Multinational company Boral has been told to take urgent action to stop pollution flowing from a disused mine site into the Wingecarribee river in the New South Wales southern highlands.

Boral now has three days left to tell the state’s environmental watchdog, the Environment Protection Authority (EPA), what it will do to stop zinc, nickel and manganese leaching into the river, which is part of Sydney’s drinking water catchment.

The pollution was discovered by an academic, University of Western Sydney water scientist Ian Wright, earlier this year.

Wright described the zinc contamination as the worst he had seen, and criticised the “soft, almost meaningless” environmental regulations applied to the mine, which include no limits on the leaching of heavy metals into the river.

He fears contamination at disused mine sites will be seen across the country in coming years.

“Whether we like it or not, a lot of coalmines are closing down; I think this is a harbinger of things to come,” Wright told Guardian Australia. “We can’t just keep dumping untreated or poorly treated mine waste into a river – the community is demanding better than that.” 

The coalmine operated from the late 1800s until 2013, perched above the river near the small villages of Medway and Berrima. It is close by to another proposed underground coalmine, Hume Coal, which Wright has similar concerns about.

Boral is still in the process of closing the site, which requires negotiations with the state government.

Wright tested water nearby earlier this year, and discovered the contamination had worsened considerably since the mine shut down.

The mine is still releasing about 30 litres of drainage a second, Wright said, the equivalent of about an Olympic swimming pool a day.

He said the discharge, given the current dry spell, was accounting for 20% to 25% of the river’s flow.

Wright’s report, handed to NSW authorities and the company in August, found zinc was being discharged, on average, at 27 times above the safe level.

“That’s the highest I’ve ever recorded coming out of a mine, and I’m studying eight of them at the moment. So I know the topic fairly well,” Wright said. “I’ve had to go to international literature to find something like this.”

Manganese was “off the chart” and higher than anything Wright had seen in Australia or abroad. Nickel concentrations in the river had doubled since the mine’s closure, and were well above safe levels.

After receiving Wright’s report, the EPA varied the mine’s licence in late September to force Boral to provide a written action plan for addressing the contamination by 13 October.

“There has been a degradation in water quality discharging from the Berrima mine since mid-2016 after old mine workings were flooded,” an EPA spokeswoman said.

“This degradation is due to naturally occurring minerals found in the geology of the area, including zinc, nickel, manganese and salt, rather than from active coalmining.

“The EPA is committed to determining the best course of action to address this mine discharge.”

Wright commended the EPA’s decision to intervene, saying it ought to be congratulated for taking action on a non-operational mine site. He also praised Boral, who he said had provided him with data to help compose his report, and appeared intent on dealing with the pollution, unlike many other companies.

But he said it should not have been discovered by a researcher like himself: “I’d rather not do this, I think it should be done independently by an independent body.

“I think it’s appropriate to have completely independent assessments, completely independent of government, like an Icac for pollution.

“I’m open in criticising the EPA because they have no limits on the most hazardous elements from this mine. Nothing.”

In a statement, Boral said it would work closely with the EPA and the state authorities on the closure.

“The mine, which had been operating for more than 50 years before Boral acquired it, ceased all mining operations in 2013,” the company said.

“Since then, it has been on care and maintenance, while we work with state authorities – including the EPA – on developing a mine closure plan.”

Boral said it would keep the local community informed about the site, including on water quality.