THE VOLUME of water at Ranger uranium mine's tailings dam could exceed the approved level if heavy rain continues, an environment group has said.

On January 28 Energy Resources Australia shut down processing of uranium for 12 weeks.

Managing director Rob Atkinson said the shutdown was a precaution to ensure any more torrential rain didn't push the tailings dam higher than allowed. He said he did not fear that the dam would overflow and contaminate Kakadu National Park and that safeguards made it impossible.

Environment Centre NT spokeswoman Cat Beaton said records showed rainfall at the mine site had exceeded the current tailings dam capacity many times in the last 40 years.

She said the Northern Territory Resources Department and the Federal Environment Department supervising scientist Alan Hughes approved ERA's request to raise the maximum water level from 52.3m to 53m.

Mr Hughes told Federal Parliament Senate estimates last week that while the water level was close to maximum, it could go to the dry season target of 53m without worry. He expects up to 500mm of rain for the rest of the Wet.

Ms Beaton said ERA was struggling to manage water at Ranger Mine and shouldn't be given approval for an expansion. She said the cumulative rainfall for March and April exceeded 500mm - the current available height left in the tailings dam - seven times since 1973 at Jabiru Airport, in 1973, 1976, 1983, 1985, 1999, 2006 and 2007.

"It's alarming that the Ranger uranium mine is operating so close to the margin, near the World Heritage listed Kakadu National Park, putting the livelihood of community and business at risk," she said.