Major and minor element chemistry, hydrogen and oxygen stable isotopes and VOCs were analyzed for the groundwaters taken from Osaka City and its surroundings, located at the alluvial plain and fluvial terrace (Uemachi terrace). Salinitization occurs in the groundwater <100m depths in the western alluvial plain from the Uemachi terrace, due to seawater invasion along river into the aquifer. The level of seawater contamination is higher in the depth between 50 and 100 m depth than in the <50 m depth. The groundwaters taken from Uemachi terrace give diluted Ca-HCO₃ type chemistry. While the fresh groundwater from the alluvial plain gives Na-HCO₃ type chemistry. However, both would be recharged from the local rain and/or river water. Fresh groundwater >100 m depth close to the coast line of Osaka Basin gives Na-HCO₃ type and low SiO₂ (<10mg/L) chemistry and lightest stable isotope ratios among the studied groundwater, suggesting that the groundwater was originated from the precipitation at the mountain area north of Osaka City, or ultrafiltrated porewater from the less permeable layer in that depth. All the studied groundwater except one do not contain VOCs, suggesting the recharging period after 1989.

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In this study, we investigated the change in the salt concentration in a lake, and the motion of interfaces between seawater and fresh water in the ground occurred by the differences in the tidal and fresh water level, using laboratory water tank experiments. Our results showed that the interface was formed under the lake or marsh, and that the configuration of the interface was flat when the fresh water level exceeded the seawater level, while the area of freshwater became smaller than the initial area when the fresh water became lower than the tidal level. In the latter situation, the fresh water flowed into a storage pond located between the land and an embankment. The storage pond water then flowed out into the ground. This work clarified that the variations in the salt concentration in the storage pond, which reproduced the lakes and marshes, must be estimated using the entire system including the water of the lakes and marshes, seawater and the subsurface fresh water.

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Pore water was extracted from sandstone at different pF values. The samples originate from three locations where sandstone rock cores of 100m length at each location were obtained. Afterwards pore water was extracted from 63 samples by centrifuge at three different values of pF (low: up to pF 2.3, medium: pF 2.3 -3.9, high: pF 3.9-4.3). For each pF range the pore water was analyzed for main anions and cations. Results show that concentrations vary with pF and depth. Based on the distribution of Ca²⁺ concentration, three zones could be defined: (1) Ca²⁺ concentration is independent of pF, (2) Ca²⁺ concentration is increasing with the value of pF, and (3) Ca²⁺ shows the same value for medium and high pF value. We conclude that water chemistry of deep pore water is likely to have reached equilibrium due to almost stagnant flow conditions, whereas shallow water is likely to participate in chemical interactions due to the relatively high flow velocity. The depths of the interfaces of these three zones are almost consistent with geological boundaries of weathered and fine sandstone and there is an evidence of relationship between pore water chemistry and physical rock properties.

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The study investigated the effect of the leakage of an inner electrode solution (3.3M KCl) for conductivity in the measurement of in situ physico-chemical parameter of groundwater without pumping. The results showed that a conductivity of groundwater in low-permeability layer (below the 10^-7m/s) was sensitive to the leakage of an inner electrode solution and the value increased continuously during monitoring campaign. In case where the conductivity of groundwater in the low permeability environment or stagnation zone increased continuously during the measurement of in situ physico-chemical parameter of groundwater without pumping, the inspection is recommendation for accurate conductivity.

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