Study on multi-recharge areas and groundwater flow paths in closed groundwater system around urban area

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Most basins, which is located in a high or low land surrounded by mountains, depends considerably on groundwater for domestic, agricultural, industrial and urban uses. An understanding of recharge zone and the flow path of the groundwater provides important strategy into the resource management and prevention of groundwater contamination.We investigated stable isotope of oxygen and hydrogen and water quality of groundwater in order to identify the recharge zones and flow paths in the Matsumoto Basin and Osaka basin. In the Matsumoto Basin, all stable isotope data fell on a meteoric line widely. The spatial distributions of the oxygen and hydrogen stable isotopic ratios, water quality and altitude effect against oxygen stable isotope of groundwater indicate that flow systems of shallow groundwater and deep groundwater, five recharge zones and seven flow paths are distinguishable in the study region. The four flow paths of shallow and deep groundwater system are along river flows. The tw … More o flow paths through each of two inferred faults, which are covered by the alluvial thin layer, are estimated by lower δ ^<18>O and δ D values. A flow path through an inferred fault into the deeper aquifer is estimated by the comparison of water compositions and the stable isotope data of the deep groundwater with those of the shallow groundwater. The NO^-_3-N from three contamination sources partially exceeded the WHO standard migrates and spreads toward the urban area along the flow paths in both the shallow and deep groundwater system. After monitoring NO^-_3-N for three years, it became apparent that NO^-_3-N of groundwater maintains a constant concentration in a shallow groundwater system, while it increases in a deep groundwater system. A flow path works as a flow barrier and causes the basin to be a closed groundwater flow system. In the Osaka basin, most stable isotope data fell on a meteoric line widely, while some data fell on the line with more gentle slope than a meteoric line and larger δ ^<18>O than -7.1 ‰. The altitude effect against oxygen stable isotope of groundwater indicate that groundwaters in recharge zone have smaller δ ^<18>O than -7.1 ‰. The shallow and deep groundwaters with these anomalously high δ ^<18>O spatially distribute at many points in the basin, which are coincident with the large pumping wells. The spatial distributions of the oxygen and hydrogen stable isotopic ratios, Cl^-and altitude effect against oxygen stable isotope of groundwater suggest that groundwaters are formed by mixing meteoric water from recharge area with sea water and Uemach terrace works as a flow barrier and causes the eastern part of the basin to be a closed groundwater flow system. Less