Civil, Environmental and Architectural Engineering

Environmental Engineers Investigate Acid Mine Drainage in Colorado Streams, continued

Eric August takes a water sample from the creek which is polluted by acid mine drainage.

Iron pyrite, exposed by mining and weathered by nature, is a source of sulfuric acid and metals that are carried with the snowmelt from the now mostly abandoned mines into streams throughout the region. Sulfuric acid raises the water's acidity and leaches metals such as aluminum and zinc from surrounding rocks, resulting in high metal concentrations. While a few insects and algae can flourish in this water, fish can't survive under the conditions described by miners as "yellow boy" or "white death." The terms refer to the presence of orange-colored iron oxides or white-colored aluminum oxides on barren streambeds. Some of the streams made toxic by these metals drain into reservoirs, which supply water to cities along the Front Range.

Noting that there would be some presence of metals in high- elevation streams even under natural conditions, McKnight says, "We've accelerated the natural weathering reactions by opening up the mountains through mining. It presents a significant risk to water quality and aquatic ecosystems."

McKnight is leading students in studies of the Snake River Basin in Summit County and headwaters of the Arkansas River in Lake County. She also belongs to a task force of stakeholders who are pursuing remediation of the Snake River. Members include federal, state and county governments, citizens and the ski industry, which wants to use additional water to expand snowmaking. One unsuccessful approach in the basin was construction of a lime-adding facility to reduce acidity. Another approach, artificial wetlands to filter out metals, was not implemented after construction of the wetlands because of liability concerns. McKnight believes large wetlands areas may be effective in treating the water, but the initiative in the Snake River Basin, she says, has been stymied by liability issues combined with uncertainty about which abandoned mines are the most important to remediate.

From an educational perspective, the complexity of the situation makes it an excellent project for interdisciplinary study. Students in engineering, geography, and EPO biology are analyzing water, plant and soil samples at various points in the basin, developing hydro-chemical transport models, and studying the public process and legal issues. "A quantitative and predictive analysis of acid mine drainage has the potential to make a real contribution," McKnight says.

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