The spill from a frac sand mine in Jackson County sent a "slurry" of water and fine sediment from a holding pond into wetlands and a creek feeding the Trempealeau River according to a Department of Natural Resources report obtained by WPR.

According to the DNR investigation, at around 8 p.m. Friday, Aug. 2, a foreman at the Wisconsin Proppants mine and processing facility in the Town of Curran began pumping water from a storage basin used for collecting fine muds into a "process water" holding pond. The holding pond stores water used to wash frac sand. The report says the storage basin contains "slurry sludge" known as fines, which are leftover from the sand washing process.

Early Saturday morning the report states the Wisconsin Proppants foreman checked the water flowing between basin and the pond before turning the pump off and noted that the water was clear. But at some point between 4 a.m. and 8 a.m. the pump began pumping "slurry/mud from the fines storage basin rather than 'clear' water from the surface of the basin."

Investigators said the mud accumulated in a "swale," which is a ditch-like depression the company uses to route water from the basin toward the process water pond.

"This mud accumulated in the swale, slowly accumulating and ultimately caused the swale to overtop with the mud and discharge the slurry sludge downhill toward the wetlands southwest of the swale. It is unclear why or how the employee did not realize this was happening when he made his checks at 0400 and 0800," said the report.

DNR warden Ryan Lowry arrived at Wisconsin Proppants around 12:45 p.m. on Saturday after receiving a complaint about a large amount of sediment in the Trempealeau River near the Village of Taylor in Jackson County. The report says when Lowry arrived, Wisconsin Proppants workers had stopped the release and were "attempting to pump impacted water back into their wet processing plant."

Lowry reported that the slurry flowed into a wetland on the Wisconsin Proppants property "at a slow enough rate not to push down vegetation next to the swale." The report states Lowry checked a culvert nearby and found "highly turbid" water flowing through it into a wetland in an adjacent property.

The water flowed through the culvert and wetlands before emptying into Curran Coulee Creek, which feeds the Trempealeau River.

The DNR found no evidence of fish or other aquatic life being killed as a result.

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On Monday, DNR hydrogeologist Matt Thompson visited the Wisconsin Proppants site and noted about 1 inch of slurry sludge in the culvert near the mine site.

In an interview with WPR Thursday, Thompson said the pump moving water from the basin holding the fine slurry materials is connected to a hose that floats on the basin's surface. He says it appears that the water level in the basin got low enough that the hose began pumping the mud instead.

"So, my understanding is that the pump was turned off at 8 o’clock in the morning because they had reached a water level within their wet plant that was acceptable to them," Thompson said. "The pump was not shut off because they noticed impacts to the creek or the river."

Thompson said based on the capacity of the pump Wisconsin Proppants was using and the 4 hour period that it was running a conservative estimate is that around 400,000 gallons of water and sediment spilled from the site.

Thompson and Lowry took samples of water and sediment from Curran Coulee Creek above the spill site and at the point of entry. But the report notes that "Given the limited apparent impact to the Trempealeau River, Warden Lowry and Matt Thompson decided not to take river samples."

The samples from the creek will be analyzed for metals. Thompson said an environmental consulting firm hired by Wisconsin Proppants has also collected samples and the company has asked for expedited test results. He said he's hopeful to get those results within the next week or two.

In May of 2018, a frac sand mine owned by Hi-Crush Proppants in neighboring Trempealeau County spilled 10 million gallons of water and fine sediment when workers emptied a process water holding pond to save a worker who had become trapped underwater in a bulldozer. Tests of that sediment showed high concentrations of heavy metals including arsenic, copper and lead. But water quality experts said those metals were "locked-up" in the sediment and did not dissolve into the water.

The DNR didn't issue any citations to Hi-Crush for the spill. The agency said the decision not to pursue enforcement was due to the life-saving measures taken which caused the sediment to be released.