ABSTRACT: Cleaning technology of contaminated groundwater includes in-situ physical and biological remediation and on-site or off-site physical, chemical and/or biological treatment. In-situ remediation requires comprehensive understanding of the site geo logical and hydrogeological conditions and history of the contamination. Various new methods of cleaning are still under investigation and trial. Large scale in situ denitrification of high nitrate content groundwater for water supply is feasible. Treatment efficiency and operation requirements are much site condition dependent. On-site and off-site decontamination technologies (pump-and-treat) are those that have been commonly practised in water and wastewater industry. Groundwater decontamination by point source must be accomplished by cleanup of the unsaturated zone where most of the contaminants are retained and released slowly.