Isotopic and Geochemical Characterization of Water Movement Through Abandoned Mine Workings, Nelson Tunnel, Creede, Colorado

Cowie, Rory

Isotopic and Geochemical Characterization of Water Movement Through Abandoned Mine Workings, Nelson Tunnel, Creede, Colorado

Monday, May 5, 2014: 2:40 p.m.

Platte River Room (Westin Denver Downtown)

Rory Cowie , Institute of Arctic and Alpine Reserach, University of Colorado Boulder, Boulder, CO

Garrett Rue , Institute of Arctic and Alpine Research, Boulder, CO

Mike Wireman , EPA, Denver, CO

Mark W. Williams , University of Colorado, Boulder, CO

Long term acid mine drainage (AMD) discharging from the portal of the Nelson Tunnel near Creede, Colorado is currently impacting water quality in West Willow Creek and the Rio Grande River. We are using established isotope and geochemical tracer techniques to quantitatively determine the sources, ages, and pathways of waters in the mine. Preliminary results indicate that waters draining the mine are well mixed and composed to some degree of old groundwater, not just meteoric inputs. The stable isotope (¹⁸O) of the mine water is steady at -15 ‰ throughout the year, suggesting a well-mixed groundwater system composed of equal parts winter snow (-20 ‰) and summer monsoon rain (-10 ‰). Strontium ratios (⁸⁷Sr/⁸⁶Sr) suggest that most of the mine source waters are traveling through similar medium. Tritium (³H) values within the tunnel are primarily “tritium-dead” indicating water that is at least older than the “bomb-spike” waters of nuclear weapons testing in the 1960s. Additionally, dissolved inorganic carbon (DIC) δ¹⁴C testing indicates mine water on the order of hundreds to thousands of years of age. Results therefore suggest that mine waters are largely not directly connected to surface waters, or to the shallow groundwater (sampled from springs and domestic wells), but rather are likely entering the tunnel at intersections with a system of watershed-wide faults. To provide age verification for the DIC δ¹⁴C results, the mine water samples were also analyzed for the δ¹⁴C of humic components of dissolved organic carbon (DOC). Additionally, fluorescence index values of the final DOC isolates were produced to identify if the organic carbon sources were of terrestrial origin or microbially influenced.

The results from this study have helped develop a hydrogeologic conceptual model of the mine complex, which will aid in the development and feasibility analysis of targeted remediation strategies.

Rory Cowie, Institute of Arctic and Alpine Reserach, University of Colorado Boulder, Boulder, CO

Rory Cowie is a Ph.D. student in the Department of Geography at the University of Colorado, and a graduate research assistant at the Institute of Arctic and Alpine Research. He received an M.A. in Geography from the University of Colorado in 2010 and a B.A. in Biology from The Colorado College in 2004. His research interest is the hydrology of mountain regions, looking at surface water and groundwater interactions using environmental isotopes and biogeochemistry. The focus of Cowie's Ph.D. research is on controlling acid mine drainage by understanding the hydrogeology of abandoned hard rock mines in Colorado.

Garrett Rue, Institute of Arctic and Alpine Research, Boulder, CO

Garrett Rue’s area of interest is in dissolved organic matter.

Mike Wireman, EPA, Denver, CO

Mike Wireman is a National Groundwater Expert at EPA Region 8.

Mark W. Williams, University of Colorado, Boulder, CO

Mark Williams is a Fellow at the Institute of Arctic and Alpine Research and a Professor of Geography at the University of Colorado. He received his Ph.D. in Biological Sciences with an emphasis in ecology from the University of California at Santa Barbara in 1991. The majority of his research has been conducted in the Rocky Mountains, Sierra Nevada of California, and the Tien Shan in China. Wireman is on the faculty of the Hydrology Program in Geography and his classes can be used to satisfy the Hydrology Certification Program in Geography.