A Monte Carlo simulation method for assessing biotransformation effects ongroundwater fuel hydrocarbon plume lengths

Biotransformation of dissolved groundwater hydrocarbon plumes emanating fro m leaking underground fuel tanks should, in principle, result in plume leng th stabilization over relatively short distances, thus diminishing the envi ronmental risk. However, because the behavior of hydrocarbon plumes is usua lly poorly constrained at most leaking underground fuel tank sites in terms of release history, groundwater velocity, dispersion, as well as the biotr ansformation rate, demonstrating such a limitation in plume length is probl ematic. Biotransformation signatures in the aquifer geochemistry, most nota bly elevated bicarbonate, may offer a means of constraining the relationshi p between plume length and the mean biotransformation rate. In this study, modeled plume lengths and spatial bicarbonate differences among a populatio n of synthetic hydrocarbon plumes, generated through Monte Carlo simulation of an analytical solute transport model, are compared to held observations from six underground storage tank (UST) sites at military bases in Califor nia. Simulation results indicate that the relationship between plume length and the distribution of bicarbonate is best explained by biotransformation rates that are consistent with ranges commonly reported in the literature. This finding suggests that bicarbonate can indeed provide an independent m eans for evaluating limitations in hydrocarbon plume length resulting from biotransformation. Published by Elsevier Science Ltd.