Stonecutters Island
The Harbour Area Treatment Scheme (HATS) is a major sewage treatment infrastructure improvement scheme designed to improve the water quality of Victoria Harbour. Originally called the Strategic Sewage Disposal Scheme, the plan was drawn up in 1989 and construction of HATS Stage 1 commenced in 1994. It comprises a system of deep tunnels to convey sewage from eight Preliminary Treatment Works to the Stonecutters Island Sewage Treatment Works, which opened in 1997. The full Stage I system, which treats 75% of the sewage generated by the urban areas around the harbour, came online in December 2001. Construction of HATS Stage 2 commenced in 2008, and stage 2A was commissioned in 2015. HATS Stage 2B, comprising an underground biological treatment facility at Stonecutters Island, has been shelved as it is felt that the existing facility is sufficient at this time.