High spring runoff sent uncontrolled releases of arsenic-laced water flowing out of an old mine tunnel at the Atlanta gold mine project into Montezuma Creek this month and last.
Atlanta Gold, the company that operates the water treatment plant, said Monday in a press release the flows from the mine caused arsenic and iron discharges that exceeded U.S. Environmental Protection Agency standards. But it did not report how much arsenic entered the creek, which runs into the Middle Fork of the Boise River near Atlanta, 60 miles upstream from Boise.
The ground in the old mine tunnel collapsed in the high flows and ran over the bulkhead Atlanta Gold had built to keep it from flowing out, flushing polluted sediment from the floor of the crosscut and carrying it downstream through a series of filters, containment ponds, the water treatment plant and eventually the creek.
The flows rose throughout the month peaking at 1,048 gallons per minute May 17t. It peaked again June 10 raising the containment ponds 24 inches, shown by an orange ring caused by the iron. Atlanta Gold took portions of the treatment plant off line for cleaning, rebuilding and maintenance.
Atlanta built the bulkhead and made other improvements to its water treatment plant after U.S. District Judge Mikel Williams ordered it to pay $2 million for repeated violations of the Clean Water Act. Atlanta Gold CEO Ernie Simmons said in 2012 the new passive filtration system reduced arsenic levels from 5,000 parts per billion to less than 50 ppb.
Simmons did not return a telephone call Monday.
Dave Tomten, the U.S. Environmental Protection Agency’s Idaho mining coordinator was skeptical the system would hold during variable flows and pollution levels from the tunnel.
“The real test will be in the spring,” he said in 2012.
The Idaho Conservation League and the Northwest Environmental Defense Center brought the lawsuit against Atlanta that led to Williams’ order.
John Robison, public lands director for the Idaho Conservation League said the spills highlight the need for the Forest Service to develop a long-term closure plan for this site and to secure a financial mechanism to pay for water treatment in perpetuity.
“We always thought it would be a matter of when, not if, these toxic spills occurred,” Robison said. We have requested a meeting with the Forest Service to learn more about the damage, the cleanup and the implications for the future of the site.”