Question 1: Will Minnesota’s water stay safe and clean?


While any kind of mining creates a certain level of environmental impact, mining sulfide ores has been shown to result in unique pollution and health risks, some quite different from those associated with iron mining. Pollution from sulfide mines can occur at various points in the mine operation, leaching from the waste rock piles and mine pit walls at the mine site, from the transportation of ore from the mine site to the processing facility, and from processing wastes disposed in tailings basins. “Waste rock” is the term given to the excavated rock that is not sent to the processing plant because it contains too little of the desired metals to be profitable to process. In sulfide mining, the vast majority of excavated rock is waste rock, while only a small fraction is sent for processing. But this sulfide-laden waste rock is the source of some very dangerous pollution.

It can sometimes be surprising to learn that naturally occurring substances on Earth are not always benign or “safe” to humans or our environment. Sulfides are those kind of substances. When left deep within the Earth, unexposed to air, they present no problem. But when brought to the surface, as is done with mineral extraction, sulfide ores undergo a chemical reaction that can createlong-lasting contamination to water and the plants and animals dependent on that water. When sulfides interact with oxygen (in our air) and water (in rain or snowmelt, for example), they create sulfuric acid – the same caustic substance used in car batteries. If this acid makes its way into streams, rivers, lakes, and groundwater in sufficient quantity, it will kill all organisms that cannot tolerate highly acidic waters.

In addition, the acids dissolve harmful metals out of the surrounding rocks. These are toxic to fish, other aquatic life, even people. A common term for this pollution is Acid Mine Drainage (AMD).

Spruce Road AMD

AMD on Spruce Road near Ely, MN

Acid mine drainage can be discharged from a variety of places in a mine, basically any place where the ore comes in contact with air and water. These places include open pit walls, waste rock piles, tailings, and underground tunnels.

Preventing this chemical reaction and toxic metal leaching is no small task for sulfide mines. The proposed PolyMet project, for example, expects to excavate and pile waste rock on the land. This waste rock mountain would be the equivalent of 500 football fields piled 20 stories tall. To keep Minnesota’s surface and ground waters free from sulfide mining pollution, none of these mountains of sulfide waste rock can ever be allowed to come into contact with oxygen and water. Or, if they do, they must be completely contained for hundreds of years while these pollutants persist. Mining operators have yet to identify a sulfide mine that has ever managed to accomplish it. AMD has devastated water bodies in many states where this kind of mining has occurred.

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In addition to acid drainage and metal contamination, chemical compounds called “sulfates” are often discharged from sulfide mining operations. Sulfates have been shown to facilitate turning non-toxic forms of mercury into toxic forms – a process called “mercury methylation.” This toxic form of mercury accumulates in fish and results in fish consumption advisories. Mercury contamination causes brain and kidney damage and behavioral disorders in humans. In a health study of newborn babies in the Lake Superior Basin conducted from 2007 to 2011, the Minnesota Department of Health found eight percent of tested newborns had mercury levels above the safe dose limit for methylmercury as set by the U.S. Environmental Protection Agency (EPA). According to the EPA, mining is the largest source of mercury contamination to the Lake Superior Basin, and new sulfide mines in the region are expected to add to this sulfate loading.


Earthworks. Fact Sheet. Hardrock Mining: Acid Mine Drainage.

Friends of the Boundary Waters Wilderness. October 2, 2010. Sulfide Mining: Spruce Road Acid Mine Drainage.

Goyer, R. August 19, 2004. Issue Paper on the Human Health Effects of Metals. U.S. Environmental Protection Agency Risk Assessment Forum

Jennings, S.R., Neuman, D.R. and Blicker, P.S. (2008). Acid Mine Drainage and Effects on Fish Health and Ecology: A Review. Reclamation Research Group Publication, Bozeman, MT.

MiningWatch Canada. December 2009. Two Million Tonnes a Day: A Mine Waste Primer.

Minnesota Department of Natural Resources Webpage. PolyMet Mining Inc./NorthMet Project EIS, Draft Environmental Impact Statement (EIS). 2001.

U.S. Environmental Protection Agency. 1994. Technical Document: Acid Mine Drainage Prediction.

Vimeo Webpage. Susan Hedman, Administrator for EPA’s Region 5 Office in Chicago at the Lake Superior Binational Forum, Friday, March 23, 2012. Ashland, Wisconsin.

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