Two workers allege they were told to keep spraying contaminated drill rig water around a gas fracking site in the Northern Territory's Beetaloo Basin, despite the gas company knowing the fluid was contaminated.
Key points:
Tamboran Resources says spraying of contaminated water stopped after one day
Workers allege spraying continued for up to five days
The gas company and NT EPA say no contaminants of concern were found
The contractors have told the ABC they now hold concerns for their health and their fellow workers who were employed last year, as well as potential impacts on the environment.
Tamboran Resources, which has the biggest gas exploration operation in the Beetaloo Basin, south of Katherine, has rejected the allegations and said there is no cause for concern.
An incident report provided to the NT government showed that in September last year, Tamboran Resources was worried it had too much water in a dam of drilling water at its Maverick 1 gas well on Tanumbirini Station.
The company ordered workers to lower the dam level.
Veteran gas worker Frank, who has asked the ABC not to use his full name because of concerns for his career, was a contractor on the site.
"It was nearly a metre too high, and they were freaking out that rains were coming at the beginning of the wet," he said.
Tamboran reported to the NT government the dam level was lowered by pumping the drilling water from it into a fresh water dam being used to damp down dust on the site and access roads.
In the environmental incident report, Tamboran said as soon as a senior manager realised the drill was being sprayed around that was immediately stopped and the government was informed.
Frank has contested those claims, telling the ABC he was directed by Tamboran to keep spraying the contaminated water.
"I was told to just continue to wet the roads, wet the camp, wet the drill pad, just keep on going until the pump couldn't pick up any more, for about three, four, five days," he said.
"It was something that they just told us to do.
"And I'm here to tell the truth; if they had have told the truth from the start I wouldn't be here sitting talking to you."
Workers say contaminated water used for up to five days
Frank said he is now worried about whether there could be health impacts for site workers.
"More for the younger ones. I'm 65, it's the long-term effects for younger people working onsite," he said.
Another tanker driver Jim, who has also asked the ABC not to use his full name, said he was also directed to keep spraying.
"We had pre-start meetings in the morning where it was brought up, but we were under direction from Tamboran to keep spraying it," he said.
"Because there was supposed to be government inspectors coming in and there was a big hurry to get rid of all this water and backfill this dam."
Jim also said he was told to keep spraying for three to five days.
He emailed the NT Environment Protection Authority in October last year to offer it information about his allegations but said he did not receive a reply.
Jim said he was also worried about the environment and workers' health.
"The people who were looking for the gas they were walking across that area all the time, the spotter, and when I'm filling up there's spray coming out as it pumps into the tank," he said.
"To me, if you're getting that overspray on workers working around that camp then there's going to be health dramas with it."
Tamboran says water contained 'no chemicals of concern'
Professor Melissa Haswell, who studies the impacts of gas and fracking operation chemicals at the University of Sydney, said it was unclear what chemicals would have been in the drill dam water during the time of the incident.
But she said shale gas drill water often contained both chemicals and naturally occurring heavy metals brought to the surface during drilling processes.
"Specific components differ, but there are heavy metals including cadmium, lead, chromium, arsenic; we also have volatile organic chemicals like benzene and polyaromatic hydrocarbons," she said.
"There are a vast array of chemicals that have been sitting on the shale for many thousands of years and can be very toxic to humans and other life."
In a statement to the ABC, a Tamboran Resources spokesperson said "the workers allegations regarding sump water being used for many days for dust suppression are false".
The spokesperson added there were "no chemicals of concern" in the fluid used for dust suppression, and that testing found it "suitable for livestock drinking".
"The fluid was a relatively low salinity brine suitable for dust suppression."
The spokesperson added that Tamboran "looks forward to progressing projects in a safe and sustainable manner with the highest environmental standards".
The NT Department of Environment, Parks and Water Security told the ABC it carried out on-site soil tests and "no contaminants of concern were detected at elevated levels".
But contractor Jim said he was worried about what will happen if potentially thousands of wells were drilled across the Beetaloo Basin.
"I think the government should have been doing a lot more research into what effect this has on the country and the land, the people and the animals," he said.