A solution for sulfate and zebra mussels

Map of St. James Mine Pit, at the edge of the town of Aurora


Dec. 21, 2023: After a century of iron and taconite mining in northern Minnesota, the landscape is dotted with former mine pits that have become lakes, some serving as municipal water supply for nearby towns. In addition to the high levels of sulfate and other pollutants that should be treated before the water is drinkable, there’s another problem: water levels have been creeping up, and a few of these “legacy pit” lakes are nearing overflow. In a July 2023 Mesabi Tribune article, “Keeping an eye on the St. James Mine Pit,” Lee Bloomquist discussed the problem for the town of Aurora.

In the St. James Pit, sulfate levels stand at 300 to 400 mg per liter (the standard for drinking water is 250 and the wild rice standard is 10 mg per liter), and there’s also a problem with zebra mussels.  Aurora officials are now in the process of switching to a different source for its water supply. But when they do, the pit’s water level will still need to be managed. In fact, it will overflow even faster without that water being drawn from it.  And with those high sulfate levels, plus the zebra mussels, it is illegal for the city or the Minnesota Department of Natural Resources to pump the water out into natural waterways, as it would further taint the ecosystem.

The Clearwater Biologic system could solve several problems at once for the DNR and the city of Aurora. Its process can reduce sulfate to near zero, eliminating zebra mussels at the same time, for water discharged from the pit lake.  With that treatment in place, water could be safely pumped out, posing no environmental problems and meeting water standards.  Clearwater Biologic leaders hope to do a pilot project at the St. James Mine Pit to show its effectiveness.

Read the Mesabi Tribune article online.

Map:  The town of Aurora lies at the edge of the St. James Mine Pit. Just to the north are several other taconite pit lakes of Erie Mining, source of the sulfate.