Pilot-scale electron donor injection enhances hexavalent chromium, Cr(VI), biochemical reduction to trivalent chromium, Cr(III), in an overburden groundwater system impacted by Cr(VI) disposal in Kanpur, Uttar Pradesh, India . The study area is located in the Indo-Gangetic alluvial plain, and is characterized by overburden stratigraphy consisting of up to about 50 meters of generally fine to medium sand interbedded with silty clay, which is underlain by about 100 meters of laterally continuous clay. The clay is underlain by interbedded fine to medium sand and clay to a depth of about 500 meters, which overlies granitic bedrock. Cr(VI) has been detected for about 20 years at concentration up to 16 milligrams per liter in groundwater samples collected from the shallower fine to medium sand unit. The source is believed to be indiscriminate dumping of wastes resulting from production of Basic Chrome Sulfate (Cr(OH)2SO4, BCS) and other reagents used by local leather tanneries. Approximately 540 kilograms of a carbohydrate-based remedial additive were injected into two wells screened in the fine to medium sand unit using about 40,000 liters of groundwater. Treatment solution make-up water was obtained from a downgradient extraction well located within the Cr(VI) plume, amended with remedial additive, and then injected into the upgradient wells to establish hydraulic control on the injection and minimize dilution. Performance monitoring included five rounds of groundwater sampling for Cr(VI), total chromium, and certain indicator parameters, including total organic carbon (TOC) as an electron donor surrogate. Pilot study results suggest that remedial additive amendment resulted in an up to 99.9% reduction in Cr(VI) concentration; an up to 97% reduction in total chromium; and up to an order of magnitude increase in TOC concentration over the four month study.
Schaffner, I. Richard Jr., P.G., C.G.W.P.; Singh, Rajiv Kumar Ph.D.; Lamb, Steven R. P.G., C.G.W.P.; and Kirkland, Donald N. P.E.
"Enhanced Bioremediation Pilot Study Of A Cr(Vi)-Impacted Overburden Groundwater System In Kanpur, Uttar Pradesh, India,"
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy: Vol. 13
, Article 8.
Available at: http://scholarworks.umass.edu/soilsproceedings/vol13/iss1/8