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Uranium found in Water Samples at Eagle Mine

The Superior Watershed Partnership (SWP) found a high concentration of uranium in water samples from the bottom layer of the Temporary Development Rock Storage Area (TDRSA) at Eagle Mine in Northern Marquette County. The samples confirm the presence of uranium at 72.6ug/L, a level of uranium that exceeds the federal maximum concentration level for drinking water.

The SWP has been conducting water quality and air quality testing at the Eagle Mine site through an agreement called the (CEMP) Community Environmental Monitoring Program. The program will monitor the Eagle mine site, the Humboldt mill and transportation routes. Rio Tinto is providing the Marquette County Community Foundation with funding ($300,000 annually) to establish the CEMP which allows the SWP to conduct environmental monitoring related to Eagle mining operations.

The lab where water samples are processed is called Underwriters Laboratory and has reported (as required by law) that the results exceed the EPA Maximum Concentration Level under the Safe Drinking Water Act, and that level for uranium is 30 ug/L.

“When the initial sample results were received, SWP notified Rio Tinto and scheduled a re-sample to verify results. SWP requested expedited reporting from Underwriters for the re-samples and the lab report confirmed the presence of uranium in the TDRSA Leak Detection Sump (61 ug/L and 58 ug/L) but not in the TDRSA Contact Water Sump (<1 ug/L or not-detected). Rio Tinto’s independent laboratory results from the re-sample also confirm the presence of uranium (56 ug/L) in the TDRSA Leak Detection Sump and at extremely low concentrations in the Contact Water Sump (0.13 ug/L)” (SWP CEMP Monitoring, April 5, 2013).

However, water in the TDRSA and the Water Treatment Plant is not regulated under the Safe Drinking Water Act. Rio Tinto’s Mine Permit and Groundwater Discharge Permit did not include regulation of uranium or limits for uranium. So the concentration of uranium is not in violation of any current state or federal permit. Water from the Leak Detection Sump will be removed and processed in the mine’s water treatment plant for ion exchange and reverse osmosis processing. Water from the WTP is either recycled through the mining process or discharged to the Treated Water Infiltration System (TWIS). The solids that are removed by the water treatment process will be disposed of at a municipal landfill.

The lab result was reported by law. “It’s a reporting requirement of the act because they don’t necessarily know what the source of that water is,” said John Becker a communications and development specialist with the SWP.

In effort to identify the extent of uranium contamination SWP will test representative core samples, a development rock sample and a sample of the aggregate imported for use in the TDRSA Leak Detection Liner. SWP will set additional parameters for testing which include but are not limited to; characterization of water in the TDRSA primary and secondary (Leak Detection) sumps, WTP influent and effluent, WTP solid waste, and related compliance wells. Further lab results are expected within one week. Some of these additional tests are intended to measure whether the water treatment plant is working. All CEMP monitoring results are available to the public at

According the EPA, “Uranium can enter the body when it is inhaled or swallowed, or under rare circumstances it may enter through cuts in the skin. Uranium does not absorb through the skin, and alpha particles released by uranium cannot penetrate the skin, so uranium that is outside the body is much less harmful than it would be if it where inhaled or swallowed. When uranium gets inside the body it can lead to cancer or kidney damage” (


The Yellow Dog Watershed Preserve will continue to follow the situation closely.


Uranium, Radiation Protection, United States Environmental Protection Agency

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