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Use of a Ferrous Sulfate - Sodium Dithionite Blend to Treat a Dissolved Phase Cr(VI) Plume
Citation:
LUDWIG, R. D., C. SU, P. J. CLARK, F. P. BECK, AND T. R. LEE. Use of a Ferrous Sulfate - Sodium Dithionite Blend to Treat a Dissolved Phase Cr(VI) Plume. Presented at The Sixth International Conference, Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 19 - 22, 2008.
Impact/Purpose:
To evaluate the use of a combination of sodium dithionite and ferrous sulfate in creating an in situ redox zone for treatment of a dissolved phase Cr(VI) plume at a former industrial site.
Description:
A field study was conducted to evaluate the use of a combination of sodium dithionite and ferrous sulfate in creating an in situ redox zone for treatment of a dissolved phase Cr(VI) plume at a former industrial site. The reductant blend was injected into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. A 1020-day monitoring program corresponding to more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from concentrations between 4 to 8 mg/L entering the treatment zone to less than 0.015 mg/L within the treatment zone. Sustained treatment is assumed to be primarily due to reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron oxide/hydroxide solid surfaces within the treatment zone. Precipitated iron phases likely include FeCO3 and FeS based on saturation index considerations and SEM/EDS analysis. The detection of solid phase sulfites and thiosulfates in aquifer sediments more than two years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI) observed.