REACTIVE TRANSPORT MODELING OF PUSH-PULL TEST DATA: EVALUATING CONTROLS ON BIOREMEDIATION OF AROMATIC HYDROCARBONS AT THE BEMIDJI, MINNESOTA SITE

Identifying an appropriate technology to cleanup sites contaminated with petroleum hydrocarbons depends on our ability to understand key controls on subsurface fate and transport processes and to accurately estimate rates of in situ bioremediation. Push-pull tests are an attractive approach to quantitatively evaluate rates of physical and biogeochemical processes influencing bioremediation at field sites; however, correctly interpreting the results of push-pull test data can be a challenge, especially in the presence of multiple competing processes (e.g., mixing and dilution versus reactions and reactions in the presence of co-contaminants). The well-characterized Bemidji site in Minnesota, a crude oil spill site where contamination percolated to the water table in addition to flowing over the land surface to a nearby wetland, represents an ideal location for conducting push-pull tests and to address several questions about factors influencing the remediation of hydrocarbons including BTEX. In this presentation we describe the application of a new reactive transport model PPTEST to interpret data from push-pull tests conducted in the aquifer (under iron-reducing conditions) and the wetland under natural (methanogenic) and nitrate reducing conditions at the Bemidji site. Tests were designed to evaluate the effects of having ethanol as a co-contaminant on transport and biodegradation processes. This study demonstrates how the model can be used to gain insight into complex processes operating at the site including sorption, diffusion, and complex reaction rate order.