The sources of city water in Mitaka city, western part of Tokyo metropolis, is mainly the groundwater from about thirty artesian wells.
One of them, which is called No.4 (300 mili - meters in diameter and 200 meters in depth), is the multiaquifer well having five punping aquifers. The well was not suitable for city water for long time because the water was 0.2 ppm in manganese content. As another multiaquifer wells were in good quality, it was an important problem to find out manganese - rich aquifer of No.4 well.
In the process of hydrogeological investgations, two unique aquifer-test apperatuses were invented by Y. Otomo. Using the water-well flow meter the direction of water flow in the well was measured under static condition. Using the special water-sumpler the water of individual aquifer was sumpled under pumping condition.
As a result of the investgations, it had existance that uppermost aquifer is essentially rich in manganese and that under static condition the groundwater flows into from the aquifer to another aquifers.
Finally after sealing up the aquifer and pumping out of water for two years, the concentration of manganese ion became 0.02 ppm. Thus nowadays No.4 well is sufficiently used as the city-water well.