THE Ranger uranium mine inside the World Heritage-listed Kakadu National Park is leaking 100,000 litres of contaminated water into the ground beneath the park every day, a Government appointed scientist has revealed.

Alan Hughes, the Commonwealth supervising scientist appointed to monitor the mine's environmental impact, confirmed at a Senate committee hearing that about 100 cubic metres a day — the equivalent of 100,000 litres or three petrol tankers — of contaminant were leaking from the mine's tailings dam into rock fissures beneath Kakadu.

There have been more than 150 leaks, spills and licence breaches at the Ranger uranium mine since it opened in 1981.

The mine's owner, Energy Resources of Australia, has been repeatedly warned about its management of the mine, with a previous government-appointed scientist declaring in 2004 that ERA was "complacent" about protecting workers and people living near the mine.

The mine was originally scheduled to cease mining last year but there are now plans to tunnel under flood plains from an open pit in a move that would extend mining to 2021.

Mr Hughes told a Senate committee late last month that ERA is responsible for recovering the contaminated water that has washed downstream, and that his office had asked the miner for more information about the leak. "We understand that they (ERA) intend to extend their monitoring program in the vicinity of the tailings dam," Mr Hughes said.

Tailings are piles of crushed radioactive rock left over after the mining process.

Mr Hughes said the extra data collected would provide "a better idea of what actually is occurring in that area". "At this stage, I do not see any significant reasons for concern."

British mining giant Rio Tinto last month refused to rule out selling its 68 per cent stake in ERA after reports that several Japanese companies were interested in buying it.

Environmentalists and the Greens say the company should be forced to halt plans to expand the mine until it explains how it intends to recover the water and meet its obligations to rehabilitate the world heritage-listed area, 250 kilometres south-east of Darwin. "The Ranger mine has a long history of cutting corners with worker and environmental safety standards and this latest leak means permanent pollution in Kakadu," said the Australian Conservation Foundation's nuclear campaigner, Dave Sweeney.

"Federal authorities should require ERA to end their expansion plans, phase out current mining, get serious about cleaning up the mountain of mess it has already caused and get out of Kakadu."

Greens Senator Scott Ludlam said Mr Hughes' until now unreported revelation about the extent of the leak during a hearing of the Senate Standing Committee on Environment was "astonishing".