It is a strategic priority for Energy Resources Australia (ERA) to comprehensively rehabilitate the Ranger Project Area.
Rehabilitation and closure planning began soon after the Ranger mine began producing uranium oxide in 1981. Mining finished in 2012 and with the completion of ore processing in 2021 the mine transitioned to its final rehabilitation and closure stage. ERA's focus is to create a positive legacy and achieve world class, sustainable rehabilitation and closure of its former mine assets.
An essential early stage to the successful rehabilitation of the site involved the enhanced consolidation of over 43 million tonnes of tailings that had been transferred to the former mine pit.
To achieve this, the design required over 41,000 Prefabricated Vertical Drains (PVDs) or 'wicks' to be installed into the tailings to depths of up to 40 metres. Once installed the PVD provides a preferential flow path for water trapped within the tailings allowing the water to be expressed and the tailings to rapidly consolidate.
Due to a covering layer of water up to five metres in depth over the tailings, a specialised delivery method would be required to achieve the projects aims.
Connecting with the right partner for a unique approach
To deliver a project of this complexity and magnitude required working with an experienced partner in environmental remediation solutions.
Ventia has 35 years' experience successfully designing and delivering a wide range of engineered solutions for the closure of mine sites, energy generators, remediation and environmental rehabilitation projects.
ERA's Project Director Bernard Toakley said progressive rehabilitation has been taking place at the Ranger Project Area since 1996 and these latest works are another step in the rehabilitation process.
To find a partner like Ventia with the unique combination of complex environmental remediation experience and also directional drilling capability, was enormously beneficial for ERA and our ongoing rehabilitation activities of the Ranger Mine Area.
Ventia was engaged to design, construct and operate a unique barge system to allow the installation of the PVDs from the waters surface. Working closely with ERA and Ventia's subcontractors, Ventia designed a barge system that could:
- be easily transported to the remote site,
- be quickly and safely assembled,
- manage the extensive forces applied to it by the two 100 tonne mobile PVD installation rigs,
- included integrated moon pools to allow wicks to be installed from within the barge footprint
- provide all necessary support functions for the works and workforce, and;
- could be positioned using a highly accurate computer controlled winching system.
Ventia also drilled three directional wells from the ex-pit natural ground surface to intersect the base of Pit 3, as part of ERA's wider upgrade of the brine injection system which manages the salt content of the process water inventory.
A commitment to safety
Safety to the workforce was of paramount importance. The challenging site conditions required a workforce to operate in close quarters to operating plant in a hot, humid tropical environment on an acidic water body.
Systems were designed and implemented prior to the commencement of works to allow the workforce to operate safely in the environment and Ventia's drive towards continuous improvement ensured processes were updated when and where potential improvements were identified.
Ventia's Senior SHEQ Engineer, Allan Garland, said the team's strong commitment to safety ensured the project was completed lost time injury free and demonstrated the value of early innovative design approaches for safety.
Completing the project
In March 2023, Ventia successfully completed the installation of 39,768 PVDs with approximately 1,268,650LM of PVD material installed into the tailings (equating to nearly the driving distance from the mine to Alice Springs NT). The works required an onsite workforce of over 70 personnel and over 101,000 hours worked on site to successfully deliver the project.
'The successful delivery of this project leveraged the innovative skills of the Ventia team to develop a safe and reliable wick installation process. Ongoing survey of the tailings indicate the wicking process has met and exceeded the expectations of ERA's model and will help ensure the success of future rehabilitation stages', said Ventia Project Manager, Jayson Gaul.