HR: 10:20h
AN: H32C-01 [Abstracts]
TI: Geochemical and Hydrogeological Controls on Arsenic
in Sand-and-Gravel Aquifers in Central Illinois, USA
AU: * Kelly, W R
EM: kelly@sws.uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495
United States
AU: Holm, T R
EM: tomholm@sws.uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495
United States
AU: Wilson, S D
EM: swilson@sws.uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495
United States
AU: Roadcap, G S
EM: george@sws.uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495
United States
AB:
A total of 176 wells in sand-and-gravel aquifers in central Illinois were sampled for arsenic and other chemical parameters.
These results were combined with archived and published data from several hundred well samples to characterize the spatial
distribution of arsenic and determine the potential geochemical controls on its solubility and mobility. There was
considerable spatial variability in the arsenic concentrations, and arsenic was not correlated with aquifer depth. There did
not appear to be any arsenic "plumes" at the scale of the sampling. Arsenic solubility appeared to be controlled by
oxidation-reduction conditions, especially the presence of organic matter. Geochemical conditions in the aquifers are
typically reducing, but only in the most reducing waters does arsenic accumulate in solution. In wells in which sulfate was
present, arsenic concentrations were low or below the detection limit (0.5 g/L). Elevated arsenic concentrations were only
found in wells where sulfate was absent or at low concentrations, indicating post-sulfate-reducing conditions. Methane was
detected and organic carbon and ammonium concentrations were generally elevated in these wells. Iron is common in the aquifer
sediments, and iron reduction appears to be occurring throughout the aquifers. Arsenic is likely released from the solid
phase as iron oxide is reduced.
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting