CHARACTERIZATION OF CHAT LEACHATE AND MINE DISCHARGE INTO TAR CREEK, OTTAWA COUNTY, OKLAHOMA

The Tar Creek Superfund site is an abandoned lead and zinc mining area located in Ottawa County, northeastern Oklahoma. Large accumulations of milled mine tailings, locally referred to as chat, and byproducts of the gravity separation process, referred to as mill pond wastes, are prevalent in the area. Chat and mill pond wastes produce leachate containing cadmium, iron, lead, and zinc that enter drainages within the mining area. Mine discharge also emanates from several locations in the mining area including unplugged shafts, vent holes, seeps, and abandoned mine dewatering wells. A segment of Tar Creek was selected to characterize and quantify metal loadings by leachate from chat piles adjacent to the study segment. Four surface-water sampling sites along the study segment were sampled seven times over 14 days following a rainfall event. Instantaneous loads of cadmium, iron, lead, and zinc were determined for each sample. A mass-balance approach was used to determine the loading due to leachate within the studied segment and compare it to loading attributable to mine discharge. Iron and zinc loadings were much greater than cadmium and lead loadings in both leachate and mine discharge. Iron loading from mine discharge was greater than iron loading from chat leachate within the study segment. Cadmium loading from chat leachate was greater than cadmium loading from mine discharge within the study segment. Zinc and lead loadings from mine discharge were comparable to zinc and lead loadings from chat leachate at the study segment except the loadings mine discharge were greater than the chat leachate on the first day following the rainfall event.