Crude Oil at the Bemidji Site: 25 Years of Monitoring, Modeling and Understanding

The long-term fate of hydrocarbons in the subsurface near Bemidji, Minnesota, has been investigated by a multi-disciplinary group of scientists for over a quarter century.  Research at Bemidji has involved extensive investigations of multiphase flow and transport, volatilization, dissolution, geochemical interactions, microbial populations and biodegradation. Early observations of ground-water geochemistry at Bemidji were among the first to document the importance of anaerobic processes for hydrocarbon removal and remediation by natural attenuation. Detailed monitoring of multiphase fluid distributions, sediment and mineral properties, ground-water concentrations, microbial populations and gas vapors has resulted in an improved understanding of the natural processes limiting the extent of the hydrocarbon plume. Spatial variability of hydraulic properties has influenced subsurface oil flow, vapor diffusion, water flow and the progression of biodegradation. Field data from the Bemidji site has made it possible to develop increasingly complex models of the fate and transport of hydrocarbons. Simulations have been used to test conceptual models, determine the relative importance of simultaneously occurring processes, and quantify field-scale reaction rates and system mass balances. Long-term field studies at Bemidji have illustrated that the fate of hydrocarbons evolves with time, and a snap-shot study of a hydrocarbon plume may not provide information that is of relevance to the long-term behavior of the plume during natural attenuation.