Environment Examples of water management Energy Resources Australia (ERA)
ERA's Ranger Mine is located 250 km southeast of Darwin in a tropical monsoon climate, with an average annual rainfall of approximately 1,500 mm. The mine is surrounded by, but remains separate from, the World Heritage listed Kakadu National Park.
As with most mines, water that comes into contact either directly with the processing plant, stockpiles, active mining areas, tailings disposal areas and pipeline corridors, is captured on site. The volume of pond and process water stored on site has increased significantly since 1995, due to a series of above average rainfall years and increasing catchment resulting from expanding mining operations. The increase is likely to continue and be exacerbated in the future by the additional process water catchment area caused by the use of the current mining pit as a tailings disposal area.
Pond water volumes are partially reduced each year through passive evaporation and irrigation systems. Apart from passive evaporation, there is currently no mechanism available to reduce the volume of the process water. Surplus process water reduces the available tailings storage capacity and compromises the consolidation rate of deposited residues. Thus, there was the need to implement a more effective process water management system to maximise the available storage of tailings, whilst facilitating the efficient use of milling consumables and enabling expeditious capping of the stored tailings and rehabilitation of the site.
A project was initiated with the objective to "remove water from the process and pond water circuits using a water treatment facility employing proven, practicable and operationally sound processes that have been endorsed by ERA's key stakeholders". Achieving this objective will require the removal of approximately 500 million litres per annum of process water and 1,000 million litres per annum of pond water over and above current passive evaporation.
- Detailed modeling of the water movement on site, including 10,000 sequences of predicted 15-year rainfall periods;
- Detailed technology reviews;
- Detailed risk assessments;
- Testwork, including bench scale, batch and continuous work, as well as a fully integrated pilot plant;
- Full scale testing of the existing, mature surface flow, constructed wetland at the Ranger Mine, to treat the discharge of the PWTP for residual ammonia removal prior to release; and
- Toxicological testwork on the PWTP product water.
The outcome of this work forms part of the ERA Strategic Water Management Plan, and provides for surety in water management issues at Ranger through to site closure. Construction of the PWTP was completed in December 2005. Commissioning will be undertaken in January and February 2006 with full operation scheduled to commence immediately thereafter.
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