The Environmental Protection Authority has approved Water Corporation plans to double the amount of treated sewage being injected into Perth's aquifers.
Stage 1 of the Perth Groundwater Replenishment Scheme scheme began at the end of 2016 with a Craigie treatment plant completing advanced purification then pumping the treated wastewater into the Gnangara aquifer at a rate of 14 billion litres a year.
The approval of the Stage 2 means another 14 billion litres annually will be pumped into the two aquifers below it, the Leederville and Yarragadee aquifers.
Water Corp would then take the same amount of groundwater from other areas for Perth's drinking supply.
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The proposal involves building another sewage treatment plant at the Craigie facility and a 12.8-kilometre pipeline to pipe the highly treated water, once it meets drinking water standards, to two existing "recharge facilities" in the City of Wanneroo.
The Leederville aquifer is often several hundred metres thick, and in some areas connects with the surface, creating wetlands and lakes.
Yarragadee, the oldest aquifer, provides a robust supply even in dry years because of its vast storage and limited connection to the surface environment, according to the Water Corporation.
Over the past 10 years Water Corp has expanded use of Yarragadee for Perth drinking water while reducing use of groundwater from superficial aquifers, lessening impacts on some wetlands and lakes.
Advanced wastewater treatment to 'top up' aquifers was a key part of its 50-year water source plan completed in 2009, which aims to ensure water supply resilience in a drying climate.
Perth is blazing the trail on this technology, repeatedly rejected by communities across Australia including in New South Wales and Queensland.
EPA chairman Tom Hatton said the proposal, including the pipeline, required clearing 2.19 hectares of native vegetation and the Water Corp would use tunnelling techniques to minimise impacts.
"Some sections of the pipeline would be constructed using technologies such as microtunnelling or horizontal directional drilling to avoid the clearing of native vegetation in sensitive Banksia woodland," he said.
The Corporation would also be required to ensure there are no indirect impacts to Banksia woodlands - now declared threatened by the federal government - within five years post construction.
The EPA has recommended Environment Minister Stephen Dawson impose conditions on the development including implementing hygiene protocols, undertaking weed control, treating and managing acid sulfate soils, and minimising impacts to animals during construction.
The EPA's report to the Minister is now open for a two-week public appeal period, closing June 12.
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