The fate of seven aromatic hydrocarbons was investigated under aerobic conditions by in situ microcosm (ISM, one-dimensional in situ column) in a sandy aquifer low in organic carbon. The results were simulated by an one-dimensional reactive solute transport model accounting for kinetically controlled sorption and degradation in order to obtain degradation parameters. The kinetic sorption process affected the fate of the aromatic hydrocarbons and must be accounted for in simulation of the degradation process. The kinetic sorption constants were determined either by laboratory batch sorption experiments or from the fate curves of a biological deactivated ISM. The fate curves of biological active ISMs were adequately described both by the first-order degradation model, including a lag phase, and by the Monod model. The first-order degradation model was preferred to the Monod model, because the Monod model approaches the first-order degradation model at the low concentrations studied (initial concentrations of the organic compounds were 150 &mgr;g L-1) and because the basic assumptions of the Monod model may be violated in a system where several aromatic hydrocarbons are present at the same time. The results obtained by the first-order degradation model showed lag phase ranging from 2--20 days. First-order degradation rate constants for aromatic hydrocarbons determined in situ ranged between 0.05 and 0.8 day-1. Sensitivity analysis revealed the importance of independent determination of sorption constants in order to obtain reliable first-order degradation rate constants. ¿ American Geophysical Union 1996