Civil Engineering June 2022 | Vol 30 No 5

The process of producing potable water starts with raw water from Spring Grove Dam being pumped into a channel, where treatment chemicals such as lime and coagulant are added. The chemicals are stored and supplied from a dry chemical building, located alongside the channel. The required mixing energy is achieved by means of hydraulic jumps throughout the channel. The water then enters the pulsator clarifiers, where up to 3 Mℓ of water pulsates to flocculate the foreign products from the raw water. The clarified water then flows by gravity into rapid gravity sand filters, using silica sand as filtration media to achieve turbidity <0.5 NTU. The final stage is the addition of chlorine for disinfection, before the potable water is stored in an on-site 5 Mℓ water reservoir, ready for discharge to the various down- stream storage reservoirs. A pumpstation was also constructed with two pump sets – one duty pump and one standby pump with a capacity of 836 m 3 /hr and 556 m 3 /hr respectively – for the Nottingham Road and Bruntville communities. Due to the hydraulics of the design, 17 000 ℓ and 14 000 ℓ surge tank vessels were also installed. The whole process is controlled via a SCADA system, which includes online quality monitoring instruments that re- cord the quality of the water at each stage of the process. The waste products from the pulsators and filters are routed to the sludge treatment facility where the water is separated from the solids via a centri- fuge. The wastewater is then recycled into the treatment process to ensure zero discharge to the environment. The dried solids are stored in storage skips. CONSTRUCTION TECHNIQUES OVERVIEW Geotechnical The site for the water treatment plant is on the slope of a hill where the drop in elevation is 45 m over the 200 m length of the site, with a high groundwater table. Subsoil drains were installed to deal with this groundwater. The ground was a silty clay with a plasticity index averaging 21. It was decided that an imported G5 layer of between 0.5 m and 1 m thick would need to be placed before any loadbearing struc- ture could be constructed. Civil Engineering June 2022 9 5 Mℓ reservoir and chorine plant Contact tanks under construction