The role of alluvial aquifer sediments in attenuating a dissolved arsenic plume

Journal of Contaminant Hydrology
By: , and 



In a crude-oil-contaminated sandy aquifer at the Bemidji site in northern Minnesota, biodegradation of petroleum hydrocarbons has resulted in release of naturally occurring As to groundwater under Fe-reducing conditions. This study used chemical extractions of aquifer sediments collected in 1993 and 2011–2014 to evaluate the relationship between Fe and As in different redox zones (oxic, methanogenic, Fe-reducing, anoxic-suboxic transition) of the contaminated aquifer over a twenty-year period. Results show that 1) the aquifer has the capacity to naturally attenuate the plume of dissolved As, primarily through sorption; 2) Fe and As are linearly correlated in sediment across all redox zones, and a regression analysis between Fe and As reasonably predicted As concentrations in sediment from 1993 using only Fe concentrations; 3) an As-rich “iron curtain,” associated with the anoxic-suboxic transition zone, migrated 30 m downgradient between 1993 and 2013 as a result of the hydrocarbon plume evolution; and 4) silt lenses in the aquifer preferentially sequester dissolved As, though As is remobilized into groundwater from sediment after reducing conditions are established. Using results of this study coupled with historical data, we develop a conceptual model which summarizes the natural attenuation of As and Fe over time and space that can be applied to other sites that experience As mobilization due to an influx of bioavailable organic matter.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The role of alluvial aquifer sediments in attenuating a dissolved arsenic plume
Series title Journal of Contaminant Hydrology
DOI 10.1016/j.jconhyd.2017.04.009
Volume 204
Year Published 2017
Language English
Publisher Elsevier
Contributing office(s) National Research Program - Eastern Branch
Description 12 p.
First page 90
Last page 101