PolyMet has done two years of humidity cell lab tests of their ore and waste rock to characterize its acid generating potential. DNR experts tell us that the ratio of sulfur to acid buffering compounds (like limestone) of the waste rockand the particle size distribution (of blasted rock) determine the acid generating potential. The smaller the particle size the higher the acid generation. Unfortunately acid mine drainage has not appeared lab tests until after five years of this test weathering (wetting and drying) and PolyMet only has two years of data. So they want to “infir” using data on rocks not from there mine to characterize its pollution potential as required by state rules. Yet at the same time they argue that “their mine is unique.”

Taconite is not being proposed as a buffering material for “hot” wastes. Limestone is proposed with gypsum as the result, which as some commercial potential, but will be landfilled for several years, maybe always. We want the mines to prove they can prevent acid mine drainage and leaching of toxic metals into surface and groundwater by the mine pit and wastes. Taconite is not involved.

We are referring to metallic sulfide mining, not taconite mining. The ore bodies do not mix. There was one taconite mine that had some metallic sulfide rock over the taconite layer. The sulfide rock was dumped into a large pile and it started generating acid mine drainage into Birch Lake. There is a passive treatment system in place there now that will have to be monitored and maintained forever. So far a mining company is paying for this, but will they eventually declare bankruptsy to get out of the obligation?