Acid rock drainage

One of the most serious environmental risks for the mining industry is 'acid rock drainage' (ARD) from mineral waste.

ARD can be created when rocks that contain naturally occurring sulphide minerals - such as pyrite - are disturbed and exposed to air and water.  This accelerates the natural weathering process and may lead to the release of low pH contact water with elevated salinity and metals concentrations.  If improperly managed, ARD can prevent revegetation of mining wastes, and degrade surface and groundwater quality. 

How we deal with ARD

To prevent or minimise these potential environmental impacts, we have developed several robust strategies.

We have adopted leading practice in mine planning, operation and waste management, while new projects are designed to ensure that the risk is minimised and that any generated ARD will be captured and treated.  Our strategies are also being refined to better characterise acid-generating materials, improve mineral waste handling procedures, develop effective closure strategies and improve collection and treatment of ARD.

We use a number of techniques to prevent or control ARD.  These include selective handling and encapsulation, disposal under water, blending waste materials and using either synthetic or engineered earth covers.

All operations where ARD could occur are required to maintain a management plan which must be reviewed every four years by an external expert.  Our internal risk reviews are now regarded as the industry benchmark in this key risk area, and we continue to play a leading role in the International Network for Acid Prevention (INAP). 

We conducted six additional ARD risk reviews in 2006 to assess the ARD hazards and management strategies at our managed operations.  Since 2003, 21 operations that were at risk of producing ARD have been visited by the ARD risk review programme. And a diagnostic tool was developed in 2006 to assist operations to improve their management of mineral waste, which is being tested at three operations.

In addition, our Acid Rock Drainage Prediction and Control Standard continues to be periodically updated in response to technological advances and new issues identified at the operations.  The Environment Due Diligence Guidance and Checklist has also been strengthened with regard to ARD issues.

Our results

All six managed operations visited by the ARD risk review program in 2006 were in compliance with the relevant government regulations and permit conditions.

Six monthly reporting by these operations indicated that significant progress has been made to address the issues raised. About a quarter of the most important findings had been addressed and actions responding to half of them are in progress. 

Given the long-term strategic nature of many of the ARD issues identified, and the long lead times to design and implement some of the studies and corrective actions, it is anticipated that this work will continue for many years.