Wetlands Treat Mine Runoff

by Frank Sanders, Sr. Sci./Proj. Mgr.; McCulley, Frick & Gilman, Inc., Boulder, CO,
John Rahe, P.E., Sr. Engr.; McCulley, Frick & Gilman, Inc., Boulder, CO,
Dan Pastor, P.E., Proj. Environmental Engr.; McCulley, Frick & Gilman, Inc., Boulder, CO,
Robert Anderson, Sr. Hydrogeologist; Hydrometrics, Inc., Helena, MT,

Serial Information: Civil Engineering—ASCE, 1999, Vol. 69, Issue 1, Pg. 52-55

Document Type: Feature article


Engineers were asked to design a treatment system for the severely acidic drainage from the Mike Horse and Anaconda metals mines in Montana. Challenges included the mountainous terrain, brutally cold temperatures, large snowfalls, and a lack of on-site electricity, as well as the composition of the drainage, which had a moderately acidic pH, moderate zinc concentrations and moderate iron concentrations. The solution is an integrated treatment system made up of flow-through plugs at the mines; in-line oxidation system (ILS) for passive oxidation of ferrous iron; a pretreatment basin for iron hydroxide settling and coprecipitation of zinc; sand filtration for iron; and polishing of residual metals in constructed wetland cells. Monitoring data from October 1998 show that the treatment system is meeting all discharge restrictions for iron, lead, copper and cadmium, and the wetland cells are still developing their capacity to retain zinc.

Subject Headings: Iron compounds | Zinc | Wetlands (fresh water) | Oxidation | Drainage | Acids | pH

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