Ironbridge was more likely to lean towards a trade sale than an IPO because local institutions had in the past shown a reluctance to pay a full price for similar assets, the source said.
Macquarie has worked with Ironbridge regularly over the past few years.
EnviroWaste is chaired by Kim Ellis, the former chief executive of NZX-listed Waste Management before the company was taken over in 2006 by Australia's Transpacific Holdings.
Ironbridge paid $365 million in December 2006 for EnviroWaste but the company later sold an asset in Canterbury to its competitor, Transpacific.
EnviroWaste later invested in acquisitions which took the invested amount back to around $365 million.
Unlike last year's IPOs, which involved only partial selldowns and listings of companies such as Summerset Holdings and Trade Me, Ironbridge could be looking at offloading 100 per cent, a financial market source said last month.
EnviroWaste's assets include the Hampton Downs landfill.
Meanwhile, Ironbridge confirmed yesterday its restructuring plan for MediaWorks had still not been finalised, and it is understood that until it is TPG is lurking in the background.
On March 1, Ironbridge announced the deal, including a $50 million cash injection.
The deal would secure banker support for three years, wipe out second-tier debt and reduce interest by $20 million a year.
It would see Ironbridge pay off the $30 million remaining from a controversial $44 million, 50-month loan by the Crown - an arrangement which enabled MediaWorks to secure its radio frequencies during tough times after the global financial crisis.