Abstract: A field survey is conducted on surface and groundwater samples collected from the Baiyangdian area in an effort to identify the scope and the impact of percolation of contaminated surface water on groundwater in the area, and to evaluate the groundwater quality for irrigation purposes. The pH, EC (Electric Conductivity) and ORP (Oxidation-Reduction Potential) values of water samples are measured, and their hydrogen and oxygen isotopic and major ion compositions are analysed. Using the linear discriminant analysis method and the R_SA(Sodium Adsorption Ratio)index, the surface water leakage and its influence on groundwater are studied and discussed. Results show that the leakage from Baiyangdian Lake can lead to an increase in EC and a decrease in ORP with heavy isotopes being enriched in shallow groundwater. The concentrations of SO₄^2- and Na⁺ in shallow groundwater around the Tang sewage reservoir have increased significantly. The extent of surface water leakages is sufficiently marked with δ¹⁸O values and the water table depth of shallow groundwater. The shallow groundwater is mainly recharged by Baiyangdian Lake. The groundwater quality around the Tang sewage reservoir area is affected by the percolation of reservoir water. The percolation of contaminated surface water has caused a general decline in groundwater quality in the area. The groundwater quality is not suitable for irrigation purpose in the west region of Baiyangdian Lake and the area around the Tang sewage reservoir.