HR: 0800h
AN: H11E-0823    [Abstracts]
TI: Controls on Aqueous Arsenic Mobilization in the Treasure Valley Shallow Aquifer, Southwestern Idaho
AU: * Busbee, M
EM: montybusbee@hotmail.com
AF: Boise State Universtiy, 1910 University Dr., Boise, ID 83725, United States
AU: Benner, S
EM: sbenner@boisestate.edu
AF: Boise State Universtiy, 1910 University Dr., Boise, ID 83725, United States
AU: Hoffman, B
EM: bernadettehoffman@mail.boisestate.edu
AF: Boise State Universtiy, 1910 University Dr., Boise, ID 83725, United States
AB: A study has been undertaken to elucidate the geochemical mechanisms by which arsenic is being stored, released and transported in the shallow sedimentary aquifer beneath the Western Snake River Plain, Idaho where groundwater arsenic concentrations exceed 100 ug/L. While arid, this region is extensively irrigated for agriculture and we are evaluating the effects of the infiltration of irrigation waters from surface and subsurface sources on the release of arsenic to the aquifer system. Our initial results indicate that while arsenic concentrations exhibit high variation over short lateral distances, throughout the affected area the highest aqueous concentrations occur in conjunction with high dissolved oxygen and low iron and manganese concentrations and near the water table. While sequential extraction and batch experiments performed on unirrigated shallow sediments from the basin show solid phase arsenic at or near average crustal abundances (n.d. to 29 mg/kg, average being 1.77 mg/kg), resultant concentrations of water soluble arsenic to >20 ug/L and of specifically adsorbed arsenic to >100 ug/L, with the highest being >500 ug/L, were observed. The highest aqueous concentrations were associated with surficial aeolian material and iron oxide coatings and concretions. Arsenic associated with the oxide operational fraction ranged from 1 to 29 mg/kg, average being 4.15 mg/kg. Analysis of flood irrigation waters indicate very little to no arsenic is currently being released from irrigated surface sediments. This data suggests that water soluble and specifically adsorbed arsenic has been flushed from the surficial sediments and that oxides/oxyhydroxides in the vadose zone and shallow aquifer may be acting as both sources and sinks for aqueous phase arsenic.
DE: 1829 Groundwater hydrology
DE: 1838 Infiltration
DE: 1842 Irrigation
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting