Factors controlling the natural attenuation of BTEX

Since 1996 investigations into the fate and transport of aromatic compounds (BTEX) have been carried out in a Quaternary porous aquifer below a former gas manufacturing plant in southwest Germany. Intrinsic bioremediati- on of the quasi-steady-state BTEX plume was found to result in significant changes in the environmental chemistry, where, besides dilution and sorption, biochemical redox processes are the controlling factors. The considerable BTEX mass loss from 23 mg l-1 near the source, to 0.1 mg l-1 about 250 m downgradient, is accompanied by characteristic changes of various electron acceptors; these include O2 under aerobic and NO3 and Fe3+, SO42 under anaerobic conditions. For the total turnover, nitrate reduction is of minor importance and sulphate and iron(III) reduction of major importance.