Field evidence for co-metabolism of trichloroethene stimulated by addition of electron donor to groundwater.

For more than 10 years, electron donor has been injected into the Snake River aquifer beneath the Test Area North site of the Idaho National Laboratory for the purpose of stimulating microbial reductive dechlorination of trichloroethene (TCE) in groundwater. This has resulted in significant TCE removal from the source area of the contaminant plume and elevated dissolved CH4 in the groundwater extending 250 m from the injection well. The δ13C of the CH4 increases from −56‰ in the source area to −13‰ with distance from the injection well, whereas the δ13C of dissolved inorganic carbon decreases from 8‰ to −13‰, indicating a shift from methanogenesis to methane oxidation. This change in microbial activity along the plume axis is confirmed by PhyloChip microarray analyses of 16S rRNA genes obtained from groundwater microbial communities, which indicate decreasing abundances of reductive dechlorinating microorganisms (e.g., Dehalococcoides ethenogenes) and increasing CH4-oxidizing microorganisms capable of aer...