Description: An Oxic Limestone Drain was constructed to treat acidity and aluminum. The treatment system consists of three series of two buried limestone cells where the acidity in the discharge water is neutralized and the pH and alkalinity are increased. Prior to treatment the discharge had low pH (3.6 to 4.2), no alkalinity, acidity (40 to 50 mg/1), negligible iron, and aluminum (1.4 to 4.9 mg/1). The discharge water requires relatively little detention time in order to successfully add the necessary alkalinity and raise the pH and remove the aluminum. The system is flushed weekly by the maintenance crew at Eagle Rock. The system was repaired after the flooding events in 2005 and 2006.