In conversation with

Stephen Bourhill  

Stephen is a Senior Project Engineer with Ventia. Over the last nine years he has worked in project management and engineering functions in Ventia's largest environmental remediation projects. He is committed to restoring contaminated land sites and is passionate about protecting the environment. Stephen has successfully delivered complex remediation projects across much of Australia using a variety of remediation approaches. His most recent project was rehabilitation works at a uranium mine in northern Australia.

He has recently shared his insights to a global audience as part of the Battelle 2024 Chlorinated Conference.

Analysis by the CSIRO projects the closure of nearly 240 Australian mines by 2040, estimating an annual expenditure ranging from $4–8 billion on mine rehabilitation and closure.*  

As more mining sites around Australia and the world reach their end of life and environmental and community standards rise, innovative solutions are required in order to ensure current mining sites are returned to their traditional state and suitable for future use.

Ventia’s environmental services team has delivered some of Australia’s largest and most complex environmental remediation projects, our team has a reputation for quality and depth of experience. 

The lessons the team learned on the Ranger Mine project, shared this week to a global audience could prove invaluable for future projects. 

 

Talk about the challenge of mine rehabilitation in general when it comes to tailings?

At the closure of most mines, tailings from mining operations, which is the material left over after milling material of value out of mined ore, are required to be contained on site as part of rehabilitation requirements. 

This is because they are often contaminated and need to be stored in a long term environmentally sounds location such as in rock underground, however they lack the geotechnical substance to effectively cap the tailings in line with rehabilitation requirements and timelines.

 

For the Ranger project what was the scope of this challenge?

In 2022-2023 Energy Resources of Australia (ERA), with Ventia as its partner in the field, installed 39,768 prefabricated vertical drains (PVDs)/wick drains within the Pit 3 tailings layer of the former mine. The purpose was to release pore pressure from the tailings, and drain water from the body, thus accelerating consolidation of the tailings from years to months and allowing the pit to be capped and returned to a state like the surrounding Kakadu National Park.

The installation of wick drains at this scale into a large body of tailings was novel - to the best of our knowledge. 

 

What were some of the innovations that might have applications elsewhere?

To meet the design during field works, specialised wick drain installation plant and equipment was developed to reach the required target depths into tailings and successfully anchor into the soupy mix, combat high excess pore pressures to succeed in installation, and protect the delicate PVD material from foreign objects during installation. 

Furthermore, as it was impossible to use the tailings layer as a working platform, a bespoke wicking barge was designed and built to float the operation above the soupy mix, all while achieving positional accuracy and station holding within an average of 89 millimetres and 1% vertical.

The combination of the bespoke barge and the specialised wicking plant and equipment was a true innovation. 

 

What have been some of the ongoing lessons you’re keen to pass on?

Within the Pit 3 tailings layer, our work successfully overcame a varying tailings condition, high excess pore pressures, and anchoring challenges to deliver this world first. Performance of the wicks has been verified through ongoing bathymetric surveys and visual confirmation as the pit gets drained by pumps.

The project required good preparation though also being adaptable and open minded throughout implementation. Lessons learned include how to use water to combat high pore pressures, what anchor plates work best, and how to adapt to the inevitable variety of conditions within the tailings body.

With more mines approaching closure and rehabilitation in Australia and the world, the lessons learned could be invaluable for future projects