Mining Program - Region 5 Success Stories
The Calfed Copper Mine Closure, Amador County

The Calfed Copper Mine Closure, Amador County

  Photographs of Mine Site

The Calfed mine is a copper mine located in Amador County, near Ione. The mine and its tailings were about 1 acre and is part of a larger 520 acre parcel owned by Calfed Bank. The mine was created by Amelsco Exploration as an exploratory excavation. They constructed a 15-foot x 15 feet by 40 feet deep shaft. There was never any commercial production at the location. During mining the mine waste was dumped adjacent to the stream that is a tributary to Sutter Creek. The tailings were generating acid waste that was being discharged into the stream.

Acidic runoff and waste were being discharged into the stream and lowering its pH from 6.75 to 5.42. There was also an increase in the electrical conductivity to 509 um/cm as the stream passed the mining waste, and copper and zinc concentrations increased from non-detect to 810 ug/l and 2000 ug/l respectively. The pH of the tailings was tested and the average result was found to be 1.9, which is considered to be hazardous under Title 22. The tailings are classified as a Group A mining waste under Title 27.

The tailings and overburden were mixed with lime to neutralize the acidity of the tailings. The lime-amended material was then placed back into the shaft and compacted, filling the shaft. Excess lime-amended material was sent to a local landfill. The soil was regraded and seeded.

The site was successfully restored, with removal of excess mine waste material and closure of the mine shaft. The pH of the soil at the site was returned to background concentrations. The stream's pH, electrical conductivity and metals concentrations were reduced to background levels. For example, the downstream pH increased to a range of 6.52-6.58 and the electrical conductivity decreased to 297 um/cm.