The iron pyrite known as fool’s gold is one type of the sulfide-bearing rock formations found throughout the gold mining district of the northern Black Hills that generate acid when exposed to air or water.
The challenge facing officials from Wharf Resources, operator of South Dakota’s last large-scale gold mine, is that veteran members of the state Board of Minerals and Environment don’t want to be played for fools again by another mining company.
Looming over the board’s hearing this week on whether to grant an expansion permit to Wharf is a legacy of pollution left to varying degrees at other gold mines such as Brohm, Richmond Hill and Golden Reward, where sulfide-bearing rock was exposed but wasn’t properly disposed.
What has continued to happen at those other now-closed mine sites in the northern Black Hills is sulfide rock has slowly oxidized as air or water reached it, gradually generating acid in amounts beyond what naturally occurs and beyond what state and federal environmental regulators deem acceptable.
Wharf officials and consultants repeatedly told the board on Wednesday and Thursday that acid rock drainage hasn’t been a problem at Wharf’s own mine. But one of the board members, Lee McCahren of Vermillion, who’s been on the panel since before surface mining for Black Hills gold erupted in the 1980s, said Thursday that promises were made in the past that acid mine drainage wouldn’t happen — but it did and hasn’t gone away.
“I at least am a little gun-shy,” McCahren said as he questioned a Wharf consultant. Minutes later he took the same tack again. “We keep being told, ‘Now things are going to be OK.’ ”
The witness, hydrogeologist Ted Cota of Denver, responded that Wharf’s plan will minimize the potential effects of acid rock drainage. He said the company has taken care when operations come into contact with pyrite and other sulfide rocks.
“But it’s possible it might occur. You can’t think of everything,” Cota said.
Wharf’s proposal includes a plan to reopen mining next door at the Golden Reward site’s old Liberty pit. As part of the work, Wharf wants to take steps that company officials said will reduce or halt water seeping down a high wall that is contributing to acid drainage there.
Several Wharf witnesses said water seems to have been getting under the cap and liner that were placed over the sulfide-bearing waste rock deposited there during the mid-1990s during the previous mining operation.
Part of the Liberty pit also would be contoured so that Terry Peak ski area could extend two runs into it. Wharf would replace the current red chairlift line with a new, longer one to accommodate the runs.
Cota, who has studied the acid-rock situation for Wharf for the past three years, said a strong possibility is that the cause at Golden Reward was a heavy rainfall in 1998 that occurred while sulfide rock was still being placed into the pit, before the cap and liner were installed.
He said the same type of circumstances might explain the acid drainage at the Richmond Hill mine.
The Brohm mine was closed after opponents successfully fought against the company being allowed to take buffer rock from U.S. Forest Service land in an attempt to neutralize acid-producing rock. Brohm is now a federal Superfund site.
Cota testified that acid rock drainage hasn’t been found in the ground water at Golden Reward, but sulfates that are a by-product do show up at higher than normal levels.
He said the water doesn’t need to be treated, but the sulfates could reach the level where aquatic life could be impaired.
South Dakota doesn’t have a sulfate standard for surface water and the standard for ground water is only secondary. Therefore, Cota said, there’s been no violation.
“This is a real minor problem,” he said.
Ron Waterland, who has been Wharf’s environmental manager for the past three years, took a similar stance regarding the potential for acid drainage at Wharf. At Golden Reward, Wharf had previously posted a $1.7 million post-closure bond that was to cover any problems for 30 years.
Waterland said the new mining plan for the Liberty pit would mitigate acid drainage there. “It’s not a risk,” he told the board.
The board’s three-day hearing is scheduled to conclude today.