Wisconsin regulators have shut down a frac sand mine for operating without a permit, dumping polluted wastewater into an unlined pond, and generally “running wild,” as one county official put it.

The 1,600 acre-Guza Pit mine is located four miles south of Independence, Wisconsin and near a stream that flows into the Mississippi River. The site produces “frac sand,” a fine, crush-resistant sand used in hydraulic fracturing, or fracking. Frac sand, which must be uniform in shape and able to withstand enormous pressures at great depth underground, is currently mined most heavily in Wisconsin and Minnesota. Due to the recent boom in shale gas extraction, Wisconsin alone is on track to extract 50 million tons of frac sand a year—the equivalent of 9,000 semi-truck loads a day.

A report released in late September revealed that frac-sand mining and processing is damaging to the environment. It uses huge amounts of groundwater and contributes to pollution by releasing “very small and very dangerous dust particles,” into the air.

The Guza Pit mine, run by Superior Silica Sands of Texas, is currently under the jurisdiction of Trempealeau County, which issued the stop-work order on Monday.