The Black Hills of South Dakota was once home to the largest underground gold mine in North America – the Homestake Mine. Following its closure in 2002, the mine was turned into the Sanford
Underground Research Facility. But, newly published
research shows evidence of the past mining activities can still be found hundreds of miles downstream.
The history of gold mining in the northern Black Hills dates back about 130 years. During the first to middle part of the 20th century, about 100-million tons of mine tailings went down Whitewood Creek and into the Belle Fourche, Cheyenne and
Missouri rivers. Research by a group of scientists, including James Stone, Ph.D., a professor of Civil and Environmental Engineering at the South
Dakota School of Mines & Technology, along with others at the USGS
Dakota Water Science Center show elevated levels of arsenic and other contaminants in these historic mine tailings.
“The concentrations in the pore waters and sediments were quite high for arsenic in some sampling sites,” says Stone.
In the 1980s, mine tailings along Whitewood Creek, found to contain arsenic, mercury and other pollutants, became an EPA Superfund Site. That clean-up project was completed in the 1990s and was reported as successful. This research examined mine tailings
further downstream that were not removed. Click here for more information on EPA Superfund.
“The concentrations are high, but the area does not have very many people,” says Stone. The sparse population means little contact with any contamination. He says the SD Mines study ended at the border of the Cheyenne River Reservation and he adds that
ongoing studies by other research teams are now underway.
Those studying this problem point out that these contaminated sediments come from historic gold mining and there is still a fair bit of gold left over in the tailings. Mining these historic tailings could be one way to reclaim these streams and remove
the contamination.
“There were some companies looking at this potential when the price of gold was high,” says Stone. “However, it’s not an easy fix. The challenge is you might remobilize those contaminants.”
The research article titled “Arsenic
Geochemistry of Alluvial Sediments and Pore Waters Affected by Mine Tailings
along the Belle Fourche and Cheyenne River Floodplains” is published in “Water,
Air, & Soil Pollution,” a scholarly journal that publishes research form around the world on these topics.