The Bureau of Mines has invented a simple, low-maintenance system to mix and aerate mine water in a pipeline. It consists of a jet pump, which entrains air by venturi action, and a static mixer, which induces turbulent flow. The system has no moving parts and is designed to use the pressure generated by an existing mine water discharge pump. The in-line aeration system has been field-tested at a minesite in Greene County, Pennsylvania, where high ferrous iron (fe2+) concentrations were causing discharge problems. Discharge concentrations of fe2+ were reduced from 10 to 20 mg/l to 0.2 to 0.9 Mg/l by installation of the aeration system. At high influent fe2+ concentrations (47 to 240 mg/l), the system also proved effective, despite low ph conditions (4.6 to 5.6). Neutralization and aeration were combined into a single step by injecting sodium hydroxide (naoh) into the port of the jet pump. This resulted in oxidation of the fe2+ within a few seconds, indicating that combining neutralization and aeration optimizes reaction rates.