On January 8, after 40 years of operations the mine officially closed, but there is still much to do at the site.

Sydney Environment Institute research affiliate Rebecca Lawrence holds high hopes one of Australia's oldest uranium mines will fit seamlessly with its surroundings - Heritage listed Kakadu National Park - at the completion of rehabilitation in 2026.

But toxic tailings buried deep in the pits and finances that will unlikely provide for future monitoring are cause for concern.

Operating for almost four decades and producing in excess of 130,000 tonnes of uranium oxide, Ranger is set to enter a five year clean up with strict requirements it can be incorporated into the surrounding Kakadu national park in five short years.

However, Gundjeihmi Aboriginal Corporation, which represents Mirarr traditional owners, is pushing for an extended rehabilitation.

"The major concern is when water flows through in the wet season we don't know what kind of toxic cocktail will be carried off-site into Kakadu National Park," Dr Lawrence said.

Energy Resources Australia, the operator of the mine, has significant data shortfalls on the risks of disposing the leftover waste in the pit, she said, highlighting concerns the site spanning 79sq km will never be the same again.

"These kind of mine sites that have toxic legacies into the future need perpetual care," Dr Lawrence said.

"The idea we can open a uranium mine, fill it up with trucks and waste and buildings with no repercussions is fanciful.

"Of course we want [rehabilitation] to be achieved... but the best possible future for the site is a compromised site with a lot of problems down the line."

The Environment Centre NT, in partnership with the Sydney Environment Institute, Australian Conservstion Foundation and Mineral Policy Institute released a report last month outlining the mammoth task ahead.

Specifically the report flags an unrealistic rehabilitation time frame, data deficiencies and technical issues - particularly around groundwater and tailings management - and the risk of contaminants entering Kakadu.

In response, Energy Resources of Australia released a statement saying the mine is "one of the most highly regulated mines in the world".

"ERA's strategic priority is the comprehensive rehabilitation of the Ranger Project Area to a standard that meets regulatory requirements and the expectations of the Traditional Landowners," the statement reads.

"ERA is committed to fulfilling the legislated timeframes and guidelines set out in the Section 41 Authority and to achieving all documented rehabilitation outcomes in its Mine Closure Plan (MCP) by January 2026."

The statement notes rehabilitation "has been underway at Ranger for over 25 years".

"The first open pit has now been fully backfilled and a revegetation program has recently commenced in that area.

"Since 2012, ERA has spent $642 million on rehabilitation and water management projects."

In previous statement's, ERA's chief executive Paul Arnold said the rehabilitation plan "reflects the complexity of rehabilitating a site in this environmentally and culturally sensitive region" and is "comprehensive and achievable".

"It is based on long term research, expert studies, best practicable technology, cultural guidance from the Mirarr traditional owners and thorough stakeholder review."

In 2019, Dr Lawrence conducted a comprehensive review of the mine's impending rehabilitation and says the risks remain.

Her research found rehabilitation will not only be complex and costly, but unless effectively carried out, threaten long term environmental harm to the region.

"Toxic waste and financial uncertainty were major red flags in 2019, and we still don't know how ERA is going to tackle these issues."

More than $1 billion has been earmarked to restore the mine to requirements which have never been set or met in Australia, Dr Lawrence said.

"Research shows mine rehab typically fails so the need for significant rehabilitation down the line is inevitable, but ERA has not even mentioned the costs for monitoring post 2026 or how it will be funded," she said.

"What that says to me is that Territorians and tax payers will be left with a site without a corporation to pay for problems sure to happen down the line."

In just five years, ERA, a subsidiary of Rio Tinto, needs to transform Ranger to fit seamlessly with the surrounding national park.

The process will involve filling gigantic holes, disposing of wastewater and tailings dams, and planting millions of trees.

A sharp lesson in community opinion and shareholder investment for mining giant Rio Tinto, who now own 90 per cent of ERA, up from 68 per cent, is likely to work in its favour, Dave Sweeney from the Australian Conservation Foundation and co-author of the Closing Ranger, Protecting Kakadu report.

"The good news is Rio Tinto and ERA have committed to rehabilitation, Rio Tinto has increased finances and have accepted they have skin in the game with a high degree of exposure and reputation on the line," Mr Sweeney said.

"Rio Tinto will be closely watched and long judged. Everyone wants it to work."

Yet, Australia's mine closure record remains shaky. It's estimated over 60,000 abandoned mines across the nation remain.

"No uranium mine has ever been successfully rehabilitated in Australia," Mr Sweeney said.

He pointed to Rio Tinto's involvement in two previous failed rehabilitiaions, Rum Jungle - Australia's first large scale uranium mine - and Mary Kathleen in Queensland.

"An unrealistic time-frame has been set that doesn't take into account COVID-19 and the Northern Territory's wet season. Boots on the ground time is going to be reduced significantly," Mr Sweeney said.

Mr Sweeney said the era for uranium is long over. The commodity price has been hammered and the need to transition to cleaner energy sources is well known.

Kakadu National Park, arts and ranger programs are increasingly being lent upon for commerce in the region, and Jabiru, built in 1982 to service the mine, has already started its monumental transition to a tourism hub, this year taking back rights to the land.

"The tourism economy is greater than the mining sector," Mr Sweeney said.

"For people concerned and uncertain about closing Ranger, for me this is an exciting and positive time.

"We are seeing a whole range of voices listened to... any transition is not without challenges, but we have commitments from companies and traditional owners that the age of uranium is over and collectively we need to fashion a different future."

While you're with us, you can now receive updates straight to your inbox each Friday at 6am from the Katherine Times. To make sure you're up to date with all the news, sign up here.