Geologic Survey Report Finds Acid Drainage Predated Mining
by Peter Shelton
Jul 04, 2012 | 3163 views | 1 1 comments | 9 9 recommendations | email to a friend | print

WESTERN SAN JUANS – An award-winning study by the Colorado Geologic Survey has bolstered claims by miners in the Ouray-Red Mountain district that highly acidic surface water preceded mining activity by thousands, perhaps millions of years.

The report, titled “Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado,” was recently given an award by the Geological Society of America as the best environmental publication of 2011. The report identifies a number of high-country streams in Colorado, including Red Mountain Creek, where surface water is acidic and has high concentrations of metals upstream of historic mining.

“Of course, the mining made it much, much worse,” commented Don Paulson, a former chemistry professor who is now curator of the Ouray County Historical Museum. Paulson has followed efforts to identify sources of stream pollution and the remedial measures undertaken to improve water quality in the Uncompahgre River and its tributaries.

There was a big push to clean up the water affected by mine waste (and the role it plays in the inability of high country waterways to support aquatic life) in the 1980s. At that time the Colorado Department of Health (now Colorado Department of Public Health and Environment) first sued under the Superfund Act, then negotiated with Idarado Mining and its parent company, Newmont Mining, substantial cleanups on both the Telluride and Ouray sides of the mountain. The Telluride side saw improvements to the water quality of the Upper San Miguel River. But the acid pH and the levels of zinc and other minerals in Red Mountain Creek has not changed significantly despite Idarado’s remediation in the area of the Treasury Tunnel.

According to the Uncompahgre Watershed Partnership, Idarado has completed all of its contracted work. That original Remedial Action Plan, or RAP, expired in 2006, and Newmont must now come up with a new Contingency Plan.

As the CGS study shows, however, at least some of the acid water in Red Mountain Creek is likely not a result of past mining. The Red Mountain district, and others around Colorado’s mineral belt, have naturally occurring, highly acid, highly mineralized waters.

Here’s how the CGS study describes the process: Hot water circulating in the earth’s crust can “hydrothermally alter” rock composition by dissolving some minerals and depositing others. In affected areas, the hydrothermal-alteration process deposited metal-sulfide minerals, commonly pyrite (fool’s gold), in the rocks. When these rocks interact with oxygen, the iron sulfide "rusts" to form iron oxide minerals, creating striking yellow, orange, and red colors – similar to the oxidation of metal in an old rusty car. “Acid rock drainage” occurs when the sulfur combines with water to form weak sulfuric acid. The acid then dissolves minerals in rock, often adding significant amounts of dissolved metals to streams.

“This is the ‘yellow boy,’ the bright yellow-orange ‘cake’ in the creek up there,” said Paulson. It’s really just rust. Red Mountain Creek was red before the miners came.” Of course, Paulson said, acid water from the Guston, the Yankee Girl, the Genesee and other mines in the district made the situation emphatically worse. It’s this acid rock drainage – natural and anthropogenic – that makes cleanup such a difficult proposition.

Neither Paulson nor Matthew Sares, one of the study authors, thinks the study will affect responsibility for cleanup of the Upper Uncompahgre. “So far, it has been difficult to decipher the proportionate sources of acid water and metals in the areas where mining has overprinted areas prone to natural acid rock drainage,” Sares wrote in an email.

“In my opinion, it doesn’t impact the responsibility for cleanup where a responsible party has been identified. That responsibility remains. If the report’s information can be used to understand the actual situation ‘on the ground,’ it can help define and make clear the final goals in new remediation efforts.”

Paulson agreed. “Absolutely. [The state] signed the agreement with Idarado and the other companies. This report is not going to change the responsibility.”

So, what is the ultimate goal for Red Mountain Creek? Blake Beyea of the state’s Water Quality Control Division asked the question rhetorically in a phone conversation. “For Red Mountain Creek, the aquatic life use has been dropped” as a goal, due in part to “irreversible man-induced conditions.” For the foreseeable future, the creek is not going to be able to support aquatic life, Beyea said, not simple organisms like bugs, let alone trout.

“This particular case is loaded with history,” Beyea said. “The complexity shoots up with the scale (the Red Mountain District covers a huge area) and the time frame associated with it (going back nearly 150 years) . . . Is all the cleanup effort and the money worth it? What can we hope to get out of it? Can we ever hope to get brown trout?”

Site-specific standards and cleanup goals “will be reassessed over time,” he said.

For an excellent primer on acid drainage, Paulson recommends a Wikipedia article:

The Colorado Geologic Survey study is not available on line. It can be purchased, for $30, on line at:

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July 05, 2012
I'm glad to see the CGS has finally "discovered" that these are "natural" systems and that mining is NOT the cause of all our problems.

During Geology Summer Camp (in 1969) we visited this area and measured a pH of 2.5 in one of these streams - with no mining being present in the watershed!

I guess we now have a naturally occurring Superfund Site.

Way to go!!