HR: 17:00h
AN: B24B-05    [Abstracts]
TI: Geochemical Controls on Natural Attenuation of Arsenic Solubilized by Human-Induced Alterations
AU: * Bilgin, A
EM: abilgin@caltech.edu
AF: California Institute of Technology, 1200 E California Blvd M/C 138-78, Pasadena, CA 91125
AU: Hering, J G
EM: jhering@caltech.edu
AF: California Institute of Technology, 1200 E California Blvd M/C 138-78, Pasadena, CA 91125
AU: Harrington, J
EM: jmharrington@arcadis-us.com
AF: ARCADIS G&M, 630 Plaza Drive, Highlands Ranch, CO 80129
AU: Horst, J
EM: jhorst@arcadis-us.com
AF: ARCADIS G&M, 630 Plaza Drive, Highlands Ranch, CO 80129
AU: Burris, D
EM: istpanamacity@aol.com
AF: Integrated Science & Technology, Inc., 1349 Olg Highway 41, Marietta, GA 30060
AU: Reisinger, H J
EM: istatlanta@aol.com
AF: Integrated Science & Technology, Inc., 1349 Olg Highway 41, Marietta, GA 30060
AB: Naturally-occurring arsenic (As) in soils can be solubilized into groundwater as a result of anthropogenic changes in subsurface redox conditions. However, the presence of As in groundwater may not lead to human exposure if As is attenuated before intercepting a water source. Dissolved As can be attenuated by sorption and precipitation processes whose effectiveness may be strongly influenced by redox transformations. Anaerobic bioremediation has been employed at a site in the Northeastern U.S. to treat a tetrachloroethene (PCE) plume in groundwater. An organic carbon source is injected via a transect of wells oriented perpendicular to groundwater flow. The resulting anaerobic reducing zone extends 30 meters down gradient of the injection transect. At the down gradient edge of the reducing zone, dissolved As and Fe concentrations have been observed at over 0.7 milligrams per liter (mg/L) and 450 mg/L, respectively. However, 60 m down gradient (and outside of the reducing zone), As and Fe concentrations have been maintained at levels below their detection limits (0.005 mg/L and 1 mg/L) for over 900 days, demonstrating natural attenuation of As. The sorption of As onto Fe and Mn oxyhydroxides under changing geochemical conditions is investigated by using the reactive transport modeling program Geochemist's Work Bench (GWB). Down gradient conditions are simulated where reduced constituents of contaminated groundwater react with Fe(III) and Mn(III, IV) oxyhydroxides in the soil/aquifer matrix or with dissolved oxygen in uncontaminated groundwater at the periphery of the reducing zone. Dissolved Fe(II) and Mn(II) are re-oxidized and precipitate as oxyhydroxide coatings on the soil or aquifer sediments. These coatings then serve as sorbents for both As(III) and As(V). Simulations allow us to examine As sequestration as a function of groundwater composition (e.g., pH and competing sorbates such as phosphate) and of the rate and extent of the precipitation of Fe(III) and Mn(III,IV) oxyhydroxides.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
DE: 0466 Modeling
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005