Artesian discharges of net alkaline, ferruginous waters from abandoned underground lead-zinc mines cause considerable surface water degradation at the Tar Creek Superfund Site, part of the historic Tri-State Mining District of Oklahoma, Kansas and Missouri. Two perennial borehole discharges, identified as the lowest elevation mine water discharge points in the district, have flowed unabated for almost 30 years and considerably degraded the physical, chemical and biological integrity of a first-order tributary to Tar Creek. Based on a comprehensive water quality and quantity characterization study, a large multi-cell passive treatment system was designed to receive approximately 1000 L/minute of mine water flowing from these abandoned boreholes (pH 5.95±0.06, total alkalinity 393±18 mg/L CaCO 3 , total acidity 364±19 mg/L CaCO 3 , Fe 192±10 mg/L, Zn 11±0.7 mg/L, Cd 17±4 ug/L, Pb 60±13 ug/L and As 64±6 ug/L). The objectives of this project include: i) remediation of polluted mine waters to acceptable quality for maintenance of the receiving water body aquatic community, ii) demonstration of the first mine water treatment facility of any kind in the Tri-State Mining District, and iii) technology transfer to speed application of this technology to other locations. The passive treatment system includes an initial oxidation pond followed by parallel treatment trains (to facilitate research and experimentation) consisting of aerobic wetlands, vertical-flow bioreactors, re-aeration ponds (with active aeration via wind and solar power) and horizontal-flow limestone beds. Waters from the parallel trains are recombined in a polishing wetland prior to final discharge. Total design surface water elevation change in the entire system is approximately 1.8 m. Prior to system implementation, the abandoned boreholes required rotosonic over-drilling to establish hydraulic control. In addition, diversion of storm water flows from an approximately 470-ha upgradient watershed was necessary. During construction, a third mine water discharge was discovered and incorporated into the design. This system represents a state of the art ecological engineering research site for passive treatment of mine waters.