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

A multi-dimensional and multi-species reactive transport model was develope d to aid in the analysis of natural attenuation design at chlorinated solve nt sites. The model can simulate several simultaneously occurring attenuati on processes including aerobic and anaerobic biological degradation process es. The developed model was applied to analyze field-scale transport and bi odegradation 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 tetrachloroeth ene (PCE), trichloroethene (TCE), dichloroethylene (DCE), vinyl chloride (V C) and chloride plumes. Field-scale decay rates of these contaminant plumes were also estimated. The decay rates are within the range of values that w ere previously estimated based on lab-scale microcosm and field-scale trans ect analyses. Model simulation results indicated that the anaerobic degrada tion rate of TCE, source loading rate, and groundwater transport rate are t he important model parameters. Sensitivity analysis of the model indicated that the shape and extent of the predicted TCE plume is most sensitive to t ransmissivity values. The total mass of the predicted TCE plume is most sen sitive to TCE anaerobic degradation rates. The numerical model developed in this study is a useful engineering tool for integrating field-scale natura l attenuation data within a rational modeling framework. The model results can be used for quantifying the relative importance of various simultaneous ly occurring natural attenuation processes. Published by Elsevier Science B .V.