Mobilization of geologic arsenic in Cache Valley, UT
Arsenic concentration in groundwater throughout Cache Valley exceeds the drinking water limit. Aquifer solids were collected from an area near the Logan Landfill. Chemical extraction procedures were used to determine whether the arsenic is associated with the local geology or is from anthropogenic sources. The results indicate that the arsenic in groundwater is from natural aquifer solids. Although mechanisms of arsenic release to groundwater from minerals have been reported in the literature, there are still disputes on specific mechanisms and the importance of contributing factors to the mobilization of arsenic. Anaerobic microcosms containing two selected aquifer solids, one site-oxidized and one site-reduced, and groundwater collected near the landfill, groundwater with the addition of glucose, and landfill leachate, were constructed and analyzed over time to evaluate the mechanism of arsenic solubilization. Microcosms were sacrificed for analysis of arsenic in solution, oxidation state of the arsenic, biogenic Fe(ll) production, changes in mineralogy, organic species, and water chemistry parameters. Reductive dissolution of iron oxides contributes to the mobilization of arsenic in the site-oxidized aquifer solid with groundwater and leachate treatments. The addition of glucose enhanced reducing conditions and the solubilization of arsenic from the host minerals. With the site-reduced sediment, the two water treatments caused reductive dissolution of iron minerals and arsenic release. The addition of glucose decreased arsenic in solution due to association of arsenic with the solid phase. The mass of arsenic mobilized into solution potentially depends on the arsenic content in the solid. By knowing the controlling factors in arsenic mobilization, the potential risk of humans being exposed to arsenic contaminated groundwater will be decreased.
Meng, X., J.E. McLean. 2010. Mobilization of geologic arsenic in Cache Valley, UT. Annual meeting Spring Runoff USU.