Abstract: Ground water pollutant floating above the water table in a water-bearing formation is removed through a well penetrating the formation by lowering the water level so that pollutant from the region surrounding the well will flow into the well due to gravitational force, and lowering a liquid-retaining vessel into the well to a depth whereby a liquid entry port in the vessel is in the pollutant layer above the water level. The vessel is constructed to receive the liquid pollutant by gravitational flow through the liquid entry port, the displaced gas leaving through a vent. A compressed air line feeds the vessel to purge its interior of accumulated liquid through an exit port on an intermittent basis. Check valves associated with each port are actuatable by the influence of the compressed air to prevent leakage of discharged pollutant back into the vessel and to provide complete and efficient purging when the compressed air is flowing.