Pilot scale studies were carried out to evaluate the suitability of bioremediation of Cr(VI) contaminated aquifers using bio-barrier and reactive zone technologies, employing chromium reducing bacteria. Experimental results showed that a 10 cm thick bio-barrier with an initial biomass concentration of 0.44 mg/g of soil was able to completely contain a Cr(VI) plume of 50 mg/L concentration, when the Darcy velocity was 0.0196 cm/h. In the case of reactive zone technology, a system with four injection wells was effective even when Cr(VI) concentration in the plume was as high as 250 mg/L, when 150g (wet weight) of bacteria were injected into each injection well. A mathematical model was proposed for simulating the bioremediation process. Though the model could predict the over all trends observed in the experiments, it is limited by the assumption of homogeneous conditions. (c) 2010 Elsevier B.V. All rights reserved.