In situ long-term reductive bioimmobilization of Cr(VI) in groundwater using hydrogen release compound

The results of a field experiment designed to test the effectiveness of a novel approach for long-term, in situ bioimmobilization of toxic and soluble Cr(VI) in groundwater using a hydrogen release compound (HRC) - a slow release glycerol polylactate - are described. The field experiment was conducted atthe Hanford Site (Washington), a U.S. Department of Energy nuclear production facility, using a combination of hydrogeological, geophysical, geochemical, and microbiological measurements and analyses of water samples and sediments. The results of this experiment show that a single HRC injection into groundwater stimulates an increase in biomass, a depletion of terminal electron acceptors O₂, NO₃^-, and SO₄^2-, and an increase in Fe²⁺, resulting in a significant decrease in soluble Cr(VI). The Cr(VI) concentration has remained belowthe background concentration in the downgradientpumping/ monitoring well, and below the detection limit in the injection well for more than 3 years after the HRC injection. The degree of sustainability of Cr(VI) reductive bioimmobilization under different redox conditions at this and other contaminated sites is currently under study.