Alexco Resource U.S. has successfully completed an emergency pit lake treatment environmental services contract at the Barite Hill gold mine that was abandoned in the 1990s near McCormick, South Carolina, USA. The pit lake contained about 227 million litres (60 million US gallons) of surface water and additionally impacted saturated waste rock fill areas, all of which contained highly contaminated strongly acidic mine drainage with metals concentrations similar to the Berkeley Pit Lake near Butte Montana and to numerous other larger acid pit lakes. Alexco completed this work under a fixed price and performance bonus contract with CMC, a site contractor to the US EPA Region IV.
The US EPA website (epaosc.net/baritehillnevadagoldfieldsremoval) recently posted treatment results for the project showing attainment of non-detectible soluble concentrations for aluminum, arsenic, cadmium, chromium, copper, lead and zinc, along with more than 95% reduction in already low concentrations of selenium, all of which are sufficient to attain the water quality criteria for the creeks leading away from the project site. Prior to commencement of treatment in late January 2008, the concentrations of several of these primary contaminants of concern exceeded Federal and State standards by hundreds to thousands of times the applicable standards. Most notably, copper concentrations were as high as 300 mg/litre prior to treatment and are now non-detectible (below 0.01 mg/litre), and zinc has been similarly reduced from 40 mg/litre to below a detection limit of 0.02 mg/litre. All of these results were achieved using Alexco’s patented technologies for pit lake, groundwater and underground mine pool treatment covered under US Patents.
The treatment used simultaneous lime neutralisation and soluble carbon source addition to reduce the toxicity, mobility and volume of the resulting metal sludges, which could not have been achieved by lime addition alone. Commenting on the successful results, US EPA On-Scene Coordinator Leo Francendese noted that “considering that titration tests showed that approximately 30 feet (9 m) of sludge would be generated by conventional lime neutralization, the resulting less than 6-in (152 mm) of precipitates formed by Alexco’s carbon addition during lime neutralisation is a remarkable result. The resulting pit lake has excellent water quality and minimal risk of remobilisation of the deposited metals. The costs to achieve these successful results were an order of magnitude less than other similar mine closures.”