(University of Oregon, 2010-06) Daigle, Ashley R., 1986-
The bedrock aquifer of the Southern Willamerte Basin, Oregon, USA, is
contaminated with arsenic at concentrations as high as several ppm. Single-well
push-pull tests were conducted to investigate how microbial metabolisms control arsenic
occurrence and levels in the aquifer. Test solutions containing ethanol were injected into
the aquifer; dissolved gases, groundwater, and sediments were then sampled to monitor
the speciation of carbon, iron, sulfur, and arsenic. Ethanol amendment stimulated a series
of microbial metabolisms, including arsenate reduction, iron reduction, and sulfate
reduction. Arsenate reduction converts arsenate to arsenite; iron reduction produces
ferrous iron; sulfate reduction releases sulfide. Arsenite and ferrous iron then combine
with sulfide and form arsenic sulfide and iron sulfide minerals. Results of the
experiments demonstrate that the interactions among microbial metabolisms and mineral precipitation influenced arsenic contamination in the aquifer. These results shed new
light on potential bioremediation strategies in the area.
