Coal tars in soil at a gasworks site in South Eastern Australia led to groundwater contamination with polycyclic aromatic hydrocarbons (PAHs), mono-aromatic compounds (BTEX) and phenols. The scope of the study included testwork in laboratory scale bioreactors and evaluation of available commercial groundwater treatment units. Two bioreactor configurations, a submerged fixed film reactor (SFFR) and a fluidized bed bioreactor (FBR) were effective, with high efficiencies of contaminant removal (typically >90%) over a range of hydraulic retention times (HRT) (3-29 h). Specifically, concentrations of total PAH, naphthalene, pyrene and total phenols in the feedstock and effluent of the SFFR were 123,60,51, 1.38 and 0.004, 0.001, 0.004, 0.1 mg/l, respectively. The FBR was only marginally less effective than the SFFR for the same groundwater contaminants. Discharge to sewer was the most appropriate end use for the effluent. SFFRs are regarded as being simpler in design and operation, and a commercially available unit has been identified which would be suitable for treating small volumes (< 10 m(3) per day) of contaminated water collected at an interception trench at the site. (C) 2002 Elsevier Science B.V. All rights reserved.