Gold exploration resumes at Keystone drill site where leak occurred
2 hours ago • Kevin Woster Journal staff
Work resumed Monday at a gold-exploration drill site in Keystone that was shut down last week after it allowed a bentonite solution to leak into Battle Creek.
The exploration company, Mineral Mountain Resources Ltd. of Vancouver, British Columbia, determined that the leak was caused by a rip in a drill sump that allowed bentonite and water to escape, said Mike Cepak, an engineering manager with the state Department of Environment and Natural Resources in Pierre.
"Mineral Mountain found the source of the leakage — a new drill sump they recently dug (the liner ripped and the bentonite/water leaked out)," Cepak told the Journal by email Monday. "They abandoned this sump, cleaned out their old sump, relined it and resumed drilling. No problems have been noted since they resumed drilling."
According to DENR, a drill sump is a hole in the ground with a liner. The sump is filled with a mixture of water and bentonite for drilling fluid, which is circulated into and out of the drill hole during operation.
Sumps eventually fill with drill cuttings and have to be cleaned up, or another sump must be dug.
Cepak said last week that the bentonite mixture wasn't hazardous and that the leak essentially stopped when the drill work at that location was suspended. Mineral Mountain notified DENR shortly after noticing the leak, he said.
The leak did create a milky stain in Battle Creek. A state Game, Fish & Parks Department official said he didn't think the leak would cause serious damage to fish life in the creek.