A Katherine resident has already made a legal claim on the Department of Defence for chemical contamination.
The “non-litigated claim” is the sole claim, believed to be for compensation, yet made on the department.
More than 250 people attended a meeting with Shine Lawyers in Katherine last week as the first steps are made to present a class action against defence.
The news that a claim has already made was presented to a Senate hearing on Wednesday.
When Senator Malarndirri McCarthy pressed the department for more information on the claim, Defence Minister Marise Payne said it “would not be appropriate”.
Under questioning from Senator McCarthy, defence also admitted it knew about the possibility of PFAS contamination from the Tindal RAAF Base years before Katherine residents were told.
Defence officials said a desktop analysis in 2012 had identified Williamtown and Oakey military bases and other military “properties”.
Senator McCarthy said it was likely Tindal was also identified then.
Oakey residents were advised in 2014.
Defence said the Katherine public were first told of the leakage of the PFAS chemicals from the base late in 2016.