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But small amounts of acrylamide have been shown to accumulate in mining waste water, and the chemical is widely considered to be present in stockpiles of discarded fines.
Mining reclamation plans call for those heaps to be buried back in the ground in unprecedented volumes — some of it at mines where digging goes well below the water table.
“There hasn’t been a lot of study about what happens to these chemicals when they get into the subsurface,” said Virginia Yingling, a hydrogeologist with the Minnesota Department of Health. “We are trying to find out if it’s a problem.”
Budinger said frac-sand companies in Wisconsin adhere to an approved products list for flocculants and other water additives. He said responsible operators continually are managing water quality and quantity with the environment in mind.
Using polyacrylamide to clarify wastewater allows mining companies to reuse the water, conserving valuable groundwater. And published studies demonstrate that polyacrylamide can degrade safely when stored above ground.
Even so, polyacrylamide and polydadmac, another widely used sand-processing flocculant, were recently added to the Health Department’s list of “chemicals of emerging concern” and will be screened for potential health risks.
The Minnesota Pollution Control Agency has its own study group on flocculants and might reassess existing permits that allow polyacrylamide use depending on findings.
Mike Caron, director of land use for Minnesota-based Tiller Corp., said the company’s frac-sand division has intentionally avoided polyacrylamide because of the unknowns. The company uses a starch-based flocculant sold by HaloSource Inc. of Bothell, Wash.
Several sand mining operations around the country have switched to greener technologies, said Frank Kneib, a HaloSource product manager.
Tiller operates a frac-sand mine near Grantsburg, Wis., and still is resolving a spill of dirty water that reached the St. Croix River last year. The U.S. Army Corps of Engineers treated it as a violation of the federal Clean Water Act and the Wisconsin Department of Justice is considering possible sanctions.
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