Water-quality Problem in Eastern Osaka and its Hydrological Interpretation

Abstract

This report treats of the groundwater condition in Eastern Osaka basin, especially of the problem of water-quality. Analytical works in the 1965-69 period on the artesian groundwater samples taken from the existing wells and test wells were summarized in several maps and diagrams ; a) isogram maps for major constituents, b) profile of chloride content, c) profile of water-quality represented by the shape diagram. The tritium content of 30 water samples was determined. Of these samples, three had less than 0.3 TU, five had less than 3.0 TU.Four main types of water based on alkalinity and chlorinity are described, with subdivision based on tritium content. The water samples characterized by the high chloride with the range of 100 to 300 ppm are distributed in the northern part of the basin. It is confirmed by the isochlor map and profile that the chloride was derived from the ancient saline water entrapped in the sediments deposited in a marine or brackish environments. The water samples of high alkalinity accompanied with nitrogen and phosphorus are found in the central part of the basin. The chemical and hydrological conditions which produce the water are discussed based on the content of the organic materials in the clayey layer.As a result of this study three discontinuous lines of water-quality ware found. One of them coincides with geological structure called Uemachi elevation, and the others lack the geological evidence. The discontinuation lying east and west provides a reasonable interpretation for the groundwater conditions as well as for the distribution of the amount of land subsidence in this area.