TRACE ELEMENTS IN FERRICRETE DEPOSITS IN A STREAM IMPACTED BY ACID MINE DRAINAGE

Iron cemented stream sediments (ferricrete deposits) line the channel substrate in West Little Sugar Creek located in west-central Indiana. The deposits formed as a result of acid mine drainage (AMD) mixing with uncontaminated stream water. The ferricrete deposits are located immediately adjacent to the abandoned Green Valley coal mine site where AMD enters West Little Sugar Creek and extend up to 4.5 km downstream of the site. Trace elements in AMD contaminated waters are generally attenuated via adsorption to or coprecipitation with Fe oxyhydroxide precipitates that form in these environments. This study evaluates the storage of trace elements in the ferricrete deposits to determine whether trace elements are being attenuated from the water column through Fe precipitation. Fifteen samples of ferricrete from West Little Sugar Creek were collected over a distance of 4.5 km downstream of the mine site. Samples were partially digested and analyzed for Fe, Al, B, As, Cd, Cr, Co, Cu, Mo, Ni, and Zn using ICPMS techniques and were compared to background concentrations in uncontaminated stream sediment samples collected upgradient of the mine site. Results of the study show that most of the ferricrete samples contained Fe, Al, Cd, Ni, and Zn at concentrations above background levels. None of these elements, however, showed decreasing concentrations with distance from the site, with Cd, Ni, and Zn being more highly concentrated at the most distal sampling point. These elements along with Fe and Al have also been detected in the contaminated water of West Little Sugar Creek where they were reported to exceed state and national water quality standards. The stream sediment data indicate these elements, and perhaps others, are being effectively attenuated via Fe precipitation and are being stored in the resulting ferricrete deposits which are more resistant to erosion than unconsolidated stream sediments.