More than 28 megalitres of concentrated saline waste will be produced from the proposed Belmont desalination plant, planning documents show.
The salt would be transferred via a 300 metre pipeline to the wastewater treatment plant before it is discharged into the ocean.
Brine is typically about twice as salty as seawater and is about a degree warmer than the ocean.
An environmental impact statement shows Hunter Water considered discharging the waste into Lake Macquarie, however, the concentration was considered too high for the lake environment to cope with.
"Both the ocean and Lake Macquarie were considered for brine discharge. However, discharging of hypersaline plumes into Lake Macquarie represents a potential issue due to inadequate mixing and has a higher regulatory approval risk," the report says.
Modelling shows the preferred option of ocean discharge will have no environmental or human health impacts.
"Overall, the key finding from the modelling assessment is that the proposed brine-effluent discharge through the existing diffuser is predicted to have the same or smaller areas of impact (or effect) in terms of marine toxicity, marine ecosystem and ambient salinity water quality objectives," the report says.
"...Therefore significant impacts to water quality objectives and associated marine ecology are not likely from the proposed brine-effluent discharge."
The report's estimates are supported by a 2018 study that concluded the effects of brine discharge were not as great as first thought.
The report, published in Water Research, found the Sydney desalination plant had a negligible effect on the offshore ecosystems during the two years it was operating before it was mothballed in mid-2012.
"We're fortunate and relieved that the ecological impacts are minor compared to what people thought might have happened ," Emma Johnston, a professor of marine ecology at the University of NSW said.
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At 100 metres from the outlet points, water salinity was barely distinguishable from the ambient conditions because of the way the brine was successfully spread in the water column, Professor Johnston said.
Construction of the Belmont plant will start when storages drop to between 35 and 40 per cent. If the current trend continues that point is likely to be reached in the middle of next year.
The Department of Planning, Industry and Environment is asking for community feedback on the application.
The proposal is on public exhibition until Thursday 19 December 2019
