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IN-SITU REDUCTION OF CHROMIUM-CONTAMINATED GROUNDWATER, SOILS, AND SEDIMENTS BY SODIUM DITHIONITE
Citation:
Paul*, C J., F A. Khan*, AND R W. Puls*. IN-SITU REDUCTION OF CHROMIUM-CONTAMINATED GROUNDWATER, SOILS, AND SEDIMENTS BY SODIUM DITHIONITE. Chapter 16, Handbook of Groundwater Remediation Using Permeable Reactive Barriers: Applications to Radionuclides, Trace Metals, and Nutrients. , 465-493, (2002).
Description:
Laboratory studies were conducted to characterize the extent of chromium contamination in the groundwater and underlying soils and sediments of a chrome-plating shop at the USCG Support Center near Elizabeth City, NC. Most of the mobile Cr(VI) is present in the capillary zone of the aquifer under oxidizing conditions. The reduction of Cr(VI) to Cr(III) through in situ redox manipulation in the presence of a reductant is an innovative technique for remediation of chromate contaminated sediments and groundwater. Three liquid reductants (sodium dithionite, l-ascorbic acid, and free hydroxylamine) were evaluated in laboratory studies to determine their ability to detoxify and immobilize chromate in situ. Sodium dithionite proved to be the most effective at reducing Cr(VI) to Cr(III) with the least side affects. A field scale pilot study was conducted in July 1999 using sodium dithionite to evaluate the effectiveness of reducing Cr(VI) in situ. Post injection monitoring results show aqueous chromate concentrations decreased from up to 5 mg/L to <0.01 mg/L in all wells within the 1 meter cylindrical zone of influence. Continued Cr(VI) reduction was seen 48 weeks post-injection, indicating that long-term reduction is occurring. Analyses of post-experimental sediment cores indicate that non-mobile reduced structural iron within the silicate minerals present in the treated sediments may be contributing to long-term remediation of Cr(VI).