The Wisconsin Department of Justice is weighing a penalty to be imposed on two sand mines for large spills in the St. Croix River.
In both of the spills, the mining companies were not meeting their permit conditions.
Wisconsin DNR enforcement specialist Deb Dix said one site had no erosion control structures, and the other used soft sand to build a berm.
"They did not construct properly, were not out there on a daily basis to watch what's going on, and with their permit conditions they should have an understanding of what they need to do so that we don't need to be out there every day," Dix said.
In one spill, sand-laden water flowed through a wetland into the St. Croix River.
Wisconsin is home to more than 63 frac sand mines and 37 processing plants. The state is experiencing a boom in mining for sand used in hydraulic fracturing used in boosting production from natural gas and oil wells.
The Wisconsin DNR's Tom Woletz said many of the companies getting into the frac sand business are new to mining.
"We're seeing fugitive dust emission issues; we're seeing stack test violations; we're seeing facilities permitted one way and built another," he said.
The agency has reassigned some staffers to work on sand mine issues.