大阪北摂地域の高塩分被圧地下水

Abstract

The high chloride groundwater in the Hokusetsu area, Osaka Prefecture was described. 1400 ppm of chloride was dissolved in the A group and 2000 ppm in the B group. These were the highest concentrations of over 740 investigations in the Eastern Osaka area. This high chloride groundwater was in one or more layers with aquifers of depths of 100m180m and it is assumed that they are present in the Osaka Group Upper Part. As the sample was composed of a water mixture from various layers, the salt concentration in a single layer is much higher. Both A and B groups are of the same origin and the groundwater was distributed in a rather wide range. The feature of the water quality is that it has low alkalinity, high chloride and contains significant amount of sulfate. Phosphorus content is low. Among cations, the content of sodium is high and that of calcium and magnesium is also high but their content is 1/11/2 of sodium. The water quality type is chloride type of 3 kinds of cations. The origin of this groundwater is sea water which has been sealed off at a certain period and remained stagnant, and the presence of sulfate is due to incomplete flushing out of saline water so low alkalinity was maintained in an environment of insufficient reduction of sulfate. The presence of large quaintities of magnesium and calcium can be explained by ion exchange between concentrated solution of the salt and clay minerals, adsorption and pricipitation.