Changi Outfall

"Conveying Treated Effluent in Singapore"

What's the most effective way to transport treated effluent from a water reclamation plant in Singapore?

That is MWH's challenge for the US $8.3 million Changi Outfall project. The effort is part of Stage 1 of Singapore's comprehensive Deep Tunnel Sewerage System (DTSS).

To be built over two decades, DTSS will consist of two large, deep tunnels that crisscross the island. It will also include two centralized water reclamation plants, deep-sea effluent pipelines and a link sewer network.

Life Span of 100 Years

MWH professionals are designing and supervising the construction of the 5.2KM-long Changi Outfall. This will convey treated effluent, not reclaimed for reuse, from the proposed Changi Water Reclamation Plant to the Straits of Singapore. The new water reclamation plant will serve more than half of Singapore's population of 4.1 million people.

MWH designed the capacity of the Changi Outfall to have a life span of 100 years, and an ultimate capacity of 4,800,000m3/day.

The complex project has presented a number of challenges.

MWH designed and is supervising construction of two parallel reinforced concrete pipes in a single trench. Each pipe measures 3m in internal diameter. To ensure proper alignment of the twin pipes, MWH employed sophisticated marine surveying technology. Marine divers are carrying out underwater inspections during the construction process.

Another challenge is the Changi Outfall is "sandwiched" between underwater fiber-optic communication cables. These are parallel to the proposed trench alignment and Singapore's new Naval Base. During construction, MWH is ensuring proper positioning of anchors to avoid damage to the cables. To avoid disrupting the nation's naval operations, MWH is coordinating closely with the Singapore Navy.

The construction and commissioning of the Changi Outfall is expected to be completed by December 2005.