Natural attenuation of chlorinated ethene compounds: model development and field-scale application at the Dover site

A multi-dimensional and multi-species reactive transport model was developed to aid in the analysis of natural attenuation design at chlorinated solvent sites. The model can simulate several simultaneously occurring attenuation processes including aerobic and anaerobic biological degradation processes. The developed model was applied to analyze field-scale transport and biodegradation processes occurring at the Area-6 site in Dover Air Force Base, Delaware. The model was calibrated to field data collected at this site. The calibrated model reproduced the general groundwater flow patterns, and also, it successfully recreated the observed distribution of Ž . Ž . Ž . Ž . tetrachloroethene PCE , trichloroethene TCE , dichloroethylene DCE , vinyl chloride VC and chloride plumes. Field-scale decay rates of these contaminant plumes were also estimated. The decay rates are within the range of values that were previously estimated based on lab-scale microcosm and field-scale transect analyses. Model simulation results indicated that the anaerobic degradation rate of TCE, source loading rate, and groundwater transport rate are the important model parameters. Sensitivity analysis of the model indicated that the shape and extent of the predicted TCE plume is most sensitive to transmissivity values. The total mass of the predicted TCE plume is most sensitive to TCE anaerobic degradation rates. The numerical model developed in this study is a useful engineering tool for integrating field-scale natural attenuation data within a rational modeling framework. The model results can be used for quantifying the relative ) Corresponding author. Ž . E-mail address: [email protected] T.P. Clement . 0169-7722r00r$ see front matter Published by Elsevier Science B.V. Ž . PII: S0169-7722 99 00098-4 ( ) T.P. Clement et al.rJournal of Contaminant Hydrology 42 2000 113–140 114 importance of various simultaneously occurring natural attenuation processes. Published by Elsevier Science B.V.