Current methods for evaluating chlorinated solvent plumes often assume that no TCE degradation occurs under aerobic conditions. It is possible that decay rates with values greater than zero exist in these plumes, but this decay may be masked by effects of parameter values in zero–decay–rate models. This hidden decay can be identified by comparing the zero–decay–rate models with others that have been created with a decay rate greater than zero. The results of this research and analysis show that it is possible to create matches between the zero–decay–rate models and models with greater than zero decay rates by adjusting model parameters other than the decay rates. The matches were closer and more easily achieved at lower decay rates than at higher ones, and increasing the number of spatial dimensions in which to match the models also increases the difficulty of creating the match. The matches are sensitive to time and do not maintain their similarity when they are examined at other discrete points in time. Time was the most important variable in making the distinction between the effects of degradation processes on the plume and those of physical processes, but the three–dimensional plume geometry is also an important factor. Because of the strong influence of time as a variable, it is crucial to collect plume data at different points in time to help constrain the models. Analysis of the results shows that it is indeed possible for rates of decay up to about 0.3 (yr-1) to be masked by model parameter values and that this misinterpretation is more likely to occur in models with lower decay rates (such as 0.1 per yr) than in models with higher rates
