After processing its last gold ore, Kennecott Ridgeway Mine was closed in 1999 and the reclamation process began. For 16 years, Schnabel provided ongoing engineering, consultation, monitoring, and testing services at the mine to Rio Tinto, one of the world’s largest mining companies. Of particular note, we provided design, consultation, and construction management services associated with its closure.

Containing the waste rock (tailings) and flooding the pits are just two of the steps needed to effectively repurpose the site. Our work included the closure of a 120-ft high, 312-acre cyanide tailings landfill dike and the development of spillways, channels, and conduits to direct surface water through the property, with final discharge into Bear Creek. We evaluated site conditions, reviewed documents, and developed a concept design for the final surface water control system. Hydrologic and hydraulic analyses of storms up to the probable maximum precipitation (PMP) event indicated the need to raise the existing tailings dike embankment, and to modify the existing spillways and emergency overflow section. We also performed dam break analyses to evaluate the impact on the integrity of the tailings embankment.

Our geotechnical engineering services included soils laboratory testing, recommendations for subgrade preparation, construction of seepage cutoffs, internal drainage systems, final slope configurations, compaction requirements, and construction procedures. We provided estimates of settlement and seepage, along with soil and rockfill slope stability analyses and site seismicity impact on design.

The existing mine pits and surrounding area were converted into wetlands and lakes used as a natural laboratory for the Clemson Ecological Restoration Institute. We prepared plans and specifications for the surface water control system, including embankments, spillways, drainage channels, and additional structural features. A combination of vegetation, turf reinforcement mats, stone riprap, and grouted geotextile mats were used to provide efficient and cost-effective stabilization. We prepared documentation for the permitting of the dams and spillways, and for the South Carolina Department of Transportation encroachment permits. Construction management services and comprehensive quality control testing were also provided.