A decision to lower the height of the Moors Drain levee bank more than 20 years ago has been blamed for ongoing flooding in surrounding properties at Williamtown.
Residents were again reminded of the fact they are living on a PFAS-contaminated floodplain when their properties were inundated following last weekend's east coast low.
"We haven't had a flood since 2016," Nelson Bay Road resident Lindsay Reinhard said.
"It normally takes about 200 millimetres (to flood) but last week we only had 130 millimetres."
"The real worry is the PFAS, which has a 50 year half-life."
Long-time Salt Ash resident Len O'Connell said the problem dated back to the late 1990s when sections of the drain's levee bank were lowered in an attempt to stop flooding at Salt Ash School and the newly created Hideaway Village.
But the move made other low-lying areas more prone to flooding.
The unsealed drain connects at the corner of Medowie Road and Nelson Bay Road and drains 10 kilometres east to Tilligerry Creek.
Port Stephens Council is responsible for maintaining the drain, which was built 120 years ago to keep water out of the extensive network of dairy farms that once dotted the area.
It was connected to the Williamtown RAAF base in 1990, which marked the start of PFAS contamination in the waterway.
Fishing was suspended in Tilligerry Creek in 2015 after surface water samples revealed high levels of chemicals - PFOS and PFOA - from a banned fire retardant foam used at the RAAF base for 50 years to 2012.
In addition to the flooding, plumes of foam have also begun appearing on inundated properties.
An EPA investigation concluded the substance was likely caused by the presence of a foaming agent such as a cleaning detergent.
As it formed it pulled PFOS from the water so the concentration of PFOS was higher in the foam residue than in the water
The EPA advised the foam should be allowed to "dissipate naturally" into the environment..
Salt Ash resident Rob Roseworne who runs a dog boarding kennel business, was also flooded, in the weekend's deluge.
"I have had a significant downturn in business since knowledge of the PFAS problem became public," Mr Roseworne said.
"The idea that PFAS from the RAAF base should be allowed to run down an earthen drain is appalling when you consider what is known about the health impacts."
A 2018 Department of Defence report warned about the environmental and health impacts of contaminated water flowing through the Moors Drain and into the catchment.
It said the areas most at risk outside of the base are those surrounding Dawsons and Moors Drain "which receive impacted water from the site".
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