In Wisconsin, frac-sand mines in Trempealeau, Buffalo and Barron counties are creating unstable piles of sand waste and illicit wastewater runoff.
In Minnesota, state health officials are studying two chemicals widely used in frac-sand processing as contaminants of "emerging concern."
Four years into a mining boom that is reshaping parts of the rural countryside, mining companies and government regulators are coming to grips with the reality that the new industry involves much more than scooping sand out of the ground and hauling it away.
The states' burgeoning frac-sand industry, they have found, creates waste streams they are scrambling to understand and control.
From pyramids of discarded sand to sludge that accumulates in filtering devices, the mines create tons of waste byproducts that must be managed until they can be plowed back into the ground as part of reclamation plans designed to protect the environment and preserve the rural landscape.
"The industry just came on too fast," said Ruth King, a stormwater specialist with the Wisconsin Department of Natural Resources. "I wish we could turn back the clock a couple of years and start over."
In a rash of continuing violations that started last year, heavy rains have combined with sand-processing water to overflow holding ponds on several mining sites. The breaches have dumped sandy sediment into public waters, where it can suffocate fish eggs, kill aquatic plants and rob fish of habitat they need to reproduce.
"It really does impact the fisheries side of it," said Roberta Walls, another Wisconsin DNR water specialist.