Abstract:

A historical underground lead-silver-zinc mine (Site) in central Colorado is located between approximately 9,500 and 12,400 feet (2,900 and 3,800 meters) above sea level and is characterized by rugged and steep terrain with a series of fault and fracture systems that allow surface water to infiltrate into the mine workings. Active reclamation is ongoing and includes water treatment operations, management of four tailings ponds, adit rehabilitation, revegetation, tailings recontouring, and cover studies. A series of surface water diversions has recently been installed to redirect precipitation and snowmelt away from fracture zones above historical underground workings and reduce metal loadings to the water treatment plant. This paper describes the development of the surface water diversion design and its overall effect on seasonal flows to the water treatment plant, metal loadings, and water quality across the Site. Initial monitoring data indicate that the diversions have reduced metal loadings to the water treatment plant, although more data are needed to evaluate performance under variable snowfall and freshet conditions. This paper also explores the challenges that are presented by the terrain, climate, hydrology, and hydrogeology of the Site.

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Sarah Walker