At the Horobetsu Sulphur Mine, a closed mine in Hokkaido, the strong acid mine water, in which its pH is 1.5-2.0, even now continues to tlow out of the underground at the rate of 4-7m³/min. The treatment of acid mine water has been carried out by the method of lime neutralization, since the mine was closed.
Recently, however, the lack of site for dumping the sludgeproduced by the water treatment has become an urRent problem to solve.
Therefore, authors have considered on sealing the mine to reduce the drainage. Consequently, the.hydrological survey on this mine district and the prediction on the mine drainage by sealing have been carried out under the request of Metal Mining Agency of Japan. Results obtained by these survey and prediction are as follows:
(1) The amount of recharged water into the ground near the top of hill side in this mine area is 6-7mm/day in rainy season and 1-3mm/day in dry season.
(2) The permeability of rock formation in this mine district is approximated to 4×10^-5cm/sec according to the wide area observation.
(3) If the level of water impounded in the underground mining zone is risen up to 50 and 100 meters vertically by sealing, the amount of mine drainage may decrease about 13 and 35%, respectively.

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