Toxic mining legacy, part two


Although I now live in Portland, Oregon, I have followed the Animas River mine drainage spill issue with extreme interest, because I spent several years studying water quality issues related to mine drainage in Colorado in the 1970s. Jonathan Thompson’s article provides the most complete description of the incident that I’ve read or heard (including anything on NPR), and it is the first to point out that the real culprit in this tragedy is Colorado’s legacy of abandoned metal mines with no culpable owners (“Animas spill,” HCN, 8/31/15).

One minor comment is that aluminum is not considered a heavy metal. Although it can be toxic to fish in acidic water, this typically occurs in poorly buffered, acidic waters impacted by acid deposition, such as in the Adirondack region of New York. In the Animas River milieu, any effects related to aluminum would likely be overwhelmed by the impacts of toxic heavy metals, such as cadmium and lead.

I do have some concern regarding possible toxic levels of cadmium that might have occurred during the downstream pulse from the Gold King mine. Cadmium is often found in Colorado metal-mine drainage, and it is toxic to rainbow trout at concentrations less than 1 microgram/liter. Although cadmium is listed in the legend of the graph shown in the article, it does not appear in the graph itself. I assume that is because the levels are so low they are hidden by the lead line, but that doesn’t mean that they are unimportant. It would have been informative to put cadmium and lead on a separate graph with a different scale so that the actual concentrations could be appraised.

Colorado has an extensive area of abandoned metal mines in the Colorado Mineral Belt, which extends from the San Juan Mountains in south-central Colorado to the Front Range in Boulder County. A colleague and I published the first statewide studies of metal mine drainage in this area in 1974 when we worked for the U.S. Geological Survey. Many studies have been done by government and academic researchers since that time to update our preliminary studies, and I am sure that similar water-quality issues related to the legacy of abandoned metal mines exist in all states of the Rocky Mountain West.

Dennis Wentz
Portland, Oregon