What risk do Larimer County waters face from mining? — the Fort Collins Coloradoan

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From the Fort Collins Coloradoan (Jacy Marmaduke):

A map released last week by the Colorado Division of Reclamation, Mining and Safety shows the majority of the mines clustered in the Silverton area and the Summit and Clear Creek county areas.

The closest leaking mines to Fort Collins are a Boulder County cluster of seven, four of which aren’t undergoing active water treatment. There are about 23,000 abandoned mines in Colorado, according to the state geographical survey.

The map also charts mine-related impaired streams — waterways with levels of potential mining-related minerals that surpass state standards. Red lines on the map denote mine-related impaired streams.

The map shows a short red section on the North Fork of the Poudre River and a lot of red lines around the Big Thompson River in the southern part of the county.

The North Fork of the Poudre is red because it contains higher-than-normal levels of lead, cadmium and copper. The Big Thompson is red because of higher levels of the same minerals, plus selenium and zinc as well as low pH levels indicating acidity.

But it’s not as bad as it sounds, said Nicole Rowan, watershed section manager with the Colorado Department of Public Health and Environment.

“It could be mining or it could be the geology of the area,” Rowan said. “This is one of the most mineralized areas in the world. That’s why people mine here.”

Federal law requires the state to assess its water quality and report the results. The map draws from the state’s last complete report in 2012. Of the Larimer County waterways included on the map, three segments are ranked high priority — meaning they’re a source of public drinking water or contain an endangered or threatened species with no plan in place to protect it.

These segments are:

•Big Thompson River’s Fish Creek below Mary’s Lake, due to low pH levels

•Big Thompson River from Rocky Mountain National Park to Home Supply Canal Diversion due to sulfide, copper, cadmium and zinc levels as well as high temperature

•Big Thompson’s North Fork due to copper levels

Zack Shelley, program director of the Big Thompson Watershed Forum, said the metals in the Big Thompson probably aren’t results of mining. The copper levels in particular are high because federal and state government used to treat algae in the river with copper sulfide, Shelley said. Other potential sources of metal in the Big Thompson include abandoned landfills, forest fires and septic systems in the area.

“To my knowledge, I don’t see a human health risk,” Shelley said, but the metals do present risks for fish and other aquatic life in the river.

The Big Thompson Watershed Forum will present new data on the river’s water quality next month.

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