Residents contacted the Mercury after the clearing started at Korrongulla Swamp which is adjacent to the Korrongulla Wetland, an annexe of Wollongong's Botanic Garden owned by the city council.

The land was previously owned by the Port Kembla Copper smelter over many years and the company had permission to place waste - slag - from its operations there, under licence from the Environment Protection Authority (EPA).

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Longtime resident Gabrielle Frawley said the land was supposed to have been rehabilitated over the years but this had not happened.

"We didn't know anything at all about it until we heard the noise and saw they'd started to clear the land," she said.

"My concerns are that there is a long history of contamination on that site. The land is in a very neglected, derelict state.

"We are marking time because we don't know what the [development application] is going to be for.

"The main concern is that they are uncovering this slag with the way they're uncovering the land. It's got a lot of dust in it and it's blowing into our properties. It contains high level heavy metals and it needs to be capped so it's not released into the atmosphere."

It is not clear what the plans are for the area.

The Mercury has not been able to contact the owners of the land.

No development applications appear to have been lodged with Wollongong City Council.

Wollongong councillor Ann Martin said residents had spoken to her.

"The concern is that by starting to clear the site, they have potentially exposed soil that is contaminated," she said. "It is rubbish he's clearing or is it trees?

"We need to make sure residents are confident that whatever happens on that site is done properly.

"I have sent emails to council and to the EPA and others saying 'what's going on here?'

"I've checked and the only DA [that was valid] over the years was to remediate the site, and it had lapsed."

She said plans for the site needed to go to consultation, and would have to include a proper contamination study, as well as an Aboriginal heritage study, and more.

Cr Martin said the former approval for waste placement was from many years ago.

"Things were different then," she said.