[en] Full text: An isotopic hydrological study was carried out on the Wei River water and shallow groundwater in the Guanzhong basin, Shaanxi, China. The study area is bordered by the Qinling Mountain in the south and by the North Mountain in the north, by the Yellow River in the east. Wei River is located in the middle of the basin and converges eastward into the Yellow River. The water supply for the major cities like Xian, Xianyang, Baoji and Weinan is from river and groundwater resources. Wei River and nearby shallow groundwater is largely used for fresh water supplies. With increasing use of the surface and groundwater, the water quality and groundwater table is decreasing. The over-exploitation of water resources is resulting in serious hydrogeological damage, such surface land depression and surface fracturing etc. The groundwater over 300 m depth is fresh from the foothill of the Qinling Mountain northward to the Wei River. The groundwater is brackish from the northeast foothill of the North Mountain southward to the Wei River, the salinity is decreasing westward and eastward. This hydrochemical trend was the foundation of a hydrogeological model in which the groundwater is recharged mainly in the Qinling Mountain and is transported relatively quickly northward and resulting in some discharge into the Wei River. Groundwater in the north bank of the Wei River is recharged in the North Mountain and move slowly southward. New isotopic and CFC data are presented to improve the interpretation for interaction between Wei River and groundwater in the Guanzhong basin. The oxygen isotopic ratios in the shallow groundwater lie within -7 per mille to -10 per mille, these are different from the more rich values of surface water, which reflect the weak link between the surface and groundwater. Deeper, warm groundwaters show a significant ¹⁸O shift due to isotope exchange with lithologies, indicating long groundwater residence times, confirmed by ¹⁴C data. Most of CFC concentrations for groundwater are very low near the Wei River, but high near the Qinling Mountain foreland alluvial fan and the North Mountain. Ratio of CFC data indicate that the groundwater near the Qinling Mountain, the North Mountain and Wei River may contain respectively as much as 20-50%, c.a. 20% (age less than 12 years), and <10% young water mixed with old regional water. Some high fraction of young water near the Wei River is related to heavy pumping. The relative high fraction of young water near the mountain areas and the Wei River in the inner basin indicates that foreland mountain areas are the recharge sources of the shallow groundwater and discharge to the Wei River. (author)