A massive leak into the St. Croix River from a sand mining operation remains under intense scrutiny from state and federal agencies charged with protecting the river from such mishaps.
Just how much damage the fine particles of sand from the Soderbeck mine inflicted on river habitat is being investigated, even as the mine operator builds stronger containment ponds to prevent a recurrence.
"Even without knowing the environmental impact they were in violation of state laws," said Deb Dix, an environmental enforcement specialist for the Wisconsin Department of Natural Resources (DNR) said of the company that operates the mine west of Grantsburg in Burnett County, Wis.
Various government agencies are trying to determine how much of the fine sand, which was being prepared at the site for oil drilling operations, was washed through a flimsy berm in late April into a nearby creek that carried it into the St. Croix River. The leak, described as the color of coffee in milk, went undiscovered until a hiker found it and took photographs.
Concern lies with the smothering effect the ultra-fine sand -- used in a controversial oil exploration process known as "fracking" -- would have on sensitive fish spawning areas and mussel beds in the St. Croix.
"It's a very critical habitat area," Dix said of the federally protected river. "It would be like filling in a wetland. You're killing everything there. It would be just like you and I in a sandstorm."
The mine is only 100 feet outside the St. Croix National Scenic Riverway, a national park. It's owned by Interstate Energy Partners of Minnetonka and operated by a Maple Grove sand and gravel company, Tiller Corp.
Mike Caron, a spokesman for Tiller, said Friday that his company is taking new steps to contain water and sand and expressed regret over the leaking berm.
"This is the last thing we'd ever want to happen at any of our facilities," he said. "We have to make sure that when we're mining those resources for use by the public that we protect the other natural resources."
Short-term problems in the river could include turbidity that leads to breathing problems for fish and other organisms, said Jill Medland, the National Park Service environmental coordinator at park headquarters in St. Croix Falls, Wis. Over time, sediment moving downriver could change river habitat because the processed sand isn't native to the St. Croix, she said.
The sand spill is possibly unprecedented in the St. Croix River, which came under federal protection in 1968, but it's one of several recent development challenges in the protected corridor. A proposed new bridge over the river at Oak Park Heights endured prolonged debate before Congress approved it this winter, and other controversies such as cell towers have entered the picture recently.
It was fortunate that Tiller wasn't using chemicals in its sand processing, Dix said. But she said that the DNR permit issued to Interstate Energy Partners required that water be "internally drained" -- soaking into the ground -- and the leak was a violation of that permit.
The DNR has issued a notice of violation and is requiring Tiller to submit weekly inspection reports, she said.
In a related matter, Tiller has proposed reopening a sand and gravel mine on the Minnesota side of the river near Scandia, in Washington County. The company will not process sand at that site, known as the Zavoral mine, should a permit be granted for operation, Caron said.
In Burnett County, conservation officer Dave Ferris said the mine is back in operation after several improvements were made to contain the water and sand.
"Everything looks fine out there," he said.
Kevin Giles • 651-925-5037 Twitter: @stribgiles