Update 5/20: This story has now been covered by Minnesota Public Radio and the St. Paul Pioneer Press, as well as published broadly via the Associated Press. Scroll to the bottom for links to those stories and new photos provided by the Wisconsin Department of Natural Resources.

The wall of a waste pond at a sand mine near Grantsburg burst in April, sending fine sediment flowing down a stream and into the St. Croix River. The Country Messenger newspaper reports:

…Tiller Corporation was unaware that the berm had been failing until authorities visited the mine. Given the time between when the complaint was first made and authorities first contacted the mine, it is possible that sediment had been seeping from the frac sand washing pond for at least three days. No estimate has been made of the amount of sediment that made its way into the river.
Caron said that the containment pond was newly constructed and that it had been in use for only ‘a couple of days.’

The St. Croix River is designated as a National Scenic Riverway, and therefore subject to federal oversight by the National Park Service (NPS). Jill Medland, who serves as Environmental Coordinator of the St. Croix National Scenic Riverway, said that unnatural quantities of sediment make their way into the river, it is cause for environmental concern.

“We don’t yet know site specific impacts, but in general, sediment has an impact on the river bottom which cumulatively impacts the sediment of the river and could affect fish spawning and mussels, and things like that,” Medland said.

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Satellite imagery showing location

View Frac Sand Mine near the St. Croix River in a larger map

The mine is operated by the Tiller Corporation, which is currently seeking to open another gravel mine on a bluff over the river in Scandia. The mine is so far the only one of its kind in the St. Croix River region, where special silica sand is extracted to be used in “fracking” for natural gas.

The booming industry has been controversial in other parts of Wisconsin and Minnesota, including in the Minnesota city of Winona. Concern about the industry growing in the St. Croix River region prompted local citizens to sponsor a forum about the issue in St. Croix Falls earlier this month.

No longer an emerging issue but now a cause of actual environmental harm, authorities are still deciding what kind of penalties might be assessed against the Grantsburg-area mine:

Officials from the NPS, WDNR, and Burnett County have continued monitoring the event and will continue to track any environmental concerns that arise. While Ferris acknowledged the mine had not been inspected regularly, he said that collective inspections by the WDNR and county would become a fixture. The most recent inspection of the mine was last fall.

Tiller Corporation has also implemented a stricter inspection schedule effective immediately.

“We’re moving forward with a more vigorous monitoring schedule that includes more frequent visual inspections and water quality monitoring,” Caron said. “When we’re mining a natural resource in close proximity to another important natural resource (St. Croix River), we have duties and responsibilities to protect it, and it’s our intention to do that.”

A joint investigation by Burnett County officials and WDNR has been launched, and should be completed within a couple of weeks. This is the first time the mine has had any violations since opening last July. Ferris was unsure what, if any, penalties would be levied against the mine or mine operator.

“We haven’t decided anything yet,” Ferris said. “Our goal was to get proper containment put in, and when they’re done with that, we’ll get together with the WDNR and talk about that (penalties).”

The National Park Service is also in the process of determining what recourse they have in terms of citing the mine.

Update 5/20

Additional media coverage:

• Minnesota Public Radio
• St. Paul Pioneer Press
• Country Messenger (Broke story)

Photos of the site:

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