IMPACT OF ACID MINE DRAINAGE ON A STREAM SYSTEM IN WESTERN INDIANA

West Little Sugar Creek is severely impacted by acid mine drainage discharging from the abandoned Green Valley coal mine in western Indiana. The acidic effluent is derived from degradation of pyrite contained in approximately 5 million tons of coal waste material stored on the surface at the site. The acidic effluent flows into West Little Sugar Creek via three constructed channels that drain from the mine site and through various groundwater seeps located in the stream bank. This study investigates the physicochemical conditions of the stream water in West Little Sugar Creek from the mine site up to 5 km downstream to further elucidate the degree and extent of contamination. Stream water pH in the uncontaminated section of the stream upgradient of the mine is slightly alkaline (pH 7.4), and the stream supports a diverse macrofauna population, including small fish, crayfish, frogs, and various aquatic insects. In the zone of mixing where effluent discharges into the stream, pH decreases to 3.0 for a distance of 518 m past the last contaminant discharge point, and acidic conditions (below pH 6.0) persist for approximately 2.4 km beyond the zone of mixing. Coinciding with the impacted zone, macroscopic aquatic life is significantly reduced compared to the uncontaminated section of West Little Sugar Creek, and in most cases, there is no visible macroscopic life in the stream for approximately 2 km downgradient of the site.

Fine-grained iron and aluminum oxy-hydroxide also form in the stream channel due to dilution and pH increase as effluent mixes with stream water. The precipitates aggregate and settle to the channel bottom forming a layer of chemical sediments up to 25 cm thick. Chemical sediments are thickest in the zone of mixing and continue to coat the channel substrate up to 5 km downstream. The sediments pose a threat to aquatic life by eliminating habitats and potentially causing respiratory dysfunction and/or interfering with metabolic processes in some organisms.