Quantitative Validation of a Model of Chlorinated Ethene Natural Attenuation

Chlorinated ethenes are among the most prevalent groundwater contaminants at hazardous waste sites nationwide. In an attempt to manage the risks posed by these contaminants, while controlling costs, monitored natural attenuation (MNA) is being considered as a remediation strategy at many sites. MNA relies on naturally occurring physical, chemical, and biological processes in the subsurface to reduce the risk posed by the contamination. The implementation of MNA, however, requires a detailed understanding of these processes, and how they impact contamination at a particular site. One way to gain this understanding is through contaminant fate and transport modeling. In this study, a deterministic model that includes relevant fate and transport processes was applied to a chlorinated ethene-contaminated field site, at which spatial and temporal data had been collected. Parameters used for model input were obtained from the literature, experimental data, and by calibrating the model using concentration data from 1993. The model was then run in a predictive mode, and simulation results were compared to field data from 1999. Model performance was measured by comparison of observed and simulated concentration contour plots and evaluation of goodness-of-fit statistics. Over the six years the model was run in a predictive mode, the model was found to predict contaminant concentrations reasonably well for the three contaminants that were monitored.