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Acid Mine Drainage: An Unavoidable Truth

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Definition

Acid mine drainage (ADM) is the outflow of acidic water from a mining site.  It is most commonly caused by hard rock mining where the precious metals are bound to sulfurous rock like iron sulfide (FeS2).Ground Truth Trekking Once this rock has been excavated and pulverized it reacts with the air and surrounding moisture to produce sulfuric acid (H2SO4).  

 

The oxidation of pyrite is a natural process,however, when it is crushed it has 100x more surface area than the naturally occurring substance making it more readily available to react with the elements.  When this happens the generation of H2SO4 exceeds the natural buffering capabilities found in host rock and water resources.2(Jennings)  The sulfuric acid that is produced mixes into the surrounding groundwater and leaches heavy metals like arsenic, lead, and mercury from the surrounding rocks.  The acid water ultimately contaminates waterways further down stream making it difficult for the flora and fauna to survive.

 

Throughout history every hardrock mine that has sulfur bearing rock as its host media has produced ADM.  Most sites have to be perpetually treated.  Mining sites in Europe from the Roman Empire (prior to 467 AD) are still producing acid mine drainage today.   

According to the U.S. Forest Service, 20,000 to 50,000 mines currently generate enough acid water to cause damage to some 8,000 to 16,000 km of streams.2   

AMD is toxic to aquatic organisms, destroys ecosystems, corrodes infrastructure, and taints water in regions where freshwater is already in short supply -  Geoffrey S. Simate

Minnesotans' Concerns