The term “dewatering” sounds harmless; it conjures up a prosaic image of someone mopping up a child’s spilled drink. But mine pit dewatering is a brutal process. Mines and quarries commonly puncture water tables and extend into local aquifers. When that happens, massive pumps must be employed to extract inflowing water so that mining can proceed without flooding.
In Minnesota there are a handful of dewatered limestone mines which have significantly lowered the local water table, caused private wells to fail and, in one case, even decreased the flow of a nearby river (the Straight River near Owatonna). The most egregious example is the Kraemer Mining and Materials quarry in Burnsville, MN. Since the operators began limestone extraction in 1959, this mine has lowered the level of the local Prairie du Chien aquifer by 70 feet as of 2015. The dewatering of this mine continues.
Currently, a permit to allow the development of an additional dewatered limestone mine in the small rural community of Waterford Township, near Northfield, is being considered by the local board. The proposed mine would cover more than 300 acres of former farmland and is expected to waste up to 10 million gallons of fresh water per day, every day, for 50 years. This mine is intensely opposed by citizens of Waterford Township, because of possible effects on drinking water, wetlands and air quality. It turns out that “dewatering” is anything but harmless.