The Environment Protection Authority has given its preliminary advice ahead of BlueScope preparing an Environmental Impact Statement for the massive project, which is planned several years out.

The No.6 blast furnace was "shuttered" in 2011 as BlueScope made dramatic cuts to production and staffing to stabilise its financial position.

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The EPA said the operation of No.5 since then had not been without its problems, which could result in air and water pollutant discharges.

"The current operational [No.5 blast furnace] periodically experiences process upsets and operational instability which can generate problematic air & water discharges such as cast house floor emissions & elevated water pollutant discharges respectively," the EPA's acting unit head Greg Newman wrote to the Department of Planning, Industry and Environment.

"Further, air emissions such as kish and granulator odours occur during routine operations.

"The development of this proposal presents an opportunity to address these matters in the refurbished [furnace]."

Kish is the airborne bulk particulate matter, iron oxide or graphite flakes, that may emerge from the furnace.

BlueScope will set about preparing an Environmental Impact Statement according to comprehensive requirements which have been outlined in the Major Projects planning process.

This will include air and water quality, noise and waste management, and technology to reduce the greenhouse gas emissions of the furnace.

Wollongong City Council said the development process should be used to define how emissions could be reduced using complementary technologies, stating that WCC had declared a climate emergency in 2019.

"BlueScope also has the capability and flexibility to adopt new technologies and iron making configurations in the medium to longer term, as and when they are technically and commercially ready," WCC wrote to DPIE.

"The EIS should detail how this might be achieved. The EIS should also detail opportunities to reduce the emissions intensity from its existing operations by outlining how progressive investment in complementary technologies such as use of renewable energy and additional on-site electricity might be implemented in line with council targets."

The reline has been given Critical State Significant Infrastructure status.

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