FOR IMMEDIATE RELEASE:
Contact: Libby London (612) 227-8407
September 26, 2025
Despite stricter permitting and monitoring since 1990, the record shows a consistent pattern: hardrock mining continues to result in long-term, often irreversible downstream water quality degradation across the U.S., even after a mine has closed.
(Ely, MN) – A new report by Save the Boundary Waters’ Northeastern Minnesotans for Wilderness entitled Modern Mine Study: Water Quality Performance and Predictions at U.S. Mines Permitted Since 1990, reviews eight hardrock mines across the United States to determine whether U.S. nonferrous hardrock metallic mineral mines permitted under modern mining regulations have degraded the quality of downstream surface waters and/or downgradient groundwaters.
The study analyzes eight operating mines alongside two proposed mines in Northeastern Minnesota as a basis for comparison, focusing on how each affects—or could affect—water quality and surrounding water resources. The study reviews water quality predictions and monitoring data for post-1990 U.S. hardrock mines with a processing capacity of more than 1,000 tons of ore per day for which adequate data were available as of the report date.
The study specifically excluded:
- Mines in desert regions.
- Mines where pollution from past mining makes it impossible to distinguish the impacts of current operations.
The mines analyzed include: Beartrack Mine in Idaho, Buckhorn Mine in Washington, Eagle Mine in Michigan, East Boulder Mine in Montana, Flambeau Mine in Wisconsin, Haile Gold Mine in South Carolina, and Kensington Mine and Pogo Mine both in Alaska.
The study finds that even under today’s mining regulations, hardrock mines across the United States are consistently polluting rivers, lakes, and groundwater.
The study found:
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All eight mines degraded the downstream surface water quality.
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Seven of the mines polluted downgradient groundwater (data unavailable for the eighth).
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At least six of the mines resulted in exceedances of water quality standards or criteria in either surface water or groundwater, while seven mines violated permit limits.
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Inaccurate predictions: At six mines where predictions could be compared with outcomes, water pollution was significantly worse than forecast. Mines underestimated acid drainage potential, leaching from “non-acid generating” rock, and the volume of water requiring long-term treatment.
Significantly, water quality impacts often worsened after mines entered closure, with pollution from sulfates, total dissolved solids, and other contaminants projected to persist for decades—or even permanently. Of the eight mines studied, three are in closure, and two have seen their worst water quality impacts after operations stopped. Most closure plans rely on indefinite water treatment, and once treatment ends, pollutants like sulfates and dissolved solids are likely to surge—causing long-term, even permanent, degradation.
Ultimately, the findings challenge assumptions that “modern” mining regulations can adequately protect water quality. Despite stricter permitting and monitoring since 1990, the record shows a consistent pattern: hardrock mining continues to result in long-term, often irreversible water quality degradation across the U.S.
Read the full report here or reach out via email or phone with any questions.
Background:
Hardrock mining is a risky type of mining considered the most toxic industry in America, and copper mining has never been done in Minnesota. 70% of Minnesotans support a ban on sulfide-ore copper mining in the Boundary Waters headwaters. The Boundary Waters is the most heavily visited Wilderness Area in the United States, attracting more than 165,000 visitors from all over the world. A vast collection of peer-reviewed science shows that if a Twin Metals copper-nickel mine were built along the rivers and streams flowing into the Boundary Waters Canoe Area Wilderness, pollution and environmental degradation would be certain.
A peer-reviewed independent study from Harvard University showed that protection of the Boundary Waters from a proposed Twin Metals sulfide-ore copper mine would result in dramatically more jobs and more income over a 20-year period.
A 2017 report by the Minnesota Pollution Control Agency describes the waters within the Boundary Waters headwaters watershed as “immaculate." The Report concludes that "the majority of the waterbodies within this watershed had exceptional biological, chemical, and physical characteristics that are worthy of additional protection."
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