Note: figures updated September 2015 to reflect average level of mercury in rainwater on site. .
Mercury is an element that commonly occurs in nature. At the PolyMet project site, mercury is found in low quantities in rock. Left in its natural state, mercury usually presents no health risk to humans or other living things as it tends to remain spread out in low concentrations within various minerals. Minnesota researchers have estimated that the mercury causing current fish consumption advisories in the region is from atmospheric deposition (for instance, rain and dust), with about 90 percent of the mercury falling in Minnesota coming from out-of-state sources.
The mining and processing of ore, however, has the potential to release mercury and other trace elements to water and air, so we take extra precautions to make sure any water and air that leaves the site doesn’t pose any health or environmental threats and remains well within strict health and safety standards set by state and federal regulators.
The Minnesota Department of Natural Resources created a helpful fact sheet [PDF] that outlines the steps PolyMet will take to protect resources in the area from mercury and other potential pollutants. This post walks through some of the fact sheet highlights and other information about mercury and how we’ll manage it.
Mercury and water
The proposed PolyMet project is located in the Lake Superior Basin, and therefore its permitted treated water discharges must meet the strict Great Lakes Initiative and Minnesota mercury standard of 1.3 nanograms per liter (ng/L). For perspective, when it comes to mercury, our discharged water will be about nine times cleaner than the rain (about 12 ng/L) that falls on the site and two to three times cleaner than what is found in natural runoff in the watershed.
When it comes to mercury, our discharged water will be about nine times cleaner than the rain that falls on the site and two to three times cleaner than what is found in natural runoff in the watershed.
To make sure we meet the Great Lakes Initiative standard, we will collect and treat water from the processing areas of the mine and plant sites to reduce or remove mercury before discharging it. These measures include installing water containment systems that capture water and route it to the treatment plants located at the mine and plant sites.
Mercury and air
According to the DNR, expected annual mercury emissions to the air are considered minimal, would not significantly affect fish in nearby water bodies, and are in line with the Minnesota Pollution Control Agency’s mercury reduction goals.
PolyMet will control air emissions at the plant using state-of-the-art technology, including low-emission burners. We also will monitor air and water quality so that we can make modifications to our systems and processes, if necessary, to address any potential issues long before they can become problems to any resources nearby.
“Mercury emitted to the air would be minimal, would not significantly affect fish in nearby water bodies, and is in line with the MPCA’s mercury reduction goals.” – DNR
Doing it right
PolyMet will use tried and tested technologies and processes to meet its moral and legal responsibilities to protect our air and water quality for generations to come.
For more information on mercury, water quality and the PolyMet project, download the complete mercury fact sheet [PDF] from the Minnesota DNR. Also, see the PolyMet Water Quality Fact Sheet.