GEOC 24 |
| Nita Sahai and Katie Thornberg. Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706 |
| The aim of our study was to determine the causes for the observed spatial and temporal variability in As contamination levels (10-12,000 ppb) in Eastern WI. Electron microprobe, XRD, HRTEM, and Raman Spectroscopy of core and hand samples of aquifer and aquitard rock, and controlled dissolution experiments for three weeks at neutral pH, indicate that oxidative dissolution of arsenic-rich pyrite/ marcasite occurring as a discrete sulfide horizon between the aquifer and aquitard, or as dispersed veins, grains and nodules mobilizes As. Concentrations peak at 1hour, with rapid resorption within 12 hours (As not detected after 5 days) on the iron oxyhydroxides formed during the oxidative dissolution reaction. The persistence of As in groundwater suggests that pumping well-water introduces a thin film of dissolved oxygen to the sulfide mineralization zone, and that As release rate is faster than resorption and oxygen diffusion rates through water. Bicarbonate in groundwater buffers pH. |
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Chemistry of Metals in Terrestrial and Aquatic Systems
8:10 AM-11:30 AM, Monday, March 29, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |