Marine
Seawater will be drawn into the plant and diffused back into the ocean through intake and outlet structures.
To protect marine and coastal environments, the intake and outlet will be tunnelled under the sand dunes, beach and seabed. They will exit the seabed beyond sensitive marine areas.
The Department of Sustainability and Environment’s Capital Projects Division developed a performance-based Environment Effects Statement (EES) and Works Approval Application. It was acknowledged that this project was being delivered as a Public Private Partnership, and that the final design may be different to the ‘Reference Project’ that was developed for the project at the time. The EES and EPA Works Approval Application (EPA WAA) stated that
“The Government has announced that the Victorian Desalination Project (the Project) will be delivered as a Public Private Partnership (PPP) under the Partnerships Victoria policy, and will be operational by the end of 2011.
The delivery of the Project will involve private sector finance, design, construction, commissioning, operation, repair, maintenance and handover of the Desalination Plant and associated infrastructure to facilitate the production and supply of desalinated water. Any works approval obtained by the Proponent is intended to be transferred to the successful bidder (the Project Company) pursuant to the terms of the Environment Protection Act 1970 (the Act). The Project Company will thereafter be solely responsible for compliance with the works approval and any licence subsequently issued by the EPA.
A detailed Reference Design (a design solution for the Project) has been developed for the Project, though the Reference Design may not be the form in which the Project may necessarily be designed and built by the Project Company. In fact, the Project as bid and built by the Project Company will almost certainly differ in some or many respects from the Reference Design.
The benefit of a PPP approach is that it encourages people to think about outputs and outcomes, rather than inputs, and encourages innovative solutions. To foster this innovation, the State has developed a detailed set of outputs known as Performance Requirements, which are intended to be the basis for any contract with the Project Company. The Performance Requirements focus on the outputs that the Project must meet, but they are not prescriptive about how they must be met, except in areas of particular, significance for instance to the environment, where constraints may apply.”
The Performance Requirements, as presented in the EES and EPA WAA, and as assessed by the EES Panel Inquiry, an Independent Expert Group and by the Minister for Planning, form the basis of ensuring the environment is protected. Design and design options are assessed by environment regulators such as the EPA, against these performance requirements, in addition to other conditions of approval required by them.
Building on the EES, AquaSure has undertaken significant investigation work, detailed design and modelling to inform the final design and location of the marine structures.
The investigations include further hydrodynamic modelling, biological studies of marine flora and fauna, water quality, water column habitat surveys, bathymetry surveys of the seabed and the construction of a large-scale physical model in a laboratory to validate results.
The final design passed a comprehensive approvals process, including review by the project’s Independent Reviewer and Environmental Auditor and final assessment by the EPA to assess its compliance with the EPA Works Approval.
The aim of the intake structures is to draw in high quality seawater, with as few impurities and particles as possible, to make it easier to filter and treat the water.
Two intake structures will be constructed. Vertical risers will connect the intake structures to a 1.2 km underground tunnel. They will draw water in so slowly that small fish and other species can easily swim in, out and around the structures. Grilles will be placed over the intake structures to prevent larger sea animals from entering.
The outlet structures will return seawater concentrate to the ocean at the end of the desalination process. Two outlet structures will be constructed. Vertical risers will connect the outlet structures to a 1.5km underground tunnel. The two structures will be fitted with nine diffuser nozzles each, designed to ensure rapid dilution of the seawater concentrate.
Due to the open ocean currents of Bass Strait, the salt content in the mixed water will drop back to standard seawater concentrations within a very short distance of the diffuser nozzles. All discharges will meet the requirements set by the EPA.
Modelling has shown that the two outlet structure design reduces the area of increased salinity. Also, evidence from other desalination plants suggests that the small area in which the seawater concentrate is most concentrated will provide habitat for salt tolerant species such as mussels, sponges and some ascidians.
The EPA will work with the Victorian Desalination Project to monitor operation of the outlet structures, which will be subject to an EPA licence prior to operation.
To see how the intake and outlet structures operate on other Australian desalination projects go to the Gallery section.
