6th Annual Judith Ramaley Celebration of Research and Creative Scholarship
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Poster #21 An Evaluation of the Performance of Passive Treatment Wetlands at the Dunka Mine in Northeastern MN Michael Carlson and Jacob Shirley
Faculty Mentor: Candace L. Kairies Beatty Acid mine drainage, a significant environmental problem impacting a number of watersheds in the United States and globally, is created when sulfide minerals are exposed to oxygen and water through mining processes, resulting in elevated concentrations of metals, sulfates and potentially acidity (if pyrite or other disulfide minerals are present) in the water. Such discharges can have a detrimental impact on aquatic ecosystems. Most of the iron ore mined in Minnesota did not contain acid-generating minerals, so little thought was given to the effects of acid mine drainage on water quality. When Dunka Mine (near Babbitt, MN) opened in 1962, the overlying Duluth Complex (primarily gabbro with high amounts of disseminated copper and nickel sulfides) was removed and stockpiled as waste rock at the site. Rainwater promoted oxidation and dissolution of the sulfide minerals in the waste rock, generating increased levels of copper, nickel, cobalt, zinc and sulfates in runoff from the rock.
Wetland systems employing peat to promote sulfate reduction and metal removal processes (through precipitation as metal sulfides and specific adsorption on the organic portion of the peat) were installed at the mine in 1992. The overall goal of this study was to assess the performance of two of the wetland systems (W1D and Seep X) to better understand and address issues related to long-term performance and management of the wetlands as well as eventual site closure. Water quality and flow data were used to calculate metal removal efficiency over time and to estimate the mass of metals removed within these systems. Results of this work will be presented along with an evaluation of the success of these systems. |
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