| Natural attenuation is an effective and feasible technology for controlling groundwater containing chlorinated hydrocarbons at contaminated sites.1,1,1-Trichloroethane (TCA) in groundwater is susceptible to a variety of natural degradation mechanisms. Advection, dispersion, adsorption and degradation are important factors affecting the transport and fate of chlorinated organics in groundwater. In this study, natural attenuation at a1,1,1-trichloroethane (TCA)-contaminated site was investigated using a column simulation experiment, reactive transport model, and16S rRNA gene cloning and sequencing to characterize its potential effectiveness and mechanisms. The results indicated that the majority of the contaminant mass was present at2-6m in depth, the contaminated area was-1000m2, and natural attenuation processes were occurring at the site. The MODFLOW groundwater model indicated that the velocity field of the groundwater relative to contaminant transport was stable and its hydraulic slope was low, which, along with the adsorption factor, slowed contaminant diffusion. The effluent breakthrough curves from the column experiments demonstrated the effectiveness of natural attenuation of TCA in the aquifer. Using the advection-dispersion-reaction equation with adsorption and degradation in one-dimensional form, the kinetic parameter of adsorption was found to be0.068m3/kg and the kinetic constant for biotic dehydrochlorination of TCA was-0.003-0.006d-1. After about5years, the contaminated area was predicted to be diminished and the maximum concentration of TCA to fall below the standard of300ug/L. We found that the dominant species in the TCA degradation bacterial community belonged to Trichococcus, Geobacteraceae, Geobacter lovleyi, Mucilaginibacter, and Arthrobacter, clarifying the degradation mechanism. This study demonstrates a method that can be used to evaluate the potential effectiveness of natural attenuation at TCA-contaminated sites. |
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