As a result of past nuclear processing activities, chromium is a common contaminant in the soils and groundwater at most DOE sites. Chromium in groundwater most commonly exists either as hexavalent chromium, Cr(VI), or trivalent chromium, Cr(III). While Cr(VI) is quite mobile and toxic in groundwater, Cr(III) complexes are much less toxic, and form insoluble and stable precipitates. A multi-institutional research team led by scientists from Lawrence Berkeley National Laboratory (LBNL) conducted field experiments in the 100-H area at the Hanford Site to test the effectiveness of a slow-release glycerol polylactate, or hydrogen release compound (HRC), to see if it would stimulate the existing microbial community to transform Cr(VI) moving in the groundwater into non toxic and insoluble Cr(III). The microbial community initially changed dramatically and then appeared to stabilize to a community with a new composition. In addition, Cr(VI) levels in wells down gradient from the HRC injection wells dropped from more than 150 micrograms/liter to an undetectable level and remained at that level for more than three years. Additional HRC and tracer injection tests are planned to further assess the biogeochemical process changes that occur as a result of HRC injection, to investigate reoxidation of Cr(III) to Cr(VI), and to develop a reactive transport model.
Reference: Environmental Science & Technology, 2008, vol 42(22):8478-8485.
Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
SC-23.1 Climate and Environmental Sciences Division, BER
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