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IN SITU ABIOTIC DETOXIFICATION AND IMMOBILIZATION OF HEXAVALENT CHROMIUM IN THE CAPILLARY FRINGE ZONE
Citation:
Khan*, F A. AND R W. Puls*. IN SITU ABIOTIC DETOXIFICATION AND IMMOBILIZATION OF HEXAVALENT CHROMIUM IN THE CAPILLARY FRINGE ZONE. Winter, GROUNDWATER MONITORING AND REMEDIATION 23(1):77-84, (2003).
Description:
Detailed site characterization data from the former electroplating shop at the U.S. Coast Guard Air Support Center, Elizabeth City, North Carolina suggested that the elevated Cr(VI) in the capillary fringe area had contaminated the ground water at the site. Most of the mobile Cr(VI) is present in the capillary fringe zone of the aquifer under an oxidizing environment. The reduction of Cr(VI) to Cr(III) through in-situ redox manipulation in the presence of a reductant is an innovative technique for remediating chromate-contaminated sediments and ground water. Sodium dithionite, a strong reductant, was injected into a capillary fringe zone where elevated Cr(VI) has been identified, and then evaluated its effectiveness in creating a reductive environment to remediate Cr(VI). Several striking changes observed in the target zone during the post-injection monitoring periods include a significant decrease in Eh(SHE), as much as ~700 mV, absence of dissolved oxygen for a period of time, and the increase of Fe(II) concentrations. Results indicated that the in situ remedial treatment of Cr(VI) in the capillary fringe area was very effective and consequently the concentration of Cr(VI) in ground water dropped below the MCLG level. This research demonstrated the effectiveness of in situ abiotic remediation by reducing Cr(VI) concentrations, mobility, and toxicity in soils and ground water within a short period time. Therefore, sodium dithionite would be a feasible and cost-effective option for a full-scale remedial approach for the contaminated site at the U.S. Coast Guard Facility.