Likelihood of Spills and Tailings Dam Failure

Results from a recent review of the spill records of fourteen copper sulfide mines in the U.S., accounting for 89% of U. S. copper production in 2010, were used to estimate the likelihood of spills and impoundment failures from the proposed PolyMet/Glencore mine. The mines reviewed share many technological designs included in PolyMet/Glencore's NorthMet proposal, and are subject to the same federal environmental regulations. Based on the 1986-2012 record during which the 14 mines had 175 spills and four impoundment failures total, we estimate that the PolyMet/Glencore mine would average five spills per decade (95% confidence interval: 3-8 spills per decade). There is less than 0.5% chance that the PolyMet impoundment would perform as designed and not fail for 500 years.

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The data is based on a report from the nonprofit Earthworks, and can be viewed here.