Cracks in containment wall at Ranger Uranium Mine
(Question No. 2568)
Senator Ludlam asked the Minister representing the Minister for Sustainability, Environment, Water, Population and Communities, upon notice, on 23 November 2012:
With reference to the 27 September 2012 NT News article indicating that cracks are appearing in the top of the northern wall of Pit 3 at the Ranger uranium mine:
(1) Has the Office of the Supervising Scientist (OSS) examined the pit wall cracks; if so, what is the OSS assessment of the potential threats posed by these cracks, particularly given the impact of recent wet seasons on mine operations.
(2) What are the implications for the overall integrity of the wall of the pit.
(3) Is the instability limited only to the road surface; if not, how far down into the pit wall does the instability go.
(4) What remediation plans, including timeframes, are in place to address the cracks appearing in the pit wall.
(5) What challenges does this situation pose for rehabilitation plans at Ranger.
Senator Conroy: The Minister for Sustainability, Environment, Water, Population and Communities has provided the following answer to the honourable senator's question:
(1) Officers from the Supervising Scientist Division (SSD), including the Supervising Scientist, have visited Ranger to examine the pit wall cracks. SSD supports ERA's view that a major wall failure is highly unlikely and in view of the actions currently being undertaken by ERA, any impact on mine operations is equally unlikely.
(2) Wall movement within the pit continues to be monitored by radar capable of detecting sub-millimeter movement. With the cessation of mining in Pit #3 wall movement has reduced and a major wall failure is highly unlikely.
(3) The cracks visible on the surface are the result of the wall settling slightly due to removal of rock at the base of the pit in a fault structure. Movement of this nature is not unusual in open pit mining.
(4) Mining in Pit #3 was completed on 24 November 2012 and backfilling operations have now commenced. A levee is also being constructed outside of the mine access road to prevent water from Magela Creek covering the area of the cracks during the wet season and possibly piping through the cracks into the pit. The levee, which is expected to be finalised by mid December 2012, will also prevent Magela Creek water from entering the pit in the highly unlikely event that a major wall failure did occur.
(5) Decommissioning the levee is a minor operation that will need to be added to the rehabilitation plan. Increased permeability in the weathered zone as a result of cracking will need to be considered in the Pit #3 closure design.