Water Journal : Water Journal December 2012
refereed paper sustainability water DECEMBER 2012 85 After considering the sustainability of each option, the relative risk, the community cost, and sensitivity of critical assumptions to alternative scenarios, collecting stormwater from a 160ha portion of the total development and treating it locally to potable standard came up most favourable (Wilson, 2010). A challenge with this project, and common to most projects aspiring to deliver better community outcomes, is that one entity may have to spend more than they would normally have had to, for others to realise these community benefits. In this case, the project only progressed because the Federal Government’s National Urban Water and Desalination Plan – Stormwater Harvesting and Reuse Projects Fund paid this difference. The scheme is presently being constructed at a cost of $21.3m and will be completed by June 2013. It will involve stormwater being harvested from the local urban catchment area via the conventional drainage system. Through the processes of natural filtration and bio-remediation, the wetlands will reduce nutrient and suspended sediment loads. Stormwater will flow by gravity from the wetlands into a 5m deep, 65ML raw water storage. Water balance modelling using the computerised hydraulic modelling software, InfoWorks, showed that the storage size will enable the potable water treatment plant to operate with an average reliability of 90%. Water will then be pumped to a nearby 1ML/ day water treatment plant designed to produce drinking standard water. It includes powdered activated carbon (PAC) dosing and coagulation, dissolved air filtration flotation (DAFF), ultra filtration (UF), advanced oxidation, granulated activated carbon (GAC), and chlorination. The Kalkallo project will demonstrate how a new development can be constructed in a greenfield site to reduce the net volume of imported water by up to 90%, decrease the urban runoff and nutrient discharged into the local stream by 45% and 25% respectively above existing best practice, use 75% less energy than desalination, and can recover the upfront capital and ongoing operational costs within a 25-year period. in-fill sites: Doncaster hill Melbourne has designated a number of high-density infill sites across the city. The intent is to encourage infill development at transport hubs and commercial centres. Thirty-three high-density infill sites have been identified within Yarra Valley Water’s service area that accordingly will need to be serviced in the future. Doncaster Hill is one of the first infill sites to be developed. The proposed Doncaster Hill Development Precinct is located approximately 20km east of the Melbourne CBD and is spread over an area of 58ha. Currently, the Doncaster Hill area is dominated by Doncaster Shopping Centre and has several other low-rise offices and retail outlets. The planned redevelopment of the region will see a number of high-rise apartment buildings constructed, increasing densification and adding up to 4,000 new dwellings. The desire for a more sustainable urban water solution was shared by Manningham City Council, Melbourne Water and Yarra Valley Water, and was consolidated in a Memorandum of Understanding (MoU). Having set the conceptual objectives the collective group engaged MWH and Bonacci to analyse all potential urban water solutions to determine which was the most sustainable for this location. A number of alternative servicing strategies were considered, including the use of rainwater tanks, stormwater capture and re-use, and the supply of Class A recycled water from treated sewage (Coombes et al., 2010). The selection of the recommended option was assessed against the sustainability objectives established in the MoU. Output from the options analysis was then used by Yarra Valley Water to develop a business case. The challenge with this project was that Yarra Valley Water had to fund an option that was more expensive to them than a traditional service – in this instance the business selected to fund the additional works. This was possible because the alternative option still returned a positive Net Present Value (NPV) (Mathieson, 2011). Sewer mining was finally selected as the preferred servicing strategy, as it provides a source of water that is not dependent on rainfall. A centralised sewer mining facility will treat sewage from a large sewer to a Class A recycled water standard and then supply it to developments via a third pipe reticulation system. Based on estimated demand and growth projections, the recycled water treatment plant will have a capacity of 35KL/day. Sewage will be sourced from the 825mm sewer from the Koonung Creek main sewer located about 1km away. A membrane bioreactor (MBR), ultra filtration (UF), ultraviolet (UV) and chlorination are being used to treat the wastewater. The Doncaster Hill project will demonstrate how a new development at in infill site can be constructed to reduce the net volume of imported water by up to 64%, decrease the urban stormwater runoff into the local stream by 42%, discharge 53% less wastewater, and use 54% less energy than desalination. Backlog areas: Kinglake Yarra Valley Water has about 17,000 properties that currently have failing septic systems that require upgrading. Many of these are located in peri-urban Figure 2. Doncaster Hill is an example of how an infill site can be serviced using 64% less reticulated water, discharge 42% less stormwater, discharge 53% less wastewater and use 54% less energy.
Water Journal February 2013
Water Journal November 2012-1