A process for remediating contaminated soil or groundwater comprises the steps: (a) treating said soil or groundwater in a bioreactor inoculated with a microorganism which biodegrades lower molecular weight polycyclic aromatic hydrocarbons, heterocyclic organic compounds and phenolics found in creosote; and (b) treating said soil or groundwater from step 1 with a microorganism which biodegrades high molecular weight polycyclic aromatic hydrocarbons or pentachlorophenol.