Modeling TEAPs and computing redox zonation in contaminated aquifers

The release of oxidizable organic contaminants in shallow aquifers leads to the segregation of the contaminated groundwater into different redox zones. This is due to the indigenous microbial reactions that can couple the oxidation of the organic compounds to the reduction of a number of electron acceptors naturally present in the aquifer system. The sequence of the TEAPs (Terminal Electron Acceptor Processes): aerobic respiration, denitrification, Mn(IV)-reduction, Fe(III)-reduction, sulfatereduction and methanogenesis is determined by the energy yield of each redox reaction (Chapelle et al., 1995). This study presents a kinetic model of the redox processes using the multispecies reactive transport code RT3D (Clement, 1997). A user-defined kinetic model (Kin_REDOX) was developed to account for the the principal biogeochemical reactions that are likely to follow the release of a generic organic contaminant (CH2O). Post processing programs have been developed to calculate point by point reaction rates of each TEAP and to display the computed redox zones. The model was tested using batch, one, and two dimensional problems.