Abstract: Apparatus for the cleaning of contaminated groundwater in an substantially vertical well. The apparatus comprises an airlift aerator comprising a plurality of vertically mounted gas lines, arranged together with separating and supporting means; a compressed gas source connected to the gas lines; and at least one pipe having an inlet for groundwater and gas and outlet for discharging lifted, aerated cleaned water, volatile pollutants and used gas. A base airlift section comprises at least one inlet at its lower circumference for receiving contaminated groundwater. At least one exchangeable airlift section is disposed, in use, between the aerator and base airlift sections for establishing an artificial groundwater level, the aerator section and exchangeable section being separated from each other by a generally watertight, aerating plug assembly and the exchangeable section and base section being separated from each other by a watertight seal.