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| 8/8/2009 6:00:00 AM | Email this article • Print this article | Group traces metals in water
By Dale Rodebaugh
Durango Herald Staff Writer
SILVERTON - The precious metals extracted from the millennia-old mountains that put this town of 500 on the map and gave it a name aren't the only minerals whose presence still affects the craggy landscape.
An all-day workshop Saturday, one of the Moving Mountain Education Seminar series sponsored by the Mountain Studies Institute here, brought together 20 people interested in talking about and seeing the consequences of acid-rock drainage - the leaching of minerals into waterways.
The workshop was led by David Borrok, a professor in the geological sciences department at the University of Texas at El Paso, and Rob Runkel, Richard Wanty and Andy Manning, all with the U.S. Geological Survey in Denver.
"The more we learn about where metals come from, how they enter waterways and how they move, the more focused, the more accurate remediation can be," Borrok said.
In the last several million years, a wealth of subterranean minerals has accumulated in this region, which has been - among other things - an ocean basin and the scene of volcanic activity.
Interest in mopping up toxic waste in the San Juan Mountains that accumulated from 100 years of mining started in earnest in the 1990s with the formation of the Animas River Stakeholders Group, a partnership of federal and state agencies and private interests.
In 1994, the federal Abandoned Mine Lands Initiative provided additional resources to quantify and set priorities for cleanup.
Numerous projects were conducted in the Upper Animas River watershed to improve water quality and fisheries.
Workshop participants, who spent the day in Prospect Gulch a few miles north of town, got an eyeful and an earful of information.
Runoff from numerous Prospect Gulch tributary watersheds feed Cement Creek, whose yellowish-colored channel is evidence of the presence of iron.
In fact, the caravan stopped twice to view ferricretes - iron oxide formations with their telltale reddish hue that are created when iron reacts with water and air. An ancient ferricrete was visible in a creekside cliff. The other - a terraced formation adjacent to the stream - is still forming.
Iron also is responsible for the color of terrain on nearby Red Mountain Pass - the reaction of pyrites (fool's gold) with air.
"Mining impacted the terrain, but a lot was going on before men began digging up rocks here," Wanty said. "Mining accelerates the process because pyrite that has been ground up in the mining process reacts more quickly with air and water than chunks of material."
The presence of ferricretes is evidence that some streams in the region were metal-rich and acidic before mining came into its own in the region in the late 1870s, Runkel said.
"Minerals are stable in the ground but react with oxygen and water when brought to the surface," Runkel said. "No one knows the quantity of metals in the water before mining started."
He cautioned that accurate hydrological studies are required to establish standards for cleaning up contaminated mines and waterways.
Later in the day Runkel demonstrated how the dilution of a tracer solution shows the level of metal loading from different sources.
Runkel poured half a bucketful of rhodamine, an organic dye, into a rivulet on the upper reaches of Prospect Gulch.
A sonde with a sensor that emits light at the same wavelength as the fluorescent dye traces the flow of the additive as it moves downstream.
Similar studies have been conducted on Cement Creek and other streams above Silverton as part of the Abandoned Mine Lands Initiative, he said.
At the Galena Queen mine, workshop participants tested the acidity and electrical conductivity of water in the shaft.
They also compared the qualities of the mine water to surface water. At a well on a bench immediately above Cement Creek, Manning explained how to age-date water.
Tritium, a radioactive isotope of hydrogen (one of the components of water) has a half-life of 13 years, meaning that in 13 years half of any tritium decays to become helium-3.
Consequently, the ratio of tritium to helium in water indicates its age. Rain will have a high ratio of tritium to helium-3 while the reverse is true for slow-moving subterranean water.
"Age-dating will tell how an aquifer works and how much water it can supply," Manning said.
Data derived from the study of mine drainage, the tour leaders said, can be useful to agencies, including the Forest Service, Bureau of Land Management, Environmental Protection Agency, Colorado Department of Public Health and Environment and private organizations such as Trout Unlimited or Animas River Stakeholders for work in the promotion of recreation and the remediation of dangerous mines.
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