Abstract: Contaminated brownfields are successfully and efficiently remediated by the sequential synchronized treatment of the native groundwater in the contaminated site, both mechanically and biologically, in a closed-loop system. The mechanical treatment comprises a high-intensity air sparger, and the biological treatment comprises a bacterial incubator initially filled with untreated (dirty) groundwater, the bacterial growth preferably being facilitated by a sample of the native bacteria in the site and/or is supplied with non-native bacteria.