MARK COLVIN: Energy Resources of Australia, ERA, is facing criticism that it's doing too little, too late, to manage radioactive waste water at its Ranger uranium mine inside Kakadu National Park. 

The company's plunging share price fell further in trade today as the market digested news that ERA was embarking on an $80 million feasibility study of a new method to concentrate its liquid waste. 

But criticism isn't just being levelled at the company. A former environmental scientist with ERA says the federal and Northern Territory regulators have also failed. 

Katrina Bolton reports.

KATRINA BOLTON: Energy Resources of Australia is struggling with the worst wet seasons on record. 

The company says nearly two-and-a-half metres of rain fell at its Ranger uranium mine this wet season, increasing the volume of waste water.

The company's already raising the wall of one of its tailings dams and it's announced it's about to spend $80 million on a feasibility study of a new water control method, which would ultimately cost close to $220 million.

It hasn't impressed Dr Gavin Mudd from Monash University, who advises the Mirrar traditional owners of the surrounding Kakadu National Park. 

GAVIN MUDD: It's too little and it's still too far away. We need something this year and we need something that works. They've been studying processed water treatment for well over a decade now. We have to get something in place. We cannot run the gauntlet of another wet season like we've just had. 

KATRINA BOLTON: The technology ERA is embarking on is a brine concentrator, which can take salty contaminated liquid and reduce its volume. 

Dr Ian Hollingsworth is an environmental scientist who spent a decade working for ERA. He says it's an expensive technology and the fact ERA is going for it shows the company is very concerned.

IAN HOLLINGSWORTH: It shows that they realise that unless they get on top of their water management issues by enhancing their disposal, they're not going to be able to process.

KATRINA BOLTON: ERA's chief executive, Rob Atkinson, says he's highly confident the brine concentrator will work to bring down the amount of waste water.

ROB ATKINSON: I would certainly prefer to be in a position where we did not have such a large inventory. It hasn't been through a lack of effort. What I'm really looking at is the investment in the brine concentrator that I'm very confident that we can tackle the process water inventory that we do have. 

KATRINA BOLTON: He says it's a proven technology.

ROB ATKINSON: It's used throughout the world in oil and gas, fertiliser, power and other mining operations and what we've just got to do is make sure that the specifications at which we get it built to is able to handle our type of water. 

KATRINA BOLTON: ERA has told the Stock Exchange the concentrator would be operational in the second half of 2013. 

Environmental scientist Ian Hollingsworth says that means the company will be rolling the dice on the next two wet seasons. He says regulators should have acted sooner. 

IAN HOLLINGSWORTH: The problems probably go back to the quality of the regulation. The regulators are not, in my opinion really, doing a great job. 

KATRINA BOLTON: Monash University's Dr Gavin Mudd wholeheartedly agrees. 

GAVIN MUDD: The fact that the company has been allowed to get this far and several years not being forced to actually build processed water treatment so that we can all achieve good quality rehabilitation, I think is a real failure of regulation. 

KATRINA BOLTON: The federal regulator couldn't respond today because staff in the Northern Territory are on a public holiday. 

The Territory Government says its monitoring is undertaken on behalf of the Commonwealth and that waste water is retained on the Ranger site.

MARK COLVIN: Katrina Bolton.