But authorities have defended a decision to keep the findings at Campvale from the public, saying only a 'trace' amount of perfluorooctane sulfonate (PFOS) was found at the Campvale Pumping Station, which feeds water directly into the dam. 

The Newcastle Herald can also reveal that PFOS was discovered above the safe US level at the poultry farm on Richardson Road, after a bore was ‘mistakenly’ tested by a Hunter Water technician. 

Hunter Water claims the worker could not find the water meter when he was sent to do routine sampling in February. 

The agency was baffled – and "immediately" informed the Environmental Protection Authority and NSW Health – when PFOS was detected at .06 micrograms per litre.

A second test returned a higher reading of .08 micrograms per litre; which exceeds US drinking water guidelines but is within Australian limits. 

Ross Wilson has owned the farm for decades and now plans to get his bore water independently tested. 

“I don’t use it on my chickens but occasionally I’ll have drink of it on a hot day,” he said. 

 Hunter Water spokesperson Jeremy Bath said it was "not physically possible" for groundwater to travel to the north because it would have to run up-hill over a divide before flowing back down into Campvale. 

He admitted authorities were not sure of the location of that divide – because it moves in wet and dry periods – but were confident it had never moved as far south as the base. 

Mr Bath suggested the contamination at the chicken farm was caused by an accident on Richardson Road in 1994 where a tanker overturned and foam was used as a suppressant. 

But Mr Wilson is not convinced.

He said he never had a problem with flooding from the base until RZM began mineral sand mining in the bushland between the base and his home. 

"Now the whole area goes under water in flood times," he said. 

Newcastle University hydrologist Dr Steven Lucas said it was impossible to say with certainty that the contaminants could not have travelled in the direction of Campvale, without testing for them and extensive modelling. 

He said sand mining and the excavation works on the base as part of a $1 billion dollar Joint Strike Fighter upgrade both had the potential to interfere with the direction of groundwater flow. 

"Things are definitely happening up there from a hydrology perspective," he said. 

"[But] to be honest, I don't know that any government or RAAF base would want to go down that track, because they don't want to know." 

Internal reports leaked to the Newcastle Herald previously showed Defence's own experts warned in 2013 the base expansion could "mobilise" contaminated material and change the direction of the groundwater flow. 

Mr Bath said the detection of PFOS at the Campvale pumping station was "so low" it was the "equivalent of less than an eye drop ...in an Olympic sized swimming pool". 

He said the pumping station only contributed between 5 and 10 per cent of the inflow into Grahamstown Dam, which had never returned a positive detection. He said the trace detection of .004 micrograms per litre caused no concern for human health and was "completely unsurprising given how widespread the compounds are in everyday household products ranging from pizza boxes to furniture to shower curtains." 

Of more than 160 samples Hunter Water has taken across its network since last October, only five have returned traces of PFOS. 

Three of those were from the Campvale pumping station, one was taken from Williamtown and the other from the Allyn River.  

Mr Bath said the pumping station was more likely to experience detections because it received stormwater run-off from Medowie. 

Residents reacted furiously to revelations they had not been told and said heads should roll within the Environmental Protection Authority (EPA), which had responsibility for informing the public. 

"If they're finding it in bores around Campvale, that just throws the whole red line out the window," Salt Ash resident Nick Marshall said. 

Mr Marshall said testing of the Grahamstown Dam needed to be more thorough, arguing sampling should include fish and target the marshy areas on its outskirts. 

"Say for example we did get a plume of algae in there, is this PFOS going to suck out of the water and attach itself to this plume – as it's supposed to do with these organic substances?" he said. 

But an Environmental Protection Authority spokesperson said it was not necessary to publicise the finding because it agreed with Hunter Water that both detects were not linked to the contamination at the RAAF base. 

“This is supported by the hydrogeological model developed by the Expert Panel’s Water Working Group,” she said. 

She said Defence was not required to do any further sampling because five bores sampled on the north of the base had showed non-detects. 

“Importantly the detection of a PFOS presence does not necessarily indicate a risk to human health,” the EPA spokesperson said. 

Labor Member for Paterson Meryl Swanson raised the potential contamination of Grahamstown Dam at a public meeting last week.

"I have been advised by Hunter Water that the dam is safe, but I can understand why people are concerned,” Ms Swanson said.