INVESTIGATION OF WATER CHEMISTRY AND PRECIPITATE COMPOSITION IN AN ACID MINE DRAINAGE SYSTEM AT THE GREEN VALLEY COAL MINE SITE, INDIANA

Acid mine drainage (AMD) at the reclaimed Green Valley coal mine site, Indiana, flows through a network of constructed channels and discharges into a nearby natural stream. Weekly monitoring of the AMD environment over a three-month period in the summer shows that effluent pH ranges from 3.0 to 3.8 and increases above 4.0 in conjunction with increased hydrologic input due to rainfall events. Preliminary analysis of the AMD by ICPMS indicates that the effluent carries up to 11,800 ppm Fe and up to 1840 ppm Al, with levels of Li, B, Ti, Cr, Co, and Ni elevated above that of normal surface water. The Fe and Al concentrations in the AMD are 10-30% higher than those measured prior to reclamation in 1994, suggesting that reclamation efforts have been ineffective in reducing metal concentration of the effluent.

Iron-rich precipitates coat the substrate of the constructed channels and consist of thin wavy laminae that alternate with thicker porous, sponge-like layers. Preliminary SEM analysis of the iron precipitates shows that they are composed of both amorphous and crystalline iron hydroxides, and to a lesser extent iron sulfates. Crystalline gypsum is also present, but at significantly lesser amounts. Interbedded within the sequence are thin (<1 mm), white layers of Al hydroxides that form when increased hydrologic input raises pH above 4.0.