Uncertainty Analyses of Fuel Hydrocarbon Biodegradation Signatures in Ground Water by Probabilistic Modeling

Natural attenuation processes, such as biodegradation, may serve as a means for remediating ground water contaminated by fuel hydrocarbons from leaking underground fuel tanks (LUFTs). Quantification of the uncertainties associated with natural attenuation, and hence the capacity to limit plume migration and restore an aquifer, is important. In this study, a probabilistic screening model is developed to quantify uncertainties involved in the impact of biodegradation on hydrocarbon plume behavior. The approach is based on Monte Carlo simulation using an analytical solution to the advective‐dispersive solute transport equation, including a first‐order degradation term, coupled with mass balance constraints on electron acceptor use. Empirical probability distributions for governing parameters are provided as input to the model. Application of the model to an existing LUFT site illustrates the degree of uncertainty associated with model‐predicted hydrocarbon concentrations and geochemical indicators at individual site monitoring wells as well as the roles of various parameter assumptions (e.g., hydraulic conductivity, first‐order decay coefficient, source term) in influencing forecasts. This information is useful for risk management planning because the degree of confidence that biodegradation will limit the impact of a hydrocarbon plume on potential receptors can be quantified.