Helena says Tenmile Creek more contaminated than EPA found

Friday, July 30, 2021

HELENA (AP) — Water samples taken by Helena City staff in Tenmile Creek following a mine waste spill earlier this month show severely higher levels of metals and arsenic than those reported by the Environmental Protection Agency, the Helena Independent Record reported.

The EPA says “a burp” caused mining sediment from the long abandoned Susie Mine, part of the Upper Tenmile Creek superfund site, to spill into the creek July 12.

EPA coordinator Duc Nguyen previously told the Independent Record that less than 100 gallons (378.5 liters) of water mixed with mining sediment was released into the creek below the city’s water treatment plant intakes, and did not impact the water’s quality.

But water samples taken by city staff on the same day showed over 100 times more arsenic compared to the sample reported by the EPA.

The level of arsenic measured by city staff was almost 3,000 times higher than the city’s discharge permit would allow, said City Manager Rachel Harlow-Schalk.

The agency recorded arsenic levels at about 0.15 milligrams per liter of water. Iron was at 0.48 milligrams per liter. Zinc was measured at 0.3 milligrams per liter. City staff recorded 31.2 milligrams of arsenic per liter of water and nearly 23 milligrams of zinc per liter of water at the site of the spill.

Discrepancies could be attributed to the location of sampling, though Harlow-Schalk said that sampling occurred in roughly the same place.

Still, Nguyen said Wednesday there is no concern.

An EPA crew has since built a settling pond below the mine entrance that will help remove the sediment before the water flows into Ten Mile Creek. A 40-foot spillway from the mine’s entrance was also built. The blockage at the entrance of the mine has been removed and the slope of earth above the entrance was re-groomed to prevent future collapses.

More than 100,000 gallons of contaminated mine runoff and acidic sludge that built up behind the section of mine that collapsed in 2016 was siphoned out and trucked away.