CERCLA RESPONSE ACTIONS APPLIED TO ARSENIC-CONTAMINATED TAILINGS AT SMALL ABANDONED GOLD MINES ON NATIONAL FORESTS IN THE SOUTHERN SIERRA NEVADA, CALIFORNIA

An estimated 67% of the 47,000 abandoned mines in California are found on Federal land including National Forests. California’s Office of Mine Reclamation suggests that 11% the State’s abandoned mines present some type of environmental hazard which would include hazardous waste. Small abandoned gold mines on National Forests are a legacy that often has roots in the late 1800s. Mines where processing of gold ore occurred commonly have tailings piles consisting of fine-grained soil-like material. It is not unusual to find elevated concentrations of arsenic within these tailings; elevated levels of lead and other heavy metals may also be present.

Seven mine sites on National Forests in the southern Sierra Nevada contained tailings with arsenic concentrations commonly greater than 500 mg/kg and as high as 60,600 mg/kg. Of 114 samples collected during characterization studies, 62% exceeded the 500 mg/kg concentration for arsenic which classifies a waste material as being”hazardous” under California regulations. The volume of tailings at an individual site varied from 110 cubic yards to about 7,000 cubic yards. The tailings are usually present in piles and devoid of vegetation. Response actions, under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), to address these wastes were necessitated by potential human exposure to the public using National Forests, the potential for erosion of tailings into stream channels and their contribution to arsenic-related water quality issues in the Tulare Basin. While arsenic levels required initiating a CERCLA response action, the specific measures taken varied depending on factors such as tailings volume, site conditions and accessibility. Remedies ranged from excavation and transport to an appropriate disposal facility to encapsulation in a designed, on-site repository.