The PolyMet NorthMet project would discharge multiple pollutants to already-impaired surrounding waters, including mercury and sulfates which have the potential to increase mercury release from wetlands and sediment. Mercury accumulates in the food chain and eating mercury-contaminated fish can result in brain damage. Children, infants and the fetus are particularly vulnerable. The potential for mercury discharge and mercury methylation from the PolyMet NorthMet mine are among the concerns that led the U.S. EPA to conclude that the project, as proposed, is “environmentally unsatisfactory.”

WaterLegacy legal counsel, Paula Maccabee, has prepared a review, MERCURY, MINING IN MINNESOTA, AND CLEAN WATER ACT PROTECTION: A REPRESENTATIVE ANALYSIS BASED ON THE PROPOSED POLYMET PROJECT published in the William Mitchell Law Review, Volume 36. 

INTRODUCTION (citations omitted):

The PolyMet Mining Corporation’s (Polymet’s) proposal to locate its NorthMet copper-nickel open pit mine and  processing facility in Northern Minnesota, draining to impaired waters within the Lake Superior Basin, is one of several proposals to increase mining and minerals processing within the Great Lakes System. This project and successive projects pose important legal questions about the application of the Clean Water Act and the Great Lakes Initiative for mercury point source discharge to impaired waters and increased mercury concentrations in the food chain resulting from nonpoint source loading. These processes pose significant risks, such as mercury air emissions and sulfate discharge within the watershed....

Point source discharge must meet wildlife-based standards for mercury concentrations in water under the Great Lakes Initiative and health-based limits on mercury in fish tissue set by Minnesota laws.  Neither mixing zones nor variances are permitted for point source discharge, and water quality may not be degraded.  Detectable mercury discharge to waters within the Great Lakes System triggers analysis of whether a new mining and processing facility causes or contributes to the violation of mercury standards or degradation of water quality.  Significantly, discharge with the potential to cause or contribute to water quality violations requires analysis through a TMDL study or comparable waste load allocation study.