Reclamation of the Silver Bell tailings impoundment, San Juan Mountains, USA

Authors: Foulk, CL; Tucker, JL; Jakubowski, RT Download Paper

DOI https://doi.org/10.36487/ACG_rep/1152_110_Foulk

Cite As:
Foulk, CL, Tucker, JL & Jakubowski, RT 2011, 'Reclamation of the Silver Bell tailings impoundment, San Juan Mountains, USA', in AB Fourie, M Tibbett & A Beersing (eds), Mine Closure 2011: Proceedings of the Sixth International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 421-431, https://doi.org/10.36487/ACG_rep/1152_110_Foulk



Abstract:
The Silver Bell tailings impoundment is located in south-western Colorado in the San Juan Mountains at an elevation of approximately 2,750 m. The impoundment contains approximately 80,000 cubic metres of sulphidic, acid rock drainage (ARD) generating tailings produced during mining activities that occurred between the 1940s and 1980s. Reclamation was conducted in 1999 and 2000 under the State of Colorado’s Voluntary Clean-up Program. Reclamation activities included regrading, placement of a soil cover and riprap, run-on diversions, seepage collection, and other closure activities. Total ARD seepage from the toe of the facility was approximately 0.3 L/s and following reclamation seepage decreased to generally less than 0.1 L/s. In 2005, the State of Colorado required the seepage discharge be permitted under the State’s industrial discharge permitting system. The established limits required water treatment measures to be implemented, which were not part of the initial design criteria. Therefore, hydrogeochemical characterisation and treatability studies were conducted as a follow-up to evaluate options for further dewatering the tailings to reduce seepage and/or to improve seepage water chemistry. These studies pointed to several options and actions including some that may have been undertaken if the discharge permit had been considered as part of the original design criteria. A major finding of these investigations revealed that a large portion of the acidic and metals loading in the seepage is the result of seepage through the oxidised coarse-grained tailings that formed the shell of the impoundment. Subsequent design modifications to address the stricter discharge quality requirements included the construction of an anoxic limestone drain (ALD), aeration channel, and sedimentation/oxic limestone treatment basins, which discharge to reconstructed wetlands. High iron concentrations in the discharge, e.g. 800 mg/l, have inhibited the effectiveness of the system. Further actions that may affect the long-term water balance of the tailings and seepage loadings have included: (1) upgrading a portion of the cover to reduce infiltration; (2) installation of pilot horizontal drains to provide a more alkaline water source for blending with discharging seepage and to help dewater the tailings; and (3) construction of an upgradient dewatering trench with a solar-powered pump to intercept shallow groundwater flow that was identified as recharging the facility.