In Situ Chemical Reduction of Cr(VI) in Groundwater Using a Combination of Ferrous Sulfate and Sodium Dithionite:  A Field Investigation

• Published in: Environmental science & technology 2007-08, Vol.41 (15), p.5299-5305
• Main Authors: Ludwig, Ralph D, Su, Chunming, Lee, Tony R, Wilkin, Richard T, Acree, Steven D, Ross, Randall R, Keeley, Ann
• Format: Article
• Language: English
• Subjects: Applied sciences; Aquifers; Chemical precipitation; Chromium - chemistry; Dithionite - chemistry; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental monitoring; Exact sciences and technology; Ferrous Compounds - chemistry; Field study; Fresh Water - chemistry; Groundwater pollution; Groundwaters; Iron - analysis; Iron compounds; Microscopy, Electron, Scanning; Natural water pollution; Oxidation-Reduction; Pollution; Pollution, environment geology; Reducing Agents - chemistry; Soil - analysis; Water treatment; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es070025z

A field study was conducted to evaluate the performance of a ferrous iron based in situ redox zone for the treatment of a dissolved phase Cr(VI) plume at a former industrial site. The ferrous iron based in situ redox zone was created by injecting a blend of 0.2 M ferrous sulfate and 0.2 M sodium dithionite into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. Monitoring data collected over a period of 1020 days after more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from initial concentrations between 4 and 8 mg/L to less than 0.015 mg/L. Sustained treatment is assumed to be primarily due to the reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron (hydr)oxide solid surfaces within the treatment zone. Precipitated 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 collected from the treatment zone more than 2 years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI).