We have been investigating field experiments on the aquifer thermal energy storage method for 9 years. As a result, the thermal recovery factor (recovered thermal energy/charged thermal energy) has improved from 23% in the first year to 63% in the 8th. We have noted the importance of ferric colloid (Fe2O3nH2O). In the aquifer, the clogging of the ferric colloidal dam in the vacant spaces of the aquifer prevented the natural flow of ground water around the well, which increased the recovery factor significantly. In this paper, a fundamental model for describing the clogging phenomena in the aquifer by the ferric colloid is proposed, and this showes a good agreement with the results of the one-dimensional experiment. The limits of the colloidal dam in the aquifer were measured by the Wenner method using 160 electrodes fixed previously from which the area of thermal energy storage could be obtained.