BIOGEOCHEMICAL MODELING OF A FIELD BIOSTIMULATION EXPERIMENT

From a field biostimulation experiment conducted at the Department of Energy's Oak Ridge Field Research Center, Tennessee, we took a time series of groundwater samples and have measured major, minor, and trace elements as well as C, N, and S stable isotopes. Data show NO3-, Mn (IV), Fe (III), U (VI), Tc (VII), and SO4-2 reduction. A zeroth order rate law generally describes the data well, but derived in situ rates are probably effective rates that mask many simultaneous and competing reactions and processes. The availability of a comprehensive suite of chemicals, stable isotopes, and characterization of the solid matrix in our study provided an opportunity to decipher a network of redox and non-redox reactions. Currently, we are using geochemical modelling to examine the complex reaction network as a result of stimulated microbial activities in the aquifer and to understand redox reactions and reaction rates in a complex geological media. Geochemical modeling can help to integrate processes and reactions in a quantitative manner to provide a more comprehensive understanding of biogeochemical processes than simply providing apparent zeroth order and first rates. This presentation will show this comprehensive data set and geochemical modeling results.