The Stonecutters Island Sewage Treatment Works was designed to handle a huge sewage flow of 1.7 million cubic metres per day under HATS Stage 1. For this purpose, a lot of sedimentation tanks occupying a large area would be required. In order to save space, double-decked sedimentation tanks are adopted. In total, there are 38 double-decked sedimentation tanks, each with a plan area of 60m by 7m.