The exact amounts each landowner can expect to receive is still unknown as details of the Defence Department in-principle offer have still not been disclosed.

It is now up to the Federal Court to apply what is believed to be a complicated formula which applies expert advice on property price falls.

Shine Lawyers class actions practice leader Joshua Aylward told a press conference yesterday it had advice of property price falls of between 15-50 per cent in various areas of Australia because of PFAS contamination.

In a regional Australia real estate market update issued today, CoreLogic says the change in median house values in Katherine over the past five years had been 15 per cent.

Katherine residents are wondering how much they might receive from the class action settlement but are also asking when it is likely to be paid?

To be eligible for compensation under the class action you need to own, or have owned, a property within the investigation area as at November 23, 2016.

The investigation area was detailed by Defence during its testing for contamination flowing from the Tindal RAAF Base.

Mr Aylward said the PFAS class actions, including Katherine, are some of the largest environmental legal actions in Australia's history.

He said the compensation would ultimately be distributed by the applicants' solicitors.

"The method of payment will be at the clients' discretion," he said.

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"The parties will work to ensure that settlement approval and settlement distribution is completed as soon as possible. This is likely to take months, not years."

The legal parties are in the process of finalising the terms of the settlement.

"These terms are confidential and are subject to formal consideration and approval by the Federal Court of Australia," a joint-statement issued by Defence Minister Linda Reynolds and Veterans Affairs Minister Darren Chester said.

Katherine's biggest real estate owner, Katherine Town Council, agreed after receiving its own legal advice in July last year to remain "opted in" to the class action.

Property owners in Katherine received letters in May last year directing them to "opt out" of the class action if they did not want to be part of the legal action.

Most did not opt out.

Those who did opt out are able to take their case for compensation direct to Defence.

Shine Lawyers and its litigation funder IMF Bentham brought the action.

"If the Class Action is successful and a judgment of damages is awarded to the people of Katherine, the costs and fees paid by the IMF Bentham, in order to bring the proceedings to a successful outcome, will be deducted from the amount of damages received from the Commonwealth of Australia. The final legal costs will depend on the amount of work, and time, required to resolve the claim."

This class action did not make any claim for personal injuries relating to exposure to PFAS contamination.

It is considered this could still happen in the future.

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