PB, in joint venture, performed conceptual engineering, engineering investigations, preliminary design, and program and construction management services for the DTSS. The firm’s early investigative work included on-shore geotechnical explorations to determine conditions along prospective alignments. The project was undertaken in three phases:

• Phase 1: Conceptual and preliminary design for Singapore's entire wastewater system.
• Phase 2: Assisting the Government of Singapore in tendering six tunnel design/build contracts that form the North System. PB also prepared the draft tender documents for the design of the link sewers, the new Changi East wastewater treatment plant, and the Changi East Outfall.
• Phase 3: Program management for the six design/build tunnel contracts.

The project is being conducted within a 10-year timeframe, with a scheduled system completion date of 2008. Tunnel excavation was completed in 2005, followed by completion of PB's contract in June 2006 with the commencement of system start-up testing.