The mammoth project consists of two cross-island tunnels and a network of link sewers that intercept sewage flows from the existing sewer reticulation system to two centralised wastewater treatment plants located at Changi East and Jurong Island reclamation areas.

The  Deep Tunnel Sewerage System Contract T-04 (Ang Mo Kio Tunnel) comprises a 7.2 kilometre long and 30 to 40 metre deep bored tunnel of 4.3 metre internal diameter, including drop shafts, access shafts, work shafts, odour control facilities, 800 metre long lateral connector and other underground wastewater structures.

The Queensway Tunnel comprises a 9.7km long and 30-45m deep bored tunnel of 3.3m internal diameter, including drop shaft, access shafts, work shafts and other underground wastewater structures. Ground material is generally of rock, soil and/or mixed-face conditions.a 9.7km long and 30-45m deep bored tunnel of 3.3m internal diameter, including drop shaft, access shafts, work shafts and other underground wastewater structures. Ground material is generally of rock, soil and/or mixed-face conditions.