Failure of Cyanide Overflow Pond Dam

An overflow pond dam at a gold mine in South Carolina failed in October 1990 approximately 2 weeks after an exceptionally large rainstorm produced more than 280 mm (11 in.) of rain in 1 day (>>2,500-year event). The pond contained a cyanide leaching solution used to extract gold from low-grade ore. The pond was lined with two geomembranes separated by a geodrain intended to serve as a leak detection system. A detailed investigation attributed the failure to internal erosion within the dam that resulted from uncontrolled natural ground-water seepage occurring below the dam. The dam was constructed of gap-graded rockfill containing significant portions of highly erodible fines. Shortcomings in the design and in the construction procedures that contributed to the failure are identified and discussed.