- Acid Rock Drainage

Acid Rock Drainage (ARD) is a natural weathering process where sulphide minerals exposed to water and air react to produce acid.  The resulting acid solution causes some minerals in rocks to dissolve which often includes metals. Resultant water with metals and acidity, if released into the natural environment, can affect water quality.  Aquatic environments, especially fish, are very sensitive to metals and acidity and may not survive with changes in water quality that could result.

Acid Rock Drainage occurs where there are large quantities of sulphur- containing rock minerals and has been observed  associated with road building, construction (including construction at an airport) and at mines.  Acid Rock Drainage or Acid Mine Drainage is a major environmental risk that is regularly assessed for new mines and is a problem at a number of historical and abandoned minesites where the potential for the problem was not identified prior to mining. ARD can often be prevented by appropriate mining plans but where not managed properly, can lead to costly collection and treatment programs that must function for many decades.

Today, mine development includes extensive evaluation of the potential for Acid Rock Drainage and prediction of water quality that may result before mining commences.  This information is normally included in the Environmental Impact Assessments required before mining begins, and also includes strategies to control or manage the problem, if there is a potential for ARD.  Only a portion of new or existing mines have the potential to generate ARD.

There are several mine sites that have had the potential for ARD and have operated and closed successfully without causing pollution problems (http://technology.infomine.com/enviromine/publicat/enviroresponse.html).  For sites where ARD is occurring, collection of acid water and treatment using lime can be a typical and useful method for controlling the problem and allowing the discharge of clean water to the environment.  However, treatment may be required for many decades. The requirements and costs for managing ARD are identified in Mine Closure Plans and the financial provisions are provided to ensure that mining companies are able to manage the long term liability.  These Closure Plans are typically filed with relevant government agencies and the liability is explained in company financial reporting.

The mining industry, governments, universities and other interested parties have been studying the problem of ARD and actively searching for solutions to eliminate the ARD problem.  These groups have been successful in improving the identification, prediction, treatment and control of ARD.  While significant progress has been made that benefits new and existing operations, work continues to search for greater understanding and improved less costly ways to solve this problem. 

Organizations that are actively working on ARD research include: The International Network for Acid Prevention (www.inap.com.au); the Mine Environment Neutral Drainage program (www.nrcan.gc.ca/ms/canmet-mtb/mmsl-lmsm/mend/); the Acid Drainage Technology Initiative (www.unr.edu/mines/adti/); the Australian Centre for Minerals Extension and Research (www.acmer.uq.edu.au/); and, the Partnership for Acid Drainage Remediation in Europe (www.padre.imwa.info/index.html).