The 360-acre Gilt Edge Mine site, leased by Coca Mines Incorporated and Thomas E. Congdon, is located east of Lead, South Dakota, in the northern Black Hills area. The contaminated area includes a former open pit and a cyanide heap-leach gold mine. The EPA and the state contend that the Gilt Edge Mine Superfund site is heavily contaminated from mining activities involving hazardous substances including arsenic, cadmium, chromium, copper, lead, manganese, nickel and zinc.
This year significant earthwork will begin addressing ARD sources remaining within the primary mine disturbance area, which includes acid-generating waste rock and fills, spent ore, exposed acid-generating bedrock in mine pit highwalls and sludge.
Approximately 14 million gallons of high-sulfate water stored in two pits will require processing in the water treatment plant. During processing, the mixing of high-sulfate water with treatment lime generates gypsum that forms a cake that tends to clog the multi-media filters, the final treatment component.
Click here for the Washington Times article, here for the EPA's current update, and here for Joy Jenkins detailed description of what must be done to bring the abandoned mine back to healthy standards.
The site had been used for hard rock mining since the late 1800s and has been extensively disturbed by mining and mineral processing operations.