 300 sub-contractors and suppliers.

Why is it shortlisted?

• The deep tunnel sewer system (DTSS) is a major step towards ensuring the long-term sustainability of Singapore's water resources. With a diameter of up to six metres, the 48km-long North Tunnel was built in six phases along a specially selected route at a depth of up to 50 metres below ground, using trenchless technology. The colossal engineering challenge is matched only by PUB's visionary foresight.

• The Changi Water Reclamation Plant, completed in 2008, will initially treat 800,000m3/d of gravity-fed wastewater from the deep tunnel. The plant is mainly built underground, and its compact design means it occupies less than a third of the area needed for a conventional layout. The treated effluent will be used to produce NEWater at a unique second plant, which will be built on the roof of the Changi WRP.

• The implementation of the DTSS will have far-reaching effects beyond wastewater treatment and reuse. Land comes at a premium in Singapore, and the decommissioning of old pumping stations and wastewater treatment plants will free up valuable land for other uses.