LEAD | To reduce the volume of contaminated water at the former Gilt Edge gold and silver mine in the Northern Black Hills, the Environmental Protection Agency is changing its method for cleaning up the site.
Project Manager Joy Jenkins said the EPA now plans to fill in the Anchor Hill Pit, a 160 million-gallon capacity reservoir that is creating water contaminated with metals and acids.
“The overall goal for the changes is to further reduce the contaminated water generated at the site," known as acid rock drainage, Jenkins said. “We’ll also be covering more mine waste materials to reduce the generation of contaminated water at the site."
The 360-acre site is 6.5 miles east of Lead.
Jenkins said preliminary activities would begin in 2015, but the majority of the filling of the reservoir would be completed in 2016. Costs for the work have not been determined, she said.
The original plan, written in 2008, has been modified as the result of studies of how to reduce the volume of contaminated water that requires collection and treatment, said Stan Christensen, a supervisor of EPA Superfund sites in South Dakota, Montana, Utah and Colorado.
“There are a lot of leftover things at this site including heap-leach pads, tailings and large quantities of waste rock,” Christensen said from his Denver office.
To date, the EPA and the State of South Dakota have spent more than $105 million to resolve longstanding environmental contamination at the Gilt Edge mine, he added. Those costs include about $2 million per year for eight to 10 employees collecting contaminated water and managing the site’s water-treatment facilities, which produce 200 to 300 gallons per minute year-round, Christensen explained.
Prospectors began mining for gold, copper and tungsten in the Gilt Edge area in 1876, and for decades, mining operations simply dumped their toxic mine tailings into Strawberry Creek and other local waterways. When Canadian-based Brohm Mining Co. took over the Gilt Edge mine in 1986, many of the streams already were contaminated with such heavy metals as arsenic, cadmium and lead.
Brohm operated the mine from 1986 until 1999, when it went bankrupt, forfeiting a $6.4 million mining bond and leaving behind 150 million gallons of contaminated acid water and millions of cubic yards of acid-generating waste rock, according to published reports. That’s when the state and the EPA stepped in. In 2000, Gilt Edge became a Superfund site, the program created in 1980 to facilitate cleanup of the nation’s worst hazardous waste sites.
From 1992, the first year for which there are records, to 1999, after Brohm entered bankruptcy, the firm extracted 102,274 ounces of gold and 172,504 ounces of silver from the mine, according to annual reports filed with the Department of Environment and Natural Resources.
In September 2012, four mining companies that had been involved, in varying degrees, in preparing the site to be mined in the late 1970s and early 1980s, agreed to contribute $30 million to the cleanup. Although the mining companies admitted no liability, Homestake Mining Co. agreed to pay $4.2 million, while Cyprus Mines Corp., Cyprus Amax Minerals Co. and Blue Tee Corp. shared $26 million in settlement costs.
Although remediation of the site will depend on additional construction and the availability of federal funding, Christensen estimated the cleanup could take as long as another decade to complete, after which it would be turned over to the state for ongoing maintenance.
“It’s a big, abandoned mine site, and we certainly have dealt with a lot of those,” he said. “I wouldn’t say this one is overly unique, but it’s pretty good-sized, and it’s going to take some effort to get it done.”
To date, the state has contributed $5.8 million to the cleanup effort, according to DENR Information Specialist Kim Smith.
Those interested in reviewing the revised EPA plan may view it online at epa.gov/region8/superfund/sd/giltedge or by visiting the Hearst Public Library, 315 Main St., in Lead.