The fines are for failing to properly maintain containment dikes around settling ponds, and for discharging fine sediment into a creek, wetland and the St. Croix River.
Court filings state that dikes around one pond failed on or before April 22, 2012 and the spill continued for at least five days. The spill was a “significant contributor of pollutants” to the waterways, according to the Wisconsin Department of Natural Resources.
The spill was first spotted by a hiker, who reported it to the DNR. When the DNR followed the muddy water to its source at the mine, the operators were unaware of the berm failure. Pollution from the spill raised concerns about fish spawning and rare mussel habitat in the St. Croix.
Tiller Corp. and Interstate Energy Partners, both based in Minnesota, agreed to the fines, without admitting liability. The mine is the only frac sand mine near the St. Croix River. Tiller recently began work on a controversial gravel mine next to the river in Scandia, MN.
Read the court documents here (PDF).