Case Studies Chapter 7

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1. The Argo Tunnel - Pulsed Limestone Bed Treatment

1. The Argo Tunnel - Pulsed Limestone Bed Treatment



The Argo Tunnel is located in Idaho Springs, Clear Creek County, Colorado, approximately 30 miles west of Denver. The tunnel was constructed to provide drainage and transportation for several connected gold mines. The tunnel continues to drain acidic mine water at an average rate of 280 gallons per minute. The environmental media affected are surface water and, to a much lesser extent, groundwater.

Treatment Applied

A conventional lime water treatment plant was constructed in 1998 and has been operating continuously. Primary contaminants include acidity and a host of heavy metals, including aluminum, copper, iron, manganese and zinc.

A pilot treatment system was operated and studied periodically from 2004 through 2007 by the United States Geological Survey (USGS) Leetown Science Center utilizing a pulsed limestone bed treatment system at 230 L/min.


Metals removal for iron and aluminum was >98%. Copper had removals of 50 to >99%, while zinc had removals from 5 to 65%. Manganese concentrations were generally unaffected. The effluent of the limestone reactor required post-treatment with lime to raise the pH high enough to remove zinc and manganese to dischargeable levels. The sludge from the limestone/lime treatment scheme had settled volumes that were 60% of the lime treatment alone.


Sibrell, P. L., T. R. Wildeman, M. Frienmuth, M. Chambers, and D. Bless. 2005. “Demonstration of a Pulsed Limestone Bed Process for the Treatment of Acid Mine Drainage at the Argo Tunnel Site.” Abstract.