Abstract
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.
