English

Abstract

To protect the Ocoee River in Tennessee (USA) from acidity and metals loadings from historical copper mining and processing activities, OXY USA is conducting removal actions to alleviate contaminant discharges from North Potato Creek (NPC). One such action is construction of an innovative in- pit lime treatment facility at the South Mine Pit designed to treat NPC flows up to a 10-yr, 24-hr storm of 1,649 m 3 /min (972 cfs) prior to discharge to the Ocoee River. OXY USA performed an Engineering Evaluation / Cost Analysis (EE/CA) to identify and evaluate alternatives to address contaminant discharges from North Potato Creek to the Ocoee River. The alternative that was determined to best meet the evaluation criteria was the in-pit treatment alternative. The in-pit treatment system treats the entire 10-yr, 24-hour storm flow of NPC by adding lime to raise the pH to the level required to precipitate dissolved metals and then settling the precipitated solids in an existing 8.1 hectare (20 acre) abandoned surface mine pit. The treatment system utilizes the existing surface mine pit as a settling pond. The in-pit treatment facility was constructed for 15% of the estimated cost of a conventional lime treatment facility capable of treating comparable NPC flows. The NPC Water Treatment Plant operations began in January 2005 and results show that reductions in aluminum, copper, iron, manganese, zinc, and other dissolved metals loading of over 360 kg (790 lbs.) per day to the Ocoee River are being achieved.