Effect of Uncertain Hydraulic Conductivity on the Simulated Fate and Transport of BTEX Compounds at a Field Site

Monte Carlo simulations were conducted to investigate the effect of uncertain hydraulic conductivity (K) on the natural attenuation of BTEX compounds (benzene, toluene, ethyl benzene, and xylenes) through aerobic respiration, denitrification, Fe(III) and sulfate reductions, and methanogenesis observed at a field site on Hill Air Force Base, Utah. First, the uncertainty in the ln?K field was represented by multiple realizations of spatially correlated random fields. The simulated BTEX plumes resulting from a light nonaqueous phase liquid source were analyzed for mass distributions and the relationships among various factors such as dissolved BTEX mass, plume spreading, and depletions of electron acceptors or productions of Fe2+ and methane. Second, additional K realizations with the same mean but different variances and correlation lengths were used to determine how the model responds to varying degrees of uncertainty in the K field. The methodology and insights are of general interest and applicable to fuel-hydrocarbon natural-attenuation sites.