Arsenic and mercury levels exceed human health standards on parts of the East Fork of the South Fork of the Salmon River and two tributaries, Meadow Creek and Sugar Creek, a U.S. Geological Survey study showed.
The study, in the historical Stibnite Mining District of central Idaho, was commissioned by Midas Gold, which hopes to open a mine in the area and the Idaho Department of Lands. USGS sampled at five sites. Only one site on Meadow Creek, did not exceed health standards for arsenic . The three sites farthest downstream in the study area had high antimony levels.
Nearly all of the mercury flowing out of the study area can be attributed to Sugar Creek, the site farthest downstream. The Sugar Creek watershed contains the former Cinnabar mercury mine.
USGS hydrologist Alexandra Etheridge said groundwater may be contributing substantial amounts of arsenic and antimony to the streams.
“This study shows for the first time that Meadow Creek upstream of the confluence with East Fork of the South Fork of the Salmon River is not the only substantial source of arsenic and antimony in the study area,” said Etheridge. “It also shows that the old mining pit... known as the Glory Hole acts as a sediment trap, especially at high flow.”
The U.S. Forest Service has issued a decision on a Midas Gold exploration proposal to conduct drilling in the area near Yellow Pine so it can develop a mining plan. The Idaho Conservation League and the Nez Perce Tribe have filed objections to the decision which was supposed to go into effect last week.
The Forest Service extended the objection period at the request of the two objectors because of ongoing talks with between them and Midas.
“The Stibnite Mining District has been impacted by a century of mining activity,” said Bob Barnes, Midas Gold CEO. “The possibility of re-mining and reclaiming the site using modern methods give us a unique opportunity to address this environmental legacy and restore the site."
John Robison of the Idaho Conservation League said the last mining company also promised to leave things cleaner than they found it but they ended up declaring bankruptcy, leaving taxpayers with contaminated water and a $13 million cleanup bill.
"The water is still contaminated," Robison said. “I appreciate Midas Gold’s intent to restore the site, but additional mining, particularly 400’ below the riverbed of the East Fork South Fork Salmon River, could make things even worse. "