The cleanup of PFAS contaminated groundwater at the Tindal RAAF Base has begun.
One of two expensive treatment plants has began work on a job which the Department of Defence has admitted "may take many years".
PFAS has been leaking from the base for 31 years, through the groundwater and underneath Katherine town, and empties into the Katherine River.
The PFAS chemicals were contained in firefighting foams which were used at the base from 1988 to 2004.
Exhaustive groundwater monitoring over the past year shows the PFAS chemicals continue to leak from base.
The Department of Defence is installing two water treatment plants at the base in an attempt to stop the leak.
There has been no information provided on the soil cleanup which defence officials have said was much more difficult than cleaning PFAS from water.
Water is extracted from groundwater at the PFAS hotspots on the base - the former firefighter training areas.
PFAS is extracted using the same synthetic resin being used on Katherine's smaller water treatment plant.
The cleaned water is being reinjected back into the aquifer in an ongoing cycle.
Combined the two base plants, sourced from the USA, are intended to clean PFAS from 10 megalitres per day or 3650 megalitres per year.
NT Government reports suggest the Tindall Aquifer has an average recharge rate of an estimated 74,000 megalitres each year.
Senior defence official, Steve Grzeskowiak, told a Senate hearing last year defence would “need to run those plants for a long time”.
“It will draw water from the ground, clean it and put it back. That's at the beginning of the remediation strategies for Tindal. That's going to be a long-term endeavour,” he said.
He said defence had taken the “best advice we can from our experts in this field about where we should site those plants”.
“Intuitively, it will start to make a difference because, for every litre of water we take some PFAS out of, we are removing PFAS from the environment.
“We're not exactly sure how that will affect the flow of PFAS in the aquifer nearby. It will affect it in a positive way, in that there will be less contaminant in the ground.””
Katherine is still waiting for more information about its own town water treatment plant while it remains on water restrictions because of PFAS.
Power and Water officials want a big plant capable of cleaning PFAS from about 10 megalitres of contaminated water per day.
The first Tindal plant, believed to have cost $5 million, is expected to treat five million litres of water per day.
The smaller Katherine town plant currently treats one million litres of water per day.
Defence this week confirmed the first plant is now fully operational.
A similar plant is operating to cleanup PFAS from the Williamtown RAAF Base in NSW.
As at February 20, approximately 16.9 megalitres of water had been treated by the fire training area’s water treatment plant.
Construction has started at the second treatment plant, located in the fire station area. It is expected to be operational in the second quarter of 2019, subject to weather conditions.
Defence has previously said once the water treatment plants were operational, data detailing laboratory analysis, from each plant, would be placed on the Defence website monthly.
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