A one-dimensional (1-D) multi-component model accounting for hydrological transport inorganic equilibrium chemistry and microbial activity during kinetically controlled biodegradation in groundwater of compounds such as benzene, toluene, ethylbenzene and xylenes (BTEX) is presented. The problem is solved numerically using an operator-splitting method to couple advective–dispersive transport of organic and inorganic solutes with a geochemical equilibrium package PHREEQC and a biodegradation module. The transport equations for inorganic solutes are solved for total aqueous component concentrations. Changes in such concentrations due to precipitation/dissolution of minerals and chemical speciation are accounted for within PHREEQC. For chemical elements occurring in multiple valence states, separate components are defined and transported. The biodegradation module simulates the sequential or parallel activity of multiple bacterial groups attached to soils and their biochemical effects. The model has been evaluated by comparison with an existing model simulation of a 1-D inorganic redox problem. An application of the model is shown for a synthetic case where BTEX compounds are degraded by sequential reduction of aqueous electron acceptors.