Grey Eagle Mine
California, United States of America
Years of Service
1984 to 1988
At the Grey Eagle Mine in northern California, gold was mined from an open pit, milled and leached in a conventional cyanide leach circuit, and tailings were disposed of in a small (15 acre) but high (420 ft toe to crest) tailings impoundment, constructed from the mine waste rock. Cyanide and metals contaminated seepage was experience from the tailings impoundment prior to mine closure. Dr. Robertson was the Project Principal for SRK for the investigation into the cause of the seepage and the evaluation and design of remediation measures.
Geotechnical and geochemical investigations, drilling and testing were performed to define the contaminant source terms and plume pathway. Of particular interest was the need to determine the long term consolidation and settlement characteristics of the tailings in order to model the long term expulsion of contaminated tailings pore water. Specialized laboratory testing was performed to enable the consolidation settlement to be determined using non-linear finite strain consolidation theory. Both self weight consolidation and consolidation under cover loads were estimated together with the long term contaminated water expulsion to both the foundation and surface discharge pathways.
Remediation measures implemented include the design and placement of a multiple layered cover over extremely soft tailings. Methods of advancing this cover over the very soft tailings were developed, tested and finally implemented.