A critical part of tackling this problem is to fully understand changing acid water conditions from underground mines over time to help in the designing efficient and cost-effective treatment measures.

 

This was the topic of a paper by J Skousen, J Demchak and L McDonald presented at the Sixth International Conference on Acid Rock Drainage held in Queensland recently. The paper looked at the discharge chemistry from above-drainage underground mines in 1968 and 2000.

 

Data was taken from more than 150 above-drainage (those not flooded after abandonment) underground mine discharges which were located and sampled during 1968 in northern West Virginia.

 

The research team then revisited 44 of those sites and measured water flow, pH, acidity, alkalinity, iron, Al, and sulfate. All 44 discharges were from mines in the Pittsburgh and Upper Freeport coal seams.

 

Past studies had reported acid water flows from underground mines for hundreds of years with little change, while others state that poor drainage quality may last only 20 to 40 years. Acid discharge from underground mines usually lasts much longer than their surface counterparts.

 

“Our data indicate that the water coming from above-drainage underground mines shows significant improvement over time,” the paper said.

 

“While significant coal seam effects were found, still a 50% to 80% reduction in acidity, iron, and sulfate were found for these mines in northern West Virginia between 1968 and 2000.”

 

The researchers also looked at water quality data from 20 mines taken in 1980, which showed that much of the improvement in water chemistry occurred between 1968 and 1980. This suggested an exponential rate of decline.

 

Given this, researchers were able to conclude the above-drainage underground mines in the region would continue to improve, and remediation strategies for above-drainage underground mines should include an assessment of the improvement in acidity and metal concentrations over time.

 

Acid mine drainage (AMD) affects approximately 10 000 kilometres of streams in Pennsylvania, Maryland, Ohio, and West Virginia, according to the US Environmental Protection Agency.

 

Many mines currently discharging AMD were operated and abandoned before enactment of the Surface Mining Control and Reclamation Act of 1977. The Act places responsibility of AMD control and treatment on the operator and has provided a means for reclaiming abandoned mines by taxing current coal operators, which generates funds for abandoned mine land reclamation programs.

 

The paper said even with millions of dollars spent in reclaiming abandoned mine lands, abandoned mines still generate more than 90 per cent of the AMD in streams and rivers in the region and most of this acidic drainage flows from underground mines.