A Critique of a Steady-State Analytical Method for Estimating Contaminant Degradation Rates

Contaminant transformation rates are routinely estimated from monitoring well data using a regression method based on a steady-state analytical model. This approach assumes one-dimensional solute transport in the presence of a continuous boundary concentration and a uniform first-order degradation coefficient. It must be recognized that this type of analysis is easily subject to misinterpretation, particularly when few monitoring points are used. This is because the dispersive nature of solute transport can produce concentration profiles which closely resemble those associated with a degrading contaminant even in the absence of any transformation processes. Monte Carlo analyses using simulated plumes suggest that this method may lead to significant overestimates of apparent transformation rates.